Effect of past peat cultivation practices on present dynamics of dissolved organic carbon.

PubMed

Frank, S; Tiemeyer, B; Bechtold, M; Lücke, A; Bol, R

2017-01-01

Peatlands are a major source of dissolved organic carbon (DOC) for aquatic ecosystems. Naturally high DOC concentrations in peatlands may be increased further by drainage. For agricultural purposes, peat has frequently been mixed with sand, but the effect of this measure on the release and cycling of DOC has rarely been investigated. This study examined the effects of (i) mixing peat with sand and (ii) water table depth (WTD) on DOC concentrations at three grassland sites on shallow organic soils. The soil solution was sampled bi-weekly for two years with suction plates at 15, 30 and 60cm depth. Selected samples were analysed for dissolved organic nitrogen (DON), δ 13 C DOM and δ 15 N DOM . Average DOC concentrations were surprisingly high, ranging from 161 to 192mgl -1 . There was no significant impact of soil organic carbon (SOC) content or WTD on mean DOC concentrations. At all sites, DOC concentrations were highest at the boundary between the SOC-rich horizon and the mineral subsoil. In contrast to the mean concentrations, the temporal patterns of DOC concentrations, their drivers and the properties of dissolved organic matter (DOM) differed between peat-sand mixtures and peat. DOC concentrations responded to changes in environmental conditions, but only after a lag period of a few weeks. At the sites with a peat-sand mixture, temperature and therefore probably biological activity determined the DOC concentrations. At the peat site, the contribution of vegetation-derived DOM was higher. The highest concentrations occurred during long, cool periods of waterlogging, suggesting a stronger physicochemical-based DOC mobilisation. Overall, these results indicate that mixing peat with sand does not improve water quality and may result in DOC losses of around 200kg DOCha -1 a -1 . Copyright © 2016 Office national des forêts. Published by Elsevier B.V. All rights reserved.

Patterns in Abundance, Cell Size and Pigment Content of Aerobic Anoxygenic Phototrophic Bacteria along Environmental Gradients in Northern Lakes

PubMed Central

Fauteux, Lisa; Cottrell, Matthew T.; Kirchman, David L.; Borrego, Carles M.; Garcia-Chaves, Maria Carolina; del Giorgio, Paul A.

2015-01-01

There is now evidence that aerobic anoxygenic phototrophic (AAP) bacteria are widespread across aquatic systems, yet the factors that determine their abundance and activity are still not well understood, particularly in freshwaters. Here we describe the patterns in AAP abundance, cell size and pigment content across wide environmental gradients in 43 temperate and boreal lakes of Québec. AAP bacterial abundance varied from 1.51 to 5.49 x 105 cells mL-1, representing <1 to 37% of total bacterial abundance. AAP bacteria were present year-round, including the ice-cover period, but their abundance relative to total bacterial abundance was significantly lower in winter than in summer (2.6% and 7.7%, respectively). AAP bacterial cells were on average two-fold larger than the average bacterial cell size, thus AAP cells made a greater relative contribution to biomass than to abundance. Bacteriochlorophyll a (BChla) concentration varied widely across lakes, and was not related to AAP bacterial abundance, suggesting a large intrinsic variability in the cellular pigment content. Absolute and relative AAP bacterial abundance increased with dissolved organic carbon (DOC), whereas cell-specific BChla content was negatively related to chlorophyll a (Chla). As a result, both the contribution of AAP bacteria to total prokaryotic abundance, and the cell-specific BChla pigment content were positively correlated with the DOC:Chla ratio, both peaking in highly colored, low-chlorophyll lakes. Our results suggest that photoheterotrophy might represent a significant ecological advantage in highly colored, low-chlorophyll lakes, where DOC pool is chemically and structurally more complex. PMID:25927833

Patterns in Abundance, Cell Size and Pigment Content of Aerobic Anoxygenic Phototrophic Bacteria along Environmental Gradients in Northern Lakes.

PubMed

Fauteux, Lisa; Cottrell, Matthew T; Kirchman, David L; Borrego, Carles M; Garcia-Chaves, Maria Carolina; Del Giorgio, Paul A

2015-01-01

There is now evidence that aerobic anoxygenic phototrophic (AAP) bacteria are widespread across aquatic systems, yet the factors that determine their abundance and activity are still not well understood, particularly in freshwaters. Here we describe the patterns in AAP abundance, cell size and pigment content across wide environmental gradients in 43 temperate and boreal lakes of Québec. AAP bacterial abundance varied from 1.51 to 5.49 x 105 cells mL-1, representing <1 to 37% of total bacterial abundance. AAP bacteria were present year-round, including the ice-cover period, but their abundance relative to total bacterial abundance was significantly lower in winter than in summer (2.6% and 7.7%, respectively). AAP bacterial cells were on average two-fold larger than the average bacterial cell size, thus AAP cells made a greater relative contribution to biomass than to abundance. Bacteriochlorophyll a (BChla) concentration varied widely across lakes, and was not related to AAP bacterial abundance, suggesting a large intrinsic variability in the cellular pigment content. Absolute and relative AAP bacterial abundance increased with dissolved organic carbon (DOC), whereas cell-specific BChla content was negatively related to chlorophyll a (Chla). As a result, both the contribution of AAP bacteria to total prokaryotic abundance, and the cell-specific BChla pigment content were positively correlated with the DOC:Chla ratio, both peaking in highly colored, low-chlorophyll lakes. Our results suggest that photoheterotrophy might represent a significant ecological advantage in highly colored, low-chlorophyll lakes, where DOC pool is chemically and structurally more complex.

Drivers of inverse DOC-nitrate loss patterns in forest soils and streams

NASA Astrophysics Data System (ADS)

Goodale, C. L.

2013-12-01

Nitrate loss from forested catchments varies greatly across sites and over time, with few reliable correlates. One of the few recurring patterns, however, is the negative nonlinear relationship that occurs regularly between surface water nitrate and dissolved organic carbon (DOC) concentrations: that is, nitrate declines sharply as DOC concentrations increase, and high nitrate levels occur only at low DOC concentrations. Several hypotheses have been proposed to explain this pattern, but its cause has remained speculative. It is likely to be driven by C- or N-limitation of biological processes such as assimilation or denitrification, but the identity of which biological process or the main landscape position of their activity are not known. We examined whether DOC and nitrate are both driven by soil C content, at scales of both soil blocks and across catchments, by measuring soil, soil extract, and surface water chemistry across nine catchments selected from long-term monitoring networks in the Catskill and Adirondack Mountains. We measured soil C and N status and solution nitrate, DOC, bioavailable DOC (bDOC), and isotopic composition (13C-DOC, 15N- and 18O-NO3) to examine whether variation in stocks of soil C partly controls DOC and nitrate loss from forested catchments in New York State. These measurements showed that surface soil C and C:N ratio together determine soil production of DOC and nitrate, reflecting assimilative demand for N by heterotrophic microbes. Yet, they also show that these processes do not produce the inverse DOC-NO3 curve observed at the catchment scale. Rather, catchment-scale DOC-nitrate patterns are more likely to be governed by the balance between excess nitrate production and its bDOC-mediated loss to denitrification.

Dissolved Organic Carbon in Headwater Streams and Riparian Soil Organic Carbon along an Altitudinal Gradient in the Wuyi Mountains, China

PubMed Central

Huang, Wei; McDowell, William H.; Zou, Xiaoming; Ruan, Honghua; Wang, Jiashe; Li, Liguang

2013-01-01

Stream water dissolved organic carbon (DOC) correlates positively with soil organic carbon (SOC) in many biomes. Does this relationship hold in a small geographic region when variations of temperature, precipitation and vegetation are driven by a significant altitudinal gradient? We examined the spatial connectivity between concentrations of DOC in headwater stream and contents of riparian SOC and water-soluble soil organic carbon (WSOC), riparian soil C:N ratio, and temperature in four vegetation types along an altitudinal gradient in the Wuyi Mountains, China. Our analyses showed that annual mean concentrations of headwater stream DOC were lower in alpine meadow (AM) than in subtropical evergreen broadleaf forest (EBF), coniferous forest (CF), and subalpine dwarf forest (SDF). Headwater stream DOC concentrations were negatively correlated with riparian SOC as well as WSOC contents, and were unrelated to riparian soil C:N ratio. Our findings suggest that DOC concentrations in headwater streams are affected by different factors at regional and local scales. The dilution effect of higher precipitation and adsorption of soil DOC to higher soil clay plus silt content at higher elevation may play an important role in causing lower DOC concentrations in AM stream of the Wuyi Mountains. Our results suggest that upscaling and downscaling of the drivers of DOC export from forested watersheds when exploring the response of carbon flux to climatic change or other drivers must done with caution. PMID:24265737

Deep nitrogen acquisition in warming permafrost soils: Contributions of belowground plant traits and fungal symbioses in the permafrost carbon feedback to climate

NASA Astrophysics Data System (ADS)

Hartnett, H. E.; Palta, M. M.; Grimm, N. B.; Ruhi, A.; van Shaijik, M.

2016-12-01

Tempe Town Lake (TTL) is a hydrologically-regulated reservoir in Tempe, Arizona. The lake has high primary production and receives dissolved organic carbon (DOC) from rainfall, storm flow, and upstream river discharge. We applied an ARIMA time-series model to a three-year period for which we have high-frequency chemistry, meteorology, and streamflow data and analyzed external (rainfall, stream flow) and internal (dissolved O2) drivers of DOC content and composition. DOC composition was represented by fluorescence-based indices (fluorescence index, humification index, freshness) related to DOC source (microbially- vs. terrestrially-derived) and reactivity DOC. Patterns in DOC concentration and composition suggest carbon cycling in the lake responds to both meteorological events and to anthropogenic activity. The fluorescence-derived DOC composition is consistent with seasonally-distinct inputs of algal- and terrestrially-derived carbon. For example, Tempe Town Lake is supersaturated in O2 over 70% of the time, suggesting the system is autotrophic and primary productivity (i.e., O2 saturation state) was the strongest driver of DOC concentration. In contrast, external drivers (rainfall pattern, streamflow) were the strongest determinants of DOC composition. Biological processes (e.g., algal growth) generate carbon in the lake during spring and summer, and high Fluorescence Index and Freshness values at this time are indicative of algal-derived material; these parameters generally decrease with rain or flow suggesting algal-derived carbon is diluted by external water inputs. During dry periods, carbon builds up on the land surface and subsequent rainfall events deliver terrestrial carbon to the lake. Further evidence that rain and streamflow deliver land-derived material are increases in the Humification Index (an indicator of terrestrial material) following rain/flow events. Our results indicate that Tempe Town Lake generates autochthonous carbon and has the capacity to process allochthonous carbon from the urban environment. Ongoing work is comparing these results to other periods in the 10-year time series to test if the driver-DOC relationships are robust over longer time-scales and evaluating how changes in lake management and climate have altered DOC over time.

Temporal Patterns in Dissolved Organic Carbon Composition in an Urban Lake

NASA Astrophysics Data System (ADS)

Hartnett, H. E.; Palta, M. M.; Grimm, N. B.; Ruhi, A.; van Shaijik, M.

2017-12-01

Tempe Town Lake (TTL) is a hydrologically-regulated reservoir in Tempe, Arizona. The lake has high primary production and receives dissolved organic carbon (DOC) from rainfall, storm flow, and upstream river discharge. We applied an ARIMA time-series model to a three-year period for which we have high-frequency chemistry, meteorology, and streamflow data and analyzed external (rainfall, stream flow) and internal (dissolved O2) drivers of DOC content and composition. DOC composition was represented by fluorescence-based indices (fluorescence index, humification index, freshness) related to DOC source (microbially- vs. terrestrially-derived) and reactivity DOC. Patterns in DOC concentration and composition suggest carbon cycling in the lake responds to both meteorological events and to anthropogenic activity. The fluorescence-derived DOC composition is consistent with seasonally-distinct inputs of algal- and terrestrially-derived carbon. For example, Tempe Town Lake is supersaturated in O2 over 70% of the time, suggesting the system is autotrophic and primary productivity (i.e., O2 saturation state) was the strongest driver of DOC concentration. In contrast, external drivers (rainfall pattern, streamflow) were the strongest determinants of DOC composition. Biological processes (e.g., algal growth) generate carbon in the lake during spring and summer, and high Fluorescence Index and Freshness values at this time are indicative of algal-derived material; these parameters generally decrease with rain or flow suggesting algal-derived carbon is diluted by external water inputs. During dry periods, carbon builds up on the land surface and subsequent rainfall events deliver terrestrial carbon to the lake. Further evidence that rain and streamflow deliver land-derived material are increases in the Humification Index (an indicator of terrestrial material) following rain/flow events. Our results indicate that Tempe Town Lake generates autochthonous carbon and has the capacity to process allochthonous carbon from the urban environment. Ongoing work is comparing these results to other periods in the 10-year time series to test if the driver-DOC relationships are robust over longer time-scales and evaluating how changes in lake management and climate have altered DOC over time.

Online stable isotope analysis of dissolved organic carbon size classes using size exclusion chromatography coupled to an isotope ratio mass spectrometer.

PubMed

Malik, Ashish; Scheibe, Andrea; LokaBharathi, P A; Gleixner, Gerd

2012-09-18

Stable isotopic content of dissolved organic carbon (δ(13)C-DOC) provides valuable information on its origin and fate. In an attempt to get additional insights into DOC cycling, we developed a method for δ(13)C measurement of DOC size classes by coupling high-performance liquid chromatography (HPLC)-size exclusion chromatography (SEC) to online isotope ratio mass spectrometry (IRMS). This represents a significant methodological contribution to DOC research. The interface was evaluated using various organic compounds, thoroughly tested with soil-water from a C3-C4 vegetation change experiment, and also applied to riverine and marine DOC. δ(13)C analysis of standard compounds resulted in excellent analytical precision (≤0.3‰). Chromatography resolved soil DOC into 3 fractions: high molecular weight (HMW; 0.4-10 kDa), low molecular weight (LMW; 50-400 Da), and retained (R) fraction. Sample reproducibility for measurement of δ(13)C-DOC size classes was ±0.25‰ for HMW fraction, ± 0.54‰ for LMW fraction, and ±1.3‰ for R fraction. The greater variance in δ(13)C values of the latter fractions was due to their lower concentrations. The limit of quantification (SD ≤0.6‰) for each size fraction measured as a peak is 200 ng C (2 mg C/L). δ(13)C-DOC values obtained in SEC mode correlated significantly with those obtained without column in the μEA mode (p < 0.001, intercept 0.17‰), which rules out SEC-associated isotopic effects or DOC loss. In the vegetation change experiment, fractions revealed a clear trend in plant contribution to DOC; those in deeper soils and smaller size fractions had less plant material. It was also demonstrated that the technique can be successfully applied to marine and riverine DOC without further sample pretreatment.

Ursodeoxycholic and deoxycholic acids: Differential effects on intestinal Ca(2+) uptake, apoptosis and autophagy of rat intestine.

PubMed

Rodríguez, Valeria A; Rivoira, María A; Pérez, Adriana del V; Marchionatti, Ana M; Tolosa de Talamoni, Nori G

2016-02-01

The aim of this work was to study the effect of sodium deoxycholate (NaDOC) and ursodeoxycholic acid (UDCA) on Ca(2+) uptake by enterocytes and the underlying mechanisms. Rats were divided into four groups: a) controls, b) treated with NaDOC, c) treated with UDCA d) treated with NaDOC and UDCA. Ca(2+) uptake was studied in enterocytes with different degrees of maturation. Apoptosis, autophagy and NO content and iNOS protein expression were evaluated. NaDOC decreased and UDCA increased Ca(2+) uptake only in mature enterocytes. The enhancement of protein expression of Fas, FasL, caspase-8 and caspase-3 activity by NaDOC indicates triggering of the apoptotic extrinsic pathway, which was blocked by UDCA. NO content and iNOS protein expression were enhanced by NaDOC, and avoided by UDCA. The increment of acidic vesicular organelles and LC3 II produced by NaDOC was also prevented by UDCA. In conclusion, the inhibitory effects of NaDOC on intestinal Ca(2+) absorption occur by decreasing the Ca(2+) uptake by mature enterocytes. NaDOC triggers apoptosis and autophagy, in part as a result of nitrosative stress. In contrast, UDCA increases the Ca(2+) uptake by mature enterocytes, and in combination with NaDOC acts as an antiapoptotic and antiautophagic agent normalizing the transcellular Ca(2+) pathway. Copyright © 2015 Elsevier Inc. All rights reserved.

A Source of Terrestrial Organic Carbon to Investigate the Browning of Aquatic Ecosystems

PubMed Central

Lennon, Jay T.; Hamilton, Stephen K.; Muscarella, Mario E.; Grandy, A. Stuart; Wickings, Kyle; Jones, Stuart E.

2013-01-01

There is growing evidence that terrestrial ecosystems are exporting more dissolved organic carbon (DOC) to aquatic ecosystems than they did just a few decades ago. This “browning” phenomenon will alter the chemistry, physics, and biology of inland water bodies in complex and difficult-to-predict ways. Experiments provide an opportunity to elucidate how browning will affect the stability and functioning of aquatic ecosystems. However, it is challenging to obtain sources of DOC that can be used for manipulations at ecologically relevant scales. In this study, we evaluated a commercially available source of humic substances (“Super Hume”) as an analog for natural sources of terrestrial DOC. Based on chemical characterizations, comparative surveys, and whole-ecosystem manipulations, we found that the physical and chemical properties of Super Hume are similar to those of natural DOC in aquatic and terrestrial ecosystems. For example, Super Hume attenuated solar radiation in ways that will not only influence the physiology of aquatic taxa but also the metabolism of entire ecosystems. Based on its chemical properties (high lignin content, high quinone content, and low C:N and C:P ratios), Super Hume is a fairly recalcitrant, low-quality resource for aquatic consumers. Nevertheless, we demonstrate that Super Hume can subsidize aquatic food webs through 1) the uptake of dissolved organic constituents by microorganisms, and 2) the consumption of particulate fractions by larger organisms (i.e., Daphnia). After discussing some of the caveats of Super Hume, we conclude that commercial sources of humic substances can be used to help address pressing ecological questions concerning the increased export of terrestrial DOC to aquatic ecosystems. PMID:24124511

Environmental assessment of different advanced oxidation processes applied to a bleaching Kraft mill effluent.

PubMed

Muñoz, Iván; Rieradevall, Joan; Torrades, Francesc; Peral, José; Domènech, Xavier

2006-01-01

Different advanced oxidation processes (AOPs) have been applied to remove the organic carbon content of a paper mill effluent originating from the Kraft pulp bleaching process. The considered AOPs were: TiO(2)-mediated heterogeneous photocatalysis, TiO(2)-mediated heterogeneous photocatalysis assisted with H(2)O(2), TiO(2)-mediated heterogeneous photocatalysis coupled with Fenton, photo-Fenton, ozonation and ozonation with UV-A light irradiation. The application of the selected AOPs all resulted in a considerable decrease in dissolved organic carbon (DOC) content with variable treatment efficiencies depending upon the nature/type of the applied AOP. A Life Cycle Assessment (LCA) study was used as a tool to compare the different AOPs in terms of their environmental impact. Heterogeneous photocatalysis coupled with the Fenton's reagent proved to have the lowest environmental impact accompanied with a moderate-to-high DOC removal rate. On the other hand, heterogeneous photocatalysis appeared to be the worst AOP both in terms of DOC abatement rate and environmental impact. For the studied AOPs, LCA has indicated that the environmental impact was attributable to the high electrical energy (power) consumption necessary to run a UV-A lamp or to produce ozone.

Effect of inorganic N enrichment on basal pelagic production in boreal unproductive lakes along a gradient of DOC concentration - results after 1 year of fertilization

NASA Astrophysics Data System (ADS)

Deininger, Anne; Bergström, Ann-Kristin

2013-04-01

Input of inorganic nitrogen (N) in boreal unproductive lakes is steadily increasing due to anthropogenic deposition and usage of artificial fertilizers. N enrichment is predicted to have a major impact on the ecosystem productivity and food web structure in unproductive clear-water and humic lakes. For a long time, pelagic primary production (PP) has been mainly regarded as being phosphorus (P) limited. However, recent studies have shown that this is not true for unproductive lakes in northern Sweden, where phytoplankton is mainly N limited. Addition of inorganic N should therefore increase phytoplankton growth in these lake ecosystems. Bacterial production (BP) in the pelagic habitat, on the other hand, is usually limited by P. Nevertheless, elevated N could have a stimulating effect on BP through enhanced leakage of dissolved organic carbon (DOC) from phytoplankton following enhanced N availability and higher PP. Further, unproductive lakes vary naturally in their DOC content which affects overall nutrient- (N and P), energy- and carbon availability (light, C) for the basal producers (phytoplankton, bacteria). It is still not clear how higher inorganic N availability affects primary- and bacterial production in the pelagic in lakes with varying DOC content. We subsequently assessed this question by conducting whole-lake fertilization experiments with inorganic N additions in 6 lakes with varying DOC concentrations (2 low DOC; 2 medium DOC; 2 high DOC). For each DOC level one lake functioned as a reference and one was fertilized with N. Year 2011 was a reference year (all lakes) and 2012 was the first year of fertilization (i.e. in 3 lakes). Measurements included basal productivity such as primary production and bacteria production, lake water chemistry and physical parameters (i.e. light, temperature). The results of this study will help to develop a conceptual understanding of how increased inorganic N availability (through land use such as forestry and/or enhanced N deposition) affects basal productivity in boreal lakes which can have consequences for overall whole lake-ecosystem productivity and functioning.

Application of a UV-Vis submersible probe for capturing changes in DOC concentrations across a mire complex during the snowmelt and summer periods

NASA Astrophysics Data System (ADS)

Avagyan, Armine; Runkle, Benjamin; Kutzbach, Lars

2013-04-01

An accurate quantification of dissolved organic carbon (DOC) is crucial for understanding changes in water resources under the influence of climate, land use and urbanization. However, the conventionally used methods do not allow high frequency in situ analyses in remote or hostile environments (e.g., industrial wastewater or during environmental high-flow events, such as snowmelt or floods). In particular, missing measurements during the snowmelt period in landscapes of the boreal region can lead to significant miscalculations in regional carbon budgets. Therefore, the aim of the study was to test the performance of a portable, submersible UV-Vis spectrophotometer (spectro::lyser, s::can Messtechnik GmbH, Austria) during the snowmelt period in a boreal mire-forest catchment, and to provide a conceptual understanding of the spatial and temporal dynamics of DOC concentrations during and after snowmelt. During 2011, water samples were collected from the near-pristine Ust-Pojeg mire complex in northwestern Russia (61° 56'N, 50° 13'E). Sampling started during the spring snowmelt period and continued until late fall. The mire presented a mosaic of different landscape units. The mire consisted of minerogeous (fen), ombrogenous (bog), and transitional forest-mire (lagg) zones. Water samples were taken from the surface across the mire (22 points at 50-m intervals). DOC concentrations were analyzed directly at the study site using a portable, submersible UV-Vis spectrophotometer, which uses high-resolution absorbance measurements over the wavelength range 200-742.5 nm at 2.5-nm intervals as a proxy for DOC content. Because the DOC composition of fluids varies by site, a local calibration replaced the default settings of the spectro::lyser (Global Calibration) to enhance the accuracy of the measurements. To evaluate the local calibration and correct for drift, the same samples (n = 157) were additionally analyzed using the wet persulfate oxidation method (O-I-Analytica, Aurora Model 1030, USA). Based on ordinary least squares regression, the local calibration showed good agreement between the results obtained from the high-resolution absorption measurements and the wet persulfate oxidation method (r2= 0.99, root-mean-square error = 1.7 mg L-1). The measurement campaign revealed spatial and temporal variability of DOC concentrations, and demonstrated that at the beginning of the snowmelt period, surface carbon was flushed away by meltwater, whereas deeper layers remained frozen. During this time, the surface DOC concentrations fluctuated within the range of 8-15 mg L-1 (April 07) across the entire mire complex. After April 18, the concentrations diverged between the sites; the DOC concentration reached 30 mg L-1in the surface water at the lagg zone but was 15 mg L-1 at the bog site (April 25). The DOC surface water concentration continued to increase during summer and fall, ranging from 19 to 74 mg L-1 across the mire, with an average of 45 ± 14 mg L-1. The study indicates that high-resolution spectroscopic measurements provide a simple, fast, robust and non-destructive method for measuring DOC contents, with a short duration (17-20 seconds) and portability of the sample analysis rendering this method particularly advantageous for in-situ measurements at remote field locations.

Dissolved organic carbon biodegradability from leaf litter leachates of riparian tropical trees

NASA Astrophysics Data System (ADS)

Bastianoni, A.; Montoya, J. V.; Mendez, C.; Paolini, J.

2012-04-01

It is generally assumed that leaf litter with varying chemical composition may show different rates of mass loss, dissolved organic carbon (DOC) release, and DOC biodegradability. Leaf litter is composed of different organic compounds, which may differ in their release rates. Some authors consider leaf litter chemical quality (carbon to nitrogen ratio (C:N) and polyphenolics content) as an indicator of leaf litter mass losses and DOC released into stream water through leaching. In this research, we determined if leachate's DOC biodegradability exhibited a positive relationship with leaf litter chemical quality and leaf litter mass loss due to leaching. In order to test these hypotheses, leaf litter from six riparian tree species (Bambusa vulgaris; Castilla elastica; Artocarpus altilis; Cecropia peltata; Hura crepitans and Ficus maxima), present in the lower reaches of a fifth-order stream in northern Venezuela was collected during the dry season of 2010. To evaluate leaf litter mass loss, air-dried leaves were incubated in Milli-Q water at room temperature in the dark. After 1h, 6h, 1d, 2d, 4d, 8d and 15d, microcosms were removed from the assay to determine remaining mass. DOC biodegradability was measured using 24 h leachates that were added into a 1L glass flask containing 250mL of unfiltered stream water, 4g of stream sediment, and nutrient amendments until all incubations had equal initial DOC concentrations. Biodegradability of DOC was measured at 0, 1, 2, 5 and 7 days as the decrease in DOC concentration through time. Chemical characterization of leaf litter involved the determination of total concentrations of C, N, and poliphenolics. Three replicates were used for all analyses. Initial chemical characterization of leaf litter showed that only two species (C. elastica and A. altilis), had similar C:N ratios (~31). The other four species, showed different C and N contents but presented C:N ratios between 21 and 23. Total polyphenolics content varied greatly among species. Based on the degree of DOC biodegradability, after 1d of incubation, all species could be grouped into three distinct categories (high, intermediate and low). Then, biodegradability of DOC declined steadily until reaching near-constant values at day 7 probably reflecting less availability of labile C compounds. Breakdown rates were not significantly correlated with DOC decay rates (r=-0.580, P =0.228, n=6). However when the remaining DOC and the remaining mass for all species was evaluated, a significant negative correlation was observed (r=-0.567, P =0.014, n=18) contradicting our initial hypothesis. Such results might be a consequence of the presence of secondary metabolites alongside labile DOC in some species leachates which could prevent microbial C consumption. Therefore, the quality of C released by leaching, measured as its biodegradability, does not seem to have a relationship with the amount of C lost by leaching. This could influence the C budget of the riparian ecosystem since the proportion of C consumed by stream microbes is affected by the chemical quality of leaf litter leachates.

Dynamic Changes of Soil Surface Organic Carbon under Different Mulching Practices in Citrus Orchards on Sloping Land

PubMed Central

Gu, Chiming; Liu, Yi; Mohamed, Ibrahim; Zhang, Runhua; Wang, Xiao; Nie, Xinxin; Jiang, Min; Brooks, Margot; Chen, Fang; Li, Zhiguo

2016-01-01

Mulching management has been used in many places all over the world to improve agricultural sustainability. However, the cycling of carbon in the soil under applications of mulch on sloping arable land is not yet fully understood. A four-year field experiment was carried out in Xiaofuling watershed of Danjiangkou reservoir in China. The object was to evaluate the effects of the application of straw mulch (ST) and grass mulch (GT) on dynamic changes in soil organic carbon and its fractions. Results showed that mulch applied on the soil surface increased the contents of SOC and its active fractions in the soil. Compared to the control without cover (CK), ST and GT treatments increased the contents of SOC, LOC, DOC, POC and EOC by 14.73%, 16.5%, 22.5%, 41.5% and 21%, respectively, in the 0–40 cm soil layer, and by 17%, 14%, 19%, and 30%, respectively, in the 0–100 cm soil layer. The contents of organic carbon and its active fractions decreased with increasing soil depth in all of the treatments. SOC was accumulated in the period of December to the following March. The contents of soil DOC and LOC were high in January to March, while the contents of soil POC and EOC were high in June to September. The relative contents of soil organic carbon fractions were POC > EOC > LOC > DOC over the four years. Straw mulching had no significant effect on the changes in soil organic carbon active fractions during the different periods. Based on this long-term field experiment in Danjiangkou reservoir, we found that straw mulching had a significant effect on soil, increasing SOC content and stock in slopping arable land, and that live grass mulching was more effective than rice straw mulching. We discuss possible optimal periods for the implementation of mulching practices on sloping land. PMID:28030551

Dynamic Changes of Soil Surface Organic Carbon under Different Mulching Practices in Citrus Orchards on Sloping Land.

PubMed

Gu, Chiming; Liu, Yi; Mohamed, Ibrahim; Zhang, Runhua; Wang, Xiao; Nie, Xinxin; Jiang, Min; Brooks, Margot; Chen, Fang; Li, Zhiguo

2016-01-01

Mulching management has been used in many places all over the world to improve agricultural sustainability. However, the cycling of carbon in the soil under applications of mulch on sloping arable land is not yet fully understood. A four-year field experiment was carried out in Xiaofuling watershed of Danjiangkou reservoir in China. The object was to evaluate the effects of the application of straw mulch (ST) and grass mulch (GT) on dynamic changes in soil organic carbon and its fractions. Results showed that mulch applied on the soil surface increased the contents of SOC and its active fractions in the soil. Compared to the control without cover (CK), ST and GT treatments increased the contents of SOC, LOC, DOC, POC and EOC by 14.73%, 16.5%, 22.5%, 41.5% and 21%, respectively, in the 0-40 cm soil layer, and by 17%, 14%, 19%, and 30%, respectively, in the 0-100 cm soil layer. The contents of organic carbon and its active fractions decreased with increasing soil depth in all of the treatments. SOC was accumulated in the period of December to the following March. The contents of soil DOC and LOC were high in January to March, while the contents of soil POC and EOC were high in June to September. The relative contents of soil organic carbon fractions were POC > EOC > LOC > DOC over the four years. Straw mulching had no significant effect on the changes in soil organic carbon active fractions during the different periods. Based on this long-term field experiment in Danjiangkou reservoir, we found that straw mulching had a significant effect on soil, increasing SOC content and stock in slopping arable land, and that live grass mulching was more effective than rice straw mulching. We discuss possible optimal periods for the implementation of mulching practices on sloping land.

Precipitation regime effects on the transport of microbial-derived organic matter from soils to surface waters

NASA Astrophysics Data System (ADS)

Pissarello, Anna; Lechtenfeld, Oliver; Miltner, Anja; Kästner, Matthias

2017-04-01

In the last decades, decreases in soil organic matter (SOM) content and increases of dissolved organic carbon (DOC) concentrations in surface water bodies have been recorded in the northern hemisphere. These have severe consequences for soil fertility and for drinking water purification, respectively. We hypothesize that microbially degraded SOM is a potential source of the additional DOC in the surface water. Recently, rain events have become more extreme, resulting in longer droughts and more intense rain events. These changes in the precipitation regime may increase the input of DOC into surface waters, which occurs mainly directly after heavy rain events. Therefore, our interest was to evaluate the role of variations of the water regime on the mobilization of the DOC from soil organic matter to soil solution. Flow-through column experiments were conducted under extreme precipitation scenarios (from continuously wet to pronounced drying and rewetting) in the laboratory in order to test how fluctuation in the water content influences DOC concentration and composition in the leachates. In our experiment we analyzed both soil respiration and DOM mobilization and found that the increased DOM mobilization after heavy rain events was also an effect of increased microbial activity after the drought stress was relieved. Furthermore, we considered that an important contribution to DOC formation and export may come from microbial processing of microbial biomass residues, residing within the particulate organic matter (POM) fraction. Therefore our aim was to link the necromass contribution to the exported DOC by characterizing DOC leachates of the soil columns at the molecular level and comparing them to fractions of bacterial DOC and POC obtained from an Escherichia coli pure culture, by using ultra-high-resolution methods such as Electrospray Ionization and Matrix assisted laser desorption/ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICR-MS and MALDI-FTICR-MS, respectively). The results help to relate the origin of organic matter to typical chemical composition patterns and to allow quantification of the relative contributions of plant and microbe-derived material to NOM and how they are affected by the different water regimes. The results of this experiment consent to link SOM degradation and DOC mobilization and to understand the role of water regime variations for these processes.

Reclamation of zinc-contaminated soil using a dissolved organic carbon solution prepared using liquid fertilizer from food-waste composting.

PubMed

Chiang, Po-Neng; Tong, Ou-Yang; Chiou, Chyow-San; Lin, Yu-An; Wang, Ming-Kuang; Liu, Cheng-Chung

2016-01-15

A liquid fertilizer obtained through food-waste composting can be used for the preparation of a dissolved organic carbon (DOC) solution. In this study, we used the DOC solutions for the remediation of a Zn-contaminated soil (with Zn concentrations up to 992 and 757 mg kg(-1) in topsoil and subsoil, respectively). We then determined the factors that affect Zn removal, such as pH, initial concentration of DOC solution, and washing frequency. Measurements using a Fourier Transform infrared spectrometer (FT-IR) revealed that carboxyl and amide were the major functional groups in the DOC solution obtained from the liquid fertilizer. Two soil washes using 1,500 mg L(-1) DOC solution with a of pH 2.0 at 25°C removed about 43% and 21% of the initial Zn from the topsoil and subsoil, respectively. Following this treatment, the pH of the soil declined from 5.4 to 4.1; organic matter content slightly increased from 6.2 to 6.5%; available ammonium (NH4(+)-N) content increased to 2.4 times the original level; and in the topsoil, the available phosphorus content and the exchangeable potassium content increased by 1.65 and 2.53 times their initial levels, respectively. Copyright © 2015 Elsevier B.V. All rights reserved.

Chemical and sensory characterization of DOC red wines from Marche (Italy) related to vintage and grape cultivars.

PubMed

Boselli, Emanuele; Boulton, Roger B; Thorngate, John H; Frega, Natale G

2004-06-16

Monomeric phenols, color and copigmentation parameters, pigments with different chemical structure, tannin, glucose, fructose, glycerol, ethanol, and organic acids were determined in DOC red wines from Marche (Italy), obtained during three different vintages ranging from 1996 to 2000. The intensity of the bitter and astringent tastes of the wines was determined with panel tastings. Lacrima di Morro and Vernaccia di Serrapetrona (obtained from local cultivars) were different from Rosso Piceno, Rosso Piceno Superiore, and Rosso Conero (produced from different percentages of Sangiovese and Montepulciano). Vernaccia, a red, sweet, "spumante" wine, was an outlier. Lacrima showed a low tannin content, a high content of small pigments and phenols, and a high ratio of copigmented color, which persisted after 3 years of aging. The chemical determinations accounted for a high percentage of variability of measured panel astringency, copigmented color, and measured wine absorbance at 520 nm. It was not possible to create a predictive model for bitterness.

δ13C Analysis of Dissolved Organic Carbon in Eastern Canadian Coastal Waters

NASA Astrophysics Data System (ADS)

Gelinas, Y.; Barber, A.

2016-12-01

The application of carbon stable isotope analysis on dissolved organic carbon (δ13C-DOC) from natural seawater samples has been limited owing to the difficulty of such analysis, with order of magnitude differences between interfering ions and analyte concentrations. High temperature catalytic oxidation allows for the separation of interferences from the organic carbon by precipitation on quartz chips upstream from the oxidation catalyst. Unlike wet chemical oxidation, where salts inhibit the oxidation of organic matter to CO2 via side reactions between the salt anions and the persulfate oxidizing agent, high temperature combustion ensures complete organic matter oxidation in a stream of O2. Using a programmable chemical trap to switch carrier gasses from O2 to He, the OI 1030C combustion unit can be coupled to and IRMS, allowing for the analysis of low DOC content saline waters with relatively high throughput. The analytical limitations and large water volumes traditionally required for these types of analyses have prevented any large-scale δ13C-DOC studies. Here we present DOC concentrations and δ13C-DOC signatures for surface and bottom waters obtained along Canada's East Coast. Included in the study are samples from the Esquiman channel (between Newfoundland and Labrador), Lake Melville, the Saglek and Nachvak Fjords, the Hudson Strait and finally covering the salinity gradient across the Gulf of the St. Lawrence, the St. Lawrence Estuary and the Saguenay Fjord. Measured δ13C-DOC signatures ranged from predominantly marine values of -21.3 ± 0.6 ‰ (vs. VPDB) off the coast of Newfoundland to predominantly terrestrial signatures of -25.8 ± 0.1‰ in Lake Melville. Overall, proper blank subtraction using the isotope mass balance equation and four replicate injections are crucial for the collection of meaningful high quality δ13C-DOC signatures on natural abundance, seawater samples.

[Effects of Different Land Uses on Soil Active Organic Carbon and Nitrogen Fractions in Jinyun Mountain].

PubMed

Qi, Xin; Jiang, Chang-sheng; Hao, Qing-ju; Li, Jian-lin

2015-10-01

In this paper, we take Jinyun Mountain where located in Beibei district of Chongqing as the research object and explore the effect of different ways of land use on soil active organic carbon, nitrogen components by collecting the soil samples from 0 to 60 cm depth in subtropical evergreen broad-leaved forest (hereinafter referred to as the forest), abandoned land, orchard, farmland and measuring the content of MBC, MBN, DOC and DON. The research results show that the contents of soil MBC, MBN, DOC, DON are reduced with the increase of soil depth in four types of land using soils. Variance analysis of the single factor shows that four kinds of land uses have no significant difference in the contents of MBC, MBN and DON, but the DOC content of the abandoned land is significantly higher than that of other three kinds. It shows that the different ways of land use have no obvious effects on soil MBC, MBN and DON but the abandonment of slope cropland can significantly increase the content of soil DOC. There is no significant difference among the distribution ratio of MBN, DOC, DON in forest, abandoned land, orchard and farmland within the soil from 0 to 60 cm, but the distribution ratio of slope MBC is significantly higher than that of other three kinds. It means farmland soil organic carbon has a higher biological activity, this could due to the application of green manure, farmland manure and other organic fertilizers. Under different land utilizations, DOC/DON is the highest, MBC/MBN is the second, and SOC/TN is the lowest. It means the biological solidification of dissolved organic matter is the strongest, and the mineralization of soil organic matter is the most obvious. Under the four kinds of land uses, there are the lowest ratios in SOC/TN, MBC/MBN and DOC/DON in the farmland. And all the ratios are less than 20, which suggest that the mineralization of farmland soil organic matter is stronger and it's easy to cause the loss of soil carbon.

Dissolved organic matter composition of Arctic rivers: Linking permafrost and parent material to riverine carbon

USGS Publications Warehouse

O’Donnell, Jonathan A.; Aiken, George R.; Swanson, David K.; Santosh, Panda; Butler, Kenna D.; Baltensperger, Andrew P.

2016-01-01

Recent climate change in the Arctic is driving permafrost thaw, which has important implications for regional hydrology and global carbon dynamics. Permafrost is an important control on groundwater dynamics and the amount and chemical composition of dissolved organic matter (DOM) transported by high-latitude rivers. The consequences of permafrost thaw for riverine DOM dynamics will likely vary across space and time, due in part to spatial variation in ecosystem properties in Arctic watersheds. Here we examined watershed controls on DOM composition in 69 streams and rivers draining heterogeneous landscapes across a broad region of Arctic Alaska. We characterized DOM using bulk dissolved organic carbon (DOC) concentration, optical properties, and chemical fractionation and classified watersheds based on permafrost characteristics (mapping of parent material and ground ice content, modeling of thermal state) and ecotypes. Parent material and ground ice content significantly affected the amount and composition of DOM. DOC concentrations were higher in watersheds underlain by fine-grained loess compared to watersheds underlain by coarse-grained sand or shallow bedrock. DOC concentration was also higher in rivers draining ice-rich landscapes compared to rivers draining ice-poor landscapes. Similarly, specific ultraviolet absorbance (SUVA254, an index of DOM aromaticity) values were highest in watersheds underlain by fine-grained deposits or ice-rich permafrost. We also observed differences in hydrophobic organic acids, hydrophilic compounds, and DOM fluorescence across watersheds. Both DOC concentration and SUVA254 were negatively correlated with watershed active layer thickness, as determined by high-resolution permafrost modeling. Together, these findings highlight how spatial variations in permafrost physical and thermal properties can influence riverine DOM.

Seasonal Dynamics of Soil Labile Organic Carbon and Enzyme Activities in Relation to Vegetation Types in Hangzhou Bay Tidal Flat Wetland

PubMed Central

Shao, Xuexin; Yang, Wenying; Wu, Ming

2015-01-01

Soil labile organic carbon and soil enzymes play important roles in the carbon cycle of coastal wetlands that have high organic carbon accumulation rates. Soils under three vegetations (Phragmites australis, Spartina alterniflora, and Scirpusm mariqueter) as well as bare mudflat in Hangzhou Bay wetland of China were collected seasonally. Seasonal dynamics and correlations of soil labile organic carbon fractions and soil enzyme activities were analyzed. The results showed that there were significant differences among vegetation types in the contents of soil organic carbon (SOC) and dissolved organic carbon (DOC), excepting for that of microbial biomass carbon (MBC). The P. australis soil was with the highest content of both SOC (7.86 g kg-1) and DOC (306 mg kg-1), while the S. mariqueter soil was with the lowest content of SOC (6.83 g kg-1), and the bare mudflat was with the lowest content of DOC (270 mg kg-1). Soil enzyme activities were significantly different among vegetation types except for urease. The P. australis had the highest annual average activity of alkaline phosphomonoesterase (21.4 mg kg-1 h-1), and the S. alterniflora had the highest annual average activities of β-glycosidase (4.10 mg kg-1 h-1) and invertase (9.81mg g-1 24h-1); however, the bare mudflat had the lowest activities of alkaline phosphomonoesterase (16.2 mg kg-1 h-1), β-glycosidase (2.87 mg kg-1 h-1), and invertase (8.02 mg g-1 24h-1). Analysis also showed that the soil labile organic carbon fractions and soil enzyme activities had distinct seasonal dynamics. In addition, the soil MBC content was significantly correlated with the activities of urease and β-glucosidase. The DOC content was significantly correlated with the activities of urease, alkaline phosphomonoesterase, and invertase. The results indicated that vegetation type is an important factor influencing the spatial-temporal variation of soil enzyme activities and labile organic carbon in coastal wetlands. PMID:26560310

Using CDOM optical properties for estimating DOC concentrations and pCO 2 in the Lower Amazon River

DOE Office of Scientific and Technical Information (OSTI.GOV)

Valerio, Aline de Matos; Kampel, Milton; Vantrepotte, Vincent

Colored dissolved organic matter (CDOM) is largely responsible for the optical properties of freshwaters and coastal areas and can be used as a proxy to assess the non-optical carbon content as the dissolved organic carbon (DOC) and the partial pressure of carbon dioxide (pCO 2). Nevertheless, riverine studies that explores the former relationship are more challenging due to the spectral mixture caused by the high content of inorganic materials in the suspended sediment. Here we evaluate the spatial-temporal variability of CDOM, DOC and pCO 2, as well as the potential of CDOM absorption coefficient (aCDOM(412)) for estimating DOC concentration andmore » pCO 2 along the lower Amazon River. Our results revealed differences in the dissolved organic matter (DOM) quality between clear water (CW) tributaries and the Amazon River mainstem. A linear relationship between DOC and CDOM was observed when tributaries and mainstem are evaluated separately (Amazon waters: N=42, R2=0.74; CW: N= 13, R2 = 0.57). However, this linear relationship was not observed during periods of higher rainfall and river discharge, requiring a model specific to these time periods to be developed (N = 25, R2 = 0.58). A strong linear positive relation was found between aCDOM(412) and pCO 2( N=69, R2=0.65) along the lower river. pCO 2 was less affected by the optical difference between tributaries and mainstem water or by the presence of higher hygrometric conditions when compared to CDOM to DOC relationships. Including the river water temperature in the model improves our ability to estimate pCO 2 (N=69; R2 = 0.80). Our results also illustrate the complexity of DOM temporal dynamics in the lower Amazon River where the occurrence of extreme high and low discharge due to factors such as El Niño, can significantly alter the expected seasonal oscillation, as was the case during this study period. The ability to remotely assess both DOC and pCO 2 from CDOM optical properties highlight the importance of using remote sensing data for monitoring carbon dynamics in large running water systems worldwide.« less

Preliminary biogeochemical assessment of EPICA LGM and Holocene ice samples

NASA Astrophysics Data System (ADS)

Bulat, S.; Alekhina, I.; Marie, D.; Wagenbach, D.; Raynaud, D.; Petit, J. R.

2009-04-01

We are investigating the biological content (biomass and microbial diversity of Aeolian origin) of EPICA ice core within the frame of EPICA Microbiology consortium*. Two ice core sections were selected from EPICA Dome C and Droning Maud Land, both from LGM and Holocene. Preliminary measurements of DOC (dissolved organic content) and microbial cell concentrations have been performed. Both analyses showed the very low biomass and ultra low DOC content. Trace DNA analyses are in a progress. The ice sections were decontaminated in LGGE cold and clean room facilities benefiting the protocol developed for Vostok ice core studies. The melt water was then shared between two party laboratories for a complementary approach in studying microbial content. Prior to biology the melt water was tested for chemical contaminant ions and organic acids, DOC and dust contents. The biological methods included all the spectra of appropriate molecular techniques (gDNA extraction, PCR, clone libraries and sequencing). As preliminary results, both LGM (well identified by dust fallout) and Holocene ice samples (EDC99 and EDML) proved to be extremely clear (i.e. pristine) in terms of biomass (less then 4 cells per ml) and DOC contents (less then 5 ppbC). There was no obvious difference between LGM and Holocene in cell counts, while LGM showed a bit high organic carbon content. The latter in terms of biology means ultra-oligotrophic conditions (i.e., no possibility for heterotrophic life style). In fact no metabolizing microbial cells or propagating populations are expected at these depths at temperature -38oC and lower (limiting life temperature threshold is -20°C). Nevertheless some life seeds brought in Antarctica with precipitation could be well preserved because the age is rather young (21 kyr and less). Trying to identify these aliens and document their distribution during last climate cycle the meltwater was concentrated about 1000 times down. The genomic DNA was extracted and very weak signals were possible to generate which are now under cloning. The signals were hard to reproduce because of rather low volume of samples. More ice volume is needed to get the biosignal stronger and reproducible. Meantime we are adjusting PCR and in addition testing DNA repair-enzyme cocktail in case of DNA damage. As a preliminary conclusion we would like to highlight the following. Both Holocene and LGM ice samples (EDC99 and EDML) are very clean in terms of Ultra low biomass and Ultra low DOC content. The most basal ice of EDC and EDML ice cores could help in assessing microbial biomass and diversity if present under the glacier at the ice-bedrock boundary. * The present-day consortium includes S. Bulat, I. Alekhina, P. Normand, D. Prieur, J-R. Petit and D. Raynaud (France) and E. Willerslev and J.P. Steffensen (Denmark)

Microbial availability and size fractionation of dissolved organic carbon after drought in an intermittent stream: biogeochemical link across the stream-riparian interface.

PubMed

Romaní, Anna M; Vázquez, Eusebi; Butturini, Andrea

2006-10-01

The evolution of dissolved organic carbon (DOC) molecular-weight fractions, DOC biodegradability (BDOC), DOC origin [fluorescence index (FI)], and enzyme activities between the stream waters (main and ephemeral channel) and ground waters (riparian and hillslope) were analyzed during the transition from drought to precipitation in a forested Mediterranean stream. After the first rains, DOC content in stream water reached its maximum value (10-18 mg L(-1)), being explained by the leaching of deciduous leaves accumulated on the stream bed during drought. During this period, the largest molecules (>10 kDa), were the most biodegradable, as indicated by high BDOC values measured during storm events and high enzymatic activities (especially for leucine-aminopeptidase). DOC >100 kDa was strongly immobilized (78%) at the stream-riparian interface, whereas the smallest molecules (<1 kDa) were highly mobile and accumulated in ground waters, indicating their greater recalcitrance. Differential enzymatic patterns between compartments showed a fast utilization of polysaccharides in the flowing water but a major protein utilization in the ground water. The results of the FI indicated a more terrestrial origin of the larger molecules in the flowing water, also suggesting that transformation of material occurs through the stream-riparian interface. Microbial immobilization and fast utilization of the most biodegradable fraction at the stream-riparian interface is suggested as a relevant DOC retention mechanism just after initial recharging of the ground water compartment. Large and rapid DOC inputs entering the intermittent river system during the transition from drought to precipitation provide available N and C sources for the heterotrophs. Heterotrophs efficiently utilize these resources that were in limited supply during the period of drought. Such changes in C cycling may highlight possible changes in organic matter dynamics under the prediction of extended drying periods in aquatic ecosystems.

How does organic matter occurrence set limit onto the use of Ce anomaly as a reliable proxy of redox conditions in shallow groundwaters?

NASA Astrophysics Data System (ADS)

Dia, A.; Gruau, G.; Davranche, M.; Vidy, A.; Henin, O.; Petitjean, P.; Le Coz-Bouhnik, M.

2003-04-01

This study is dedicated to the effects of organic matter on the hydrochemistry of Rare Earth Elements (REE) and the ability of using the Ce anomaly as a reliable proxy of redox conditions in surface waters when organic matter occurs. The data include a : i) two-year survey of SREE and Ce anomalies in organic-rich waters recovered from a catchment located in Brittany (western Europe) and (ii) experimental incubation of organic soils from this catchment set under controlled conditions, as well as, (iii) a REE speciation calculation in both the natural organic-rich waters from the wetlands and the experimental solutions. Field and experimental data appear to be extremely coherent, displaying good correlation between the SREE, the Dissolved Organic Carbon (DOC) contents and the redox state. The field data show a strong increase of the SREE and DOC concentrations in soil waters when the environment becomes more reducing. The onset of DOC and SREE contents is seen to be in phase with the increase of dissolved Fe and Mn. The role of Fe-, Mn-oxyhydroxides is confirmed by the experimental data as the maximum of DOC and SREE content is reached when Fe2+ reaches a maximum in the soil solution, suggesting that reductive dissolution of Fe, Mn-oxyhydroxides happens. Despite the strong redox changes and the known redox sensitive behaviour of Ce as compared to other REE, none Ce anomaly variation is observed during either, the experimental procedure, or the field survey through time. Speciation calculations were performed showing that in both such pH range and moderately oxidizing waters in DOC-rich waters, REE should have an organic speciation. Such an organic speciation prevents the formation of Ce(IV) and therefore the development of any Ce anomaly. However, since the studied waters are highly oxidizing (high nitrate contents), the nitrates impose the redox formation of Ce(IV) and a Ce anomaly should appear. Therefore, Ce(IV) is not formed in these waters either because (i) the reaction kinetic might be so slow that the anomaly has no time to ever happen in the field, or (ii) Ce(IV) might be linked to the organic colloidal fraction. Since the thermodynamic modelling does not help getting information, further experimental kinetics or ultrafiltration studies will be required to clarify these latter points. This has to be fixed to be able to use the Ce anomaly as a reliable proxy of redox conditions in organic-rich environment.

Effect of disinfection upon dissolved organic carbon (DOC) in wastewater: bacterial bioassays.

PubMed

Arana, I; Santorum, P; Muela, A; Barcina, I

2000-08-01

Quantitative and qualitative changes in organic matter content of wastewater effluents attributable to chlorination and ozonation have been analysed using bioassays as well as organic carbon direct measures. Bioassays were carried out using the bacterial populations of wastewater and two Escherichia coli strains as test micro-organisms. Our results indicate that pure strains present some advantages over indigenous bacteria. Although wastewater bacterial populations are better adapted to growth in wastewater, E. coli strains are more sensitive to changes in dissolved organic carbon (DOC) content. Moreover, the use of pure cultures allows estimation of the portion of DOC which can be converted in cell biomass, the assimilable organic carbon (AOC). Finally, the results obtained using prototrophic and the auxotrophic strains of E. coli suggested that ozonation alters the amino acid composition of wastewater while chlorination does not change the quantity nor the quality of the DOC present in effluents.

Analysis and modeling of metals release from MBT wastes through batch and up-flow column tests.

PubMed

Pantini, Sara; Verginelli, Iason; Lombardi, Francesco

2015-04-01

The leaching behavior of wastes coming out from Mechanical Biological Treatment (MBT) plants is still poorly investigated in literature. This work presents an attempt to provide a deeper insight about the contaminants release from this type of waste. To this end, results of several batch and up-flow percolation tests, carried out on different biologically treated waste samples collected from an Italian MBT plant, are reported. The obtained results showed that, despite MBT wastes are characterized by relatively high heavy metals content, only a limited amount was actually soluble and thus bioavailable. Namely, the release percentage was generally lower than 5% of the total content with the only exception of dissolved organic carbon (DOC), Zn, Ni and Co with release percentages up to 20%. The information provided by the different tests also allowed to highlight some key factors governing the kinetics release of DOC and metals from this type of material. In particular, results of up-flow column percolation tests showed that metals such as Cr, Mg, Ni and Zn followed essentially the leaching trend of DOC suggesting that these elements were mainly released as organo-compounds. Actually, a strong linear correlation (R(2) > 0.8) between DOC and metals concentration in eluates was observed, especially for Cr, Ni and Zn (R(2)>0.94). Thus, combining the results of batch and up-flow column percolation tests, partition coefficients between DOC and metals concentration were derived. These data, coupled with a simplified screening model for DOC release, allowed to get a very good prediction of metal release during the different column tests. Finally, combining the experimental data with a simplified model provided some useful indications for the evaluation of long-term emissions from this type of waste in landfill disposal scenarios. Copyright © 2014 Elsevier Ltd. All rights reserved.

Chemical characteristics and acidity of soluble organic substances from a northern hardwood forest floor, central Maine, USA

NASA Astrophysics Data System (ADS)

Vance, George F.; David, Mark B.

1991-12-01

Our understanding of the chemistry, structure, and reactions of organic substances in forest floor leachates is limited and incomplete. Therefore, we examined the organic and inorganic chemistry of forest floor leachates collected from a hardwood forest in central Maine over a two-year period (1987-1989), including detailed study of dissolved organic carbon (DOC). Seasonal variations in NH 4+, NO 3-, K +, and total Al were believed due to organic matter decomposition and release. Leaching of other base cations closely followed that of NO 3-. Snowmelt resulted in NO 3- levels that decreased in time due to flushing of mineralization/nitrification by-products that had accumulated during the winter months. Total DOC ranged from 2228 to 7193 μmol L -1 with an average of 4835 μmol L -1. Monosaccharides and polyphenols constituted 3.9% (range of 3.4 to 4.4%) and 3.0% (2.2 to 3.7%) of the DOC, respectively, which suggests DOC may contain partially oxidized products that are possibly of a lignocellulose nature. Fractionation of the forest floor DOC indicated high organic acid contents (hydrophobic and hydrophilic acids) that averaged 92% of the total DOC. Organic acids were isolated and analyzed for elemental content (C, H, N, and S), and determination of UV absorptivity ( E 4/E 6) ratios, CuO oxidation products, FT-IR and 13C-NMR spectra, and acidity by potentiometric titration. Results from these analyses indicate the organic acids in the forest floor leachates are similar to fulvic acids. Hydrophobic and hydrophilic acids had average exchange acidities of 0.126 and 0.148 μeq μmol -1 C, respectively, and pKa, of 4.23 and 4.33. Their FT-IR and 13C-NMR spectra suggest they are primarily carboxylic acids, with aliphatic and aromatic structure. An organic charge contribution model was developed using titration data, DOC fractionation percentages, and the total DOC in the forest floor leachates. Application of the model to all solutions accounted for 97% of the charge balance deficits. Adjusted values for the flux of C and organic acidity due to organic solutes in forest floor leachates indicated translocation of 112 to 260 kg C ha -1 yr -1 and 460 to 1330 eq ha -1 yr -1, respectively, to the underlying mineral subsurface horizons.

[Interactions of straw, nitrogen fertilizer and bacterivorous nematodes on soil labile carbon and nitrogen and greenhouse gas emissions].

PubMed

Zhang, Teng-Hao; Wang, Nan; Liu, Man-Qiang; Li, Fang-Hui; Zhu, Kang-Li; Li, Hui-Xin; Hu, Feng

2014-11-01

A 3 x 2 factorial design of microcosm experiment was conducted to investigate the interactive effects of straw, nitrogen fertilizer and bacterivorous nematodes on soil microbial biomass carbon (C(mic)) and nitrogen (N(mic)), dissolved organic carbon (DOC) and nitrogen (DON), mineral nitrogen (NH(4+)-N and NO(3-)-N), and greenhouse gas (CO2, N2O and CH4) emissions. Results showed that straw amendment remarkably increased the numbers of bacterivorous nematodes and the contents of Cmic and Nmic, but Cmic and Nmic decreased with the increasing dose of nitrogen fertilization. The effects of bacterivorous nematodes strongly depended on either straw or nitrogen fertilization. The interactions of straw, nitrogen fertilization and bacterivorous nematodes on soil DOC, DON and mineral nitrogen were strong. Straw and nitrogen fertilization increased DOC and mineral nitrogen contents, but their influences on DON depended on the bacterivorous nematodes. The DOC and mineral nitrogen were negatively and positively influenced by the bacterivorous nematodes, re- spectively. Straw significantly promoted CO2 and N2O emissions but inhibited CH4 emission, while interactions between nematodes and nitrogen fertilization on emissions of greenhouse gases were obvious. In the presence of straw, nematodes increased cumulative CO2 emissions with low nitrogen fertilization, but decreased CO2 and N2O emissions with high nitrogen fertilization on the 56th day after incubation. In summary, mechanical understanding the soil ecological process would inevitably needs to consider the roles of soil microfauna.

A novel approach combining self-organizing map and parallel factor analysis for monitoring water quality of watersheds under non-point source pollution

PubMed Central

Zhang, Yixiang; Liang, Xinqiang; Wang, Zhibo; Xu, Lixian

2015-01-01

High content of organic matter in the downstream of watersheds underscored the severity of non-point source (NPS) pollution. The major objectives of this study were to characterize and quantify dissolved organic matter (DOM) in watersheds affected by NPS pollution, and to apply self-organizing map (SOM) and parallel factor analysis (PARAFAC) to assess fluorescence properties as proxy indicators for NPS pollution and labor-intensive routine water quality indicators. Water from upstreams and downstreams was sampled to measure dissolved organic carbon (DOC) concentrations and excitation-emission matrix (EEM). Five fluorescence components were modeled with PARAFAC. The regression analysis between PARAFAC intensities (Fmax) and raw EEM measurements indicated that several raw fluorescence measurements at target excitation-emission wavelength region could provide similar DOM information to massive EEM measurements combined with PARAFAC. Regression analysis between DOC concentration and raw EEM measurements suggested that some regions in raw EEM could be used as surrogates for labor-intensive routine indicators. SOM can be used to visualize the occurrence of pollution. Relationship between DOC concentration and PARAFAC components analyzed with SOM suggested that PARAFAC component 2 might be the major part of bulk DOC and could be recognized as a proxy indicator to predict the DOC concentration. PMID:26526140

[Seasonality and contribution to acid rain of the carbon abundance in rainwater].

PubMed

Xu, Tao; Song, Zhi-guang; Liu, Jun-feng; Wang, Cui-ping

2008-02-01

This paper reports the results from a study of the carbon abundance in rainwater of Guangzhou city, China. The determination of TOC, DOC, POC and PEC helps to study the seasonality of carbon abundance and its contribution to the acid rain. The results display the fact that the average contents of TOC, DOC, POC and PEC are 7.10 mg/L, 3.58 mg/L, 3.60 mg/L and 0.72 mg/L, respectively. These results confirm the deep effect of the organic pollutant to the rain. The seasonality exists in the carbon abundance of rainwater. The contents of TOC and DOC are up to the maximum in spring and the minimum in summer; the contribution of POC to TOC in summer is obviously higher than that in other seasons; and the relative content of POC is clearly higher in dry season than that in wet season. The seasonality reflects the more emission of the total pollutant in spring and the solid particle pollutant in summer than those in other seasons. Moreover, the emission of the organic pollutant from the mobile vehicles is more obvious in dry season than that in wet season. The contents of TOC and DOC have the negative correlation to the pH values, which confirms the contribution effect of the organic pollutant, such as vehicle emission, to the acid rain.

Linking aboveground net primary productivity to soil carbon and dissolved organic carbon in complex terrain

NASA Astrophysics Data System (ADS)

Peterson, Fox S.; Lajtha, Kate J.

2013-07-01

Factors influencing soil organic matter (SOM) stabilization and dissolved organic carbon (DOC) content in complex terrain, where vegetation, climate, and topography vary over the scale of a few meters, are not well understood. We examined the spatial correlations of lidar and geographic information system-derived landscape topography, empirically measured soil characteristics, and current and historical vegetation composition and structure versus SOM fractions and DOC pools and leaching on a small catchment (WS1) in the H.J. Andrews Experimental Forest, located in the western Cascades Range of Oregon, USA. We predicted that aboveground net primary productivity (ANPP), litter fall, and nitrogen mineralization would be positively correlated with SOM, DOC, and carbon (C) content of the soil based on the principle that increased C inputs cause C stores in and losses from in the soil. We expected that in tandem, certain microtopographical and microclimatic characteristics might be associated with elevated C inputs and correspondingly, soil C stores and losses. We confirmed that on this site, positive relationships exist between ANPP, C inputs (litter fall), and losses (exportable DOC), but we did not find that these relationships between ANPP, inputs, and exports were translated to SOM stores (mg C/g soil), C content of the soil (% C/g soil), or DOC pools (determined with salt and water extractions). We suggest that the biogeochemical processes controlling C storage and lability in soil may relate to longer-term variability in aboveground inputs that result from a heterogeneous and evolving forest stand.

Analysis of selected chemical parameters in Piemontese wines.

PubMed

Stępień, Agnieszka E; Stawarczyk, Kinga; Bilek, Maciej; Kędziora, Katarzyna M

2015-01-01

Piemontese wines are well known and valued all over the world. The most popular of them are Barolo and Barbaresco wines. However, in Poland, they are still little known and only now are being gradually introduced to a wider range of consumers. The aim of this study was to evaluate the content of inorganic anions, minerals, sugars and glycerol of Piemontese wines from micro-region Langhe, classified as DOCG ("Denominazione di Origine Controllata e Garantita", ie. controlled designation of origin guaranteed) and DOC ("Denominazione di Origine Controllata", ie. controlled designation of origin) products. Seven types of red wines and one type of white wine were tested. High Performance Ion Chromatography with conductometric detection (HPLC-CD) was used to measure the content of inorganic anions, ie. fluorides, chlorides, sulfates and phosphates. Flame atomic absorption spectrometry (F-AAS) was used to measure the content of minerals, ie. magnesium, calcium, sodium, copper, potassium, zinc and iron, while High Performance Liquid Chromatography with charged aerosol detection (HPLC-CAD) was used to measure the content of glycerol and sugars, ie. fructose, glucose and sucrose. Our studies show that although Piemontese wines are characterized by a relatively low content of minerals in comparison with the wines from other regions, they contain a lot of ingredients that have beneficial effects for human health. Moreover, we observed that the studied wines contain particularly high concentration of inorganic ions--phosphates and fluorides. Furthermore, all tested red wines show far reaching similarities in their chemical properties, which is possibly a direct consequence of using in their production locally cultivated grape varieties. Analysis of the wines from the Piemont region, classified as DOCG, DOC, confirmed that these are dry wines of a high quality.

The Effects of Permafrost Thaw on Organic Matter Quality and Availability Along a Hill Slope in Northeastern Siberia

NASA Astrophysics Data System (ADS)

Connolly, C. T.; Spawn, S.; Ludwig, S.; Schade, J. D.; Natali, S.

2014-12-01

Climate warming and permafrost thaw in northeastern Siberia are expected to change the quantity and quality of organic matter (OM) transported through watersheds, releasing previously frozen carbon (C) to biologically available pool. Hill slopes have shown to influence the distribution of OM, resulting in a downhill accumulation of available C and nutrients relative to uphill. Here we examine how future permafrost thaw will change OM quality and availability along a hill slope in a larch-dominated watershed. We collected soils from the thawed organic and mineral layers, and 1m deep permafrost cores for dissolved organic C (DOC) and total dissolved N (TDN), C composition from measures of colored dissolved organic matter (CDOM), DOC lability from biodegradable DOC (BDOC) incubations, C and nutrient availability from extracellular-enzyme assays (EEA's), and microbial respiration from aerobic soil incubations. Here we show that organic soils (O), in comparison to mineral soils (M) and permafrost (P) are the most abundant source of C (avg O DOC: 51.6mg/L), exhibiting low molecular complexity (avg O SUVA254: 4.05) and high quality. Evidence suggests permafrost OM may be an equally abundant, and more labile source of C than mineral soils (highest P DOC: 16.1 mg/L, lowest P SUVA254: 6.32; median M DOC: 18.5 mg/L, median M SUVA254: 24.0). Furthermore, we demonstrate that there may be a positive relationship in the rate of C mineralization and distance downhill, showing 15-30% greater CO2 production/gC downhill relative to uphill. Evidence also supports a similar relationship in permafrost DOC content and molecular complexity, showing more DOC of a lower complexity further downhill. This indicates DOC transport may have been occurring through the active layer and downhill during ice-rich permafrost formation, and may supply a labile source of carbon to lowland areas and adjacent stream networks upon thaw.

Geochemistry of aquatic humic substances in the Lake Fryxell basin, Antarctica

USGS Publications Warehouse

Aiken, G.; McKnight, D.; Harnish, R.; Wershaw, R.

1996-01-01

Dissolved organic carbon (DOC) in Lake Fryxell, 10 streams flowing into the lake, and the moat surrounding the lake was studied to determine the influence of sources and biogeochemical processes on its distribution and chemical nature. Lake Fryxell is an amictic, permanently ice-covered lake in the McMurdo Dry Valleys which contains benthic and planktonic microbial populations, but receives essentially no input of organic material from the ahumic soils of the watershed. Biological activity in the water column does not appear to influence the DOC depth profile, which is similar to the profiles for conservative inorganic constituents. DOC values for the streams varied with biomass in the stream channel, and ranged from 0.2 to 9.7 mg C/L. Fulvic acids in the streams were a lower percentage of the total DOC than in the lake. These samples contain recent carbon and appear to be simpler mixtures of compounds than the lake samples, indicating that they have undergone less humification. The fulvic acids from just above the sediments of the lake have a high sulfur content and are highly aliphatic. The main transformations occurring as these fractions diffuse upward in the water column are 1) loss of sulfur groups through the oxycline and 2) decrease in aliphatic carbon and increase in the heterogeneity of aliphatic moieties. The fraction of modem 14C content of the lake fulvic acids range from a minimum of 0.68 (approximately 3000 years old) at 15m depth to 0.997 (recent material) just under the ice. The major processes controlling the DOC in the lake appear to be: 1) The transport of organic matter by the inflow streams resulting in the addition of recent organic material to the moat and upper waters of the lake; 2) The diffusion of organic matter composed of relict organic material and organic carbon resulting from the degradation of algae and bacteria from the bottom waters or sediments of the lake into overlying glacial melt water; 3) The addition of recent organic matter to the bottom waters of the lake from the moat.

Relationships between Δ14C and the molecular quality of dissolved organic carbon in rivers draining to the coast from the conterminous United States

USGS Publications Warehouse

Butman, David; Raymond, Peter A.; Butler, Kenna D.; Aiken, George R.

2012-01-01

Dissolved organic carbon (DOC) in natural waters possesses chemical and molecular qualities indicative of its source and age. The apportionment of DOC by age into millennial and decadal pools is necessary to understand the temporal connection between terrestrial and aquatic ecosystems in the global carbon cycle. We measured Δ14C-DOC and chemical composition indices (specific ultraviolet absorbance (SUVA254), fluorescence index (FI), hydrophobic organic acid fraction (HPOA) content) for 15 large river basins in the conterminous United States. Across all rivers the average proportion of HPOA in DOC correlated strongly with SUVA254 (r2 = 0.93 p < 0.001). Individual Δ14C-DOC ranged from a low of −92.9‰ (726 y.b.p.) in the Colorado River to 73.4‰ (>Modern) in the Altamaha River for the year 2009. When adjusted by total discharge, these U.S. Rivers export modern carbon at between 34 and 46‰, a signal dominated by the Mississippi River. The variation in Δ14C correlates to indices of the aromaticity of the DOC measured by the SUVA254 (r2 = 0.87, p < 0.001), and FI (r2 = 0.6; p < 0.001) as well as differences in annual river discharge (r2 = 0.46, p < 0.006). SUVA254 was further correlated to broad scale vegetation phenology estimated from the Enhanced Vegetation Index derived from the NASA Moderate Resolution Imaging Spectrometer (MODIS). We show that basins with high discharge, high proportions of vegetation cover, and low human population densities export DOC enriched in aromatic material that corresponds to recently fixed atmospheric CO2. Conversely old DOC is exported from low discharge watersheds draining arid regions, and watersheds more strongly impacted by humans. The potential influence from fossil carbon from human inputs to aquatic systems may be important and requires more research.

[Effects of nitrogen addition and elevated CO2 concentration on soil dissolved organic carbon and nitrogen in rhizosphere and non-rhizosphere of Bothriochloa ischaemum].

PubMed

Xiao, Lie; Liu, Guo Bin; Li, Peng; Xue, Sha

2017-01-01

A pot experiment was conducted to study soil dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) in the rhizosphere and non-rhizosphere of Bothriochloa ischaemum in loess hilly-gully region under the different treatments of CO 2 concentrations (400 and 800 μmol·mol -1 ) and nitrogen addition (0, 2.5, 5.0 g N·m -2 ·a -1 ). The results showed that eleva-ted CO 2 treatments had no significant effect on the contents of DOC, dissolved total nitrogen (DTN), DON, dissolved ammonium nitrogen (NH 4 + -N) and dissolved nitrate nitrogen (NO 3 - -N) in the soil of rhizosphere and non-rhizosphere of B. ischaemum. The contents of DTN, DON, and NO 3 - -N in the rhizosphere soil were significantly increased with the nitrogen application and the similar results of DTN and NO 3 - -N also were observed in the non-rhizosphere of B. ischaemum. Nitrogen application significantly decreased DOC/DON in the rhizosphere of B. ischaemum. The contents of DTN, NO 3 - -N and DON in the soil of rhizosphere were significantly lower than that in the non-rhizosphere soil, and DOC/DON was significantly higher in the rhizosphere soil than that in the non-rhizosphere soil. It indicated that short-term elevated CO 2 concentration had no significant influence on the contents of soil dissolved organic carbon and nitrogen. Simulated nitrogen deposition, to some extent, increased the content of soil dissolved nitrogen, but it was still insufficient to meet the demand of dissolved nitrogen for plant growing.

Environmental Dynamics of Dissolved Black Carbon in the Amazon River

NASA Astrophysics Data System (ADS)

Roebuck, J. A., Jr.; Gonsior, M.; Enrich-Prast, A.; Jaffe, R.

2016-02-01

Dissolve black carbon (DBC) is an important component in the global carbon cycle and constitutes a significant portion of dissolved organic carbon (DOC) in aquatic systems. While global fluxes of DBC may be well understood, little is known about systematic processing of this carbon pool in fluvial systems. Similar to DOC, DBC composition may change as it moves throughout a river continuum before it is eventually deposited into the ocean. This is especially important for large river systems that are major sources of DOC to the ocean and may have significant impacts on ocean biogeochemistry and carbon cycling. To better understand variations in DBC dynamics throughout a large fluvial system, DBC was quantified using the benzene polycarboxylic acid method (BPCA) in three major tributaries of the Amazon River, each with varying biogeochemical characteristics. Principal component analysis of the BPCA abundances was used to assess the DBC compositional differences between sampling locations. In some rivers, light availability appeared to influence both DBC quantity and quality. Higher concentrations of DBC characterized by a larger, more aromatic DBC pool was found in the Rio Negro, a black water river with high levels of chromophoric dissolved organic matter and low light penetration. In the Rio Tapajós, a clear water river with higher light penetration, lower DBC concentrations characterized by higher abundances of the less polycondensed DBC pool provided evidence of photodecomposition under such conditions. The Rio Madeira, characterized as a white water river with high suspended sediment yields and high mineral/clay content, had the lowest DBC concentrations and the least polycondensed DBC content, suggesting a preferential adsorption of the more highly polycondensed DBC components onto clay particles.

DocML: A Digital Library of University Data.

ERIC Educational Resources Information Center

Papadakis, Ioannis; Karakoidas, Vassileios; Chrissikopoulos, Vassileios

2002-01-01

Describes DocML, a Web-based digital library of university data that is used to build a system capable of preserving and managing student assignments. Topics include requirements for a digital library of university data; metadata and XML; three-tier architecture; user interface; searching; browsing; content delivery; and administrative issues.…

Assimilation of old carbon by stream food webs in arctic Alaska

NASA Astrophysics Data System (ADS)

O'Donnell, J. A.; Carey, M.; Xu, X.; Koch, J. C.; Walker, J. C.; Zimmerman, C. E.

2017-12-01

Permafrost thaw in arctic and sub-arctic region is mobilizing old carbon (C) from perennially frozen soils, driving the release of old C to the atmosphere and to aquatic ecosystems. Much research has focused on the transport and lability of old dissolved organic C (DOC) as a possible feedback to the climate system following thaw. However, little is known about the role of old C as a source to aquatic food webs in watersheds underlain by thawing permafrost. To quantify the contributions of old C to Arctic stream food-webs, we measured the radiocarbon (Δ14C) and stable isotope (δ13C, δ15N) contents of periphyton, macroinvertebrates, and resident fish species (Arctic Grayling (Thymallus arcticus) and Dolly Varden (Salvelinus malma)). We also characterized the isotopic composition of possible C sources, including DOC, dissolved inorganic carbon (DIC), and soil organic matter. Samples were collected across 10 streams in Arctic Alaska, draining watersheds underlain by varying parent material and ground-ice content, from ice-poor bedrock to ice-rich loess (i.e. Yedoma). Fraction modern (FM) values for Arctic Grayling and Dolly Varden ranged from 0.6720 to 1.0101 (3195 years BP to modern) across all streams, and closely tracked spatial variation in Δ14C content of periphyton. Parent material and ground-ice content appear to govern the age and form of dissolved C sources to stream biota. For instance, in watersheds underlain by ice-poor bedrock, old DIC (< 5000 years BP) was the dominant C source to stream biota, reflecting contributions from carbonate weathering and soil respiration. In streams draining ice-rich Yedoma, high concentrations of younger DOC were the primary C source to stream biota, reflecting leaching of DOC from saturated, peaty soils of the active layer. These findings highlight the importance of permafrost characteristics as a control on subsurface hydrology and the delivery of aged C to surface waters. Given the large stores Pleistocene-aged organic C in Yedoma deposits, we hypothesize that older C may become a more important contribution to stream biota under warmer conditions that promote thaw.

Determining sources of dissolved organic carbon and disinfection byproduct precursors to the McKenzie River, Oregon

USGS Publications Warehouse

Kraus, Tamara E.C.; Anderson, Chauncey W.; Morgenstern, Karl; Downing, Bryan D.; Pellerin, Brian A.; Bergamaschi, Brian A.

2010-01-01

This study was conducted to determine the main sources of dissolved organic carbon (DOC) and disinfection byproduct (DBP) precursors to the McKenzie River, Oregon (USA). Water samples collected from the mainstem, tributaries, and reservoir outflows were analyzed for DOC concentration and DBP formation potentials (trihalomethanes [THMFPs] and haloacetic acids [HAAFPs]). In addition, optical properties (absorbance and fluorescence) of dissolved organic matter (DOM) were measured to provide insight into DOM composition and assess whether optical properties are useful proxies for DOC and DBP precursor concentrations. Optical properties indicative of composition suggest that DOM in the McKenzie River mainstem was primarily allochthonous - derived from soils and plant material in the upstream watershed. Downstream tributaries had higher DOC concentrations than mainstem sites (1.6 ?? 0.4 vs. 0.7 ?? 0.3 mg L-1) but comprised <5% of mainstem flows and had minimal effect on overall DBP precursor loads. Water exiting two large upstream reservoirs also had higher DOC concentrations than the mainstem site upstream of the reservoirs, but optical data did not support in situ algal production as a source of the added DOC during the study. Results suggest that the first major rain event in the fall contributes DOM with high DBP precursor content. Although there was interference in the absorbance spectra in downstream tributary samples, fluorescence data were strongly correlated to DOC concentration (R 2 = 0.98), THMFP (R2 = 0.98), and HAAFP (R2 = 0.96). These results highlight the value of using optical measurements for identifying the concentration and sources of DBP precursors in watersheds, which will help drinking water utilities improve source water monitoring and management programs. Copyright ?? 2010 by the American Society of Agronomy.

Process Inference from High Frequency Temporal Variations in Dissolved Organic Carbon (DOC) Dynamics Across Nested Spatial Scales

NASA Astrophysics Data System (ADS)

Tunaley, C.; Tetzlaff, D.; Lessels, J. S.; Soulsby, C.

2014-12-01

In order to understand aquatic ecosystem functioning it is critical to understand the processes that control the spatial and temporal variations in DOC. DOC concentrations are highly dynamic, however, our understanding at short, high frequency timescales is still limited. Optical sensors which act as a proxy for DOC provide the opportunity to investigate near-continuous DOC variations in order to understand the hydrological and biogeochemical processes that control concentrations at short temporal scales. Here we present inferred 15 minute stream water DOC data for a 12 month period at three nested scales (1km2, 3km2 and 31km2) for the Bruntland Burn, a headwater catchment in NE Scotland. High frequency data were measured using FDOM and CDOM probes which work by measuring the fluorescent component and coloured component, respectively, of DOC when exposed to ultraviolet light. Both FDOM and CDOM were strongly correlated (r2 >0.8) with DOC allowing high frequency estimations. Results show the close coupling of DOC with discharge throughout the sampling period at all three spatial scales. However, analysis at the event scale highlights anticlockwise hysteresis relationships between DOC and discharge due to the delay in DOC being flushed from the increasingly large areas of peaty soils as saturation zones expand and increase hydrological connectivity. Lag times vary between events dependent on antecedent conditions. During a 10 year drought period in late summer 2013 it was apparent that very small changes in discharge on a 15 minute timescale result in high increases in DOC. This suggests transport limitation during this period where DOC builds up in the soil and is not flushed regularly, therefore any subsequent increase in discharge results in large DOC peaks. The high frequency sensors also reveal diurnal variability during summer months related to the photo-oxidation, evaporative and biological influences of DOC during the day. This relationship is less significant during the winter months.

Linking major and trace element headwater stream concentrations to DOC release and hydrologic conditions in a bog and peaty riparian zone

NASA Astrophysics Data System (ADS)

Broder, Tanja; Biester, Harald

2017-04-01

Peatlands and organic-rich riparian zones are known to export large amounts of dissolved organic carbon (DOC) to surface water. In organic-rich, acidic headwater streams main carriers for element export are dissolved organic matter (DOM) and organic-iron complexes. In this environment DOM might also act as major carrier for metals, which otherwise may have a low solubility. This study examines annual and short term event-based variations of major and trace elements in a headwater catchment. Patterns are used to trace hydrological pathways and element sources under different hydrologic preconditions. Furthermore, it elucidates the importance of DOC as carrier of different elements in a bog and a peaty riparian catchment. The study was conducted in a small headwater stream draining an ombrotrophic peatland with an adjacent forested area with peaty riparian soils in the Harz Mountains (Germany). Discharge sampling was conducted weekly at two sites from snowmelt to begin of snowfall and in high resolution during selected discharge events in 2013 and 2014. Element concentrations were measured by means of ICP-MS and ICP-OES. A PCA was performed for each site and for annual and event datasets. Results show that a large number of element concentrations strongly correlate with DOC concentrations at the bog site. Even elements like Ca and Mg, which are known to have a low affinity to DOC. Congruently, the first principal component integrates the DOC pattern (element loadings > 0.8: Ca, Fe, Mg, Mn, Zn, As, Sr, Cd, DOC) and explained about 35 % of total variance and even 50 % during rain events (loadings > 0.8: Al, Ca, Fe, Mg, Mn, Zn, Li, Co, As, Sr, Cd, Pb, DOC). The study cannot verify that all correlating elements bind to DOC. It is likely that also a common mobilization pattern in the upper peat layer by plant decomposition causes the same response to changes in hydrologic pathways. Additionally, a low mineral content and an enrichment of elements like Fe and Mn in the upper peat layers due to prevailing redox conditions might play a major role in a bog environment. At the peaty riparian zone only Ca, Fe, and Sr strongly correlated with DOC over the annual record. The PCA of the annual record display no clear DOC component here, but indicates that DOC is influenced by Component one (element loadings > 0.8: Ca, Mg, Zn, Co, Sr) and two (Al, V, La, Pb, U) suggesting different DOC sources in the peaty riparian zone. A large number of elements correlate with DOC during rain event sampling at the riparian zone. In contrast to the bog site the event-based riparian zone PCA distinguished a clear discharge related component with mineral, groundwater related elements (K, Rb, In, Cs, NO3- and SO42-). Pattern of the mineral and DOC components prove that during base flow discharge is generated in a shallow groundwater layer and successively increases upward to the organic-rich upper soil layer with increasing discharge. Contrarily, bog element pattern confirm a dominating surface-near discharge, due to high hydraulic conductivities.

TOC/DOC: "It Has Changed the Way I Do Science".

ERIC Educational Resources Information Center

Douglas, Kimberly; Roth, Dana L.

1997-01-01

Describes a user-based automated service developed at the California Institute of Technology that combines access to journal article databases with an in-house document delivery system. TOC/DOC (Tables of Contents/Document Delivery) has undergone a conceptual change from a catalog of locally-held journal articles to a broader, more retrospective…

Major 20th century changes of the content and chemical speciation of organic carbon archived in Alpine ice cores: Implications for the long-term change of organic aerosol over Europe

NASA Astrophysics Data System (ADS)

Legrand, M.; Preunkert, S.; May, B.; Guilhermet, J.; Hoffman, H.; Wagenbach, D.

2013-05-01

Dissolved organic carbon (DOC) and an extended array of organic compounds were investigated in an Alpine ice core covering the 1920-1988 time period. Based on this, a reconstruction was made of the long-term trends of water-soluble organic carbon (WSOC) aerosol in the European atmosphere. It is shown that light mono- and dicarboxylates, humic-like substances, and formaldehyde account together for more than half of the DOC content of ice. This extended chemical speciation of DOC is used to estimate the DOC fraction present in ice that is related to WSOC aerosol and its change over the past. It is suggested that after World War II, the WSOC levels have been enhanced by a factor of 2 and 3 in winter and summer, respectively. In summer, the fossil fuel contribution to the enhancement is estimated to be rather small, suggesting that it arises mainly from an increase in biogenic sources of WSOC.

[Vertical distribution of soil active carbon and soil organic carbon storage under different forest types in the Qinling Mountains].

PubMed

Wang, Di; Geng, Zeng-Chao; She, Diao; He, Wen-Xiang; Hou, Lin

2014-06-01

Adopting field investigation and indoor analysis methods, the distribution patterns of soil active carbon and soil carbon storage in the soil profiles of Quercus aliena var. acuteserrata (Matoutan Forest, I), Pinus tabuliformis (II), Pinus armandii (III), pine-oak mixed forest (IV), Picea asperata (V), and Quercus aliena var. acuteserrata (Xinjiashan Forest, VI) of Qinling Mountains were studied in August 2013. The results showed that soil organic carbon (SOC), microbial biomass carbon (MBC), dissolved organic carbon (DOC), and easily oxidizable carbon (EOC) decreased with the increase of soil depth along the different forest soil profiles. The SOC and DOC contents of different depths along the soil profiles of P. asperata and pine-oak mixed forest were higher than in the other studied forest soils, and the order of the mean SOC and DOC along the different soil profiles was V > IV > I > II > III > VI. The contents of soil MBC of the different forest soil profiles were 71.25-710.05 mg x kg(-1), with a content sequence of I > V > N > III > II > VI. The content of EOC along the whole soil profile of pine-oak mixed forest had a largest decline, and the order of the mean EOC was IV > V> I > II > III > VI. The sequence of soil organic carbon storage of the 0-60 cm soil layer was V > I >IV > III > VI > II. The MBC, DOC and EOC contents of the different forest soils were significanty correlated to each other. There was significant positive correlation among soil active carbon and TOC, TN. Meanwhile, there was no significant correlation between soil active carbon and other soil basic physicochemical properties.

Effect of algal flocculation on dissolved organic matters using cationic starch modified soils.

PubMed

Shi, Wenqing; Bi, Lei; Pan, Gang

2016-07-01

Modified soils (MSs) are being increasingly used as geo-engineering materials for the sedimentation removal of cyanobacterial blooms. Cationic starch (CS) has been tested as an effective soil modifier, but little is known about its potential impacts on the treated water. This study investigated dissolved organic matters in the bloom water after algal removal using cationic starch modified soils (CS-MSs). Results showed that the dissolved organic carbon (DOC) could be decreased by CS-MS flocculation and the use of higher charge density CS yielded a greater DOC reduction. When CS with the charge density of 0.052, 0.102 and 0.293meq/g were used, DOC was decreased from 3.4 to 3.0, 2.3 and 1.7mg/L, respectively. The excitation-emission matrix fluorescence spectroscopy and UV254 analysis indicated that CS-MS exhibits an ability to remove some soluble organics, which contributed to the DOC reduction. However, the use of low charge density CS posed a potential risk of DOC increase due to the high CS loading for effective algal removal. When CS with the charge density of 0.044meq/g was used, DOC was increased from 3.4 to 3.9mg/L. This study suggested, when CS-MS is used for cyanobacterial bloom removal, the content of dissolved organic matters in the treated water can be controlled by optimizing the charge density of CS. For the settled organic matters, other measures (e.g., capping treatments using oxygen loaded materials) should be jointly applied after algal flocculation. Copyright © 2016. Published by Elsevier B.V.

Relation between Soil Order and Sorptive Capacity for Dissolved Organic Carbon

DOE Office of Scientific and Technical Information (OSTI.GOV)

Heal, Katherine R; Brandt, Craig C; Mayes, Melanie

2012-01-01

Soils have historically been considered a temporary sink for organic C, but deeper soils may serve as longer term C sinks due to the sorption of dissolved organic C (DOC) onto Fe- and clay-rich mineral soil particles. This project provides an improved understanding and predictive capability of the physical and chemical properties of deep soils that control their sorptive capacities for DOC. Two hundred thirteen subsurface soil samples (72 series from five orders) were selected from the eastern and central United States. A characterized natural DOC source was added to the soils, and the Langmuir sorption equation was fitted tomore » the observed data by adjusting the maximum DOC sorption capacity (Q{sub max}) and the binding coefficient (k). Different isotherm shapes were observed for Ultisols, Alfisols, and Mollisols due to statistically significant differences in the magnitude of k, while Q{sub max} was statistically invariant among these three orders. Linear regressions were performed on the entire database and as a function of soil order to correlate Langmuir fitted parameters with measured soil properties, e.g., pH, clay content, total organic C (TOC), and total Fe oxide content. Together, textural clay and Fe oxide content accounted for 35% of the variation in Q{sub max} in the database, and clay was most important for Alfisols and Ultisols. The TOC content, however, accounted for 27% of the variation in Q{sub max} in Mollisols. Soil pH accounted for 45% of the variation in k for the entire database, 41% for Mollisols, and 22% for Alfisols. Our findings demonstrate that correlations between Langmuir parameters and soil properties are different for different soil orders and that k is a more sensitive parameter for DOC sorption than is Q{sub max} for temperate soils from the central and eastern United States.« less

Hidden cycle of dissolved organic carbon in the deep ocean.

PubMed

Follett, Christopher L; Repeta, Daniel J; Rothman, Daniel H; Xu, Li; Santinelli, Chiara

2014-11-25

Marine dissolved organic carbon (DOC) is a large (660 Pg C) reactive carbon reservoir that mediates the oceanic microbial food web and interacts with climate on both short and long timescales. Carbon isotopic content provides information on the DOC source via δ(13)C and age via Δ(14)C. Bulk isotope measurements suggest a microbially sourced DOC reservoir with two distinct components of differing radiocarbon age. However, such measurements cannot determine internal dynamics and fluxes. Here we analyze serial oxidation experiments to quantify the isotopic diversity of DOC at an oligotrophic site in the central Pacific Ocean. Our results show diversity in both stable and radio isotopes at all depths, confirming DOC cycling hidden within bulk analyses. We confirm the presence of isotopically enriched, modern DOC cocycling with an isotopically depleted older fraction in the upper ocean. However, our results show that up to 30% of the deep DOC reservoir is modern and supported by a 1 Pg/y carbon flux, which is 10 times higher than inferred from bulk isotope measurements. Isotopically depleted material turns over at an apparent time scale of 30,000 y, which is far slower than indicated by bulk isotope measurements. These results are consistent with global DOC measurements and explain both the fluctuations in deep DOC concentration and the anomalous radiocarbon values of DOC in the Southern Ocean. Collectively these results provide an unprecedented view of the ways in which DOC moves through the marine carbon cycle.

Hidden cycle of dissolved organic carbon in the deep ocean

PubMed Central

Follett, Christopher L.; Repeta, Daniel J.; Rothman, Daniel H.; Xu, Li; Santinelli, Chiara

2014-01-01

Marine dissolved organic carbon (DOC) is a large (660 Pg C) reactive carbon reservoir that mediates the oceanic microbial food web and interacts with climate on both short and long timescales. Carbon isotopic content provides information on the DOC source via δ13C and age via Δ14C. Bulk isotope measurements suggest a microbially sourced DOC reservoir with two distinct components of differing radiocarbon age. However, such measurements cannot determine internal dynamics and fluxes. Here we analyze serial oxidation experiments to quantify the isotopic diversity of DOC at an oligotrophic site in the central Pacific Ocean. Our results show diversity in both stable and radio isotopes at all depths, confirming DOC cycling hidden within bulk analyses. We confirm the presence of isotopically enriched, modern DOC cocycling with an isotopically depleted older fraction in the upper ocean. However, our results show that up to 30% of the deep DOC reservoir is modern and supported by a 1 Pg/y carbon flux, which is 10 times higher than inferred from bulk isotope measurements. Isotopically depleted material turns over at an apparent time scale of 30,000 y, which is far slower than indicated by bulk isotope measurements. These results are consistent with global DOC measurements and explain both the fluctuations in deep DOC concentration and the anomalous radiocarbon values of DOC in the Southern Ocean. Collectively these results provide an unprecedented view of the ways in which DOC moves through the marine carbon cycle. PMID:25385632

Temporal trends in organic carbon content in the main Swiss rivers, 1974-2010.

PubMed

Rodríguez-Murillo, J C; Zobrist, J; Filella, M

2015-01-01

Increases in dissolved organic carbon (DOC) concentrations have often been reported in rivers and lakes of the Northern Hemisphere over the last few decades. High-quality organic carbon (OC) concentration data have been used to study the change in DOC and total (TOC) organic carbon concentrations in the main rivers of Switzerland (Rhône, Rhine, Thur and Aar) between 1974 and 2010. These rivers are characterized by high discharge regimes (due to their Alpine origin) and by running in populated areas. Small long term trends (a general statistically significant decrease in TOC and a less clear increase in DOC concentrations), on the order of 1% of mean OC concentration per year, have been observed. An upward trend before 1999 reversed direction to a more marked downward trend from 1999 to 2010. Of the potential causes of OC temporal variation analysed (water temperature, dissolved reactive phosphorus and river discharge), only discharge explains a significant, albeit still small, part of TOC variability (8-31%), while accounting for barely 2.5% of DOC variability. Estimated anthropogenic TOC and DOC loads (treated sewage) to the rivers could account for a maximum of 4-20% of the temporal trends. Such low predictability is a good example of the limitations faced when studying causality and drivers behind small variations in complex systems. River export of OC from Switzerland has decreased significantly over the period. Since about 5.5% of estimated NEP of Switzerland is exported by the rivers, riverine OC fluxes should be taken into account in a detailed carbon budget of the country. Copyright © 2014 Elsevier B.V. All rights reserved.

Simultaneous effect of dissolved organic carbon, surfactant, and organic acid on the desorption of pesticides investigated by response surface methodology.

PubMed

Trinh, Ha Thu; Duong, Hanh Thi; Ta, Thao Thi; Van Cao, Hoang; Strobel, Bjarne W; Le, Giang Truong

2017-08-01

Desorption of pesticides (fenobucarb, endosulfan, and dichlorodiphenyltrichloroethane (DDT)) from soil to aqueous solution with the simultaneous presence of dissolved organic carbon (DOC), sodium dodecyl sulfate (SDS), and sodium oxalate (Oxa) was investigated in batch test by applying a full factorial design and the Box-Behnken response surface methodology (RSM). Five concentration levels of DOC (8 to 92 mg L -1 ), SDS (0 to 6.4 critical micelle concentration (CMC)), and Oxa (0 to 0.15 M) were used for the experiments with a rice field topsoil. The results of RSM analysis and analysis of variance (ANOVA) have shown that the experimental data could be well described by quadratic regression equations with determination coefficients (R 2 ) of 0.990, 0.976, and 0.984 for desorption of fenobucarb, endosulfan, and DDT, respectively. The individual effects and interaction of DOC, SDS, and Oxa were evaluated through quadratic regression equations. When the aqueous solution includes 50 mg L -1 DOC, 3.75 CMC SDS, and 0.1 M Oxa, the maximum desorption concentrations of fenobucarb, endosulfan, and DDT were 96, 80, and 75 μg L -1 , respectively. The lowest concentration of SDS, DOC, and Oxa caused the minimum desorption. This point at conditions of concern for flooding water is high content of organic compounds causing potentially high contamination by desorption, and the remarkably lower desorption at organic matter-free conditions. The suspended organic matter is one of the common characteristics of flooding and irrigation water in rice fields, and surfactants from pollution increase the problem with desorption of legacy pesticides in the rice fields.

Dynamics of hydrophobic organic contaminants in the Baltic proper pelagial

DOE Office of Scientific and Technical Information (OSTI.GOV)

Axelman, J.; Broman, D.; Naef, C.

Hydrophobic organic contaminants occur in different forms in natural water. Apart from being truly dissolved in water they partition into dissolved organic carbon (DOC) and particles of different sizes including pelagic bacteria, phytoplankton and zooplankton. The distribution between the different forms is dependent on carbon turnover rates in and transport between the different compartments and on the physical and chemical properties of the compound in focus. The water phase, the DOC-phase and two particle size fractions, 0.2--2pm and 2--20 pm representing the base of the pelagic food web, were analyzed for their content of PCBs and PAHs during summer andmore » winter conditions in the open sea in the Baltic proper. New methods for separating truly dissolved from DOC-bound compounds have been developed using a high capacity perfusion adsorbent and large scale gas sparging. The small particle size fraction was sampled using high volume tangential flow filtration. The possibility to separate between these four different compartments has given a more detailed picture of the short term dynamics of hydrophobic organic compounds in the important base of the pelagial food web.« less

Effects of nutrient enrichment on the release of dissolved organic carbon and nitrogen by the scleractinian coral Montipora digitata

NASA Astrophysics Data System (ADS)

Tanaka, Y.; Ogawa, H.; Miyajima, T.

2010-09-01

The effects of nutrient enrichment on the release of dissolved organic carbon and nitrogen (DOC and DON, respectively) from the coral Montipora digitata were investigated in the laboratory. Nitrate (NO3 -) and phosphate (PO4 3-) were supplied to the aquarium to get the final concentrations of 10 and 0.5 μmol l-1, respectively, and the corals were incubated for 8 days. The release rate of DON per unit coral surface area significantly decreased after the nutrient enrichment, while the release rate of DOC was constant. Because the chlorophyll a (chl a) content of zooxanthellae per unit surface area increased, the release rate of DOC significantly decreased when normalized to unit chl a. These results suggested that the incorporation of NO3 - and PO4 3- stimulated the synthesis of new cellular components in the coral colonies and consequently, reduced extracellular release of DOC and DON. Actually, significant increase in N and P contents relative to C content was observed in the coral’s tissue after the nutrient enrichment. The present study has concluded that inorganic nutrient enrichment not only affects coral-algal metabolism inside the colony but also affects a microbial community around the coral because the organic matter released from corals functions as energy carrier in the coral reef ecosystem.

Contrasting dissolved organic carbon dynamics at two forested catchments interpreted from high-frequency optical sensor measurements

NASA Astrophysics Data System (ADS)

Saraceno, J.; Shanley, J. B.

2015-12-01

Stream dissolved organic carbon (DOC) concentrations can change rapidly during high-flow events. The timing and magnitude of these changes relative to the event hydrograph can yield insights about possible DOC sources its flow paths to the stream. In situ fluorescent dissolved organic matter (FDOM) sensors that generate high-frequency observations enable detailed examination of high-flow DOC- discharge hysteresis. In this presentation, we interpret high-flow DOC dynamics at two of the five U.S. Geological Survey (USGS) Water, Energy, and Biogeochemical Budgets (WEBB) sites - Panola Mountain, Georgia and Sleepers River, Vermont. Based on laboratory analyses of weekly and event grab samples, both USGS WEBB sites had a similar DOC ranges: from ~1 milligrams per liter (mg/L) at base flow to ~11-15 mg/L during the largest events. A curvilinear relationship between DOC and FDOM (corrected for temperature and turbidity interferences) was used to model a continuous time series of DOC. At the Sleepers River site, DOC showed a seasonal pattern of increasing DOC response; from fairly subdued during spring snowmelt, to a maximum during autumn leaf-fall. The DOC response to discharge showed a consistent clockwise hysteresis (DOC peak, lagged discharge peak). At the Panola Mountain site, maximum event DOC response was lower during wet conditions in the winter and spring. Hysteresis was less expressed at Panola Mountain relative to Sleepers River and displayed both clockwise and counterclockwise patterns, which were dependent on antecedent moisture conditions. The greater synchrony of DOC and discharge peaks at Panola Mountain suggests that DOC sources are closer to the stream and (or) move to the stream more quickly, than at Sleepers River.

Nitrogen addition shifts the microbial community in the rhizosphere of Pinus tabuliformis in Northwestern China

PubMed Central

Lv, Fenglian; Xue, Sha; Wang, Guoliang; Zhang, Chao

2017-01-01

Atmospheric nitrogen (N) deposition profoundly alters the soil microbial communities and will thus affect nutrient cycles. The effects of N availability on microbial community, however, are not clear. We used PLFA analysis to evaluate the effects of a gradient of N addition (0, 2.8, 5.6, 11.2, and 22.4 g N m-2 y-1) for three years on the rhizospheric microbial community of Pinus tabuliformis seedlings. The main factors influencing the community were quantified using structural equation modelling and redundancy analysis. At the microbial-community level, N addition increased the total phospholipid fatty acids content by increasing the dissolved organic carbon (DOC) and root biomass. Increases in soil microbial biomass carbon and N, however, was attributed to the increased DOC, N content and decreased pH. At the microbial-groups level, Fungal, arbuscular mycorrhizal fungal (AMF), gram-positive bacterial (GP) abundances and the GP:GN ratio first increased and then decreased with N addition. Nitrogen addition increased the abundances of bacteria, fungi, and actinomycetes mainly by increasing the DOC content and decreasing root biomass. Additionally, the decrease of pH and ammonium N caused by N addition increased the fungal abundances and reduced actinomycete abundances, respectively. Nitrogen addition shifted the rhizospheric microbial community mainly by altering the DOC content and root biomass. The current rate of N deposition (2.5 g N m-2 y-1) benefits plant growth and increases the abundances of fungi, arbuscular mycorrhizal fungi, GP, actinomycetes and the GP:GN ratio. PMID:28234932

Speciation of Se and DOC in soil solution and their relation to Se bioavailability.

PubMed

Weng, Liping; Vega, Flora Alonso; Supriatin, Supriatin; Bussink, Wim; Van Riemsdijk, Willem H

2011-01-01

A 0.01 M CaCl(2) extraction is often used to asses the bioavailability of plant nutrients in soils. However, almost no correlation was found between selenium (Se) in the soil extraction and Se content in grass. The recently developed anion Donnan membrane technique was used to analyze chemical speciation of Se in the 0.01 M CaCl(2) extractions of grassland soils and fractionation of DOC (dissolved organic carbon). The results show that most of Se (67-86%) in the extractions (15 samples) are colloidal-sized Se. Only 13-34% of extractable Se are selenate, selenite and small organic Se (<1 nm). Colloidal Se is, most likely, Se bound to or incorporated in colloidal-sized organic matter. The dominant form of small Se compounds (selenate, selenite/small organic compounds) depends on soil. A total of 47-85% of DOC is colloidal-sized and 15-53% are small organic molecules (<1 nm). In combination with soluble S (sulfur) and/or P (phosphor), concentration of small DOC can explain most of the variability of Se content in grass. The results indicate that mineralization of organic Se is the most important factor that controls Se availability in soils. Competition with sulfate and phosphate needs to be taken into account. Further research is needed to verify if concentration of small DOC is a good indicator of mineralization of soil organic matter.

Influence of allochthonous dissolved organic matter on pelagic basal production in a northerly estuary

NASA Astrophysics Data System (ADS)

Andersson, A.; Brugel, S.; Paczkowska, J.; Rowe, O. F.; Figueroa, D.; Kratzer, S.; Legrand, C.

2018-05-01

Phytoplankton and heterotrophic bacteria are key groups at the base of aquatic food webs. In estuaries receiving riverine water with a high content of coloured allochthonous dissolved organic matter (ADOM), phytoplankton primary production may be reduced, while bacterial production is favoured. We tested this hypothesis by performing a field study in a northerly estuary receiving nutrient-poor, ADOM-rich riverine water, and analyzing results using multivariate statistics. Throughout the productive season, and especially during the spring river flush, the production and growth rate of heterotrophic bacteria were stimulated by the riverine inflow of dissolved organic carbon (DOC). In contrast, primary production and photosynthetic efficiency (i.e. phytoplankton growth rate) were negatively affected by DOC. Primary production related positively to phosphorus, which is the limiting nutrient in the area. In the upper estuary where DOC concentrations were the highest, the heterotrophic bacterial production constituted almost 100% of the basal production (sum of primary and bacterial production) during spring, while during summer the primary and bacterial production were approximately equal. Our study shows that riverine DOC had a strong negative influence on coastal phytoplankton production, likely due to light attenuation. On the other hand DOC showed a positive influence on bacterial production since it represents a supplementary food source. Thus, in boreal regions where climate change will cause increased river inflow to coastal waters, the balance between phytoplankton and bacterial production is likely to be changed, favouring bacteria. The pelagic food web structure and overall productivity will in turn be altered.

Characterising Event-Based DOM Inputs to an Urban Watershed

NASA Astrophysics Data System (ADS)

Croghan, D.; Bradley, C.; Hannah, D. M.; Van Loon, A.; Sadler, J. P.

2017-12-01

Dissolved Organic Matter (DOM) composition in urban streams is dominated by terrestrial inputs after rainfall events. Urban streams have particularly strong terrestrial-riverine connections due to direct input from terrestrial drainage systems. Event driven DOM inputs can have substantial adverse effects on water quality. Despite this, DOM from important catchment sources such as road drains and Combined Sewage Overflows (CSO's) remains poorly characterised within urban watersheds. We studied DOM sources within an urbanised, headwater watershed in Birmingham, UK. Samples from terrestrial sources (roads, roofs and a CSO), were collected manually after the onset of rainfall events of varying magnitude, and again within 24-hrs of the event ending. Terrestrial samples were analysed for fluorescence, absorbance and Dissolved Organic Carbon (DOC) concentration. Fluorescence and absorbance indices were calculated, and Parallel Factor Analysis (PARAFAC) was undertaken to aid sample characterization. Substantial differences in fluorescence, absorbance, and DOC were observed between source types. PARAFAC-derived components linked to organic pollutants were generally highest within road derived samples, whilst humic-like components tended to be highest within roof samples. Samples taken from the CSO generally contained low fluorescence, however this likely represents a dilution effect. Variation within source groups was particularly high, and local land use seemed to be the driving factor for road and roof drain DOM character and DOC quantity. Furthermore, high variation in fluorescence, absorbance and DOC was apparent between all sources depending on event type. Drier antecedent conditions in particular were linked to greater presence of terrestrially-derived components and higher DOC content. Our study indicates that high variations in DOM character occur between source types, and over small spatial scales. Road drains located on main roads appear to contain the poorest quality DOM of the sources studied due to the presence of hydrocarbons. In order to prevent storm-derived DOM degradation of water quality of urban streams, greater knowledge of links between these drainage sources, and their pathways to streams is required.

Does quinone or phenol enrichment of humic substances alter the primary compound from a non-algicidal to an algicidal preparation?

PubMed

Bährs, Hanno; Menzel, Ralph; Kubsch, Georg; Stösser, Reinhardt; Putschew, Anke; Heinze, Tobias; Steinberg, Christian E W

2012-06-01

Dissolved organic matter (DOM) has been shown to affect phytoplankton species directly. These interactions largely depend on the origin and molecular size of DOM and are different in prokaryotes and eukaryotes. In a preceding study, however, two humic substance preparations did not adversely affect coccal green algae or cyanobacterial growth even at high concentrations of dissolved organic carbon (DOC). These results contradicted previous findings, showing a clear, negative response of different phototrophs to much lower DOC concentrations. To test whether or not at least defined building blocks of humic substances (HSs) are effective algicidal structures, we enriched two humic preparations with hydroquinone and p-benzoquinone, respectively, and exposed two different green algae, Pseudokirchneriella subcapitata and Monoraphidium braunii, and two cyanobacterial species, Synechocystis sp. and Microcystis aeruginosa, to the unmodified and enriched HSs. As response variables, growth rates in terms of biomass increase, chlorophyll-a content, and photosynthetic yield were measured. The highest concentration (4.17 mM DOC) of the modified HSs clearly inhibited growth; the cyanobacterial species were much more sensitive than the green algal species. However, realistic ecological concentrations did not adversely affect growth. Aerating the exposure solution for 24 h strongly reduced the inhibitory effect of the modified HSs. The algicidal effect was obviously caused by monomers and not by polymerised high molecular weight HSs themselves. Furthermore, the maximum quantum yield (Φ PSII max) was stimulated in the green algal species by low and medium DOC concentrations, but reduced in the cyanobacterial species upon exposure to higher HS concentrations. The quinone- and phenol-enriched HSs only showed algicidal activity at high concentrations of 4.17 mM DOC and lost their effects over time, presumably by oxidation and subsequent polymerisation. This study confirms that the applied humic substances themselves are not effective algicides even if enriched in effective structures. Copyright © 2012 Elsevier Ltd. All rights reserved.

Estimating grassland curing with remotely sensed data

NASA Astrophysics Data System (ADS)

Chaivaranont, Wasin; Evans, Jason P.; Liu, Yi Y.; Sharples, Jason J.

2018-06-01

Wildfire can become a catastrophic natural hazard, especially during dry summer seasons in Australia. Severity is influenced by various meteorological, geographical, and fuel characteristics. Modified Mark 4 McArthur's Grassland Fire Danger Index (GFDI) is a commonly used approach to determine the fire danger level in grassland ecosystems. The degree of curing (DOC, i.e. proportion of dead material) of the grass is one key ingredient in determining the fire danger. It is difficult to collect accurate DOC information in the field, and therefore ground-observed measurements are rather limited. In this study, we explore the possibility of whether adding satellite-observed data responding to vegetation water content (vegetation optical depth, VOD) will improve DOC prediction when compared with the existing satellite-observed data responding to DOC prediction models based on vegetation greenness (normalised difference vegetation index, NDVI). First, statistically significant relationships are established between selected ground-observed DOC and satellite-observed vegetation datasets (NDVI and VOD) with an r2 up to 0.67. DOC levels estimated using satellite observations were then evaluated using field measurements with an r2 of 0.44 to 0.55. Results suggest that VOD-based DOC estimation can reasonably reproduce ground-based observations in space and time and is comparable to the existing NDVI-based DOC estimation models.

Direct analysis of δ13C and concentration of dissolved organic carbon (DOC) in environmental samples by TOC-IRMS

NASA Astrophysics Data System (ADS)

Kirkels, Frédérique; Cerli, Chiara; Federherr, Eugen; Kalbitz, Karsten

2014-05-01

Dissolved organic carbon (DOC) plays an important role in carbon cycling in terrestrial and aquatic systems. Stable isotope analysis (delta 13C) of DOC could provide valuable insights in its origin, fluxes and environmental fate. Precise and routine analysis of delta 13C and DOC concentration are therefore highly desirable. A promising, new system has been developed for this purpose, linking a high-temperature combustion TOC analyzer trough an interface with a continuous flow isotope ratio mass spectrometer (Elementar group, Hanau, Germany). This TOC-IRMS system enables simultaneous stable isotope (bulk delta 13C) and concentration analysis of DOC, with high oxidation efficiency by high-temperature combustion for complex mixtures as natural DOC. To give delta 13C analysis by TOC-IRMS the necessary impulse for broad-scale application, we present a detailed evaluation of its analytical performance for realistic and challenging conditions inclusive low DOC concentrations and environmental samples. High precision (standard deviation, SD predominantly < 0.15 permil) and accuracy (R2 = 0.9997, i.e. comparison TOC-IRMS and conventional EA-IRMS) were achieved by TOC-IRMS for a broad diversity of DOC solutions. This precision is comparable or even slightly better than that typically reported for EA-IRMS systems, and improves previous techniques for δ13C analysis of DOC. Simultaneously, very good precision was obtained for DOC concentration measurements. Assessment of natural abundance and slightly 13C enriched DOC, a wide range of concentrations (0.2-150 mgC/L) and injection volumes (0.05-3 ml), demonstrated good analytical performance with negligible memory effects, no concentration/volume effects and a wide linearity. Low DOC concentrations (< 2 mgC/L), were correctly analyzed without any pre-concentration. Moreover, TOC-IRMS was successfully applied to analyze DOC from diverse terrestrial, freshwater and marine environments (SD < 0.23 permil). In summary, the TOC-IRMS performs fast and reliable analysis of DOC concentration and δ13C in aqueous samples, without any pre-concentration/freeze-drying. Flexible usage is highlighted by automated, online analysis, a variable injection volume, high throughput and no extensive maintenance. Sample analysis is simple, using small aliquots and with minimal sample preparation. Further investigations should focus on complex, saline matrices and very low DOC concentrations, to achieve a potential lower limit of 0.2 mgC/L. High-resolution, routine delta 13C analysis of DOC by TOC-IRMS offers opportunities for wide-scale application in terrestrial, freshwater and marine research to elucidate the role of DOC in biogeochemical processes and ecosystem functioning.

Depth distribution of abiotic drivers of N mineralization and methane emission from a continuously and intermittently flooded Bangladeshi paddy soil

NASA Astrophysics Data System (ADS)

Akter, Masuda; Kader, Md. Abdul; Pierreux, Sofie; Boeckx, Pascal; Kamal, Ahammad Mostafa; Sleutel, Steven

2016-04-01

Water-saving irrigation such as AWD may significantly alter depth profiles of moisture content, pH, Eh and soil microbial activity. Modelling the effect of irrigation management on soil N mineralization, therefore requires detailed insight into depth distribution of these variables and dissolved organic carbon (DOC), and evolution of electron acceptors. We set up a field experiment at Bangladesh Agricultural University from January to May' 2015. The cultivated rice variety (BRRI dhan28) was grown under continuous flooding (CF) and alternate wetting and drying (AWD) management, with 120 kg N ha-1(N120) or without (N0)N fertilizer application. We measured soil mineral N and plant N uptake to evaluate N mineralization. CH4 emissions were monitored with timely gas sample collection and GC-analysis. Soil Eh at four depths and temperature at two depths were monitored continuously by Eh/T°-probes connected to a HYPNOS III data logger (MVH, The Netherlands). Simultaneously, soil solution from three depths were sampled with rhizon samplers to track DOC, Fe and Mn in solution. Over the growing season soil and air temperature increased by 8°C, and soil pH stayed near neutral (6.7 to 7.8). In all depths of AWD and CF, Eh dropped sharply to methanic conditions within 21 days after transplanting (DAT). Low redox-potential continued until 77DAT in all cases, except in the puddle layers under AWD, where redox raised to -200mV during drainage. Fe and Mn in soil solution increased gradually over the growing season, indicating continued reductive dissolution of Fe and Mn (hydro-)oxides. DOC increased continuously as well in all depths. Besides to release of DOC bound to pedogenic oxides upon their reductive dissolution, higher plant and soil microbial activity with increasing soil temperature (till 28°C) through the growing season explains the increasing DOC levels. Increasing methanogenic activity as indicated by the high CH4 emissions at 70-84DAT under both CF and AWD is logically linked. The elevated redox potential in puddle layer depth increments during AWD drainage events, significantly (p<0.01) declined the cumulative CH4 emission by 47% when compared to CF management. Moreover, seasonal CH4 emissions in N-fertilized fields (N120) decreased by 29 and 8% under CF and AWD, respectively relative to the control (N0), possibly due to promotion of methanotrophs, which were N-limited in N0. Mostly, mineral N content in N120 plots of AWD and CF exceeded contents in the N0 fields. Contrary to CH4 emission, irrigation management did not affect evolutions of pH, Fe, Mn and DOC in soil solution. Likewise, soil exchangeable N content evolution was unaffected and followed zero-order kinetics (N120: R2=0.53 to 0.81; N0: R2=0.12 to 0.48). Our results generally indicate that in Northern Bangladesh's Boro season, evolutions in paddy soil solution chemistry and CH4 emission are strongly depending on course soil temperature and only secondarily on irrigation management. Whether temperature steers microbial activity and methanogenesis directly or via concomitant plant activity and exudation is not known. Key words: Redox, CH4, emission, mineralization, Fe, Mn, DOC, water management

How appetizing is the dissolved organic matter (DOM) trees lose during rainfall?

NASA Astrophysics Data System (ADS)

Howard, D.; Van Stan, J. T., II; Whitetree, A.; Zhu, L.; Stubbins, A.

2017-12-01

Dissolved organic carbon (DOC) is the chemical backbone of dissolved organic matter (DOM), which is important because it drives many processes in soils and waterways. Current DOC work has paid little attention to interactions between rain and plant canopies, where rainfall is partitioned into throughfall and stemflow. Even less DOC research has investigated the effect of arboreal epiphytes on throughfall and stemflow DOC. The purpose of this study is twofold: (1) assess the degree and timing of DOC consumption by microbial communities (biolability) in throughfall and stemflow, and (2) determine whether the presence of arboreal epiphytes in the canopy affect DOC biolability. Biolability of stemflow and throughfall DOC from Juniperus virginiana (cedar) was determined by incubating samples for 14 days. Throughfall and stemflow DOC was highly biolabile with DOC concentrations decreasing by 30-60%. Throughfall DOC was more biolabile than stemflow DOC. DOC in both throughfall and stemflow from epiphyte-covered cedars was less biolabile than DOC from trees without epiphytes. The high biolability of tree-derived DOC indicates that its supply provides carbon substrates to the microbial community at the forest floor, in soils and the rhizosphere. Epiphytes appear to be important in determining the biolability of DOC and therefore the size of this carbon subsidy to the soil ecosystem.

Impact of hurricanes on the flux of rainwater and Cape Fear River water dissolved organic carbon to Long Bay, southeastern United States

NASA Astrophysics Data System (ADS)

Avery, G. Brooks; Kieber, Robert J.; Willey, Joan D.; Shank, G. Christopher; Whitehead, Robert F.

2004-09-01

The hurricane flux of rain and river water dissolved organic carbon (DOC) to Long Bay located on the southeastern coast of the United States was determined for four hurricanes that made landfall in the Cape Fear region of North Carolina. Riverine flux of DOC following hurricanes Fran (1996) and Floyd (1999) represented one third and one half of the entire annual river flux of DOC to Long Bay, respectively. The majority of this DOC was recalcitrant and not available for biological consumption. The high flux of DOC from hurricane Floyd resulted from extremely high precipitation amounts (in excess of 50 cm) associated with the hurricane and subsequent flooding. High riverine DOC fluxes were observed following hurricane Fran but not hurricanes Bertha (1996) and Bonnie (1998). The westerly path of Fran deposited rain inland along the Cape Fear River watershed, causing high river flow conditions, while Bonnie and Bertha took an eastern path, resulting in a minimal effect to the Cape Fear River flow rates. The rainwater flux of total DOC to Long Bay from the four hurricanes was not as dramatic as that observed for riverine fluxes. However, unlike river water DOC that is refractory, rainwater DOC is highly labile. Rainwater from the four hurricanes in this study deposited 2-5 times the DOC deposited in an average storm. This represented a flux of 3-9% of the entire annual budget of bioavailable DOC to Long Bay being deposited over a 1 or 2 day period, likely spurring short-term secondary productivity following the hurricanes.

Dissolved Organic Carbon in the Yukon, Tanana and Porcupine Rivers, Alaska

NASA Astrophysics Data System (ADS)

Aiken, G. R.; Striegl, R. G.; Wickland, K. P.; Dornblaser, M. M.; Raymond, P. A.

2006-12-01

The spatial and temporal variability of dissolved organic carbon (DOC) in the Yukon River (YR) and two major tributaries, the Porcupine River (PR), a black water river draining a watershed almost entirely underlain by permafrost, and the Tanana River (TR), a glacial dominated river, are being studied to better define processes controlling DOC in these systems. Five-year seasonal averages indicate DOC concentrations follow the discharge hydrograph, with highest daily and seasonal flux occurring during spring in YR and PR and during summer-autumn in TR. Largest DOC concentrations and specific UV absorption (SUVA) values, a measure of aromatic carbon content of the DOC and an indicator of DOC source, occurred at all locations during spring snowmelt. Lowest DOC concentration and SUVA occurred during low-flow in winter due to greatly reduced contributions of soil organic matter and to relatively greater influences of ground water. While all sites had comparable DOC concentration during winter, DOC concentration was greatest at PR during spring and summer-autumn, whereas TR had the lowest average DOC and SUVA values. Within the YR, average DOC concentration and SUVA values in spring and summer-autumn increase downriver due to contributions from organic carbon rich tributaries, such as PR, that increase in number and significance as the river flows through Alaska. Most the DOC in each system was comprised of hydrophobic organic acids (HPOA) derived from terrestrial vegetation. During winter, the hydrophilic fraction, determined to be the most biodegradable, was a larger percentage of the DOC than during spring-autumn. During spring, HPOA concentration and SUVA increased significantly at all sites, suggesting that most DOC in spring is derived from terrestrial organic matter that was frozen on the land surface over winter. During spring-autumn, PR had the largest concentration of HPOA and TR had the least. Like DOC concentration, HPOA concentration and SUVA increased down river. 14C-DOC values correspond to radiocarbon ages of modern (PR), 282 (TR), and 328 (YR) yrs B.P, indicating the presence of some aged DOC in YR and TR. Comparison of the chemical character of DOC from sites along the YR suggests that most DOC is transported from its source to the Bering Sea with little within river chemical or biological alteration, a result supported by laboratory biodegradation experiments.

Temporal Variability of Stemflow Dissolved Organic Carbon (DOC) Concentrations and Quality from Morphologically Contrasting Deciduous Canopies

NASA Astrophysics Data System (ADS)

van Stan, J. T.; Levia, D. F.; Inamdar, S. P.; Mitchell, M. J.; Mage, S. M.

2010-12-01

Dissolved organic carbon (DOC) inputs from canopy-derived hydrologic fluxes play a significant role in the terrestrial carbon budgets of forested ecosystems. However, no studies known to the authors have examined the variability of both DOC concentrations and quality for stemflow across time scales, nor has any study to date evaluated the effects of canopy structure on stemflow DOC characteristics. This investigation seeks to rectify this knowledge gap by examining the variability of stemflow DOC concentrations and quality across contrasting canopy morphologies and time scales (seasonal, storm and intrastorm). Bulk and intrastorm stemflow samples from a less dense, rough-barked, more plagiophile (Liriodendron tulipifera L. (tulip poplar)) and a denser, thin-barked, more erectophile (Fagus grandifolia Ehrh. (American beech)) canopy were collected and analyzed for DOC quality using metrics derived from UV-vis spectroscopy (E2:E3 ratio, SUVA254, select spectral slope (S), and spectral slope ratios (SR)). Our results suggest that stemflow DOC concentrations and quality change as crown architectural traits enhance or diminish hydrologic retention time within the canopy. The architecture of L. tulipifera canopies likely retards the flow of intercepted water, increasing chemical exchange with bark and foliar surfaces. UV-vis metrics indicated that this increased chemical exchange, particularly with bark surfaces, generally enhanced aromatic hydrocarbon content and increased molecular weight. Because leaf presence influenced DOC quality, stemflow DOC characteristics also varied seasonally in response to canopy condition. At the inter- and intrastorm scale, stemflow DOC concentration and quality varied with meteorological and antecedent canopy conditions. Since recent studies have linked stemflow production to preferential subsurface transport of dissolved chemistries, trends in DOC speciation and fluxes described in this study may impact soil environments within wooded ecosystems.

Hydrologically transported dissolved organic carbon influences soil respiration in a tropical rainforest

NASA Astrophysics Data System (ADS)

Zhou, Wen-Jun; Lu, Hua-Zheng; Zhang, Yi-Ping; Sha, Li-Qing; Schaefer, Douglas Allen; Song, Qing-Hai; Deng, Yun; Deng, Xiao-Bao

2016-10-01

To better understand the effect of dissolved organic carbon (DOC) transported by hydrological processes (rainfall, throughfall, litter leachate, and surface soil water; 0-20 cm) on soil respiration in tropical rainforests, we detected the DOC flux in rainfall, throughfall, litter leachate, and surface soil water (0-20 cm), compared the seasonality of δ13CDOC in each hydrological process, and δ13C in leaves, litter, and surface soil, and analysed the throughfall, litter leachate, and surface soil water (0-20 cm) effect on soil respiration in a tropical rainforest in Xishuangbanna, south-west China. Results showed that the surface soil intercepted 94.4 ± 1.2 % of the annual litter leachate DOC flux and is a sink for DOC. The throughfall and litter leachate DOC fluxes amounted to 6.81 and 7.23 % of the net ecosystem exchange respectively, indicating that the DOC flux through hydrological processes is an important component of the carbon budget, and may be an important link between hydrological processes and soil respiration in a tropical rainforest. Even the variability in soil respiration is more dependent on the hydrologically transported water than DOC flux insignificantly, soil temperature, and soil-water content (at 0-20 cm). The difference in δ13C between the soil, soil water (at 0-20 cm), throughfall, and litter leachate indicated that DOC is transformed in the surface soil and decreased the sensitivity indices of soil respiration of DOC flux to water flux, which suggests that soil respiration is more sensitive to the DOC flux in hydrological processes, especially the soil-water DOC flux, than to soil temperature or soil moisture.

Dissolved Organic Matter Composition and Export from U.S. Rivers

NASA Astrophysics Data System (ADS)

Aiken, G.; Butman, D. E.; Spencer, R. G.; Raymond, P.

2012-12-01

Dissolved organic matter (DOM) chemistry and flux are potentially useful indicators of watershed characteristics, climate influences on watershed hydrology and soils, and changes associated with water and land resource management. Organic source materials, watershed geochemistry, oxidative processes and hydrology strongly influence the nature and reactivity of DOM in aquatic systems. The molecules that comprise DOM, in turn, control a number of environmental processes important for ecosystem function including light penetration and photochemistry, microbial activity, mineral dissolution/precipitation, and the transport and reactivity of hydrophobic compounds and metals. In particular, aromatic molecules derived from higher plants exert strong controls on aquatic photochemistry, and on the transport and biogeochemistry of metals. Assessment of DOM composition and transport, therefore, can provide a basis for understanding watershed processes and biogeochemistry of rivers and streams. Here we present results of a multi-year study designed to assess the seasonal and spatial variability of DOM quantity and quality for 15 large North American river basins. Samples were collected from the mouths of the rivers using a sampling program designed to capture hydrologic and seasonal variability of DOM export. DOM concentrations and composition, based on DOM fractionation on XAD resins, chromophoric dissolved organic matter (CDOM) parameters (ultraviolet /visible absorption and fluorescence spectroscopy), specific compound analyses, and DO14C content varied greatly both between sites and seasonally within a given site. DOM in these rivers exhibited a wide range of concentration and carbon specific ultra-violet absorbance at 254 nm (SUVA254), an optical measurement that is an indicator of DOM aromatic carbon content. In almost all systems, CDOM optical parameters correlated strongly with DOC concentration and hydrophobic organic acid (HPOA) content (aquatic humic substances). In particular, SUVA254 was found to correlate strongly with the proportion of HPOA and Δ14C. Relationships between dissolved organic carbon (DOC) concentration and absorbance for individual rivers were quite variable due to differences in the fraction of non-chromophoric DOM. Notably, the relationship between UV absorption coefficients and DOC concentration for four rivers that drain arid regions and/or are heavily influenced by impoundments were statistically weak.although similar trends for these rivers were not observed for Δ14C. Basins with high discharge, high density of vegetation cover, and low population densities exported younger, more aromatic DOM. Conversely, old DOM was exported from low discharge watersheds draining arid regions and watersheds impacted by high population densities. While individual watershed characteristics control DOC concentrations, CDOM parameters and DO14C content, overall discharge dominated the flux of both CDOM and DO14C to coastal waters. The link between the nature and reactivity of DOM and its optical properties can be exploited to provide powerful monitoring tools to assess the impacts of climate change, land-use change, and management practices on overall water quality and on DOM transport and transformation.

Physical access for residue-mineral interactions controls organic carbon retention in an Oxisol soil.

PubMed

Ye, Chenglong; Bai, Tongshuo; Yang, Yi; Zhang, Hao; Guo, Hui; Li, Zhen; Li, Huixin; Hu, Shuijin

2017-07-24

Oxisol soils are widely distributed in the humid tropical and subtropical regions and are generally characterized with high contents of metal oxides. High metal oxides are believed to facilitate organic carbon (C) accumulation via mineral-organic C interactions but Oxisols often have low organic C. Yet, the causes that constrain organic C accumulation in Oxisol soil are not exactly clear. Here we report results from a microcosm experiment that evaluated how the quantity and size of crop residue fragments affect soil C retention in a typical Oxisol soil in southeast China. We found that there were significantly higher levels of dissolved organic C (DOC), microbial biomass C (MBC) and C accumulation in the heavy soil fraction in soil amended with fine-sized (<0.2 mm) compared with coarse-sized (5.0 mm) fragments. Attenuated total reflectance-Fourier transform infrared spectroscopy analysis further showed that fine-sized residues promoted stabilization of aliphatic C-H and carboxylic C=O compounds associated with mineral phases. In addition, correlation analysis revealed that the increased content of organic C in the heavy soil fraction was positively correlated with increased DOC and MBC. Together, these results suggest that enhancement of contact between organic materials and soil minerals may promote C stabilization in Oxisols.

Multi-facetted Metadata - Describing datasets with different metadata schemas at the same time

NASA Astrophysics Data System (ADS)

Ulbricht, Damian; Klump, Jens; Bertelmann, Roland

2013-04-01

Inspired by the wish to re-use research data a lot of work is done to bring data systems of the earth sciences together. Discovery metadata is disseminated to data portals to allow building of customized indexes of catalogued dataset items. Data that were once acquired in the context of a scientific project are open for reappraisal and can now be used by scientists that were not part of the original research team. To make data re-use easier, measurement methods and measurement parameters must be documented in an application metadata schema and described in a written publication. Linking datasets to publications - as DataCite [1] does - requires again a specific metadata schema and every new use context of the measured data may require yet another metadata schema sharing only a subset of information with the meta information already present. To cope with the problem of metadata schema diversity in our common data repository at GFZ Potsdam we established a solution to store file-based research data and describe these with an arbitrary number of metadata schemas. Core component of the data repository is an eSciDoc infrastructure that provides versioned container objects, called eSciDoc [2] "items". The eSciDoc content model allows assigning files to "items" and adding any number of metadata records to these "items". The eSciDoc items can be submitted, revised, and finally published, which makes the data and metadata available through the internet worldwide. GFZ Potsdam uses eSciDoc to support its scientific publishing workflow, including mechanisms for data review in peer review processes by providing temporary web links for external reviewers that do not have credentials to access the data. Based on the eSciDoc API, panMetaDocs [3] provides a web portal for data management in research projects. PanMetaDocs, which is based on panMetaWorks [4], is a PHP based web application that allows to describe data with any XML-based schema. It uses the eSciDoc infrastructures REST-interface to store versioned dataset files and metadata in a XML-format. The software is able to administrate more than one eSciDoc metadata record per item and thus allows the description of a dataset according to its context. The metadata fields can be filled with static or dynamic content to reduce the number of fields that require manual entries to a minimum and, at the same time, make use of contextual information available in a project setting. Access rights can be adjusted to set visibility of datasets to the required degree of openness. Metadata from separate instances of panMetaDocs can be syndicated to portals through RSS and OAI-PMH interfaces. The application architecture presented here allows storing file-based datasets and describe these datasets with any number of metadata schemas, depending on the intended use case. Data and metadata are stored in the same entity (eSciDoc items) and are managed by a software tool through the eSciDoc REST interface - in this case the application is panMetaDocs. Other software may re-use the produced items and modify the appropriate metadata records by accessing the web API of the eSciDoc data infrastructure. For presentation of the datasets in a web browser we are not bound to panMetaDocs. This is done by stylesheet transformation of the eSciDoc-item. [1] http://www.datacite.org [2] http://www.escidoc.org , eSciDoc, FIZ Karlruhe, Germany [3] http://panmetadocs.sf.net , panMetaDocs, GFZ Potsdam, Germany [4] http://metaworks.pangaea.de , panMetaWorks, Dr. R. Huber, MARUM, Univ. Bremen, Germany

Multistage treatment system for raw leachate from sanitary landfill combining biological nitrification-denitrification/solar photo-Fenton/biological processes, at a scale close to industrial--biodegradability enhancement and evolution profile of trace pollutants.

PubMed

Silva, Tânia F C V; Silva, M Elisabete F; Cunha-Queda, A Cristina; Fonseca, Amélia; Saraiva, Isabel; Sousa, M A; Gonçalves, C; Alpendurada, M F; Boaventura, Rui A R; Vilar, Vítor J P

2013-10-15

A multistage treatment system, at a scale close to the industrial, was designed for the treatment of a mature raw landfill leachate, including: a) an activated sludge biological oxidation (ASBO), under aerobic and anoxic conditions; b) a solar photo-Fenton process, enhancing the bio-treated leachate biodegradability, with and without sludge removal after acidification; and c) a final polishing step, with further ASBO. The raw leachate was characterized by a high concentration of humic substances (HS) (1211 mg CHS/L), representing 39% of the dissolved organic carbon (DOC) content, and a high nitrogen content, mainly in the form of ammonium nitrogen (>3.8 g NH4(+)-N/L). In the first biological oxidation step, a 95% removal of total nitrogen and a 39% mineralization in terms of DOC were achieved, remaining only the recalcitrant fraction, mainly attributed to HS (57% of DOC). Under aerobic conditions, the highest nitrification rate obtained was 8.2 mg NH4(+)-N/h/g of volatile suspended solids (VSS), and under anoxic conditions, the maximum denitrification rate obtained was 5.8 mg (NO2(-)-N + NO3(-)-N)/h/g VSS, with a C/N consumption ratio of 2.4 mg CH3OH/mg (NO2(-)-N + NO3(-)-N). The precipitation of humic acids (37% of HS) after acidification of the bio-treated leachate corresponds to a 96% DOC abatement. The amount of UV energy and H2O2 consumption during the photo-Fenton reaction was 30% higher in the experiment without sludge removal and, consequently, the reaction velocity was 30% lower. The phototreatment process led to the depletion of HS >80%, of low-molecular-weight carboxylate anions >70% and other organic micropollutants, thus resulting in a total biodegradability increase of >70%. The second biological oxidation allowed to obtain a final treated leachate in compliance with legal discharge limits regarding water bodies (with the exception of sulfate ions), considering the experiment without sludge. Finally, the high efficiency of the overall treatment process was further reinforced by the total removal percentages attained for the identified organic trace contaminants (>90%). Copyright © 2013 Elsevier Ltd. All rights reserved.

Transformation of molecular weight distributions of dissolved organic carbon and UV-absorbing compounds at full-scale wastewater-treatment plants.

PubMed

Esparza-Soto, Mario; Fox, Peter; Westerhoff, Paul

2006-03-01

The molecular-weight distribution (MWD) of wastewater dissolved-organic carbon (DOC) was determined in samples from seven full-scale wastewater-treatment plants (WWTPs) that use different biological treatments (air activated sludge [air-AS], pure-oxygen AS [O2-AS], and trickling filters). The research objective was to determine how different biological treatments influenced the MWD of wastewater DOC. Primary sedimentation effluent DOC from most of the WWTPs exhibited a skewed distribution toward the low-molecular-weight fraction (MWF) (40 to 50%, < 0.5 K Daltons [KDa]). The Air-AS effluent DOC exhibited a centrally clustered distribution, with the majority of DOC in the intermediate MWF (0.5 to 3 KDa). The O2-AS effluent DOC exhibited a skewed distribution toward the high MWF (> 3 KDa). The removal of DOC by air- and O2-AS bacteria followed trends predicted by a macromolecule degradation model. Trickling-filter effluent DOC exhibited a skewed distribution toward the high MWF (50% DOC, > 3 KDa).

Fluvial dissolved organic carbon composition varies spatially and seasonally in a small catchment draining a wind farm and felled forestry.

PubMed

Zheng, Ying; Waldron, Susan; Flowers, Hugh

2018-06-01

Assessing whether land use, from activities such as wind farm construction and tree-felling, impacts on terrestrial C delivery to rivers has focused on quantifying the loss of dissolved organic carbon (DOC), and not the composition changes. Here we explore how land use influences DOC composition by considering fluvial DOC concentration, [DOC], and spectrophotometric composition of a river draining a peat-rich catchment. We find that in this 5.7km 2 catchment differences occur in both the concentration and composition of the DOC in its sub-catchments. This is attributed to differences in how land was used: one tributary (D-WF) drains an area with wind farm construction and forestry in the headwaters, and one tributary (D-FF) drains an area with felled plantation trees. Generally, [DOC] in both streams showed similar seasonal variation, and autumn maxima. However, the felled catchment had greater mean [DOC] than the wind farm catchment. The SUVA 254 and E 4 /E 6 indicated DOC in both streams had similar aromaticity and fulvic:humic acid for most of the time, but SUVA 410 and E 2 /E 4 indicated less DOC humification in the felled catchment. This may be due to young DOC from the breakdown of residual branches and roots, or more humification in soils in the wind farm area. During the dry months, DOC composition showed more spatial variation: the D-WF DOC had smaller SUVA 254 (less total aromatic material) and SUVA 410 (fewer humic substances). The decreased E 2 /E 4 in both streams indicated the total aromatic carbon decreased more than humic substances content. Moreover, the larger E 4 /E 6 for D-WF in summer indicated that the humic substances were richer in fulvic acids than humic acids. Soil disturbance associated with forestry-felling likely contributed to the higher [DOC] and release of less-humified material in D-FF. This research indicates drivers of different DOC concentration and composition can exist even in small catchments. Copyright © 2018 Elsevier B.V. All rights reserved.

Microbial degradation of plant leachate alters lignin phenols and trihalomethane precursors

USGS Publications Warehouse

Pellerin, Brian A.; Hernes, Peter J.; Saraceno, John Franco; Spencer, Robert G.M.; Bergamaschi, Brian A.

2010-01-01

Although the importance of vascular plant-derived dissolved organic carbon (DOC) in freshwater systems has been studied, the role of leached DOC as precursors of disinfection byproducts (DBPs) during drinking water treatment is not well known. Here we measured the propensity of leachates from four crops and four aquatic macrophytes to form trihalomethanes (THMs)—a regulated class of DBPs—before and after 21 d of microbial degradation. We also measured lignin phenol content and specific UV absorbance (SUVA254) to test the assumption that aromatic compounds from vascular plants are resistant to microbial degradation and readily form DBPs. Leaching solubilized 9 to 26% of total plant carbon, which formed 1.93 to 6.72 mmol THM mol C-1 However, leachate DOC concentrations decreased by 85 to 92% over the 21-d incubation, with a concomitant decrease of 67 to 92% in total THM formation potential. Carbon-normalized THM yields in the residual DOC pool increased by 2.5 times on average, consistent with the preferential uptake of nonprecursor material. Lignin phenol concentrations decreased by 64 to 96% over 21 d, but a lack of correlation between lignin content and THM yields or SUVA254 suggested that lignin-derived compounds are not the source of increased THM precursor yields in the residual DOC pool. Our results indicate that microbial carbon utilization alters THM precursors in ecosystems with direct plant leaching, but more work is needed to identify the specific dissolved organic matter components with a greater propensity to form DBPs and affect watershed management, drinking water quality, and human health.

Seasonal change in precipitation, snowpack, snowmelt, soil water and streamwater chemistry, northern Michigan

USGS Publications Warehouse

Stottlemyer, R.; Toczydlowski, D.

1999-01-01

We have studied weekly precipitation, snowpack, snowmelt, soil water and streamwater chemistry throughout winter for over a decade in a small (176 ha) northern Michigan watershed with high snowfall and vegetated by 60 to 80 year-old northern hardwoods. In this paper, we examine physical, chemical, and biological processes responsible for observed seasonal change in streamwater chemistry based upon intensive study during winter 1996-1997. The objective was to define the contributions made to winter and spring streamwater chemical concentration and flux by processes as snowmelt, over-winter forest floor and surface soil mineralization, immobilization, and exchange, and subsurface flowpath. The forest floor and soil were unfrozen beneath the snowpack which permitted most snowmelt to enter. Over-winter soil mineralization and other biological processes maintain shallow subsurface ion and dissolved organic carbon (DOC) reservoirs. Small, but steady, snowmelt throughout winter removed readily mobilized soil NO3- which resulted in high over-winter streamwater concentrations but little flux. Winter soil water levels and flowpaths were generally deep which increased soil water and streamwater base cation (C(B)), HCO3-, and Si concentrations. Spring snowmelt increased soil water levels and removal of ions and DOC from the biologically active forest floor and shallow soils. The snowpack solute content was a minor component in determining streamwater ion concentration or flux during and following peak snowmelt. Exchangeable ions, weakly adsorbed anions, and DOC in the forest floor and surface soils dominated the chemical concentration and flux in soil water and streamwater. Following peak snowmelt, soil microbial immobilization and rapidly increased plant uptake of limiting nutrients removed nearly all available nitrogen from soil water and streamwater. During the growing season high evapotranspiration increased subsurface flowpath depth which in turn removed weathering products, especially C(B), HCO3-, and Si, from deeper soils. Soil water was a major component in the hydrologic and chemical budgets.We have studied weekly precipitation, snowpack, snowmelt, soil water and streamwater chemistry throughout winter for over a decade in a small (176 ha) northern Michigan watershed with high snowfall and vegetated by 60 to 80 year-old northern hardwoods. In this paper, we examine physical, chemical, and biological processes responsible for observed seasonal change in streamwater chemistry based upon intensive study during winter 1996-1997. The objective was to define the contributions made to winter and spring streamwater chemical concentration and flux by processes as snowmelt, over-winter forest floor and surface soil mineralization, immobilization, and exchange, and subsurface flowpath. The forest floor and soils were unfrozen beneath the snowpack which permitted most snowmelt to enter. Over-winter soil mineralization and other biological processes maintain shallow subsurface ion and dissolved organic carbon (DOC) reservoirs. Small, but steady, snowmelt throughout winter removed readily mobilized soil NO3- which resulted in high over-winter streamwater concentrations but little flux. Winter soil water levels and flowpaths were generally deep which increased soil water and streamwater base cation (CB), HCO3-, and Si concentrations. Spring snowmelt increased soil water levels and removal of ions and DOC from the biologically active forest floor and shallow soils. The snowpack solute content was a minor component in determining streamwater ion concentration or flux during and following peak snowmelt. Exchangeable ions, weakly adsorbed anions, and DOC in the forest floor and surface soils dominated the chemical concentration and flux in soil water and streamwater. Following peak snowmelt, soil microbial immobilization and rapidly increased plant uptake of limiting nutrients removed nearly all available nitrogen from soil water and streamwater. D

Evaluation of specific ultraviolet absorbance as an indicator of the chemical composition and reactivity of dissolved organic carbon

USGS Publications Warehouse

Weishaar, J.L.; Aiken, George R.; Bergamaschi, Brian A.; Fram, Miranda S.; Fujii, Roger; Mopper, K.

2003-01-01

Specific UV absorbance (SUVA) is defined as the UV absorbance of a water sample at a given wavelength normalized for dissolved organic carbon (DOC) concentration. Our data indicate that SUVA, determined at 254 nm, is strongly correlated with percent aromaticity as determined by 13C NMR for 13 organic matter isolates obtained from a variety of aquatic environments. SUVA, therefore, is shown to be a useful parameter for estimating the dissolved aromatic carbon content in aquatic systems. Experiments involving the reactivity of DOC with chlorine and tetramethylammonium hydroxide (TMAH), however, show a wide range of reactivity for samples with similar SUVA values. These results indicate that, while SUVA measurements are good predictors of general chemical characteristics of DOC, they do not provide information about reactivity of DOC derived from different types of source materials. Sample pH, nitrate, and iron were found to influence SUVA measurements.

Advances in the Control System for a High Precision Dissolved Organic Carbon Analyzer

NASA Astrophysics Data System (ADS)

Liao, M.; Stubbins, A.; Haidekker, M.

2017-12-01

Dissolved organic carbon (DOC) is a master variable in aquatic ecosystems. DOC in the ocean is one of the largest carbon stores on earth. Studies of the dynamics of DOC in the ocean and other low DOC systems (e.g. groundwater) are hindered by the lack of high precision (sub-micromolar) analytical techniques. Results are presented from efforts to construct and optimize a flow-through, wet chemical DOC analyzer. This study focused on the design, integration and optimization of high precision components and control systems required for such a system (mass flow controller, syringe pumps, gas extraction, reactor chamber with controlled UV and temperature). Results of the approaches developed are presented.

Carbon Isotope Composition as an Indicator of DOC Sources to a Stream During Events in a Temperate Forested Catchment

NASA Astrophysics Data System (ADS)

Doctor, D. H.; Sebestyen, S. D.; Aiken, G. R.; Shanley, J. B.; Kendall, C.; Boyer, E. W.

2006-12-01

Increased DOC flux in streams and rivers is commonly observed during high runoff regimes, however DOC concentrations alone do not provide information about multiple sources or pathways of DOC to streams. In an effort to gain this information, we measured DOC concentrations and stable carbon isotope composition (δ13C-DOC) on samples collected at high-frequency during events at Sleepers River Research Watershed in Vermont, USA. During snowmelt and storm events, peaks in stream DOC concentration (up to 10.5 mg/L) were coincident with peaks in flow. Stream water δ13C-DOC measurements ranged between -23.7‰ and - 28.9‰ and indicated changing sources of DOC during events; the highest δ13C-DOC values occurred consistently at the lowest flows, and the lowest δ13C-DOC values occurred with peaks in discharge. Water samples collected from shallow wells and stacked soil lysimeters showed the highest DOC concentrations in the most shallow (<0.5 m) lysimeter waters, and the lowest concentrations in the deeper (>1.5 m) well waters. Wells and lysimeters exhibited a range of δ13C-DOC values similar to those observed in the stream; however, samples collected from shallow horizons at nested wells and lysimeters consistently showed lower δ13C-DOC values than those from greater depths. Maple leaf litter collected from across the watershed provided an end-member of fresh organic material, with average δ13C composition of -31.3±0.7‰ (n=57), which is lower than the lowest measured DOC values in any of the stream, well, or lysimeter waters. A subset of stream waters were fractionated onto XAD4 and XAD8 resins; the hydrophobic acid fraction (XAD8) had consistently lower δ13C values than the transphilic acid fraction (XAD4), and both of these were lower than those of the bulk DOC. Samples with lower δ13C-DOC values also exhibited higher SUVA-254 values, i.e. greater aromaticity. Thus, lower δ13C-DOC values are interpreted as an indicator of relatively "fresh", more aromatic and more biologically labile material while higher δ13C-DOC values indicate relatively more degraded material. Since lower δ13C-DOC values were observed in the shallowest well and lysimeter waters and in stream water during periods of highest DOC flux, we surmise that fresh DOC is mobilized to the stream along relatively shallow flowpaths during high flows, and that a second source of more degraded DOC supplies background concentrations to the stream at lower flows.

The Age of Terrestrial Carbon Export and Rainfall Intensity in a Temperate River Headwater System

NASA Astrophysics Data System (ADS)

Tittel, J.; Büttner, O.; Freier, K.; Heiser, A.; Sudbrack, R.; Ollesch, G.

2013-12-01

Riverine dissolved organic carbon (DOC) supports the production of estuaries and coastal ecosystems, constituting one of the most actively recycled pools of the global carbon cycle. A substantial proportion of DOC entering oceans is highly aged, but its origins remain unclear. Significant fluxes of old DOC have never been observed in temperate headwaters where terrestrial imports take place. Here, we studied the radiocarbon age of DOC in three streams draining forested headwater catchments of the river Mulde (Ore Mountains, Germany). We found modern DOC at moderately dry and moderately wet conditions as well as at high discharges during snowmelt. Old groundwater carbon contributed to stream DOC during the summer drought, although the yield was negligible. However, in a four-week summer precipitation event DOC aged at between 160 and 270 years was delivered into the watershed. In one stream, the DOC was modern but depleted in radiocarbon compared to other hydrological conditions. The yield was substantial and corresponded to 20 to 52% of the annual DOC yields in wet and dry years, respectively. Time-integrating samples of a downstream reservoir also revealed modern DOC ages under moderate conditions and old DOC from the rainfall event. Earlier studies suggested that increasing precipitation escalates the contribution of modern DOC from topsoil layers to surface runoff. Our results demonstrate a step change occurring if rainfall intensities increase and become extreme; then the consequences lead to the mobilization of old carbon in exceptionally high concentrations. The runoff/precipitation ratios of rainfall events indicated that during extreme events upland areas of the catchments were hydrologically connected to the stream and upland DOC was activated. Furthermore, the analysis of long-term data suggested that the DOC export in extreme precipitation events added to the annual yield and was not compensated for by lower exports in remaining periods. We conclude that climate change, along with additional processes associated with human activities, channels old soil carbon into more rapidly cycled carbon pools of the hydrosphere.

Response of oxidative enzyme activities to nitrogen deposition affects soil concentrations of dissolved organic carbon

USGS Publications Warehouse

Waldrop, M.P.; Zak, D.R.

2006-01-01

Recent evidence suggests that atmospheric nitrate (NO3- ) deposition can alter soil carbon (C) storage by directly affecting the activity of lignin-degrading soil fungi. In a laboratory experiment, we studied the direct influence of increasing soil NO 3- concentration on microbial C cycling in three different ecosystems: black oak-white oak (BOWO), sugar maple-red oak (SMRO), and sugar maple-basswood (SMBW). These ecosystems span a broad range of litter biochemistry and recalcitrance; the BOWO ecosystem contains the highest litter lignin content, SMRO had intermediate lignin content, and SMBW leaf litter has the lowest lignin content. We hypothesized that increasing soil solution NO 3- would reduce lignolytic activity in the BOWO ecosystem, due to a high abundance of white-rot fungi and lignin-rich leaf litter. Due to the low lignin content of litter in the SMBW, we further reasoned that the NO3- repression of lignolytic activity would be less dramatic due to a lower relative abundance of white-rot basidiomycetes; the response in the SMRO ecosystem should be intermediate. We increased soil solution NO3- concentrations in a 73-day laboratory incubation and measured microbial respiration and soil solution dissolved organic carbon (DOC) and phenolics concentrations. At the end of the incubation, we measured the activity of ??-glucosidase, N-acetyl-glucosaminidase, phenol oxidase, and peroxidase, which are extracellular enzymes involved with cellulose and lignin degradation. We quantified the fungal biomass, and we also used fungal ribosomal intergenic spacer analysis (RISA) to gain insight into fungal community composition. In the BOWO ecosystem, increasing NO 3- significantly decreased oxidative enzyme activities (-30% to -54%) and increased DOC (+32% upper limit) and phenolic (+77% upper limit) concentrations. In the SMRO ecosystem, we observed a significant decrease in phenol oxidase activity (-73% lower limit) and an increase in soluble phenolic concentrations (+57% upper limit) in response to increasing NO 3- in soil solution, but there was no significant change in DOC concentration. In contrast to these patterns, increasing soil solution NO3- in the SMBW soil resulted in significantly greater phenol oxidase activity (+700% upper limit) and a trend toward lower DOC production (-52% lower limit). Nitrate concentration had no effect on microbial respiration or ??-glucosidase or N-acetyl-glucosaminidase activities. Fungal abundance and basidiomycete diversity tended to be highest in the BOWO soil and lowest in the SMBW, but neither displayed a consistent response to NO 3- additions. Taken together, our results demonstrate that oxidative enzyme production by microbial communities responds directly to NO3- deposition, controlling extracellular enzyme activity and DOC flux. The regulation of oxidative enzymes by different microbial communities in response to NO3- deposition highlights the fact that the composition and function of soil microbial communities directly control ecosystem-level responses to environmental change. ?? 2006 Springer Science+Business Media, Inc.

Web-based Loansome Doc, librarians, and end users: results from a survey of the Southeast Region.

PubMed

Paden, S L; Batson, A L; Wallace, R L

2001-07-01

The study examines how Loansome Doc services are implemented and used by libraries in the Southeast Region and describe end users' experiences with and attitudes toward Loansome Doc. 251 active DOCLINE libraries and 867 Loansome Doc users were surveyed. Roughly one half of the libraries offered Loansome Doc services. Of those that did not, most indicated no plans to offer it in the future. The majority had a small number of end users and experienced minimal increases in interlibrary loan activity. Problems were relatively rare. Satisfaction with Loansome Doc was high among all types of libraries. End users were usually physicians or other health care professionals who requested articles for research and patient care. Most learned about Loansome Doc through PubMed or Internet Grateful Med. End users appeared to be largely self-taught or received informal instruction in Loansome Doc. Loansome Doc filled document requests in a timely manner, and end users reported being satisfied with the service. Greater promotion of what Loansome Doc is and how it can benefit libraries can increase the number of participating libraries. While satisfaction of Loansome Doc end users is high, satisfaction could be increased with more help on the PubMed screen, more library training, and faster delivery methods.

The effectiveness of arbuscular-mycorrhizal fungi and Aspergillus niger or Phanerochaete chrysosporium treated organic amendments from olive residues upon plant growth in a semi-arid degraded soil.

PubMed

Medina, A; Roldán, A; Azcón, R

2010-12-01

Arbuscular mycorrhizal (AM) fungi and a residue from dry olive cake (DOC) supplemented with rock phosphate (RP) and treated with either Aspergillus niger (DOC-A) or Phanerochaete chrysosporium (DOC-P), were assayed in a natural, semi-arid soil using Trifolium repens or Dorycnium pentaphyllum plants. The effects of the AM fungi and/or DOC-A were compared with P-fertilisation (P) over eleven successive harvests to evaluate the persistence of the effectiveness of the treatments. The biomass of dually-treated plants after four successive harvests was greater than that obtained for non-treated plants or those receiving the AM inoculum or DOC-A treatments after eleven yields. The AM inoculation was critical for obtaining plant growth benefit from the application of fermented DOC-A residue. The abilities of the treatments to prevent plant drought stress were also assayed. Drought-alleviating effects were evaluated in terms of plant growth, proline and total sugars concentration under alternative drought and re-watering conditions (8th and 9th harvests). The concentrations of both compounds in plant biomass increased under drought when DOC-A amendment and AM inoculation were employed together: they reinforced the plant drought-avoidance capabilities and anti-oxidative defence. Water stress was less compensated in P-fertilised than in DOC-A-treated plants. DOC-P increased D. pentaphyllum biomass, shoot P content, nodule number and AM colonisation, indicating the greater DOC-transforming ability of P. chrysosporium compared to A. niger. The lack of AM colonisation and nodulation in this soil was compensated by the application of DOC-P, particularly with AM inoculum. The management of natural resources (organic amendments and soil microorganisms) represents an important strategy that assured the growth, nutrition and plant establishment in arid, degraded soils, preventing the damage that arises from limited water and nutrient supply. Copyright © 2010 Elsevier Ltd. All rights reserved.

Dynamics of dissolved organic carbon (DOC) through stormwater basins designed for groundwater recharge in urban area: Assessment of retention efficiency.

PubMed

Mermillod-Blondin, Florian; Simon, Laurent; Maazouzi, Chafik; Foulquier, Arnaud; Delolme, Cécile; Marmonier, Pierre

2015-09-15

Managed aquifer recharge (MAR) has been developed in many countries to limit the risk of urban flooding and compensate for reduced groundwater recharge in urban areas. The environmental performances of MAR systems like infiltration basins depend on the efficiency of soil and vadose zone to retain stormwater-derived contaminants. However, these performances need to be finely evaluated for stormwater-derived dissolved organic matter (DOM) that can affect groundwater quality. Therefore, this study examined the performance of MAR systems to process DOM during its transfer from infiltration basins to an urban aquifer. DOM characteristics (fluorescent spectroscopic properties, biodegradable and refractory fractions of dissolved organic carbon -DOC-, consumption by micro-organisms during incubation in slow filtration sediment columns) were measured in stormwater during its transfer through three infiltration basins during a stormwater event. DOC concentrations sharply decreased from surface to the aquifer for the three MAR sites. This pattern was largely due to the retention of biodegradable DOC which was more than 75% for the three MAR sites, whereas the retention of refractory DOC was more variable and globally less important (from 18% to 61% depending on MAR site). Slow filtration column experiments also showed that DOC retention during stormwater infiltration through soil and vadose zone was mainly due to aerobic microbial consumption of the biodegradable fraction of DOC. In parallel, measurements of DOM characteristics from groundwaters influenced or not by MAR demonstrated that stormwater infiltration increased DOC quantity without affecting its quality (% of biodegradable DOC and relative aromatic carbon content -estimated by SUVA254-). The present study demonstrated that processes occurring in soil and vadose zone of MAR sites were enough efficient to limit DOC fluxes to the aquifer. Nevertheless, the enrichments of DOC concentrations measured in groundwater below infiltration basins need to be considered in future studies to especially assess their impact on groundwater quality. Copyright © 2015 Elsevier Ltd. All rights reserved.

Identifying sources of dissolved organic carbon in agriculturally dominated rivers using radiocarbon age dating: Sacramento-San Joaquin River Basin, California

USGS Publications Warehouse

Sickman, James O.; DiGiorgio, Carol L.; Davisson, M. Lee; Lucero, Delores M.; Bergamaschi, Brian A.

2010-01-01

We used radiocarbon measurements of dissolved organic carbon (DOC) to resolve sources of riverine carbon within agriculturally dominated landscapes in California. During 2003 and 2004, average Δ14C for DOC was −254‰ in agricultural drains in the Sacramento–San Joaquin Delta, −218‰ in the San Joaquin River, −175‰ in the California State Water Project and −152‰ in the Sacramento River. The age of bulk DOC transiting the rivers of California’s Central Valley is the oldest reported for large rivers and suggests wide-spread loss of soil organic matter caused by agriculture and urbanization. Using DAX 8 adsorbent, we isolated and measured 14C concentrations in hydrophobic acid fractions (HPOA); river samples showed evidence of bomb-pulse carbon with average Δ14C of 91 and 76‰ for the San Joaquin and Sacramento Rivers, respectively, with older HPOA, −204‰, observed in agricultural drains. An operationally defined non-HPOA fraction of DOC was observed in the San Joaquin River with seasonally computed Δ14C values of between −275 and −687‰; the source of this aged material was hypothesized to be physically protected organic-matter in high clay-content soils and agrochemicals (i.e., radiocarbon-dead material) applied to farmlands. Mixing models suggest that the Sacramento River contributes about 50% of the DOC load in the California State Water Project, and agricultural drains contribute approximately one-third of the load. In contrast to studies showing stabilization of soil carbon pools within one or two decades following land conversion, sustained loss of soil organic matter, occurring many decades after the initial agricultural-land conversion, was observed in California’s Central Valley.

Greywater as a sustainable water source: A photocatalytic treatment technology under artificial and solar illumination.

PubMed

Tsoumachidou, Sophia; Velegraki, Theodora; Antoniadis, Apostolos; Poulios, Ioannis

2017-06-15

Greywater considers being a highly reclaimable water source particularly important for water-stressed nations. In this work, heterogeneous photocatalysis using artificial and solar illumination has been applied for the mineralization of simulated light greywater (effluents from dishwashers and kitchen sinks were excluded from the study). The effects on the process' efficiency of TiO 2 P25 catalyst's concentration, initial concentration of H 2 O 2 and Fe 3+ , pH of the solution, as well as the type of radiation, were evaluated in a bench-scale Pyrex reactor and a pilot-scale slurry fountain photoreactor. The treatment efficiency has been followed through the evolution of the organic matter content expresses as dissolved organic carbon (DOC). Best results were obtained with the photo-Fenton-assisted TiO 2 photocatalytic process with 72% DOC removal after 210 min of bench scale treatment, while under the same photocatalytic conditions in the pilot reactor the DOC removal reached almost 64%. Moreover, the decrease in toxicity, phytotoxicity and biodegradability of the simulated wastewater has been observed after solar-induced photocatalytic treatment. Copyright © 2016 Elsevier Ltd. All rights reserved.

Nutrient and dissolved organic carbon removal from natural waters using industrial by-products.

PubMed

Wendling, Laura A; Douglas, Grant B; Coleman, Shandel; Yuan, Zheng

2013-01-01

Attenuation of excess nutrients in wastewater and stormwater is required to safeguard aquatic ecosystems. The use of low-cost, mineral-based industrial by-products with high Ca, Mg, Fe or Al content as a solid phase in constructed wetlands potentially offers a cost-effective wastewater treatment option in areas without centralised water treatment facilities. Our objective was to investigate use of water treatment residuals (WTRs), coal fly ash (CFA), and granular activated carbon (GAC) from biomass combustion in in-situ water treatment schemes to manage dissolved organic carbon (DOC) and nutrients. Both CaO- and CaCO(3)-based WTRs effectively attenuated inorganic N species but exhibited little capacity for organic N removal. The CaO-based WTR demonstrated effective attenuation of DOC and P in column trials, and a high capacity for P sorption in batch experiments. Granular activated carbon proved effective for DOC and dissolved organic nitrogen (DON) removal in column trials, but was ineffective for P attenuation. Only CFA demonstrated effective removal of a broad suite of inorganic and organic nutrients and DOC; however, Se concentrations in column effluents exceeded Australian and New Zealand water quality guideline values. Water treated by filtering through the CaO-based WTR exhibited nutrient ratios characteristic of potential P-limitation with no potential N- or Si-limitation respective to growth of aquatic biota, indicating that treatment of nutrient-rich water using the CaO-based WTR may result in conditions less favourable for cyanobacterial growth and more favourable for growth of diatoms. Results show that selected industrial by-products may mitigate eutrophication through targeted use in nutrient intervention schemes. Crown Copyright © 2012. Published by Elsevier B.V. All rights reserved.

Influence of natural dissolved organic carbon on the bioavailability of mercury to a freshwater alga

USGS Publications Warehouse

Gorski, P.R.; Armstrong, D.E.; Hurley, J.P.; Krabbenhoft, D.P.

2008-01-01

Bioavailability of mercury (Hg) to Selenastrum capricornutum was assessed in bioassays containing field-collected freshwater of varying dissolved organic carbon (DOC) concentrations. Bioconcentration factor (BCF) was measured using stable isotopes of methylmercury (MeHg) and inorganic Hg(II). BCFs for MeHg in low-DOC lake water were significantly larger than those in mixtures of lake water and high-DOC river water. The BCF for MeHg in rainwater (lowest DOC) was the largest of any treatment. Rainwater and lake water also had larger BCFs for Hg(II) than river water. Moreover, in freshwater collected from several US and Canadian field sites, BCFs for Hg(II) and MeHg were low when DOC concentrations were >5 mg L-1. These results suggest high concentrations of DOC inhibit bioavailability, while low concentrations may provide optimal conditions for algal uptake of Hg. However, variability of BCFs at low DOC indicates that DOC composition or other ligands may determine site-specific bioavailability of Hg.

The two faces of DOC.

PubMed

Wood, Chris M; Al-Reasi, H A; Smith, D Scott

2011-10-01

Dissolved organic carbon (DOC), through its ability to complex metals and thereby reduce their bioavailability, plays a major role in ameliorating metal toxicity in natural waters. Indeed DOC is a key variable in the Biotic Ligand Model (BLM) for predicting metal toxicity on a site-specific basis. However, recent evidence indicates that all DOCs are not alike, but rather heterogeneous in their ability to protect organisms against metal toxicity, at least in fresh water. The degree of protection appears to correlate with optical properties, such that dark, aromatic-rich compounds of allochthonous origin, with greater humic acid content, are more effective in this regard, particularly against Cu, Ag, and Pb toxicity. The specific absorption coefficient of the DOC in the 300-350nm range (SAC(300-350)) has proven to be a simple and effective index of this protective ability. PARAFAC, a multivariate statistical technique for analysis of excitation-emission fluorescence spectroscopy data, also holds promise for quantifying the humic-like and fulvic-like fluorophores, which tend to be positively and negatively correlated with protective ability, respectively. However, what has been largely missing in the toxicological realm is any appreciation that DOC may also affect the physiology of target organisms, such that part of the protection may occur by a mechanism other than metal complexation. Recently published evidence demonstrates that DOC has effects on Na(+) transport, diffusive permeability, and electrical properties of the gills in fish and crustaceans in a manner which will promote Na(+) homeostasis. These actions could thereby protect against metal toxicity by physiological mechanisms. Future research should investigate potential direct interactions of DOC molecules with the branchial epithelium. Incorporation of optical properties of DOC could be used to improve the predictive capabilities of the BLM. 2011 Elsevier B.V. All rights reserved.

Assessing the contribution of wetlands and subsided islands to dissolved organic matter and disinfection byproduct precursors in the Sacramento-San Joaquin River Delta: A geochemical approach

USGS Publications Warehouse

Kraus, T.E.C.; Bergamaschi, B.A.; Hernes, P.J.; Spencer, R.G.M.; Stepanauskas, R.; Kendall, C.; Losee, R.F.; Fujii, R.

2008-01-01

This study assesses how rivers, wetlands, island drains and open water habitats within the Sacramento-San Joaquin River Delta affect dissolved organic matter (DOM) content and composition, and disinfection byproduct (DBP) formation. Eleven sites representative of these habitats were sampled on six dates to encompass seasonal variability. Using a suite of qualitative analyses, including specific DBP formation potential, absorbance, fluorescence, lignin content and composition, C and N stable isotopic compositions, and structural groupings determined using CPMAS (cross polarization, magic angle spinning) 13C NMR, we applied a geochemical fingerprinting approach to characterize the DOM from different Delta habitats, and infer DOM and DBP precursor sources and estimate the relative contribution from different sources. Although river input was the predominant source of dissolved organic carbon (DOC), we observed that 13-49% of the DOC exported from the Delta originated from sources within the Delta, depending on season. Interaction with shallow wetlands and subsided islands significantly increased DOC and DBP precursor concentrations and affected DOM composition, while deep open water habitats had little discernable effect. Shallow wetlands contributed the greatest amounts of DOM and DBP precursors in the spring and summer, in contrast to island drains which appeared to be an important source during winter months. The DOM derived from wetlands and island drains had greater haloacetic acid precursor content relative to incoming river water, while two wetlands contributed DOM with greater propensity to form trihalomethanes. These results are pertinent to restoration of the Delta. Large scale introduction of shallow wetlands, a proposed restoration strategy, could alter existing DOC and DBP precursor concentrations, depending on their hydrologic connection to Delta channels. ?? 2008 Elsevier Ltd.

The relationship between soil heterotrophic activity, soil dissolved organic carbon (DOC) leachate, and catchment-scale DOC export in headwater catchments

USGS Publications Warehouse

Brooks, P.D.; McKnight, Diane M.; Bencala, K.E.

1999-01-01

Dissolved organic carbon (DOC) from terrestrial sources forms the major component of the annual carbon budget in many headwater streams. In high-elevation catchments in the Rocky Mountains, DOC originates in the upper soil horizons and is flushed to the stream primarily during spring snowmelt. To identify controls on the size of the mobile soil DOC pool available to be transported during the annual melt event, we measured soil DOC production across a range of vegetation communities and soil types together with catchment DOC export in paired watersheds in Summit County, Colorado. Both surface water DOC concentrations and watershed DOC export were lower in areas where pyrite weathering resulted in lower soil pH. Similarly, the amount of DOC leached from organic soils was significantly smaller (p < 0.01) at sites having low soil pH. Scaling point source measurements of DOC production and leaching to the two basins and assuming only vegetated areas contribute to DOC production, we calculated that the amount of mobile DOC available to be leached to surface water during melt was 20.3 g C m−2 in the circumneutral basin and 17.8 g C m−2 in the catchment characterized by pyrite weathering. The significant (r2=0.91 and p < 0.05), linear relationship between over-winter CO2 flux and the amount of DOC leached from upper soil horizons during snowmelt suggests that the mechanism for the difference in production of mobile DOC was heterotrophic processing of soil carbon in snow-covered soil. Furthermore, this strong relationship between over-winter heterotrophic activity and the size of the mobile DOC pool present in a range of soil and vegetation types provides a likely mechanism for explaining the interannual variability of DOC export observed in high-elevation catchments.

[The remove characteristics of dissolved organic matter in landfill leachate during the treatment process].

PubMed

He, Xiao-Song; Yu, Jing; Xi, Bei-Dou; Jiang, Yong-Hai; Zhang, Jin-Bao; Li, Dan; Pan, Hong-Wei; Liu, Hong-Liang

2012-09-01

In order to investigate remove characteristics of dissolved organic matter in landfill leachate, leachates were sampled during the process (i. e. , adjusting tank, anaerobic zone, oxidation ditch and MBR processing). Dissolved organic matter was extracted and its content and structure were characterized by fluorescence excitation-emission matrix spectra, UV-Vis specrtra and FTIR spectra. The results showed that an amount of 377.6 mg x L(-1) dissolved organic carbon (DOC) was removed during the whole treatment process, and the total removal rate was up to 78.34%. The 25.56% of DOC in the adjusting tank was removed during the anaerobic zone, 41.58% of DOC in anaerobic effluent was removed during the oxidation ditch, while 50.19% of DOC in the oxidation ditch effluent decreased in the MBR process. The anaerobic process increased the content of unsaturated compound and polysaccharides in leachate DOM, which improved the leachate biochemical characteristics. The unsaturated compound and polysaccharides were removed effectively during being in oxidation ditch. Protein-like and humic-like fluorescence peaks were observed in the adjusting tank and anaerobic zone, while humic-like fluorescence peaks were just presented in the oxidation ditch and MBR processing. Protein-like and fulvic-like substances were biodegraded in the adjusting tank and anaerobic zone, while humic-like materials were removed in the MBR process.

Temporal changes in photoreactivity of dissolved organic carbon and implications for aquatic carbon fluxes from peatlands

NASA Astrophysics Data System (ADS)

Pickard, Amy E.; Heal, Kate V.; McLeod, Andrew R.; Dinsmore, Kerry J.

2017-04-01

Aquatic systems draining peatland catchments receive a high loading of dissolved organic carbon (DOC) from the surrounding terrestrial environment. Whilst photo-processing is known to be an important process in the transformation of aquatic DOC, the drivers of temporal variability in this pathway are less well understood. In this study, 8 h laboratory irradiation experiments were conducted on water samples collected from two contrasting peatland aquatic systems in Scotland: a peatland stream and a reservoir in a catchment with high percentage peat cover. Samples were collected monthly at both sites from May 2014 to May 2015 and from the stream system during two rainfall events. DOC concentrations, absorbance properties and fluorescence characteristics were measured to investigate characteristics of the photochemically labile fraction of DOC. CO2 and CO produced by irradiation were also measured to determine gaseous photoproduction and intrinsic sample photoreactivity. Significant variation was seen in the photoreactivity of DOC between the two systems, with total irradiation-induced changes typically 2 orders of magnitude greater at the high-DOC stream site. This is attributed to longer water residence times in the reservoir rendering a higher proportion of the DOC recalcitrant to photo-processing. During the experimental irradiation, 7 % of DOC in the stream water samples was photochemically reactive and direct conversion to CO2 accounted for 46 % of the measured DOC loss. Rainfall events were identified as important in replenishing photoreactive material in the stream, with lignin phenol data indicating mobilisation of fresh DOC derived from woody vegetation in the upper catchment. This study shows that peatland catchments produce significant volumes of aromatic DOC and that photoreactivity of this DOC is greatest in headwater streams; however, an improved understanding of water residence times and DOC input-output along the source to sea aquatic pathway is required to determine the fate of peatland carbon.

Multi-residue analysis of pharmaceuticals in aqueous environmental samples by online solid-phase extraction-ultra-high-performance liquid chromatography-tandem mass spectrometry: optimisation and matrix effects reduction by quick, easy, cheap, effective, rugged and safe extraction.

PubMed

Bourdat-Deschamps, Marjolaine; Leang, Sokha; Bernet, Nathalie; Daudin, Jean-Jacques; Nélieu, Sylvie

2014-07-04

The aim of this study was to develop and optimise an analytical method for the quantification of a bactericide and 13 pharmaceutical products, including 8 antibiotics (fluoroquinolones, tetracyclines, sulfonamides, macrolide), in various aqueous environmental samples: soil water and aqueous fractions of pig slurry, digested pig slurry and sewage sludge. The analysis was performed by online solid-phase extraction coupled to ultra-high performance liquid chromatography with tandem mass spectrometry (online SPE-UHPLC-MS-MS). The main challenge was to minimize the matrix effects observed in mass spectrometry, mostly due to ion suppression. They depended on the dissolved organic carbon (DOC) content and its origin, and ranged between -22% and +20% and between -38% and -93% of the signal obtained without matrix, in soil water and slurry supernatant, respectively. The very variable levels of these matrix effects suggested DOC content cut-offs above which sample purification was required. These cut-offs depended on compounds, with concentrations ranging from 30 to 290mgC/L for antibiotics (except tylosine) up to 600-6400mgC/L for the most apolar compounds. A modified Quick, Easy, Cheap, Effective, Rugged and Safe (QuEChERS) extraction procedure was therefore optimised using an experimental design methodology, in order to purify samples with high DOC contents. Its performance led to a compromise, allowing fluoroquinolone and tetracycline analysis. The QuEChERS extraction salts consisted therefore of sodium acetate, sodium sulfate instead of magnesium sulfate, and sodium ethylenediaminetetraacetate (EDTA) as a ligand of divalent cations. The modified QuEChERS procedure employed for the extraction of pharmaceuticals in slurry and digested slurry liquid phases reduced the matrix effects for almost all the compounds, with extraction recoveries generally above 75%. The performance characteristics of the method were evaluated in terms of linearity, intra-day and inter-day precision, accuracy and limits of quantification, which reached concentration ranges of 5-270ng/L in soil water and sludge supernatant, and 31-2400ng/L in slurry and digested slurry supernatants, depending on the compounds. The new method was then successfully applied for the determination of the target compounds in environmental samples. Copyright © 2014 Elsevier B.V. All rights reserved.

Arsenic in New Jersey Coastal Plain streams, sediments, and shallow groundwater: effects from different geologic sources and anthropogenic inputs on biogeochemical and physical mobilization processes

USGS Publications Warehouse

Barringer, Julia L.; Reilly, Pamela A.; Eberl, Dennis D.; Mumford, Adam C.; Benzel, William M.; Szabo, Zoltan; Shourds, Jennifer L.; Young, Lily Y.

2013-01-01

With a history of agriculture in the New Jersey Coastal Plain, anthropogenic inputs of As, such as residues from former pesticide applications in soils, can amplify any geogenic As in runoff. Such inputs contribute to an increased total As load to a stream at high stages of flow. As a result of yet another anthropogenic influence, microbes that reduce and mobilize As beneath the streambeds are stimulated by inputs of dissolved organic carbon (DOC). Although DOC is naturally occurring, anthropogenic contributions from wastewater inputs may deliver increased levels of DOC to subsurface soils and ultimately groundwater. Arsenic concentrations may increase with the increases in pH of groundwater and stream water in developed areas receiving wastewater inputs, as As mobilization caused by pH-controlled sorption and desorption reactions are likely to occur in waters of neutral or alkaline pH (for example, Nimick and others, 1998; Barringer and others, 2007b). Because of the difference in As content of the geologic materials in the two sub-provinces of the Coastal Plain, the amount of As that is mobile in groundwater and stream water is, potentially, substantially greater in the Inner Coastal Plain than in the Outer Coastal Plain. In turn, streams within the Inner and Outer Coastal Plain can receive substantially more As in groundwater discharge from developed areas than from environments where DOC appears to be of natural origin.

Differences in dissolved organic matter between reclaimed water source and drinking water source.

PubMed

Hu, Hong-Ying; Du, Ye; Wu, Qian-Yuan; Zhao, Xin; Tang, Xin; Chen, Zhuo

2016-05-01

Dissolved organic matter (DOM) significantly affects the quality of reclaimed water and drinking water. Reclaimed water potable reuse is an effective way to augment drinking water source and de facto reuse exists worldwide. Hence, when reclaimed water source (namely secondary effluent) is blended with drinking water source, understanding the difference in DOM between drinking water source (dDOM) and reclaimed water source (rDOM) is essential. In this study, composition, transformation, and potential risk of dDOM from drinking water source and rDOM from secondary effluent were compared. Generally, the DOC concentration of rDOM and dissolved organic nitrogen (DON) content in reclaimed water source were higher but rDOM exhibited a lower aromaticity. Besides, rDOM comprises a higher proportion of hydrophilic fractions and more low-molecular weight compounds, which are difficult to be removed during coagulation. Although dDOM exhibited higher specific disinfection byproducts formation potential (SDBPFP), rDOM formed more total disinfection byproducts (DBPs) during chlorination including halomethanes (THMs) and haloacetic acids (HAAs) due to high DOC concentration. Likewise, in consideration of DOC basis, rDOM contained more absolute assimilable organic carbon (AOC) despite showing a lower specific AOC (normalized AOC per unit of DOC). Besides, rDOM exhibited higher biotoxicity including genotoxicity and endocrine disruption. Therefore, rDOM presents a greater potential risk than dDOM does. Reclaimed water source needs to be treated carefully when it is blended with drinking water source. Copyright © 2015. Published by Elsevier B.V.

High light intensity mediates a shift from allochthonous to autochthonous carbon use in phototrophic stream biofilms

NASA Astrophysics Data System (ADS)

Wagner, Karoline; Bengtsson, Mia M.; Findlay, Robert H.; Battin, Tom J.; Ulseth, Amber J.

2017-07-01

Changes in the riparian vegetation along stream channels, diurnal light availability, and longitudinal fluctuations in the local light regime in streams influence primary production and carbon (C) cycling in benthic stream biofilms. To investigate the influence of light availability on the uptake dynamics of autochthonous and allochthonous dissolved organic carbon (DOC) in benthic biofilms, we experimentally added 13C-labeled allochthonous DOC to biofilms grown under light intensities ranging from 5 to 152 μmol photons m-2 s-1. We calculated the net C flux, which showed that benthic biofilms released autochthonous DOC across the entire light gradient. Light availability and diurnal light patterns influenced C uptake by benthic biofilms. More allochthonous DOC was respired under low light availability and at night, whereas under high light availability and during the day mainly autochthonous C was respired by the benthic biofilm community. Furthermore, phenol oxidase activity (indicative of allochthonous DOC uptake) was more elevated under low light availability, whereas beta-glucosidase activity (indicative of autochthonous DOC use) increased with light intensity. Collectively, our results suggest that biofilms exposed to high light inputs preferentially used autochthonous DOC, whereas biofilms incubated at attenuated levels showed greater use of allochthonous DOC. This has implications for the spatial dynamics of DOC uptake in streams and speaks against the occurrence of priming effects in algal-dominated stream biofilms.

The Emerging Diabetes Online Community

PubMed Central

Hilliard, Marisa E.; Sparling, Kerri M.; Hitchcock, Jeff; Oser, Tamara K.; Hood, Korey K.

2015-01-01

Abstract: Background Diabetes self-management is complex and demanding, and isolation and burnout are common experiences. The Internet provides opportunities for people with diabetes to connect with one another to address these challenges. The aims of this paper are to introduce readers to the platforms on which Diabetes Online Community (DOC) participants interact, to discuss reasons for and risks associated with diabetes-related online activity, and to review research related to the potential impact of DOC participation on diabetes outcomes. Methods Research and online content related to diabetes online activity is reviewed, and DOC writing excerpts are used to illustrate key themes. Guidelines for meaningful participation in DOC activities for people with diabetes, families, health care providers, and industry are provided. Results Common themes around DOC participation include peer support, advocacy, self-expression, seeking and sharing diabetes information, improving approaches to diabetes data management, and humor. Potential risks include access to misinformation and threats to individuals’ privacy, though there are limited data on negative outcomes resulting from such activities. Likewise, few data are available regarding the impact of DOC involvement on glycemic outcomes, but initial research suggests a positive impact on emotional experiences, attitudes toward diabetes, and engagement in diabetes management behaviors. Conclusion The range of DOC participants, activities, and platforms is growing rapidly. The Internet provides opportunities to strengthen communication and support among individuals with diabetes, their families, health care providers, the health care industry, policy makers, and the general public. Research is needed to investigate the impact of DOC participation on self-management, quality of life, and glycemic control, and to design and evaluate strategies to maximize its positive impact. PMID:25901500

The emerging diabetes online community.

PubMed

Hilliard, Marisa E; Sparling, Kerri M; Hitchcock, Jeff; Oser, Tamara K; Hood, Korey K

2015-01-01

Diabetes self-management is complex and demanding, and isolation and burnout are common experiences. The Internet provides opportunities for people with diabetes to connect with one another to address these challenges. The aims of this paper are to introduce readers to the platforms on which Diabetes Online Community (DOC) participants interact, to discuss reasons for and risks associated with diabetes-related online activity, and to review research related to the potential impact of DOC participation on diabetes outcomes. Research and online content related to diabetes online activity is reviewed, and DOC writing excerpts are used to illustrate key themes. Guidelines for meaningful participation in DOC activities for people with diabetes, families, health care providers, and industry are provided. Common themes around DOC participation include peer support, advocacy, self-expression, seeking and sharing diabetes information, improving approaches to diabetes data management, and humor. Potential risks include access to misinformation and threats to individuals' privacy, though there are limited data on negative outcomes resulting from such activities. Likewise, few data are available regarding the impact of DOC involvement on glycemic outcomes, but initial research suggests a positive impact on emotional experiences, attitudes toward diabetes, and engagement in diabetes management behaviors. The range of DOC participants, activities, and platforms is growing rapidly. The Internet provides opportunities to strengthen communication and support among individuals with diabetes, their families, health care providers, the health care industry, policy makers, and the general public. Research is needed to investigate the impact of DOC participation on self-management, quality of life, and glycemic control, and to design and evaluate strategies to maximize its positive impact.

Flux of carbon from 14C-enriched leaf litter throughout a forest soil mesocosm

DOE Office of Scientific and Technical Information (OSTI.GOV)

Froberg, Mats J.; Hanson, Paul J; Trumbore, Susan E.

2009-01-01

The role of DOC for the build-up of soil organic carbon pools is still not well known, but it is thought to play a role in the transport of carbon to a greater depth where it becomes more stable. The aim of this study was to elucidate within-year dynamics of carbon transport from litter to the O (Oe and Oa) and A horizons. Mesocosms with constructed soil profiles were used to study dynamics of C transport from 14C-enriched (about 1000 ) leaf litter to the Oe/Oa and A horizons as well as the mineralization of leaf litter. The mesocosms weremore » placed in the field for 17 months during which time fluxes and 14C content of DOC and CO2 were measured. Changes in 14C in leaf litter and bulk soil C pools were also recorded. Significant simultaneous release and immobilization of DOC occurring in both the O and A horizons was hypothesized. Contrary to our hypothesis, DOC released from the labeled Oi horizon was not retained within the Oe/Oa layer. DOC originating in the unlabeled Oe/Oa layer was also released for transport. Extensive retention of DOC occurred in the A horizon. DOC leaching from A horizon consisted of a mix of DOC from different sources, with a main fraction originating in the A horizon and a smaller fraction leached from the overlaying horizons. The C and 14C budget for the litter layer also indicated a surprisingly large amount of carbon with ambient Δ14C-signature to be respired from this layer. Data for this site also suggested significant contributions from throughfall to dissolved organic carbon (DOC) transport into and respiration from the litter layer. The results from this study showed that DOC retentionwas low in the O horizon and therefore not important for the O horizon carbon budget. In the A horizon DOC retention was extensive, but annual DOC input was small compared to C stocks and therefore not important for changes in soil C on an annual timescale.« less

Dissolved Organic Carbon in the North Atlantic Meridional Overturning Circulation.

PubMed

Fontela, Marcos; García-Ibáñez, Maribel I; Hansell, Dennis A; Mercier, Herlé; Pérez, Fiz F

2016-05-31

The quantitative role of the Atlantic Meridional Overturning Circulation (AMOC) in dissolved organic carbon (DOC) export is evaluated by combining DOC measurements with observed water mass transports. In the eastern subpolar North Atlantic, both upper and lower limbs of the AMOC transport high-DOC waters. Deep water formation that connects the two limbs of the AMOC results in a high downward export of non-refractory DOC (197 Tg-C·yr(-1)). Subsequent remineralization in the lower limb of the AMOC, between subpolar and subtropical latitudes, consumes 72% of the DOC exported by the whole Atlantic Ocean. The contribution of DOC to the carbon sequestration in the North Atlantic Ocean (62 Tg-C·yr(-1)) is considerable and represents almost a third of the atmospheric CO2 uptake in the region.

Dissolved Organic Carbon in the North Atlantic Meridional Overturning Circulation

PubMed Central

Fontela, Marcos; García-Ibáñez, Maribel I.; Hansell, Dennis A.; Mercier, Herlé; Pérez, Fiz F.

2016-01-01

The quantitative role of the Atlantic Meridional Overturning Circulation (AMOC) in dissolved organic carbon (DOC) export is evaluated by combining DOC measurements with observed water mass transports. In the eastern subpolar North Atlantic, both upper and lower limbs of the AMOC transport high-DOC waters. Deep water formation that connects the two limbs of the AMOC results in a high downward export of non-refractory DOC (197 Tg-C·yr−1). Subsequent remineralization in the lower limb of the AMOC, between subpolar and subtropical latitudes, consumes 72% of the DOC exported by the whole Atlantic Ocean. The contribution of DOC to the carbon sequestration in the North Atlantic Ocean (62 Tg-C·yr−1) is considerable and represents almost a third of the atmospheric CO2 uptake in the region. PMID:27240625

Distinct expression of alkaline phosphatase activity in epilimnetic bacteria: Implication for persistent DOC consumption in a P-limited reservoir

NASA Astrophysics Data System (ADS)

Tseng, Y.; Kao, S.; Shiah, F.

2013-12-01

In a P-deficient system, P availability usually controls the microbial activity and thus the ecosystem function. Thingstad et al. (1997) first addressed a 'Malfunctioning Microbial-loop' theory, which stated that low bacterial production (BP) caused by insufficient nutrient supply would result in DOC accumulation in an oligotrophic ecosystem. In this study we re-examined the theory by conducting seasonal patterns and correlations among soluble reactive phosphate (SRP) and DOC, microbial abundances (picocyanobacteria, bacteria, and heterotrophic nanoflagellate; HNF) and activities (primary production, bacterial production, and alkaline phosphatase activity; APA) coupled with enzyme-labeled fluorescence (ELF) assays on bacterioplankton in a subtropical reservoir sharing the common features, nitrate-replete and P-deficient, with most natural freshwater system during Oct 2007-Oct 2008. Persistently high APA was recorded during most of time, implying that the system was P-deficient. Size fractionated APA and ELF assay revealed that bacteria were the major APA contributor. However, significantly low epilimnion DOC was recorded during the stratified summer season accompanying with high BP and APA as well as high PP, implying that heterotrophic bacteria can well sustain in P-deficient system by utilizing DOP to rapidly lower down DOC under relatively high PP. Such findings oppose the 'Malfunctioning Microbial-loop' theory. On the other hand, strong epilimnetic DOC accumulation occurred in Oct 2007 under low light and low PP condition accompanying with high abundance of HNF, implying that HNF grazing may contribute to a certain degree of DOC accumulation. Correlation matrix supported our suggestions. This study testified the DOC dynamics in P-deficient ecosystem are tightly coupled with the source (PP and grazing) and sink (BP). We also suggested that in SRP-limited freshwater systems bacteria are capable of breaking down autochthonous DOC to reduce the chance of DOC accumulation during transport even dam construction continues to increase.

TogoDoc server/client system: smart recommendation and efficient management of life science literature.

PubMed

Iwasaki, Wataru; Yamamoto, Yasunori; Takagi, Toshihisa

2010-12-13

In this paper, we describe a server/client literature management system specialized for the life science domain, the TogoDoc system (Togo, pronounced Toe-Go, is a romanization of a Japanese word for integration). The server and the client program cooperate closely over the Internet to provide life scientists with an effective literature recommendation service and efficient literature management. The content-based and personalized literature recommendation helps researchers to isolate interesting papers from the "tsunami" of literature, in which, on average, more than one biomedical paper is added to MEDLINE every minute. Because researchers these days need to cover updates of much wider topics to generate hypotheses using massive datasets obtained from public databases or omics experiments, the importance of having an effective literature recommendation service is rising. The automatic recommendation is based on the content of personal literature libraries of electronic PDF papers. The client program automatically analyzes these files, which are sometimes deeply buried in storage disks of researchers' personal computers. Just saving PDF papers to the designated folders makes the client program automatically analyze and retrieve metadata, rename file names, synchronize the data to the server, and receive the recommendation lists of newly published papers, thus accomplishing effortless literature management. In addition, the tag suggestion and associative search functions are provided for easy classification of and access to past papers (researchers who read many papers sometimes only vaguely remember or completely forget what they read in the past). The TogoDoc system is available for both Windows and Mac OS X and is free. The TogoDoc Client software is available at http://tdc.cb.k.u-tokyo.ac.jp/, and the TogoDoc server is available at https://docman.dbcls.jp/pubmed_recom.

TogoDoc Server/Client System: Smart Recommendation and Efficient Management of Life Science Literature

PubMed Central

Takagi, Toshihisa

2010-01-01

In this paper, we describe a server/client literature management system specialized for the life science domain, the TogoDoc system (Togo, pronounced Toe-Go, is a romanization of a Japanese word for integration). The server and the client program cooperate closely over the Internet to provide life scientists with an effective literature recommendation service and efficient literature management. The content-based and personalized literature recommendation helps researchers to isolate interesting papers from the “tsunami” of literature, in which, on average, more than one biomedical paper is added to MEDLINE every minute. Because researchers these days need to cover updates of much wider topics to generate hypotheses using massive datasets obtained from public databases or omics experiments, the importance of having an effective literature recommendation service is rising. The automatic recommendation is based on the content of personal literature libraries of electronic PDF papers. The client program automatically analyzes these files, which are sometimes deeply buried in storage disks of researchers' personal computers. Just saving PDF papers to the designated folders makes the client program automatically analyze and retrieve metadata, rename file names, synchronize the data to the server, and receive the recommendation lists of newly published papers, thus accomplishing effortless literature management. In addition, the tag suggestion and associative search functions are provided for easy classification of and access to past papers (researchers who read many papers sometimes only vaguely remember or completely forget what they read in the past). The TogoDoc system is available for both Windows and Mac OS X and is free. The TogoDoc Client software is available at http://tdc.cb.k.u-tokyo.ac.jp/, and the TogoDoc server is available at https://docman.dbcls.jp/pubmed_recom. PMID:21179453

Photooxidation and Microbial Processing of Ancient and Modern Dissolved Organic Carbon in the Kolyma River, Siberia.

NASA Astrophysics Data System (ADS)

Behnke, M. I.; Mann, P. J.; Schade, J. D.; Spawn, S.; Zimov, N.

2015-12-01

Permafrost soils in northern high latitudes store large quantities of organic carbon that have remained frozen for thousands of years. As global temperatures increase, permafrost deposits have begun to thaw, releasing previously stored ancient carbon to streams and rivers in the form of dissolved organic carbon (DOC). Newly mobilized DOC is then subjected to processing by photooxidation and microbial metabolism. Permafrost-derived DOC is highly bioavailable directly upon release relative to modern DOC derived from plants and surface active layer soils. Our objectives were to assess the interaction of photodegradation and microbial processing, and to quantify any light priming effect on the microbial consumption of both ancient and modern sourced DOC pools. We exposed sterilized mixtures of ancient and modern DOC to ambient sunlight for six days, and then inoculated mixtures (0, 1, 10, 25, 50 & 100% ancient DOC) with microbes from both modern and ancient water sources. After inoculation, samples were incubated in the dark for five days. We measured biological oxygen demand, changes in absorbance, and DOC concentrations to quantify microbial consumption of DOC and identify shifts in DOC composition and biolability. We found evidence of photobleaching during irradiation (decreasing S275-295, increasing slope ratio, and decreasing SUVA254). Once inoculated, mixtures with more ancient DOC showed initially increased microbial respiration compared to mixtures with primarily modern DOC. During the first 24 hours, the light-exposed mixture with 50% ancient DOC showed 47.6% more oxygen consumption than did the dark 50% mixture, while the purely modern DOC showed 11.5% greater oxygen consumption after light exposure. After 5 days, the modern light priming was comparable to the 50% mixture (31.2% compared to 20.5%, respectively). Our results indicate that natural photoexposure of both modern and newly released DOC increases microbial processing rates over non photo-exposed DOC.

Stable and radiocarbon isotopic composition of dissolved organic matter in the Gulf of Mexico

NASA Astrophysics Data System (ADS)

Walker, B. D.; Druffel, E. R. M.; Kolasinski, J.; Roberts, B. J.; Xu, X.; Rosenheim, B. E.

2017-08-01

Dissolved organic carbon (DOC) is of primary importance to marine ecosystems and the global carbon cycle. Stable carbon (δ13C) and radiocarbon (Δ14C) isotopic measurements are powerful tools for evaluating DOC sources and cycling. However, the isotopic signature of DOC in the Gulf of Mexico (GOM) remains almost completely unknown. Here we present the first DOC Δ14C and δ13C depth profiles from the GOM. Our results suggest the Mississippi River exports large amounts of DOC with an anthropogenic "bomb" Δ14C signature. Riverine DOC is removed and recycled offshore, and some marine production of DOC is observed in the river plume. Offshore profiles show that DOC has higher Δ14C than its Caribbean feed waters, indicative of a modern deep DOC source in the GOM basin. Finally, high DOC with negative δ13C and Δ14C values were observed near the Macondo Wellhead, suggesting a transformation of Deepwater Horizon hydrocarbons into a persistent population of DOC.

Degradation potentials of dissolved organic carbon (DOC) from thawed permafrost peat

PubMed Central

Panneer Selvam, Balathandayuthabani; Lapierre, Jean-François; Guillemette, Francois; Voigt, Carolina; Lamprecht, Richard E.; Biasi, Christina; Christensen, Torben R.; Martikainen, Pertti J.; Berggren, Martin

2017-01-01

Global warming can substantially affect the export of dissolved organic carbon (DOC) from peat-permafrost to aquatic systems. The direct degradability of such peat-derived DOC, however, is poorly constrained because previous permafrost thaw studies have mainly addressed mineral soil catchments or DOC pools that have already been processed in surface waters. We incubated peat cores from a palsa mire to compare an active layer and an experimentally thawed permafrost layer with regard to DOC composition and degradation potentials of pore water DOC. Our results show that DOC from the thawed permafrost layer had high initial degradation potentials compared with DOC from the active layer. In fact, the DOC that showed the highest bio- and photo-degradability, respectively, originated in the thawed permafrost layer. Our study sheds new light on the DOC composition of peat-permafrost directly upon thaw and suggests that past estimates of carbon-dioxide emissions from thawed peat permafrost may be biased as they have overlooked the initial mineralization potential of the exported DOC. PMID:28378792

[Three dimensional fluorescent characteristics of soil dissolved organic matter (DOM) in Jiaozhou Bay coastal wetlands, China].

PubMed

Zi, Yuan Yuan; Kong, Fan Long; Xi, Min; Li, Yue; Yang, Ling

2016-12-01

In order to elucidate the structure characteristics of soil dissolved organic matter (DOM) and analyze the sources in Jiaozhou Bay coastal wetlands, four typical types of wetlands around Jiaozhou Bay were chosen, including Spartina anglica wetland, the barren wetland, Suaeda glauca wetland and Phragmites australis wetland. The soil samples were collected in January 2014. The contents of soil DOM were determined and the spectral analysis was made by three-dimensional fluorescent technology. The results showed that the contents of soil dissolved organic carbon (DOC) in four types of wetlands all decreased with the increasing soil depth, and S. anglica wetland ranked the first in the contents of soil DOC, followed by the barren wetland, S. glauca wetland and P. australis wetland. Five fluorescence peaks including B, T, A, D and C were found in the three-dimensional fluorescence spectrum (3DEEMs), indicating tyrosine-like, tryptophan-like, phenol-like, soluble microbial byproduct-like and humic acid-like- substances, respectively. Fluorescence integration (FRI) was applied in the qualitative analysis of five components. The results showed that tryptophan-like, phenol-like and tyrosine-like substances ranked in top three in content, followed by soluble microbial byproduct-like and humic acid-like substances which were not significantly different. Pearson correlation analysis demonstrated that a positive correlation existed between any two of the five components of DOM, and they were all positively related to DOC content. In addition, there existed different correlations between the five components of DOM and total phosphorus (TP), available phosphorus (AP) and total nitrogen (TN). The soil DOM in the four types of wetlands was mainly produced by biotic interactions, and the degree of humification was relatively low.

First dynamic model of dissolved organic carbon derived directly from high-frequency observations through contiguous storms.

PubMed

Jones, Timothy D; Chappell, Nick A; Tych, Wlodek

2014-11-18

The first dynamic model of dissolved organic carbon (DOC) export in streams derived directly from high frequency (subhourly) observations sampled at a regular interval through contiguous storms is presented. The optimal model, identified using the recently developed RIVC algorithm, captured the rapid dynamics of DOC load from 15 min monitored rainfall with high simulation efficiencies and constrained uncertainty with a second-order (two-pathway) structure. Most of the DOC export in the four headwater basins studied was associated with the faster hydrometric pathway (also modeled in parallel), and was soon exhausted in the slower pathway. A delay in the DOC mobilization became apparent as the ambient temperatures increased. These features of the component pathways were quantified in the dynamic response characteristics (DRCs) identified by RIVC. The model and associated DRCs are intended as a foundation for a better understanding of storm-related DOC dynamics and predictability, given the increasing availability of subhourly DOC concentration data.

Removing organic and nitrogen content from a highly saline municipal wastewater reverse osmosis concentrate by UV/H2O2-BAC treatment.

PubMed

Pradhan, Shovana; Fan, Linhua; Roddick, Felicity A

2015-10-01

Reverse osmosis (RO) concentrate (ROC) streams generated from RO-based municipal wastewater reclamation processes pose potential health and environmental risks on their disposal to confined water bodies such as bays. A UV/H2O2 advanced oxidation process followed by a biological activated carbon (BAC) treatment was evaluated at lab-scale for the removal of organic and nutrient content from a highly saline ROC (TDS 16 g L(-1), EC 23.5 mS cm(-1)) for its safe disposal to the receiving environment. Over the 230-day operation of the UV/H2O2-BAC process, the colour and UV absorbance (254 nm) of the ROC were reduced to well below those of the influent to the reclamation process. The concentrations of DOC and total nitrogen (TN) were reduced by approximately 60% at an empty bed contact time (EBCT) of 60 min. The reduction in ammonia nitrogen by the BAC remained high under all conditions tested (>90%). Further investigation confirmed that the presence of residual peroxide in the UV/H2O2 treated ROC was beneficial for DOC removal, but markedly inhibited the activities of the nitrifying bacteria (i.e., nitrite oxidising bacteria) in the BAC system and hence compromised total nitrogen removal. This work demonstrated that the BAC treatment could be acclimated to the very high salinity environment, and could be used as a robust method for the removal of organic matter and nitrogen from the pre-oxidised ROC under optimised conditions. Copyright © 2015 Elsevier Ltd. All rights reserved.

Winter to spring variations of chromophoric dissolved organic matter in a temperate estuary (Po River, northern Adriatic Sea).

PubMed

Berto, D; Giani, M; Savelli, F; Centanni, E; Ferrari, C R; Pavoni, B

2010-07-01

The light absorbing fraction of dissolved organic carbon (DOC), known as chromophoric dissolved organic matter (CDOM) showed wide seasonal variations in the temperate estuarine zone in front of the Po River mouth. DOC concentrations increased from winter through spring mainly as a seasonal response to increasing phytoplankton production and thermohaline stratification. The monthly dependence of the CDOM light absorption by salinity and chlorophyll a concentrations was explored. In 2003, neither DOC nor CDOM were linearly correlated with salinity, due to an exceptionally low Po river inflow. Though the CDOM absorbance coefficients showed a higher content of chromophoric dissolved organic matter in 2004 with respect to 2003, the spectroscopic features confirmed that the qualitative nature of CDOM was quite similar in both years. CDOM and DOC underwent a conservative mixing, only after relevant Po river freshets, and a change in optical features with an increase of the specific absorption coefficient was observed, suggesting a prevailing terrestrial origin of dissolved organic matter. Published by Elsevier Ltd.

Linking soil DOC production rates and transport processes from landscapes to sub-basin scales

NASA Astrophysics Data System (ADS)

Tian, Y. Q.; Yu, Q.; Li, J.; Ye, C.

2014-12-01

Recent research rejects the traditional perspective that dissolved organic carbon (DOC) component in global carbon cycle are simply trivial, and in fact evidence demonstrates that lakes likely mediate carbon dynamics on a global scale. Riverine and estuarine carbon fluxes play a critical role in transporting and recycling carbon and nutrients, not only within watersheds but in their receiving waters. However, the underlying mechanisms that drive carbon fluxes, from land to rivers, lake and oceans, remain poorly understood. This presentation will report a research result of the scale-dependent DOC production rate in coastal watersheds and DOC transport processes in estuarine regions. We conducted a series of controlled experiments and field measurements for examining biogeochemical, biological, and geospatial variables that regulate downstream processing on global-relevant carbon fluxes. Results showed that increased temperatures and raised soil moistures accelerate decomposition rates of organic matter with significant variations between vegetation types. The measurements at meso-scale ecosystem demonstrated a good correlation to bulk concentration of DOC monitored in receiving waters at the outlets of sub-basins (R2 > 0.65). These field and experimental measurements improved the model of daily carbon exports through below-ground processes as a function of the organic matter content of surface soils, forest litter supply, and temperature. The study demonstrated a potential improvement in modeling the co-variance of CDOM and DOC with the unique terrestrial sources. This improvement indicated a significant promise for monitoring riverine and estuarine carbon flux from satellite images. The technical innovations include deployments of 1) mini-ecosystem (mesocosms) with soil as replicate controlled experiments for DOC production and leaching rates, and 2) aquatic mesocosms for co-variances of DOC and CDOM endmembers, and an instrumented incubation experiment for determining degradation rates.

Investigating Forest Harvest Effects on DOC Concentration and Quality: An In Situ, High Resolution Approach to Quantifying DOC Export Dynamics

NASA Astrophysics Data System (ADS)

Jollymore, A. J.; Johnson, M. S.; Hawthorne, I.

2013-12-01

Justification: Forest harvest effects on water quality can signal alterations in hydrologic and ecologic processes incurred as a result of forest harvest activities. Organic matter (OM), specifically dissolved organic carbon (DOC), plays a number of important roles mediating UV-light penetration, redox reactivity and microbial activity within aquatic ecosystems. Quantification of DOC is typically pursued via grab sampling followed by chemical or spectrophotometric analysis, limiting the temporal resolution obtained as well as the accuracy of export calculations. The advent of field-deployable sensors capable of measuring DOC concentration and certain quality characteristics in situ provides the ability to observe dynamics at temporal scales necessary for accurate calculation of DOC flux, as well as the observation of dynamic changes in DOC quality on timescales impossible to observe through grab sampling. Methods: This study utilizes a field deployable UV-Vis spectrophotometer (spectro::lyzer, s::can, Austria) to investigate how forest harvest affects DOC export. The sensor was installed at an existing hydrologic monitoring site at the outlet of a headwater stream draining a small (91 hectare) second growth Douglasfir-dominated catchment near Campbell River on Vancouver Island, British Columbia. Measurement began late in 2009, prior to forest harvest and associated activities such as road building (which commenced in October 2010 and ended in early 2011), and continues to present. During this time - encompassing the pre, during and post-harvest conditions - the absorbance spectrum of stream water from 200 to 750 nm was measured. DOC concentration and spectroscopic indices related to DOC quality (including SUVA, which relates to the concentration of aromatic carbon, and spectral slope) were subsequently calculated for each spectra obtained at 30-minute intervals. Results and conclusions: High frequency measurements of DOC show that overall export of OM increased in the months following harvest. A major advantage of this study is the use of in situ measurements, allowing for high temporal resolution of DOC dynamics occurring within specific hydrologic events. For example, concentration-discharge relationships for both the pre- and post-logging periods demonstrate similar clockwise hysteresis during individual storm events, while the magnitude of change dramatically increased during the post-logging period. However, in situ measurements of SUVA over this period suggest that DOC quality may be less affected by forest harvest than overall DOC concentration, where high frequency data also allows for the observation of SUVA and spectral slope responses to specific hydrologic events during the pre- and post- harvest period.

Effects of High Dissolved Inorganic and Organic Carbon Availability on the Physiology of the Hard Coral Acropora millepora from the Great Barrier Reef

PubMed Central

Meyer, Friedrich W.; Vogel, Nikolas; Diele, Karen; Kunzmann, Andreas; Uthicke, Sven; Wild, Christian

2016-01-01

Coral reefs are facing major global and local threats due to climate change-induced increases in dissolved inorganic carbon (DIC) and because of land-derived increases in organic and inorganic nutrients. Recent research revealed that high availability of labile dissolved organic carbon (DOC) negatively affects scleractinian corals. Studies on the interplay of these factors, however, are lacking, but urgently needed to understand coral reef functioning under present and near future conditions. This experimental study investigated the individual and combined effects of ambient and high DIC (pCO2 403 μatm/ pHTotal 8.2 and 996 μatm/pHTotal 7.8) and DOC (added as Glucose 0 and 294 μmol L-1, background DOC concentration of 83 μmol L-1) availability on the physiology (net and gross photosynthesis, respiration, dark and light calcification, and growth) of the scleractinian coral Acropora millepora (Ehrenberg, 1834) from the Great Barrier Reef over a 16 day interval. High DIC availability did not affect photosynthesis, respiration and light calcification, but significantly reduced dark calcification and growth by 50 and 23%, respectively. High DOC availability reduced net and gross photosynthesis by 51% and 39%, respectively, but did not affect respiration. DOC addition did not influence calcification, but significantly increased growth by 42%. Combination of high DIC and high DOC availability did not affect photosynthesis, light calcification, respiration or growth, but significantly decreased dark calcification when compared to both controls and DIC treatments. On the ecosystem level, high DIC concentrations may lead to reduced accretion and growth of reefs dominated by Acropora that under elevated DOC concentrations will likely exhibit reduced primary production rates, ultimately leading to loss of hard substrate and reef erosion. It is therefore important to consider the potential impacts of elevated DOC and DIC simultaneously to assess real world scenarios, as multiple rather than single factors influence key physiological processes in coral reefs. PMID:26959499

Effects of High Dissolved Inorganic and Organic Carbon Availability on the Physiology of the Hard Coral Acropora millepora from the Great Barrier Reef.

PubMed

Meyer, Friedrich W; Vogel, Nikolas; Diele, Karen; Kunzmann, Andreas; Uthicke, Sven; Wild, Christian

2016-01-01

Coral reefs are facing major global and local threats due to climate change-induced increases in dissolved inorganic carbon (DIC) and because of land-derived increases in organic and inorganic nutrients. Recent research revealed that high availability of labile dissolved organic carbon (DOC) negatively affects scleractinian corals. Studies on the interplay of these factors, however, are lacking, but urgently needed to understand coral reef functioning under present and near future conditions. This experimental study investigated the individual and combined effects of ambient and high DIC (pCO2 403 μatm/ pHTotal 8.2 and 996 μatm/pHTotal 7.8) and DOC (added as Glucose 0 and 294 μmol L-1, background DOC concentration of 83 μmol L-1) availability on the physiology (net and gross photosynthesis, respiration, dark and light calcification, and growth) of the scleractinian coral Acropora millepora (Ehrenberg, 1834) from the Great Barrier Reef over a 16 day interval. High DIC availability did not affect photosynthesis, respiration and light calcification, but significantly reduced dark calcification and growth by 50 and 23%, respectively. High DOC availability reduced net and gross photosynthesis by 51% and 39%, respectively, but did not affect respiration. DOC addition did not influence calcification, but significantly increased growth by 42%. Combination of high DIC and high DOC availability did not affect photosynthesis, light calcification, respiration or growth, but significantly decreased dark calcification when compared to both controls and DIC treatments. On the ecosystem level, high DIC concentrations may lead to reduced accretion and growth of reefs dominated by Acropora that under elevated DOC concentrations will likely exhibit reduced primary production rates, ultimately leading to loss of hard substrate and reef erosion. It is therefore important to consider the potential impacts of elevated DOC and DIC simultaneously to assess real world scenarios, as multiple rather than single factors influence key physiological processes in coral reefs.

A global hotspot for dissolved organic carbon in hypermaritime watersheds of coastal British Columbia

NASA Astrophysics Data System (ADS)

Oliver, Allison A.; Tank, Suzanne E.; Giesbrecht, Ian; Korver, Maartje C.; Floyd, William C.; Sanborn, Paul; Bulmer, Chuck; Lertzman, Ken P.

2017-08-01

The perhumid region of the coastal temperate rainforest (CTR) of Pacific North America is one of the wettest places on Earth and contains numerous small catchments that discharge freshwater and high concentrations of dissolved organic carbon (DOC) directly to the coastal ocean. However, empirical data on the flux and composition of DOC exported from these watersheds are scarce. We established monitoring stations at the outlets of seven catchments on Calvert and Hecate islands, British Columbia, which represent the rain-dominated hypermaritime region of the perhumid CTR. Over several years, we measured stream discharge, stream water DOC concentration, and stream water dissolved organic-matter (DOM) composition. Discharge and DOC concentrations were used to calculate DOC fluxes and yields, and DOM composition was characterized using absorbance and fluorescence spectroscopy with parallel factor analysis (PARAFAC). The areal estimate of annual DOC yield in water year 2015 was 33.3 Mg C km-2 yr-1, with individual watersheds ranging from an average of 24.1 to 37.7 Mg C km-2 yr-1. This represents some of the highest DOC yields to be measured at the coastal margin. We observed seasonality in the quantity and composition of exports, with the majority of DOC export occurring during the extended wet period (September-April). Stream flow from catchments reacted quickly to rain inputs, resulting in rapid export of relatively fresh, highly terrestrial-like DOM. DOC concentration and measures of DOM composition were related to stream discharge and stream temperature and correlated with watershed attributes, including the extent of lakes and wetlands, and the thickness of organic and mineral soil horizons. Our discovery of high DOC yields from these small catchments in the CTR is especially compelling as they deliver relatively fresh, highly terrestrial organic matter directly to the coastal ocean. Hypermaritime landscapes are common on the British Columbia coast, suggesting that this coastal margin may play an important role in the regional processing of carbon and in linking terrestrial carbon to marine ecosystems.

Dissolved organic carbon from the upper Rio Negro protects zebrafish (Danio rerio) against ionoregulatory disturbances caused by low pH exposure

PubMed Central

Duarte, Rafael M.; Smith, D. Scott; Val, Adalberto L.; Wood, Chris M.

2016-01-01

The so-called “blackwaters” of the Amazonian Rio Negro are rich in highly coloured dissolved organic carbon (DOC), but ion-poor and very acidic, conditions that would cause fatal ionoregulatory failure in most fish. However these blackwaters support 8% of the world’s ichthyofauna. We tested the hypothesis that native DOC provides protection against ionoregulatory dysfunction in this extreme environment. DOCs were isolated by reverse-osmosis from two Rio Negro sites. Physico-chemical characterization clearly indicated a terrigenous origin, with a high proportion of hydroxyl and phenolic sites, high chemical reactivity to protons, and unusual proteinaceous fluorescence. When tested using zebrafish (a model organism), Rio Negro DOC provided almost perfect protection against ionoregulatory disturbances associated with acute exposure to pH 4.0 in ion-poor water. DOC reduced diffusive losses of Na+ and Cl−, and promoted a remarkable stimulation of Na+ uptake that otherwise would have been completely inhibited. Additionally, prior acclimation to DOC at neutral pH reduced rates of branchial Na+ turnover, and provided similar protection against acid-induced ionoregulatory disturbances, even if the DOC was no longer present. These results reinforce the important roles that DOC molecules can play in the regulation of gill functions in freshwater fish, particularly in ion-poor, acidic blackwaters. PMID:26853589

Relationship between THMs/NDMA formation potential and molecular weight of organic compounds for source and treated water in Shanghai, China.

PubMed

An, Dong; Gu, Bin; Sun, Sainan; Zhang, Han; Chen, Yanan; Zhu, Huifeng; Shi, Jian; Tong, Jun

2017-12-15

Molecular weight (MW) distributions in source and treated water in Shanghai, China were investigated to understand the relationship between trihalomethanes formation potential/N-nitrosodimethylamine formation potential (THMFP/NDMAFP) and dissolved organic carbon (DOC) for different MW ranges (<1K, 1-10K, 10-30K, >30KDa). The result of MW distributions in source water indicated a relationship between THMFP/NDMAFP and DOC such that DOC for <1K and 1-30KDa DOC were linearly related to THMFP and NDMAFP, respectively. In treated water, >30KDa THMFP was totally removed whereas <1KDa THMFP showed linear relationships with R 2 =0.88 and 0.83 after sand and granular activated carbon (GAC) filtration, respectively. DOC content for 1-10KDa tended to form NDMA according to the results for treated water between DOC and NDMAFP (R 2 =0.94 and 0.93 for sand and GAC filtration, respectively). The results may provide researchers with targeted treatment strategies to destroy, remove, or reduce the occurrence of THMs and NDMA precursors. The findings presented in this study will be of great value in future work for selecting suitable drinking water treatment processes to minimize the formation of disinfection by-products using chlorine or chloramine disinfection. Copyright © 2017 Elsevier B.V. All rights reserved.

Constraining the sources and cycling of dissolved organic carbon in a large oligotrophic lake using radiocarbon analyses

NASA Astrophysics Data System (ADS)

Zigah, Prosper K.; Minor, Elizabeth C.; McNichol, Ann P.; Xu, Li; Werne, Josef P.

2017-07-01

We measured the concentrations and isotopic compositions of solid phase extracted (SPE) dissolved organic carbon (DOC) and high molecular weight (HMW) DOC and their constituent organic components in order to better constrain the sources and cycling of DOC in a large oligotrophic lacustrine system (Lake Superior, North America). SPE DOC constituted a significant proportion (41-71%) of the lake DOC relative to HMW DOC (10-13%). Substantial contribution of 14C-depleted components to both SPE DOC (Δ14C = 25-43‰) and HMW DOC (Δ14C = 22-32‰) was evident during spring mixing, and depressed their radiocarbon values relative to the lake dissolved inorganic carbon (DIC; Δ14C ∼ 59‰). There was preferential removal of 14C-depleted (older) and thermally recalcitrant components from HMW DOC and SPE DOC in the summer. Contemporary photoautotrophic addition to HMW DOC was observed during summer stratification in contrast to SPE DOC, which decreased in concentration during stratification. Serial thermal oxidation radiocarbon analysis revealed a diversity of sources (both contemporary and older) within the SPE DOC, and also showed distinct components within the HMW DOC. The thermally labile components of HMW DOC were 14C-enriched and are attributed to heteropolysaccharides (HPS), peptides/amide and amino sugars (AMS) relative to the thermally recalcitrant components reflecting the presence of older material, perhaps carboxylic-rich alicyclic molecules (CRAM). The solvent extractable lipid-like fraction of HMW DOC was very 14C-depleted (as old as 1270-2320 14C years) relative to the carbohydrate-like and protein-like substances isolated by acid hydrolysis of HMW DOC. Our data constrain relative influences of contemporary DOC and old DOC, and DOC cycling in a modern freshwater ecosystem.

Characterization of dissolved organic matter from surface waters with low to high dissolved organic carbon and the related disinfection byproduct formation potential.

PubMed

Li, Angzhen; Zhao, Xu; Mao, Ran; Liu, Huijuan; Qu, Jiuhui

2014-04-30

In this study, the disinfection byproduct formation potential (DBPFP) of three surface waters with the dissolved organic carbon (DOC) content of 2.5, 5.2, and 7.9mg/L was investigated. The formation and distribution of trihalomethanes and haloacetic acids were evaluated. Samples collected from three surface waters in China were fractionated based on molecular weight and hydrophobicity. The raw water containing more hydrophobic (Ho) fraction exhibited higher formation potentials of haloacetic acid and trihalomethane. The DBPFP of the surface waters did not correlate with the DOC value. The values of DBPFP per DOC were correlated with the specific ultraviolet absorbance (SUVA) for Ho and Hi fractions. The obtained results suggested that SUVA cannot reveal the ability of reactive sites to form disinfection byproducts for waters with few aromatic structures. Combined with the analysis of FTIR and nuclear magnetic resonance spectra of the raw waters and the corresponding fractions, it was concluded that the Ho fraction with phenolic hydroxyl and conjugated double bonds was responsible for the production of trichloromethanes and trichloroacetic acids. The Hi fraction with amino and carboxyl groups had the potential to form dichloroacetic acids and chlorinated trihalomethanes. Copyright © 2014. Published by Elsevier B.V.

Organic Carbon Loading in Tropical Near-Shore Ecosystems: the Role of Mangrove Lagoons and Channels in Coastal Ocean Acidification

NASA Astrophysics Data System (ADS)

García, E.; Morell, J. M.

2016-02-01

Low energy tropical Caribbean shores are often dominated by highly productive mangrove ecosystems that thrive on land borne inorganic nutrient inputs and whose net production results in significant export of litter and dissolved organic compounds (DOC). These organic matrixes can be effectively transported to nearby ecosystems, including coral reefs whose vulnerability to excessive organic loading has been widely documented. This study documents the seaward transport and transformation of organic carbon from mangrove bays, trough near-shore reef ecosystems and out to open waters in the La Parguera Marine Reserve (LPMR). Considering in-situ colored dissolved organic matter (CDOM) as a tracer for DOC, absorption coefficient values (a350) were observed in the 6.13-0.02 m-1 and 14.08-0.06 m-1 during the dry (from 0 to 0.18 inches of rain) and wet seasons (from 0.68 to 4.76 inches of rain), respectively. Spectral properties (S275-295 and SR) calculations indicate that DOC is predominantly of terrestrial origin and found in high concentrations in enclosed mangrove bays and canals. Data evidences a strong gradient in CDOM concentration decreasing t from inshore to outer shelf waters. Rain precipitation correlated well with high CDOM values (aλ values doubled) and forced LPMR to behave similarly to a river influenced estuary as shown when CDOM is correlated with salinity, contrary to its predominant negative estuary profile. When correlating CDOM with pH and dissolved oxygen concentrations, it is evident that high organic matter content is driving ocean acidification in the nearshore areas. The non-conservative behavior of CDOM implies that other processes besides dilution may play a significant role in its spatial distribution.

Dissolved organic carbon in soil solution of peat-moorsh soils on Kuwasy Mire

NASA Astrophysics Data System (ADS)

Jaszczyński, J.; Sapek, A.

2009-04-01

Key words: peat-moorsh soils, soil solution, dissolved organic carbon (DOC), temperature of soil, redox potential. The objective this study was the dissolved organic carbon concentration (DOC) in soil solution on the background of soil temperature, moisture and redox potential. The investigations were localized on the area of drained and agricultural used Kuwasy Mire, which are situated in the middle basin of Biebrza River, in North-East Poland. Research point was placed on a low peat soil of 110 cm depth managed as extensive grassland. The soil was recognized as peat-moorsh with the second degree of the moorshing process (with 20 cm of moorsh layer). The ceramic suction cups were installed in three replications at 30 cm depth of soil profile. The soil solution was continuously sampled by pomp of the automatic field station. The successive samples comprised of solution collected at the intervals of 21 days. Simultaneously, at the 20, 30 and 40 cm soil depths the measurements of temperature and determination of soil moisture and redox potential were made automatically. The mean twenty-four hours data were collected. The concentrations of DOC were determined by means of the flow colorimeter using the Skalar standard methods. Presented observations were made in 2001-2006. Mean DOC concentration in soil solution was 66 mg.dm-3 within all research period. A significant positive correlation between studied compound concentration and temperature of soil at 30 cm depth was observed; (correlation coefficient - r=0.55, number of samples - n=87). The highest DOC concentrations were observed during the season from July to October, when also a lower ground water level occurred. The DOC concentration in soil solution showed as well a significant correlation with the soil redox potential at 20 cm level. On this depth of describing soil profile a frontier layer between moorshing layer and peat has been existed. This layer is the potentially most active in the respect to biochemical transformation. On the other hand it wasn't possible to shown dependences on the DOC concentration from soil moisture. That probably results from a huge water-holding capacity of these type of peat soils, which are keeping a high moisture content even at a long time after decreasing of the groundwater table.

High dissolved organic carbon release by benthic cyanobacterial mats in a Caribbean reef ecosystem

NASA Astrophysics Data System (ADS)

Brocke, Hannah J.; Wenzhoefer, Frank; de Beer, Dirk; Mueller, Benjamin; van Duyl, Fleur C.; Nugues, Maggy M.

2015-03-01

Benthic cyanobacterial mats (BCMs) are increasing in abundance on coral reefs worldwide. However, their impacts on biogeochemical cycling in the surrounding water and sediment are virtually unknown. By measuring chemical fluxes in benthic chambers placed over sediment covered by BCMs and sediment with BCMs removed on coral reefs in Curaçao, Southern Caribbean, we found that sediment covered by BCMs released 1.4 and 3.5 mmol C m-2 h-1 of dissolved organic carbon (DOC) during day and night, respectively. Conversely, sediment with BCMs removed took up DOC, with day and night uptake rates of 0.9 and 0.6 mmol C m-2 h-1. DOC release by BCMs was higher than reported rates for benthic algae (turf and macroalgae) and was estimated to represent 79% of the total DOC released over a 24 h diel cycle at our study site. The high nocturnal release of DOC by BCMs is most likely the result of anaerobic metabolism and degradation processes, as shown by high respiration rates at the mat surface during nighttime. We conclude that BCMs are significant sources of DOC. Their increased abundance on coral reefs will lead to increased DOC release into the water column, which is likely to have negative implications for reef health.

High dissolved organic carbon release by benthic cyanobacterial mats in a Caribbean reef ecosystem.

PubMed

Brocke, Hannah J; Wenzhoefer, Frank; de Beer, Dirk; Mueller, Benjamin; van Duyl, Fleur C; Nugues, Maggy M

2015-03-09

Benthic cyanobacterial mats (BCMs) are increasing in abundance on coral reefs worldwide. However, their impacts on biogeochemical cycling in the surrounding water and sediment are virtually unknown. By measuring chemical fluxes in benthic chambers placed over sediment covered by BCMs and sediment with BCMs removed on coral reefs in Curaçao, Southern Caribbean, we found that sediment covered by BCMs released 1.4 and 3.5 mmol C m(-2) h(-1) of dissolved organic carbon (DOC) during day and night, respectively. Conversely, sediment with BCMs removed took up DOC, with day and night uptake rates of 0.9 and 0.6 mmol C m(-2) h(-1). DOC release by BCMs was higher than reported rates for benthic algae (turf and macroalgae) and was estimated to represent 79% of the total DOC released over a 24 h diel cycle at our study site. The high nocturnal release of DOC by BCMs is most likely the result of anaerobic metabolism and degradation processes, as shown by high respiration rates at the mat surface during nighttime. We conclude that BCMs are significant sources of DOC. Their increased abundance on coral reefs will lead to increased DOC release into the water column, which is likely to have negative implications for reef health.

Organic carbon transport through a discontinuous fluvial system in a Mediterranean catchment after a greening-up process

NASA Astrophysics Data System (ADS)

Boix-Fayos, Carolina; Almagro, María; Díaz-Pereira, Elvira; Pérez-Cutillas, Pedro; de Vente, Joris; Martínez-Mena, María

2017-04-01

Quantification of different organic carbon pools mobilized by lateral fluxes is important to close organic carbon (OC) budgets at the catchment scale. This quantification helps to identify in which forms OC is transferred, deposited, and mineralized during the erosion cycle. Many Mediterranean mountain catchments have experienced important land use changes in the last 50 years leading to a recovery of the vegetation in many cases. Furthermore, many of them are characterized by stream discontinuity with high runoff rates responding to intensive hydrological pulses. There is a current lack of knowledge on fluvial OC fluxes and their relation to soil organic carbon stocks in these systems. The objective of this research was to quantify the amount of organic carbon transported by these systems in a catchment representative of Mediterranean conditions and to explore how intermittent fluvial systems can affect organic carbon transported by lateral flows. During six years OC fluvial fluxes in a catchment of 77 km2 in SE Spain were monitored. The catchment experienced a greening-up process in the last 50 years through a conversion mainly from agricultural use (decrease 44%) to forest (increase 45%). Data on water discharge, sediment concentration, total organic carbon (OC) of suspended sediments and dissolved organic carbon (DOC) were collected throughout 32 rainfall events and 13 sampling periods with base flow conditions. The data were collected from two monitoring stations located on two nested subcatchments covering permanent and ephemeral flow conditions. We found no significant differences in OC concentrations in suspended sediments (10.1 ± 5 g kg-1) and DOC (0.014 ± 0.010 g kg-1) between the ephemeral and the permanent streams. However, sediment concentration, index of aggregation and silt content of suspended load were significantly higher in the ephemeral stream than in the permanent one. OC concentration of suspended sediments was much lower than OC concentration of the catchment soils (20.5 ± 7 g kg-1), and it showed a strong positive correlation with clay content. DOC concentrations were quite high, being in the upper limit of the mean values reported for European rivers and close to DOC values of runoff generated in natural forests from similar areas. A strong positive correlation between DOC and sediment concentration was also observed. DOC represents a 20% and 12% of the total OC fluvial flux in the permanent and ephemeral streams, respectively. OC in suspended solids represents an 80% and 88% of the total OC fluvial flux in the permanent and ephemeral streams, respectively. The ephemeral stream (with a contribution of 70% to the total catchment area) provides up to 20% to the total transported OC downstream. The OC transported to the catchment outlet (1.97 g C m-2 year-1) constitutes 33 % of the OC lateral flux mobilized in the upper subcatchment areas (6 g C m-2 year-1). These findings highlight the strong dynamic character of organic carbon during transport in these fluvial systems and the important role of the hydrological regime for carbon transport and stability.

Analysis of dissolved organic carbon concentration and 13C isotopic signature by TOC-IRMS - assessment of analytical performance

NASA Astrophysics Data System (ADS)

Kirkels, Frédérique; Cerli, Chiara; Federherr, Eugen; Kalbitz, Karsten

2013-04-01

Stable carbon isotopes provide a powerful tool to assess carbon pools and their dynamics. Dissolved organic carbon (DOC) has been recognized to play an important role in ecosystem functioning and carbon cycling and has therefore gained increased research interest. However, direct measurement of 13C isotopic signature of carbon in the dissolved phase is technically challenging particularly using high temperature combustion. Until recently, mainly custom-made systems existed which were modified for coupling of TOC instruments with IRMS for simultaneous assessment of C content and isotopic signature. The variety of coupled systems showed differences in their analytical performances. For analysis of DOC high temperature combustion is recognized as best performing method, owing to its high efficiency of conversion to CO2 also for highly refractory components (e.g. humic, fulvic acids) present in DOC and soil extracts. Therefore, we tested high temperature combustion TOC coupled to IRMS (developed by Elementar Group) for bulk measurements of DOC concentration and 13C signature. The instruments are coupled via an Interface to exchange the carrier gas from O2 to He and to concentrate the derived CO2 for the isotope measurement. Analytical performance of the system was assessed for a variety of organic compounds characterized by different stability and complexity, including humic acid and DOM. We tested injection volumes between 0.2-3 ml, thereby enabling measurement of broad concentration ranges. With an injection volume of 0.5 ml (n=3, preceded by 1 discarded injection), DOC and 13C signatures for concentrations between 5-150 mg C/L were analyzed with high precision (standard deviation (SD) predominantly <0.1‰), good accuracy and linearity (overall SD <0.9‰). For the same settings, slightly higher variation in precision was observed among the lower concentration range and depending upon specific system conditions. Differences in 13C signatures of about 50‰ among samples did not affect the precision of the analysis of natural abundance and labeled samples. Natural DOM, derived from different soils and assessed at various concentrations, was measured with similar good analytical performance, and also tested for the effect of freezing and re-dissolving. We found good performance of TOC-IRMS in comparison with other systems capable of determining C concentration and isotopic signatures. We recognize the advantages of this system providing: - High sample throughput, short measurement time (15 minutes), flexible sample volume - Easy maintenance, handling, rapid sample preparation (no pretreatment) This preliminary assessment highlights wide-ranging opportunities for further research on concentrations and isotopic signatures by TOC-IRMS to elucidate the role of dissolved carbon in terrestrial and aquatic systems.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Qichun; Zhang, Xuesong; Xu, Xingya

Riverine carbon cycling is an important, but insufficiently investigated component of the global carbon cycle. Analyses of environmental controls on riverine carbon cycling are critical for improved understanding of mechanisms regulating carbon processing and storage along the terrestrial-aquatic continuum. Here, we compile and analyze riverine dissolved organic carbon (DOC) concentration data from 1402 United States Geological Survey (USGS) gauge stations to examine the spatial variability and environmental controls of DOC concentrations in the United States (U.S.) surface waters. DOC concentrations exhibit high spatial variability, with an average of 6.42 ± 6.47 mg C/ L (Mean ± Standard Deviation). In general,more » high DOC concentrations occur in the Upper Mississippi River basin and the Southeastern U.S., while low concentrations are mainly distributed in the Western U.S. Single-factor analysis indicates that slope of drainage areas, wetlands, forests, percentage of first-order streams, and instream nutrients (such as nitrogen and phosphorus) pronouncedly influence DOC concentrations, but the explanatory power of each bivariate model is lower than 35%. Analyses based on the general multi-linear regression models suggest DOC concentrations are jointly impacted by multiple factors. Soil properties mainly show positive correlations with DOC concentrations; forest and shrub lands have positive correlations with DOC concentrations, but urban area and croplands demonstrate negative impacts; total instream phosphorus and dam density correlate positively with DOC concentrations. Notably, the relative importance of these environmental controls varies substantially across major U.S. water resource regions. In addition, DOC concentrations and environmental controls also show significant variability from small streams to large rivers, which may be caused by changing carbon sources and removal rates by river orders. In sum, our results reveal that general multi-linear regression analysis of twenty one terrestrial and aquatic environmental factors can partially explain (56%) the DOC concentration variation. In conclusion, this study highlights the complexity of the interactions among these environmental factors in determining DOC concentrations, thus calls for processes-based, non-linear methodologies to constrain uncertainties in riverine DOC cycling.« less

Characterization of Greenbeard Genes Involved in Long-Distance Kind Discrimination in a Microbial Eukaryote

PubMed Central

Heller, Jens; Zhao, Jiuhai; Rosenfield, Gabriel; Kowbel, David J.; Gladieux, Pierre; Glass, N. Louise

2016-01-01

Microorganisms are capable of communication and cooperation to perform social activities. Cooperation can be enforced using kind discrimination mechanisms in which individuals preferentially help or punish others, depending on genetic relatedness only at certain loci. In the filamentous fungus Neurospora crassa, genetically identical asexual spores (germlings) communicate and fuse in a highly regulated process, which is associated with fitness benefits during colony establishment. Recognition and chemotropic interactions between isogenic germlings requires oscillation of the mitogen-activated protein kinase (MAPK) signal transduction protein complex (NRC-1, MEK-2, MAK-2, and the scaffold protein HAM-5) to specialized cell fusion structures termed conidial anastomosis tubes. Using a population of 110 wild N. crassa isolates, we investigated germling fusion between genetically unrelated individuals and discovered that chemotropic interactions are regulated by kind discrimination. Distinct communication groups were identified, in which germlings within one communication group interacted at high frequency, while germlings from different communication groups avoided each other. Bulk segregant analysis followed by whole genome resequencing identified three linked genes (doc-1, doc-2, and doc-3), which were associated with communication group phenotype. Alleles at doc-1, doc-2, and doc-3 fell into five haplotypes that showed transspecies polymorphism. Swapping doc-1 and doc-2 alleles from different communication group strains was necessary and sufficient to confer communication group affiliation. During chemotropic interactions, DOC-1 oscillated with MAK-2 to the tips of conidial anastomosis tubes, while DOC-2 was statically localized to the plasma membrane. Our data indicate that doc-1, doc-2, and doc-3 function as “greenbeard” genes, involved in mediating long-distance kind recognition that involves actively searching for one’s own type, resulting in cooperation between non-genealogical relatives. Our findings serve as a basis for investigations into the mechanisms associated with attraction, fusion, and kind recognition in other eukaryotic species. PMID:27077707

Dissolved organic matter composition of winter flow in the Yukon River basin: Implications of permafrost thaw and increased groundwater discharge

USGS Publications Warehouse

O'Donnell, Jonathan A.; Aiken, George R.; Walvoord, Michelle Ann; Butler, Kenna D.

2012-01-01

Groundwater discharge to rivers has increased in recent decades across the circumpolar region and has been attributed to thawing permafrost in arctic and subarctic watersheds. Permafrost-driven changes in groundwater discharge will alter the flux of dissolved organic carbon (DOC) in rivers, yet little is known about the chemical composition and reactivity of dissolved organic matter (DOM) of groundwater in permafrost settings. Here, we characterize DOM composition of winter flow in 60 rivers and streams of the Yukon River basin to evaluate the biogeochemical consequences of enhanced groundwater discharge associated with permafrost thaw. DOC concentration of winter flow averaged 3.9 ± 0.5 mg C L−1, yet was highly variable across basins (ranging from 20 mg C L−1). In comparison to the summer-autumn period, DOM composition of winter flow had lower aromaticity (as indicated by specific ultraviolet absorbance at 254 nm, or SUVA254), lower hydrophobic acid content, and a higher proportion of hydrophilic compounds (HPI). Fluorescence spectroscopy and parallel factor analysis indicated enrichment of protein-like fluorophores in some, but not all, winter flow samples. The ratio of DOC to dissolved organic nitrogen, an indicator of DOM biodegradability, was positively correlated with SUVA254 and negatively correlated with the percentage of protein-like compounds. Using a simple two-pool mixing model, we evaluate possible changes in DOM during the summer-autumn period across a range of conditions reflecting possible increases in groundwater discharge. Across three watersheds, we consistently observed decreases in DOC concentration and SUVA254 and increases in HPI with increasing groundwater discharge. Spatial patterns in DOM composition of winter flow appear to reflect differences in the relative contributions of groundwater from suprapermafrost and subpermafrost aquifers across watersheds. Our findings call for more explicit consideration of DOC loss and stabilization pathways associated with changing subsurface hydrology in watersheds underlain by thawing permafrost.

Acid-induced changes in DOC quality in an experimental whole-lake manipulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Donahue, W.F.; Schindler, D.W.; Page, S.J.

1998-10-01

Fluorescence analyses of archived water samples were used to typify dissolved organic carbon (DOC) quality in experimentally acidified lakes and reference lakes at the Experimental Lakes Area, in northwestern Ontario. Carbon-specific DOC fluorescence (CSF) during peak acidification was 40--50% of that for a high-DOC reference lake and similar to a low-DOC reference lake. Reference lakes showed similar but smaller decreases in CSF during several years of prolonged drought in the late 1980s. During the 1990s, recovery from acidification resulted in increased CSF, whereas reference lakes remained unchanged during the same time period. In addition to causing decreased [DOC], acidification causesmore » changes in fluorescence-peak geometry that indicate a switch in DOC quality from allochthonous to autochthonous-like during acidification. The acid-induced change in DOC quality was likely due to increased chemical oxidation or precipitation of the UV-absorbent aromatic portions of allochthonous DOC molecules, leaving more UV-transparent aliphatic chains. The change in the nature of DOC following acidification and drought may have an important role in physical, biological, and chemical processes within these lakes. With recovery from acidification, DOC quality has also recovered.« less

Geochemistry and Flux of Terrigenous Dissolved Organic Matter to the Arctic Ocean

NASA Astrophysics Data System (ADS)

Spencer, R. G.; Mann, P. J.; Hernes, P. J.; Tank, S. E.; Striegl, R. G.; Dyda, R. Y.; Peterson, B. J.; McClelland, J. W.; Holmes, R. M.

2011-12-01

Rivers draining into the Arctic Ocean exhibit high concentrations of terrigenous dissolved organic carbon (DOC) and recent studies indicate that DOC export is changing due to climatic warming and alteration in permafrost condition. The fate of exported DOC in the Arctic Ocean is of key importance for understanding the regional carbon cycle and remains a point of discussion in the literature. As part of the Arctic Great Rivers Observatory (Arctic-GRO) project, samples were collected for DOC, chromophoric dissolved organic matter (CDOM) and lignin phenols from the Ob', Yenisey, Lena, Kolyma, Mackenzie and Yukon rivers in 2009 - 2010. DOC and lignin concentrations were elevated during the spring freshet and measurements related to DOC composition indicated an increasing contribution from terrestrial vascular plant sources at this time of year (e.g. lignin carbon-normalized yield, CDOM spectral slope, SUVA254, humic-like fluorescence). CDOM absorption was found to correlate strongly with both DOC (r2=0.83) and lignin concentration (r2=0.92) across the major arctic rivers. Utilizing these relationships we modeled loads for DOC and lignin export from high-resolution CDOM measurements (daily across the freshet) to derive improved flux estimates, particularly from the dynamic spring discharge maxima period when the majority of DOC and lignin export occurs. The new load estimates for DOC and lignin are higher than previous evaluations, emphasizing that if these are more representative of current arctic riverine export, terrigenous DOC is transiting through the Arctic Ocean at a faster rate than previously thought. It is apparent that higher resolution sampling of arctic rivers is exceptionally valuable with respect to deriving accurate fluxes and we highlight the potential of CDOM in this role for future studies and the applicability of in-situ CDOM sensors.

The role of irrigation runoff and winter rainfall on dissolved organic carbon loads in an agricultural watershed

USGS Publications Warehouse

Oh, Neung-Hwan; Pellerin, Brian A.; Bachand, Philip A.M.; Hernes, Peter J.; Bachand, Sandra M.; Ohara, Noriaki; Kavvas, M. Levent; Bergamaschi, Brian A.; Horwath, William R.

2013-01-01

We investigated the role of land use/land cover and agriculture practices on stream dissolved organic carbon (DOC) dynamics in the Willow Slough watershed (WSW) from 2006 to 2008. The 415 km2watershed in the northern Central Valley, California is covered by 31% of native vegetation and the remaining 69% of agricultural fields (primarily alfalfa, tomatoes, and rice). Stream discharge and weekly DOC concentrations were measured at eight nested subwatersheds to estimate the DOC loads and yields (loads/area) using the USGS developed stream load estimation model, LOADEST. Stream DOC concentrations peaked at 18.9 mg L−1 during summer irrigation in the subwatershed with the highest percentage of agricultural land use, demonstrating the strong influence of agricultural activities on summer DOC dynamics. These high concentrations contributed to DOC yields increasing up to 1.29 g m−2 during the 6 month period of intensive agricultural activity. The high DOC yields from the most agricultural subwatershed during the summer irrigation period was similar throughout the study, suggesting that summer DOC loads from irrigation runoff would not change significantly in the absence of major changes in crops or irrigation practices. In contrast, annual DOC yields varied from 0.89 to 1.68 g m−2 yr−1 for the most agricultural watershed due to differences in winter precipitation. This suggests that variability in the annual DOC yields will be largely determined by the winter precipitation, which can vary significantly from year to year. Changes in precipitation patterns and intensities as well as agricultural practices have potential to considerably alter the DOC dynamics.

Seasonal Dynamics of Dissolved Organic Carbon Under Complex Circulation Schemes on a Large Continental Shelf: The Northern South China Sea

NASA Astrophysics Data System (ADS)

Meng, Feifei; Dai, Minhan; Cao, Zhimian; Wu, Kai; Zhao, Xiaozheng; Li, Xiaolin; Chen, Junhui; Gan, Jianping

2017-12-01

We examined the distribution and seasonality of dissolved organic carbon (DOC) based on a large data set collected from the northern South China Sea (NSCS) shelf under complex circulation schemes influenced by river plume, coastal upwelling, and downwelling. The highest surface values of ˜117 μmol L-1 were observed nearshore in summer suggesting high DOC supplies from the river inputs, whereas the lowest surface values of ˜62 μmol L-1 were on the outer shelf in winter due to entrainment of DOC-poor subsurface water under strengthened vertical mixing. While the summer coastal upwelling brought lower DOC from offshore depth to the nearshore surface, the winter coastal downwelling delivered higher surface DOC to the midshelf deep waters from the inner shelf fueled by the China Coastal Current (CCC) transporting relatively high DOC from the East China Sea to the NSCS. The intensified winter downwelling generated a cross-shelf DOC transport of 3.1 × 1012 g C over a large shelf area, which induced a significant depression of the NSCS DOC inventory in winter relative to in autumn. In addition to the variable physical controls, net biological production of DOC was semiquantified in both the river plume (2.8 ± 3.0 μmol L-1) and coastal upwelling (3.1 ± 1.3 μmol L-1) in summer. We demonstrated that the NSCS shelf had various origins of DOC including riverine inputs, inter-shelf transport and in situ production. Via cross-shelf transport, the accumulated DOC would be exported to and stored in the deep ocean, suggesting that continental shelves are a potentially effective carbon sink.

Controls on accumulation and soil solution partitioning of heavy metals across upland sites in United Kingdom (UK).

PubMed

Zia, Afia; van den Berg, Leon; Ahmad, Muhammad Nauman; Riaz, Muhammad; Zia, Dania; Ashmore, Mike

2018-05-31

A significant body of knowledge suggests that soil solution pH and dissolved organic carbon (DOC) strongly influence metal concentrations and speciation in porewater, however, these effects vary between different metals. This study investigated the factors influencing soil and soil solution concentrations of copper (Cu), lead (Pb), nickel (Ni) and zinc (Zn) under field conditions in upland soils from UK having a wide range of pH, DOC and organic matter contents. The study primarily focussed on predicting soil and soil solution metal concentrations from the data on total soil metal concentrations (HNO 3 extracts) and soil and soil solution properties (pH, DOC and organic matter content). We tested the multiple regression models proposed by Tipping et al. (2003) to predict heavy metal concentrations in soil solutions and the results indicated a better fit (higher R 2 values) in both studies for Pb compared to the Zn and Cu concentrations. Both studies observed consistent negative relationships of metals with pH and loss on ignition (LOI) suggesting an increase in soil solution metal concentrations with increasing acidity. The positive relationship between Pb concentrations in porewater and HNO 3 extracts was similar for both studies, however, similar relationships were not found for the Zn and Cu concentrations because of the negative coefficients for these metals in our study. The results of this study conclude that the predictive equations of Tipping et al. (2003) may not be applicable to the field sites where the range of DOC and metal concentrations is much lower than their study. Our study also suggests that the extent to which metals are partitioned into soil solution is lower in soils with a higher organic matter contents due to binding of these metals to soil organic matter. Copyright © 2018 Elsevier Ltd. All rights reserved.

The Role of YKL-40 in Predicting Resistance to Docetaxel Chemotherapy in Prostate Cancer.

PubMed

Darr, Christopher; Krafft, Ulrich; Hadaschik, Boris; Tschirdewahn, Stephan; Sevcenco, Sabina; Csizmarik, Anita; Nyirady, Peter; Küronya, Zsófia; Reis, Henning; Maj-Hes, Agnieszka; Shariat, Shahrokh F; Kramer, Gero; Szarvas, Tibor

2018-06-27

High baseline YKL-40 serum levels are associated with drug resistance in several solid tumours. However, their role in predicting docetaxel (DOC) resistance in prostate cancer (PCa) is unknown. Pre-treatment serum levels of YKL-40 and prostate-specific antigen (PSA) were analyzed in 109 castration-resistant prostate cancer patients who underwent DOC-therapy. Responsive patients were retreated by repeated series of DOC. Results were compared with the clinical parameters as well as overall (OS) and disease-specific survival (DSS). YKL-40 but not PSA serum levels were significantly higher in patients with baseline resistance to DOC (p = 0.035). Higher YKL-40 and PSA levels were detected in patients with bone metastasis (p = 0.032; p = 0.010) and in those who were not pre-treated with radical prostatectomy (p = 0.011, p = 0.008). High YKL-40 levels were associated with shorter OS (p = 0.037) and DSS (p = 0.017) in patients who received DOC in the first-line setting. In multivariable analysis, ECOG performance status (p = 0.009), presence of any metastases (p = 0.016) and high PSA levels (p = 0.005) remained independent predictors for DSS. YKL-40 may help to identify patients with baseline resistance to DOC and therefore may help to optimize treatment decisions. In accordance, high pre-treatment YKL-40 serum levels were associated with shorter OS and DSS in patients who received DOC as first-line therapy. © 2018 S. Karger AG, Basel.

Concentration, sources, and flux of dissolved organic carbon of precipitation at Lhasa city, the Tibetan Plateau.

PubMed

Li, Chaoliu; Yan, Fangping; Kang, Shichang; Chen, Pengfei; Qu, Bin; Hu, Zhaofu; Sillanpää, Mika

2016-07-01

Dissolved organic carbon (DOC) plays an important role in the climate system, but few data are available on the Tibetan Plateau (TP). In this study, 89 precipitation samples were collected at Lhasa, the largest city of southern Tibet, from March to December 2013. The average concentration and wet deposition flux of DOC was 1.10 mg C L(-1) and 0.63 g C m(-2) year(-1), respectively. Seasonally, low DOC concentration and high flux appeared during the monsoon period, which were in line with heavy precipitation amount, reflecting dilution effect of precipitation for the DOC. Compared to other regions, the values of Lhasa were lower than those of large cities (e.g., Beijing and Seoul) mainly because of less air pollution of Lhasa. The principal component analysis (PCA) of DOC and ions (Ca(2+), Mg(2+), Na(+), K(+), NH4 (+), Cl(-), NO3 (-), and SO4 (2-)) showed that DOC of Lhasa was derived mainly from the natural sources, followed by anthropogenic burning activities. Furthermore, △(14)C value of DOC indicated that fossil fuel combustion contributed around 28 % of the rainwater DOC of Lhasa, indicating that the atmosphere of Lhasa has been influenced by emission from fossil fuel combustion or high-temperature industrial processes.

Photochemical alteration of organic carbon draining permafrost soils shifts microbial metabolic pathways and stimulates respiration.

PubMed

Ward, Collin P; Nalven, Sarah G; Crump, Byron C; Kling, George W; Cory, Rose M

2017-10-03

In sunlit waters, photochemical alteration of dissolved organic carbon (DOC) impacts the microbial respiration of DOC to CO 2 . This coupled photochemical and biological degradation of DOC is especially critical for carbon budgets in the Arctic, where thawing permafrost soils increase opportunities for DOC oxidation to CO 2 in surface waters, thereby reinforcing global warming. Here we show how and why sunlight exposure impacts microbial respiration of DOC draining permafrost soils. Sunlight significantly increases or decreases microbial respiration of DOC depending on whether photo-alteration produces or removes molecules that native microbial communities used prior to light exposure. Using high-resolution chemical and microbial approaches, we show that rates of DOC processing by microbes are likely governed by a combination of the abundance and lability of DOC exported from land to water and produced by photochemical processes, and the capacity and timescale that microbial communities have to adapt to metabolize photo-altered DOC.The role of dissolved organic carbon (DOC) photo-alteration in the microbial respiration of DOC to CO 2 is unclear. Here, the authors show that the impact of this mechanism depends on whether photo-alteration of DOC produces or removes molecules used by native microbial communities prior to light exposure.

Comparing Stream DOC Fluxes from Sensor- and Sample-Based Approaches

NASA Astrophysics Data System (ADS)

Shanley, J. B.; Saraceno, J.; Aulenbach, B. T.; Mast, A.; Clow, D. W.; Hood, K.; Walker, J. F.; Murphy, S. F.; Torres-Sanchez, A.; Aiken, G.; McDowell, W. H.

2015-12-01

DOC transport by streamwater is a significant flux that does not consistently show up in ecosystem carbon budgets. In an effort to quantify stream DOC flux, we analyzed three to four years of high-frequency in situ fluorescing dissolved organic matter (FDOM) concentrations and turbidity measured by optical sensors at the five diverse forested and/or alpine headwater sites of the U.S. Geological Survey (USGS) Water, Energy, and Biogeochemical Budgets (WEBB) program. FDOM serves as a proxy for DOC. We also took discrete samples over a range of hydrologic conditions, using both manual weekly and automated event-based sampling. After compensating FDOM for temperature effects and turbidity interference - which was successful even at the high-turbidity Luquillo, PR site -- we evaluated the DOC-FDOM relation based on discrete sample DOC analyses matched to corrected FDOM at the time of sampling. FDOM was a moderately robust predictor of DOC, with r2 from 0.60 to more than 0.95 among sites. We then formed continuous DOC time series by two independent approaches: (1) DOC predicted from FDOM; and (2) the composite method, based on modeled DOC from regression on stream discharge, season, air temperature, and time, forcing the model to observations and adjusting modeled concentrations between observations by linearly-interpolated model residuals. DOC flux from each approach was then computed directly as concentration times discharge. DOC fluxes based on the sensor approach were consistently greater than the sample-based approach. At Loch Vale, CO (2.5 years) and Panola Mountain GA (1 year), the difference was 5-17%. At Sleepers River, VT (3 years), preliminary differences were greater than 20%. The difference is driven by the highest events, but we are investigating these results further. We will also present comparisons from Luquillo, PR, and Allequash Creek, WI. The higher sensor-based DOC fluxes could result from their accuracy during hysteresis, which is difficult to model. In at least one case the higher sensor-based DOC flux was linked to an unsampled event outside the range of the concentration model. Sensors require upkeep and vigilance with the data, but have the potential to yield more accurate fluxes than sample-based approaches.

Carbon and nitrogen stoichiometry across stream ecosystems

NASA Astrophysics Data System (ADS)

Wymore, A.; Kaushal, S.; McDowell, W. H.; Kortelainen, P.; Bernhardt, E. S.; Johnes, P.; Dodds, W. K.; Johnson, S.; Brookshire, J.; Spencer, R.; Rodriguez-Cardona, B.; Helton, A. M.; Barnes, R.; Argerich, A.; Haq, S.; Sullivan, P. L.; López-Lloreda, C.; Coble, A. A.; Daley, M.

2017-12-01

Anthropogenic activities are altering carbon and nitrogen concentrations in surface waters globally. The stoichiometry of carbon and nitrogen regulates important watershed biogeochemical cycles; however, controls on carbon and nitrogen ratios in aquatic environments are poorly understood. Here we use a multi-biome and global dataset (tropics to Arctic) of stream water chemistry to assess relationships between dissolved organic carbon (DOC) and nitrate, ammonium and dissolved organic nitrogen (DON), providing a new conceptual framework to consider interactions between DOC and the multiple forms of dissolved nitrogen. We found that across streams the total dissolved nitrogen (TDN) pool is comprised of very little ammonium and as DOC concentrations increase the TDN pool shifts from nitrate to DON dominated. This suggests that in high DOC systems, DON serves as the primary source of nitrogen. At the global scale, DOC and DON are positively correlated (r2 = 0.67) and the average C: N ratio of dissolved organic matter (molar ratio of DOC: DON) across our data set is approximately 31. At the biome and smaller regional scale the relationship between DOC and DON is highly variable (r2 = 0.07 - 0.56) with the strongest relationships found in streams draining the mixed temperate forests of the northeastern United States. DOC: DON relationships also display spatial and temporal variability including latitudinal and seasonal trends, and interactions with land-use. DOC: DON ratios correlated positively with gradients of energy versus nutrient limitation pointing to the ecological role (energy source versus nutrient source) that DON plays with stream ecosystems. Contrary to previous findings we found consistently weak relationships between DON and nitrate which may reflect DON's duality as an energy or nutrient source. Collectively these analyses demonstrate how gradients of DOC drive compositional changes in the TDN pool and reveal a high degree of variability in the C: N ratio (3-100) of stream water dissolved organic matter.

Direct quantitative detection of Doc2b-induced hemifusion in optically trapped membranes

NASA Astrophysics Data System (ADS)

Brouwer, Ineke; Giniatullina, Asiya; Laurens, Niels; van Weering, Jan R. T.; Bald, Dirk; Wuite, Gijs J. L.; Groffen, Alexander J.

2015-09-01

Ca2+-sensor proteins control the secretion of many neuroendocrine substances. Calcium-secretion coupling may involve several mechanisms. First, Ca2+-dependent association of their tandem C2 domains with phosphatidylserine may induce membrane curvature and thereby enhance fusion. Second, their association with SNARE complexes may inhibit membrane fusion in the absence of a Ca2+ trigger. Here we present a method using two optically trapped beads coated with SNARE-free synthetic membranes to elucidate the direct role of the C2AB domain of the soluble Ca2+-sensor Doc2b. Contacting membranes are often coupled by a Doc2b-coated membrane stalk that resists forces up to 600 pN upon bead separation. Stalk formation depends strictly on Ca2+ and phosphatidylserine. Real-time fluorescence imaging shows phospholipid but not content mixing, indicating membrane hemifusion. Thus, Doc2b acts directly on membranes and stabilizes the hemifusion intermediate in this cell-free system. In living cells, this mechanism may co-occur with progressive SNARE complex assembly, together defining Ca2+-secretion coupling.

Physicochemical, microbiological and sensory evaluation of beef patties incorporated with destoned olive cake powder.

PubMed

Hawashin, Majed D; Al-Juhaimi, Fahad; Ahmed, Isam A Mohamed; Ghafoor, Kashif; Babiker, Elfadil E

2016-12-01

The biological efficacy of different concentrations (2%, 4%, and 6%) of destoned olive cake (DOC) as improvers of the quality, storability, and safety of beef patties was investigated. Increasing the percentage of DOC in the patties improved (P≤0.05) the protein and fat contents, cooking yield, moisture and fat retention, total phenolic, and DPPH radical scavenging activity, while the dimensional shrinkage and TBARS showed a progressive reduction. The pH of the patties decreased gradually with the storage time. DOC-incorporated patties showed significantly (P≤0.05) lower total plate count than untreated. Surface color values of raw beef patties were decreased gradually with the storage time. Throughout the storage period, all the sensory traits of non-formulated patties were significantly (P≤0.05) reduced, whereas the formulated patties revealed considerable stability of all characters. Overall, this study identified antioxidant and antimicrobial potentiality of DOC, which could pave the way for its use as an extender of the shelf life of the patties. Copyright © 2016 Elsevier Ltd. All rights reserved.

What advice is given to newly qualified doctors on Twitter? An analysis of #TipsForNewDocs tweets.

PubMed

Rashid, Mohammed Ahmed; McKechnie, Doug; Gill, Deborah

2018-07-01

Twitter is a social media platform on which users post very brief messages that can be rapidly communicated across wide geographical areas and audiences. Many doctors use Twitter for personal as well as professional communications and networking. The #TipsForNewDocs hashtag is used on Twitter to give advice to newly qualified doctors as they commence their careers. This study explores the nature and focus of such advice. An analysis of Twitter activity containing the #TipsForNewDocs hashtag was performed using Symplur health care analytics software. Tweets sent during a peak 48-hour period in 2016 (immediately preceding the first day of work for newly qualified UK doctors) were studied. The geographical locations and professional backgrounds of participants were categorised and the content of tweets was subjected to thematic analysis. During 1 and 2 August 2016, 661 unique #TipsForNewDocs tweets were posted. A total of 621 (94.0%) were posted by people in the UK; 522 (79.0%) were posted by doctors, and the remainder by allied health care professionals and patients. The majority of included tweets focused on aspects of professional development, improving personal or professional knowledge, particularly tacit knowledge, and developing 'know-how'. These aspects of professional knowledge have previously been described as fundamental to professional education and training. However, a significant subset of tweets focused on accelerating socialisation into the profession, an essential step in joining a professional community. The tweets relating to socialisation were often humorous and colloquial in nature. Despite their brief and often jocular nature, #TipsForNewDocs tweets provided meaningful advice for newcomers to the profession, often focusing on tacit learning and professional socialisation. Hashtag-driven enquiries can be a valuable and time-efficient way of accessing and sharing tacitly held knowledge. Social media content analysis can provide valuable insights into key educational issues. © 2018 John Wiley & Sons Ltd and The Association for the Study of Medical Education.

Fingerprinting Dissolved Organic Carbon (DOC) Sources with Specific UV Absorbance (SUVA) and Fluorescence

NASA Astrophysics Data System (ADS)

van Verseveld, W. J.; Lajtha, K.; McDonnell, J. J.

2007-12-01

DOC is an important water quality constituent because it is an important food source for stream biota, it plays a significant role in metal toxicity and transport, and protects aquatic organisms by absorbing visible and UV light. However, sources of stream DOC and changes in DOC quality at storm and seasonal scales remain poorly understood. We characterized DOC concentrations and SUVA (as an indicator of aromaticity) at the plot, hillslope and catchment scale during and between five storm events over the period Fall 2004 until Spring 2005, in WS10, H.J. Andrews, Oregon, USA. This study site has hillslopes that issue directly into the stream. This enabled us to compare a trenched hillslope response to the stream response without the influence of a riparian zone. The main result of this study was that SUVA in addition to DOC was needed to fingerprint sources of DOC. Stream water and lateral subsurface flow showed a clockwise DOC and SUVA hysteresis pattern. Both organic horizon water and transient groundwater were characterized by high DOC concentrations and SUVA values, while DOC concentrations and SUVA values in soil water decreased with depth in the soil profile. This indicates transient groundwater was an important contributor to high DOC concentrations and SUVA values during storm events. During the falling limb of the hydrograph deep soil water and seepage groundwater based on SUVA values contributed significantly to lateral subsurface flow and stream water. Preliminary results showed that fluorescence of stream water and lateral subsurface flow continuously measured with a fluorometer was significantly related to UV-absorbance during a December storm event. Finally, SUVA of lateral subsurface flow was lower than SUVA of stream water at the seasonal scale, indicating a difference in mixing of water sources at the hillslope and catchment scale. Overall, our results show that SUVA and fluorescence are useful tracers for fingerprinting DOC sources.

Wetlands receiving water treated with coagulants improve water quality by removing dissolved organic carbon and disinfection byproduct precursors.

PubMed

Hansen, Angela M; Kraus, Tamara E C; Bachand, Sandra M; Horwath, William R; Bachand, Philip A M

2018-05-01

Constructed wetlands are used worldwide to improve water quality while also providing critical wetland habitat. However, wetlands have the potential to negatively impact drinking water quality by exporting dissolved organic carbon (DOC) that upon disinfection can form disinfection byproducts (DBPs) like trihalomethanes (THMs) and haloacetic acids (HAAs). We used a replicated field-scale study located on organic rich soils in California's Sacramento-San Joaquin Delta to test whether constructed flow-through wetlands which receive water high in DOC that is treated with either iron- or aluminum-based coagulants can improve water quality with respect to DBP formation. Coagulation alone removed DOC (66-77%) and THM (67-70%) precursors, and was even more effective at removing HAA precursors (77-90%). Passage of water through the wetlands increased DOC concentrations (1.5-7.5mgL -1 ), particularly during the warmer summer months, thereby reversing some of the benefits from coagulant addition. Despite this addition, water exiting the wetlands treated with coagulants had lower DOC and DBP precursor concentrations relative to untreated source water. Benefits of the coagulation-wetland systems were greatest during the winter months (approx. 50-70% reduction in DOC and DBP precursor concentrations) when inflow water DOC concentrations were higher and wetland DOC production was lower. Optical properties suggest DOC in this system is predominantly comprised of high molecular weight, aromatic compounds, likely derived from degraded peat soils. Published by Elsevier B.V.

Spatiotemporal Variation of Dissolved Carbon in Semi-humid/arid Inland Waters: A Case Study from Songnen Plain, China

NASA Astrophysics Data System (ADS)

Song, K.; Li, L.; Zang, S.; Zhao, Y.

2012-12-01

Spatial and seasonal variations of dissolved organic carbon (DOC) and inorganic carbon (DIC) in 34 waters across the semi-humid/arid Songnen Plain, China were examined with 320 samples collected in 2011-2012. Large variations in both the concentration and quality of DOC are revealed, ranging from 0.47 mgL-1 to 720 mgL-1, which is mainly caused by the hydro-climatic condition in the plain. Large variations of DOC and DIC concentrations are observed between open (mean ± sd: 5.6 ± 2.4 mgL-1, 57.4 ± 34.7 mgL-1) and closed lakes (43.3 ± 7.9 mgL-1, 172.9 ± 113.3 mgL-1). Temporally, higher DOC and DIC concentrations are measured for ice-underlying water in winter than ice-free seasons. Colored dissolved organic matter (CDOM) and DOC concentrations are higher after high discharge events with terrigenous sources of CDOM/DOC dominated, while autochthonous sources also contributed to CDOM/DOC concentrations during algal bloom seasons. An interesting result of this study is that the non-outflow conditions for various water catchments had condensed effects on the dissolved carbon, resulting in close relationships between salinity and dissolved carbon parameters, e.g. salinity vs DOC (R2 = 0.83, p < 0.001), DIC (R2 = 0.96, p < 0.0001) using data set collected in 2011. Independent data set collected in May 2012 also confirmed this finding, yielding high correlation for salinity vs DOC (R2 = 0.79, p < 0.001), salinity vs DIC (R2 = 0.91, p < 0.0001), highlighting the potential of quantifying DOC/DIC from salinity measurements for thousand of waters dispersed in the semi-arid Songnen Plain. Indices based on CDOM absorption spectra, e.g. E250:365, DOC specific CDOM absorption (SUVA254) and spectral slope ratio (Sr, S275-295/S350-400), were applied to characterize DOM components and sources. Our results indicate high molecular weight CDOM fractions are more abundant in open waters than closed waters.

Major and trace element geochemistry of Lake Bogoria and Lake Nakuru, Kenya, during extreme draught.

PubMed

Jirsa, Franz; Gruber, Martin; Stojanovic, Anja; Omondi, Steve Odour; Mader, Dieter; Körner, Wilfried; Schagerl, Michael

2013-10-01

The physico-chemical properties of water samples from the two athalassic endorheic lakes Bogoria and Nakuru in Kenya were analysed. Surface water samples were taken between July 2008 and October 2009 in weekly intervals from each lake. The following parameters were determined: pH, salinity, electric conductivity, dissolved organic carbon (DOC), the major cations (FAAS and ICP-OES) and the major anions (IC), as well as certain trace elements (ICP-OES). Samples of superficial sediments were taken in October 2009 and examined using Instrumental Neutron Activation Analysis (INAA) for their major and trace element content including rare earth elements (REE). Both lakes are highly alkaline with a dominance of Na > K > Si > Ca in cations and HCO 3  > CO 3  > Cl > F > SO 4 in anions. Both lakes also exhibited high concentrations of Mo, As and fluoride. Due to an extreme draught from March to October 2009, the water level of Lake Nakuru dropped significantly. This created drastic evapoconcentration, with the total salinity rising from about 20‰ up to 63‰. Most parameters (DOC, Na, K, Ca, F, Mo and As) increased with falling water levels. A clear change in the quality of DOC was observed, followed by an almost complete depletion of dissolved Fe from the water phase. In Lake Bogoria the evapoconcentration effects were less pronounced (total salinity changed from about 40‰ to 48‰). The distributions of REE in the superficial sediments of Lake Nakuru and Lake Bogoria are presented here for the first time. The results show a high abundance of the REE and a very distinct Eu depletion of Eu/Eu* = 0.33-0.45.

Major and trace element geochemistry of Lake Bogoria and Lake Nakuru, Kenya, during extreme draught

PubMed Central

Jirsa, Franz; Gruber, Martin; Stojanovic, Anja; Omondi, Steve Odour; Mader, Dieter; Körner, Wilfried; Schagerl, Michael

2013-01-01

The physico-chemical properties of water samples from the two athalassic endorheic lakes Bogoria and Nakuru in Kenya were analysed. Surface water samples were taken between July 2008 and October 2009 in weekly intervals from each lake. The following parameters were determined: pH, salinity, electric conductivity, dissolved organic carbon (DOC), the major cations (FAAS and ICP-OES) and the major anions (IC), as well as certain trace elements (ICP-OES). Samples of superficial sediments were taken in October 2009 and examined using Instrumental Neutron Activation Analysis (INAA) for their major and trace element content including rare earth elements (REE). Both lakes are highly alkaline with a dominance of Na > K > Si > Ca in cations and HCO3 > CO3 > Cl > F > SO4 in anions. Both lakes also exhibited high concentrations of Mo, As and fluoride. Due to an extreme draught from March to October 2009, the water level of Lake Nakuru dropped significantly. This created drastic evapoconcentration, with the total salinity rising from about 20‰ up to 63‰. Most parameters (DOC, Na, K, Ca, F, Mo and As) increased with falling water levels. A clear change in the quality of DOC was observed, followed by an almost complete depletion of dissolved Fe from the water phase. In Lake Bogoria the evapoconcentration effects were less pronounced (total salinity changed from about 40‰ to 48‰). The distributions of REE in the superficial sediments of Lake Nakuru and Lake Bogoria are presented here for the first time. The results show a high abundance of the REE and a very distinct Eu depletion of Eu/Eu* = 0.33–0.45. PMID:25843965

Assessment of benthic flux of dissolved organic carbon in wetland and estuarine sediments using the eddy-correlation technique

NASA Astrophysics Data System (ADS)

Swett, M. P.; Amirbahman, A.; Boss, E.

2009-12-01

Wetland and estuarine sediments release significant amounts of dissolved organic carbon (DOC) due to high levels of microbial activity, particularly sulfate reduction. Changes in climate and hydrologic conditions have a potential to alter DOC release from these systems as well. This is a concern, as high levels of DOC can lead to mobilization of toxic metals and organics in natural waters. In addition, source waters high in DOC produce undesirable disinfection byproducts in water treatment. Various in situ methods, such as peepers and sediment core centrifugation, exist to quantify vertical benthic fluxes of DOC and other dissolved species from the sediment-water interface (SWI). These techniques, however, are intrusive and involve disturbance of the sediment environment. Eddy-correlation allows for real-time, non-intrusive, in situ flux measurement of important analytes, such as O2 and DOC. An Acoustic Doppler Velocimeter (ADV) is used to obtain three-dimensional fluid velocity measurements. The eddy-correlation technique employs the mathematical separation of fluid velocity into mean velocity and fluctuating velocity components, with the latter representing turbulent eddy velocity. DOC concentrations are measured using a colored dissolved organic matter (CDOM) fluorometer, and instantaneous vertical flux is determined from the correlated data. This study assesses DOC flux at three project sites: a beaver pond in the Lower Penobscot Watershed, Maine; a mudflat in Penobscot River, Maine; and a mudflat in Great Bay, New Hampshire. Eddy flux values are compared with results obtained using peepers and centrifugation, as well as vertical profiling.

Diagnosis of Processes Controlling Dissolved Organic Carbon (DOC) Export in a Subarctic Region by a Dynamic Ecosystem Model

NASA Astrophysics Data System (ADS)

Tang, J.

2015-12-01

Permafrost thawing in high latitudes allows more soil organic carbon (SOC) to become hydrologically accessible. This can increase dissolved organic carbon (DOC) exports and carbon release to the atmosphere as CO2 and CH4, with a positive feedback to regional and global climate warming. However, this portion of carbon loss through DOC export is often neglected in ecosystem models. In this paper, we incorporate a set of DOC-related processes (DOC production, mineralization, diffusion, sorption-desorption and leaching) into an Arctic-enabled version of the dynamic ecosystem model LPJ-GUESS (LPJ-GUESS WHyMe) to mechanistically model the DOC export, and to link this flux to other ecosystem processes. The extended LPJ-GUESS WHyMe with these DOC processes is applied to the Stordalen catchment in northern Sweden. The relative importance of different DOC-related processes for mineral and peatland soils for this region have been explored at both monthly and annual scales based on a detailed variance-based Sobol sensitivity analysis. For mineral soils, the annual DOC export is dominated by DOC fluxes in snowmelt seasons and the peak in spring is related to the runoff passing through top organic rich layers. Two processes, DOC sorption-desorption and production, are found to contribute most to the annual variance in DOC export. For peatland soils, the DOC export during snowmelt seasons is constrained by frozen soils and the processes of DOC production and mineralization, determining the magnitudes of DOC desorption in snowmelt seasons as well as DOC sorption in the rest of months, play the most important role in annual variances of DOC export. Generally, the seasonality of DOC fluxes is closely correlated with runoff seasonality in this region. The current implementation has demonstrated that DOC-related processes in the framework of LPJ-GUESS WHyMe are at an appropriate level of complexity to represent the main mechanism of DOC dynamics in soils. The quantified contributions from different processes on DOC export dynamics could be further linked to the climate change, vegetation composition change and permafrost thawing in this region.

Laboratory Experiments to Evaluate Matrix Diffusion of Dissolved Organic Carbon Carbon-14 in Southern Nevada Fractured-rock Aquifers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hershey, Ronald L.; Fereday, Wyatt

Dissolved inorganic carbon (DIC) carbon-14 ( 14C) is used to estimate groundwater ages by comparing the DIC 14C content in groundwater in the recharge area to the DIC 14C content in the downgradient sampling point. However, because of chemical reactions and physical processes between groundwater and aquifer rocks, the amount of DIC 14C in groundwater can change and result in 14C loss that is not because of radioactive decay. This loss of DIC 14C results in groundwater ages that are older than the actual groundwater ages. Alternatively, dissolved organic carbon (DOC) 14C in groundwater does not react chemically with aquifermore » rocks, so DOC 14C ages are generally younger than DIC 14C ages. In addition to chemical reactions, 14C ages may also be altered by the physical process of matrix diffusion. The net effect of a continuous loss of 14C to the aquifer matrix by matrix diffusion and then radioactive decay is that groundwater appears to be older than it actually is. Laboratory experiments were conducted to measure matrix diffusion coefficients for DOC 14C in volcanic and carbonate aquifer rocks from southern Nevada. Experiments were conducted using bromide (Br-) as a conservative tracer and 14C-labeled trimesic acid (TMA) as a surrogate for groundwater DOC. Outcrop samples from six volcanic aquifers and five carbonate aquifers in southern Nevada were used. The average DOC 14C matrix diffusion coefficient for volcanic rocks was 2.9 x 10 -7 cm 2/s, whereas the average for carbonate rocks was approximately the same at 1.7 x 10 -7 cm 2/s. The average Br- matrix diffusion coefficient for volcanic rocks was 10.4 x 10 -7 cm 2/s, whereas the average for carbonate rocks was less at 6.5 x 10 -7 cm 2/s. Carbonate rocks exhibited greater variability in DOC 14C and Br- matrix diffusion coefficients than volcanic rocks. These results confirmed, at the laboratory scale, that the diffusion of DOC 14C into southern Nevada volcanic and carbonate aquifers is slower than DIC 14C. Because of the apparent sorption of 14C-labeled TMA in the experiments, matrix diffusion coefficients are likely even lower. The reasons for the higher than expected Br-/ 14C-labeled TMA are unknown. Because the molecular size of TMA is on the low end of the range in molecular size for typical humic substances, the matrix diffusion coefficients for the 14C-labeled TMA likely represent close to the maximum diffusion rates for DOC 14C in the volcanic and carbonate aquifers in southern Nevada.« less

Hot Moments in Cold Spots - Investigating Reactive Transport Patterns at Aquifer-River Interfaces by Heat Tracers and Distributed Sensor Networks

NASA Astrophysics Data System (ADS)

Krause, Stefan; Angermann, Lisa; Naden, Emma; Cassidy, Nigel; Blume, Theresa

2010-05-01

The mixing of groundwater and surface water in hyporheic zones often coincides with high redox reactivity and chemical transformation potential. Depending on redox conditions and reaction types, hyporheic mixing of groundwater and surface water can lead to either attenuation or enrichment of pollutants or nutrients with diametrical implications for stream and aquifer hydro-ecological conditions. This study investigates the reactive transport of nitrate and a chlorinated solvent (Trichloroethylene - TCE) at the aquifer-river interface of a UK lowland river. In this study, distributed temperature sensor networks and hydro-geophysical methods, which have been applied for identifying structural streambed heterogeneity and tracing aquifer river exchange, were combined with hydro-chemical analyses of hyporheic multi-component reactive transport. In stream Electric Resistivity Tomography has been applied to map the complex spatial distribution of highly conductive sandy and gravely sediments in contrast to semi-confining, low conductivity peat lenses. Reach scale (1km) spatial patterns and temporal dynamics of aquifer-river exchange have been identified by heat tracer experiments based on fibre-optic Distributed Temperature Sensing in combination with 2D thermocouple-arrays and small scale heat pulse injection methods for tracing shallow (25 cm) hyporheic flow paths. Spatial patterns of hyporheic redox conditions, dissolved oxygen and organic carbon (DOC) content as well as concentrations of major anions, TCE and its decay products have been observed in 48 nested multi-level piezometers and passive DET (Diffusive Equilibrium in Thin film) gel probes. Our results indicate that patterns of cold spots in streambed sediments can be attributed to fast groundwater up-welling in sandy and gravely sediments resulting in low hyporheic residence times. Contrasting conditions were found at warmer areas at the streambed surface where groundwater - surface water exchange was inhibited by the existence of peat or clay lenses within the streambed. These flow-inhibiting structures have been shown to cause semi-confined conditions in the up-welling groundwater, resulting in long residence times and increased redox-reactivity. Anoxic conditions and high DOC contents combined with long residence times underneath peat layers cause highly efficient denitrification rates, reducing nitrate concentrations from > 50mg/l to below the level of detection. In contrast, sandy and gravely areas of fast groundwater up-welling where characterized by only marginal changes in nitrate concentrations. Observation of the reactive transport of the chlorinated solvent groundwater plume into the river suggest that natural attenuation of TCE, which competes with nitrate for DOC as reductive agent, is limited to the semi-confined, anoxic, low nitrate - high DOC groundwater pockets underneath streambed peat lenses. The investigations supported the development of a conceptual model of aquifer - river exchange and hyporheic reactivity in lowland rivers including temperature traceable "hyporheic super-reactors" of great importance for river restoration, water quality and ecology status.

Hot Moments in Cold Spots - Using Heat Tracers and Distributed Sensor Networks to Investigate Reactive Transport Patterns at Aquifer-River Interfaces

NASA Astrophysics Data System (ADS)

Krause, S.; Angermann, L.; Naden, E.; Cassidy, N. J.

2009-12-01

The mixing of groundwater and surface water in hyporheic zones often coincides high redox reactivity and chemical transformation potential. Depending on redox conditions and reaction types, hyporheic mixing of groundwater and surface water can lead to either attenuation or enrichment of pollutants or nutrients with diametrical implications for stream and aquifer hydro-ecology. This study investigates the reactive transport of nitrate and the chlorinated solvent Trichloroethylene (TCE) at the aquifer-river interface of a UK lowland river. The investigations are based on novel distributed sensor networks and hydro-geophysical methods for the identification of structural streambed heterogeneity and the tracing of aquifer river exchange combined with hydro-chemical analyses of hyporheic multi-component reactive transport. In stream Electric Resistivity Tomography and Ground Penetrating Radar have been applied to map the complex spatial distribution of highly conductive sandy and gravely sediments in contrast to semi-confining, low conductivity peat lenses. Reach scale (1km) spatial patterns and temporal dynamics of aquifer-river exchange have been identified by heat tracer experiments based on fibre-optic Distributed Temperature Sensing in combination with 2D thermocouple-arrays and small scale heat pulse injection methods for tracing shallow (25 cm) hyporheic flow paths. Spatial patterns of hyporheic redox conditions, dissolved oxygen and organic carbon (DOC) content as well as concentrations of major anions, TCE and its decay products have been observed in 48 nested multi-level piezometers and passive DET (Diffusive Equilibrium in Thin film) gel probes. Our results indicate that patterns of cold spots in streambed sediments can be attributed to fast groundwater up-welling in sandy and gravely sediments resulting in low hyporheic residence times. Contrasting conditions were found at warmer areas at the streambed surface where groundwater - surface water exchange was inhibited by the existence of peat or clay lenses within the streambed. These flow-inhibiting structures have been shown to cause semi-confined conditions in the up-welling groundwater, resulting in long residence times and increased redox-reactivity. Anoxic conditions and high DOC contents combined with long residence times underneath peat layers cause highly efficient denitrification rates, reducing nitrate concentrations from > 50mg/l to below the level of detection. In contrast, sandy and gravely areas of fast groundwater up-welling where characterized by only marginal changes in nitrate concentrations. Observation of the reactive transport of the chlorinated solvent groundwater plume into the river suggest that natural attenuation of TCE, which competes with nitrate for DOC as reductive agent, is limited to the semi-confined, anoxic, low nitrate - high DOC groundwater pockets underneath streambed peat lenses. The investigations supported the development of a conceptual model of aquifer - river exchange and hyporheic reactivity in lowland rivers including temperature traceable “hyporheic super-reactors” of great importance for river restoration, water quality and ecology status.

[Short-term effects of low intensity thinning simulated by gap on ground microclimate and soil nutrients of pure spruce plantation].

PubMed

Wang, Cheng; Pang, Xue-Yong; Bao, Wei-Kai

2010-03-01

Taking a dense spruce pure plantation as test object and simulating the formation of natural forest gap, this paper studied the effects of low intensity thinning by gap creation on the ground temperature, ground humidity, and nutrient contents in different soil layers of the plantation. In the first year of gap creation, the mean diurnal temperature in the gap across the growth season (May - September) increased, while the mean diurnal humidity decreased. The soil organic matter (SOM) and NH4(+) -N contents in O-horizon (humus layer) increased by 19.62% and 283.85%, and the dissolved organic carbon (DOC) and NO3(-) -N contents decreased by 77.86% and 23.60%, respectively. The SOM, total nitrogen (TN), and NO3(-) -N contents in 0-10 cm soil layer increased by 45.77%, 37.14%, and 75.11%, and the NH4(+) -N, DOC, and total phosphorus (TP) contents decreased by 48.56%, 33.33%, and 13.11%, respectively. All the results suggested that low intensity thinning by gap creation could rapidly improve the ground microclimate of the plantation, and consequently, promote the soil microbial activity and mineralization processes in O-horizon, the release of soil nutrients, and the restoration of soil fertility.

Diel fluctuations of viscosity-driven riparian inflow affect streamflow DOC concentration

NASA Astrophysics Data System (ADS)

Schwab, Michael P.; Klaus, Julian; Pfister, Laurent; Weiler, Markus

2018-04-01

Diel fluctuations of stream water DOC concentrations are generally explained by a complex interplay of different instream processes. We measured the light absorption spectrum of water and DOC concentrations in situ and with high frequency by means of a UV-Vis spectrometer during 18 months at the outlet of a forested headwater catchment in Luxembourg (0.45 km2). We generally observed diel DOC fluctuations with a maximum in the afternoon during days that were not affected by rainfall-runoff events. We identified an increased inflow of terrestrial DOC to the stream in the afternoon, causing the DOC maxima in the stream. The terrestrial origin of the DOC was derived from the SUVA-254 (specific UV absorbance at 254 nm) index, which is a good indicator for the aromaticity of DOC. In the studied catchment, the most likely process that can explain the diel DOC input variations towards the stream is the so-called viscosity effect. The water temperature in the upper parts of the saturated riparian zone is increasing during the day, leading to a lower viscosity and therefore a higher hydraulic conductivity. Consequently, more water from areas that are rich in terrestrial DOC passes through the saturated riparian zone and contributes to streamflow in the afternoon. We believe that not only diel instream processes, but also viscosity-driven diel fluctuations of terrestrial DOC input should be considered to explain diel DOC patterns in streams.

Feed Me! Rethinking Traditional Modes of Library Access and Content Delivery

ERIC Educational Resources Information Center

Hutchens, Chad; Clark, Jason

2008-01-01

At their core, XML feeds are content-delivery vehicles. This fact has not always been highlighted in library conversations surrounding RSS and ATOM. The authors have looked to extend the conversation by offering a proof of concept application using RSS as a means to deliver all types of library data: PDFs, docs, images, video--to people where and…

Response of Bacterial Metabolic Activity to Riverine Dissolved Organic Carbon and Exogenous Viruses in Estuarine and Coastal Waters: Implications for CO2 Emission

PubMed Central

Xu, Jie; Sun, Mingming; Shi, Zhen; Harrison, Paul J.; Liu, Hongbin

2014-01-01

A cross-transplant experiment between estuarine water and seawater was conducted to examine the response of bacterial metabolic activity to riverine dissolved organic carbon (DOC) input under virus-rich and virus-free conditions, as well as to exogenous viruses. Riverine DOC input increased bacterial production significantly, but not bacterial respiration (BR) because of its high lability. The bioavailable riverine DOC influenced bulk bacterial respiration in two contrasting ways; it enhanced the bulk BR by stimulating bacterial growth, but simultaneously reduced the cell-specific BR due to its high lability. As a result, there was little stimulation of the bulk BR by riverine DOC. This might be partly responsible for lower CO2 degassing fluxes in estuaries receiving high sewage-DOC that is highly labile. Viruses restricted microbial decomposition of riverine DOC dramatically by repressing the growth of metabolically active bacteria. Bacterial carbon demand in the presence of viruses only accounted for 7–12% of that in the absence of viruses. Consequently, a large fraction of riverine DOC was likely transported offshore to the shelf. In addition, marine bacteria and estuarine bacteria responded distinctly to exogenous viruses. Marine viruses were able to infect estuarine bacteria, but not as efficiently as estuarine viruses, while estuarine viruses infected marine bacteria as efficiently as marine viruses. We speculate that the rapid changes in the viral community due to freshwater input destroyed the existing bacteria-virus relationship, which would change the bacterial community composition and affect the bacterial metabolic activity and carbon cycling in this estuary. PMID:25036641

Response of bacterial metabolic activity to riverine dissolved organic carbon and exogenous viruses in estuarine and coastal waters: implications for CO2 emission.

PubMed

Xu, Jie; Sun, Mingming; Shi, Zhen; Harrison, Paul J; Liu, Hongbin

2014-01-01

A cross-transplant experiment between estuarine water and seawater was conducted to examine the response of bacterial metabolic activity to riverine dissolved organic carbon (DOC) input under virus-rich and virus-free conditions, as well as to exogenous viruses. Riverine DOC input increased bacterial production significantly, but not bacterial respiration (BR) because of its high lability. The bioavailable riverine DOC influenced bulk bacterial respiration in two contrasting ways; it enhanced the bulk BR by stimulating bacterial growth, but simultaneously reduced the cell-specific BR due to its high lability. As a result, there was little stimulation of the bulk BR by riverine DOC. This might be partly responsible for lower CO2 degassing fluxes in estuaries receiving high sewage-DOC that is highly labile. Viruses restricted microbial decomposition of riverine DOC dramatically by repressing the growth of metabolically active bacteria. Bacterial carbon demand in the presence of viruses only accounted for 7-12% of that in the absence of viruses. Consequently, a large fraction of riverine DOC was likely transported offshore to the shelf. In addition, marine bacteria and estuarine bacteria responded distinctly to exogenous viruses. Marine viruses were able to infect estuarine bacteria, but not as efficiently as estuarine viruses, while estuarine viruses infected marine bacteria as efficiently as marine viruses. We speculate that the rapid changes in the viral community due to freshwater input destroyed the existing bacteria-virus relationship, which would change the bacterial community composition and affect the bacterial metabolic activity and carbon cycling in this estuary.

Export of dissolved organic carbon and nitrate from grassland in winter using high temporal resolution, in situ UV sensing.

PubMed

Sandford, Richard C; Hawkins, Jane M B; Bol, Roland; Worsfold, Paul J

2013-07-01

Co-deployment of two reagentless UV sensors for high temporal resolution (15 min) real time determination of wintertime DOC and nitrate-N export from a grassland lysimeter plot (North Wyke, Devon, UK) is reported. They showed rapid, transient but high impact perturbations of DOC (5.3-23 mg CL(-1)) and nitrate-N export after storm/snow melt which discontinuous sampling would not have observed. During a winter freeze/thaw cycle, DOC export (1.25 kg Cha(-1)d(-1)) was significantly higher than typical UK catchment values (maximum 0.25 kg Chad(-1)) and historical North Wyke data (0.7 kg Cha(-1)d(-1)). DOC concentrations were inversely correlated with the key DOC physico-chemical drivers of pH (January r=-0.65), and conductivity (January r=-0.64). Nitrate-N export (0.8-1.5 mg NL(-1)) was strongly correlated with DOC export (r ≥ 0.8). The DOC:NO3-N molar ratios showed that soil microbial N assimilation was not C limited and therefore high N accrual was not promoted in the River Taw, which is classified as a nitrate vulnerable zone (NVZ). The sensor was shown to be an effective sentinel device for identifying critical periods when rapid ecosystem N accumulation could be triggered by a shift in resource stoichiometry. It is therefore a useful tool to help evaluate land management strategies and impacts from climate change and intensive agriculture. Copyright © 2013 Elsevier B.V. All rights reserved.

Adsorption-desorption of dimethenamid and fenarimol onto three agricultural soils as affected by treated wastewater and fresh sewage sludge-derived dissolved organic carbon.

PubMed

Rodríguez-Liébana, José Antonio; Peña, Aránzazu

2018-07-01

The use of treated wastewaters (TWW) in agriculture is widening in areas suffering drought, such as southern Europe, to preserve freshwater supply for human consumption. The composition of TWW, especially concerning their organic carbon (OC) content, has been demonstrated to influence the processes governing the behavior of non-ionic pesticides in soils. Three OC-poor agricultural soils (SV, RM1 and RM3) from the province of Granada (Spain) were chosen for the assessment of the adsorption and desorption of the herbicide dimethenamid (DIM) and the fungicide fenarimol (FEN). TWW and sewage sludge extracts at different dissolved OC (DOC) concentrations (30, 90 and 300 mg L -1 ) were considered to evaluate their effect on pesticide adsorption-desorption. As expected by their properties, DIM and FEN were weakly and moderately adsorbed to the soils, respectively. Soil OC seemed to be the major factor controlling FEN adsorption, whereas the mineral fraction played a key role in DIM adsorption, especially in RM1 with high clay:OC ratio. Although TWW did not significantly modify the adsorption of pesticides, it enhanced DIM desorption from the three soils. Adsorption of FEN to SV and RM3 was directly related to the concentration of DOC, possibly due to co-sorption phenomena. Hysteretic desorption was found in all cases, indicating partially reversible adsorption. While FEN desorption was not altered by the solutions, the use of sludge extracts at the highest DOC concentration (300 mg L -1 ) enhanced DIM desorption as occurred with TWW. Interactions with DOC in solution seemed to predominate for this less hydrophobic compound, thus increasing the risk of natural waters contamination if TWW will be used. Copyright © 2018 Elsevier Ltd. All rights reserved.

An Analysis of Terrestrial and Aquatic Environmental Controls of Riverine Dissolved Organic Carbon in the Conterminous United States

DOE PAGES

Yang, Qichun; Zhang, Xuesong; Xu, Xingya; ...

2017-05-29

Riverine carbon cycling is an important, but insufficiently investigated component of the global carbon cycle. Analyses of environmental controls on riverine carbon cycling are critical for improved understanding of mechanisms regulating carbon processing and storage along the terrestrial-aquatic continuum. Here, we compile and analyze riverine dissolved organic carbon (DOC) concentration data from 1402 United States Geological Survey (USGS) gauge stations to examine the spatial variability and environmental controls of DOC concentrations in the United States (U.S.) surface waters. DOC concentrations exhibit high spatial variability, with an average of 6.42 ± 6.47 mg C/ L (Mean ± Standard Deviation). In general,more » high DOC concentrations occur in the Upper Mississippi River basin and the Southeastern U.S., while low concentrations are mainly distributed in the Western U.S. Single-factor analysis indicates that slope of drainage areas, wetlands, forests, percentage of first-order streams, and instream nutrients (such as nitrogen and phosphorus) pronouncedly influence DOC concentrations, but the explanatory power of each bivariate model is lower than 35%. Analyses based on the general multi-linear regression models suggest DOC concentrations are jointly impacted by multiple factors. Soil properties mainly show positive correlations with DOC concentrations; forest and shrub lands have positive correlations with DOC concentrations, but urban area and croplands demonstrate negative impacts; total instream phosphorus and dam density correlate positively with DOC concentrations. Notably, the relative importance of these environmental controls varies substantially across major U.S. water resource regions. In addition, DOC concentrations and environmental controls also show significant variability from small streams to large rivers, which may be caused by changing carbon sources and removal rates by river orders. In sum, our results reveal that general multi-linear regression analysis of twenty one terrestrial and aquatic environmental factors can partially explain (56%) the DOC concentration variation. In conclusion, this study highlights the complexity of the interactions among these environmental factors in determining DOC concentrations, thus calls for processes-based, non-linear methodologies to constrain uncertainties in riverine DOC cycling.« less

Understanding the relationship between DOC and nitrate export and dominant rainfall-runoff processes through long-term high frequency measurements

NASA Astrophysics Data System (ADS)

Schwab, Michael; Klaus, Julian; Pfister, Laurent; Weiler, Markus

2016-04-01

Over the past decades, stream sampling protocols for hydro-geochemical parameters were often limited by logistical and technological constraints. While long-term monitoring protocols were typically based on weekly sampling intervals, high frequency sampling was commonly limited to a few single events. In our study, we combined high frequency and long-term measurements to understand the DOC and nitrate behaviour and dynamics for different runoff events and seasons. Our study area is the forested Weierbach catchment (0.47 km2) in Luxembourg. The fractured schist bedrock is covered by cambisol soils. The runoff response of the catchment is characterized by a double peak behaviour. A first discharge peak occurs during or right after a rainfall event (triggered by fast near surface runoff generation processes), while a second delayed peak lasts several days (generated by subsurface flow/ shallow groundwater flow). Peaks in DOC concentrations are closely linked to the first discharge peak, whereas nitrate concentrations follow the second peak. Our observations were carried out with the field deployable instrument spectro::lyser (scan Messtechnik GmbH). This instrument relies on the principles of UV-Vis spectrometry and measures DOC and nitrate concentrations. The measurements were carried out at a high frequency of 15 minutes in situ in the Weierbach creek for more than two years. In addition, a long-term validation was carried out with data obtained from the analysis of water collected with automatic samplers. The long-term, high-frequency measurements allowed us to calculate a complete and detailed balance of DOC and nitrate export over two years. Transport behaviour of the DOC and nitrate showed different dynamics between the first and second hydrograph peaks. DOC is mainly exported during first peaks, while nitrate is mostly exported during the delayed second peaks. In combination with other measurements in the catchment, the long and detailed observations have enabled us to derive relationships between DOC and nitrate export and different catchment states: soil wetness and groundwater levels, precipitation and seasonality. Altogether, the long-term and high-frequency time series provides the opportunity to study DOC and nitrate export without having to just rely only on either a few single event measurements or coarse measurement protocols.

Plant diversity induces a shift of DOC concentration over time - results from long term and large scale experiment

NASA Astrophysics Data System (ADS)

Lange, Markus; Gleixner, Gerd

2016-04-01

Plant diversity has been demonstrated as a crucial factor for soil organic carbon (SOC) storage. The horizontal SOC formation in turn is strongly impacted by the relative small but consistent flow of dissolved organic carbon (DOC) in soils. In this process, pore water leaches plant material and already stored SOC while simultaneously these leachates are transported downwards. However, there is a big uncertainty about the drivers of DOC flux; in particular about the importance of biological processes. We investigated the impact of plant diversity and other biotic drivers on DOC concentrations and total DOC fluxes (concentration × sampled water amount). In addition, we considered abiotic factors such as weather and soil conditions to assess the relative importance of biotic and abiotic drivers and how their importance changes over time. We used a comprehensive data set, gathered in the frame of the long-term biodiversity experiment "The Jena Experiment". Permanent monitoring started directly after establishment of the field site in 2002 and is still running. This enabled us to trace the impact of plant communities with their increasing establishment over the time on DOC concentration. We found the amount of sampled pore water best explained by rainfall, while it was not related to plant associated variables. Directly after establishing the experimental site, DOC concentrations were highest and then decreasing with time. In the first period of the experiment plant diversity had no or even a slightly negative impact on DOC concentrations. The direction of the plant diversity effect on DOC concentrations changed over time; namely in later phases we observed highest DOC concentrations on plots with high plant diversity. Moreover, DOC concentrations were negatively affected by increased amounts of sampled pore water indicating a dilution effect. Even though this impact was highly significant; its effect size was even less pronounced at later time points. In summary, inter annual differences of total DOC fluxes reflect patterns of sampled soil water, indicating the major driver of total DOC flux is driven by rainfall. In contrast, intra annually the DOC flux reflects the patterns of the DOC concentrations with a strengthening positive impact of plant diversity among time. Our results show that variations of the total DOC fluxes are more affected by the pore water flux than by the differences in DOC concentrations as the magnitude of the pore water flux exceeds the magnitude of concentrations by a factor of 20. This indicates that abiotic conditions set the frame in which biotic properties can drive the DOC flux. However, the biotic drivers are getting more important over time and might outperform the dominating role of the abiotic conditions on the longer term.

Duplicate document detection in DocBrowse

NASA Astrophysics Data System (ADS)

Chalana, Vikram; Bruce, Andrew G.; Nguyen, Thien

1998-04-01

Duplicate documents are frequently found in large databases of digital documents, such as those found in digital libraries or in the government declassification effort. Efficient duplicate document detection is important not only to allow querying for similar documents, but also to filter out redundant information in large document databases. We have designed three different algorithm to identify duplicate documents. The first algorithm is based on features extracted from the textual content of a document, the second algorithm is based on wavelet features extracted from the document image itself, and the third algorithm is a combination of the first two. These algorithms are integrated within the DocBrowse system for information retrieval from document images which is currently under development at MathSoft. DocBrowse supports duplicate document detection by allowing (1) automatic filtering to hide duplicate documents, and (2) ad hoc querying for similar or duplicate documents. We have tested the duplicate document detection algorithms on 171 documents and found that text-based method has an average 11-point precision of 97.7 percent while the image-based method has an average 11- point precision of 98.9 percent. However, in general, the text-based method performs better when the document contains enough high-quality machine printed text while the image- based method performs better when the document contains little or no quality machine readable text.

Carbonaceous composition changes of heavy-duty diesel engine particles in relation to biodiesels, aftertreatments and engine loads.

PubMed

Cheng, Man-Ting; Chen, Hsun-Jung; Young, Li-Hao; Yang, Hsi-Hsien; Tsai, Ying I; Wang, Lin-Chi; Lu, Jau-Huai; Chen, Chung-Bang

2015-10-30

Three biodiesels and two aftertreatments were tested on a heavy-duty diesel engine under the US FTP transient cycle and additional four steady engine loads. The objective was to examine their effects on the gaseous and particulate emissions, with emphasis given to the organic and elemental carbon (OC and EC) in the total particulate matter. Negligible differences were observed between the low-sulfur (B1S50) and ultralow-sulfur (B1S10) biodiesels, whereas small reductions of OC were identified with the 10% biodiesel blend (B10). The use of diesel oxidation catalyst (DOC1) showed moderate reductions of EC and particularly OC, resulting in the OC/EC ratio well below unity. The use of DOC plus diesel particulate filter (DOC2+DPF) yielded substantial reductions of OC and particularly EC, resulting in the OC/EC ratio well above unity. The OC/EC ratios were substantially above unity at idle and low load, whereas below unity at medium and high load. The above changes in particulate OC and EC are discussed with respect to the fuel content, pollutant removal mechanisms and engine combustion conditions. Overall, the present study shows that the carbonaceous composition of PM could change drastically with engine load and aftertreatments, and to a lesser extent with the biodiesels under study. Copyright © 2015 Elsevier B.V. All rights reserved.

Does DOM properties or the amount of DOC induces iron reduction in topsoil porewater?

NASA Astrophysics Data System (ADS)

Szalai, Zoltán; Ringer, Marianna; Kiss, Klaudia; Perényi, Katalin; Jakab, Gergely

2017-04-01

Iron content of porewater in hydromorphic soils shows high temporal variability. This usually correlates with dissolved organic carbon (DOC) content, but the correlation can be weak in some cases. Some studies suggest that ferrous iron stabilizes organic carbon in dissolved state. On the contrary, other papers report about dissolved iron stabilization by dissolved organic matter (DOM). Present study focuses on this apparent contradiction and on the interaction of organic carbon and iron in hydromorphic soils. Studied gleyic Phaeozems (3 profiles) and mollic Gleysols (3 profiles) are located in Geresdi-dombság (Hungary) and in Danube-Tisza Interfluve (Hungary) respectively. Dynamics of porewater pH, EH, have been recorded by field stations at 20, 40 and 100 cm depth during the growing season with 10 min temporal resolution. Porewater occasionally have also been sampled in each depth. The presence of ferrous iron was detected by dipyridil field test. DOC, dissolved nitrogen (DN) and iron were measured by TOC analyser and fl-AAS. Molecular size and molecular weight were measured by photon correlation spectroscope (DLS and SLS). Textural and mineralogical properties of studied soils were also determined. Relationships among studied parameters were tested by Spearman's rank correlation. The seasonal dynamics of redox potential is primarily controlled by saturation, but spatial differences are also driven by vegetation. The environment is usually reductive for iron oxides between March and July, but intensive daily redox fluctuations could be measured in June and July in some topsoils. Short term temporal variability of redox conditions is depended on the physiological activity of plants. Most of the papers published a range between +100 and +50 mV for iron reduction in aquatic systems. Topsoil porewater measurements show three redox ranges where concentration of dissolved iron has been increased: +320 to +200, +80 to +20 and below-160 mV. These ranges were identified independently from each other in various topsoils and subsoils. DOC was correlated with dissolved iron only in the most oxidative topsoils. Therefore we did not find correlation between DOC and dissolved iron in the studied topsoils of Gleysols. Molecular size and molecular weight of DOM have correlated with dissolved iron in all topsoils. We did not find any relationship between dissolved iron and any other properties at 100 cm depth. Presence of colour reaction and the colour intensity of dipyridil test also did not show correlation with measured dissolved iron in all studied topsoils. High ratio of dithionite and oxalate extractable iron of the solid phase and the molecular size measurements suggest that this observation can be explained by an intensive complex formation of ferric iron with low molecular size DOM. This research was supported by Hungarian Scientific Research Fund (OTKA K100180) and Gergely Jakab was supported by János Bolyai Fellowship of the MTA.

The physiological response of two green calcifying algae from the Great Barrier Reef towards high dissolved inorganic and organic carbon (DIC and DOC) availability.

PubMed

Meyer, Friedrich Wilhelm; Vogel, Nikolas; Teichberg, Mirta; Uthicke, Sven; Wild, Christian

2015-01-01

Increasing dissolved inorganic carbon (DIC) concentrations associated with ocean acidification can affect marine calcifiers, but local factors, such as high dissolved organic carbon (DOC) concentrations through sewage and algal blooms, may interact with this global factor. For calcifying green algae of the genus Halimeda, a key tropical carbonate producer that often occurs in coral reefs, no studies on these interactions have been reported. These data are however urgently needed to understand future carbonate production. Thus, we investigated the independent and combined effects of DIC (pCO2 402 μatm/ pHtot 8.0 and 996 μatm/ pHtot 7.7) and DOC (added as glucose in 0 and 294 μmol L-1) on growth, calcification and photosynthesis of H. macroloba and H. opuntia from the Great Barrier Reef in an incubation experiment over 16 days. High DIC concentrations significantly reduced dark calcification of H. opuntia by 130 % and led to net dissolution, but did not affect H. macroloba. High DOC concentrations significantly reduced daily oxygen production of H. opuntia and H. macroloba by 78 % and 43 %, respectively, and significantly reduced dark calcification of H. opuntia by 70%. Combined high DIC and DOC did not show any interactive effects for both algae, but revealed additive effects for H. opuntia where the combination of both factors reduced dark calcification by 162 % compared to controls. Such species-specific differences in treatment responses indicate H. opuntia is more susceptible to a combination of high DIC and DOC than H. macroloba. From an ecological perspective, results further suggest a reduction of primary production for Halimeda-dominated benthic reef communities under high DOC concentrations and additional decreases of carbonate accretion under elevated DIC concentrations, where H. opuntia dominates the benthic community. This may reduce biogenic carbonate sedimentation rates and hence the buffering capacity against further ocean acidification.

High-frequency DOC and nitrate measurements provide new insights into their export and their relationships to rainfall-runoff processes

NASA Astrophysics Data System (ADS)

Schwab, Michael; Klaus, Julian; Pfister, Laurent; Weiler, Markus

2015-04-01

Over the past decades, stream sampling protocols for environmental tracers were often limited by logistical and technological constraints. Long-term sampling programs would typically rely on weekly sampling campaigns, while high-frequency sampling would remain restricted to a few days or hours at best. We stipulate that the currently predominant sampling protocols are too coarse to capture and understand the full amplitude of rainfall-runoff processes and its relation to water quality fluctuations. Weekly sampling protocols are not suited to get insights into the hydrological system during high flow conditions. Likewise, high frequency measurements of a few isolated events do not allow grasping inter-event variability in contributions and processes. Our working hypothesis is based on the potential of a new generation of field-deployable instruments for measuring environmental tracers at high temporal frequencies over an extended period. With this new generation of instruments we expect to gain new insights into rainfall-runoff dynamics, both at intra- and inter-event scales. Here, we present the results of one year of DOC and nitrate measurements with the field deployable UV-Vis spectrometer spectro::lyser (scan Messtechnik GmbH). The instrument measures the absorption spectrum from 220 to 720 nm in situ and at high frequencies and derives DOC and nitrate concentrations. The measurements were carried out at 15 minutes intervals in the Weierbach catchment (0.47 km2) in Luxemburg. This fully forested catchment is characterized by cambisol soils and fractured schist as underlying bedrock. The time series of DOC and nitrate give insights into the high frequency dynamics of stream water. Peaks in DOC concentrations are closely linked to discharge peaks that occur during or right after a rainfall event. Those first discharge peaks can be linked to fast near surface runoff processes and are responsible for a remarkable amount of DOC export. A special characterisation of the Weierbach catchment are the delayed second peaks a few days after the rainfall event. Nitrate concentrations are following this second peak. We assume that this delayed response is going back to subsurface or upper groundwater flows, with nitrate enriched water. On an inter-event scale during low flow / base flow conditions, we observe interesting diurnal patterns of both DOC and nitrate concentrations. Overall, the long-term high-frequency measurements of DOC and nitrate provide us the opportunity to separate different rainfall-runoff processes and link the amount of DOC and nitrate export to them to quantify the overall relevance of the different processes.

CDOM fluorescence as a proxy of DOC concentration in natural waters: a comparison of four contrasting tropical systems.

PubMed

Rochelle-Newall, E; Hulot, F D; Janeau, J L; Merroune, A

2014-01-01

Chromophoric dissolved organic matter (CDOM) fluorescence or absorption is often proposed as a rapid alternative to chemical methods for the estimation of bulk dissolved organic carbon (DOC) concentration in natural waters. However, the robustness of this method across a wide range of systems remains to be shown. We measured CDOM fluorescence and DOC concentration in four tropical freshwater and coastal environments (estuary and coastal, tropical shallow lakes, water from the freshwater lens of two small islands, and soil leachates). We found that although this method can provide an estimation of DOC concentration in sites with low variability in DOC and CDOM sources in systems where the variability of DOC and CDOM sources are high, this method should not be used as it will lead to errors in the estimation of the bulk DOC concentration.

75 FR 77007 - Notice of Information Collection

Federal Register 2010, 2011, 2012, 2013, 2014

2010-12-10

... works with K-12 teachers to provide content and curricular support selected as the best from among the... Parker, NASA Clearance Officer. [FR Doc. 2010-31038 Filed 12-9-10; 8:45 am] BILLING CODE 7510-13-P ...

Habitat, not resource availability, limits consumer production in lake ecosystems

USGS Publications Warehouse

Craig, Nicola; Jones, Stuart E.; Weidel, Brian C.; Solomon, Christopher T.

2015-01-01

Food web productivity in lakes can be limited by dissolved organic carbon (DOC), which reduces fish production by limiting the abundance of their zoobenthic prey. We demonstrate that in a set of 10 small, north temperate lakes spanning a wide DOC gradient, these negative effects of high DOC concentrations on zoobenthos production are driven primarily by availability of warm, well-oxygenated habitat, rather than by light limitation of benthic primary production as previously proposed. There was no significant effect of benthic primary production on zoobenthos production after controlling for oxygen, even though stable isotope analysis indicated that zoobenthos do use this resource. Mean whole-lake zoobenthos production was lower in high-DOC lakes with reduced availability of oxygenated habitat, as was fish biomass. These insights improve understanding of lake food webs and inform management in the face of spatial variability and ongoing temporal change in lake DOC concentrations.

Quality transformation of dissolved organic carbon during water transit through lakes: contrasting controls by photochemical and biological processes

NASA Astrophysics Data System (ADS)

Berggren, Martin; Klaus, Marcus; Panneer Selvam, Balathandayuthabani; Ström, Lena; Laudon, Hjalmar; Jansson, Mats; Karlsson, Jan

2018-01-01

Dissolved organic carbon (DOC) may be removed, transformed, or added during water transit through lakes, resulting in changes in DOC composition and pigmentation (color). However, the process-based understanding of these changes is incomplete, especially for headwater lakes. We hypothesized that because heterotrophic bacteria preferentially consume noncolored DOC, while photochemical processing removes colored fractions, the overall changes in DOC color upon water passage through a lake depend on the relative importance of these two processes, accordingly. To test this hypothesis we combined laboratory experiments with field studies in nine boreal lakes, assessing both the relative importance of different DOC decay processes (biological or photochemical) and the loss of color during water transit time (WTT) through the lakes. We found that influence from photo-decay dominated changes in DOC quality in the epilimnia of relatively clear headwater lakes, resulting in systematic and selective net losses of colored DOC. However, in highly pigmented brown-water lakes (absorbance at 420 nm > 7 m-1) biological processes dominated, and there was no systematic relationship between color loss and WTT. Moreover, in situ data and dark experiments supported our hypothesis on the selective microbial removal of nonpigmented DOC, mainly of low molecular weight, leading to persistent water color in these highly colored lakes. Our study shows that brown headwater lakes may not conform to the commonly reported pattern of the selective removal of colored constituents in freshwaters, as DOC can show a sustained degree of pigmentation upon transit through these lakes.

Source water controls on the character and origin of dissolved organic matter in streams of the Yukon River basin, Alaska

USGS Publications Warehouse

O'Donnell, Jonathan A.; Aiken, George R.; Kane, Evan S.; Jones, Jeremy B.

2010-01-01

Climate warming and permafrost degradation at high latitudes will likely impact watershed hydrology, and consequently, alter the concentration and character of dissolved organic carbon (DOC) in northern rivers. We examined seasonal variation of DOC chemistry in 16 streams of the Yukon River basin, Alaska. Our primary objective was to evaluate the relationship between source water (shallow versus deep groundwater flow paths) and DOC chemical composition. Using base cation chemistry and principal component analysis, we observed high contributions of deep groundwater to glacial and clearwater streams, whereas blackwater streams received larger contributions from shallow groundwater sources. DOC concentration and specific ultraviolet absorbance peaked during spring snowmelt in all streams, and were consistently higher in blackwater streams than in glacial and clearwater streams. The hydrophobic acid fraction of DOC dominated across all streams and seasons, comprising between 35% and 56% of total DOC. The hydrophilic acid fraction of DOC was more prominent in glacial (23% ± 3%) and clearwater streams (19% ± 1%) than in blackwater streams (16% ± 1%), and was enriched during winter base flow (29% ± 1%) relative to snowmelt and summer base flow. We observed that an increase in the contribution of deep groundwater to streamflow resulted in decreased DOC concentration, aromaticity, and DOC-to-dissolved organic nitrogen ratio, and an increase in the proportion of hydrophilic acids relative to hydrophobic acids. Our findings suggest that future permafrost degradation and higher contributions of groundwater to streamflow may result in a higher fraction of labile DOM in streams of the Yukon basin.

Dissolved Organic Carbon 14C in Southern Nevada Groundwater and Implications for Groundwater Travel Times

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hershey, Ronald L.; Fereday, Wyall; Thomas, James M

Dissolved inorganic carbon (DIC) carbon-14 ( 14C) ages must be corrected for complex chemical and physical reactions and processes that change the amount of 14C in groundwater as it flows from recharge to downgradient areas. Because of these reactions, DIC 14C can produce unrealistically old ages and long groundwater travel times that may, or may not, agree with travel times estimated by other methods. Dissolved organic carbon (DOC) 14C ages are often younger than DIC 14C ages because there are few chemical reactions or physical processes that change the amount of DOC 14C in groundwater. However, there are several issuesmore » that create uncertainty in DOC 14C groundwater ages including limited knowledge of the initial (A 0) DOC 14C in groundwater recharge and potential changes in DOC composition as water moves through an aquifer. This study examines these issues by quantifying A 0 DOC 14C in recharge areas of southern Nevada groundwater flow systems and by evaluating changes in DOC composition as water flows from recharge areas to downgradient areas. The effect of these processes on DOC 14C groundwater ages is evaluated and DOC and DIC 14C ages are then compared along several southern Nevada groundwater flow paths. Twenty-seven groundwater samples were collected from springs and wells in southern Nevada in upgradient, midgradient, and downgradient locations. DOC 14C for upgradient samples ranged from 96 to 120 percent modern carbon (pmc) with an average of 106 pmc, verifying modern DOC 14C ages in recharge areas, which decreases uncertainty in DOC 14C A 0 values, groundwater ages, and travel times. The HPLC spectra of groundwater along a flow path in the Spring Mountains show the same general pattern indicating that the DOC compound composition does not change along this flow path. Although DOC concentration decreases from recharge-area to downgradient groundwater, the organic compounds are similar, indicating that DOC 14C is unaffected by other processes such as microbial degradation. A small amount of organic carbon was leached from crushed volcanic and carbonate aquifer outcrop rock in rock-leaching experiments. The leached DOC was high in 14C (75 pmc carbonate rocks, 91 pmc volcanic) suggesting that the leached DOC likely came from microbes in the rock samples. The small amount of DOC and high 14C indicates that the amount of old organic carbon in these rocks is low so there should be minimal impact on groundwater DOC 14C ages. Based on the results from this study, DOC 14C ages do not require additional corrections. Several correction models were applied to DIC 14C ages to correct for water-rock reactions along two carbonate and two volcanic flow paths and the corresponding travel times were compare to DOC 14C travel times. The DOC 14C travel times were hundreds to thousands of years shorter than uncorrected and corrected DIC 14C travel times except for the upper section of one carbonate flow path. DOC 14C travel times ranged from 400 to 5,400 years as compared to DIC 14C that ranged from modern to 20,900 years. The DIC 14C ages are greatly influenced by carbonate mineral and gas reactions and other processes such as matrix diffusion, isotope exchange, or adsorption, which are not always adequately accounted for in DIC 14C groundwater age correction models.« less

Dissolved Organic Matter Land-Ocean Linkages in the Arctic

NASA Astrophysics Data System (ADS)

Mann, P. J.; Spencer, R. M.; Hernes, P. J.; Tank, S. E.; Striegl, R.; Dyda, R. Y.; Peterson, B. J.; McClelland, J. W.; Holmes, R. M.

2012-04-01

Rivers draining into the Arctic Ocean exhibit high concentrations of terrigenous dissolved organic carbon (DOC), and recent studies indicate that DOC export is changing due to climatic warming and alteration in permafrost condition. The fate of exported DOC in the Arctic Ocean is important for understanding the regional carbon cycle and remains a point of discussion in the literature. As part of the NSF funded Arctic Great Rivers Observatory (Arctic-GRO) project, samples were collected for DOC, chromophoric and fluorescent dissolved organic matter (CDOM & FDOM) and lignin phenols from the Ob', Yenisey, Lena, Kolyma, Mackenzie and Yukon rivers in 2009 - 2010. DOC and lignin concentrations were elevated during the spring freshet and measurements related to DOC composition indicated an increasing contribution from terrestrial vascular plant sources at this time of year (e.g. lignin carbon-normalized yield, CDOM spectral slope, SUVA254, humic-like fluorescence). CDOM absorption was found to correlate strongly with both DOC (r2=0.83) and lignin concentration (r2=0.92) across the major arctic rivers. Lignin composition was also successfully modeled using FDOM measurements decomposed using PARAFAC analysis. Utilizing these relationships we modeled loads for DOC and lignin export from high-resolution CDOM measurements (daily across the freshet) to derive improved flux estimates, particularly from the dynamic spring discharge maxima period when the majority of DOC and lignin export occurs. The new load estimates for DOC and lignin are higher than previous evaluations, emphasizing that if these are more representative of current arctic riverine export, terrigenous DOC is transiting through the Arctic Ocean at a faster rate than previously thought. It is apparent that higher resolution sampling of arctic rivers is exceptionally valuable with respect to deriving accurate fluxes and we highlight the potential of CDOM in this role for future studies and the applicability of in-situ CDOM sensors.

Sedimentary sources of old high molecular weight dissolved organic carbon from the ocean margin benthic nepheloid layer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guo, L. Santschi, P.H.

2000-02-01

Average {sup 14}C ages of dissolved organic carbon (DOC) in the ocean are 3--6,000 years, and are influenced by old DOC from continental margins. However, sources of DOC from terrestrial, autochthonous, and sedimentary organic carbon seem to be too young to be responsible for the old DOC observed in the ocean. Since colloidal organic carbon (COC, i.e., high molecular weight DOC), which is chemically very similar to that of bulk DOC, can be effectively isolated from seawater using cross-flow ultrafiltration, it can hold clues to sources and pathways of DOC turnover in the ocean. Radiocarbon measurements on COC in themore » water column and benthic nepheloid layer (BNL) from two continental margin areas (the Middle Atlantic Bight and the Gulf of Mexico) and controlled laboratory experiments were carried out to study sources of old DOC in the ocean margin areas. Vertical distributions of suspended particulate matter (SPM), particulate organic carbon (POC), nitrogen (PON), and DOC in the water column and bottom waters near the sediment-water interface all demonstrate a well developed benthic nepheloid layer in both ocean margin areas. COC from the BNL was much older than COC from the overlying water column. These results, together with strong concentration gradients of SPM, POC, PON, and DOC, suggest a sedimentary source for organic carbon species and possibly for old COC as well in BNL waters. This is confirmed by the results from controlled laboratory experiments. The heterogeneity of {Delta}{sup 14}C signatures in bulk SOC thus points to a preferential release of old organic components from sediment resuspension, which can be the transport mechanism of the old benthic COC observed in ocean margin areas. Old COC from continental margin nepheloid layers may thus be a potential source of old DOC to the deep ocean.« less

Deconstructing the Effects of Flow on DOC, Nitrate, and Major Ion Interactions Using a High-Frequency Aquatic Sensor Network

NASA Astrophysics Data System (ADS)

Koenig, L. E.; Shattuck, M. D.; Snyder, L. E.; Potter, J. D.; McDowell, W. H.

2017-12-01

Streams provide a physical linkage between land and downstream river networks, delivering solutes derived from multiple catchment sources. We analyzed high-frequency time series of stream solutes to characterize the timing and magnitude of major ion, nutrient, and organic matter transport over event, seasonal, and annual timescales as well as to assess whether nitrate (NO3-) and dissolved organic carbon (DOC) transport are coupled in catchments, which would be expected if they are subject to similar biogeochemical controls throughout the watershed. Our data set includes in situ observations of NO3-, fluorescent dissolved organic matter (DOC proxy), and specific conductance spanning 2-4 years in 10 streams and rivers across New Hampshire, including observations of nearly 700 individual hydrologic events. We found a positive response of NO3- and DOC to flow in forested streams, but watershed development led to a negative relationship between NO3- and discharge, and thus a decoupling of the overall NO3- and DOC responses to flow. On event and seasonal timescales, NO3- and DOC consistently displayed different behaviors. For example, in several streams, FDOM yield was greatest during summer storms while NO3- yield was greatest during winter storms. Most streams had generalizable storm NO3- and DOC responses, but differences in the timing of NO3- and DOC transport suggest different catchment sources. Further, certain events, including rain-on-snow and summer storms following dry antecedent conditions, yielded disproportionate NO3- responses. High-frequency data allow for increased understanding of the processes controlling solute variability and will help reveal their responses to changing climatic regimes.

Submersible UV-Vis Spectroscopy for Quantifying Streamwater Organic Carbon Dynamics: Implementation and Challenges before and after Forest Harvest in a Headwater Stream

PubMed Central

Jollymore, Ashlee; Johnson, Mark S.; Hawthorne, Iain

2012-01-01

Organic material, including total and dissolved organic carbon (DOC), is ubiquitous within aquatic ecosystems, playing a variety of important and diverse biogeochemical and ecological roles. Determining how land-use changes affect DOC concentrations and bioavailability within aquatic ecosystems is an important means of evaluating the effects on ecological productivity and biogeochemical cycling. This paper presents a methodology case study looking at the deployment of a submersible UV-Vis absorbance spectrophotometer (UV-Vis spectro∷lyzer model, s∷can, Vienna, Austria) to determine stream organic carbon dynamics within a headwater catchment located near Campbell River (British Columbia, Canada). Field-based absorbance measurements of DOC were made before and after forest harvest, highlighting the advantages of high temporal resolution compared to traditional grab sampling and laboratory measurements. Details of remote deployment are described. High-frequency DOC data is explored by resampling the 30 min time series with a range of resampling time intervals (from daily to weekly time steps). DOC export was calculated for three months from the post-harvest data and resampled time series, showing that sampling frequency has a profound effect on total DOC export. DOC exports derived from weekly measurements were found to underestimate export by as much as 30% compared to DOC export calculated from high-frequency data. Additionally, the importance of the ability to remotely monitor the system through a recently deployed wireless connection is emphasized by examining causes of prior data losses, and how such losses may be prevented through the ability to react when environmental or power disturbances cause system interruption and data loss. PMID:22666002

Submersible UV-Vis spectroscopy for quantifying streamwater organic carbon dynamics: implementation and challenges before and after forest harvest in a headwater stream.

PubMed

Jollymore, Ashlee; Johnson, Mark S; Hawthorne, Iain

2012-01-01

Organic material, including total and dissolved organic carbon (DOC), is ubiquitous within aquatic ecosystems, playing a variety of important and diverse biogeochemical and ecological roles. Determining how land-use changes affect DOC concentrations and bioavailability within aquatic ecosystems is an important means of evaluating the effects on ecological productivity and biogeochemical cycling. This paper presents a methodology case study looking at the deployment of a submersible UV-Vis absorbance spectrophotometer (UV-Vis spectro::lyzer model, s::can, Vienna, Austria) to determine stream organic carbon dynamics within a headwater catchment located near Campbell River (British Columbia, Canada). Field-based absorbance measurements of DOC were made before and after forest harvest, highlighting the advantages of high temporal resolution compared to traditional grab sampling and laboratory measurements. Details of remote deployment are described. High-frequency DOC data is explored by resampling the 30 min time series with a range of resampling time intervals (from daily to weekly time steps). DOC export was calculated for three months from the post-harvest data and resampled time series, showing that sampling frequency has a profound effect on total DOC export. DOC exports derived from weekly measurements were found to underestimate export by as much as 30% compared to DOC export calculated from high-frequency data. Additionally, the importance of the ability to remotely monitor the system through a recently deployed wireless connection is emphasized by examining causes of prior data losses, and how such losses may be prevented through the ability to react when environmental or power disturbances cause system interruption and data loss.

Sources of dissolved and particulate organic material in Loch Vale Watershed, Rocky Mountain National Park, Colorado, USA

USGS Publications Warehouse

Baron, Jill S.; McKnight, Diane M.; Denning, A. Scott

1991-01-01

The sources of both dissolved organic carbon (DOC) and particulate organic carbon (POC) to an alpine (Sky Pond) and a subalpine lake (The Loch) in Rocky Mountain National Park were explored for four years. The importance of both autochthonous and allochthonous sources of organic matter differ, not only between alpine and subalpine locations, but also seasonally. Overall, autochthonous sources dominate the organic carbon of the alpine lake, while allochthonous sources are a more significant source of organic carbon to the subalpine lake. In the alpine lake, Sky Pond, POC makes up greater than one third of the total organic matter content of the water column, and is related to phytoplankton abundance. Dissolved organic carbon is a product of within-lake activity in Sky Pond except during spring snowmelt and early summer (May–July), when stable carbon isotope ratios suggest a terrestrial source. In the subalpine lake, The Loch, DOC is a much more important constituent of water column organic material than POC, comprising greater than 90% of the spring snowmelt organic matter, and greater than 75% of the organic matter over the rest of the year. Stable carbon isotope ratios and a very strong relation of DOC with soluble Al(tot) indicate DOC concentrations are almost entirely related to flushing of soil water from the surrounding watershed during spring snowmelt. Stable carbon isotope ratios indicate that, for both lakes, phytoplankton is an important source of DOC in the winter, while terrestrial material of plant or microbial origin contributes DOC during snowmelt and summer.

Spatial Variability of Dissolved Organic Carbon in Headwater Wetlands in Central Pennsylvania

NASA Astrophysics Data System (ADS)

Reichert-Eberhardt, A. J.; Wardrop, D.; Boyer, E. W.

2011-12-01

Dissolved organic carbon (DOC) is known to be of an important factor in many microbially mediated biochemical processes, such as denitrification, that occur in wetlands. The spatial variability of DOC within a wetland could impact the microbes that fuel these processes, which in turn can affect the ecosystem services provided by wetlands. However, the amount of spatial variability of DOC in wetlands is generally unknown. Furthermore, it is unknown how disturbance to wetlands can affect spatial variability of DOC. Previous research in central Pennsylvania headwater wetland soils has shown that wetlands with increased human disturbance had decreased heterogeneity in soil biochemistry. To address groundwater chemical variability 20 monitoring wells were installed in a random pattern in a 400 meter squared plot in a low-disturbance headwater wetland and a high-disturbance headwater wetland in central Pennsylvania. Water samples from these wells will be analyzed for DOC, dissolved inorganic carbon, nitrate, ammonia, and sulfate concentrations, as well as pH, conductivity, and temperature on a seasonal basis. It is hypothesized that there will be greater spatial variability of groundwater chemistry in the low disturbance wetland than the high disturbance wetland. This poster will present the initial data concerning DOC spatial variability in both the low and high impact headwater wetlands.

Carbon isotope analysis of dissolved organic carbon in fresh and saline (NaCl) water via continuous flow cavity ring-down spectroscopy following wet chemical oxidation

USGS Publications Warehouse

Conaway, Christopher; Thomas, Randal B.; Saad, Nabil; Thordsen, James J.; Kharaka, Yousif K.

2015-01-01

This work examines the performance and limitations of a wet chemical oxidation carbon analyser interfaced with a cavity ring-down spectrometer (WCO-CRDS) in a continuous flow (CF) configuration for measuring δ13C of dissolved organic carbon (δ13C-DOC) in natural water samples. Low-chloride matrix (<5 g Cl/L) DOC solutions were analysed with as little as 2.5 mg C/L in a 9 mL aliquot with a precision of 0.5 ‰. In high-chloride matrix (10–100 g Cl/L) DOC solutions, bias towards lighter δ13C-DOC was observed because of incomplete oxidation despite using high-concentration oxidant, extended reaction time, or post-wet chemical oxidation gas-phase combustion. However, through a combination of dilution, chloride removal, and increasing the oxidant:sample ratio, high-salinity samples with sufficient DOC (>22.5 µg C/aliquot) may be analysed. The WCO-CRDS approach requires more total carbon (µg C/aliquot) than conventional CF-isotope ratio mass spectrometer, but is nonetheless applicable to a wide range of DOC concentration and water types, including brackish water, produced water, and basinal brines.

Near-surface Heating of Young Rift Sediment Causes Mass Production and Discharge of Reactive Dissolved Organic Matter

PubMed Central

Lin, Yu-Shih; Koch, Boris P.; Feseker, Tomas; Ziervogel, Kai; Goldhammer, Tobias; Schmidt, Frauke; Witt, Matthias; Kellermann, Matthias Y.; Zabel, Matthias; Teske, Andreas; Hinrichs, Kai-Uwe

2017-01-01

Ocean margin sediments have been considered as important sources of dissolved organic carbon (DOC) to the deep ocean, yet the contribution from advective settings has just started to be acknowledged. Here we present evidence showing that near-surface heating of sediment in the Guaymas Basin, a young extensional depression, causes mass production and discharge of reactive dissolved organic matter (DOM). In the sediment heated up to ~100 °C, we found unexpectedly low DOC concentrations in the pore waters, reflecting the combined effect of thermal desorption and advective fluid flow. Heating experiments suggested DOC production to be a rapid, abiotic process with the DOC concentration increasing exponentially with temperature. The high proportions of total hydrolyzable amino acids and presence of chemical species affiliated with activated hydrocarbons, carbohydrates and peptides indicate high reactivity of the DOM. Model simulation suggests that at the local scale, near-surface heating of sediment creates short and massive DOC discharge events that elevate the bottom-water DOC concentration. Because of the heterogeneous distribution of high heat flow areas, the expulsion of reactive DOM is spotty at any given time. We conclude that hydrothermal heating of young rift sediments alter deep-ocean budgets of bioavailable DOM, creating organic-rich habitats for benthic life. PMID:28327661

Influence of soil conditions on dissolved organic matter leached from forest and wetland soils: a controlled growth chamber study.

PubMed

Kim, Eun-Ah; Nguyen, Hang Vo-Minh; Oh, Hae Sung; Hur, Jin; Choi, Jung Hyun

2016-03-01

This study investigated the effects of various soil conditions, including drying-rewetting, nitrogen deposition, and temperature rise, on the quantities and the composition of dissolved organic matter leached from forest and wetland soils. A set of forest and wetland soils with and without the nitrogen deposition were incubated in the growth chambers under three different temperatures. The moisture contents were kept constant, except for two-week drying intervals. Comparisons between the original and the treated samples revealed that drying-rewetting was a crucial environmental factor driving changes in the amount of dissolved organic carbon (DOC). The DOC was also notably increased by the nitrogen deposition to the dry forest soil and was affected by the temperature of the dry wetland soil. A parallel factor (PARAFAC) analysis identified three sub-fractions of the fluorescent dissolved organic matter (FDOM) from the fluorescence excitation-emission matrices (EEMs), and their compositions depended on drying-rewetting. The data as a whole, including the DOC and PARAFAC components and other optical indices, were possibly explained by the two main variables, which were closely related with the PARAFAC components and DOC based on principal component analysis (PCA). Our results suggested that the DOC and PARAFAC component information could provide a comprehensive interpretation of the changes in the soil-leached DOM in response to the different environmental conditions.

Carbonyl emission and toxicity profile of diesel blends with an animal-fat biodiesel and a tire pyrolysis liquid fuel.

PubMed

Ballesteros, R; Guillén-Flores, J; Martínez, J D

2014-02-01

In this paper, two diesel fuels, an animal-fat biodiesel and two diesel blends with the animal-fat biodiesel (50vol.%) and with a tire pyrolysis liquid (TPL) fuel (5vol.%) have been tested in a 4-cylinder, 4-stroke, turbocharged, intercooled, 2.0L Nissan diesel automotive engine (model M1D) with common-rail injection system and diesel oxidation catalyst (DOC). Carbonyl emissions have been analyzed both before and after DOC and specific reactivity of carbonyl profile has been calculated. Carbonyl sampling was carried out by means of a heated line, trapping the gas in 2,4-DNPH cartridges. The eluted content was then analyzed in an HPLC system, with UV-VIS detection. Results showed, on the one hand, an increase in carbonyl emissions with the biodiesel fraction in the fuel. On the other hand, the addition of TPL to diesel also increased carbonyl emissions. These trends were occasionally different if the emissions were studied after the DOC, as it seems to be selectivity during the oxidation process. The specific reactivity was also studied, finding a decrease with the oxygen content within the fuel molecule, although the equivalent ozone emissions slightly increased with the oxygen content. Finally, the emissions toxicity was also studied, comparing them to different parameters defined by different organizations. Depending on the point of study, emissions were above or below the established limits, although acrolein exceeded them as it has the least permissive values. Copyright © 2013 Elsevier Ltd. All rights reserved.

Dynamics, chemical properties and bioavailability of DOC in an early successional catchment

NASA Astrophysics Data System (ADS)

Risse-Buhl, U.; Hagedorn, F.; Dümig, A.; Gessner, M. O.; Schaaf, W.; Nii-Annang, S.; Gerull, L.; Mutz, M.

2013-01-01

The dynamics of dissolved organic carbon (DOC) have been intensively studied in mature ecosystems, but little is known about DOC dynamics and the significance of DOC as a substrate for microbial activity in early-successional catchments. We determined the concentration, chemical composition, source, radiocarbon age, and bioavailability of DOC along the hydrological flow path from soil solution to a downstream pond in a recently constructed catchment (Chicken Creek Catchment, Germany). Soil solution, upwelling ground water, subsurface water in an alluvial fan, and pond water all had high DOC concentrations (averages of 6.0-11.6 mg DOC L-1), despite small carbon stocks in either vegetation or soil of the early-successional catchment. The mean 14C age of DOC in upwelling ground water was 2600 to 2800 yr. Solid-state CPMAS 13C NMR revealed a higher proportion of aromatic compounds (32%) and a lower proportion of carbohydrates (33%) in upwelling ground water than in pond water (18% and 45%, respectively). The 14C age and 13C NMR spectra suggest that DOC was partly mobilized from charred organic matter of the Quaternary substrate. In an experimental 70-days incubation experiment, 20% of the total DOC was found to be bioavailable, irrespective of the water type. Origin of microbial communities (enriched from soil, stream sediment or pond water) had only marginal effects on overall DOC utilization. Overall, these data suggest that the old DOC can support microbial activity during early ecosystem succession to some extent, although the largest fraction is recalcitrant DOC that is exported from the catchment once it has been mobilized.

Dynamics, chemical properties and bioavailability of DOC in an early successional catchment

NASA Astrophysics Data System (ADS)

Risse-Buhl, U.; Hagedorn, F.; Dümig, A.; Gessner, M. O.; Schaaf, W.; Nii-Annang, S.; Gerull, L.; Mutz, M.

2013-07-01

The dynamics of dissolved organic carbon (DOC) have been intensively studied in mature ecosystems, but little is known about DOC dynamics and the significance of DOC as a substrate for microbial activity in early-successional catchments. We determined the concentration, chemical composition, source, radiocarbon age, and bioavailability of DOC along the hydrological flow path from soil solution to a downstream pond in a recently constructed catchment (Chicken Creek Catchment, Germany). Soil solution, upwelling ground water, stream water, subsurface water in an alluvial fan, and pond water all had high DOC concentrations (averages: 6.0-11.6 mg DOC L-1), despite small carbon stocks in both vegetation and soil of the catchment. Solid-state CPMAS 13C NMR of DOC in upwelling ground water revealed a higher proportion of aromatic compounds (32%) and a lower proportion of carbohydrates (33%) than in pond water (18% and 45%, respectively). The average 14C age of DOC in upwelling ground water was 2600 to 2900 yr, while organic matter of the Quaternary substrate of the catchment had a 14C age of 3000 to 16 000 yr. Both the 14C age data and 13C NMR spectra suggest that DOC partly derived from organic matter of the Quaternary substrate (about 40 to 90% of the C in the DOC), indicating that both recent and old C of the DOC can support microbial activity during early ecosystem succession. However, in a 70 day incubation experiment, only about 11% of the total DOC was found to be bioavailable. This proportion was irrespective of the water type. Origin of the microbial communities within the catchment (enriched from soil, stream sediment or pond water) also had only a marginal effect on overall DOC utilization.

Reactivity of Triplet Excited States of Dissolved Natural Organic Matter in Stormflow from Mixed-Use Watersheds.

PubMed

McCabe, Andrew J; Arnold, William A

2017-09-05

Dissolved organic matter (DOM) quantity and composition control the rate of formation (R f,T ) of triplet excited states of dissolved natural organic matter ( 3 DOM*) and the efficiency of 3 DOM* formation (the apparent quantum yield, AQY T ). Here, the reactivity of 3 DOM* in stormflow samples collected from watersheds with variable land covers is examined. Stormflow DOM reflects variability in DOM quantity and composition as a function of land cover and may be important in controlling the fate of cotransported pollutants. R f,T and AQY T were measured using 2,4,6-trimethylphenol in stormflow samples under simulated sunlight. The DOM source and composition was characterized using absorbance and fluorescence spectroscopies and high-resolution mass spectrometry. R f,T and the total rate of light absorption by the water samples (R a ) increased with the dissolved organic carbon (DOC) concentration. AQY T was independent of DOC concentration, but varied with DOM source: developed land cover (4-6%) ≈ open water > vegetated land cover (3%). AQY T was positively related to an index for microbial/algal DOM content and negatively related to DOM molecular weight, DOM aromaticity, and the content of polyphenols. This work demonstrates that TMP is an effective probe for the determination of R f,T and AQY T in whole water samples after accounting for the inhibition of TMP photodegradation by DOM.

Identification and analysis of low-molecular-weight dissolved organic carbon in subglacial basal ice ecosystems by ion chromatography

NASA Astrophysics Data System (ADS)

O'Donnell, Emily C.; Wadham, Jemma L.; Lis, Grzegorz P.; Tranter, Martyn; Pickard, Amy E.; Stibal, Marek; Dewsbury, Paul; Fitzsimons, Sean

2016-07-01

Determining the concentration and composition of dissolved organic carbon (DOC) in glacial ecosystems is important for assessments of in situ microbial activity and contributions to wider biogeochemical cycles. Nonetheless, there is limited knowledge of the abundance and character of DOC in basal ice and the subglacial environment and a lack of quantitative data on low-molecular-weight (LMW) DOC components, which are believed to be highly bioavailable to microorganisms. We investigated the abundance and composition of DOC in basal ice via a molecular-level DOC analysis. Spectrofluorometry and a novel ion chromatographic method, which has been little utilized in glacial science for LMW-DOC determinations, were employed to identify and quantify the major LMW fractions (free amino acids, carbohydrates, and carboxylic acids) in basal ice from four glaciers, each with a different type of overridden material (i.e. the pre-entrainment sedimentary type such as lacustrine material or palaeosols). Basal ice from Joyce Glacier (Antarctica) was unique in that 98 % of the LMW-DOC was derived from the extremely diverse free amino acid (FAA) pool, comprising 14 FAAs. LMW-DOC concentrations in basal ice were dependent on the bioavailability of the overridden organic carbon (OC), which in turn was influenced by the type of overridden material. Mean LMW-DOC concentrations in basal ice from Russell Glacier (Greenland), Finsterwalderbreen (Svalbard), and Engabreen (Norway) were low (0-417 nM C), attributed to the relatively refractory nature of the OC in the overridden palaeosols and bedrock. In contrast, mean LMW-DOC concentrations were an order of magnitude higher (4430 nM C) in basal ice from Joyce Glacier, a reflection of the high bioavailability of the overridden lacustrine material (> 17 % of the sediment OC comprised extractable carbohydrates, a proxy for bioavailable OC). We find that the overridden material may act as a direct (via abiotic leaching) and indirect (via microbial cycling) source of DOC to the subglacial environment and provides a range of LMW-DOC compounds that may stimulate microbial activity in wet subglacial sediments.

DOC and nitrate export linked to dominant rainfall-runoff processes, end-members and seasonality - a long-term high frequency measurement campaign

NASA Astrophysics Data System (ADS)

Schwab, M. P.; Klaus, J.; Pfister, L.; Weiler, M.

2016-12-01

Over the past decades, stream sampling protocols for hydro-geochemical parameters were often limited by logistical and technological constraints. While long-term monitoring protocols were typically based on weekly sampling intervals, high frequency sampling was commonly limited to a few single events. In this contribution, we combined high frequency and long-term measurements to understand DOC and nitrate dynamics in a forest headwater for different runoff events and seasons. Our study area is the forested Weierbach catchment (0.47 km2) in Luxembourg, where the fractured schist bedrock is covered by cambisol soils. The runoff response is characterized by a double peak behaviour. The first peak occurs during or right after a rainfall event triggered by fast near surface runoff generation processes, while a second delayed peak lasts several days and is generated by subsurface flow. This second peak occurs only if a distinct storage threshold of the catchment is exceeded. Our observations were carried out with a field deployable UV-Vis spectrometer measuring DOC and nitrate concentrations in-situ at 15 min intervals for more than two years. In addition, a long-term validation was carried out with data obtained from the analysis of water collected with grab samples. The long-term, high-frequency measurements allowed us to calculate a complete and detailed balance of DOC and nitrate export over two years. Transport behaviour of the DOC and nitrate showed different dynamics between the first and second hydrograph peaks. DOC is mainly exported during the first peaks, while nitrate is mostly exported during the delayed second peaks. Biweekly end-member measurement of soil and groundwater over several years enables us to link the behaviour of DOC and nitrate export to various end-members in the catchment. Altogether, the long-term and high-frequency time series provides the opportunity to study DOC and nitrate export processes without having to just rely only on either a few single event measurements or coarse measurement protocols.

Sensitivity of Deep Soil Organic Carbon Age to Sorption, Transport and Microbial Interactions - Insights from a Calibrated Process Model

NASA Astrophysics Data System (ADS)

Ahrens, B.; Schrumpf, M.; Reichstein, M.

2013-12-01

Subsoil soil organic carbon (SOC) is characterized by conventional radiocarbon ages on the order of centuries to millennia. Most vertically explicit SOC turnover models represent this persistence of deep SOC by one pool that has millennial turnover times. This approach lumps different stabilizing mechanisms such as chemical recalcitrance, sorptive stabilization and energy limitation into a single rate constant. As an alternative, we present a continuous, vertically explicit SOC decomposition model that allows for stabilization via sorption and microbial interactions (COMISSION model). We compare the COMISSION model with the SOC profile of a Haplic Podzol under a Norway spruce forest. In the COMISSION model two pools receive aboveground litter input and vertically distributed root litter input. The readily leachable and soluble fraction of litter input enters a dissolved organic carbon pool (DOC), while the rest enters the residue pool which represents polymeric, non-soluble SOC. The residue pool is depolymerized with extracellular enzymes produced by a microbial pool to enter the DOC pool which represents SOC potentially available for assimilation by microbes. The adsorption/desorption of DOC from/to mineral surfaces controls the availability of carbon in the DOC pool for assimilatory uptake by microbes. The sorption of DOC is modeled with dynamic Langmuir equations. The desorbed part of the DOC pool not only constitutes the substrate for the microbial pool, but is also transported via advection. Interactions of microbes with the residue and DOC pool are modeled with Michaelis-Menten kinetics - this not only allows representing ';priming', but also the retardation of decomposition via energy limitation in the deep soil where substrate is scarce. Further, soil organic matter is recycled within the soil profile through microbial processing - dead microbes either enter the DOC or the residue pool, and thereby also contribute to longer residence times with soil depth. First results of a calibration against SOC, SO14C, MOC and MO14C profiles (mineral associated organic carbon, density fraction >1.6 g cm-3) of a Haplic Podzol of the Waldstein site (Germany) show that we can use the maximum sorption capacity (qmax) estimated from batch sorption experiments to parameterize the dynamic Langmuir sorption equation. qmax could potentially be extrapolated to other soil profiles based on relations to iron and aluminum oxide contents. Although we are able to capture the secondary maximum of SOC contents in the Bh horizon with qmax from batch sorption experiments, our results indicate that the adsorption and desorption rates retrieved from batch sorption experiments are too fast to explain the low Δ14C values of the MOC. This could point to other processes apart from DOC sorption that trigger stabilization by organo-mineral associations with a stronger apparent irreversibility (e.g. inclusion in small pores). Alternatively, the conditions of batch sorption experiments (constant shaking in centrifuge tubes) might not be representative for in situ sorption conditions. Overall, we show how effective decomposition rates and 14C ages readily emerge from a combination of known stabilizing and destabilizing mechanisms and we discuss how to identify these processes with a model-data fusion framework.

Organic Carbon and Trace Element Cycling in a River-Dominated Tidal Coastal Wetland System (Tampa Bay, FL, USA)

NASA Astrophysics Data System (ADS)

Moyer, R. P.; Smoak, J. M.; Engelhart, S. E.; Powell, C. E.; Chappel, A. R.; Gerlach, M. J.; Kemp, A.; Breithaupt, J. L.

2016-02-01

Tampa Bay is the largest open water, river-fed estuary in Florida (USA), and is characterized by the presence of both mangrove and salt marsh ecosystems. Both coastal wetland systems, and small rivers such as the ones draining into Tampa Bay have historically been underestimated in terms of their role in the global carbon and elemental cycles. Climate change and sea-level rise (SLR) are major threats in Tampa Bay and stand to disrupt hydrologic cycles, compromising sediment accumulation and the rate of organic carbon (OC) burial. This study evaluates organic carbon content, sediment accumulation, and carbon burial rates in salt marsh and mangrove ecosystems, along with measurements of fluxes of dissolved OC (DOC) and trace elements in the water column of the Little Manatee River (LMR) in Tampa Bay. The characterization of OC and trace elements in tidal rivers and estuaries is critical for quantitatively constraining these systems in local-to-regional scale biogeochemical budgets, and provide insight into biogeochemical processes occurring with the estuary and adjacent tidal wetlands. Material fluxes of DOC and trace elements were tied to discharge irrespective of season, and the estuarine habitats removed 15-65% of DOC prior to export to Tampa Bay and the Gulf of Mexico. Thus, material is available for cycling and burial within marsh and mangrove peats, however, LMR mangrove peats have higher OC content and burial rates than adjacent salt marsh peats. Sedimentary accretion rates in LMR marshes are not currently keeping pace with SLR, thus furthering the rapid marsh-to-mangrove conversions that have been seen in Tampa Bay over the past half-century. Additionally, wetlands in Tampa Bay tend to have a lower rate of carbon burial than other Florida tidal wetlands, demonstrating their high sensitivity to climate change and SLR.

Local and regional scale exchanges of dissolved organic carbon (DOC) between tidal wetlands and their adjacent coastal waters

NASA Astrophysics Data System (ADS)

Osburn, C. L.; Joshi, I.; Lebrasse, M. C.; Oviedo-Vargas, D.; Bianchi, T. S.; Bohnenstiehl, D. R.; D'Sa, E. J.; He, R.; Ko, D.; Arellano, A.; Ward, N. D.

2017-12-01

The contribution of blue carbon from tidal wetlands to the coastal ocean in the form of dissolved organic carbon (DOC) represents a terrestrial-aquatic linkage of increasing importance. DOC flux results will be presented from local (tidal creek) and regional (bays) scale studies in which various combinations of field observations, ocean-color satellite observations, and the outputs of high-resolution hydrodynamic models were used to estimate DOC export. The first project was located in Bald Head Creek, a tributary to the Cape Fear River estuary in eastern North Carolina (NC). DOC fluxes were computed using a bathymetric data collected via unmanned surface vehicle (USV) and a numerical hydrodynamic model (SCHISM) based on the relationships between colored dissolved organic matter (CDOM) absorption, DOC concentration, and salinity taken from field observations. Model predictions estimated an annual net export of DOC at 54 g C m-2 yr-1 from the tidal creek to the adjacent estuary. Carbon stable isotope (δ13C) values were used to estimate the contribution of wetland carbon to this export. In the second project, DOC fluxes from the Apalachicola Bay, FL, Barataria Bay, LA, were based on the development of algorithms between DOC and CDOM absorption derived from the VIIRS ocean color sensor. The Navy Coastal Ocean Model (NCOM) was used to compute salt flux estimates from each bay to the Louisiana-Texas shelf. The relationship between salinity and CDOM was used to estimate net annual DOC exports of 8.35 x 106 g C m-2 y-1 (Apalachicola Bay) and 7.14 x 106 g C m-2 yr-1 (Barataria Bay). These values approximate 13% and 9% of the annual loads of DOC from the Mississippi River to the Gulf of Mexico, respectively. CDOM and lignin were used in a mixing model to estimate wetland-derived DOC were 2% for Apalachicola Bay and 13% for Barataria Bay, the latter having one of the highest rates of relative sea level rise in North America. Results from our project demonstrated the utility of CDOM, amenable to high resolution observations from multiple platforms, as a basis for constraining the heterogeneity of DOC exports from tidal wetlands to estuaries and coastal waters using numerical models at local and regional scales.

Hydrological controls on DOC  :  nitrate resource stoichiometry in a lowland, agricultural catchment, southern UK

NASA Astrophysics Data System (ADS)

Heppell, Catherine M.; Binley, Andrew; Trimmer, Mark; Darch, Tegan; Jones, Ashley; Malone, Ed; Collins, Adrian L.; Johnes, Penny J.; Freer, Jim E.; Lloyd, Charlotte E. M.

2017-09-01

The role that hydrology plays in governing the interactions between dissolved organic carbon (DOC) and nitrogen in rivers draining lowland, agricultural landscapes is currently poorly understood. In light of the potential changes to the production and delivery of DOC and nitrate to rivers arising from climate change and land use management, there is a pressing need to improve our understanding of hydrological controls on DOC and nitrate dynamics in such catchments. We measured DOC and nitrate concentrations in river water of six reaches of the lowland river Hampshire Avon (Wiltshire, southern UK) in order to quantify the relationship between BFI (BFI) and DOC : nitrate molar ratios across contrasting geologies (Chalk, Greensand, and clay). We found a significant positive relationship between nitrate and BFI (p < 0. 0001), and a significant negative relationship between DOC and BFI (p < 0. 0001), resulting in a non-linear negative correlation between DOC : nitrate molar ratio and BFI. In the Hampshire Avon, headwater reaches which are underlain by clay and characterized by a more flashy hydrological regime are associated with DOC : nitrate ratios > 5 throughout the year, whilst groundwater-dominated reaches underlain by Chalk, with a high BFI have DOC : nitrate ratios in surface waters that are an order of magnitude lower (< 0.5). Our analysis also reveals significant seasonal variations in DOC : nitrate transport and highlights critical periods of nitrate export (e.g. winter in sub-catchments underlain by Chalk and Greensand, and autumn in drained, clay sub-catchments) when DOC : nitrate molar ratios are low, suggesting low potential for in-stream uptake of inorganic forms of nitrogen. Consequently, our study emphasizes the tight relationship between DOC and nitrate availability in agricultural catchments, and further reveals that this relationship is controlled to a great extent by the hydrological setting.

The conservative behavior of dissolved organic carbon in surface waters of the southern Chukchi Sea, Arctic Ocean, during early summer

PubMed Central

Tanaka, Kazuki; Takesue, Nobuyuki; Nishioka, Jun; Kondo, Yoshiko; Ooki, Atsushi; Kuma, Kenshi; Hirawake, Toru; Yamashita, Youhei

2016-01-01

The spatial distribution of dissolved organic carbon (DOC) concentrations and the optical properties of dissolved organic matter (DOM) determined by ultraviolet-visible absorbance and fluorescence spectroscopy were measured in surface waters of the southern Chukchi Sea, western Arctic Ocean, during the early summer of 2013. Neither the DOC concentration nor the optical parameters of the DOM correlated with salinity. Principal component analysis using the DOM optical parameters clearly separated the DOM sources. A significant linear relationship was evident between the DOC and the principal component score for specific water masses, indicating that a high DOC level was related to a terrigenous source, whereas a low DOC level was related to a marine source. Relationships between the DOC and the principal component scores of the surface waters of the southern Chukchi Sea implied that the major factor controlling the distribution of DOC concentrations was the mixing of plural water masses rather than local production and degradation. PMID:27658444

Modeling the production, decomposition, and transport of dissolved organic carbon in boreal soils

USGS Publications Warehouse

Fan, Zhaosheng; Neff, Jason C.; Wickland, Kimberly P.

2010-01-01

The movement of dissolved organic carbon (DOC) through boreal ecosystems has drawn increased attention because of its potential impact on the feedback of OC stocks to global environmental change in this region. Few models of boreal DOC exist. Here we present a one-dimensional model with simultaneous production, decomposition, sorption/desorption, and transport of DOC to describe the behavior of DOC in the OC layers above the mineral soils. The field-observed concentration profiles of DOC in two moderately well-drained black spruce forest sites (one with permafrost and one without permafrost), coupled with hourly measured soil temperature and moisture, were used to inversely estimate the unknown parameters associated with the sorption/desorption kinetics using a global optimization strategy. The model, along with the estimated parameters, reasonably reproduces the concentration profiles of DOC and highlights some important potential controls over DOC production and cycling in boreal settings. The values of estimated parameters suggest that humic OC has a larger potential production capacity for DOC than fine OC, and most of the DOC produced from fine OC was associated with instantaneous sorption/desorption whereas most of the DOC produced from humic OC was associated with time-dependent sorption/desorption. The simulated DOC efflux at the bottom of soil OC layers was highly dependent on the component and structure of the OC layers. The DOC efflux was controlled by advection at the site with no humic OC and moist conditions and controlled by diffusion at the site with the presence of humic OC and dry conditions.

On the Use of Ocean Color Remote Sensing to Measure the Transport of Dissolved Organic Carbon by the Mississippi River Plume

NASA Technical Reports Server (NTRS)

DelCastillo, Carlos E.; Miller, Richard L.

2007-01-01

We investigated the use of ocean color remote sensing to measure transport of dissolved organic carbon (DOC) by the Mississippi River to the Gulf of Mexico. From 2000 to 2005 we recorded surface measurements of DOC, colored dissolved organic matter (CDOM), salinity, and water-leaving radiances during five cruises to the Mississippi River Plume. These measurements were used to develop empirical relationships to derive CDOM, DOC, and salinity from monthly composites of SeaWiFS imagery collected from 1998 through 2005. We used river flow data and a two-end-member mixing model to derive DOC concentrations in the river end-member, river flow, and DOC transport using remote sensing data. We compared our remote sensing estimates of river flow and DOC transport with data collected by the United States Geological Survey (USGS) from 1998 through 2005. Our remote sensing estimates of river flow and DOC transport correlated well (r2 0.70) with the USGS data. Our remote sensing estimates and USGS field data showed low variability in DOC concentrations in the river end-member (7-11%), and high seasonal variability in river flow (50%). Therefore, changes in river flow control the variability in DOC transport, indicating that the remote sensing estimate of river flow is the most critical element of our DOC transport measurement. We concluded that it is possible to use this method to estimate DOC transport by other large rivers if there are data on the relationship between CDOM, DOC, and salinity in the river plume.

An effective method of UV-oxidation of dissolved organic carbon in natural waters for radiocarbon analysis by accelerator mass spectrometry

NASA Astrophysics Data System (ADS)

Xue, Yuejun; Ge, Tiantian; Wang, Xuchen

2015-12-01

Radiocarbon (14C) measurement of dissolved organic carbon (DOC) is a very powerful tool to study the sources, transformation and cycling of carbon in the ocean. The technique, however, remains great challenges for complete and successful oxidation of sufficient DOC with low blanks for high precision carbon isotopic ratio analysis, largely due to the overwhelming proportion of salts and low DOC concentrations in the ocean. In this paper, we report an effective UV-Oxidation method for oxidizing DOC in natural waters for radiocarbon analysis by accelerator mass spectrometry (AMS). The UV-oxidation system and method show 95%±4% oxidation efficiency and high reproducibility for DOC in both river and seawater samples. The blanks associated with the method was also low (about 3 µg C) that is critical for 14C analysis. As a great advantage of the method, multiple water samples can be oxidized at the same time so it reduces the sample processing time substantially compared with other UV-oxidation method currently being used in other laboratories. We have used the system and method for 14C studies of DOC in rivers, estuaries, and oceanic environments and have received promise results.

A study of dissolved organic carbon and nitrate export in Catskill Mountain watersheds

NASA Astrophysics Data System (ADS)

Son, K.; Moore, K. E.; Lin, L.; Schneiderman, E. M.; Band, L. E.

2016-12-01

Watersheds in the Catskill Mountain region of New York State have historically experienced soil and stream acidification due to deposition of acidic compounds created from atmospheric SO2 and NOx. Recent studies in this region, and elsewhere in North America and Europe, have shown increases in dissolved organic carbon (DOC) in streams and lakes. Watersheds in the Catskills are the major source of drinking water for New York City and other communities in the region. Due to use of chlorine for disinfection, there is potential for the increase in DOC to lead to increased levels of disinfection byproducts in treated drinking water. Therefore, developing an improved understanding of the sources, fate and transport mechanisms, and export patterns for nitrate and DOC is important for informing watershed and water supply management. In this study, we analyzed the relationships between watershed characteristics, nitrate, and DOC for 12 gauged streams in the Neversink River watershed. Watershed characteristics included topography (elevation, slope, topographic wetness index), vegetation (leaf area index, species composition), soil (soil hydraulic parameters, soil carbon, wetland soil), atmospheric deposition (SO2, NOx), and climate (precipitation, temperature). Our preliminary analysis showed that both watershed slope and baseflow ratio are negatively correlated with annual median DOC concentration. At Biscuit Brook in the Neversink watershed, annual precipitation explained about 25% of annual DOC median concentration. DOC concentration was highly correlated with storm runoff in spring, summer, and fall, but stream nitrate concentration was weakly correlated with storm runoff in most seasons except summer when it was highly correlated with baseflow. We also applied a process-based ecohydrologic model (Regional Hydrologic Ecologic System Simulation, RHESSys) to the Biscuit Brook watershed to explore sources of nitrate and DOC and their movement within the watershed. We expect that this study will increase our understanding of how, when, and where DOC and nitrate are stored and transported to streams, as well as give insights into the key controls on nitrate and DOC processes in Catskill Mountain watersheds.

Temperature sensitivity of DOC production and transformation in organic soils of the Yukon River Basin, Alaska

NASA Astrophysics Data System (ADS)

O'Donnell, J.; Butler, K. D.; Aiken, G.

2012-12-01

The flux of dissolved organic carbon (DOC) from terrestrial to aquatic ecosystems represents a critical component of the high-latitude carbon balance. In the Yukon River basin (YRB), DOC fluxes have declined in recent decades, likely in response to regional permafrost thaw and increased groundwater discharge to river flow. Despite improved flux estimates for many arctic rivers, considerable uncertainty exists regarding the potential response of DOC fluxes to projected warming. To improve estimates of future DOC dynamics, it is important to develop a process-based approach whereby empirical constraints are placed on source and sink terms in both soil and river systems. Here, we examine variability in DOC production and microbially mediated transformations as a function of both temperature and organic matter (OM) composition in soils of the YRB. We conducted "tea" experiments by incubating three organic-soil types that vary with depth and decomposition extent (live/dead moss, fibric OM and humic OM) at two temperatures (4 vs. 20 °C). Leachate samples were collected periodically over a 30-day incubation and characterized for DOC concentration, optical properties (specific UV absorbance at 254 nm or SUVA254, fluorescence), and major chemical fractions using XAD8/XAD4 resins. We observed a non-linear increase in DOC production over time, characterized by a rapid initial release of DOC from soils followed by a slower rise in DOC concentration in subsequent weeks. Mean DOC concentration was described by a significant interaction between organic-soil type and temperature, indicating a strong relationship between temperature sensitivity of net DOC production and the decomposition extent of soil OM. On average across all sampling dates, DOC concentrations were highest in leachate from fibric OM (13.4 to 17.8 mgC L-1), and lowest in leachate from humic OM (3.5 to 8.5 mgC L-1). However, the temperature sensitivity of net DOC production was highest in the humic OM treatment, with mean DOC concentrations increasing by 145% between the 4 and 20°C temperature treatments, whereas DOC concentrations in leachate from fibric OM only increased by 33%. We also observed compositional differences in dissolved organic matter (DOM) across experimental treatments and over time, as reflected by UV absorbance and fluorescence measurements. For instance, mean SUVA254 values increased from near-surface soil (live/dead moss = 2.28 ± 0.27 L mgC m-1) to deeper organic horizons (humic OM = 3.86 ± 0.60 L mgC m-1). SUVA254 also increased over time, suggesting selective mineralization of low-molecular weight compounds and enrichment of the aromatic DOM pool. Together, these data help to distinguish vertical differences in DOM origin and composition through soil profiles, and can be used to track the fate of terrestrial DOC under future warming at high latitudes.

Structural properties of dissolved organic carbon in deep soil horizons of an arable and temporarily grassland.

NASA Astrophysics Data System (ADS)

Lavaud, A.; Chabbi, A.; Croue, J. P.

2009-04-01

It is commonly accepted that dissolved organic carbon (DOC) is the bio-available fraction of the largest amount of soil organic matter (SOM), even if it does represent only a very small proportion. Because most of the studies on DOC dynamics were mainly restricted to forest soils, studies on the factors governing the dynamics of DOC in deep soil horizons (>1 m) in arable system are still very little limited. The objective of this work is to better define the proportion of DOC in deep soil horizons and indicate their main characteristics and structural properties. The study was conducted on the long term observatory for environmental research- biogeochemical cycles and biodiversity Lusignan site). DOC collected using lysimeters plates inserted to a depth of 105 cm was fractionated into 3 fractions using the two column array of XAD-8 and XAD-4 resins. The HPO (hydrophobic) fraction (i.e. humic substances) isolated from the XAD-8 resin, the TPH (Transphilic) fraction from the XAD-4 resin and the HPI (hydrophilic) fraction which corresponds to the DOC that does not adsorbed onto the two resins under the acid condition used (pH 2). DOM adsorbed onto the resins is recovered with a 75%/25% acetonitrile/water mixture and lyophilized. Depend on the amount of material; the chemical composition of DOC was performed using UV254 nm, fluorescence EEM, NMR and HPSEC/UV/COD. The results show that the concentration and structural properties of DOC in deep soil horizon were similar to those of groundwater (low SUVA (1.2 m-1.L.mg C-1), structures composed mainly of low molecular weight). Because of the relatively recent establishment of the treatment, the monitoring of the dynamics of the DOC concentrations did not show significant differences between arable and grassland. However, the temporal dynamic shows a slight increase in the DOC content regardless of the of land use. DOC concentrations between winter and the middle of spring tend to double going from 1 to 2.5 mg / L and then to 4-5 mg / L in summer time. The structural analysis reveals significant input of terpenoid derived organic matter was confirmed in the HPO fraction of DOC a results supported by the data of 13C NMR, Infra Red and Micro Scale Sealed Vessel / pyrolysis GC / MS. The chromatographic profiles obtained by flash pyrolysis GC / MS highlight the presence of phenol and alkyl phenols, generally attributed to structures polyhydroxyaromatiques (lignin / tannins), but acetamide, pyrolysis product of amino sugars constituents of the wall microbial cells. The thermochimiolyse (TMAH) / GC / MS confirmed the presence of hydroxy aromatic structures in the extracts, however, their precise origin (lignin, tannins ...) remains uncertain. The results so far indicate that the DOC in deep soil horizons is marked by low aromaticity and dominated by small size molecules. This would consist of carbon derived from terpenoids, lignin degraded and amino sugars.

Biodegradation of crude oil into nonvolatile organic acids in a contaminated aquifer near Bemidji, Minnesota

USGS Publications Warehouse

Thorn, K.A.; Aiken, G.R.

1998-01-01

As the result of a pipeline burst, a body of light aliphatic crude oil floats atop the groundwater in a shallow sand and gravel aquifer in a remote area outside Bemidji, Minnesota. Biodegradation has resulted in the formation of a plume of DOC downgradient from the oil body. Groundwater has also been contaminated in an area known as the spray zone, from vertical infiltration of DOC resulting from biodegradation of crude oil in the overlying unsaturated zone. The majority of DOC in the contaminated groundwater is in the form of nonvolatile organic acids (NVOA's) which represent the partial oxidation products of the crude oil constituents. The NVOA's have been classified into three fractions according to their isolation on XAD resins: hydrophobic neutrals (HPO-N), hydrophobic acids (HPO-A) and hydrophilic acids (HPI-A). These fractions of NVOA's were isolated from a well downgradient from the oil body (well 530; DOC=21 mg C/l), from a well in the spray zone (well 603; DOC=15 mg C/l) and from an uncontaminated well upgradient of the oil body where the naturally occurring DOC is 2.9 mg C/l (well 310). The three sets of NVOA's were characterized by elemental analyses, molecular weight determinations, 14C ages and liquid phase 1H and 13C NMR. The crude oil and the saturate, aromatic, resin and asphaltene fractions of the crude oil were similarly analyzed by elemental analysis and NMR. The NVOA's from the contaminated wells were clearly distinguishable from the naturally occurring groundwater DOC. Based upon molecular weights, sulfur contents, aromaticities and the presence of methyl groups bonded to aromatic rings, the characterization data suggests that the NVOA's originate from the C18 or greater alkylaromatic, naphthenoaromatic and sulfur-containing constituents of the crude oil, including possibly the resins and asphaltenes.

Aquatic export of young dissolved and gaseous carbon from a pristine boreal fen: Implications for peat carbon stock stability.

PubMed

Campeau, Audrey; Bishop, Kevin H; Billett, Michael F; Garnett, Mark H; Laudon, Hjalmar; Leach, Jason A; Nilsson, Mats B; Öquist, Mats G; Wallin, Marcus B

2017-12-01

The stability of northern peatland's carbon (C) store under changing climate is of major concern for the global C cycle. The aquatic export of C from boreal peatlands is recognized as both a critical pathway for the remobilization of peat C stocks as well as a major component of the net ecosystem C balance (NECB). Here, we present a full year characterization of radiocarbon content ( 14 C) of dissolved organic carbon (DOC), carbon dioxide (CO 2 ), and methane (CH 4 ) exported from a boreal peatland catchment coupled with 14 C characterization of the catchment's peat profile of the same C species. The age of aquatic C in runoff varied little throughout the year and appeared to be sustained by recently fixed C from the atmosphere (<60 years), despite stream DOC, CO 2 , and CH 4 primarily being sourced from deep peat horizons (2-4 m) near the mire's outlet. In fact, the 14 C content of DOC, CO 2 , and CH 4 across the entire peat profile was considerably enriched with postbomb C compared with the solid peat material. Overall, our results demonstrate little to no mobilization of ancient C stocks from this boreal peatland and a relatively large resilience of the source of aquatic C export to forecasted hydroclimatic changes. © 2017 The Authors Global Change Biology Published by John Wiley & Sons Ltd.

A systematic examination of the relationships between CDOM and DOC in inland waters in China

NASA Astrophysics Data System (ADS)

Song, Kaishan; Zhao, Ying; Wen, Zhidan; Fang, Chong; Shang, Yingxin

2017-10-01

Chromophoric dissolved organic matter (CDOM) plays a vital role in the biogeochemical cycle in aquatic ecosystems. The relationship between CDOM and dissolved organic carbon (DOC) has been investigated, and this significant relationship lays the foundation for the estimation of DOC using remotely sensed imagery data. The current study examined samples from freshwater lakes, saline lakes, rivers and streams, urban water bodies, and ice-covered lakes in China for tracking the variation of the relationships between DOC and CDOM. The regression model slopes for DOC vs. aCDOM (275) ranged from extremely low 0.33 (highly saline lakes) to 1.03 (urban waters) and 3.01 (river waters). The low values were observed in saline lake waters and waters from semi-arid or arid regions, where strong photobleaching is expected due to less cloud cover, longer water residence time, and daylight hours. In contrast, high values were found in waters developed in wetlands or forest in Northeast China, where more organic matter was transported from catchment to waters. The study also demonstrated that closer relationships between CDOM and DOC were revealed when aCDOM (275) were sorted by the ratio of aCDOM(250)/aCDOM (365), which is a measure for the CDOM absorption with respect to its composition, and the determination of coefficient of the regression models ranged from 0.79 to 0.98 for different groups of waters. Our results indicate the relationships between CDOM and DOC are variable for different inland waters; thus, models for DOC estimation through linking with CDOM absorption need to be tailored according to water types.

Re-evaluation of colorimetric Cl- data from natural waters with DOC

USGS Publications Warehouse

Norton, S.A.; Handlet, M.J.; Kahl, J.S.; Peters, N.E.

1996-01-01

Colorimetric Cl- data from natural solutions that contain dissolved organic carbon (DOC) may be biased high. We evaluated aquatic Cl- concentrations in ecosystem compartments at the Bear Brook Watershed, Maine, and from lakes in Maine, using ion chromatography and colorimetry. DOC imparts a positive interference on colorimetric Cl- results proportional to DOC concentrations at approximately 0.8 ??eq Cl-/L per mg DOC/L. The interference is not a function of Cl- concentration. The resulting bias in concentrations of Cl- may be 50% or more of typical environmental values for Cl- in areas remote from atmospheric deposition of marine aerosols. Such biased data in the literature appear to have led to spurious conclusions about recycling of Cl- by forests, the usefulness of Cl- as a conservative tracer in watershed studies, and calculations of elemental budgets, ion balance, charge density of DOC, and dry deposition factors.

Vegetation and climate controls on potential CO2, DOC and DON production in northern latitude soils

USGS Publications Warehouse

Neff, J.C.; Hooper, D.U.

2002-01-01

Climatic change may influence decomposition dynamics in arctic and boreal ecosystems, affecting both atmospheric CO2 levels, and the flux of dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) to aquatic systems. In this study, we investigated landscape-scale controls on potential production of these compounds using a one-year laboratory incubation at two temperatures (10?? and 30??C). We measured the release of CO2, DOC and DON from tundra soils collected from a variety of vegetation types and climatic regimes: tussock tundra at four sites along a latitudinal gradient from the interior to the north slope of Alaska, and soils from additional vegetation types at two of those sites (upland spruce at Fairbanks, and wet sedge and shrub tundra at Toolik Lake in northern Alaska). Vegetation type strongly influenced carbon fluxes. The highest CO2 and DOC release at the high incubation temperature occurred in the soils of shrub tundra communities. Tussock tundra soils exhibited the next highest DOC fluxes followed by spruce and wet sedge tundra soils, respectively. Of the fluxes, CO2 showed the greatest sensitivity to incubation temperatures and vegetation type, followed by DOC. DON fluxes were less variable. Total CO2 and total DOC release were positively correlated, with DOC fluxes approximately 10% of total CO2 fluxes. The ratio of CO2 production to DOC release varied significantly across vegetation types with Tussock soils producing an average of four times as much CO2 per unit DOC released compared to Spruce soils from the Fairbanks site. Sites in this study released 80-370 mg CO2-C g soil C-1 and 5-46 mg DOC g soil C-1 at high temperatures. The magnitude of these fluxes indicates that arctic carbon pools contain a large proportion of labile carbon that could be easily decomposed given optimal conditions. The size of this labile pool ranged between 9 and 41% of soil carbon on a g soil C basis, with most variation related to vegetation type rather than climate.

Electrochemical degradation of perfluoroalkyl and polyfluoroalkyl substances (PFASs) in groundwater.

PubMed

Trautmann, A M; Schell, H; Schmidt, K R; Mangold, K-M; Tiehm, A

2015-01-01

Perfluoroalkyl and polyfluoroalkyl substances (PFASs) represent hazardous pollutants and are frequently detected in the environment, e.g. in contaminated groundwater. PFASs are persistent to biodegradation and conventional oxidation processes such as ozonation. In this study electrochemical degradation of PFASs on boron-doped diamond (BDD) electrodes is demonstrated. Experiments were performed with model solutions and contaminated groundwater with a dissolved organic carbon (DOC) content of 13 mg/L. The perfluorinated carboxylic acids (PFCAs) perfluorobutanoate, perfluoropentanoate, perfluorohexanoate, perfluoroheptanoate and perfluorooctanoate, and the perfluorinated sulfonic acids (PFSAs) perfluorobutane sulfonate, perfluorohexane sulfonate, perfluorooctane sulfonate and 6:2 fluorotelomer sulfonate were detected in the groundwater samples. At PFAS concentrations ranging from 0.26 to 34 mg/L (0.7 to 79 μM), the degradation of PFASs was achieved despite of the high DOC background. Pseudo first-order kinetic constants of PFSA degradation increased with the increase of carbon chain length. Fluoride formation as well as the generation of PFCAs with shortened chain lengths was observed. Inorganic byproducts such as perchlorate were also formed and have to be considered in further process optimization.

PanMetaDocs - A tool for collecting and managing the long tail of "small science data"

NASA Astrophysics Data System (ADS)

Klump, J.; Ulbricht, D.

2011-12-01

In the early days of thinking about cyberinfrastructure the focus was on "big science data". Today, the challenge is not anymore to store several terabytes of data, but to manage data objects in a way that facilitates their re-use. Key to re-use by a user as a data consumer is proper documentation of the data. Also, data consumers need discovery metadata to find the data they need and they need descriptive metadata to be able to use the data they retrieved. Thus, data documentation faces the challenge to extensively and completely describe these objects, hold the items easily accessible at a sustainable cost level. However, data curation and documentation do not rank high in the everyday work of a scientist as a data producer. Data producers are often frustrated by being asked to provide metadata on their data over and over again, information that seemed very obvious from the context of their work. A challenge to data archives is the wide variety of metadata schemata in use, which creates a number of maintenance and design challenges of its own. PanMetaDocs addresses these issues by allowing an uploaded files to be described by more than one metadata object. PanMetaDocs, which was developed from PanMetaWorks, is a PHP based web application that allow to describe data with any xml-based metadata schema. Its user interface is browser based and was developed to collect metadata and data in collaborative scientific projects situated at one or more institutions. The metadata fields can be filled with static or dynamic content to reduce the number of fields that require manual entries to a minimum and make use of contextual information in a project setting. In the development of PanMetaDocs the business logic of panMetaWorks is reused, except for the authentication and data management functions of PanMetaWorks, which are delegated to the eSciDoc framework. The eSciDoc repository framework is designed as a service oriented architecture that can be controlled through a REST interface to create version controlled items with metadata records in XML format. PanMetaDocs utilizes the eSciDoc items model to add multiple metadata records that describe uploaded files in different metadata schemata. While datasets are collected and described, shared to collaborate with other scientists and finally published, data objects are transferred from a shared data curation domain into a persistent data curation domain. Through an RSS interface for recent datasets PanMetaWorks allows project members to be informed about data uploaded by other project members. The implementation of the OAI-PMH interface can be used to syndicate data catalogs to research data portals, such as the panFMP data portal framework. Once data objects are uploaded to the eSciDoc infrastructure it is possible to drop the software instance that was used for collecting the data, while the compiled data and metadata are accessible for other authorized applications through the institution's eSciDoc middleware. This approach of "expendable data curation tools" allows for a significant reduction in costs for software maintenance as expensive data capture applications do not need to be maintained indefinitely to ensure long term access to the stored data.

Development of a combined isotopic and mass-balance approach to determine dissolved organic carbon sources in eutrophic reservoirs.

PubMed

Pierson-Wickmann, Anne-Catherine; Gruau, Gérard; Jardé, Emilie; Gaury, Nicolas; Brient, Luc; Lengronne, Marion; Crocq, André; Helle, Daniel; Lambert, Thibault

2011-04-01

A combined mass-balance and stable isotope approach was set up to identify and quantify dissolved organic carbon (DOC) sources in a DOC-rich (9mgL(-1)) eutrophic reservoir located in Western France and used for drinking water supply (so-called Rophemel reservoir). The mass-balance approach consisted in measuring the flux of allochthonous DOC on a daily basis, and in comparing it with the effective (measured) DOC concentration of the reservoir. The isotopic approach consisted, for its part, in measuring the carbon isotope ratios (δ(13)C values) of both allochthonous and autochthonous DOC sources, and comparing these values with the δ(13)C values of the reservoir DOC. Results from both approaches were consistent pointing out for a DOC of 100% allochthonous origin. In particular, the δ(13)C values of the DOC recovered in the reservoir (-28.5±0.2‰; n=22) during the algal bloom season (May-September) showed no trace of an autochthonous contribution (δ(13)C in algae=-30.1±0.3‰; n=2) being indistinguishable from the δ(13)C values of allochthonous DOC from inflowing rivers (-28.6±0.1‰; n=8). These results demonstrate that eutrophication is not responsible for the high DOC concentrations observed in the Rophemel reservoir and that limiting eutrophication of this reservoir will not reduce the potential formation of disinfection by-products during water treatment. The methodology developed in this study based on a complementary isotopic and mass-balance approach provides a powerful tool, suitable to identify and quantify DOC sources in eutrophic, DOC-contaminated reservoirs. Copyright © 2010 Elsevier Ltd. All rights reserved.

The influence of reservoirs, climate, land use and hydrologic conditions on loads and chemical quality of dissolved organic carbon in the Colorado River

USGS Publications Warehouse

Miller, Matthew P.

2012-01-01

Longitudinal patterns in dissolved organic carbon (DOC) loads and chemical quality were identified in the Colorado River from the headwaters in the Rocky Mountains to the United States-Mexico border from 1994 to 2011. Watershed- and reach-scale climate, land use, river discharge and hydrologic modification conditions that contribute to patterns in DOC were also identified. Principal components analysis (PCA) identified site-specific precipitation and reach-scale discharge as being correlated with sites in the upper basin, where there were increases in DOC load from the upstream to downstream direction. In the lower basin, where DOC load decreased from upstream to downstream, sites were correlated with site-specific temperature and reach-scale population, urban land use and hydrologic modification. In the reaches containing Lakes Powell and Mead, the two largest reservoirs in the United States, DOC quantity decreased, terrestrially derived aromatic DOC was degraded and/or autochthonous less aromatic DOC was produced. Taken together, these results suggest that longitudinal patterns in the relatively unregulated upper basin are influenced by watershed inputs of water and DOC, whereas DOC patterns in the lower basin are reflective of a balance between watershed contribution of water and DOC to the river and loss of water and DOC due to hydrologic modification and/or biogeochemical processes. These findings suggest that alteration of constituent fluxes in rivers that are highly regulated may overshadow watershed processes that would control fluxes in comparable unregulated rivers. Further, these results provide a foundation for detailed assessments of factors controlling the transport and chemical quality of DOC in the Colorado River.

Source water controls on the character and origin of dissolved organic matter in streams of the Yukon River basin, Alaska

Treesearch

Jonathan A. O' Donnell; George R. Aiken; Evan S. Kane; Jeremy B. Jones

2010-01-01

Climate warming and permafrost degradation at high latitudes will likely impact watershed hydrology, and consequently, alter the concentration and character of dissolved organic carbon (DOC) in northern rivers. We examined seasonal variation of DOC chemistry in 16 streams of the Yukon River basin, Alaska. Our primary objective was to evaluate DOC chemical composition....

Cross-regional prediction of long-term trajectory of stream water DOC response to climate change

Treesearch

H. Laudon; J.M. Buttle; S.K. Carey; J.J. McDonnell; K.J. McGuire; J. Seibert; J. Shanley; C. Soulsby; D. Tetzlaff

2012-01-01

There is no scientific consensus about how dissolved organic carbon (DOC) in surface waters is regulated. Here we combine recent literature data from 49 catchments with detailed stream and catchment process information from nine well established research catchments at mid- to high latitudes to examine the question of how climate controls stream water DOC. We show for...

Effect of DOC on evaporation from small Wisconsin lakes

NASA Astrophysics Data System (ADS)

Watras, C. J.; Morrison, K. A.; Rubsam, J. L.

2016-09-01

Evaporation (E) dominates the loss of water from many small lakes, and the balance between precipitation and evaporation (P-E) often governs water levels. In this study, evaporation rates were estimated for three small Wisconsin lakes over several years using 30-min data from floating evaporation pans (E-pans). Measured E was then compared to the output of mass transfer models driven by local conditions over daily time scales. The three lakes were chosen to span a range of dissolved organic carbon (DOC) concentrations (3-20 mg L-1), a solute that imparts a dark, tea-stain color which absorbs solar energy and limits light penetration. Since the lakes were otherwise similar, we hypothesized that a DOC-mediated increase in surface water temperature would translate directly to higher rates of evaporation thereby informing climate response models. Our results confirmed a DOC effect on surface water temperature, but that effect did not translate to enhanced evaporation. Instead the opposite was observed: evaporation rates decreased as DOC increased. Ancillary data and prior studies suggest two explanatory mechanisms: (1) disproportionately greater radiant energy outflux from high DOC lakes, and (2) the combined effect of wind speed (W) and the vapor pressure gradient (es - ez), whose product [W(es - ez)] was lowest on the high DOC lake, despite very low wind speeds (<1.5 m s-1) and steep forested uplands surrounding all three lakes. Agreement between measured (E-pan) and modeled evaporation rates was reasonably good, based on linear regression results (r2: 0.6-0.7; slope: 0.5-0.7, for the best model). Rankings based on E were similar whether determined by measured or modeled criteria (high DOC < low DOC). Across the 3 lakes and 4 years, E averaged ∼3 mm d-1 (C.V. 9%), but statistically significant differences between lakes resulted in substantial differences in cumulative E that were consistent from year to year. Daily water budgets for these lakes show that inputs were dominated by P and outputs by E; and our findings indicate that subtle changes in the variables that drive E can have measurable effects on water levels by shifting the balance between P and E.

Anthropogenic inputs of dissolved organic matter in New York Harbor

NASA Astrophysics Data System (ADS)

Gardner, G. B.; Chen, R. F.; Olavasen, J.; Peri, F.

2016-02-01

The Hudson River flows into the Atlantic Ocean through a highly urbanized region which includes New York City to the east and Newark, New Jersey to the west. As a result, the export of Dissolved Organic Carbon (DOC) from the Hudson to the Atlantic Ocean includes a significant anthropogenic component. A series of high resolution studies of the DOC dynamics of this system were conducted between 2003 and 2010. These included both the Hudson and adjacent large waterways (East River, Newark Bay, Kill Van Kull and Arthur Kill) using coastal research vessels and smaller tributaries (Hackensack, Pasaic and Raritan rivers) using a 25' boat. In both cases measurements were made using towed instrument packages which could be cycled from near surface to near bottom depths with horizontal resolution of approximately 20 to 200 meters depending on depth and deployment strategy. Sensors on the instrument packages included a CTD to provide depth and salinity information and a chromophoric dissolved organic matter(CDOM) fluorometer to measure the fluorescent fraction of the DOC. Discrete samples allowed calibration of the fluorometer and the CDOM data to be related to DOC. The combined data set from these cruises identified multiple scales of source and transport processes for DOC within the Hudson River/New York Harbor region. The Hudson carries a substantial amount of natural DOC from its 230 km inland stretch. Additional sources exist in fringing salt marshes adjacent to the Hackensack and Raritan rivers. However the lower Hudson/New Harbor region receives a large input of DOC from multiple publically owned treatment works (POTW) discharges. The high resolution surveys allowed us to elucidate the distribution of these sources and the manner in which they are rapidly mixed to create the total export. We estimate that anthropogenic sources account for up to 2.5 times the DOC flux contributed by natural processes.

Impact of managed moorland burning on DOC concentrations in soil solutions and stream waters

NASA Astrophysics Data System (ADS)

Palmer, Sheila; Wearing, Catherine; Johnson, Kerrylyn; Holden, Joseph; Brown, Lee

2013-04-01

In the UK uplands, prescribed burning of moorland vegetation is a common practice to maintain suitable habitats for game birds. Many of these landscapes are in catchments covered by significant deposits of blanket peat (typically one metre or more in depth). There is growing interest in the effect of land management on the stability of these peatland carbon stores, and their contribution to dissolved and particulate organic carbon in surface waters (DOC and POC, respectively) and subsequent effects on stream biogeochemistry and ecology. Yet there are surprisingly few published catchment-scale studies on the effect of moorland burning on DOC and POC. As part of the EMBER project, stream chemistry data were collected approximately monthly in ten upland blanket peat catchments in the UK, five of which acted as controls and were not subject to burning. The other five catchments were subject to a history of prescribed burning, typically in small patches (300-900 m2) in rotations of 8-25 years. Soil solution DOC was also monitored at four depths at two intensively studied sites (one regularly burned and one control). At the two intensive sites, soil solution DOC was considerably higher at the burned site, particularly in surface solutions where concentrations in excess of 100 mg/L were recorded on several occasions (median 37 mg/L over 18 months). The high soil solution DOC concentrations at the burned site occurred in the most recently burned plots (less than 2 years prior to start of sampling) and the lowest DOC concentrations were observed in plots burned 15-25 years previously. On average, median stream DOC and POC concentrations were approximately 43% and 35% higher respectively in burned catchments relative to control catchments. All streams exhibited peak DOC in late summer/early autumn with higher peak DOC concentrations in burned catchments (20-66 mg/L) compared to control catchments (18-54 mg/L). During winter months, DOC concentrations were low in control catchments (typically less than 15 mg/L) but were highly variable in burned catchments (9-40 mg/L), implying some instability of peat carbon stores and/or fluctuation in source. The results offer strong evidence for an impact of burning on the delivery of DOC to streams, possibly through increased surface run-off from bare or partially vegetated patches.

Modeling nonlinear responses of DOC transport in boreal catchments in Sweden

NASA Astrophysics Data System (ADS)

Kasurinen, Ville; Alfredsen, Knut; Ojala, Anne; Pumpanen, Jukka; Weyhenmeyer, Gesa A.; Futter, Martyn N.; Laudon, Hjalmar; Berninger, Frank

2016-07-01

Stream water dissolved organic carbon (DOC) concentrations display high spatial and temporal variation in boreal catchments. Understanding and predicting these patterns is a challenge with great implications for water quality projections and carbon balance estimates. Although several biogeochemical models have been used to estimate stream water DOC dynamics, model biases common during both rain and snow melt-driven events. The parsimonious DOC-model, K-DOC, with 10 calibrated parameters, uses a nonlinear discharge and catchment water storage relationship including soil temperature dependencies of DOC release and consumption. K-DOC was used to estimate the stream water DOC concentrations over 5 years for eighteen nested boreal catchments having total area of 68 km2 (varying from 0.04 to 67.9 km2). The model successfully simulated DOC concentrations during base flow conditions, as well as, hydrological events in catchments dominated by organic and mineral soils reaching NSEs from 0.46 to 0.76. Our semimechanistic model was parsimonious enough to have all parameters estimated using statistical methods. We did not find any clear differences between forest and mire-dominated catchments that could be explained by soil type or tree species composition. However, parameters controlling slow release and consumption of DOC from soil water behaved differently for small headwater catchments (less than 2 km2) than for those that integrate larger areas of different ecosystem types (10-68 km2). Our results emphasize that it is important to account for nonlinear dependencies of both, soil temperature, and catchment water storage, when simulating DOC dynamics of boreal catchments.

Contrasts in Flushing Patterns Among Solutes

NASA Astrophysics Data System (ADS)

Shanley, J. B.; Sebestyen, S. D.; Boyer, E. W.; Ross, D. S.

2005-12-01

High-frequency sampling since 1991 at the 41-ha forested W-9 catchment at Sleepers River, Vermont provides a wealth of data to evaluate catchment flushing responses. Snowmelt and rain-on-snow account for about half the annual flow at Sleepers River during a 6-week period in early spring. Summer and fall storms produce frequent high-flows of short duration. Flushing of weathering products (Ca, Mg, Na, K, SO4 ANC, Si) is generally supply-limited, and is masked by rapid dilution with meteoric and soil water during events. In contrast, flushing dominates the stream dynamics of atmospheric and pedogenic solutes (NO3, DOC, Hg), causing concentration increases with increasing flow. During snowmelt, NO3 peaks well before the peak in discharge, whereas DOC tracks discharge closely and peaks concurrently. These patterns suggest that NO3 is supply-limited and DOC is transport-limited; W-9 is not N saturated and the available NO3 supply is readily leached from the soil, whereas stream DOC progressively increases as rising water tables and expanding saturated areas connect with new source areas. In summer storms, DOC and NO3 both peak simultaneously with discharge. Unlike DOC, however, NO3 concentrations are attenuated with subsequent storms that follow within a few days, consistent with a depletion of the NO3 pool available for flushing as observed during snowmelt. Sleepers River contrasts with the Snake River in Colorado, where NO3 and DOC reverse roles; DOC peaks early in snowmelt and may be supply-limited due to the paucity of organic matter. An ample supply of NO3 is available due to N saturation and N fixation, but NO3 may be transport-limited due to primary N sources in talus deposits far from the stream. Hg is an atmospheric solute that accumulates in soils because of its affinity for organic matter, and is flushed by high flows, mostly in association with suspended sediment. The concept of flushing provides a useful context for understanding the variable responses of solutes to the expansion of catchment saturation during high flow events.

Urbanization and agriculture increase exports and differentially alter elemental stoichiometry of dissolved organic matter (DOM) from tropical catchments.

PubMed

Gücker, Björn; Silva, Ricky C S; Graeber, Daniel; Monteiro, José A F; Boëchat, Iola G

2016-04-15

Many tropical biomes are threatened by rapid land-use change, but its catchment-wide biogeochemical effects are poorly understood. The few previous studies on DOM in tropical catchments suggest that deforestation and subsequent land use increase stream water dissolved organic carbon (DOC) concentrations, but consistent effects on DOM elemental stoichiometry have not yet been reported. Here, we studied stream water DOC concentrations, catchment DOC exports, and DOM elemental stoichiometry in 20 tropical catchments at the Cerrado-Atlantic rainforest transition, dominated by natural vegetation, pasture, intensive agriculture, and urban land cover. Streams draining pasture could be distinguished from those draining natural catchments by their lower DOC concentrations, with lower DOM C:N and C:P ratios. Catchments with intensive agriculture had higher DOC exports and lower DOM C:P ratios than natural catchments. Finally, with the highest DOC concentrations and exports, as well as the highest DOM C:P and N:P ratios, but the lowest C:N ratios among all land-use types, urbanized catchments had the strongest effects on catchment DOM. Thus, urbanization may have alleviated N limitation of heterotrophic DOM decomposition, but increased P limitation. Land use-especially urbanization-also affected the seasonality of catchment biogeochemistry. While natural catchments exhibited high DOC exports and concentrations, with high DOM C:P ratios in the rainy season only, urbanized catchments had high values in these variables throughout the year. Our results suggest that urbanization and pastoral land use exerted the strongest impacts on DOM biogeochemistry in the investigated tropical catchments and should thus be important targets for management and mitigation efforts. Copyright © 2016 Elsevier B.V. All rights reserved.

Distribution characteristic of soil organic carbon fraction in different types of wetland in Hongze Lake of China.

PubMed

Lu, Yan; Xu, Hongwen

2014-01-01

Soil organic carbon fractions included microbial biomass carbon (MBC), dissolved organic carbon (DOC), and labile organic carbon (LOC), which was investigated over a 0-20 cm depth profile in three types of wetland in Hongze Lake of China. Their ecoenvironmental effect and the relationships with soil organic carbon (SOC) were analyzed in present experiment. The results showed that both active and SOC contents were in order reduced by estuarine wetland, flood plain, and out-of-lake wetland. Pearson correlative analysis indicated that MBC and DOC were positively related to SOC. The lowest ratios of MBC and DOC to SOC in the estuarine wetland suggested that the turnover rate of microbial active carbon pool was fairly low in this kind of wetland. Our results showed that estuarine wetland had a strong carbon sink function, which played important role in reducing greenhouse gas emissions; besides, changes of water condition might affect the accumulation and decomposition of organic carbon in the wetland soils.

Distribution Characteristic of Soil Organic Carbon Fraction in Different Types of Wetland in Hongze Lake of China

PubMed Central

Lu, Yan; Xu, Hongwen

2014-01-01

Soil organic carbon fractions included microbial biomass carbon (MBC), dissolved organic carbon (DOC), and labile organic carbon (LOC), which was investigated over a 0–20 cm depth profile in three types of wetland in Hongze Lake of China. Their ecoenvironmental effect and the relationships with soil organic carbon (SOC) were analyzed in present experiment. The results showed that both active and SOC contents were in order reduced by estuarine wetland, flood plain, and out-of-lake wetland. Pearson correlative analysis indicated that MBC and DOC were positively related to SOC. The lowest ratios of MBC and DOC to SOC in the estuarine wetland suggested that the turnover rate of microbial active carbon pool was fairly low in this kind of wetland. Our results showed that estuarine wetland had a strong carbon sink function, which played important role in reducing greenhouse gas emissions; besides, changes of water condition might affect the accumulation and decomposition of organic carbon in the wetland soils. PMID:24971377

Groundwater nitrate remediation using plant-chip bioreactors under phosphorus-limited environment

NASA Astrophysics Data System (ADS)

Satake, Shunichi; Tang, Changyuan

2018-02-01

Groundwater denitrification bioreactors under limited phosphorus conditions were studied in column experiments using four types of plant-chips. When the phosphate-P concentration in the influent increased from 0.04 mg/L to 0.4 mg/L, the nitrate removal ratio increased from 61.6% to 86.1% in reed, from 7.2% to 12.6% in Japanese cedar, from 37.0% to 73.6% in Moso bamboo, and from 19.2% to 50.5% in Lithocarpus edulis. The carbon source of the denitrifiers' growth was indicated by the content of acid detergent soluble organic matter in the chips. Furthermore, according to the modified Michaelis-Menten-type equation proposed in the study, the denitrification rate was largely limited by the phosphate-P concentration in reed and L. eduilis, and by the dissolved organic carbon (DOC) in Japanese cedar. Denitrification in Moso bamboo was affected by both phosphate-P and DOC. Besides the DOC, phosphorus emerged as an important limiting element of denitrification in some bioreactor plant-chips.

Scaling Effects of Riparian Peatlands on Stable Isotopes in Runoff and DOC Mobilization

NASA Astrophysics Data System (ADS)

Tetzlaff, D.; Tunaley, C.; Soulsby, C.

2016-12-01

We combined 13 months of daily isotope measurements in stream water with daily DOC and 15 minute FDOM (fluorescent component of dissolved organic matter) data at three nested scales to identify how riparian peatlands generate runoff and influence DOC dynamics in streams. We investigated how runoff generation processes in a small, riparian peatland dominated headwater catchment (0.65 km2) propagate to larger scales (3.2 km2 and 31 km2) with decreasing percentage of riparian peatland coverage. Isotope damping was most pronounced in the 0.65 km2 headwater catchment due to high water storage in the organic soils which encourage tracer mixing. At the largest scale, stream flow and water isotope dynamics showed a more flashy response. The isotopic difference between the sites was most pronounced in the summer months when stream water signatures were enriched. During the winter months, the inter-site difference reduced. The isotopes also revealed evaporative fractionation in the peatland dominated catchment, in particular during summer low flows, which implied high hydrological connectivity in form of constant seepage from the peatlands sustaining high baseflows at the headwater scale. This connectivity resulted in high DOC concentrations at the peatland site during baseflow ( 5 mg l-1). In contrast, at the larger scales, DOC was minimal during low flows ( 2 mg l-1) due to increased groundwater influence and the disconnection between DOC sources and the stream. High frequency data also revealed diel variability during low flows. Insights into event dynamics through the analysis of hysteresis loops showed slight dilution on the rising limb, the strong influence of dry antecedent conditions and a quick recovery between events at the riparian peatland site. Again, these dynamics are driven by the tight coupling and high connectivity of the landscape to the stream. At larger scales, the disconnection between the landscape units increase and the variable connectivity controls runoff generation and DOC dynamics. The results presented here suggest that the processes occurring in riparian peatlands in headwater catchments are less evident at larger scales which may have implications for the larger scale impact of peatland restoration projects.

Scaling effects of riparian peatlands on stable isotopes in runoff and DOC mobilisation

NASA Astrophysics Data System (ADS)

Tunaley, C.; Tetzlaff, D.; Soulsby, C.

2017-06-01

We combined 13 months of daily isotope measurements in stream water with daily DOC and 15 min FDOM (fluorescent component of dissolved organic matter) data at three nested scales to identify how riparian peatlands generate runoff and influence DOC dynamics in streams. We investigated how runoff generation processes in a small, riparian peatland-dominated headwater catchment (0.65 km2) propagate to larger scales (3.2 km2 and 31 km2) with decreasing percentage of riparian peatland coverage. Isotope damping was most pronounced in the 0.65 km2 headwater catchment due to high water storage in the organic soils encouraging tracer mixing. At the largest scale, stream flow and water isotope dynamics showed a more flashy response. The isotopic difference between the sites was most pronounced in the summer months when stream water signatures were enriched. During the winter months, the inter-site difference reduced. The isotopes also revealed evaporative fractionation in the peatland dominated catchment, in particular during summer low flows, which implied high hydrological connectivity in the form of constant seepage from the peatlands sustaining high baseflows at the headwater scale. This connectivity resulted in high DOC concentrations at the peatland site during baseflow (∼5 mg l-1). In contrast, at the larger scales, DOC was minimal during low flows (∼2 mg l-1) due to increased groundwater influence and the disconnection between DOC sources and the stream. High frequency data also revealed diel variability during low flows. Insights into event dynamics through the analysis of hysteresis loops showed slight dilution on the rising limb, the strong influence of dry antecedent conditions and a quick recovery between events at the riparian peatland site. Again, these dynamics are driven by the tight coupling and high connectivity of the landscape to the stream. At larger scales, the disconnection between the landscape units increases and the variable connectivity controls runoff generation and DOC dynamics. The results presented here suggest that the processes occurring in riparian peatlands in headwater catchments are less evident at larger scales which may have implications for the larger scale impact of peatland restoration projects.

panMetaDocs and DataSync - providing a convenient way to share and publish research data

NASA Astrophysics Data System (ADS)

Ulbricht, D.; Klump, J. F.

2013-12-01

In recent years research institutions, geological surveys and funding organizations started to build infrastructures to facilitate the re-use of research data from previous work. At present, several intermeshed activities are coordinated to make data systems of the earth sciences interoperable and recorded data discoverable. Driven by governmental authorities, ISO19115/19139 emerged as metadata standards for discovery of data and services. Established metadata transport protocols like OAI-PMH and OGC-CSW are used to disseminate metadata to data portals. With the persistent identifiers like DOI and IGSN research data and corresponding physical samples can be given unambiguous names and thus become citable. In summary, these activities focus primarily on 'ready to give away'-data, already stored in an institutional repository and described with appropriate metadata. Many datasets are not 'born' in this state but are produced in small and federated research projects. To make access and reuse of these 'small data' easier, these data should be centrally stored and version controlled from the very beginning of activities. We developed DataSync [1] as supplemental application to the panMetaDocs [2] data exchange platform as a data management tool for small science projects. DataSync is a JAVA-application that runs on a local computer and synchronizes directory trees into an eSciDoc-repository [3] by creating eSciDoc-objects via eSciDocs' REST API. DataSync can be installed on multiple computers and is in this way able to synchronize files of a research team over the internet. XML Metadata can be added as separate files that are managed together with data files as versioned eSciDoc-objects. A project-customized instance of panMetaDocs is provided to show a web-based overview of the previously uploaded file collection and to allow further annotation with metadata inside the eSciDoc-repository. PanMetaDocs is a PHP based web application to assist the creation of metadata in any XML-based metadata schema. To reduce manual entries of metadata to a minimum and make use of contextual information in a project setting, metadata fields can be populated with static or dynamic content. Access rights can be defined to control visibility and access to stored objects. Notifications about recently updated datasets are available by RSS and e-mail and the entire inventory can be harvested via OAI-PMH. panMetaDocs is optimized to be harvested by panFMP [4]. panMetaDocs is able to mint dataset DOIs though DataCite and uses eSciDocs' REST API to transfer eSciDoc-objects from a non-public 'pending'-status to the published status 'released', which makes data and metadata of the published object available worldwide through the internet. The application scenario presented here shows the adoption of open source applications to data sharing and publication of data. An eSciDoc-repository is used as storage for data and metadata. DataSync serves as a file ingester and distributor, whereas panMetaDocs' main function is to annotate the dataset files with metadata to make them ready for publication and sharing with your own team, or with the scientific community.

DOC quantity and quality in northeastern USA catchments

NASA Astrophysics Data System (ADS)

Shanley, J. B.; Sebestyen, S. D.; Aiken, G.; Pellerin, B. A.

2011-12-01

At the Sleepers River Research Watershed in Vermont we have studied interactions of dissolved organic carbon (DOC) cycling and hydrological processes for nearly 20 years to determine how and when DOC is transported through the landscape. Stream DOC concentration in this cool temperate forested catchment varies from ~1 to ~15 mg L-1 and is transport-limited; concentrations increase with increasing flow, even under the wettest conditions, suggesting shifting but non-depletable sources. Specific UV absorbance (SUVA) also increases consistently with flow. Source strength does vary seasonally, however, evidenced by higher DOC for a given flow during autumn leaf fall relative to spring snowmelt. Recent high-frequency optical sensor measurements have revealed fine-scale structure in the temporal DOC pattern not possible from discrete sampling. We observe a consistent counterclockwise hysteresis and diurnal cycles with seasonally variable amplitude. In this presentation we infer DOC sources and processes through analysis of antecedent moisture conditions and concurrent variations in nitrate, dissolved organic nitrogen, and SUVA. With sensors and sampling in place at several other research catchments, we are investigating the similarity of patterns across the northeastern USA.

Secondary Psychometric Examination of the Dimensional Obsessive-Compulsive Scale: Classical Testing, Item Response Theory, and Differential Item Functioning.

PubMed

Thibodeau, Michel A; Leonard, Rachel C; Abramowitz, Jonathan S; Riemann, Bradley C

2015-12-01

The Dimensional Obsessive-Compulsive Scale (DOCS) is a promising measure of obsessive-compulsive disorder (OCD) symptoms but has received minimal psychometric attention. We evaluated the utility and reliability of DOCS scores. The study included 832 students and 300 patients with OCD. Confirmatory factor analysis supported the originally proposed four-factor structure. DOCS total and subscale scores exhibited good to excellent internal consistency in both samples (α = .82 to α = .96). Patient DOCS total scores reduced substantially during treatment (t = 16.01, d = 1.02). DOCS total scores discriminated between students and patients (sensitivity = 0.76, 1 - specificity = 0.23). The measure did not exhibit gender-based differential item functioning as tested by Mantel-Haenszel chi-square tests. Expected response options for each item were plotted as a function of item response theory and demonstrated that DOCS scores incrementally discriminate OCD symptoms ranging from low to extremely high severity. Incremental differences in DOCS scores appear to represent unbiased and reliable differences in true OCD symptom severity. © The Author(s) 2014.

Natural organic matters removal efficiency by coagulation

NASA Astrophysics Data System (ADS)

Sapingi, Mohd Sharizal Mohd; Pishal, Munirah; Murshed, Mohamad Fared

2017-10-01

The presence of Natural Organic Matter (NOM) in surface water results in unwanted characteristics in terms of color, odor, and taste. NOM content reaction with free chlorine in treated water lowers the water quality further. Chlorine is added for disinfection and produces undesirable disinfection by-products (DPBs). DBPs in drinking water are carcinogenic to consumers and may promote cancerous cell development in the human body. This study was performed to compare the coagulant efficiency of aluminum sulfate (Alum) and ferric chloride (FeCl3) on NOM removal (as in UV254 absorbance) and turbidity removal under three pH conditions (pH 6, pH 7, and sample actual pH). The three sampling points for these studies were Jalan Baru River, Kerian River, and Redac Pond. Additional sampling points, such as Lubuk Buntar and a tubewell located in the Civil Engineering School, were included to observe differences in characteristics. DOC, UV absorbance, and full wavelength were tested, after which samples treated with alum were also tested to further analyze the NOM content. Based on UV254 absorbance and DOC data, specific UV value was calculated to obtain vital synopsis of the characteristics of NOM content, as well as coagulation efficiency.

Seasonal estimates of DOC standing stocks in Apalachicola Bay estuary: Towards a better understanding using field, ocean color and model data

NASA Astrophysics Data System (ADS)

D'Sa, E. J.; Joshi, I.; Osburn, C. L.; Bianchi, T. S.; Ko, D. S.; Oviedo-Vargas, D.; Arellano, A.; Ward, N.

2016-12-01

Apalachicola Bay, a semi-enclosed estuary located in Florida's panhandle, is well known for its water quality and oyster yields. We present the use of combined field and ocean color satellite observations and the outputs of a high-resolution hydrodynamic model to study the influence of physical processes on the distribution and the transport of terrestrially derived CDOM and DOC to shelf waters during the spring and fall of 2015. Determination of DOC stocks were based on the development of a CDOM algorithm (R2 = 0.87, N = 9) for the VIIRS ocean color sensor, and the assessment of CDOM - DOC relationships (R2 = 0.88, N = 13 in March; R2 = 0.83, N = 24 in November) for the Apalachicola Bay. Satellite-derived CDOM and DOC maps together with model-based salinity distributions revealed their spatial extent, sources and transport to the shelf water. Furthermore, strong seasonal influence on DOM distribution in the bay was associated with inputs from Apalachicola and Carrabelle Rivers and the surrounding marshes. Estimates of DOC standing stocks in the bay obtained using ocean color data and high-resolution bathymetry showed relatively higher stocks in November ( 3.71 × 106 kg C, 560 km2) than in March ( 4.07 × 106 kg C, 560 km2) despite lower river discharge in dry season. Results of DOC flux estimates from the bay to coastal waters will also be presented.

Identification and analysis of low molecular weight dissolved organic carbon in subglacial basal ice ecosystems by ion chromatography

NASA Astrophysics Data System (ADS)

Lawson, E. C.; Wadham, J. L.; Lis, G. P.; Tranter, M.; Pickard, A. E.; Stibal, M.; Dewsbury, P.; Fitzsimons, S.

2015-08-01

Glacial runoff is an important source of dissolved organic carbon (DOC) for downstream heterotrophic activity, despite the low overall DOC concentrations. This is because of the abundance of bioavailable, low molecular weight (LMW) DOC species. However, the provenance and character of LMW-DOC is not fully understood. We investigated the abundance and composition of DOC in subglacial environments via a molecular level DOC analysis of basal ice, which forms by water/sediment freeze-on to the glacier sole. Spectrofluorometry and a novel ion chromatographic method, which has been little utilised in glacial science for LMW-DOC determinations, were employed to identify and quantify the major LMW fractions (free amino acids, carbohydrates and carboxylic acids) in basal ice from four glaciers, each with a different basal debris type. Basal ice from Joyce Glacier (Antarctica) was unique in that 98 % of the LMW-DOC was derived from the extremely diverse FAA pool, comprising 14 FAAs. LMW-DOC concentrations in basal ice were dependent on the bioavailability of the overridden organic carbon (OC), which in turn, was influenced by the type of overridden material. Mean LMW-DOC concentrations in basal ice from Russell Glacier (Greenland), Finsterwalderbreen (Svalbard) and Engabreen (Norway) were low (0-417 nM C), attributed to the relatively refractory nature of the OC in the overridden paleosols and bedrock. In contrast, mean LMW-DOC concentrations were an order of magnitude higher (4430 nM C) in basal ice from Joyce Glacier, a reflection of the high bioavailability of the overridden lacustrine material (>17 % of the sediment OC comprised extractable carbohydrates, a proxy for bioavailable OC). We find that the overridden material may act as a direct (via abiotic leaching) and indirect (via microbial cycling) source of DOC to the subglacial environment and provides a range of LMW-DOC compounds that may stimulate microbial activity in wet sediments in current subglacial environments.

Permafrost conditions in peatlands regulate magnitude, timing, and chemical composition of catchment dissolved organic carbon export.

PubMed

Olefeldt, David; Roulet, Nigel T

2014-10-01

Permafrost thaw in peatlands has the potential to alter catchment export of dissolved organic carbon (DOC) and thus influence downstream aquatic C cycling. Subarctic peatlands are often mosaics of different peatland types, where permafrost conditions regulate the hydrological setting of each type. We show that hydrological setting is key to observed differences in magnitude, timing, and chemical composition of DOC export between permafrost and nonpermafrost peatland types, and that these differences influence the export of DOC of larger catchments even when peatlands are minor catchment components. In many aspects, DOC export from a studied peatland permafrost plateau was similar to that of a forested upland catchment. Similarities included low annual export (2-3 g C m(-2) ) dominated by the snow melt period (~70%), and how substantial DOC export following storms required wet antecedent conditions. Conversely, nonpermafrost fens had higher DOC export (7 g C m(-2) ), resulting from sustained hydrological connectivity during summer. Chemical composition of catchment DOC export arose from the mixing of highly aromatic DOC from organic soils from permafrost plateau soil water and upland forest surface horizons with nonaromatic DOC from mineral soil groundwater, but was further modulated by fens. Increasing aromaticity from fen inflow to outlet was substantial and depended on both water residence time and water temperature. The role of fens as catchment biogeochemical hotspots was further emphasized by their capacity for sulfate retention. As a result of fen characteristics, a 4% fen cover in a mixed catchment was responsible for 34% higher DOC export, 50% higher DOC concentrations and ~10% higher DOC aromaticity at the catchment outlet during summer compared to a nonpeatland upland catchment. Expansion of fens due to thaw thus has potential to influence landscape C cycling by increasing fen capacity to act as biogeochemical hotspots, amplifying aquatic C cycling, and increasing catchment DOC export. © 2014 John Wiley & Sons Ltd.

Ancient low-molecular-weight organic acids in permafrost fuel rapid carbon dioxide production upon thaw.

PubMed

Drake, Travis W; Wickland, Kimberly P; Spencer, Robert G M; McKnight, Diane M; Striegl, Robert G

2015-11-10

Northern permafrost soils store a vast reservoir of carbon, nearly twice that of the present atmosphere. Current and projected climate warming threatens widespread thaw of these frozen, organic carbon (OC)-rich soils. Upon thaw, mobilized permafrost OC in dissolved and particulate forms can enter streams and rivers, which are important processors of OC and conduits for carbon dioxide (CO2) to the atmosphere. Here, we demonstrate that ancient dissolved organic carbon (DOC) leached from 35,800 y B.P. permafrost soils is rapidly mineralized to CO2. During 200-h experiments in a novel high-temporal-resolution bioreactor, DOC concentration decreased by an average of 53%, fueling a more than sevenfold increase in dissolved inorganic carbon (DIC) concentration. Eighty-seven percent of the DOC loss to microbial uptake was derived from the low-molecular-weight (LMW) organic acids acetate and butyrate. To our knowledge, our study is the first to directly quantify high CO2 production rates from permafrost-derived LMW DOC mineralization. The observed DOC loss rates are among the highest reported for permafrost carbon and demonstrate the potential importance of LMW DOC in driving the rapid metabolism of Pleistocene-age permafrost carbon upon thaw and the outgassing of CO2 to the atmosphere by soils and nearby inland waters.

Sunlight, iron and radicals to tackle the resistant leftovers of biotreated winery wastewater.

PubMed

Ioannou, Lida; Velegraki, Theodora; Michael, Costas; Mantzavinos, Dionissios; Fatta-Kassinos, Despo

2013-04-01

Winery wastewater is characterized by high organic content consisting of alcohols, acids and recalcitrant high-molecular-weight compounds (e.g. polyphenols, tannins and lignins). So far, biological treatment constitutes the best available technology for such effluents that are characterized by high seasonal variability; however the strict legislation applied on the reclamation and reuse of wastewaters for irrigation purposes introduces the need for further treatment of the bioresistant fraction of winery effluents. In this context, the use of alternative treatment technologies, aiming to mineralize or transform refractory molecules into others which could be further biodegraded, is a matter of great concern. In this study, a winery effluent that had already been treated in a sequencing batch reactor was subjected to further purification by homogeneous and heterogeneous solar Fenton oxidation processes. The effect of various operating variables such as catalyst and oxidant concentration, initial pH, temperature and lamp power on the abatement of chemical oxygen demand (COD), dissolved organic carbon (DOC), color, total phenolics and ecotoxicity has been assessed in the homogeneous solar Fenton process. In addition, a comparative assessment between homogeneous and heterogeneous solar Fenton processes was performed. In the present study the homogeneous solar Fenton process has been demonstrated to be the most effective process, yielding COD, DOC and total phenolics removal of about 69%, 48% and 71% in 120 min of the photocatalytic treatment, respectively.

Bioavailable dissolved and particulate organic carbon flux from coastal temperate rainforest watersheds

NASA Astrophysics Data System (ADS)

Fellman, J.; Hood, E. W.; D'Amore, D. V.; Moll, A.

2017-12-01

Coastal temperate rainforest (CTR) watersheds of southeast Alaska have dense soil carbon stocks ( 300 Mg C ha-1) and high specific discharge (1.5-7 m yr-1) driven by frontal storms from the Gulf of Alaska. As a result, dissolved organic carbon (DOC) fluxes from Alaskan CTR watersheds are estimated to exceed 2 Tg yr-1; however, little is known about the export of particulate organic carbon (POC). The magnitude and bioavailability of this land-to-ocean flux of terrigenous organic matter ultimately determines how much metabolic energy is translocated to downstream and coastal marine ecosystems in this region. We sampled streamwater weekly from May through October from four watersheds of varying landcover (gradient of wetland to glacial coverage) to investigate changes in the concentration and flux of DOC and POC exported to the coastal ocean. We also used headspace analysis of CO2 following 14 day laboratory incubations to determine the flux of bioavailable DOC and POC exported from CTR watersheds. Across all sites, bioavailable DOC concentrations ranged from 0.2 to 1.9 mg L-1 but were on average 0.6 mg L-1. For POC, bioavailable concentrations ranged from below detection to 0.3 mg L-1 but were on average 0.1 mg L-1. The concentration, flux and bioavailability of DOC was higher than for POC highlighting the potential importance of DOC as a metabolic subsidy to downstream and coastal environments. Ratios of DOC to POC decreased during high flow events because the increase in POC concentrations with discharge exceeds that for DOC. Overall, our findings suggest that projected increases in precipitation and storm intensity will drive changes in the speciation, magnitude and bioavailability of the organic carbon flux from CTR watersheds.

How we used two social media tools to enhance aspects of active learning during lectures.

PubMed

George, Daniel R; Dreibelbis, Tomi D; Aumiller, Betsy

2013-12-01

Medical education is evolving to include active learning approaches, yet some courses will remain lecture-based. Social media tools used by students may foster collaborative learning during lectures. We present preliminary results from a pilot study that integrated two 'social' technologies, Google Docs and SurveyMonkey, into 22 hour-long lectures for a course called "Social Influences on Health" attended by 154 students. At the conclusion of the semester, we reviewed student usage patterns with both technologies and collected data from students via course evaluations that included a standard Likert Scale. We used thematic analysis to identify emergent themes from evaluations. On average, students contributed 6 comments/questions to the Google Doc in each lecture, and 35 students participated in SurveyMonkey. Engagement with both technologies increased throughout the semester and no unprofessional incidents were observed. The mean student rating for integration of Google Docs and SurveyMonkey was 3.4 or "above average" (SD = 1.17). Thematic analysis identified perceived strengths of this approach as well as areas for improvement. Social media such as Google Docs and SurveyMonkey can facilitate interaction and provide students with control over content and flow of lecture-based courses, but educators must be mindful of practical and conceptual limitations.

Biochemical methane potential of fractions of organic matter extracted from a municipal solid waste leachate: Impact of their hydrophobic character.

PubMed

Baccot, Camille; Pallier, Virginie; Feuillade-Cathalifaud, Geneviève

2017-05-01

Many data on anaerobic digestion (AD) and co-digestion of municipal solid waste leachate (MSWL) are already available in literature. They mainly deal with its performances to decrease the chemical oxygen demand (COD) of MSWL and no information is given on the impact of the specific characteristics of the dissolved organic matter (DOM) in leachate on these performances. DOM in leachate evolves towards more aromatic and hydrophobic compounds during landfilling with increasing specific ultra-violet absorbance index (SUVA) and hydrophobic character. However, according to the humification stages, this DOM would not present the same aptitude for AD. This research thus focused on (i) optimizing a biochemical methane potential (BMP) test applied to MSWL by using the Taguchi method and (ii) evaluating the impact of the hydrophobic character of the DOM in leachate on the BMP of MSWL to finally define the humification degree more suitable for AD. Hydrophobic-like (HPO ∗ ) and transphilic-like (TPH ∗ ) compounds extracted from leachate by a fractionation protocol were tested because of their high content in MSWL during acetogenesis and methanogenesis steps. After 275days of AD, the content in hydrophobic compounds and the SUVA indexes increased in the digestates. Moreover, even if the biogas and methane productions were not significantly different during the whole tests (4072±350mLgDOC -1 and 2370±95mLgDOC -1 respectively), the volume of biogas produced directly correlated with the TPH ∗ fraction content in the initial digestates. On the contrary, the methane percentage in biogas was anti-correlated with the hydrophilic-like compounds content. The hydrophobic-like molecules seem thus not to be directly involved in the methanogenic step, however they promote the increase of the methane percent in the biogas. Copyright © 2016 Elsevier Ltd. All rights reserved.

Flushing of distal hillslopes as an alternative source of stream dissolved organic carbon in a headwater catchment

USGS Publications Warehouse

Gannon, John P; Bailey, Scott W.; McGuire, Kevin J.; Shanley, James B.

2015-01-01

We investigated potential source areas of dissolved organic carbon (DOC) in headwater streams by examining DOC concentrations in lysimeter, shallow well, and stream water samples from a reference catchment at the Hubbard Brook Experimental Forest. These observations were then compared to high-frequency temporal variations in fluorescent dissolved organic matter (FDOM) at the catchment outlet and the predicted spatial extent of shallow groundwater in soils throughout the catchment. While near-stream soils are generally considered a DOC source in forested catchments, DOC concentrations in near-stream groundwater were low (mean = 2.4 mg/L, standard error = 0.6 mg/L), less than hillslope groundwater farther from the channel (mean = 5.7 mg/L, standard error = 0.4 mg/L). Furthermore, water tables in near-stream soils did not rise into the carbon-rich upper B or O horizons even during events. In contrast, soils below bedrock outcrops near channel heads where lateral soil formation processes dominate had much higher DOC concentrations. Soils immediately downslope of bedrock areas had thick eluvial horizons indicative of leaching of organic materials, Fe, and Al and had similarly high DOC concentrations in groundwater (mean = 14.5 mg/L, standard error = 0.8 mg/L). Flow from bedrock outcrops partially covered by organic soil horizons produced the highest groundwater DOC concentrations (mean = 20.0 mg/L, standard error = 4.6 mg/L) measured in the catchment. Correspondingly, stream water in channel heads sourced in part by shallow soils and bedrock outcrops had the highest stream DOC concentrations measured in the catchment. Variation in FDOM concentrations at the catchment outlet followed water table fluctuations in shallow to bedrock soils near channel heads. We show that shallow hillslope soils receiving runoff from organic matter-covered bedrock outcrops may be a major source of DOC in headwater catchments in forested mountainous regions where catchments have exposed or shallow bedrock near channel heads.

Dissolved Organic Carbon in Marginal, Damaged Peatlands: Using 14C to Understand DOC Losses

NASA Astrophysics Data System (ADS)

Luscombe, D.; Grand-Clement, E.; Garnett, M.; Anderson, K.; Gatis, N.; Benaud, P.; Brazier, R.

2013-12-01

Peatlands are widely represented throughout the world and act as an important store of carbon, as well as providing society with a range of other ecosystem services, such as drinking water or the support of rare habitats. However, the combination of historical management practices, and the predicted impact of climate change means that they are now largely under threat. In the shallow peatlands of Exmoor National Park (South West UK), peat cutting and intensive drainage in the 19th and 20th century for agricultural reclamation have changed the hydrological behaviour of the peat. This damage has dried out the upper layers, causing oxidation, erosion and vegetation change. In addition, their location on the southernmost limit of peatlands geographical extent in northern Europe makes them particularly vulnerable to the predicted changes in rainfall and temperature. Recent modelling work has shown that such marginal peatlands may disappear as early as 2050. Restoration programs are currently in place, aiming to restore the hydrological functioning of the peat. However, current dissolved organic carbon (DOC) losses from damaged peatlands are especially of concern, because of the contribution of the aquatic pathways in the C flux, and because of the impact on water quality. DOC has been shown to originate from the drainage of highly-aged organic matter. In stream waters, DOC from low flow tends to contain a larger component of older C compared to that of high flow. Both the impact of extensive drainage on where DOC is originating from and the effect of peatland restoration on this process remain poorly understood. We used 14C dating of DOC from streams and pore water, as well as from damaged peat, in order to gain a better understanding of the process and origin of DOC loss in drained shallow peatlands. This will further help us understand the potential for peatland restoration. Work was carried out in a small intensively monitored catchment in Exmoor. Samples were taken in an area of shallow peat (ca. 20-30 cm depth) drained by a medium size ditch (50 x 50 cm). Samples of DOC from stream water were taken at low and high flow during 3 separate rain events in Winter- Spring 2013 using automatic pump samplers. Samples of DOC in pore water were taken 2 m away from the ditch at 5 and 15 cm depth on two occasions. Finally, matching bulk peat samples were collected at 5 and 15 cm depth. Intensive monitoring data also provides information on water table depth and level in streams. A neighbouring pristine peat area was used as a control, and DOC pore water and bulk peat soil samples were taken at 5, 15 and 45 cm depth on two occasions. Preliminary results show that DOC lost in streams at high flow contains a greater contribution of bomb-14C compared to that at low flow (107 and 101 % modern respectively). Stream water DOC at low flow had a 14C concentration lower than that in pore water at both 5 and 15 cm depth (105 and 102% modern, respectively), suggesting that low flow stream water DOC is predominantly older than that found in pore water at depth.

Transgender Inmates in Prisons.

PubMed

Routh, Douglas; Abess, Gassan; Makin, David; Stohr, Mary K; Hemmens, Craig; Yoo, Jihye

2017-05-01

Transgender inmates provide a conundrum for correctional staff, particularly when it comes to classification, victimization, and medical and health issues. Using LexisNexis and WestLaw and state Department of Corrections (DOC) information, we collected state statutes and DOC policies concerning transgender inmates. We utilized academic legal research with content analysis to determine whether a statute or policy addressed issues concerning classification procedures, access to counseling services, the initiation and continuation of hormone therapy, and sex reassignment surgery. We found that while more states are providing either statutory or policy guidelines for transgender inmates, a number of states are lagging behind and there is a shortage of guidance dealing with the medical issues related to being transgender.

Nonlinear and threshold-dominated runoff generation controls DOC export in a small peat catchment

NASA Astrophysics Data System (ADS)

Birkel, C.; Broder, T.; Biester, H.

2017-03-01

We used a relatively simple two-layer, coupled hydrology-biogeochemistry model to simultaneously simulate streamflow and stream dissolved organic carbon (DOC) concentrations in a small lead and arsenic contaminated upland peat catchment in northwestern Germany. The model procedure was informed by an initial data mining analysis, in combination with regression relationships of discharge, DOC, and element export. We assessed the internal model DOC processing based on stream DOC hysteresis patterns and 3-hourly time step groundwater level and soil DOC data for two consecutive summer periods in 2013 and 2014. The parsimonious model (i.e., few calibrated parameters) showed the importance of nonlinear and rapid near-surface runoff generation mechanisms that caused around 60% of simulated DOC load. The total load was high even though these pathways were only activated during storm events on average 30% of the monitoring time—as also shown by the experimental data. Overall, the drier period 2013 resulted in increased nonlinearity but exported less DOC (115 kg C ha-1 yr-1 ± 11 kg C ha-1 yr-1) compared to the equivalent but wetter period in 2014 (189 kg C ha-1 yr-1 ± 38 kg C ha-1 yr-1). The exceedance of a critical water table threshold (-10 cm) triggered a rapid near-surface runoff response with associated higher DOC transport connecting all available DOC pools and subsequent dilution. We conclude that the combination of detailed experimental work with relatively simple, coupled hydrology-biogeochemistry models not only allowed the model to be internally constrained but also provided important insight into how DOC and tightly coupled pollutants or trace elements are mobilized.

Long-term anoxia and release of ancient, labile carbon upon thaw of Pleistocene permafrost

USGS Publications Warehouse

Ewing, Stephanie A.; O'Donnell, Jonathan A.; Aiken, George R.; Butler, Kenna D.; Butman, David; Windham-Myers, Lisamarie; Kanevskiy, Mikhail

2015-01-01

The fate of permafrost carbon upon thaw will drive feedbacks to climate warming. Here we consider the character and context of dissolved organic carbon (DOC) in yedoma permafrost cores from up to 20 m depth in central Alaska. We observed high DOC concentrations (4 to 129 mM) and consistent low molecular weight organic acid concentrations in three cores. We estimate a DOC production rate of 12 µmol DOC m−2 yr−1 based on model ages of up to ~200 kyr derived from uranium isotopes. Acetate C accounted for 24 ± 1% of DOC in all samples. This proportion suggests long-term anaerobiosis and is likely to influence thaw outcomes due to biolability of acetate upon release in many environments. The combination of uranium isotopes, ammonium concentrations, and calcium concentrations explained 86% of the variation in thaw water DOC concentrations, suggesting that DOC production may be related to both reducing conditions and mineral dissolution over time.

Microbial Growth and Metabolism in Soil - Refining the Interpretation of Carbon Use Efficiency

NASA Astrophysics Data System (ADS)

Geyer, K.; Frey, S. D.

2016-12-01

Carbon use efficiency (CUE) describes a critical step in the terrestrial carbon cycle where microorganisms partition organic carbon (C) between stabilized organic forms and CO2. Application of this concept, however, begins with accurate measurements of CUE. Both traditional and developing approaches still depend on numerous assumptions that render them difficult to interpret and potentially incompatible with one another. Here we explore the soil processes inherent to traditional (e.g., substrate-based, biomass-based) and emerging (e.g., growth rate-based, calorimetry) CUE techniques in order to better understand the information they provide. Soil from the Harvard Forest Long Term Ecological Research (LTER) site in Massachusetts, USA, was amended with both 13C-glucose and 18O-water and monitored over 72 h for changes in dissolved organic carbon (DOC), respiration (R), microbial biomass (MB), DNA synthesis, and heat flux (Q). Four different CUE estimates were calculated: 1) (ΔDOC - R)/ΔDOC (substrate-based), 2) Δ13C-MB/(Δ13C-MB + R) (biomass-based), 3) Δ18O-DNA/(Δ18O-DNA + R) (growth rate-based), 4) Q/R (energy-based). Our results indicate that microbial growth (estimated by both 13C and 18O techniques) was delayed for 40 h after amendment even though DOC had declined to pre-amendment levels within 48 h. Respiration and heat flux also peaked after 40 h. Although these soils have a relatively high organic C content (5% C), respired CO2 was greater than 88% glucose-derived throughout the experiment. All estimates of microbial growth (Spearman's ρ >0.83, p<0.01) and efficiency (Spearman's ρ >0.65, p<0.05) were positively correlated, but strong differences in the magnitude of CUE suggest incomplete C accounting. This work increases the transparency of CUE techniques for researchers looking to choose the most appropriate measure for their scale of inquiry or to use CUE estimates in modeling applications.

Organic carbon and nitrogen concentrations and annual organic carbon load of six selected rivers of the United States

USGS Publications Warehouse

Malcolm, R.L.; Durum, W.H.

1976-01-01

The organic carbon load during 1969-70 of each of the six rivers in this study is substantial. The 3.4-billion-kilogram (3.7-million-ton) and 47-million-kilogram (52-thousandton) annual organic carbon loads of the Mississippi River and the Brazos River (Tex.), respectively, were approximately equally distributed between dissolved and suspended phases, whereas the 725-million-kilogram (79.8-million-ton) organic load of the Missouri River was primarily in the suspended phase. The major portion of the 6.4-million-kilogram (7.3 thousand-ton) and the 19-million-kilogram (21-thousand-ton) organic carbon loads of the Sopchoppy River (Fla.) and the Neuse River (N.C.), respectively, was in the dissolved phase. DOC (dissolved organic carbon) concentrations in most rivers were usually less than 8 milligrams per litre. SOC (suspended organic carbon) concentrations fluctuated markedly with discharge, ranging between 1 and 14 percent, by weight, in sediment of most rivers. DOC concentrations were found to be independent of discharge, whereas SOC and SIC (suspended inorganic carbon) concentrations were positively correlated with discharge. Seasonal fluctuations in DOC and SOC were exhibited by the Missouri, Neuse, Ohio, and Brazos Rivers, but both SOC and DOC concentrations were relatively constant throughout the year in the Mississippi and Sopchoppy Rivers. The carbon-nitrogen ratio in the sediment phase of all river waters averaged less than 8 1 as compared with 12:1 or greater for most soils. This high nitrogen content shows a nitrogen enrichment of the stream sediment over that in adjacent soils, which suggests that different decomposition and humification processes are operating in streams than in the soils. The abundance of organic material in the dissolved and suspended phase of all river waters in this study indicate a large capacity factor for various types of organic reactivity within all streams and the quantitative importance of organic constituents in relation to the water quality of rivers and streams.

Catchment-Scale Sampling Reveals the Consistent Function of the Sediment-Water Interface to Remove Landscape Scale Dissolved Organic Carbon Properties

NASA Astrophysics Data System (ADS)

Lee-Cullin, J. A.; Zarnetske, J. P.; Wiewiora, E.; Ruhala, S.; Hampton, T. B.

2016-12-01

Dissolved organic carbon (DOC) is a critical component to biogeochemical cycling and water quality in surface waters. As DOC moves through stream networks, from headwaters to higher order streams, the sediment-water interface (SWI), where streams and groundwater readily interact, exerts a strong influence on DOC concentrations and compositional characteristics (i.e., molecular properties). Few studies examine SWI patterns at larger spatial scales, instead focusing primarily on site-level studies because sampling in the SWI is methodologically time and labor intensive. It is presently unknown how land use and landcover influence the fate of DOC in the SWI and therefore the function of the SWI on catchment-scale DOC conditions. Here, we performed a catchment-scale, high spatial-resolution SWI sampling campaign to test how landscape pattern DOC signatures are propagated into the stream and groundwater, and to assess the fate of these signatures when DOC travels through the SWI. We sampled across 39 sites composed of first-, second-, and third-order locations in a lowland, third-order catchment composed of diverse landscape units and properties, including wetland, upland forest, and agriculture. At each of these locations, surface water, groundwater, and SWI water were collected, including six discrete depths across the SWI. The major land use and landcover properties were also determined for each of these locations. We developed two simple generalized linear models to identify the landscape properties with greatest explanatory power for DOC conditions - one for stream water and one for groundwater. The correlation between landscape properties and surface water DOC characteristics was stronger than between landscape properties and groundwater DOC characteristics. To test if the DOC properties from surface and groundwater were preserved or removed by the SWI, the resulting best-fit models for each water source were used to predict the DOC conditions across the SWI. The models were unable to predict SWI DOC conditions, indicating that the landscape signature present in both the surface water and groundwater is removed by processes occurring in the SWI. Overall, this suggests that the SWI functions as and effective zone for processing the landscape-derived DOC signatures.

Catchment-Scale Sampling Reveals the Consistent Function of the Sediment-Water Interface to Remove Landscape Scale Dissolved Organic Carbon Properties

NASA Astrophysics Data System (ADS)

Lee-Cullin, J. A.; Zarnetske, J. P.; Wiewiora, E.; Ruhala, S.; Hampton, T. B.

2017-12-01

Dissolved organic carbon (DOC) is a critical component to biogeochemical cycling and water quality in surface waters. As DOC moves through stream networks, from headwaters to higher order streams, the sediment-water interface (SWI), where streams and groundwater readily interact, exerts a strong influence on DOC concentrations and compositional characteristics (i.e., molecular properties). Few studies examine SWI patterns at larger spatial scales, instead focusing primarily on site-level studies because sampling in the SWI is methodologically time and labor intensive. It is presently unknown how land use and landcover influence the fate of DOC in the SWI and therefore the function of the SWI on catchment-scale DOC conditions. Here, we performed a catchment-scale, high spatial-resolution SWI sampling campaign to test how landscape pattern DOC signatures are propagated into the stream and groundwater, and to assess the fate of these signatures when DOC travels through the SWI. We sampled across 39 sites composed of first-, second-, and third-order locations in a lowland, third-order catchment composed of diverse landscape units and properties, including wetland, upland forest, and agriculture. At each of these locations, surface water, groundwater, and SWI water were collected, including six discrete depths across the SWI. The major land use and landcover properties were also determined for each of these locations. We developed two simple generalized linear models to identify the landscape properties with greatest explanatory power for DOC conditions - one for stream water and one for groundwater. The correlation between landscape properties and surface water DOC characteristics was stronger than between landscape properties and groundwater DOC characteristics. To test if the DOC properties from surface and groundwater were preserved or removed by the SWI, the resulting best-fit models for each water source were used to predict the DOC conditions across the SWI. The models were unable to predict SWI DOC conditions, indicating that the landscape signature present in both the surface water and groundwater is removed by processes occurring in the SWI. Overall, this suggests that the SWI functions as and effective zone for processing the landscape-derived DOC signatures.

Dissolved organic carbon fluxes in the Middle Atlantic Bight: An integrated approach based on satellite data and ocean model products

NASA Astrophysics Data System (ADS)

Mannino, Antonio; Signorini, Sergio R.; Novak, Michael G.; Wilkin, John; Friedrichs, Marjorie A. M.; Najjar, Raymond G.

2016-02-01

Continental margins play an important role in global carbon cycle, accounting for 15-21% of the global marine primary production. Since carbon fluxes across continental margins from land to the open ocean are not well constrained, we undertook a study to develop satellite algorithms to retrieve dissolved organic carbon (DOC) and combined these satellite data with physical circulation model products to quantify the shelf boundary fluxes of DOC for the U.S. Middle Atlantic Bight (MAB). Satellite DOC was computed through seasonal relationships of DOC with colored dissolved organic matter absorption coefficients, which were derived from an extensive set of in situ measurements. The multiyear time series of satellite-derived DOC stocks (4.9 Teragrams C; Tg) shows that freshwater discharge influences the magnitude and seasonal variability of DOC on the continental shelf. For the 2010-2012 period studied, the average total estuarine export of DOC into the MAB shelf is 0.77 Tg C yr-1 (year). The integrated DOC tracer fluxes across the shelf boundaries are 12.1 Tg C yr-1 entering the MAB from the southwest alongshore boundary, 18.5 Tg C yr-1 entering the MAB from the northeast alongshore boundary, and 29.0 Tg C yr-1 flowing out of the MAB across the entire length of the 100 m isobath. The magnitude of the cross-shelf DOC flux is quite variable in time (monthly) and space (north to south). The highly dynamic exchange of water along the shelf boundaries regulates the DOC budget of the MAB at subseasonal time scales.

The Influence of Submarine Groundwater Discharge on Nearshore Marine Dissolved Organic Carbon Reactivity, Concentration Dynamics, and Offshore Export

NASA Astrophysics Data System (ADS)

Goodridge, B.

2017-12-01

Dissolved organic carbon (DOC) is the largest pool of reduced carbon in the oceans, with a reservoir equivalent to atmospheric CO2. In nearshore marine regions, DOC sources include primary production, terrestrial DOC delivered by river discharge, and/or terrestrial and marine DOC delivered via submarine groundwater discharge (SGD). While the importance of SGD to coastal carbon cycling has been implicated, the actual influence of this process on nearshore carbon dynamics and offshore export has not been explicitly identified. This study, conducted at a predominantly marine-influenced intertidal beach-nearshore ocean system along the Santa Barbara, California coastline, aimed to address this knowledge gap. I coupled dark, temperature-controlled laboratory incubations, radioisotopic (Rn-222) SGD estimates, and a DOC box model to identify the influence of pore water mixing with seawater on nearshore DOC reactivity, concentration dynamics, and offshore export. Even with a relatively low volumetric contribution, SGD pore water mixing altered nearshore DOC reactivity, and elevated the nearshore DOC concentration by 0.9 to 5.6 µmol L-1 over nearshore seawater residence times ranging from 1 to 6 days. These elevated DOC concentrations were equivalent to 1.2 to 7.5% of the mean offshore DOC concentration taken during the summer months in the Santa Barbara Channel, when the coastal water column is highly thermally stratified. Despite the challenge of assessing carbon dynamics in physically and biogeochemically complex nearshore marine regions, this study demonstrates the need for future investigations to assess and account for SGD as a non-trivial component of coastal marine carbon cycles.

Dissolved organic carbon fluxes in the Middle Atlantic Bight: An integrated approach based on satellite data and ocean model products.

PubMed

Mannino, Antonio; Signorini, Sergio R; Novak, Michael G; Wilkin, John; Friedrichs, Marjorie A M; Najjar, Raymond G

2016-02-01

Continental margins play an important role in global carbon cycle, accounting for 15-21% of the global marine primary production. Since carbon fluxes across continental margins from land to the open ocean are not well constrained, we undertook a study to develop satellite algorithms to retrieve dissolved organic carbon (DOC) and combined these satellite data with physical circulation model products to quantify the shelf boundary fluxes of DOC for the U.S. Middle Atlantic Bight (MAB). Satellite DOC was computed through seasonal relationships of DOC with colored dissolved organic matter absorption coefficients, which were derived from an extensive set of in situ measurements. The multiyear time series of satellite-derived DOC stocks (4.9 Teragrams C; Tg) shows that freshwater discharge influences the magnitude and seasonal variability of DOC on the continental shelf. For the 2010-2012 period studied, the average total estuarine export of DOC into the MAB shelf is 0.77 Tg C yr -1 (year). The integrated DOC tracer fluxes across the shelf boundaries are 12.1 Tg C yr -1 entering the MAB from the southwest alongshore boundary, 18.5 Tg C yr -1 entering the MAB from the northeast alongshore boundary, and 29.0 Tg C yr -1 flowing out of the MAB across the entire length of the 100 m isobath. The magnitude of the cross-shelf DOC flux is quite variable in time (monthly) and space (north to south). The highly dynamic exchange of water along the shelf boundaries regulates the DOC budget of the MAB at subseasonal time scales.

Variation in fish mercury concentrations in streams of the Adirondack region, New York: A simplified screening approach using chemical metrics

USGS Publications Warehouse

Burns, Douglas A.; Riva-Murray, Karen

2018-01-01

Simple screening approaches for the neurotoxicant methylmercury (MeHg) in aquatic ecosystems may be helpful in risk assessments of natural resources. We explored the development of such an approach in the Adirondack Mountains of New York, USA, a region with high levels of MeHg bioaccumulation. Thirty-six perennial streams broadly representative of 1st and 2nd order streams in the region were sampled during summer low flow and analyzed for several solutes and for Hg concentrations in fish. Several landscape and chemical metrics that are typically strongly related to MeHg concentrations in aquatic biota were explored for strength of association with fish Hg concentrations. Data analyses were based on site mean length-normalized and standardized Hg concentrations (assumed to be dominantly MeHg) in whole juvenile and adult Brook Trout Salvelinus fontinalis, Creek Chub Semotilus atromaculatus, Blacknose Dace Rhinichthys atratulus, and Central Mudminnow Umbra limi, as well as on multi-species z-scores. Surprisingly, none of the landscape metrics was related significantly to regional variation in fish Hg concentrations or to z-scores across the study streams. In contrast, several chemical metrics including dissolved organic carbon (DOC) concentrations, sulfate concentrations (SO42−), pH, ultra-violet absorbance (UV254), and specific ultra-violet absorbance were significantly related to regional variation in fish Hg concentrations. A cluster analysis based on DOC, SO42−, and pH identified three distinct groups of streams: (1) high DOC, acidic streams, (2) moderate DOC, slightly acidic streams, and (3) low DOC circum-neutral streams with relatively high SO42−. Preliminary analysis indicated no significant difference in fish Hg z-scores between the moderate and high DOC groups, so these were combined for further analysis. The resulting two groups showed strong differences (p < 0.001) in DOC and SO42−concentrations as well as in pH and UV254 values. Median fish z-scores were significantly higher (p = 0.002) in the group of streams with higher DOC and UV254 and lower pH and SO42−. Screening values of DOC >6.9 mg/L, SO42− <2.8 mg/L, pH <6.6, and UV254>0.31 cm−1 were tested as thresholds to identify Adirondack stream sites likely to have higher fish Hg concentrations. By applying a combined threshold of exceedance for either pH or UV254, sites with fish Hg concentrations that exceeded a wildlife guideline of 100 ng/g were correctly identified about 75% of the time among the 36 study streams. An estimate of Hg risk applied to a data set of 391 streams based on DOC concentrations showed that about 28% were likely to pose high risk to wildlife; most of these streams were located in the western Adirondacks.

Organic matter dynamics in a karstic watershed: Example from Santa Fe River, Florida, USA

NASA Astrophysics Data System (ADS)

Jin, J.; Khadka, M. B.; Martin, J. B.; Zimmerman, A. R.

2011-12-01

Organic matter (OM) dynamics in karstic watersheds can involve a range of interactions between organic and inorganic phases of carbon. These interactions include OM remineralization, which will changes its lability, increase dissolved inorganic carbon (DIC) concentrations, reduce pH, and enhance carbonate mineral dissolution. Dissolved organic carbon (DOC) concentrations are elevated in black-water rivers of northern Florida from both allochthonous and autochthonous sources and these rivers flow into and interact with the karstic Floridan Aquifer. One such river, the Santa Fe River, is split into upper confined and lower unconfined watersheds by the Cody Scarp, which represent the erosional edge of a regional confining unit. Water samples were collected from 8 sites across the entire Santa Fe River watershed (SFRW) during 9 sampling trips from December 2009 to May 2011 at flow conditions that ranged from 27 to 39 m3/s, with the highest flow about 45% higher than baseflow. At sites above the Cody Scarp, the river has elevated DOC concentrations, which decrease downstream, while dissolved inorganic carbon (DIC) and δ13C-DIC show opposite trends. At high flow, DOC concentrations progressively decrease downstream from dilution by low-DOC water discharging from the Floridan Aquifer. At low flow, the water chemistry varies little from upstream to downstream, largely because the composition of upstream water becomes similar to that of downstream water. DOC is inversely and linearly correlated with DIC and δ13C-DIC, but the slope of the correlations vary with discharge, with low flow having more negative slopes than high flow. The OM becomes more labile with distance downstream as assessed using two fluorescence indices, biological/autochthonous index (BIX) and humification index (HIX). This increase in lability suggests that DOC is produced in the river, and this production is reflected in a downstream increase in DOC flux regardless of dilution by the influx of low-DOC groundwater. Primary production was 5 to 25 times higher during high and low flow, respectively, in the lower than in the upper SFRW. No decrease in DOC with a concomitant increase in DIC was observed, however, suggesting observations of microbial consumption of OM is masked by primary production and gain of DIC-rich and DOC-poor groundwater. The upper SFRW has lower saturation index (SI; -2.9 and -0.7 for high and low flow, respectively) than the lower SFRW (0.0 and 0.3 for high and low flow, respectively). The downstream shift in SI reflects dissolution of the carbonate minerals and gain of water from the Floridan Aquifer that had equilibrated with carbonate minerals. OM dynamics in the SFRW are closely linked to the allochthonous OM derived from the upper SFRW, as well as primary production in the lower watershed. Both allochthonous and autochthonous OM can be important in abiotic processes such as carbonate mineral dissolution, but flow conditions mediate the magnitudes of the reactions.

Publishing datasets with eSciDoc and panMetaDocs

NASA Astrophysics Data System (ADS)

Ulbricht, D.; Klump, J.; Bertelmann, R.

2012-04-01

Currently serveral research institutions worldwide undertake considerable efforts to have their scientific datasets published and to syndicate them to data portals as extensively described objects identified by a persistent identifier. This is done to foster the reuse of data, to make scientific work more transparent, and to create a citable entity that can be referenced unambigously in written publications. GFZ Potsdam established a publishing workflow for file based research datasets. Key software components are an eSciDoc infrastructure [1] and multiple instances of the data curation tool panMetaDocs [2]. The eSciDoc repository holds data objects and their associated metadata in container objects, called eSciDoc items. A key metadata element in this context is the publication status of the referenced data set. PanMetaDocs, which is based on PanMetaWorks [3], is a PHP based web application that allows to describe data with any XML-based metadata schema. The metadata fields can be filled with static or dynamic content to reduce the number of fields that require manual entries to a minimum and make use of contextual information in a project setting. Access rights can be applied to set visibility of datasets to other project members and allow collaboration on and notifying about datasets (RSS) and interaction with the internal messaging system, that was inherited from panMetaWorks. When a dataset is to be published, panMetaDocs allows to change the publication status of the eSciDoc item from status "private" to "submitted" and prepare the dataset for verification by an external reviewer. After quality checks, the item publication status can be changed to "published". This makes the data and metadata available through the internet worldwide. PanMetaDocs is developed as an eSciDoc application. It is an easy to use graphical user interface to eSciDoc items, their data and metadata. It is also an application supporting a DOI publication agent during the process of publishing scientific datasets as electronic data supplements to research papers. Publication of research manuscripts has an already well established workflow that shares junctures with other processes and involves several parties in the process of dataset publication. Activities of the author, the reviewer, the print publisher and the data publisher have to be coordinated into a common data publication workflow. The case of data publication at GFZ Potsdam displays some specifics, e.g. the DOIDB webservice. The DOIDB is a proxy service at GFZ for the DataCite [4] DOI registration and its metadata store. DOIDB provides a local summary of the dataset DOIs registered through GFZ as a publication agent. An additional use case for the DOIDB is its function to enrich the datacite metadata with additional custom attributes, like a geographic reference in a DIF record. These attributes are at the moment not available in the datacite metadata schema but would be valuable elements for the compilation of data catalogues in the earth sciences and for dissemination of catalogue data via OAI-PMH. [1] http://www.escidoc.org , eSciDoc, FIZ Karlruhe, Germany [2] http://panmetadocs.sf.net , panMetaDocs, GFZ Potsdam, Germany [3] http://metaworks.pangaea.de , panMetaWorks, Dr. R. Huber, MARUM, Univ. Bremen, Germany [4] http://www.datacite.org

[Redacted] Settlement Agreement - Docket No. CERCLA-04-2009-3978 (Appendix A Withheld)

EPA Pesticide Factsheets

Contains legal agreement for the Granville High School Mercury Superfund site under CERCLA Section 122(h)(1), Creedmoor, Granville County, North Carolina, November 13, 2009 DocID: 10760173 , DocDate: 11-13-2009

Relationships between colored dissolved organic matter and dissolved organic carbon in different coastal gradients of the Baltic Sea.

PubMed

Harvey, E Therese; Kratzer, Susanne; Andersson, Agneta

2015-06-01

Due to high terrestrial runoff, the Baltic Sea is rich in dissolved organic carbon (DOC), the light-absorbing fraction of which is referred to as colored dissolved organic matter (CDOM). Inputs of DOC and CDOM are predicted to increase with climate change, affecting coastal ecosystems. We found that the relationships between DOC, CDOM, salinity, and Secchi depth all differed between the two coastal areas studied; the W Gulf of Bothnia with high terrestrial input and the NW Baltic Proper with relatively little terrestrial input. The CDOM:DOC ratio was higher in the Gulf of Bothnia, where CDOM had a greater influence on the Secchi depth, which is used as an indicator of eutrophication and hence important for Baltic Sea management. Based on the results of this study, we recommend regular CDOM measurements in monitoring programmes, to increase the value of concurrent Secchi depth measurements.

Human Systems Engineering and Program Success - A Retrospective Content Analysis

DTIC Science & Technology

2016-01-01

collected from the 546 documents and entered into SPSS Statistics Version 22.0 for Windows. HSI words within the sampled doc- uments ranged from zero to...engineers. The approach used a retrospective content analysis of documents from weapon systems acquisi- tion programs, namely Major Defense Acquisition...January 2016, Vol. 23 No. 1 : 78–101 January 2016 The interaction between humans and the systems they use affects program success, as well as life-cycle

Drivers of dissolved organic carbon export in a subarctic catchment: Importance of microbial decomposition, sorption-desorption, peatland and lateral flow.

PubMed

Tang, Jing; Yurova, Alla Y; Schurgers, Guy; Miller, Paul A; Olin, Stefan; Smith, Benjamin; Siewert, Matthias B; Olefeldt, David; Pilesjö, Petter; Poska, Anneli

2018-05-01

Tundra soils account for 50% of global stocks of soil organic carbon (SOC), and it is expected that the amplified climate warming in high latitude could cause loss of this SOC through decomposition. Decomposed SOC could become hydrologically accessible, which increase downstream dissolved organic carbon (DOC) export and subsequent carbon release to the atmosphere, constituting a positive feedback to climate warming. However, DOC export is often neglected in ecosystem models. In this paper, we incorporate processes related to DOC production, mineralization, diffusion, sorption-desorption, and leaching into a customized arctic version of the dynamic ecosystem model LPJ-GUESS in order to mechanistically model catchment DOC export, and to link this flux to other ecosystem processes. The extended LPJ-GUESS is compared to observed DOC export at Stordalen catchment in northern Sweden. Vegetation communities include flood-tolerant graminoids (Eriophorum) and Sphagnum moss, birch forest and dwarf shrub communities. The processes, sorption-desorption and microbial decomposition (DOC production and mineralization) are found to contribute most to the variance in DOC export based on a detailed variance-based Sobol sensitivity analysis (SA) at grid cell-level. Catchment-level SA shows that the highest mean DOC exports come from the Eriophorum peatland (fen). A comparison with observations shows that the model captures the seasonality of DOC fluxes. Two catchment simulations, one without water lateral routing and one without peatland processes, were compared with the catchment simulations with all processes. The comparison showed that the current implementation of catchment lateral flow and peatland processes in LPJ-GUESS are essential to capture catchment-level DOC dynamics and indicate the model is at an appropriate level of complexity to represent the main mechanism of DOC dynamics in soils. The extended model provides a new tool to investigate potential interactions among climate change, vegetation dynamics, soil hydrology and DOC dynamics at both stand-alone to catchment scales. Copyright © 2017 Elsevier B.V. All rights reserved.

Effects of humic substances on the bioconcentration of polycyclic aromatic hydrocarbons: Correlations with spectroscopic and chemical properties of humic substances

USGS Publications Warehouse

Haitzer, M.; Abbt-Braun, G.; Traunspurger, W.; Steinberg, C.E.W.

1999-01-01

The presence of dissolved humic substances (HS, fulvic and humic acids) generally reduces the uptake of hydrophobic organic compounds into aquatic organisms. The extent of this effect depends both on the concentration and on the origin of the HS. The aim of this study was to investigate the role of qualitative differences between HS from different origins. The effects of seven different HS on the bioconcentration of pyrene and benzo[a]pyrene (BaP) in the nematode Caenorhabditis elegans were related to the spectroscopic and chemical properties of the HS. The effect of each humic material on the bioconcentration of pyrene or BaP was quantified as a 'biologically determined' partition coefficient K(DOC). We observed significant linear relationships between K(DOC) and the atomic H/C ratio, the specific absorptivity at 254 nm, the content of aromatic carbons (as determined by 13C nuclear magnetic resonance spectroscopy, the copper-complexing capacity, the content of phenolic OH groups, and the molecular weight of the HS. There was no discernible relationship of K(DOC) with the atomic (N + O)/C ratio, an indicator of the polarity of HS. Taken together, our results show that the variability in the effects of HS from different origins could be related to variations in bulk properties of the HS. Parameters describing the aromaticity of the humic materials seemed to be most useful for estimating effects of HS on the bioconcentration of pyrene and BaP.

Biochar feedstock and pyrolysis temperature effects on leachate: DOC characteristics and nitrate losses from a Brazilian Cerrado Arenosol mixed with agricultural waste biochars.

PubMed

Speratti, Alicia B; Johnson, Mark S; Sousa, Heiriane Martins; Dalmagro, Higo J; Couto, Eduardo Guimarães

2018-04-01

Dissolved organic carbon (DOC) leached from Brazilian Cerrado Arenosols can lead to carbon (C) losses and lower soil fertility, while excessive nutrient, e.g. nitrate (NO 3 - ), leaching can potentially cause water contamination. As biochar has been shown to stabilize C and retain soil nutrients, a greenhouse experiment was conducted to test different biochars' contributions to DOC and NO 3 - leaching from a sandy soil. Biochars were made from four local agricultural waste feedstocks (cotton residue, swine manure, eucalyptus sawmill residue, sugarcane filtercake) pyrolysed at 400, 500 and 600 °C. Biochar was mixed with soil at 5% weight in pots and maize seeds planted. Leachate was collected weekly for six weeks and analyzed for DOC and NO 3 - concentrations, while fluorescence spectroscopy with parallel factor analysis (PARAFAC) was used to interpret DOC characteristics. Cotton and swine manure biochar treatments had higher DOC and NO 3 - losses than eucalyptus biochar, filtercake biochar, and control treatments. Cotton and swine manure biochar treatments at high temperatures lost mostly terrestrial, humified DOC, while swine manure, filtercake, and eucalyptus biochars at low temperatures lost mostly labile, microbially-derived DOC. Through the practical use of fluorescence spectroscopy, our study identified filtercake and eucalyptus biochars as most promising for retaining DOC and NO 3 - in a Cerrado Arenosol, potentially reducing stable C and nutrient losses. Copyright © 2018 Elsevier Ltd. All rights reserved.

Improved automation of dissolved organic carbon sampling for organic-rich surface waters.

PubMed

Grayson, Richard P; Holden, Joseph

2016-02-01

In-situ UV-Vis spectrophotometers offer the potential for improved estimates of dissolved organic carbon (DOC) fluxes for organic-rich systems such as peatlands because they are able to sample and log DOC proxies automatically through time at low cost. In turn, this could enable improved total carbon budget estimates for peatlands. The ability of such instruments to accurately measure DOC depends on a number of factors, not least of which is how absorbance measurements relate to DOC and the environmental conditions. Here we test the ability of a S::can Spectro::lyser™ for measuring DOC in peatland streams with routinely high DOC concentrations. Through analysis of the spectral response data collected by the instrument we have been able to accurately measure DOC up to 66 mg L(-1), which is more than double the original upper calibration limit for this particular instrument. A linear regression modelling approach resulted in an accuracy >95%. The greatest accuracy was achieved when absorbance values for several different wavelengths were used at the same time in the model. However, an accuracy >90% was achieved using absorbance values for a single wavelength to predict DOC concentration. Our calculations indicated that, for organic-rich systems, in-situ measurement with a scanning spectrophotometer can improve fluvial DOC flux estimates by 6 to 8% compared with traditional sampling methods. Thus, our techniques pave the way for improved long-term carbon budget calculations from organic-rich systems such as peatlands. Copyright © 2015 Elsevier B.V. All rights reserved.

Determination and theoretical aspects of the equilibrium between dissolved organic matter and hydrophobic organic micropollutants in water (Kdoc).

PubMed

Krop, H B; van Noort, P C; Govers, H A

2001-01-01

Literature on the equilibrium constant for distribution between dissolved organic carbon (DOC) (Kdoc) data of strongly hydrophobic organic contaminants were collected and critically analyzed. About 900 Kdoc entries for experimental values were retrieved and tabulated, including those factors that can influence them. In addition, quantitative structure-activity relationship (QSAR) prediction equations were retrieved and tabulated. Whether a partition or association process between the contaminant and DOC takes place could not be fully established, but indications toward an association process are strong in several cases. Equilibrium between a contaminant and DOC in solution was shown to be achieved within a minute. When the equilibrium shifts in time, this was caused by either a physical or chemical change of the DOC, affecting the lighter fractions most. Adsorption isotherms turned out to be linear in the contaminant concentration for the relevant DOC concentration up to 100 mg of C/L. Eighteen experimental methods have been developed for the determination of the pertinent distribution constant. Experimental Kdoc values revealed the expected high correlation with partition coefficients over n-octanol and water (Kow) for all experimental methods, except for the HPLC and apparent solubility (AS) method. Only fluorescence quenching (FQ) and solid-phase microextraction (SPME) methods could quantify fast equilibration. Only 21% of the experimental values had a 95% confidence interval, which was statistically significantly different from zero. Variation in Kdoc values was shown to be high, caused mainly by the large variation of DOC in water samples. Even DOC from one sample gave different equilibrium constants for different DOC fractions. Measured Kdoc values should, therefore, be regarded as average values. Kdoc was shown to increase on increasing molecular mass, indicating that the molecular mass distribution is a proper normalization function for the average Kdoc at the current state of knowledge. The weakly bound fraction could easily be desorbed when other adsorbing media, such as a SepPak column or living organism, are present. The amount that moves from the DOC to the other medium will depend, among other reasons, on the size of the labile DOC fraction and the equilibrium constant of the other medium. Variation of Kdoc with temperature turned out to be small, probably caused by a small enthalpy of transfer from water to DOC. Ionic strength turned out to be more important, leading to changes of a factor of 2-5. The direction of this effect depends on the type of ion. With respect to QSAR relationships between Kdoc and macroscopic or molecular descriptors, it was concluded that only a small number of equations are available in the literature, for apolar compounds only, and with poor statistics and predictive power. Therefore, a first requirement is the improvement of the availability and quality of experimental data. Along with this, theoretical (mechanistic) models for the relationship between DOC plus contaminant descriptors on the one side and Kdoc on the other should be further developed. Correlations between Kdoc and Kow and those between the soil-water partition constant (Koc) and Kow were significantly different only in the case of natural aquatic DOC, pointing at substantial differences between these two types of organic material and at a high correspondence for other types of commercial and natural DOC.

'invisible' DOM in hourly-resolved headwater river records from Northern Amazonia

NASA Astrophysics Data System (ADS)

Pereira, R.; Bovolo, C.; Spencer, R. G.; Hernes, P. J.; Tipping, E.; Vieth-Hillebrand, A.; Chappell, N.; Lewis-Franklin, A.; Parkin, G.; Wagner, T.

2012-12-01

Global river networks annually process ~3 billion tonnes of organic carbon but only ~17% reaches the ocean. These estimates suggest rivers are not mere transportation pipes but biogeochemical reactors. Inland waters are therefore fundamental to the understanding of carbon and nutrient interactions between land and ocean. Within these global estimates, tropical rivers contribute ~two-thirds of the global dissolved organic matter flux to the ocean. Recent studies suggest that up to 50% of the CO2 outgassed from tropical rivers is derived from terrestrial organic matter and that the terrestrial-aquatic interface in river headwaters are hotspots of biochemical activity. However, to date, most tropical riverine studies focus on the main river stem or mouth and therefore the dynamics of tropical headwater organic matter cycling within the global carbon cycle are unknown. We present a geochemical and hydrological time-series (sub-hourly resolution) of river water DOC concentration, source and composition from a pristine lowland rainforest headwater of the Burro Burro River, a tributary of the Essequibo River, the 3rd largest river in S. America. We show that during and after a rainstorm event, DOC concentrations increase an order of magnitude (10 to 114mg/L) in less than 30 mins, far exceeding the entire seasonal DOC range measured in 2010 and 2011 (17-28mg/L). The source (δ13C-DOC) of DOC during the rainstorm event changes from microbial/aquatic (-21.9‰ to -25.7‰) at low/intermediate DOC concentration to C3 vegetation supply (-26.8‰ to -30.3‰) during peak DOC flushing. First radiocarbon data shows that riverine DOC is relatively young (106.8-110.9 %modern), however, tropical soils suggest a potential for organic matter to be preserved (360-1200 BP). The fundamental relationship between DOC and coloured dissolved organic matter (CDOM), measured as UV absorbance (SUVA254), holds only for low riverine DOC concentrations with proportionally high lignin contribution, whereas high levels in DOC are not explained by humic substances. Size exclusion chromatography confirms that the DOM pool is divided into two main fractions, humic substances and 'invisible' DOM, or 'iDOM'. The latter group includes non UV-absorbing organic compounds of mono- and oligosaccharides, alcohols, aldehydes, ketones and amino sugars. Our new records from Guyana show that whilst lignin phenols are present and closely track the UV absorbance (R2 = 0.97), it is iDOM that dominates the total DOC pool at peak concentrations (up to 84%). Notably, iDOM is still found in the main Burro Burro River (20-40%), indicating that iDOM has some potential to survive transport downstream. The results suggest that DOC could be significantly underestimated in tropical systems due to the observed decoupling of DOC, water colour (CDOM) and river flux related to large amounts of iDOM entering the river during rainstorm events and wet seasons. Furthermore, given that headwaters represent roughly 50-85% of the total area of tropical river catchments, it is likely that iDOM is a significant component of the terrestrial carbon and nutrient cycles. It is therefore necessary to conduct further field studies that will produce high resolution (temporal and spatial) geochemical records from a large number of tropical systems to better quantify the role of tropical inland waters in carbon and nutrient cycling.

Estimating dissolved organic carbon concentration in turbid coastal waters using optical remote sensing observations

NASA Astrophysics Data System (ADS)

Cherukuru, Nagur; Ford, Phillip W.; Matear, Richard J.; Oubelkheir, Kadija; Clementson, Lesley A.; Suber, Ken; Steven, Andrew D. L.

2016-10-01

Dissolved Organic Carbon (DOC) is an important component in the global carbon cycle. It also plays an important role in influencing the coastal ocean biogeochemical (BGC) cycles and light environment. Studies focussing on DOC dynamics in coastal waters are data constrained due to the high costs associated with in situ water sampling campaigns. Satellite optical remote sensing has the potential to provide continuous, cost-effective DOC estimates. In this study we used a bio-optics dataset collected in turbid coastal waters of Moreton Bay (MB), Australia, during 2011 to develop a remote sensing algorithm to estimate DOC. This dataset includes data from flood and non-flood conditions. In MB, DOC concentration varied over a wide range (20-520 μM C) and had a good correlation (R2 = 0.78) with absorption due to coloured dissolved organic matter (CDOM) and remote sensing reflectance. Using this data set we developed an empirical algorithm to derive DOC concentrations from the ratio of Rrs(412)/Rrs(488) and tested it with independent datasets. In this study, we demonstrate the ability to estimate DOC using remotely sensed optical observations in turbid coastal waters.

Photochemical dissolution of organic matter from resuspended sediments: Impact of source and diagenetic state on photorelease

NASA Astrophysics Data System (ADS)

Helms, J. R.; Glinski, D. A.; Mead, R. N.; Southwell, M.; Avery, G. B., Jr.; Kieber, R. J.; Skrabal, S. A.

2015-12-01

Resuspended sediments exposed to simulated solar radiation release dissolved organic carbon (DOC). However, it is unclear how the provenance of sedimentary organic matter (OM) impacts this photorelease. In the first geographically extensive study of this phenomenon, twenty three size fractionated, fine grained sediments (< ca. 10-20 μm) from a variety of drainage basins were resuspended (at suspended solid loading of 29- 255 mg/l) and exhibited a net photochemical DOC release ranging from 2 to 178 μmol/g/h. There was a logarithmic increase in photoreleased DOC vs. the proportion of sedimentary OC (%), most likely due to photon limitation at high sedimentary OC loading (i.e. high mass-specific absorption limiting light penetration). Sediment source and quality - determined using lipid biomarkers - had a significant effect on DOC photorelease. The fatty acid terrestrial aquatic ratio (TARFA) indicated that terrestrially derived sediments exhibited relatively greater DOC photorelease. The long chain carbon preference index (CPI24-34) indicated that diagenetically unaltered terrestrial OM photoreleased more DOC than diagenetically altered terrestrial OM. The short chain carbon preference index (CPI14-22) demonstrated that sediments containing diagenetically altered planktonic or algal derived OM had a greater photorelease rate of DOC than fresh algal OM. This suggests that humic substances (humus and/or adsorbed humic and fulvic acids) play an important role in the photochemical dissolution of OC regardless of whether or not they are imported from upstream (i.e. terrestrial humics) or generated within the depositional or sedimentary environment (i.e. humification of algal dissolved OM).

Flux and Seasonality of Dissolved Organic Matter From the Northern Dvina (Severnaya Dvina) River, Russia

NASA Astrophysics Data System (ADS)

Johnston, Sarah Ellen; Shorina, Natalia; Bulygina, Ekaterina; Vorobjeva, Taisya; Chupakova, Anna; Klimov, Sergey I.; Kellerman, Anne M.; Guillemette, Francois; Shiklomanov, Alexander; Podgorski, David C.; Spencer, Robert G. M.

2018-03-01

Pan-Arctic riverine dissolved organic carbon (DOC) fluxes represent a major transfer of carbon from land-to-ocean, and past scaling estimates have been predominantly derived from the six major Arctic rivers. However, smaller watersheds are constrained to northern high-latitude regions and, particularly with respect to the Eurasian Arctic, have received little attention. In this study, we evaluated the concentration of DOC and composition of dissolved organic matter (DOM) via optical parameters, biomarkers (lignin phenols), and ultrahigh resolution mass spectrometry in the Northern Dvina River (a midsized high-latitude constrained river). Elevated DOC, lignin concentrations, and aromatic DOM indicators were observed throughout the year in comparison to the major Arctic rivers with seasonality exhibiting a clear spring freshet and also some years a secondary pulse in the autumn concurrent with the onset of freezing. Chromophoric DOM absorbance at a350 was strongly correlated to DOC and lignin across the hydrograph; however, the relationships did not fit previous models derived from the six major Arctic rivers. Updated DOC and lignin fluxes were derived for the pan-Arctic watershed by scaling from the Northern Dvina resulting in increased DOC and lignin fluxes (50 Tg yr-1 and 216 Gg yr-1, respectively) compared to past estimates. This leads to a reduction in the residence time for terrestrial carbon in the Arctic Ocean (0.5 to 1.8 years). These findings suggest that constrained northern high-latitude rivers are underrepresented in models of fluxes based from the six largest Arctic rivers with important ramifications for the export and fate of terrestrial carbon in the Arctic Ocean.

Effect of biological and coagulation pre-treatments to control organic and biofouling potential components of ultrafiltration membrane in the treatment of lake water.

PubMed

Pramanik, Biplob Kumar; Kajol, Annaduzzaman; Suja, Fatihah; Md Zain, Shahrom

2017-03-01

Biological aerated filter (BAF), sand filtration (SF), alum and Moringa oleifera coagulation were investigated as a pre-treatment for reducing the organic and biofouling potential component of an ultrafiltration (UF) membrane in the treatment of lake water. The carbohydrate content was mainly responsible for reversible fouling of the UF membrane compared to protein or dissolved organic carbon (DOC) content. All pre-treatment could effectively reduce these contents and led to improve the UF filterability. Both BAF and SF markedly led to improvement in flux than coagulation processes, and alum gave greater flux than M. oleifera. This was attributed to the effective removal and/or breakdown of high molecular weight (MW) organics by biofilters. BAF led to greater improvement in flux than SF, due to greater breakdown of high MW organics, and this was also confirmed by the attenuated total reflection-Fourier transform infrared spectroscopy analysis. Coagulation processes were ineffective in removing biofouling potential components, whereas both biofilters were very effective as shown by the reduction of low MW organics, biodegradable dissolved organic carbon and assimilable organic carbon contents. This study demonstrated the potential of biological pre-treatments for reducing organic and biofouling potential component and thus improving flux for the UF of lake water treatment.

Outcome Prediction of Consciousness Disorders in the Acute Stage Based on a Complementary Motor Behavioural Tool.

PubMed

Pignat, Jean-Michel; Mauron, Etienne; Jöhr, Jane; Gilart de Keranflec'h, Charlotte; Van De Ville, Dimitri; Preti, Maria Giulia; Meskaldji, Djalel E; Hömberg, Volker; Laureys, Steven; Draganski, Bogdan; Frackowiak, Richard; Diserens, Karin

2016-01-01

Attaining an accurate diagnosis in the acute phase for severely brain-damaged patients presenting Disorders of Consciousness (DOC) is crucial for prognostic validity; such a diagnosis determines further medical management, in terms of therapeutic choices and end-of-life decisions. However, DOC evaluation based on validated scales, such as the Revised Coma Recovery Scale (CRS-R), can lead to an underestimation of consciousness and to frequent misdiagnoses particularly in cases of cognitive motor dissociation due to other aetiologies. The purpose of this study is to determine the clinical signs that lead to a more accurate consciousness assessment allowing more reliable outcome prediction. From the Unit of Acute Neurorehabilitation (University Hospital, Lausanne, Switzerland) between 2011 and 2014, we enrolled 33 DOC patients with a DOC diagnosis according to the CRS-R that had been established within 28 days of brain damage. The first CRS-R assessment established the initial diagnosis of Unresponsive Wakefulness Syndrome (UWS) in 20 patients and a Minimally Consciousness State (MCS) in the remaining13 patients. We clinically evaluated the patients over time using the CRS-R scale and concurrently from the beginning with complementary clinical items of a new observational Motor Behaviour Tool (MBT). Primary endpoint was outcome at unit discharge distinguishing two main classes of patients (DOC patients having emerged from DOC and those remaining in DOC) and 6 subclasses detailing the outcome of UWS and MCS patients, respectively. Based on CRS-R and MBT scores assessed separately and jointly, statistical testing was performed in the acute phase using a non-parametric Mann-Whitney U test; longitudinal CRS-R data were modelled with a Generalized Linear Model. Fifty-five per cent of the UWS patients and 77% of the MCS patients had emerged from DOC. First, statistical prediction of the first CRS-R scores did not permit outcome differentiation between classes; longitudinal regression modelling of the CRS-R data identified distinct outcome evolution, but not earlier than 19 days. Second, the MBT yielded a significant outcome predictability in the acute phase (p<0.02, sensitivity>0.81). Third, a statistical comparison of the CRS-R subscales weighted by MBT became significantly predictive for DOC outcome (p<0.02). The association of MBT and CRS-R scoring improves significantly the evaluation of consciousness and the predictability of outcome in the acute phase. Subtle motor behaviour assessment provides accurate insight into the amount and the content of consciousness even in the case of cognitive motor dissociation.

Bacterial production in the water column of small streams highly depends on terrestrial dissolved organic carbon

NASA Astrophysics Data System (ADS)

Graeber, Daniel; Poulsen, Jane R.; Rasmussen, Jes J.; Kronvang, Brian; Zak, Dominik; Kamjunke, Norbert

2016-04-01

In the recent years it has become clear that the largest part of the terrestrial dissolved organic carbon (DOC) pool is removed on the way from the land to the ocean. Yet it is still unclear, where in the freshwater systems terrestrial DOC is actually taken up, and for streams DOC uptake was assumed to happen mostly at the stream bottom (benthic zone). However, a recent monitoring study implies that water column but not benthic bacteria are strongly affected by the amount and composition of DOM entering streams from the terrestrial zone. We conducted an experiment to compare the reaction of the bacterial production and heterotrophic uptake in the water column and the benthic zone to a standardized source of terrestrial DOC (leaf leachate from Beech litter). In detail, we sampled gravel and water from eight streams with a gradient in stream size and land use. For each stream four different treatments were incubated at 16°C for three days and each stream: filtered stream water with gravel stones (representing benthic zone bacteria) or unfiltered stream water (representing water column bacteria), both either with (n = 5) or, without (n = 3) leaf leachate. We found that the bacterial uptake of leaf litter DOC was higher for the benthic zone likely due to the higher bacterial production compared to the water column. In contrast, the bacterial production per amount of leaf leachate DOC taken up was significantly higher for the bacteria in the water column than for those in the benthic zone. This clearly indicates a higher growth efficiency with the leaf leachate DOC for the bacteria in the water column than in the benthic zone. We found a high variability for the growth efficiency in the water column, which was best explained by a negative correlation of the DOC demand with stream width (R² = 0.86, linear correlation of log-transformed data). This was not the case for the benthic zone bacteria (R² = 0.02). This implies that water column bacteria in very small streams are more dependent on terrestrial DOC sources for their growth than those in larger streams. Based on this experiment and literature data we hypothesize that: I) The response of the bacterial production to terrestrial DOC in the water column is stronger than for the benthic zone and is decreasing with increasing stream size, likely due to the increase of autochthonous DOC production within the stream. II) Independent of stream size there is only a small reaction to terrestrial DOC for the bacterial production in the benthic zone, either due to internal DOC production or a stronger dependency on particulate organic carbon. We propose that this terrestrial DOC dependency concept is generally applicable, however, its potential underlying mechanisms and concept predictions need to be tested further for other stream and river ecosystems.

Dilute Oxygen Combustion Phase IV Final Report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Riley, M.F.

2003-04-30

Novel furnace designs based on Dilute Oxygen Combustion (DOC) technology were developed under subcontract by Techint Technologies, Coraopolis, PA, to fully exploit the energy and environmental capabilities of DOC technology and to provide a competitive offering for new furnace construction opportunities. Capital cost, fuel, oxygen and utility costs, NOx emissions, oxide scaling performance, and maintenance requirements were compared for five DOC-based designs and three conventional air5-fired designs using a 10-year net present value calculation. A furnace direct completely with DOC burners offers low capital cost, low fuel rate, and minimal NOx emissions. However, these benefits do not offset the costmore » of oxygen and a full DOC-fired furnace is projected to cost $1.30 per ton more to operate than a conventional air-fired furnace. The incremental cost of the improved NOx performance is roughly $6/lb NOx, compared with an estimated $3/lb. NOx for equ8pping a conventional furnace with selective catalytic reduction (SCCR) technology. A furnace fired with DOC burners in the heating zone and ambient temperature (cold) air-fired burners in the soak zone offers low capital cost with less oxygen consumption. However, the improvement in fuel rate is not as great as the full DOC-fired design, and the DOC-cold soak design is also projected to cost $1.30 per ton more to operate than a conventional air-fired furnace. The NOx improvement with the DOC-cold soak design is also not as great as the full DOC fired design, and the incremental cost of the improved NOx performance is nearly $9/lb NOx. These results indicate that a DOC-based furnace design will not be generally competitive with conventional technology for new furnace construction under current market conditions. Fuel prices of $7/MMBtu or oxygen prices of $23/ton are needed to make the DOC furnace economics favorable. Niche applications may exist, particularly where access to capital is limited or floor space limitations are critical. DOC technology will continue to have a highly competitive role in retrofit applications requiring increases in furnace productivity.« less

Radiocarbon Depression in Aquatic Foodwebs of the Colorado River, USA: Coupling Between Carbonate Weathering and the Biosphere

NASA Astrophysics Data System (ADS)

Sickman, J. O.; Huang, W.; Lucero, D.; Anderson, M.

2012-12-01

The 14C isotopic composition of living organisms is generally considered to be in isotopic equilibrium with atmosphere CO2. During the course of investigations of aquatic foodwebs of the Colorado River, we measured substantial radiocarbon depression of organisms within planktonic and benthic foodwebs of Copper Basin Reservoir, a short residence-time water body at the intake to the Colorado River Aqueduct. All trophic levels had depressed radiocarbon content with inferred "age" of ca. 1,200 radiocarbon years (range: 0.85 to 0.87 fraction modern carbon (fmc)). Additional measurements of the radiocarbon content of dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC) were made in other major rivers in California (New (near Salton Sea), Santa Ana (near Riverside), San Joaquin (near Fresno) and Salinas (near San Luis Obispo)). In the New River (which is composed primarily of irrigation tailwater derived from the Colorado River), the radiocarbon values for DIC closely matched those found in biota of the Copper Basin Reservoir (0.85 to 0.87 fmc), but radiocarbon values for DOC were slightly higher (0.91 to 0.95 fmc). In the other California rivers, radiocarbon concentrations in DIC were generally below modern and lower than corresponding levels in DOC; in the case of the Santa Ana River, DOC was older than DIC as a result of wastewater inputs from upstream treatment plants. Together these data suggest that the carbonate equilibrium of California rivers is influenced by weathering of carbonate minerals which produces HCO3- with no 14C. We hypothesize that this dead carbon can move into aquatic foodwebs via algae and phytoplankton uptake during photosynthesis, depressing the 14C content of aquatic foodwebs below that of the atmosphere. Based on a simple two-component mixing model incorporating carbonate weathering and atmospheric CO2, we estimate that 15-17% of the carbon in the aquatic foodweb of Copper Basin is derived directly from mineral weathering of carbonate minerals in the Colorado River basin. Worldwide, only a few cases of radiocarbon depression have been reported for aquatic ecosystems. The extent of 14C depression in the Colorado River is much larger than that observed in the Arctic or deep ocean environments.

Influences of glacial melt and permafrost thaw on the age of dissolved organic carbon in the Yukon River basin

USGS Publications Warehouse

Aiken, George R.; Spencer, Robert G.M.; Striegl, Robert G.; Schuster, Paul F.; Raymond, Peter A.

2014-01-01

Responses of near-surface permafrost and glacial ice to climate change are of particular significance for understanding long-term effects on global carbon cycling and carbon export by high-latitude northern rivers. Here we report Δ14C-dissolved organic carbon (DOC) values and dissolved organic matter optical data for the Yukon River, 15 tributaries of the Yukon River, glacial meltwater, and groundwater and soil water end-member sources draining to the Yukon River, with the goal of assessing mobilization of aged DOC within the watershed. Ancient DOC was associated with glacial meltwater and groundwater sources. In contrast, DOC from watersheds dominated by peat soils and underlain by permafrost was typically enriched in Δ14C indicating that degradation of ancient carbon stores is currently not occurring at large enough scales to quantitatively influence bulk DOC exports from those landscapes. On an annual basis, DOC exported was predominantly modern during the spring period throughout the Yukon River basin and became older through summer-fall and winter periods, suggesting that contributions of older DOC from soils, glacial meltwaters, and groundwater are significant during these months. Our data indicate that rapidly receding glaciers and increasing groundwater inputs will likely result in greater contributions of older DOC in the Yukon River and its tributaries in coming decades.

36 year trends in dissolved organic carbon export from Finnish rivers to the Baltic Sea.

PubMed

Räike, Antti; Kortelainen, Pirkko; Mattsson, Tuija; Thomas, David N

2012-10-01

Increasing dissolved organic carbon (DOC) concentrations in lakes, rivers and streams in northern mid latitudes have been widely reported during the last two decades, but relatively few studies have dealt with trends in DOC export. We studied the export of DOC from Finnish rivers to the Baltic Sea between 1975 and 2010, and estimated trends in DOC fluxes (both flow normalised and non-normalised). The study encompassed the whole Finnish Baltic Sea catchment area (301,000 km(2)) covering major land use patterns in the boreal zone. Finnish rivers exported annually over 900,000 t DOC to the Baltic Sea, and the mean area specific export was 3.5 t km(-2). The highest export (7.3t km(-2)) was measured in peat dominated catchments, whereas catchments rich in lakes had the lowest export (2.2 t km(-2)). Inter-annual variation in DOC export was high and controlled mainly by hydrology. There was no overall trend in the annual water flow, although winter flow increased in northern Finland over 36 years. Despite the numerous studies showing increases in DOC concentrations in streams and rivers in the northern hemisphere, we could not find any evidence of increases in DOC export to the northern Baltic Sea from Finnish catchments since 1975. Copyright © 2012 Elsevier B.V. All rights reserved.

Greenland Ice Sheet exports labile organic carbon to the Arctic oceans

NASA Astrophysics Data System (ADS)

Lawson, E. C.; Wadham, J. L.; Tranter, M.; Stibal, M.; Lis, G. P.; Butler, C. E. H.; Laybourn-Parry, J.; Nienow, P.; Chandler, D.; Dewsbury, P.

2013-12-01

Runoff from small glacier systems contains dissolved organic carbon (DOC), rich in protein-like, low molecular weight (LMW) compounds, designating glaciers as an important source of bioavailable carbon for downstream heterotrophic activity. Fluxes of DOC and particulate organic carbon (POC) exported from large Greenland catchments, however, remain unquantified, despite the Greenland Ice Sheet (GrIS) being the largest source of global glacial runoff (ca. 400 km3 yr-1). We report high and episodic fluxes of POC and DOC from a large (1200 km2) GrIS catchment during contrasting melt seasons. POC dominates organic carbon (OC) export (70-89% on average), is sourced from the ice sheet bed and contains a significant bioreactive component (9% carbohydrates). A major source for the "bioavailable" (free carbohydrates) LMW-DOC fraction is microbial activity on the ice sheet surface, with some further addition of LMW-DOC to meltwaters by biogeochemical processes at the ice sheet bed. The bioavailability of the exported DOC (30-58%) to downstream marine microorganisms is similar to that reported from other glacial watersheds. Annual fluxes of DOC and free carbohydrates during two melt seasons were similar, despite the ~ 2 fold difference in runoff fluxes, suggesting production-limited DOC sources. POC fluxes were also insensitive to an increase in seasonal runoff volumes, indicating supply-limitation of suspended sediment in runoff. Scaled to the GrIS, the combined DOC and POC fluxes (0.13-0.17 Tg C yr-1 DOC, 0.36-1.52 Tg C yr-1 mean POC) are of a similar order of magnitude to a large Arctic river system, and hence represent an important OC source to the North Atlantic, Greenland and Labrador Seas.

Dissolved organic carbon fluxes in the Middle Atlantic Bight: An integrated approach based on satellite data and ocean model products

PubMed Central

Mannino, Antonio; Signorini, Sergio R.; Novak, Michael G.; Wilkin, John; Friedrichs, Marjorie A. M.; Najjar, Raymond G.

2017-01-01

Continental margins play an important role in global carbon cycle, accounting for 15–21% of the global marine primary production. Since carbon fluxes across continental margins from land to the open ocean are not well constrained, we undertook a study to develop satellite algorithms to retrieve dissolved organic carbon (DOC) and combined these satellite data with physical circulation model products to quantify the shelf boundary fluxes of DOC for the U.S. Middle Atlantic Bight (MAB). Satellite DOC was computed through seasonal relationships of DOC with colored dissolved organic matter absorption coefficients, which were derived from an extensive set of in situ measurements. The multiyear time series of satellite-derived DOC stocks (4.9 Teragrams C; Tg) shows that freshwater discharge influences the magnitude and seasonal variability of DOC on the continental shelf. For the 2010–2012 period studied, the average total estuarine export of DOC into the MAB shelf is 0.77 Tg C yr−1 (year). The integrated DOC tracer fluxes across the shelf boundaries are 12.1 Tg C yr−1 entering the MAB from the southwest alongshore boundary, 18.5 Tg C yr−1 entering the MAB from the northeast alongshore boundary, and 29.0 Tg C yr−1 flowing out of the MAB across the entire length of the 100 m isobath. The magnitude of the cross-shelf DOC flux is quite variable in time (monthly) and space (north to south). The highly dynamic exchange of water along the shelf boundaries regulates the DOC budget of the MAB at subseasonal time scales. PMID:29201582

Character, quality and bioavailability of Dissolved Organic Carbon (DOC) in a boreal stream network (Invited)

NASA Astrophysics Data System (ADS)

Laudon, H.; Berggren, M.; Agren, A.; Jansson, M.

2010-12-01

The conceptual understanding of the role of terrestrially derived dissolved organic carbon (DOC) in freshwaters has been changing rapidly. While it was once considered mainly a pool of recalcitrant compounds, DOC is now better known for its interactivity and ability to affect both the biogeochemistry and ecology of streams, rivers and lakes. Here we summarize the recent work from the multi-investigatory project conducted in the Krycklan Catchment Study in Sweden with an emphasis on the spatial and temporal variability of the character and bioavailability of DOC. In total, 15 streams and their adjacent soils have been investigated. The streams cover a forest-wetland gradient, spanning from 0% to 69% wetland coverage (hence with a 100% to 31% forest cover). Lower values of the ratio between absorbance measured at 254 nm and 365 nm (A254/A365), in both soil plots and streams, indicated that wetland-derived DOC has a higher average molecular weight than forest DOC. Higher SUVA254 (DOC specific ultraviolet absorption at 254 nm) in wetland runoff indicated more aromatic DOC from wetlands than forests. In accordance, low molecular weight non-aromatic compounds such as free organic acids (OA), amino acids (AA) and carbohydrates (CH) had higher quantities in the forested streams. We have shown that a variety of the OA, AA and CH compounds can be significantly assimilated by bacteria, meeting 15-100% of the bacterial carbon demand and explaining most of the observed variance in bacterial growth efficiency. We can now also show that in small homogenous catchments, the hydrological functioning provides a first order control on the temporal variability of stream water DOC and its quality. As a consequence, streams with heterogeneous catchments undergo a temporal switch in the DOC source. In a typical boreal catchment of 10-20% wetlands, DOC originates predominantly from wetland sources during low flow conditions whereas the major source of DOC originates from forested areas of the catchment during high flow resulting in dramatic shifts in the character and bioavailability of DOC during different flow conditions. By connecting knowledge about the sources and quality of DOC with detailed hydrological process understanding, an improved representation of stream water DOC regulation can be provided. This work also illustrates that the sensitivity of stream water DOC in the boreal landscape ultimately depends on how individual landscape elements are affected, the proportion of these landscape elements and how these changes are propagated downstream.

Estuarine studies in upper Grays Harbor, Washington

USGS Publications Warehouse

Beverage, Joseph P.; Swecker, Milton N.

1969-01-01

Improved management of the water resources of Grays Harbor, Wash., requires more data on the water quality of the harbor and a better understanding of the influences of industrial and domestic wastes on the local fisheries resources. To provide a more comprehensive understanding of these influences, the U.S. Geological Survey joined other agencies in a cooperative study of Grays Harbor. This report summarizes the Survey's study of circulation patterns, description of water-quality conditions, and characterization of bottom material in the upper harbor. Salt water was found to intrude at least as far as Montesano, 28.4 nautical miles from the mouth of the harbor. Longitudinal salinity distributions were used to compute dispersion (diffusivity) coefficients ranging from 842 to 3,520 square feet per second. These values were corroborated by half-tidal-cycle dye studies. The waters of the harbor were found to be well mixed after extended periods of low fresh-water flow but stratified at high flows. Salinity data were used lo define the cumulative 'mean age' of the harbor water, which may be used to approximate a mean 'flushing time.' Velocity-time curves for the upper harbor are distorted from simple harmonic functions owing to channel geometry and frictional effects. Surface and bottom velocity data were used to estimate net tidal 'separation' distance, neglecting vertical mixing. Net separation distances between top and bottom water ranged from 1.65 nautical miles when fresh-water inflow was 610 cubic feet per second to 13.4 miles when inflow was 15,900 cubic feet per second. The cumulative mean age from integration of the fresh-water velocity equation was about twice that obtained from the salinity distribution. Excursion distances obtained with dye over half-tidal cycles exceeded those estimated from longitudinal salinity distributions and those obtained by earlier investigators who used floats. Net tidal excursions were as much as twice those obtained with floats. The carbon content of bottom materials was related to channel fine material: C= 0.315+0.0238 F where C is in percent by dry weight, and F is percent by weight finer than 0.062 millimeter. Carbon content was low upstream and downstream of the upper harbor area, and high in the Cow Point-Rennie Island reach. The high-carbon-content reach coincides with the general area of a dissolved-oxygen sag. The logarithm of the fresh-water discharge gave a high degree of correlation with daily maximum specific conductance at Cosmopolis. The regression equation is: Kc max---- 76.4-- 17.7 logl0 Qf where Kc max is in millimhos at 25 ? Celsius (centigrade), and Qf is the estimated daily fresh-water discharge, in cubic feet per second. Dissolved oxygen is the most critical water-quality parameter in Grays Harbor. At Cosmopolis, the daily minimum dissolved oxygen content, DOc min, correlated well with discharge and tidal range, delta H. The regression equation relating the variables is: DOc min---- 6.03 + 0.00096 Qf - 0.291 delta H in which DOc min is in milligrams per liter and delta H is in feet. The upper harbor was found to contain 250 million cubic feet less water than average during the critical low-flow period, on the basis of the frequency distribution of predicted tides. About 78,000 pounds of dissolved oxygen is thus unavailable for oxidation of waste during summer.

Ionic strength and DOC determinations from various freshwater sources to the San Francisco Bay

USGS Publications Warehouse

Hunter, Y.R.; Kuwabara, J.S.

1994-01-01

An exact estimation of dissolved organic carbon (DOC) within the salinity gradient of zinc and copper metals is significant in understanding the limit to which DOC could influence metal speciation. A low-temperature persulfate/oxygen/ultraviolet wet oxidation procedure was utilized for analyzing DOC samples adapted for ionic strength from major freshwater sources of the northern and southern regions of San Francisco Bay. The ionic strength of samples was modified with a chemically defined seawater medium up to 0.7M. Based on the results, a minimum effect of ionic strength on oxidation proficiency for DOC sources to the Bay over an ionic strength gradient of 0.0 to 0.7 M was observed. There was no major impacts of ionic strength on two Suwanee River fulvic acids. In general, the noted effects associated with ionic strength were smaller than the variances seen in the aquatic environment between high- and low-temperature methods.

Influence of water chemistry on the acute toxicity of copper and zinc to the cladoceran Ceriodaphnia cf dubia.

PubMed

Hyne, Ross V; Pablo, Fleur; Julli, Moreno; Markich, Scott J

2005-07-01

This study determined the influence of key water chemistry parameters (pH, alkalinity, dissolved organic carbon [DOC], and hardness) on the aqueous speciation of copper and zinc and its relationship to the acute toxicity of these metals to the cladoceran Ceriodaphnia cf dubia. Immobilization tests were performed for 48-h in synthetic or natural waters buffered at various pH values from 5.5 to 8.4 (other chemical parameters held constant). The toxicity of copper to C. cf dubia decreased fivefold with increasing pH, whereas the toxicity of zinc increased fivefold with increasing pH. The effect of DOC on copper and zinc toxicity to C. cf dubia was determined using natural fulvic acid in the synthetic water. Increasing DOC was found to decrease linearly the toxicity of copper, with the mean effect concentration of copper that immobilized 50% of the cladocerans (EC50) value 45 times higher at 10 mg/L, relative to 0.1 mg/L DOC at pH 6.5. In contrast, the addition of 10 mg/L DOC only resulted in a very small (1.3-fold) reduction in the toxicity of zinc to C. cf dubia. Copper toxicity to C. cf dubia generally did not vary as a function of hardness, whereas zinc toxicity was reduced by a factor of only two, with an increase in water hardness from 44 to 374 mg CaCO3/L. Increasing bicarbonate alkalinity of synthetic waters (30-125 mg/L as CaCO3) decreased the toxicity of copper up to fivefold, which mainly could be attributed to the formation of copper-carbonate complexes, in addition to a pH effect. The toxicity of copper added to a range of natural waters with varying DOC content, pH, and hardness was consistent with the toxicity predicted using the data obtained from the synthetic waters.

Stoichiometric determination of nitrate fate in agricultural ecosystems during rainfall events.

PubMed

Xu, Zuxin; Wang, Yiyao; Li, Huaizheng

2015-01-01

Ecologists have found a close relationship between the concentrations of nitrate (NO3-) and dissolved organic carbon (DOC) in ecosystems. However, it is difficult to determine the NO3- fate exactly because of the low coefficient in the constructed relationship. In the present paper, a negative power-function equation (r(2) = 0.87) was developed by using 411 NO3- data points and DOC:NO3- ratios from several agricultural ecosystems during different rainfall events. Our analysis of the stoichiometric method reveals several observations. First, the NO3- concentration demonstrated the largest changes when the DOC:NO3- ratio increased from 1 to 10. Second, the biodegradability of DOC was an important factor in controlling the NO3- concentration of agricultural ecosystems. Third, sediment was important not only as a denitrification site, but also as a major source of DOC for the overlying water. Fourth, a high DOC concentration was able to maintain a low NO3- concentration in the groundwater. In conclusion, this new stoichiometric method can be used for the accurate estimation and analysis of NO3- concentrations in ecosystems.

Stabilization/solidification of an alkyd paint waste by carbonation of waste-lime based formulations.

PubMed

Arce, R; Galán, B; Coz, A; Andrés, A; Viguri, J R

2010-05-15

The application of solvent-based paints by spraying in paint booths is extensively used in a wide range of industrial activities for the surface treatment of a vast array of products. The wastes generated as overspray represent an important environmental and managerial problem mainly due to the hazardous characteristics of the organic solvent, rendering it necessary to appropriately manage this waste. In this paper a solidification/stabilization (S/S) process based on accelerated carbonation was investigated as an immobilization pre-treatment prior to the disposal, via landfill, of an alkyd solvent-based paint waste coming from the automotive industry; the purpose of this S/S process was to immobilize the contaminants and reduce their release into the environment. Different formulations of paint waste with lime, lime-coal fly-ash and lime-Portland cement were carbonated to study the effect of the water/solid ratio and carbonation time on the characteristics of the final product. To assess the efficiency of the studied S/S process, metals, anions and dissolved organic carbon (DOC) were analyzed in the leachates obtained from a battery of compliance and characterization leaching tests. Regarding the carbonation of paint waste-lime formulations, a mathematical expression has been proposed to predict the results of the leachability of DOC from carbonated mixtures working at water/solid ratios from 0.2 to 0.6. However, lower DOC concentrations in leachates (400mg/kg DOC in L/S=10 batch leaching test) were obtained when carbonation of paint waste-lime-fly-ash mixtures was used at 10h carbonation and water to solid ratio of 0.2. The flammability characteristics, the total contents of contaminants and the contaminant release rate in compliance leaching tests provide evidence for a final product suitable for deposition in non-hazardous landfills. The characterization of this carbonated sample using a dynamic column leaching test shows a high stabilization of metals, partial immobilization of Cl(-), SO(4)(2-), F(-) and limited retention of DOC. However, the obtained results improve the previous findings obtained after the paint waste S/S using uncarbonated formulations and would be a useful pre-treatment technique of the alkyd paint waste prior to its disposal in a landfill. Copyright (c) 2009 Elsevier B.V. All rights reserved.

Effect of dissolved organic matter (DOM) of contrasting origins on Cu and Pb speciation and toxicity to Paracentrotus lividus larvae.

PubMed

Sánchez-Marín, Paula; Santos-Echeandía, Juan; Nieto-Cid, Mar; Alvarez-Salgado, Xosé Antón; Beiras, Ricardo

2010-01-31

Water samples of contrasting origin, including natural seawater, two sediment elutriates and sewage-influenced seawater, were collected and obtained to examine the effect of the dissolved organic matter (DOM) present on metal bioavailability. The carbon content (DOC) and the optical properties (absorbance and fluorescence) of the coloured DOM fraction (CDOM) of these materials were determined. Cu and Pb complexation properties were measured by anodic stripping voltammetry (ASV) and the effect of DOM on Cu and Pb bioavailability was studied by means of the Paracentrotus lividus embryo-larval bioassay. Sediment elutriates and sewage-influenced water (1) were enriched 1.4-1.7 times in DOC; (2) absorbed and reemitted more light; and (3) presented higher Cu complexation capacities (L(Cu)) than the natural seawater used for their preparation. L(Cu) varied from 0.08 microM in natural seawater to 0.3 and 0.5 microM in sediment elutriates and sewage-influenced water, respectively. Differences in DOC, CDOM and Cu complexation capacities were reflected in Cu toxicity. DOM enriched samples presented a Cu EC(50) of 0.64 microM, significantly higher than the Cu EC(50) of natural and artificial seawater, which was 0.38 microM. The protecting effect of DOM on Cu toxicity greatly disappeared when the samples were irradiated with high intensity UV-light. Cu toxicity could be successfully predicted considering ASV-labile Cu concentrations in the samples. Pb complexation by DOM was only detected in the DOM-enriched samples and caused little effect on Pb EC(50). This effect was contrary for both elutriates: one elutriate reduced Pb toxicity in comparison with the control artificial seawater, while the other increased it. UV irradiation of the samples caused a marked increase in Pb toxicity, which correlated with the remaining DOC concentration. DOM parameters were related to Cu speciation and toxicity: good correlations were found between DOC and Cu EC(50), while L(Cu) correlated better with the fluorescence of marine humic substances. The present results stress the importance of characterizing not only the amount but also the quality of seawater DOM to better predict ecological effects from total metal concentration data. Copyright (c) 2009 Elsevier B.V. All rights reserved.

The effects of salinity, pH, and dissolved organic matter on acute copper toxicity to the rotifer, Brachionus plicatilis ("L" strain).

PubMed

Arnold, W R; Diamond, R L; Smith, D S

2010-08-01

This paper presents data from original research for use in the development of a marine biotic ligand model and, ultimately, copper criteria for the protection of estuarine and marine organisms and their uses. Ten 48-h static acute (unfed) copper toxicity tests using the euryhaline rotifer Brachionus plicatilis ("L" strain) were performed to assess the effects of salinity, pH, and dissolved organic matter (measured as dissolved organic carbon; DOC) on median lethal dissolved copper concentrations (LC50). Reconstituted and natural saltwater samples were tested at seven salinities (6, 11, 13, 15, 20, 24, and 29 g/L), over a pH range of 6.8-8.6 and a range of dissolved organic carbon of <0.5-4.1 mg C/L. Water chemistry analyses (alkalinity, calcium, chloride, DOC, hardness, magnesium, potassium, sodium, salinity, and temperature) are presented for input parameters to the biotic ligand model. In stepwise multiple regression analysis of experimental results where salinity, pH, and DOC concentrations varied, copper toxicity was significantly related only to the dissolved organic matter content (pH and salinity not statistically retained; alpha=0.05). The relationship of the 48-h dissolved copper LC50 values and dissolved organic carbon concentrations was LC50 (microg Cu/L)=27.1xDOC (mg C/L)1.25; r2=0.94.

Seasonal Changes of DOC Composition of Rivers in Temperate Monsoon Climates

NASA Astrophysics Data System (ADS)

Oh, N. H.; Shin, Y.; Lee, E. J.; Hur, J.

2014-12-01

The spatial and seasonal dynamics of dissolved organic carbon (DOC) composition and biodegradability were investigated for the five largest rivers in the Republic of Korea during the years 2012 - 2013 using dark incubation experiments and spectroscopic measurements, including parallel factor analysis (PARAFAC). The DOC concentrations of the rivers in relatively steep and forest-dominated basins were <~2 mg L-1, and remained relatively constant over the seasons. In contrast, those of the rivers influenced by urban and agricultural activities rose up to 5.4 mg L-1, which was decreased to ~2 mg L-1 during the summer monsoon period, indicating that increased precipitation had the effect of dilution. Among the fluorescence components, terrestrial humic-like components were dominant in all the rivers except for one, where tyrosine- or tryptophan-like compounds were the major component. However, terrestrial humic-like components became dominant in all five of the rivers after high precipitation which occurred during the monsoon season, during which ~76% of the annual precipitation was received. Considering that 64% of South Korea is forested, our results suggest that the forests could be a large source of riverine DOC, elevating the DOC loads during monsoon rainfall. Although more DOC could be degraded when DOC input increased, regardless of its sources, the percent biodegradability was reduced with increased proportions of terrestrially derived and aromatic compounds. These results suggest that the relatively stable and terrestrial humic-like compounds released during the monsoon rainfall could reduce the potential of microbial respiration of riverine DOC and evasion of river CO2 to the atmosphere, despite of the increase in the DOC load.

Dissolved organic carbon fluxes from soils in the Alaskan coastal temperate rainforest

NASA Astrophysics Data System (ADS)

D'Amore, D. V.; Edwards, R.; Hood, E. W.; Herendeen, P. A.; Valentine, D.

2011-12-01

Soil saturation and temperature are the primary factors that influence soil carbon cycling. Interactions between these factors vary by soil type, climate, and landscape position, causing uncertainty in predicting soil carbon flux from. The soils of the North American perhumid coastal temperate rainforest (NCTR) store massive amounts of carbon, yet there is no estimate of dissolved organic carbon (DOC) export from different soil types in the region. There are also no working models that describe the influence of soil saturation and temperature on the export of DOC from soils. To address this key information gap, we measured soil water table elevation, soil temperature, and soil and stream DOC concentrations to calculate DOC flux across a soil hydrologic gradient that included upland soils, forested wetland soils, and sloping bog soils in the NCTR of southeast Alaska. We found that increased soil temperature and frequent fluctuations of soil water tables promoted the export of large quantities of DOC from wetland soils and relatively high amounts of DOC from mineral soils. Average area-weighted DOC flux ranged from 7.7 to 33.0 g C m-2 y-1 across a gradient of hydropedologic soil types. The total area specific export of carbon as DOC for upland, forested wetland and sloping bog catchments was 77, 306, and 329 Kg C ha-1 y-1 respectively. The annual rate of carbon export from wetland soils in this region is among the highest reported in the literature. These findings highlight the importance of terrestrial-aquatic fluxes of DOC as a pathway for carbon loss in the NCTR.

Multi-site Field Verification of Laboratory Derived FDOM Sensor Corrections: The Good, the Bad and the Ugly

NASA Astrophysics Data System (ADS)

Saraceno, J.; Shanley, J. B.; Aulenbach, B. T.

2014-12-01

Fluorescent dissolved organic matter (FDOM) is an excellent proxy for dissolved organic carbon (DOC) in natural waters. Through this relationship, in situ FDOM can be utilized to capture both high frequency time series and long term fluxes of DOC in small streams. However, in order to calculate accurate DOC fluxes for comparison across sites, in situ FDOM data must be compensated for matrix effects. Key matrix effects, include temperature, turbidity and the inner filter effect due to color. These interferences must be compensated for to develop a reasonable relationship between FDOM and DOC. In this study, we applied laboratory-derived correction factors to real time data from the five USGS WEBB headwater streams in order to gauge their effectiveness across a range of matrix effects. The good news is that laboratory derived correction factors improved the predicative relationship (higher r2) between DOC and FDOM when compared to uncorrected data. The relative importance of each matrix effect (i.e. temperature) varied by site and by time, implying that each and every matrix effect should be compensated for when available. In general, temperature effects were more important on longer time scales, while corrections for turbidity and DOC inner filter effects were most prevalent during hydrologic events, when the highest instantaneous flux of DOC occurred. Unfortunately, even when corrected for matrix effects, in situ FDOM is a weaker predictor of DOC than A254, a common surrogate for DOC, implying that either DOC fluoresces at varying degrees (but should average out over time), that some matrix effects (e.g. pH) are either unaccounted for or laboratory-derived correction factors do not encompass the site variability of particles and organics. The least impressive finding is that the inherent dependence on three variables in the FDOM correction algorithm increases the likelihood of record data gaps which increases the uncertainty in calculated DOC flux values.

Decreasing DOC trends in soil solution along the hillslopes at two IM sites in southern Sweden--geochemical modeling of organic matter solubility during acidification recovery.

PubMed

Löfgren, Stefan; Gustafsson, Jon Petter; Bringmark, Lage

2010-12-01

Numerous studies report increased concentrations of dissolved organic carbon (DOC) during the last two decades in boreal lakes and streams in Europe and North America. Recently, a hypothesis was presented on how various spatial and temporal factors affect the DOC dynamics. It was concluded that declining sulphur deposition and thereby increased DOC solubility, is the most important driver for the long-term DOC concentration trends in surface waters. If this recovery hypothesis is correct, the DOC levels should increase both in the soil solution as well as in the surrounding surface waters as soil pH rises and the ionic strength declines due to the reduced input of SO(4)(2-) ions. In this project a geochemical model was set up to calculate the net humic charge and DOC solubility trends in soils during the period 1996-2007 at two integrated monitoring sites in southern Sweden, showing clear signs of acidification recovery. The Stockholm Humic Model was used to investigate whether the observed DOC solubility is related to the humic charge and to examine how pH and ionic strength influence it. Soil water data from recharge and discharge areas, covering both podzols and riparian soils, were used. The model exercise showed that the increased net charge following the pH increase was in many cases counteracted by a decreased ionic strength, which acted to decrease the net charge and hence the DOC solubility. Thus, the recovery from acidification does not necessarily have to generate increasing DOC trends in soil solution. Depending on changes in pH, ionic strength and soil Al pools, the trends might be positive, negative or indifferent. Due to the high hydraulic connectivity with the streams, the explanations to the DOC trends in surface waters should be searched for in discharge areas and peat lands. Copyright © 2010 Elsevier B.V. All rights reserved.

Prokaryotic degradation of high molecular weight dissolved organic matter in the deep-sea waters of NW Mediterranean Sea under in situ temperature and pressure conditions during contrasted hydrological conditions

NASA Astrophysics Data System (ADS)

Tamburini, C.; Boutrif, M.; Garel, M.; Sempéré, R.; Repeta, D.; Charriere, B.; Nerini, D.; Panagiotopoulos, C.

2016-02-01

The contribution of the semi-labile dissolved organic carbon (DOC) to the global prokaryotic production has been assessed in very few previous studies. Some experiments show rapid utilization of semi-reactive DOC by prokaryotes, while other experiments show almost no utilization at all. However, all these studies did not take into account the role of hydrostatic pressure for the degradation of organic matter. In this study, we investigate (1) the degradation of "natural" high molecular weight DOM HMW-DOM (obtained after ultrafiltration) and (2) the uptake of labeled extracellular polymeric substances (3H-EPS) incubated with deep-sea water samples (2000 m-depth, NW Mediterranean Sea) under in situ pressure conditions (HP) and under atmospheric compression after decompression of the deep samples (ATM) during stratified and mixed water conditions (deep sea convection). Our results indicated that during HP incubations DOC exhibited the highest degradation rates (kHP DOC = 0.82 d-1) compared to the ATM conditions were no or few degradation was observed (kATM DOC= 0.007 d-1). An opposite trend was observed for the HP incubations from mixed deep water masses. HP incubation measurements displayed the lowest DOC degradation (kHP DOC=0.031 d-1) compared to the ATM conditions (kATM DOC=0.62 d-1). These results imply the presence of allochthonous prokaryotic cells in deep-sea samples after a winter water mass convection. Same trends were found using 3H-EPS uptake rates which were higher at HP than at ATM conditions during stratified period conditions whereas the opposite patterns were observed during deep-sea convection event. Moreover, we found than Euryarchaea were the main contributors to 3H-EPS assimilation at 2000m-depth, representing 58% of the total cells actively assimilating 3H-EPS. This study demonstrates that remineralization rates of semi-labile DOC in deep NW Med. Sea are controlled by the prokaryotic communities, which are influenced by the hydrological conditions of the water column.

Dissolved organic carbon modulates mercury concentrations in insect subsidies from streams to terrestrial consumers

PubMed Central

Chaves-Ulloa, Ramsa; Taylor, Brad W.; Broadley, Hannah J.; Cottingham, Kathryn L.; Baer, Nicholas A.; Weathers, Kathleen C.; Ewing, Holly A.; Chen, Celia Y.

2016-01-01

Mercury (Hg) concentrations in aquatic environments have increased globally, exposing consumers of aquatic organisms to high Hg levels. For both aquatic and terrestrial consumers, exposure to Hg depends on their food sources as well as environmental factors influencing Hg bioavailability. The majority of the research on the transfer of methylmercury (MeHg), a toxic and bioaccumulating form of Hg, between aquatic and terrestrial food webs has focused on terrestrial piscivores. However, a gap exists in our understanding of the factors regulating MeHg bioaccumulation by non-piscivorous terrestrial predators, specifically consumers of adult aquatic insects. Because dissolved organic carbon (DOC) binds tightly to MeHg, affecting its transport and availability in aquatic food webs, we hypothesized that DOC affects MeHg transfer from stream food webs to terrestrial predators feeding on emerging adult insects. We tested this hypothesis by collecting data over two years from 10 low-order streams spanning a broad DOC gradient in the Lake Sunapee watershed in New Hampshire. We found that streamwater MeHg concentration increased linearly with DOC concentration. However, streams with the highest DOC concentrations had emerging stream prey and spiders with lower MeHg concentrations than streams with intermediate DOC concentrations; a pattern that is similar to fish and larval aquatic insects. Furthermore, high MeHg concentrations found in spiders show that MeHg transfer in adult aquatic insects is an overlooked but potentially significant pathway of MeHg bioaccumulation in terrestrial food webs. Our results suggest that although MeHg in water increases with DOC, MeHg concentrations in stream and terrestrial consumers did not consistently increase with increases in streamwater MeHg concentrations. In fact, there was a change from a positive to a negative relationship between aqueous exposure and bioaccumulation at streamwater MeHg concentrations associated with DOC above around 5 mg/L. Thus, our study highlights the importance of stream DOC for MeHg dynamics beyond stream boundaries, and shows that factors modulating MeHg bioavailability in aquatic systems can affect the transfer of MeHg to terrestrial predators via aquatic subsidies. PMID:27755696

Riverine organic matter composition and fluxes to Hudson Bay

NASA Astrophysics Data System (ADS)

Kuzyk, Z. Z. A.; Macdonald, R. W.; Goni, M. A.; Godin, P.; Stern, G. A.

2016-12-01

With warming in northern regions, many changes including permafrost degradation, vegetation alteration, and wildfire incidence will impact the carbon cycle. Organic carbon (OC) carried by river runoff to northern oceans has the potential to provide integrated evidence of these impacts. Here, concentrations of dissolved (DOC) and particulate (POC) OC are used to estimate terrestrial OC transport in 17 major rivers draining varied vegetative and permafrost conditions into Hudson Bay and compositional data (lignin and 14C) to infer OC sources. Hudson Bay lies just south of the Arctic Circle in Canada and is surrounded by a large drainage basin (3.9 × 106 km2) dominated by permafrost. Analysis of POC and DOC in the 17 rivers indicates that DOC dominates the total OC load. The southern rivers dominate. The Nelson and Churchill Rivers to the southwest are particularly important suppliers of OC partly because of large drainage basins but also perhaps because of impacts by hydroelectric development, as suggested by a 14C age of DOC in the Churchill River of 2800 years. Higher DOC and POC concentrations in the southern rivers, which have substantive areas only partially covered by permafrost, compared to northern rivers draining areas with complete permafrost cover, implies that warming - and hence permafrost thawing - will lead to progressively higher DOC and POC loads for these rivers. Lignin composition in the organic matter (S/V and C/V ratios) reveals mixed sources of OC consistent with the dominant vegetation in the river basins. This vegetation is organized by latitude with southern regions below the tree line enriched by woody gymnosperm sources (boreal forest) and northern regions enriched with organic matter from non-woody angiosperms (flowering shrubs, tundra). Acid/Aldehyde composition together with Δ14C data for selected DOC samples suggest that most of the lignin has undergone oxidative degradation, particularly the DOC component. However, high Δ14C ages did not co-occur with high [Ad/Al] ratios, suggesting that riverine DOC preserved (frozen) for extensive periods is now being released. Although permafrost thaw within the Hudson Bay drainage has already commenced, this meridional river study provides a benchmark against which to evaluate future change.

Dissolved organic carbon modulates mercury concentrations in insect subsidies from streams to terrestrial consumers.

PubMed

Chaves-Ulloa, Ramsa; Taylor, Brad W; Broadley, Hannah J; Cottingham, Kathryn L; Baer, Nicholas A; Weathers, Kathleen C; Ewing, Holly A; Chen, Celia Y

2016-09-01

Mercury (Hg) concentrations in aquatic environments have increased globally, exposing consumers of aquatic organisms to high Hg levels. For both aquatic and terrestrial consumers, exposure to Hg depends on their food sources as well as environmental factors influencing Hg bioavailability. The majority of the research on the transfer of methylmercury (MeHg), a toxic and bioaccumulating form of Hg, between aquatic and terrestrial food webs has focused on terrestrial piscivores. However, a gap exists in our understanding of the factors regulating MeHg bioaccumulation by non-piscivorous terrestrial predators, specifically consumers of adult aquatic insects. Because dissolved organic carbon (DOC) binds tightly to MeHg, affecting its transport and availability in aquatic food webs, we hypothesized that DOC affects MeHg transfer from stream food webs to terrestrial predators feeding on emerging adult insects. We tested this hypothesis by collecting data over 2 years from 10 low-order streams spanning a broad DOC gradient in the Lake Sunapee watershed in New Hampshire, USA. We found that streamwater MeHg concentration increased linearly with DOC concentration. However, streams with the highest DOC concentrations had emerging stream prey and spiders with lower MeHg concentrations than streams with intermediate DOC concentrations; a pattern that is similar to fish and larval aquatic insects. Furthermore, high MeHg concentrations found in spiders show that MeHg transfer in adult aquatic insects is an overlooked but potentially significant pathway of MeHg bioaccumulation in terrestrial food webs. Our results suggest that although MeHg in water increases with DOC, MeHg concentrations in stream and terrestrial consumers did not consistently increase with increases in streamwater MeHg concentrations. In fact, there was a change from a positive to a negative relationship between aqueous exposure and bioaccumulation at streamwater MeHg concentrations associated with DOC above ~5 mg/L. Thus, our study highlights the importance of stream DOC for MeHg dynamics beyond stream boundaries, and shows that factors modulating MeHg bioavailability in aquatic systems can affect the transfer of MeHg to terrestrial predators via aquatic subsidies. © 2016 by the Ecological Society of America.

Hydrologically mediated iron reduction/oxidation fluctuations and dissolved organic carbon exports in tidal wetlands

NASA Astrophysics Data System (ADS)

Guimond, J. A.; Seyfferth, A.; Michael, H. A.

2017-12-01

Salt marshes are biogeochemical hotspots where large quantities of carbon are processed and stored. High primary productivity and deposition of carbon-laden sediment enable salt marsh soils to accumulate and store organic carbon. Conversely, salt marshes can laterally export carbon from the marsh platform to the tidal channel and eventually the ocean via tidal pumping. However, carbon export studies largely focus on tidal channels, missing key physical and biogeochemical mechanisms driving the mobilization of dissolved organic carbon (DOC) within the marsh platform and limiting our understanding of and ability to predict coastal carbon dynamics. We hypothesize that iron redox dynamics mediate the mobilization/immobilization of DOC in the top 30 cm of salt marsh sediment near tidal channels. The mobilized DOC can then diffuse into the flooded surface water or be advected to tidal channels. To elucidate DOC dynamics driven by iron redox cycles, we measured porewater DOC, Fe(II), total iron, total sulfate, pH, redox potential, and electrical conductivity (EC) beside the creek, at the marsh levee, and in the marsh interior in a mid-latitude tidal salt marsh in Dover, Delaware. Samples were collected at multiple tide stages during a spring and neap tide at depths of 5-75cm. Samples were also collected from the tidal channel. Continuous Eh measurements were made using in-situ electrodes. A prior study shows that DOC and Fe(II) concentrations vary spatially across the marsh. Redox conditions near the creek are affected by tidal oscillations. High tides saturate the soil and decrease redox potential, whereas at low tide, oxygen enters the sediment and increases the Eh. This pattern is always seen in the top 7-10cm of sediment, with more constant low Eh at depth. However, during neap tides, this signal penetrates deeper. Thus, between the creek and marsh levee, hydrology mediates redox conditions. Based on porewater chemistry, if DOC mobilization can be linked to redox cycles, then hydrologic oscillations can be tied to DOC dynamics and predicted with hydrologic models. By elucidating the mechanisms driving the mobilization of DOC, we can begin to better understand, quantify, and forecast coastal carbon dynamics.

Sources and fate of organic (DOC, POC, CDOM) and inorganic (DIC) carbon in a mangrove dominated estuary (French Guiana)

NASA Astrophysics Data System (ADS)

Ray, R.; Michaud, E.; Vantrepotte, V.; Aller, R. C.; Morvan, S.; Thouzeau, G.

2016-12-01

We studied the mangrove dominated Sinnamary estuarine system in French Guiana during the dry and wet seasons in 2015 to examine the sources, transport and fate of surface water DOC, POC and DIC along the salinity gradient and the effect of tidal fluctuations on carbon dynamics. Elemental ratios, stable isotopes and optical properties (absorption) were applied as proxies to delineate the sources and molecular structure of the organic carbon. Results showed that during the wet season there were significant net inputs of POC and DOC along the salinity gradient from mangroves and enhanced surface runoff. Time series performed during the dry season at a station in channel water adjacent to mangroves revealed mangrove-derived export and exchanges of DOC and POC during the ebb and marine algae import during the flood. DOC was the dominant form of carbon in both seasons with DOC:POC ratios typically between 13 and 40. Both δ13DOC and CDOM descriptors (e.g., S275-295 and a*412) confirmed mangrove litter leaching to be the primary contributor of high molecular weight dissolved organic matter in the wet season which was replaced by marine phytoplanktonic OC during transport offshore in the dry season. CDOM aromaticity is lower in the dry season as mangrove inputs decrease. POC showed similar trends as DOC, with maximum contributions of terrestrial litter in the river and mixing zone, and in situ production dominant in the marine zone. The entire estuary is heterotrophic, exhibiting high pCO2 (837-5575µatm) and oxygen undersaturation (59-86%) in both seasons, and substantial CO2 emission fluxes (278-3671mmol m-2 d-1). Intense local remineralization and laterally transported CO2 originating from mangrove benthic respiration could account for the water column pCO2 enrichment during low tide and night time. Keywords: Organic carbon, stable isotopes, CDOM, pCO2, mangrove, French Guiana

The role of iron and reactive oxygen species in the production of CO2 in arctic soil waters

NASA Astrophysics Data System (ADS)

Trusiak, Adrianna; Treibergs, Lija A.; Kling, George W.; Cory, Rose M.

2018-03-01

Hydroxyl radical (radOH) is a highly reactive oxidant of dissolved organic carbon (DOC) in the environment. radOH production in the dark was observed through iron and DOC mediated Fenton reactions in natural environments. Specifically, when dissolved oxygen (O2) was added to low oxygen and anoxic soil waters in arctic Alaska, radOH was produced in proportion to the concentrations of reduced iron (Fe(II)) and DOC. Here we demonstrate that Fe(II) was the main electron donor to O2 to produce radOH. In addition to quantifying radOH production, hydrogen peroxide (H2O2) was detected in soil waters as a likely intermediate in radOH production from oxidation of Fe(II). For the first time in natural systems we detected carbon dioxide (CO2) production from radOH oxidation of DOC. More than half of the arctic soil waters tested showed production of CO2 under conditions conducive for production of radOH. Findings from this study strongly suggest that DOC is the main sink for radOH, and that radOH can oxidize DOC to yield CO2. Thus, this iron-mediated, dark chemical oxidation of DOC may be an important component of the arctic carbon cycle.

Higher order scaffoldin assembly in Ruminococcus flavefaciens cellulosome is coordinated by a discrete cohesin-dockerin interaction.

PubMed

Bule, Pedro; Pires, Virgínia M R; Alves, Victor D; Carvalho, Ana Luísa; Prates, José A M; Ferreira, Luís M A; Smith, Steven P; Gilbert, Harry J; Noach, Ilit; Bayer, Edward A; Najmudin, Shabir; Fontes, Carlos M G A

2018-05-03

Cellulosomes are highly sophisticated molecular nanomachines that participate in the deconstruction of complex polysaccharides, notably cellulose and hemicellulose. Cellulosomal assembly is orchestrated by the interaction of enzyme-borne dockerin (Doc) modules to tandem cohesin (Coh) modules of a non-catalytic primary scaffoldin. In some cases, as exemplified by the cellulosome of the major cellulolytic ruminal bacterium Ruminococcus flavefaciens, primary scaffoldins bind to adaptor scaffoldins that further interact with the cell surface via anchoring scaffoldins, thereby increasing cellulosome complexity. Here we elucidate the structure of the unique Doc of R. flavefaciens FD-1 primary scaffoldin ScaA, bound to Coh 5 of the adaptor scaffoldin ScaB. The RfCohScaB5-DocScaA complex has an elliptical architecture similar to previously described complexes from a variety of ecological niches. ScaA Doc presents a single-binding mode, analogous to that described for the other two Coh-Doc specificities required for cellulosome assembly in R. flavefaciens. The exclusive reliance on a single-mode of Coh recognition contrasts with the majority of cellulosomes from other bacterial species described to date, where Docs contain two similar Coh-binding interfaces promoting a dual-binding mode. The discrete Coh-Doc interactions observed in ruminal cellulosomes suggest an adaptation to the exquisite properties of the rumen environment.

Implementation and Early Outcomes of the Comprehensive School Reform Demonstration (CSRD) Program. Doc # 2004-15

ERIC Educational Resources Information Center

LaPointe, Michelle; Stullich, Stephanie

2004-01-01

The Comprehensive School Reform (CSR) program provides financial assistance to help schools develop and implement systematic approaches to schoolwide improvement that are grounded in scientifically based research and effective practices. The goal of the program is to enable all children to meet challenging state academic content and achievement…

Seasonal and air mass trajectory effects on dissolved organic matter of bulk deposition at a coastal town in south-western Europe.

PubMed

Santos, Patrícia S M; Santos, Eduarda B H; Duarte, Armando C

2013-01-01

Rainwater contains a complex mixture of organic compounds which may influence climate, terrestrial and maritime ecosystems and thus human health. In this work, the characteristics of DOM of bulk deposition at a coastal town on the southwest of Europe were assessed by UV-visible and three-dimensional excitation-emission matrix fluorescence spectroscopies and by dissolved organic carbon (DOC) content. The seasonal and air mass trajectory effects on dissolved organic matter (DOM) of bulk deposition were evaluated. The absorbance at 250 nm (UV(250 nm)) and integrated fluorescence showed to be positively correlated with each other, and they were also positively correlated to the DOC in bulk deposition, which suggest that a constant fraction of DOM is likely to fluoresce. There was more chromophoric dissolved organic matter (CDOM) present in summer and autumn seasons than in winter and spring. Bulk deposition associated with terrestrial air masses contained a higher CDOM content than bulk deposition related to marine air masses, thus highlighting the contribution of terrestrial/anthropogenic sources.

Non-linear, connectivity and threshold-dominated runoff-generation controls DOC and heavy metal export in a small peat catchment

NASA Astrophysics Data System (ADS)

Birkel, Christian; Broder, Tanja; Biester, Harald

2017-04-01

Peat soils act as important carbon sinks, but they also release large amounts of dissolved organic carbon (DOC) to the aquatic system. The DOC export is strongly tied to the export of soluble heavy metals. The accumulation of potentially toxic substances due to anthropogenic activities, and their natural export from peat soils to the aquatic system is an important health and environmental issue. However, limited knowledge exists as to how much of these substances are mobilized, how they are mobilized in terms of flow pathways and under which hydrometeorological conditions. In this study, we report from a combined experimental and modelling effort to provide greater process understanding from a small, lead (Pb) and arsenic (As) contaminated upland peat catchment in northwestern Germany. We developed a minimally parameterized, but process-based, coupled hydrology-biogeochemistry model applied to simulate detailed hydrometric and biogeochemical data. The model was based on an initial data mining analysis, in combination with regression relationships of discharge, DOC and element export. We assessed the internal model DOC-processing based on stream-DOC hysteresis patterns and 3-hourly time step groundwater level and soil DOC data (not used for calibration as an independent model test) for two consecutive summer periods in 2013 and 2014. We found that Pb and As mobilization can be efficiently predicted from DOC transport alone, but Pb showed a significant non-linear relationship with DOC, while As was linearly related to DOC. The relatively parsimonious model (nine calibrated parameters in total) showed the importance of non-linear and rapid near-surface runoff-generation mechanisms that caused around 60% of simulated DOC load. The total load was high even though these pathways were only activated during storm events on average 30% of the monitoring time - as also shown by the experimental data. Overall, the drier period 2013 resulted in increased nonlinearity, but exported less DOC (115 kg C ha-1 yr-1 ± 11 kg C ha-1 yr-1) compared to the equivalent but wetter period in 2014 (189 kg C ha-1 yr-1 ± 38 kg C ha-1 yr-1). The exceedance of a critical water table threshold (-10 cm) triggered a rapid near-surface runoff response with associated higher DOC transport connecting all available DOC pools, and with subsequent dilution. We conclude that the combination of detailed experimental work with relatively simple, coupled hydrology-biogeochemistry models allowed not only the model to be internally constrained, but also provided important insight into how DOC and tightly coupled heavy metals are mobilized.

Regulation of stream water dissolved organic carbon concentrations ([DOC]) during snowmelt in forest streams; the role of discharge, winter climate and memory effects

NASA Astrophysics Data System (ADS)

Ågren, A.; Haei, M.; Öquist, M.; Buffam, I.; Ottosson-Löfvenius, M.; Kohler, S.; Bishop, K.; Blomkvist, P.; Laudon, H.

2011-12-01

Using 15 year stream records from two forested northern boreal catchments, coupled with soil frost experiments in the riparian zone, we demonstrate the complex inter-annual control on [DOC] and export during snowmelt. Stream [DOC] varied by a factor of 2 during those 15 years with no consistent trend. Based on our long-term analysis, we demonstrate, for the first time, that stream water [DOC] is strongly linked to the climatic conditions during the preceding winter, but that there is also a long-term memory effect in the catchment soils, related to the extent of the previous export from the catchment. Hydrology had a first order control on the inter-annual variation in concentrations, and the length of the winter was more important than the memory effect. By removing the effect of discharge on [DOC], using a conceptual hydrological model, we could detect processes that would otherwise have been overshadowed. A short and intense snowmelt gave higher [DOC] in the stream. During a prolonged snowmelt, one soil layer at the time might have been "flushed" from easily exported DOC, resulting in slightly lower stream [DOC] during such years. We found that longer and colder winters resulted in higher [DOC] during the subsequent snowmelt. A soil frost manipulation experiment in the riparian soils of the study catchment showed that the DOC concentrations in the soil water increased with the duration of the soil frost. A high antecedent DOC export during the preceding summer and autumn resulted in lower concentrations during the following spring, indicating a long-term "memory effect" of the catchment soils. In a nearby stream draining mire, we found a different response to hydrology but similar response to climate and memory effect. The inter-annual variation in snowmelt DOC exports was mostly controlled by the amount of runoff, but the variability in [DOC] also exerted a significant control on the exports, accounting for 15% of the variance in exports. We conclude that winter climatic conditions can play a substantial role in controlling stream [DOC] in ways not previously understood. These findings are especially important for northern latitude regions expected to be most affected by climate change. It's difficult to directly translate this to a future climate change prediction. If warmer winters with less insulating snow cover increase the soil frost, the results from the soil frost manipulation experiment then suggest increasing [DOC] in a future climate. At the same time the statistical analysis of the stream records suggest that a shorter and warmer winter would decrease the [DOC]. Our results do, however, highlight the role of winter climate for regulating DOC in areas with seasonally frozen soils which should be considered when resolving the sensitivity of stream [DOC] to global environmental change.

Switching predominance of organic versus inorganic carbon exports from an intermediate-size subarctic watershed

USGS Publications Warehouse

Dornblaser, Mark M.; Striegl, Robert G.

2015-01-01

Hydrologic exports of dissolved inorganic and organic carbon (DIC, DOC) reflect permafrost conditions in arctic and subarctic river basins. DIC yields in particular, increase with decreased permafrost extent. We investigated the influence of permafrost extent on DIC and DOC yield in a tributary of the Yukon River, where the upper watershed has continuous permafrost and the lower watershed has discontinuous permafrost. Our results indicate that DIC versus DOC predominance switches with interannual changes in water availability and flow routing in intermediate-size watersheds having mixed permafrost coverage. Large water yield and small concentrations from mountainous headwaters and small water yield and high concentrations from lowlands produced similar upstream and downstream carbon yields. However, DOC export exceeded DIC export during high-flow 2011 while DIC predominated during low-flow 2010. The majority of exported carbon derived from near-surface organic sources when landscapes were wet or frozen and from mineralized subsurface sources when infiltration increased.

Dissolved Organic Carbon and Natural Terrestrial Sequestration Potential in Volcanic Terrain, San Juan Mountains, Colorado

NASA Astrophysics Data System (ADS)

Yager, D. B.; Burchell, A.; Johnson, R. H.; Kugel, M.; Aiken, G.; Dick, R.

2009-12-01

The need to reduce atmospheric CO2 levels has stimulated studies to understand and quantify carbon sinks and sources. Soils represent a potentially significant natural terrestrial carbon sequestration (NTS) reservoir. This project is part of a collaborative effort to characterize carbon (C) stability in temperate soils. To examine the potential for dissolved organic carbon (DOC) values as a qualitative indicator of C-stability, peak-flow (1500 ft3/s) and low-flow (200 ft3/s) samples from surface and ground waters were measured for DOC. DOC concentrations are generally low. Median peak-flow values from all sample sites (mg/L) were: streams (0.9); seeps (1.2); wells (0.45). Median low-flow values were: streams (0.7); seeps (0.75); wells (0.5). Median DOC values decrease between June and September 0.45 mg/L for seeps, and 0.2 mg/L for streams. Elevated DOC in some ground waters as compared to surface waters indicates increased contact time with soil organic matter. Elevated peak-flow DOC in areas with propylitically-altered bedrocks, composed of a secondary acid neutralizing assemblage of calcite-chlorite-epidote, reflects increased microbial and vegetation activity as compared to reduced organic matter accumulation in highly-altered terrain composed of an acid generating assemblage with abundant pyrite. Waters sampled in propylitically-altered bedrock terrain exhibit the lowest values during low-flow and suggest bedrock alteration type may influence DOC. Previous studies revealed undisturbed soils sampled have 2 to 6 times greater total organic soil carbon (TOSC) than global averages. Forest soils underlain by intermediate to mafic volcanic bedrock have the highest C (34.15 wt%), C: N (43) and arylsulfatase enzyme activity (ave. 278, high 461 µg p-nitrophenol/g/h). Unreclaimed mine sites have the lowest C (0 to 0.78 wt%), and arylsulfatase enzyme activity (0 to 41). Radiocarbon dates on charcoal collected from paleo-burn horizons illustrate Rocky Mountain soils may represent an old and if undisturbed, stable carbon pool (500 -5,440 ± 40 yrs B.P). Undisturbed and reclaimed soils derived from propylitic bedrocks also exhibit high TOSC (13.5 - 25.6 wt%), C: N (27), arylsulfatase (338). This is consistent with earlier studies in which propylitic bedrocks were identified as having a high acid-neutralizing capacity (ANC). Observations at natural reclamation sites suggest “bio-geo-mimicry” techniques that use ANC rock plus other soil amendments (biochar, nutrients, mycorrhizea, seeding) may aid reclamation measures and support carbon sequestration. The data demonstrate that volcanic-hosted watersheds may exhibit both high TOSC and low DOC. This is attributed to: host rock-weathering release of nutrients important for soil productivity, ANC, formation of secondary mineral carbonates; development of intermediate soil aggregates and adsorption-enhancing clays that stabilize C and N, environmental factors such as climate, moisture retention, and land use. Future work will explore the potential of DOC flux as a proxy for NTS potential.

Rising susceptibility of freshwater DOC inputs to extreme events? The implications of underlying changes in atmospheric deposition and land-management. (Invited)

NASA Astrophysics Data System (ADS)

Evans, C.; Monteith, D.; Jones, T.; Burden, A.; Peacock, M.; Gauci, V.; Page, S. E.; Moore, S.

2013-12-01

Dissolved organic carbon (DOC) represents a significant loss term within the carbon (C) balance of many terrestrial ecosystems, and a quantitatively important and reactive C input to many freshwater ecosystems. DOC concentrations have risen dramatically, over a period of decades, in rivers and lakes draining semi-natural catchments across large areas of Northern Europe and Northeast North America, with wide-ranging consequences for C cycling, aquatic ecosystem functioning and drinking water treatment. These increases have been variously attributed to climatic changes, including increased incidence of extreme events, as well as land-management factors and changes in atmospheric deposition. A growing body of evidence now indicates that the primary driver of rising DOC has been ecosystem recovery from the historic effects of acid deposition, and thus that observed increases - whilst sometimes economically problematic - may represent a return to pre-industrial baseline conditions. In light of the apparent dominance of acidity change as a driver of recent freshwater DOC increases, we consider whether or not other potential drivers of change, including climatic extremes and management-related disturbances, are likely to exert a significant influence on the transport of DOC from catchments to surface waters. We conclude that the alleviation of acidification pressures has now made catchments in regions formerly impacted by sulphur pollution much more susceptible to extreme events and disturbances. Drawing on monitoring and experimental case studies from the UK, we suggest that DOC export from organic soils may be shifting from ';solubility controlled' to ';supply controlled', and that climatic events leading to enhanced DOC production (e.g. high temperatures or drought-rewet cycles) and/or shallow lateral transport (e.g. high flow events) are now generating freshwater DOC peaks that are unprecedented in the monitoring record. We also examine the role of land-management as a control on DOC leaching, focusing on the influence of peatland drainage on sites ranging from the UK to Southeast Asia. Again, we conclude that anthropogenic modification of peat hydrology has contributed both to increases in baseline rates of DOC export, and to the enhanced susceptibility of these ecosystems to extreme events. An example is presented of the impact of an uncontrolled fire on DOC export from a drained peatland in Borneo. We develop a conceptual model of the integrated effect of multiple environmental drivers on DOC export from peats and organo-mineral soils, and consider how projected changes in these drivers might be expected to alter the supply and behaviour of freshwater DOC in future. References Evans CD, Jones TG, Burden A et al. (2012) Acidity controls on dissolved organic carbon mobility in organic soils. Global Change Biology 18, 3317-3331. Monteith DT, Stoddard JL, Evans CD et al. (2007). Rising freshwater dissolved organic carbon driven by changes in atmospheric deposition. Nature 450, 537-540. Moore S, Evans CD, Page SE et al. (2013). Deep instability of deforested tropical peatlands revealed by fluvial organic carbon fluxes, Nature 493, 660-664.

The Pulse of the Amazon

NASA Astrophysics Data System (ADS)

Spencer, R. G.; Moura, J. M. S.; Mitsuya, M.; Peucker-Ehrenbrink, B.; Holmes, R. M.; Galy, V.; Drake, T.

2017-12-01

Rivers integrate over a fixed and definable area (the watershed), with their discharge and chemistry at any given point a function of upstream processes. As a consequence, examination of riverine discharge and chemistry can provide powerful indictors of change within a watershed. To assess the validity of this approach long-term datasets are required from fluvial environments around the globe. The Amazon River delivers one-fifth of the total freshwater discharged to the ocean and so represents a fundamentally important site for examination of long-term major ion, trace element, nutrient, and organic matter (OM) export. Here we describe data from a multi-year, monthly sampling campaign of the Amazon River at Obidos (Para, Brazil). Clear seasonality in all analyte fluxes is apparent and is linked to hydrology, however dissolved OM composition appears dominated by allochthonous sources throughout the year as evidenced by optical parameters indicative of high molecular weight and high relative aromatic content. Annual loads of some analytes for 2011-2013 inclusive varied by up to 50%, highlighting significant variability in flux from year to year that was linked to inter-annual hydrologic shifts (i.e. higher fluxes in wetter years). Finally, encompassing both intra- and inter-annual variability, a robust correlation was observed between chromophoric dissolved OM (CDOM) absorbance and dissolved organic carbon (DOC) concentration highlighting the potential to improve DOC flux estimates at this globally significant site via CDOM measurements from in situ technologies or remote sensing techniques.

Nitrate loading and CH4 and N2O Flux from headwater streams

NASA Astrophysics Data System (ADS)

Sousa, C. H. R. D.; Hilker, T.; Hall, F. G.; Moura, Y. M.; McAdam, E.

2014-12-01

Freshwater ecosystems transport and process significant amounts of terrestrial carbon and can be considerable sources of CO2, CH4, and N2O. A great deal of uncertainty, however, remains in both global estimates and our understanding of drivers of freshwater greenhouse gas emissions. Furthermore, small headwater streams have received insufficient attention to date and may contribute disproportionately to global GHG flux. Our objective was to quantify GHG flux and assess the impact of changes in DOC and NO3 concentrations in surface and subsurface water on flux rates in three streams in the Lamprey River watershed in New Hampshire, USA, that contrast in surface water DOC:NO3. We measured DOC, NO3 and dissolved gas concentrations in surface waters of each stream monthly from May 2011 to April 2012. Empirical measurements of reaeration coefficients were used to convert dissolved gas concentrations to fluxes. We found higher GHG concentrations and fluxes in the two streams with high DOC concentrations, particularly gases produced by anaerobic metabolism (CH4, N2O from methanogenesis and denitrification, respectively). The stream with high DOC and high NO3 showed high N2O and low CH4 flux, while the high DOC, low NO3 stream showed high CH4 and low N2O flux. Our results are consistent with a model in which C inputs drive total GHG production, while NO3 input regulates the relative importance of CH4 and N2O by suppressing methanogenesis and stimulating denitrification. The magnitude of GHG fluxes suggests that streams in this region are likely to be small sources of CO2, but potentially important sources of CH4 and N2O. Since CH4 and N2O are many times more powerful than CO2 at trapping heat in the atmosphere, freshwater emissions of these gases have the potential to offset a significant proportion of the climate benefits of the terrestrial carbon sink, a possibility that has not been sufficiently incorporated into climate models.

Nitrate loading and CH4 and N2O Flux from headwater streams

NASA Astrophysics Data System (ADS)

Schade, J. D.; Bailio, J.; McDowell, W. H.

2015-12-01

Freshwater ecosystems transport and process significant amounts of terrestrial carbon and can be considerable sources of CO2, CH4, and N2O. A great deal of uncertainty, however, remains in both global estimates and our understanding of drivers of freshwater greenhouse gas emissions. Furthermore, small headwater streams have received insufficient attention to date and may contribute disproportionately to global GHG flux. Our objective was to quantify GHG flux and assess the impact of changes in DOC and NO3 concentrations in surface and subsurface water on flux rates in three streams in the Lamprey River watershed in New Hampshire, USA, that contrast in surface water DOC:NO3. We measured DOC, NO3 and dissolved gas concentrations in surface waters of each stream monthly from May 2011 to April 2012. Empirical measurements of reaeration coefficients were used to convert dissolved gas concentrations to fluxes. We found higher GHG concentrations and fluxes in the two streams with high DOC concentrations, particularly gases produced by anaerobic metabolism (CH4, N2O from methanogenesis and denitrification, respectively). The stream with high DOC and high NO3 showed high N2O and low CH4 flux, while the high DOC, low NO3 stream showed high CH4 and low N2O flux. Our results are consistent with a model in which C inputs drive total GHG production, while NO3 input regulates the relative importance of CH4 and N2O by suppressing methanogenesis and stimulating denitrification. The magnitude of GHG fluxes suggests that streams in this region are likely to be small sources of CO2, but potentially important sources of CH4 and N2O. Since CH4 and N2O are many times more powerful than CO2 at trapping heat in the atmosphere, freshwater emissions of these gases have the potential to offset a significant proportion of the climate benefits of the terrestrial carbon sink, a possibility that has not been sufficiently incorporated into climate models.

Organic carbon export from the Greenland Ice Sheet: sources, sinks and downstream fluxes

NASA Astrophysics Data System (ADS)

Wadham, J. L.; Lawson, E.; Tranter, M.; Stibal, M.; Telling, J.; Lis, G. P.; Nienow, P. W.; Anesio, A. M.; Butler, C. E.

2012-12-01

Runoff from small glacier systems has been shown to contain dissolved organic carbon (DOC) rich in low molecular weight (LMW), and hence more labile forms, designating glaciers as an important source of carbon for downstream heterotrophic activity. Here we assess glacier surfaces as potential sources of labile DOC to downstream ecosystems, presenting data from a wide range of glacier systems to determine sources and sinks of DOC in glacial and proglacial systems. We subsequently focus upon the Greenland Ice Sheet (GrIS) which is the largest source of glacial runoff at present (400 km3 yr-1), with predicted increases in future decades. We report high fluxes of particulate organic carbon (POC), DOC and LMW labile fractions from a large GrIS catchment during two contrasting melt seasons. POC dominates OC export, is sourced from the ice sheet bed and contains a significant bioreactive component (~10% carbohydrates). The LMW-DOC "labile" fraction derives almost entirely from microbial activity on the ice sheet surface, which is supported by data from glacier systems also presented here. Annual fluxes of DOC, POC and labile components were lower in 2010 than 2009, despite a ~2 fold increase in runoff fluxes in 2010, suggesting production-limited DOC/POC sources. Scaled to the entire ice sheet, combined DOC and POC fluxes are of a similar order of magnitude to other large Arctic river systems and may represent an important source of organic carbon to the North Atlantic, Greenland and Labrador Seas.

Coupled mobilization of dissolved organic matter and metals (Cu and Zn) in soil columns

NASA Astrophysics Data System (ADS)

Zhao, Lu Y. L.; Schulin, Rainer; Weng, Liping; Nowack, Bernd

2007-07-01

Dissolved organic carbon (DOC) is a key component involved in metal displacement in soils. In this study, we investigated the concentration profiles of soil-borne DOC, Cu and Zn at various irrigation rates with synthetic rain water under quasi steady-state conditions, using repacked soil columns with a metal-polluted topsoil and two unpolluted subsoils. Soil solution was collected using suction cups installed at centimeter intervals over depth. In the topsoil the concentrations of DOC, dissolved metals (Zn and Cu), major cations (Ca 2+ and Mg 2+) and anions ( NO3- and SO42-) increased with depth. In the subsoil, the Cu and Zn concentrations dropped to background levels within 2 cm. All compounds were much faster mobilized in the first 4 cm than in the rest of the topsoil. DOC and Cu concentrations were higher at higher flow rates for a given depth, whereas the concentrations of the other ions decreased with increasing flow rate. The decomposition of soil organic matter resulted in the formation of DOC, SO42-, and NO3- and was the main driver of the system. Regression analysis indicated that Cu mobilization was governed by DOC, whereas Zn mobilization was primarily determined by Ca and to a lesser extent by DOC. Labile Zn and Cu 2+ concentrations were well predicted by the NICA-Donnan model. The results highlight the value of high-resolution in-situ measurements of DOC and metal mobilization in soil profiles.

Remediation of a winery wastewater combining aerobic biological oxidation and electrochemical advanced oxidation processes.

PubMed

Moreira, Francisca C; Boaventura, Rui A R; Brillas, Enric; Vilar, Vítor J P

2015-05-15

Apart from a high biodegradable fraction consisting of organic acids, sugars and alcohols, winery wastewaters exhibit a recalcitrant fraction containing high-molecular-weight compounds as polyphenols, tannins and lignins. In this context, a winery wastewater was firstly subjected to a biological oxidation to mineralize the biodegradable fraction and afterwards an electrochemical advanced oxidation process (EAOP) was applied in order to mineralize the refractory molecules or transform them into simpler ones that can be further biodegraded. The biological oxidation led to above 97% removals of dissolved organic carbon (DOC), chemical oxygen demand (COD) and 5-day biochemical oxygen demand (BOD5), but was inefficient on the degradation of a bioresistant fraction corresponding to 130 mg L(-1) of DOC, 380 mg O2 L(-1) of COD and 8.2 mg caffeic acid equivalent L(-1) of total dissolved polyphenols. Various EAOPs such as anodic oxidation with electrogenerated H2O2 (AO-H2O2), electro-Fenton (EF), UVA photoelectro-Fenton (PEF) and solar PEF (SPEF) were then applied to the recalcitrant effluent fraction using a 2.2 L lab-scale flow plant containing an electrochemical cell equipped with a boron-doped diamond (BDD) anode and a carbon-PTFE air-diffusion cathode and coupled to a photoreactor with compound parabolic collectors (CPCs). The influence of initial Fe(2+) concentration and current density on the PEF process was evaluated. The relative oxidative ability of EAOPs increased in the order AO-H2O2 < EF < PEF ≤ SPEF. The SPEF process using an initial Fe(2+) concentration of 35 mg L(-1), current density of 25 mA cm(-2), pH of 2.8 and 25 °C reached removals of 86% on DOC and 68% on COD after 240 min, regarding the biologically treated effluent, along with energy consumptions of 45 kWh (kg DOC)(-1) and 5.1 kWh m(-3). After this coupled treatment, color, odor, COD, BOD5, NH4(+), NO3(-) and SO4(2-) parameters complied with the legislation targets and, in addition, a total dissolved polyphenols content of 0.35 mg caffeic acid equivalent L(-1) was found. Respirometry tests revealed low biodegradability enhancement along the SPEF process. Copyright © 2015 Elsevier Ltd. All rights reserved.

Carbon, nitrogen, and phosphorus transport by world rivers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meybeck, M.

1982-04-01

The various forms (dissolved and particulate, organic and inorganic) of carbon, nitrogen, and phosphorus in world rivers are reviewed from literature data. Natural levels are based mainly on major rivers for the subarctic and tropical zones which are still unpolluted and on smaller streams for the temperate zone. Atmospheric fallout is also reviewed. Natural contents of dissolved organic carbon (DOC) are mainly dependent on environmental conditions: DOC varies from 1 mg 1/sup -1/ in the mountainous alpine environments to 20 mg 1/sup -1/ in some taiga rivers. The world DOC average is 5.75 mg l/sup -1/. Nitrogen forms include dissolvedmore » organic nitrogen (DON), dissolved inorganic nitrogen (DIN = N - NH/sub 4//sup +/ + N - NO/sub 3//sup -/ + N - NO/sub 2//sup -/), and particulate organic nitrogen (PON). Natural levels are very low: DIN = 120 ..mu..g 1/sup -1/ of which only 15 percent is present as ammonia, and 1 percent as nitrite. Phosphorus is naturally present in very low amounts: around 10 ..mu..g 1/sup -1/ for P-PO/sub 4//sup 3/ and 25 ..mu..g 1/sup -1/ for total dissolved phosphorus (TDP which includes the organic form). The average nutrient content of rains has been estimated with a set of unpolluted stations: P - PO/sub 4/ = 5 ..mu..g 1/sup -1/, TDP = 10, N - NO/sub 2/ = 5, N - NH/sub 4/ = 225, DON = 225, and N - NO/sub 3/ = 175 ..mu..g 1/sup -1/. TOC levels are probably around several mg 1/sup -1/. These contents are very similar to those found in unpolluted rivers. Man's influence on surface waters has now greatly increased natural nutrient levels. Total dissolved P and N have globally increased by a factor of two and locally (Western Europe, North America) by factors of 10 to 50. These increases were found to be directly proportional to the watershed population and to its energy consumption.« less

Effects of humic substances on the bioconcentration of polycyclic aromatic hydrocarbons: Correlations with spectroscopic and chemical properties of humic substances

DOE Office of Scientific and Technical Information (OSTI.GOV)

Haitzer, M.; Abbt-Braun, G.; Traunspurger, W.

1999-12-01

The presence of dissolved humic substances (HS, fulvic and humic acids) generally reduces the uptake of hydrophobic organic compounds into aquatic organisms. The extent of this effect depends both on the concentration and on the origin of the HS. The aim of this study was to investigate the role of qualitative differences between HS from different origins. The effects of seven different HS on the bioconcentration of pyrene and benzo[a]pyrene (BaP) in the nematode Caenorhabditis elegans were related to the spectroscopic and chemical properties of the HS. The effect of each humic material on the bioconcentration of pyrene or BaPmore » was quantified as a biologically determined partition coefficient K{sub DOC}. The authors observed significant linear relationships between K{sub DOC} and the atomic H/C ratio, the specific absorptivity at 254 nm, the content of aromatic carbons as determined by {sup 13}C nuclear magnetic resonance spectroscopy, the copper-complexing capacity, the content of phenolic OH groups, and the molecular weight of the HS. There was no discernible relationship of K{sub DOC} with the atomic (N + O)/C ratio, an indicator of the polarity of HS. Taken together, their results show that the variability in the effects of HS from different origins could be related to variations in bulk properties of the HS. Parameters describing the aromaticity of the humic materials seemed to be most useful for estimating effects of HS on the bioconcentration of pyrene and BaP.« less

Greenland Ice Sheet exports labile organic carbon to the Arctic oceans

NASA Astrophysics Data System (ADS)

Lawson, E. C.; Wadham, J. L.; Tranter, M.; Stibal, M.; Lis, G. P.; Butler, C. E. H.; Laybourn-Parry, J.; Nienow, P.; Chandler, D.; Dewsbury, P.

2014-07-01

Runoff from small glacier systems contains dissolved organic carbon (DOC) rich in protein-like, low molecular weight (LMW) compounds, designating glaciers as an important source of bioavailable carbon for downstream heterotrophic activity. Fluxes of DOC and particulate organic carbon (POC) exported from large Greenland catchments, however, remain unquantified, despite the Greenland Ice Sheet (GrIS) being the largest source of global glacial runoff (ca. 400 km3 yr-1). We report high and episodic fluxes of POC and DOC from a large (>600 km2) GrIS catchment during contrasting melt seasons. POC dominates organic carbon (OC) export (70-89% on average), is sourced from the ice sheet bed, and contains a significant bioreactive component (9% carbohydrates). A major source of the "bioavailable" (free carbohydrate) LMW-DOC fraction is microbial activity on the ice sheet surface, with some further addition of LMW-DOC to meltwaters by biogeochemical processes at the ice sheet bed. The bioavailability of the exported DOC (26-53%) to downstream marine microorganisms is similar to that reported from other glacial watersheds. Annual fluxes of DOC and free carbohydrates during two melt seasons were similar, despite the approximately two-fold difference in runoff fluxes, suggesting production-limited DOC sources. POC fluxes were also insensitive to an increase in seasonal runoff volumes, indicating a supply limitation in suspended sediment in runoff. Scaled to the GrIS, the combined DOC (0.13-0.17 Tg C yr-1 (±13%)) and POC fluxes (mean = 0.36-1.52 Tg C yr-1 (±14%)) are of a similar order of magnitude to a large Arctic river system, and hence may represent an important OC source to the near-coastal North Atlantic, Greenland and Labrador seas.

Low dose combinations of 2-methoxyestradiol and docetaxel block prostate cancer cells in mitosis and increase apoptosis.

PubMed

Reiner, Teresita; de las Pozas, Alicia; Gomez, Lourdes A; Perez-Stable, Carlos

2009-04-08

Clinical trials have shown that chemotherapy with docetaxel (Doc) combined with prednisone can improve survival of patients with androgen-independent prostate cancer (AI-PC). It is likely that the combination of Doc with other novel agents would also improve the survival of AI-PC patients. We investigated whether the combination of Doc and 2-methoxyestradiol (2ME2), an endogenous metabolite of estradiol promising for cancer therapy, can increase apoptotic cell death in prostate cancer cells. Low concentration 2ME2 (0.5-1 microM)+Doc (0.05-0.1 nM) combinations inhibit cell growth, increase G2/M cell cycle arrest, and increase apoptosis more effectively than the single concentrations in a variety of human AI-PC cells. Effects on apoptosis were associated with an increase in p53 protein and a decrease in cyclin A-dependent kinase activity. We then investigated whether the combination of 2ME2+Doc can increase apoptotic cell death and inhibit the growth of prostate tumors in the FG/Tag transgenic mouse model of AI-PC. Doses of 2ME2 and Doc that increase mitotic cell cycle arrest result in an increase in apoptosis and lower primary prostate tumor weights in FG/Tag mice. High dose 2ME2+Doc combinations did not increase G2/M cell cycle arrest or apoptosis in AI-PC cell lines and in the FG/Tag mice more than the single drugs. Overall, our data indicate that low dose 2ME2+Doc combinations may provide a treatment strategy that can improve therapeutic efficacy against AI-PC while reducing toxicity often seen in patients treated with Doc.

A mobile water analysis laboratory for the study of stream nutrient and DOC dynamics

NASA Astrophysics Data System (ADS)

Echevarria Roman, Y.; Pullin, M. J.; Schwingle, R.; Gabrielsen, P. J.

2013-12-01

The dynamics of nutrient and dissolved organic carbon (DOC) quantity and composition in streams vary with season and in response to hydrologic events. Periodic grab sampling can capture some of this variation, but has also been shown to miss high flow events. Sampling during winter, during thunderstorms, and at night is difficult and sometimes hazardous. For these reasons, we have developed a mobile laboratory that autonomously determines pH, Eh, conductivity, dissolved oxygen, turbidity, nitrate, phosphate, DOC, DIC, as well as DOC fluorescence and absorbance continuously on a minutes timescale. The laboratory includes a Labview operated computer system that allows remote control and interaction with pumps, pressure, temperature, and flow sensors as well as the analytical instruments. Climate control allows for operation in winter. The design and operation of this laboratory will be presented. We will also discuss example data showing diurnal changes and responses to hydrologic events in DOC quantity and quality in the East Fork of the Jemez River, New Mexico.

Spatial and temporal patterns of dissolved organic matter quantity and quality in the Mississippi River Basin, 1997–2013

USGS Publications Warehouse

Stackpoole, Sarah M.; Stets, Edward G.; Clow, David W.; Burns, Douglas A.; Aiken, George R.; Aulenbach, Brent T.; Creed, Irena F.; Hirsch, Robert M.; Laudon, Hjalmar; Pellerin, Brian; Striegl, Robert G.

2017-01-01

Recent studies have found insignificant or decreasing trends in time-series dissolved organic carbon (DOC) datasets, questioning the assumption that long-term DOC concentrations in surface waters are increasing in response to anthropogenic forcing, including climate change, land use, and atmospheric acid deposition. We used the weighted regressions on time, discharge, and season (WRTDS) model to estimate annual flow-normalized concentrations and fluxes to determine if changes in DOC quantity and quality signal anthropogenic forcing at 10 locations in the Mississippi River Basin. Despite increases in agriculture and urban development throughout the basin, net increases in DOC concentration and flux were significant at only 3 of 10 sites from 1997 to 2013 and ranged between −3.5% to +18% and −0.1 to 19%, respectively. Positive shifts in DOC quality, characterized by increasing specific ultraviolet absorbance at 254 nm, ranged between +8% and +45%, but only occurred at one of the sites with significant DOC quantity increases. Basinwide reductions in atmospheric sulfate deposition did not result in large increases in DOC either, likely because of the high buffering capacity of the soil. Hydroclimatic factors including annual discharge, precipitation, and temperature did not significantly change during the 17-year timespan of this study, which contrasts with results from previous studies showing significant increases in precipitation and discharge over a century time scale. Our study also contrasts with those from smaller catchments, which have shown stronger DOC responses to climate, land use, and acidic deposition. This temporal and spatial analysis indicated that there was a potential change in DOC sources in the Mississippi River Basin between 1997 and 2013. However, the overall magnitude of DOC trends was not large, and the pattern in quantity and quality increases for the 10 study sites was not consistent throughout the basin.

Satellite-Derived Distributions, Inventories and Fluxes of Dissolved and Particulate Organic Matter Along the Northeastern U.S. Continental Margin

NASA Technical Reports Server (NTRS)

Mannino, A.; Hooker, S. B.; Hyde, K.; Novak, M. G.; Pan, X.; Friedrichs, M.; Cahill, B.; Wilkin, J.

2011-01-01

Estuaries and the coastal ocean experience a high degree of variability in the composition and concentration of particulate and dissolved organic matter (DOM) as a consequence of riverine and estuarine fluxes of terrigenous DOM, sediments, detritus and nutrients into coastal waters and associated phytoplankton blooms. Our approach integrates biogeochemical measurements, optical properties and remote sensing to examine the distributions and inventories of organic carbon in the U.S. Middle Atlantic Bight and Gulf of Maine. Algorithms developed to retrieve colored DOM (CDOM), Dissolved (DOC) and Particulate Organic Carbon (POC) from NASA's MODIS-Aqua and SeaWiFS satellite sensors are applied to quantify the distributions and inventories of DOC and POC. Horizontal fluxes of DOC and POC from the continental margin to the open ocean are estimated from SeaWiFS and MODIS-Aqua distributions of DOC and POC and horizontal divergence fluxes obtained from the Northeastern North Atlantic ROMS model. SeaWiFS and MODIS imagery reveal the importance of estuarine outflow to the export of CDOM and DOC to the coastal ocean and a net community production of DOC on the shelf.

Experimental investigation and modeling of dissolved organic carbon removal by coagulation from seawater.

PubMed

Jeong, Sanghyun; Sathasivan, Arumugam; Kastl, George; Shim, Wang Geun; Vigneswaran, Saravanamuthu

2014-01-01

Coagulation removes colloidal matters and dissolved organic carbon (DOC) which can cause irreversible membrane fouling. However, how DOC is removed by coagulant is not well-known. Jar test was used to study the removal of hydrophobic and hydrophilic DOC fractions at various doses (0.5-8.0 mg-Fe(+3) L(-1)) of ferric chloride (FeCl3) and pH (5.0-9.0). Natural organic matter (NOM) in seawater and treated seawater were fractionated by liquid chromatography-organic carbon detector (LC-OCD). Compared to surface water, the removal of DOC in seawater by coagulation was remarkably different. Majority of DOC could be easily removed with very low coagulant dose (<5.0 mg-Fe(+3) L(-1)) and the removal efficiency did not vary with pH, but the DOC composition in treated water had significantly changed. Hydrophobic fraction (HB) was better removed at high pH while hydrophilic fraction (HF) was better removed at low pH. A modified model of Kastl et al. (2004) which assumed that the removal occurred by adsorption of un-dissociated compounds onto ferric hydroxide was formulated and successfully validated against the jar test data. Copyright © 2013 Elsevier Ltd. All rights reserved.

Long-lasting repetitive transcranial magnetic stimulation modulates electroencephalography oscillation in patients with disorders of consciousness.

PubMed

Xia, Xiaoyu; Liu, Yang; Bai, Yang; Liu, Ziyuan; Yang, Yi; Guo, Yongkun; Xu, Ruxiang; Gao, Xiaorong; Li, Xiaoli; He, Jianghong

2017-10-18

Repetitive transcranial magnetic stimulation (rTMS) has been applied for the treatment of patients with disorders of consciousness (DOC). Timely and accurate assessments of its modulation effects are very useful. This study evaluated rTMS modulation effects on electroencephalography (EEG) oscillation in patients with chronic DOC. Eighteen patients with a diagnosis of DOC lasting more than 3 months were recruited. All patients received one session of 10-Hz rTMS at the left dorsolateral prefrontal cortex and then 12 of them received consecutive rTMS treatment everyday for 20 consecutive days. Resting-state EEGs were recorded before the experiment (T0) after one session of rTMS (T1) and after the entire treatment (T2). The JFK Coma Recovery Scale-Revised scale scores were also recorded at the time points. Our data showed that application of 10-Hz rTMS to the left dorsolateral prefrontal cortex decreased low-frequency band power and increased high-frequency band power in DOC patients, especially in minimal conscious state patients. Considering the correlation of the EEG spectrum with the consciousness level of patients with DOC, quantitative EEG might be useful for assessment of the effect of rTMS in DOC patients.

Pyrolysis temperature-dependent release of dissolved organic carbon from plant, manure, and biorefinery wastes

USDA-ARS?s Scientific Manuscript database

Limited information is available to understand the chemical structure of biochar’s labile dissolved organic carbon (DOC) fraction that will change amended soil’s DOC composition. This study utilized the high sensitivity of fluorescence excitation-emission (EEM) spectrophotometry to understand the s...

Tidally driven export of dissolved organic carbon, total mercury, and methylmercury from a mangrove-dominated estuary

USGS Publications Warehouse

Bergamaschi, B.A.; Krabbenhoft, D.P.; Aiken, G.R.; Patino, E.; Rumbold, D.G.; Orem, W.H.

2012-01-01

The flux of dissolved organic carbon (DOC) from mangrove swamps accounts for 10% of the global terrestrial flux of DOC to coastal oceans. Recent findings of high concentrations of mercury (Hg) and methylmercury (MeHg) in mangroves, in conjunction with the common co-occurrence of DOC and Hg species, have raised concerns that mercury fluxes may also be large. We used a novel approach to estimate export of DOC, Hg, and MeHg to coastal waters from a mangrove-dominated estuary in Everglades National Park (Florida, USA). Using in situ measurements of fluorescent dissolved organic matter as a proxy for DOC, filtered total Hg, and filtered MeHg, we estimated the DOC yield to be 180 (??12.6) g C m -2 yr -1, which is in the range of previously reported values. Although Hg and MeHg yields from tidal mangrove swamps have not been previously measured, our estimated yields of Hg species (28 ?? 4.5 ??g total Hg m -2 yr -1 and 3.1 ?? 0.4 ??g methyl Hg m -2 yr -1) were five times greater than is typically reported for terrestrial wetlands. These results indicate that in addition to the well documented contributions of DOC, tidally driven export from mangroves represents a significant potential source of Hg and MeHg to nearby coastal waters. ?? 2011 American Chemical Society.

Influence of the segmentation on the characterization of cerebral networks of structural damage for patients with disorders of consciousness

NASA Astrophysics Data System (ADS)

Martínez, Darwin; Mahalingam, Jamuna J.; Soddu, Andrea; Franco, Hugo; Lepore, Natasha; Laureys, Steven; Gómez, Francisco

2015-01-01

Disorders of consciousness (DOC) are a consequence of a variety of severe brain injuries. DOC commonly results in anatomical brain modifications, which can affect cortical and sub-cortical brain structures. Postmortem studies suggest that severity of brain damage correlates with level of impairment in DOC. In-vivo studies in neuroimaging mainly focus in alterations on single structures. Recent evidence suggests that rather than one, multiple brain regions can be simultaneously affected by this condition. In other words, DOC may be linked to an underlying cerebral network of structural damage. Recently, geometrical spatial relationships among key sub-cortical brain regions, such as left and right thalamus and brain stem, have been used for the characterization of this network. This approach is strongly supported on automatic segmentation processes, which aim to extract regions of interests without human intervention. Nevertheless, patients with DOC usually present massive structural brain changes. Therefore, segmentation methods may highly influence the characterization of the underlying cerebral network structure. In this work, we evaluate the level of characterization obtained by using the spatial relationships as descriptor of a sub-cortical cerebral network (left and right thalamus) in patients with DOC, when different segmentation approaches are used (FSL, Free-surfer and manual segmentation). Our results suggest that segmentation process may play a critical role for the construction of robust and reliable structural characterization of DOC conditions.

Tidally Driven Export of Dissolved Organic Carbon, Total Mercury, and Methylmercury from a Mangrove-Dominated Estuary

PubMed Central

2011-01-01

The flux of dissolved organic carbon (DOC) from mangrove swamps accounts for 10% of the global terrestrial flux of DOC to coastal oceans. Recent findings of high concentrations of mercury (Hg) and methylmercury (MeHg) in mangroves, in conjunction with the common co-occurrence of DOC and Hg species, have raised concerns that mercury fluxes may also be large. We used a novel approach to estimate export of DOC, Hg, and MeHg to coastal waters from a mangrove-dominated estuary in Everglades National Park (Florida, USA). Using in situ measurements of fluorescent dissolved organic matter as a proxy for DOC, filtered total Hg, and filtered MeHg, we estimated the DOC yield to be 180 (±12.6) g C m–2 yr–1, which is in the range of previously reported values. Although Hg and MeHg yields from tidal mangrove swamps have not been previously measured, our estimated yields of Hg species (28 ± 4.5 μg total Hg m–2 yr–1 and 3.1 ± 0.4 μg methyl Hg m–2 yr–1) were five times greater than is typically reported for terrestrial wetlands. These results indicate that in addition to the well documented contributions of DOC, tidally driven export from mangroves represents a significant potential source of Hg and MeHg to nearby coastal waters. PMID:22206226

Linking aboveground net primary productivity to soil carbon and dissolved organic carbon in complex terrain

Treesearch

F.S. Peterson; K. Lajtha

2013-01-01

Factors influencing soil organic matter (SOM) stabilization and dissolved organic carbon (DOC) content in complex terrain, where vegetation, climate, and topography vary over the scale of a few meters, are not well understood. We examined the spatial correlations of lidar and geographic information system-derived landscape topography, empirically measured soil...

Carbon dynamics in peatland pool systems: the role of light

NASA Astrophysics Data System (ADS)

Pickard, Amy; Heal, Kate; McLeod, Andy; Dinsmore, Kerry

2016-04-01

Open-water pools are widespread in peatlands and are considered to represent biogeochemical hotspots within the peatland landscape. However the contribution of pool systems to wider peatland C cycling has not been quantified fully and there is a lack of knowledge of the role of photochemical processes in such environments. In this study, light exposure experiments were conducted in two contrasting pools to test the reactivity of aquatic C. The first study site was located at Cross Lochs (CL), Forsinard, in the Flow Country of Northern Scotland, in a 412 m2 pool characterised by low dissolved organic carbon (DOC) concentrations (˜15 mg C L-1). The second site was located at Red Moss of Balerno (RM), a raised bog in central Scotland, in a 48 m2 pool with high DOC concentrations (˜35 mg C L-1). Experiments took place over 9 days in situ at each pool in mid-summer 2015, with 500 mL water samples contained in bags transparent to sunlight and in opaque control bags. After field exposure, optical, chemical and stable C isotope analyses were conducted on the samples. Significant differences in biogeochemical cycling of DOC were detected between the two systems, with DOC losses as a percentage of the total C pool 15% higher at RM than at CL after light exposure. The mean DOC concentration of light exposed samples at RM declined steeply initially, with 83% observed DOC degradation occurring by day 3 of the experiment. Total losses of 7.9 mg DOC L-1were observed in light exposed samples at RM, along with decreasing E4:E6 ratios, suggesting that material remaining at the end of the experiment was humified. Depletion of DOC was positively correlated with production of CO2 at both sites, with concentrations of up to 4.3 mg CO2-C L-1 recorded at RM. Stable C isotope signatures at both sites were altered under light treatment, as demonstrated by the production of enriched δ13C-DOC (+0.46 ‰ relative to opaque bags) and depleted δ13C-DIC (-0.97 ‰ relative to opaque bags) at RM. However, at CL, the δ13C-DOC signature in both the light exposed and opaque bags was depleted (-0.2‰ and -0.4 ‰ respectively), suggesting that microbial processing was the preferential DOC processing pathway in this system. These results show that C in peatland pools is highly reactive and further demonstrate the importance of photochemical processing of C, which should be considered as a significant driver of biogeochemical cycling.

Influence of organic carbon loading, sediment associated metal oxide content and sediment grain size distributions upon Cryptosporidium parvum removal during riverbank filtration operations, Sonoma County, CA.

PubMed

Metge, D W; Harvey, R W; Aiken, G R; Anders, R; Lincoln, G; Jasperse, J

2010-02-01

This study assessed the efficacy for removing Cryptosporidium parvum oocysts of poorly sorted, Fe- and Al-rich, subsurface sediments collected from 0.9 to 4.9 and 1.7-13.9 m below land surface at an operating riverbank filtration (RBF) site (Russian River, Sonoma County, CA). Both formaldehyde-killed oocysts and oocyst-sized (3 microm) microspheres were employed in sediment-packed flow-through and static columns. The degree of surface coverage of metal oxides on sediment grain surfaces correlated strongly with the degrees of oocyst and microsphere removals. In contrast, average grain size (D(50)) was not a good indicator of either microsphere or oocyst removal, suggesting that the primary mechanism of immobilization within these sediments is sorptive filtration rather than physical straining. A low specific UV absorbance (SUVA) for organic matter isolated from the Russian River, suggested that the modest concentration of the SUVA component (0.8 mg L(-1)) of the 2.2 mg L(-1) dissolved organic carbon (DOC) is relatively unreactive. Nevertheless, an amendment of 2.2 mg L(-1) of isolated river DOC to column sediments resulted in up to a 35.7% decrease in sorption of oocysts and (or) oocyst-sized microspheres. Amendments (3.2 microM) of the anionic surfactant, sodium dodecyl benzene sulfonate (SDBS) also caused substantive decreases (up to 31.9 times) in colloid filtration. Although the grain-surface metal oxides were found to have a high colloid-removal capacity, our study suggested that any major changes within the watershed that would result in long-term alterations in either the quantity and (or) the character of the river's DOC could alter the effectiveness of pathogen removal during RBF operations. Published by Elsevier Ltd.

Experimental determinations of soil copper toxicity to lettuce (Lactuca sativa) growth in highly different copper spiked and aged soils.

PubMed

Christiansen, Karen S; Borggaard, Ole K; Holm, Peter E; Vijver, Martina G; Hauschild, Michael Z; Peijnenburg, Willie J G M

2015-04-01

Accurate knowledge about factors and conditions determining copper (Cu) toxicity in soil is needed for predicting plant growth in various Cu-contaminated soils. Therefore, effects of Cu on growth (biomass production) of lettuce (Lactuca sativa) were tested on seven selected, very different soils spiked with Cu and aged for 2 months at 35 °C. Cu toxicity was expressed as pEC50(Cu(2+)), i.e., the negative logarithm of the EC50(Cu(2+)) activity to plant growth. The determined pEC50(Cu(2+)) was significantly and positively correlated with both the analytically readily available soil pH and concentration of dissolved organic carbon [DOC] which together could explain 87% of the pEC50(Cu(2+)) variation according to the simple equation: pEC50(Cu(2+)) = 0.98 × pH + 345 × [DOC] - 0.27. Other soil characteristics, including the base cation concentrations (Na(+), K(+), Ca(2+), Mg(2+)), the cation exchange capacity at soil pH (ECEC), and at pH 7 (CEC7), soil organic carbon, clay content, and electric conductivity as well as the distribution coefficient (Kd) calculated as the ratio between total soil Cu and water-extractable Cu did not correlate significantly with pEC50(Cu(2+)). Consequently, Cu toxicity, expressed as the negative log of the Cu(2+) activity, to plant growth increases at increasing pH and DOC, which needs to be considered in future management of plant growth on Cu-contaminated soils. The developed regression equation allows identification of soil types in which the phytotoxicity potential of Cu is highest.

Simulated climate change impact on summer dissolved organic carbon release from peat and surface vegetation: implications for drinking water treatment.

PubMed

Ritson, Jonathan P; Bell, Michael; Graham, Nigel J D; Templeton, Michael R; Brazier, Richard E; Verhoef, Anne; Freeman, Chris; Clark, Joanna M

2014-12-15

Uncertainty regarding changes in dissolved organic carbon (DOC) quantity and quality has created interest in managing peatlands for their ecosystem services such as drinking water provision. The evidence base for such interventions is, however, sometimes contradictory. We performed a laboratory climate manipulation using a factorial design on two dominant peatland vegetation types (Calluna vulgaris and Sphagnum Spp.) and a peat soil collected from a drinking water catchment in Exmoor National Park, UK. Temperature and rainfall were set to represent baseline and future conditions under the UKCP09 2080s high emissions scenario for July and August. DOC leachate then underwent standard water treatment of coagulation/flocculation before chlorination. C. vulgaris leached more DOC than Sphagnum Spp. (7.17 versus 3.00 mg g(-1)) with higher specific ultraviolet (SUVA) values and a greater sensitivity to climate, leaching more DOC under simulated future conditions. The peat soil leached less DOC (0.37 mg g(-1)) than the vegetation and was less sensitive to climate. Differences in coagulation removal efficiency between the DOC sources appears to be driven by relative solubilisation of protein-like DOC, observed through the fluorescence peak C/T. Post-coagulation only differences between vegetation types were detected for the regulated disinfection by-products (DBPs), suggesting climate change influence at this scale can be removed via coagulation. Our results suggest current biodiversity restoration programmes to encourage Sphagnum Spp. will result in lower DOC concentrations and SUVA values, particularly with warmer and drier summers. Copyright © 2014 Elsevier Ltd. All rights reserved.

CDOM-DOC relationship in contrasted coastal waters: implication for DOC retrieval from ocean color remote sensing observation.

PubMed

Vantrepotte, Vincent; Danhiez, François-Pierre; Loisel, Hubert; Ouillon, Sylvain; Mériaux, Xavier; Cauvin, Arnaud; Dessailly, David

2015-01-12

Increasing our knowledge on dissolved organic carbon (DOC) spatio-temporal distribution in the coastal ocean represents a crucial challenge for better understanding the role of these ecosystems in the global oceanic carbon cycle. The assessment of DOC concentration from the absorption properties of the colored part of the dissolved organic matter (a(cdom)) was investigated from an extensive data set covering a variety of coastal environments. Our results confirmed that variation in the a(cdom)(412) to DOC ratio (a*(cdom)(412)) can be depicted from the CDOM spectral slope in the UV domain (S(275-295)). They also evidenced that regional first order variation in both a*(cdom)(412) and S(275-295) are highly correlated to variation in a(cdom)(412). From these observations, generalized relationships for estimating a*(cdom)(412) from S(275-295) or a(cdom)(412) were parameterized from our development sites (N = 158; English Channel, French Guiana, Hai Phong Bay) and tested against an independent data set covering others coastal regions (N = 223; French Polynesia, Rhone River estuary, Gulf of Maine, Chesapeake Bay, Southern Middle Atlantic Bight) demonstrating the possibility to derive DOC estimates from in situ CDOM optical properties with an average accuracy of ~16% over very contrasted coastal environments (with DOC ranging from 50 to 250 µmol.L(-1)). The applicability of these generalized approaches was evaluated in the context of ocean color remote sensing observation emphasizing the limits of S(275-295)-based formulations and the potential for a(cdom)-based approaches to represent a compelling alternative for assessing synoptic DOC distribution.

Hydrologic flow paths control dissolved organic carbon fluxes and metabolism in an Alpine stream hyporheic zone

NASA Astrophysics Data System (ADS)

Battin, Tom J.

1999-10-01

The objective of the present paper was to link reach-scale streambed reactive uptake of dissolved organic carbon (DOC) and dissolved oxygen (DO) to subsurface flow paths in an alpine stream (Oberer Seebach (OSB)). The topography adjacent to the stream channel largely determined flow paths, with shallow hillslope groundwater flowing beneath the stream and entering the alluvial groundwater at the opposite bank. As computed from hydrometric data, OSB consistently lost stream water to groundwater with fluxes out of the stream averaging 943 ± 47 and 664 ± 45 L m-2 h-1 at low (Q < 600 L s-1) and high (Q > 600 L s-1) flow, respectively. Hydrometric segregation of streambed fluxes and physicochemical mixing analysis indicated that stream water was the major input component to the streambed with average contributions of 70-80% to the hyporheic zone (i.e., the subsurface zone where shallow groundwater and stream water mix). Surface water was also the major source of DOC with 0.512 ± 0.043 mg C m-2 h-1 to the streambed. The DOC flux from shallow riparian groundwater was lower (0.309 ± 0.071 mg C m-2 h-1) and peaked in autumn with 1.011 mg C m-2 h-1. I computed the relative proportion of downstream discharge through the streambed as the ratio of the downstream length (Ssw) a stream water parcel travels before entering the streambed to the downstream length (Shyp) a streambed water parcel travels before returning to the stream water. The relative streambed DOC retention efficiency, calculated as (input-output)/input of interstitial DOC, correlated with the proportion (Ssw/Shyp) of downstream discharge (r2 = 0.76, p = 0.006). Also, did the streambed metabolism (calculated as DO uptake from mass balance) decrease with low subsurface downstream routing, whereas elevated downstream discharge through the streambed stimulated DO uptake (r2 = 0.69, p = 0.019)? Despite the very short DOC turnover times (˜0.05 days, calculated as mean standing stock/annual input) within the streambed, the latter constitutes a net sink of DOC (˜14 mg C m-2 h-1). Along with high standing stocks of sediment associated particulate organic carbon, these results suggest microbial biofilms as the major retention and storage site of DOC in an alpine stream where large hydrologic exchange controls DOC fluxes.

[Distribution characteristics of soil organic carbon of burned area under different restorations.

PubMed

Li, Hong Yun; Xin, Ying; Zhao, Yu Sen

2016-09-01

The distribution characteristics of soil organic carbon (SOC), soil dissolved organic carbon (DOC) and soil microbial biomass carbon (MBC) under different restorations were studied in Larix gmelinii plantation, Pinus sylvestris var. mongolica plantation, artificial promotion poplar-birch forest and the natural secondary poplar-birch forest restored from burned area after the severe fire of Greater Xing' an Mountains in 1987. The results showed that the variations in SOC, DOC and MBC ranged from 9.63 to 79.72 g·kg -1 , from 33.21 to 186.30 mg·kg -1 and from 200.85 to 1755.63 mg·kg -1 , respectively, which decreased with soil depth increasing. There was significant diffe-rence in SOC, DOC and MBC among different restorations, with the maximum carbon contents for artificial promotion poplar-birch forest, followed by L. gmelinii plantation, natural secondary poplar-birch forest and P. sylvestris var. mongolica plantation successively. The soil microbial quotient va-ried from 1.1% under P. sylvestris var. mongolica plantation to 2.3% under artificial promotion poplar-birch forest, and its vertical distributions were different in the four restoration forests. Correlation analysis indicated that MBC had a significant positive correlation with SOC and DOC, respectively. The activity of soil organic carbon in artificial promotion poplar-birch forest was higher than in other forest stands, suggesting a stronger capacity of the soil carbon cycle through natural regeneration with artificial promotion on burned area in Greater Xing'an Mountains.

Biogeochemistry of a treeline watershed, northwestern Alaska

USGS Publications Warehouse

Stottlemyer, R.

2001-01-01

Since 1950, mean annual temperatures in northwestern Alaska have increased. Change in forest floor and soil temperature or moisture could alter N mineralization rates, production of dissolved organic carbon (DOC) and organic nitrogen (DON), and their export to the aquatic ecosystem. In 1990, we began study of nutrient cycles in the 800-ha Asik watershed, located at treeline in the Noatak National Preserve, northwestern Alaska. This paper summarizes relationships between topographic aspect, soil temperature and moisture, inorganic and organic N pools, C pools, CO2 efflux, growing season net N mineralization rates, and stream water chemistry. Forest floor (O2) C/N ratios, C pools, temperature, and moisture were greater on south aspects. More rapid melt of the soil active layer (zone of annual freeze-thaw) and permafrost accounted for the higher moisture. The O2 C and N content were correlated with moisture, inorganic N pools, CO2 efflux, and inversely with temperature. Inorganic N pools were correlated with temperature and CO2 efflux. Net N mineralization rates were positive in early summer, and correlated with O2 moisture, temperature, and C and N pools. Net nitrification rates were inversely correlated with moisture, total C and N. The CO2 efflux increased with temperature and moisture, and was greater on south aspects. Stream ion concentrations declined and DOC increased with discharge. Stream inorganic nitrogen (DIN) output exceeded input by 70%. Alpine stream water nitrate (NO-3) and DOC concentrations indicated substantial contributions to the watershed DIN and DOC budgets.

Biogeochemistry of a treeline watershed, northwestern Alaska.

PubMed

Stottlemyer, R

2001-01-01

Since 1950, mean annual temperatures in northwestern Alaska have increased. Change in forest floor and soil temperature or moisture could alter N mineralization rates, production of dissolved organic carbon (DOC) and organic nitrogen (DON), and their export to the aquatic ecosystem. In 1990, we began study of nutrient cycles in the 800-ha Asik watershed, located at treeline in the Noatak National Preserve, northwestern Alaska. This paper summarizes relationships between topographic aspect, soil temperature and moisture, inorganic and organic N pools, C pools, CO2 efflux, growing season net N mineralization rates, and stream water chemistry. Forest floor (O2) C/N ratios, C pools, temperature, and moisture were greater on south aspects. More rapid melt of the soil active layer (zone of annual freeze-thaw) and permafrost accounted for the higher moisture. The O2 C and N content were correlated with moisture, inorganic N pools, CO2 efflux, and inversely with temperature. Inorganic N pools were correlated with temperature and CO2 efflux. Net N mineralization rates were positive in early summer, and correlated with O2 moisture, temperature, and C and N pools. Net nitrification rates were inversely correlated with moisture, total C and N. The CO2 efflux increased with temperature and moisture, and was greater on south aspects. Stream ion concentrations declined and DOC increased with discharge. Stream inorganic nitrogen (DIN) output exceeded input by 70%. Alpine stream water nitrate (NO3-) and DOC concentrations indicated substantial contributions to the watershed DIN and DOC budgets.

Variation of the isotopic composition of dissolved organic carbon during the runoff cycle in the Amazon River and the floodplains

NASA Astrophysics Data System (ADS)

Albéric, Patrick; Pérez, Marcela A. P.; Moreira-Turcq, Patricia; Benedetti, Marc F.; Bouillon, Steven; Abril, Gwenaël

2018-01-01

Given the relative scarcity of stable isotope data on dissolved organic carbon (DOC) in the Amazon Basin, we hypothesized that the variability in DOC sources may be underestimated in such major river basins. To explore the links between the mainstem and tributaries and the floodplain, particular efforts were made during five distinct cruises at different stages of the hydrograph between October 2008 and January 2011, to document the spatial and temporal variation of DOC concentrations and δ13C-DOC in the central Amazon River system (Brazil). Based on more than 200 data, the spatial and temporal variability of δ13C-DOC values was found to be larger than previously reported in the same area. Although a small range of variation was observed throughout the hydrological cycle in the upper reach of the studied section (-29.2 to -29.5‰ in the Rio Negro and -28.7 to -29.0‰ in the Rio Solimões), a much larger one (-28.0 to -34.6‰) was found in the lower reach of the river, as the proportion of open lakes increased downstream in the floodplains. The low variability in the upper reaches suggests constant and homogeneous DOC sources from upland soils and flooded forest, while lower δ13C-DOC values recorded in the lower reach mainstem at high and falling waters can be attributed to a greater export of plankton-derived 13C-depleted DOC from flooded lakes. Noteworthy are the higher δ13C-DOC values measured in the Rio Madeira and the associated flooded lakes (-26.5 to -28.8‰), which may reflect the imprint from upland headwaters and a weaker density of flooded forest in the watershed. The higher δ13C-DOC values observed in the lower reach during low waters are still not fully understood. Floating meadows principally consisting of C4 macrophytes were found to increase δ13C-DOC values by ∼1.5‰ in their vicinity, but this impact was no longer noticeable at distances of ∼10 m from the plant rafts. This rather modest 13C-enrichment suggests rapid decomposition and/or dilution of this wetland-derived DOC.

Identifying dissolved organic carbon sources at a gaged headwater catchment using FDOM sensors

NASA Astrophysics Data System (ADS)

Malzone, J. M.; Shanley, J. B.

2014-12-01

The United States Geological Survey's (USGS) W-9 gage at the headwaters of Sleepers River, Vermont has been monitored for dissolved organic carbon (DOC) concentration for more than 20 years. However, the sources of this DOC during base flow and hydrologic events remain unclear. The major objectives of this research were to identify sources of DOC during storm events and to explain the observed DOC-streamflow counterclockwise hysteresis during hydrologic events. Two main hypotheses to explain hysteresis during hydrologic events were tested: (1) distant headwater wetlands are the major DOC source, which lags behind peak flow due to travel time; and (2) the entire watershed contributes to the DOC at the gage, but the response of DOC lags behind the period when groundwater contributes most to streamflow. Sources of DOC were tracked using fluorescent dissolved organic matter (FDOM) sensors in surface water and groundwater wells. Wells were installed at four depths, 0.3, 0.6, 0.9, and 1.2 m, at four sites: a peaty low-gradient riparian area near the headwaters; a mid-hillslope area on a long hillslope mid-watershed; a near-stream area on a long hillslope mid-watershed; and a low-gradient tributary confluence area just above the gage. During storm events, FDOM and hydraulic head were measured at the nested groundwater wells. Samples for DOC analysis were also taken to determine the relationship between FDOM and DOC. Results suggest that both distant sources and the greater watershed played a role in the transport of DOC to the W-9 gage. Distant peaty sources dominated during large storms and contributed the highest surface water FDOM measurements. The peak FDOM at the gage was therefore best described as a result of transport. However, export from these distant sources terminated rapidly and did not explain continued elevated FDOM at the gage. Groundwater across the watershed exhibited hysteresis analogous to that in the stream itself, with FDOM peaking as head receded. As groundwater is recharged, the water table intersects more carbon rich soil layers. Pre-event water is flushed out first before event water mobilizes DOC, causing the groundwater hysteresis. High FDOM groundwater discharging to the stream likely sustained elevated FDOM at the gage. The gage hysteresis, therefore, seems to be a result of both hypotheses tested.

First assessment of water and carbon cycles in two tropical coastal rivers of south-west India: an isotopic approach.

PubMed

Tripti, M; Lambs, L; Otto, T; Gurumurthy, G P; Teisserenc, R; Moussa, I; Balakrishna, K; Probst, J L

2013-08-15

The contribution of tropical coastal rivers to the global carbon budget remains unmeasured, despite their high water dynamics, i.e. higher run-off with their basin characteristic of warm temperature. Two rivers draining the western part of the Western Ghats, the Swarna (length 80 km) and Nethravati (147 km) Rivers, were studied for water and carbon cycles. The stable isotope ratios of oxygen (δ(18) O values), hydrogen (δ(2) H values) and carbon (δ(13) C values) were used to understand the water circulation, the weathering processes and the carbon biogeochemical cycle. The river water samples were collected during the dry post-monsoonal season (November 2011). The δ(18) O and δ(2) H values of river water suggested that the monsoonal vapour source and its high recycling have a dominant role because of the orographical and tropical conditions. The absence of calcareous rocks has led to dissolved inorganic carbon (DIC) mainly originating from atmospheric/soil CO2 , via rock-weathering processes, and the low soil organic matter combined with high run-off intensity has led to low riverine dissolved organic carbon (DOC) contents. The δ(13) C values increase from upstream to downstream and decrease with increasing pCO2 . There is a positive relationship between the δ(13) CDIC values and the DOC concentrations in these two rivers that is contrary to that in most of the studied rivers of the world. The higher evapotranspiration supported by tropical conditions suggests that there are higher vapour recycling process in the Swarna and Nethravati basins as studied from the water δ(18) O and δ(2) H values. The basin characteristics of higher rainfall/run-off accompanied by warm temperature suggest that the δ(13) C value of riverine DIC is mainly controlled by the weathering of source rocks (silicates) with variation along the river course by CO2 degassing from the river water to the atmosphere and is less dominated by the oxidation of DOC. Copyright © 2013 John Wiley & Sons, Ltd.

Influence of intermittent stream connectivity on water quality and salmonid survivorship.

NASA Astrophysics Data System (ADS)

Hildebrand, J.; Woelfle-Erskine, C. A.; Larsen, L.

2014-12-01

Anthropogenic stress and climate change are causing an increasing number of California streams to become intermittent and are driving earlier and more severe summertime drying. The extent to which emerging water conservation alternatives impact flows or habitat quality (e.g. temperature, DO) for salmonids remains poorly understood. Here, we investigate the proximal drivers of salmonid mortality over a range of connectivity conditions during summertime intermittency in Salmon Creek watershed, Sonoma County, CA. Through extensive sampling in paired subwatersheds over a period of two years, we tested the hypothesis that accumulation of readily bioavailable DOC in poorly flushed pools drives DO decline associated with loss of salmonids. We then traced the origin and flow pathways of DOC throughout the watershed using Parallel Factor Analysis (PARAFAC). We obtained samples for DOC and stable isotope analyses at monthly intervals from 20 piezometers and surface water in the study reaches and from private wells and springs distributed throughout the watersheds. We also obtained in situ DO, conductivity and pH readings within stream study reaches. We determined DOC quality by SUVA (specific UV absorbance) and fluorescence index. We calculated stream metabolism rates using the single station method. In pools instrumented with DO sensors, we compared changing DOC quality during the summer months to changes in DO concentrations and stream metabolism. Our results show that the duration of complete disconnection of pools during the summer months and stream metabolic rates are positively correlated with salmonid mortality. Furthermore, our results indicate that salmonid mortality is greatest in disconnected pools with low DOC fluorescence indices and high SUVA values, indicative of terrestrially derived DOC and little or no groundwater inflow. Conversely low salmonid mortality was found in disconnected pools with high fluorescence index and low SUVA, indicative of microbially derived DOC. These pools showed clear signs of hyporheic inflow during summertime drying despite complete surficial disconnection. PARAFAC analysis pinpointed groundwater sources of hyporheic flow in the watershed, suggesting that targeted aquifer recharge may contribute to salmonid recovery by augmenting flow in summer refugia.

Patterns in DOC Concentration and Composition in Tundra Watersheds in the Kolyma River Basin

NASA Astrophysics Data System (ADS)

Behnke, M. I.; Schade, J. D.; Fiske, G. J.; Whittinghill, K. A.; Zimov, N.

2014-12-01

Much of the world's soil carbon is frozen in permafrost in the Arctic. As the climate warms and permafrost thaws, this carbon will again be actively cycled. Whether it is exported to the ocean or released as greenhouse gases to the atmosphere depends on the form of carbon compounds and conditions encountered during transport, and will determine the strength of permafrost thaw as a feedback on climate change. To better understand the fate of this carbon, we determined how and where in the landscape dissolved organic carbon (DOC) breaks down as water transports it from tundra to ocean. We compared DOC concentration and composition along flowpaths within watersheds and at the mouths of watersheds differing in drainage area. We incubated filtered water samples in light and dark, including filter-sterilized samples, to assess the interactions between light and microbial processing as mechanisms of DOC loss. Composition was assessed using optical measurements associated with the structure of organic compounds. DOC concentration declined along flowpaths within watersheds, with most loss occurring in aquatic environments high in the landscape. We also found a negative correlation between watershed size and DOC concentration. These results suggest that much of the processing of organic carbon occurs in small streams. In addition, the relationship with drainage area suggests that residence time in streams has a large impact on transformation of terrestrial carbon during transport. We found no substantial differences in optical characteristics of DOC, indicating that breakdown processes were not selective, and that light caused much of the breakdown. This conclusion is supported by the incubation experiment, which showed greater breakdown by light, and evidence that light stimulated higher rates of microbial processing. These results highlight the importance of inland aquatic ecosystems as processors of organic matter, and suggest that organic carbon from permafrost thaw is likely to be processed high in the landscape rather than transported to the ocean. Furthermore, the importance of light-induced breakdown as a mechanism for carbon loss suggests that the timing of DOC transport relative to seasonal changes in light intensity may influence the impact of permafrost thaw on climate change.

Contrasting vulnerability of drained tropical and high-latitude peatlands to fluvial loss of stored carbon

NASA Astrophysics Data System (ADS)

Evans, Chris D.; Page, Susan E.; Jones, Tim; Moore, Sam; Gauci, Vincent; Laiho, Raija; Hruška, Jakub; Allott, Tim E. H.; Billett, Michael F.; Tipping, Ed; Freeman, Chris; Garnett, Mark H.

2014-11-01

Carbon sequestration and storage in peatlands rely on consistently high water tables. Anthropogenic pressures including drainage, burning, land conversion for agriculture, timber, and biofuel production, cause loss of pressures including drainage, burning, land conversion for agriculture, timber, and biofuel production, cause loss of peat-forming vegetation and exposure of previously anaerobic peat to aerobic decomposition. This can shift peatlands from net CO2 sinks to large CO2 sources, releasing carbon held for millennia. Peatlands also export significant quantities of carbon via fluvial pathways, mainly as dissolved organic carbon (DOC). We analyzed radiocarbon (14C) levels of DOC in drainage water from multiple peatlands in Europe and Southeast Asia, to infer differences in the age of carbon lost from intact and drained systems. In most cases, drainage led to increased release of older carbon from the peat profile but with marked differences related to peat type. Very low DOC-14C levels in runoff from drained tropical peatlands indicate loss of very old (centuries to millennia) stored peat carbon. High-latitude peatlands appear more resilient to drainage; 14C measurements from UK blanket bogs suggest that exported DOC remains young (<50 years) despite drainage. Boreal and temperate fens and raised bogs in Finland and the Czech Republic showed intermediate sensitivity. We attribute observed differences to physical and climatic differences between peatlands, in particular, hydraulic conductivity and temperature, as well as the extent of disturbance associated with drainage, notably land use changes in the tropics. Data from the UK Peak District, an area where air pollution and intensive land management have triggered Sphagnum loss and peat erosion, suggest that additional anthropogenic pressures may trigger fluvial loss of much older (>500 year) carbon in high-latitude systems. Rewetting at least partially offsets drainage effects on DOC age.

Changes in the quality of river water before, during and after a major flood event associated with a La Niña cycle and treatment for drinking purposes.

PubMed

Murshed, Mohamad Fared; Aslam, Zeeshan; Lewis, Rosmala; Chow, Christopher; Wang, Dongsheng; Drikas, Mary; van Leeuwen, John

2014-10-01

The treatment of organics present in the lower reaches of a major river system (the Murray-Darling Basin, Australia) before (March-July 2010), during (December 2010-May 2011) and after (April-December 2012) a major flood period was investigated. The flood period (over 6months) occurred during an intense La Niña cycle, leading to rapid and high increases in river flows and organic loads in the river water. Dissolved organic carbon (DOC) increased (2-3 times) to high concentrations (up to 16mg/L) and was found to correlate with river flow rates. The treatability of organics was studied using conventional jar tests with alum and an enhanced coagulation model (mEnCo©). Predicted mean alum dose rates (per mg DOC) were higher before (9.1mg alum/mg DOC) and after (8.5mg alum/mg DOC) than during the flood event (8.0mg alum/mg DOC), indicating differences in the character of the organics in raw waters. To assess the character of natural organic matter present in raw and treated waters, high performance size exclusion chromatography with UV and fluorescence detectors were used. During the flood period, high molecular weight UV absorbing compounds (>2kDa) were mostly detected in waters collected, but were not evident in waters collected before and afterwards. The relative abundances of humic-like and protein-like compounds during and following the flood period were also investigated and found to be of a higher molecular weight during the flood period. The treatability of the organics was found to vary over the three climate conditions investigated. Copyright © 2014. Published by Elsevier B.V.

Evaluating the sorption of organophosphate esters to different sourced humic acids and its effects on the toxicity to Daphnia magna.

PubMed

Pang, Long; Liu, Jingfu; Yin, Yongguang; Shen, Mohai

2013-12-01

Because of large usage as flame retardants and additives, organophosphate esters (OPEs) are widely detected in the environment and regarded as emerging contaminants. However, the sorption of OPEs to organic matter and its effects have scarcely been studied. In the present study, the sorption of 9 commonly used OPEs to 4 representative humic acids--Elliott Soil humic acid, Suwannee River humic acid, Aldrich humic acid, and Acros humic acid--in the range of 0 mg/L to 50 mg/L dissolved organic carbon (DOC), was evaluated with negligible-depletion solid-phase microextraction and verified by its impacts on the toxicity to the aquatic invertebrate Daphnia magna. Whereas OPEs with a high octanol/water partition coefficient (log K(OW)=4.51-6.64) were associated with humic acids mainly by hydrophobic interaction with DOC partition coefficient (K(DOC)) in the range of 10²·²² to 10⁵·³¹, the sorption of low-K(OW) OPEs (log K(OW)=-0.65 to 2.59) to humic acids was not hydrophobic interaction-dominant, with K(DOC) in the range of 10³·⁴⁷ to 10⁴·²⁹. These results were corroborated by the effects of humic acids on the acute toxicity of 3 high-K(OW) OPEs to D. magna. The sorption of OPEs to Suwannee River humic acid was weak and had negligible effects on the toxicity of high-K(OW) OPEs; the presence of terrestrial Acros humic acid (50 mg/L DOC), however, significantly decreased the toxicity by 53% to 60%. The results indicated that the strong sorption between high-K(OW) OPEs and terrestrial humic acid might affect their transportation and bioavailability. © 2013 SETAC.

Using stable isotopes to identify the scaling effects of riparian peatlands on runoff generation processes and DOC mobilisation

NASA Astrophysics Data System (ADS)

Tunaley, Claire; Tetzlaff, Doerthe; Soulsby, Chris

2017-04-01

Knowledge of hydrological sources, flow paths, and their connectivity is fundamental to understanding stream flow generation and surface water quality in peatlands. Stable isotopes are proven tools for tracking the sources and flow paths of runoff. However, relativity few studies have used isotopes in peat-dominated catchments. Here, we combined 13 months (June 2014 - July 2015) of daily isotope measurements in stream water with daily DOC and 15 minute FDOM (fluorescent component of dissolved organic matter) data, at three nested scales in NE Scotland, to identify the hydrological processes occurring in riparian peatlands. We investigated how runoff generation processes in a small, riparian peatland dominated headwater catchment (0.65 km2) propagate to larger scales (3.2 km2 and 31 km2) with decreasing percentage of riparian peatland coverage. Isotope damping was most pronounced in the 0.65 km2 catchment due to high water storage in the organic soils which encouraged tracer mixing and resulted in attenuated runoff peaks. At the largest scale, stream flow and water isotope dynamics showed a more flashy response. Particularly insightful in this study was calculating the deviation of the isotopes from the local meteoric water line, the lc-excess. The lc-excess revealed evaporative fractionation in the peatland dominated catchment, particularly during summer low flows. This implied high hydrological connectivity in the form of constant seepage from the peatlands sustaining high baseflows at the headwater scale. This constant connectivity resulted in high DOC concentrations at the peatland site during baseflow ( 5 mg l-1). In contrast, at the larger scales, DOC was minimal during low flows ( 2 mg l-1) due to increased groundwater influence and the disconnection between DOC sources and the stream. Insights into event dynamics through the analysis of DOC hysteresis loops showed slight dilution on the rising limb, the strong influence of dry antecedent conditions and a quick recovery between events at the riparian peatland site. Again, these dynamics were driven by the tight coupling and high connectivity of the landscape to the stream. At larger scales, the disconnection between the landscape units increased and the variable connectivity controlled runoff generation and DOC dynamics. The results presented here suggest that the hydrological processes occurring in riparian peatlands in headwater catchments are less evident at larger scales which may have implications for the larger scale impact of peatland restoration projects.

Concentration and age of DOC transported from thawing permafrost soils into Arctic headwater streams

NASA Astrophysics Data System (ADS)

Romano, E. L.; Wickland, K.; Ebert, C.; Schuur, E.

2017-12-01

As Arctic permafrost stability decreases due to global climate change, hydrologic dynamics in catchments underlain by permafrost are expected to shift. The thickness of seasonally thawed surface soils is an important driver of the extent to which carbon (C) that was previously stored as frozen soil organic carbon (SOC) will be transported laterally as dissolved organic carbon (DOC). The concentration and radiocarbon (14C) age of newly thawed DOC that moves downslope through tundra soils and is delivered to headwater streams is an important indicator of changing C dynamics. Understanding the timing and quantity of C loss in this form is imperative for greenhouse gas emission and soil C stock estimates, as well as predicting the impact of permafrost thaw on aquatic ecosystems. In this study we examined the relationship between DOC concentrations, 14C-DOC, and active layer thickness (ALT) in thawing soils over time. Water samples were collected once in July 2016 and weekly in 2017 from late May to late August from wells within a long-term tundra soil warming experiment (n=36), located in a discontinuous permafrost zone in Interior Alaska. Preliminary data from 2016 shows average maximum ALT at wells within the warming treatment of 68.9 cm, while wells from control averaged 86.6 cm. 2016 water sample data from wells within the warming treatment showed higher mean DOC concentrations (103.1 ± 32.5 mg/L) and older 14C-DOC values (-28.7 ± 21.1 ‰) than samples from the control (44.5 ± 3.0 mg/L and 11.3 ± 8.6 ‰). To assess inter-annual changes in DOC delivery to local headwater streams, DOC concentration and 14C-DOC were also measured on water samples taken in late summer of 2007, 2008, and 2016 from streams within the watershed surrounding the experimental sites. Weekly sampling in 2017 allowed analysis of seasonal patterns of DOC concentration for that year. Values increased slightly over time at some stream sites (ranging from 4-33 mg/L in 2012 to 2-80 mg/L in 2016). Seasonal and inter-annual permafrost thaw appears to drive the release of previously stored old C in the form of DOC, which increases downslope mobility. In-situ terrestrial greenhouse gas emission estimates may therefore underestimate C losses, especially when precipitation is high or early in the season when spring snowmelt and shallow ALT promote lateral transport of DOC.

Arsenic in the rhizosphere soil solution of ferns.

PubMed

Wei, Chaoyang; Zheng, Huan; Yu, Jiangping

2012-12-01

The aim of this study was to explore the evidence of arsenic hyperaccumulation in plant rhizosphere solutions. Six common fern plants were selected and grown in three types of substrate: arsenic (As) -tailings, As-spiked soil, and soil-As-tailing composites. A rhizobox was designed with an in-situ collection of soil solutions to analyze changes in the As concentration and valence as well as the pH, dissolved organic carbon (DOC) and total nitrogen (TN). Arsenite composed less than 20% of the total As, and As depletion was consistent with N depletion in the rhizosphere solutions of the various treatments. The As concentrations in the rhizosphere and non-rhizosphere solutions in the presence of plants were lower than in the respective controls without plants, except for in the As-spiked soils. The DOC concentrations were invariably higher in the rhizosphere versus non-rhizosphere solutions from the various plants; however, no significant increase in the DOC content was observed in Pteris vittata, in which only a slight decrease in pH appeared in the rhizosphere compared to non-rhizosphere solutions. The results showed that As reduction by plant roots was limited, acidification-induced solubilization was not the mechanism for As hyperaccumulation.

Impact of drainage on wettability of fen peat-moorsh soils

NASA Astrophysics Data System (ADS)

Szajdak, L.; Szatyłowicz, J.; Brandyk, T.

2009-04-01

High water retention in peat is attributed to structural voids (macro-pores) due to the partial degradation of the structure of peat-forming plants, and molecular absorption sites (micro-pores) associated with the formation of humic substances. Water retention by the heterogeneously-structured system in peat organic matter depends on the chemical structure of solid surfaces. These naturally wet solids, if dried sufficiently, lose the ability to rewet quickly when immersed in water. The ability of peat surfaces to attract and hold water is attributed to hydrophilic functional groups which characterize the organic substances of peat. The investigations of chemical and physical properties were performed for three different peat-moorsh soils located in the Biebrza River Valley in Poland. All examined soils were used as meadow. Soil samples were taken from two depths: 5-10 cm (moorsh) and 50-80 cm (peat). Total organic carbon (TOC), dissolved organic carbon (DOC) and humic acids (HA) extracted from these samples were analysed. Also basic physical properties such as ash content and bulk density were measured. Wetting behavior of soils was quantified using water drop penetration time test (WDPT) and measured values of the soil-water contact angle using sessile drop method. The measurements were conducted on air-dry soil samples which volumetric moisture content was not exceeding 7%. The significant differences in the concentrations of TOC, DOC and properties of HA between two investigated depth of among peat and moorsh samples were observed. The measured concentrations of total organic carbon in the considered soils ranged from 37.2 to 45.6%. Generally, the decrease of total organic carbon concentration with depth of profiles was observed. The contents of dissolved organic carbon in the soils ranged from 5.3 to 19.4%. The quantities of dissolved organic carbon decreased simultaneously with E4/E6 values and with the depth of the soil profiles. For the investigated peat's, an increase of the depth is accompanied by the decrease in the degree of humification or an increase in chemical maturity of HA. The measured values of the contact angle for investigated soils were in the range from 81.4˚ to 114.3˚ what indicates their high water repellency. The WDPT was positively correlated with total organic carbon, organic matter and humic acids content while ash content, soil bulk density, pH and absorbance were correlated negatively. The highest value of correlation coefficient (statistically significant) was obtained for relation between WDPT and ash content. The soil water contact angle was less correlated with peat-moorsh soil properties in comparison with WDPT with one exception pH. The pH against the contact angle indicates tendency of increasing the contact angle with decreasing pH.

Uranium isotopes and dissolved organic carbon in loess permafrost: Modeling the age of ancient ice

USGS Publications Warehouse

Ewing, Stephanie A.; Paces, James B.; O'Donnell, J.A.; Jorgenson, M.T.; Kanevskiy, M.Z.; Aiken, George R.; Shur, Y.; Harden, Jennifer W.; Striegl, Robert G.

2015-01-01

The residence time of ice in permafrost is an indicator of past climate history, and of the resilience and vulnerability of high-latitude ecosystems to global change. Development of geochemical indicators of ground-ice residence times in permafrost will advance understanding of the circumstances and evidence of permafrost formation, preservation, and thaw in response to climate warming and other disturbance. We used uranium isotopes to evaluate the residence time of segregated ground ice from ice-rich loess permafrost cores in central Alaska. Activity ratios of 234U vs. 238U (234U/238U) in water from thawed core sections ranged between 1.163 and 1.904 due to contact of ice and associated liquid water with mineral surfaces over time. Measured (234U/238U) values in ground ice showed an overall increase with depth in a series of five neighboring cores up to 21 m deep. This is consistent with increasing residence time of ice with depth as a result of accumulation of loess over time, as well as characteristic ice morphologies, high segregated ice content, and wedge ice, all of which support an interpretation of syngenetic permafrost formation associated with loess deposition. At the same time, stratigraphic evidence indicates some past sediment redistribution and possibly shallow thaw among cores, with local mixing of aged thaw waters. Using measures of surface area and a leaching experiment to determine U distribution, a geometric model of (234U/238U) evolution suggests mean ages of up to ∼200 ky BP in the deepest core, with estimated uncertainties of up to an order of magnitude. Evidence of secondary coatings on loess grains with elevated (234U/238U) values and U concentrations suggests that refinement of the geometric model to account for weathering processes is needed to reduce uncertainty. We suggest that in this area of deep ice-rich loess permafrost, ice bodies have been preserved from the last glacial period (10–100 ky BP), despite subsequent fluctuations in climate, fire disturbance and vegetation. Radiocarbon (14C) analysis of dissolved organic carbon (DOC) in thaw waters supports ages greater than ∼40 ky BP below 10 m. DOC concentrations in thaw waters increased with depth to maxima of >1000 ppm, despite little change in ice content or cryostructures. These relations suggest time-dependent production of old DOC that will be released upon permafrost thaw at a rate that is mediated by sediment transport, among other factors.

Drain blocking: an effective treatment for reducing dissolved organic carbon loss and water discolouration in a drained peatland.

PubMed

Wallage, Zoe E; Holden, Joseph; McDonald, Adrian T

2006-08-31

Peatlands are an important terrestrial carbon store. However, heightened levels of degradation in response to environmental change have resulted in an increased loss of dissolved organic carbon (DOC) and an associated rise in the level of discolouration in catchment waters. A significant threat to peatland sustainability has been the installation of artificial drainage ditches. However, recent restoration schemes have pursued drain blocking as a possible strategy for reducing degradation, fluvial carbon loss and water discolouration. This paper investigates the effect of open cut drainage and the impact of drain blocking on DOC and colour dynamics in blanket peat soil-water solutions. Three treatments (intact peat, drained peat and drain-blocked peat) were monitored in an upland blanket peat catchment in the UK. DOC and colour values were significantly higher on the drained slopes compared with those of the intact peat, which in turn had greater DOC and colour values than the drain-blocked slopes. Consequently, drain blocking is shown to be a highly successful technique in reducing both the DOC concentration and level of discolouration in soil waters, even to values lower than those observed for the intact site, which suggests a process of store exhaustion and flushing may operate. The colour per carbon unit (C/C) ratio was significantly higher at the drain-blocked site than either the intact or the drained treatments, while the E4/E6 ratio (fulvic acid/humic acid) was significantly lower at the blocked site compared to the two other treatments. The high C/C and low E4/E6 ratios indicate that drain blocking also modifies the composition of DOC, such that darker-coloured humic substances become more dominant compared to the intact site. This implies disturbance to DOC production and/or transportation processes operating within the peat.

Digital optical computer II

NASA Astrophysics Data System (ADS)

Guilfoyle, Peter S.; Stone, Richard V.

1991-12-01

OptiComp is currently completing a 32-bit, fully programmable digital optical computer (DOC II) that is designed to operate in a UNIX environment running RISC microcode. OptiComp's DOC II architecture is focused toward parallel microcode implementation where data is input in a dual rail format. By exploiting the physical principals inherent to optics (speed and low power consumption), an architectural balance of optical interconnects and software code efficiency can be achieved including high fan-in and fan-out. OptiComp's DOC II program is jointly sponsored by the Office of Naval Research (ONR), the Strategic Defense Initiative Office (SDIO), NASA space station group and Rome Laboratory (USAF). This paper not only describes the motivational basis behind DOC II but also provides an optical overview and architectural summary of the device that allows the emulation of any digital instruction set.

Effect of salinity on soil respiration in relation to dissolved organic carbon and microbial characteristics of a wetland in the Liaohe River estuary, Northeast China.

PubMed

Yang, Jisong; Zhan, Chao; Li, Yunzhao; Zhou, Di; Yu, Yang; Yu, Junbao

2018-06-18

Increasing salinity has important impacts on biogeochemical processes in estuary wetlands, with the potential to influence the soil respiration, dissolved organic carbon (DOC) and microbial population. However, it is unclear how soil respiration is related to changes in the DOC and microbial community composition with increasing salinity. In this study, soil cores were sampled from a brackish wetland in the Liaohe River estuary and treated by salinity solutions at four levels (fresh water, 3‰, 5‰, and 10‰). Samples of gas, water and soil were collected to determine the respiration rates and microbial community structure of the soil and the DOC leaching from the soil. Compared to the low-salinity treatments (fresh water and 3‰), the high-salinity treatments (5‰ and 10‰) decreased the soil respiration rates by 45-57% and decreased the DOC concentrations by 47-55%. However, no significant differences were observed within the low-salinity treatments nor the high-salinity treatments. There is a positive correlation between the soil respiration rates and DOC concentrations in all treatments, but it does not indicate a genetic cause-effect relationship between them. The microbial community structure varied with the salinity level, with higher β- and δ-Proteobacteria abundance, as well as higher Anaerolineae, and lower Clostridia abundance in the high-salinity treatments. The respiration rates were slightly negatively related to the richness of Proteobacteria and positively related to the richness of Clostridia. This study suggests that there may be a salinity threshold (3-10‰) impacting the organic carbon loss from estuarine brackish wetlands. In addition, the response of soil respiration to increasing salinity may be mainly linked to changes in the microbial community composition rather than changes in the DOC quantity. Copyright © 2018. Published by Elsevier B.V.

G-DOC: A Systems Medicine Platform for Personalized Oncology1

PubMed Central

Madhavan, Subha; Gusev, Yuriy; Harris, Michael; Tanenbaum, David M; Gauba, Robinder; Bhuvaneshwar, Krithika; Shinohara, Andrew; Rosso, Kevin; Carabet, Lavinia A; Song, Lei; Riggins, Rebecca B; Dakshanamurthy, Sivanesan; Wang, Yue; Byers, Stephen W; Clarke, Robert; Weiner, Louis M

2011-01-01

Currently, cancer therapy remains limited by a “one-size-fits-all” approach, whereby treatment decisions are based mainly on the clinical stage of disease, yet fail to reference the individual's underlying biology and its role driving malignancy. Identifying better personalized therapies for cancer treatment is hindered by the lack of high-quality “omics” data of sufficient size to produce meaningful results and the ability to integrate biomedical data from disparate technologies. Resolving these issues will help translation of therapies from research to clinic by helping clinicians develop patient-specific treatments based on the unique signatures of patient's tumor. Here we describe the Georgetown Database of Cancer (G-DOC), a Web platform that enables basic and clinical research by integrating patient characteristics and clinical outcome data with a variety of high-throughput research data in a unified environment. While several rich data repositories for high-dimensional research data exist in the public domain, most focus on a single-data type and do not support integration across multiple technologies. Currently, G-DOC contains data from more than 2500 breast cancer patients and 800 gastrointestinal cancer patients, G-DOC includes a broad collection of bioinformatics and systems biology tools for analysis and visualization of four major “omics” types: DNA, mRNA, microRNA, and metabolites. We believe that G-DOC will help facilitate systems medicine by providing identification of trends and patterns in integrated data sets and hence facilitate the use of better targeted therapies for cancer. A set of representative usage scenarios is provided to highlight the technical capabilities of this resource. PMID:21969811

The Influence of Wetland Cover and Dissolved Organic Carbon on Mercury Export in Forest Landscapes, Northeastern USA

NASA Astrophysics Data System (ADS)

Dittman, J. A.; Shanley, J. B.; Driscoll, C. T.; Aiken, G.; Chalmers, A.; Towse, J.

2007-12-01

Mercury (Hg) contamination is widespread in remote areas of the northeastern USA. Atmospheric Hg is deposited on terrestrial uplands and subsequently mobilized to downstream aquatic ecosystems. We are investigating the fate of Hg deposited in forested watersheds by quantifying stream transport of Hg, and the interactions with dissolved and particulate organic matter. We hypothesize that the landscape characteristics controlling the production and mobility of organic matter will likewise control the mobility of Hg. This research was conducted at three sites in the Northeast that represent a range of hydrochemical conditions and span a range of wetland cover. Most stream export of Hg occurs at high flow; therefore we collected samples during snowmelt and storms. Mercury concentrations increase with discharge at all three sites; however the partitioning of Hg fractions (dissolved vs. particulate) differs among sites during high flow events. At the Hubbard Brook Experimental Forest, NH (watershed 6), there are no true wetlands and dissolved organic carbon (DOC) and total Hg (THg) concentrations, and suspended sediment concentration (SSC) (mean DOC = 3.1 mg C L-1; THg = 1.5 ng L-1; SSC < 50 mg L-1) are low even during the highest of flow events. At Sleepers River, VT (watershed 9), SSC can be elevated during events (SSC > 500 mg L-1), consequently the particulate Hg fraction can range as high as 95% of the THg concentration (mean particulate Hg concentration = 10.2 ng L- 1). At Archer Creek (Huntington Forest, NY), which has the greatest percent wetland cover (10%) of our three sites, DOC concentrations are high (mean DOC = 7.5 mg C L-1), while SSC are low (SSC < 10 mg L- 1). At Archer Creek, Hg is largely in the dissolved form (~75% of Hg) and strongly correlated with DOC (r2 = 0.90). The hydrophobic organic acid (HPOA) fraction of DOC is most effective at mobilizing Hg and is strongly correlated to Hg concentrations in stream water. This research suggests that high concentrations of Hg can be present in stream water from forest watersheds during high flow events, and that wetlands and suspended sediment favor Hg export. However, it is not clear to what degree this Hg is bioavailable for potential uptake by organisms in aquatic ecosystems following mobilization.

Spatiotemporal characterization of dissolved carbon for inland waters in semi-humid/semi-arid region, China

NASA Astrophysics Data System (ADS)

Song, K. S.; Zang, S. Y.; Zhao, Y.; Li, L.; Du, J.; Zhang, N. N.; Wang, X. D.; Shao, T. T.; Guan, Y.; Liu, L.

2013-10-01

Spatiotemporal variations of dissolved organic carbon (DOC) and inorganic carbon (DIC) in 26 waters across the semi-humid/semi-arid Songnen Plain, China, were examined with data collected during 2008-2011. Fresh (n = 14) and brackish (n = 12) waters were grouped according to electrical conductivity (threshold = 1000 μS cm-1) Significant differences in the average DOC and DIC concentrations were observed between the fresh (5.63 mg L-1, 37.39 mg L-1) and the brackish waters (15.33 mg L-1, 142.93 mg L-1). Colored dissolved organic matter (CDOM) and DOC concentrations were mainly controlled by climatic-hydrologic conditions. The investigation indicated that the outflow conditions in the semi-arid region had condensed effects on the dissolved carbon, resulting in close relationships between salinity vs. DOC (R2 = 0.66), and salinity vs. DIC (R2 = 0.94). An independent data set collected in May 2012 also confirmed this finding (DOC: R2 = 0.79, DIC: R2 = 0.91), highlighting the potential of quantifying DOC and DIC via salinity measurements for waters dispersed in the plain. Indices based on the CDOM absorption spectra (e.g., the DOC-specific CDOM absorption (SUVA254), absorption ratio a250 : a365 (E250 : E365) and the spectral slope ratio (Sr, S275-295/S350-400) were applied to characterize CDOM composition and quality. Our results indicate that high molecular weight CDOM fractions are more abundant in the fresh waters than the brackish waters.

Spatiotemporal characterization of dissolved carbon for inland waters in semi-humid/semiarid region, China

NASA Astrophysics Data System (ADS)

Song, K. S.; Zang, S. Y.; Zhao, Y.; Du, J.; Li, L.; Zhang, N. N.; Wang, X. D.; Shao, T. T.; Guan, Y.; Liu, L.

2013-05-01

Spatiotemporal variations of dissolved organic carbon (DOC), inorganic carbon (DIC) in 26 waters across the semi-humid/semi-arid Songnen Plain, China were examined with data collected during 2008-2011. Fresh (n = 14) and brackish (n = 12) waters were grouped according to electrical conductivity (threshold = 1000 μS cm-1). Significant differences in the mean DOC/DIC concentrations were observed between fresh (5.63 mg L-1, 37.39 mg L-1) and brackish waters (15.33 mg L-1, 142.93 mg L-1). Colored dissolved organic matter (CDOM) and DOC concentrations were mainly controlled by climatic-hydrologic conditions. The observation indicated that the outflow conditions in the semi-endorheic region had condensed effects on the dissolved carbon, resulting in close relationships between salinity vs. DOC (R2 = 0.66), and vs. DIC (R2 = 0.94). Independent data set collected in May 2012 also confirmed this finding (DOC: R2 = 0.79), (DIC: R2 = 0.91), highlighting the potential of quantifying DOC/DIC via salinity measurements for waters dispersed in the plain. Indices based on CDOM absorption spectra, e.g. DOC specific CDOM absorption (SUVA254), absorption ratio a250 : a365 (E250:365) and spectral slope ratio (Sr, S275-295/S350-400), were applied to characterize DOM composition and quality. Our results indicate high molecular weight CDOM fractions are more abundant in fresh waters than brackish waters.

Feasibility and toxicity of docetaxel before or after fluorouracil, epirubicin and cyclophosphamide as adjuvant chemotherapy for early breast cancer.

PubMed

Abe, Hajime; Mori, Tsuyoshi; Kawai, Yuki; Cho, Hirotomi; Kubota, Yoshihiro; Umeda, Tomoko; Kurumi, Yoshimasa; Tani, Tohru

2013-06-01

The tolerance and safety associated with the administration order of the anthracycline and taxane drugs have not been evaluated. Breast cancer patients with node-positive or high-risk patients with node-negative were eligible. The feasibility and toxicity were evaluated in the following regimens--arm A, 3 courses of fluorouracil 500 mg/m(2), epirubicin 100 mg/m(2) and cyclophosphamide 500 mg/m(2) (FEC) followed by 3 courses of docetaxel 100 mg/m(2) (DOC); arm B, 3 courses of DOC followed by 3 courses of FEC. Forty-two patients were registered. The relative dose intensity was 94.2 % for FEC and 97.8 % for DOC in arm A, and 98.9 % for DOC and 95.2 % for FEC in arm B. In arm A, grade 3 or higher hematological toxicity was observed in nine patients, and febrile neutropenia developed in three patients with FEC. In arm B, grade 3 or higher hematological toxicity was observed in seven patients, but febrile neutropenia was not noted in any patient. The regimens in both arms A and B were safe regarding adjuvant chemotherapy for early breast cancer. However, DOC followed by FEC might be more tolerable. Further studies will maximize the results obtained with DOC followed by FEC.

The Earth System Documentation (ES-DOC) Software Process

NASA Astrophysics Data System (ADS)

Greenslade, M. A.; Murphy, S.; Treshansky, A.; DeLuca, C.; Guilyardi, E.; Denvil, S.

2013-12-01

Earth System Documentation (ES-DOC) is an international project supplying high-quality tools & services in support of earth system documentation creation, analysis and dissemination. It is nurturing a sustainable standards based documentation eco-system that aims to become an integral part of the next generation of exa-scale dataset archives. ES-DOC leverages open source software, and applies a software development methodology that places end-user narratives at the heart of all it does. ES-DOC has initially focused upon nurturing the Earth System Model (ESM) documentation eco-system and currently supporting the following projects: * Coupled Model Inter-comparison Project Phase 5 (CMIP5); * Dynamical Core Model Inter-comparison Project (DCMIP); * National Climate Predictions and Projections Platforms Quantitative Evaluation of Downscaling Workshop. This talk will demonstrate that ES-DOC implements a relatively mature software development process. Taking a pragmatic Agile process as inspiration, ES-DOC: * Iteratively develops and releases working software; * Captures user requirements via a narrative based approach; * Uses online collaboration tools (e.g. Earth System CoG) to manage progress; * Prototypes applications to validate their feasibility; * Leverages meta-programming techniques where appropriate; * Automates testing whenever sensibly feasible; * Streamlines complex deployments to a single command; * Extensively leverages GitHub and Pivotal Tracker; * Enforces strict separation of the UI from underlying API's; * Conducts code reviews.

Ancient low–molecular-weight organic acids in permafrost fuel rapid carbon dioxide production upon thaw

USGS Publications Warehouse

Drake, Travis W.; Wickland, Kimberly P.; Spencer, Robert G. M.; McKnight, Diane M.; Striegl, Robert G.

2015-01-01

Northern permafrost soils store a vast reservoir of carbon, nearly twice that of the present atmosphere. Current and projected climate warming threatens widespread thaw of these frozen, organic carbon (OC)-rich soils. Upon thaw, mobilized permafrost OC in dissolved and particulate forms can enter streams and rivers, which are important processors of OC and conduits for carbon dioxide (CO2) to the atmosphere. Here, we demonstrate that ancient dissolved organic carbon (DOC) leached from 35,800 y B.P. permafrost soils is rapidly mineralized to CO2. During 200-h experiments in a novel high–temporal-resolution bioreactor, DOC concentration decreased by an average of 53%, fueling a more than sevenfold increase in dissolved inorganic carbon (DIC) concentration. Eighty-seven percent of the DOC loss to microbial uptake was derived from the low–molecular-weight (LMW) organic acids acetate and butyrate. To our knowledge, our study is the first to directly quantify high CO2 production rates from permafrost-derived LMW DOC mineralization. The observed DOC loss rates are among the highest reported for permafrost carbon and demonstrate the potential importance of LMW DOC in driving the rapid metabolism of Pleistocene-age permafrost carbon upon thaw and the outgassing of CO2 to the atmosphere by soils and nearby inland waters.

Ancient low–molecular-weight organic acids in permafrost fuel rapid carbon dioxide production upon thaw

PubMed Central

Drake, Travis W.; Wickland, Kimberly P.; Spencer, Robert G. M.; McKnight, Diane M.; Striegl, Robert G.

2015-01-01

Northern permafrost soils store a vast reservoir of carbon, nearly twice that of the present atmosphere. Current and projected climate warming threatens widespread thaw of these frozen, organic carbon (OC)-rich soils. Upon thaw, mobilized permafrost OC in dissolved and particulate forms can enter streams and rivers, which are important processors of OC and conduits for carbon dioxide (CO2) to the atmosphere. Here, we demonstrate that ancient dissolved organic carbon (DOC) leached from 35,800 y B.P. permafrost soils is rapidly mineralized to CO2. During 200-h experiments in a novel high–temporal-resolution bioreactor, DOC concentration decreased by an average of 53%, fueling a more than sevenfold increase in dissolved inorganic carbon (DIC) concentration. Eighty-seven percent of the DOC loss to microbial uptake was derived from the low–molecular-weight (LMW) organic acids acetate and butyrate. To our knowledge, our study is the first to directly quantify high CO2 production rates from permafrost-derived LMW DOC mineralization. The observed DOC loss rates are among the highest reported for permafrost carbon and demonstrate the potential importance of LMW DOC in driving the rapid metabolism of Pleistocene-age permafrost carbon upon thaw and the outgassing of CO2 to the atmosphere by soils and nearby inland waters. PMID:26504243

Bioaccessibility of polycyclic aromatic hydrocarbons in activated carbon or biochar amended vegetated (Salix viminalis) soil.

PubMed

Oleszczuk, Patryk; Godlewska, Paulina; Reible, Danny D; Kraska, Piotr

2017-08-01

The aim of the present study was to determine the effect of activated carbon (AC) or biochars on the bioaccessibility (C bioacc ) of polycyclic aromatic hydrocarbons (PAHs) in soils vegetated with willow (Salix viminalis). The study determined the effect of willow on the C bioacc PAHs and the effect of the investigated amendments on changes in dissolved organic carbon (DOC), crop yield and the content of PAHs in plants. PAH-contaminated soil was amended with 2.5 wt% AC or biochar. Samples from individual plots with and without plants were collected at the beginning of the experiment and after 3, 6, 12 and 18 months. The C bioacc PAHs were determined using sorptive bioaccessibility extraction (SBE) (silicon rods and hydroxypropyl-β-cyclodextrin). Both AC and biochar caused a decrease in the C bioacc PAHs. Immediately after adding AC, straw-derived biochar or willow-derived biochar to the soil, the reduction in the sum of 16 (Σ16) C bioacc PAHs was 70.3, 38.0, and 29.3%, respectively. The highest reduction of C bioacc was observed for 5- and 6-ring PAHs (from 54.4 to 100%), whereas 2-ring PAHs were reduced only 8.0-25.4%. The reduction of C bioacc PAHs increased over time. Plants reduced C bioacc in all soils although effects varied by soil treatment and PAH. Willow grown in AC- and biochar-amended soil accumulated less phenanthrene than in the control soil. The presence of AC in the soil also affected willow yield and shoot length and DOC was reduced from 53.5 to 66.9% relative to unamended soils. In the biochars-amended soil, no changes in soil DOC content were noted nor effects on willow shoot length. Copyright © 2017 Elsevier Ltd. All rights reserved.

Dissolved organic carbon in rainwater from areas heavily impacted by sugar cane burning

NASA Astrophysics Data System (ADS)

Coelho, C. H.; Francisco, J. G.; Nogueira, R. F. P.; Campos, M. L. A. M.

This work reports on rainwater dissolved organic carbon (DOC) from Ribeirão Preto (RP) and Araraquara over a period of 3 years. The economies of these two cities, located in São Paulo state (Brazil), are based on agriculture and related industries, and the region is strongly impacted by the burning of sugar cane foliage before harvesting. Highest DOC concentrations were obtained when air masses traversed sugar cane fields burned on the same day as the rain event. Significant increases in the DOC volume weighted means (VWM) during the harvest period, for both sites, and a good linear correlation ( r = 0.83) between DOC and K (a biomass burning marker) suggest that regional scale organic carbon emissions prevail over long-range transport. The DOC VWMs and standard deviations were 272 ± 22 μmol L -1 ( n = 193) and 338 ± 40 μmol L -1 ( n = 80) for RP and Araraquara, respectively, values which are at least two times higher than those reported for other regions influenced by biomass burning, such as the Amazon. These high DOC levels are discussed in terms of agricultural activities, particularly the large usage of biogenic fuels in Brazil, as well as the analytical method used in this work, which includes volatile organic carbon when reporting DOC values. Taking into account rainfall volume, estimated annual rainwater DOC fluxes for RP (4.8 g C m -2 yr -1) and Araraquara (5.4 g C m -2 yr -1) were close to that previously found for the Amazon region (4.8 g C m -2 yr -1). This work also discusses whether previous calculations of the global rainwater carbon flux may have been underestimated, since they did not consider large inputs from biomass combustion sources, and suffered from a possible analytical bias.

Vegetation succession influences soil carbon sequestration in coastal alkali-saline soils in southeast China.

PubMed

Li, Niu; Shao, Tianyun; Zhu, Tingshuo; Long, Xiaohua; Gao, Xiumei; Liu, Zhaopu; Shao, Hongbo; Rengel, Zed

2018-06-27

The area of saline soils accounts for 8% of the earth's surface, making these soils an important terrestrial carbon sink. Soil organic carbon (SOC), microbial biomass carbon (MBC), dissolved organic carbon (DOC), soil enzyme activity, and soil bacterial abundance and biodiversity were measured in four successive coastal tidal flat ecosystems representing: bare saline soil (BS), Suaeda glauca land (SL), Imperata cylindrica grassland (IG), and Jerusalem artichoke field (JF). A decrease in soil salt content resulted in increased SOC content. With vegetation succession, MBC and DOC concentrations showed a positive trend, and activities of soil urease, catalase, invertase and alkaline phosphatase increased. A next-generation, Illumina-based sequencing approach showed that Proteobacteria, Acidobacteria, Chloroflexi, Bacteroidetes, Gemmatimonadetes, Actinobacteria, Nitrospirae and Planctomycetes were the dominant bacterial communities (a total of 597 taxa were detected, and 27 genera showed significant differences among the vegetation communities). Bacterial diversity at two soil depths was enhanced with the succession of vegetation ecosystems, with the increases in operational taxonomic units (OTUs) and the Shannon and Chao1 indices ranked in the order: JF > IG > SL > BS. The SOC and C/N were the most determinant factors influencing diversity of bacterial communities in the succession ecosystems.

Laboratory investigations into the potential for transformation of POC to dissolved and gaseous forms

NASA Astrophysics Data System (ADS)

Goulsbra, Claire; Evans, Martin; Allott, Tim; Evans, Chris; Flint, Rebecca; Mcmorron, Katherine

2014-05-01

In eroding peatland systems POC is the dominant component of the fluvial carbon flux, with POC flux to up to circa 80 g C m-2 yr-1. The fate of this POC has remained uncertain, however, and at present many carbon models exclude POC flux from estimations of atmospherically active carbon budgets. Recent work on headwater systems with high POC concentrations has demonstrated that POC:DOC ratios decrease rapidly downstream, hypothesised to be due the physical and microbial breakdown of POC in the fluvial system and transformation of soil carbon to dissolved and gaseous phases. To assess this hypothesis, laboratory investigations of the potential for transformation of POC to dissolved and gaseous forms were undertaken. POC derived from an exposed gully face was mixed with stream waters collected from Upper North Grain, an eroded peatland catchment in the South Pennines, UK, to simulate typical storm flow suspended sediment concentrations. The solutions were agitated using a magnetic stirring system for one week and subsamples of the solution were extracted at intervals of 0.5, 1, 1.5, 2, 3, 4, 5 and 6 hours, and 1, 2, 3, 4, and 7 days. Samples were analysed for POC and DOC concentration using a Shimadzu total carbon analyser and absorbance was measured spectrophotometrically at 254, 400 465 and 665 nm wavelengths as a proxy for DOC quality. In a parallel experiment CO2 emissions to the mixing flask were measured using an infra-red gas analyser (IRGA). To isolate the role of microbial versus physical breakdown, both experiments were replicated with POM and streamwater which had been sterilised by gamma irradiation. The experiments were further repeated to assess the impact of variations in pH and the initial DOC concentration of the stream water on rates of POC conversion to on DOC and CO2. The results of these experiments will be presented here. Initial results show that peat-derived POC was found to be reactive in streamwater, leading to a rapid in DOC within 24 hours of the start of mixing experiments, thought to occur via physicochemical processes. Mixing of POC with streamwater also led to rapid CO2 emissions, possibly via a DOC intermediary, and overall CO2 production exceeded that of DOC. These results strongly indicate that POC is actively converted to other carbon forms in high-POC waters over the timescale of water residence in typical UK river systems, and that a high proportion of this carbon is emitted to the atmosphere as CO2.

Composition and Biolability of Dissolved Organic Matter Leached from the Dominant Endmembers of the Siberian Arctic

NASA Astrophysics Data System (ADS)

Borgen, M.; Spencer, R. G.; Mann, P. J.; Vonk, J. E.; Bulygina, E. B.; Holmes, R. M.

2012-12-01

Terrigenous dissolved organic matter (DOM) has historically been thought to be refractory as it is mobilized into and transported through Arctic fluvial networks. However, a growing body of evidence suggests that this DOM, largely leached from vegetation, soils, and litter during the annual freshet, is highly biolabile. This study examined DOM leached from these dominant endmembers of the Kolyma River watershed in the Siberian Arctic. As leachates progressed through time, measurements of dissolved organic carbon (DOC), optical parameters to assess DOM composition, and biodegradation incubations were undertaken. This suite of measurements allowed examination of the rate and composition of leached DOC into the aquatic system and quantification of the biolability of the DOM from the diverse range of endmembers examined. Of all the endmembers, vascular plants leached the greatest amount of DOC and results will be presented relating DOC concentration and DOM composition to initial source material. Furthermore, controls on DOM biolability, enzymatic activity, and the ultimate fate of terriginous DOC in Siberian fluvial systems will be discussed.

The role of DOM in nitrogen processing in streams across arctic regions affected by fire

NASA Astrophysics Data System (ADS)

Rodriguez-Cardona, B.; Schade, J. D.; Holmes, R. M.; Natali, S.; Mann, P. J.; Wymore, A.; Coble, A. A.; Prokishkin, A. S.; Zito, P.; Podgorski, D. C.; Spencer, R. G.; McDowell, W. H.

2017-12-01

In stream ecosystems, inputs of dissolved organic carbon (DOC) have a strong influence on nitrogen (N) processing. Previous studies have demonstrated that increases in DOC concentrations can promote greater N removal in many stream ecosystems. Most of what we know about C and N coupling comes from studies of temperate streams; less is known about this relationship in the Arctic. Streams in Arctic ecosystems are facing rapid changes in climate and disturbance regimes, in particular increasing fire frequencies that are likely to alter biogeochemical cycles. Although fires can lead to increases in NO3 concentrations in streams, the effects of fire on DOC (concentration and composition) have been difficult to generalize. We studied the relationships between DOC and N in two locations; the Central Siberian Plateau, Russia and the Yukon-Kuskokwim (YK) River Delta, Alaska. Streams in both regions show increases in NO3 concentrations after fire, while DOC concentrations decrease in Siberia but increase in streams within the YK-Delta. These patterns in DOC and NO3 create a gradient in DOC and nutrient concentrations, allowing us to study this coupling in a wider Pan-Arctic scope. In order to assess the role of DOC in Arctic N processing, we conducted NO3 and NH4 additions to stream microcosms at the Alaskan site as well as whole-stream additions in Siberia. We hypothesized that nutrient uptake would be high in older burn sites of Siberia and recently burned sites in the YK-Delta, due to greater DOC concentrations and availability. Our results suggest that nitrogen dynamics in the Alaskan sites is strongly responsive to C availability, but is less so in Siberian sites. The potential impacts of permafrost thawing and fires on DOM and nutrient dynamics thus appear to not be consistent across the Arctic suggesting that different regions of the Arctic have unique biogeochemical controls.

Preliminary assessment of DOC and THM precursor loads from a freshwater restored wetland, an agricultural field, and a tidal wetland in the Sacramento-San Joaquin River Delta

USGS Publications Warehouse

Fujii, R.; Bergamaschi, B.A.; Ganju, N.K.; Fleck, J.A.; Burow-Fogg, K.R.; Schoellhamer, D.; Deverel, S.J.

2003-01-01

Water exported from the Sacramento-San Joaquin River Delta supplies drinking water to more than 22 million people in California. At certain times of the year, Delta waters contain relatively high concentrations of dissolved organic carbon (DOC) and bromide. During these times, chlorination of Delta water for drinking water disinfection will form disinfection byproducts, such as trihalomethanes (THMs), that can exceed the U.S. Environmental Protection Agency's maximum contaminant level for THMs of 80 mg/L. Important sources of DOC and THM precursors (types of DOC that form THMs when chlorinated) to the Delta include rivers, drainage water from peat islands, water from wetlands and areas with extensive riparian vegetation, and in-channel growth of algae and macrophytes. Due to proposed ecosystem restoration and creation of wetlands in the Delta, there is an urgent need for information on the relative loads of DOC and THM precursors produced from three different land uses: restored wetlands constructed for subsidence mitigation, tidal wetlands, and agricultural operations. We have been conducting research in the Delta to provide this information. A restored wetland and agricultural field located on Twitchell Island, and a tidal wetland on Browns Island have been monitored for flow, DOC, and THM precursors. Initial results indicate that the loads of DOC and THM precursors are similar for the restored wetland (surface water only) and the agricultural field. These land uses produce DOC loads of about 14 and 11 g C/m2/yr, respectively, and THM precursor loads of about 1.7 and 1.0 g THM/m2/yr, respectively. Estimates of DOC and THM precursor loads for the tidal wetland site on Browns Island and seepage associated with the restored wetland are being developed.

Potential vulnerability of southeast Alaskan wetland soil carbon stocks to climate warming

NASA Astrophysics Data System (ADS)

Fellman, J.; D'Amore, D. V.; Hood, E. W.

2015-12-01

Carbon cycling along the high latitude coastal margins of Alaska is poorly understood relative to boreal and arctic ecosystems. The perhumid coastal temperate rainforest (PCTR) of southeast Alaska has some of the densest carbon stocks (>300 Mg C ha-1) in the world but the fate of these stocks with continued warming will balance on the poorly constrained rates of carbon accumulation and loss. We quantified the rate of dissolved organic carbon (DOC) and carbon dioxide (CO2) production from four different wetland types (rich fen, poor fen, forested wetland and cedar wetland) using controlled laboratory incubations of surface (10 cm) and subsurface (25 cm) soils incubated at 8 ºC and 15 ºC for 37 weeks. This design allowed us to determine the potential vulnerability of wetland soil carbon stocks to climate warming and partition organic matter mineralization into DOC and CO2 fluxes and its controls (e.g., wetland type and temperature). Furthermore, we used fluorescence characterization of DOC and laboratory bioassays to assess how climate warming may impact the quality and bioavailability of DOC delivered to fluvial systems. Soil depth and temperature strongly influenced carbon loss in all four wetland types with the greatest CO2 fluxes observed in the rich fen and greatest DOC fluxes observed in the poor fen. Of the fluxes, CO2 was the most sensitive to incubation temperature but DOC showed more variation with wetland type. Fluxes of DOC and CO2 were positively correlated only during the last few months of the incubation suggesting strong biotic control of DOC production developed as soil organic matter decomposition progressed. Moreover, bioavailable DOC and protein-like fluorescence were greatest in the initial soil extractions but dramatically decreased over the length of the incubations. Our findings suggest that soil organic matter decomposition will increase as the PCTR continues to warm, but this response will also will vary with wetland type.

UV-visible absorbance spectroscopy as a proxy for peatland dissolved organic carbon (DOC) quantity and quality: considerations on wavelength and absorbance degradation.

PubMed

Peacock, Mike; Evans, Chris D; Fenner, Nathalie; Freeman, Chris; Gough, Rachel; Jones, Timothy G; Lebron, Inma

2014-05-01

Absorbance in the UV or visible spectrum (UV-vis) is commonly used as a proxy for DOC concentrations in waters draining upland catchments. To determine the appropriateness of different UV-vis measurements we used surface and pore water samples from two Welsh peatlands in four different experiments: (i) an assessment of single wavelength proxies (1 nm increments between 230-800 nm) for DOC concentration demonstrated that 254 nm was more accurate than 400 nm. The highest R(2) values between absorbance and DOC concentration were generated using 263 nm for one sample set (R(2) = 0.91), and 230 nm for the other three sample sets (respective R(2) values of 0.86, 0.81, and 0.93). (ii) A comparison of different DOC concentration proxies, including single wavelength proxies, a two wavelength model, a proxy using phenolic concentration, and a proxy using the area under a UV spectrum at 250-350 nm. It was found that both a single wavelength proxy (≤263 nm) and a two wavelength model performed well for both pore water and surface water. (iii) An evaluation of the E2 : E3, E2 : E4, E4 : E6 ratios, and SUVA (absorbance at 254 nm normalised to DOC concentration) as indicators of DOC quality showed that the E4 : E6 ratio was subject to extensive variation over time, and was highly correlated between surface water and pore water, suggesting that it is a useful metric to determine temporal changes in DOC quality. (iv) A repeated weekly analysis over twelve weeks showed no consistent change in UV-vis absorbance, and therefore an inferred lack of degradation of total DOC in samples that were filtered and stored in the dark at 4 °C.

Microbial and Dissolved Organic Carbon Characterization of Stormflow in the Santa Ana River at Imperial Highway, Southern California, 1999-2002

USGS Publications Warehouse

Izbicki, John A.; Pimentel, M. Isabel; Leddy, Menu; Bergamaschi, Brian A.

2004-01-01

The Santa Ana River drains about 2,670 square miles of densely populated coastal southern California, near Los Angeles. Almost all the flow in the river, more than 200,000 acre-feet annually, is diverted to ponds where it infiltrates and recharges underlying aquifers pumped to supply water for more than 2 million people. Base flow in the river is almost entirely treated municipal wastewater discharged from upstream treatment plants and, in the past, stormflow was considered a source of high-quality water suitable for use as a source of ground-water recharge that would dilute poorer quality water recharged during base flow. Stormflow in the Santa Ana River at the Imperial Highway diversion contains total coliform bacteria concentrations as high as 3,400,000 colonies per 100 mL (milliliters). Fecal indicator bacteria concentrations, including fecal coliforms, Escherichia coli, and enterococci, were as high as 310,000, 84,000, and 102,000 colonies per 100 mL, respectively. Although concentrations were high owing to urban runoff during the first stormflow of the rainy season, the highest concentrations occurred during the recessional flows of the first stormflow of the rainy season after streamflow returned to pre-storm conditions. Molecular indicators of microbiological organisms in stormflow, including phospholipid fatty acid (PLFA) and genetic data, show that the diversity of the total microbial population decreases during stormflow while fecal indicator bacteria concentrations increase. This suggests that the source of the bacteria must be poorly diverse and dominated by only a few types of bacteria. Although direct runoff of fecal indicator bacteria from urban areas occurs, this process cannot explain the very high concentrations of fecal indicator bacteria in runoff from upstream parts of the basin characterized by urban, agricultural (including more than 300,000 head of dairy cattle), and other land uses. Although other explanations are possible, fecal indicator bacteria concentrations and molecular microbiological data indicate accumulation and extended survival of bacteria in streambed sediments, and subsequent mobilization of those sediments and associated bacteria during stormflow. Both PLFA and genetic data indicate that water from dairy-waste storage ponds was not present during sampled stormflows. This is consistent with the relatively dry conditions and the absence of large stormflows during the study. Dissolved organic carbon (DOC) concentrations in stormflow ranged from 3 to 15.3 mg/L. In general, concentrations increased during stormflow and were distributed across the stormflow hydrograph in a manner similar to that of fecal indicator bacteria. DOC concentrations typically remained high for several days after flow returned to pre-storm conditions. Ultraviolet absorbance, excitation emission spectroscopy, and sequential fractionation of DOC using XAD-8 and XAD-4 resins showed that the composition of DOC changed rapidly during stormflow. Hydrophobic and hydrophilic acids were the largest fraction of DOC composing between 27 and 45 percent and between 24 and 37 percent of the DOC, respectively. The fraction of DOC composed of hydrophobic acids decreased due to urban runoff and increased during the recession of the first stormflow of the rainy season; the hydrophilic-acid fraction generally decreased throughout the stormflow hydrograph; the transhydrophilic-acid fraction did not vary greatly during stormflow; and the hydrophobic-neutral fraction increased from low values in base flow to almost 30 percent of the DOC after more soluble and more mobile hydrophobic and hydrophilic acids were washed from urban areas. Comparison of ultraviolet absorbance data with data collected during previous studies shows that the optical properties and, presumably, the composition of the DOC were different in this study than DOC collected during wetter periods. Samples of shallow ground water collec

Dissolved organic carbon in coral-reef lagoons, by high temperature catalytic oxidation and UV spectrometry

NASA Astrophysics Data System (ADS)

Pagès, Jean; Torréton, Jean-Pascal; Sempéré, Richard

1997-06-01

Two surveys were carried out on ten atolls in the Tuamotu archipelago (French Polynesia, Pacific Ocean). In vitro UV (250-400 nm) spectra of water samples gave absorption at 254 nm, A 254, and spectrum slope, S ⋆ (computed from In A λ versus λ).These two descriptors are negatively correlated, and data points are arrayed along a hyperbola spanned between an oceanic pole (high S ⋆, low A 254) and a confined pole (low 5 ⋆, high A 254). Dissolved organic carbon (DOC) concentrations, [C], as assessed by HTCO, exhibit a narrow range (0.7-1.0 mg C.L -1 for most lagoons) contrasting with the wide diversity of optical characteristics. [C] and A 254 are positively correlated, with a significant intercept (0.5 mg C.L -1) representing non-chromophoric DOC. Carbon-specific absorption, ɛ 254 increases (from 0.4 to 1.3 m 2.g -1) with increasing [C], mainly according to the literature) owing to increased average molecular weight (MW) of the chromophoric DOC fraction, which also lowers S ⋆. Our optical data thus illustrate a gradient of confinement (or residence time) that corresponds to a continuum in DOC nature, especially in MW and hence in bioavailability. Optical methods are confirmed as quick and effective means of assessing DOM distribution.

Dynamics and sources of reduced sulfur, humic substances and dissolved organic carbon in a temperate river system affected by agricultural practices.

PubMed

Marie, Lauriane; Pernet-Coudrier, Benoît; Waeles, Matthieu; Gabon, Marine; Riso, Ricardo

2015-12-15

Although reduced organic sulfur substances (RSS) as well as humic substances (HS) are widely suspected to play a role in, for example, metal speciation or used as a model of dissolved organic carbon (DOC) in laboratory studies, reports of their quantification in natural waters are scarce. We have examined the dynamics and sources of reduced sulfur, HS and DOC over an annual cycle in a river system affected by agricultural practices. The new differential pulse cathodic stripping voltammetry was successfully applied to measure glutathione-like compounds (GSHs), thioacetamide-like compounds (TAs) and the liquid chromatography coupled to organic detector to analyze HS and DOC at high frequency in the Penzé River (NW France). The streamflow-concentration patterns, principal components analysis and flux analysis allowed discrimination of the source of each organic compound type. Surprisingly, the two RSS and HS detected in all samples, displayed different behavior. As previously shown, manuring practice is the main source of DOC and HS in this watershed where agricultural activity is predominant. The HS were then transferred to the river systems via runoff, particularly during the spring and autumn floods, which are responsible of >60% of the annual flux. TAs had a clear groundwater source and may be formed underground, whereas GSHs displayed two sources: one aquagenic in spring and summer probably linked to the primary productivity and a second, which may be related to bacterial degradation. High sampling frequency allowed a more accurate assessment of the flux values which were 280 tC y(-1) for DOC representing 20 kg C ha(-1) y(-1). HS, TAs and GSHs fluxes represented 60, 13, and 4% of the total annual DOC export, respectively. Copyright © 2015 Elsevier B.V. All rights reserved.

Real Time Monitoring of Dissolved Organic Carbon Concentration and Disinfection By-Product Formation Potential in a Surface Water Treatment Plant with Simulaneous UV-VIS Absorbance and Fluorescence Excitation-Emission Mapping

NASA Astrophysics Data System (ADS)

Gilmore, A. M.

2015-12-01

This study describes a method based on simultaneous absorbance and fluorescence excitation-emission mapping for rapidly and accurately monitoring dissolved organic carbon concentration and disinfection by-product formation potential for surface water sourced drinking water treatment. The method enables real-time monitoring of the Dissolved Organic Carbon (DOC), absorbance at 254 nm (UVA), the Specific UV Absorbance (SUVA) as well as the Simulated Distribution System Trihalomethane (THM) Formation Potential (SDS-THMFP) for the source and treated water among other component parameters. The method primarily involves Parallel Factor Analysis (PARAFAC) decomposition of the high and lower molecular weight humic and fulvic organic component concentrations. The DOC calibration method involves calculating a single slope factor (with the intercept fixed at 0 mg/l) by linear regression for the UVA divided by the ratio of the high and low molecular weight component concentrations. This method thus corrects for the changes in the molecular weight component composition as a function of the source water composition and coagulation treatment effects. The SDS-THMFP calibration involves a multiple linear regression of the DOC, organic component ratio, chlorine residual, pH and alkalinity. Both the DOC and SDS-THMFP correlations over a period of 18 months exhibited adjusted correlation coefficients with r2 > 0.969. The parameters can be reported as a function of compliance rules associated with required % removals of DOC (as a function of alkalinity) and predicted maximum contaminant levels (MCL) of THMs. The single instrument method, which is compatible with continuous flow monitoring or grab sampling, provides a rapid (2-3 minute) and precise indicator of drinking water disinfectant treatability without the need for separate UV photometric and DOC meter measurements or independent THM determinations.

The sensitivity of peat soil and peatland vegetation to drought: release of dissolved organic carbon (DOC) on rewetting

NASA Astrophysics Data System (ADS)

Ritson, Jonathan; Graham, Nigel; Templeton, Michael; Freeman, Christopher; Clark, Joanna

2015-04-01

Organic rich peat soils are a major store of carbon worldwide. Their existence is predicated on high year-round water tables which create an anoxic environment, thus limiting decay, and also to the recalcitrance of plant litter (dead plant material) commonly found in peatland areas. Climate change threatens the stability of peat soils by altering the biogeochemical cycles which control plant decay, lowering water tables so that oxic degradation can occur and by changing habitat niches such that less recalcitrant species can thrive in peatlands. One of the major fluxes of carbon from peatlands is through dissolved organic carbon (DOC) in surface waters. As peatland areas in the UK are often used as source waters for drinking water supply this presents a problem to water utilities as DOC must be effectively removed to limit colour, odour and the formation of potentially carcinogenic by-products on disinfection. Changes in catchment vegetation may occur due to climate change, nutrient deposition and changing bioclimatic envelopes. How different peatland vegetation contribute to DOC flux and how this may change in the future is therefore of interest. A six week laboratory simulation was performed on typical peatland litter (Sphagnum spp., Calluna vulgaris, Molinea caerulea, Juncus effusus) and a peat soil collected from Exmoor National Park, UK. The simulation monitored DOC flux from the decaying litter/soil and considered the impact of different drought severities using the 50th, 25th, 10th and 5th percentiles of the mean July/August monthly rainfall for Exmoor. On rewetting following the drought, all sources produced significantly different amounts of DOC (Tukey HSD p<0.05) in the order Molinia>Juncus>Calluna>Sphagnum>peat. The source also had a significant (ANOVA p<0.001) effect on coagulation removal efficiency, a typical method of removing DOC during drinking water treatment, with Juncus DOC proving the easiest to remove whilst Sphagnum DOC was the most difficult. Sphagnum DOC had the lowest ratio of humic-like to protein-like fluorescence, which is indicative of DOC which is poorly removed by coagulation. An interactive effect was noted between DOC source and the drought treatment which was explored further using a one-way ANOVA with a Holm-Šidák correction. This suggested peat will produce significantly more DOC when affected by drought (p=0.010), possibly explained by increased oxygenation engaging the 'enzymatic latch' mechanism. A similar analysis was performed on the interaction between drought and DOC source for the specific UV absorbance at 254nm (SUVA) value (a measure of aromaticity). This suggested that Molinea caerulea produces DOC of significantly (p=0.001) higher aromaticity following periods of drought. Comparisons between drought and DOC source factors suggest the source in more important than climatic conditions of decay which is consistent with our previously published findings. These results have implications for marginal peatlands which may be at risk from increased water table drawdown in the future as climate changes and where Molinea caerulea, typically a fen species, is encroaching on bog communities.

Pushing Boreal Headwaters: Responses of Dissolved Organic Carbon to Increased Hydro-Meteorological Forcing by Forest Harvesting

NASA Astrophysics Data System (ADS)

Schelker, J.; Grabs, T. J.; Bishop, K. H.; Laudon, H.

2012-12-01

Concentrations of dissolved organic carbon (DOC) in stream water show large variations as a response to disturbances such as forestry operations. We used a paired catchment experiment in northern Sweden which shows well quantified increases of DOC concentrations and C-exports as a result of forest harvesting. To identify the drivers of these increases, a physically-based process model (Riparian Flow Integration Model, RIM) was used to inversely simulate the DOC availability in the peat-rich riparian soils of the catchments. DOC availability in soils followed a seasonal signal paralleling the seasonality of soil-temperatures (min: February; max: August) during 2005-2011. Further, high-frequency event sampling of DOC during spring and summer seasons of 2007, 2008 and 2009, respectively, revealed that event size acted as a secondary control of DOC in streams: Spring snowmelt events (as well as one major event in 2009) showed clockwise hysteresis, whereas minor runoff episodes during summer (when DOC availability in soils was highest) were characterized by a counterclockwise behavior. The higher hydro-meteorological forcing consisting of increases of soil temperature and soil moisture after the forest removal governed additional increases in DOC availability in soils. The higher DOC concentrations observed in streams after forest harvesting can therefore be ascribed to i) the increased climatic forcing comprising higher water flows through riparian soils, ii) increased soil temperatures and soil moisture, respectively, favoring an increased production of DOC, and iii) additional variation by event size. Overall these results underline the large impact of forestry operations on stream water quality as well as DOC exports leaving managed boreal forests. Simulated and measured soil water TOC concentration profiles within the three Balsjö catchments (CC-4 = clear-cut with 67% harvest; NO-5 = 35% harvest; NR-7 = northern reference). The simulated curves represent the inversely modeled soil profiles using the average f-parameter calculated for August 2009 for each catchment. Measured values represent TOC concentrations of soil water sampled in mid August 2009. Sample numbers (soil depth in bracket) are given as: n (-0.2m) = 16; n (-0.6m) = 17; n (-0.9m) = 15. Horizontal whiskers indicate the standard deviation of measured values for each soil depth.

The geochemical characteristics of soil water and epikarst springs and their response to vegetation-soil degradation in a karst area

NASA Astrophysics Data System (ADS)

Xiao, D. A.; Xu, H.

2012-04-01

Samples of soil waters and epi-karst springs in four vegetation types were collected at Maolan nature reserve in Libo county, which including protogenetic arbors, secondary arbor-shrub, shrubs and shrub-grass, to analyze their hydro-geochemical properties and the variations of nutrient elements, and further to illustrate the intrinsic correlations of vegetation, soil, environment changes and their geochemical information. The conclusions have been concluded as follows: (1) The pH of soil waters in the study area varies between 5.32 and 7.93, with a mean value of 6.78, and the conductivity changes between 31.82 and 353.65 μS/cm, with a mean value of 126.19 μS/cm. Both descend as the vegetation degrades. The hydro-chemistry of soil waters are Ca- HCO3-, and their ions mainly consist of Ca2+, Mg2+, HCO3-, SO42-. Ca2+, Mg2+, HCO3-are very sensitive to vegetations degradation. Ion contents are high in rain seasons and low in dry ones. (2) The pH of surface karst springs in the study area vary between 6.7 and 8.42, with a mean value of 7.65, and the conductivity between 125.6 and 452 μS/cm, with a mean value of 288.09 μS/cm. The hydro-chemistry of surface karst springs are Ca- HCO3-. HCO3-and SO42-are the main anions while Ca2+and Mg2+as main cations. The chemical properties and geochemical process of surface springs are mainly controlled by the solubility equilibrium of carbonate rocks, thus not sensitive to vegetation degradations. (3) All the calcite saturation indices of soil waters in four vegetation types are below 0, while most indices of surface karst springs are above 0, demonstrating greater denudation of soil waters than surface karst springs. As soil waters flow to surface springs, the partial pressure of CO2decreases, the denudation of water lessens, and saturation index, Ca2+, HCO3-, consequently, pH and conductivity increase. (4) Inorganic nitrogen in soil waters exist mainly as N-NO3- and N-NH4+, accounting ~ 95% of the 3 Ns. As vegetation degrades, nitrate nitrogen, organic nitrogen and total nitrogen change in follow way, protogenetic arbors > secondary arbor-shrub, shrubs > shrub-grass, but the differences among all vegetation types are not prominent. Ammonia nitrogen, however, changes otherwise as follows: shrubs, shrub-grass > protogenetic arbors, secondary arbor-shrub. In surface springs, few inorganic nitrogen exists as NO2--N ( 2 μg/L on average ), and most exists as NO3-N ( 215 μg/L on average ), and NH4+-N is 185μg/L on average. In general, NH4+-N, NO3--N and TN formations in the four vegetation types are: protogenetic arbors > secondary arbor-shrub > shrubs > shrub-grass. (5) DOC content in soil waters vary between 1.88 and 10.37 mg/L, with an average 4.8 mg/L. DOC content in surface karst springs changes between 0.39 and 9.98 mg/L, with an average 2.25 mg/L. DOCs in soil waters are greater than those in surface karst springs in all four vegetation types, and have sharp differences ( P≤0.01 ). DOCs in soil waters and surface karst springs share a great relationship and a similar change tendency, which well illustrates a main source of surface springs from soil waters. In both of them, DOCs are larger in original vegetations than in degraded vegetations. This is because the soil-vegetation system is stable in an original ecology environment which free from outside disturbs. By contrast, a degraded system is unstable, weak at beating disturbs, and conserves less but loses more. Key words: soil waters, epi-karst springs, hydro-geochemical, vegetation, karst area, Maolan in Guizhou

Controls on the dynamics of dissolved organic matter in soils: A review

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kalbitz, K.; Solinger, S.; Park, J.H.

Dissolved organic matter (DOM) in soils plays an important role in the biogeochemistry of carbon, nitrogen, and phosphorus, in pedogenesis, and in the transport of pollutants in soils. The aim of this review is to summarize the recent literature about controls on DOM concentrations and fluxes in soils. The authors focus on comparing results between laboratory and field investigations and on the differences between the dynamics of dissolved organic carbon (DOC), nitrogen (DON), and phosphorus (DOP). Both laboratory and field studies show that litter and humus are the most important DOM sources in soils. However, it is impossible to quantifymore » the individual contributions of each of these sources to DOM release. In addition, it is not clear how changes in the pool sizes of litter or humus may affect DOM release. High microbial activity, high fungal abundance, and any conditions that enhance mineralization all promote high DOM concentrations. However, under field conditions, hydrologic variability in soil horizons with high carbon contents may be more important than biotic controls. In subsoil horizons with low carbon contents, DOM may be adsorbed strongly to mineral surfaces, resulting in low DOM concentrations in the soil solution. There are strong indications that microbial degradation of DOM also controls the fate of DOM in the soil.« less

Matrices and scaffolds for drug delivery in dental, oral and craniofacial tissue engineering☆

PubMed Central

Moioli, Eduardo K.; Clark, Paul A.; Xin, Xuejun; Lal, Shan; Mao, Jeremy J.

2010-01-01

Current treatments for diseases and trauma of dental, oral and craniofacial (DOC) structures rely on durable materials such as amalgam and synthetic materials, or autologous tissue grafts. A paradigm shift has taken place to utilize tissue engineering and drug delivery approaches towards the regeneration of these structures. Several prototypes of DOC structures have been regenerated such as temporomandibular joint (TMJ) condyle, cranial sutures, tooth structures and periodontium components. However, many challenges remain when taking in consideration the high demand for esthetics of DOC structures, the complex environment and yet minimal scar formation in the oral cavity, and the need for accommodating multiple tissue phenotypes. This review highlights recent advances in the regeneration of DOC structures, including the tooth, periodontium, TMJ, cranial sutures and implant dentistry, with specific emphasis on controlled release of signaling cues for stem cells, biomaterial matrices and scaffolds, and integrated tissue engineering approaches. PMID:17499385

Progress in the Development of Direct Osmotic Concentration Wastewater Recovery Process for Advanced Life Support Systems

NASA Technical Reports Server (NTRS)

Cath, Tzahi Y.; Adams, Dean V.; Childress, Amy; Gormly, Sherwin; Flynn, Michael

2005-01-01

Direct osmotic concentration (DOC) has been identified as a high potential technology for recycling of wastewater to drinking water in advanced life support (ALS) systems. As a result the DOC process has been selected for a NASA Rapid Technology Development Team (RTDT) effort. The existing prototype system has been developed to a Technology Readiness Level (TRL) 3. The current project focuses on advancing the development of this technology from TRL 3 to TRL 6 (appropriate for human rated testing). A new prototype of a DOC system is been designed and fabricated that addresses the deficiencies encountered during the testing of the original system and allowing the new prototype to achieve TRL 6. Background information is provided about the technologies investigated and their capabilities, results from preliminary tests, and the milestones plan and activities for the RTDT program intended to develop a second generation prototype of the DOC system.

Carbon speciation and surface tension of fog

USGS Publications Warehouse

Capel, P.D.; Gunde, R.; Zurcher, F.; Giger, W.

1990-01-01

The speciation of carbon (dissolved/particulate, organic/inorganic) and surface tension of a number of radiation fogs from the urban area of Zurich, Switzerland, were measured. The carbon species were dominated by "dissolved" organic carbon (DOC; i.e., the fraction that passes through a filter), which was typically present at levels of 40-200 mg/L. Less than 10% of the DOC was identified as specific individual organic compounds. Particulate organic carbon (POC) accounted for 26-41% of the mass of the particles, but usually less than 10% of the total organic carbon mass. Inorganic carbon species were relatively minor. The surface tensions of all the measured samples were less than pure water and were correlated with their DOC concentrations. The combination of high DOC and POC and low surface tension suggests a mechanism for the concentration of hydrophobic organic contaminants in the fog droplet, which have been observed by numerous investigators. ?? 1990 American Chemical Society.

Factors affecting the mobilization of DOC and metals in a peat soil under a warmer scenario

NASA Astrophysics Data System (ADS)

Carrera, Noela; Barreal, María. Esther; Briones, María. Jesús I.

2010-05-01

Most climate change models predict an increase of temperature of 3-5°C in Southern Europe by the end of this century (IPCC 2007). However, changes in summer precipitations are more uncertain, and although a decrease in rainfall inputs is forecasted by most models, the magnitude of this effect has not been assessed properly (Rowell & Jones 2006). Peatland areas are very sensitive to climate change. In Galicia they survive in upland areas where cold temperatures and continuous moisture supply allow their presence. Besides abiotic factors, alterations in soil fauna activities can also affect peat turnover. Among them, enchytraeids are usually the most numerous invertebrate group in these systems and both temperature and moisture content regulate their abundances and vertical distribution. Previous studies have demonstrated that changes in their populations associated to increasing temperatures can significantly affect metal mobilization, namely iron and aluminium, together with an important decline in the acidity of the soil solution, which possibly eliminates one of the critical mechanisms restricting DOC release (Carrera et al., 2009). In this study we investigated whether changes in water content of the peat soil and soil invertebrate activities associated to increasing temperatures could alter the mobilization rates of Fe and Al and in turn, DOC. 72 undisturbed soil cores (6 cm diameter x 10 cm deep) with their associated vegetation were taken from a blanket bog in Galicia (NW Spain). Back at the laboratory they were sliced horizontally into two layers, (0-5cm and 5-10cm) which were defaunated by means of a wet extraction. Thereafter, the two soil layers derived from the same core were introduced in each microcosm by placing them in their original position but separated by a 1 mm nylon mesh to allow the vertical movements of the organisms. Half of the experimental units were adjusted to the used moisture values observed in the field (80% SWC, H1), whereas in the remaining half the moisture content was decreased to a lower value so that the activities of the soil organisms remained unaffected (60%, H2). Sixty enchytraeid individuals were inoculated into 18 units of each moisture treatment resulting in two animal treatments (+E and -E). Nine replicates of each treatment were incubated at 14°C and the rest were maintained at 19°C. Changes in enchytraeid populations during incubation were monitored by using a parallel series of 120 experimental units consisting of plastic containers which contained defaunated soil samples (two soil layers) separated by the nylon mesh and with the two moisture treatments as the microcosms (H1 and H2) following the same procedures as before. Next, the same number of enchytraeids was re-inoculated in half of these experimental units (+E and -E). The experiment run for 13 weeks; every 15 days, enchytraeid numbers, DOC, Fe and Al content in the leachates collected from each individual layer were determined. Results showed that both high temperature and moisture values promoted enchytraeid reproduction, with most individuals concentrated in the upper layer. This abundant enchytraeid population favoured the mobilization of DOC, Fe and Al to the soil solution. These findings suggest that modifications in soil faunal populations due to abiotic changes could enhance organic matter decomposition, contributing to the destabilization of these peatland systems. Increasing leaching of dissolved organic matter and metals could have negative implications, not only in terms of possible feed-backs to global warming but also as potential contaminants for aquatic ecosystems. References • Carrera N., Barreal M.E., Gallego P. & Briones M.J.I. (2009). Soil invertebrates control peatland C fluxes in response to warming. Functional Ecology 23: 637-648. • IPCC 2007. Climate change 2007. The Physical Science Basis. Solomon S., Qin D., Manning M., Chen Z., Marquis M., Averyt K.B., Tignor M. & Miller H.L. (Eds.). Cambridge University Press, Cambridge, UK. • Rowell D.P. & Jones R.G. (2006). Causes and uncertainty of future summer drying over Europe. Climate Dynamics 27: 281-299.

Influence of fresh water, nutrients and DOC in two submarine-groundwater-fed estuaries on the west of Ireland.

PubMed

Smith, Aisling M; Cave, Rachel R

2012-11-01

Coastal fresh water sources, which discharge to the sea are expected to be directly influenced by climate change (e.g. increased frequency of extreme weather events). Sea-level rise and changes in rainfall patterns, changes in demand for drinking water and contamination caused by population and land use change, will also have an impact. Coastal waters with submarine groundwater discharge are of particular interest as this fresh water source is very poorly quantified. Two adjacent bays which host shellfish aquaculture sites along the coast of Co. Galway in the west of Ireland have been studied to establish the influence of fresh water inputs on nutrients and dissolved organic carbon (DOC) in each bay. Neither bay has riverine input and both are underlain by the karst limestone of the Burren and are susceptible to submarine groundwater discharge. Water and suspended matter samples were collected half hourly over 13 h tidal cycles over several seasons. Water samples were analysed for nutrients and DOC, while suspended matter was analysed for organic/inorganic content. Temperature and salinity measurements were recorded during each tidal station by SBE 37 MicroCAT conductivity/temperature sensors. Long-term mooring data were used to track freshwater input for Kinvara and Aughinish Bays and compare it with rainfall data. Results show that Kinvara Bay is much more heavily influenced by fresh water input than Aughinish Bay, and this is a strong source of fixed nitrogen to Kinvara Bay. Only during flood events is there a significant input of inorganic nitrogen from fresh water to Aughinish Bay, such as in late November 2009. Fresh water input does not appear to be a significant source of dissolved inorganic phosphate (DIP) to either bay, but is a source of DOC to both bays. C:N ratios of DOC/DON show a clear distinction between marine and terrestrially derived dissolved organic material. Copyright © 2012. Published by Elsevier B.V.

Comparison of pharmaceutical abatement in various water matrices by conventional ozonation, peroxone (O3/H2O2), and an electro-peroxone process.

PubMed

Wang, Huijiao; Zhan, Juhong; Yao, Weikun; Wang, Bin; Deng, Shubo; Huang, Jun; Yu, Gang; Wang, Yujue

2018-03-01

Pharmaceutical abatement in a groundwater (GW), surface water (SW), and secondary effluent (SE) by conventional ozonation, the conventional peroxone (O 3 /H 2 O 2 ), and the electro-peroxone (E-peroxone) processes was compared in batch tests. SE had significantly more fast-reacting dissolved organic matter (DOM) moieties than GW and SW. Therefore, O 3 decomposed much faster in SE than in GW and SW. At specific ozone doses of 0.5-1.5 mg O 3 /mg dissolved organic carbon (DOC), the application of O 3 /H 2 O 2 and E-peroxone process (by adding external H 2 O 2 stocks or in-situ generating H 2 O 2 from cathodic O 2 reduction during ozonation) similarly enhanced the OH yield from O 3 decomposition by ∼5-12% and 5-7% in GW and SW, respectively, compared to conventional ozonation. In contrast, due to the slower reaction kinetics of O 3 with H 2 O 2 than O 3 with fast-reacting DOM moieties, the addition or electro-generation of H 2 O 2 hardly increased the OH yield (<4% increases) in SE. Corresponding to the changes in the OH yields, the abatement efficiencies of ozone-resistant pharmaceuticals (ibuprofen and clofibric acid) increased evidently in GW (up to ∼14-18% at a specific ozone dose of 1.5 mg O 3 /mg DOC), moderately in SW (up to 6-10% at 0.5 mg O 3 /mg DOC), and negligibly in SE during the O 3 /H 2 O 2 and E-peroxone treatment compared to conventional ozonation. These results indicate that similar to the conventional O 3 /H 2 O 2 process, the E-peroxone process can more pronouncedly enhance O 3 transformation to OH, and thus increase the abatement efficiency of ozone-resistant pharmaceuticals in water matrices exerting relatively high ozone stability (e.g., groundwater and surface water with low DOM contents). Therefore, by installing electrodes in existing ozone reactors, the E-peroxone process may provide a convenient way to enhance pharmaceutical abatement in drinking water applications, where groundwater and surface water with low DOM contents are used as the source waters. Copyright © 2017 Elsevier Ltd. All rights reserved.

Investigation of water-soluble organic matter extracted from shales during leaching experiments

NASA Astrophysics Data System (ADS)

Zhu, Yaling; Vieth-Hillebrand, Andrea; Wilke, Franziska D. H.; Horsfield, Brian

2017-04-01

The huge volumes and unknown composition of flowback and produced waters cause major public concerns about the environmental and social compatibility of hydraulic fracturing and the exploitation of gas from unconventional reservoirs. Flowback and produced waters contain not only residues of fracking additives but also chemical species that are dissolved from the shales themselves during fluid-rock interaction. Knowledge of the composition, size and structure of dissolved organic carbon (DOC) as well as the main controls on the release of DOC are a prerequisite for a better understanding of these interactions and its effects on composition of flowback and produced water. Black shales from four different geological settings and covering a maturity range Ro = 0.3-2.6% were extracted with deionized water. The DOC yields were found to decrease rapidly with increasing diagenesis and remain low throughout catagenesis. Four DOC fractions have been qualitatively and quantitatively characterized using size-exclusion chromatography. The concentrations of individual low molecular weight organic acids (LMWOA) decrease with increasing maturity of the samples except for acetate extracted from the overmature Posidonia shale, which was influenced by hydrothermal brines. The oxygen content of the shale organic matter also shows a significant influence on the release of organic acids, which is indicated by the positive trend between oxygen index (OI) and the concentrations of formate and acetate. Based on our experiments, both the properties of the organic matter source and the thermal maturation progress of the shale organic matter significantly influence the amount and quality of extracted organic compounds during the leaching experiments.

Global distribution of dissolved organic matter along the aquatic continuum: Across rivers, lakes and oceans.

PubMed

Massicotte, Philippe; Asmala, Eero; Stedmon, Colin; Markager, Stiig

2017-12-31

Based on an extensive literature survey containing more than 12,000 paired measurements of dissolved organic carbon (DOC) concentrations and absorption of chromophoric dissolved organic matter (CDOM) distributed over four continents and seven oceans, we described the global distribution and transformation of dissolved organic matter (DOM) along the aquatic continuum across rivers and lakes to oceans. A strong log-linear relationship (R 2 =0.92) between DOC concentration and CDOM absorption at 350nm was observed at a global scale, but was found to be ecosystem-dependent at local and regional scales. Our results reveal that as DOM is transported towards the oceans, the robustness of the observed relation decreases rapidly (R 2 from 0.94 to 0.44) indicating a gradual decoupling between DOC and CDOM. This likely reflects the decreased connectivity between the landscape and DOM along the aquatic continuum. To support this hypothesis, we used the DOC-specific UV absorbance (SUVA) to characterize the reactivity of the DOM pool which decreased from 4.9 to 1.7m 2 × gC -1 along the aquatic continuum. Across the continuum, a piecewise linear regression showed that the observed decrease of SUVA occurred more rapidly in freshwater ecosystems compared to marine water ecosystems, suggesting that the different degradation processes act preferentially on CDOM rather than carbon content. The observed change in the DOM characteristics along the aquatic continuum also suggests that the terrestrial DOM pool is gradually becoming less reactive, which has profound consequences on cycling of organic carbon in aquatic ecosystems. Copyright © 2017 Elsevier B.V. All rights reserved.

Seasonality of major redox constituents in a shallow subterranean estuary

NASA Astrophysics Data System (ADS)

O'Connor, Alison E.; Krask, Julie L.; Canuel, Elizabeth A.; Beck, Aaron J.

2018-03-01

The subterranean estuary (STE), the subsurface mixing zone of outflowing fresh groundwater and infiltrating seawater, is an area of extensive geochemical reactions that determine the composition of groundwater that flows into coastal environments. This study examined the porewater composition of a shallow STE (<5 m depth) in Gloucester Point, VA (USA) over two years to determine seasonal variations in dissolved organic carbon (DOC) and the reduced metabolites Fe, Mn, and sulfide. An additional aim of this study was to investigate the relative importance of salinity gradients (which have great geochemical influence in surface estuaries) versus redox gradients on STE geochemistry. Two freshwater endmembers were identified, between which redox potential and composition varied with depth-a shallow freshwater endmember was oxidizing and high in DOC, whereas a deep freshwater endmember was reducing, lower in DOC, and high in sulfide. Results showed that dissolved Fe, Mn, and sulfide varied along a redox gradient distinct from the salinity gradient, and that three-endmember mixing was required to quantify non-conservative chemical addition/removal in the STE. In addition to salinity, humic carbon was used as a quasi-conservative tracer to quantify mixing according to a three-endmember model. The vertical distributions of DOC and reduced metabolites remained approximately constant over time, but concentrations varied with season. Dissolved organic carbon concentrations were greatest in the summer, and shallow meteoric groundwater supplied the majority of DOC to the STE. In summer, there was additional evidence for shallow non-conservative addition of DOC. Dissolved Fe and Mn were highest in a subsurface plume through the middle of the STE (100-140 cm below sediment surface at the high tide line) which was characterized by higher concentrations and greater non-conservative addition in the winter. In contrast, sulfide was higher in summer at depths within the Fe and Mn plume (100-140 cm). We attribute the contrasting seasonal patterns of dissolved Fe, Mn, and sulfide to differences in microbial response to temperature changes and organic matter availability, and to competition at the ferrous-sulfidic transition zone between dissimilatory metal reduction and sulfate reduction, leading to sulfate/sulfur reducing bacteria (SRB) being more active in summer and metal reducers being more active in winter. Throughout the STE, seasonal temperature and DOC variations determined the spatial distribution and geochemical cycling of Fe, Mn, and sulfur.

DOC Dynamics in Small Headwater Streams: the Role of Hydrology, Climate, and Land Management

NASA Astrophysics Data System (ADS)

Lajtha, K.; Lee, B. S.; Jones, J. A.

2015-12-01

Dissolved organic carbon (DOC) is a critical component of the carbon (C) cycle of both terrestrial and aquatic systems. For small headwater allochthonous streams, terrestrial C delivery fuels the metabolism of receiving waters and significantly influences biotic diversity and function. While nutrient fluxes in streams have long been used as indicators of terrestrial ecosystem processes, less attention has been given to terrestrial controls on DOC export. We used the long-term stream chemistry records from the H.J. Andrews Forest LTER to examine forest management, climatic, and hydrologic controls on both seasonal and annual DOC fluxes. Within a watershed, annual DOC flux was highly related to annual discharge (Q), although considerable variability in higher discharge years suggested a role for indices of storminess, especially early in the water year. Among watersheds, younger, previously harvested watersheds generally had significantly lower DOC fluxes for a given Q than old-growth watersheds, even 4+ decades after harvest. The exception to this pattern was a harvested watershed that had significant downed wood retained on site, and had densities of coarse woody debris (CWD) close to that of the old-growth watersheds even though live tree biomass was similar to the other harvested watersheds. Other climatic factors did not appear to have significant roles in predicting either seasonal or annual fluxes of DOC. This is in sharp contrast to fluxes of nitrate at our site, which appears to be related most significantly to the presence of alder within the watershed. Taken together, our data suggest a persistent and cascading role for CWD in old-growth forest ecosystems.

Distributions of nutrients, dissolved organic carbon and carbohydrates in the western Arctic Ocean

NASA Astrophysics Data System (ADS)

Wang, Deli; Henrichs, Susan M.; Guo, Laodong

2006-09-01

Seawater samples were collected from stations along a transect across the shelf-basin interface in the western Arctic Ocean during September 2002, and analyzed for nutrients, dissolved organic carbon (DOC), and total dissolved carbohydrate (TDCHO) constituents, including monosaccharides (MCHO) and polysaccharides (PCHO). Nutrients (nitrate, ammonium, phosphate and dissolved silica) were depleted at the surface, especially nitrate. Their concentrations increased with increasing depth, with maxima centered at ˜125 m depth within the halocline layer, then decreased with increasing depth below the maxima. Both ammonium and phosphate concentrations were elevated in shelf bottom waters, indicating a possible nutrient source from sediments, and in a plume that extended into the upper halocline waters offshore. Concentrations of DOC ranged from 45 to 85 μM and had an inverse correlation with salinity, indicating that mixing is a control on DOC concentrations. Concentrations of TDCHO ranged from 2.5 to 19 μM-C, comprising 13-20% of the bulk DOC. Higher DOC concentrations were found in the upper water column over the shelf along with higher TDCHO concentrations. Within the TDCHO pool, the concentrations of MCHO ranged from 0.4 to 8.6 μM-C, comprising 20-50% of TDCHO, while PCHO concentrations ranged from 0.5 to 13.6 μM-C, comprising 50-80% of the TDCHO. The MCHO/TDCHO ratio was low in the upper 25 m of the water column, followed by a high MCHO/TDCHO ratio between 25 and 100 m, and a low MCHO/TDCHO ratio again below 100 m. The high MCHO/TDCHO ratio within the halocline layer likely resulted from particle decomposition and associated release of MCHO, whereas the low MCHO/TDCHO (or high PCHO/TDCHO) ratio below the halocline layer could have resulted from slow decomposition and additional particulate CHO sources.

Evaluation of Dermatology Practice Online Reviews: Lessons From Qualitative Analysis.

PubMed

Smith, Robert J; Lipoff, Jules B

2016-02-01

Patient satisfaction is an increasingly important component of health care quality measures. Online reviews of physicians represent a promising platform for capturing patient perspectives of care. To identify qualitative themes associated with patient reviews of dermatologic care on consumer reporting websites. A qualitative analysis was conducted of patient-generated reviews of dermatology practices on 2 consumer review platforms. Yelp is an online consumer portal for users to review their experience with local businesses; ZocDoc is an online patient-scheduling portal that provides opportunity for patients to write reviews of physician practices. A total of 518 reviews from 45 dermatology practices on Yelp and 4921 reviews from 45 dermatology providers on ZocDoc were collected from 3 geographically diverse cities: Philadelphia, Pennsylvania; Houston, Texas; and Seattle, Washington. The study was conducted from January 15 to July 15, 2015. Reviews were separated into high-scoring and low-scoring groups. An inductive qualitative method was used to code and identify key themes associated with positive and negative patient experiences. Analysis was completed upon reaching thematic saturation. Reported as mean (95% CI), the overall Yelp score for the 45 selected practices was 3.46 of 5 stars (3.17-3.75) and overall ZocDoc score for the 45 selected practices was 4.72 of 5 stars (4.47-4.80). The proportion of individual reviews giving a score of 5.0 was significantly higher on ZocDoc (3986 [81.0%]) than on Yelp (229 [44.2%]) (P < .001). Qualitative themes centered on characteristics of the physician and the practice. Themes that emerged from the high-scoring and low-scoring reviews were similar in content but opposite in valence. Physician-specific themes included temperament, knowledge and competency, physical examination, communication abilities, and mindfulness of cost. Practice-specific themes included scheduling, staff temperament, office cleanliness, waiting room, and insurance. Patients appreciated physicians who are kind, respectful, and thorough with the physical examination; empathetic about the emotional difficulty of skin disease; and cognizant of cost. Negative experiences were frequently affected by considerations outside of the physician-patient interaction, such as curt interactions with staff, difficulty with scheduling, practice cleanliness, and insurance problems. Patients reported relying on consumer websites to identify dermatology providers. Online consumer review websites are designed to facilitate instantaneous and public communication among patients. These platforms provide elaborate and timely data for dermatologists to garner insight into their patients' experiences. The themes identified in this study are consistent with past satisfaction studies and may aid dermatologists in optimizing the patient care experience.

Effect of exchangeable cation concentration on sorption and desorption of dissolved organic carbon in saline soils.

PubMed

Setia, Raj; Rengasamy, Pichu; Marschner, Petra

2013-11-01

Sorption is a very important factor in stabilization of dissolved organic carbon (DOC) in soils and thus C sequestration. Saline soils have significant potential for C sequestration but little is known about the effect of type and concentration of cations on sorption and release of DOC in salt-affected soils. To close this knowledge gap, three batch sorption and desorption experiments were conducted using soils treated with solutions either low or high in salinity. In Experiment 1, salinity was developed with either NaCl or CaCl2 to obtain an electrical conductivity (EC) in a 1:5 soil: water extract (EC1:5) of 2 and 4 dS m(-1). In Experiments 2 and 3, NaCl and CaCl2 were added in various proportions (between 25 and 100%) to obtain an EC1:5 of 0.5 and 4 dS m(-1), respectively. At EC1:5 of 4 dS m(-1), the sorption of DOC (derived from wheat straw) was high even at a low proportion of added Ca(2+) and did not change with proportion of Ca added, but at EC1:5 of 0.5 dS m(-1) increasing proportion of Ca(2+) added increased DOC sorption. This can be explained by the differences in exchangeable Ca(2+) at the two salinity levels. At EC1:5 of 4 dS m(-1), the exchangeable Ca(2+) concentration did not increase beyond a proportion of 25% Ca(2+), whereas it increased with increasing Ca(2+) proportion in the treatments at EC1:5 of 0.5 dS m(-1). The DOC sorption was lowest with a proportion of 100% as Na(+). When Ca(2+) was added, DOC sorption was highest, but least was desorbed (with deionised water), thus sorption and desorption of added DOC were inversely related. The results of this study suggest that DOC sorption in salt-affected soils is mainly controlled by the levels of exchangeable Ca(2+) irrespective of the Ca(2+) concentration in the soil solution which has implications on carbon stabilization in salt-affected soils. Copyright © 2013 Elsevier B.V. All rights reserved.

Flushing of distal hillslopes as an alternative source of stream dissolved organic carbon in a headwater catchment

Treesearch

John P. Gannon; Scott W. Bailey; Kevin J. McGuire; James B. Shanley

2015-01-01

We investigated potential source areas of dissolved organic carbon (DOC) in headwater streams by examining DOC concentrations in lysimeter, shallow well, and stream water samples from a reference catchment at the Hubbard Brook Experimental Forest. These observations were then compared to high-frequency temporal variations in fluorescent dissolved organic matter (FDOM)...

Origins and bioavailability of dissolved organic matter in groundwater

USGS Publications Warehouse

Shen, Yuan; Chapelle, Francis H.; Strom, Eric W.; Benner, Ronald

2015-01-01

Dissolved organic matter (DOM) in groundwater influences water quality and fuels microbial metabolism, but its origins, bioavailability and chemical composition are poorly understood. The origins and concentrations of dissolved organic carbon (DOC) and bioavailable DOM were monitored during a long-term (2-year) study of groundwater in a fractured-rock aquifer in the Carolina slate belt. Surface precipitation was significantly correlated with groundwater concentrations of DOC, bioavailable DOM and chromophoric DOM, indicating strong hydrological connections between surface and ground waters. The physicochemical and biological processes shaping the concentrations and compositions of DOM during its passage through the soil column to the saturated zone are conceptualized in the regional chromatography model. The model provides a framework for linking hydrology with the processes affecting the transformation, remineralization and microbial production of DOM during passage through the soil column. Lignin-derived phenols were relatively depleted in groundwater DOM indicating substantial removal in the unsaturated zone, and optical properties of chromophoric DOM indicated lower molecular weight DOM in groundwater relative to surface water. The prevalence of glycine, γ-aminobutyric acid, and d-enantiomers of amino acids indicated the DOM was highly diagenetically altered. Bioassay experiments were used to establish DOC-normalized yields of amino acids as molecular indicators of DOM bioavailability in groundwater. A relatively small fraction (8 ± 4 %) of DOC in groundwater was bioavailable. The relatively high yields of specific d-enantiomers of amino acids indicated a substantial fraction (15–34 %) of groundwater DOC was of bacterial origin.

Reference Architecture for MNE 5 Technical System

DTIC Science & Technology

2007-05-30

of being available in most experiments. Core Services A core set of applications whi directories, web portal and collaboration applications etc. A...classifications Messages (xml, JMS, content level…) Meta data filtering, who can initiate services Web browsing Collaboration & messaging Border...Exchange Ref Architecture for MNE5 Tech System.doc 9 of 21 audit logging Person and machine Data lev objects, web services, messages rification el

Soil-solution partitioning of DOC in acid organic soils: Results from a UK field acidification and alkalization experiment

NASA Astrophysics Data System (ADS)

Oulehle, Filip; Jones, Timothy; Burden, Annette; Evans, Chris

2013-04-01

Dissolved organic carbon (DOC) is an important component of the global carbon (C) cycle and has profound impacts on water chemistry and metabolism in lakes and rivers. Reported increases of DOC concentration in surface waters across Europe and Northern America have been attributed to several drivers; from changing climate and land-use to eutrophication and declining acid deposition. The last of these suggests that acidic deposition suppressed the solubility of DOC, and that this historic suppression is now being reversed by reducing emissions of acidifying pollutants. We studied a set of four parallel acidification and alkalization experiments in organic rich soils which, after three years of manipulation, have shown clear soil solution DOC responses to acidity change. We tested whether these DOC concentration changes were related to changes in the acid/base properties of DOC. Based on laboratory determination of DOC site density (S.D. = amount of carboxylic groups per milligram DOC) and charge density (C.D. = organic acid anion concentration per milligram DOC) we found that the change in DOC soil-solution partitioning was tightly related to the change in degree of dissociation (α = C.D./S.D. ratio) of organic acids (R2=0.74, p<0.01). Carbon turnover in soil organic matter (SOM), determined by soil respiration and β-D-glucosidase enzyme activity measurements, also appears to have some impact on DOC leaching, via constraints on the actual supply of available DOC from SOM; when the turnover rate of C in SOM is low, the effect of α on DOC leaching is reduced. Thus, differences in the magnitude of DOC changes seen across different environments might be explained by interactions between physicochemical restrictions of DOC soil-solution partitioning, and SOM carbon turnover effects on DOC supply.

Effect of Photochemical Transformation on Dissolved Organic Carbon Concentration and Bioavailability from Watersheds with Varying Landcover

NASA Astrophysics Data System (ADS)

Vermilyea, A.; Sanders, A.; Vazquez, E.

2017-12-01

The transformation of freshwater dissolved organic carbon (DOC) can have important implications for water quality, aquatic ecosystem health, and our climate. DOC is an important nutrient for heterotrophic microorganisms near the base of the aquatic food chain and the extent of conversion of DOC to CO2 is a critical piece of the global carbon cycle. Photochemical pathways have the potential to transform recalcitrant DOC into more labile forms that can then be converted to smaller DOC molecules and eventually be completely mineralized to CO2. This may lead to a DOC pool with different bioavailability depending on the structural composition of the original DOC pool and the mechanistic pathways undergone during transformation. This study aimed to measure the changes in DOC concentration and bioavailability due solely to photochemical processes in three watersheds of northern Vermont, USA that have varied land cover, land use (LCLU) attributes. Our hypothesis was that photochemical transformations will lead to (1) an overall loss of DOC due to mineralization to CO2 and (2) a relative increase in the bioavailable fraction of DOC. Additionally, the influence of LCLU and base flow versus storm flow on both mineralization rates and changes in DOC bioavailability was investigated. Irradiation of filtered samples in quartz vessels under sunlight led to small changes in DOC concentration over time, but significant changes in DOC bioavailability. In general, fluorescence excitation-emission matrices (EEMs) showed a shift from an initially more humic-like DOC pool, to a more protein-like (bioavailable) DOC pool. Specific UV index (SUVA) along with bioavailable DOC (BDOC) incubations were also used to characterize DOC and its bioavailability. There were only small differences in the DOC transformation that took place among sites, possibly due to only small differences in the initial bioavailability and fluorescent properties between water samples. Photochemical transformation appears to play an important role in the transformation of a more recalcitrant (humic) pool of DOC into a more bioavailable DOC pool that can then be utilized by aquatic heterotrophs and ultimately be converted to CO2.

Dams impact carbon dynamics in U.S. rivers

NASA Astrophysics Data System (ADS)

Bhattacharya, Atreyee

2012-09-01

Dissolved organic carbon (DOC)—which leaches into freshwater systems from plants, soils, and sediments, and from other detritus present in the water itself—is the major food supplement for microorganisms and plays an important role in several environmental processes and in the global carbon cycle. In some aquatic systems such as estuaries, the optically measurable colored component of dissolved organic matter (CDOM) is often proportional to the concentration of DOC. CDOM forms when light-absorbing compounds are released into the water by decaying organic material and through photochemical degradation of certain organic compounds. Hence, CDOM reflects not just the environment and ecosystem, which is the source of the detritus, but also the processes that deliver the organic matter into aquatic systems. Human activities, such as logging, agriculture, and waste water treatment, also affect CDOM levels in aquatic systems. It is relatively easy and inexpensive to measure the CDOM content in small volumes of water.

Acute toxicity of heavy metals for benthic epiphytic foraminifera Pararotalia spinigera (Le Calvez) and influence of seaweed-derived DOC

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bresler, V.; Yanko, V.

1995-10-01

The acute toxicity of cadmium, copper, and mercury to the benthic epiphytic foraminiferan Pararotalia spinigera (Le Calvez) was investigated using seven different vital cytophysiological and cytochemical methods. The ability to enzymatically hydrolyze the fluorogenic substrates fluorescein diacetate or fluorescein dibutyrate was the most sensitive method of LC50 value determination. The LC50 (24-h) values for cadmium, copper, and mercury determined by this assay with fluorescein diacetate was 0.56, 1.4, and 0.07 {micro}M, respectively. The content of seaweed-derived dissolved organic carbon (DOC), measured by absorbance at 436 nm, produced a dramatic increase of LC50 values for the heavy metals in a dose-dependentmore » manner. ``Intact`` epiphytic foraminifera attached to seaweeds are less sensitive to acute toxicity of cadmium, copper, and mercury than are ``detached`` foraminifera.« less

Dissolved Organic Matter (DOM) Export from Watersheds to Coastal Oceans

NASA Astrophysics Data System (ADS)

Chen, R. F.; Gardner, G. B.; Peri, F.

2016-02-01

Dissolved organic matter (DOM) from terrestrial plants and soils is transported by surface waters and groundwaters to coastal ocean waters. Along the way, photochemical and biological degradation can remove DOM, and in situ processes such as phytoplankton leaching and sediment sources can add to the DOM in the river water. Wetlands, especially coastal wetlands can add significant amounts of DOM that is carried by rivers and is exported through estuaries to coastal systems. We will present observational data from a variety of coastal systems (San Francisco Bay, Boston Harbor, Chesapeake Bay, Hudson River, the Mississippi River, and a small salt marsh in the Gulf of Mexico). High resolution measurements of chromophoric dissolved organic matter (CDOM) can be correlated with dissolved organic carbon (DOC) so can be used to estimate DOC in specific systems and seasons. Gradients in CDOM/DOC combined with water fluxes can be used to estimate DOC fluxes from a variety of coastal watersheds to coastal systems. Influences of land use, system size, residence time, DOM quality, and photochemical and biological degradation will be discussed. The significance of coastal wetlands in the land-to-ocean export of DOC will be emphasized.

Effects of wildfire on source-water quality and aquatic ecosystems, Colorado Front Range

USGS Publications Warehouse

Writer, Jeffrey H.; McCleskey, R. Blaine; Murphy, Sheila F.; Stone, Mike; Collins, Adrian; Thoms, Martin C.

2012-01-01

Watershed erosion can dramatically increase after wildfire, but limited research has evaluated the corresponding influence on source-water quality. This study evaluated the effects of the Fourmile Canyon wildfire (Colorado Front Range, USA) on source-water quality and aquatic ecosystems using high- frequency sampling. Dissolved organic carbon (DOC) and nutrient loads in stream water were evaluated for a one-year period during different types of runoff events, including spring snowmelt, and both frontal and summer convective storms. DOC export from the burned watershed did not increase relative to the unburned watershed during spring snowmelt, but substantial increases in DOC export were observed during summer convective storms. Elevated nutrient export from the burned watershed was observed during spring snowmelt and summer convective storms, which increased the primary productivity of stream biofilms. Wildfire effects on source-water quality were shown to be substantial following high-intensity storms, with the potential to affect drinking-water treatment processes.

Application of advanced high speed turboprop technology to future civil short-haul transport aircraft design

NASA Technical Reports Server (NTRS)

Conlon, J. A.; Bowles, J. V.

1978-01-01

With an overall goal of defining the needs and requirements for short-haul transport aircraft research and development, the objective of this paper is to determine the performance and noise impact of short-haul transport aircraft designed with an advanced turboprop propulsion system. This propulsion system features high-speed propellers that have more blades and reduced diameters. Aircraft are designed for short and medium field lengths; mission block fuel and direct operating costs (DOC) are used as performance measures. The propeller diameter was optimized to minimize DOC. Two methods are employed to estimate the weight of the acoustic treatment needed to reduce interior noise to an acceptable level. Results show decreasing gross weight, block fuel, DOC, engine size, and optimum propfan diameter with increasing field length. The choice of acoustic treatment method has a significant effect on the aircraft design.

Photodemethylation of Methylmercury in Eastern Canadian Arctic Thaw Pond and Lake Ecosystems.

PubMed

Girard, Catherine; Leclerc, Maxime; Amyot, Marc

2016-04-05

Permafrost thaw ponds of the warming Eastern Canadian Arctic are major landscape constituents and often display high levels of methylmercury (MeHg). We examined photodegradation potentials in high-dissolved organic matter (DOC) thaw ponds on Bylot Island (BYL) and a low-DOC oligotrophic lake on Cornwallis Island (Char Lake). In BYL, the ambient MeHg photodemethylation (PD) rate over 48 h of solar exposure was 6.1 × 10(-3) m(2) E(-1), and the rate in MeHg amended samples was 9.3 × 10(-3) m(2) E(-1). In contrast, in low-DOC Char Lake, PD was only observed in the first 12 h, which suggests that PD may not be an important loss process in polar desert lakes. Thioglycolic acid addition slowed PD, while glutathione and chlorides did not impact northern PD rates. During an ecosystem-wide experiment conducted in a covered BYL pond, there was neither net MeHg increase in the dark nor loss attributable to PD following re-exposure to sunlight. We propose that high-DOC Arctic thaw ponds are more prone to MeHg PD than nearby oligotrophic lakes, likely through photoproduction of reactive species rather than via thiol complexation. However, at the ecosystem level, these ponds, which are widespread through the Arctic, remain likely sources of MeHg for neighboring systems.

Reservoirs as hotspots of fluvial carbon cycling in peatland catchments.

PubMed

Stimson, A G; Allott, T E H; Boult, S; Evans, M G

2017-02-15

Inland water bodies are recognised as dynamic sites of carbon processing, and lakes and reservoirs draining peatland soils are particularly important, due to the potential for high carbon inputs combined with long water residence times. A carbon budget is presented here for a water supply reservoir (catchment area~9km 2 ) draining an area of heavily eroded upland peat in the South Pennines, UK. It encompasses a two year dataset and quantifies reservoir dissolved organic carbon (DOC), particulate organic carbon (POC) and aqueous carbon dioxide (CO 2 (aq)) inputs and outputs. The budget shows the reservoir to be a hotspot of fluvial carbon cycling, as with high levels of POC influx it acts as a net sink of fluvial carbon and has the potential for significant gaseous carbon export. The reservoir alternates between acting as a producer and consumer of DOC (a pattern linked to rainfall and temperature) which provides evidence for transformations between different carbon species. In particular, the budget data accompanied by 14 C (radiocarbon) analyses provide evidence that POC-DOC transformations are a key process, occurring at rates which could represent at least ~10% of the fluvial carbon sink. To enable informed catchment management further research is needed to produce carbon cycle models more applicable to these environments, and on the implications of high POC levels for DOC composition. Copyright © 2016 Elsevier B.V. All rights reserved.

Are variations in heterotrophic soil respiration related to changes in substrate availability and microbial biomass carbon in the subtropical forests?

PubMed

Wei, Hui; Chen, Xiaomei; Xiao, Guoliang; Guenet, Bertrand; Vicca, Sara; Shen, Weijun

2015-12-16

Soil temperature and moisture are widely-recognized controlling factors on heterotrophic soil respiration (Rh), although they often explain only a portion of Rh variability. How other soil physicochemical and microbial properties may contribute to Rh variability has been less studied. We conducted field measurements on Rh half-monthly and associated soil properties monthly for two years in four subtropical forests of southern China to assess influences of carbon availability and microbial properties on Rh. Rh in coniferous forest was significantly lower than that in the other three broadleaf species-dominated forests and exhibited obvious seasonal variations in the four forests (P < 0.05). Temperature was the primary factor influencing the seasonal variability of Rh while moisture was not in these humid subtropical forests. The quantity and decomposability of dissolved organic carbon (DOC) were significantly important to Rh variations, but the effect of DOC content on Rh was confounded with temperature, as revealed by partial mantel test. Microbial biomass carbon (MBC) was significantly related to Rh variations across forests during the warm season (P = 0.043). Our results suggest that DOC and MBC may be important when predicting Rh under some conditions, and highlight the complexity by mutual effects of them with environmental factors on Rh variations.

Poster — Thur Eve — 52: A Web-based Platform for Collaborative Document Management in Radiotherapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kildea, J.; Joseph, A.

We describe DepDocs, a web-based platform that we have developed to manage the committee meetings, policies, procedures and other documents within our otherwise paperless radiotherapy clinic. DepDocs is essentially a document management system based on the popular Drupal content management software. For security and confidentiality, it is hosted on a linux server internal to our hospital network such that documents are never sent to the cloud or outside of the hospital firewall. We used Drupal's in-built role-based user rights management system to assign a role, and associated document editing rights, to each user. Documents are accessed for viewing using eithermore » a simple Google-like search or by generating a list of related documents from a taxonomy of categorization terms. Our system provides document revision tracking and an document review and approval mechanism for all official policies and procedures. Committee meeting schedules, agendas and minutes are maintained by committee chairs and are restricted to committee members. DepDocs has been operational within our department for over six months and has already 45 unique users and an archive of over 1000 documents, mostly policies and procedures. Documents are easily retrievable from the system using any web browser within our hospital's network.« less

The effects of temperature on decomposition and allelopathic phytotoxicity of boneseed litter.

PubMed

Al Harun, Md Abdullah Yousuf; Johnson, Joshua; Uddin, Md Nazim; Robinson, Randall W

2015-07-01

Decomposition of plant litter is a fundamental process in ecosystem function, carbon and nutrient cycling and, by extension, climate change. This study aimed to investigate the role of temperature on the decomposition of water soluble phenolics (WSP), carbon and soil nutrients in conjunction with the phytotoxicity dynamics of Chrysanthemoides monilifera subsp. monilifera (boneseed) litter. Treatments consisted of three factors including decomposition materials (litter alone, litter with soil and soil alone), decomposition periods and temperatures (5-15, 15-25 and 25-35°C (night/day)). Leachates were collected on 0, 5, 10, 20, 40 and 60th days to analyse physico-chemical parameters and phytotoxicity. Water soluble phenolics and dissolved organic carbon (DOC) increased with increasing temperature while nutrients like SO4(-2) and NO3(-1) decreased. Speed of germination, hypocotyl and radical length and weight of Lactuca sativa exposed to leachates were decreased with increasing decomposition temperature. All treatment components had significant effects on these parameters. There had a strong correlation between DOC and WSP, and WSP content of the leachates with radical length of test species. This study identified complex interactivity among temperature, WSP, DOC and soil nutrient dynamics of litter occupied soil and that these factors work together to influence phytotoxicity. Copyright © 2015. Published by Elsevier B.V.

The Comparison of Different Heterotrophic Bacteria on the Decomposition of DOC molecule

NASA Astrophysics Data System (ADS)

Xie, R.; Zheng, Q.; Jiao, N.

2016-02-01

Marine dissolved organic carbon (DOC) pool is one of the largest reservoirs of organic carbon on Earth. Heterotrophic bacteria are the primary biotic force regulating the fate of marine DOC. Comparison of genomic data, microbes belonging to different clades have diverse DOC molecule utilization genes. That's give us a hint that different microbial groups may have their own pattern to decompose DOC, biosynthesize diverse DOC molecule and contribute to the in situ DOC reservoirs in the ocean. The interaction between marine microbes and DOC molecule is hotspots in current research. We will choose some important microbial groups (e.g., Roseobacter, Altermonas, Halomonas, SAR11 and CFB) to identify their contribution to environmental DOC pool and their specific recalcitrant DOC component using ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Combined with the composition of hydrolases, lyases and ligases in their genomes, we try to establish a linkage between the specific DOC composition and microbial genetic information. Future more the environmental metagenomic data would help us understand the relationship between the endemic DOC composition and microbial communities in the environment.

Changes in metal mobility associated with bark beetle-induced tree mortality.

PubMed

Mikkelson, Kristin M; Bearup, Lindsay A; Navarre-Sitchler, Alexis K; McCray, John E; Sharp, Jonathan O

2014-05-01

Recent large-scale beetle infestations have caused extensive mortality to conifer forests resulting in alterations to dissolved organic carbon (DOC) cycling, which in turn can impact metal mobility through complexation. This study analyzed soil-water samples beneath impacted trees in concert with laboratory flow-through soil column experiments to explore possible impacts of the bark beetle infestation on metal release and transport. The columns mimicked field conditions by introducing pine needle leachate and artificial rainwater through duplicate homogenized soil columns and measuring effluent metal (focusing on Al, Cu, and Zn) and DOC concentrations. All three metals were consistently found in higher concentrations in the effluent of columns receiving pine needle leachate. In both the field and laboratory, aluminum mobility was largely correlated with the hydrophobic fraction of the DOC, while copper had the largest correlation with total DOC concentrations. Geochemical speciation modeling supported the presence of DOC-metal complexes in column experiments. Copper soil water concentrations in field samples supported laboratory column results, as they were almost twice as high under grey phase trees than under red phase trees further signifying the importance of needle drop. Pine needle leachate contained high concentrations of Zn (0.1 mg l(-1)), which led to high effluent zinc concentrations and sorption of zinc to the soil matrix representing a future potential source for release. In support, field soil-water samples underneath beetle-impacted trees where the needles had recently fallen contained approximately 50% more zinc as samples from under beetle-impacted trees that still held their needles. The high concentrations of carbon in the pine needle leachate also led to increased sorption in the soil matrix creating the potential for subsequent carbon release. While unclear if manifested in adjacent surface waters, these results demonstrate an increased potential for Zn, Cu, and Al mobility, along with increased deposition of metals and carbon beneath beetle-impacted trees.

Biodegradability of dissolved organic carbon in permafrost soils and aquatic systems: a meta-analysis

USGS Publications Warehouse

Jorien E. Vonk,; Tank, Suzanne E.; Paul J. Mann,; Robert G.M. Spencer,; Treat, Claire C.; Striegl, Robert G.; Benjamin W. Abbott,; Wickland, Kimberly P.

2015-01-01

As Arctic regions warm and frozen soils thaw, the large organic carbon pool stored in permafrost becomes increasingly vulnerable to decomposition or transport. The transfer of newly mobilized carbon to the atmosphere and its potential influence upon climate change will largely depend on the degradability of carbon delivered to aquatic ecosystems. Dissolved organic carbon (DOC) is a key regulator of aquatic metabolism, yet knowledge of the mechanistic controls on DOC biodegradability is currently poor due to a scarcity of long-term data sets, limited spatial coverage of available data, and methodological diversity. Here, we performed parallel biodegradable DOC (BDOC) experiments at six Arctic sites (16 experiments) using a standardized incubation protocol to examine the effect of methodological differences commonly used in the literature. We also synthesized results from 14 aquatic and soil leachate BDOC studies from across the circum-arctic permafrost region to examine pan-arctic trends in BDOC.An increasing extent of permafrost across the landscape resulted in higher DOC losses in both soil and aquatic systems. We hypothesize that the unique composition of (yedoma) permafrost-derived DOC combined with limited prior microbial processing due to low soil temperature and relatively short flow path lengths and transport times, contributed to a higher overall terrestrial and freshwater DOC loss. Additionally, we found that the fraction of BDOC decreased moving down the fluvial network in continuous permafrost regions, i.e. from streams to large rivers, suggesting that highly biodegradable DOC is lost in headwater streams. We also observed a seasonal (January–December) decrease in BDOC in large streams and rivers, but saw no apparent change in smaller streams or soil leachates. We attribute this seasonal change to a combination of factors including shifts in carbon source, changing DOC residence time related to increasing thaw-depth, increasing water temperatures later in the summer, as well as decreasing hydrologic connectivity between soils and surface water as the thaw season progresses. Our results suggest that future climate warming-induced shifts of continuous permafrost into discontinuous permafrost regions could affect the degradation potential of thaw-released DOC, the amount of BDOC, as well as its variability throughout the Arctic summer. We lastly recommend a standardized BDOC protocol to facilitate the comparison of future work and improve our knowledge of processing and transport of DOC in a changing Arctic.

Soil Dissolved Organic Carbon Fluxes are Controlled by both Precipitation and Longer-Term Climate Effects on Boreal Forest Ecosystems

NASA Astrophysics Data System (ADS)

Hotchkiss, E. R.; Ziegler, S. E.; Edwards, K. A.; Bowering, K.

2017-12-01

Water acts as a control on the cycling of organic carbon (OC). Forest productivity responses to climate change are linked to water availability while water residence time is a major control on OC loss in aquatic ecosystems. However, controls on the export of terrestrial OC to the aquatic environment remains poorly understood. Transport of dissolved OC (DOC) through soils both vertically to deeper soil horizons and into aquatic systems is a key flux of terrestrial OC, but the climate drivers controlling OC mobilized from soils is poorly understood. We installed zero-tension lysimeters across similar balsam fir forest sites within three regions that span a MAT gradient of 5.2˚C and MAP of 1050-1500 mm. Using soil water collected over all seasons for four years we tested whether a warmer and wetter climate promotes greater DOC fluxes in ecosystems experiencing relatively high precipitation. Variability within and between years was compared to that observed across climates to test the sensitivity of this flux to shorter relative to longer-term climate effects on this flux. The warmest and wettest southern site exhibited the greatest annual DOC flux (25 to 28 g C m-2 y-1) in contrast to the most northern site (8 to 10 g C m -2 y-1). This flux represented 10% of litterfall C inputs across sites and surpassed the DOC export from associated forested headwater streams (1 to 16 g C m-2 y-1) suggesting terrestrial to aquatic interface processing. Historical climate and increased soil C inputs explain the greater DOC flux in the southern region. Even in years with comparable annual precipitation among regions the DOC flux differed by climate region. Furthermore, neither quantity nor form of precipitation could explain inter-annual differences in DOC flux within each region. Region specific relationships between precipitation and soil water flux instead suggest historical climate effects may impact soil water transport efficiency thereby controlling the regional variation in the DOC flux. As these forests are exposed to a warmer and wetter climate, DOC transport from organic soils will likely increase. Although precipitation changes will impact this C flux, longer-term climate effects impacting soil inputs, composition and structure of these forests will play an important role in controlling DOC transport in a warmer and wetter future.

Biodegradability of dissolved organic carbon in permafrost soils and aquatic systems: a meta-analysis

NASA Astrophysics Data System (ADS)

Vonk, J. E.; Tank, S. E.; Mann, P. J.; Spencer, R. G. M.; Treat, C. C.; Striegl, R. G.; Abbott, B. W.; Wickland, K. P.

2015-12-01

As Arctic regions warm and frozen soils thaw, the large organic carbon pool stored in permafrost becomes increasingly vulnerable to decomposition or transport. The transfer of newly mobilized carbon to the atmosphere and its potential influence upon climate change will largely depend on the degradability of carbon delivered to aquatic ecosystems. Dissolved organic carbon (DOC) is a key regulator of aquatic metabolism, yet knowledge of the mechanistic controls on DOC biodegradability is currently poor due to a scarcity of long-term data sets, limited spatial coverage of available data, and methodological diversity. Here, we performed parallel biodegradable DOC (BDOC) experiments at six Arctic sites (16 experiments) using a standardized incubation protocol to examine the effect of methodological differences commonly used in the literature. We also synthesized results from 14 aquatic and soil leachate BDOC studies from across the circum-arctic permafrost region to examine pan-arctic trends in BDOC. An increasing extent of permafrost across the landscape resulted in higher DOC losses in both soil and aquatic systems. We hypothesize that the unique composition of (yedoma) permafrost-derived DOC combined with limited prior microbial processing due to low soil temperature and relatively short flow path lengths and transport times, contributed to a higher overall terrestrial and freshwater DOC loss. Additionally, we found that the fraction of BDOC decreased moving down the fluvial network in continuous permafrost regions, i.e. from streams to large rivers, suggesting that highly biodegradable DOC is lost in headwater streams. We also observed a seasonal (January-December) decrease in BDOC in large streams and rivers, but saw no apparent change in smaller streams or soil leachates. We attribute this seasonal change to a combination of factors including shifts in carbon source, changing DOC residence time related to increasing thaw-depth, increasing water temperatures later in the summer, as well as decreasing hydrologic connectivity between soils and surface water as the thaw season progresses. Our results suggest that future climate warming-induced shifts of continuous permafrost into discontinuous permafrost regions could affect the degradation potential of thaw-released DOC, the amount of BDOC, as well as its variability throughout the Arctic summer. We lastly recommend a standardized BDOC protocol to facilitate the comparison of future work and improve our knowledge of processing and transport of DOC in a changing Arctic.

Retrogressive thaw slumps temper dissolved organic carbon delivery to streams of the Peel Plateau, NWT, Canada

NASA Astrophysics Data System (ADS)

Littlefair, Cara A.; Tank, Suzanne E.; Kokelj, Steven V.

2017-12-01

In Siberia and Alaska, permafrost thaw has been associated with significant increases in the delivery of dissolved organic carbon (DOC) to recipient stream ecosystems. Here, we examine the effect of retrogressive thaw slumps (RTSs) on DOC concentration and transport, using data from eight RTS features on the Peel Plateau, NWT, Canada. Like extensive regions of northwestern Canada, the Peel Plateau is comprised of thick, ice-rich tills that were deposited at the margins of the Laurentide Ice Sheet. RTS features are now widespread in this region, with headwall exposures up to 30 m high and total disturbed areas often exceeding 20 ha. We find that intensive slumping on the Peel Plateau is universally associated with decreasing DOC concentrations downstream of slumps, even though the composition of slump-derived dissolved organic matter (DOM; assessed using specific UV absorbance and slope ratios) is similar to permafrost-derived DOM from other regions. Comparisons of upstream and downstream DOC flux relative to fluxes of total suspended solids suggest that the substantial fine-grained sediments released by RTS features may sequester DOC. Runoff obtained directly from slump rill water, above entry into recipient streams, indicates that the deepest RTS features, which thaw the greatest extent of buried, Pleistocene-aged glacial tills, release low-concentration DOC when compared to paired upstream, undisturbed locations, while shallower features, with exposures that are more limited to a relict Holocene active layer, have within-slump DOC concentrations more similar to upstream sites. Finally, fine-scale work at a single RTS site indicates that temperature and precipitation serve as primary environmental controls on above-slump and below-slump DOC flux, but it also shows that the relationship between climatic parameters and DOC flux is complex for these dynamic thermokarst features. These results demonstrate that we should expect clear variation in thermokarst-associated DOC mobilization across Arctic regions. However, they also show that within-region variation in thermokarst intensity and landscape composition is critical for determining the biogeochemical response. Geological and climate legacy shape the physical and chemical composition of permafrost and thermokarst potential. As such, these factors must be considered in predictions of land-to-water carbon mobilization in a warming Arctic.

Hydrologic controls on DOC, As and Pb export from a polluted peatland - the importance of heavy rain events, antecedent moisture conditions and hydrological connectivity

NASA Astrophysics Data System (ADS)

Broder, T.; Biester, H.

2015-08-01

Bogs can store large amounts of lead (Pb) and arsenic (As) from atmospheric deposition of anthropogenic emissions. Pb and As are exported along with dissolved organic carbon (DOC) from these organic-rich systems, but it is not yet clear which hydrological (pre)conditions favor their export. This study combines a 1-year monitoring of precipitation, bog water level and pore water concentration changes with bog discharge and DOC, iron, As and Pb stream concentrations. From these data, annual DOC, As, and Pb exports were calculated. Concentrations ranged from 5 to 30 mg L-1 for DOC, 0.2 to 1.9 μg L-1 for As, and 1.3 to 12 μg L-1 for Pb, with highest concentrations in late summer. As and Pb concentrations significantly correlated with DOC concentrations. Fluxes depended strongly on discharge, as 40 % of As and 43 % of Pb were exported during 10 % of the time with the highest discharge, pointing out the over-proportional contribution of short-time, high-discharge events to annual As, Pb and DOC export. Exponential increase in element export from the bog is explained by connection of additional DOC, As and Pb pools in the acrotelm during water table rise, which is most pronounced after drought. Pb, As and DOC concentrations in pore water provide evidence of an increase in the soluble Pb pool as soon as the peat layer becomes hydrologically connected, while DOC and As peak concentrations in runoff lag behind in comparison to Pb. Our data indicate a distinct bog-specific discharge threshold of 8 L s-1, which is thought to depend mainly on the bogs size and drainage conditions. Above this threshold, element concentrations do not further increase and discharge becomes diluted. Combining pore water and discharge data shows that As and Pb exports are dependent on not only the amount of precipitation and discharge but also on the frequency and depth of water table fluctuations. Comparing the annual bog As and Pb export with element inventories indicates that As is much more mobilized than Pb, with annual fluxes accounting for 0.85 and 0.27 ‰ of total As and Pb inventory, respectively.

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2013-03-26

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Characteristics of wet dissolved carbon deposition in a semi-arid catchment at the Loess Plateau, China

NASA Astrophysics Data System (ADS)

Wang, Linhua; Yen, Haw; Chen, Liding; E, Xinhui; Wang, Yafeng

2018-06-01

Wet dissolved carbon deposition is a critical node of the global carbon cycle, but little is known about dissolved organic and inorganic carbon (DOC and DIC) concentrations and fluxes in the semi-arid areas of the Loess Plateau Region (LPR). In this study, we measured variations in DOC and DIC concentrations in rainfalls at Yangjuangou Ecological Restoration and Soil and Water Observatory. Rainwater samples were collected in 16 rainfall events from July to September and the event-based, monthly concentrations and fluxes of DOC and DIC were quantified. The results showed that the event-based concentrations and fluxes of DOC and DIC were highly variable, ranging from 0.56 to 28.71 mg C L-1 and from 3.47 to 17.49 mg C L-1, respectively. The corresponding event-based fluxes ranged from 0.21-258.36 mg C m-2 and from 4.12 to 42.32 mg C m-2. The monthly concentrations of DOC and DIC were 24.62 and 4.30 (July), 3.58 and 10.52 (August), and 1.01 and 5.89 (September) mg C L-1, respectively. Thus, the monthly deposition fluxes of DOC and DIC were 541.64/94.60, 131.03/385.03, and 44.44/259.16 mg C m-2 for July, August, and September, respectively. In addition, the concentrations of DOC and DIC for the concentrated rainfall season (July-September) in the studied catchment were 7.06 and 7.00 mg C L-1, respectively. The estimated annual wet dissolved carbon depositions were 1.91 and 1.89 g C m-2 yr-1 for DOC and DIC, respectively. The results of this study suggest the variation in concentrations and fluxes of DOC and DIC and explore that these variation may be related to the dissolved carbon source and the rainfall characteristics during the concentrated rainfall season in the semi-arid catchment of the LPR. Furthermore, these results also suggest that dissolved carbon may be an important external input of carbon into terrestrial ecosystems.

The carbon commute: Effects of urbanization on dissolved organic carbon quality on a suburban New England river network

NASA Astrophysics Data System (ADS)

Balch, E.; Robison, A.; Wollheim, W. M.

2017-12-01

Understanding anthropogenic influence on the sources and fluxes of carbon is necessary for interpreting the carbon cycle and contaminant transport throughout a river system. As urbanization increases worldwide, it is critical to understand how urbanization affects the carbon cycle so that we may be able to predict future changes. Rivers act as both transporters of terrestrial dissolved organic carbon (DOC) to coastal regions, and active transformers of DOC. The character (lability) of the carbon found within a river network is influenced by its sources and fluxes, as determined by the ecological processes, land use, and discharge, which vary throughout the network. We have characterized DOC quantity and quality throughout a suburban New England river network (Ipswich River, MA) in an attempt to provide a detailed picture of how DOC quality varies within a network, and how urbanization influences these changes. We conducted a synoptic survey of 45 sites over two hydrologically similar days in the Ipswich River network in northeast Massachusetts, USA. We collected discrete grab samples for DOC quantity and quality analyses. We also collected dissolved oxygen, conductivity, and nutrients (major anions and cations) as an extension of the synoptic survey. We plan to determine the source of the DOC by using excitation-emission matrices (EEMs), and specific UV absorption (SUVA) at 254 nm. These analyses will provide us with a detailed picture of how DOC quality varies within a network, and how urbanization influences these changes. Using land use data of the Ipswich River watershed, we are able to model the changes in DOC quality throughout the network. In highly urbanized headwaters, through the progressively more forested and wetland dominated main stem reaches, we expect to see the imprint of urbanization throughout the network due to its decreased lability. Studying the imprint of urbanization on DOC throughout a river network helps us complete our understanding of freshwater carbon processes. Rivers are an important component of the global carbon balance, and monitoring the effect of urbanization on the carbon cycle in freshwater systems is integral to understanding their role in the global carbon system.

Hydrologic controls on DOC, As and Pb export from a polluted peatland - the importance of heavy rain events, antecedent moisture conditions and hydrological connectivity

NASA Astrophysics Data System (ADS)

Broder, T.; Biester, H.

2015-03-01

Bogs can store large amounts of lead (Pb) and arsenic (As) attributed to atmospheric deposition of anthropogenic emissions. Pb and As are exported along with dissolved organic carbon (DOC) in these organic-rich systems, but it is not yet clear which hydrological (pre-)conditions favor their export. This study combines one year continuous monitoring of precipitation, bog water level and pore water concentration changes with bog discharge, DOC, As and Pb stream concentrations and fluxes. Concentrations ranged from 5 to 30 mg L-1 for DOC, 0.2 to 1.9 μg L-1 for As and 1.3 to 12 μg L-1 for Pb with highest concentrations in late summer. As and Pb concentrations significantly correlated with DOC concentrations. Fluxes depended strongly on discharge, as 40% of As and 43% of Pb were exported by the upper 10% of discharge, pointing out the over-proportional contribution of heavy rain and high discharge events to annual As, Pb and DOC export. Exponential increase in element export from the bog is explained by connection of additional DOC, As and Pb pools in the acrotelm during water table rise, which is most pronounced after drought. Pb, As and DOC concentrations in pore water provide evidence of an increase of the soluble Pb pool as soon as the peat layer gets hydrologically connected, while DOC and As peak concentrations in runoff lag in comparison to Pb. Our data indicates a distinct bog-specific discharge threshold of 8 L s-1, which is thought to depend mainly on the bogs size and drainage conditions. Above this threshold element concentration do not further increase and discharge gets diluted. Combining pore water and discharge data shows that As and Pb exports are not only dependent on the amount of precipitation and discharge, but on the frequency and depth of water table fluctuations. Comparing the annual bog As and Pb export with element inventories indicates that As is much more mobilized than Pb, with annual fluxes accounting for 0.85 and 0.27‰ of total As and Pb inventory, respectively.

Influence of moisture content and temperature on degree of carbonation and the effect on Cu and Cr leaching from incineration bottom ash.

PubMed

Lin, Wenlin Yvonne; Heng, Kim Soon; Sun, Xiaolong; Wang, Jing-Yuan

2015-09-01

This study investigated the influence of moisture content and temperature on the degree of carbonation of municipal solid waste (MSW) incineration bottom ash (IBA) from two different incineration plants in Singapore. The initial rate of carbonation was affected by the nominal moisture content used. Carbonation temperature seemed to play a part in changing the actual moisture content of IBA during carbonation, which in turn affected the degree of carbonation. Results showed that 2h of carbonation was sufficient for the samples to reach a relatively high degree of carbonation that was close to the degree of carbonation observed after 1week of carbonation. Both Cu and Cr leaching also showed significant reduction after only 2h of carbonation. Therefore, the optimum moisture content and temperature were selected based on 2h of carbonation. The optimum moisture content was 15% for both incineration plants while the optimum temperature was different for the two incineration plants, at 35°C and 50°C. The effect on Cu and Cr leaching from IBA after accelerated carbonation was evaluated as a function of carbonation time. Correlation coefficient, Pearson's R, was used to determine the dominant leaching mechanism. The reduction in Cu leaching was found to be contributed by both formation of carbonate mineral and reduction of DOC leaching. On the other hand, Cr leaching seemed to be dominantly controlled by pH. Copyright © 2015 Elsevier Ltd. All rights reserved.

The role of dissolved organic carbon concentration and composition on nickel toxicity to early life-stages of the blue mussel Mytilus edulis and purple sea urchin Strongylocentrotus purpuratus.

PubMed

Blewett, Tamzin A; Dow, Elissa M; Wood, Chris M; McGeer, James C; Smith, D Scott

2018-05-24

Nickel (Ni) emissions resulting from production and transportation raise concerns about the impact of Ni exposure to marine ecosystems. Ni bioavailability models are established for FW systems, but the influence of chemical parameters (e.g. dissolved organic carbon (DOC)) on Ni toxicity within marine systems is less well understood. To examine the effects of DOC concentration and composition on Ni toxicity, acute toxicity tests were conducted on early life-stages of blue mussels (Mytilus edulis) and sea urchin embryos (Strongylocentrotus purpuratus) in full strength sea water (32 ppt). Nine different field collected samples of water with varying concentration (up to 4.5 mg C/L) and composition of DOC were collected from the east coast of the United States. Organic matter compositional analysis included molecular fluorescence and absorbance spectroscopy. The different DOC sources had different protective effects against embryo toxicity. The control (no DOC) Ni 48 h-EC 50 for Mytilus embryos was 133 µg/L (95% confidence interval (C.I.) of 123-144 µg/L), while Strongylocentrotus embryos displayed control 96-h EC 50 values of 207 µg/L (167-247 µg/L). The most significantly protective sample had high humic acid concentrations (as determined from fluorescence spectroscopy), which yielded an EC 50 of 195 µg/L (169-222 µg/L) for Mytilus, and an EC 50 of 394 µg/L (369-419 µg/L) for S. purpuratus. Among all samples, protection was related to both DOC quantity and quality, with fluorescence-resolved humic and fulvic acid concentrations showing the strongest correlations with protection for both species. These data suggest that DOC is protective against Ni toxicity in M. edulis and S. purpuratus, and that accounting for a DOC quality factor will improve predictive toxicity models such as the biotic ligand model. Copyright © 2018 Elsevier Inc. All rights reserved.

[Removal of DON in micro-polluted raw water by coagulation and adsorption using activated carbon].

PubMed

Liu, Bing; Yu, Guo-Zhong; Gu, Li; Zhao, Cheng-Mei; Li, Qing-Fei; Zhai, Hui-Min

2013-04-01

Dissolved organic nitrogen as a precursor of new type nitrogenous disinfection by-products in drinking water attracted gradually the attention of scholars all over the world. In order to explore the mechanism of DON removal in micro-polluted raw water by coagulation and adsorption, water quality parameters, such as DON, DOC, NH4(+) -N, UV254, pH and dissolved oxygen, were determined in raw water and the molecular weight distribution of the DON and DOC was investigated. The variations in DON, DOC and UV254 in the coagulation and adsorption tests were investigated, and the changes of DON in raw water were characterized using three-dimensional fluorescence spectroscopy. The results showed that DON, DOC and UV254 were 1.28 mg x L(-1), 8.56 mg x L(-1), 0.16 cm(-1), and DOC/DON and SUVA were 6.69 mg x mg(-1), 1.87 m(-1) x (mg x L(-1))(-1) in raw water, respectively. The molecular weight distribution of the DON in raw water showed a bimodal distribution. The small molecular weight (< 6 000) fractions accounted for a high proportion of 68% and the large (> 20 000) fractions accounted for about 22%. The removal of DON, DOC and UV254 was about 20%, 26% and 70%, respectively, in the coagulation test and the dosage of coagulant was 10 mg x L(-1). The removal of DON, DOC and UV254 was about 60%, 35% and 100%, respectively, in the adsorption test and the dosage of activated carbon was 1.0 g. In the combination of coagulation and adsorption, the removal of DON and DOC reached approximately 82% and 64%, respectively. 3DEEM revealed that the variation of DON in the coagulation and adsorption tests depended intimately on tryptophan protein-like substances, aromatic protein-like substances and fulvic acid-like substances.

After the flood: consistency in DOM response to the 2010/2011 Australian floods

NASA Astrophysics Data System (ADS)

Shutova, Y.; Baker, A.; Bridgeman, J.; Henderson, R.

2014-12-01

The 2010/2011 floods in Eastern Australia were one of the worst on record, causing more than one billion AUD of damages and killing 35 people. This field campaign, monitoring raw water DOM concentration and character on three contrasting rivers across the region captured the late recession curve (October 2011- September 2012). DOM was characterized using fluorescence excitation-emission matrix (EEM) spectra with PARAFAC analysis; δ 13C-DOC; and molecular size using liquid chromatography with organic carbon, UV254 and nitrogen detection (LC-OCD) to identify DOC fractions: biopolymers, humic substance (HS), building blocks (BB), low molecular weight acids, and low molecular weight neutrals. Despite the difference in catchment and climatic zones, similar trends were observed in all three rivers, where DOC concentrations gradually decreased in river streams over a year from 8-11 mgCL-1 to 3-4 mgCL-1, followed by similar changes of HS, BB and fluorescent terrestrially delivered DOM components (C1-C3). In Allyn and Patterson rivers the proportion of HS, fluorescent terrestrially delivered DOM components (C1, C2) in DOC have decreased, in contrast to Logan River, where the ratio of HS/DOC was highly variable and showed no particular trends. The proportion of other DOC components remained almost the same. Molecular weight of the HS declined from 700 gmol-1 to 610 gmol-1 in all sites. δ 13C-DOC increased during monitoring, this could be linked to general decrease of DOM proportion delivered from C4 type plants after the flood. Overall, although DOC concentration decreased over the year post flood at all sites, most importantly the composition of DOM changed, with major changes occurring in proportion of humic-like and fluorescent terrestrially delivered DOM. Therefore it is important to monitor DOM character to be able to assess the impact of climate change and extreme weather events on the DOM transport and transformation.

Fermi/LAT search for counterpart to the IceCube event 67093193 (run 127853)

NASA Astrophysics Data System (ADS)

Vianello, G.; Magill, J. D.; Omodei, N.; Kocevski, D.; Ajello, M.; Buson, S.; Krauss, F.; Chiang, J.

2016-04-01

on behalf of the Fermi-LAT team: We have searched the Fermi Large Area Telescope data for a high-energy gamma-ray counterpart for the IceCube High Energy Starting Event (HESE) 67093193, detected in run 127853 on 2016-04-27 05:52:32.00 UT (AMON GCN notice rev. 2, http://gcn.gsfc.nasa.gov/notices_amon/67093193_127853.amon . See http://gcn.gsfc.nasa.gov/doc/Public_Doc_AMON_IceCube_GCN_Alerts_v2.pdf for a description of HESE events and related GCN notices).

Coagulant recovery and reuse for drinking water treatment.

PubMed

Keeley, James; Jarvis, Peter; Smith, Andrea D; Judd, Simon J

2016-01-01

Coagulant recovery and reuse from waterworks sludge has the potential to significantly reduce waste disposal and chemicals usage for water treatment. Drinking water regulations demand purification of recovered coagulant before they can be safely reused, due to the risk of disinfection by-product precursors being recovered from waterworks sludge alongside coagulant metals. While several full-scale separation technologies have proven effective for coagulant purification, none have matched virgin coagulant treatment performance. This study examines the individual and successive separation performance of several novel and existing ferric coagulant recovery purification technologies to attain virgin coagulant purity levels. The new suggested approach of alkali extraction of dissolved organic compounds (DOC) from waterworks sludge prior to acidic solubilisation of ferric coagulants provided the same 14:1 selectivity ratio (874 mg/L Fe vs. 61 mg/L DOC) to the more established size separation using ultrafiltration (1285 mg/L Fe vs. 91 mg/L DOC). Cation exchange Donnan membranes were also examined: while highly selective (2555 mg/L Fe vs. 29 mg/L DOC, 88:1 selectivity), the low pH of the recovered ferric solution impaired subsequent treatment performance. The application of powdered activated carbon (PAC) to ultrafiltration or alkali pre-treated sludge, dosed at 80 mg/mg DOC, reduced recovered ferric DOC contamination to <1 mg/L but in practice, this option would incur significant costs. The treatment performance of the purified recovered coagulants was compared to that of virgin reagent with reference to key water quality parameters. Several PAC-polished recovered coagulants provided the same or improved DOC and turbidity removal as virgin coagulant, as well as demonstrating the potential to reduce disinfection byproducts and regulated metals to levels comparable to that attained from virgin material. Copyright © 2015 Elsevier Ltd. All rights reserved.

New insights into the source of decadal increase in chemical oxygen demand associated with dissolved organic carbon in Dianchi Lake.

PubMed

Guo, Wei; Yang, Feng; Li, Yanping; Wang, Shengrui

2017-12-15

Dissolved organic carbon (DOC) can be used an alternative index of water quality instead of chemical oxygen demand (COD) to reflect the organic pollution in water. The monitoring data of water quality in a long-term (1990-2013) from Dianchi Lake confirmed the increase trend of COD concentration in the lake since 2007. The similarities and differences in the DOC components between the lake and its sources and the contribution from allochthonous and autochthonous DOC to the total DOC in this lake were determined to elucidate the reason of COD increase based on C/N atomic ratios, stable isotope abundance of carbon and nitrogen, UV-visible spectroscopy, three-dimensional excitation-emission matrix (3DEEM) fluorescence spectroscopy. The terrigenous organic matter showed humic-like fluorescence, and the autochthonous organic matter showed tryptophan-like components. Agricultural runoff (9.5%), leaf litter (7.5%) and urban runoff (13.2%) were the main sources of DOC in the lake. Sewage tail was a major source of organic materials, 3DEEM for the indicates that sewage tail DOC composition did not change markedly over the biodegradation period, indicating that sewage tail contains a high load of DOC that is resistant to further biodegradation and subsequently accumulates in the lake. The change of land use in the catchment and the increase of sewage tail load into the lake are the key factors for the increase in COD concentration in Dianchi Lake. Thus, the lake should be protected by controlling the pollution from the urban nonpoint sources and refractory composition in point sources. Copyright © 2017 Elsevier B.V. All rights reserved.

Hydrological mobilization of mercury and dissolved organic carbon in a snow-dominated, forested watershed: Conceptualization and modeling

USGS Publications Warehouse

Schelker, J.; Burns, Douglas A.; Weiler, M.; Laudon, H.

2011-01-01

The mobilization of mercury and dissolved organic carbon (DOC) during snowmelt often accounts for a major fraction of the annual loads. We studied the role of hydrological connectivity of riparian wetlands and upland/wetland transition zones to surface waters on the mobilization of Hg and DOC in Fishing Brook, a headwater of the Adirondack Mountains, New York. Stream water total mercury (THg) concentrations varied strongly (mean = 2.25 ?? 0.5 ng L -1), and the two snowmelt seasons contributed 40% (2007) and 48% (2008) of the annual load. Methyl mercury (MeHg) concentrations ranged up to 0.26 ng L-1, and showed an inverse log relationship with discharge. TOPMODEL-simulated saturated area corresponded well with wetland areas, and the application of a flow algorithm based elevation-above-creek approach suggests that most wetlands become well connected during high flow. The dynamics of simulated saturated area and soil storage deficit were able to explain a large part of the variation of THg concentrations (r2 = 0.53 to 0.72). In contrast, the simulations were not able to explain DOC variations and DOC and THg concentrations were not correlated. These results indicate that all three constituents, THg, MeHg, and DOC, follow different patterns at the outlet: (1) the mobilization of THg is primarily controlled by the saturation state of the catchment, (2) the dilution of MeHg suggests flushing from a supply limited pool, and (3) DOC dynamics follow a pattern different from THg dynamics, which likely results from differing gain and/or loss processes for THg and/or DOC within the Fishing Brook catchment. Copyright 2011 by the American Geophysical Union.

Dissolved carbon and nitrogen dynamics in paddy fields under different water management practices and implications on green-house gas emissions

NASA Astrophysics Data System (ADS)

Miniotti, Eleonora; Said-Pullicino, Daniel; Bertora, Chiara; Pelissetti, Simone; Sacco, Dario; Grignani, Carlo; Lerda, Cristina; Romani, Marco; Celi, Luisella

2013-04-01

The alternation of oxidizing and reducing conditions in paddy soils results in considerable complexity in the biogeochemical cycling of elements and their interactions, influencing important soil processes. Water management practices may play an important role in controlling the loss of nutrients from rice paddies to surface and subsurface waters, as well as soil organic matter (SOM) stabilization and the emission of green-house gases (GHG) such as methane and nitrous oxide. The aim of this study was therefore to evaluate the interaction between changes in soil redox conditions and element cycling in temperate paddy soils as a function of different water management practices. The research was carried out within an experimental platform (1.2 ha) located at the Rice Research Center of Ente Nazionale Risi (Castello d'Agogna, PV, NW Italy) where three water management practices are being compared with two plots for each treatment. These included (i) rice cultivation under traditional submerged conditions (FLD); (ii) seeding under dry soil conditions and flooding delayed by about 40 days (DRY); (iii) seeding under dry soil conditions and rotational irrigation (IRR). Surface and subsurface (25, 50 and 75 cm) water samples were collected at regular intervals over the cropping season from V-notch weirs and porous ceramic suction cups installed in each plot, and subsequently analyzed for DOC, SUVA, Fe(II), ammonium and nitrate-N. Moreover, methane and nitrous oxide fluxes were measured in situ by the closed-chamber technique. DOC concentrations in soil solutions were generally higher in FLD and DRY treatments with respect to IRR throughout the cropping season. Higher DOC contents after field flooding in FLD and DRY treatments also corresponded with greater concentrations of reduced Fe, higher SUVA values, lower Eh values and higher pH values, suggesting that desorption of more aromatic, mineral-associated SOM could be responsible for the observed increase in DOC. These trends were not observed in the IRR treatment. The differences in DOC contents and in Eh trend between treatments could possibly explain the increasing trend in cumulative methane emissions in the order IRR<

Dissolved organic carbon in runoff and tile-drain water under corn and forage fertilized with hog manure.

PubMed

Royer, Isabelle; Angers, Denis A; Chantigny, Martin H; Simard, Régis R; Cluis, Daniel

2007-01-01

Dissolved organic carbon (DOC) export from soils can play a significant role in soil C cycling and in nutrient and pollutant transport. However, information about DOC losses from agricultural soils as influenced by management practices is scarce. We compared the effects of mineral fertilizer (MF) and liquid hog manure (LHM) applications on the concentration and molecular size of DOC released in runoff and tile-drain water under corn (Zea mays L.) and forage cropping systems. Runoff and tile-drain water samples were collected during a 2-mo period (October to December 1998) and DOC concentration was measured. Characterization of DOC was performed by tangential ultrafiltration with nominal cut-offs at 3 and 100 kDa. Mean concentration of DOC in runoff water (12.7 mg DOC L(-1)) was higher than in tile-drain water (6.5 mg DOC L(-1)). Incorporation of corn residues increased the DOC concentration by 6- to 17-fold in surface runoff, but this effect was short-lived. In runoff water, the relative size of the DOC molecules increased when corn residues and LHM were applied probably due to partial microbial breakdown of these organic materials and to a faster decomposition or preferential adsorption of the small molecules. The DOC concentration in tile-drain water was slightly higher under forage (7.5 mg DOC L(-1)) than under corn (5.4 mg DOC L(-1)) even though the application rates of LHM were higher in corn plots. We suggest that preferential flow facilitated the migration of DOC to tile drains in forage plots. In conclusion, incorporation of corn residues and LHM increased the concentration of DOC and the relative size of the molecules in surface runoff water, whereas DOC in tile-drain water was mostly influenced by the cropping system with relatively more DOC and larger molecules under forage than corn.

ORCHILEAK (revision 3875): a new model branch to simulate carbon transfers along the terrestrial-aquatic continuum of the Amazon basin

NASA Astrophysics Data System (ADS)

Lauerwald, Ronny; Regnier, Pierre; Camino-Serrano, Marta; Guenet, Bertrand; Guimberteau, Matthieu; Ducharne, Agnès; Polcher, Jan; Ciais, Philippe

2017-10-01

Lateral transfer of carbon (C) from terrestrial ecosystems into the inland water network is an important component of the global C cycle, which sustains a large aquatic CO2 evasion flux fuelled by the decomposition of allochthonous C inputs. Globally, estimates of the total C exports through the terrestrial-aquatic interface range from 1.5 to 2.7 Pg C yr-1 (Cole et al., 2007; Battin et al., 2009; Tranvik et al., 2009), i.e. of the order of 2-5 % of the terrestrial NPP. Earth system models (ESMs) of the climate system ignore these lateral transfers of C, and thus likely overestimate the terrestrial C sink. In this study, we present the implementation of fluvial transport of dissolved organic carbon (DOC) and CO2 into ORCHIDEE (Organising Carbon and Hydrology in Dynamic Ecosystems), the land surface scheme of the Institut Pierre-Simon Laplace ESM. This new model branch, called ORCHILEAK, represents DOC production from canopy and soils, DOC and CO2 leaching from soils to streams, DOC decomposition, and CO2 evasion to the atmosphere during its lateral transport in rivers, as well as exchange with the soil carbon and litter stocks on floodplains and in swamps. We parameterized and validated ORCHILEAK for the Amazon basin, the world's largest river system with regard to discharge and one of the most productive ecosystems in the world. With ORCHILEAK, we are able to reproduce observed terrestrial and aquatic fluxes of DOC and CO2 in the Amazon basin, both in terms of mean values and seasonality. In addition, we are able to resolve the spatio-temporal variability in C fluxes along the canopy-soil-water continuum at high resolution (1°, daily) and to quantify the different terrestrial contributions to the aquatic C fluxes. We simulate that more than two-thirds of the Amazon's fluvial DOC export are contributed by the decomposition of submerged litter. Throughfall DOC fluxes from canopy to ground are about as high as the total DOC inputs to inland waters. The latter, however, are mainly sustained by litter decomposition. Decomposition of DOC and submerged plant litter contributes slightly more than half of the CO2 evasion from the water surface, while the remainder is contributed by soil respiration. Total CO2 evasion from the water surface equals about 5 % of the terrestrial NPP. Our results highlight that ORCHILEAK is well suited to simulate carbon transfers along the terrestrial-aquatic continuum of tropical forests. It also opens the perspective that provided parameterization, calibration and validation is performed for other biomes, the new model branch could improve the quantification of the global terrestrial C sink and help better constrain carbon cycle-climate feedbacks in future projections.

Chemical and carbon isotopic composition of dissolved organic carbon in a regional confined methanogenic aquifer

USGS Publications Warehouse

Aravena, R.; Wassenaar, L.I.; Spiker, E. C.

2004-01-01

This study demonstrates the advantage of a combined use of chemical and isotopic tools to understand the dissolved organic carbon (DOC) cycle in a regional confined methanogenic aquifer. DOC concentration and carbon isotopic data demonstrate that the soil zone is a primary carbon source of groundwater DOC in areas close to recharge zones. An in-situ DOC source linked to organic rich sediments present in the aquifer matrix is controlling the DOC pool in the central part of the groundwater flow system. DOC fractions, 13C-NMR on fulvic acids and 14C data on DOC and CH4 support the hypothesis that the in-situ DOC source is a terrestrial organic matter and discard the Ordovician bedrock as a source of DOC. ?? 2004 Taylor and Francis Ltd.

Export of dissolved organic matter in relation to land use along a European climatic gradient.

PubMed

Mattsson, Tuija; Kortelainen, Pirkko; Laubel, Anker; Evans, Dylan; Pujo-Pay, Mireille; Räike, Antti; Conan, Pascal

2009-03-01

The terrestrial export of dissolved organic matter (DOM) is associated with climate, vegetation and land use, and thus is under the influence of climatic variability and human interference with terrestrial ecosystems, their soils and hydrological cycles. We present a data-set including catchments from four areas covering the major climate and land use gradients within Europe: a forested boreal zone (Finland), a temperate agricultural area (Denmark), a wet and temperate mountain region in Wales, and a warm Mediterranean catchment draining into the Gulf of Lyon. In all study areas, DOC (dissolved organic carbon) was a major fraction of DOM, with much lower proportions of DON (dissolved organic nitrogen) and DOP (dissolved organic phosphorus). A south-north gradient with highest DOC concentrations and export in the northernmost catchments was recorded: DOC concentrations and loads were highest in Finland and lowest in France. These relationships indicate that DOC concentrations/export are controlled by several factors including wetland and forest cover, precipitation and hydrological processes. DON concentrations and loads were highest in the Danish catchments and lowest in the French catchments. In Wales and Finland, DON concentrations increased with the increasing proportion of agricultural land in the catchment, whereas in Denmark and France no such relationship was found. DOP concentrations and loads were low compared to DOC and DON. The highest DOP concentrations and loads were recorded in catchments with a high extent of agricultural land, large urban areas or a high population density, reflecting the influence of human impact on DOP loads.

Tidal Marshes as Pulsing Systems: New Estimates of Marsh-Carbon Export and Fate

NASA Astrophysics Data System (ADS)

Logozzo, L. A.; Neale, P.; Tzortziou, M.; Nelson, N.; Megonigal, P.

2016-02-01

We investigated wetland-estuarine exchanges of dissolved organic carbon (DOC), chromophoric dissolved organic matter (CDOM), dissolved inorganic carbon (DIC), and chlorophyll a (chl a) in the Chesapeake Bay Kirkpatrick wetlands, an ecosystem that is representative of brackish marshes with organic-rich soils in North America. 1 L water samples were collected every hour over multiple semidiurnal tidal cycles (24 h deployments) and the flow was continuously measured every minute over the course of the study. DIC samples were collected and filtered on site. Fluxes were estimated using the measured flow and concentrations of biogeochemical variables (DOC, DIC, and chl a as a measure of algal biomass). aCDOM(300) was used as a proxy for CDOM amount to observe variations over two semidiurnal tidal cycles. Relative to high tide water, low tide water was consistently enriched in DOC, DIC, and CDOM, whereas it was consistently depleted in chl a. Initial estimates of fluxes over the tidal cycle showed net export of DIC and DOC from the marsh, and net import of chl a into the marsh. These results are consistent with DOC flux estimates from previous studies, but our method utilizes high temporal resolution flow measurements, improving flux estimate accuracy. Transect sampling from the marsh into the sub-estuary during ebbing tide indicated a strong negative gradient in a­CDOM­(300) and non-conservative mixing with salinity. The observed gradients in CDOM absorption spectral shape (slope and slope ratios) and the relative changes in the major fluorescence components identified in 3D fluorescence excitation-emission-matrices, indicated strong photochemical degradation in the estuary and a shift from higher to lower molecular-weight organic compounds. The weaker gradients observed for DOC and DIC compared to aCDOM(300) indicate that while microbial degradation does occur, photobleaching is the dominant degradation mechanism for CDOM in the estuary.

Modeling the Space-Time Destiny of Pan-Arctic Permafrost DOC in a Global Land Surface Model: Feedback Implications

NASA Astrophysics Data System (ADS)

Bowring, S.; Lauerwald, R.; Guenet, B.; Zhu, D.; Ciais, P.

2017-12-01

Most global climate models do not represent the unique permafrost soil environment and its respective processes. This significantly contributes to uncertainty in estimating their responses, and that of the planet at large, to warming. Here, the production, transport and atmospheric release of dissolved organic carbon (DOC) from high-latitude permafrost soils into inland waters and the ocean is explicitly represented for the first time in the land surface component (ORCHIDEE-MICT) of a CMIP6 global climate model (IPSL). This work merges two models that are able to mechanistically simulate complex processes for 1) snow, ice and soil phenomena in high latitude environments, and 2) DOC production and lateral transport through soils and the river network, respectively, at 0.5° to 2° resolution. The resulting model is subjected to a wide range of input forcing data, parameter testing and contentious feedback phenomena, including microbial heat generation as the active layer deepens. We present results for the present and future Pan-Arctic and Eurasia, with a focus on the Lena and Mackenzie River basins, and show that soil DOC concentrations, their riverine transport and atmospheric evasion are reasonably well represented as compared to observed stocks, fluxes and seasonality. We show that most basins exhibit large increases in DOC transport and riverine CO2 evasion across the suite of RCP scenarios to 2100. We also show that model output is strongly influenced by choice of input forcing data. The riverine component of what is known as the `boundless carbon cycle' is little-recognized in global climate modeling. Hydrological mobilization to the river network results either in sedimentary settling or atmospheric `evasion', presently amounting to 0.5-1.8 PgC yr-1. Our work aims at filling in these knowledge gaps, and the response of these DOC-related processes to thermal forcing. Potential feedbacks owing to such a response are of particular relevance, given the magnitude of the permafrost carbon pool.

An audiovisual BCI system for assisting clinical communication assessment in patients with disorders of consciousness: a case study.

PubMed

Fei Wang; Yanbin He; Jun Qu; Qiuyou Xie; Qing Lin; Xiaoxiao Ni; Yan Chen; Ronghao Yu; Chin-Teng Lin; Yuanqing Li

2016-08-01

The JFK Coma Recovery Scale-Revised (JFK CRS-R), a behavioral scale, is often used for clinical assessments of patients with disorders of consciousness (DOC), such as patients in a vegetative state. However, there has been a high rate of clinical misdiagnosis with the JFK CRS-R because patients with severe brain injures cannot provide sufficient behavioral responses. It is particularly difficult to evaluate the communication function in DOC patients using the JFK CRS-R because a higher level of behavioral responses is needed for communication assessments than for many other assessments, such as an auditory startle assessment. Brain-computer interfaces (BCIs), which provide control and communication by detecting changes in brain signals, can be used to evaluate patients with DOC without the need of behavioral expressions. In this paper, we proposed an audiovisual BCI system to supplement the JFK CRS-R in assessing the communication ability of patients with DOC. In the graphic user interface of the BCI system, two word buttons ("Yes" and "No" in Chinese) were randomly displayed in the left and right sides and flashed in an alternating manner. When a word button flashed, its corresponding spoken word was broadcast from an ipsilateral headphone. The use of semantically congruent audiovisual stimuli improves the detection performance of the BCI system. Similar to the JFK CRS-R, several situation-orientation questions were presented one by one to patients with DOC. For each question, the patient was required to provide his/her answer by selectively focusing on an audiovisual stimulus (audiovisual "Yes" or "No"). As a case study, we applied our BCI system in a patient with DOC who was clinically diagnosed as being in a minimally conscious state (MCS). According to the JFK CRS-R assessment, this patient was unable to communicate consistently. However, he achieved a high accuracy of 86.5% in our BCI experiment. This result indicates his reliable communication ability and demonstrates the effectiveness of our system.

High mobilization of arsenic, metals and rare earth elements in seepage waters driven by respiration of old allochthonous organic carbon.

PubMed

Weiske, Arndt; Schaller, Jörg; Hegewald, Tilo; Machill, Susanne; Werner, Ingo; Dudel, E Gert

2013-12-01

Metal and metalloid mobilization processes within seepage water are of major concern in a range of water reservoir systems. The mobilization process of arsenic and heavy metals within a dam and sediments of a drinking water reservoir was investigated. Principle component analysis (PCA) on time series data of seepage water showed a clear positive correlation of arsenic with iron and DOC (dissolved organic carbon), and a negative correlation with nitrate due to respiratory processes. A relationship of reductive metal and metalloid mobilization with respiration of old carbon was shown. The system is influenced by sediment layers as well as a recent DOC input from degraded ombrotrophic peatbogs in the catchment area. The isotopic composition ((12)C, (13)C and (14)C) of DOC is altered along the path from basin to seepage water, but no significant changes in structural parameters (LC-OCD-OND, FT-IR) could be seen. DIC (dissolved inorganic carbon) in seepage water partly originates from respiratory processes, and a higher relationship of it with sediment carbon than with the DOC inventory of infiltrating water was found. This study revealed the interaction of respiratory processes with metal and metalloid mobilization in sediment water flows. In contrast to the presumption that emerging DOC via respiratory processes mainly controls arsenic and metal mobilization it could be shown that the presence of aged carbon compounds is essential. The findings emphasize the importance of aged organic carbon for DOC, DIC, arsenic and metal turnover.

Atmospheric inputs of organic matter to a forested watershed: Variations from storm to storm over the seasons

NASA Astrophysics Data System (ADS)

Iavorivska, Lidiia; Boyer, Elizabeth W.; Miller, Matthew P.; Brown, Michael G.; Vasilopoulos, Terrie; Fuentes, Jose D.; Duffy, Christopher J.

2016-12-01

The objectives of this study were to determine the quantity and chemical composition of precipitation inputs of dissolved organic carbon (DOC) to a forested watershed; and to characterize the associated temporal variability. We sampled most precipitation that occurred from May 2012 through August 2013 at the Susquehanna Shale Hills Critical Zone Observatory (Pennsylvania, USA). Sub-event precipitation samples (159) were collected sequentially during 90 events; covering various types of synoptic meteorological conditions in all climatic seasons. Precipitation DOC concentrations and rates of wet atmospheric DOC deposition were highly variable from storm to storm, ranging from 0.3 to 5.6 mg C L-1 and from 0.5 to 32.8 mg C m-2 h-1, respectively. Seasonally, storms in spring and summer had higher concentrations of DOC and more optically active organic matter than in winter. Higher DOC concentrations resulted from weather types that favor air advection, where cold frontal systems, on average, delivered more than warm/stationary fronts and northeasters. A mixed modeling statistical approach revealed that factors related to storm properties, emission sources, and to the chemical composition of the atmosphere could explain more than 60% of the storm to storm variability in DOC concentrations. This study provided observations on changes in dissolved organic matter that can be useful in modeling of atmospheric oxidative chemistry, exploring relationships between organics and other elements of precipitation chemistry, and in considering temporal changes in ecosystem nutrient balances and microbial activity.

Characteristics of dissolved organic matter in the Upper Klamath River, Lost River, and Klamath Straits Drain, Oregon and California

USGS Publications Warehouse

Goldman, Jami H.; Sullivan, Annett B.

2017-12-11

Concentrations of particulate organic carbon (POC) and dissolved organic carbon (DOC), which together comprise total organic carbon, were measured in this reconnaissance study at sampling sites in the Upper Klamath River, Lost River, and Klamath Straits Drain in 2013–16. Optical absorbance and fluorescence properties of dissolved organic matter (DOM), which contains DOC, also were analyzed. Parallel factor analysis was used to decompose the optical fluorescence data into five key components for all samples. Principal component analysis (PCA) was used to investigate differences in DOM source and processing among sites.At all sites in this study, average DOC concentrations were higher than average POC concentrations. The highest DOC concentrations were at sites in the Klamath Straits Drain and at Pump Plant D. Evaluation of optical properties indicated that Klamath Straits Drain DOM had a refractory, terrestrial source, likely extracted from the interaction of this water with wetland peats and irrigated soils. Pump Plant D DOM exhibited more labile characteristics, which could, for instance, indicate contributions from algal or microbial exudates. The samples from Klamath River also had more microbial or algal derived material, as indicated by PCA analysis of the optical properties. Most sites, except Pump Plant D, showed a linear relation between fluorescent dissolved organic matter (fDOM) and DOC concentration, indicating these measurements are highly correlated (R2=0.84), and thus a continuous fDOM probe could be used to estimate DOC loads from these sites.

How reservoirs alter drinking water quality: Organic matter sources, sinks, and transformations

USGS Publications Warehouse

Kraus, Tamara E.C.; Bergamaschi, Brian A.; Hernes, Peter J.; Doctor, Daniel H.; Kendall, Carol; Downing, Bryan D.; Losee, Richard F.

2011-01-01

Within reservoirs, production, transformation, and loss of dissolved organic matter (DOM) occur simultaneously. While the balance between production and loss determines whether a reservoir is a net sink or source of DOM, changes in chemical composition are also important because they affect DOM reactivity with respect to disinfection by-product (DBP) formation. The composition of the DOM pool also provides insight into DOM sources and processing, which can inform reservoir management. We examined the concentration and composition of DOM in San Luis Reservoir, a large off-stream impoundment of the California State Water Project. We used a wide array of DOM chemical tracers including dissolved organic carbon (DOC) concentration, trihalomethane and haloacetic acid formation potentials (THMFP and HAAFP, respectively), absorbance properties, isotopic composition, lignin phenol content, and structural groupings determined by 13C nuclear magnetic resonance (NMR). There were periods when the reservoir was a net source of DOC due to the predominance of algal production (summer), a net sink due to the predominance of degradation (fall–winter), and balanced between production and consumption (spring). Despite only moderate variation in bulk DOC concentration (3.0–3.6 mg C/L), changes in DOM composition indicated that terrestrial-derived material entering the reservoir was being degraded and replaced by aquatic-derived DOM produced within the reservoir. Substantial changes in the propensity of the DOM pool to form THMs and HAAs illustrate that the DBP precursor pool was not directly coupled to bulk DOC concentration and indicate that algal production is an important source of DBP precursors. Results suggest reservoirs have the potential to attenuate DOM amount and reactivity with respect to DBP precursors via degradative processes; however, these benefits can be decreased or even negated by the production of algal-derived DOM.

The effect of microbial activity and adsorption processes on groundwater dissolved organic carbon character and concentration

NASA Astrophysics Data System (ADS)

Meredith, K.; McDonough, L.; Oudone, P.; Rutlidge, H.; O'Carroll, D. M.; Andersen, M. S.; Baker, A.

2017-12-01

Balancing the terrestrial global carbon budget has proven to be a significant challenge. Whilst the movement of carbon in the atmosphere, rivers and oceans has been extensively studied, the potential for groundwater to act as a carbon source or sink through both microbial activity and sorption to and from mineral surfaces, is poorly understood. To investigate the biodegradable component of groundwater dissolved organic carbon (DOC), groundwater samples were collected from multiple coastal and inland sites. Water quality parameters such as pH, electrical conductivity, temperature, dissolved oxygen were measured in the field. Samples were analysed and characterised for their biodegradable DOC content using spectrofluorometric and Liquid Chromatography-Organic Carbon Detection (LC-OCD) techniques at set intervals within a 28 day period. Further to this, we performed laboratory sorption experiments on our groundwater samples using different minerals to examine the effect of adsorption processes on DOC character and concentration. Calcium carbonate, quartz and iron coated quartz were heated to 400ºC to remove potential carbon contamination, and then added at various known masses (0 mg to 10 g) to 50 mL of groundwater. Samples were then rotated for two hours, filtered at 0.2 μm and analysed by LC-OCD. This research forms part of an ongoing project which will assist in identifying the factors affecting the mobilisation, transport and removal of DOC in uncontaminated groundwater. By quantifying the relative importance of these processes, we can then determine whether the groundwater is a carbon source or sink. Importantly, this information will help guide policy and identify the need to include groundwater resources as part of the carbon economy.

Bamboo biochar amendment improves the growth and reproduction of Eisenia fetida and the quality of green waste vermicompost.

PubMed

Gong, Xiaoqiang; Cai, Linlin; Li, Suyan; Chang, Scott X; Sun, Xiangyang; An, Zhengfeng

2018-07-30

Vermicomposting is a promising method for reusing urban green waste. However, high lignin content in the green waste could hinder the development of earthworm and microorganisms and the vermicomposting process, resulting in a low-quality vermicompost product. The objective of this study was to evaluate the effect of bamboo biochar addition (at 0%, 3%, and 6% on a dry w/w basis) on the activity of Eisenia fetida and the obtained vermicompost. Biochar addition increased (P < 0.05) earthworm biomass, juvenile and cocoon numbers of Eisenia fetida, as well as the activities of dehydrogenase, cellulase, urease and alkaline phosphatase. Compared to the control, lignin degradation rate was enhanced up to 13.89% by biochar addition. Biochar addition also improved the vermicompost quality in terms of cation exchange capacity (CEC), dissolved organic carbon (DOC) degradation, humification, nitrogen transformation, toxicity to germinating seeds (Brassica rapa L., Chinensis group) and heavy metals concentrations. The 6% bamboo biochar addition rate achieved maturity after 60 days of vermicomposting and resulted in the highest quality vermicompost based on parameters such as CEC, DOC, NH 4 + -N/NO 3 - -N ratio, germination index and heavy metal concentration. We conclude that 6% biochar addition promoted earthworm growth and the vermicomposting of green waste. Copyright © 2018 Elsevier Inc. All rights reserved.

Assessing contribution of DOC from sediments to a drinking-water reservoir using optical profiling

USGS Publications Warehouse

Downing, Bryan D.; Bergamaschi, Brian A.; Evans, David G.; Boss, Emmanuel

2008-01-01

Understanding the sources of dissolved organic carbon (DOC) in drinking-water reservoirs is an important management issue because DOC may form disinfection by-products, interfere with disinfection, or increase treatment costs. DOC may be derived from a host of sources-algal production of DOC in the reservoir, marginal production of DOC from mucks and vascular plants at the margins, and sediments in the reservoir. The purpose of this study was to assess if release of DOC from reservoir sediments containing ferric chloride coagulant was a significant source of DOC to the reservoir. We examined the source-specific contributions of DOC using a profiling system to measure the in situ distribution of optical properties of absorption and fluorescence at various locations in the reservoir. Vertical optical profiles were coupled with discrete water samples measured in the laboratory for DOC concentration and optical properties: absorption spectra and excitation emission matrix spectra (EEMs). Modeling the in situ optical data permitted estimation of the bulk DOC profile in the reservoir as well as separation into source-specific contributions. Analysis of the source-specific profiles and their associated optical characteristics indicated that the sedimentary source of DOC to the reservoir is significant and that this DOC is labile in the reservoir. We conclude that optical profiling is a useful technique for understanding complex biogeochemical processes in a reservoir.

Associations of free-living bacteria and dissolved organic compounds in a plume of contaminated groundwater

USGS Publications Warehouse

Harvey, R.W.; Barber, L.B.; ,

1992-01-01

Associations of free-living bacteria (FLB) and dissolved organic contaminants in a 4-km-long plume of sewage-contaminated groundwater were investigated. Abundance of FLB in the core of the plume (as delineated by maximum specific conductance) steadily decreased in the direction of flow from a point 0.25 km downgradient from the source to the toe of the plume. At 0.25 km downgradient, FLB comprised up to 31% of the total bacterial population, but constituted < 7% of the population at 2 km downgradient. Abundance of FLB correlated strongly (r = 0.80 n = 23) with total dissolved organic carbon (DOC) in contaminated groundwater between 0.64 and 2.1 km downgradient, although distributions of individual contaminants such as di-, tri- and tetrachloroethene were highly variable, and their association with FLB less clear. Numbers of FLB in the downgradient portion of the plume which is contaminated with branched-chain alkylbenzenesulfonate (ABS) surfactants were low (< 5??108/L) in spite of relatively high levels of DOC (up to 4 mg/L). However, abundance of FLB correlated strongly with non-surfactant DOC along vertical transects through the plume. The ratio of FLB to DOC and the ratio of FLB to attached bacteria generally decreased in the direction of flow and, consequently, with the age of the organic contaminants.

Effect of spent mushroom substrate applied to vineyard soil on the behaviour of copper-based fungicide residues.

PubMed

Herrero-Hernández, E; Andrades, M S; Rodríguez-Cruz, M S; Sánchez-Martín, M J

2011-07-01

The effect of the addition of spent mushroom substrate (SMS) to the soil as an amendment on the distribution and/or fate of copper from a copper-based fungicide applied to a vineyard soil in La Rioja (N. Spain) was studied. The study was carried out on experimental plots amended or not with SMS at rates of 40 and 100 t ha(-1). The variation in total Cu content in the topsoil (0-10 cm) and in the soil profile (0-50 cm), and the distribution of Cu in different fractions of the topsoil were studied as a function of the dose of Cu added (5 and 10 kg ha(-1)) and of the time elapsed since application (0-12 months). In addition, the changes in the chemical properties (solid organic carbon (OC), dissolved organic carbon (DOC) and pH) of the soils were studied. A greater capacity for Cu retention by the amended soils than by the unamended one was observed only when the fungicide was applied at the high dose. No effect of the amendment rate was noted on this retention capacity. The metal content in the topsoil decreased over time in step with the disappearance of the OC in the amended soil due to its oxidation, mineralization and/or leaching. This decrease in total Cu content was possibly due to the formation of soluble Cu complexes with the DOC, which facilitated its transport through the soil. A re-distribution of Cu in the different soil fractions was also observed over time, mainly from the organic to the residual fraction. The results obtained indicate that the increase in OC due to the application of SMS at the rates used does not lead to any significant increase in the persistence of Cu in the soil over time. Of greater interest would be the assessment of the risk for groundwater quality, owing to possible leaching of the fungicide enhanced by the SMS when SMS and Cu-based fungicides are jointly applied to vineyard soils. Copyright © 2011 Elsevier Ltd. All rights reserved.

Relationship between the colored dissolved organic matter and dissolved organic carbon and the application on remote sensing in East China Sea

NASA Astrophysics Data System (ADS)

Qiong, Liu; Pan, Delu; Huang, Haiqing; Lu, Jianxin; Zhu, Qiankun

2011-11-01

A cruise was conducted in the East China Sea (ECS) in autumn 2010 to collect Dissolved Organic Carbon (DOC) and Colored Dissolved Organic Matter (CDOM) samples. The distribution of DOC mainly controlled by the hydrography since the relationship between DOC and salinity was significant in both East China Sea. The biological activity had a significant influence on the concentration of DOC with a close correlation between DOC and Chl a. The absorption coefficient of CDOM (a355) decreased with the salinity increasing in the shelf of East China Sea (R2=0.9045). CDOM and DOC were significantly correlated in ECS where DOC distribution was dominated largely by the Changjiang diluted water. Based on the relationship of CDOM and DOC, we estimated the DOC concentration of the surface in ECS from satellite-derived CDOM images. Some deviations induced by the biological effect and related marine DOC accumulations were discussed.

Overview of a simple model describing variation of dissolved organic carbon in an upland catchment

USGS Publications Warehouse

Boyer, Elizabeth W.; Hornberger, George M.; Bencala, Kenneth E.; McKnight, Diane M.

1996-01-01

Hydrological mechanisms controlling the variation of dissolved organic carbon (DOC) were investigated in the Deer Creek catchment located near Montezuma, CO. Patterns of DOC in streamflow suggested that increased flows through the upper soil horizon during snowmelt are responsible for flushing this DOC-enriched interstitial water to the streams. We examined possible hydrological mechanisms to explain the observed variability of DOC in Deer Creek by first simulating the hydrological response of the catchment using TOPMODEL and then routing the predicted flows through a simple model that accounted for temporal changes in DOC. Conceptually the DOC model can be taken to represent a terrestrial (soil) reservoir in which DOC builds up during low flow periods and is flushed out when infiltrating meltwaters cause the water table to rise into this “reservoir”. Concentrations of DOC measured in the upper soil and in streamflow were compared to model simulations. The simulated DOC response provides a reasonable reproduction of the observed dynamics of DOC in the stream at Deer Creek.

Influence of organic carbon loading, sediment associated metal oxide content and sediment grain size distributions upon Cryptosporidium parvum removal during riverbank filtration operations, Sonoma County, CA

USGS Publications Warehouse

Metge, D.W.; Harvey, R.W.; Aiken, G.R.; Anders, R.; Lincoln, G.; Jasperse, James

2010-01-01

This study assessed the efficacy for removing Cryptosporidium parvum oocysts of poorly sorted, Fe- and Al-rich, subsurface sediments collected from 0.9 to 4.9 and 1.7–13.9 m below land surface at an operating riverbank filtration (RBF) site (Russian River, Sonoma County, CA). Both formaldehyde-killed oocysts and oocyst-sized (3 μm) microspheres were employed in sediment-packed flow-through and static columns. The degree of surface coverage of metal oxides on sediment grain surfaces correlated strongly with the degrees of oocyst and microsphere removals. In contrast, average grain size (D50) was not a good indicator of either microsphere or oocyst removal, suggesting that the primary mechanism of immobilization within these sediments is sorptive filtration rather than physical straining. A low specific UV absorbance (SUVA) for organic matter isolated from the Russian River, suggested that the modest concentration of the SUVA component (0.8 mg L−1) of the 2.2 mg L−1dissolved organic carbon (DOC) is relatively unreactive. Nevertheless, an amendment of 2.2 mg L−1 of isolated river DOC to column sediments resulted in up to a 35.7% decrease in sorption of oocysts and (or) oocyst-sized microspheres. Amendments (3.2 μM) of the anionic surfactant, sodium dodecyl benzene sulfonate (SDBS) also caused substantive decreases (up to 31.9 times) in colloid filtration. Although the grain-surface metal oxides were found to have a high colloid-removal capacity, our study suggested that any major changes within the watershed that would result in long-term alterations in either the quantity and (or) the character of the river's DOC could alter the effectiveness of pathogen removal during RBF operations.

In‐stream sorption of fulvic acid in an acidic stream: A stream‐scale transport experiment

USGS Publications Warehouse

McKnight, Diane M.; Hornberger, George M.; Bencala, Kenneth E.; Boyer, Elizabeth W.

2002-01-01

The variation of concentration and composition of dissolved organic carbon (DOC) in stream waters cannot be explained solely on the basis of soil processes in contributing subcatchments. To investigate in‐stream processes that control DOC, we injected DOC‐enriched water into a reach of the Snake River (Summit County, Colorado) that has abundant iron oxyhydroxides coating the streambed. The injected water was obtained from the Suwannee River (Georgia), which is highly enriched in fulvic acid. The fulvic acid from this water is the standard reference for aquatic fulvic acid for the International Humic Substances Society and has been well characterized. During the experimental injection, significant removal of sorbable fulvic acid occurred within the first 141 m of stream reach. We coinjected a conservative tracer (lithium chloride) and analyzed the results with the one‐dimensional transport with inflow and storage (OTIS) stream solute transport model to quantify the physical transport mechanisms. The downstream transport of fulvic acid as indicated by absorbance was then simulated using OTIS with a first‐order kinetic sorption rate constant applied to the sorbable fulvic acid. The “sorbable” fraction of injected fulvic acid was irreversibly sorbed by streambed sediments at rates (kinetic rate constants) of the order of 10−4–10−3 s−1. In the injected Suwannee River water, sorbable and nonsorbable fulvic acid had distinct chemical characteristics identified in 13C‐NMR spectra. The 13C‐NMR spectra indicate that during the experiment, the sorbable “signal” of greater aromaticity and carboxyl content decreased downstream; that is, these components were preferentially removed. This study illustrates that interactions between the water and the reactive surfaces will modify significantly the concentration and composition of DOC observed in streams with abundant chemically reactive surfaces on the streambed and in the hyporheic zone.

A study on the reactivity characteristics of dissolved effluent organic matter (EfOM) from municipal wastewater treatment plant during ozonation.

PubMed

Jin, Pengkang; Jin, Xin; Bjerkelund, Viggo A; Østerhus, Stein W; Wang, Xiaochang C; Yang, Lei

2016-01-01

The reactivity of dissolved effluent organic matter (EfOM) in the process of ozonation was examined. Under different ozone dosages (0.42 ± 0.09, 0.98 ± 0.11 and 2.24 ± 0.17 mgO3/mg DOC), the EfOM before and after ozonation could be classified into four fractions according to their hydrophobicities. By ozonation, the hydrophobic fractions, especially hydrophobic acid (HOA) and hydrophobic neutral (HON), were found to undergo a process of transformation into hydrophilic fractions (HI), of which the HOA were first transformed into HON, and then the majority of the HON fraction was later converted to HI by further ozonation. It was noticeable that after ozonation, the fluorescence intensity in the humic-like and protein-like regions decreased as indicated by the excitation and emission matrix (EEM) spectra for the hydrophobic fractions. By coupling the EEM spectra with the molecular size analysis using high performance size exclusion chromatography (HPSEC), the difference between the characteristic distributions of the humic-like and protein-like fluorophores were further revealed. It could thus be extrapolated that ozone might have preferentially reacted with the protein-like hydrophobic fraction with molecular weight (MW) less than 100 kDa. Moreover, by X-ray photoelectron spectroscopy (XPS) analysis, it was identified that with increasing ozone dosage (from 0 to 2.24 ± 0.17 mgO3/mg DOC), the aromaticity of HON decreased dramatically, while aliphatics and ketones increased especially at the low ozone dose (0.42 ± 0.09 mgO3/mg DOC). Of the EfOM fractions, the HON fraction would have a higher content of electron enriched aromatics which could preferentially react with ozone rather than the HOA fraction. Copyright © 2015 Elsevier Ltd. All rights reserved.

Heavy metal stabilization in contaminated road-derived sediments.

PubMed

Rijkenberg, Micha J A; Depree, Craig V

2010-02-01

There is increasing interest in the stabilization of heavy metals in road-derived sediments (RDS), to enable environmentally responsible reuse applications and circumvent the need for costly landfill disposal. To reduce the mobility of heavy metals (i.e. Cu, Pb and Zn) the effectiveness of amendments using phosphate, compost and fly ash addition were investigated using batch leaching experiments. In general, phosphate amendments of RDS were found to be ineffective at stabilizing heavy metals, despite being used successfully in soils. Phosphate amendment resulted in enhanced concentrations of dissolved organic carbon (DOC), which increased the solubilisation of heavy metals via complexation. Amendment with humified organic matter (compost) successfully stabilized Cu and Pb in high DOC leaching RDS with an optimum loading of 15-20% (w/w). Compost, however, was ineffective at stabilizing Zn. Increasing the pH by amending RDS/compost blends with 2.5-15% (w/w) coal fly ash resulted in the stabilization of Zn, Cu and Pb. However, above a pH of approximately 7.5 and 8 enhanced leaching of organic matter resulted in an increase in leached Cu and Pb, respectively. Accordingly, the optimum level of fly ash amendment for the RDS/compost blends was estimated to be ca. 10%. Boosted regression trees analysis (BRT) of the data revealed that DOC accounted for 56% and 65% of the Cu and Pb leaching, respectively, whereas pH only accounted for ca. 18% of Cu and Pb leaching. RDS sample characteristics (i.e. metal concentrations, size fractionation and organic matter content) were more important at reconciling the leaching concentrations of copper Cu (27%) than Pb (16%). The most important parameter explaining Zn leaching was pH. Overall, the choice of a suitable stabilization agent/s depends on the composition of RDS with respect to the amount of organic matter present, and the sorption chemistry of the heavy metal of interest. Copyright 2009 Elsevier B.V. All rights reserved.

Dissolved organic carbon and major and trace elements in peat porewater of sporadic, discontinuous, and continuous permafrost zones of western Siberia

NASA Astrophysics Data System (ADS)

Raudina, Tatiana V.; Loiko, Sergey V.; Lim, Artyom G.; Krickov, Ivan V.; Shirokova, Liudmila S.; Istigechev, Georgy I.; Kuzmina, Daria M.; Kulizhsky, Sergey P.; Vorobyev, Sergey N.; Pokrovsky, Oleg S.

2017-07-01

Mobilization of dissolved organic carbon (DOC) and related trace elements (TEs) from the frozen peat to surface waters in the permafrost zone is expected to enhance under ongoing permafrost thaw and active layer thickness (ALT) deepening in high-latitude regions. The interstitial soil solutions are efficient tracers of ongoing bio-geochemical processes in the critical zone and can help to decipher the intensity of carbon and metals migration from the soil to the rivers and further to the ocean. To this end, we collected, across a 640 km latitudinal transect of the sporadic to continuous permafrost zone of western Siberia peatlands, soil porewaters from 30 cm depth using suction cups and we analyzed DOC, dissolved inorganic carbon (DIC), and 40 major elements and TEs in 0.45 µm filtered fraction of 80 soil porewaters. Despite an expected decrease in the intensity of DOC and TE mobilization from the soil and vegetation litter to the interstitial fluids with the increase in the permafrost coverage and a decrease in the annual temperature and ALT, the DOC and many major and trace elements did not exhibit any distinct decrease in concentration along the latitudinal transect from 62.2 to 67.4° N. The DOC demonstrated a maximum of concentration at 66° N, on the border of the discontinuous/continuous permafrost zone, whereas the DOC concentration in peat soil solutions from the continuous permafrost zone was equal to or higher than that in the sporadic/discontinuous permafrost zone. Moreover, a number of major (Ca, Mg) and trace (Al, Ti, Sr, Ga, rare earth elements (REEs), Zr, Hf, Th) elements exhibited an increasing, not decreasing, northward concentration trend. We hypothesize that the effects of temperature and thickness of the ALT are of secondary importance relative to the leaching capacity of peat, which is in turn controlled by the water saturation of the peat core. The water residence time in peat pores also plays a role in enriching the fluids in some elements: the DOC, V, Cu, Pb, REEs, and Th were a factor of 1.5 to 2.0 higher in mounds relative to hollows. As such, it is possible that the time of reaction between the peat and downward infiltrating waters essentially controls the degree of peat porewater enrichments in DOC and other solutes. A 2° northward shift in the position of the permafrost boundaries may bring about a factor of 1.3 ± 0.2 decrease in Ca, Mg, Sr, Al, Fe, Ti, Mn, Ni, Co, V, Zr, Hf, Th, and REE porewater concentration in continuous and discontinuous permafrost zones, and a possible decrease in DOC, specific ultraviolet absorbency (SUVA), Ca, Mg, Fe, and Sr will not exceed 20 % of their current values. The projected increase in ALT and vegetation density, northward migration of the permafrost boundary, or the change of hydrological regime is unlikely to modify chemical composition of peat porewater fluids larger than their natural variations within different micro-landscapes, i.e., within a factor of 2. The decrease in DOC and metal delivery to small rivers and lakes by peat soil leachate may also decrease the overall export of dissolved components from the continuous permafrost zone to the Arctic Ocean. This challenges the current paradigm on the increase in DOC export from the land to the ocean under climate warming in high latitudes.

The Earth System Documentation (ES-DOC) project

NASA Astrophysics Data System (ADS)

Murphy, S.; Greenslade, M. A.; Treshansky, A.; DeLuca, C.; Guilyardi, E.; Denvil, S.

2013-12-01

Earth System Documentation (ES-DOC) is an international project supplying high quality tools and services in support of Earth system documentation creation, analysis and dissemination. It is nurturing a sustainable standards based documentation ecosystem that aims to become an integral part of the next generation of exa-scale dataset archives. ES-DOC leverages open source software, and applies a software development methodology that places end-user narratives at the heart of all it does. ES-DOC has initially focused upon nurturing the Earth System Model (ESM) documentation eco-system. Within this context ES-DOC leverages the emerging Common Information Model (CIM) metadata standard, which has supported the following projects: ** Coupled Model Inter-comparison Project Phase 5 (CMIP5); ** Dynamical Core Model Inter-comparison Project (DCMIP-2012); ** National Climate Predictions and Projections Platforms (NCPP) Quantitative Evaluation of Downscaling Workshop (QED-2013). This presentation will introduce the project to a wider audience and will demonstrate the current production level capabilities of the eco-system: ** An ESM documentation Viewer embeddable into any website; ** An ESM Questionnaire configurable on a project by project basis; ** An ESM comparison tool reusable across projects; ** An ESM visualization tool reusable across projects; ** A search engine for speedily accessing published documentation; ** Libraries for streamlining document creation, validation and publishing pipelines.

Leakage of soluble microbial products from biological activated carbon filtration in drinking water treatment plants and its influence on health risks.

PubMed

Hong, Shen; Xian-Chun, Tang; Nan-Xiang, Wu; Hong-Bin, Chen

2018-07-01

The application of ozone-biological activated carbon (O 3 -BAC) as an advanced treatment method in drinking water treatment plants (DWTPs) can help to remove organic micropollutants and further decrease the dissolved organic carbon (DOC) level in finished water. With the increase attention to microbial safety of drinking water, a pre-positioned O 3 -BAC followed by a sand filter has been implanted into DWTP located in Shanghai, China to increase the biostability of effluents. The results showed that BAC had high removal efficiencies of UV 254 , DOC and disinfection by-product formation potential (DBPFP). The removal efficiencies between pre- and post-positioned BAC filtrations were similar. Based on the analyses of fluorescence excitation-emission matrix spectrophotometry (FEEM), the generation and leakage of soluble microbial products (SMPs) were found in both two BAC filtrations on account of the increased fluorescence intensities and fluorescence regional integration (FRI) distribution of protein-like organics, as well as the enhanced biological index (BIX). The leakage of SMPs produced by metabolism of microbes during BAC process resulted in increased DBPFP yield and carcinogenic factor per unit of DOC (CF/DOC). Although BAC filtration reduced the DBPFP and CF, there still was high health risk of effluents for the production of SMPs. Therefore, the health risks for SMPs generated by BAC filtration in drinking water advanced treatment process should be addressed, especially with that at high temperature. Copyright © 2018 Elsevier Ltd. All rights reserved.

Removal of terrestrial DOC in aquatic ecosystems of a temperate river network

USGS Publications Warehouse

Wollheim, W.M.; Stewart, R. J.; Aiken, George R.; Butler, Kenna D.; Morse, Nathaniel B.; Salisbury, J.

2015-01-01

Surface waters play a potentially important role in the global carbon balance. Dissolved organic carbon (DOC) fluxes are a major transfer of terrestrial carbon to river systems, and the fate of DOC in aquatic systems is poorly constrained. We used a unique combination of spatially distributed sampling of three DOC fractions throughout a river network and modeling to quantify the net removal of terrestrial DOC during a summer base flow period. We found that aquatic reactivity of terrestrial DOC leading to net loss is low, closer to conservative chloride than to reactive nitrogen. Net removal occurred mainly from the hydrophobic organic acid fraction, while hydrophilic and transphilic acids showed no net change, indicating that partitioning of bulk DOC into different fractions is critical for understanding terrestrial DOC removal. These findings suggest that river systems may have only a modest ability to alter the amounts of terrestrial DOC delivered to coastal zones.

Long-term decomposition of DOC from experimental diatom blooms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fry, B.; Hopkinson, C.S. Jr.; Nolin, A.

1996-09-01

Decomposition of {sup 13}C-labeled dissolved organic carbon (DOC) produced in two marine diatom blooms was followed for 2.5 yr with large volume (20 liter) incubations performed in the dark. The {sup 13}C tracer was used to partition decomposition dynamics of the fresh diatom-derived DOC and the turnover of background DOC from Woods Hole Harbor. DOC from Woods Hole harbor proved largely refractory, with DOC concentrations falling from 122 to {approximately} 100 {mu}M C in 2.5 yr. DOC from the diatom blooms was more labile, but was also incompletely mineralized, with 25-35% remaining after 2.5 yr. Neither nutrients nor labile carbonmore » (dextrose) added at 1.5 yr significantly stimulated DOC mineralization. The experiments indicate that DOC produced in short-term blooms can be surprisingly resistant to microbial attack. 21 refs., 1 fig., 1 tab.« less

Response Characteristics of Dissolved Organic Carbon Flushing in a Subarctic Alpine Catchment

NASA Astrophysics Data System (ADS)

Carey, S. K.

2002-12-01

Dissolved organic carbon (DOC) is an important part of ecosystem-scale carbon balances and in the transport of contaminants as it interacts with other dissolved substances including trace metals. It also can be used as a surrogate hydrological tracer in permafrost regions as near-surface waters are often DOC enriched due to the presence of thick organic soils. In a small subarctic alpine catchment within the Wolf Creek Research Basin, Yukon, Canada, DOC was studied in the summer of 2001 and spring of 2002 to determine the role frost (both permanent and seasonal), snowmelt and summer storms on DOC flushing. Peak DOC concentrations occurred during the snowmelt period, approximately one week prior to peak discharge. However, peak discharge took place several weeks after snow on south facing exposures had melted. Within the hillslopes, DOC concentrations were three to five times greater in wells underlain with permafrost compared with seasonal frost. Groundwater DOC concentrations declined during snowmelt, yet remained at levels above the streamflow. After peaking, streamflow DOC concentrations declined exponentially suggesting a simple flushing mechanism, however there did not appear to be a relation between DOC and topographic position. Following melt, permafrost underlain slopes had near-surface water tables and retained elevated levels of DOC, whereas slopes without permafrost had rapidly declining water tables at upslope locations with low DOC concentrations at all positions except near-stream riparian zones. The influence of summer rainstorms on DOC was monitored on three occasions. In each case DOC peaked on the ascending limb of the runoff hydrograph and declined exponentially on the receding limb and hysteretic behavior occurred between discharge and DOC during all events. Patterns of DOC within the hillslopes and streams suggest that runoff from permafrost-underlain slopes control DOC flushing within the stream during both snowmelt and summer periods. This flushing mechanism conforms with conceptual models of runoff generation in discontinuous permafrost catchments whereby water tables within permafrost-underlain slopes rise into porous organic-layers, whereupon DOC is leached into the water and rapidly conveyed to the stream.

Does wildfire cause cascading effects on aquatic C cycling? A study of soil, well and lake DOC composition and bio/photolability

NASA Astrophysics Data System (ADS)

Olefeldt, D.; Turetsky, M. R.; Devito, K. J.; Blodau, C.

2012-12-01

In May 2011 a wildfire broke out north of Utikuma Lake in central Alberta, Canada, which eventually burned an area of ~880 km2. Wildfire alters soil properties, potentially altering the chemical composition of terrestrial DOC that reaches downstream aquatic environments. In order to study the potential effects of wildfire on lake carbon cycling, we sampled and incubated DOC from soil samples (n=52), wells (n=35) and lakes (n=32) from within and outside the recent fire perimeter. We incubated the DOC samples under both dark and UV conditions to assess both bio- and photolability, and followed DOC composition throughout the incubations by measuring DOC absorbing and fluorescing properties. A strong effect of wildfire was found among DOC samples leached from surface peatland and upland soils - with fire yielding increased DOC aromaticity associated with decreased biodegradability but also increased photolability. Parallel factor analysis of fluorescence matrices revealed distinct regions that were associated with DOC leached from charred soils, potentially linked to their lower biodegradability. Dark and UV conditions gave rise to very different trajectories of changes to DOC composition throughout incubations, with preferential losses of non-aromatic DOC under dark conditions and aromatic DOC under UV conditions. The DOC composition index that was found to best predict both DOC bio- and photolability was specific UV absorbance, which is also a very simple and quick index to measure. For lakes, we found that the primary influences on DOC composition and bio-/photolability was linked to lake size and hydrogeological setting (whether located on a lacustrine clay plain or in a moraine/outwash region) that controls groundwater influence and the hydrological connectivity to adjacent peatlands. Further analysis of well and lake water incubations will be used to detect whether wildfire can be detected to have a subtle secondary effect on DOC composition and lability or if the potential for cascading effects on lake C cycling due to altered soil DOC sources remain unrealized in the study region.

Chado controller: advanced annotation management with a community annotation system.

PubMed

Guignon, Valentin; Droc, Gaëtan; Alaux, Michael; Baurens, Franc-Christophe; Garsmeur, Olivier; Poiron, Claire; Carver, Tim; Rouard, Mathieu; Bocs, Stéphanie

2012-04-01

We developed a controller that is compliant with the Chado database schema, GBrowse and genome annotation-editing tools such as Artemis and Apollo. It enables the management of public and private data, monitors manual annotation (with controlled vocabularies, structural and functional annotation controls) and stores versions of annotation for all modified features. The Chado controller uses PostgreSQL and Perl. The Chado Controller package is available for download at http://www.gnpannot.org/content/chado-controller and runs on any Unix-like operating system, and documentation is available at http://www.gnpannot.org/content/chado-controller-doc The system can be tested using the GNPAnnot Sandbox at http://www.gnpannot.org/content/gnpannot-sandbox-form valentin.guignon@cirad.fr; stephanie.sidibe-bocs@cirad.fr Supplementary data are available at Bioinformatics online.

Assessing chromophoric dissolved organic matter (CDOM) distribution, stocks, and fluxes in Apalachicola Bay using combined field, VIIRS ocean color, and model observations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Joshi, Ishan D.; D'Sa, Eurico J.; Osburn, Christopher L.

Understanding the role of estuarine-carbon fluxes is essential to improve estimates of the global carbon budget. Dissolved organic matter (DOM) plays an important role in aquatic carbon cycling. Here, the chromophoric fraction of DOM (CDOM) can be readily detected via in situ and remotely-sensed optical measurements. DOM properties, including CDOM absorption coefficient at 412 nm (a g412) and dissolved organic carbon (DOC) concentrations were examined in Apalachicola Bay, a national estuarine research reserve located in the northeast Gulf of Mexico, using in situ and satellite observations during the spring and fall of 2015. Synoptic and accurate representation of estuarine-scale processesmore » using satellite ocean color imagery necessitates the removal of atmospheric contribu- tion (~90%) to signals received by satellite sensors to successfully link to in situ observations. Three atmospheric correction schemes (e.g., Standard NIR correction, Iterative NIR correction, and SWIR correction) were tested first to find a suitable correction scheme for the VIIRS imagery in low to moderately turbid Apalachicola Bay. The iterative NIR correction performed well, and validation showed high correlation (R 2 = 0.95, N = 25) against in situ light measurements. A VIIRS-based CDOM algorithm was developed (R 2 = 0.87, N = 9) and validated (R 2 = 0.76, N = 20, RMSE = 0.29 m -1) against in situ observations. Subsequently, ag412 was used as a proxy of DOC in March (DOC = 1.08 + 0.94 × a g412,R 2 =0.88, N = 13)and in November (DOC= 1.61 + 1.33 × a g412, R 2 = 0.83, N = 24) to derive DOC maps that provided synoptic views of DOC distribution, sources, and their transport to the coastal waters during the wet and dry seasons. The estimated DOC stocks were ~3.71 × 10 6 kg C in March and ~4.07 × 10 6 kg C in November over an area of ~560 km2. Volume flux (out of the bay) almost doubled for March 24 (735 m 3 s -1) relative to November 4 (378 m 3 s -1). However, estimates of DOC fluxes exported out of the bay from model-derived currents and satellite-derived DOC were only marginally greater in March (0.163 × 10 6 kg C d -1) than in November (0.124 × 10 6 kg C d -1) and reflected greater DOC stocks in the fall. Finally, the combination of satellite-, field-, and model-based observations revealed the strong linkage between the Apalachicola River plume, a major source of DOM, and the overall hydrodynamic forcing that controlled distributions of CDOM abundance, DOC concentration, stocks, and fluxes in the bay.« less

Assessing chromophoric dissolved organic matter (CDOM) distribution, stocks, and fluxes in Apalachicola Bay using combined field, VIIRS ocean color, and model observations

DOE PAGES

Joshi, Ishan D.; D'Sa, Eurico J.; Osburn, Christopher L.; ...

2017-02-06

Understanding the role of estuarine-carbon fluxes is essential to improve estimates of the global carbon budget. Dissolved organic matter (DOM) plays an important role in aquatic carbon cycling. Here, the chromophoric fraction of DOM (CDOM) can be readily detected via in situ and remotely-sensed optical measurements. DOM properties, including CDOM absorption coefficient at 412 nm (a g412) and dissolved organic carbon (DOC) concentrations were examined in Apalachicola Bay, a national estuarine research reserve located in the northeast Gulf of Mexico, using in situ and satellite observations during the spring and fall of 2015. Synoptic and accurate representation of estuarine-scale processesmore » using satellite ocean color imagery necessitates the removal of atmospheric contribu- tion (~90%) to signals received by satellite sensors to successfully link to in situ observations. Three atmospheric correction schemes (e.g., Standard NIR correction, Iterative NIR correction, and SWIR correction) were tested first to find a suitable correction scheme for the VIIRS imagery in low to moderately turbid Apalachicola Bay. The iterative NIR correction performed well, and validation showed high correlation (R 2 = 0.95, N = 25) against in situ light measurements. A VIIRS-based CDOM algorithm was developed (R 2 = 0.87, N = 9) and validated (R 2 = 0.76, N = 20, RMSE = 0.29 m -1) against in situ observations. Subsequently, ag412 was used as a proxy of DOC in March (DOC = 1.08 + 0.94 × a g412,R 2 =0.88, N = 13)and in November (DOC= 1.61 + 1.33 × a g412, R 2 = 0.83, N = 24) to derive DOC maps that provided synoptic views of DOC distribution, sources, and their transport to the coastal waters during the wet and dry seasons. The estimated DOC stocks were ~3.71 × 10 6 kg C in March and ~4.07 × 10 6 kg C in November over an area of ~560 km2. Volume flux (out of the bay) almost doubled for March 24 (735 m 3 s -1) relative to November 4 (378 m 3 s -1). However, estimates of DOC fluxes exported out of the bay from model-derived currents and satellite-derived DOC were only marginally greater in March (0.163 × 10 6 kg C d -1) than in November (0.124 × 10 6 kg C d -1) and reflected greater DOC stocks in the fall. Finally, the combination of satellite-, field-, and model-based observations revealed the strong linkage between the Apalachicola River plume, a major source of DOM, and the overall hydrodynamic forcing that controlled distributions of CDOM abundance, DOC concentration, stocks, and fluxes in the bay.« less

The topographic wetness index as a predictor for hot spots of DOC export from catchments

NASA Astrophysics Data System (ADS)

Musolff, Andreas; Oosterwoud, Marieke; Tittel, Jörg; Selle, Benny; Fleckenstein, Jan H.

2015-04-01

Dissolved organic carbon (DOC) concentrations in the discharge of many catchments in Europe and North America are rising. This increase is of concern for the drinking water supply from reservoirs since high DOC concentrations cause additional costs in water treatment and potentially the formation of harmful disinfection by-products. A prerequisite for understanding this increase is the knowledge on the spatial distribution of dominant soil DOC sources within catchments and on mobilization as well as transfer processes to the surface water. A number of studies identified wetland soils as the dominant source with fast mobilization and short transit times to the receiving surface water. However, most studies have either focussed on smaller, hillslope and single catchment or on larger scale multi-catchment assessments. Moreover, information on the distribution of soil types in catchments is not always readily available. This study brings together both types of assessment in a data-driven top-down approach: (i) a detailed survey on DOC concentration and loads over the course of one year within two paired data-rich catchments discharging into a large drinking water reservoir in central Germany and (ii) a database of hydrochemistry and physio-geographic characteristics of 113 catchments draining into 58 reservoirs across Germany over the course of 16 years. The objective is to define hot spots of DOC export within the catchments for both types of assessments (i, ii) and to test the suitability of the topographic wetness index (TWI) as a proxy for well-connected wetland soils at various spatial scales. In the sub-catchments of assessment (i) the spatial variability of concentrations and loads was much smaller than expected. None of the studied sub-catchments was a predominant producer of the total DOC loads exported from the catchments. We found the mean concentrations and loads to be positively correlated with the share of groundwater-dominated soils in the sub-catchments. These soils are distributed in riparian wetlands along all streams within the catchments. As a readily available proxy for wetland soils percentiles of the probability distribution of the TWI in the sub-catchments were found to be good predictors for mean DOC concentrations in catchment outlet as well as for loads. In the larger dataset across Germany (ii) we also found a surprisingly good correlation between the TWI within the catchments and mean DOC concentrations. Thus we can show that, despite the wide range of topographies, land use types, geological setups and climatic conditions within this dataset the dominant source zones of DOC export is well captured by the TWI as a proxy for the share of wetland soils and DOC source zones within the catchments.

Process Simulation and Modeling for Advanced Intermetallic Alloys.

DTIC Science & Technology

1994-06-01

calorimetry, using a Stanton Redfera/Omnitherm DOC 1500 thermal analysis system, was the primary experimental tool for this investigation...samples during both heating and cooling in a high purity argon atmosphere at a rate of 20K/min. The DSC instrumental baseline was obtained using both empty...that is capable of fitting the observed data to given cell structures using a least squares procedure. RESULTS The results of the DOC observations are

Transcriptional Changes Underlying Elemental Stoichiometry Shifts in a Marine Heterotrophic Bacterium

PubMed Central

Chan, Leong-Keat; Newton, Ryan J.; Sharma, Shalabh; Smith, Christa B.; Rayapati, Pratibha; Limardo, Alexander J.; Meile, Christof; Moran, Mary Ann

2012-01-01

Marine bacteria drive the biogeochemical processing of oceanic dissolved organic carbon (DOC), a 750-Tg C reservoir that is a critical component of the global C cycle. Catabolism of DOC is thought to be regulated by the biomass composition of heterotrophic bacteria, as cells maintain a C:N:P ratio of ∼50:10:1 during DOC processing. Yet a complicating factor in stoichiometry-based analyses is that bacteria can change the C:N:P ratio of their biomass in response to resource composition. We investigated the physiological mechanisms of resource-driven shifts in biomass stoichiometry in continuous cultures of the marine heterotrophic bacterium Ruegeria pomeroyi (a member of the Roseobacter clade) under four element limitation regimes (C, N, P, and S). Microarray analysis indicated that the bacterium scavenged for alternate sources of the scarce element when cells were C-, N-, or P-limited; reworked the ratios of biomolecules when C- and P- limited; and exerted tighter control over import/export and cytoplasmic pools when N-limited. Under S limitation, a scenario not existing naturally for surface ocean microbes, stress responses dominated transcriptional changes. Resource-driven changes in C:N ratios of up to 2.5-fold and in C:P ratios of up to sixfold were measured in R. pomeroyi biomass. These changes were best explained if the C and P content of the cells was flexible in the face of shifting resources but N content was not, achieved through the net balance of different transcriptional strategies. The cellular-level metabolic trade-offs that govern biomass stoichiometry in R. pomeroyi may have implications for global carbon cycling if extendable to other heterotrophic bacteria. Strong homeostatic responses to N limitation by marine bacteria would intensify competition with autotrophs. Modification of cellular inventories in C- and P-limited heterotrophs would vary the elemental ratio of particulate organic matter sequestered in the deep ocean. PMID:22783226

Controls on soil solution nitrogen along an altitudinal gradient in the Scottish uplands.

PubMed

Jackson-Blake, L; Helliwell, R C; Britton, A J; Gibbs, S; Coull, M C; Dawson, L

2012-08-01

Nitrogen (N) deposition continues to threaten upland ecosystems, contributing to acidification, eutrophication and biodiversity loss. We present results from a monitoring study aimed at investigating the fate of this deposited N within a pristine catchment in the Cairngorm Mountains (Scotland). Six sites were established along an elevation gradient (486-908 m) spanning the key habitats of temperate maritime uplands. Bulk deposition chemistry, soil carbon content, soil solution chemistry, soil temperature and soil moisture content were monitored over a 5 year period. Results were used to assess spatial variability in soil solution N and to investigate the factors and processes driving this variability. Highest soil solution inorganic N concentrations were found in the alpine soils at the top of the hillslope. Soil carbon stock, soil solution dissolved organic carbon (DOC) and factors representing site hydrology were the best predictors of NO(3)(-) concentration, with highest concentrations at low productivity sites with low DOC and freely-draining soils. These factors act as proxies for changing net biological uptake and soil/water contact time, and therefore support the hypothesis that spatial variations in soil solution NO(3)(-) are controlled by habitat N retention capacity. Soil percent carbon was a better predictor of soil solution inorganic N concentration than mass of soil carbon. NH(4)(+) was less affected by soil hydrology than NO(3)(-) and showed the effects of net mineralization inputs, particularly at Racomitrium heath and peaty sites. Soil solution dissolved organic N concentration was strongly related to both DOC and temperature, with a stronger temperature effect at more productive sites. Due to the spatial heterogeneity in N leaching potential, a fine-scale approach to assessing surface water vulnerability to N leaching is recommended over the broad scale, critical loads approach currently in use, particularly for sensitive areas. Copyright © 2012 Elsevier B.V. All rights reserved.

Organic Carbon Mobilisation Mechanisms: Evidence from Globally Distributed Stalagmite Records

NASA Astrophysics Data System (ADS)

Baldini, J. U. L.; Fairchild, I. J.; Wynn, P.; Bourdin, C.; Muller, W.; Hartland, A.; Perrette, Y.; Worrall, F.; Bartlett, R.

2017-12-01

Identifying the cause of widespread increases in surface water dissolved organic carbon (DOC) concentrations in recent years is the subject of a contentious debate. Although DOC trends may partially reflect climate change, in many catchments they may also result from increased soil carbon solubility associated with decreases in acid rain due to lower atmospheric sulphur emissions. However, the lack of long-term DOC records hampers constraining climate's role in modulating DOC trends versus that of recovery from acidification. Here we help clarify the causes of recent DOC increases by using a combination of laboratory soil experiments and new stalagmite geochemical data. Laboratory experiments with soils sampled from above several key caves simulate the effect of acidity, temperature, and soil microbial processes on DOC release. These experiments are used to inform records of DOC encoded within several stalagmites from currently acidified, previously acidified, and unacidified sites, and which collectively yield insights into the timing of DOC change in the past. These records of stalagmite DOC concentration and composition are discussed within the context of the ongoing debate regarding the mechanism responsible for DOC release.

Minor contribution of small thaw ponds to the pools of carbon and methane in the inland waters of the permafrost-affected part of the Western Siberian Lowland

NASA Astrophysics Data System (ADS)

Polishchuk, Y. M.; Bogdanov, A. N.; Muratov, I. N.; Polishchuk, V. Y.; Lim, A.; Manasypov, R. M.; Shirokova, L. S.; Pokrovsky, O. S.

2018-04-01

Despite the potential importance of small (< 1000 m2) thaw ponds and thermokarst lakes in greenhouse gas (GHG) emissions from inland waters of high latitude and boreal regions, these features have not been fully inventoried and the volume of GHG and carbon in thermokarst lakes remains poorly constrained. This is especially true for the vast Western Siberia Lowland (WSL) which is subject to strong thermokarst activity. We assessed the number of thermokarst lakes and their size distribution for the permafrost-affected WSL territory based on a combination of medium-resolution Landsat-8 images and high-resolution Kanopus-V scenes on 78 test sites across the WSL in a wide range of lake sizes (from 20 to 2 × 108 m2). The results were in fair agreement with other published data for world lakes including those in circum-polar regions. Based on available measurements of CH4, CO2, and dissolved organic carbon (DOC) in thermokarst lakes and thaw ponds of the permafrost-affected part of the WSL, we found an inverse relationship between lake size and concentration, with concentrations of GHGs and DOC being highest in small thaw ponds. However, since these small ponds represent only a tiny fraction of the landscape (i.e. ~1.5% of the total lake area), their contribution to the total pool of GHG and DOC in inland lentic water of the permafrost-affected part of the WSL is less than 2%. As such, despite high concentrations of DOC and GHG in small ponds, their role in overall C storage can be negated. Ongoing lake drainage due to climate warming and permafrost thaw in the WSL may lead to a decrease in GHG emission potential from inland waters and DOC release from lakes to rivers.

Direct observation and determination of the mechanisms governing mobility of asbestos in porous media

NASA Astrophysics Data System (ADS)

Seiphoori, A.; Ortiz, C. P.; Jerolmack, D. J.

2017-12-01

Transport of asbestos through soil by groundwater is typically considered to be negligible. There are indications, however, that under some conditions of pore-water/soil chemistry asbestos may become mobile, implying that buried contaminants could migrate from a disposal site and surface elsewhere. Shape, size and surface charge may influence the physical and chemical interactions of colloids with the soil matrix, and asbestos consists of elongated particles with different size and unique surface charge properties. Although chemical factors such as pH and ionic strength of pore water may affect the transport properties, the presence of dissolved organic carbon (DOC) has been identified to remarkably enhance the mobility of colloids including asbestos. To date, there is no explanation for how the presence of DOC may facilitate the mobilization of asbestos in soil - mainly because the soil medium has been treated as a black box without the possibility of observing particles within the matrix. Here, we investigated the mobility of chrysotile asbestos particles ( 10 um long) in porous media by developing a flow cell with an optically-transparent porous medium composed of granules of a refractive-index matched material. This enabled us to observe and track the particles within the water-saturated porous medium using in situ microscopy. The aqueous suspension of asbestos fibers was passed through this artificial soil, while the physical and chemical interaction of asbestos particles with the medium and their pore-scale distribution were analyzed. We studied the effects of changing solution chemistry (e.g., ionic strength, pH, and DOC content) on transport, attachment and aggregation of chrysotile particles. Experiments revealed a novel mechanism where the DOC-associated nanoparticles attach to chrysotile fibers by an electrostatic attraction, which facilitates their mobilization through the porous medium while modulating aggregation among fibers. Although pH and ionic strength also influenced aggregation and the attachment rate of particles to the substrate, the effect of DOC was more pronounced. This work may lead to enhanced predictions for the fate and transport of asbestos (as well as other contaminants) in the environment, and has implications for the mobility of asbestos particles in the human body.

Antarctic snow: metals bound to high molecular weight dissolved organic matter.

PubMed

Calace, Nicoletta; Nardi, Elisa; Pietroletti, Marco; Bartolucci, Eugenia; Pietrantonio, Massimiliana; Cremisini, Carlo

2017-05-01

In this paper we studied some heavy metals (Cu, Zn, Cd, Pb, As, U) probably associated to high molecular weight organic compounds present in the Antarctic snow. Snow-pit samples were collected and analysed for high molecular weight fraction and heavy metals bound to them by means of ultrafiltration treatment. High molecular weight dissolved organic matter (HMW-DOM) recovered by ultrafiltration showed a dissolved organic carbon concentration (HMW-DOC) of about 18-83% of the total dissolved organic carbon measured in Antarctic snow. The characterisation of HMW-DOM fraction evidenced an ageing of organic compounds going from surface layers to the deepest ones with a shift from aliphatic compounds and proteins/amino sugars to more high unsaturated character and less nitrogen content. The heavy metals associated to HMW-DOM fraction follows the order: Zn > Cu > Pb > Cd ∼ As ∼ U. The percentage fraction of metals bound to HMW-DOM respect to total metal content follows the order: Cu > Pb > Zn, Cd in agreement with humic substance binding ability (Irwing-William series). Going down to depth of trench, all metals except arsenic, showed a high concentration peak corresponding to 2.0-2.5 m layer. This result was attributed to particular structural characteristic of organic matter able to form different type of complexes (1:1, 1:2, 1:n) with metals. Copyright © 2017 Elsevier Ltd. All rights reserved.

Distribution characteristics of dissolved organic carbon in annular wetland soil-water solutions through soil profiles in the Sanjiang Plain, northeast China.

PubMed

Xi, Min; Lu, Xian-Guo; Li, Yue; Kong, Fan-Long

2007-01-01

Overwhelming evidence reveals that concentrations of dissolved organic carbon (DOC) have increased in streams which brings negative environmental impacts. DOC in stream flow is mainly originated from soil-water solutions of watershed. Wetlands prove to be the most sensitive areas as an important DOC reserve between terrestrial and fluvial biogeosystems. This reported study was focused on the distribution characteristics and the controlling factors of DOC in soil-water solutions of annular wetland, i.e., a dishing wetland and a forest wetland together, in the Sanjiang Plain, Northeast China. The results indicate that DOC concentrations in soil-water solutions decreased and then increased with increasing soil depth in the annular wetland. In the upper soil layers of 0-10 cm and 10-20 cm, DOC concentrations in soil-water solutions linearly increased from edge to center of the annular wetland (R2 = 0.3122 and R2 = 0.443). The distribution variations were intimately linked to DOC production and utilization and DOC transport processes in annular wetland soil-water solutions. The concentrations of total organic carbon (TOC), total carbon (TC) and Fe(II), DOC mobility and continuous vertical and lateral flow affected the distribution variations of DOC in soil-water solutions. The correlation coefficients between DOC concentrations and TOC, TC and Fe(II) were 0.974, 0.813 and 0.753 respectively. These distribution characteristics suggested a systematic response of the distribution variations of DOC in annular wetland soil-water solutions to the geometry of closed depressions on a scale of small catchments. However, the DOC in soil pore water of the annular wetland may be the potential source of DOC to stream flow on watershed scale. These observations also implied the fragmentation of wetland landscape could bring the spatial-temporal variations of DOC distribution and exports, which would bring negative environmental impacts in watersheds of the Sanjiang Plain.

Characterization and comparison of hydrophobic neutral and hydrophobic acid dissolved organic carbon isolated from three municipal landfill leachates

USGS Publications Warehouse

Nanny, Mark A.; Ratasuk, Nopawan

2002-01-01

The acid-precipitated (AP) and acid-soluble (AS) fractions of the combined hydrophobic neutral and hydrophobic acid dissolved organic carbon (DOC) were isolated from leachate collected from three municipal landfills of different age and redox conditions. The AP and the AS combined hydrophobic neutral and hydrophobic acid DOC comprised 6–15% and 51–66%, respectively, of the leachate nonpurgable organic carbon. Elemental analysis, infra-red spectroscopy, 13C CP-MAS nuclear magnetic resonance spectroscopy and dipolar dephasing experiments, and thermochemolysis gas chromatography/mass spectrometry results showed that the AP and AS fractions of hydrophobic neutral and hydrophobic acid DOC are highly aliphatic, with linear and branching moieties, and less oxidized than most terrestrial and aquatic humic substances. Very little, if any, polysaccharide or cellulose, lignin, or cutin components comprise these fractions. It is hypothesized that a majority of the organic carbon in these fractions originates highly branched, cyclic aliphatic organic compounds.

[Response of mineralization of dissolved organic carbon to soil moisture in paddy and upland soils in hilly red soil region].

PubMed

Chen, Xiang-Bi; Wang, Ai-Hua; Hu, Le-Ning; Huang, Yuan; Li, Yang; He, Xun-Yang; Su, Yi-Rong

2014-03-01

Typical paddy and upland soils were collected from a hilly subtropical red-soil region. 14C-labeled dissolved organic carbon (14C-DOC) was extracted from the paddy and upland soils incorporated with 14C-labeled straw after a 30-day (d) incubation period under simulated field conditions. A 100-d incubation experiment (25 degrees C) with the addition of 14C-DOC to paddy and upland soils was conducted to monitor the dynamics of 14C-DOC mineralization under different soil moisture conditions [45%, 60%, 75%, 90%, and 105% of the field water holding capacity (WHC)]. The results showed that after 100 days, 28.7%-61.4% of the labeled DOC in the two types of soils was mineralized to CO2. The mineralization rates of DOC in the paddy soils were significantly higher than in the upland soils under all soil moisture conditions, owing to the less complex composition of DOC in the paddy soils. The aerobic condition was beneficial for DOC mineralization in both soils, and the anaerobic condition was beneficial for DOC accumulation. The biodegradability and the proportion of the labile fraction of the added DOC increased with the increase of soil moisture (45% -90% WHC). Within 100 days, the labile DOC fraction accounted for 80.5%-91.1% (paddy soil) and 66.3%-72.4% (upland soil) of the cumulative mineralization of DOC, implying that the biodegradation rate of DOC was controlled by the percentage of labile DOC fraction.

Understanding the role of soil erosion on co2-c loss using (13)c isotopic signatures in abandoned Mediterranean agricultural land.

PubMed

Novara, Agata; Keesstra, Saskia; Cerdà, Artemio; Pereira, Paulo; Gristina, Luciano

2016-04-15

Understanding soil water erosion processes is essential to evaluate the redistribution of soil organic carbon (SOC) within a landscape and is fundamental to assess the role of soil erosion in the global carbon (C) budget. The main aim of this study was to estimate the C redistribution and losses using (13)C natural abundance. Carbon losses in soil sediment, dissolved organic carbon (DOC) and CO2 emission were determined. Four bounded parallel plots were installed on a 10% slope. In the upper part of the plots, C3soil was replaced with C4soil. The SOC and δ(13)C were measured after 145.2mm rainfall in the upper (2m far from C4strip), middle (4m far from C4strip) lower (6m far from C4strip) trams of the plot and in the sediments collected in the Gerlach collector at the lower part of the plot. A laboratory incubation experiment was performed to evaluate the CO2 emission rate of soils in each area. OC was mainly lost in the sediments as 2.08g(-)(2) of C was lost after 145.2mm rainfall. DOC losses were only 5.61% of off-site OC loss. Three months after the beginning of the experiment, 15.90% of SOC in the upper tram of the plot had a C4 origin. The C4-SOC content decreased along the 6m length of the plot, and in the sediments collected by the Gerlach collector. CO2 emission rate was high in the upper plot tram due to the high SOC content. The discrimination of CO2 in C3 and C4 portion permitted to increase our level of understanding on the stability of SOC and its resilience to decomposition. The transport of sediments along the plot increased SOC mineralization by 43%. Our study underlined the impact of rainfall in C losses in soil and water in abandoned Mediterranean agriculture fields and the consequent implications on the C balance. Copyright © 2016 Elsevier B.V. All rights reserved.

Utilizing chromophoric dissolved organic matter measurements to derive export and reactivity of dissolved organic carbon exported to the Arctic Ocean: A case study of the Yukon River, Alaska

USGS Publications Warehouse

Spencer, R.G.M.; Aiken, G.R.; Butler, K.D.; Dornblaser, M.M.; Striegl, Robert G.; Hernes, P.J.

2009-01-01

The quality and quantity of dissolved organic matter (DOM) exported by Arctic rivers is known to vary with hydrology and this exported material plays a fundamental role in the biogeochemical cycling of carbon at high latitudes. We highlight the potential of optical measurements to examine DOM quality across the hydrograph in Arctic rivers. Furthermore, we establish chromophoric DOM (CDOM) relationships to dissolved organic carbon (DOC) and lignin phenols in the Yukon River and model DOC and lignin loads from CDOM measurements, the former in excellent agreement with long-term DOC monitoring data. Intensive sampling across the historically under-sampled spring flush period highlights the importance of this time for total export of DOC and particularly lignin. Calculated riverine DOC loads to the Arctic Ocean show an increase from previous estimates, especially when new higher discharge data are incorporated. Increased DOC loads indicate decreased residence times for terrigenous DOM in the Arctic Ocean with important implications for the reactivity and export of this material to the Atlantic Ocean. Citation: Spencer, R. G. M., G. R. Aiken, K. D. Butler, M. M. Dornblaser, R. G. Striegl, and P. J. Hernes (2009), Utilizing chromophoric dissolved organic matter measurements to derive export and reactivity of dissolved organic carbon exported to the Arctic Ocean: A case study of the Yukon River, Alaska, Geophys. Res. Lett., 36, L06401, doi:10.1029/ 2008GL036831. Copyright 2009 by the American Geophysical Union.

Influence of Flood and Drought Conditions on Dissolved Organic Matter Distribution in Northern Gulf of Mexico Shelf Waters

NASA Astrophysics Data System (ADS)

Shank, G. C.; Liu, Q.; Patterson, L.; Kowalczuk, P.

2012-12-01

DOC, CDOM, and EEM PARAFAC analyses were used to examine DOM distribution along the Louisiana (LA) and Texas (TX) continental shelves in the northern Gulf of Mexico during cruises in May and August of the 2011 Mississippi basin flood year, and May, June, and August of the 2012 Mississippi basin drought year. For both 2011 and 2012, CDOM and DOC levels were well-correlated with salinity on the LA shelf. However, the mixing curves for each parameter were markedly different between 2011 and 2012 and CDOM:DOC ratios, indicative of terrestrial organic matter inputs, were much higher during 2011 than during 2012. EEM PARAFAC results confirmed a much higher terrestrial DOM signature in LA shelf waters for 2011, but also a higher terrestrial DOM signature for TX waters in 2012 as the drought in the western Gulf region subsided. CDOM:DOC ratios were anomalously high offshore of Atchafalaya Bay and the Breton-Chandeleur Sound complex indicating coastal wetlands augment the terrestrial DOM discharged through the Mississippi and Atchafalaya Rivers. At several sites along the LA and TX shelves during both 2011 and 2012, CDOM was higher near bottom than at mid-depth without concomitant DOC increases, possibly due to microbial processing of settling phytoplankton cells, sedimentary fluxes, and benthic algal activity which was especially prevalent along the TX shelf. Results from simulated solar radiation experiments indicate that shelf water CDOM readily photobleaches with losses of >50% likely in surface waters over the summer, while DOC photooxidation is at least an order of magnitude slower than CDOM photobleaching.;

Atmospheric inputs of organic matter to a forested watershed: Variations from storm to storm over the seasons

USGS Publications Warehouse

Iavorivska , Lidiia; Boyer, Elizabeth W.; Miller, Matthew P.; Brown, Michael G.; Vasilopoulos , Terrie; Fuentes, Jose D.; Duffy, Christopher J.

2016-01-01

The objectives of this study were to determine the quantity and chemical composition of precipitation inputs of dissolved organic carbon (DOC) to a forested watershed; and to characterize the associated temporal variability. We sampled most precipitation that occurred from May 2012 through August 2013 at the Susquehanna Shale Hills Critical Zone Observatory (Pennsylvania, USA). Sub-event precipitation samples (159) were collected sequentially during 90 events; covering various types of synoptic meteorological conditions in all climatic seasons. Precipitation DOC concentrations and rates of wet atmospheric DOC deposition were highly variable from storm to storm, ranging from 0.3 to 5.6 mg C L−1 and from 0.5 to 32.8 mg C m−2 h−1, respectively. Seasonally, storms in spring and summer had higher concentrations of DOC and more optically active organic matter than in winter. Higher DOC concentrations resulted from weather types that favor air advection, where cold frontal systems, on average, delivered more than warm/stationary fronts and northeasters. A mixed modeling statistical approach revealed that factors related to storm properties, emission sources, and to the chemical composition of the atmosphere could explain more than 60% of the storm to storm variability in DOC concentrations. This study provided observations on changes in dissolved organic matter that can be useful in modeling of atmospheric oxidative chemistry, exploring relationships between organics and other elements of precipitation chemistry, and in considering temporal changes in ecosystem nutrient balances and microbial activity.

Variability of dissolved organic carbon in precipitation during storms at the Shale Hills Critical Zone Observatory

USGS Publications Warehouse

Iavorivska , Lidiia; Boyer, Elizabeth W.; Grimm, Jeffrey W.; Miller, Matthew P.; DeWalle, David R.; Davis, Kenneth J.; Kaye, Margot W.

2017-01-01

Organic compounds are removed from the atmosphere and deposited to the earth's surface via precipitation. In this study, we quantified variations of dissolved organic carbon (DOC) in precipitation during storm events at the Shale Hills Critical Zone Observatory, a forested watershed in central Pennsylvania (USA). Precipitation samples were collected consecutively throughout the storm during 13 events, which spanned a range of seasons and synoptic meteorological conditions, including a hurricane. Further, we explored factors that affect the temporal variability by considering relationships of DOC in precipitation with atmospheric and storm characteristics. Concentrations and chemical composition of DOC changed considerably during storms, with the magnitude of change within individual events being comparable or higher than the range of variation in average event composition among events. While some previous studies observed that concentrations of other elements in precipitation typically decrease over the course of individual storm events, results of this study show that DOC concentrations in precipitation are highly variable. During most storm events concentrations decreased over time, possibly as a result of washing out of the below-cloud atmosphere. However, increasing concentrations that were observed in the later stages of some storm events highlight that DOC removal with precipitation is not merely a dilution response. Increases in DOC during events could result from advection of air masses, local emissions during breaks in precipitation, or chemical transformations in the atmosphere that enhance solubility of organic carbon compounds. This work advances understanding of processes occurring during storms that are relevant to studies of atmospheric chemistry, carbon cycling, and ecosystem responses.

Dissolved Organic Carbon and Disinfection By-Product Precursor Release from Managed Peat Soils

USGS Publications Warehouse

Fleck, J.A.; Bossio, D.A.; Fujii, R.

2004-01-01

A wetland restoration demonstration project examined the effects of a permanently flooded wetland on subsidence of peat soils. The project, started in 1997, was done on Twitchell Island, in the Sacramento-San Joaquin Delta of California. Conversion of agricultural land to a wetland has changed many of the biogeochemical processes controlling dissolved organic carbon (DOC) release from the peat soils, relative to the previous land use. Dissolved organic C in delta waters is a concern because it reacts with chlorine, added as a disinfectant in municipal drinking waters, to form carcinogenic disinfection byproducts (DBPs), including trihalomethanes (THMs) and haloacetic acids (HAAs). This study explores the effects of peat soil biogeochemistry on DOC and DBP release under agricultural and wetland management. Results indicate that organic matter source, extent of soil organic matter decomposition, and decomposition pathways all are factors in THM formation. The results show that historical management practices dominate the release of DOC and THM precursors. However, within-site differences indicate that recent management decisions can contribute to changes in DOC quality and THM precursor formation. Not all aromatic forms of carbon are highly reactive and certain environmental conditions produce the specific carbon structures that form THMs. Both HAA and THM precursors are elevated in the DOC released under wetland conditions. The findings of this study emphasize the need to further investigate the roles of organic matter sources, microbial decomposition pathways, and decomposition status of soil organic matter in the release of DOC and DBP precursors from delta soils under varying land-use practices.

Representation of riverine DOC within a GCM: First framework for coupling soil carbon and lateral hydrology in MPI-ESM

NASA Astrophysics Data System (ADS)

Brovkin, V.; Gehlot, S.; Hagemann, S.

2017-12-01

The current state of the art General Circulation Models (GCMs) do not consider the lateral transport of dissolved organic carbon (DOC) from land to ocean via rivers/streams and the global carbon budget is primarily evaluated based only on vertical gas exchange processes between land or ocean carbon reservoirs. In high latitudes, the permafrost plays an important role in contributing to riverine organic carbon. Moreover, the vertical gas exchange processes are active during the lateral riverine carbon transport but are not considered in the impact of thawing permafrost on global climate. The interplay between permafrost and lateral hydrology is a substantial factor impacting the organic carbon inflow to the Arctic and its associated atmospheric exchange. In this research, we propose a framework of coupling the soil carbon transport via rivers using the hydrological discharge scheme (HD-Model) of MPI-ESM (Max-Planck Institute for Meteorology Earth System Model). The soil carbon classification is based on the solubility (YASSO soil carbon pools) and their subsequent attribution to the dissolved organic carbon via runoff (fast carbon pool) and baseflow (slow carbon pool). The HD-model, which simulates the river discharge for all land areas at a resolution of 0.5 degree, will be modified with inclusion of the DOC as tracer over test areas. Evaluation of DOC transport scheme is intended at reservoir level via available site measurements. The analysis will include global river networks for organic carbon transport with focus on permafrost and high latitude areas. Decomposition of DOC en-route land to ocean via vertical gas exchange processes will be included.

Benthic fluxes of dissolved organic carbon from gas hydrate sediments in the northern South China Sea

PubMed Central

Hung, Chia-Wei; Huang, Kuo-Hao; Shih, Yung-Yen; Lin, Yu-Shih; Chen, Hsin-Hung; Wang, Chau-Chang; Ho, Chuang-Yi; Hung, Chin-Chang; Burdige, David J.

2016-01-01

Hydrocarbon vents have recently been reported to contribute considerable amounts of dissolved organic carbon (DOC) to the oceans. Many such hydrocarbon vents widely exist in the northern South China Sea (NSCS). To investigate if these hydrocarbon vent sites release DOC, we used a real-time video multiple-corer to collect bottom seawater and surface sediments at vent sites. We analyzed concentrations of DOC in these samples and estimated DOC fluxes. Elevated DOC concentrations in the porewaters were found at some sites suggesting that DOC may come from these hydrocarbon vents. Benthic fluxes of DOC from these sediments were 28 to 1264 μmol m−2 d−1 (on average ~321 μmol m−2 d−1) which are several times higher than most DOC fluxes in coastal and continental margin sediments. The results demonstrate that the real-time video multiple-corer can precisely collect samples at vent sites. The estimated benthic DOC flux from the methane venting sites (8.6 × 106 mol y−1), is 24% of the DOC discharge from the Pearl River to the South China Sea, indicating that these sediments make an important contribution to the DOC in deep waters. PMID:27432631

Inverse coupling of DOC and nitrate export from soils and streams

NASA Astrophysics Data System (ADS)

Goodale, Christine

2013-04-01

Over the last two decades, nitrate concentrations in surface waters have decreased across the Northeastern United States and parts of northern Europe. Many hypotheses have been proposed to explain this decrease, but the cause remains unclear. One control may be associated with increasing abundance of dissolved organic carbon (DOC), which in turn may be a result of soil recovery from acidification. Compared across catchments, surface water NO3- decreases sharply with increasing DOC concentration. Here, we used measurements of soil and solution nitrate, DOC, and their isotopic composition (13C-DOC, 15N- and 18O-NO3) to test several related hypotheses that changing acidification affects the release of DOC and bio-available DOC (bDOC) from soil, and that variation in stocks of soil C and release of bDOC partly control NO3- export from forested catchments in New York State, USA. We examined whether DOC and NO3- are both driven by soil C processes that produce inverse coupling at the scale of soil cores as well as across catchments, through comparison of soil and surface water chemistry across nine catchments selected from long-term monitoring networks in the Catskill and Adirondack Mountains. In addition, we conducted a series of soil core leaching experiments to examine the role of acidification and recovery in driving the net production of DOC and NO3- from soils. Over 8 months, soil cores were leached biweekly with simulated rainfall solutions of varying pH (3.6 to 7.0) from additions of H2SO4, CaCO3 and NaOH. These experiments did not yield a pH-induced change in DOC quantity, but did show a change in DOC quality, in that acidified cores released more bio-available DOC with less depleted 13C-DOC than cores with experimentally increased pH. All cores leached substantial amounts of nitrate. Together, these lab- and field comparisons are being used to identify the role of soil production and consumption processes in driving cross-watershed differences in DOC and NO3- loss, or whether other factors (e.g., riparian, in-stream or hydrologic processes) likely explain this relationship.

Characterisation of DOC and its relation to the deep terrestrial biosphere

NASA Astrophysics Data System (ADS)

Vieth, Andrea; Vetter, Alexandra; Sachse, Anke; Horsfield, Brian

2010-05-01

The deep subsurface is populated by a large number of microorganisms playing a pivotal role in the carbon cycling. The question arises as to the origin of the potential carbon sources that support deep microbial communities and their possible interactions within the deep subsurface. As the carbon sources need to be dissolved in formation fluids to become available to microorganisms, the dissolved organic carbon (DOC) needs further characterisation as regards concentration, structural as well as molecular composition and origin. The Malm carbonates in the Molasse basin of southern Germany are of large economic potential as they are targets for both hydrocarbon and geothermal exploration (ANDREWS et al., 1987). Five locations that differ in their depth of the Malm aquifer between 220 m and 3445 m below surface have been selected for fluid sampling. The concentration and the isotopic composition of the DOC have been determined. To get a better insight into the structural composition of the DOC, we also applied size exclusion chromatography and quantified the amount of low molecular weight organic acids (LMWOA) by ion chromatography. With increasing depth of the aquifer the formation fluids show increasing salinity as chloride concentrations increase from 2 to 300 mg/l and also the composition of the DOC changes. Water samples from greater depth (>3000 m) showed that the DOC mainly consists of LMWOA (max. 83 %) and low percentages of neutral compounds (alcohols, aldehyde, ketones, amino acids) as well as "building blocks". Building blocks have been described to be the oxidation intermediates from humic substances to LMWOA. With decreasing depth of the aquifer, the DOC of the fluid becomes increasingly dominated by neutral compounds and the percentage of building blocks increases to around 27%. The fluid sample from 220 m depth still contains a small amount of humic substances. The DOC of formation fluids in some terrestrial sediments may originate from organic-rich layers like coals and source rocks which may provide carbon sources for the deep biosphere by leaching water soluble organic compounds. We investigated the potential of a series of Eocene-Pleistocene coals, mudstones and sandstones from New Zealand with different maturities (Ro between 0.29 and 0.39) and total organic carbon content (TOC) regarding their potential to release such compounds. The water extraction of these New Zealand coals using Soxhlet apparatus resulted in yields of LMWOA that may feed the local deep terrestrial biosphere over geological periods of time (VIETH et al., 2008). However, the DOC of the water extracts mainly consisted of humic substances. To investigate the effect of thermal maturity of the organic matter as well as the effect of the organic matter type on the extraction yields, we examined additional coal samples (Ro between 0.29 and 0.80) and source rock samples from low to medium maturity (Ro between 0.3 to 1.1). Within our presentation we would like to show the compositional diversity and variability of dissolved organic compounds in natural formation fluids as well as in water extracts from a series of very different lithologies and discuss their effects on the carbon cycling in the deep terrestrial subsurface. References: Andrews, J. N., Youngman, M. J., Goldbrunner, J. E., and Darling, W. G., 1987. The geochemistry of formation waters in the Molasse Basin of Upper Austria. Environmental Geology 10, 43-57. Vieth, A., Mangelsdorf, K., Sykes, R., and Horsfield, B., 2008. Water extraction of coals - potential to estimate low molecular weight organic acids as carbon feedstock for the deep terrestrial biosphere? Organic Geochemistry 39, 985-991.

Sources and yields of dissolved carbon in northern Wisconsin stream catchments with differing amounts of Peatland

USGS Publications Warehouse

Elder, J.F.; Rybicki, N.B.; Carter, V.; Weintraub, V.

2000-01-01

In five tributary streams (four inflowing and one outflowing) of 1600-ha Trout Lake in northern Wisconsin, USA, we examined factors that can affect the magnitude of stream flow and transport of dissolved organic and inorganic carbon (DOC and DIC) through the streams to the lake. One catchment, the Allequash Creek basin, was investigated in more detail to describe the dynamics of carbon flow and to identify potential carbon sources. Stream flows and carbon loads showed little or no relation to surface-water catchment area. They were more closely related to ground-water watershed area because ground-water discharge, from both local and regional sources, is a major contributor to the hydrologic budgets of these catchments. An important factor in determining carbon influx to the stream is the area of peatland in the catchment. Peatland porewaters contain DOC concentrations up to 40 mg l-1 and are a significant potential carbon source. Ground-water discharge and lateral flow through peat are the suspected mechanisms for transport of that carbon to the streams. Carbon and nitrogen isotopes suggested that the sources of DOC in Allequash Creek above Allequash Lake were wetland vegetation and peat and that the sources below Allequash Lake were filamentous algae and wild rice. Catchments with high proportions of peatland, including the Allequash Creek catchment, tended to have elevated DOC loads in outflowing stream water. Respiration and carbon mineralization in lakes within the system tend to produce low DOC and low DOC/DIC in lake outflows, especially at Trout Lake. In Allequash Lake, however, the shallow peat island and vegetation-filled west end were sources of DOC. Despite the vast carbon reservoir in the peatlands, carbon yields were very low in these catchments. Maximum yields were on the order of 2.5 g m-2 y-1 DOC and 5.5 g m-2 y-1 DIC. The small yields were attributable to low stream flows due to lack of significant overland runoff and very limited stream channel coverage of the total catchment area.

Transport of suspended sediment and organic carbon during storm events in a large agricultural catchment, southwest France.

NASA Astrophysics Data System (ADS)

Chantha, Oeurng; Sabine, Sauvage; David, Baqué; Alexandra, Coynel; Eric, Maneux; Henri, Etcheber; José-Miguel, Sánchez-Pérez

2010-05-01

Intensive agriculture has led to environmental degradation through soil erosion and carbon loss transferred from agricultural land to the stream networks. Suspended sediment transport from the agricultural catchment to the watercourses is responsible for aquatic habitat degradation, reservoir sedimentation, and for transporting sediment associated pollutants (pesticides, nutrient, heavy metals and other toxic substances). Consequently, the temporal transport of suspended sediment (SS), dissolved and particulate organic carbon (DOC and POC) was investigated during 18 months from January 2008 to June 2009 within a large agricultural catchment in southwest France. This study is based on an extensive dataset with high temporal resolution using manual and automatic sampling, especially during 15 flood events. Two main objectives aim at: (i) studying temporal transport in suspended sediment (SS), DOC and POC with factors explaining their dynamics and (ii) analysing the relationships between discharge, SSC, DOC and POC during flood events. The study demonstrates there is a strong variability of SS, POC and DOC during flood events. The SS transport during different seasonal floods varied by event from 513 to 41 750 t; POC transport varied from 12 to 748 t and DOC transport varied from 9 to 218 t. The specific yield of the catchment represents 76 t km-2 y-1 of sediment, 1.8 t km-2 y-1 of POC and 0.7 t km-2 y-1 of DOC, respectively. The POC associated with sediment transport from the catchment accounted for ~2.5% of the total sediment load. Flood duration and flood magnitude are key factors in determining the sediment and organic carbon transport. Statistical analyses revealed strong correlations between total precipitation, flood discharge, total water yield with suspended sediment and organic transport. The relationships of SSC, POC and DOC versus discharge over temporal flood events resulted in different hysteresis patterns which were used to suggest those dissolved and particulate origins. POC for both clockwise and anticlockwise also mostly followed the same patterns of discharge and suspended sediment hysteresis. DOC and discharge relationship were mainly dominated by mixing pattern of clockwise and anticlockwise due to dilution effects of water originating from different sources in the whole catchment.

Humic substances-part 7: the biogeochemistry of dissolved organic carbon and its interactions with climate change.

PubMed

Porcal, Petr; Koprivnjak, Jean-François; Molot, Lewis A; Dillon, Peter J

2009-09-01

Dissolved organic matter, measured as dissolved organic carbon (DOC), is an important component of aquatic ecosystems and of the global carbon cycle. It is known that changes in DOC quality and quantity are likely to have ecological repercussions. This review has four goals: (1) to discuss potential mechanisms responsible for recent changes in aquatic DOC concentrations; (2) to provide a comprehensive overview of the interactions between DOC, nutrients, and trace metals in mainly boreal environments; (3) to explore the impact of climate change on DOC and the subsequent effects on nutrients and trace metals; and (4) to explore the potential impact of DOC cycling on climate change. We review recent research on the mechanisms responsible for recent changes in aquatic DOC concentrations, DOC interactions with trace metals, N, and P, and on the possible impacts of climate change on DOC in mainly boreal lakes. We then speculate on how climate change may affect DOC export and in-lake processing and how these changes might alter nutrient and metal export and processing. Furthermore, the potential impacts of changing DOC cycling patterns on climate change are examined. It has been noted that DOC concentrations in lake and stream waters have increased during the last 30 years across much of Europe and North America. The potential reasons for this increase include increasing atmospheric CO(2) concentration, climate warming, continued N deposition, decreased sulfate deposition, and hydrological changes due to increased precipitation, droughts, and land use changes. Any change in DOC concentrations and properties in lakes and streams will also impact the acid-base chemistry of these waters and, presumably, the biological, chemical, and photochemical reactions taking place. For example, the interaction of trace metals with DOC may be significantly altered by climate change as organically complexed metals such as Cu, Fe, and Al are released during photo-oxidation of DOC. The production and loss of DOC as CO(2) from boreal lakes may also be affected by changing climate. Climate change is unlikely to be uniform spatially with some regions becoming wetter while others become drier. As a result, rates of change in DOC export and concentrations will vary regionally and the changes may be non-linear. Climate change models predict that higher temperatures are likely to occur over most of the boreal forests in North America, Europe, and Asia over the next century. Climate change is also expected to affect the severity and frequency of storm and drought events. Two general climate scenarios emerge with which to examine possible DOC trends: warmer and wetter or warmer and drier. Increasing temperature and hydrological changes (specifically, runoff) are likely to lead to changes in the quality and quantity of DOC export from terrestrial sources to rivers and lakes as well as changes in DOC processing rates in lakes. This will alter the quality and concentrations of DOC and its constituents as well as its interactions with trace metals and the availability of nutrients. In addition, export rates of nutrients and metals will also change in response to changing runoff. Processing of DOC within lakes may impact climate depending on the extent to which DOC is mineralized to dissolved inorganic carbon (DIC) and evaded to the atmosphere or settles as particulate organic carbon (POC) to bottom sediments and thereby remaining in the lake. The partitioning of DOC between sediments and the atmosphere is a function of pH. Decreased DOC concentrations may also limit the burial of sulfate, as FeS, in lake sediments, thereby contributing acidity to the water by increasing the formation of H(2)S. Under a warmer and drier scenario, if lake water levels fall, previously stored organic sediments may be exposed to greater aeration which would lead to greater CO(2) evasion to the atmosphere. The interaction of trace metals with DOC may be significantly altered by climate change. Iron enhances the formation of POC during irradiation of lake water with UV light and therefore may be an important pathway for transfer of allochthonous DOC to the sediments. Therefore, changing Fe/DOC ratios could affect POC formation rates. If climate change results in altered DOC chemistry (e.g., fewer and/or weaker binding sites) more trace metals could be present in their toxic and bioavailable forms. The availability of nutrients may be significantly altered by climate change. Decreased DOC concentrations in lakes may result in increased Fe colloid formation and co-incident loss of adsorbable P from the water column. Climate change expressed as changes in runoff and temperature will likely result in changes in aquatic DOC quality and concentration with concomitant effects on trace metals and nutrients. Changes in the quality and concentration of DOC have implications for acid-base chemistry and for the speciation and bioavailability of certain trace metals and nutrients. Moreover, changes in DOC, metals, and nutrients are likely to drive changes in rates of C evasion and storage in lake sediments. The key controls on allochthonous DOC quality, quantity, and catchment export in response to climate change are still not fully understood. More detailed knowledge of these processes is required so that changes in DOC and its interactions with nutrients and trace metals can be better predicted based on changes caused by changing climate. More studies are needed concerning the effects of trace metals on DOC, the effects of changing DOC quality and quantity on trace metals and nutrients, and how runoff and temperature-related changes in DOC export affect metal and nutrient export to rivers and lakes.

Fate and Transport of Organic Contaminants in Coastal Marsh Sediments Resulting from the 2010 Gulf Oil Spill

NASA Astrophysics Data System (ADS)

Natter, M.; Keevan, J.; Lee, M.; Keimowitz, A.; Savrda, C.; Son, A.; Okeke, B.; Wang, Y.

2011-12-01

The devastating explosion and subsequent sinking of the oil platform Deepwater Horizon at the British Petroleum Macondo-1 well in the Northern Gulf of Mexico on April 20, 2010, released approximately 4.9 million barrels of crude oil into the Gulf before the well was capped on July 15, 2010. Although most light compounds of oil may be easily degraded by natural microbes on the short term, saturated heavy oil (e.g., asphaltenes, resins, polycyclic aromatics, etc.) and those adsorbed by sediments could persist in the environment for decades. The long-term effects of high levels of persistent oil compounds on biogeochemical evolution and ecosystems of salt marshes remain unclear. This research investigates the spatial range and changes in levels of oil and their biogeochemical impacts. A total of ten marsh sampling sites that varied from pristine, non-effected marshes (e.g., Weeks Bay and Wolf Bay, Alabama) to heavily oiled wetlands (e.g., Bay Jimmy and Bayou Dulac, Louisiana) were utilized for this study. Sediment cores, bulk sediments, surface water samples, degraded oil, oiled dead marsh grass, and live marsh grass were collected from these sites in an attempt to study the source, distribution, and evolution of organic compounds and oil present in sediments and pore-waters. Geochemical analyses show alarmingly high organic carbon loads in pore-waters and sediments at heavily contaminated sites months after the influx of oil ceased. Very high levels (10-28%) of total organic carbon (TOC) within the heavily oiled sediments (down to 30 cm) are clearly distinguished from those found in pristine wetland sediments (generally < 5%). TOC levels are elevated in the deeper sediments while being depleated in the uppermost ones at certain locations. The TOC contents in uppermost sediments may be reduced by microbial degradation, water mixing, and the use of oil dispersants. Furthermore, dissolved organic carbon (DOC) levels of pore-waters extracted from oiled sediments, ranging up to hundreds of mg/kg, are on the order of one to two magnitudes higher than those at pristine and slightly contaminated sites. These DOC levels also interestingly increase with depth, possibly indicating saltwater-freshwater mixing near the sediment surface or freshwater recharge from rainfall. The spatial changes in DOC indicate that seawater and oil invaded along the deeper portion of the marsh sediments due to their higher density with respect to freshwater. TOC and DOC data clearly indicate that not all the spilled oil rose to the water surface and washed on-shore. Plumes of partially degraded oil could be spreading at various levels of the water column and feeding the underlying sediments. Geochemical biomarkers and stable isotopes (carbon and nitrogen) analyses of wetland plants, oiled sediments, and initial crude oils are underway to trace the sources of oil and the extent of oil degradation in impacted wetlands.

The Extent of Denitrification in Long Island Groundwater using MIMS

NASA Astrophysics Data System (ADS)

Young, C.; Hanson, G. N.; Kroeger, K. D.

2009-12-01

Long Island drinking water is provided by a sole source aquifer with nitrate levels in some North Shore communities approaching or exceeding the drinking water standard of 10 mgL-1. Previous workers, using mass balance approaches, suggested that the primary source of nitrogen is sewage effluent and observed a 50% deficit of nitrate in Long Island’s groundwater system. We analyzed dissolved N2/Ar ratios in groundwater from wells to determine if groundwater denitrification is the cause of the nitrogen deficit at two locations where septic tanks are used for sewage treatment and the effluent leaches to the groundwater; a suburban community on the north shore of Long Island (Northport, NY) and parkland on a barrier island at the south shore of Long Island (Watch Hill, Fire Island National Seashore). In Northport we found 0 to 20 % of the nitrate in groundwater denitrified with excess N-NO3- concentrations ranging from 0 to 1.5 mgL-1. These samples had concentrations high in dissolved oxygen (DO), 6 to 11 mgL-1, and low in dissolved organic carbon (DOC), 0.4 to 2.8 mgL-1. At Watch Hill nitrogen is primarily retained as ammonium or dissolved organic nitrogen. Where nitrate is formed, we found up to 99% denitrification. Excess N-NO3- ranged from 0 to 8 mgL-1 with concentrations low in DO, 0.3 to 3.4 mgL-1, and high in DOC, 5.3 to 18.4 mgL-1. The vadose zone in the Northport area has an average thickness of 10-100 feet whereas at Watch Hill it is 1 - 2 feet thick. We hypothesize that the vadose zone thickness affects the extent of denitrification by controlling the amount of DOC and DO that reaches the groundwater. A thick vadose zone allows for more extensive interaction of infiltrating sewage effluent with atmospheric oxygen in the vadose zone which oxidizes DOC. In Northport groundwater has high DO, low DOC and essentially no denitrification leaving 2 to 11 mgL-1 N-NO3- remaining. At the Watch Hill site a thin vadose zone below the sewage leach field provides anaerobic conditions under which DOC is recharged with the sewage to the groundwater. Under these conditions any nitrate in the groundwater is denitrified and the groundwater has less than 0.01 mgL-1 nitrate remaining.

Variable flushing mechanisms and landscape structure control stream DOC export during snowmelt in a set of nested catchments

Treesearch

Vincent J. Pacific; Kelsey G. Jencso; Brian L. McGlynn

2010-01-01

Stream DOC dynamics during snowmelt have been the focus of much research, and numerous DOC mobilization and delivery mechanisms from riparian and upland areas have been proposed. However, landscape structure controls on DOC export from riparian and upland landscape elements remains poorly understood. We investigated stream and groundwater DOC dynamics across three...

Dissolved Organic Carbon along the Louisiana coast from MODIS and MERIS satellite data

NASA Astrophysics Data System (ADS)

Chaichi Tehrani, N.; D'Sa, E. J.

2012-12-01

Dissolved organic carbon (DOC) plays a critical role in the coastal and ocean carbon cycle. Hence, it is important to monitor and investigate its the distribution and fate in coastal waters. Since DOC cannot be measured directly through satellite remote sensors, chromophoric dissolved organic matter (CDOM) as an optically active fraction of DOC can be used as an alternative proxy to trace DOC concentrations. Here, satellite ocean color data from MODIS, MERIS, and field measurements of CDOM and DOC were used to develop and assess CDOM and DOC ocean color algorithms for coastal waters. To develop a CDOM retrieval algorithm, empirical relationships between CDOM absorption coefficient at 412 nm (aCDOM(412)) and reflectance ratios Rrs(488)/Rrs(555) for MODIS and Rrs(510)/Rrs(560) for MERIS were established. The performance of two CDOM empirical algorithms were evaluated for retrieval of (aCDOM(412)) from MODIS and MERIS in the northern Gulf of Mexico. Further, empirical algorithms were developed to estimate DOC concentration using the relationship between in situ aCDOM(412) and DOC, as well as using the newly developed CDOM empirical algorithms. Accordingly, our results revealed that DOC concentration was strongly correlated to aCDOM (412) for summer and spring-winter periods (r2 = 0.9 for both periods). Then, using the aCDOM(412)-Rrs and the aCDOM(412)-DOC relationships derived from field measurements, a relationship between DOC-Rrs was established for MODIS and MERIS data. The DOC empirical algorithms performed well as indicated by match-up comparisons between satellite estimates and field data (R2=0.52 and 0.58 for MODIS and MERIS for summer period, respectively). These algorithms were then used to examine DOC distribution along the Louisiana coast.

Algorithm Development and Validation for Satellite-Derived Distributions of DOC and CDOM in the US Middle Atlantic Bight

NASA Technical Reports Server (NTRS)

Mannino, Antonio; Russ, Mary E.; Hooker, Stanford B.

2007-01-01

In coastal ocean waters, distributions of dissolved organic carbon (DOC) and chromophoric dissolved organic matter (CDOM) vary seasonally and interannually due to multiple source inputs and removal processes. We conducted several oceanographic cruises within the continental margin of the U.S. Middle Atlantic Bight (MAB) to collect field measurements in order to develop algorithms to retrieve CDOM and DOC from NASA's MODIS-Aqua and SeaWiFS satellite sensors. In order to develop empirical algorithms for CDOM and DOC, we correlated the CDOM absorption coefficient (a(sub cdom)) with in situ radiometry (remote sensing reflectance, Rrs, band ratios) and then correlated DOC to Rrs band ratios through the CDOM to DOC relationships. Our validation analyses demonstrate successful retrieval of DOC and CDOM from coastal ocean waters using the MODIS-Aqua and SeaWiFS satellite sensors with mean absolute percent differences from field measurements of < 9 %for DOC, 20% for a(sub cdom)(355)1,6 % for a(sub cdom)(443), and 12% for the CDOM spectral slope. To our knowledge, the algorithms presented here represent the first validated algorithms for satellite retrieval of a(sub cdom) DOC, and CDOM spectral slope in the coastal ocean. The satellite-derived DOC and a(sub cdom) products demonstrate the seasonal net ecosystem production of DOC and photooxidation of CDOM from spring to fall. With accurate satellite retrievals of CDOM and DOC, we will be able to apply satellite observations to investigate interannual and decadal-scale variability in surface CDOM and DOC within continental margins and monitor impacts of climate change and anthropogenic activities on coastal ecosystems.

Commonalities in Mercury Behavior in Contrasting Northeastern USA Landscapes

NASA Astrophysics Data System (ADS)

Shanley, J. B.; Scherbatskoy, T.; Schuster, P. F.; Reddy, M. M.; Chalmers, A.

2001-05-01

Generally less than 20% of atmospherically deposited mercury is exported from watersheds in streamflow, but the mercury export that does occur is highly episodic. Our research from diverse landscapes in northern New England, including small forested, agricultural, and urban watersheds as well as some larger rivers discharging to Lake Champlain and the Atlantic Ocean, indicates a consistent positive correlation between Hg concentrations and stream discharge. This relation appears to be driven by increased DOC, POC, and suspended sediment concentrations at increased streamflow. Streamwater Hg analyses pooled from 10 watersheds of diverse size and land use during the 2000 snowmelt within the Sleepers River Research Watershed in northeastern Vermont displayed a high correlation between (1) dissolved Hg and DOC, and (2) particulate Hg and POC. The same correlations held at Nettle Brook, a forested Vermont watershed 100 km west of Sleepers River. At Nettle Brook, DOC and dissolved mercury concentrations were both greater than at Sleepers River but the relation at the two sites was co-linear. In an agricultural watershed in northwestern Vermont, particulate Hg concentrations in streamflow were comparable to those at Nettle Brook despite markedly higher suspended sediment (and presumably POC) concentrations, suggesting the soil Hg pool is depleted by more frequent erosional events. The coupling of organic carbon with mercury may originate in the shallow soil zone; high concentrations of DOC and dissolved Hg were observed in O-horizon soil solution both at Nettle Brook and at some sites in the Adirondack Mountains of New York. Our findings underscore the importance of sampling during high-flow to determine accurate fluxes of Hg in streamflow. It is not clear, however, whether organic carbon actually controls Hg mobility, or whether organic carbon and Hg move in tandem simply as a result of their common source in soil organic matter.