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Sample records for comparing ecosystem exchange

  1. Comparing the Net Ecosystem Exchange of Two Cropping Systems for Dairy Feed Production

    NASA Astrophysics Data System (ADS)

    Sulaiman, M. F.; Wagner-Riddle, C.; Brown, S. E.

    2015-12-01

    A three-year study was conducted from 2012 to 2014 to determine the net CO2 fluxes from corn and hay, the two main feed crops used in dairy production. The aim of this study is to better understand the net ecosystem exchange (NEE) in annual and perennial cropping systems used in dairy production to benefit greenhouse gas emission model developments and the life cycle analysis of dairy production. The study was conducted on two 4-ha plots where one plot was a 5-year old hayfield and the other plot was planted in a continuous cycle corn. All plots were continuously monitored using the flux-gradient method deployed with a tunable diode laser trace gas analyzer and sonic anemometers. All plots received dairy manure as fertilizer applied according to common practice. The cumulative NEE for the three years of the study was -873.15 g C m-2 for corn and -409.36 g C m-2 for hay. Differences in respiration between the two cropping systems was found to be the larger factor compared to differences in gross ecosystem production (GEP) that resulted in the contrasting cumulative NEE where cumulative respiration for the three years for hay was 3094.23 g C m-2 as opposed to 2078.11 g C m-2 for corn. Cumulative GEP for the three years was 3503.60 and 2951.31 g C m-2 for hay and corn respectively. Inter-annual and inter-crop variability of the NEE, GEP and respiration will be discussed in relation to biomass production, climatic conditions and crop physiological characteristics.

  2. Comparative studies of land-atmosphere energy exchange in high and low Arctic tundra ecosystems

    NASA Astrophysics Data System (ADS)

    Stiegler, Christian; Lindroth, Anders; Lund, Magnus; Tamstorf, Mikkel P.

    2013-04-01

    The energy balance of arctic terrestrial ecosystems is of crucial importance to understand future climate change in high northern latitudes. Despite a growing interest in the Arctic local measurements and observations of climate characteristics are still scarce. Therefore, we present first results of comparative short- and long-term eddy covariance and energy balance measurements of high and low Arctic terrestrial ecosystems in Greenland. The study area covers high Arctic tundra heath and fen ecosystems in Zackenberg (Northeast Greenland National Park, 74°30'N, 21°00'W) and low Arctic terrestrial ecosystems in the Kobbefjord area close to the city of Nuuk (West Greenland, 64°07'N, 51°21'W). By using a mobile eddy covariance and energy balance tower we collected data during late winter (April 2012), early summer (June/July 2012) and late summer (August 2012). Mobile eddy covariance and energy balance measurements during late winter in Zackenberg focus on the energy balance of undisturbed snow covered surfaces with variable snow depth and snow layer structure. Data collection on thin snow layers with disturbed surfaces and exposed vegetation also show the impact of Muskox cratering on the surface energy balance. Measurements during early summer in the Kobbefjord area were conducted on characteristic bare soils with scattered cushion plants, on grasslands with sedge vegetation and on shrub vegetation up to 100 cm in height. Late summer measurements of energy balance and eddy covariance in the Zackenberg valley focus on transect measurements of energy balance components and active layer thickness of adjacent high arctic fen and heath ecosystems. In addition to the short-term mobile measurements we use and analyse data sets from permanent stations monitoring eddy covariance and energy balance on heath and fen sites in both high and low Arctic environments. Long-term measurements provide continuous data since early April 2012 and in this study we compare our mobile

  3. Comparing net ecosystem carbon dioxide exchange at adjacent commercial bioenergy and conventional cropping systems in Lincolnshire, United Kingdom

    NASA Astrophysics Data System (ADS)

    Morrison, Ross; Brooks, Milo; Evans, Jonathan; Finch, Jon; Rowe, Rebecca; Rylett, Daniel; McNamara, Niall

    2016-04-01

    The conversion of agricultural land to bioenergy plantations represents one option in the national and global effort to reduce greenhouse gas emissions whilst meeting future energy demand. Despite an increase in the area of (e.g. perennial) bioenergy crops in the United Kingdom and elsewhere, the biophysical and biogeochemical impacts of large scale conversion of arable and other land cover types to bioenergy cropping systems remain poorly characterised and uncertain. Here, the results of four years of eddy covariance (EC) flux measurements of net ecosystem CO2 exchange (NEE) obtained at a commercial farm in Lincolnshire, United Kingdom (UK) are reported. CO2 flux measurements are presented and compared for arable crops (winter wheat, oilseed rape, spring barely) and plantations of the perennial biofuel crops Miscanthus x. giganteus (C4) and short rotation coppice (SRC) willow (Salix sp.,C3). Ecosystem light and temperature response functions were used to analyse and compare temporal trends and spatial variations in NEE across the three land covers. All three crops were net in situ sinks for atmospheric CO2 but were characterised by large temporal and between site variability in NEE. Environmental and biological controls driving the spatial and temporal variations in CO2 exchange processes, as well as the influences of land management, will be analysed and discussed.

  4. Long term flux ecosystem exchange over a Mediterranean shrubland ecosystem

    NASA Astrophysics Data System (ADS)

    Spano, D.; Sirca, C.; Marras, S.; Carta, M.; Zara, P.; Arca, A.; Duce, P.

    2011-12-01

    Only a few long-term studies on inter-annual variability in energy and mass exchanges of Mediterranean shrubland ecosystems have been recently published. Since maquis ecosystems experience a wide variation in inter-annual rainfall and temperature, inter-annual differences in CO2 fluxes are expected. Mediterranean-type ecosystems normally show two main peaks of growth (in spring and fall) and experience sometimes pronounced summer drought periods. Consequently, Mediterranean-type ecosystem behavior is even more complex and responds more dramatically to perturbations in water conditions. In this paper, six years of energy and mass fluxes measured using eddy covariance (EC) technique over a secondary succession shrubland ecosystem (maquis) located in Sardinia, Italy are reported. The main objectives are to understand dynamics of ecosystem carbon cycling and to identify the driving factors affecting ecosystem exchanges. Eddy flux and meteorological data are presented along with soil respiration information. Footprint analysis, friction velocity method, and other turbulent parameters were calculated to verify the accuracy of the eddy covariance CO2 measurements. The energy partitioning exhibited clear seasonal patterns with increasing Bowen ratio values during the drought season. Peak CO2 uptake occurred during spring and autumn showing an evident decrease in summer. The estimate of NEE showed differences among years depending on drought and temperature conditions. The surface conductance was clearly depressed during long-term drought period. In general, NEE was relatively low compared to other forest ecosystems. A good relationship was found between GPP and LE. Our data show that the inter-annual differences in NEE of the maquis ecosystem depend mainly on seasonal climate rather than on mean annual air temperature or precipitation. In addition, extreme weather events can also contribute to NEE inter-annual variability.

  5. Thermal adaptation of net ecosystem exchange

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Thermal adaptation of gross primary production and ecosystem respiration has been well documented over broad thermal gradients. However, no study has examined their interaction as a function of temperature, i.e. the thermal responses of net ecosystem exchange of carbon (NEE). In this study, we const...

  6. Turbulence Considerations for Comparing Ecosystem Exchange over Old-Growth and Clear-Cut Stands For Limited Fetch and Complex Canopy Flow Conditions

    SciTech Connect

    Wharton, S; Schroeder, M; Paw U, K T; Falk, M; Bible, K

    2009-01-08

    Carbon dioxide, water vapor and energy fluxes were measured using eddy covariance (EC) methodology over three adjacent forests in southern Washington State to identify stand-level age-effects on ecosystem exchange. The sites represent Douglas-fir forest ecosystems at two contrasting successional stages: old-growth (OG) and early seral (ES). Here we present eddy flux and meteorological data from two early seral stands and the Wind River AmeriFlux old-growth forest during the growing season (March-October) in 2006 and 2007. We show an alternative approach to the usual friction velocity (u*) method for determining periods of adequate atmospheric boundary layer (ABL) mixing based on the ratio of mean horizontal ({bar u}) and vertical ({bar w}) wind flow to a modified turbulent kinetic energy scale (uTKE). This new parameter in addition to footprint modeling showed that daytime CO{sub 2} fluxes (F{sub NEE}) in small clear-cuts (< 10 hectares) can be measured accurately with EC if micrometeorological conditions are carefully evaluated. Peak midday CO{sub 2} fluxes (F{sub NEE} = -14.0 to -12.3 {micro}mol m{sup -2} s{sup -1}) at OG were measured in April in both 2006 and 2007 before bud break when air and soil temperatures and vapor pressure deficit were relatively low, and soil moisture and light levels were favorable for photosynthesis. At the early seral stands, peak midday CO{sub 2} fluxes (F{sub NEE} = -11.0 to -8.7 {micro}mol m{sup -2} s{sup -1}) were measured in June and July while spring-time CO{sub 2} fluxes were much smaller (F{sub NEE} = -3.8 to -3.6 {micro}mol m{sup -2} s{sup -1}). Overall, we measured lower evapotranspiration (OG = 230 mm; ES = 297 mm) higher midday F{sub NEE} (OG F{sub NEE} = -9.0 {micro}mol m{sup -2} s{sup -1}; ES F{sub NEE} = -7.3 {micro}mol m{sup -2} s{sup -1}) and higher Bowen ratios (OG {beta} = 2.0. ES {beta} = 1.2) at the old-growth forest than at the ES sites during the summer months (May-August). Eddy covariance studies such as ours

  7. Trophic cascade alters ecosystem carbon exchange

    PubMed Central

    Strickland, Michael S.; Hawlena, Dror; Reese, Aspen; Bradford, Mark A.; Schmitz, Oswald J.

    2013-01-01

    Trophic cascades—the indirect effects of carnivores on plants mediated by herbivores—are common across ecosystems, but their influence on biogeochemical cycles, particularly the terrestrial carbon cycle, are largely unexplored. Here, using a 13C pulse-chase experiment, we demonstrate how trophic structure influences ecosystem carbon dynamics in a meadow system. By manipulating the presence of herbivores and predators, we show that even without an initial change in total plant or herbivore biomass, the cascading effects of predators in this system begin to affect carbon cycling through enhanced carbon fixation by plants. Prolonged cascading effects on plant biomass lead to slowing of carbon loss via ecosystem respiration and reallocation of carbon among plant aboveground and belowground tissues. Consequently, up to 1.4-fold more carbon is retained in plant biomass when carnivores are present compared with when they are absent, owing primarily to greater carbon storage in grass and belowground plant biomass driven largely by predator nonconsumptive (fear) effects on herbivores. Our data highlight the influence that the mere presence of predators, as opposed to direct consumption of herbivores, can have on carbon uptake, allocation, and retention in terrestrial ecosystems. PMID:23776213

  8. Comparative review of multifunctionality and ecosystem services in sustainable agriculture.

    PubMed

    Huang, Jiao; Tichit, Muriel; Poulot, Monique; Darly, Ségolène; Li, Shuangcheng; Petit, Caroline; Aubry, Christine

    2015-02-01

    Two scientific communities with broad interest in sustainable agriculture independently focus on multifunctional agriculture or ecosystem services. These communities have limited interaction and exchange, and each group faces research challenges according to independently operating paradigms. This paper presents a comparative review of published research in multifunctional agriculture and ecosystem services. The motivation for this work is to improve communication, integrate experimental approaches, and propose areas of consensus and dialog for the two communities. This extensive analysis of publication trends, ideologies, and approaches enables formulation of four main conclusions. First, the two communities are closely related through their use of the term "function." However, multifunctional agriculture considers functions as agricultural activity outputs and prefers farm-centred approaches, whereas ecosystem services considers ecosystem functions in the provision of services and prefers service-centred approaches. Second, research approaches to common questions in these two communities share some similarities, and there would be great value in integrating these approaches. Third, the two communities have potential for dialog regarding the bundle of ecosystem services and the spectrum of multifunctional agriculture, or regarding land sharing and land sparing. Fourth, we propose an integrated conceptual framework that distinguishes six groups of ecosystem services and disservices in the agricultural landscape, and combines the concepts of multifunctional agriculture and ecosystem services. This integrated framework improves applications of multifunctional agriculture and ecosystem services for operational use. Future research should examine if the framework can be readily adapted for modelling specific problems in agricultural management.

  9. Global simulation of the carbon isotope exchange of terrestrial ecosystems

    NASA Astrophysics Data System (ADS)

    Ito, A.; Terao, Y.; Mukai, H.

    2009-12-01

    There remain large uncertainties in our quantification of global carbon cycle, which has close interactions with the climate system and is subject to human-induced global environmental change. Information on carbon isotopes is expected to reduce the uncertainty by providing additional constraints on net atmosphere-ecosystem exchange. This study attempted to simulate the dynamics of carbon isotopes at the global scale, using a process-based terrestrial ecosystem model: Vegetation Integrative SImulator for Trace gases (VISIT). The base-model of carbon cycle (Sim-CYCLE, Ito 2003) has already considered stable carbon isotope composition (13C/12C), and here radioactive carbon isotope (14C) was included. The isotope ratios characterize various aspects of terrestrial carbon cycle, which is difficult to be constrained by sole mass balance. For example, isotopic discrimination by photosynthetic assimilation is closely related with leaf stomatal conductance and composition of C3 and C4 plant in grasslands. Isotopic disequilibrium represents mean residence time of terrestrial carbon pools. In this study, global simulations (spatial resolution 0.5-deg, time-step 1-month) were conducted during the period 1901 to 2100 on the basis of observed and projected atmospheric CO2, climate, and land-use conditions. As anthropogenic CO2 accumulates in the atmosphere, heavier stable carbon isotope (13C) was diluted, while radioactive carbon isotope (14C) is strongly affected by atomic bomb experiments mainly in the 1950s and 1960s. The model simulated the decadal change in carbon isotope compositions. Leaf carbon with shorter mean residence time responded rapidly to the atmospheric change, while plant stems and soil humus showed substantial time-lag, leading to large isotopic disequilibrium. In the future, the isotopic disequilibrium was estimated to augment, due to accelerated rate of anthropogenic CO2 accumulation. Spatial distribution of stable isotope composition (12C/13C, or d13C) was

  10. Greenhouse gas exchange in tropical mountain ecosystems in Tanzania

    NASA Astrophysics Data System (ADS)

    Gerschlauer, Friederike; Kikoti, Imani; Kiese, Ralf

    2014-05-01

    Tropical mountain ecosystems with their mostly immense biodiversity are important regions for natural resources but also for agricultural production. Their supportive ecosystem processes are particularly vulnerable to the combined impacts of global warming and the conversion of natural to human-modified landscapes. Data of impacts of climate and land use change on soil-atmosphere interactions due to GHG (CO2, CH4, and N2O) exchange from these ecosystems are still scarce, in particular for Africa. Tropical forest soils are underestimated as sinks for atmospheric CH4 with regard to worldwide GHG budgets (Werner et al. 2007, J GEOPHYS RES Vol. 112). Even though these soils are an important source for the atmospheric N2O budget, N2O emissions from tropical forest ecosystems are still poorly characterized (Castaldi et al. 2013, Biogeosciences 10). To obtain an insight of GHG balances of selected ecosystems soil-atmosphere exchange of N2O, CH4 and CO2 was investigated along the southern slope of Mt. Kilimanjaro, Tanzania. We will present results for tropical forests in three different altitudes (lower montane, Ocotea, and Podocarpus forest), home garden (extensive agro-forestry), and coffee plantation (intensive agro-forestry). Therefore we used a combined approach consisting of a laboratory parameterization experiment (3 temperature and 2 moisture levels) and in situ static chamber measurements for GHG exchange. Field measurements were conducted during different hygric seasons throughout two years. Seasonal variation of temperature and especially of soil moisture across the different ecosystems resulted in distinct differences in GHG exchange. In addition environmental parameters like soil bulk density and substrate availability varying in space strongly influenced the GHG fluxes within sites. The results from parameterization experiments and in situ measurements show that natural forest ecosystems and extensive land use had higher uptakes of CH4. For the investigated

  11. Growing season net ecosystem CO2 exchange of two desert ecosystems with alkaline soils in Kazakhstan

    PubMed Central

    Li, Longhui; Chen, Xi; van der Tol, Christiaan; Luo, Geping; Su, Zhongbo

    2014-01-01

    Central Asia is covered by vast desert ecosystems, and the majority of these ecosystems have alkaline soils. Their contribution to global net ecosystem CO2 exchange (NEE) is of significance simply because of their immense spatial extent. Some of the latest research reported considerable abiotic CO2 absorption by alkaline soil, but the rate of CO2 absorption has been questioned by peer communities. To investigate the issue of carbon cycle in Central Asian desert ecosystems with alkaline soils, we have measured the NEE using eddy covariance (EC) method at two alkaline sites during growing season in Kazakhstan. The diurnal course of mean monthly NEE followed a clear sinusoidal pattern during growing season at both sites. Both sites showed significant net carbon uptake during daytime on sunny days with high photosynthetically active radiation (PAR) but net carbon loss at nighttime and on cloudy and rainy days. NEE has strong dependency on PAR and the response of NEE to precipitation resulted in an initial and significant carbon release to the atmosphere, similar to other ecosystems. These findings indicate that biotic processes dominated the carbon processes, and the contribution of abiotic carbon process to net ecosystem CO2 exchange may be trivial in alkaline soil desert ecosystems over Central Asia. PMID:24455157

  12. Thermal Acclimation and Adaptation of Net Ecosystem Carbon Exchange (Invited)

    NASA Astrophysics Data System (ADS)

    Luo, Y.; Niu, S.; Fei, S.; Yuan, W.; Zhang, Z.; Schimel, D.; Fluxnet Pis, .

    2010-12-01

    Ecosystem responses to temperature change are collectively determined by its constituents, which are plants, animals, microbes, and their interactions. It has been long documented that all plant, animals, and microbial carbon metabolism (photosynthesis, respiration) can acclimate and respond to changing temperatures, influencing the response of ecosystem carbon fluxes to climate change. Climate change also can induce competition between species with different thermal responses leading to changes in community composition. While a great deal of research has been done on species-level responses to temperature, it is yet to examine thermal acclimation of adaptation of ecosystem carbon processes to temperature change. With the advent of eddy flux measurements, it is possible to directly characterize the ecosystem-scale temperature response of carbon storage. In this study, we quantified the temperature response functions of net ecosystem carbon exchange (NEE), from which the responses of apparent optimal temperatures across broad spatial and temporal scales were examined. While temperature responses are normally parameterized in terms of the physiological variables describing photosynthesis and respiration, we focus on the apparent optimal behavior of NEE. Because the measurement integrated over multiple individuals and species within the footprint of the measurement (100s to 1000s of ha), it is challenging to interpret this measurement in terms of classical physiological variables such as the Q10. Rather we focus on the realized behavior of the ecosystem and its sensitivity to temperature. These empirical response functions can then be used as a benchmark for model evaluation and testing. Our synthesis of 656 site-years of eddy covariance data over the world shows that temperature response curves of NEE are parabolic, with their optima temperature strongly correlated with site growing season temperature across the globe and with annual mean temperature over years at

  13. Continuous In-situ Measurements of Carbonyl Sulfide to Constrain Ecosystem Carbon and Water Exchange

    NASA Astrophysics Data System (ADS)

    Rastogi, B.; Kim, Y.; Berkelhammer, M. B.; Noone, D. C.; Lai, C. T.; Hollinger, D. Y.; Bible, K.; Leen, J. B.; Gupta, M.; Still, C. J.

    2014-12-01

    Understanding the processes that control the terrestrial exchange of carbon and water are critical for examining the role of forested ecosystems in changing climates. A small but increasing number of studies have identified Carbonyl Sulfide (OCS) as a potential tracer for photosynthesis. OCS is hydrolyzed by an irreversible reaction in leaf mesophyll cells that is catalyzed by the enzyme, carbonic anhydrase. Leaf-level field and greenhouse studies indicate that OCS uptake is controlled by stomatal activity and that the ratio of OCS and CO2 uptake is reasonably constant. Existing studies on ecosystem OCS exchange have been based on laboratory measurements or short field campaigns and therefore little information on OCS exchange in a natural ecosystem over longer timescales is available. The objective of this study is to further assess the stability of OCS as a tracer for canopy photosynthesis in an active forested ecosystem and also to assess its utility for constraining transpiration, since both fluxes are mediated by canopy stomatal conductance. An off-axis integrated cavity output spectroscopy analyzer (Los Gatos Research Inc.) was deployed at the Wind River Experimental Forest in Washington (45.8205°N, 121.9519°W). Canopy air was sampled from three heights to measure vertical gradients of OCS within the canopy, and OCS exchange between the forest and the atmosphere. Here we take advantage of simultaneous measurements of the stable isotopologues of H2O and CO2 at corresponding heights as well as NEE (Net Ecosystem Exchange) from eddy covariance measurements to compare GPP (Gross Primary Production) and transpiration estimates from a variety of independent techniques. Our findings seek to allow assessment of the environmental and ecophysicological controls on evapotranspiration rates, which are projected to change in coming decades, and are otherwise poorly constrained.

  14. Effects of Fire on Ecosystem Carbon Exchange in Siberian Larch Forest

    NASA Astrophysics Data System (ADS)

    Natali, S.; Alexander, H. D.; Davydov, S. P.; Loranty, M. M.; Mack, M. C.; Zimov, N.

    2014-12-01

    Fire frequency and severity have been increasing across the Arctic, and fires are expected to intensify as the climate becomes warmer and dryer. Fire plays a prominent role in global carbon cycling through direct emissions of greenhouse gases from organic matter combustion as well as through indirect effects of vegetation changes and permafrost thaw, both of which can impact ecosystem carbon exchange over timescales ranging from years to centuries. We examined the indirect effects of fire (i.e., years to decades timescales) on ecosystem carbon exchange in Siberian larch (Larix cajanderi) forests underlain by continuous permafrost and carbon-rich yedoma deposits. We measured understory net ecosystem exchange (NEE) and ecosystem respiration (Reco) from experimental burns, and from larch stands of varying stand densities occurring within a 75-yr burn scar in the vicinity of Cherskiy, Russia. The plot-level (4 m2) experimental burns were conducted in 2012 and comprise four burn treatments based on residual soil organic layer (SOL) depths: control, low severity (> 8 cm), moderate severity (5-8 cm), and high severity (2-5 cm). After three growing seasons, thaw depth was 6%, 11% and 30% deeper in the low, mid, and high severity burn plots compared to control. Immediately following the burns, Reco declined and was related to burn severity; Reco in the mid and high severity plots was fourfold lower than in low severity and control. In the second and third growing seasons, understory Reco continued to be lower in the burn plots relative to control, but effects of burn severity varied across measurement years. While Reco declined as a result of fire, there was a greater net release of CO2 (i.e., NEE) from the burn plots compared to control because there was limited carbon uptake by the regenerating plant community. In the 75-yr burn, we found that variation in stand density, which was likely related to fire severity, significantly impacted understory CO2 exchange through

  15. Sensitivity of Prosopis velutina to Summer Rainfall and Consequences for Seasonal Patterns of Ecosystem Carbon Exchange

    NASA Astrophysics Data System (ADS)

    Potts, D. L.; Cable, J. M.; Scott, R. L.; Williams, D. G.; Goodrich, D. C.; Huxman, T. E.

    2005-12-01

    Future changes in dryland vegetation composition will interact with climate variability to influence carbon and water cycling in unforeseen ways. Observed increases in the density of woody plants in North America's savanna ecosystems may be an important terrestrial carbon sink and could alter patterns of regional hydrologic cycling. During the 2005 growing season we compared seasonal patterns of Prosopis velutina plant water status and leaf gas exchange in upland and riparian savannas. Previous work suggested the plant size class constrained alluvial groundwater access and that mature individuals were less sensitive to the onset of summer rains at the riparian site. We predicted that at the upland site, where groundwater was unavailable, mature and juvenile plants would respond similarly to the onset of summer rains. Furthermore, we predicted that this increased sensitivity by the dominant vegetation to seasonal rainfall would be reflected in NEE data collected by eddy-covariance at both sites. Results indicate that mesquite performance and the duration and magnitude of ecosystem carbon exchanges are tightly linked to precipitation at the upland site. Comparing upland and riparian sites demonstrates how seasonal pattern of precipitation, plant-available alluvial groundwater and vegetation structure interact to govern ecosystem carbon balance in savanna ecosystems.

  16. Whole ecosystem estimates of carbon exchange and storage in a New England salt marsh

    NASA Astrophysics Data System (ADS)

    Forbrich, I.; Giblin, A.

    2013-12-01

    flooding. To partition the net flux into its component fluxes gross primary production (GPP) and ecosystem respiration (Reco), these tidal influences have to be incorporated in the NEE model. Differences in GPP and Reco during high tide and low tide events can be used to constrain estimates of lateral carbon transport. These will need to be compared to direct measurements of tidal carbon fluxes to determine how much of the reduction in atmospheric fluxes is due to metabolic changes and how much is due to the exchange of carbon between the marsh and water.

  17. Effects of Water and Nitrogen Addition on Ecosystem Carbon Exchange in a Meadow Steppe

    PubMed Central

    Wang, Yunbo; Jiang, Qi; Yang, Zhiming; Sun, Wei; Wang, Deli

    2015-01-01

    A changing precipitation regime and increasing nitrogen deposition are likely to have profound impacts on arid and semiarid ecosystem C cycling, which is often constrained by the timing and availability of water and nitrogen. However, little is known about the effects of altered precipitation and nitrogen addition on grassland ecosystem C exchange. We conducted a 3-year field experiment to assess the responses of vegetation composition, ecosystem productivity, and ecosystem C exchange to manipulative water and nitrogen addition in a meadow steppe. Nitrogen addition significantly stimulated aboveground biomass and net ecosystem CO2 exchange (NEE), which suggests that nitrogen availability is a primary limiting factor for ecosystem C cycling in the meadow steppe. Water addition had no significant impacts on either ecosystem C exchange or plant biomass, but ecosystem C fluxes showed a strong correlation with early growing season precipitation, rather than whole growing season precipitation, across the 3 experimental years. After we incorporated water addition into the calculation of precipitation regimes, we found that monthly average ecosystem C fluxes correlated more strongly with precipitation frequency than with precipitation amount. These results highlight the importance of precipitation distribution in regulating ecosystem C cycling. Overall, ecosystem C fluxes in the studied ecosystem are highly sensitive to nitrogen deposition, but less sensitive to increased precipitation. PMID:26010888

  18. Growing season ecosystem and leaf-level gas exchange of an exotic and native semiarid bunchgrass.

    PubMed

    Hamerlynck, Erik P; Scott, Russell L; Moran, M Susan; Keefer, Timothy O; Huxman, Travis E

    2010-07-01

    The South African grass, Lehmann lovegrass (Eragrostis lehmanniana), may alter ecosystem processes across extensive semiarid grasslands and savannahs of western North America. We compared volumetric soil moisture (theta), total and green tissue leaf area index (LAI), ecosystem (i.e. whole-plant and soil), and leaf-level gas exchange of Lehmann lovegrass and the native bush muhly (Muhlenbergia porteri) over the 2008 monsoon season in a semiarid savanna in southern Arizona, USA, to see if these were consistent with high productivity associated with lovegrass invasive success. theta across 0-5 and 0-25 cm was higher while evapotranspiration (ET) was similar between lovegrass and bush muhly plots, except shortly after rainfall, when ET was 32-81% higher in lovegrass plots. Lehmann lovegrass had lower, quickly developing LAI with greater leaf proportions than bush muhly. When early season theta was high, net ecosystem CO(2) exchange (NEE) was similar, but as storm frequency and theta declined, NEE was more negative in lovegrass (-0.69 to -3.00 micromol m(-2) s(-1)) than bush muhly (+1.75 to -1.55 micromol m(-2) s(-1)). Ecosystem respiration (R (eco)) responded quickly to monsoon onset and late-season rains, and was lower in lovegrass (2.44-3.74 micromol m(-2) s(-1)) than bush muhly (3.60-5.3 micromol m(-2) s(-1)) across the season. Gross ecosystem photosynthesis (GEP) was greater in Lehmann lovegrass, concurrent with higher leaf-level photosynthesis and stomatal conductance. We conclude that canopy structure facilitates higher theta under Lehmann lovegrass, reducing phenological constraints and stomatal limitations to whole-plant carbon uptake through the short summer monsoon growing season.

  19. Modeling snow season controls on northern net ecosystem exchange

    NASA Astrophysics Data System (ADS)

    Luus, K. A.; Lin, J. C.; Kelly, R. E.

    2011-12-01

    Recent field studies have indicated that the timing of snow melt and snow fall, the quantity of snow, and soil temperature are important controls on snow season net ecosystem exchange (NEE). The low thermal conductivity of snow reduces soil heat loss, thereby enabling a greater rate of subnivean respiration under deeper snowpacks, whereas snow melt and snow fall alter the seasonal timing of photosynthetic uptake. Although a substantial portion of annual NEE in northern regions occurs during the snow season, model estimates have not previously included representations of snow season controls on NEE. The objective of this study was therefore to 1) incorporate remotely sensed estimates of snow water equivalent, soil temperature, and the timing of initial snow fall and final snow melt into model estimates of northern NEE; and 2) examine whether incorporating representations of key snow season variables reduces model uncertainty. NEE was estimated using the Vegetation Photosynthesis Respiration Model (VPRM), a simple diagnostic biosphere model that relies on a remote sensing based approach. Findings indicate that a potential exists to improve northern estimates of NEE by incorporating information on snow season controls from remote sensing observations. Soil respiration can be better assessed using soil temperature rather than surface air temperature. The influence of changes in snow water equivalent on soil temperature dynamics can be assessed using remotely sensed estimates of snow water equivalent. Incorporating remotely sensed estimates of snow cover area can improve the timing of seasonal changes in photosynthetic uptake. Furthermore, including snow season controls on northern NEE can enable experiments to be run analyzing the influence of changes in snowpack dynamics, the frequency of extreme winter warming events, and the timing of the snow season on northern NEE.

  20. Delayed responses of an Arctic ecosystem to an extremely dry summer: impacts on net ecosystem exchange and vegetation functioning

    NASA Astrophysics Data System (ADS)

    Zona, D.; Lipson, D. A.; Richards, J. H.; Phoenix, G. K.; Liljedahl, A. K.; Ueyama, M.; Sturtevant, C. S.; Oechel, W. C.

    2013-12-01

    The importance and mode of action of extreme events on the global carbon budget are inadequately understood. This includes the differential impact of extreme events on various ecosystem components, lag effects, recovery times, and compensatory processes. Summer 2007 in Barrow, Arctic Alaska, experienced unusually high air temperatures (fifth warmest over a 65 yr period) and record low precipitation (lowest over a 65 yr period). These abnormal conditions resulted in strongly reduced net Sphagnum CO2 uptake, but no effect neither on vascular plant development nor on net ecosystem exchange (NEE) from this arctic tundra ecosystem. Gross primary production (GPP) and ecosystem respiration (Reco) were both generally greater during most of this extreme summer. Cumulative ecosystem C uptake in 2007 was similar to the previous summers, showing the capacity of the ecosystem to compensate in its net ecosystem exchange (NEE) despite the impact on other functions and structure such as substantial necrosis of the Sphagnum layer. Surprisingly, the lowest ecosystem C uptake (2005-2009) was observed during the 2008 summer, i.e the year directly following the extremely summer. In 2008, cumulative C uptake was ∼70% lower than prior years. This reduction cannot solely be attributed to mosses, which typically contribute with ∼40% - of the entire ecosystem C uptake. The minimum summer cumulative C uptake in 2008 suggests that the entire ecosystem experienced difficulty readjusting to more typical weather after experiencing exceptionally warm and dry conditions. Importantly, the return to a substantial cumulative C uptake occurred two summers after the extreme event, which suggest a high resilience of this tundra ecosystem. Overall, these results show a highly complex response of the C uptake and its sub-components to atypically dry conditions. The impact of multiple extreme events still awaits further investigation.

  1. Spatial assessment of atmosphere-ecosystem exchanges via micrometeorological measurements and footprint modelling over complex terrain

    NASA Astrophysics Data System (ADS)

    Zhao, Peng; Lüers, Johannes; Foken, Thomas

    2010-05-01

    Anthropogenic impacts on natural and managed ecosystems have increased seriously during recent years. Ecosystem functions are modified as a result, which have an apparent influence on ecosystem services. TERRECO, a joint activity of the University of Bayreuth, Kangwon National University in Korea, and Korean Forest Research Institute, focuses the goal on building a bridge between ecosystem performance in mountainous terrain and derived ecosystem services that are critical for human well being. As a sub-program of TERRECO, our study is concentrated in Haean-Myun Catchment, an intensively used landscape within the Soyang Lake watershed including Soyang Lake Reservoir, and a sub-catchment of the Han River system which drains 26% of the land surface of South Korea. The aim of our study is to better understand the energy and matter exchange above farmlands (rice fields and/or dry crops) during the whole growing period including monsoon seasons in such a complex terrain as Haean Basin in Korea. To determine reliable evaporation and net ecosystem exchange (NEE), and to determine reliable information about near surface atmospheric stratification conditions, including convective events in Haean Basin, an eddy covariance complex (USA-1, LI-7500) will be installed above a typical farmland in Haean Basin to collect the 3D wind vector, water vapor and carbon dioxide concentration. It will be running at a sampling frequency of 20 Hz continuously, from late April to October in 2010. A post-processing software packages called TK2 will be used to obtain reliable sensible and latent heat and carbon dioxide fluxes with a high standard in data quality. Ongoing Footprint analysis will give an opportunity to track the spatial contribution of the surrounding land uses to the observed heat and CO2 fluxes helping to interpret the data. Useful data will be picked out to determine the variability of the stratification of the near surface boundary atmospheric layer to better understand the

  2. Scaling hyporheic exchange and its influence on biogeochemical reactions in aquatic ecosystems

    NASA Astrophysics Data System (ADS)

    O'Connor, Ben L.; Harvey, Judson W.

    2008-12-01

    Hyporheic exchange and biogeochemical reactions are difficult to quantify because of the range in fluid-flow and sediment conditions inherent to streams, wetlands, and nearshore marine ecosystems. Field measurements of biogeochemical reactions in aquatic systems are impeded by the difficulty of measuring hyporheic flow simultaneously with chemical gradients in sediments. Simplified models of hyporheic exchange have been developed using Darcy's law generated by flow and bed topography at the sediment-water interface. However, many modes of transport are potentially involved (molecular diffusion, bioturbation, advection, shear, bed mobility, and turbulence) with even simple models being difficult to apply in complex natural systems characterized by variable sediment sizes and irregular bed geometries. In this study, we synthesize information from published hyporheic exchange investigations to develop a scaling relationship for estimating mass transfer in near-surface sediments across a range in fluid-flow and sediment conditions. Net hyporheic exchange was quantified using an effective diffusion coefficient (De) that integrates all of the various transport processes that occur simultaneously in sediments, and dimensional analysis was used to scale De to shear stress velocity, roughness height, and permeability that describe fluid-flow and sediment characteristics. We demonstrated the value of the derived scaling relationship by using it to quantify dissolved oxygen (DO) uptake rates on the basis of DO profiles in sediments and compared them to independent flux measurements. The results support a broad application of the De scaling relationship for quantifying coupled hyporheic exchange and biogeochemical reaction rates in streams and other aquatic ecosystems characterized by complex fluid-flow and sediment conditions.

  3. Scaling hyporheic exchange and its influence on biogeochemical reactions in aquatic ecosystems

    USGS Publications Warehouse

    O'Connor, B.L.; Harvey, J.W.

    2008-01-01

    Hyporheic exchange and biogeochemical reactions are difficult to quantify because of the range in fluid-flow and sediment conditions inherent to streams, wetlands, and nearshore marine ecosystems. Field measurements of biogeochemical reactions in aquatic systems are impeded by the difficulty of measuring hyporheic flow simultaneously with chemical gradients in sediments. Simplified models of hyporheic exchange have been developed using Darcy's law generated by flow and bed topography at the sediment-water interface. However, many modes of transport are potentially involved (molecular diffusion, bioturbation, advection, shear, bed mobility, and turbulence) with even simple models being difficult to apply in complex natural systems characterized by variable sediment sizes and irregular bed geometries. In this study, we synthesize information from published hyporheic exchange investigations to develop a scaling relationship for estimating mass transfer in near-surface sediments across a range in fluid-flow and sediment conditions. Net hyporheic exchange was quantified using an effective diffusion coefficient (De) that integrates all of the various transport processes that occur simultaneously in sediments, and dimensional analysis was used to scale De to shear stress velocity, roughness height, and permeability that describe fluid-flow and sediment characteristics. We demonstrated the value of the derived scaling relationship by using it to quantify dissolved oxygen (DO) uptake rates on the basis of DO profiles in sediments and compared them to independent flux measurements. The results support a broad application of the De scaling relationship for quantifying coupled hyporheic exchange and biogeochemical reaction rates in streams and other aquatic ecosystems characterized by complex fluid-flow and sediment conditions.

  4. Typhoons exert significant but differential impact on net carbon ecosystem exchange of subtropical mangrove ecosystems in China

    NASA Astrophysics Data System (ADS)

    Chen, H.; Lu, W.; Yan, G.; Yang, S.; Lin, G.

    2014-06-01

    Typhoons are very unpredictable natural disturbances to subtropical mangrove forests in Asian countries, but litter information is available on how these disturbances affect ecosystem level carbon dioxide (CO2) exchange of mangrove wetlands. In this study, we examined short-term effect of frequent strong typhoons on defoliation and net ecosystem CO2 exchange (NEE) of subtropical mangroves, and also synthesized 19 typhoons during a 4-year period between 2009 and 2012 to further investigate the regulation mechanisms of typhoons on ecosystem carbon and water fluxes following typhoon disturbances. Strong wind and intensive rainfall caused defoliation and local cooling effect during typhoon season. Daily total NEE values were decreased by 26-50% following some typhoons (e.g. W28-Nockten, W35-Molave and W35-Lio-Fan), but were significantly increased (43-131%) following typhoon W23-Babj and W38-Megi. The magnitudes and trends of daily NEE responses were highly variable following different typhoons, which were determined by the balance between the variances of gross ecosystem production (GEP) and ecosystem respiration (RE). Furthermore, results from our synthesis indicated that the landfall time of typhoon, wind speed and rainfall were the most important factors controlling the CO2 fluxes following typhoon events. These findings not only indicate that mangrove ecosystems have strong resilience to the frequent typhoon disturbances, but also demonstrate the damage of increasing typhoon intensity and frequency on subtropical mangrove ecosystems under future global climate change scenarios.

  5. Current net ecosystem exchange of CO2 in a young mixed forest: any heritage from the previous ecosystem?

    NASA Astrophysics Data System (ADS)

    Violette, Aurélie; Heinesch, Bernard; Erpicum, Michel; Carnol, Monique; Aubinet, Marc; François, Louis

    2013-04-01

    For 15 years, networks of flux towers have been developed to determine accurate carbon balance with the eddy-covariance method and determine if forests are sink or source of carbon. However, for prediction of the evolution of carbon cycle and climate, major uncertainties remain on the ecosystem respiration (Reco, which includes the respiration of above ground part of trees, roots respiration and mineralization of the soil organic matter), the gross primary productivity (GPP) and their difference, the net ecosystem exchange (NEE) of forests. These uncertainties are consequences of spatial and inter-annual variability, driven by previous and current climatic conditions, as well as by the particular history of the site (management, diseases, etc.). In this study we focus on the carbon cycle in two mixed forests in the Belgian Ardennes. The first site, Vielsalm, is a mature stand mostly composed of beeches (Fagus sylvatica) and douglas fir (Pseudotsuga menziesii) from 80 to 100 years old. The second site, La Robinette, was covered before 1995 with spruces. After an important windfall and a clear cutting, the site was replanted, between 1995 and 2000, with spruces (Piceas abies) and deciduous species (mostly Betula pendula, Aulnus glutinosa and Salix aurita). The challenge here is to highlight how initial conditions can influence the current behavior of the carbon cycle in a growing stand compared to a mature one, where initial conditions are supposed to be forgotten. A modeling approach suits particularly well for sensitivity tests and estimation of the temporal lag between an event and the ecosystem response. We use the forest ecosystem model ASPECTS (Rasse et al., Ecological Modelling 141, 35-52, 2001). This model predicts long-term forest growth by calculating, over time, hourly NEE. It was developed and already validated on the Vielsalm forest. Modelling results are confronted to eddy-covariance data on both sites from 2006 to 2011. The main difference between both

  6. Contrasting tropical estuarine ecosystem functioning and stability: A comparative study

    NASA Astrophysics Data System (ADS)

    Villanueva, Maria Ching

    2015-03-01

    A comparative study of the Sine-saloum (Senegal) and Gambia (The Gambia) estuaries was performed based on trophic model outputs that describe the system structure and functioning. These trophic models were constructed such as to differentiate main energetic flows in the systems and express how climate change may have impacted ecosystem resilience to change. Estuarine fish assemblages are highly resilient despite exposure to vast hydrodynamic variations and stress. Coupled with strong anthropogenic-driven stresses such as fisheries and climate change, ecosystems may undergo severe regime shifts that may weaken their resilience and stability. Taxonomically related and morphologically similar species do not necessarily play similar ecological roles in these two ecosystems. Biomass and production in the Sine-saloum are concentrated at trophic levels (TLs) 2 and 3, while for the Gambia, both are concentrated at TL3. Higher TL biomasses in Gambia compared to Sine-Saloum may be explained by the latter ecosystem being characterized by inverse hypersalinity. Higher TL of production in Sine-Saloum is due to higher exploitations compared to Gambia where fishing activities are still less developed. High production and consumption rates of some groups in both ecosystems indicate high system productivity. Elevated productivity may be due to higher abundance of juvenile fishes in most groups that utilize the latter as refuge and/or nursery zones. Both ecosystems are phytoplankton-driven. Differences in group trophic and ecological roles are mainly due to adaptive responses of these species to seasonal and long-term climate and anthropogenic stressors. System indicators suggest different levels of ecosystem resilience and stability as a function of biodiversity. Relevance of other observations on ecosystem functioning and indicators in relation to perturbation is discussed.

  7. Large interannual variability in net ecosystem carbon dioxide exchange of a disturbed temperate peatland.

    PubMed

    Aslan-Sungur, Guler; Lee, Xuhui; Evrendilek, Fatih; Karakaya, Nusret

    2016-06-01

    Peatland ecosystems play an important role in the global carbon (C) cycle as significant C sinks. However, human-induced disturbances can turn these sinks into sources of atmospheric CO2. Long-term measurements are needed to understand seasonal and interannual variability of net ecosystem CO2 exchange (NEE) and effects of hydrological conditions and their disturbances on C fluxes. Continuous eddy-covariance measurements of NEE were conducted between August 2010 and April 2014 at Yenicaga temperate peatland (Turkey), which was drained for agricultural usage and for peat mining until 2009. Annual NEE during the three full years of measurement indicated that the peatland acted as a CO2 source with large interannual variability, at rates of 246, 244 and 663 g Cm(-2)yr(-1) for 2011, 2012, and 2013 respectively, except for June 2011, and May to July 2012. The emission strengths were comparable to those found for severely disturbed tropical peatlands. The peak CO2 emissions occurred in the dry summer of 2013 when water table level (WTL) was below a threshold value of -60 cm and soil water content (SCW) below a threshold value of 70% by volume. Water availability index was found to have a stronger explanatory power for variations in monthly ecosystem respiration (ER) than the traditional water status indicators (SCW and WTL). Air temperature, evapotranspiration and vapor pressure deficient were the most significant variables strongly correlated with NEE and its component fluxes of gross primary production and ER. PMID:26950633

  8. Ecosystem carbon exchange in response to locust outbreaks in a temperate steppe.

    PubMed

    Song, Jian; Wu, Dandan; Shao, Pengshuai; Hui, Dafeng; Wan, Shiqiang

    2015-06-01

    It is predicted that locust outbreaks will occur more frequently under future climate change scenarios, with consequent effects on ecological goods and services. A field manipulative experiment was conducted to examine the responses of gross ecosystem productivity (GEP), net ecosystem carbon dioxide (CO2) exchange (NEE), ecosystem respiration (ER), and soil respiration (SR) to locust outbreaks in a temperate steppe of northern China from 2010 to 2011. Two processes related to locust outbreaks, natural locust feeding and carcass deposition, were mimicked by clipping 80 % of aboveground biomass and adding locust carcasses, respectively. Ecosystem carbon (C) exchange (i.e., GEP, NEE, ER, and SR) was suppressed by locust feeding in 2010, but stimulated by locust carcass deposition in both years (except SR in 2011). Experimental locust outbreaks (i.e., clipping plus locust carcass addition) decreased GEP and NEE in 2010 whereas they increased GEP, NEE, and ER in 2011, leading to neutral changes in GEP, NEE, and SR across the 2 years. The responses of ecosystem C exchange could have been due to the changes in soil ammonium nitrogen, community cover, and aboveground net primary productivity. Our findings of the transient and neutral changes in ecosystem C cycling under locust outbreaks highlight the importance of resistance, resilience, and stability of the temperate steppe in maintaining reliable ecosystem services, and facilitate the projections of ecosystem functioning in response to natural disturbance and climate change.

  9. Continuous In-situ Measurements of Carbonyl Sulfide (OCS) and Carbon Dioxide Isotopes to Constrain Ecosystem Carbon and Water Exchanges

    NASA Astrophysics Data System (ADS)

    Rastogi, B.; Still, C. J.; Noone, D. C.; Berkelhammer, M. B.; Whelan, M.; Lai, C. T.; Hollinger, D. Y.; Gupta, M.; Leen, J. B.; Huang, Y. W.

    2015-12-01

    Understanding the processes that control the terrestrial exchange of carbon and water are critical for examining the role of forested ecosystems in changing climates. A small but increasing number of studies have identified Carbonyl Sulfide (OCS) as a potential tracer for photosynthesis. OCS is hydrolyzed by an irreversible reaction in leaf mesophyll cells that is catalyzed by the enzyme, carbonic anhydrase. Leaf- level field and greenhouse studies indicate that OCS uptake is controlled by stomatal activity and that the ratio of OCS and CO2 uptake is reasonably constant. Existing studies on ecosystem OCS exchange have been based on laboratory measurements or short field campaigns and therefore little information on OCS exchange in a natural ecosystem over longer timescales is available. The objective of this study is to further assess the stability of OCS as a tracer for canopy photosynthesis in an active forested ecosystem and also to assess its utility for constraining transpiration, since both fluxes are mediated by canopy stomatal conductance. An off-axis integrated cavity output spectroscopy analyzer (Los Gatos Research Inc.) was deployed at the Wind River Experimental Forest in Washington (45.8205°N, 121.9519°W). Canopy air was sampled from four heights as well as the soil to measure vertical gradients of OCS within the canopy, and OCS exchange between the forest and the atmosphere for the growing season. Here we take advantage of simultaneous measurements of the stable isotopologues of H2O and CO2 at corresponding heights as well as NEE (Net Ecosystem Exchange) from eddy covariance measurements to compare GPP (Gross Primary Production) and transpiration estimates from a variety of independent techniques. Our findings also seek to allow assessment of the environmental and ecophysicological controls on evapotranspiration rates, which are projected to change in coming decades, and are otherwise poorly constrained.

  10. Regional Ecosystem-Atmosphere CO2 Exchange Via Atmospheric Budgets

    SciTech Connect

    Davis, K J; Richardson, S J; Miles, N L

    2007-03-07

    Inversions of atmospheric CO2 mixing ratio measurements to determine CO2 sources and sinks are typically limited to coarse spatial and temporal resolution. This limits our ability to evaluate efforts to upscale chamber- and stand-level CO2 flux measurements to regional scales, where coherent climate and ecosystem mechanisms govern the carbon cycle. As a step towards the goal of implementing atmospheric budget or inversion methodology on a regional scale, a network of five relatively inexpensive CO2 mixing ratio measurement systems was deployed on towers in northern Wisconsin. Four systems were distributed on a circle of roughly 150-km radius, surrounding one centrally located system at the WLEF tower near Park Falls, WI. All measurements were taken at a height of 76 m AGL. The systems used single-cell infrared CO2 analyzers (Licor, model LI-820) rather than the siginificantly more costly two-cell models, and were calibrated every two hours using four samples known to within ± 0.2 ppm CO2. Tests prior to deployment in which the systems sampled the same air indicate the precision of the systems to be better than ± 0.3 ppm and the accuracy, based on the difference between the daily mean of one system and a co-located NOAA-ESRL system, is consistently better than ± 0.3 ppm. We demonstrate the utility of the network in two ways. We interpret regional CO2 differences using a Lagrangian parcel approach. The difference in the CO2 mixing ratios across the network is at least 2-3 ppm, which is large compared to the accuracy and precision of the systems. Fluxes estimated assuming Lagrangian parcel transport are of the same sign and magnitude as eddy-covariance flux measurements at the centrally-located WLEF tower. These results indicate that the network will be useful in a full inversion model. Second, we present a case study involving a frontal passage through the region. The progression of a front across the network is evident; changes as large as four ppm in one minute

  11. A long term monitoring of Net Ecosystem Exchanges of the chaparral ecosystem in Southern California

    NASA Astrophysics Data System (ADS)

    Rossi, A.; Oechel, W. C.; Murphy, P.; Ikawa, H.; Sturtevant, C. S.

    2012-12-01

    Arid and semiarid woody shrublands represent approximately 35% of the global terrestrial surface area and 24% of the global soil organic carbon, and 16% of the global aboveground biomass (Atjay et al., 1979; Shmida, 1985). Therefore, these areas potentially have a large contribution to the global carbon budget. However, the assessment of carbon uptake for the old-growth shrubland has remained largely unexplored. Therefore, a long-term observation of CO2 flux with the eddy covariance technique has started since 1997 at Sky Oaks Field Station in Southern California. The research site is categorized at the climatic gradient between desert and semiarid area and that experiences a Mediterranean climate. The long term record of CO2 flux showed the area has been a sink of CO2 of up to -0.2 kgCm-2yr-1. In addition to evaluating vertical carbon fluxes, we initiated a project to evaluate lateral carbon transports using litter traps, sediment fences and two small weirs adjacent to the eddy covariance site in 2011. Preliminary results indicate that the lateral carbon efflux from the system may offset the vertical influx to the shrub ecosystem. However, it is still necessary to develop the methodology to compare vertical carbon flux and the lateral carbon fluxes more accurately.

  12. Delayed responses of an Arctic ecosystem to an extreme summer: impacts on net ecosystem exchange and vegetation functioning

    NASA Astrophysics Data System (ADS)

    Zona, D.; Lipson, D. A.; Richards, J. H.; Phoenix, G. K.; Liljedahl, A. K.; Ueyama, M.; Sturtevant, C. S.; Oechel, W. C.

    2014-10-01

    The importance and consequences of extreme events on the global carbon budget are inadequately understood. This includes the differential impact of extreme events on various ecosystem components, lag effects, recovery times, and compensatory processes. In the summer of 2007 in Barrow, Arctic Alaska, there were unusually high air temperatures (the fifth warmest summer over a 65-year period) and record low precipitation (the lowest over a 65-year period). These abnormal conditions were associated with substantial desiccation of the Sphagnum layer and a reduced net Sphagnum CO2 sink but did not affect net ecosystem exchange (NEE) from this wet-sedge arctic tundra ecosystem. Microbial biomass, NH4+ availability, gross primary production (GPP), and ecosystem respiration (Reco) were generally greater during this extreme summer. The cumulative ecosystem CO2 sink in 2007 was similar to the previous summers, suggesting that vascular plants were able to compensate for Sphagnum CO2 uptake, despite the impact on other functions and structure such as desiccation of the Sphagnum layer. Surprisingly, the lowest ecosystem CO2 sink over a five summer record (2005-2009) was observed during the 2008 summer (~70% lower), directly following the unusually warm and dry summer, rather than during the extreme summer. This sink reduction cannot solely be attributed to the potential damage to mosses, which typically contribute ~40% of the entire ecosystem CO2 sink. Importantly, the return to a substantial cumulative CO2 sink occurred two summers after the extreme event, which suggests a substantial resilience of this tundra ecosystem to at least an isolated extreme event. Overall, these results show a complex response of the CO2 sink and its sub-components to atypically warm and dry conditions. The impact of multiple extreme events requires further investigation.

  13. Combining Ballast Water Exchange and Treatment To Maximize Prevention of Species Introductions to Freshwater Ecosystems.

    PubMed

    Briski, Elizabeta; Gollasch, Stephan; David, Matej; Linley, R Dallas; Casas-Monroy, Oscar; Rajakaruna, Harshana; Bailey, Sarah A

    2015-08-18

    The most effective way to manage species transfers is to prevent their introduction via vector regulation. Soon, international ships will be required to meet numeric ballast discharge standards using ballast water treatment (BWT) systems, and ballast water exchange (BWE), currently required by several countries, will be phased out. However, there are concerns that BWT systems may not function reliably in fresh and/or turbid water. A land-based evaluation of simulated "BWE plus BWT" versus "BWT alone" demonstrated potential benefits of combining BWE with BWT for protection of freshwater ecosystems. We conducted ship-based testing to compare the efficacy of "BWE plus BWT" versus "BWT alone" on voyages starting with freshwater ballast. We tested the hypotheses that there is an additional effect of "BWE plus BWT" compared to "BWT alone" on the reduction of plankton, and that taxa remaining after "BWE plus BWT" will be marine (low risk for establishment at freshwater recipient ports). Our study found that BWE has significant additional effect on the reduction of plankton, and this effect increases with initial abundance. As per expectations, "BWT alone" tanks contained higher risk freshwater or euryhaline taxa at discharge, while "BWE plus BWT" tanks contained mostly lower risk marine taxa unlikely to survive in recipient freshwater ecosystems.

  14. Drivers of long-term variability in CO2 net ecosystem exchange in a temperate peatland

    NASA Astrophysics Data System (ADS)

    Helfter, C.; Campbell, C.; Dinsmore, K. J.; Drewer, J.; Coyle, M.; Anderson, M.; Skiba, U.; Nemitz, E.; Billett, M. F.; Sutton, M. A.

    2014-10-01

    Land-atmosphere exchange of carbon dioxide (CO2) in peatlands exhibits marked seasonal and inter-annual variability, which subsequently affects the carbon sink strength of catchments across multiple temporal scales. Long-term studies are needed to fully capture the natural variability and therefore identify the key hydrometeorological drivers in the net ecosystem exchange (NEE) of CO2. NEE has been measured continuously by eddy-covariance at Auchencorth Moss, a temperate lowland peatland in central Scotland, since 2002. Hence this is one of the longest peatland NEE studies to date. For 11 yr, the site was a consistent, yet variable, atmospheric CO2 sink ranging from -5.2 to -135.9 g CO2-C m-2 yr-1 (mean of -64.1 ± 33.6 g CO2-C m-2 yr-1). Inter-annual variability in NEE was positively correlated to the length of the growing season. Mean winter air temperature explained 87% of the inter-annual variability in the sink strength of the following summer, indicating a phenological memory-effect. Plant productivity exhibited a marked hysteresis with respect to photosynthetically active radiation (PAR) over the growing season, indicative of two separate growth regimes. Ecosystem respiration (Reco) and gross primary productivity (GPP) were closely correlated (ratio 0.74), suggesting that autotrophic processes were dominant. Whilst the site was wet most of the year (water table depth <5 cm) there were indications that heterotrophic respiration was enhanced by drought, which also depressed GPP. NEE was compared to 5 other peatland sites which have published long-term NEE records. The CO2 uptake rate during the growing season was comparable to 3 other European sites, however the emission rate during the dormant season was significantly higher.

  15. Carbon dioxide exchange in a temperate grassland ecosystem

    NASA Technical Reports Server (NTRS)

    Kim, Joon; Verma, Shashi B.

    1990-01-01

    Carbon dioxide exchange was measured, using the eddy correlation technique, over a tallgrass prairie in northeastern Kansas, U.S.A., during a six-month period in 1987. The diurnal patterns of daytime and nocturnal CO2 fluxes are presented on eight selected days. These days were distributed throughout most of the growing season and covered a wide range of meteorological and soil water conditions. The midday CO2 flux reached a maximum of 1.3 mg/sq m (ground area)/s during early July and was near zero during the dry period in late July. The dependence of the daytime carbon dioxide exchange on pertinent controlling variables, particularly photosynthetically active radiation, vapor pressure deficit, and soil water content is discussed. The nocturnal CO2 flux (soil plus plant respiration) averaged -0.4 m sq m (ground area)/s during early July and was about -0.2 mg sq/m during the dry period.

  16. Comparison of net ecosystem carbon exchange estimation in a mixed temperate forest using field eddy covariance and MODIS data.

    PubMed

    Wang, Yuandong; Tang, Xuguang; Yu, Lianfang; Hou, Xiyong; Munger, J William

    2016-01-01

    Quantification of net ecosystem carbon exchange (NEE) between the atmosphere and vegetation is of great importance for regional and global studies of carbon balance. The eddy covariance technique can quantify carbon budgets and the effects of environmental controls for many forest types across the continent but it only provides integrated CO2 flux measurements within tower footprints and need to be scaled up to large areas in combination with remote sensing observations. In this study we compare a multiple-linear regression (MR) model which relates enhanced vegetation index and land surface temperature derived from the moderate resolution imaging spectroradiometer (MODIS), and photosynthetically active radiation with the site-level NEE, for estimating carbon flux exchange between the ecosystem and the environment at the deciduous-dominated Harvard Forest to three other methods proposed in the literature. Six years (2001-2006) of eddy covariance and MODIS data are used and results show that the MR model has the best performance for both training (2001-2004, R (2) = 0.84, RMSE = 1.33 g Cm(-2) day(-1)) and validation (2005-2006, R (2) = 0.76, RMSE = 1.54 g Cm(-2) day(-1)) datasets comparing to the other ones. It provides the potential to estimate carbon flux exchange across different ecosystems at various time intervals for scaling up plot-level NEE of CO2 to large spatial areas.

  17. Characterization of total ecosystem-scale biogenic VOC exchange at a Mediterranean oak-hornbeam forest

    NASA Astrophysics Data System (ADS)

    Schallhart, Simon; Rantala, Pekka; Nemitz, Eiko; Taipale, Ditte; Tillmann, Ralf; Mentel, Thomas F.; Loubet, Benjamin; Gerosa, Giacomo; Finco, Angelo; Rinne, Janne; Ruuskanen, Taina M.

    2016-06-01

    Recently, the number and amount of biogenically emitted volatile organic compounds (VOCs) has been discussed in great detail. Depending on the ecosystem, the published number varies between a dozen and several hundred compounds. We present ecosystem exchange fluxes from a mixed oak-hornbeam forest in the Po Valley, Italy. The fluxes were measured by a proton transfer reaction-time-of-flight (PTR-ToF) mass spectrometer and calculated using the eddy covariance (EC) method. Detectable fluxes were observed for up to 29 compounds, dominated by isoprene, which comprised over 60 % of the total upward flux (on a molar basis). The daily average of the total VOC upward flux was 10.4 nmol m-2 s-1. Methanol had the highest concentration and accounted for the largest downward flux. Methanol seemed to be deposited to dew, as the downward flux happened in the early morning, right after the calculated surface temperature came closest to the calculated dew point temperature.We estimated that up to 30 % of the upward flux of methyl vinyl ketone (MVK) and methacrolein (MACR) originated from atmospheric oxidation of isoprene. A comparison between two methods for the flux detection (manual and automated) was made. Their respective advantages and disadvantages were discussed and the differences in their results shown. Both provide comparable results.

  18. Characterization of total ecosystem scale biogenic VOC exchange at a Mediterranean oak-hornbeam forest

    NASA Astrophysics Data System (ADS)

    Schallhart, S.; Rantala, P.; Nemitz, E.; Mogensen, D.; Tillmann, R.; Mentel, T. F.; Rinne, J.; Ruuskanen, T. M.

    2015-10-01

    Recently, the number and amount of biogenically emitted volatile organic compounds (VOCs) has been discussed vigorously. Depending on the ecosystem the published number varies between a dozen and several hundred compounds. We present ecosystem exchange fluxes from a mixed oak-hornbeam forest in the Po Valley, Italy. The fluxes were measured by a proton transfer reaction-time-of-flight (PTR-ToF) mass spectrometer and calculated by the eddy covariance (EC) method. Detectable fluxes were observed for twelve compounds, dominated by isoprene, which comprised over 65 % of the total flux emission. The daily average of the total VOC emission was 9.5 nmol m-2 s-1. Methanol had the highest concentration and accounted for the largest deposition. Methanol seemed to be deposited to dew, as the deposition happened in the early morning, right after the calculated surface temperature came closest to the calculated dew point temperature. We estimated that up to 27 % of the upward flux of methyl vinyl ketone (MVK) and methacrolein (MACR) originated from atmospheric oxidation of isoprene. A comparison between two flux detection methods (classical/visual and automated) was made. Their respective advantages and disadvantages were discussed and the differences in their results shown. Both provide comparable results; however we recommend the automated method with a compound filter, which combines the fast analysis and better flux detection, without the overestimation due to double counting.

  19. Drivers of long-term variability in CO2 net ecosystem exchange in a temperate peatland

    NASA Astrophysics Data System (ADS)

    Helfter, C.; Campbell, C.; Dinsmore, K. J.; Drewer, J.; Coyle, M.; Anderson, M.; Skiba, U.; Nemitz, E.; Billett, M. F.; Sutton, M. A.

    2015-03-01

    Land-atmosphere exchange of carbon dioxide (CO2) in peatlands exhibits marked seasonal and inter-annual variability, which subsequently affects the carbon (C) sink strength of catchments across multiple temporal scales. Long-term studies are needed to fully capture the natural variability and therefore identify the key hydrometeorological drivers in the net ecosystem exchange (NEE) of CO2. Since 2002, NEE has been measured continuously by eddy-covariance at Auchencorth Moss, a temperate lowland peatland in central Scotland. Hence this is one of the longest peatland NEE studies to date. For 11 years, the site was a consistent, yet variable, atmospheric CO2 sink ranging from -5.2 to -135.9 g CO2-C m-2 yr-1 (mean of -64.1 ± 33.6 g CO2-C m-2 yr-1). Inter-annual variability in NEE was positively correlated to the length of the growing season. Mean winter air temperature explained 87% of the inter-annual variability in the sink strength of the following summer, indicating an effect of winter climate on local phenology. Ecosystem respiration (Reco) was enhanced by drought, which also depressed gross primary productivity (GPP). The CO2 uptake rate during the growing season was comparable to three other sites with long-term NEE records; however, the emission rate during the dormant season was significantly higher. To summarise, the NEE of the peatland studied is modulated by two dominant factors: - phenology of the plant community, which is driven by winter air temperature and impacts photosynthetic potential and net CO2 uptake during the growing season (colder winters are linked to lower summer NEE), - water table level, which enhanced soil respiration and decreased GPP during dry spells. Although summer dry spells were sporadic during the study period, the positive effects of the current climatic trend towards milder winters on the site's CO2 sink strength could be offset by changes in precipitation patterns especially during the growing season.

  20. Comparative biogeochemistry-ecosystem-human interactions on dynamic continental margins

    USGS Publications Warehouse

    Levin, Lisa A.; Liu, Kon-Kee; Emeis, Kay-Christian; Breitburg, Denise L.; Cloern, James; Deutsch, Curtis; Giani, Michele; Goffart, Anne; Hofmann, Eileen E.; Lachkar, Zouhair; Limburg, Karin; Liu, Su-Mei; Montes, Enrique; Naqvi, Wajih; Ragueneau, Olivier; Rabouille, Christophe; Sarkar, Santosh Kumar; Swaney, Dennis P.; Wassman, Paul; Wishner, Karen F.

    2014-01-01

    The ocean’s continental margins face strong and rapid change, forced by a combination of direct human activity, anthropogenic CO2-induced climate change, and natural variability. Stimulated by discussions in Goa, India at the IMBER IMBIZO III, we (1) provide an overview of the drivers of biogeochemical variation and change on margins, (2) compare temporal trends in hydrographic and biogeochemical data across different margins (3) review ecosystem responses to these changes, (4) highlight the importance of margin time series for detecting and attributing change and (5) examine societal responses to changing margin biogeochemistry and ecosystems. We synthesize information over a wide range of margin settings in order to identify the commonalities and distinctions among continental margin ecosystems. Key drivers of biogeochemical variation include long-term climate cycles, CO2-induced warming, acidification, and deoxygenation, as well as sea level rise, eutrophication, hydrologic and water cycle alteration, changing land use, fishing, and species invasion. Ecosystem responses are complex and impact major margin services including primary production, fisheries production, nutrient cycling, shoreline protection, chemical buffering, and biodiversity. Despite regional differences, the societal consequences of these changes are unarguably large and mandate coherent actions to reduce, mitigate and adapt to multiple stressors on continental margins.

  1. Comparative biogeochemistry-ecosystem-human interactions on dynamic continental margins

    NASA Astrophysics Data System (ADS)

    Levin, Lisa A.; Liu, Kon-Kee; Emeis, Kay-Christian; Breitburg, Denise L.; Cloern, James; Deutsch, Curtis; Giani, Michele; Goffart, Anne; Hofmann, Eileen E.; Lachkar, Zouhair; Limburg, Karin; Liu, Su-Mei; Montes, Enrique; Naqvi, Wajih; Ragueneau, Olivier; Rabouille, Christophe; Sarkar, Santosh Kumar; Swaney, Dennis P.; Wassman, Paul; Wishner, Karen F.

    2015-01-01

    The oceans' continental margins face strong and rapid change, forced by a combination of direct human activity, anthropogenic CO2-induced climate change, and natural variability. Stimulated by discussions in Goa, India at the IMBER IMBIZO III, we (1) provide an overview of the drivers of biogeochemical variation and change on margins, (2) compare temporal trends in hydrographic and biogeochemical data across different margins, (3) review ecosystem responses to these changes, (4) highlight the importance of margin time series for detecting and attributing change and (5) examine societal responses to changing margin biogeochemistry and ecosystems. We synthesize information over a wide range of margin settings in order to identify the commonalities and distinctions among continental margin ecosystems. Key drivers of biogeochemical variation include long-term climate cycles, CO2-induced warming, acidification, and deoxygenation, as well as sea level rise, eutrophication, hydrologic and water cycle alteration, changing land use, fishing, and species invasion. Ecosystem responses are complex and impact major margin services. These include primary production, fisheries production, nutrient cycling, shoreline protection, chemical buffering, and biodiversity. Despite regional differences, the societal consequences of these changes are unarguably large and mandate coherent actions to reduce, mitigate and adapt to multiple stressors on continental margins.

  2. [Ecosystem carbon exchange in Artemisia ordosica shrubland of Ordos Plateau in two different precipitation years].

    PubMed

    Gao, Li; Dong, Ting-Ting; Wang, Yu-Qing; Yan, Zhi-Jian; Baoyin, Tao-ge-tao; Wang, Hui; Dai, Ya-Ting

    2014-08-01

    Characteristics of ecosystem carbon exchange and its impact factors in Artemisia ordosica shrubland in 2011 (low precipitation) and 2012 (high precipitation), Ordos Plateau, were studied using eddy covariance methods. The results showed that the diurnal dynamics of ecosystem carbon exchange could be expressed as single-peak and double-peak curves in the two different precipitation years. In 2011, three carbon absorption peaks and three carbon release peaks of ecosystem carbon exchange presented in the growing season. In 2012, four carbon absorption peaks and one carbon release peak appeared in the growing season. The A. ordosica shrubland was a net carbon sink from June to September and a carbon source in October in 2011. In 2012, A. ordosica shrubland was a net carbon sink in the whole growing season. The amount of carbon fixed by A. ordosica shrubland in the growing season in 2012 was 268.90 mg CO2 x m(-2) x s(-1) higher than that in 2011. The ecosystem carbon exchange of A. ordosica shrubland was controlled by PAR (photosynthetically active radiation) on the day scale, and affected by both abiotic (precipitation and soil water content) and biotic (aboveground net primary, productivity) factors on the growing season scale.

  3. Simulating the impacts of land use in northwest Europe on Net Ecosystem Exchange (NEE): the role of arable ecosystems, grasslands and forest plantations in climate change mitigation.

    PubMed

    Abdalla, Mohamed; Saunders, Matthew; Hastings, Astley; Williams, Mike; Smith, Pete; Osborne, Bruce; Lanigan, Gary; Jones, Mike B

    2013-11-01

    In this study, we compared measured and simulated Net Ecosystem Exchange (NEE) values from three wide spread ecosystems in the southeast of Ireland (forest, arable and grassland), and investigated the suitability of the DNDC (the DeNitrification-DeComposition) model to estimate present and future NEE. Although, the field-DNDC version overestimated NEE at temperatures >5 °C, forest-DNDC under-estimated NEE at temperatures >5 °C. The results suggest that the field/forest DNDC models can successfully estimate changes in seasonal and annual NEE from these ecosystems. Differences in NEE were found to be primarily land cover specific. The annual NEE was similar for the grassland and arable sites, but due to the contribution of exported carbon, the soil carbon increased at the grassland site and decreased at the arable site. The NEE of the forest site was an order of magnitude larger than that of the grassland or arable ecosystems, with large amounts of carbon stored in woody biomass and the soil. The average annual NEE, GPP and Reco values over the measurement period were -904, 2379 and 1475 g C m(-2) (forest plantations), -189, 906 and 715 g C m(-2) (arable systems) and -212, 1653 and 1444 g C m(-2) (grasslands), respectively. The average RMSE values were 3.8 g C m(-2) (forest plantations), 0.12 g C m(-2) (arable systems) and 0.21 g C m(-2) (grasslands). When these models were run with climate change scenarios to 2060, predictions show that all three ecosystems will continue to operate as carbon sinks. Further, climate change may decrease the carbon sink strength in the forest plantations by up to 50%. This study supports the use of the DNDC model as a valid tool to predict the consequences of climate change on NEE from different ecosystems.

  4. Simulating the impacts of land use in northwest Europe on Net Ecosystem Exchange (NEE): the role of arable ecosystems, grasslands and forest plantations in climate change mitigation.

    PubMed

    Abdalla, Mohamed; Saunders, Matthew; Hastings, Astley; Williams, Mike; Smith, Pete; Osborne, Bruce; Lanigan, Gary; Jones, Mike B

    2013-11-01

    In this study, we compared measured and simulated Net Ecosystem Exchange (NEE) values from three wide spread ecosystems in the southeast of Ireland (forest, arable and grassland), and investigated the suitability of the DNDC (the DeNitrification-DeComposition) model to estimate present and future NEE. Although, the field-DNDC version overestimated NEE at temperatures >5 °C, forest-DNDC under-estimated NEE at temperatures >5 °C. The results suggest that the field/forest DNDC models can successfully estimate changes in seasonal and annual NEE from these ecosystems. Differences in NEE were found to be primarily land cover specific. The annual NEE was similar for the grassland and arable sites, but due to the contribution of exported carbon, the soil carbon increased at the grassland site and decreased at the arable site. The NEE of the forest site was an order of magnitude larger than that of the grassland or arable ecosystems, with large amounts of carbon stored in woody biomass and the soil. The average annual NEE, GPP and Reco values over the measurement period were -904, 2379 and 1475 g C m(-2) (forest plantations), -189, 906 and 715 g C m(-2) (arable systems) and -212, 1653 and 1444 g C m(-2) (grasslands), respectively. The average RMSE values were 3.8 g C m(-2) (forest plantations), 0.12 g C m(-2) (arable systems) and 0.21 g C m(-2) (grasslands). When these models were run with climate change scenarios to 2060, predictions show that all three ecosystems will continue to operate as carbon sinks. Further, climate change may decrease the carbon sink strength in the forest plantations by up to 50%. This study supports the use of the DNDC model as a valid tool to predict the consequences of climate change on NEE from different ecosystems. PMID:23384575

  5. Carbondioxide exchange of biological soil crusts compared to disturbed soil / sand in semi arid areas

    NASA Astrophysics Data System (ADS)

    Wilske, B.; Yakir, D.; Burgheimer, J.; Karnieli, A.; Zaady, E.; Kesselmeier, J.

    2003-04-01

    Sparse vegetation in semi arid and arid lands is associated with low productivity and minor contribution to biosphere-atmosphere exchange of greenhouse gases, on an area basis. Dryland ecosystems, however, cover large land areas that are continuously increasing. Two third of global population live in semi arid and arid regions and its direct impact contributes to the expansion of dryland ecosystems. Satellite images at the start of the wet season in natural dryland ecosystems clearly show significant photosynthetic activity at a time when most vascular plants are yet inactive or undeveloped, indicating a possibly neglected CO_2 sink. This can likely be assigned to the so-called biological soil crusts (BSC) that consist of poikilohydric microphytes such as cyanobacteria, lichens, green algae, and mosses, which can rapidly recover photosynthesis in response to the earliest water supply. Such non-vascular vegetation activities are an important feature of dryland ecosystems worldwide, often complementary to that of vascular plants. We report on the rates of CO_2 exchange of BSC as measured at two field sites in the northern Negev desert during six months during 2001/2002. Peak rates of net photosynthesis (1.5 - 2 μmol m-2 s-1) were in the range observed in vascular plants, but periods with low or no activities were considerable. Rates of CO_2 exchange of BSC was always compared with that of bare soil / sand. This allowed both estimating net local land surface exchange, and assessing the influence of disturbance, mainly by uncontrolled land use, of the highly vulnerable BSC ecosystems. Simultaneous measurements of spectral reflectance properties of BSC in this study aim to allow calibration of airborne remote sensing for large-scale BSC activity studies.

  6. Interannual variability of Net Ecosystem CO2 Exchange and its component fluxes in a subalpine Mediterranean ecosystem (SE Spain)

    NASA Astrophysics Data System (ADS)

    Chamizo, Sonia; Serrano-Ortiz, Penélope; Sánchez-Cañete, Enrique P.; Domingo, Francisco; Arnau-Rosalén, Eva; Oyonarte, Cecilio; Pérez-Priego, Óscar; López-Ballesteros, Ana; Kowalski, Andrew S.

    2015-04-01

    Recent decades under climate change have seen increasing interest in quantifying the carbon (C) balance of different terrestrial ecosystems, and their behavior as sources or sinks of C. Both CO2 exchange between terrestrial ecosystems and the atmosphere and identification of its drivers are key to understanding land-surface feedbacks to climate change. The eddy covariance (EC) technique allows measurements of net ecosystem C exchange (NEE) from short to long time scales. In addition, flux partitioning models can extract the components of net CO2 fluxes, including both biological processes of photosynthesis or gross primary production (GPP) and respiration (Reco), and also abiotic drivers like subsoil CO2 ventilation (VE), which is of particular relevance in semiarid environments. The importance of abiotic processes together with the strong interannual variability of precipitation, which strongly affects CO2 fluxes, complicates the accurate characterization of the C balance in semiarid landscapes. In this study, we examine 10 years of interannual variability of NEE and its components at a subalpine karstic plateau, El Llano de los Juanes, in the Sierra de Gádor (Almería, SE Spain). Results show annual NEE ranging from 55 g C m-2 (net emission) to -54 g C m-2 (net uptake). Among C flux components, GPP was the greatest contributing 42-57% of summed component magnitudes, while contributions by Reco and VE ranged from 27 to 46% and from 3 to 18%, respectively. Annual precipitation during the studied period exhibited high interannual variability, ranging from 210 mm to 1374 mm. Annual precipitation explained 50% of the variance in Reco, 59% of that in GPP, and 56% for VE. While Reco and GPP were positively correlated with annual precipitation (correlation coefficient, R, of 0.71 and 0.77, respectively), VE showed negative correlation with this driver (R = -0.74). During the driest year (2004-2005), annual GPP and Reco reached their lowest values, while contribution of

  7. Enhanced Seasonal Exchange of CO2 by Northern Ecosystems - Observations and Models

    NASA Astrophysics Data System (ADS)

    Graven, H. D.; Keeling, R. F.; Piper, S. C.; Patra, P. K.; Stephens, B. B.; Wofsy, S. C.; Welp, L. R.; Sweeney, C.; Tans, P. P.; Kelley, J. J.; Daube, B. C.; Kort, E. A.; Santoni, G.; Bent, J. D.; Thomas, R.; Prentice, I. C.

    2014-12-01

    Long-term measurements of atmospheric CO2 have revealed increasing amplitude in seasonal variations at Northern Hemisphere sites. In a recent paper1, we extended the analysis of seasonal CO2 amplitude using aircraft data from 1958-61 and 2009-11 and found large increases of 50% in the mid-troposphere north of 45°N. Changes in amplitude south of 45°N were less than 25%. The observations indicate that seasonal CO2 exchanges with northern terrestrial ecosystems must have increased by 30-60% over the past 50 years. The increased exchange is likely widespread over northern ecosystems but it must be focused in boreal forests to match the observed spatial pattern in the aircraft data. Small decreases in seasonal CO2 exchange of subtropical and tropical regions may also contribute to CO2 amplitude changes. The required increases in seasonal CO2 exchange in northern ecosystems are larger than simulated by terrestrial models, indicating the models do not capture substantial ecological changes occurring since 1960. This presentation will give an overview of the recent paper1, highlighting the atmospheric evidence for a dominant influence from boreal forests and from the main growing season months. It will also expand on the investigation of modeled changes in seasonal CO2 flux using CMIP5 and other model intercomparisons, including the modeled influences of carbon vs climate drivers. 1. Graven et al. 2013, Enhanced Seasonal Exchange of CO2 by Northern Ecosystems Since 1960, Science, 341, 6150, 1085-1089. DOI: 10.1126/science.1239207

  8. Assessing net ecosystem carbon exchange of U S terrestrial ecosystems by integrating eddy covariance flux measurements and satellite observations

    SciTech Connect

    Zhuang, Qianlai; Law, Beverly E.; Baldocchi, Dennis; Ma, Siyan; Chen, Jiquan; Richardson, Andrew; Melillo, Jerry; Davis, Ken J.; Hollinger, D.; Wharton, Sonia; Falk, Matthias; Paw, U. Kyaw Tha; Oren, Ram; Katulk, Gabriel G.; Noormets, Asko; Fischer, Marc; Verma, Shashi; Suyker, A. E.; Cook, David R.; Sun, G.; McNulty, Steven G.; Wofsy, Steve; Bolstad, Paul V; Burns, Sean; Monson, Russell K.; Curtis, Peter; Drake, Bert G.; Foster, David R.; Gu, Lianhong; Hadley, Julian L.; Litvak, Marcy; Martin, Timothy A.; Matamala, Roser; Meyers, Tilden; Oechel, Walter C.; Schmid, H. P.; Scott, Russell L.; Torn, Margaret S.

    2011-01-01

    More accurate projections of future carbon dioxide concentrations in the atmosphere and associated climate change depend on improved scientific understanding of the terrestrial carbon cycle. Despite the consensus that U.S. terrestrial ecosystems provide a carbon sink, the size, distribution, and interannual variability of this sink remain uncertain. Here we report a terrestrial carbon sink in the conterminous U.S. at 0.63 pg C yr 1 with the majority of the sink in regions dominated by evergreen and deciduous forests and savannas. This estimate is based on our continuous estimates of net ecosystem carbon exchange (NEE) with high spatial (1 km) and temporal (8-day) resolutions derived from NEE measurements from eddy covariance flux towers and wall-to-wall satellite observations from Moderate Resolution Imaging Spectroradiometer (MODIS). We find that the U.S. terrestrial ecosystems could offset a maximum of 40% of the fossil-fuel carbon emissions. Our results show that the U.S. terrestrial carbon sink varied between 0.51 and 0.70 pg C yr 1 over the period 2001 2006. The dominant sources of interannual variation of the carbon sink included extreme climate events and disturbances. Droughts in 2002 and 2006 reduced the U.S. carbon sink by 20% relative to a normal year. Disturbances including wildfires and hurricanes reduced carbon uptake or resulted in carbon release at regional scales. Our results provide an alternative, independent, and novel constraint to the U.S. terrestrial carbon sink.

  9. Growing Season Length as a Key Factor of Cumulative Net Ecosystem Exchange Over the Pine Forest Ecosystems in Europe

    NASA Astrophysics Data System (ADS)

    Danielewska, Alina; Urbaniak, Marek; Olejnik, Janusz

    2015-04-01

    The Scots pine is one of the most important species in European and Asian forests. Due to a widespread occurrence of pine forests, their significance in the energy and mass exchange between the Earth surface and the atmosphere is also important, particularly in the context of climate change and greenhouse gases balance. The aim of this work is to present the relationship between the average annual net ecosystem productivity and growing season length, latitude and air temperature (tay) over Europe. Therefore, CO2 flux measurement data from eight European pine dominated forests were used. The observations suggest that there is a correlation between the intensity of CO2 uptake or emission by a forest stand and the above mentioned parameters. Based on the obtained results, all of the selected pine forest stands were CO2 sinks, except a site in northern Finland. The carbon dioxide uptake increased proportionally with the increase of growing season length (9.212 g C m-2 y-1 per day of growing season, R2 = 0.53, p = 0.0399). This dependency showed stronger correlation and higher statistical significance than both relationships between annual net ecosystem productivity and air temperature (R2 = 0.39, p = 0.096) and annual net ecosystem productivity and latitude (R2 = 0.47, p = 0.058). The CO2 emission surpassed assimilation in winter, early spring and late autumn. Moreover, the appearance of late, cold spring and early winter, reduced annual net ecosystem productivity. Therefore, the growing season length can be considered as one of the main factor affecting the annual carbon budget of pine forests.

  10. Net Ecosystem Exchange and Net Biome Productivity of different land use in eastern Germany

    NASA Astrophysics Data System (ADS)

    Grünwald, Thomas; Prescher, Anne-Katrin; Bernhofer, Christian

    2010-05-01

    The carbon (CO2-C) budgets of a managed forest (spruce), grassland and a cropland (crop rotation) have been determined and compared. The sites are part of the Tharandt cluster which features low intersite variability in climate due to the small distances between the sites. This allows the comparison of management effects on the carbon budget of different land use among other things. At the forest site, continuous CO2 flux measurements are available from 1997 to 2008, the common observation period of the grassland and cropland sites was 2005 to 2008. With regard to annual net ecosystem exchange NEE (based on eddy covariance flux measurements), the forest showed the highest net sink (-698 g C m-2 (1999) to -444 g C m-2 (2003)). In contrast the grassland and cropland sites were significantly lower sinks in terms of NEE (-177 g C m-2 (2004) to -62 g C m-2 (2005) and -115 g C m-2 (2005) to -32 g C m-2 (2007 and 2008), respectively). To quantify the net biome productivity (NBP) carbon exports due to thinning or harvest as well as carbon imports due to organic fertilisation are considered besides NEE. Carbon exports and imports change the carbon budget in terms of NBP. At the forest site only the 2002 NBP is a carbon source (+221 g C m-2) due to the thinning in April 2002 when around 43 m3 ha-1 solid wood was removed from the ecosystem. After the thinning the annual NEE is reduced by around 100 g C m-2 until 2007. The grassland NBP alternated between carbon source and sink (+25 g C m-2 (2008) to -28 g C m-2 (2006)) indicating the carbon balance was approximately neutral. Low NEE and NBP values at the grassland site were a consequence of carbon export due to several cuts per year. The NBP of the cropland ecosystem was mainly influenced by the crop type (winter or spring crop) and the application of organic fertiliser (manure) resulting in carbon budgets between +484 g C m-2 (2007) and -89 g C m-2 (2006). The different timing and length of the growing season of winter and

  11. Effects of temperature, moisture, and permafrost thaw on ecosystem carbon exchange in Alaskan tundra.

    NASA Astrophysics Data System (ADS)

    Natali, S.; Schuur, E. A.; Webb, E.

    2012-12-01

    Carbon has been accumulating in northern high latitude ecosystems for thousands of years because cold and moist conditions have protected soil organic matter from microbial decomposition. Over the past several decades, warming surface air temperatures have been accompanied by thawing of the perennially frozen permafrost layer where much of the accumulated carbon is stored. In addition to its role in carbon storage, permafrost regulates surface hydrology by restricting vertical water flow, thereby maintaining a water table that remains close to the ground surface. In the absence of the permafrost layer, enhanced water drainage will result in increased water table depth and decreased soil moisture. The biological availability of permafrost carbon may increase in a warmer and drier soil environment, as is expected for the region of this study. To determine the effects of warming temperatures and changes in soil moisture on ecosystem carbon exchange, we established a water table drawdown experiment within the footprint of the Carbon in Permafrost Experimental Heating Research (CiPEHR) project, an ecosystem warming experiment in Interior Alaska that warms air and soil temperatures and degrades permafrost. Here we present ecosystem carbon balance results from combined warming and moisture manipulation treatments at the CiPEHR project. Soil warming increased soil temperature by 2-3o C and resulted in a 10% increase in growing season thaw depth. Surprisingly, the additional 2 kg of thawed soil C m-2 in the warmed plots did not increase net growing season CO2 loss from this ecosystem. In contrast, soil warming and permafrost thaw increased growing season CO2 uptake, which was a result of both higher net primary productivity and an inhibition of microbial decomposition by soil saturation at the base of the active layer. The drying treatment (i.e., water table drawdown) decreased soil moisture by 25%, which led to an increase in ecosystem respiration and decrease in net

  12. Active atmosphere-ecosystem exchange of the vast majority of detected volatile organic compounds.

    PubMed

    Park, J-H; Goldstein, A H; Timkovsky, J; Fares, S; Weber, R; Karlik, J; Holzinger, R

    2013-08-01

    Numerous volatile organic compounds (VOCs) exist in Earth's atmosphere, most of which originate from biogenic emissions. Despite VOCs' critical role in tropospheric chemistry, studies for evaluating their atmosphere-ecosystem exchange (emission and deposition) have been limited to a few dominant compounds owing to a lack of appropriate measurement techniques. Using a high-mass resolution proton transfer reaction-time of flight-mass spectrometer and an absolute value eddy-covariance method, we directly measured 186 organic ions with net deposition, and 494 that have bidirectional flux. This observation of active atmosphere-ecosystem exchange of the vast majority of detected VOCs poses a challenge to current emission, air quality, and global climate models, which do not account for this extremely large range of compounds. This observation also provides new insight for understanding the atmospheric VOC budget.

  13. Bi-directional exchange of ammonia in a pine forest ecosystem - a model sensitivity analysis

    NASA Astrophysics Data System (ADS)

    Moravek, Alexander; Hrdina, Amy; Murphy, Jennifer

    2016-04-01

    Ammonia (NH3) is a key component in the global nitrogen cycle and of great importance for atmospheric chemistry, neutralizing atmospheric acids and leading to the formation of aerosol particles. For understanding the role of NH3 in both natural and anthropogenically influenced environments, the knowledge of processes regulating its exchange between ecosystems and the atmosphere is essential. A two-layer canopy compensation point model is used to evaluate the NH3 exchange in a pine forest in the Colorado Rocky Mountains. The net flux comprises the NH3 exchange of leaf stomata, its deposition to leaf cuticles and exchange with the forest ground. As key parameters the model uses in-canopy NH3 mixing ratios as well as leaf and soil emission potentials measured at the site in summer 2015. A sensitivity analysis is performed to evaluate the major exchange pathways as well as the model's constraints. In addition, the NH3 exchange is examined for an extended range of environmental conditions, such as droughts or varying concentrations of atmospheric pollutants, in order to investigate their influence on the overall net exchange.

  14. [Effect of air temperature and rainfall on wetland ecosystem CO2 exchange in China].

    PubMed

    Chu, Xiao-jing; Han, Guang-xuan

    2015-10-01

    Wetland can be a potential efficient sink to reduce global warming due to its higher primary productivity and lower carbon decomposition rate. While there has been a series progress on the influence mechanism of ecosystem CO2 exchange over China' s wetlands, a systematic metaanalysis of data still needs to be improved. We compiled data of ecosystem CO2 exchange of 21 typical wetland vegetation types in China from 29 papers and carried out an integrated analysis of air temperature and precipitation effects on net ecosystem CO2 exchange (NEE), ecosystem respiration (Reco), gross primary productivity (GPP), the response of NEE to PAR, and the response of Reco to temperature. The results showed that there were significant responses (P<0.05) of NEE (R2 = 50%, R2=57%), GPP (R2 = 60%, R2 = 50%) Reco (R2 = 44%, R2=50%) with increasing air temperature and enhanced precipitation on the annual scale. On the growing season scale, air temperature accounted for 50% of the spatial variation of NEE, 36% of GPP and 19% of Reco, respectively. Both NEE (R2 = 33%) and GPP (R2 =25%) were correlated positively with precipitation (P<0.05). However, the relationship between Reco and precipitation was not significant (P>0.05). Across different Chinese wetlands, both precipitation and temperature had no significant effect on apparent quantum yield (α) or ecosystem respiration in the daytime (Reco,day, P>0.05). The maximum photosynthesis rate (Amax) was remarkably correlated with precipitation (P <0.01), but not with air temperature. Besides, there was no significant correlation between basal respiration (Rref) and precipitation (P>0.05). Precipitation was negatively correlated with temperature sensitivity of Reco (Q10, P<0.05). Furthermore, temperature accounted for 35% and 46% of the variations in temperature sensitivity of Reco (Q10) and basal respiration (Rref P<0.05), respectively. PMID:26995905

  15. Impacts of Precipitation Diurnal Timing on Ecosystem Carbon Exchanges in Grasslands: A Synthesis of AmeriFlux Data

    NASA Astrophysics Data System (ADS)

    Song, X.; Xu, X.; Tweedie, C. E.

    2015-12-01

    Drylands have been found playing an important role regulating the seasonality of global atmospheric carbon dioxide concentrations. Precipitation is a primary control of ecosystem carbon exchanges in drylands where a large proportion of the annual total rainfall arrives through a small number of episodic precipitation events. While a large number of studies use the concept of "precipitation pulses" to explore the effects of short-term precipitation events on dryland ecosystem function, few have specifically evaluated the importance of the diurnal timing of these events. The primary goal of this study was to determine how the diurnal timing of rainfall events impacts land-atmosphere net ecosystem CO2 exchanges (NEE) and ecosystem respiration in drylands. Our research leverages a substantial and existing long-term database (AmeriFlux) that describes NEE, Reco and meteorological conditions at 11 sites situated in different dryland ecosystems in South West America. All sites employ the eddy covariance technique to measure land-atmosphere the CO2 exchange rates between atmosphere and ecosystem. Data collected at these sites range from 4 to 10 years, totaling up to 73 site-years. We found that episodic precipitation events stimulate not only vegetation photosynthesis but also ecosystem respiration. Specifically, the morning precipitation events decrease photosynthesis function at daytime and increase ecosystem respiration at nighttime; the afternoon precipitation events do not stimulate ecosystem photosynthesis at daytime, while stimulate ecosystem respiration; the night precipitations suppress photosynthesis at daytime, and enhance ecosystem respiration at nighttime.

  16. Dynamic exchanges between DOM and POM pools in coastal and inland aquatic ecosystems: A review.

    PubMed

    He, Wei; Chen, Meilian; Schlautman, Mark A; Hur, Jin

    2016-05-01

    Dynamic exchanges between dissolved organic matter (DOM) and particulate organic matter (POM) plays a critical role in organic carbon cycling in coastal and inland aquatic ecosystems, interactions with aquatic organisms, mobility and bioavailability of pollutants, among many other ecological and geochemical phenomena. Although DOM-POM exchange processes have been widely studied from different aspects, little to no effort has been made to date to provide a comprehensive, mechanistic, and micro-spatial schema for understanding various exchange processes occurring in different aquatic ecosystems in a unified way. The phenomena occurring between DOM and POM were explained here with the homogeneous and heterogeneous mechanisms. In the homogeneous mechanism, the participating components are only organic matter (OM) constituents themselves with aggregation and dissolution involved, whereas OM is associated with other components such as minerals and particulate colloids in the heterogeneous counterpart. Besides the generally concerned processes of aggregation/dissolution and adsorption/desorption, other ecological factors such as sunlight and organisms can also participate in DOM-POM exchanges through altering the chemical nature of OM. Despite the limitation of current analytical technologies, many unknown and/or unquantified processes need to be identified to unravel the complicated exchanges of OM between its dissolved and particulate states. Based on the review of several previous mathematical models, we proposed a unified conceptual model to describe all major dynamic exchange mechanisms on the basis of exergy theory. More knowledge of dynamic DOM-POM exchanges is warranted to overcome the potential problems arising from a simple division of OM into dissolved versus particulate states and to further develop more sophisticated mathematic models.

  17. Comparison of net ecosystem carbon exchange estimation in a mixed temperate forest using field eddy covariance and MODIS data.

    PubMed

    Wang, Yuandong; Tang, Xuguang; Yu, Lianfang; Hou, Xiyong; Munger, J William

    2016-01-01

    Quantification of net ecosystem carbon exchange (NEE) between the atmosphere and vegetation is of great importance for regional and global studies of carbon balance. The eddy covariance technique can quantify carbon budgets and the effects of environmental controls for many forest types across the continent but it only provides integrated CO2 flux measurements within tower footprints and need to be scaled up to large areas in combination with remote sensing observations. In this study we compare a multiple-linear regression (MR) model which relates enhanced vegetation index and land surface temperature derived from the moderate resolution imaging spectroradiometer (MODIS), and photosynthetically active radiation with the site-level NEE, for estimating carbon flux exchange between the ecosystem and the environment at the deciduous-dominated Harvard Forest to three other methods proposed in the literature. Six years (2001-2006) of eddy covariance and MODIS data are used and results show that the MR model has the best performance for both training (2001-2004, R (2) = 0.84, RMSE = 1.33 g Cm(-2) day(-1)) and validation (2005-2006, R (2) = 0.76, RMSE = 1.54 g Cm(-2) day(-1)) datasets comparing to the other ones. It provides the potential to estimate carbon flux exchange across different ecosystems at various time intervals for scaling up plot-level NEE of CO2 to large spatial areas. PMID:27186455

  18. Unmasking the effect of a precipitation pulse on the biological processes composing Net Ecosystem Carbon Exchange

    NASA Astrophysics Data System (ADS)

    Lopez-Ballesteros, Ana; Sanchez-Cañete, Enrique P.; Serrano-Ortiz, Penelope; Oyonarte, Cecilio; Kowalski, Andrew S.; Perez-Priego, Oscar; Domingo, Francisco

    2015-04-01

    Drylands occupy 47.2% of the global terrestrial area and are key ecosystems that significantly determine the inter-annual variability of the global carbon balance. However, it is still necessary to delve into the functional behavior of arid and semiarid ecosystems due to the complexity of drivers and interactions between underpinning processes (whether biological or abiotic) that modulate net ecosystem CO2 exchange (NEE). In this context, water inputs are crucial to biological organisms survival in arid ecosystems and frequently arrive via rain events that are commonly stochastic and unpredictable (i.e. precipitation pulses) and strongly control arid land ecosystem structure and function. The eddy covariance technique can be used to investigate the effect of precipitation pulses on NEE, but provide limited understanding of what exactly happens after a rain event. The chief reasons are that, firstly, we cannot measure separately autotrophic and heterotrophic components, and secondly, the partitioning techniques widely utilized to separate Gross Primary Production and Total Ecosystem Respiration, do not work properly in these water-limited ecosystems, resulting in biased estimations of plant and soil processes. Consequently, it is essential to combine eddy covariance measurements with other techniques to disentangle the different biological processes composing NEE that are activated by a precipitation pulse. Accordingly, the main objectives of this work were: (i) to quantify the contribution of precipitation pulse events to annual NEE using the eddy covariance technique in a semiarid steppe located in Almería (Spain), and (ii) to simulate a realistic precipitation pulse in order to understand its effect on the ecosystem, soil and plant CO2 exchanges by using a transitory-state closed canopy chamber, soil respiration chambers and continuous monitoring CO2 sensors inserted in the subsoil. Preliminary results showed, as expected, a delay between soil and plant

  19. Modeling net ecosystem carbon exchange of alpine grasslands with a satellite-driven model.

    PubMed

    Yan, Wei; Hu, Zhongmin; Zhao, Yuping; Zhang, Xianzhou; Fan, Yuzhi; Shi, Peili; He, Yongtao; Yu, Guirui; Li, Yingnian

    2015-01-01

    Estimate of net ecosystem carbon exchange (NEE) between the atmosphere and terrestrial ecosystems, the balance of gross primary productivity (GPP) and ecosystem respiration (Reco) has significant importance for studying the regional and global carbon cycles. Using models driven by satellite data and climatic data is a promising approach to estimate NEE at regional scales. For this purpose, we proposed a semi-empirical model to estimate NEE in this study. In our model, the component GPP was estimated with a light response curve of a rectangular hyperbola. The component Reco was estimated with an exponential function of soil temperature. To test the feasibility of applying our model at regional scales, the temporal variations in the model parameters derived from NEE observations in an alpine grassland ecosystem on Tibetan Plateau were investigated. The results indicated that all the inverted parameters exhibit apparent seasonality, which is in accordance with air temperature and canopy phenology. In addition, all the parameters have significant correlations with the remote sensed vegetation indexes or environment temperature. With parameters estimated with these correlations, the model illustrated fair accuracy both in the validation years and at another alpine grassland ecosystem on Tibetan Plateau. Our results also indicated that the model prediction was less accurate in drought years, implying that soil moisture is an important factor affecting the model performance. Incorporating soil water content into the model would be a critical step for the improvement of the model. PMID:25849325

  20. Modeling Net Ecosystem Carbon Exchange of Alpine Grasslands with a Satellite-Driven Model

    PubMed Central

    Zhao, Yuping; Zhang, Xianzhou; Fan, Yuzhi; Shi, Peili; He, Yongtao; Yu, Guirui; Li, Yingnian

    2015-01-01

    Estimate of net ecosystem carbon exchange (NEE) between the atmosphere and terrestrial ecosystems, the balance of gross primary productivity (GPP) and ecosystem respiration (Reco) has significant importance for studying the regional and global carbon cycles. Using models driven by satellite data and climatic data is a promising approach to estimate NEE at regional scales. For this purpose, we proposed a semi-empirical model to estimate NEE in this study. In our model, the component GPP was estimated with a light response curve of a rectangular hyperbola. The component Reco was estimated with an exponential function of soil temperature. To test the feasibility of applying our model at regional scales, the temporal variations in the model parameters derived from NEE observations in an alpine grassland ecosystem on Tibetan Plateau were investigated. The results indicated that all the inverted parameters exhibit apparent seasonality, which is in accordance with air temperature and canopy phenology. In addition, all the parameters have significant correlations with the remote sensed vegetation indexes or environment temperature. With parameters estimated with these correlations, the model illustrated fair accuracy both in the validation years and at another alpine grassland ecosystem on Tibetan Plateau. Our results also indicated that the model prediction was less accurate in drought years, implying that soil moisture is an important factor affecting the model performance. Incorporating soil water content into the model would be a critical step for the improvement of the model. PMID:25849325

  1. Modeling net ecosystem carbon exchange of alpine grasslands with a satellite-driven model.

    PubMed

    Yan, Wei; Hu, Zhongmin; Zhao, Yuping; Zhang, Xianzhou; Fan, Yuzhi; Shi, Peili; He, Yongtao; Yu, Guirui; Li, Yingnian

    2015-01-01

    Estimate of net ecosystem carbon exchange (NEE) between the atmosphere and terrestrial ecosystems, the balance of gross primary productivity (GPP) and ecosystem respiration (Reco) has significant importance for studying the regional and global carbon cycles. Using models driven by satellite data and climatic data is a promising approach to estimate NEE at regional scales. For this purpose, we proposed a semi-empirical model to estimate NEE in this study. In our model, the component GPP was estimated with a light response curve of a rectangular hyperbola. The component Reco was estimated with an exponential function of soil temperature. To test the feasibility of applying our model at regional scales, the temporal variations in the model parameters derived from NEE observations in an alpine grassland ecosystem on Tibetan Plateau were investigated. The results indicated that all the inverted parameters exhibit apparent seasonality, which is in accordance with air temperature and canopy phenology. In addition, all the parameters have significant correlations with the remote sensed vegetation indexes or environment temperature. With parameters estimated with these correlations, the model illustrated fair accuracy both in the validation years and at another alpine grassland ecosystem on Tibetan Plateau. Our results also indicated that the model prediction was less accurate in drought years, implying that soil moisture is an important factor affecting the model performance. Incorporating soil water content into the model would be a critical step for the improvement of the model.

  2. Climatic regulation of seasonal and inter-annual variability in net ecosystem exchange of CO2 on rangelands

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Net ecosystem exchange of CO2 (NEE) from terrestrial ecosystems varies seasonally and inter-annually because of temporal variation in climate. If we are predict climate-caused variation in NEE, we must understand how climatic variation influences NEE and its components, CO2 uptake and CO2 loss. ...

  3. Seasonal variations of net CO2 exchange in European Arctic ecosystems

    NASA Astrophysics Data System (ADS)

    Laurila, T.; Soegaard, H.; Lloyd, C. R.; Aurela, M.; Tuovinen, J.-P.; Nordstroem, C.

    The carbon dioxide exchange in arctic and subarctic terrestrial ecosystems has been measured using the eddy-covariance method at sites representing the latitudinal and longitudinal extremes of the European Arctic sea areas as part of the Land Arctic Physical Processes (LAPP) project. The sites include two fen (Kaamanen and Kevo) and one mountain birch ecosystems in subarctic northern Finland (69°N) fen, heathland, and snowbed willow ecosystems in northeastern Greenland (74°N) and a polar semidesert site in Svalbard (79°N). The measurement results, which are given as weekly average diurnal cycles, show the striking seasonal development of the net CO2 fluxes. The seasonal periods important for the net CO2 fluxes, i.e. winter, thaw, pre-leaf, summer, and autumn can be identified from measurements of the physical environment, such as temperature, albedo, and greenness. During the late winter period continuous efflux is observed at the permafrost-free Kaamanen site. At the permafrost sites, efflux begins during the thaw period, which lasts about 3-5 weeks, in contrast to the Kaamanen site where efflux continues at the same rate as during the winter. Seasonal efflux maximum is during the pre-leaf period, which lasts about 2-5 weeks. The summer period lasts 6 weeks in NE Greenland but 10-14 weeks in northern Finland. During a high summer week, the mountain birch ecosystem had the highest gross photosynthetic capacity, GPmax, followed by the fen ecosystems. The polar semidesert ecosystem had the lowest GPmax. By the middle of August, noon uptake fluxes start to decrease as the solar elevation angle decreases and senescence begins within the vascular plants. At the end of the autumn period, which lasts 2-5 weeks, topsoil begins to freeze at the end of August in Svalbard; at the end of September at sites in eastern Greenland; and one month later at sites in northern Finland.

  4. Carbon exchange between ecosystems and atmosphere in the Czech Republic is affected by climate factors.

    PubMed

    Marek, Michal V; Janouš, Dalibor; Taufarová, Klára; Havránková, Kateřina; Pavelka, Marian; Kaplan, Věroslav; Marková, Irena

    2011-05-01

    By comparing five ecosystem types in the Czech Republic over several years, we recorded the highest carbon sequestration potential in an evergreen Norway spruce forest (100%) and an agroecosystem (65%), followed by European beech forest (25%) and a wetland ecosystem (20%). Because of a massive ecosystem respiration, the final carbon gain of the grassland was negative. Climate was shown to be an important factor of carbon uptake by ecosystems: by varying the growing season length (a 22-d longer season in 2005 than in 2007 increased carbon sink by 13%) or by the effect of short- term synoptic situations (e.g. summer hot and dry days reduced net carbon storage by 58% relative to hot and wet days). Carbon uptake is strongly affected by the ontogeny and a production strategy which is demonstrated by the comparison of seasonal course of carbon uptake between coniferous (Norway spruce) and deciduous (European beech) stands.

  5. Modelling Net Ecosystem Exchange and LUE in Mediterranean Oak Forest by Satellite Remote Sensing

    NASA Astrophysics Data System (ADS)

    Tramontana, Gianluca; Papale, Dario

    2011-01-01

    Net Ecosystem Exchange (NEE) is a key factor defining CO2 fluxes between atmosphere and ecosystems and CO2 flux measurements at individual eddy covariance flux sites provide valuable information on the seasonal dynamics of NEE. In this work, we developed and validated a satellite-based Light Use Efficiency (LUE) model to estimate NEE for a typical oak forest located in Central Italy. Satellite data were acquired by Moderate resolution spectroradiometer (MODIS) sensor installed on board Terra satellite. Oak forest studied is coppice managed; 2 eddy-covariance towers are located inside two forests parcels having different ages. We proposed to estimate LUE like function of mean brightness temperature, Normalized Difference Water Index (NDWI) and Photochemical Reflectance Index (PRI). Empirical multiple regressions models (MR) and Artificial Neural Network (ANN) were parameterized and validated using subset of data acquired by both the stations. Daily, 8-day and monthly temporal resolutions were investigated and accuracy estimation in space and time was performed.

  6. Structure, function and evolution of the gas exchangers: comparative perspectives

    PubMed Central

    Maina, JN

    2002-01-01

    Over the evolutionary continuum, animals have faced similar fundamental challenges of acquiring molecular oxygen for aerobic metabolism. Under limitations and constraints imposed by factors such as phylogeny, behaviour, body size and environment, they have responded differently in founding optimal respiratory structures. A quintessence of the aphorism that ‘necessity is the mother of invention’, gas exchangers have been inaugurated through stiff cost–benefit analyses that have evoked transaction of trade-offs and compromises. Cogent structural–functional correlations occur in constructions of gas exchangers: within and between taxa, morphological complexity and respiratory efficiency increase with metabolic capacities and oxygen needs. Highly active, small endotherms have relatively better-refined gas exchangers compared with large, inactive ectotherms. Respiratory structures have developed from the plain cell membrane of the primeval prokaryotic unicells to complex multifunctional ones ofthe modern Metazoa. Regarding the respiratory medium used to extract oxygen from, animal life has had only two choices – water or air – within the biological range of temperature and pressure the only naturally occurring respirable fluids. In rarer cases, certain animalshave adapted to using both media. Gills (evaginated gas exchangers) are the primordial respiratory organs: they are the archetypal water breathing organs. Lungs (invaginated gas exchangers) are the model air breathing organs. Bimodal (transitional) breathers occupy the water–air interface. Presentation and exposure of external (water/air) and internal (haemolymph/blood) respiratory media, features determined by geometric arrangement of the conduits, are important features for gas exchange efficiency: counter-current, cross-current, uniform pool and infinite pool designs have variably developed. PMID:12430953

  7. Structure, function and evolution of the gas exchangers: comparative perspectives.

    PubMed

    Maina, J N

    2002-10-01

    Over the evolutionary continuum, animals have faced similar fundamental challenges of acquiring molecular oxygen for aerobic metabolism. Under limitations and constraints imposed by factors such as phylogeny, behaviour, body size and environment, they have responded differently in founding optimal respiratory structures. A quintessence of the aphorism that 'necessity is the mother of invention', gas exchangers have been inaugurated through stiff cost-benefit analyses that have evoked transaction of trade-offs and compromises. Cogent structural-functional correlations occur in constructions of gas exchangers: within and between taxa, morphological complexity and respiratory efficiency increase with metabolic capacities and oxygen needs. Highly active, small endotherms have relatively better-refined gas exchangers compared with large, inactive ectotherms. Respiratory structures have developed from the plain cell membrane of the primeval prokaryotic unicells to complex multifunctional ones of the modern Metazoa. Regarding the respiratory medium used to extract oxygen from, animal life has had only two choices--water or air--within the biological range of temperature and pressure the only naturally occurring respirable fluids. In rarer cases, certain animals have adapted to using both media. Gills (evaginated gas exchangers) are the primordial respiratory organs: they are the archetypal water breathing organs. Lungs (invaginated gas exchangers) are the model air breathing organs. Bimodal (transitional) breathers occupy the water-air interface. Presentation and exposure of external (water/air) and internal (haemolymph/blood) respiratory media, features determined by geometric arrangement of the conduits, are important features for gas exchange efficiency: counter-current, cross-current, uniform pool and infinite pool designs have variably developed. PMID:12430953

  8. Estimation of Net Ecosystem Carbon Exchange for the Conterminous United States by Combining MODIS and AmeriFlux Data 1961

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Eddy covariance flux towers provide continuous measurements of net ecosystem carbon exchange (NEE) for a wide range of climate and biome types. However, these measurements only represent the carbon fluxes at the scale of the tower footprint. To quantify the net exchange of carbon dioxide between the...

  9. Uncertainty analysis of gross primary production partitioned from net ecosystem exchange measurements

    NASA Astrophysics Data System (ADS)

    Raj, Rahul; Hamm, Nicholas Alexander Samuel; van der Tol, Christiaan; Stein, Alfred

    2016-03-01

    Gross primary production (GPP) can be separated from flux tower measurements of net ecosystem exchange (NEE) of CO2. This is used increasingly to validate process-based simulators and remote-sensing-derived estimates of simulated GPP at various time steps. Proper validation includes the uncertainty associated with this separation. In this study, uncertainty assessment was done in a Bayesian framework. It was applied to data from the Speulderbos forest site, The Netherlands. We estimated the uncertainty in GPP at half-hourly time steps, using a non-rectangular hyperbola (NRH) model for its separation from the flux tower measurements. The NRH model provides a robust empirical relationship between radiation and GPP. It includes the degree of curvature of the light response curve, radiation and temperature. Parameters of the NRH model were fitted to the measured NEE data for every 10-day period during the growing season (April to October) in 2009. We defined the prior distribution of each NRH parameter and used Markov chain Monte Carlo (MCMC) simulation to estimate the uncertainty in the separated GPP from the posterior distribution at half-hourly time steps. This time series also allowed us to estimate the uncertainty at daily time steps. We compared the informative with the non-informative prior distributions of the NRH parameters and found that both choices produced similar posterior distributions of GPP. This will provide relevant and important information for the validation of process-based simulators in the future. Furthermore, the obtained posterior distributions of NEE and the NRH parameters are of interest for a range of applications.

  10. Drivers of inter-annual variability in Net Ecosystem Exchange in a semi-arid savanna ecosystem, South Africa

    NASA Astrophysics Data System (ADS)

    Archibald, S. A.; Kirton, A.; van der Merwe, M. R.; Scholes, R. J.; Williams, C. A.; Hanan, N.

    2009-02-01

    Inter-annual variability in primary production and ecosystem respiration was explored using eddy-covariance data at a semi-arid savanna site in the Kruger Park, South Africa. New methods of extrapolating night-time respiration to the entire day and filling gaps in eddy-covariance data in semi-arid systems were developed. Net ecosystem exchange (NEE) in these systems occurs as pulses associated with rainfall events, a pattern not well-represented in current standard gap-filling procedures developed primarily for temperate flux sites. They furthermore do not take into account the decrease in respiration at high soil temperatures. An artificial neural network (ANN) model incorporating these features predicted measured fluxes accurately (MAE 0.42 gC/m2/day), and was able to represent the seasonal patterns of photosynthesis and respiration at the site. The amount of green leaf area (indexed using satellite-derived estimates of fractional interception of photosynthetically active radiation fAPAR), and the timing and magnitude of rainfall events, were the two most important predictors used in the ANN model. These drivers were also identified by multiple linear regressions (MLR), with strong interactive effects. The annual integral of the filled NEE data was found to range from -138 to +155 g C/m2/y over the 5 year eddy covariance measurement period. When applied to a 25 year time series of meteorological data, the ANN model predicts an annual mean NEE of 75(±105) g C/m2/y. The main correlates of this inter-annual variability were found to be variation in the amount of absorbed photosynthetically active radiation (APAR), length of the growing season, and number of days in the year when moisture was available in the soil.

  11. Drivers of interannual variability in Net Ecosystem Exchange in a semi-arid savanna ecosystem, South Africa

    NASA Astrophysics Data System (ADS)

    Archibald, S.; Kirton, A.; van der Merwe, M.; Scholes, R. J.; Williams, C. A.; Hanan, N.

    2008-08-01

    Inter-annual variability in primary production and ecosystem respiration was explored using eddy-covariance data at a semi-arid savanna site in the Kruger Park, South Africa. New methods of extrapolating night-time respiration to the entire day and filling gaps in eddy-covariance data in semi-arid systems were developed. Net ecosystem exchange (NEE) in these systems occurs as pulses associated with rainfall events, a pattern not well-represented in current standard gap-filling procedures developed primarily for temperate flux sites. They furthermore do not take into account the decrease in respiration at high soil temperatures. An artificial neural network (ANN) model incorporating these features predicted measured fluxes accurately (MAE 0.42 g C/m2/day), and was able to represent the seasonal patterns of photosynthesis and respiration at the site. The amount of green leaf area (indexed using satellite-derived estimates of fractional interception of photosynthetically active radiation fAPAR), and the timing and magnitude of rainfall events, were the two most important predictors used in the ANN model. These drivers were also identified by multiple linear models (MLR), with strong interactive effects. The annual integral of the filled NEE data was found to range from -138 to +155 g C/m2/y over the 5 year eddy covariance measurement period. When applied to a 25 year time series of meteorological data, the ANN model predicts an annual mean NEE of 75 (±105) g C/m2/y. The main correlates of this inter-annual variability were found to be variation in the amount of absorbed photosynthetically active radiation (APAR), length of the growing season, and number of days in the year when moisture was available in the soil.

  12. Spatial Distribution of Hydrologic Ecosystem Service Estimates: Comparing Two Models

    NASA Astrophysics Data System (ADS)

    Dennedy-Frank, P. J.; Ghile, Y.; Gorelick, S.; Logsdon, R. A.; Chaubey, I.; Ziv, G.

    2014-12-01

    We compare estimates of the spatial distribution of water quantity provided (annual water yield) from two ecohydrologic models: the widely-used Soil and Water Assessment Tool (SWAT) and the much simpler water models from the Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) toolbox. These two models differ significantly in terms of complexity, timescale of operation, effort, and data required for calibration, and so are often used in different management contexts. We compare two study sites in the US: the Wildcat Creek Watershed (2083 km2) in Indiana, a largely agricultural watershed in a cold aseasonal climate, and the Upper Upatoi Creek Watershed (876 km2) in Georgia, a mostly forested watershed in a temperate aseasonal climate. We evaluate (1) quantitative estimates of water yield to explore how well each model represents this process, and (2) ranked estimates of water yield to indicate how useful the models are for management purposes where other social and financial factors may play significant roles. The SWAT and InVEST models provide very similar estimates of the water yield of individual subbasins in the Wildcat Creek Watershed (Pearson r = 0.92, slope = 0.89), and a similar ranking of the relative water yield of those subbasins (Spearman r = 0.86). However, the two models provide relatively different estimates of the water yield of individual subbasins in the Upper Upatoi Watershed (Pearson r = 0.25, slope = 0.14), and very different ranking of the relative water yield of those subbasins (Spearman r = -0.10). The Upper Upatoi watershed has a significant baseflow contribution due to its sandy, well-drained soils. InVEST's simple seasonality terms, which assume no change in storage over the time of the model run, may not accurately estimate water yield processes when baseflow provides such a strong contribution. Our results suggest that InVEST users take care in situations where storage changes are significant.

  13. Estimation of Ecosystem Parameters of the Community Land Model with DREAM: Evaluation of the Potential for Upscaling Net Ecosystem Exchange

    NASA Astrophysics Data System (ADS)

    Hendricks Franssen, H. J.; Post, H.; Vrugt, J. A.; Fox, A. M.; Baatz, R.; Kumbhar, P.; Vereecken, H.

    2015-12-01

    Estimation of net ecosystem exchange (NEE) by land surface models is strongly affected by uncertain ecosystem parameters and initial conditions. A possible approach is the estimation of plant functional type (PFT) specific parameters for sites with measurement data like NEE and application of the parameters at other sites with the same PFT and no measurements. This upscaling strategy was evaluated in this work for sites in Germany and France. Ecosystem parameters and initial conditions were estimated with NEE-time series of one year length, or a time series of only one season. The DREAM(zs) algorithm was used for the estimation of parameters and initial conditions. DREAM(zs) is not limited to Gaussian distributions and can condition to large time series of measurement data simultaneously. DREAM(zs) was used in combination with the Community Land Model (CLM) v4.5. Parameter estimates were evaluated by model predictions at the same site for an independent verification period. In addition, the parameter estimates were evaluated at other, independent sites situated >500km away with the same PFT. The main conclusions are: i) simulations with estimated parameters reproduced better the NEE measurement data in the verification periods, including the annual NEE-sum (23% improvement), annual NEE-cycle and average diurnal NEE course (error reduction by factor 1,6); ii) estimated parameters based on seasonal NEE-data outperformed estimated parameters based on yearly data; iii) in addition, those seasonal parameters were often also significantly different from their yearly equivalents; iv) estimated parameters were significantly different if initial conditions were estimated together with the parameters. We conclude that estimated PFT-specific parameters improve land surface model predictions significantly at independent verification sites and for independent verification periods so that their potential for upscaling is demonstrated. However, simulation results also indicate

  14. Comparative analysis of compact heat exchangers for application as the intermediate heat exchanger for advanced nuclear reactors

    SciTech Connect

    Bartel, N.; Chen, M.; Utgikar, V. P.; Sun, X.; Kim, I. -H.; Christensen, R.; Sabharwall, P.

    2015-04-04

    A comparative evaluation of alternative compact heat exchanger designs for use as the intermediate heat exchanger in advanced nuclear reactor systems is presented in this article. Candidate heat exchangers investigated included the Printed circuit heat exchanger (PCHE) and offset strip-fin heat exchanger (OSFHE). Both these heat exchangers offer high surface area to volume ratio (a measure of compactness [m2/m3]), high thermal effectiveness, and overall low pressure drop. Helium–helium heat exchanger designs for different heat exchanger types were developed for a 600 MW thermal advanced nuclear reactor. The wavy channel PCHE with a 15° pitch angle was found to offer optimum combination of heat transfer coefficient, compactness and pressure drop as compared to other alternatives. The principles of the comparative analysis presented here will be useful for heat exchanger evaluations in other applications as well.

  15. Comparative analysis of compact heat exchangers for application as the intermediate heat exchanger for advanced nuclear reactors

    DOE PAGES

    Bartel, N.; Chen, M.; Utgikar, V. P.; Sun, X.; Kim, I. -H.; Christensen, R.; Sabharwall, P.

    2015-04-04

    A comparative evaluation of alternative compact heat exchanger designs for use as the intermediate heat exchanger in advanced nuclear reactor systems is presented in this article. Candidate heat exchangers investigated included the Printed circuit heat exchanger (PCHE) and offset strip-fin heat exchanger (OSFHE). Both these heat exchangers offer high surface area to volume ratio (a measure of compactness [m2/m3]), high thermal effectiveness, and overall low pressure drop. Helium–helium heat exchanger designs for different heat exchanger types were developed for a 600 MW thermal advanced nuclear reactor. The wavy channel PCHE with a 15° pitch angle was found to offer optimummore » combination of heat transfer coefficient, compactness and pressure drop as compared to other alternatives. The principles of the comparative analysis presented here will be useful for heat exchanger evaluations in other applications as well.« less

  16. Multivariate Comparative Analysis of Stock Exchanges: The European Perspective

    NASA Astrophysics Data System (ADS)

    Koralun-Bereźnicka, Julia

    The aim of the research is to perform a multivariate comparative analysis of 20 European stock exchanges in order to identify the main similarities between the objects. Due to the convergence process of capital markets in Europe the similarities between stock exchanges could be expected to increase over time. The research is meant to show whether and how these similarities change. Consequently, the distances between clusters of similar stock exchanges should become less significant, which the analysis also aims at verifying. The basis of comparison is a set of 48 monthly variables from the period January, 2003 to December, 2006. The variables are classified into three categories: size of the market, equity trading and bonds. The paper aims at identifying the clusters of alike stock exchanges and at finding the characteristic features of each of the distinguished groups. The obtained categorization to some extent corresponds with the division of the European Union into “new” and “old” member countries. Clustering method, performed for each quarter separately, also reveals that the classification is fairly stable in time. The factor analysis, which was carried out to reduce the number of variables, reveals three major factors behind the data, which are related with the earlier mentioned categories of variables.

  17. Post-Fire Evapotranspiration and Net Ecosystem Exchange over A Semi-Arid Grassland in Arizona

    NASA Astrophysics Data System (ADS)

    Krishnan, P.; Meyers, T. P.; Heuer, M.

    2015-12-01

    The seasonal and interannual variability of evapotranspiration (E) and net ecosystem exchange (NEE) following a fire disturbance over a semi -arid grassland located on the Audubon Research Ranch in south western Arizona (31.5907N, 110.5104W, elevation 1496 m), USA, and their relationships to environmental variables were examined using continuous measurements of water vapour and CO2 fluxes made from first week of June 2002 to 2009 using the eddy covariance technique. The research ranch was established in 1969 as an ecological research preserve and it is now one of the largest ungrazed, privately managed grassland sites in Arizona. A wild fire occurred in April - May 2002, and burned all the standing vegetation and litter on in research ranch (~38,000 acres) including 500 acres of grassland. The mean annual temperature and precipitation (P) at this site were ~16 deg C and ~370 mm, respectively. More than 60% of the annual P was received during the North American monsoon period (July-September) with the lowest annual P in the drought years of 2004 and 2009. Drastic changes in albedo, vegetation growth and evapotranspiration occurred following the onset of the monsoon season in July. The ecosystem was mostly a carbon sink during monsoon period. Daily total evapotranspiration during July-August increased from 2 mm d-1 in 2002 to >3 mm d-1 in 2007. The mean annual E over the site was during 2003 -2009 was 352 ±75 mm. With the onset of monsoon the ecosystem turned to carbon sink in 2002, with daily total net ecosystem exchange (NEE) varying up to ~<-2 g C m-2, by mid-July to August 2002. It was followed by one of the driest monsoon period on the record (2003) with <50% of normal July-September P. Because of this, the recovery of the ecosystem was delayed. During 2002-2009, the ecosystem was mostly a carbon source except in 2006 an year with high growing season Normalized-difference vegetation index, longest monsoon growing season and the highest annual and July

  18. Biophysical controls on net ecosystem CO2 exchange over a semiarid shrubland in northwest China

    NASA Astrophysics Data System (ADS)

    Jia, X.; Zha, T. S.; Wu, B.; Zhang, Y. Q.; Gong, J. N.; Qin, S. G.; Chen, G. P.; Kellomäki, S.; Peltola, H.

    2014-03-01

    The carbon (C) cycling in semiarid and arid areas remains largely unexplored, despite the wide distribution of drylands globally. Rehabilitation practices have been carried out in many desertified areas, but information on the C sequestration potential of recovering vegetation is still largely lacking. Using the eddy-covariance technique, we measured the net ecosystem CO2 exchange (NEE) over a recovering shrub ecosystem in northwest China throughout 2012 in order to (1) quantify NEE and its components, (2) examine the dependence of C fluxes on biophysical factors at multiple timescales. The annual budget showed a gross ecosystem productivity (GEP) of 456 ± 8 g C m-2 yr-1 and an ecosystem respiration (Re) of 379 ± 3 g C m-2 yr-1, resulting in a net C sink of 77 ± 7 g C m-2 yr-1. The maximum daily NEE, GEP and Re were -4.7, 6.8 and 3.3 g C m-2 day-1, respectively. Both the maximum C assimilation rate (i.e., at optimum light intensity) and the quantum yield varied strongly over the growing season, being higher in summer and lower in spring and autumn. At the half-hourly scale, water stress exerted a major control over daytime NEE, and interacted with heat stress and photoinhibition in constraining C fixation by the vegetation. Low soil moisture also reduced the temperature sensitivity of Re (Q10). At the synoptic scale, rain events triggered immediate pulses of C release from the ecosystem, followed by peaks of CO2 uptake 1-2 days later. Over the entire growing season, leaf area index accounted for 45 and 65% of the seasonal variation in NEE and GEP, respectively. There was a linear dependence of daily Re on GEP, with a slope of 0.34. These results highlight the role of abiotic stresses and their alleviation in regulating C cycling in the face of an increasing frequency and intensity of extreme climatic events.

  19. Partitioning of catchment water budget and its implications for ecosystem carbon exchange

    NASA Astrophysics Data System (ADS)

    Lee, D.; Kim, J.; Lee, K.-S.; Kim, S.

    2010-06-01

    Spatially averaged annual carbon budget is one of the key information needed to understand ecosystem response and feedback to climate change. Water availability is a primary constraint of carbon uptake in many ecosystems and therefore the estimation of ecosystem water use may serve as an alternative to quantify Gross Primary Productivity (GPP). To examine this concept, we estimated a long-term steady state water budget for the Han River basin (~26 000 km2) in Korea and examined its application for catchment scale carbon exchange. For this, the catchment scale evapotranspiration (ET) was derived from the long term precipitation (P) and discharge (Q) data. Then, using stable isotope data of P and Q along with other hydrometeorological information, ET was partitioned into evaporation from soil and water surfaces (ES), evaporation from intercepted rainfall (EI, and transpiration (T). ES was identified as a minor component of ET in the study areas regardless of the catchment scales. The annual T, estimated from ET after accounting for EI and ES for the Han River basin from 1966 to 2007, was 22~31% of annual P and the proportion decreased with increasing P. Assuming that T further constrains the catchment scale GPP in terms of water use efficiency (WUE), we examined the possibility of using T as a relative measure for the strength and temporal changes of carbon uptake capacity. The proposed relationship would provide a simple and practical way to assess the spatial distribution of ecosystem GPP, provided the WUE estimates in terms of GPP/T at ecosystem scale could be obtained. For carbon and water tracking toward a sustainable Asia, ascertaining such a spatiotemporally representative WUE and their variability is a requisite facing the flux measurement and modeling communities.

  20. Representing Sub-Plot Canopy Heterogeneity Improves Model Prediction of Net Ecosystem Exchange in a Mixed-Deciduous Forest

    NASA Astrophysics Data System (ADS)

    Frasson, R. P. M.; Bohrer, G.; Medvigy, D.; Vogel, C. S.; Gough, C. M.; Curtis, P.

    2014-12-01

    Canopy density and composition may vary within an eddy covariance tower's footprint in response to small-scale topographic features, biotic interactions such as herbivory, local disturbances, etc. We are investigating how different representations of canopy heterogeneity influence predictions of net ecosystem CO2 exchange in a mixed-deciduous forest by an age/plant functional type structured ecosystem model. Our study area is located at the University of Michigan Biological Station (UMBS) where two eddy covariance towers and periodic tree censuses provide a rich long-term record of ecosystem structure, weather, and carbon uptake. Meteorological measurements collected at the US-UMB AmeriFlux tower served to force, optimize, and evaluate the Ecosystem Demography model version 2 (ED2), while tree census information was used to initialize ED2. To test the influence that representing canopy heterogeneity has on model-tower agreement, we ran a set of ED2 site-level simulations with an increasing number of sub-grid patches. The first simulation, which we call 'aggregated', had one large patch explicitly containing all trees. The aggregated canopy represents a case where different size cohorts of each plant functional type are distributed homogeneously throughout the plot with uniform stem density. Six other simulations represented patch-level canopies with varying degrees of heterogeneity, ranging from 5 to 64 sub-plot patches; each patch represented from one to several of the 0.1 ha tree census plots. A preliminary comparison of the aggregated and the 20-plot heterogeneous simulations showed that including patch-level heterogeneity in the canopy description improved model prediction quality. For example, compared to the single-patch, aggregated simulation, including 20 sub-plot patches improved model bias in the estimated accumulated 5-year net ecosystem exchange from 17% to 5%, which is smaller than our tower observation uncertainty. As a result of this study, we will

  1. Sensitivity analysis of a model of CO2 exchange in tundra ecosystems by the adjoint method

    NASA Technical Reports Server (NTRS)

    Waelbroek, C.; Louis, J.-F.

    1995-01-01

    A model of net primary production (NPP), decomposition, and nitrogen cycling in tundra ecosystems has been developed. The adjoint technique is used to study the sensitivity of the computed annual net CO2 flux to perturbation in initial conditions, climatic inputs, and model's main parameters describing current seasonal CO2 exchange in wet sedge tundra at Barrow, Alaska. The results show that net CO2 flux is most sensitive to parameters characterizing litter chemical composition and more sensitive to decomposition parameters than to NPP parameters. This underlines the fact that in nutrient-limited ecosystems, decomposition drives net CO2 exchange by controlling mineralization of main nutrients. The results also indicate that the short-term (1 year) response of wet sedge tundra to CO2-induced warming is a significant increase in CO2 emission, creating a positive feedback to atmosphreic CO2 accumulation. However, a cloudiness increase during the same year can severely alter this response and lead to either a slight decrease or a strong increase in emitted CO2, depending on its exact timing. These results demonstrate that the adjoint method is well suited to study systems encountering regime changes, as a single run of the adjoint model provides sensitivities of the net CO2 flux to perturbations in all parameters and variables at any time of the year. Moreover, it is shown that large errors due to the presence of thresholds can be avoided by first delimiting the range of applicability of the adjoint results.

  2. Sensitivity analysis of a model of CO2 exchange in tundra ecosystems by the adjoint method

    SciTech Connect

    Waelbroek, C.; Louis, J.F. |

    1995-02-01

    A model of net primary production (NPP), decomposition, and nitrogen cycling in tundra ecosystems has been developed. The adjoint technique is used to study the sensitivity of the computed annual net CO2 flux to perturbation in initial conditions, climatic inputs, and model`s main parameters describing current seasonal CO2 exchange in wet sedge tundra at Barrow, Alaska. The results show that net CO2 flux is most sensitive to parameters characterizing litter chemical composition and more sensitive to decomposition parameters than to NPP parameters. This underlines the fact that in nutrient-limited ecosystems, decomposition drives net CO2 exchange by controlling mineralization of main nutrients. The results also indicate that the short-term (1 year) response of wet sedge tundra to CO2-induced warming is a significant increase in CO2 emission, creating a positive feedback to atmosphreic CO2 accumulation. However, a cloudiness increase during the same year can severely alter this response and lead to either a slight decrease or a strong increase in emitted CO2, depending on its exact timing. These results demonstrate that the adjoint method is well suited to study systems encountering regime changes, as a single run of the adjoint model provides sensitivities of the net CO2 flux to perturbations in all parameters and variables at any time of the year. Moreover, it is shown that large errors due to the presence of thresholds can be avoided by first delimiting the range of applicability of the adjoint results.

  3. Pan-Arctic modelling of net ecosystem exchange of CO2

    PubMed Central

    Shaver, G. R.; Rastetter, E. B.; Salmon, V.; Street, L. E.; van de Weg, M. J.; Rocha, A.; van Wijk, M. T.; Williams, M.

    2013-01-01

    Net ecosystem exchange (NEE) of C varies greatly among Arctic ecosystems. Here, we show that approximately 75 per cent of this variation can be accounted for in a single regression model that predicts NEE as a function of leaf area index (LAI), air temperature and photosynthetically active radiation (PAR). The model was developed in concert with a survey of the light response of NEE in Arctic and subarctic tundras in Alaska, Greenland, Svalbard and Sweden. Model parametrizations based on data collected in one part of the Arctic can be used to predict NEE in other parts of the Arctic with accuracy similar to that of predictions based on data collected in the same site where NEE is predicted. The principal requirement for the dataset is that it should contain a sufficiently wide range of measurements of NEE at both high and low values of LAI, air temperature and PAR, to properly constrain the estimates of model parameters. Canopy N content can also be substituted for leaf area in predicting NEE, with equal or greater accuracy, but substitution of soil temperature for air temperature does not improve predictions. Overall, the results suggest a remarkable convergence in regulation of NEE in diverse ecosystem types throughout the Arctic. PMID:23836790

  4. Autochamber measurements of Net Ecosystem (CO2) Exchange at a subarctic mire in Northern Sweden

    NASA Astrophysics Data System (ADS)

    Walthall, M.; Parker-Smith, X.; Lawrence, R. D.; Crill, P. M.

    2015-12-01

    Northern latitude wetlands (>~50°N) are characterized by cold and wet conditions that result in low decomposition rates for plant litter. This process promotes the sequestration of carbon (C) in the form of organic matter (i.e. peat) and the formation of widespread peatands. Peatlands, particularly in the Northern Hemisphere, have accumulated C by removing atmospheric CO2 for approximately the past 10,000 years. Historically, peatlands represent a net C sink; however, increases in the global average temperature could alter peatlands ability to store carbon. With a warming climate and permafrost thaw, the pool of once stable soil organic C available for decomposition is increasing. Like all terrestrial ecosystems, a number of environmental factors (e.g. peat temperature and vegetation) play important roles in governing the fate of C in peatlands. Projected climate change is expected to affect these regulating factors. Subarctic peatlands in zones of discontinuous permafrost are experiencing widespread environmental changes due to climate warming. In this study, we present net ecosystem (CO2) exchange and δ13C-CO2 data from Stordalen Mire in northern Sweden (68°22'N, 19°03'E). Measurements were made using a quantum cascade laser spectrometer connected to automatic chambers placed in the three predominant ecosystems (a dry, elevated Palsa; an intermediate thaw regime dominated by Sphagnum spp. and; a completely thawed, inundated site dominated by Eriophorum angustifolium). Team was mentored by Mr. Ryan Lawrence from The University of New Hampshire.

  5. Comparative assessment of the methods for exchangeable acidity measuring

    NASA Astrophysics Data System (ADS)

    Vanchikova, E. V.; Shamrikova, E. V.; Bespyatykh, N. V.; Zaboeva, G. A.; Bobrova, Yu. I.; Kyz"yurova, E. V.; Grishchenko, N. V.

    2016-05-01

    A comparative assessment of the results of measuring the exchangeable acidity and its components by different methods was performed for the main mineral genetic horizons of texturally-differentiated gleyed and nongleyed soddy-podzolic and gley-podzolic soils of the Komi Republic. It was shown that the contents of all the components of exchangeable soil acidity determined by the Russian method (with potassium chloride solution as extractant, c(KCl) = 1 mol/dm3) were significantly higher than those obtained by the international method (with barium chloride solution as extractant, c(BaCl2) = 0.1 mol/dm3). The error of the estimate of the concentration of H+ ions extracted with barium chloride solution equaled 100%, and this allowed only qualitative description of this component of the soil acidity. In the case of the extraction with potassium chloride, the error of measurements was 50%. It was also shown that the use of potentiometric titration suggested by the Russian method overestimates the results of soil acidity measurement caused by the exchangeable metal ions (Al(III), Fe(III), and Mn(II)) in comparison with the atomic emission method.

  6. Uncertainties in the Net Ecosystem Exchange of Europe and North America

    NASA Astrophysics Data System (ADS)

    Tomelleri, E.; Migliavacca, M.; Carvalhais, N.; Reichstein, M.

    2008-12-01

    Here present a thorough upscaling of carbon balance estimates from eddy covariance flux towers to Europe and North America with an estimate of uncertainties by means of model data integration techniques. Model parameter regionalization approaches aim to spatially discriminate ecosystem properties, embodying the concept that different parameters control different processes hence requiring different extrapolation strategies. In this perspective, the consideration of a multivariate space for model parameter extrapolation strategies should rely on spatially distributed variables, supporting the identification of upscaling regions. This target can be partly achieved by the use of variables derived from remote sensing as model drivers. These act as weights for the flux variability in the upscaling exercise, by adding information about the spatial structure in the land surface exchanges. In this perspective, the quantification of the FLUXNET representativeness and heterogeneity is fundamental to assess the upscaling potential of both model parameters and observed processes. These issues can be better addressed for geographical regions such as Europe or North America where FLUXNET, albeit confined to individual sites, is already gaining pseudo- spatial characteristics. We integrated eddy covariance measurements, partitioned into primary productivity and ecosystem respiration into the parameterization of a primary productivity empirical light-use efficiency model combined with a semi-empirical respiration model. We stratified the measurement sites per ecosystem type and climate classification. For the integration we adopted a Markov Chain Monte Carlo approach, which permitted us to estimate a posteriori joint probability functions of model parameters. These were used for extrapolating uncertainties of the regional carbon budgets for Europe and North America. For doing this, the Markovian Chains of model parameters from each site/year optimization were sub-sampled in such a

  7. A Constructed Freshwater Wetland Shows Signs of Declining Net Ecosystem Exchange

    NASA Astrophysics Data System (ADS)

    Anderson, F. E.; Bergamaschi, B. A.; Windham-Myers, L.; Byrd, K. B.; Drexler, J. Z.; Fujii, R.

    2014-12-01

    The USGS constructed a freshwater-wetland complex on Twitchell Island in the Sacramento-San Joaquin Delta (Delta), California, USA, in 1997 and maintained it until 2012 to investigate strategies for biomass accretion and reduction of oxidative soil loss. We studied an area of the wetland complex covered mainly by dense patches of hardstem bulrush (Schoenoplectus acutus) and cattails (Typha spp.), with smaller areas of floating and submerged vegetation, that was maintained at an average depth of 55 cm. Using eddy covariance measurements of carbon and energy fluxes, we found that the combination of water management and the region's Mediterranean climate created conditions where peak growing season daily means of net ecosystem exchange (NEE) reached -45 gCO2 m-2 d-1 and averaged around -30 gCO2 m-2 d-1 between 2002 through 2004. However, when measurements resumed in 2010, NEE rates were a fraction of the rates previously measured, approximately -6 gCO2 m-2 d-1. Interestingly, NEE rates in 2011 doubled compared to 2010 (-13 gCO2 m-2 d-1). Methane fluxes, collected in 2010 to assess a complete atmospheric carbon budget, were positive throughout the year, with daily mean flux values ranging from 50 to 300 mg CH4 m-2 d-1. As a result, methane flux reduced NEE values by approximately one-third, and when the global warming potential was considered, the wetland became a net global warming potential source. We found that carbon cycling in a constructed wetland is complex and can change over annual and decadal timescales. We investigated possible reasons for differences between flux measurements from 2002 to 2004 and those from 2010 and 2011: (1) changes in methodology, (2) differences in weather conditions, (3) differences in gross primary productivity relative to respiration rates, and (4) the amount of living plant tissue relative to brown accumulations of senesced plant litter. We hypothesize that large mats of senesced material within the flux footprint could have

  8. Comparing three methods of NEE-flux partitioning from the same grassland ecosystem: the 13C, 18O isotope approach and using simulated Ecosystem respiration

    NASA Astrophysics Data System (ADS)

    Siegwolf, R.; Bantelmann, E.; Saurer, M.; Eugster, W.; Buchmann, N.

    2007-12-01

    As a change in the global climate occurs with increasing temperatures, the Carbon exchange processes of terrestrial ecosystems will change as well. However, it is difficult to quantify the degree to what ecosystem respiration will change relative to the CO2 uptake by photosynthesis. To estimate the carbon sequestration potential of terrestrial vegetation cover it is essential to know both fluxes: ecosystem respiration and the carbon uptake by the vegetation cover. Therefore the net ecosystem exchange of CO2 (NEE) was measured with the eddy covariance method and separated into assimilation and respiration flux. We applied three different approaches, 1) the conventional method, applying the nighttime relationship between soil temperature and NEE for calculating the respiration flux during the day, 2) the use of stable carbon and 3) oxygen isotopes. We compared the results of the three partitioning exercises for a temperate grassland ecosystem in the pre-Alps of Switzerland for four days in June 2004. The assimilation flux derived with the conventional NEE partitioning approach, was best represented at low PAR and low temperatures, in the morning between 5 and 9 am. With increasing temperature and PAR the assimilation for the whole canopy was underestimated. For partitioning NEE via 18O approach, correlations of temperature and radiation with assimilation and respiration flux were significantly higher for the partitioning approach with 18O than for the 13C NEE partitioning. A sensitivity analysis showed the importance of an accurate determination of the equilibrium term θ between CO2 and leaf water δ18O for the NEE partitioning with 18O. For using 13C to partition NEE, the correct magnitude of the 13C fractionation and for the respiration term is essential. The analysis of the data showed that for low light and low morning temperatures the conventional method delivers reasonably good results. When the temperatures exceeded 21°C the isotope approach provided the

  9. The impact of land use on the net ecosystem CO2 exchanges in the West African Sudanian Savannas

    NASA Astrophysics Data System (ADS)

    Mauder, Matthias; Quansah, Emmanuel; Annor, Thompson; Balogun, Ahmed A.; Amekudzi, Leonard K.; Bliefernicht, Jan; Heinzeller, Dominikus; Kunstmann, Harald

    2016-04-01

    The land surface in West Africa has been considerably changed within the past decade due to various anthropogenic measures such as an increased agricultural activity. However, the impact of these land use changes on land-atmosphere exchange processes such as net ecosystems exchange is not well known for this highly vulnerable region. To tackle this problem, the effects of land use on the net ecosystem exchange of CO2 (NEE) along a transect of three contrasting ecosystems have been investigated on seasonal and annual time scales using the Eddy Covariance method. The ecosystems were grassland (GL), a mixture of fallow and cropland (CR) in the Upper East Region of Ghana, and a nature reserve (NR) near Pô in the Nahouri Province of Burkina Faso. The results for January to December 2013 showed that the ecosystems of the three sites served as net sinks of CO2 during the rainy season (May to October) and net sources of CO2 during the dry season (November to April). However, NR was a net sink of CO2 during the wet to dry transition period (November to December). On an annual timescale, only NR served as a net sink of CO2 from the atmosphere into the ecosystem, while the others were net sources of CO2 into the atmosphere. Furthermore, the study revealed that the three contrasting ecosystems responded to environmental and physiological factors based on the ecosystem functional types. This suggests that land use and land use management may play a significant role in the diurnal to annual sequestration and efflux patterns of NEE and its composite fluxes, gross primary production (GPP) and ecosystem respiration (ER), over the West African Sudanian Savannas.

  10. Biophysical controls on net ecosystem CO2 exchange over a semiarid shrubland in northwest China

    NASA Astrophysics Data System (ADS)

    Jia, X.; Zha, T. S.; Wu, B.; Zhang, Y. Q.; Gong, J. N.; Qin, S. G.; Chen, G. P.; Qian, D.; Kellomäki, S.; Peltola, H.

    2014-09-01

    The carbon (C) cycling in semiarid and arid areas remains largely unexplored, despite the wide distribution of drylands globally. Rehabilitation practices have been carried out in many desertified areas, but information on the C sequestration capacity of recovering vegetation is still largely lacking. Using the eddy-covariance technique, we measured the net ecosystem CO2 exchange (NEE) over a recovering shrub ecosystem in northwest China throughout 2012 in order to (1) quantify NEE and its components and to (2) examine the dependence of C fluxes on biophysical factors at multiple timescales. The annual budget showed a gross ecosystem productivity (GEP) of 456 g C m-2 yr-1 (with a 90% prediction interval of 449-463 g C m-2 yr-1) and an ecosystem respiration (Re) of 379 g C m-2 yr-1 (with a 90% prediction interval of 370-389 g C m-2 yr-1), resulting in a net C sink of 77 g C m-2 yr-1 (with a 90% prediction interval of 68-87 g C m-2 yr-1). The maximum daily NEE, GEP and Re were -4.7, 6.8 and 3.3 g C m-2 day-1, respectively. Both the maximum C assimilation rate (i.e., at the optimum light intensity) and the quantum yield varied over the growing season, being higher in summer and lower in spring and autumn. At the half-hourly scale, water deficit exerted a major control over daytime NEE, and interacted with other stresses (e.g., heat and photoinhibition) in constraining C fixation by the vegetation. Low soil moisture also reduced the temperature sensitivity of Re (Q10). At the synoptic scale, rain events triggered immediate pulses of C release from the ecosystem, followed by peaks of CO2 uptake 1-2 days later. Over the entire growing season, leaf area index accounted for 45 and 65% of the seasonal variation in NEE and GEP, respectively. There was a linear dependence of daily Re on GEP, with a slope of 0.34. These results highlight the role of abiotic stresses and their alleviation in regulating C cycling in the face of an increasing frequency and intensity of extreme

  11. Modeling net ecosystem exchange of carbon dioxide in a beetle-attacked subalpine forest using a data-constrained ecosystem model

    NASA Astrophysics Data System (ADS)

    Peckham, S. D.; Ewers, B. E.; Mackay, D. S.; Frank, J. M.; Massman, W. J.; Ryan, M. G.; Scott, H.; Pendall, E.

    2012-12-01

    The mountain pine and spruce bark beetles and associated blue-stain fungi have caused widespread mortality in the forests of the western U.S. during the past decade, impacting over 1.6 Mha in Northern Colorado and Southeast Wyoming alone. Both the beetles and fungi they carry block tree xylem and eventually cause mortality due to hydraulic failure. Previous studies of bark beetle mortality in Canadian forests have suggested a net loss of carbon following beetle attack. This study aimed to determine if forests in the southern Rocky Mountains showed a similar response. We simulated carbon fluxes over a time period of six years (2005-2010) at the Glacier Lakes Ecosystem Experiment sites (GLEES) Ameriflux site using the Terrestrial Regional Ecosystem Exchange Simulator (TREES) model. This time period included a beetle infestation during the last three years that resulted in mortality of 51% of the spruce trees that accounted for 90% of the spruce basal area. Model estimates of net ecosystem exchange of CO2 (NEE) were compared to eddy-covariance measurements before, during, and after beetle attack. Model predictions of NEE were generated two ways, 1) using the standard set of maintenance respiration coefficients, and 2) constraining modeled respiration using equations derived from field measurements of stem, leaf, and soil respiration at GLEES, and were compared to NEE observations before, during, and after the presence of bark beetles. Model changes included both simple modification of the exponential temperature response curve (Q10) and adding new equations based on both temperature and live tissue nitrogen content. Pre-beetle observed growing season mean NEE averaged -1.49 μmol C m-2 s-1 and simulation means ranged from -4.10 to 0.64 μmol C m-2 s-1. Changing the model's computation of maintenance respiration to incorporate site-specific temperature response (Q10) resulted in an over-prediction of nighttime NEE by up to 100%, but a 10-30% improvement during the day

  12. Diurnal and seasonal variations in carbon dioxide exchange in ecosystems in the Zhangye oasis area, Northwest China.

    PubMed

    Zhang, Lei; Sun, Rui; Xu, Ziwei; Qiao, Chen; Jiang, Guoqing

    2015-01-01

    Quantifying carbon dioxide exchange and understanding the response of key environmental factors in various ecosystems are critical to understanding regional carbon budgets and ecosystem behaviors. For this study, CO2 fluxes were measured in a variety of ecosystems with an eddy covariance observation matrix between June 2012 and September 2012 in the Zhangye oasis area of Northwest China. The results show distinct diurnal variations in the CO2 fluxes in vegetable field, orchard, wetland, and maize cropland. Diurnal variations of CO2 fluxes were not obvious, and their values approached zero in the sandy desert, desert steppe, and Gobi ecosystems. Additionally, daily variations in the Gross Primary Production (GPP), Ecosystem Respiration (Reco) and Net Ecosystem Exchange (NEE) were not obvious in the sandy desert, desert steppe, and Gobi ecosystems. In contrast, the distributions of the GPP, Reco, and NEE show significant daily variations, that are closely related to the development of vegetation in the maize, wetland, orchard, and vegetable field ecosystems. All of the ecosystems are characterized by their carbon absorption during the observation period. The ability to absorb CO2 differed significantly among the tested ecosystems. We also used the Michaelis-Menten equation and exponential curve fitting methods to analyze the impact of Photosynthetically Active Radiation (PAR) on the daytime CO2 flux and impact of air temperature on Reco at night. The results show that PAR is the dominant factor in controlling photosynthesis with limited solar radiation, and daytime CO2 assimilation increases rapidly with PAR. Additionally, the carbon assimilation rate was found to increase slowly with high solar radiation. The light response parameters changed with each growth stage for all of the vegetation types, and higher light response values were observed during months or stages when the plants grew quickly. Light saturation points are different for different species. Nighttime

  13. Tracking CO2 flux: Seasonal Patterns, Net Ecosystem Exchange and Site Comparisons of Environmental Variables at a Boreal Peatland

    NASA Astrophysics Data System (ADS)

    Bhatia, G.; Bubier, J. L.

    2001-05-01

    Peatlands play a significant role in the global carbon cycle sequestering approximately one-third of the global pool of soil carbon. An increased understanding of the carbon cycle in these critical ecosystems is imperative to further our comprehension of the role they play in future global warming. Net ecosystem exchange (NEE) of carbon dioxide was measured at Mer Bleue Bog in Ottawa, Ontario, Canada from May through August 2000. Dominant species at Mer Bleue included Ledum groenlandicum, Chamaedaphne calyculata, Eriophorum vaginatum, Carex oligosperma and Sphagnum species. In order to understand the controls and variability of NEE a range of sites were considered, including a beaver pond, a bog and a poor fen. This study aimed at comparing overall seasonal patterns and ranges of NEE, photosynthesis and respiration and understanding the relationships with photosynthetically active radiation (PAR), water table, temperature, species composition and plant biomass. A clear lexan and teflon film climate-controlled chamber was used to measure the rate of respiration and photosynthesis on a bi-weekly basis in all sites. The chamber was attached to a LI-COR 6200 portable photosynthesis system, which included a LI-6250 infrared gas analyzer, quantum sensor and data logger. Shrouds of different mesh sizes were used to regulate the amount of light entering the chamber in order to measure NEE at a wide range of PAR. An opaque shroud was used to measure ecosystem respiration. Photosynthesis was calculated as the difference between NEE and respiration. Seasonal patterns showed a peak season from June 23rd through July 15th where higher PAR and temperature levels led to increased photosynthesis and respiration measurements. Although NEE rates at the sites varied, during peak season NEE ranged in increasing order: bog hummock and hollow (6 to -6.5 μ mol CO2 m{-2} s{-1}) < beaver pond (6 to -7 μ mol CO2 m{-2} s{-1}) < poor fen (10 to -8 μ mol CO2 m{-2}s {-1}).

  14. Measurement-based upscaling of Pan Arctic Net Ecosystem Exchange: the PANEEx project

    NASA Astrophysics Data System (ADS)

    Njuabe Mbufong, Herbert; Kusbach, Antonin; Lund, Magnus; Persson, Andreas; Christensen, Torben R.; Tamstorf, Mikkel P.; Connolly, John

    2016-04-01

    The high variability in Arctic tundra net ecosystem exchange (NEE) of carbon (C) can be attributed to the high spatial heterogeneity of Arctic tundra due to the complex topography. Current models of C exchange handle the Arctic as either a single or few ecosystems, responding to environmental change in the same manner. In this study, we developed and tested a simple pan Arctic NEE (PANEEx) model using the Misterlich light response curve (LRC) function with photosynthetic photon flux density (PPFD) as the main driving variable. Model calibration was carried out with eddy covariance carbon dioxide (CO2) data from 12 Arctic tundra sites. The model input parameters (Fcsat, Rd and α) were estimated as a function of air temperature (AirT) and leaf area index (LAI) and represent specific characteristics of the NEE-PPFD relationship, including the saturation flux, dark respiration and initial light use efficiency, respectively. LAI and air temperature were respectively estimated from empirical relationships with remotely sensed normalized difference vegetation index (NDVI) and land surface temperature (LST). These are available as MODIS Terra product MOD13Q1 and MOD11A1 respectively. Therefore, no specific knowledge of the vegetation type is required. The PANEEx model captures the spatial heterogeneity of the Arctic tundra and was effective in simulating 77% of the measured fluxes (r2 = 0.72, p < 0.001) at the 12 sites used in the calibration of the model. Further, the model effectively estimates NEE in three disparate Alaskan ecosystems (heath, tussock and fen) with an estimation ranging between 10 - 36% of the measured fluxes. We suggest that the poor agreement between the measured and modeled NEE may result from the disparity between ground-based measured LAI (used in model calibration) and remotely sensed LAI (estimated from NDVI and used in NEE estimation). Moreover, our results suggests that using simple linear regressions may be inadequate as parameters estimated

  15. Biophysical drivers of net ecosystem exchange in shrublands of the northern Chihuahuan Desert

    NASA Astrophysics Data System (ADS)

    Jaimes, A.; Laney, C.; Tweedie, C. E.

    2013-12-01

    In the northern Chihuahuan Desert, large areas of southern New Mexico that were formerly dominated by perennial grasses, including black grama (Bouteloua eriopa) and mesa dropseed (Sporobolus flexus) have been replaced by desert shrubland species, in particular creosote bush (Larrea tridentata) and honey mesquite (Prosopis glandulosa). Recent studies suggest that these changes in land cover have the ability to modify near surface microclimate such as soil water holding capacity, albedo, carbon dioxide sequestration, and increases in local air temperature, respiration, sensible heat and evapotranspiration. Despite the recognized importance of the consequences of land cover change in the ecosystem, the rates and tipping points at which these changes occur are not well understood. This knowledge is key to improve predictions in regional and global models, as the region is expected to go through an imminent transition from warm to warmer climate in this century. This study analyze three years of data (2010-2012) from our multi sensor platform situated on the USDA ARS Jornada Experimental Range (JER), about 25 km northeast of Las Cruces, New Mexico, USA. A robust data set that combines high frequency micrometeorological data, plot phenology estimates and spectral indices was used. A combination of statistical analyses based on clustering methods (self-organizing maps) and simple nonparametric regression techniques (regression trees) were used to identify factors controlling fluxes and likely biophysical thresholds and tipping points indicative of different functional system states. Both analyses were implemented through the use of Neural Network Toolbox and Statistics toolbox within MATLAB 7.0. During the period of study the shrubland acted as a carbon sink ranging between -105 to -134 gCO2 m-2 y-1. The largest variation between years in the annual estimated fluxes was the slight decrease of total annual net ecosystem exchange during 2011 (-105 g m-2 s-1) in comparison

  16. Contrasting the patterns of aspen forest and sagebrush shrubland gross ecosystem exchange in montane Idaho, USA

    NASA Astrophysics Data System (ADS)

    Fellows, A.; Flerchinger, G. N.; Seyfried, M. S.

    2015-12-01

    We investigated the environmental controls on Gross Ecosystem Exchange (GEE) at an aspen forest and a sagebrush shrubland in southwest Idaho. The two sites were situated within a mosaic of vegetation that included temperate deciduous trees, shrublands, and evergreen conifer trees. The distribution of vegetation was presumably linked to water availability; aspen were located in wetter high-elevations sites, topographic drainages, or near snow drifts. Local temperatures have increased by ~2-3 °C over the past 50 years and less precipitation has arrived as snow. These ongoing changes in weather may impact snow water redistribution, plant-water availability, and plant-thermal stress, with associated impacts on vegetation health and production. We used eddy covariance to measure the exchange of water and carbon dioxide above the two sites and partitioned the net carbon flux to determine GEE. The sagebrush record was from 2003-2007 and the aspen record was from 2007-12. The region experienced a modest-to-severe drought in 2007, with ~73% of typical precipitation. We found that aspen were local "hotspots" for carbon exchange; peak rates of aspen GEE were ~ 60% greater than the peak rates of sagebrush GEE. Light, temperature, and water availability were dominant controls on the seasonality of GEE at both sites. Sagebrush and aspen were dormant during winter, limited by cold temperatures during winter and early spring, and water availability during mid-late summer. The onset of summer drought was typically later in the aspen than in the sagebrush. Drifting snow, lateral water redistribution, or increased rooting depths may have increased water availability in the aspen stand. Seasonal patterns of observed soil moisture and evaporation indicated aspen were rooted to >= 1 m. The sagebrush and aspen both responded strongly to the 2007 drought; peak GEE decreased by ~75%, peak GEE shifted to earlier parts of the year, and mid-summer GEE was decreased. We consider potential

  17. The Inter-Annual Variability Analysis of Carbon Exchange in Low Artic Fen Uncovers The Climate Sensitivity And The Uncertainties Around Net Ecosystem Exchange Partitioning

    NASA Astrophysics Data System (ADS)

    Blanco, E. L.; Lund, M.; Williams, M. D.; Christensen, T. R.; Tamstorf, M. P.

    2015-12-01

    An improvement in our process-based understanding of CO2 exchanges in the Arctic, and their climate sensitivity, is critical for examining the role of tundra ecosystems in changing climates. Arctic organic carbon storage has seen increased attention in recent years due to large potential for carbon releases following thaw. Our knowledge about the exact scale and sensitivity for a phase-change of these C stocks are, however, limited. Minor variations in Gross Primary Production (GPP) and Ecosystem Respiration (Reco) driven by changes in the climate can lead to either C sink or C source states, which likely will impact the overall C cycle of the ecosystem. Eddy covariance data is usually used to partition Net Ecosystem Exchange (NEE) into GPP and Reco achieved by flux separation algorithms. However, different partitioning approaches lead to different estimates. as well as undefined uncertainties. The main objectives of this study are to use model-data fusion approaches to (1) determine the inter-annual variability in C source/sink strength for an Arctic fen, and attribute such variations to GPP vs Reco, (2) investigate the climate sensitivity of these processes and (3) explore the uncertainties in NEE partitioning. The intention is to elaborate on the information gathered in an existing catchment area under an extensive cross-disciplinary ecological monitoring program in low Arctic West Greenland, established under the auspices of the Greenland Ecosystem Monitoring (GEM) program. The use of such a thorough long-term (7 years) dataset applied to the exploration in inter-annual variability of carbon exchange, related driving factors and NEE partition uncertainties provides a novel input into our understanding about land-atmosphere CO2 exchange.

  18. Biometric and Eddy-Covariance Based Estimates of Ecosystem Carbon Exchange in an Age-Sequence of Temperate Pine Forests

    NASA Astrophysics Data System (ADS)

    Peichl, M.; Arain, M. A.; Brodeur, J. J.; Khomik, M.

    2009-05-01

    We determined and compared annual carbon (C) exchanges from biometric and eddy-covariance (EC) measurements in an age-sequence (6-, 19-, 34-, 69-years old) of managed pine (Pinus strobus L.) forests in southern Ontario from 2005-2007. The biometric approach determined annual above- and belowground tree biomass production from site-specific allometric biomass equations depending on either tree diameter at breast height (DBH) only (method B1) or on DBH with tree height as additional variable (method B2). In addition, detritus production and heterotrophic soil respiration were determined. Data from continuous closed- path measurements at the oldest site and from a roving open-path system among the three younger sites provided EC-based estimates of C exchanges (method EC). The contribution of individual net primary productivity (NPP) components varied considerably with stand age, suggesting different dominant fluxes and uncertainty levels occurring at various forest development stages. All methods produced similar patterns for inter-annual variations with highest (lowest) C fluxes in 2006 (2005). While on an annual basis, differences between methods ranged from ± 4-67% for estimates of annual net ecosystem productivity (NEP), the differences were within ± 15% when averaged over three years, except for the 34-year old stand. Mean annual NEP was estimated by the biometric method B1 (B2) as 1 (N.A.), 394 (634), 134 (265), and 124 (272) g C m-2 y-1 compared to 47, 724, 408, and 119 g C m-2 y-1 by the EC method for the 6-, 19-, 34-, 69-years old stands, respectively. The biometric method B1 agreed best with the EC estimates in the youngest and the oldest stand, but estimated considerably lower productivity rates than the EC method in the two middle-age stands in which method B2 showed a better agreement with method EC by accounting for the vigorous height growth in these stands. Thus, our comparison study shows that the use of inadequate allometric equations may

  19. ELEVATED CO2 AND TEMPERATURE ALTER THE ECOSYSTEM C EXCHANGE IN A YOUNG DOUGLAS FIR MESOCOSM EXPERIMENT

    EPA Science Inventory

    We investigated the effects of elevated CO2 (EC) [ambient CO2 (AC) + 190 ppm] and elevated temperature (ET) [ambient temperature (AT) + 3.6 °C] on net ecosystem exchange (NEE) of seedling Douglas fir (Pseudotsuga menziesii) mesocosms. As the study utilized seedlings in reconstruc...

  20. Controls for multi-scale temporal variation in ecosystem methane exchange during the growing season of a permanently inundated fen

    NASA Astrophysics Data System (ADS)

    Koebsch, Franziska; Jurasinski, Gerald; Koch, Marian; Hofmann, Joachim; Glatzel, Stephan

    2014-05-01

    Temperature and phenology trigger seasonal variation of CH4 emissions in many ecosystems. However, ecosystem CH4 exchange varies also considerably on smaller temporal scales such as days or weeks. Indeed, we are aware of many processes that control CH4 emissions on the local soil-plant-atmosphere continuum, but their interaction on ecosystem level is not well understood yet. We used a quasi-continuous Eddy Covariance CH4 flux time series and wavelet analysis to describe the temporal variation of ecosystem CH4 exchange within the growing season of a permanently inundated temperate fen. Moreover, we assigned time scale-specific controls and investigated whether their impact changes during the course of the growing season. Water/soil temperature correlated with ecosystem CH4 exchange at time scales of 6-11 and 22 days which exceeds the time scales that are typically associated with the passage of weather fronts. The low response time might be due to the high heat capacity of the water column. On a daily scale, shear-induced turbulence (presented by friction velocity) and plant activity (presented by canopy photosynthesis) caused a diurnal variation of ecosystem CH4 exchange with peak time around noon. However, this pattern was apparent only at the beginning of the growing season (April/May). In the following, convective mixing of the water column (presented by the water temperature gradient) gradually gained importance and caused high night-time CH4 emissions, thereby levelling off the diurnal CH4 emission pattern. Our study highlights the need for multi-scale approaches that consider the non-stationarity of the underlying processes to adequately describe the complexity of ecosystem CH4 exchange. Moreover, we show that CH4 release processes such as convective mixing of the water column which has been mainly known from aquatic ecosystems until recently (Godwin et al. 2013), might be also of importance in shallowly flooded terrestrial ecosystems. Citation: Godwin CM, Mc

  1. Invasive C4 Perennial Grass Alters Net Ecosystem Exchange in Mixed C3/C4 Savanna Grassland

    NASA Astrophysics Data System (ADS)

    Basham, T. S.; Litvak, M.

    2006-12-01

    The invasion of ecosystems by non-native plants that differ from native plants in physiological characteristics and phenology has the potential to alter ecosystem function. In Texas and other regions of the southern central plains of the United States, the introduced C4 perennial grass, Bothriochloa ischaemum, invades C3/C4 mixed grasslands and savannas, resulting in decreased plant community diversity (Gabbard 2003; Harmoney et al 2004). The objective of this study was to quantify how the conversion of these mixed grass communities to C4 dominated, B. ischaemum monocultures impacts carbon cycling and sequestration. Seasonal measurements of Net Ecosystem Exchange (NEE) of CO2, leaf level gas exchange and soil respiration were compared between savanna grassland plots composed of either naturally occurring B. ischaemum monocultures or native mixed grasses (n=16). NEE was measured using a closed system chamber that attached to permanently installed stainless steel bases. Temperature, soil moisture, aerial percent species cover and leaf area index were also monitored in plots to explain variability in measured responses. Results showed that NEE differed seasonally between invaded and native plots due to 1) greater leaf surface area per unit ground area in invaded plots, 2) differences in phenological patterns of plant activity and 3) differences in responses to water limitation between invaded and native plots. Cold season and summer drought NEE were driven primarily by belowground respiration in both plot types, however spring uptake activity commenced two months later in invaded plots. This later start in invaded plots was compensated for by greater uptake throughout the growing season and in particular during the drier summer months. Differences in NEE between plot types were not due to differences in soil respiration nor were they due to greater leaf level photosynthetic capabilities of B. ischaemum relative to the dominant native grasses. NEE, soil respiration and

  2. Effects of grazing on ecosystem CO₂ exchange in a meadow grassland on the Tibetan Plateau during the growing season.

    PubMed

    Chen, Ji; Shi, Weiyu; Cao, Junji

    2015-02-01

    Effects of human activity on ecosystem carbon fluxes (e.g., net ecosystem exchange (NEE), ecosystem respiration (R(eco)), and gross ecosystem exchange (GEE)) are crucial for projecting future uptake of CO2 in terrestrial ecosystems. However, how ecosystem that carbon fluxes respond to grazing exclusion is still under debate. In this study, a field experiment was conducted to study the effects of grazing exclusion on R(eco), NEE, and GEE with three treatments (free-range grazing (FG) and grazing exclusion for 3 and 5 years (GE3 and GE5, respectively)) in a meadow grassland on the Tibetan Plateau. Our results show that grazing exclusion significantly increased NEE by 47.37 and 15.84%, and R eco by 33.14 and 4.29% under GE3 and GE5 plots, respectively, although carbon sinks occurred in all plots during the growing season, with values of 192.11, 283.12, and 222.54 g C m(-2) for FG, GE3, and GE5, respectively. Interestingly, grazing exclusion increased temperature sensitivity (Q10) of R eco with larger increases at the beginning and end of growing season (i.e., May and October, respectively). Soil temperature and soil moisture were key factors on controlling the diurnal and seasonal variations of R(eco), NEE, and GEE, with soil temperature having a stronger influence. Therefore, the combined effects of grazing and temperature suggest that grazing should be taken into consideration in assessing global warming effects on grassland ecosystem CO2 exchange.

  3. Effects of grazing on ecosystem CO₂ exchange in a meadow grassland on the Tibetan Plateau during the growing season.

    PubMed

    Chen, Ji; Shi, Weiyu; Cao, Junji

    2015-02-01

    Effects of human activity on ecosystem carbon fluxes (e.g., net ecosystem exchange (NEE), ecosystem respiration (R(eco)), and gross ecosystem exchange (GEE)) are crucial for projecting future uptake of CO2 in terrestrial ecosystems. However, how ecosystem that carbon fluxes respond to grazing exclusion is still under debate. In this study, a field experiment was conducted to study the effects of grazing exclusion on R(eco), NEE, and GEE with three treatments (free-range grazing (FG) and grazing exclusion for 3 and 5 years (GE3 and GE5, respectively)) in a meadow grassland on the Tibetan Plateau. Our results show that grazing exclusion significantly increased NEE by 47.37 and 15.84%, and R eco by 33.14 and 4.29% under GE3 and GE5 plots, respectively, although carbon sinks occurred in all plots during the growing season, with values of 192.11, 283.12, and 222.54 g C m(-2) for FG, GE3, and GE5, respectively. Interestingly, grazing exclusion increased temperature sensitivity (Q10) of R eco with larger increases at the beginning and end of growing season (i.e., May and October, respectively). Soil temperature and soil moisture were key factors on controlling the diurnal and seasonal variations of R(eco), NEE, and GEE, with soil temperature having a stronger influence. Therefore, the combined effects of grazing and temperature suggest that grazing should be taken into consideration in assessing global warming effects on grassland ecosystem CO2 exchange. PMID:25355630

  4. The contribution of advective fluxes to net ecosystem exchange in a high-elevation, subalpine forest.

    PubMed

    Yi, Chuixiang; Anderson, Dean E; Turnipseed, Andrew A; Burns, Sean P; Sparks, Jed P; Stannard, David I; Monson, Russell K

    2008-09-01

    The eddy covariance technique, which is used in the determination of net ecosystem CO2 exchange (NEE), is subject to significant errors when advection that carries CO2 in the mean flow is ignored. We measured horizontal and vertical advective CO2 fluxes at the Niwot Ridge AmeriFlux site (Colorado, USA) using a measurement approach consisting of multiple towers. We observed relatively high rates of both horizontal (F(hadv)) and vertical (F(vadv)) advective fluxes at low surface friction velocities (u(*)) which were associated with downslope katabatic flows. We observed that F(hadv) was confined to a relatively thin layer (0-6 m thick) of subcanopy air that flowed beneath the eddy covariance sensors principally at night, carrying with it respired CO2 from the soil and lower parts of the canopy. The observed F(vadv) came from above the canopy and was presumably due to the convergence of drainage flows at the tower site. The magnitudes of both F(hadv) and F(vadv) were similar, of opposite sign, and increased with decreasing u(*), meaning that they most affected estimates of the total CO2 flux on calm nights with low wind speeds. The mathematical sign, temporal variation and dependence on u(*) of both F(hadv) and F(vadv) were determined by the unique terrain of the Niwot Ridge site. Therefore, the patterns we observed may not be broadly applicable to other sites. We evaluated the influence of advection on the cumulative annual and monthly estimates of the total CO2 flux (F(c)), which is often used as an estimate of NEE, over six years using the dependence of F(hadv) and F(vadv) on u(*). When the sum of F(hadv) and F(vadv) was used to correct monthly F(c), we observed values that were different from the monthly F(c) calculated using the traditional u(*)-filter correction by--16 to 20 g C x m(-2) x mo(-1); the mean percentage difference in monthly Fc for these two methods over the six-year period was 10%. When the sum of F(hadv) and F(vadv) was used to correct annual Fc

  5. Inter-annual variability in Alaskan net ecosystem CO2 exchange

    NASA Astrophysics Data System (ADS)

    Luus, Kristina; Lindaas, Jakob; Commane, Roisin; Euskirchen, Eugenie; Oechel, Walter; Zona, Donatella; Chang, Rachel; Kelly, Richard; Miller, Charles; Wofsy, Steven; Lin, John

    2015-04-01

    The high-latitude biospheric carbon cycle's responses to climate change are predicted to have an important role in determining future atmospheric concentrations of CO2. In response to warming soil and air temperatures, Arctic wetlands have been observed to increase rates of both soil C efflux and vegetation C uptake through photosynthesis. However, insights into the regional-scale consequences of these processes for net C uptake have been limited by the large uncertainties existing in process-based model estimates of Arctic net ecosystem CO2 exchange (NEE). The Polar Vegetation Photosynthesis and Respiration Model (PolarVPRM) instead provides data-driven, satellite-based estimates of high-latitude NEE, using a framework which specifically accounts for polar influences on NEE. PolarVPRM calculates NEE as the sum of respiration (R) and gross ecosystem exchange (GEE), where GEE refers to the light-dependent portion of NEE: NEE= -GEE + R. Meteorological inputs for PolarVPRM are provided by the North American Regional Reanalysis (NARR), and land surface inputs are acquired from the Moderate Resolution Imaging Spectroradiometer (MODIS). Growing season R is calculated from air temperature, and subnivean R is calculated according to soil temperature. GEE is calculated according to shortwave radiation, air temperature, and MODIS-derived estimates of soil moisture and vegetation biomass. Previously, model validation has indicated that PolarVPRM showed reasonably good agreement with eddy covariance observations at nine North American Arctic sites, of which three were used for calibration purposes. For this project, PolarVPRM NEE was calculated year-round across Alaska at a three-hourly temporal resolution and a spatial resolution of 1 6°×1 4° (latitude × longitude). The objective of this work was to gain insight into inter-annual variability in Alaskan NEE, R and GEE, and an understanding of which meteorological and land surface drivers account for these observed patterns

  6. Disentangling leaf area and environmental effects on the response of the net ecosystem CO2 exchange to diffuse radiation.

    PubMed

    Wohlfahrt, Georg; Hammerle, Albin; Haslwanter, Alois; Bahn, Michael; Tappeiner, Ulrike; Cernusca, Alexander

    2008-08-01

    There is an ongoing discussion about why the net ecosystem CO2 exchange (NEE) of some ecosystems is less sensitive to diffuse radiation than others and about the role other environmental factors play in determining the response of NEE to diffuse radiation. Using a six-year data set from a temperate mountain grassland in Austria we show that differences between ecosystems may be reconciled based on their green area index (GAI; square meter green plant area per square meter ground area) - the sensitivity to diffuse radiation increasing with GAI. Our data suggest diffuse radiation to have a negligible influence on NEE below a GAI of 2 m(2) m(-2). Changes in air/soil temperature and air humidity concurrent with the fraction of diffuse radiation were found to amplify the sensitivity of the investigated temperate mountain grassland ecosystem to diffuse radiation.

  7. Plant carbon-nutrient interactions control CO{sub 2} exchange in Alaskan wet sedge tundra ecosystems

    SciTech Connect

    Johnson, L.C.; Shaver, G.R.; Cades, D.H.; Rastetter, E.; Nadelhoffer, K.; Giblin, A.; Laundre, J.; Stanley, A.

    2000-02-01

    The authors explored the long-term (8-yr) effects of separate field manipulations of temperature and nutrient availability on carbon balance in wet sedge tundra near the Arctic Long Term Ecological Research (LTER) site at Toolik Lake, Alaska. Their goals were (1) to assess the relative importance of chronic warming (with field greenhouses) and increased N and P availability (by fertilization) in controlling gross ecosystem photosynthesis, ecosystem respiration, and ultimately ecosystem C balance; and (2) to attempt to partition ecosystem responses to these treatments between plant and soil contributions. The authors present results of the effects of these manipulations on whole-system CO{sub 2} exchange over seasonal and duel cycles, and on nonrhizosphere soil microbial respiration using in situ soil incubations.

  8. Net ecosystem exchange related to different rewetting intensities of a drained coastal fen

    NASA Astrophysics Data System (ADS)

    Koebsch, F.; Jurasinski, G.; Glatzel, S.

    2012-04-01

    Peatlands are important carbon (C) reservoirs. Although they account for only 3% of total global area they store 550 Gt C. This corresponds to 75% of atmospheric C. Drainage and agricultural use of peatlands cause considerable release of climate relevant carbon dioxide (CO2). Thus, rewetting measures attempt to re-activate C storage potentials of peatlands. Yet, further research is needed about the biogeochemical processes related to rewetting. We present results of net ecosystem exchange (NEE) measurements of a rewetted coastal fen from two vegetation periods with different rewetting intensities. In 2009 mean water level was short below ground surface whilst 2010 implicated a year-round flooding. Measurements were conducted with the Eddy-Covariance method which provides quasi-continuous flux measurements on ecosystem scale. Vegetation period 2009 exhibited a high negative NEE indicating considerable CO2 storage of the coastal fen. Flooding decreased the amount of stored CO2 for approximately 50% during the vegetation period 2010. Since a significant part of local vegetation (above all Carex acutiformis stands) was killed by the increased water level, we assume NEE to be dampened by a lower gross primary production. Additionally, the plant residuals may provide a labile C source for microbial respiration. Flooding affects the element budget of peatlands dramatically and causes a considerable element outflow, detectable e. g. as CO2 emission. Our results display only the initial phase of flooding. Long time studies are necessary to investigate whether CO2 will be stored after a certain period of time. Nevertheless, the climate effects of flooding should be considered when rewetting measures are assessed

  9. Promoting Value for Consumers: Comparing Individual Health Insurance Markets Inside and Outside the ACA's Exchanges.

    PubMed

    McCue, Michael J; Hall, Mark A

    2016-06-01

    The new health insurance exchanges are the core of the Affordable Care Act's (ACA) insurance reforms, but insurance markets beyond the exchanges also are affected by the reforms. This issue brief compares the markets for individual coverage on and off of the exchanges, using insurers' most recent projections for ACA-compliant policies. In 2016, insurers expect that less than one-fifth of ACA-compliant coverage will be sold outside of the exchanges. Insurers that sell mostly through exchanges devote a greater portion of their premium dollars to medical care than do insurers selling only off of the exchanges, because exchange insurers project lower administrative costs and lower profit margins. Premium increases on exchange plans are less than those for off-exchange plans, in large part because exchange enrollment is projected to shift to closed-network plans. Finally, initial concerns that insurers might seek to segregate higher-risk subscribers on the exchanges have not been realized. PMID:27290751

  10. Comparing soil biogeochemical processes in novel and natural boreal forest ecosystems

    NASA Astrophysics Data System (ADS)

    Quideau, S. A.; Swallow, M. J. B.; Prescott, C. E.; Grayston, S. J.; Oh, S.-W.

    2013-04-01

    Emulating the variability that exists in the natural landscape prior to disturbance should be a goal of soil reconstruction and land reclamation efforts following resource extraction. Long-term ecosystem sustainability within reclaimed landscapes can only be achieved with the re-establishment of biogeochemical processes between reconstructed soils and plants. In this study, we assessed key soil biogeochemical attributes (nutrient availability, organic matter composition, and microbial communities) in reconstructed, novel, anthropogenic ecosystems covering different reclamation treatments following open-cast mining for oil extraction. We compared the attributes to those present in a range of natural soils representative of mature boreal forest ecosystems in the same area of northern Alberta. Soil nutrient availability was determined in situ with resin probes, organic matter composition was described with 13C nuclear magnetic resonance spectroscopy and soil microbial community structure was characterized using phospholipid fatty acid analysis. Significant differences among natural ecosystems were apparent in nutrient availability and seemed more related to the dominant tree cover than to soil type. When analyzed together, all natural forests differed significantly from the novel ecosystems, in particular with respect to soil organic matter composition. However, there was some overlap between the reconstructed soils and some of the natural ecosystems in nutrient availability and microbial communities, but not in organic matter characteristics. Hence, our results illustrate the importance of considering the range of natural landscape variability, and including several soil biogeochemical attributes when comparing novel, anthropogenic ecosystems to the mature ecosystems that constitute ecological targets.

  11. Comparing soil biogeochemical processes in novel and natural boreal forest ecosystems

    NASA Astrophysics Data System (ADS)

    Quideau, S. A.; Swallow, M. J. B.; Prescott, C. E.; Grayston, S. J.; Oh, S.-W.

    2013-08-01

    Emulating the variability that exists in the natural landscape prior to disturbance should be a goal of soil reconstruction and land reclamation efforts following resource extraction. Long-term ecosystem sustainability within reclaimed landscapes can only be achieved with the re-establishment of biogeochemical processes between reconstructed soils and plants. In this study, we assessed key soil biogeochemical attributes (nutrient availability, organic matter composition, and microbial communities) in reconstructed, novel, anthropogenic ecosystems, covering different reclamation treatments following open-cast mining for oil extraction. We compared the attributes to those present in a range of natural soils representative of mature boreal forest ecosystems in the same area of Northern Alberta. Soil nutrient availability was determined in situ with resin probes, organic matter composition was described with 13C nuclear magnetic resonance spectroscopy and soil microbial community structure was characterized using phospholipid fatty acid analysis. Significant differences among natural ecosystems were apparent in nutrient availability and seemed more related to the dominant tree cover than to soil type. When analyzed together, all natural forests differed significantly from the novel ecosystems, in particular with respect to soil organic matter composition. However, there was some overlap between the reconstructed soils and some of the natural ecosystems in nutrient availability and microbial communities, but not in organic matter characteristics. Hence, our results illustrate the importance of considering the range of natural landscape variability and including several soil biogeochemical attributes when comparing novel, anthropogenic ecosystems to the mature ecosystems that constitute ecological targets.

  12. Comparing two tools for ecosystem service assessments regarding water resources decisions.

    PubMed

    Dennedy-Frank, P James; Muenich, Rebecca Logsdon; Chaubey, Indrajeet; Ziv, Guy

    2016-07-15

    We present a comparison of two ecohydrologic models commonly used for planning land management to assess the production of hydrologic ecosystem services: the Soil and Water Assessment Tool (SWAT) and the Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) annual water yield model. We compare these two models at two distinct sites in the US: the Wildcat Creek Watershed in Indiana and the Upper Upatoi Creek Watershed in Georgia. The InVEST and SWAT models provide similar estimates of the spatial distribution of water yield in Wildcat Creek, but very different estimates of the spatial distribution of water yield in Upper Upatoi Creek. The InVEST model may do a poor job estimating the spatial distribution of water yield in the Upper Upatoi Creek Watershed because baseflow provides a significant portion of the site's total water yield, which means that storage dynamics which are not modeled by InVEST may be important. We also compare the ability of these two models, as well as one newly developed set of ecosystem service indices, to deliver useful guidance for land management decisions focused on providing hydrologic ecosystem services in three particular decision contexts: environmental flow ecosystem services, ecosystem services for potable water supply, and ecosystem services for rainfed irrigation. We present a simple framework for selecting models or indices to evaluate hydrologic ecosystem services as a way to formalize where models deliver useful guidance. PMID:27111651

  13. Multiple independent constraints help resolve net ecosystem carbon exchange under nutrient limitation

    NASA Astrophysics Data System (ADS)

    Thornton, P. E.; Metcalfe, D.; Oren, R.; Ricciuto, D. M.

    2014-12-01

    The magnitude, spatial distribution, and variability of land net ecosystem exchange of carbon (NEE) are important determinants of the trajectory of atmospheric carbon dioxide concentration. Independent observational constraints provide important clues regarding NEE and its component fluxes, with information available at multiple spatial scales: from cells, to leaves, to entire organisms and collections of organisms, to complex landscapes and up to continental and global scales. Experimental manipulations, ecosystem observations, and process modeling all suggest that the components of NEE (photosynthetic gains, and respiration and other losses) are controlled in part by the availability of mineral nutrients, and that nutrient limitation is a common condition in many biomes. Experimental and observational constraints at different spatial scales provide a complex and sometimes puzzling picture of the nature and degree of influence of nutrient availability on carbon cycle processes. Photosynthetic rates assessed at the cellular and leaf scales are often higher than the observed accumulation of carbon in plant and soil pools would suggest. We infer that a down-regulation process intervenes between carbon uptake and plant growth under conditions of nutrient limitation, and several down-regulation mechanisms have been hypothesized and tested. A recent evaluation of two alternative hypotheses for down-regulation in the light of whole-plant level flux estimates indicates that some plants take up and store extra carbon, releasing it to the environment again on short time scales. The mechanism of release, either as additional autotrophic respiration or as exudation belowground is unclear, but has important consequences for long-term ecosystem state and response to climate change signals. Global-scale constraints from atmospheric concentration and isotopic composition data help to resolve this question, ultimately focusing attention on land use fluxes as the most uncertain

  14. Are BVOC exchanges in agricultural ecosystems overestimated? Insights from fluxes measured in a maize field over a whole growing season

    NASA Astrophysics Data System (ADS)

    Bachy, Aurélie; Aubinet, Marc; Schoon, Niels; Amelynck, Crist; Bodson, Bernard; Moureaux, Christine; Heinesch, Bernard

    2016-04-01

    Although maize is the second most important crop worldwide, and the most important C4 crop, no study on biogenic volatile organic compounds (BVOCs) has yet been conducted on this crop at ecosystem scale and over a whole growing season. This has led to large uncertainties in cropland BVOC emission estimations. This paper seeks to fill this gap by presenting, for the first time, BVOC fluxes measured in a maize field at ecosystem scale (using the disjunct eddy covariance by mass scanning technique) over a whole growing season in Belgium. The maize field emitted mainly methanol, although exchanges were bi-directional. The second most exchanged compound was acetic acid, which was taken up mainly in the growing season. Bi-directional exchanges of acetaldehyde, acetone and other oxygenated VOCs also occurred, whereas the terpenes, benzene and toluene exchanges were small, albeit significant. Surprisingly, BVOC exchanges were of the same order of magnitude on bare soil and on well developed vegetation, suggesting that soil is a major BVOC reservoir in agricultural ecosystems. Quantitatively, the maize BVOC emissions observed were lower than those reported in other maize, crops and grasses studies. The standard emission factors (SEFs) estimated in this study (231 ± 19 µg m-2 h-1 for methanol, 8 ± 5 µg m-2 h-1 for isoprene and 4 ± 6 µg m-2 h-1 for monoterpenes) were also much lower than those currently used by models for C4 crops, particularly for terpenes. These results suggest that maize fields are small BVOC exchangers in north-western Europe, with a lower BVOC emission impact than that modelled for growing C4 crops in this part of the world. They also reveal the high variability in BVOC exchanges across world regions for maize and suggest that SEFs should be estimated for each region separately.

  15. Long-term impacts of peatland restoration on the net ecosystem exchange (NEE) of blanket bogs in Northern Scotland.

    NASA Astrophysics Data System (ADS)

    Hambley, Graham; Hill, Timothy; Saunders, Matthew; Arn Teh, Yit

    2016-04-01

    Unmanaged peatlands represent an important long-term C sink and thus play an important part of the global C cycle. Despite covering only 12 % of the UK land area, peatlands are estimated to store approximately 20 times more carbon than the UK's forests, which cover 13% of the land area. The Flow Country of Northern Scotland is the largest area of contiguous blanket bog in the UK, and one of the biggest in Europe, covering an area in excess of 4000 km2 and plays a key role in mediating regional atmospheric exchanges of greenhouse gases (GHGs) such as carbon dioxide (CO2), and water vapour (H2O). However, these peatlands underwent significant afforestation in the 1980s, when over 670 km2 of blanket bog were drained and planted with Sitka spruce (Picea sitchensis) and Lodgepole pine (Pinus contorta). This resulted in modifications to hydrology, micro-topography, vegetation and soil properties all of which are known to influence the production, emission and sequestration of key GHGs. Since the late 1990s restoration work has been carried out to remove forest plantations and raise water tables, by drain blocking, to encourage the recolonisation of Sphagnum species and restore ecosystem functioning. Here, we report findings of NEE and its constituent fluxes, GPP and Reco, from a study investigating the impacts of restoration on C dynamics over a chronosequence of restored peatlands. The research explored the role of environmental variables and microtopography in modulating land-atmosphere exchanges, using a multi-scale sampling approach that incorporated eddy covariance measurements with dynamic flux chambers. Key age classes sampled included an undrained peatland; an older restored peatland (17 years old); and a more recently restored site (12 years old). The oldest restored site showed the strongest uptake of C, with an annual assimilation rate of 858 g C m-2 yr-1 compared to assimilation rates of 501g C m-2 yr-1 and 575g C m-2 yr-1 from the younger restored site and

  16. Assessing net ecosystem carbon exchange of U.S. terrestrial ecosystems by integrating eddy covariance flux measurements and satellite observations

    Technology Transfer Automated Retrieval System (TEKTRAN)

    More accurate projections of future carbon dioxide concentrations in the atmosphere and associated climate change as well as carbon accounting and climate policy-making depend on improved scientific understanding of the terrestrial carbon cycle. Despite the consensus that U.S. terrestrial ecosystems...

  17. The Oncor Geodatabase for the Columbia Estuary Ecosystem Restoration Program: Handbook of Data Reduction Procedures, Workbooks, and Exchange Templates

    SciTech Connect

    Sather, Nichole K.; Borde, Amy B.; Diefenderfer, Heida L.; Serkowski, John A.; Coleman, Andre M.; Johnson, Gary E.

    2013-12-31

    This Handbook of Data Reduction Procedures, Workbooks, and Exchange Templates is designed to support the Oncor geodatabase for the Columbia Estuary Ecosystem Restoration Program (CEERP). The following data categories are covered: water-surface elevation and temperature, sediment accretion rate, photo points, herbaceous wetland vegetation cover, tree plots and site summaries, fish catch and density, fish size, fish diet, fish prey, and Chinook salmon genetic stock identification. The handbook is intended for use by scientists collecting monitoring and research data for the CEERP. The ultimate goal of Oncor is to provide quality, easily accessible, geospatial data for synthesis and evaluation of the collective performance of CEERP ecosystem restoration actions at a program scale.

  18. Typhoons exert significant but differential impacts on net ecosystem carbon exchange of subtropical mangrove forests in China

    NASA Astrophysics Data System (ADS)

    Chen, H.; Lu, W.; Yan, G.; Yang, S.; Lin, G.

    2014-10-01

    Typhoons are very unpredictable natural disturbances to subtropical mangrove forests in Asian countries, but little information is available on how these disturbances affect ecosystem level carbon dioxide (CO2) exchange of mangrove wetlands. In this study, we examined short-term effect of frequent strong typhoons on defoliation and net ecosystem CO2 exchange (NEE) of subtropical mangroves, and also synthesized 19 typhoons during a 4-year period between 2009 and 2012 to further investigate the regulation mechanisms of typhoons on ecosystem carbon and water fluxes following typhoon disturbances. Strong wind and intensive rainfall caused defoliation and local cooling effect during the typhoon season. Daily total NEE values decreased by 26-50% following some typhoons (e.g., W28-Nockten, W35-Molave and W35-Lio-Fan), but significantly increased (43-131%) following typhoon W23-Babj and W38-Megi. The magnitudes and trends of daily NEE responses were highly variable following different typhoons, which were determined by the balance between the variances of gross ecosystem production (GEP) and ecosystem respiration (RE). Furthermore, results from our synthesis indicated that the landfall time of typhoon, wind speed and rainfall were the most important factors controlling the CO2 fluxes following typhoon events. These findings indicate that different types of typhoon disturbances can exert very different effects on CO2 fluxes of mangrove ecosystems and that typhoon will likely have larger impacts on carbon cycle processes in subtropical mangrove ecosystems as the intensity and frequency of typhoons are predicted to increase under future global climate change scenarios.

  19. Enhanced seasonal CO2 exchange caused by amplified plant productivity in northern ecosystems

    NASA Astrophysics Data System (ADS)

    Forkel, Matthias; Carvalhais, Nuno; Rödenbeck, Christian; Keeling, Ralph; Heimann, Martin; Thonicke, Kirsten; Zaehle, Sönke; Reichstein, Markus

    2016-04-01

    Atmospheric monitoring has shown an increase in the seasonal cycle of carbon dioxide (CO2) in high northern latitudes (> 40°N) since the 1960s. The much stronger increase of the seasonal CO2 amplitude in high latitudes compared to low latitudes suggests that northern ecosystems are experiencing large changes in carbon cycle dynamics. However the underlying mechanisms are not yet fully understood and current climate/carbon cycle models under-estimate observed changes in the seasonal CO2 amplitude. Here we aim to explain the observed latitudinal gradient of seasonal CO2 amplitude trends by contrasting observations from long-term monitoring sites of atmospheric CO2 concentration, satellite observation of vegetation greenness, and global observation-based datasets of gross primary production and net biome productivity, with results from the LPJmL dynamic global vegetation model coupled to the TM3 atmospheric transport model. Our results demonstrate that the latitudinal gradient of the enhanced seasonal CO2 amplitude is mainly driven by positive trends in photosynthetic carbon uptake caused by recent climate change and mediated by changing vegetation cover in boreal and arctic ecosystems. Climate change affects processes such as plant physiology, phenology, water availability, and vegetation dynamics, ultimately leading to increased plant productivity and vegetation cover in northern ecosystems in the last decades. Thereby photosynthetic carbon uptake has reacted much more strongly to warming than respiratory carbon release processes. Continued long-term observation of atmospheric CO2 together with ground and satellite observations of land surface and vegetation dynamics will be the key to detect, model, and better predict changes in high-latitude land/carbon cycle dynamics.

  20. Biosphere/atmosphere CO2 exchange in tundra ecosystems - Community characteristics and relationships with multispectral surface reflectance

    NASA Technical Reports Server (NTRS)

    Whiting, Gary J.; Bartlett, David S.; Fan, Song-Miao; Bakwin, Peter S.; Wofsy, Steven C.

    1992-01-01

    CO2 exchange rates were measured at selected tundra sites near Bethel, Alaska using portable, climate-controlled, instrumented enclosures. The empirically modeled exchange rate for a representative area of vegetated tundra was 1.2 +/- 1.2 g/sq m/d, compared to a tower-measured exchange over the same time period of 1.1 +.0- 1.2 g/sq m/d. Net exchange in response to varying light levels was compared to wet meadow and dry upland tundra, and to the net exchange measured by the micrometeoroidal tower technique. The multispectral reflectance properties of the sites were measured and related to exchange rates in order to provide a quantitative foundation for the use of satellite remote sensing to monitor biosphere/atmosphere CO2 exchange in the tundra biome.

  1. Biosphere/atmosphere CO[sub 2] exchange in tundra ecosystems - community characteristics and relationships with multispectral surface reflectance

    SciTech Connect

    Whiting, G.J.; Bartlett, D.S.; Fan, Songmiao; Bakwin, P.S.; Wofsy, S.C. New Hampshire Univ., Durham Harvard Univ., Cambridge, MA )

    1992-10-01

    CO2 exchange rates were measured at selected tundra sites near Bethel, Alaska using portable, climate-controlled, instrumented enclosures. The empirically modeled exchange rate for a representative area of vegetated tundra was 1.2 +/- 1.2 g/sq m/d, compared to a tower-measured exchange over the same time period of 1.1 +.0- 1.2 g/sq m/d. Net exchange in response to varying light levels was compared to wet meadow and dry upland tundra, and to the net exchange measured by the micrometeoroidal tower technique. The multispectral reflectance properties of the sites were measured and related to exchange rates in order to provide a quantitative foundation for the use of satellite remote sensing to monitor biosphere/atmosphere CO[sub 2] exchange in the tundra biome. 28 refs.

  2. What are the instrumentation requirements for measuring the isotopic composition of net ecosystem exchange of CO2 using eddy covariance methods?

    PubMed

    Saleska, Scott R; Shorter, Joanne H; Herndon, Scott; Jiménez, Rodrigo; McManus, J Barry; Munger, J William; Nelson, David D; Zahniser, Mark S

    2006-06-01

    Better quantification of isotope ratios of atmosphere-ecosystem exchange of CO2 could substantially improve our ability to probe underlying physiological and ecological mechanisms controlling ecosystem carbon exchange, but the ability to make long-term continuous measurements of isotope ratios of exchange fluxes has been limited by measurement difficulties. In particular, direct eddy covariance methods have not yet been used for measuring the isotopic composition of ecosystem fluxes. In this article, we explore the feasibility of such measurements by (a) proposing a general criterion for judging whether a sensor's performance is sufficient for making such measurements (the criterion is met when the contribution of sensor error to the flux measurement error is comparable to or less than the contribution of meteorological noise inherently associated with turbulence flux measurements); (b) using data-based numerical simulations to quantify the level of sensor precision and stability required to meet this criterion for making direct eddy covariance measurements of the 13C/12C ratio of CO2 fluxes above a specific ecosystem (a mid-latitude temperate forest in central Massachusetts, USA); (c) testing whether the performance of a new sensor-a prototype pulsed quantum cascade laser (QCL) based isotope-ratio absorption spectrometer (and plausible improvements thereon)-is sufficient for meeting the criterion in this ecosystem. We found that the error contribution from a prototype sensor (approximately 0.2 per thousand, 1 SD of 10 s integrations) to total isoflux measurement error was comparable to (1.5 to 2x) the irreducible 'meteorological' noise inherently associated with turbulent flux measurements above this ecosystem (daytime measurement error SD of approximately 60% of flux versus meteorological noise of 30-40% for instantaneous half-hour fluxes). Our analysis also shows that plausible instrument improvements (increase of sensor precision to approximately 0.1 per

  3. [CO2-exchange in tundra ecosystems of Vaygach Island during the unusually warm and dry vegetation season].

    PubMed

    Zamolodchikov, D G

    2015-01-01

    In summer of 2013, field studies of CO2-exchange in tundra ecosystems of Vaygach Island have been conducted using the chamber method. The models are developed that establish relationships between CO2 fluxes and key ecological factors such as temperature, photosynthetic active radiation, leaf mass of vascular plants, and depth of thawing. According to the model estimates, in 2013 vegetation season tundra ecosystems of Vaygach Island have been appearing to be a CO2 source to the atmosphere (31.9 ± 17.1 g C m(-2) season(-1)) with gross primary production equal to 136.6 ± 18.9 g C m(-2) season(-1) and ecosystem respiration of 168.5 ± ± 18.4 g C m(-2) season(-1). Emission of CO2 from the soil surface (soil respiration) has been equal, on the average, to 67.3% of the ecosystem respiration. The reason behind carbon losses by tundra ecosystems seems to be unusually warm and dry weather conditions in 2013 summer. The air temperature during summer months has been twice as high as the climatic norm for 1961-1990. Last decades, researches in the circumpolar Arctic revealed a growing trend to the carbon sink from the atmosphere to tundra ecosystems. This trend can be interrupted by unusually warm weather situations becoming more frequent and of larger scale.

  4. Diurnal and Seasonal Variations in Carbon Dioxide Exchange in Ecosystems in the Zhangye Oasis Area, Northwest China

    PubMed Central

    Zhang, Lei; Sun, Rui; Xu, Ziwei; Qiao, Chen; Jiang, Guoqing

    2015-01-01

    Quantifying carbon dioxide exchange and understanding the response of key environmental factors in various ecosystems are critical to understanding regional carbon budgets and ecosystem behaviors. For this study, CO2 fluxes were measured in a variety of ecosystems with an eddy covariance observation matrix between June 2012 and September 2012 in the Zhangye oasis area of Northwest China. The results show distinct diurnal variations in the CO2 fluxes in vegetable field, orchard, wetland, and maize cropland. Diurnal variations of CO2 fluxes were not obvious, and their values approached zero in the sandy desert, desert steppe, and Gobi ecosystems. Additionally, daily variations in the Gross Primary Production (GPP), Ecosystem Respiration (Reco) and Net Ecosystem Exchange (NEE) were not obvious in the sandy desert, desert steppe, and Gobi ecosystems. In contrast, the distributions of the GPP, Reco, and NEE show significant daily variations, that are closely related to the development of vegetation in the maize, wetland, orchard, and vegetable field ecosystems. All of the ecosystems are characterized by their carbon absorption during the observation period. The ability to absorb CO2 differed significantly among the tested ecosystems. We also used the Michaelis-Menten equation and exponential curve fitting methods to analyze the impact of Photosynthetically Active Radiation (PAR) on the daytime CO2 flux and impact of air temperature on Reco at night. The results show that PAR is the dominant factor in controlling photosynthesis with limited solar radiation, and daytime CO2 assimilation increases rapidly with PAR. Additionally, the carbon assimilation rate was found to increase slowly with high solar radiation. The light response parameters changed with each growth stage for all of the vegetation types, and higher light response values were observed during months or stages when the plants grew quickly. Light saturation points are different for different species. Nighttime

  5. Diurnal and seasonal variations in carbon dioxide exchange in ecosystems in the Zhangye oasis area, Northwest China.

    PubMed

    Zhang, Lei; Sun, Rui; Xu, Ziwei; Qiao, Chen; Jiang, Guoqing

    2015-01-01

    Quantifying carbon dioxide exchange and understanding the response of key environmental factors in various ecosystems are critical to understanding regional carbon budgets and ecosystem behaviors. For this study, CO2 fluxes were measured in a variety of ecosystems with an eddy covariance observation matrix between June 2012 and September 2012 in the Zhangye oasis area of Northwest China. The results show distinct diurnal variations in the CO2 fluxes in vegetable field, orchard, wetland, and maize cropland. Diurnal variations of CO2 fluxes were not obvious, and their values approached zero in the sandy desert, desert steppe, and Gobi ecosystems. Additionally, daily variations in the Gross Primary Production (GPP), Ecosystem Respiration (Reco) and Net Ecosystem Exchange (NEE) were not obvious in the sandy desert, desert steppe, and Gobi ecosystems. In contrast, the distributions of the GPP, Reco, and NEE show significant daily variations, that are closely related to the development of vegetation in the maize, wetland, orchard, and vegetable field ecosystems. All of the ecosystems are characterized by their carbon absorption during the observation period. The ability to absorb CO2 differed significantly among the tested ecosystems. We also used the Michaelis-Menten equation and exponential curve fitting methods to analyze the impact of Photosynthetically Active Radiation (PAR) on the daytime CO2 flux and impact of air temperature on Reco at night. The results show that PAR is the dominant factor in controlling photosynthesis with limited solar radiation, and daytime CO2 assimilation increases rapidly with PAR. Additionally, the carbon assimilation rate was found to increase slowly with high solar radiation. The light response parameters changed with each growth stage for all of the vegetation types, and higher light response values were observed during months or stages when the plants grew quickly. Light saturation points are different for different species. Nighttime

  6. Ion-exchange method in the collection of nitrate from freshwater ecosystems for nitrogen and oxygen isotope analysis: a review.

    PubMed

    Li, Wen-Bing; Song, Yao-Bin; Xu, Hong-Ke; Chen, Ling-Yun; Dai, Wen-Hong; Dong, Ming

    2015-07-01

    Nitrate (NO3(-)) contamination of freshwater is considered one of the most prevalent global environmental problems. Dual stable isotopic compositions (δ(15)N and δ(18)O) of NO3(-) can provide helpful information and have been well documented as being a powerful tool to track the source of NO3(-) in freshwater ecosystems. The ion-exchange method is a reliable and precise technique for measuring the δ(15)N and δ(18)O of NO3(-) and has been widely employed to collect NO3(-) from freshwater ecosystems. This review summarizes and presents the principles, affecting factors and corresponding significant improvements of the ion-exchange method. Finally, potential improvements and perspectives for the applicability of this method are also discussed, as are suggestions for further research and development drawn from the overall conclusions.

  7. Are BVOC exchanges in agricultural ecosystems overestimated? Insights from fluxes measured in a maize field over a whole growing season

    NASA Astrophysics Data System (ADS)

    Bachy, Aurélie; Aubinet, Marc; Schoon, Niels; Amelynck, Crist; Bodson, Bernard; Moureaux, Christine; Heinesch, Bernard

    2016-04-01

    Maize is the most important C4 crop worldwide. It is also the second most important crop worldwide (C3 and C4 mixed), and is a dominant crop in some world regions. Therefore, it can potentially influence local climate and air quality through its exchanges of gases with the atmosphere. Among others, biogenic volatile organic compounds (BVOC) are known to influence the atmospheric composition and thereby modify greenhouse gases lifetime and pollutant formation in the atmosphere. However, so far, only two studies have dealt with BVOC exchanges from maize. Moreover, these studies were conducted on a limited range of meteorological and phenological conditions, so that the knowledge of BVOC exchanges by this crop remains poor. Here, we present the first BVOC measurement campaign performed at ecosystem-scale on a maize field during a whole growing season. It was carried out in the Lonzée Terrestrial Observatory (LTO), an ICOS site. BVOC fluxes were measured by the disjunct by mass-scanning eddy covariance technique with a proton transfer reaction mass spectrometer for BVOC mixing ratios measurements. Outstanding results are (i) BVOC exchanges from soil were as important as BVOC exchanges from maize itself; (ii) BVOC exchanges observed on our site were much lower than exchanges observed by other maize studies, even under normalized temperature and light conditions, (iii) they were also lower than those observed on other crops grown in Europe. Lastly (iv), BVOC exchanges observed on our site under standard environmental conditions, i.e., standard emission factors SEF, were much lower than those currently considered by BVOC exchange up-scaling models. From those observations, we deduced that (i) soil BVOC exchanges should be better understood and should be incorporated in terrestrial BVOC exchanges models, and that (ii) SEF for the C4 crop plant functional type cannot be evaluated at global scale but should be determined for each important agronomic and pedo-climatic region

  8. Long-term dynamics of production, respiration, and net CO2 exchange in two sagebrush-steppe ecosystems

    USGS Publications Warehouse

    Gilmanov, T.G.; Svejcar, T.J.; Johnson, D.A.; Angell, R.F.; Saliendra, Nicanor Z.; Wylie, B.K.

    2006-01-01

    We present a synthesis of long-term measurements of CO2 exchange in 2 US Intermountain West sagebrush-steppe ecosystems. The locations near Burns, Oregon (1995-2001), and Dubois, Idaho (1996-2001), are part of the AgriFlux Network of the Agricultural Research Service, United States Department of Agriculture. Measurements of net ecosystem CO2 exchange (F c) during the growing season were continuously recorded at flux towers using the Bowen ratio-energy balance technique. Data were partitioned into gross primary productivity (Pg) and ecosystem respiration (Re) using the light-response function method. Wintertime fluxes were measured during 1999/2000 and 2000/2001 and used to model fluxes in other winters. Comparison of daytime respiration derived from light-response analysis with nighttime tower measurements showed close correlation, with daytime respiration being on the average higher than nighttime respiration. Maxima of Pg and Re at Burns were both 20 g CO2?? m-2??d-1 in 1998. Maxima of Pg and R e at Dubois were 37 and 35 g CO2??m -2??d-1, respectively, in 1997. Mean annual gross primary production at Burns was 1 111 (range 475-1 715) g CO2?? m-2??y-1 about 30% lower than that at Dubois (1 602, range 963-2 162 g CO2??m-2??y-1). Across the years, both ecosystems were net sinks for atmospheric CO2 with a mean net ecosystem CO2 exchange of 82 g CO2?? m-2??y-1 at Burns and 253 g CO2?? m-2??y-1 at Dubois, but on a yearly basis either site could be a C sink or source, mostly depending on precipitation timing and amount. Total annual precipitation is not a good predictor of carbon sequestration across sites. Our results suggest that Fc should be partitioned into Pg and Re components to allow prediction of seasonal and yearly dynamics of CO2 fluxes.

  9. Net Ecosystem Exchange in a Tall Tower Footprint: Reconciling Observations, Modeling, and Remote Sensing

    NASA Astrophysics Data System (ADS)

    Braswell, B.; Braswell, B.; Churkina, G.; Schimel, D.; Davis, K.

    2001-05-01

    In this study we investigate the controls on monthly-to-interannual terrestrial NEP within the footprint of the WLEF tall tower. This footprint is large enough (>1 km2) to be considered as a single example of a global ecosystem model or global remote sensing grid cell. We compare the observed NEE from 1997-1999 with predictions of the Biome-BGC model and attempt to associate discrepancies with specific processes, including plant phenology and soil respiration. The remote sensing observations are used in this exercise to help diagnose interannual variability in growing season length and to characterize the distribution of landcover within the footprint. We consider also inherent limitations in the data, especially the uncertainty associated with data gap-filling methods.

  10. Improved determination of daytime net ecosystem exchange of carbon dioxide at croplands

    NASA Astrophysics Data System (ADS)

    Zhao, P.; Lüers, J.

    2012-03-01

    The eddy-covariance technique is applied worldwide to acquire information about carbon exchange between a variety of ecosystems and atmosphere, but the data acquisition only covers, on average, two-thirds of the whole year due to system failures and data rejection. Therefore, data must be corrected and data gaps must be filled to provide seasonal or annual budgets. The gap-filing strategies, however, are still under discussion within the research community. Presently the major gap-filling methods work quite well for long-time running sites over slow-developing biosphere surfaces such as long-living evergreen forests, but difficulties appear for short-living and fast-growing croplands. In this study we developed a new Multi-Step Error Filter procedure to gain good-quality data as input for different parameterizations of the light response function of plants for two cropland sites (rice and potatoes), and we could prove that the conventional temperature binning approach is inadequate. The presented time-window scheme showed best results with a four-day time window for the potato field and an eight-day time window for the rice field. The influence of vapor pressure deficit was tested as well, but in our case it plays a minor role at both the potato and the rice fields with the exception of the early growing stage of the potatoes. Completing our research, we suggest an innovative method by introducing a Leaf Area Index factor to capture the seasonal vegetation development. With this method we are now able to fill the large gaps between observation periods when conventional methods are invalid.

  11. Net ecosystem exchange of CO2 with rapidly changing high Arctic landscapes.

    PubMed

    Emmerton, Craig A; St Louis, Vincent L; Humphreys, Elyn R; Gamon, John A; Barker, Joel D; Pastorello, Gilberto Z

    2016-03-01

    High Arctic landscapes are expansive and changing rapidly. However, our understanding of their functional responses and potential to mitigate or enhance anthropogenic climate change is limited by few measurements. We collected eddy covariance measurements to quantify the net ecosystem exchange (NEE) of CO2 with polar semidesert and meadow wetland landscapes at the highest latitude location measured to date (82°N). We coupled these rare data with ground and satellite vegetation production measurements (Normalized Difference Vegetation Index; NDVI) to evaluate the effectiveness of upscaling local to regional NEE. During the growing season, the dry polar semidesert landscape was a near-zero sink of atmospheric CO2 (NEE: -0.3 ± 13.5 g C m(-2) ). A nearby meadow wetland accumulated over 300 times more carbon (NEE: -79.3 ± 20.0 g C m(-2) ) than the polar semidesert landscape, and was similar to meadow wetland NEE at much more southerly latitudes. Polar semidesert NEE was most influenced by moisture, with wetter surface soils resulting in greater soil respiration and CO2 emissions. At the meadow wetland, soil heating enhanced plant growth, which in turn increased CO2 uptake. Our upscaling assessment found that polar semidesert NDVI measured on-site was low (mean: 0.120-0.157) and similar to satellite measurements (mean: 0.155-0.163). However, weak plant growth resulted in poor satellite NDVI-NEE relationships and created challenges for remotely detecting changes in the cycling of carbon on the polar semidesert landscape. The meadow wetland appeared more suitable to assess plant production and NEE via remote sensing; however, high Arctic wetland extent is constrained by topography to small areas that may be difficult to resolve with large satellite pixels. We predict that until summer precipitation and humidity increases enough to offset poor soil moisture retention, climate-related changes to productivity on polar semideserts may be restricted.

  12. Net Ecosystem Exchange of CO2 with Rapidly Changing High Arctic Landscapes

    NASA Astrophysics Data System (ADS)

    Emmerton, C. A.

    2015-12-01

    High Arctic landscapes are expansive and changing rapidly. However our understanding of their functional responses and potential to mitigate or enhance anthropogenic climate change is limited by few measurements. We collected eddy covariance measurements to quantify the net ecosystem exchange (NEE) of CO2 with polar semidesert and meadow wetland landscapes at the highest-latitude location measured to date (82°N). We coupled these rare data with ground and satellite vegetation production measurements (Normalized Difference Vegetation Index; NDVI) to evaluate the effectiveness of upscaling local to regional NEE. During the growing season, the dry polar semidesert landscape was a near zero sink of atmospheric CO2 (NEE: -0.3±13.5 g C m-2). A nearby meadow wetland accumulated over two magnitudes more carbon (NEE: -79.3±20.0 g C m-2) than the polar semidesert landscape, and was similar to meadow wetland NEE at much more southern latitudes. Polar semidesert NEE was most influenced by moisture, with wetter surface soils resulting in greater soil respiration and CO2 emissions. At the meadow wetland, soil heating enhanced plant growth, which in turn increased CO2 uptake. Our upscaling assessment found that polar semidesert NDVI measured on site was low (mean: 0.120-0.157) and similar to satellite measurements (mean: 0.155-0.163). However, weak plant growth resulted in poor satellite NDVI-NEE relationships and created challenges for remotely-detecting changes in the cycling of carbon on the polar semidesert landscape. The meadow wetland appeared more suitable to assess plant production and NEE via remote-sensing, however high Arctic wetland extent is constrained by topography to small areas that may be difficult to resolve with large satellite pixels. We predict that until summer precipitation and humidity increases substantially, climate-related changes of dry high Arctic landscapes may be restricted by poor soil moisture retention, and therefore have some inertia against

  13. Effects of Pre-industrial and Future Atmospheric CO2 concentration on Net Ecosystem Exchange on Arid and Semi-Arid Ecosystems

    NASA Astrophysics Data System (ADS)

    Kalhori, A. A. M.; Deutschman, D.; Cheng, Y.; Oechel, W. C.

    2014-12-01

    Ecosystem carbon dioxide flux was studied between 1997 and 2000 under six different CO2 concentrations (250 ppm, 350 ppm, 450 ppm, 550 ppm, 650 ppm, and 750 ppm) using CO2 LT (CO2 controlled, naturally Lit, Temperature controlled) null balance chambers in Southern California chaparral dominated by Adenostoma fasciculatum. The purpose of this study is to evaluate possible effects of altered levels of atmospheric CO2 concentrations on carbon fluxes in a natural chaparral ecosystem. Here we present that the increase of CO2 from near pre-industrial levels of around 250 ppm to recent past CO2 levels of 350 ppm are sufficient to increase NEE. These data indicate that chaparral ecosystems will increase carbon sequestration under elevated CO2 levels and that under elevated atmospheric CO2 there will be greater sink or reduced source of ecosystem CO2 to the atmosphere as a result of improved moisture status. The effect of elevated CO2 on increasing NEE was greatest during the warm and dry season versus the cold and wet season. Further, it appears that increasing atmospheric CO2 will have greater relative effects in areas of increasing water stress as CO2 treatment effects on NEE were greater in modestly dry years and with longer periods of drought. The daily maximum NEE difference between the lowest (250 ppm) and the highest (750 ppm) CO2 concentrations treatments for January was -0.127gC m-2 h-1, but for June was -0.267 gC m-2 h-1 in this study, which was a 210 percent increase. The differences between the lower treatments and higher treatments were greater in the later years indicating there was an accumulative effect. Cumulative of net ecosystem exchange (gC m-2) between 1/1/1997 and 1/1/2001 under six different CO2 concentration is presented in the figure attached.

  14. Impact of extreme inter-annual climatic differences on the net ecosystem carbon dioxide exchange of a Sitka spruce forest.

    NASA Astrophysics Data System (ADS)

    Saunders, Matthew; Tobin, Brian; Gioria, Margherita; Benanti, Giuseppe; Cacciotti, Erica; Osborne, Bruce

    2013-04-01

    Sitka spruce forest plantations are well suited to growing in the temperate climate of Ireland and represent some of the most productive forest stands in Europe, assimilating between 8-10 t C ha-1 yr-1. Temperature and precipitation are key drivers of the global carbon cycle and both inter-annual climatic variability and extreme climatic events have been shown to influence rates of carbon sequestration and greenhouse gas mitigation potential within terrestrial biological ecosystems. The impacts of the timing, intensity and duration of extreme climatic events, characterised by major differences in rainfall and minimum temperatures, were assessed using long-term eddy covariance measurements of net ecosystem carbon dioxide exchange (2002-2012). Precipitation in 2009 and 2010 was 1156 mm and 741 mm, respectively and was approximately 35% higher and 16% lower than the 30 year mean precipitation for this region (1978-2007). The difference in precipitation in 2009 was not uniformly distributed throughout the year and occurred largely during the growing season (April-August). The mean annual air temperature in 2010 (8.2°C) was also 1.7°C lower than the 30 year mean, and was characterised by a number of extended sub-zero temperature events during the winter months. Despite these differences, annual estimates of NEE were remarkably similar between years, ranging between 8.14 ± 1.94 t C ha yr-1 and 8.18 ± 0.88 t C ha yr-1 in 2009 and 2010 respectively. However, the measured NEE in both 2009 and 2010 were approximately 6% lower than the long-term mean measured at this site (2002-2008; 8.62 ± 1.39 t C ha yr-1). The components of NEE, gross primary productivity (GPP) and ecosystem respiration (Reco) did, however, show differences between years. In 2009, GPP was ~15% lower when compared to 2010, most likely due to a reduction in stand photosynthesis at higher irradiances during the growing season that was related to higher water availability in the surface layers of the soil

  15. Differential responses of net ecosystem exchange of carbon dioxide to light and temperature between spring and neap tides in subtropical mangrove forests.

    PubMed

    Li, Qing; Lu, Weizhi; Chen, Hui; Luo, Yiqi; Lin, Guanghui

    2014-01-01

    The eddy flux data with field records of tidal water inundation depths of the year 2010 from two mangroves forests in southern China were analyzed to investigate the tidal effect on mangrove carbon cycle. We compared the net ecosystem exchange (NEE) and its responses to light and temperature, respectively, between spring tide and neap tide inundation periods. For the most time of the year 2010, higher daytime NEE values were found during spring tides than during neap tides at both study sites. Regression analysis of daytime NEE to photosynthetically active radiation (PAR) using the Landsberg model showed increased sensitivity of NEE to PAR with higher maximum photosynthetic rate during spring tides than neap tides. In contrast, the light compensation points acquired from the regression function of the Landsberg model were smaller during spring tides than neap tides in most months. The dependence of nighttime NEE on soil temperature was lower under spring tide than under neap tides. All these results above indicated that ecosystem carbon uptake rates of mangrove forests were strengthened, while ecosystem respirations were inhibited during spring tides in comparison with those during neap tides, which needs to be considered in modeling mangrove ecosystem carbon cycle under future sea level rise scenarios.

  16. Differential Responses of Net Ecosystem Exchange of Carbon Dioxide to Light and Temperature between Spring and Neap Tides in Subtropical Mangrove Forests

    PubMed Central

    Li, Qing; Lu, Weizhi; Chen, Hui; Luo, Yiqi; Lin, Guanghui

    2014-01-01

    The eddy flux data with field records of tidal water inundation depths of the year 2010 from two mangroves forests in southern China were analyzed to investigate the tidal effect on mangrove carbon cycle. We compared the net ecosystem exchange (NEE) and its responses to light and temperature, respectively, between spring tide and neap tide inundation periods. For the most time of the year 2010, higher daytime NEE values were found during spring tides than during neap tides at both study sites. Regression analysis of daytime NEE to photosynthetically active radiation (PAR) using the Landsberg model showed increased sensitivity of NEE to PAR with higher maximum photosynthetic rate during spring tides than neap tides. In contrast, the light compensation points acquired from the regression function of the Landsberg model were smaller during spring tides than neap tides in most months. The dependence of nighttime NEE on soil temperature was lower under spring tide than under neap tides. All these results above indicated that ecosystem carbon uptake rates of mangrove forests were strengthened, while ecosystem respirations were inhibited during spring tides in comparison with those during neap tides, which needs to be considered in modeling mangrove ecosystem carbon cycle under future sea level rise scenarios. PMID:25133267

  17. Differential responses of net ecosystem exchange of carbon dioxide to light and temperature between spring and neap tides in subtropical mangrove forests.

    PubMed

    Li, Qing; Lu, Weizhi; Chen, Hui; Luo, Yiqi; Lin, Guanghui

    2014-01-01

    The eddy flux data with field records of tidal water inundation depths of the year 2010 from two mangroves forests in southern China were analyzed to investigate the tidal effect on mangrove carbon cycle. We compared the net ecosystem exchange (NEE) and its responses to light and temperature, respectively, between spring tide and neap tide inundation periods. For the most time of the year 2010, higher daytime NEE values were found during spring tides than during neap tides at both study sites. Regression analysis of daytime NEE to photosynthetically active radiation (PAR) using the Landsberg model showed increased sensitivity of NEE to PAR with higher maximum photosynthetic rate during spring tides than neap tides. In contrast, the light compensation points acquired from the regression function of the Landsberg model were smaller during spring tides than neap tides in most months. The dependence of nighttime NEE on soil temperature was lower under spring tide than under neap tides. All these results above indicated that ecosystem carbon uptake rates of mangrove forests were strengthened, while ecosystem respirations were inhibited during spring tides in comparison with those during neap tides, which needs to be considered in modeling mangrove ecosystem carbon cycle under future sea level rise scenarios. PMID:25133267

  18. Stable oxygen isotope and flux partitioning demonstrates understory of an oak savanna contributes up to half of ecosystem carbon and water exchange.

    PubMed

    Dubbert, Maren; Piayda, Arndt; Cuntz, Matthias; Correia, Alexandra C; Costa E Silva, Filipe; Pereira, Joao S; Werner, Christiane

    2014-01-01

    Semi-arid ecosystems contribute about 40% to global net primary production (GPP) even though water is a major factor limiting carbon uptake. Evapotranspiration (ET) accounts for up to 95% of the water loss and in addition, vegetation can also mitigate drought effects by altering soil water distribution. Hence, partitioning of carbon and water fluxes between the soil and vegetation components is crucial to gain mechanistic understanding of vegetation effects on carbon and water cycling. However, the possible impact of herbaceous vegetation in savanna type ecosystems is often overlooked. Therefore, we aimed at quantifying understory vegetation effects on the water balance and productivity of a Mediterranean oak savanna. ET and net ecosystem CO2 exchange (NEE) were partitioned based on flux and stable oxygen isotope measurements and also rain infiltration was estimated. The understory vegetation contributed importantly to total ecosystem ET and GPP with a maximum of 43 and 51%, respectively. It reached water-use efficiencies (WUE; ratio of carbon gain by water loss) similar to cork-oak trees. The understory vegetation inhibited soil evaporation (E) and, although E was large during wet periods, it did not diminish WUE during water-limited times. The understory strongly increased soil water infiltration, specifically following major rain events. At the same time, the understory itself was vulnerable to drought, which led to an earlier senescence of the understory growing under trees as compared to open areas, due to competition for water. Thus, beneficial understory effects are dominant and contribute to the resilience of this ecosystem. At the same time the vulnerability of the understory to drought suggests that future climate change scenarios for the Mediterranean basin threaten understory development. This in turn will very likely diminish beneficial understory effects like infiltration and ground water recharge and therefore ecosystem resilience to drought. PMID

  19. Stable oxygen isotope and flux partitioning demonstrates understory of an oak savanna contributes up to half of ecosystem carbon and water exchange.

    PubMed

    Dubbert, Maren; Piayda, Arndt; Cuntz, Matthias; Correia, Alexandra C; Costa E Silva, Filipe; Pereira, Joao S; Werner, Christiane

    2014-01-01

    Semi-arid ecosystems contribute about 40% to global net primary production (GPP) even though water is a major factor limiting carbon uptake. Evapotranspiration (ET) accounts for up to 95% of the water loss and in addition, vegetation can also mitigate drought effects by altering soil water distribution. Hence, partitioning of carbon and water fluxes between the soil and vegetation components is crucial to gain mechanistic understanding of vegetation effects on carbon and water cycling. However, the possible impact of herbaceous vegetation in savanna type ecosystems is often overlooked. Therefore, we aimed at quantifying understory vegetation effects on the water balance and productivity of a Mediterranean oak savanna. ET and net ecosystem CO2 exchange (NEE) were partitioned based on flux and stable oxygen isotope measurements and also rain infiltration was estimated. The understory vegetation contributed importantly to total ecosystem ET and GPP with a maximum of 43 and 51%, respectively. It reached water-use efficiencies (WUE; ratio of carbon gain by water loss) similar to cork-oak trees. The understory vegetation inhibited soil evaporation (E) and, although E was large during wet periods, it did not diminish WUE during water-limited times. The understory strongly increased soil water infiltration, specifically following major rain events. At the same time, the understory itself was vulnerable to drought, which led to an earlier senescence of the understory growing under trees as compared to open areas, due to competition for water. Thus, beneficial understory effects are dominant and contribute to the resilience of this ecosystem. At the same time the vulnerability of the understory to drought suggests that future climate change scenarios for the Mediterranean basin threaten understory development. This in turn will very likely diminish beneficial understory effects like infiltration and ground water recharge and therefore ecosystem resilience to drought.

  20. Satellite Remote Sensing of Net Ecosystem CO2 Exchange Using Optical-IR and Microwave Sensors: Algorithm Development for the SMAP Decadal Survey Mission

    NASA Astrophysics Data System (ADS)

    Jones, L. A.; Kimball, J. S.; Reichle, R. H.; Zhang, K.; McDonald, K. C.

    2009-12-01

    The global balance between photosynthesis, respiration, and disturbance determines whether ecosystems will continue to offset human CO2 emissions. Changes in temperature and moisture constraints can differentially affect photosynthesis and respiration, whereas disturbance and stand succession can push ecosystems far from steady state, shifting carbon source-sink dynamics. Remote sensing and ecosystem process model simulations allow us to characterize the climatic sensitivity of this balance, but effective model parameters are uncertain at continental scales. We developed a carbon model to derive daily net ecosystem exchange of CO2 (NEE) using MODIS GPP and surface soil moisture and temperature retrievals from AMSR-E as driving data. We apply Bayesian synthesis to parameterize the model with a range of FLUXNET tower CO2 measurements across representative global biomes, while accounting for error in flux observations, driving data, and model structure. Model fit diagnostics are compared to determine the relative value of remotely sensed information for accurate prediction of carbon fluxes. Model parameters vary with ecosystem type and indicate that most ecosystems have not reached soil organic carbon pools expected for steady state. Model fit is relatively more impacted by MODIS GPP than by AMSR-E temperature and moisture. AMSR-E moisture explains arid region fluxes, whereas temperature is a stronger predictor for high-latitude locations. The results of this study offer a benchmark for calibrating and assessing the incremental value of Soil Moisture Active Passive (SMAP) mission observations over information available from existing sensors. The Soil Moisture Active Passive (SMAP) mission with scheduled 2013 launch date will provide moderate resolution soil moisture (10 km) and freeze-thaw state (1-3 km) information potentially providing new estimates of land surface processes, including daily NEE. This work was performed at The University of Montana and Jet

  1. Stable oxygen isotope and flux partitioning demonstrates understory of an oak savanna contributes up to half of ecosystem carbon and water exchange

    PubMed Central

    Dubbert, Maren; Piayda, Arndt; Cuntz, Matthias; Correia, Alexandra C.; Costa e Silva, Filipe; Pereira, Joao S.; Werner, Christiane

    2014-01-01

    Semi-arid ecosystems contribute about 40% to global net primary production (GPP) even though water is a major factor limiting carbon uptake. Evapotranspiration (ET) accounts for up to 95% of the water loss and in addition, vegetation can also mitigate drought effects by altering soil water distribution. Hence, partitioning of carbon and water fluxes between the soil and vegetation components is crucial to gain mechanistic understanding of vegetation effects on carbon and water cycling. However, the possible impact of herbaceous vegetation in savanna type ecosystems is often overlooked. Therefore, we aimed at quantifying understory vegetation effects on the water balance and productivity of a Mediterranean oak savanna. ET and net ecosystem CO2 exchange (NEE) were partitioned based on flux and stable oxygen isotope measurements and also rain infiltration was estimated. The understory vegetation contributed importantly to total ecosystem ET and GPP with a maximum of 43 and 51%, respectively. It reached water-use efficiencies (WUE; ratio of carbon gain by water loss) similar to cork-oak trees. The understory vegetation inhibited soil evaporation (E) and, although E was large during wet periods, it did not diminish WUE during water-limited times. The understory strongly increased soil water infiltration, specifically following major rain events. At the same time, the understory itself was vulnerable to drought, which led to an earlier senescence of the understory growing under trees as compared to open areas, due to competition for water. Thus, beneficial understory effects are dominant and contribute to the resilience of this ecosystem. At the same time the vulnerability of the understory to drought suggests that future climate change scenarios for the Mediterranean basin threaten understory development. This in turn will very likely diminish beneficial understory effects like infiltration and ground water recharge and therefore ecosystem resilience to drought. PMID

  2. A carbon budget of Arizona: Comparing Natural Ecosystems with Emissions from Human Activities

    NASA Astrophysics Data System (ADS)

    Ford, A. C.; Finley, B. K.; Koch, G. W.; Hungate, B. A.

    2011-12-01

    A carbon budget of Arizona was constructed to examine the potential for carbon uptake by the state's ecosystems to mitigate human-caused emissions of greenhouse gases. The NASA-CASA (Carnegie Ames Stanford Approach) carbon flux model was used to estimate annual ecosystem CO2 exchange and the State's 2006 greenhouse gas inventory provided data on emissions from transportation, industry, waste, agriculture, electricity, industrial, and residential fuel use. The net carbon flux from primary production in the eight major land resource areas in the state averaged -1.56 million metric tons of carbon (MMTC) per year between 2001 and 2004. This net uptake from the atmosphere amounts to only 1.5% of statewide anthropogenic emissions of 99 MMTCE per year. Given this large imbalance and that projected climate trends for the region are likely to reduce C stocks in the state's forest and woodland ecosystems, land management to promote ecosystem carbon uptake is not a realistic solution to mitigate Arizona's anthropogenic greenhouse gas emissions.

  3. Ecosystem carbon balance in a drier future: land-atmosphere exchanges of CO2, water and energy across semiarid southwestern North America

    NASA Astrophysics Data System (ADS)

    Biederman, J. A.; Scott, R. L.; Goulden, M.; Litvak, M. E.; Kolb, T.; Yépez, E. A.; Oechel, W. C.; Meyers, T. P.; Papuga, S. A.; Ponce-Campos, G.; Krofcheck, D. J.; Maurer, G. E.; Dore, S.; Garatuza, J.; Bell, T. W.; Krishnan, P.

    2015-12-01

    The southwest US and northwest Mexico are predicted to become warmer and drier, increasing disturbance, shifting ecosystem composition, and altering global CO2 cycling. However, direct measurements of ecosystem land-atmosphere carbon and water exchange in this region have lagged behind those in wetter regions. In this presentation we present a synthesis of CO2, water, and energy exchanges made at 25 Southwest eddy covariance sites (3-10 years each, n = 174 years). This regional gradient includes desert shrublands, grasslands, savannas, and forests and spans ranges of 200 - 800 mm in mean annual precipitation and 2 - 24 ⁰C mean annual temperature, a climate space that has been underrepresented in flux databases and publications. We compare measured fluxes against state-of-the-art remote sensing and modeling products representing current best regional estimates. We find that 65% of annual net ecosystem production of CO2 (NEP) is explained by water availability. Meanwhile, most of the unexplained NEP variability is related to site-specific differences persisting over the observation years, suggesting slow-changing controls such as demography (plant type, age, structure) and legacies of disturbance. Disturbances that kill plants without removing biomass, such as drought, tend to decrease productivity and increase respiration, shifting sites from carbon sinks to sources. However, following disturbances that removed biomass, such as fire, both productivity and respiration decline, with minimal impacts on NEP. Remote sensing and modeling match mean CO2 uptake measurements across spatial gradients in climate and plant functional type. However, measured uptake reveals 200-400% greater interannual variability than model estimates. High variability and sensitivity to water help us understand why semiarid ecosystems dominate the interannual variability of the terrestrial carbon sink in global accounting studies.

  4. A comparative assessment of tools for ecosystem services quantification and valuation

    USGS Publications Warehouse

    Bagstad, Kenneth J.; Semmens, Darius; Waage, Sissel; Winthrop, Robert

    2013-01-01

    To enter widespread use, ecosystem service assessments need to be quantifiable, replicable, credible, flexible, and affordable. With recent growth in the field of ecosystem services, a variety of decision-support tools has emerged to support more systematic ecosystem services assessment. Despite the growing complexity of the tool landscape, thorough reviews of tools for identifying, assessing, modeling and in some cases monetarily valuing ecosystem services have generally been lacking. In this study, we describe 17 ecosystem services tools and rate their performance against eight evaluative criteria that gauge their readiness for widespread application in public- and private-sector decision making. We describe each of the tools′ intended uses, services modeled, analytical approaches, data requirements, and outputs, as well time requirements to run seven tools in a first comparative concurrent application of multiple tools to a common location – the San Pedro River watershed in southeast Arizona, USA, and northern Sonora, Mexico. Based on this work, we offer conclusions about these tools′ current ‘readiness’ for widespread application within both public- and private-sector decision making processes. Finally, we describe potential pathways forward to reduce the resource requirements for running ecosystem services models, which are essential to facilitate their more widespread use in environmental decision making.

  5. The strength of contributions from topography mismatch and measurement filtering to simulated net ecosystem exchange in complex terrain

    NASA Astrophysics Data System (ADS)

    Brooks, B.; Desai, A. R.; Stephens, B. B.; Jacobson, A. R.

    2011-12-01

    Global scale carbon cycle inverse models provide invaluable information for the construction of empirically based carbon budgets based on in situ measurements. In landscapes of predominantly smooth topography inverse carbon cycle models are useful for diagnosing the magnitude and climate sensitivity of different regional carbon sinks. However, in landscapes of predominately complex topography inversion model results come with strong caveats for two reasons: 1) Coarse gridding of model topography can lead the model to sample observations at elevations far above the model surface, and 2) Transport wind fields over smoothed model representations of mountain regions are not always sufficiently resolved to inform the model about the source region for assimilated measurements. The uncertainty contributed by incorrect winds and topography mismatches (e.g., differences between the actual measurement elevation and model surface on the order of 1,000 m) is thought to be smaller for higher resolution regional inversion models (e.g., Gockede et al., 2010; Schuh et al. 2010), but these uncertainties are not well constrained for larger scale inversion systems (e.g., Peters et al., 2010), which are one of few ways for determining the relative priority of regional sinks. In this work we examine the effects on net ecosystem exchange (NEE) for a global scale inversion system when 1) topography mismatches are ameliorated, and 2) subset observations consistent with model resolution are used rather than observation-based subsets. Our focus is to use an example inversion model system, CarbonTracker (Peters et al., 2007; 2010), driven by CO2 mixing ratio measurements, including the RACCOON Network in the United States Mountain West (raccoon.ucar.edu), to quantify and compare the contribution to NEE from tower elevation mismatches and filtering strategies across biomes and and in terms of forecast skill (model data mismatch). We further compare our results to the differences in NEE over

  6. The Ecohydrological Consequences of Woody Plant Encroachment: How Accessibility to Deep Soil Water Resources Affects Ecosystem Carbon and Water Exchange

    NASA Astrophysics Data System (ADS)

    Scott, R. L.; Huxman, T. E.; Barron-Gafford, G.; Jenerette, D.; Young, J. M.

    2013-12-01

    Woody plant encroachment into grassland systems, a process that has increased rapidly over the last century, has potentially broad ecohydrological consequences by affecting the way ecosystems use water and cycle carbon. This study examines the influence of precipitation- and groundwater-derived water availability by comparing eddy covariance measurements of water vapor and carbon dioxide fluxes over a riparian grassland, shrubland, and woodland, and an upland grassland site in southeastern Arizona USA. Compared to the upland grassland, the riparian sites exhibited greater net carbon uptake (NEP) and higher evapotranspiration (ET) across a longer portion of the year. Among the riparian sites, however, the grassland was less able to take advantage of the stable groundwater supply. Increasing woody plant density facilitated greater water and carbon exchange that became increasingly decoupled from incident precipitation (P). How groundwater accessibility affected NEP was more complex than ET. Respiration (Reco) costs were higher for the riparian grassland so, while it had a similar ET and gross carbon uptake (GEP) to the shrubland, its NEP was substantially less. Also, riparian grassland fluxes were much more variable due to flooding that occurred at the site, which could stimulate or inhibit NEP. Woodland NEP was largest but surprisingly similar to the less mature and dense shrubland even while having much greater GEP. Woodland NEP responded negatively to P, due to the stimulation of Reco likely due to greater amounts of aboveground and soil carbon. With many areas of the world experiencing woody plants encroachment, encroachment into areas where there are additional deep soil water sources, such as in riparian settings or in areas of deep soil moisture recharge, will likely increase carbon sequestration but at the expense of higher water use.

  7. Net ecosystem exchange of CO2 with rapidly changing high Arctic landscapes.

    PubMed

    Emmerton, Craig A; St Louis, Vincent L; Humphreys, Elyn R; Gamon, John A; Barker, Joel D; Pastorello, Gilberto Z

    2016-03-01

    High Arctic landscapes are expansive and changing rapidly. However, our understanding of their functional responses and potential to mitigate or enhance anthropogenic climate change is limited by few measurements. We collected eddy covariance measurements to quantify the net ecosystem exchange (NEE) of CO2 with polar semidesert and meadow wetland landscapes at the highest latitude location measured to date (82°N). We coupled these rare data with ground and satellite vegetation production measurements (Normalized Difference Vegetation Index; NDVI) to evaluate the effectiveness of upscaling local to regional NEE. During the growing season, the dry polar semidesert landscape was a near-zero sink of atmospheric CO2 (NEE: -0.3 ± 13.5 g C m(-2) ). A nearby meadow wetland accumulated over 300 times more carbon (NEE: -79.3 ± 20.0 g C m(-2) ) than the polar semidesert landscape, and was similar to meadow wetland NEE at much more southerly latitudes. Polar semidesert NEE was most influenced by moisture, with wetter surface soils resulting in greater soil respiration and CO2 emissions. At the meadow wetland, soil heating enhanced plant growth, which in turn increased CO2 uptake. Our upscaling assessment found that polar semidesert NDVI measured on-site was low (mean: 0.120-0.157) and similar to satellite measurements (mean: 0.155-0.163). However, weak plant growth resulted in poor satellite NDVI-NEE relationships and created challenges for remotely detecting changes in the cycling of carbon on the polar semidesert landscape. The meadow wetland appeared more suitable to assess plant production and NEE via remote sensing; however, high Arctic wetland extent is constrained by topography to small areas that may be difficult to resolve with large satellite pixels. We predict that until summer precipitation and humidity increases enough to offset poor soil moisture retention, climate-related changes to productivity on polar semideserts may be restricted. PMID:26279166

  8. Net ecosystem CO2 exchange and evapotranspiration of a sphagnum mire: field measurements and model simulations

    NASA Astrophysics Data System (ADS)

    Olchev, Alexander; Volkova, Elena; Karataeva, Tatiana; Zatsarinnaya, Dina; Novenko, Elena

    2014-05-01

    The spatial and temporal variability of net ecosystem exchange of CO2 (NEE) and evapotranspiration (ET) of a karst-hole sphagnum peat mire situated at the boundary between broad-leaved and forest-steppe zones in the central part of European Russia (54.06N, 37.59E, 260 m a.s.l.) was described using results of field measurements and simulations with Mixfor-3D model. The area of the mire is about 1.2 ha and it is surrounded by a broadleaved forest stand. It is a typical peat mire according to water and mineral supply as well as to vegetation composition. The vegetation of the peripheral parts of the mire is typical eutrophic whereas the vegetation in its central part is represented by meso-oligothrophic plant communities. To describe the spatial variability of NEE and ET within the mire a portable measuring system consisting of a transparent ventilated chamber combined with an infrared CO2 and H2O analyzer LI-840A (Li-Cor, USA) was used. The measurements were provided along a transect from the southern peripheral part of the mire to its center under sunny clear-sky weather conditions in the period from May to September of 2012 and from May 2013 to October 2013. The chamber method was used for measurements of NEE and ET fluxes because of small size of the mire, a very uniform surrounding forest stand and the mosaic mire vegetation. All these factors promote very heterogeneous exchange conditions within the mire and make it difficult to apply, for example, an eddy covariance method that is widely used for flux measurements in the field. The results of the field measurements showed a significant spatial and temporal variability of NEE and ET that was mainly influenced by incoming solar radiation, air temperature and ground water level. During the entire growing season the central part of the mire was a sink of CO2 for the atmosphere (up to 6.8±4.2 µmol m-2 s-1 in June) whereas its peripheral part, due to strong shading by the surrounding forest, was mainly a source of

  9. Impact of extreme inter-annual climatic events on the net ecosystem carbon dioxide exchange of a Sitka spruce forest

    NASA Astrophysics Data System (ADS)

    Saunders, M.; Tobin, B.; Gioria, M.; Cacciotti, E.; Benanti, G.; Osborne, B. A.

    2013-12-01

    Temperature and precipitation are key climatic drivers of the global carbon cycle and play an important role in the greenhouse gas mitigation potential of terrestrial ecosystems. The impacts of extreme climatic variability, which in this study were defined by differences in rainfall and temperature of >5% (IPCC, 2012) relative to the long-term site mean (1978-2007), were assessed using eddy covariance-based measurements of net ecosystem carbon dioxide exchange (NEE). Precipitation in 2009 and 2010 was 1156 mm and 741 mm, respectively and approximately 35% higher and 16% lower than the 30 year mean for this region (1978-2007). The differences in precipitation in 2009 were not uniformly distributed throughout the year and occurred largely during the growing season (April-August). The mean annual air temperature in 2010 was ~17% lower than the 30 year mean, and characterized by a number of extended sub-zero temperature events during the winter months. These climatic differences resulted in a 1.07 t C ha yr-1 difference between the annual estimates of NEE in 2009 (8.14 × 1.94 t C ha yr-1) and 2010 (9.21 × 0.99 t C ha yr-1) respectively. The measured NEE in 2009 and 2010 represented a 5.6% decrease and a 6.9% increase relative to the long-term mean measured at this site (2002-2008; 8.62 × 1.39 t C ha yr-1). The components of NEE, gross primary productivity (GPP) and ecosystem respiration (Reco), also showed differences between years. In 2009, GPP was ~19% lower when compared to 2010, most likely due to a reduction in stand photosynthesis at higher irradiances during the growing season that was correlated with higher soil water availability. The extended sub-zero temperatures experienced during the winter of 2010 had a greater impact on GPP, relative to Reco, resulting in a net loss of carbon during these periods. Variations in GPP were, however, positively correlated with Reco in both years. NEE was correlated with temperature in all years, with a slope (negative) of

  10. Effects of episodic flooding on the net ecosystem CO2 exchange of a supratidal wetland in the Yellow River Delta

    NASA Astrophysics Data System (ADS)

    Han, Guangxuan; Chu, Xiaojing; Xing, Qinghui; Li, Dejun; Yu, Junbao; Luo, Yiqi; Wang, Guangmei; Mao, Peili; Rafique, Rashad

    2015-08-01

    Episodic flooding due to intense rainfall events is characteristic in many wetlands, which may modify wetland-atmosphere exchange of CO2. However, the degree to which episodic flooding affects net ecosystem CO2 exchange (NEE) is poorly documented in supratidal wetlands of coastal zone, where rainfall-driven episodic flooding often occurs. To address this issue, the ecosystem CO2 fluxes were continuously measured using the eddy covariance technique for 4 years (2010-2013) in a supratidal wetland in the Yellow River Delta. Our results showed that over the growing season, the daily average uptake in the supratidal wetland was -1.4, -1.3, -1.0, and -1.3 g C m-2 d-1 for 2010, 2011, 2012, and 2013, respectively. On the annual scale, the supratidal wetland functioned as a strong sink for atmospheric CO2, with the annual NEE of -223, -164, and -247 g C m-2 yr-1 for 2011, 2012, and 2013, respectively. The mean diurnal pattern of NEE exhibited a smaller range of variation before episodic flooding than after it. Episodic flooding reduced the average daytime net CO2 uptake and the maximum rates of photosynthesis. In addition, flooding clearly suppressed the nighttime CO2 release from the wetland but increased its temperature sensitivity. Therefore, effects of episodic flooding on the direction and magnitude of NEE should be considered when predicting the ecosystem responses to future climate change in supratidal wetlands.

  11. Hydrological exchanges and Organic Matter dynamics in highly vulnerable tidal wetland ecosystems at the land-ocean interface

    NASA Astrophysics Data System (ADS)

    Tzortziou, M.; Neale, P.; Megonigal, P.; Loughner, C.

    2014-12-01

    Occupying a critical interface between the land and the sea, tidal wetlands are amongst the most ecologically valuable and economically important ecosystems on Earth, but also especially vulnerable to human pressures and climate change. These rich in biodiversity and highly productive ecosystems are hot spots of biogeochemical transformations, consistently exchanging Organic Matter with adjacent estuarine waters through tidal flushing. Here we discuss new results on the amount and directions of biogeochemical exchanges at the tidal wetland-estuary interface. Detailed microbial and photochemical degradation experiments and high resolution bio-optical observations in tidal freshwater and salt marsh systems of the Eastern US coast provide insights on the quality and fate of the organic compounds exported from tidal marshes and their influence on near-shore biological processes, biogeochemical cycles and optical variability. Impacts of anthropogenic activities and resulting air-pollution are also discussed. High resolution model runs were performed using the Community Multi-scale Air Quality (CMAQ) model, to examine atmospheric composition along the shoreline where processes such as sea and bay breeze circulations often favor the accumulation and air-deposition of atmospheric pollutants, impacting biogeochemical processes in sensitive tidal wetland ecosystems.

  12. The Effect of Temperature and Increased Rainfall on Carbon Dioxide Exchange in a High Arctic Ecosystem: Improving Models and Testing Linearity of Response

    NASA Astrophysics Data System (ADS)

    Steltzer, H.; Welker, J.; Sullivan, P.

    2006-12-01

    Ecosystem carbon dioxide exchange determines the terrestrial flux of carbon dioxide to the atmosphere through the two component processes of photosynthesis and respiration. Temperature and water availability are dominant factors that regulate carbon dioxide exchange and ecosystem productivity across the globe. Yet, in many ecosystems, the complex interaction of temperature and water availability and their individual and combined effects on photosynthesis and respiration make it difficult to predict how climate change will affect carbon dioxide exchange. For example, climate warming can increase carbon dioxide uptake in wetter Arctic ecosystems, but leads to the loss of carbon dioxide to the atmosphere in drier Arctic ecosystems. Characterizing how temperature and water availability affect ecosystem carbon exchange in the Arctic is essential to determine whether the rate of climate warming could accelerate due to carbon dioxide losses from Arctic ecosystems. We conducted a multi-level warming experiment that included control plots and two- levels of warming in a widespread High Arctic ecosystem. Infrared lamps were used to warm the tundra during the growing season and rainfall was increased by 50 percent in control plots and the higher level warming treatment. Carbon dioxide exchange was measured using chamber techniques over several 24-hour periods during the growing season for three years and was resolved into the component fluxes. Climate and biophysical variables that affect carbon dioxide exchange rates were measured in coordination with these flux measurements. We chose to analyze the data from this experiment by fitting the data to light and temperature response functions for gross ecosystem photosynthesis and ecosystem respiration, respectively. Based on our sample size of 30 experimental plots (5 treatments x 6 replicates), we selected relatively simple models of carbon dioxide exchange to minimize overfitting, but considered linear and nonlinear models

  13. Geospatial variability of soil CO2-C exchange in the main terrestrial ecosystems of Keller Peninsula, Maritime Antarctica.

    PubMed

    Thomazini, A; Francelino, M R; Pereira, A B; Schünemann, A L; Mendonça, E S; Almeida, P H A; Schaefer, C E G R

    2016-08-15

    Soils and vegetation play an important role in the carbon exchange in Maritime Antarctica but little is known on the spatial variability of carbon processes in Antarctic terrestrial environments. The objective of the current study was to investigate (i) the soil development and (ii) spatial variability of ecosystem respiration (ER), net ecosystem CO2 exchange (NEE), gross primary production (GPP), soil temperature (ST) and soil moisture (SM) under four distinct vegetation types and a bare soil in Keller Peninsula, King George Island, Maritime Antarctica, as follows: site 1: moss-turf community; site 2: moss-carpet community; site 3: phanerogamic antarctic community; site 4: moss-carpet community (predominantly colonized by Sanionia uncinata); site 5: bare soil. Soils were sampled at different layers. A regular 40-point (5×8 m) grid, with a minimum separation distance of 1m, was installed at each site to quantify the spatial variability of carbon exchange, soil moisture and temperature. Vegetation characteristics showed closer relation with soil development across the studied sites. ER reached 2.26μmolCO2m(-2)s(-1) in site 3, where ST was higher (7.53°C). A greater sink effect was revealed in site 4 (net uptake of 1.54μmolCO2m(-2)s(-1)) associated with higher SM (0.32m(3)m(-3)). Spherical models were fitted to describe all experimental semivariograms. Results indicate that ST and SM are directly related to the spatial variability of CO2 exchange. Heterogeneous vegetation patches showed smaller range values. Overall, poorly drained terrestrial ecosystems act as CO2 sink. Conversely, where ER is more pronounced, they are associated with intense soil carbon mineralization. The formations of new ice-free areas, depending on the local soil drainage condition, have an important effect on CO2 exchange. With increasing ice/snow melting, and resulting widespread waterlogging, increasing CO2 sink in terrestrial ecosystems is expected for Maritime Antarctica. PMID:27110991

  14. Effect of land use on carbon dioxide, water vapour and energy exchange over terrestrial ecosystems in Southwestern France during the CERES campaign

    NASA Astrophysics Data System (ADS)

    Jarosz, N.; Béziat, P.; Bonnefond, J. M.; Brunet, Y.; Calvet, J. C.; Ceschia, E.; Elbers, J. A.; Hutjes, R. W. A.; Traullé, O.

    2009-03-01

    Eddy fluxes were measured over different ecosystems, winter and summer crops, a maritime pine forest at different stages of development and grassland, from 17 May to 26 June 2005 in the southwestern region of France. During the experiment, summer crops started growing whereas winter crops and grassland achieved their senescence. Comparatively, the other ecosystems had a much slower growth emphasized by soil water deficit at forest sites. The ten ecosystems showed different partitioning of available energy. Net radiation was the highest above the maritime pine forest, followed, in decreasing order, by the crops, the vineyard and the grassland. Over the whole campaign period, the Bowen ratio (β=H/LE) was larger above the forest sites than for the other sites. The various vegetation types also showed contrasting net ecosystem exchange (NEE) dynamics following their growth status and respective behaviour in response to drought. Both the clearcut and summer crops before irrigation and plant growth behaved as sources of CO2, whereas the vineyard, the mature forest and winter crops acted as sinks. However the maize crops became substantial sinks of CO2 after the start of irrigation and canopy growth, with fluxes twice as large as for the mature pine forest. Finally, throughout the experiment, forest, grassland and crops sequestrated from about 50 gC m-2 to 230 gC m-2, while the cleacut and the beans crop rejected about 30 gC m-2. These results support the idea that converting a mature forest to a clearcut or bare soil available to agricultural use enhances the sensible heat flux and shifts the ecosystem from a sink to a source of carbon.

  15. Long term carbon dioxide exchange above a mixed forest in the Belgian Ardennes: evaluation of different approaches to deduce total ecosystem respiration from Eddy covariance measurements

    NASA Astrophysics Data System (ADS)

    Jérôme, Elisabeth; Aubinet, Marc; Heinesch, Bernard

    2010-05-01

    The general aim of this research is to analyze inter annual variability of carbon dioxide (CO2) fluxes exchanged by a mixed forest located at the Vielsalm experimental site in Belgium. At this site, CO2 flux measurements started in 1996 and are still going on. Thirteen complete years of measurements are thus available. Net Ecosystem Exchange (NEE) inter annual variability may be driven by gross primary productivity (GPP) or Total Ecosystem Respiration (TER), which should thus be both quantified. Using flux partitioning methods, TER is deduced from NEE measurements. GPP is then obtained by subtracting TER from NEE. Initially, a robust estimation of TER is required. This work seeks to compare two independent approaches to assess TER in order to quantify the implications on inter-annual variability. The comparison was performed on twelve complete years. TER estimates can be deduced by extrapolating to the whole day NEE measurements taken during selected night or day periods. In both case, the extrapolation is performed by using a respiration response to temperature. The first approach, referred as the night-time approach, consisted in calculating TER using a temperature response function derived from night-time data sets (Reichstein et al., 2005). The second approach, referred as the daytime approach, consisted in assessing TER from the intercept of the NEE/Photosynthetically Photon Flux Density (PPFD) response (Wohlfahrt et al., 2005). For each approach, different modalities were compared: the use of long term (annual) or short term (15 days) data sets for the night-time approach and the use of different types of regression for the daytime approach. In addition, the impact of the temperature choice was studied for each of the approaches. For the night-time approach, main results showed that air temperature sensitivity of ecosystem respiration derived from annual data did not reflect the short-term air temperature sensitivity. Vielsalm is a summer active ecosystem

  16. Comparing Individual Health Coverage On and Off the Affordable Care Act's Insurance Exchanges.

    PubMed

    McCue, Michael J; Hall, Mark A

    2015-08-01

    The new health insurance exchanges are the core of the Affordable Care Act's (ACA) reforms, but how the law improves the nonsubsidized portion of the individual market is also important. This issue brief compares products sold on and off the exchanges to gain insight into how the ACA's market reforms are functioning. Initial concerns that insurers might seek to enroll lower-risk customers outside the exchanges have not been realized. Instead, more-generous benefit plans, which appeal to people with health problems, constitute a greater portion of plans sold off-exchange than those sold on-exchange. Although insur­ers that sell mostly on the exchanges incur an additional fee, they still devote a greater portion of their premium dollars to medical care. Their projected admin­istrative costs and profit margins are lower than are those of insurers selling only off the exchanges. PMID:26372970

  17. Effects of cloud optical thickness on net ecosystem exchange in a Northern U.S. temperate forest

    NASA Astrophysics Data System (ADS)

    Cheng, S. J.; Steiner, A. L.; Nadelhoffer, K.; Bohrer, G.; Curtis, P.

    2011-12-01

    Surface observations show that since the 1950s, the amount of cloud cover has increased over the United States. Changes in cloud properties could affect the degree to which forests act as carbon sinks, since clouds influence the amount and quality of light that reaches and penetrates forest canopies. Canopy photosynthesis can be higher under cloudy conditions than under clear skies because scattered, diffuse light can penetrate deeper into canopies and reach leaves that would otherwise be light-limited. As forests undergo canopy structural modifications during succession, cloud impacts on forest carbon storage may change. Most studies related to this topic use measured sunlight at the Earth's surface as a proxy for cloud cover. To determine a more precise relationship between cloud conditions and forest carbon storage, cloud optical thickness values from 2000-2010 were retrieved from NASA's Moderate Resolution Imaging Spectroradiometer (MODIS). These values are used to evaluate the amount of radiation extinguished by clouds and its impact on net ecosystem exchange (NEE), gross primary production (GPP) and respiration in a regionally representative forest equipped with an Ameriflux eddy co-variance tower at the University of Michigan Biological Station (UMBS). Comparisons of the Ameriflux site with the UMBS Forest Accelerated Succession ExperimenT (FASET) allow testing of how later successional forests may respond to cloud conditions. In the FASET experiment, more than 6,700 early successional aspen and birch trees (~35% leaf area index) were stem-girdled to create a later-successional forest. NEE, GPP and respiration relationships measured by the FASET tower are compared to those seen at the Ameriflux site. The interaction between cloud optical thickness and other environmental factors, such as air temperature and soil moisture, is also examined to determine which conditions result in stronger effects of clouds on forest processes.

  18. [Characteristics of net ecosystem flux exchanges over Stipa krylovii steppe in Inner Mongolia].

    PubMed

    Yang, Juan; Zhou, Guang-Sheng; Wang, Yun-Long; Wang, Yu-Hui

    2008-03-01

    Based on an entire year continuous measurement of surface fluxes by eddy covariance (EC) tower and micro-climate gradient observation system, the diurnal and seasonal dynamics of net ecosystem fluxes including carbon, water, and heat fluxes over Stipa krylovii steppe in Inner Mongolia were investigated. The results indicated that the diurnal pattern of carbon fluxes during growing season could be expressed as U curve. S. krylovii steppe ecosystem emitted CO2 before the sunrise and absorbed CO2 after the sunrise, with the maximum CO2 uptake around noon. The ecosystem had weaker CO2 uptake after the noon, and turned to emit CO2 after sunset. The CO2 uptake by S. krylovii steppe ecosystem reached the maximum in September, followed in August, and got the minimum in October. The diurnal dynamic patterns of sensible heat flux (Hs) and latent heat flux (LE) could be expressed as inverse U curves. The Hs and LE over S. krylovii steppe ecosystem were positive during the daytime, while Hs was negative and LE was close to zero during the nighttime. The ecosystem had the highest Hs and LE in May and September, respectively. In winter, the steppe acted as a weak carbon source, with the CO2 flux being small; while in summer, it became an obvious carbon sink.

  19. Responses of ecosystem carbon dioxide exchange to nitrogen addition in a freshwater marshland in Sanjiang Plain, Northeast China.

    PubMed

    Zhang, Lihua; Song, Changchun; Nkrumah, Philip N

    2013-09-01

    It has widely been documented that nitrogen (N) stimulates plant growth and net primary production. But how N affects net ecosystem CO2 exchange (NEE) is still dispute. We conduct an experimental study to assess the response of NEE to N addition in a freshwater marsh. Experimental treatments involved elevated N and control treatments on triplicate 1 m(2) plots. Gas exchange, air temperature, plant biomass and leaf area as well as N% of leaf were measured from 2004 to 2005. The results indicated that N addition initially decreased the CO2 sequestration but the trend changed in the second year. It was concluded that N addition enhanced the greenhouse effect in marshland as far as global warming potential (GWP) is concerned. This increase was attributed to a substantial increase in CH4 and N2O emissions after N addition. We recommended long-term studies to further clarify the effect of N addition on NEE. PMID:23727568

  20. Flax pond ecosystem study: exchanges of CO/sub 2/ between a salt marsh and the atmosphere

    SciTech Connect

    Houghton, R.A.; Woodwell, G.M.

    1980-12-01

    Profiles of CO/sub 2/ concentration, windspeed, and temperature were used in the aerodynamic flux technique to calculate the CO/sub 2/ exchange between a Long Island salt marsh and the atmosphere. Uptake of CO/sub 2/ by the marsh during hours of sunlight and release during the night occurred during all times of the year. The rates of CO/sub 2/ exchange were highest during midsummer, 2.3 g CO/sub 2/.m/sup -2/.h/sup -1/ averaged over the daylight hours of July, and 1.3 g CO/sub 2/.m/sup -2/.h/sup -1/ for both uptake and release. The net 24-h exchange rates followed Spartina growth and senescence during the summer and fall, and photosynthesis of benthic algae during late winter and spring. There was a net uptake of Co/sub 2/ over 24 h by the marsh during all seasons except autumn. The net annual flow of carbon was from the atmosphere to Flax Pond (approx. = 300 g C.m/sup -2/.yr/sup -1/ averaged over the entire marsh ecosystem). This flux was larger than the net exchange of carbon between the marsh and either uplands, sediments, or coastal waters. The net uptake of CO/sub 2/ during summer was less than the net productivity of the vascular plants, indicating that some of the CO/sub 2/ assimilated by the plants came from heterotrophic respiration within the marsh. Nevertheless, respiration by the plants was by far the largest source of CO/sub 2/ from the marsh surface. Nighttime respiration of the ecosystem released a total of approx. = 510 g C.m/sup -2/.yr/sup -1/ to the atmosphere.

  1. Atmospheric N deposition and feedbacks on net ecosystem CO2 exchange at a semi-natural peatland site

    NASA Astrophysics Data System (ADS)

    Hurkuck, Miriam; Brümmer, Christian; Spott, Oliver; Flessa, Heinz; Kutsch, Werner L.

    2013-04-01

    Large areas of Northern Germany have been converted from natural peat bogs to arable land and were subjected to draining and peat cutting in the past. The few protected peatland areas remaining are affected by high nitrogen (N) deposition. This is the case at our study site - a semi-natural raised bog - which although located in a natural park, is surrounded by highly fertilized agricultural land and highly emitting animal husbandry farms. In this study, we use a combined approach of two independent methods to quantify atmospheric N deposition. We further investigate possible feedbacks of seasonal variation in N deposition on net ecosystem CO2 exchange (NEE). Fluxes of ammonia (NH3) and its atmospheric reactants are measured by a KAPS-denuder system. Additionally, total N input from the atmosphere into a soil-plant model ecosystem is investigated by a 15N dilution method called 'Integrated Total Nitrogen Input' (ITNI). With this approach, we allocate atmospheric N after its uptake by the ecosystem into its different fractions and investigate both plant-species effects (Lolium multiflorum, Eriophorum vaginatum) and influences of the plant biomass production induced by different amounts of fertilizer addition. Continuous eddy-covariance measurements are carried out to measure NEE. Maximum NH3 depositions of 0.41 ± 0.04 kg ha-1 week-1 were found in spring 2012. The proportion of fluxes of other N compounds such as HNO3, aerosol NH4 and NO3 was usually around 20 % of total dry N measured by KAPS denuders. In total, dry N deposition was 11.2 ± 0.9 kg N ha-1 yr-1 over the first year of experiments. Complemented with wet N measurements using bulk samplers, total N depositions of about 25.0 kg ha-1 yr-1 were found. The mean atmospheric N uptake determined with the ITNI system was 3.99 ± 0.82 mg N g-1 dry weight from July to October 2011. About two third of total deposited airborne N was allocated in above-ground plant biomass and roots. Upscaling of data based on pot

  2. Ambient ammonia in terrestrial ecosystems: a comparative study in the Tennessee Valley, USA.

    PubMed

    Allen, Ridwaana; Myles, LaToya; Heuer, Mark W

    2011-06-15

    Atmospheric ammonia has been shown to degrade regional air quality and affect environmental health. In-situ measurements of ammonia are needed to determine how ambient concentrations vary in different ecosystems and the extent to which emission sources contribute to those levels. The objective of this study was to measure and compare ammonia concentrations in two Tennessee Valley (USA) ecosystems: a forested rural area and a metropolitan site adjacent to a main transportation route. Integrated samples of atmospheric ammonia were collected with annular denuder systems for ~4 weeks during the summer of 2009 in both ecosystems. Ancillary measurements of meteorological variables, such as wind direction and precipitation, were also conducted to determine any relationships with ammonia concentration. Measurements in the two ecosystems revealed ammonia concentrations that were mostly representative of background levels. Arithmetic means were 1.57±0.68 μg m(-3) at the metropolitan site and 1.60±0.77 μg m(-3) in the forest. The geometric mean concentrations for both sites were ~1.46 μg m(-3). Wind direction, and to a lesser extent air temperature and precipitation, did influence measured concentrations. At the metropolitan site, ammonia concentrations were slightly higher in winds emanating from the direction of the interstate highway. Meteorological variables, such as wind direction, and physical factors, such as topography, can affect measurement of ambient ammonia concentrations, especially in ecosystems distant from strong emission sources. The 12-h integrated sampling method used in this study was unable to measure frequent changes in ambient ammonia concentrations and illustrates the need for measurements with higher temporal resolution, at least ~1-2h, in a variety of diverse ecosystems to determine the behavior of atmospheric ammonia and its environmental effects.

  3. Annual net ecosystem exchanges of carbon dioxide and methane from a temperate brackish marsh: should the focus of marsh restoration be on brackish environments?

    NASA Astrophysics Data System (ADS)

    Windham-Myers, L.; Anderson, F. E.; Bergamaschi, B. A.; Ferner, M. C.; Schile, L. M.; Spinelli, G.

    2015-12-01

    The exchange and transport of carbon in tidally driven, saline marsh ecosystems provide habitat and trophic support for coastal wildlife and fisheries, while potentially accumulating and storing carbon at some of the highest rates compared to other ecosystems. However, due to the predicted rise in sea level over the next century, the preservation and restoration of estuarine habitats is necessary to compensate for their expected decline. In addition, restoration of these marsh systems can also reduce the impacts of global climate change as they assimilate as much carbon as their freshwater counterparts, while emitting less methane due to the higher concentrations of sulfate in seawater. Unfortunately, in brackish marshes, with salinity concentrations less than 18 parts per thousand (ppt), simple relationships between methane production, salinity and sulfate concentrations are not well known. Here we present the net ecosystem exchange (NEE) of carbon dioxide and methane, as calculated by the eddy covariance method, from a brackish marsh ecosystem in the San Francisco Estuary where salinity ranges from oligohaline (0.5-5 ppt) to mesohaline (5-18 ppt) conditions. Daily rates of carbon dioxide and methane NEE ranged from approximately 10 gC-CO2 m-2 d-1 and 0 mgC-CH4 m-2 d-1, during the winter to -15 gC-CO2 m-2 d-1 and 30 mgC-CH4 m-2 d-1, in the summer growing season. A comparison between similar measurements made from freshwater wetlands in the Sacramento-San Joaquin Delta found that the daily rates of carbon dioxide NEE were similar, but daily rates of methane NEE were just a small fraction (0-15%). Our research also shows that the daily fluxes of carbon dioxide and methane at the brackish marsh were highly variable and may be influenced by the tidal exchanges of seawater. Furthermore, the observed decline in methane production from summer to fall may have resulted from a rise in salinity and/or a seasonal decline in water and air temperatures. Our research goals are

  4. The Development of Community-Based Health Information Exchanges: A Comparative Assessment of Organizational Models

    ERIC Educational Resources Information Center

    Champagne, Tiffany

    2013-01-01

    The purpose of this dissertation research was to critically examine the development of community-based health information exchanges (HIEs) and to comparatively analyze the various models of exchanges in operation today nationally. Specifically this research sought to better understand several aspects of HIE: policy influences, organizational…

  5. Comparative analysis of European wide marine ecosystem shifts: a large-scale approach for developing the basis for ecosystem-based management.

    PubMed

    Möllmann, Christian; Conversi, Alessandra; Edwards, Martin

    2011-08-23

    Abrupt and rapid ecosystem shifts (where major reorganizations of food-web and community structures occur), commonly termed regime shifts, are changes between contrasting and persisting states of ecosystem structure and function. These shifts have been increasingly reported for exploited marine ecosystems around the world from the North Pacific to the North Atlantic. Understanding the drivers and mechanisms leading to marine ecosystem shifts is crucial in developing adaptive management strategies to achieve sustainable exploitation of marine ecosystems. An international workshop on a comparative approach to analysing these marine ecosystem shifts was held at Hamburg University, Institute for Hydrobiology and Fisheries Science, Germany on 1-3 November 2010. Twenty-seven scientists from 14 countries attended the meeting, representing specialists from seven marine regions, including the Baltic Sea, the North Sea, the Barents Sea, the Black Sea, the Mediterranean Sea, the Bay of Biscay and the Scotian Shelf off the Canadian East coast. The goal of the workshop was to conduct the first large-scale comparison of marine ecosystem regime shifts across multiple regional areas, in order to support the development of ecosystem-based management strategies.

  6. Impact of inter-annual climatic variability on ecosystem carbon exchange in two grazed temperate grasslands with contrasting drainage regimes

    NASA Astrophysics Data System (ADS)

    Choncubhair, Órlaith Ní; Humphreys, James; Lanigan, Gary

    2014-05-01

    Temperate grasslands constitute over 30% of the Earth's naturally-occurring biomes and make an important contribution towards the partial mitigation of anthropogenic greenhouse gas emissions by terrestrial ecosystems. Accumulation of carbon (C) in grassland systems predominantly takes place in below-ground repositories, enhanced by the presence of a stable soil environment with low carbon turnover rates, active rhizodeposition and high levels of residue and organic inputs. Predicted future warming is expected to increase productivity in temperate zones, thereby enhancing rates of terrestrial carbon sequestration. However, the susceptibility of many ecosystems, including grasslands, to extreme climatic events and inter-annual variability has been demonstrated previously. Temperature anomalies as well as modifications in the temporal pattern and quantity of precipitation alter the balance between carbon uptake and release processes and a mechanistic understanding of ecosystem response to such changes is still lacking. In the present study, the impact of extreme inter-annual variability in summer rainfall and temperature on carbon dynamics in two rotationally-grazed grasslands in Ireland was examined. The sites experience similar temperate climatic regimes but differ in soil drainage characteristics. Eddy covariance measurements of net ecosystem exchange of carbon were complemented by regular assessment of standing biomass, leaf cover, harvest exports and organic amendment inputs. The summers of 2012 and 2013 showed contrasting climatic conditions, with summer precipitation 93% higher and 25% lower respectively than long-term means. In addition, soil temperatures were 7% lower and 11% higher than expected. Cool, wet conditions in 2012 facilitated net carbon uptake for more than ten months of the year at the poorly-drained site, however the ecosystem switched to a net source of carbon in 2013 during months with significantly reduced rainfall. In contrast, net C

  7. Ecosystem-Atmosphere Exchange of Carbon, Water and Energy over a Mixed Deciduous Forest in the Midwest

    SciTech Connect

    Danilo Dragoni; Hans Peter Schmid; C.S.B. Grimmond; J.C. Randolph; J.R. White

    2012-12-17

    During the project period we continued to conduct long-term (multi-year) measurements, analysis, and modeling of energy and mass exchange in and over a deciduous forest in the Midwestern United States, to enhance the understanding of soil-vegetation-atmosphere exchange of carbon. At the time when this report was prepared, results from nine years of measurements (1998 - 2006) of above canopy CO2 and energy fluxes at the AmeriFlux site in the Morgan-Monroe State Forest, Indiana, USA (see Table 1), were available on the Fluxnet database, and the hourly CO2 fluxes for 2007 are presented here (see Figure 1). The annual sequestration of atmospheric carbon by the forest is determined to be between 240 and 420 g C m-2 a-1 for the first ten years. These estimates are based on eddy covariance measurements above the forest, with a gap-filling scheme based on soil temperature and photosynthetically active radiation. Data gaps result from missing data or measurements that were rejected in qua)lity control (e.g., during calm nights). Complementary measurements of ecological variables (i.e. inventory method), provided an alternative method to quantify net carbon uptake by the forest, partition carbon allocation in each ecosystem components, and reduce uncertainty on annual net ecosystem productivity (NEP). Biometric datasets are available on the Fluxnext database since 1998 (with the exclusion of 2006). Analysis for year 2007 is under completion.

  8. Interannual hypoxia variability in a coastal upwelling system: Ocean shelf exchange, climate and ecosystem-state implications

    NASA Astrophysics Data System (ADS)

    Monteiro, P. M. S.; van der Plas, A. K.; Mélice, J.-L.; Florenchie, P.

    2008-04-01

    In this study we use multi-year time series to examine the dynamic characteristics of coupled physical-biogeochemical processes that modulate interannual coastal hypoxia in the Benguela upwelling system in the southeast Atlantic. The results confirmed earlier findings on the role of advection to explain much of the seasonal-decadal variability. These results challenge the predominantly biogeochemical basis, namely benthic-pelagic coupling, to understand the variability of hypoxia and its ecosystem implications. Unexpectedly, the results showed that the variability was insensitive to changes in the electron-donating capacity (carbon export fluxes) but strongly dependent on the advected oxygen fluxes. The dynamics of the interaction of equatorial and polar boundary conditions (ocean-shelf exchange) and seasonally phased shelf advection were the key forcing functions that explained hypoxia variability in seasonal-decadal time scales. The vulnerability of the system to climate change lies in the long-term response of the equatorial system that governs seasonal and interannual warming at the Angola-Benguela front as well as wind stress in the Luderitz southern boundary that governs ventilation. The proposed model was able to explain most of the decadal scale variability of two different ecosystem-state indicators. The model predicts a long-term decline of present ecosystem function with climate change.

  9. Thermal optimality of net ecosystem exchange of carbon dioxide and underlying mechanisms

    Technology Transfer Automated Retrieval System (TEKTRAN)

    It has been well established that individual organisms can acclimate and adapt to temperature change to optimize their performance (i.e., achieve thermal optimality). However, whether ecosystems with an assembly of organisms would also undergo thermal optimization has not been examined on a broader ...

  10. Comparing the performance of two ecosystem models in the North Atlantic

    NASA Astrophysics Data System (ADS)

    Daewel, Ute; Samuelsen, Annette

    2015-04-01

    Comparing different biogeochemical models allows for understanding process interactions within model formulations and hence constitutes a good starting point for advanced model development. But 3d biogeochemical models are combinations of coupled modules, representing different aspects of the ecosystem (i.e. physics, ecosystem dynamics, carbon chemistry), and a set of different forcing fields. This creates difficulties in understanding the results from inter-model comparison studies as differences between model results might either stem from each of the modules or from the choice of the forcing fields. Here we present an inter-model comparison study for the North Atlantic ecosystem using two different NPZD type ecosystem models (NORWECOM and ECOSMO) solved in exactly the same physical setup. This approach allows disentangling differences and uncertainties caused by the chosen NPZD model and better understanding the choice of model formulation and parameterisation. Both models were coupled to a North Atlantic version of HYCOM (HYbrid Coordinate Ocean model) forced by the ERA-interim atmospheric reanalysis. ECOSMO is a model originally developed for the North Sea and Baltic Sea ecosystem that has previously been successfully applied to the Barents Sea ecosystem. It resolves 15 state variables including nitrate, ammonia, phosphate, silicate, oxygen, 2 types of phytoplankton, diatoms and flagellates, and 2 types of zooplankton, divided in functional groups based on their feeding preferences, DOM, detritus, opal and 3 types of sediments. This version of NORWECOM in contrast has earlier been used to simulate the North Atlantic ecosystem. It contains 11 state variables including nitrate, phosphate, silicate, oxygen, diatoms and flagellates, 2 size classes of zooplankton, 2 types of detritus, and opal. The aim of the study is to understand the relevance of different model formulation and parameterisations for the solution of the model system and to use this information to

  11. Enhanced seasonal CO2 exchange caused by amplified plant productivity in northern ecosystems.

    PubMed

    Forkel, Matthias; Carvalhais, Nuno; Rödenbeck, Christian; Keeling, Ralph; Heimann, Martin; Thonicke, Kirsten; Zaehle, Sönke; Reichstein, Markus

    2016-02-12

    Atmospheric monitoring of high northern latitudes (above 40°N) has shown an enhanced seasonal cycle of carbon dioxide (CO2) since the 1960s, but the underlying mechanisms are not yet fully understood. The much stronger increase in high latitudes relative to low ones suggests that northern ecosystems are experiencing large changes in vegetation and carbon cycle dynamics. We found that the latitudinal gradient of the increasing CO2 amplitude is mainly driven by positive trends in photosynthetic carbon uptake caused by recent climate change and mediated by changing vegetation cover in northern ecosystems. Our results underscore the importance of climate-vegetation-carbon cycle feedbacks at high latitudes; moreover, they indicate that in recent decades, photosynthetic carbon uptake has reacted much more strongly to warming than have carbon release processes.

  12. Comparing employer-sponsored and federal exchange plans: wide variations in cost sharing for prescription drugs.

    PubMed

    Buttorff, Christine; Andersen, Martin S; Riggs, Kevin R; Alexander, G Caleb

    2015-03-01

    Just under seven million Americans acquired private insurance through the new health insurance exchanges, or Marketplaces, in 2014. The exchange plans are required to cover essential health benefits, including prescription drugs. However, the generosity of prescription drug coverage in the plans has not been well described. Our primary objective was to examine the variability in drug coverage in the exchanges across plan types (health maintenance organization or preferred provider organization) and metal tiers (bronze, silver, gold, and platinum). Our secondary objective was to compare the exchange coverage to employer-sponsored coverage. Analyzing prescription drug benefit design data for the federally facilitated exchanges, we found wide variation in enrollees' out-of-pocket costs for generic, preferred brand-name, nonpreferred brand-name, and specialty drugs, not only across metal tiers but also within those tiers across plan types. Compared to employer-sponsored plans, exchange plans generally had lower premiums but provided less generous drug coverage. However, for low-income enrollees who are eligible for cost-sharing subsidies, the exchange plans may be more comparable to employer-based coverage. Policies and programs to assist consumers in matching their prescription drug needs with a plan's benefit design may improve the financial protection for the newly insured. PMID:25732498

  13. Effects of vegetation structure on soil carbon, nutrients and greenhouse gas exchange in a savannah ecosystem of Mount Kilimanjaro Region

    NASA Astrophysics Data System (ADS)

    Becker, J.

    2015-12-01

    The savannah biome is a hotspot for biodiversity and wildlife conservation in Africa and recently got in the focus of research on carbon sequestration. Savannah ecosystems are under strong pressure from climate and land-use change, especially around populous areas like the Mt. Kilimanjaro region. Savannah vegetation consists of grassland with isolated trees and is therefore characterized by high spatial variation of canopy cover, aboveground biomass and root structure. The canopy structure is a major regulator for soil ecological parameters and soil-atmospheric trace gas exchange (CO2, N2O, CH4) in water limited environments. The spatial distribution of these parameters and the connection between above and belowground processes are important to understand and predict ecosystem changes and estimate its vulnerability. Our objective was to determine spatial trends and changes of soil parameters and relate their variability to the vegetation structure. We chose three trees from each of the two most dominant species (Acacia nilotica and Balanites aegyptiaca) in our research area. For each tree, we selected transects with nine sampling points of the same relative distances to the stem. At these each sampling point a soil core was taken and separated in 0-10 cm and 10-30 cm depth. We measured soil carbon (C) and nitrogen (N) storage, microbial biomass C and N, Natural δ13C, soil respiration, available nutrients, pH, cation exchange capacity (CEC) as well as root biomass and -density, soil temperature and soil water content. Concentrations and stocks of C and N fractions, CEC and K+ decreased up to 50% outside the crown covered area. Microbial C:N ratio and CO2 efflux was about 30% higher outside the crown. This indicates N limitation and low C use efficiency in soil outside the crown area. We conclude that the spatial structure of aboveground biomass in savanna ecosystems leads to a spatial variance in nutrient limitation. Therefore, the capability of a savanna ecosystem

  14. Environment and phenology: CO2 net ecosystem exchange and CO2 flux partitioning at an acid and oligotrophic mire system in northern Sweden

    NASA Astrophysics Data System (ADS)

    Gažovič, Michal; Peichl, Matthias; Vermeij, Ilse; Limpens, Juul; Nilsson, Mats. B.

    2015-04-01

    Static chamber and environmental measurements in combination with vegetation indices (i.e. vascular green area (VGA) and the greenness chromatic color index (gcc) derived from digital camera images) were used to investigate effects of environment and phenology on the CO2 net ecosystem exchange (NEE) and CO2 flux partitioning at the Degerö Stormyr site in northern Sweden (64°11' 23.565" N, 19°33' 55.291 E) during two environmentally different years. Our measurement design included a control plot, a moss plot (where vascular plants were removed by clipping) and four heterotrophic respiration (RH) collars (where all green moss and vascular plant biomass were removed) to partition between soil heterotrophic and plant autotrophic (moss and vascular plants) respiration (RA), as well as between moss and vascular plant gross primary production (GPP). Environmental conditions, especially the shallow snow cover, peat soil frost and cold spring in 2014 caused delayed onset of spring green up, reduced soil respiration flux and reduced GPP of vascular plants. Soil temperature measured in 26 cm depth started to rise from spring temperatures of ~ 0.6 °C in 2013 and 0.15 °C in 2014 about 20 days earlier in 2013 compared to 2014. With earlier onset of the growing season and higher soil temperatures in 2013, heterotrophic soil respiration was higher in year 2013 than in year 2014. In 2013, RH dominated the total ecosystem respiration in all months but June and August. On contrary, autotrophic respiration dominated ecosystem respiration in all months of 2014. In both years, vascular plants and mosses were more or less equally contributing to autotrophic respiration. We measured higher GPP in year 2013 compared to year 2014. Also VGA and gcc were higher in spring and throughout the rest of 2013 compared to 2014. The onset of VGA was delayed by ~ 10 days in 2014. In general, total GPP was dominated by GPP of vascular plants in both years, although moss GPP had substantial

  15. Ecosystem scale VOC exchange measurements at Bosco Fontana (IT) and Hyytiälä (FI)

    NASA Astrophysics Data System (ADS)

    Schallhart, S.; Rantala, P.; Taipale, R.; Nemitz, E.; Tillmann, R.; Mentel, T. F.; Ruuskanen, T.; Rinne, J.

    2013-12-01

    The ozone production and destruction mechanisms in the troposphere depend on the abundance of NOx and volatile organic compounds (VOCs). As the latter originate not only from human activities, but to a large extent from vegetation it is important to quantify these biogenic sources as well. The VOC-fluxes were measured in Bosco Fontana forest as a part of an intensive measurement campaign of the Eclaire project, which investigates how climate change alters the threat of air pollution. Measurements were carried out at the Nature Reserve 'Bosco della Fontana' in the Po valley, Italy. The area of the forest is 198 ha and the dominanting tree species are Quercus robur (English oak), Quercus cerris (Turkey oak) and Carpinus betulus (hornbeam). The fluxes were measured on at a height of 32 metres using the eddy covariance method. A PTR-TOF (Ionicon Analytik, Austria) measured volatile organic compounds up to a mass of 300 atomic mass units. The instrument is capable of recording full spectra of VOCs in real-time with a resolution of 10 Hz. In addition to the mass spectrometer a 3D Anemometer was placed next to the inlet. Results will be presented and compared with disjunct eddy covariance measurements (Taipale et al. 2011) from a Pinus sylvestris (Scots Pine) dominated forest in Hyytiälä, Finland. The two forests are characterized by a different emission profile; the Bosco Fontana forest emits large amounts of isoprene, whereas the terpenoid emissions from Hyytiälä forest are dominated by monoterpenes. The magnitude of the emissions differs as emission from Bosco Fontana is much higher. The monoterpene emission from Bosco Fontana is likely to follow different dynamics than that from Hyytiälä as it correlates well with the radiation. This leads to the conclusion, that monoterpenes are released right after they are produced (de novo). In Hyytiälä the emissions are light and temperature dependent, which is caused by de novo and storage emissions. Pines have large

  16. Estimating impacts of snow cover on net ecosystem exchange near Daring Lake, NWT, Canada (65oN, 111oW)

    NASA Astrophysics Data System (ADS)

    Luus, K. A.; Kelly, R. E.; Lin, J. C.; Humphreys, E. R.; Lafleur, P.

    2010-12-01

    Arctic CO2 flux is influenced by the spatial distribution, accumulation, and phenology of snow. Regions with greater net primary productivity tend to accumulate greater snowfall, and areas receiving greater snowfall have higher soil temperatures, enabling greater rates of winter respiration. During snow melt, the spatial distributions of remaining snow influence the patterns of CO2 release. However, cryospheric influences on CO2 distributions are not typically included in models of net ecosystem exchange. The objective of this research was therefore to investigate: 1) the influence of snow cover distributions on CO2 flux during snow melt at four sites located near Daring Lake, NWT, Canada; and 2) the amount of variation in CO2 flux due to arctic land cover class and snow distributions captured by the remote sensing based Vegetation Photosysthesis and Respiration Model (VPRM), which does not contain explicit arctic land cover class or cryospheric parameterizations. Snow cover distributions were monitored twice daily throughout the 2010 snow melt period (May-June) using Moultrie I-65 game cameras over four arctic land cover classes: fen, tall shrub, short shrub and mixed tundra. At each site, CO2 flux data was collected using an open path infrared gas analyzer eddy covariance system. Initial analysis consisted of classifying snow cover locations and extent in each image. Footprint modeling was then conducted in order to assess the impact of snow cover distributions on CO2 flux during melt. In order to assess the amount of variability in net ecosystem exchange due to snow cover captured by VPRM, associations between vegetation cover, snow extents and CO2 flux were first upscaled using classification of Landsat snow cover and land cover class. VPRM was then run over the same region. VPRM output was statistically compared to upscaled CO2. Although VPRM contains few land surface parameters, it is not hindered by gaps in Landsat data due to cloud cover, or diminished

  17. The REFLEX project: Comparing different algorithms and implementations for the inversion of a terrestrial ecosystem model against eddy covariance data

    SciTech Connect

    Fox, Andrew; Williams, Mathew; Richardson, Andrew D.; Cameron, David; Gove, Jeffrey H.; Quaife, Tristan; Ricciuto, Daniel M; Reichstein, Markus; Tomelleri, Enrico; Trudinger, Cathy; Van Wijk, Mark T.

    2009-10-01

    We describe a model-data fusion (MDF) inter-comparison project (REFLEX), which compared various algorithms for estimating carbon (C) model parameters consistent with both measured carbon fluxes and states and a simple C model. Participants were provided with the model and with both synthetic net ecosystem exchange (NEE) ofCO2 and leaf area index (LAI) data, generated from the model with added noise, and observed NEE and LAI data from two eddy covariance sites. Participants endeavoured to estimate model parameters and states consistent with the model for all cases over the two years for which data were provided, and generate predictions for one additional year without observations. Nine participants contributed results using Metropolis algorithms, Kalman filters and a genetic algorithm. For the synthetic data case, parameter estimates compared well with the true values. The results of the analyses indicated that parameters linked directly to gross primary production (GPP) and ecosystem respiration, such as those related to foliage allocation and turnover, or temperature sensitivity of heterotrophic respiration,were best constrained and characterised. Poorly estimated parameters were those related to the allocation to and turnover of fine root/wood pools. Estimates of confidence intervals varied among algorithms, but several algorithms successfully located the true values of annual fluxes from synthetic experiments within relatively narrow 90% confidence intervals, achieving>80% success rate and mean NEE confidence intervals <110 gCm-2 year-1 for the synthetic case. Annual C flux estimates generated by participants generally agreed with gap-filling approaches using half-hourly data. The estimation of ecosystem respiration and GPP through MDF agreed well with outputs from partitioning studies using half-hourly data. Confidence limits on annual NEE increased by an average of 88% in the prediction year compared to the previous year, when data were available. Confidence

  18. A multiscale and multidisciplinary investigation of ecosystem-atmosphere CO2 exchange over the rocky mountains of colorado

    USGS Publications Warehouse

    Sun, Jielun; Oncley, S.P.; Burns, Sean P.; Stephens, B.B.; Lenschow, D.H.; Campos, T.; Monson, Russell K.; Schimel, D.S.; Sacks, W.J.; De Wekker, S. F. J.; Lai, C.-T.; Lamb, B.; Ojima, D.; Ellsworth, P.Z.; Sternberg, L.S.L.; Zhong, S.; Clements, C.; Moore, D.J.P.; Anderson, D.E.; Watt, A.S.; Hu, Jiawen; Tschudi, M.; Aulenbach, S.; Allwine, E.; Coons, T.

    2010-01-01

    A field study combined with modeling investigation demonstrated that the organization of CO2 transport by mountain terrain strongly affects the regional CO2 budget. Atmospheric dynamics can lead to complicated flows generated by inhomogeneous landscapes, topography or synoptic weather systems. The field campaign conducted of a ground deployment, the Carbon in the Mountain Experiment (CME04), and an aircraft deployment of the national Center for Atmospheric Research (NCAR) C-130, the Airborne Carbon in the Mountains Experiment (ACME04) over the period of spring to fall of 2004 to cover the seasonal variation of ecosystem-atmosphere carbon exchange. The role of the mountain circulation in CO2 transport can be played over seemingly flat terrain by mesoscale flows generated by various physical processes. The three dimensional observation strategy considered can also be applied over flat terrain.

  19. Sensitivity analysis of a model of CO{sub 2} exchange in tundra ecosystems by the adjoint method

    SciTech Connect

    Waelbroeck, C.; Louis, J.F.

    1995-02-20

    A model of net primary production (NPP), decomposition, and nitrogen cycling in tundra ecosystems has been developed. The adjoint technique is used to study the sensitivity of the computed annual net CO{sub 2} flux to perturbations in initial conditions, climatic inputs, and model`s main parameters describing current seasonal CO{sub 2} exchange in wet sedge tundra at Barrow, Alaska. The results show that net CO{sub 2} flux is more sensitive to decomposition parameters than to NPP parameters. This underlines the fact that in nutrient-limited ecosystems, decomposition drives net CO{sub 2} exchange by controlling mineralization of main nutrients. The results also indicate that the short-term (1 year) response of wet sedge tundra to CO{sub 2}-induced warming is a significant increase in CO{sub 2} emission, creating a positive feedback to atmospheric CO{sub 2} accumulation. However, a cloudiness increase during the same year can severely alter this response and lead to either a slight decrease or a strong increase in emitted CO{sub 2}, depending on its exact timing. These results demonstrate that the adjoint method is well suited to study systems encountering regime changes, as a single run of the adjoint model provides sensitivities of the net CO{sub 2} flux to perturbations in all parameters and variables at any time of the year. Moreover, it is shown that large errors due to the presence of thresholds can be avoided by first delimiting the range of applicability of the adjoint results. 38 refs., 10 figs., 7 tabs.

  20. Estimation of net ecosystem carbon exchange for the conterminous United States by combining MODIS and AmeriFlux data

    SciTech Connect

    Xiao, Jingfeng; Zhuang, Qianlai; Baldocchi, Dennis D.; Bolstad, Paul V.; Burns, Sean P.; Chen, Jiquan; Cook, David R.; Curtis, Peter S.; Drake, Bert G.; Foster, David R.; Gu, Lianhong; Hadley, Julian L.; Hollinger, David Y.; Katul, Gabriel G.; Law, Beverly E.; Litvak, Marcy; Ma, Siyan; Martin, Timothy A.; Matamala, Roser; McNulty, Steve; Meyers, Tilden P.; Monson, Russell K.; Munger, J. William; Noormets, Asko; Oechel, Walter C.; Oren, Ram; Richardson, Andrew D.; Schmid, Hans Peter; Scott, Russell L.; Starr, Gregory; Sun, Ge; Suyker, Andrew E.; Torn, Margaret S.; Paw, Kyaw; Verma, Shashi B.; Wharton, Sonia; Wofsy, Steven C.

    2008-10-01

    Eddy covariance flux towers provide continuous measurements of net ecosystem carbon exchange (NEE) for a wide range of climate and biome types. However, these measurements only represent the carbon fluxes at the scale of the tower footprint. To quantify the net exchange of carbon dioxide between the terrestrial biosphere and the atmosphere for regions or continents, flux tower measurements need to be extrapolated to these large areas. Here we used remotely sensed data from the Moderate Resolution Imaging Spectrometer (MODIS) instrument on board the National Aeronautics and Space Administration's (NASA) Terra satellite to scale up AmeriFlux NEE measurements to the continental scale. We first combined MODIS and AmeriFlux data for representative U.S. ecosystems to develop a predictive NEE model using a modified regression tree approach. The predictive model was trained and validated using eddy flux NEE data over the periods 2000-2004 and 2005-2006, respectively. We found that the model predicted NEE well (r = 0.73, p < 0.001). We then applied the model to the continental scale and estimated NEE for each 1 km x 1 km cell across the conterminous U.S. for each 8-day interval in 2005 using spatially explicit MODIS data. The model generally captured the expected spatial and seasonal patterns of NEE as determined from measurements and the literature. Our study demonstrated that our empirical approach is effective for scaling up eddy flux NEE measurements to the continental scale and producing wall-to-wall NEE estimates across multiple biomes. Our estimates may provide an independent dataset from simulations with biogeochemical models and inverse modeling approaches for examining the spatiotemporal patterns of NEE and constraining terrestrial carbon budgets over large areas.

  1. Estimation of Net Ecosystem Carbon Exchange for the Conterminous UnitedStates by Combining MODIS and AmeriFlux Data

    SciTech Connect

    Xiao, Jingfeng; Zhuang, Qianlai; Baldocchi, Dennis D.; Law, Beverly E.; Richardson, Andrew D.; Chen, Jiquan; Oren, Ram; Starr, Gregory; Noormets, Asko; Ma, Siyan; Verma, Shashi B.; Wharton, Sonia; Wofsy, Steven C.; Bolstad, Paul V.; Burns, Sean P.; Cook, David R.; Curtis, Peter S.; Drake, Bert G.; Falk, Matthias; Fischer, Marc L.; Foster, David R.; Gu, Lianhong; Hadley, Julian L.; Hollinger, David Y.; Katul, Gabriel G.; Litvak, Marcy; Martin, Timothy A.; Matamala, Roser; McNulty, Steve; Meyers, Tilden P.; Monson, Russell K.; Munger, J. William; Oechel, Walter C.; U, Kyaw Tha Paw; Schmid, Hans Peter; Scott, Russell L.; Sun, Ge; Suyker, Andrew E.; Torn, Margaret S.

    2009-03-06

    Eddy covariance flux towers provide continuous measurements of net ecosystem carbon exchange (NEE) for a wide range of climate and biome types. However, these measurements only represent the carbon fluxes at the scale of the tower footprint. To quantify the net exchange of carbon dioxide between the terrestrial biosphere and the atmosphere for regions or continents, flux tower measurements need to be extrapolated to these large areas. Here we used remotely-sensed data from the Moderate Resolution Imaging Spectrometer (MODIS) instrument on board NASA's Terra satellite to scale up AmeriFlux NEE measurements to the continental scale. We first combined MODIS and AmeriFlux data for representative U.S. ecosystems to develop a predictive NEE model using a regression tree approach. The predictive model was trained and validated using NEE data over the periods 2000-2004 and 2005-2006, respectively. We found that the model predicted NEE reasonably well at the site level. We then applied the model to the continental scale and estimated NEE for each 1 km x 1 km cell across the conterminous U.S. for each 8-day period in 2005 using spatially-explicit MODIS data. The model generally captured the expected spatial and seasonal patterns of NEE. Our study demonstrated that our empirical approach is effective for scaling up eddy flux NEE measurements to the continental scale and producing wall-to-wall NEE estimates across multiple biomes. Our estimates may provide an independent dataset from simulations with biogeochemical models and inverse modeling approaches for examining the spatiotemporal patterns of NEE and constraining terrestrial carbon budgets for large areas.

  2. Estimation of net ecosystem carbon exchange for the conterminous United States by combining MODIS and AmeriFlux data

    SciTech Connect

    Xiao, Jingfeng; Zhuang, Qianlai; Baldocchi, Dennis; Ma, Siyan; Law, Beverly E.; Richardson, Andrew D; Chen, Jiquan; Oren, Ram

    2008-10-01

    Eddy covariance flux towers provide continuous measurements of net ecosystem carbon exchange (NEE) for a wide range of climate and biome types. However, these measurements only represent the carbon fluxes at the scale of the tower footprint. To quantify the net exchange of carbon dioxide between the terrestrial biosphere and the atmosphere for regions or continents, flux tower measurements need to be extrapolated to these large areas. Here we used remotely sensed data from the Moderate Resolution Imaging Spectrometer (MODIS) instrument on board the National Aeronautics and Space Administration s (NASA) Terra satellite to scale up AmeriFlux NEE measurements to the continental scale.We first combined MODIS and AmeriFlux data for representative U.S. ecosystems to develop a predictive NEE model using a modified regression tree approach. The predictive model was trained and validated using eddy flux NEE data over the periods 2000 2004 and 2005 2006, respectively. We found that the model predicted NEE well (r = 0.73, p < 0.001). We then applied the model to the continental scale and estimated NEE for each 1 km 1 km cell across the conterminous U.S. for each 8-day interval in 2005 using spatially explicit MODIS data. The model generally captured the expected spatial and seasonal patterns of NEE as determined from measurements and the literature. Our study demonstrated that our empirical approach is effective for scaling up eddy flux NEE measurements to the continental scale and producing wall-to-wall NEE estimates across multiple biomes. Our estimates may provide an independent dataset from simulations with biogeochemical models and inverse modeling approaches for examining the spatiotemporal patterns of NEE and constraining terrestrial carbon budgets over large areas.

  3. El Niño Southern Oscillation (ENSO) enhances CO2 exchange rates in freshwater Marsh ecosystems in the Florida everglades.

    PubMed

    Malone, Sparkle L; Staudhammer, Christina L; Oberbauer, Steven F; Olivas, Paulo; Ryan, Michael G; Schedlbauer, Jessica L; Loescher, Henry W; Starr, Gregory

    2014-01-01

    This research examines the relationships between El Niño Southern Oscillation (ENSO), water level, precipitation patterns and carbon dioxide (CO2) exchange rates in the freshwater wetland ecosystems of the Florida Everglades. Data was obtained over a 5-year study period (2009-2013) from two freshwater marsh sites located in Everglades National Park that differ in hydrology. At the short-hydroperiod site (Taylor Slough; TS) and the long-hydroperiod site (Shark River Slough; SRS) fluctuations in precipitation patterns occurred with changes in ENSO phase, suggesting that extreme ENSO phases alter Everglades hydrology which is known to have a substantial influence on ecosystem carbon dynamics. Variations in both ENSO phase and annual net CO2 exchange rates co-occurred with changes in wet and dry season length and intensity. Combined with site-specific seasonality in CO2 exchanges rates, El Niño and La Niña phases magnified season intensity and CO2 exchange rates at both sites. At TS, net CO2 uptake rates were higher in the dry season, whereas SRS had greater rates of carbon sequestration during the wet season. As La Niña phases were concurrent with drought years and extended dry seasons, TS became a greater sink for CO2 on an annual basis (-11 to -110 g CO2 m-2 yr-1) compared to El Niño and neutral years (-5 to -43.5 g CO2 m-2 yr-1). SRS was a small source for CO2 annually (1.81 to 80 g CO2 m-2 yr-1) except in one exceptionally wet year that was associated with an El Niño phase (-16 g CO2 m-2 yr-1). Considering that future climate predictions suggest a higher frequency and intensity in El Niño and La Niña phases, these results indicate that changes in extreme ENSO phases will significantly alter CO2 dynamics in the Florida Everglades.

  4. El Niño Southern Oscillation (ENSO) Enhances CO2 Exchange Rates in Freshwater Marsh Ecosystems in the Florida Everglades

    PubMed Central

    Malone, Sparkle L.; Staudhammer, Christina L.; Oberbauer, Steven F.; Olivas, Paulo; Ryan, Michael G.; Schedlbauer, Jessica L.; Loescher, Henry W.; Starr, Gregory

    2014-01-01

    This research examines the relationships between El Niño Southern Oscillation (ENSO), water level, precipitation patterns and carbon dioxide (CO2) exchange rates in the freshwater wetland ecosystems of the Florida Everglades. Data was obtained over a 5-year study period (2009–2013) from two freshwater marsh sites located in Everglades National Park that differ in hydrology. At the short-hydroperiod site (Taylor Slough; TS) and the long-hydroperiod site (Shark River Slough; SRS) fluctuations in precipitation patterns occurred with changes in ENSO phase, suggesting that extreme ENSO phases alter Everglades hydrology which is known to have a substantial influence on ecosystem carbon dynamics. Variations in both ENSO phase and annual net CO2 exchange rates co-occurred with changes in wet and dry season length and intensity. Combined with site-specific seasonality in CO2 exchanges rates, El Niño and La Niña phases magnified season intensity and CO2 exchange rates at both sites. At TS, net CO2 uptake rates were higher in the dry season, whereas SRS had greater rates of carbon sequestration during the wet season. As La Niña phases were concurrent with drought years and extended dry seasons, TS became a greater sink for CO2 on an annual basis (−11 to −110 g CO2 m−2 yr−1) compared to El Niño and neutral years (−5 to −43.5 g CO2 m−2 yr−1). SRS was a small source for CO2 annually (1.81 to 80 g CO2 m−2 yr−1) except in one exceptionally wet year that was associated with an El Niño phase (−16 g CO2 m−2 yr−1). Considering that future climate predictions suggest a higher frequency and intensity in El Niño and La Niña phases, these results indicate that changes in extreme ENSO phases will significantly alter CO2 dynamics in the Florida Everglades. PMID:25521299

  5. Using a spectral approach to compare dynamic and static head driven hyporheic exchange

    NASA Astrophysics Data System (ADS)

    Wörman, Anders; Morén, Ida; Riml, Joakim

    2016-04-01

    Hyporheic exchange is an important process controlling the transportation and fate of solutes in natural streams. The exchange is driven by the hydraulic head gradients over the stream bottom and occurs on a wide range of spatial scales. The hydraulic head gradient is either dominated by the static head, originating from water surface elevation differences or it is dominated by the dynamic head that is created when the velocity head of the stream is transformed to pressure variations along an uneven bed surface. This article uses a power spectral approach to compare the exchange due to the static and dynamic head occurring over a range of spatial scales in the Tullstorps Brook. Prediction of hyporheic exchange is restrained by the complications of performing measurements of high quality and quantity in the field. In this study bottom elevation and water depth was measured with a levelling instrument every 2.56 - 16.83 m along a 500 m long reach of the Tullstorps Brook. The velocity head was calculated at the same sections based on the measured cross section area of the stream and the average discharge during the day when the measurements were done. Parallel to the head investigations a Rhodamine WT tracer test was performed in the reach and the parameters controlling hyporheic exchange was estimated through inverse modelling. These tracer test parameters were compared with theoretical parameters obtained from a spectral model. Hyporheic exchange is often modelled by assuming the head variations to be harmonic with a certain wavelength and amplitude. In the reality the head variation cannot be represented by a single harmonic function, but the representation of head geometry can be improved by superimposing a large number of harmonic functions. Here, to be able to include the whole range of harmonics, we used a power spectral approach to analyse the hydraulic head measurements from the field. The Fourier power spectrum of the data was calculated for the water

  6. Elevated CO(2) and temperature alter net ecosystem C exchange in a young Douglas fir mesocosm experiment.

    PubMed

    Tingey, David T; Lee, E Henry; Phillips, Donald L; Rygiewicz, Paul T; Waschmann, Ronald S; Johnson, Mark G; Olszyk, David M

    2007-11-01

    We investigated the effects of elevated CO(2) (EC) [ambient CO(2) (AC) + 190 ppm] and elevated temperature (ET) [ambient temperature (AT) + 3.6 degrees C] on net ecosystem exchange (NEE) of seedling Douglas fir (Pseudotsuga menziesii) mesocosms. As the study utilized seedlings in reconstructed soil-litter-plant systems, we anticipated greater C losses through ecosystem respiration (R(e)) than gains through gross photosynthesis (GPP), i.e. negative NEE. We hypothesized that: (1) EC would increase GPP more than R(e), resulting in NEE being less negative; and (2) ET would increase R(e) more than GPP, resulting in NEE being more negative. We also evaluated effects of CO(2) and temperature on light inhibition of dark respiration. Consistent with our hypothesis, NEE was a smaller C source in EC, not because EC increased photosynthesis but rather because of decreased respiration resulting in less C loss. Consistent with our hypothesis, NEE was more negative in ET because R(e) increased more than GPP. The light level that inhibited respiration varied seasonally with little difference among CO(2) and temperature treatments. In contrast, the degree of light inhibition of respiration was greater in AC than EC. In our system, respiration was the primary control on NEE, as EC and ET caused greater changes in respiration than photosynthesis.

  7. Unexpected sensitivity of the annual net ecosystem exchange to the high frequency loss corrections in a grazed grassland site in Belgium

    NASA Astrophysics Data System (ADS)

    Mamadou, Ossenatou; Gourlez de la Motte, Louis; De Ligne, Anne; Bernard, Heineisch; Aubinet, Marc

    2016-04-01

    Although widely used to measure CO2 and other gas fluxes, the eddy covariance technique still needs methodological improvements. This research focuses on the high frequency loss corrections, which are especially important when using a closed-path infrared gas analyzer. We compared three approaches to implement these corrections for CO2 fluxes and evaluated their impact on the carbon balance at the Dorinne Terrestrial Observatory (DTO), an intensively grazed grassland site in Belgium. The carbon balance at DTO is also the object of a separate analysis (Gourlez de la Motte et al., Geophysical Research Abstract, Vol. 18, EGU2016-6813-1, 2016). In the first approach, the computation of correction factors was based on the measured sensible heat cospectra ('local' cospectra), whereas the other two were based on theoretical models (Kaimal et al., 1972). The correction approaches were validated by comparing the nighttime eddy covariance CO2 fluxes corrected with each approach and in situ soil respiration measurements. We found that the local cospectra differed from the Kaimal theoretical shape, although the site could not be considered 'difficult' (i.e., fairly flat, homogeneous, low vegetation, sufficient measurement height), appearing less peaked in the inertial subrange. This difference greatly affected the correction factor, especially for night fluxes. Night fluxes measured by eddy covariance were found to be in good agreement with in situ soil respiration measurements when corrected with local cospectra and to be overestimated when corrected with Kaimal cospectra. As the difference between correction factors was larger in stable than unstable conditions, this acts as a selective systematic error and has an important impact on annual fluxes. On the basis of a 4-year average, at DTO, the errors reach 71-150 g C m-2 y-1 for net ecosystem exchange (NEE), 280-562 g C m-2 y-1 for total ecosystem respiration (TER) and 209-412 g C m-2 y-1 for gross primary productivity (GPP

  8. Age-dependent impacts of peatland restoration on the net ecosystem CO2 exchange of blanket bogs in Northern Scotland

    NASA Astrophysics Data System (ADS)

    Hambley, Graham; Hill, Timothy; Saunders, Matthew; Arn Teh, Yit

    2015-04-01

    The Flow Country of Northern Scotland is the largest area of contiguous blanket bog in the UK covering an area in excess of 400 km2. This region is the single largest peat and soil C repository in the UK, and plays a key role in mediating regional atmospheric exchanges of greenhouse gases (GHGs) such as carbon dioxide (CO2), methane (CH4) and water vapour (H2O). However, these peatlands were subject to significant afforestation in the 1980s, where large areas of blanket bog were drained and planted with Sitka spruce (Picea sitchensis) and Lodgepole Pine (Pinus contorta), resulting in modifications to micro-topographic features, vegetation composition and soil properties such as bulk density and water holding capacity, all of which are known to influence the production and emission of key GHGs. Since the late 1990s restoration work has been undertaken to remove forest plantations and to restore the peatland areas by raising the water table, predominantly by drain and furrow blocking, in order to encourage the recolonisation of Sphagnum species. Here we report findings from an eddy covariance study of CO2 and H2O exchange from an unmanaged peatland and a chronosequence of restored peatland sites, which were felled in 1998 and 2004. Located within the Forsinard Flows National Nature Reserve in Northern Scotland, these sites are being studied to better understand the key drivers of carbon dynamics in these ecosystems and also assess the age-dependent impacts of peatland restoration on the net CO2 sink strength. Preliminary data show rates of CO2 uptake increased with time since restoration, with peak assimilation rates of -9.9 and -14.4 micro mol CO2 m-2 s-1 measured at the 10 and 16 year old restoration sites, respectively. Carbon losses through ecosystem respiration followed a similar pattern. The data collected to date indicates that while peatland restoration is actively increasing CO2 uptake at each of the sites, more long-term observational data is required to

  9. Comparing approaches to spatially explicit ecosystem service modeling: a case study from the San Pedro River, Arizona

    USGS Publications Warehouse

    Bagstad, Kenneth J.; Semmens, Darius J.; Winthrop, Robert

    2013-01-01

    Although the number of ecosystem service modeling tools has grown in recent years, quantitative comparative studies of these tools have been lacking. In this study, we applied two leading open-source, spatially explicit ecosystem services modeling tools – Artificial Intelligence for Ecosystem Services (ARIES) and Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) – to the San Pedro River watershed in southeast Arizona, USA, and northern Sonora, Mexico. We modeled locally important services that both modeling systems could address – carbon, water, and scenic viewsheds. We then applied managerially relevant scenarios for urban growth and mesquite management to quantify ecosystem service changes. InVEST and ARIES use different modeling approaches and ecosystem services metrics; for carbon, metrics were more similar and results were more easily comparable than for viewsheds or water. However, findings demonstrate similar gains and losses of ecosystem services and conclusions when comparing effects across our scenarios. Results were more closely aligned for landscape-scale urban-growth scenarios and more divergent for a site-scale mesquite-management scenario. Follow-up studies, including testing in different geographic contexts, can improve our understanding of the strengths and weaknesses of these and other ecosystem services modeling tools as they move closer to readiness for supporting day-to-day resource management.

  10. EXCHANGE

    SciTech Connect

    Boltz, J.C.

    1992-09-01

    EXCHANGE is published monthly by the Idaho National Engineering Laboratory (INEL), a multidisciplinary facility operated for the US Department of Energy (DOE). The purpose of EXCHANGE is to inform computer users about about recent changes and innovations in both the mainframe and personal computer environments and how these changes can affect work being performed at DOE facilities.

  11. Net ecosystem CO2 exchange measured by autochambers during the snow-covered season at a temperate peatland

    NASA Astrophysics Data System (ADS)

    Bubier, Jill; Crill, Patrick; Mosedale, Andrew

    2002-12-01

    Net ecosystem exchange of CO2 was measured at a temperate peatland in southeastern New Hampshire. Classified as a mineral-poor fen owing to deep, water-logged peats that are influenced to a limited extent by groundwater, the ecosystem is dominated by plants such as sedges (Carex spp.) and evergreen shrubs. Ten automatic chambers measured fluxes every 3 h by sampling changes in headspace concentration of CO2 from November 2000 through March 2001. The fen was covered in snow for most of this period and CO2 was emitted from the snow pack throughout the winter. The largest fluxes were associated with ground temperatures of 0°C and with declining atmospheric pressure. CO2 effluxes up to 3 µmol m-2 s-1 were recorded when the ground temperature reached the thaw point. Fluxes were lower when the ground temperature rose above 0°C, however, suggesting that the large fluxes were associated with a build up and release of stored CO2 degassing as soon as the ground thawed, or by enhanced microbial activity associated with freeze-thaw dynamics. The large number of thaw events coupled with frequent short-term releases of CO2 suggest that degassing occurred on a regular basis with changes in atmospheric pressure and/or microbial decomposition occurred beneath the snowpack. The extent of soil freezing prior to thaw was also an important factor, with colder soils yielding smaller CO2 emissions upon thaw. Although most of the observed CO2 flux was efflux from the ecosystem, occasional CO2 uptake by the ecosystem of up to 1 µmol m-2 s-1 was also observed, indicating small rates of photosynthesis even during winter. Photosynthesis occurred only when the ground temperature was >0°C. The implications for a warmer climate are unclear. If warmer winter temperatures yield less snow in the temperate region, then soils could freeze more deeply and result in lower CO

  12. Comparative diversity analysis in sandy littoral ecosystems of the western Mediterranean

    NASA Astrophysics Data System (ADS)

    Colombini, I.; Fallaci, M.; Milanesi, F.; Scapini, F.; Chelazzi, L.

    2003-10-01

    A comparative faunal analysis was carried out in sandy littoral localities differing both morphologically and in human impact. The study sites were located in the western Mediterranean basin along the coasts of Morocco, Tunisia, the Maltese Islands and Italy. These were typical beach-dune ecosystems more (Smir, Morocco; Zouara, Tunisia; Burano, Italy) or less (Ir-Ramla tat-Torri, Malta and Ir-Ramla l-Hamra, Gozo) structurally developed accordingly. Species richness was evaluated using standard trapping techniques with pitfall traps along the transects perpendicular to the shoreline. Only isopods and coleopterans were used in the analysis. In each locality, an analysis was conducted on both the beach and the dune separately, and on the entire ecosystem in the two seasons (spring and autumn). Species were studied both quantitatively and qualitatively using ecological coefficients (relative abundance) and Fisher's diversity index. To evaluate the evenness of the community, Shannon-Weaver index was calculated and compared with Brillouin index. For both indices, the maximum values were computed and were used to obtain the evenness of the community through Pielou index. In addition, Simpson's dominance index was considered. Percentages of similarities between localities were analysed in the two seasons and in total using the Renkonen index. The overall analysis showed that general trends could be found for both orders that were studied and gave indications on habitat quality. The study showed that when monitoring was carried out systematically both in space and time, arthropods could be used as important tool to assess beach health.

  13. On the relationship between ecosystem-scale hyperspectral reflectance and CO2 exchange in European mountain grasslands

    NASA Astrophysics Data System (ADS)

    Balzarolo, M.; Vescovo, L.; Hammerle, A.; Gianelle, D.; Papale, D.; Wohlfahrt, G.

    2014-07-01

    In this paper we explore the use of hyperspectral reflectance measurements and vegetation indices (VIs) derived therefrom in estimating carbon dioxide (CO2) fluxes (net ecosystem exchange - NEE; gross primary production - GPP), and some key ecophysiological variables related to NEE and GPP (light use efficiency - ɛ; initial quantum yield - α; and GPP at saturating light - GPPmax) for grasslands. Hyperspectral reflectance data (400-1000 nm), CO2 fluxes and biophysical parameters were measured at three grassland sites located in European mountain regions. The relationships between CO2 fluxes, ecophysiological variables and VIs derived using all two-band combinations of wavelengths available from the whole hyperspectral data space were analysed. We found that hyperspectral VIs generally explained a large fraction of the variability in the investigated dependent variables and that they generally exhibited more skill in estimating midday and daily average GPP and NEE, as well as GPPmax, than α and ɛ. Relationships between VIs and CO2 fluxes and ecophysiological parameters were site-specific, likely due to differences in soils, vegetation parameters and environmental conditions. Chlorophyll and water content related VIs (e.g. CI, NPCI, WI), reflecting seasonal changes in biophysical parameters controlling the photosynthesis process, explained the largest fraction of variability in most of the dependent variables. A limitation of the hyperspectral sensors is that their cost is still high and the use laborious. At the eddy covariance with a limited budget and without technical support, we suggest to use at least dual or four channels low cost sensors in the the following spectral regions: 400-420 nm; 500-530 nm; 750-770 nm; 780-800 nm and 880-900 nm. In addition, our findings have major implications for up-scaling terrestrial CO2 fluxes to larger regions and for remote and proximal sensing sampling and analysis strategies and call for more cross-site synthesis studies

  14. Impact of active layer detachments on carbon exchange in a high-Arctic ecosystem, Cape Bounty, Nunavut, Canada

    NASA Astrophysics Data System (ADS)

    Scott, N. A.; Beamish, A.; Neil, A.; Wagner, I.

    2011-12-01

    High Arctic ecosystems are experiencing some of the earliest and most extreme changes in climate, including increases in both temperature and precipitation leading to a deepening and destabilization of the active layer. This destabilization of shallow slopes can lead to disturbances such as active layer detachments (ALD), which could further alter soil temperature and moisture regimes, potentially releasing carbon (C) and nutrients previously unavailable to soil microbes. We explored the impact of ALD's on carbon dioxide (CO2) exchange at the Cape Bounty Arctic Watershed Observatory on Melville Island, Canada over two growing seasons. CO2 exchange under light and dark conditions was measured approximately every five to nine days across both growing seasons for a total of five sampling day in 2009 and nine sampling days in 2010. Sampling was stratified to include highly disturbed, moderately disturbed, and undisturbed areas. Transparent static chambers were equipped with a Vaisala GMP343 CO2 sensor to measure changes in CO2 concentration over time. Based on static chamber C flux measurements during the growing seasons of 2009 and 2010, we found that the moderately disturbed sites were net sinks of CO2 (-6.44gC m-2 season-1, -8.21gC m-2 season-1, respectively). The highly disturbed sites however were net sources of CO2 in both seasons (3.01gC m-2 season-1, 30.01gC m-2 season-1, respectively). Control sites in 2009 were a net C sink (-6.48gC m-2 season-1) while in 2010 they represented a net C source (16.75gC m-2 season-1). Overall, the formation of ALD's led to highly disturbed areas (roughly 40% of the area of an ALD) becoming C sources, but appeared to enhance C uptake in moderately disturbed areas. Active layer depth explained little of the variation in any of the C fluxes, while combinations of soil moisture, temperature, and air temperature explained up to roughly 40% of the variation in C fluxes. These findings have important implications if temperature and

  15. Net Ecosystem Carbon Exchange and Evapotranspiration After the Felling of an Eucalyptus Forest

    NASA Astrophysics Data System (ADS)

    Pita, Gabriel; Rodrigues, Abel; Mateus, Antonio; Pereira, Santos J.

    2011-01-01

    Espirra site (38o38’N,8o36’W) is located in a 300ha Eucalyptus globulus plantation, with a Mediterranean type climate with a mean annual precipitation of 709mm and a mean annual air temperature of 15.9oC. The plantation was established in 1986 with about 1100 trees ha-1. A 33m observation tower was installed in 2002, with an eddy covariance system. A harvesting of trees was made at the end of the 2nd rotation period, from November to December 2006. During the last four years of the second rotation the coppice were 20m height. Harvesting was planned in order to initiate a new 12 year productive cycle. In October 2008 a first thinning was made in three fourths of emerging stems from stumps. At this stage the forest trees had a mean height of 6m. During the period of analyses the total annual precipitation has varied between a minimum of 248mmYr-1 (2005) to a maximum of 796mm Yr-1 (2007), pattern typical of a Mediterranean climate. The diminution of precipitation (and also how it is distributed along the year) affects the forest uptake of Carbon .The GPP and the TER show lower values in dry years, both in the adult forest as in the young one. The GPP of the growing eucalyptus has been affected by the dry year but also by the thinning that took place in Oct 2008. The Ecosystem total respiration shows high values after the felling ( the same order of magnitude as the forest before the felling) due to the leaves and branches that were left over the soil after the harvesting. Three years after the felling the GPP of the young forest is 61% the value of the adult forest (mean value, excluding the dry year). The seasonal pattern of TER is similar before and after the felling, but in the young forest the GPP is lower and the NEE becomes positive in winter time. In an annual base the growing eucalyptus forest only in the first year after felling was a source of carbon.

  16. Differences in plant cover and species composition of semiarid grassland communities of Central Mexico and its effects on net ecosystem exchange

    NASA Astrophysics Data System (ADS)

    Delgado-Balbuena, J.; Arredondo, J. T.; Loescher, H. W.; Huber-Sannwald, E.; Chavez-Aguilar, G.; Luna-Luna, M.; Barretero-Hernandez, R.

    2012-12-01

    Changes in land use across the semiarid grasslands of Northern Mexico have driven a decline of plant cover and alteration of plant species composition. A number of different plant communities have resulted from these changes, however, their implications on the carbon cycle and regional carbon balance are still poorly understood. Here, we examined the effects of plant cover loss and changes in species composition on net ecosystem CO2 exchange (NEE) and their biotic and abiotic controls. Five typical plant community types were examined in the semiarid grassland by encasing the entire above-ground ecosystem using the geodesic dome method. Sites included an oat crop (crop), a moderately grazed grassland (moderate grazing), a 28 yr-old grazing exclosure (exclosure), an overgrazed site with low perennial grass cover (overgrazed), and an overgrazed site presenting shrub encroachment (shrub encroachment). For natural vegetation, rates of daytime NEE for sites with a high plant cover (exclosure and moderate grazing) were similar (P>0.05) as compared to sites with low plant cover (overgrazed and shrub encroachment). However, night time NEE (carbon loss) was more than double (P<0.05) for sites with high plant cover compared to sites with low cover, resulting into slight C sinks for the low plant cover sites and neutral or sources for the high plant cover sites on an annual basis. Differences in plant cover and its associated biomass defined the sensitivity to environmental controls. Thus, daytime NEE in low plant cover sites reached light compensation points at lower PPFD values than those from high plant cover sites. Differences in species composition did not influence NEE rates even though there were transient or permanent changes in C3 vs. C4 functional groups.

  17. Isotopic partitioning of net ecosystem CO2 exchange reveals the importance of methane oxidation in a boreal peatland

    NASA Astrophysics Data System (ADS)

    Hasselquist, Niles; Peichl, Matthias; Öquist, Mats; Crill, Patrick; Nilsson, Mats

    2016-04-01

    Partitioning net ecosystem CO2 exchange (NEE) into its different flux components is crucial as it provides a mechanistic framework to better assess how the terrestrial carbon cycle may respond to projected environmental change. This is especially important for northern boreal peatlands, which store approximately one-quarter of the world's soil carbon and yet at the same time are projected to experience some of the greatest environmental changes in the future. Using an experimental setup with automated chambers for measuring NEE (transparent chambers), ecosystem respiration (Reco; opaque chambers) and heterotrophic respiration (Rh; opaque chambers on vegetation-free trenched plots) in combination with continuous measurements of δ13C using near-infrared, diode-laser-based cavity-ring down spectroscopy (Picarro G1101-i analyzer), we partitioned NEE of CO2 into gross primary productivity (GPP), ecosystem respiration (Reco), heterotrophic respiration (Rh) and autotrophic respiration (Ra) using two different approaches (i.e., chamber- and isotope-based methods) in a boreal peatland in northern Sweden (Degerö). Given that δ13C was continuously measured in each chamber, we were also able to further partition Rh into soil organic matter (SOM) mineralization by saprotrophic microbes and the oxidation of methane (CH4) by methanotrophic bacteria. During the ten day measurement period (in late July 2014), the average daily NEE flux at the mire was -0.6 g C m-2 d-1. Overall, the two partitioning approaches yielded similar estimates for the different NEE component fluxes. Average daily fluxes of Rh and Ra were similar in magnitude, yet these two flux components showed contrasting diurnal responses: Ra was greatest during the day whereas there was little diurnal variation in Rh. In general, average 13C signature of CO2 efflux from the Rh chambers (-41.1 ± 0.6 ‰) was between the 13C signature of SOM (-25.8 ± 0.6 ‰) and CH4 in pore water (-69.0 ± 0.8 ‰). Assuming that

  18. Comparing terrestrial, satellite, and ecosystem model output data for the Batéké Plateau, Gabon.

    NASA Astrophysics Data System (ADS)

    Fletcher, Charlotte; Petritsch, Richard; Pietsch, Stephan

    2010-05-01

    Productivity estimates hold an important role in decision making processes involving carbon sequestration and ecosystem management. They are also an integrated part of our efforts in understanding the effects of climate change on ecosystems. Yet exhaustive measurements of Net Primary Production (NPP) are difficult to accomplish, and the relationship between site-level and ecosystem model biomass estimates, and satellite and ecosystem model NPP estimates, is, as yet, not clearly defined. Past research undertaken in Austria suggests that (i) satellite-driven NPP estimates are similar to those of the ecosystem model's self-initialisation which represents potential NPP; (ii) NPP derived from field observations are correlated to the model results on actual ecosystem NPP; and (iii) correlations between satellite-derived versus terrestrial estimates are relatively poor. This study builds on the above-mentioned research within a different environmental context. Correlations between terrestrial data-driven biomass and NPP estimates and those derived from satellite imagery and an ecosystem model are analysed for the Batéké Plateau, Gabon - an area of savannah grasslands in the Congo basin. The biomass and NPP outputs of a biogeochemical (BGC) ecosystem model will be compared with biomass estimates calculated from field data, and NPP estimates as derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) available on the internet, respectively. One potential reason offered for the lack of correlation between satellite-derived and terrestrial estimates of NPP is that the different estimation methods act on different scales. Indeed, prior results indicate that satellite and terrestrial estimates are more highly correlated for homogenous landscapes compared to ‘patchy' landscapes. The Batéké Plateau has a more homogenous landscape compared to the intensively managed, patchwork landscape of Austria. It is therefore predicted that this study will show stronger

  19. Variability in net ecosystem exchange from hourly to inter-annual time scales at adjacent pine and hardwood forests: a wavelet analysis.

    PubMed

    Stoy, Paul C; Katul, Gabriel G; Siqueira, Mario B S; Juang, Jehn-Yih; McCarthy, Heather R; Kim, Hyun-Seok; Oishi, A Christopher; Oren, Ram

    2005-07-01

    Orthonormal wavelet transformation (OWT) is a computationally efficient technique for quantifying underlying frequencies in nonstationary and gap-infested time series, such as eddy-covariance-measured net ecosystem exchange of CO2 (NEE). We employed OWT to analyze the frequency characteristics of synchronously measured and modeled NEE at adjacent pine (PP) and hardwood (HW) ecosystems. Wavelet cospectral analysis showed that NEE at PP was more correlated to light and vapor pressure deficit at the daily time scale, and NEE at HW was more correlated to leaf area index (LAI) and temperature, especially soil temperature, at seasonal time scales. Models were required to disentangle the impacts of environmental drivers on the components of NEE, ecosystem carbon assimilation (Ac) and ecosystem respiration (RE). Sensitivity analyses revealed that using air temperature rather than soil temperature in RE models improved the modeled wavelet spectral frequency response on time scales longer than 1 day at both ecosystems. Including LAI improved RE model fit on seasonal time scales at HW, and incorporating parameter variability improved the RE model response at annual time scales at both ecosystems. Resolving variability in canopy conductance, rather than leaf-internal CO2, was more important for modeling Ac at both ecosystems. The PP ecosystem was more sensitive to hydrologic variables that regulate canopy conductance: vapor pressure deficit on weekly time scales and soil moisture on seasonal to interannual time scales. The HW ecosystem was sensitive to water limitation on weekly time scales. A combination of intrinsic drought sensitivity and non-conservative water use at PP was the basis for this response. At both ecosystems, incorporating variability in LAI was required for an accurate spectral representation of modeled NEE. However, nonlinearities imposed by canopy light attenuation were of little importance to spectral fit. The OWT revealed similarities and differences in

  20. Net ecosystem CO2 exchange of an invasive plant infestation: new insights on the effects of phenology and management practices on structure and functioning

    NASA Astrophysics Data System (ADS)

    Sonnentag, Oliver; Detto, Matteo; Runkle, Benjamin; Hatala, Jaclyn; Vargas, Rodrigo; Kelly, Maggi; Baldocchi, Dennis

    2010-05-01

    effects of measurement year and flowering/ mowing on the variable parameters of the non-linear responses of FA to light and FAR to air temperature. We address two specific questions with our research. First, how do year-round grazing and spring mowing affect the timing (i.e., onset) of pepperweed's key phenological phases? Second, we focus on pepperweed flowering, the spectrally most notable phenological phase. Thus we ask does the onset of flowering trigger changes in structural canopy development (i.e., z0m) and functioning (i.e., FA; FAR)? Over the summers (1 May - 30 September) of 2007 and 2009 the site was either almost neutral with respect to CO2 (-26 g C m-2 period-1 in 2007) or a moderate net CO2 source (89 g C m-2 period-1 in 2009). In contrast, the pepperweed infestation acted as a net CO2 sink (-162 g C m-2 period-1) over the summer of 2008 when the site was mowed once in May during flowering to reduce the reproductive success of pepperweed. Preliminary results show that year-round grazing inhibited the accumulation of dead stalks causing earlier pepperweed green-up. The onset of flowering had no substantial impact on z0m. In contrast, the onset of flowering significantly reduced maximum photosynthetic capacity compared to non-flowering pepperweed, resulting in reduced photosynthetic CO2 uptake. Similarly, FAR was slightly reduced in response to flowering, most likely due to the due to the close coupling of growth respiration to FA. In contrast, mowing early during flowering prevented the decrease in photosynthetic CO2 uptake and the associated decrease in FAR due to immediate pepperweed regrowth. Our study highlights the impact of invasive plants' unique ecophysiological features and applied management practices on net ecosystem CO2 exchange of infested ecosystems.

  1. Climate Effects on Carbon and Water Exchange of Young and Intermediate-growth Ponderosa Pine Ecosystems in Central Oregon

    NASA Astrophysics Data System (ADS)

    Kurpius, M. R.; Irvine, J.; Law, B. E.; Unsworth, M. H.

    2002-12-01

    Carbon and water fluxes were measured continuously by eddy covariance above young- and intermediate-aged ponderosa pine (Pinus ponderosa Dougl. Ex P. and C. Laws.) stands in a seasonally semiarid environment in central Oregon. Ecophysiological measurements of processes contributing to fluxes were also made (soil CO2 effluxes, transpiration). The young stand (YS) is ~17 years old, and has a total LAI of 1.5, with 40% of the leaf area in understory shrubs. The intermediate stand (IS), ~1.5 km from the YS, is ~56 years old, with total LAI ~3.1 (5% in understory shrubs). Our goal was to examine how seasonal weather patterns and age-related site characteristics affect CO2 and H2O exchange at these sites. Throughout the measurement period, water vapor exchange for both sites was similar in magnitude and trend. Net ecosystem exchange (NEE) was similar in magnitude (-1 to +1 mmol m-2 s-1) for both sites from January 2002 through March. As the rainy season ended, carbon uptake at both sites increased in April, and reached a maximum in early June. Early summer daytime mean NEE was greater at the IS (-6 to -8 mmol m-2 s-1) than at the YS (-3 to -4 mmol m-2 s-1). While the YS had higher summer soil CO2 efflux during this period, NEE remained higher at the IS due to higher GEP. Air temperature, vapor pressure deficit (VPD), and incident PAR were similar at both sites, but greater snow cover at the IS resulted in twice the soil moisture of the YS until July, when both sites reached low values (12% and 9%, respectively). A combination of higher leaf area and soil moisture likely accounts for higher early summer carbon uptake at the IS. NEE became strongly correlated with VPD in June as soil moisture levels were rapidly declining. VPD caused lowered NEE at both sites but the IS decreased more substantially than the YS and by mid-July NEE at both sites was -2 to -4 mmol m-2 s-1. Even with the diminished carbon uptake at the IS due to the strong coupling between VPD and NEE, we

  2. Ecosystem CO2/H2O fluxes are explained by hydraulically limited gas exchange during tree mortality from spruce bark beetles

    NASA Astrophysics Data System (ADS)

    Frank, John M.; Massman, William J.; Ewers, Brent E.; Huckaby, Laurie S.; Negrón, José F.

    2014-06-01

    Disturbances are increasing globally due to anthropogenic changes in land use and climate. This study determines whether a disturbance that affects the physiology of individual trees can be used to predict the response of the ecosystem by weighing two competing hypothesis at annual time scales: (a) changes in ecosystem fluxes are proportional to observable patterns of mortality or (b) to explain ecosystem fluxes the physiology of dying trees must also be incorporated. We evaluate these hypotheses by analyzing 6 years of eddy covariance flux data collected throughout the progression of a spruce beetle (Dendroctonus rufipennis) epidemic in a Wyoming Engelmann spruce (Picea engelmannii)-subalpine fir (Abies lasiocarpa) forest and testing for changes in canopy conductance (gc), evapotranspiration (ET), and net ecosystem exchange (NEE) of CO2. We predict from these hypotheses that (a) gc, ET, and NEE all diminish (decrease in absolute magnitude) as trees die or (b) that (1) gc and ET decline as trees are attacked (hydraulic failure from beetle-associated blue-stain fungi) and (2) NEE diminishes both as trees are attacked (restricted gas exchange) and when they die. Ecosystem fluxes declined as the outbreak progressed and the epidemic was best described as two phases: (I) hydraulic failure caused restricted gc, ET (28 ± 4% decline, Bayesian posterior mean ± standard deviation), and gas exchange (NEE diminished 13 ± 6%) and (II) trees died (NEE diminished 51 ± 3% with minimal further change in ET to 36 ± 4%). These results support hypothesis b and suggest that model predictions of ecosystem fluxes following massive disturbances must be modified to account for changes in tree physiological controls and not simply observed mortality.

  3. [Evaluation of remote sensing extraction methods for vegetation phenology based on flux tower net ecosystem carbon exchange data].

    PubMed

    Mou, Min-Jie; Zhu, Wen-Quan; Wang, Ling-Li; Xu, Ying-Jun; Liu, Jian-Hong

    2012-02-01

    Taking the vegetation phenological metrics derived from the net ecosystem carbon exchange (NEE) data of 72 flux towers in North America as the references, a comprehensive evaluation was conducted on the three typical classes of remote sensing extraction methods (threshold method, moving average method, and function fitting method) for vegetation phenology from the aspects of feasibility and accuracy. The results showed that the local midpoint threshold method had the highest feasibility and accuracy for extracting vegetation phenology, followed by the first derivative method based on fitted Logistic function. The feasibility and accuracy of moving average method were determined by the moving window size. As for the MODJS 16 d composited time-series normalized difference vegetation index (NDVI), the moving average method had preferable performance when the window size was set as 15. The global threshold method performed quite poor in the feasibility and accuracy. Though the values of the phenological metrics extracted by the curvature change rate method based on fitted Logistic function and the corresponding ones derived from NEE data had greater differences, there existed a strong correlation between them, indicating that the vegetation phenological metrics extracted by the curvature change rate method could reflect the real temporal and spatial variations of vegetation phenology.

  4. Response of net ecosystem gas exchange to a simulated precipitation pulse in a semi-arid grassland: the role of native versus non-native grasses and soil texture.

    PubMed

    Huxman, Travis E; Cable, Jessica M; Ignace, Danielle D; Eilts, J Alex; English, Nathan B; Weltzin, Jake; Williams, David G

    2004-10-01

    Physiological activity and structural dynamics in arid and semi-arid ecosystems are driven by discrete inputs or "pulses" of growing season precipitation. Here we describe the short-term dynamics of ecosystem physiology in experimental stands of native (Heteropogon contortus) and invasive (Eragrostis lehmanniana) grasses to an irrigation pulse across two geomorphic surfaces with distinctly different soils: a Pleistocene-aged surface with high clay content in a strongly horizonated soil, and a Holocene-aged surface with low clay content in homogenously structured soils. We evaluated whole-ecosystem and leaf-level CO2 and H2O exchange, soil CO2 efflux, along with plant and soil water status to understand potential constraints on whole-ecosystem carbon exchange during the initiation of the summer monsoon season. Prior to the irrigation pulse, both invasive and native grasses had less negative pre-dawn water potentials (Psipd), greater leaf photosynthetic rates (Anet) and stomatal conductance (gs), and greater rates of net ecosystem carbon exchange (NEE) on the Pleistocene surface than on the Holocene. Twenty-four hours following the experimental application of a 39 mm irrigation pulse, soil CO2 efflux increased leading to all plots losing CO2 to the atmosphere over the course of a day. Invasive species stands had greater evapotranspiration rates (ET) immediately following the precipitation pulse than did native stands, while maximum instantaneous NEE increased for both species and surfaces at roughly the same rate. The differential ET patterns through time were correlated with an earlier decline in NEE in the invasive species as compared to the native species plots. Plots with invasive species accumulated between 5% and 33% of the carbon that plots with the native species accumulated over the 15-day pulse period. Taken together, these results indicate that system CO2 efflux (both the physical displacement of soil CO2 by water along with plant and microbial respiration

  5. Anywhere the Wind Blows does Really Matter to Net Ecosystem Carbon Exchange.

    NASA Astrophysics Data System (ADS)

    Montaldo, Nicola; Oren, Ram

    2013-04-01

    Mistral wind (from North-west direction) affects climate of western Mediterranean basin. Coming from north -east, it crosses France, Sardinia and finally reaches South Italy. Recent studies showed that climate change is affecting wind speed and directions. In particular, in the case of the Mistral over the Mediterranean area a decrease of the wind speed and changes of the wind direction in the Summer months are predicted using global climate models. We point out that these climate changes can affect land surface fluxes -- evapotranspiration (ET) and carbon exchanges (Fc). Indeed, considering data from an eddy covariance tower in Sardinia (Italy) we show that wind direction and velocity represent larger scale weather conditions affecting land surface fluxes independently of footprint properties in what might be a confounding fashion, requiring extra care in linking footprint properties to flux rates. Hence, we demonstrate that more important can be the large scale (e.g., regional) impact of the wind direction and speed on land surface fluxes. The island of Sardinia is strongly representative of the Mediterranean region. We consider a representative case study site within the Flumendosa river basin on Sardinia in Orroli, a mixed grass-woodland site on a shallow soil. During 2004 - 2007 a micrometeorological towers with eddy covariance instrumentation monitored land surface fluxes of energy, water, and CO2. In Sardinia Mistral is characterized by the highest wind speed (> 3 m/s). Analyzing meteorological conditions under Mistral over Sardinia we observe a decrease of the air temperature and vapor pressure deficit (VPD). We concentrate on the Summer period during which air temperature and light are not limiting factors of ET and Fc. We distinguish the surprising effect of the mistral on ET and Fc. At the Orroli site the Summer 2005 was characterized by a soil moisture drying due to a small rain event at the end of June followed by an extreme dry period until September

  6. CO2 and CH4 exchanges between land ecosystems and the atmosphere in northern high latitudes over the 21st century

    USGS Publications Warehouse

    Zhuang, Q.; Melillo, J.M.; Sarofim, M.C.; Kicklighter, D.W.; McGuire, A.D.; Felzer, B.S.; Sokolov, A.; Prinn, R.G.; Steudler, P.A.; Hu, S.

    2006-01-01

    Terrestrial ecosystems of the northern high latitudes (above 50??N) exchange large amounts of CO2 and CH4 with the atmosphere each year. Here we use a process-based model to estimate the budget of CO 2 and CH4 of the region for current climate conditions and for future scenarios by considering effects of permafrost dynamics, CO 2 fertilization of photosynthesis and fire. We find that currently the region is a net source of carbon to the atmosphere at 276 Tg C yr -1. We project that throughout the 21st century, the region will most likely continue as a net source of carbon and the source will increase by up to 473 Tg C yr-1 by the end of the century compared to the current emissions. However our coupled carbon and climate model simulations show that these emissions will exert relatively small radiative forcing on global climate system compared to large amounts of anthropogenic emissions. Copyright 2006 by the American Geophysical Union.

  7. Evaluating atmospheric CO2 effects on gross primary productivity and net ecosystem exchanges of terrestrial ecosystems in the conterminous United States using the AmeriFlux data and an artificial neural network approach

    DOE PAGES

    Liu, Shaoqing; Zhuang, Qianlai; He, Yujie; Noormets, Asko; Chen, Jiquan; Gu, Lianhong

    2016-01-21

    Quantitative understanding of regional gross primary productivity (GPP) and net ecosystem exchanges (NEE) and their responses to environmental changes are critical to quantifying the feedbacks of ecosystems to the global climate system. Numerous studies have used the eddy flux data to upscale the eddy covariance derived carbon fluxes from stand scales to regional and global scales. However, few studies incorporated atmospheric carbon dioxide (CO2) concentrations into those extrapolations. In this study, we consider the effect of atmospheric CO2 using an artificial neural network (ANN) approach to upscale the AmeriFlux tower of NEE and the derived GPP to the conterminous Unitedmore » States. Two ANN models incorporating remote sensing variables at an 8-day time step were developed. One included CO2 as an explanatory variable and the other did not. The models were first trained, validated using eddy flux data, and then extrapolated to the region at a 0.05° × 0.05° (latitude × longitude) resolution from 2001 to 2006. We found that both models performed well in simulating site-level carbon fluxes. The spatially-averaged annual GPP with and without considering the atmospheric CO2 were 789 and 788 g C m-2 yr-1, respectively (for NEE, the values were -112 and -109 g C m-2 yr-1, respectively). Model predictions were comparable with previous published results and MODIS GPP products. However, the difference in GPP between the two models exhibited a great spatial and seasonal variability, with an annual difference of 200 g C m-2 yr-1. Further analysis suggested that air temperature played an important role in determining the atmospheric CO2 effects on carbon fluxes. In addition, the simulation that did not consider atmospheric CO2 failed to detect ecosystem responses to droughts in part of the US in 2006. In conclusion, we suggest that the spatially and temporally varied atmospheric CO2 concentrations should be factored into carbon quantification when scaling eddy flux

  8. Evaluating atmospheric CO2 effects on gross primary productivity and net ecosystem exchanges of terrestrial ecosystems in the conterminous United States using the AmeriFlux data and an artificial neural network approach

    SciTech Connect

    Liu, Shaoqing; Zhuang, Qianlai; He, Yujie; Noormets, Asko; Chen, Jiquan; Gu, Lianhong

    2016-01-01

    Quantitative understanding of regional gross primary productivity (GPP) and net ecosystem exchanges (NEE) and their responses to environmental changes are critical to quantifying the feedbacks of ecosystems to the global climate system. Numerous studies have used the eddy flux data to upscale the eddy covariance derived carbon fluxes from stand scales to regional and global scales. However, few studies incorporated atmospheric carbon dioxide (CO2) concentrations into those extrapolations. Here, we consider the effect of atmospheric CO2 using an artificial neural network (ANN) approach to upscale the AmeriFlux tower of NEE and the derived GPP to the conterminous United States. Two ANN models incorporating remote sensing variables at an 8-day time step were developed. One included CO2 as an explanatory variable and the other did not. The models were first trained, validated using eddy flux data, and then extrapolated to the region at a 0.05 degrees x 0.05 degrees (latitude x longitude) resolution from 2001 to 2006. We found that both models performed well in simulating site-level carbon fluxes. The spatially averaged annual GPP with and without considering the atmospheric CO2 were 789 and 788 g Cm-2 yr(-1), respectively (for NEE, the values were 112 and 109 g Cm-2 yr(-1), respectively). Model predictions were comparable with previous published results and MODIS GPP products. However, the difference in GPP between the two models exhibited a great spatial and seasonal variability, with an annual difference of 200 g Cm-2 yr(-1). Further analysis suggested that air temperature played an important role in determining the atmospheric CO2 effects on carbon fluxes. In addition, the simulation that did not consider atmospheric CO2 failed to detect ecosystem responses to droughts in part of the US in 2006. The study suggests that the spatially and temporally varied atmospheric CO2 concentrations should be factored into carbon quantification when scaling eddy flux data to a

  9. Seasonal and inter-annual variability of the net ecosystem CO2 exchange of a temperate mountain grassland: effects of climate and management

    PubMed Central

    Wohlfahrt, Georg; Hammerle, Albin; Haslwanter, Alois; Bahn, Michael; Tappeiner, Ulrike; Cernusca, Alexander

    2013-01-01

    The role and relative importance of climate and cutting for the seasonal and inter-annual variability of the net ecosystem CO2 (NEE) of a temperate mountain grassland was investigated. Eddy covariance CO2 flux data and associated measurements of the green area index and the major environmental driving forces acquired during 2001-2006 at the study site Neustift (Austria) were analyzed. Driven by three cutting events per year which kept the investigated grassland in a stage of vigorous growth, the seasonal variability of NEE was primarily modulated by gross primary productivity (GPP). The role of environmental parameters in modulating the seasonal variability of NEE was obscured by the strong response of GPP to changes in the amount of green area, as well as the cutting-mediated decoupling of phenological development and the seasonal course of climate drivers. None of the climate and management metrics examined was able to explain the inter-annual variability of annual NEE. This is thought to result from (1) a high covariance between GPP and ecosystem respiration (Reco) at the annual time scale which results in a comparatively small inter-annual variation of NEE, (2) compensating effects between carbon exchange during and outside the management period, and (3) changes in the biotic response to rather than the climate variables per se. GPP was more important in modulating inter-annual variations in NEE in spring and before the first and second cut, while Reco explained a larger fraction of the inter-annual variability of NEE during the remaining, in particular the post-cut, periods. PMID:24383047

  10. Seasonal and inter-annual variability of the net ecosystem CO2 exchange of a temperate mountain grassland: effects of climate and management.

    PubMed

    Wohlfahrt, Georg; Hammerle, Albin; Haslwanter, Alois; Bahn, Michael; Tappeiner, Ulrike; Cernusca, Alexander

    2008-04-27

    The role and relative importance of climate and cutting for the seasonal and inter-annual variability of the net ecosystem CO2 (NEE) of a temperate mountain grassland was investigated. Eddy covariance CO2 flux data and associated measurements of the green area index and the major environmental driving forces acquired during 2001-2006 at the study site Neustift (Austria) were analyzed. Driven by three cutting events per year which kept the investigated grassland in a stage of vigorous growth, the seasonal variability of NEE was primarily modulated by gross primary productivity (GPP). The role of environmental parameters in modulating the seasonal variability of NEE was obscured by the strong response of GPP to changes in the amount of green area, as well as the cutting-mediated decoupling of phenological development and the seasonal course of climate drivers. None of the climate and management metrics examined was able to explain the inter-annual variability of annual NEE. This is thought to result from (1) a high covariance between GPP and ecosystem respiration (Reco) at the annual time scale which results in a comparatively small inter-annual variation of NEE, (2) compensating effects between carbon exchange during and outside the management period, and (3) changes in the biotic response to rather than the climate variables per se. GPP was more important in modulating inter-annual variations in NEE in spring and before the first and second cut, while Reco explained a larger fraction of the inter-annual variability of NEE during the remaining, in particular the post-cut, periods. PMID:24383047

  11. Comparative impacts of two major hurricane seasons on the Neuse River and western Pamlico Sound ecosystems.

    PubMed

    Burkholder, JoAnn; Eggleston, David; Glasgow, Howard; Brownie, Cavell; Reed, Robert; Janowitz, Gerald; Posey, Martin; Melia, Greg; Kinder, Carol; Corbett, Reide; Toms, David; Alphin, Troy; Deamer, Nora; Springer, Jeffrey

    2004-06-22

    Ecosystem-level impacts of two hurricane seasons were compared several years after the storms in the largest lagoonal estuary in the U.S., the Albemarle-Pamlico Estuarine System. A segmented linear regression flow model was developed to compare mass-water transport and nutrient loadings to a major artery, the Neuse River Estuary (NRE), and to estimate mean annual versus storm-related volume delivery to the NRE and Pamlico Sound. Significantly less water volume was delivered by Hurricane Fran (1996), but massive fish kills occurred in association with severe dissolved oxygen deficits and high contaminant loadings (total nitrogen, total phosphorus, suspended solids, and fecal bacteria). The high water volume of the second hurricane season (Hurricanes Dennis, Floyd, and Irene in 1999) delivered generally comparable but more dilute contaminant loads, and no major fish kills were reported. There were no discernable long-term adverse impacts on water quality. Populations of undesirable organisms, such as toxic dinoflagellates, were displaced down-estuary to habitats less conducive for growth. The response of fisheries was species-dependent: there was no apparent impact of the hurricanes on commercial landings of bivalve molluscs or shrimp. In contrast, interacting effects of hurricane floodwaters in 1999 and intensive fishing pressure led to striking reductions in blue crabs. Overall, the data support the premise that, in shallow estuaries frequently disturbed by hurricanes, there can be relatively rapid recovery in water quality and biota, and benefit from the scouring activity of these storms.

  12. Influence of clouds and diffuse radiation on ecosystem-atmosphere CO2 and CO18O exchanges

    NASA Astrophysics Data System (ADS)

    Still, C. J.; Riley, W. J.; Biraud, S. C.; Noone, D. C.; Buenning, N. H.; Randerson, J. T.; Torn, M. S.; Welker, J.; White, J. W. C.; Vachon, R.; Farquhar, G. D.; Berry, J. A.

    2009-03-01

    This study evaluates the potential impact of clouds on ecosystem CO2 and CO2 isotope fluxes ("isofluxes") in two contrasting ecosystems (a broadleaf deciduous forest and a C4 grassland) in a region for which cloud cover, meteorological, and isotope data are available for driving the isotope-enabled land surface model (ISOLSM). Our model results indicate a large impact of clouds on ecosystem CO2 fluxes and isofluxes. Despite lower irradiance on partly cloudy and cloudy days, predicted forest canopy photosynthesis was substantially higher than on clear, sunny days, and the highest carbon uptake was achieved on the cloudiest day. This effect was driven by a large increase in light-limited shade leaf photosynthesis following an increase in the diffuse fraction of irradiance. Photosynthetic isofluxes, by contrast, were largest on partly cloudy days, as leaf water isotopic composition was only slightly depleted and photosynthesis was enhanced, as compared to adjacent clear-sky days. On the cloudiest day, the forest exhibited intermediate isofluxes: although photosynthesis was highest on this day, leaf-to-atmosphere isofluxes were reduced from a feedback of transpiration on canopy relative humidity and leaf water. Photosynthesis and isofluxes were both reduced in the C4 grass canopy with increasing cloud cover and diffuse fraction as a result of near-constant light limitation of photosynthesis. These results suggest that some of the unexplained variation in global mean δ18O of CO2 may be driven by large-scale changes in clouds and aerosols and their impacts on diffuse radiation, photosynthesis, and relative humidity.

  13. Carbonyl sulfide exchange in soils for better estimates of ecosystem carbon uptake

    NASA Astrophysics Data System (ADS)

    Whelan, Mary E.; Hilton, Timothy W.; Berry, Joseph A.; Berkelhammer, Max; Desai, Ankur R.; Campbell, J. Elliott

    2016-03-01

    Carbonyl sulfide (COS) measurements are one of the emerging tools to better quantify gross primary production (GPP), the largest flux in the global carbon cycle. COS is a gas with a similar structure to CO2; COS uptake is thought to be a proxy for GPP. However, soils are a potential source or sink of COS. This study presents a framework for understanding soil-COS interactions. Excluding wetlands, most of the few observations of isolated soils that have been made show small uptake of atmospheric COS. Recently, a series of studies at an agricultural site in the central United States found soil COS production under hot conditions an order of magnitude greater than fluxes at other sites. To investigate the extent of this phenomenon, soils were collected from five new sites and incubated in a variety of soil moisture and temperature states. We found that soils from a desert, an oak savannah, a deciduous forest, and a rainforest exhibited small COS fluxes, behavior resembling previous studies. However, soil from an agricultural site in Illinois, > 800 km away from the initial central US study site, demonstrated comparably large soil fluxes under similar conditions. These new data suggest that, for the most part, soil COS interaction is negligible compared to plant uptake of COS. We present a model that anticipates the large agricultural soil fluxes so that they may be taken into account. While COS air-monitoring data are consistent with the dominance of plant uptake, improved interpretation of these data should incorporate the soil flux parameterizations suggested here.

  14. Carbonyl sulfide exchange in soils for better estimates of ecosystem carbon uptake

    DOE PAGES

    Whelan, Mary E.; Hilton, Timothy W.; Berry, Joseph A.; Berkelhammer, Max; Desai, Ankur R.; Campbell, J. Elliott

    2016-03-21

    Carbonyl sulfide (COS) measurements are one of the emerging tools to better quantify gross primary production (GPP), the largest flux in the global carbon cycle. COS is a gas with a similar structure to CO2; COS uptake is thought to be a proxy for GPP. However, soils are a potential source or sink of COS. This study presents a framework for understanding soil–COS interactions. Excluding wetlands, most of the few observations of isolated soils that have been made show small uptake of atmospheric COS. Recently, a series of studies at an agricultural site in the central United States found soilmore » COS production under hot conditions an order of magnitude greater than fluxes at other sites. To investigate the extent of this phenomenon, soils were collected from five new sites and incubated in a variety of soil moisture and temperature states. We found that soils from a desert, an oak savannah, a deciduous forest, and a rainforest exhibited small COS fluxes, behavior resembling previous studies. However, soil from an agricultural site in Illinois, >800 km away from the initial central US study site, demonstrated comparably large soil fluxes under similar conditions. These new data suggest that, for the most part, soil COS interaction is negligible compared to plant uptake of COS. We present a model that anticipates the large agricultural soil fluxes so that they may be taken into account. Furthermore, while COS air-monitoring data are consistent with the dominance of plant uptake, improved interpretation of these data should incorporate the soil flux parameterizations suggested here.« less

  15. Carbon storage, timber production, and biodiversity: comparing ecosystem services with multi-criteria decision analysis.

    PubMed

    Schwenk, W Scott; Donovan, Therese M; Keeton, William S; Nunery, Jared S

    2012-07-01

    Increasingly, land managers seek ways to manage forests for multiple ecosystem services and functions, yet considerable challenges exist in comparing disparate services and balancing trade-offs among them. We applied multi-criteria decision analysis (MCDA) and forest simulation models to simultaneously consider three objectives: (1) storing carbon, (2) producing timber and wood products, and (3) sustaining biodiversity. We used the Forest Vegetation Simulator (FVS) applied to 42 northern hardwood sites to simulate forest development over 100 years and to estimate carbon storage and timber production. We estimated biodiversity implications with occupancy models for 51 terrestrial bird species that were linked to FVS outputs. We simulated four alternative management prescriptions that spanned a range of harvesting intensities and forest structure retention. We found that silvicultural approaches emphasizing less frequent harvesting and greater structural retention could be expected to achieve the greatest net carbon storage but also produce less timber. More intensive prescriptions would enhance biodiversity because positive responses of early successional species exceeded negative responses of late successional species within the heavily forested study area. The combinations of weights assigned to objectives had a large influence on which prescriptions were scored as optimal. Overall, we found that a diversity of silvicultural approaches is likely to be preferable to any single approach, emphasizing the need for landscape-scale management to provide a full range of ecosystem goods and services. Our analytical framework that combined MCDA with forest simulation modeling was a powerful tool in understanding trade-offs among management objectives and how they can be simultaneously accommodated. PMID:22908717

  16. Uncertainty Analysis of Gross Primary Production Separated from Net Ecosystem Exchange Measurements at Speulderbos Forest, The Netherlands

    NASA Astrophysics Data System (ADS)

    Raj, Rahul; Hamm, Nicholas Alexander Samuel; van der Tol, Christiaan; Stein, Alfred

    2015-04-01

    Gross primary production (GPP), separated from the flux tower measurements of net ecosystem exchange (NEE) of CO2, is used increasingly to validate process-based simulators and remote sensing-derived estimates of simulated GPP at various time scales. Proper implementation of validation requires knowledge of the uncertainty associated with the separated GPP at different time scales so that the propagated uncertainty can be determined. We estimate the uncertainty in GPP at half-hourly to yearly time scales. Flux tower measurements of NEE results from two major fluxes GPP and ecosystem respiration (Reco) as NEE = GPP - Reco and therefore GPP can be separated from NEE. We used a non-rectangular hyperbola (NRH) model to separate half-hourly GPP from the three years of continuous flux tower measurements of half-hourly NEE at the Speulderbos forest site, The Netherlands. NRH includes the variables that influence GPP, in particular radiation, vapor pressure deficit, and temperature. In addition, NRH model provides a robust empirical relationship between radiation and GPP by including the degree of curvature of light response curve. NRH was fitted to the measured NEE data on a daily basis. Variation in the parameters of this model was studied within each year. We did not obtain a single optimized value of each parameter of NRH model, instead we defined the prior distribution of each parameters based on literature search. We adopted a Bayesian approach, which was implemented using Markov chain Monte Carlo (MCMC) simulation to update the prior distribution of each parameter on a daily basis. This allowed us to estimate the uncertainty in the separated GPP at the half-hourly time scale. The results of this approach generated the empirical distribution of GPP at each half-hour, which are a measure of uncertainty. The time series of empirical distributions of half-hourly GPP values also allowed us to estimate the uncertainty at daily, monthly and yearly time scales. Our research

  17. Mathematical modeling of the "plant community -soil-like substrate -gas exchange with the human" closed ecosystem

    NASA Astrophysics Data System (ADS)

    Barkhatov, Yuri; Gubanov, Vladimir; Tikhomirov, Alexander A.; Degermendzhy, Andrey G.

    A mathematical model of the "plant community -soil-like substrate -gas exchange with the human" experimental biological life support system (BLSS) has been constructed to predict its functioning and estimate feasibility of controlling it. The mathematical model consists of three compartments -two `phytotron' models (with wheat and radish) and the `mycotron' model (for mushrooms). The following components are included in the model: edible mushrooms (mushroom fruit bodies and mycelium); wheat; radish; straw (processed by mycelium); dead organic matter in the phytotron (separately for the wheat unit and for the radish unit); worms; worms' coprolites; vermicompost used as a soil-like substrate (SLS); bacterial microflora; min-eral nitrogen, phosphorus and iron; products of the system intended for humans (wheat grains, radish roots and mushroom fruit bodies); oxygen and carbon dioxide. Under continuous gas exchange, the mass exchange between the compartments occurs at the harvesting time. The conveyor character of the closed ecosystem functioning has been taken into account -the num-ber of culture age groups can be regulated (in experiments -4 and 8 age groups). The conveyor cycle duration can be regulated as well. The module is designed for the food and gas exchange requirements of 1/30 of a virtually present human. Aim of model analysis is determination of investigation direction in real experimental BLSS. The model allows doing dynamic calcu-lations of closure coefficient based on the main elements taken into account in the model and evaluating all dynamic components of the system under different conditions and modes of its operation, especially under the conditions that can hardly be created experimentally. One of the sustainability conditions can be long-duration functioning of the system under the light-ing that is far from the optimum. The mathematical model of the system can demonstrate variants of its sustainable functioning or ruin under various critical

  18. Comparative study of key exchange and authentication methods in application, transport and network level security mechanisms

    NASA Astrophysics Data System (ADS)

    Fathirad, Iraj; Devlin, John; Jiang, Frank

    2012-09-01

    The key-exchange and authentication are two crucial elements of any network security mechanism. IPsec, SSL/TLS, PGP and S/MIME are well-known security approaches in providing security service to network, transport and application layers; these protocols use different methods (based on their requirements) to establish keying materials and authenticates key-negotiation and participated parties. This paper studies and compares the authenticated key negotiation methods in mentioned protocols.

  19. Effects of winter temperature and summer drought on net ecosystem exchange of CO2 in a temperate peatland

    NASA Astrophysics Data System (ADS)

    Helfter, Carole; Campbell, Claire; Dinsmore, Kerry; Drewer, Julia; Coyle, Mhairi; Anderson, Margaret; Skiba, Ute; Nemitz, Eiko; Billett, Michael; Sutton, Mark

    2014-05-01

    Northern peatlands are one of the most important global sinks of atmospheric carbon dioxide (CO2); their ability to sequester C is a natural feedback mechanism controlled by climatic variables such as precipitation, temperature, length of growing season and period of snow cover. In the UK it has been predicted that peatlands could become a net source of carbon in response to climate change with climate models predicting a rise in global temperature of ca. 3oC between 1961-1990 and 2100. Land-atmosphere exchange of CO2in peatlands exhibits marked seasonal and inter-annual variations, which have significant short- and long-term effects on carbon sink strength. Net ecosystem exchange (NEE) of CO2 has been measured continuously by eddy-covariance (EC) at Auchencorth Moss (55° 47'32 N, 3° 14'35 W, 267 m a.s.l.), a temperate peatland in central Scotland, since 2002. Auchencorth Moss is a low-lying, ombrotrophic peatland situated ca. 20 km south-west of Edinburgh. Peat depth ranges from 5 m and the site has a mean annual precipitation of 1155 mm. The vegetation present within the flux measurement footprint comprises mixed grass species, heather and substantial areas of moss species (Sphagnum spp. and Polytrichum spp.). The EC system consists of a LiCOR 7000 closed-path infrared gas analyser for the simultaneous measurement of CO2 and water vapour and of a Gill Windmaster Pro ultrasonic anemometer. Over the 10 year period, the site was a consistent yet variable sink of CO2 ranging from -34.1 to -135.9 g CO2-C m-2 yr-1 (mean of -69.1 ± 33.6 g CO2-C m-2 yr-1). Inter-annual variability in NEE was positively correlated to the length of the growing seasons and mean winter air temperature explained 93% of the variability in summertime sink strength, indicating a phenological memory-effect. Plant development and productivity were stunted by colder winters causing a net reduction in the annual carbon sink strength of this peatland where autotrophic processes are thought to be

  20. Calcium Carbonate Phosphate Binding Ion Exchange Filtration and Accelerated Denitrification Improve Public Health Standards and Combat Eutrophication in Aquatic Ecosystems

    PubMed Central

    Yanamadala, Vijay

    2010-01-01

    Hektoen agar. Initial analyses suggest a strong correlation between phosphate concentrations and bacterial populations; a 66% decrease in phosphate resulted in a 35% reduction in bacterial populations and a 45% reduction in enteropathogenic populations. Likewise, a strong correlation was shown between calcium carbonate concentrations and bacterial reduction greater than that which can be attributed to the phosphate reduction alone. This was followed by the construction of various phosphate binding calcium carbonate filters, which used the ion exchange principle, including a spring loading filter, PVC pipe filter, and a galvanized filter. All were tested with the aid of Stoke's law formulation. The experiment was extremely successful in designing a working phosphate-binding and ammonia-reducing filter, and a large-scale agitator-clarifier filter system is currently being planned for construction in Madrona Marsh; this filter will reduce phosphate and ammonia levels substantially in the following years, bringing ecological, economical, and health-related improvements to the overall ecosystem and habitat. PMID:16381147

  1. Evaluating Eddy Covariance Flux Filtering Methods For Producing Ecosystem-Representative Carbon Exchange Estimates For A Fetch-Limited Temperate Forest

    NASA Astrophysics Data System (ADS)

    Bowling, D. R.; Bird, J. A.; Schmidt, S. K.

    2011-12-01

    Producing time-integrated (daily to annual) estimates of ecosystem-atmosphere carbon exchanges from eddy covariance (EC) measurements requires the careful exclusion of non-representative fluxes prior to gap-filling model application. Half-hourly fluxes are typically excluded when atmospheric turbulence is below an acceptable level (friction velocity threshold, u*Th), or when the relative contribution from non-target surfaces is greater than a tolerable amount (footprint threshold, fpTh). In this study, we compare and evaluate a variety of commonly-used footprint- and friction velocity-filtering methods applied to six years (2006-2011) of carbon flux estimates for a fetch-limited, 74-year old planted Eastern white pine (Pinus Strobus L.) forest in southern Ontario, Canada. A data-driven approach was used, where factorial combinations of footprint models, fpTh values and u*Th determination methods were applied prior to gap-filling. Filtering applications were compared in terms of the quantity and distribution of data removed, while ANOVA and multiple comparison tests were used to quantify the influence of these applications on annual estimates of Net Ecosystem Productivity (NEP), Ecosystem Respiration (RE) and Gross Ecosystem Productivity (GEP). Finally, preferred filtering applications were selected using an objective evaluation of gap-filling model performance metrics to provide information on the internal consistency of the filtered data. Results showed that the choice of footprint model and fpTh exerted a greater influence on NEP, RE and GEP estimates than the u*Th estimation method used. Variation in u*Th estimates were partly explained by footprint filtering specifications, indicating significant u*Th differences between the target forest and the surrounding forested and agricultural land. Applying the footprint model of Kljun (2004. Bound. Layer Met. 112[3]) at fpTh = 0.8 resulted in greatest improvement in model performance; increasing fpTh above this value

  2. Evaluating Eddy Covariance Flux Filtering Methods For Producing Ecosystem-Representative Carbon Exchange Estimates For A Fetch-Limited Temperate Forest

    NASA Astrophysics Data System (ADS)

    Brodeur, J. J.; Peichl, M.; Arain, M.

    2013-12-01

    Producing time-integrated (daily to annual) estimates of ecosystem-atmosphere carbon exchanges from eddy covariance (EC) measurements requires the careful exclusion of non-representative fluxes prior to gap-filling model application. Half-hourly fluxes are typically excluded when atmospheric turbulence is below an acceptable level (friction velocity threshold, u*Th), or when the relative contribution from non-target surfaces is greater than a tolerable amount (footprint threshold, fpTh). In this study, we compare and evaluate a variety of commonly-used footprint- and friction velocity-filtering methods applied to six years (2006-2011) of carbon flux estimates for a fetch-limited, 74-year old planted Eastern white pine (Pinus Strobus L.) forest in southern Ontario, Canada. A data-driven approach was used, where factorial combinations of footprint models, fpTh values and u*Th determination methods were applied prior to gap-filling. Filtering applications were compared in terms of the quantity and distribution of data removed, while ANOVA and multiple comparison tests were used to quantify the influence of these applications on annual estimates of Net Ecosystem Productivity (NEP), Ecosystem Respiration (RE) and Gross Ecosystem Productivity (GEP). Finally, preferred filtering applications were selected using an objective evaluation of gap-filling model performance metrics to provide information on the internal consistency of the filtered data. Results showed that the choice of footprint model and fpTh exerted a greater influence on NEP, RE and GEP estimates than the u*Th estimation method used. Variation in u*Th estimates were partly explained by footprint filtering specifications, indicating significant u*Th differences between the target forest and the surrounding forested and agricultural land. Applying the footprint model of Kljun (2004. Bound. Layer Met. 112[3]) at fpTh = 0.8 resulted in greatest improvement in model performance; increasing fpTh above this value

  3. Biodiversity mediates top-down control in eelgrass ecosystems: a global comparative-experimental approach.

    PubMed

    Duffy, J Emmett; Reynolds, Pamela L; Boström, Christoffer; Coyer, James A; Cusson, Mathieu; Donadi, Serena; Douglass, James G; Eklöf, Johan S; Engelen, Aschwin H; Eriksson, Britas Klemens; Fredriksen, Stein; Gamfeldt, Lars; Gustafsson, Camilla; Hoarau, Galice; Hori, Masakazu; Hovel, Kevin; Iken, Katrin; Lefcheck, Jonathan S; Moksnes, Per-Olav; Nakaoka, Masahiro; O'Connor, Mary I; Olsen, Jeanine L; Richardson, J Paul; Ruesink, Jennifer L; Sotka, Erik E; Thormar, Jonas; Whalen, Matthew A; Stachowicz, John J

    2015-07-01

    Nutrient pollution and reduced grazing each can stimulate algal blooms as shown by numerous experiments. But because experiments rarely incorporate natural variation in environmental factors and biodiversity, conditions determining the relative strength of bottom-up and top-down forcing remain unresolved. We factorially added nutrients and reduced grazing at 15 sites across the range of the marine foundation species eelgrass (Zostera marina) to quantify how top-down and bottom-up control interact with natural gradients in biodiversity and environmental forcing. Experiments confirmed modest top-down control of algae, whereas fertilisation had no general effect. Unexpectedly, grazer and algal biomass were better predicted by cross-site variation in grazer and eelgrass diversity than by global environmental gradients. Moreover, these large-scale patterns corresponded strikingly with prior small-scale experiments. Our results link global and local evidence that biodiversity and top-down control strongly influence functioning of threatened seagrass ecosystems, and suggest that biodiversity is comparably important to global change stressors.

  4. From carbon numbers to ecosystem services: usable results comparing natural versus managed lands

    NASA Astrophysics Data System (ADS)

    Bachelet, D. M.; Ferschweiler, K.; Sheehan, T.; Sleeter, B. M.; Zhu, Z.

    2015-12-01

    We ran the MC2 dynamic vegetation model for the conterminous US at 30 arc sec with and without land use and fire suppression for several climate change scenarios. We translated model results into key ecosystem services (ES) such as climate regulation through carbon uptake and sequestration (global climate) or through transpiration (regional climate) as well as water provision through runoff and throughflow. We also projected timber production and gauged the risk of production lost to fire and/or drought by simulating fuel loads and forest vigor annually through the 21st century. We calculated the rising irrigation demand for agricultural land which, coupled with available information on groundwater resources, could help plan for future cropping systems. By combining these results we can evaluate land cover value across the country in terms of quantity and quality of services rendered. By comparing projections with and without landuse and fire suppression we can illustrate differences in regulating and provisioning services between managed and natural lands.

  5. Comparison between eddy covariance and automatic chamber techniques for measuring net ecosystem exchange of carbon dioxide in cotton and wheat fields

    NASA Astrophysics Data System (ADS)

    Wang, K.; Liu, C.; Zheng, X.; Pihlatie, M.; Li, B.; Haapanala, S.; Vesala, T.; Liu, H.; Wang, Y.; Liu, G.; Hu, F.

    2013-05-01

    Static and transparent automatic chamber (AC) technique is a~necessary choice for measuring net ecosystem exchange (NEE) of carbon dioxide (CO2) in circumstances where eddy covariance (EC) technique is not applicable. However, a comparison of the two techniques for measurements on croplands has seldom been undertaken. We carried out NEE observations in a cotton field (for one year) and a winter wheat field (for one cropping season) using both AC and EC techniques, to (a) compare the NEE fluxes measured using each technique, and (b) test the NEE measurement performance of an automatic chamber system (AMEG), which was designed for simultaneous flux measurements of multiple gases. The half-hourly NEE fluxes measured with the two techniques were in approximate agreement, with the AC fluxes being 0.78 (cotton) and 1.06 (wheat) times those of the EC. When integrated to daily timescale, the fluxes of the two techniques were in better agreement, showing an average ratio of 0.94 and 1.00 for the cotton and wheat, respectively. During the periods with comparable field conditions and normal performance of both instruments, the cumulative NEE fluxes revealed small differences between the two techniques (-9.0 ~ 6.7%, with a mean of 0.1%). The measurements resulted in annual cumulative NEE of -40 g C m-2 yr-1 (EC) and -42 g C m-2 yr-1 (AC) in the cotton field and seasonal cumulative NEE of -251 g C m-2 (EC) and -205 g C m-2 (AC) in the wheat field. Our results indicate that, for cropland populated by short plants, the AMEG system and the data processing procedures applied in this study are able to provide NEE estimates comparable to those from EC measurements, although either technique may lead to an overestimation of the loss rate (or underestimation of the gain rate) of the soil organic carbon stock of an ecosystem, in particular with calcareous soils exposed to increasing atmospheric acid deposition.

  6. Comparison between eddy covariance and automatic chamber techniques for measuring net ecosystem exchange of carbon dioxide in cotton and wheat fields

    NASA Astrophysics Data System (ADS)

    Wang, K.; Liu, C.; Zheng, X.; Pihlatie, M.; Li, B.; Haapanala, S.; Vesala, T.; Liu, H.; Wang, Y.; Liu, G.; Hu, F.

    2013-11-01

    Static and transparent automatic chamber (AC) technique is a necessary choice for measuring net ecosystem exchange (NEE) of carbon dioxide (CO2) in circumstances where eddy covariance (EC) technique is not applicable. However, a comparison of the two techniques for measurements on croplands has seldom been undertaken. We carried out NEE observations in a cotton field (for one year) and a winter wheat field (for one cropping season) using both AC and EC techniques, to (a) compare the NEE fluxes measured using each technique, and (b) test the NEE measurement performance of an automatic chamber system (AMEG), which was designed for simultaneous flux measurements of multiple gases. The half-hourly NEE fluxes measured with the two techniques were in approximate agreement, with the AC fluxes being 0.78 (cotton) and 1.06 (wheat) times the size of the EC fluxes. When integrated to daily timescale, the fluxes of the two techniques were in better agreement, showing an average ratio of 0.94 and 1.00 for the cotton and wheat, respectively. During the periods with comparable field conditions and normal performance of both instruments, the cumulative NEE fluxes revealed small differences between the two techniques (-9.0% ~ 7%, with a mean of 0.1%). The measurements resulted in an annual cumulative NEE of -40 g C m-2 yr-1 (EC) and -42 g C m-2 yr-1 (AC) in the cotton field, and a seasonal cumulative NEE of -251 g C m-2 (EC) and -205 g C m-2 (AC) in the wheat field. Our results indicate that, for cropland populated by short plants, the AMEG system and the data processing procedures applied in this study are able to provide NEE estimates comparable to those from EC measurements.

  7. Comparing Measures of Estuarine Ecosystem Production in a Temperate New England Estuary

    EPA Science Inventory

    Anthropogenic nutrient enrichments and concerted efforts at nutrient reductions, compounded with the influences of climate change, are likely changing the net ecosystem production (NEP) of our coastal systems. To quantify these changes, scientists monitor a range of physical, che...

  8. Comparing bioenergy production sites in the Southeastern US regarding ecosystem service supply and demand.

    PubMed

    Meyer, Markus A; Chand, Tanzila; Priess, Joerg A

    2015-01-01

    Biomass for bioenergy is debated for its potential synergies or tradeoffs with other provisioning and regulating ecosystem services (ESS). This biomass may originate from different production systems and may be purposefully grown or obtained from residues. Increased concerns globally about the sustainable production of biomass for bioenergy has resulted in numerous certification schemes focusing on best management practices, mostly operating at the plot/field scale. In this study, we compare the ESS of two watersheds in the southeastern US. We show the ESS tradeoffs and synergies of plantation forestry, i.e., pine poles, and agricultural production, i.e., wheat straw and corn stover, with the counterfactual natural or semi-natural forest in both watersheds. The plantation forestry showed less distinct tradeoffs than did corn and wheat production, i.e., for carbon storage, P and sediment retention, groundwater recharge, and biodiversity. Using indicators of landscape composition and configuration, we showed that landscape planning can affect the overall ESS supply and can partly determine if locally set environmental thresholds are being met. Indicators on landscape composition, configuration and naturalness explained more than 30% of the variation in ESS supply. Landscape elements such as largely connected forest patches or more complex agricultural patches, e.g., mosaics with shrub and grassland patches, may enhance ESS supply in both of the bioenergy production systems. If tradeoffs between biomass production and other ESS are not addressed by landscape planning, it may be reasonable to include rules in certification schemes that require, e.g., the connectivity of natural or semi-natural forest patches in plantation forestry or semi-natural landscape elements in agricultural production systems. Integrating indicators on landscape configuration and composition into certification schemes is particularly relevant considering that certification schemes are governance

  9. Comparing Bioenergy Production Sites in the Southeastern US Regarding Ecosystem Service Supply and Demand

    PubMed Central

    Meyer, Markus A.; Chand, Tanzila; Priess, Joerg A.

    2015-01-01

    Biomass for bioenergy is debated for its potential synergies or tradeoffs with other provisioning and regulating ecosystem services (ESS). This biomass may originate from different production systems and may be purposefully grown or obtained from residues. Increased concerns globally about the sustainable production of biomass for bioenergy has resulted in numerous certification schemes focusing on best management practices, mostly operating at the plot/field scale. In this study, we compare the ESS of two watersheds in the southeastern US. We show the ESS tradeoffs and synergies of plantation forestry, i.e., pine poles, and agricultural production, i.e., wheat straw and corn stover, with the counterfactual natural or semi-natural forest in both watersheds. The plantation forestry showed less distinct tradeoffs than did corn and wheat production, i.e., for carbon storage, P and sediment retention, groundwater recharge, and biodiversity. Using indicators of landscape composition and configuration, we showed that landscape planning can affect the overall ESS supply and can partly determine if locally set environmental thresholds are being met. Indicators on landscape composition, configuration and naturalness explained more than 30% of the variation in ESS supply. Landscape elements such as largely connected forest patches or more complex agricultural patches, e.g., mosaics with shrub and grassland patches, may enhance ESS supply in both of the bioenergy production systems. If tradeoffs between biomass production and other ESS are not addressed by landscape planning, it may be reasonable to include rules in certification schemes that require, e.g., the connectivity of natural or semi-natural forest patches in plantation forestry or semi-natural landscape elements in agricultural production systems. Integrating indicators on landscape configuration and composition into certification schemes is particularly relevant considering that certification schemes are governance

  10. Two years with extreme and little snowfall: effects on energy partitioning and surface energy exchange in a high-Arctic tundra ecosystem

    NASA Astrophysics Data System (ADS)

    Stiegler, Christian; Lund, Magnus; Røjle Christensen, Torben; Mastepanov, Mikhail; Lindroth, Anders

    2016-07-01

    Snow cover is one of the key factors controlling Arctic ecosystem functioning and productivity. In this study we assess the impact of strong variability in snow accumulation during 2 subsequent years (2013-2014) on the land-atmosphere interactions and surface energy exchange in two high-Arctic tundra ecosystems (wet fen and dry heath) in Zackenberg, Northeast Greenland. We observed that record-low snow cover during the winter 2012/2013 resulted in a strong response of the heath ecosystem towards low evaporative capacity and substantial surface heat loss by sensible heat fluxes (H) during the subsequent snowmelt period and growing season. Above-average snow accumulation during the winter 2013/2014 promoted summertime ground heat fluxes (G) and latent heat fluxes (LE) at the cost of H. At the fen ecosystem a more muted response of LE, H and G was observed in response to the variability in snow accumulation. Overall, the differences in flux partitioning and in the length of the snowmelt periods and growing seasons during the 2 years had a strong impact on the total accumulation of the surface energy balance components. We suggest that in a changing climate with higher temperature and more precipitation the surface energy balance of this high-Arctic tundra ecosystem may experience a further increase in the variability of energy accumulation, partitioning and redistribution.

  11. Old and Not-So-Old: Examining Changes in Forest Ecosystem Carbon Exchange With Stand Age in the Upper Midwest U.S.

    NASA Astrophysics Data System (ADS)

    Desai, A. R.; Cook, B.; Davis, K. J.; Bolstad, P.; Carey, E.; Martin, J.; Kreller, L.; Wang, W.

    2003-12-01

    Forest stand age is an important determinant of ecosystem carbon uptake. Though there are biometric measurements and ecological models for forests of all ages, there are few stand-scale eddy-flux measurements of net carbon exchange in older forests, though the number is increasing. In order to scale carbon fluxes from sites to regions, where stands of multiple ages may exist, it is necessary to measure to the effect of stand age on carbon exchange. Measuring the effect of stand age on carbon exchange is also necessary when trying to predict future or past carbon exchange (scaling across time). Many researchers have noted that site disturbance history is the fundamental factor in determining carbon uptake by forests over time scales of decades to centuries. The 8,500 ha Sylvania Wilderness in the upper peninsula of Michigan is one of several large tracts of old-growth forest in the Midwest. Trees range from 0-350 years old. Primary species are sugar maple, eastern hemlock and yellow birch. Catastrophic disturbance is rare. A research plot near the wilderness was established in late 2001 to measure the net ecosystem exchange (NEE) of carbon and water using eddy-flux, component flux and biometric methods. This site is part of the Chequamegon Ecosystem Atmosphere Study (ChEAS, http://cheas.psu.edu), a loose affiliation of researchers conducting carbon and water research in northern Wisconsin and upper Michigan. Another similar research plot within ChEAS and not far from Sylvania is the Willow Creek mature uplands site. This forest is about 70 years old and the primary species are sugar maple, basswood and green ash. The site had presettlement old-growth vegetation similar to what is currently seen in the Sylvania Wilderness. Thus, the carbon exchange seen at Sylvania may be representative of carbon uptake at Willow Creek had it not been logged in the early 20th century, and may also represent the future (or past) carbon uptake for similar forests in northern Wisconsin

  12. Differences in plant cover and species composition of semiarid grassland communities of central Mexico and its effects on net ecosystem exchange

    NASA Astrophysics Data System (ADS)

    Delgado-Balbuena, J.; Arredondo, J. T.; Loescher, H. W.; Huber-Sannwald, E.; Chavez-Aguilar, G.; Luna-Luna, M.; Barretero-Hernandez, R.

    2013-07-01

    Changes in land use across the semiarid grasslands of northern Mexico have driven a decline of plant cover and alteration of plant species composition. A number of different plant communities have resulted from these changes. Their implications, however, on the carbon (C) cycle and regional carbon balance are still poorly understood. Here, we examined the effects of plant cover loss and changes in species composition on net ecosystem CO2 exchange (NEE) and their biotic and abiotic controls. NEE was measured in five representative plant community types within a semiarid grassland by temporarily enclosing the entire aboveground ecosystem using a chamber method (i.e., geodesic dome). Sites included an oat crop (crop), a moderately grazed grassland (moderate grazing), a 28 yr-old grazing exclosure (exclosure), an overgrazed site with low perennial grass cover (overgrazed), and an overgrazed site presenting shrub encroachment (shrub encroachment). For natural vegetation, rates of standardized daytime NEE for sites with a high plant cover (exclosure and moderate grazing) were similar (P > 0.05) as compared to sites with low plant cover (overgrazed and shrub encroachment). However, yearly total nighttime NEE (carbon loss) was more than double (P < 0.05) for sites with high plant cover compared to sites with low cover, resulting to slight C sinks for the low plant cover sites, and neutral or sources for the high plant cover sites as accounted by daytime and nighttime NEE annual balance. Differences in plant cover and its associated biomass defined the sensitivity to environmental controls. Thus, daytime NEE in low plant cover sites reached light compensation points at lower photosynthetic photon flux density than those from high plant cover sites. Differences in species composition did not influence NEE rates even though there were transient or permanent changes in C3 vs. C4 functional groups. Our results allowed the detection of the large variability and contribution of

  13. A Comparative Data-Based Modeling Study on Respiratory CO2 Gas Exchange during Mechanical Ventilation

    PubMed Central

    Kim, Chang-Sei; Ansermino, J. Mark; Hahn, Jin-Oh

    2016-01-01

    The goal of this study is to derive a minimally complex but credible model of respiratory CO2 gas exchange that may be used in systematic design and pilot testing of closed-loop end-tidal CO2 controllers in mechanical ventilation. We first derived a candidate model that captures the essential mechanisms involved in the respiratory CO2 gas exchange process. Then, we simplified the candidate model to derive two lower-order candidate models. We compared these candidate models for predictive capability and reliability using experimental data collected from 25 pediatric subjects undergoing dynamically varying mechanical ventilation during surgical procedures. A two-compartment model equipped with transport delay to account for CO2 delivery between the lungs and the tissues showed modest but statistically significant improvement in predictive capability over the same model without transport delay. Aggregating the lungs and the tissues into a single compartment further degraded the predictive fidelity of the model. In addition, the model equipped with transport delay demonstrated superior reliability to the one without transport delay. Further, the respiratory parameters derived from the model equipped with transport delay, but not the one without transport delay, were physiologically plausible. The results suggest that gas transport between the lungs and the tissues must be taken into account to accurately reproduce the respiratory CO2 gas exchange process under conditions of wide-ranging and dynamically varying mechanical ventilation conditions. PMID:26870728

  14. A Portable Eddy Covariance System for the Measurement of Ecosystem-Atmosphere Exchange of CO{sub 2}, Water Vapor, and Energy

    SciTech Connect

    Billesbach, D.P.; Fischer, M.L.; Torn, M.S.; Berry, J.A.

    2003-01-02

    To facilitate the study of flux heterogeneity within a region, the authors have designed and field-tested a portable eddy covariance system to measure exchange of CO{sub 2}, water vapor, and energy between the land surface and the atmosphere. The combination of instrumentation used in this system allows high precision flux measurements without requiring on-site infrastructure such as prepositioned towers or line power. In addition, the system contains sensors to measure a suit of soil, climatic, and energy-related parameters that are needed to quality control the fluxes and to characterize the flux footprint. The physical design and instrument packaging used in the system allows for simple transport (fits in a standard minivan) and for rapid deployment with a minimal number of field personnel (usually less than a day for one person). The power requirement for the entire system (instruments and data loggers) is less than 35 W, which is provided by a companion solar power system. Side-by-side field comparisons between this system and two permanent AmeriFlux sites and between the roving AmeriFlux intercomparison system are described here. Results of these comparisons indicate that the portable system is capable of absolute flux resolutions of about {+-}1.2 {micro}mol m{sup -2} s{sup -1} for CO{sub 2}, {+-}15 W m{sup -2} for LE, {+-}7 W m{sup -2} for H, and {+-}0.06 m s{sup -1} for u* between any given 30-min averaging periods. It is also found that, compared to a permanent Ameriflux site, the relative accuracy of this flux estimates is between 1 percent and 7 percent. Based on these results, it is concluded that this portable system is capable of making ecosystem flux measurements with an accuracy and precision comparable to most permanent AmeriFlux systems.

  15. Disentangling the confounding effects of PAR and air temperature on net ecosystem exchange in time and scale

    NASA Astrophysics Data System (ADS)

    yang, Z.; Chen, J.; Becker, R.; Chu, H.; Xie, J.; Shao, C.

    2013-12-01

    Net ecosystem exchange of CO2 (NEE) in temperate forests is modulated by microclimatic factors. The effects of those factors differ at different time scales and during different time periods. Some of them are correlated across a number of time scales, so their effects on NEE are confounded by each other. PAR and air temperature (Ta) are among the two most important drivers of NEE in temperate forests, and among the two most correlated microclimatic factors. PAR and Ta have similar daily, seasonal, and annual cycles. Their influence on NEE is confounded by each other and entangled together especially at those scales. In this study, we tried to disentangle the confounding effects of them on NEE at different time scales and during different time periods. To accomplish this objective, we applied the innovative spectral analysis techniques including Continuous Wavelet Transformation (CWT), Cross Wavelet Transformation (XWT), Wavelet Coherent (WTC), and Partial Wavelet Coherence (PWC) on seven years time series (2004-2010) of PAR, Ta and NEE from the Ohio Oak Openings site (N 41.5545°, W 83.8438°), USA for spectral analysis. We found that PAR is the major driver at short time scales (e.g. semidiurnal and daily) and Ta is the major driver at long time scales (e.g. seasonal and annual). At daily scale during growing seasons, PAR is anti-phase with NEE with no time delay while Ta lagged PAR about 2-3 hours, which could be explained by the strong dependence of photosynthesis on PAR and a 2-3 hours lags of the daily course of Ta to PAR. At daily scale during non-growing season, NEE has little variation and thus neither Ta nor PAR has high common wavelet power and significant coherence with NEE. At annual scale, Ta is anti-phase with NEE and PAR leads NEE about 34 days, which could be explained by the strong dependence of LAI dynamics on Ta and the lag between the LAI/biomass development and the progress of sunlight. We also found that NEE distributes most of its variation

  16. Comparing marine and terrestrial ecosystems: Implications for the design of coastal marine reserves

    USGS Publications Warehouse

    Carr, M.H.; Neigel, J.E.; Estes, J.A.; Andelman, S.; Warner, R.R.; Largier, J. L.

    2003-01-01

    Concepts and theory for the design and application of terrestrial reserves is based on our understanding of environmental, ecological, and evolutionary processes responsible for biological diversity and sustainability of terrestrial ecosystems and how humans have influenced these processes. How well this terrestrial-based theory can be applied toward the design and application of reserves in the coastal marine environment depends, in part, on the degree of similarity between these systems. Several marked differences in ecological and evolutionary processes exist between marine and terrestrial ecosystems as ramifications of fundamental differences in their physical environments (i.e., the relative prevalence of air and water) and contemporary patterns of human impacts. Most notably, the great extent and rate of dispersal of nutrients, materials, holoplanktonic organisms, and reproductive propagules of benthic organisms expand scales of connectivity among near-shore communities and ecosystems. Consequently, the "openness" of marine populations, communities, and ecosystems probably has marked influences on their spatial, genetic, and trophic structures and dynamics in ways experienced by only some terrestrial species. Such differences appear to be particularly significant for the kinds of organisms most exploited and targeted for protection in coastal marine ecosystems (fishes and macroinvertebrates). These and other differences imply some unique design criteria and application of reserves in the marine environment. In explaining the implications of these differences for marine reserve design and application, we identify many of the environmental and ecological processes and design criteria necessary for consideration in the development of the analytical approaches developed elsewhere in this Special Issue.

  17. Warmer temperatures stimulate respiration and reduce net ecosystem productivity in a northern Great Plains grassland: Analysis of CO2 exchange in automatic chambers

    NASA Astrophysics Data System (ADS)

    Flanagan, L. B.

    2013-12-01

    The interacting effects of altered temperature and precipitation are expected to have significant consequences for ecosystem net carbon storage. Here I report the results of an experiment that evaluated the effects of elevated temperature and altered precipitation on ecosystem CO2 exchange in a northern Great Plains grassland, near Lethbridge, Alberta Canada. Open-top chambers were used to establish an experiment in 2012 with three treatments (control, warmed, warmed plus 50% of normal precipitation input). A smaller experiment with only the two temperature treatments (control and warmed) was conducted in 2013. Continuous half-hourly net CO2 exchange measurements were made using nine automatic chambers during May-October in both years. My objectives were to determine the sensitivity of the ecosystem carbon budget to temperature and moisture manipulations, and to test for direct and indirect effects of the environmental changes on ecosystem CO2 exchange. The experimental manipulations resulted primarily in a significant increase in air temperature in the warmed treatment plots. A cumulative net loss of carbon or negative net ecosystem productivity (NEP) occurred during May through September in the warmed treatment (NEP = -659 g C m-2), while in the control treatment there was a cumulative net gain of carbon (NEP = +50 g C m-2). An eddy covariance system that operated at the site, over a footprint region that was not influenced by the experimental treatments, also showed a net gain of carbon by the ecosystem. The reduced NEP was due to higher plant and soil respiration rates in the warmed treatment that appeared to be caused by a combination of: (i) higher carbon substrate availability indirectly stimulating soil respiration in the warmed relative to the control treatment, and (ii) a strong increase in leaf respiration likely caused by a shift in electron partitioning to the alternative pathway respiration in the warmed treatment, particularly when exposed to high

  18. Mechanistic insights on the responses of plant and ecosystem gas exchange to global environmental change: lessons from Biosphere 2.

    PubMed

    Gonzalez-Meler, Miquel A; Rucks, Jessica S; Aubanell, Gerard

    2014-09-01

    Scaling up leaf processes to canopy/ecosystem level fluxes is critical for examining feedbacks between vegetation and climate. Collectively, studies from Biosphere 2 Laboratory have provided important insight of leaf-to-ecosystem investigations of multiple environmental parameters that were not before possible in enclosed or field studies. B2L has been a testing lab for the applicability of new technologies such as spectral approaches to detect spatial and temporal changes in photosynthesis within canopies, or for the development of cavity ring-down isotope applications for ecosystem evapotranspiration. Short and long term changes in atmospheric CO2, drought or temperature allowed for intensive investigation of the interactions between photosynthesis and leaf, soil and ecosystem respiration. Experiments conducted in the rainforest biome have provided some of the most comprehensive dataset to date on the effects of climate change variables on tropical ecosystems. Results from these studies have been later corroborated in natural rainforest ecosystems and have improved the predictive capabilities of models that now show increased resilience of tropics to climate change. Studies of temperature and CO2 effects on ecosystem respiration and its leaf and soil components have helped reconsider the use of simple first-order kinetics for characterizing respiration in models. The B2L also provided opportunities to quantify the rhizosphere priming effect, or establish the relationships between net primary productivity, atmospheric CO2 and isoprene emissions.

  19. The Use of Bayesian Modeling to Assess the Impact of Altered Precipitation on Leaf-level Carbon Exchange in Four Desert Savanna Ecosystems

    NASA Astrophysics Data System (ADS)

    Patrick, L.; Ogle, K.; Tissue, D.; Cable, J.

    2007-12-01

    Savannas are complex ecosystems with diverse plant communities and spatially variable nutrient and carbon dynamics. In semi-arid regions, savannas are rapidly changing as a result of climate change and/or land-use, both of which have the potential to alter carbon cycling processes. To determine the potential impacts of climate change on savanna systems, it is critical to understand the processes governing vegetation dynamics across the diverse range of savanna ecosystem types. Because water is the primary driver of biological activity in these ecosystems, changes in precipitation frequency and magnitude may significantly affect plant community composition and ecosystem carbon cycling through effects on leaf-level carbon dynamics. Here, we utilized photosynthesis data and models to explore the underlying mechanisms responsible for changes in leaf-level carbon exchange under altered precipitation. Our objective was to determine whether dominant plants in four North American deserts exhibited a common photosynthetic response to precipitation manipulations. In the summer of 2005 and 2006, photosynthetic CO2- and light-response curves were measured on the dominant plant functional groups (grasses and shrubs) in the Great Basin, Mojave, Sonoran, and Chihuahuan deserts. We used a hierarchical Bayesian modeling framework to integrate the extensive field data with a biochemical-based photosynthesis model, yielding estimates of photosynthetic parameters (e.g. rate of daytime respiration, maximum rate of carboxylation, and maximum rate of electron transport). The modeling results indicated that, generally, plant photosynthesis parameters were conserved across all desert sites and plant species. There is, however, evidence that supplemental precipitation affected photosynthetic responses as some species differed in key biochemical parameters under this treatment. This result suggests that in these ecosystems changes in precipitation associated with climate change have the

  20. Ecosystem modeling of coastal acidification and hypoxia and structural uncertainties in the representation of sediment-water exchanges

    EPA Science Inventory

    Numerical ecosystem models of coastal acidification (CA) and hypoxia have been developed to synthesize current scientific understanding and provide predictions for nutrient management and policy. However, there is not a scientific consensus about the structure of these models an...

  1. An automated dynamic chamber system for surface exchange measurement of non-reactive and reactive trace gases of grassland ecosystems

    NASA Astrophysics Data System (ADS)

    Pape, L.; Ammann, C.; Nyfeler-Brunner, A.; Spirig, C.; Hens, K.; Meixner, F. X.

    2009-03-01

    We present an automated dynamic chamber system which is optimised for continuous unattended flux measurements of multiple non-reactive and reactive trace gases on grassland ecosystems. Main design features of our system are (a) highly transparent chamber walls consisting of chemically inert material, (b) individual purging flow units for each chamber, and (c) a movable lid for automated opening and closing of the chamber. The purging flow rate was chosen high enough to keep the mean residence time of the chamber air below one minute. This guarantees a proven efficient mixing of the chamber volume and a fast equilibration after lid closing. The dynamic chamber system is able to measure emission as well as deposition fluxes of trace gases. For the latter case, the modification of the turbulent transport by the chamber (compared to undisturbed ambient conditions) is quantitatively described by a bulk resistance concept. Beside a detailed description of the design and functioning of the system, results of field applications at two grassland sites are presented. In the first experiment, fluxes of five trace gases (CO2, H2O, NO, NO2, O3) were measured simultaneously on small grassland plots. It showed that the dynamic chamber system is able to detect the characteristic diurnal cycles with a sufficient temporal resolution. The results also demonstrated the importance of considering the chemical source/sink in the chamber due to gas phase reactions for the reactive compounds of the NO-NO2-O3 triad. In a second field experiment, chamber flux measurements of CO2 and methanol were compared to simultaneous independent eddy covariance flux measurements on the field scale. The fluxes obtained with the two methods showed a very good agreement indicating a minimal disturbance of the chambers on the physiological activity of the enclosed vegetation.

  2. An automated dynamic chamber system for surface exchange measurement of non-reactive and reactive trace gases of grassland ecosystems

    NASA Astrophysics Data System (ADS)

    Pape, L.; Ammann, C.; Nyfeler-Brunner, A.; Spirig, C.; Hens, K.; Meixner, F. X.

    2008-08-01

    We present an automated dynamic chamber system which is optimised for continuous unattended flux measurements of multiple non-reactive and reactive trace gases on grassland ecosystems. Main design features of our system are (a) highly transparent chamber walls consisting of chemically inert material, (b) individual purging flow units for each chamber, and (c) a movable lid for automated opening and closing of the chamber. The purging flow rate was chosen high enough to keep the mean residence time of the chamber air below one minute. This guarantees a proven efficient mixing of the chamber volume and a fast equilibration after lid closing. The dynamic chamber system is able to measure emission as well as deposition fluxes of trace gases. For the latter case, the modification of the turbulent transport by the chamber (compared to undisturbed ambient conditions) is quantitatively described by a bulk resistance concept. Beside a detailed description of the design and functioning of the system, results of field applications at two grassland sites are presented. In the first experiment, fluxes of five trace gases (CO2, H2O, NO, NO2, O3) were measured simultaneously on small grassland plots. It showed that the dynamic chamber system is able to detect the characteristic diurnal cycles with a sufficient temporal resolution. The results also demonstrated the importance of considering the chemical source/sink in the chamber due to gas phase reactions for the reactive compounds of the NO-NO2-O3 triad. In a second field experiment, chamber flux measurements of CO2 and methanol were compared to simultaneous independent eddy covariance flux measurements on the field scale. The fluxes obtained with the two methods showed a very good agreement indicating a minimal disturbance of the chambers on the physiological activity of the enclosed vegetation.

  3. Comparing carbon storage of Siberian tundra and taiga permafrost ecosystems at very high spatial resolution

    NASA Astrophysics Data System (ADS)

    Siewert, Matthias B.; Hanisch, Jessica; Weiss, Niels; Kuhry, Peter; Maximov, Trofim C.; Hugelius, Gustaf

    2015-10-01

    Permafrost-affected ecosystems are important components in the global carbon (C) cycle that, despite being vulnerable to disturbances under climate change, remain poorly understood. This study investigates ecosystem carbon storage in two contrasting continuous permafrost areas of NE and East Siberia. Detailed partitioning of soil organic carbon (SOC) and phytomass carbon (PC) is analyzed for one tundra (Kytalyk) and one taiga (Spasskaya Pad/Neleger) study area. In total, 57 individual field sites (24 and 33 in the respective areas) have been sampled for PC and SOC, including the upper permafrost. Landscape partitioning of ecosystem C storage was derived from thematic upscaling of field observations using a land cover classification from very high resolution (2 × 2 m) satellite imagery. Nonmetric multidimensional scaling was used to explore patterns in C distribution. In both environments the ecosystem C is mostly stored in the soil (≥86%). At the landscape scale C stocks are primarily controlled by the presence of thermokarst depressions (alases). In the tundra landscape, site-scale variability of C is controlled by periglacial geomorphological features, while in the taiga, local differences in catenary position, soil texture, and forest successions are more important. Very high resolution remote sensing is highly beneficial to the quantification of C storage. Detailed knowledge of ecosystem C storage and ground ice distribution is needed to predict permafrost landscape vulnerability to projected climatic changes. We argue that vegetation dynamics are unlikely to offset mineralization of thawed permafrost C and that landscape-scale reworking of SOC represents the largest potential changes to C cycling.

  4. Hydrological Controls on Ecosystem CO2 and CH4 Exchange in a MIXED Tundra and a FEN within an Arctic Landscape UNDER Current and Future Climates

    NASA Astrophysics Data System (ADS)

    Grant, R. F.; Humphreys, E.; Lafleur, P.

    2014-12-01

    Variation in CO2 and CH4 exchange in years with contrasting weather is strongly affected by hydrology in landscapes underlain by permafrost. Hypotheses for this variation were incorporated into the ecosystem model ecosys which simulated CO2 and CH4 fluxes along a topographic gradient within an arctic landscape at Daring Lake, NWT, Canada. Fluxes modelled at mixed tundra and fen sites within the gradient were compared with CO2 fluxes measured at eddy covariance towers from 2006 to 2009, and with CH4 fluxes measured with surface chambers in 2008. Slopes and correlation coefficients from regressions of modelled vs. measured CO2 fluxes were 1.0 ± 0.1 and 0.7 - 0.8 for both sites in all years. At the mixed tundra site, rises in net CO2 uptake in warmer years with earlier snowmelt were constrained by midafternoon declines in CO2 influxes when vapor pressure deficits (D) exceeded 1.5 kPa, and by rises in CO2 effluxes with greater active layer depth (ALD). Consequently annual net CO2 uptake at this site rose little with warming. At the fen site, CO2 influxes declined less with D and CO2 effluxes rose less with warming, so that rises in net CO2 uptake in warmer years were greater than those at the mixed tundra site. The greater declines in CO2 influxes with warming at the mixed tundra site were modelled from greater soil-plant-atmosphere water potential gradients that developed in drier soil, and the smaller rises in CO2 effluxes with warming at the fen site were modelled from O2 constraints to heterotrophic and below-ground autotrophic respiration that limited their responses to greater ALD. Modelled and measured CH4 exchange during July and August indicated very small influxes at the mixed tundra site, and larger emissions at the fen site. Emissions of CH4 modelled during soil freezing in October - November contributed about one-third of the annual total, and so should be included in estimates of annual emissions. These contrasting responses to warming under current

  5. Modelling the impact of soil Carbonic Anhydrase on the net ecosystem exchange of OCS at Harvard forest using the MuSICA model

    NASA Astrophysics Data System (ADS)

    Launois, Thomas; Ogée, Jérôme; Commane, Roisin; Wehr, Rchard; Meredith, Laura; Munger, Bill; Nelson, David; Saleska, Scott; Wofsy, Steve; Zahniser, Mark; Wingate, Lisa

    2016-04-01

    The exchange of CO2 between the terrestrial biosphere and the atmosphere is driven by photosynthetic uptake and respiratory loss, two fluxes currently estimated with considerable uncertainty at large scales. Model predictions indicate that these biosphere fluxes will be modified in the future as CO2 concentrations and temperatures increase; however, it still unclear to what extent. To address this challenge there is a need for better constraints on land surface model parameterisations. Additional atmospheric tracers of large-scale CO2 fluxes have been identified as potential candidates for this task. In particular carbonyl sulphide (OCS) has been proposed as a complementary tracer of gross photosynthesis over land, since OCS uptake by plants is dominated by carbonic anhydrase (CA) activity, an enzyme abundant in leaves that catalyses CO2 hydration during photosynthesis. However, although the mass budget at the ecosystem is dominated by the flux of OCS into leaves, some OCS is also exchanged between the atmosphere and the soil and this component of the budget requires constraining. In this study, we adapted the process-based isotope-enabled model MuSICA (Multi-layer Simulator of the Interactions between a vegetation Canopy and the Atmosphere) to include the transport, reaction, diffusion and production of OCS within a forested ecosystem. This model was combined with 3 years (2011-2013) of in situ measurements of OCS atmospheric concentration profiles and fluxes at the Harvard Forest (Massachussets, USA) to test hypotheses on the mechanisms responsible for CA-driven uptake by leaves and soils as well as possible OCS emissions during litter decomposition. Model simulations over the three years captured well the impact of diurnally and seasonally varying environmental conditions on the net ecosystem OCS flux. A sensitivity analysis on soil CA activity and soil OCS emission rates was also performed to quantify their impact on the vertical profiles of OCS inside the

  6. Digital photography for assessing the link between vegetation phenology and CO2 exchange in two contrasting northern ecosystems

    NASA Astrophysics Data System (ADS)

    Linkosalmi, Maiju; Aurela, Mika; Tuovinen, Juha-Pekka; Peltoniemi, Mikko; Tanis, Cemal M.; Arslan, Ali N.; Kolari, Pasi; Böttcher, Kristin; Aalto, Tuula; Rainne, Juuso; Hatakka, Juha; Laurila, Tuomas

    2016-09-01

    Digital repeat photography has become a widely used tool for assessing the annual course of vegetation phenology of different ecosystems. By using the green chromatic coordinate (GCC) as a greenness measure, we examined the feasibility of digital repeat photography for assessing the vegetation phenology in two contrasting high-latitude ecosystems. Ecosystem-atmosphere CO2 fluxes and various meteorological variables were continuously measured at both sites. While the seasonal changes in GCC were more obvious for the ecosystem that is dominated by annual plants (open wetland), clear seasonal patterns were also observed for the evergreen ecosystem (coniferous forest). Daily and seasonal time periods with sufficient solar radiation were determined based on images of a grey reference plate. The variability in cloudiness had only a minor effect on GCC, and GCC did not depend on the sun angle and direction either. The daily GCC of wetland correlated well with the daily photosynthetic capacity estimated from the CO2 flux measurements. At the forest site, the correlation was high in 2015 but there were discernible deviations during the course of the summer of 2014. The year-to-year differences were most likely generated by meteorological conditions, with higher temperatures coinciding with higher GCCs. In addition to depicting the seasonal course of ecosystem functioning, GCC was shown to respond to environmental changes on a timescale of days. Overall, monitoring of phenological variations with digital images provides a powerful tool for linking gross primary production and phenology.

  7. Causes of interannual variability in ecosystem-atmosphere CO2 exchange in a northern Wisconsin forest using a Bayesian model calibration

    SciTech Connect

    Ricciuto, Daniel M; Butler, Martha; Davis, Kenneth; Cook, Bruce D

    2008-01-01

    Carbon dioxide fluxes were examined over the growing seasons of 2002 and 2003 from 14 different sites in Upper Midwest (USA) to assess spatial variability of ecosystem-atmosphere CO2 exchange. These sites were exposed to similar temperature/precipitation regimes and spanned a range of vegetation types typical of the region (northern hardwood, mixed forest, red pine, jack pine, pine barrens and shrub wetland). The hardwood and red pine sites also spanned a range of stand ages (young, intermediate, mature). While seasonal changes in net ecosystem exchange (NEE) and photosynthetic parameters were coherent across the 2 years at most sites, changes in ecosystem respiration (ER) and gross ecosystem production (GEP) were not. Canopy height and vegetation type were important variables for explaining spatial variability of CO2 fluxes across the region. Light-use efficiency (LUE) was not as strongly correlated to GEP as maximum assimilation capacity (Amax). A bottom-up multi-tower land cover aggregated scaling of CO2 flux to a 2000 km(2) regional flux estimate found June to August 2003 NEE, ER and GEP to be -290 +/- 89, 408 +/- 48, and 698 +/- 73 gC m(-2), respectively. Aggregated NEE, ER and GEP were 280% larger, 32% smaller and 3% larger, respectively, than that observed from a regionally integrating 447 m tall flux tower. However, when the tall tower fluxes were decomposed using a footprint-weighted influence function and then re-aggregated to a regional estimate, the resulting NEE, ER and GEP were within 11% of the multi-tower aggregation. Excluding wetland and young stand age sites from the aggregation worsened the comparison to observed fluxes. These results provide insight on the range of spatial sampling, replication, measurement error and land cover accuracy needed for multi-tiered bottom-up scaling of CO2 fluxes in heterogeneous regions such as the Upper Midwest, USA. (C) 2007 Elsevier B.V. All rights reserved.

  8. Combining Microbial Enzyme Kinetics Models with Light Use Efficiency Models to Predict CO2 and CH4 Ecosystem Exchange from Flooded and Drained Peatland Systems

    NASA Astrophysics Data System (ADS)

    Oikawa, P. Y.; Jenerette, D.; Knox, S. H.; Sturtevant, C. S.; Verfaillie, J. G.; Baldocchi, D. D.

    2014-12-01

    Under California's Cap-and-Trade program, companies are looking to invest in land-use practices that will reduce greenhouse gas (GHG) emissions. The Sacramento-San Joaquin River Delta is a drained cultivated peatland system and a large source of CO2. To slow soil subsidence and reduce CO2 emissions, there is growing interest in converting drained peatlands to wetlands. However, wetlands are large sources of CH4 that could offset CO2-based GHG reductions. The goal of our research is to provide accurate measurements and model predictions of the changes in GHG budgets that occur when drained peatlands are restored to wetland conditions. We have installed a network of eddy covariance towers across multiple land use types in the Delta and have been measuring CO2 and CH4 ecosystem exchange for multiple years. In order to upscale these measurements through space and time we are using these data to parameterize and validate a process-based biogeochemical model. To predict gross primary productivity (GPP), we are using a simple light use efficiency (LUE) model which requires estimates of light, leaf area index and air temperature and can explain 90% of the observed variation in GPP in a mature wetland. To predict ecosystem respiration we have adapted the Dual Arrhenius Michaelis-Menten (DAMM) model. The LUE-DAMM model allows accurate simulation of half-hourly net ecosystem exchange (NEE) in a mature wetland (r2=0.85). We are working to expand the model to pasture, rice and alfalfa systems in the Delta. To predict methanogenesis, we again apply a modified DAMM model, using simple enzyme kinetics. However CH4 exchange is complex and we have thus expanded the model to predict not only microbial CH4 production, but also CH4 oxidation, CH4 storage and the physical processes regulating the release of CH4 to the atmosphere. The CH4-DAMM model allows accurate simulation of daily CH4 ecosystem exchange in a mature wetland (r2=0.55) and robust estimates of annual CH4 budgets. The LUE

  9. Analysis of the influence of climatic and physiological parameters on the net ecosystem carbon exchange of an apple orchard

    NASA Astrophysics Data System (ADS)

    Zanotelli, Damiano; Montagnani, Leonardo; Scandellari, Francesca; Tagliavini, Massimo

    2013-04-01

    Net ecosystem carbon exchange (NEE) of an apple orchard located in South Tyrol (Caldaro, Bolzano, Italy) was monitored continuously since March 2009 via eddy covariance technique. Contemporary measurements of the main environmental parameters (temperature, photosynthetic active photon flux density, soil water content, vapor pressure deficit) were taken at the same field site. Leaf Area Index was also determined biometrically starting from spring 2010. Objectives of this work were (i) to assess the influence of these environmental and physiological parameters on NEE, (ii) to set up a model capable to fill large gap occurring in the dataset and (iii) predict inter-annual variability of fluxes based on the measurements of the selected explanatory variables. Daily cumulated values of the response variable (NEE, g C d-1) and mean daily value of the five explanatory variables considered (air T, ° C; SWC, m3m-3; PPFD, μmol m-2s-1; VPD, hPa, LAI m2m-2) were used in this analysis. The complex interactions between the explanatory variables and NEE were analyzed with the tree model approach which draws a picture of the complexity of data structure and highlights the explanatory variable that explain the greater amount of deviance of the response variable. NEE variability was mostly explained by LAI and PPFD. The most positive values of NEE occurred below the LAI threshold of 1.16 m2m-2 while above that LAI threshold and with an average daily PPFD above 13.2 μmol m-2s-1, the orchard resulted always a sink of carbon (negative daily NEE). On half of the available data (only alternate months of the considered period were considered), a stepwise multiple regression approach was used to model NEE using the variables indicated above. Simplification by deletion of the non-significant terms was carried out until all parameters where highly significant (p < 0.05) and a significant increase in deviance was observed when deleting further variables. Since heteroscedasticity and non

  10. Comparative dynamics of pelagic and benthic micro-algae in a coastal ecosystem

    NASA Astrophysics Data System (ADS)

    Chatterjee, Arnab; Klein, Cécile; Naegelen, Aurore; Claquin, Pascal; Masson, Annick; Legoff, Manon; Amice, Erwan; L'Helguen, Stéphane; Chauvaud, Laurent; Leynaert, Aude

    2013-11-01

    Together with phytoplankton, microphytobenthos (MPB) play an important role in the overall food web structure of coastal ecosystems by regulating nutrient fluxes, oxygen concentration and sediment stability in the ecosystem. Although there are many studies on phytoplankton, MPB dynamics in the subtidal zone are largely unknown. In this study, we carried out a whole-year survey to investigate the seasonal dynamics of phytoplankton and MPB biomass simultaneously in relation to the environmental physico-chemical parameters. We show that phytoplankton and MPB do not follow the same dynamics with MPB being the first to increase in the season. It constitutes a large energy input to the ecosystem from the beginning of spring (with 60% of the total biomass until April). The system then moves from a system dominated by benthic biomass in early spring to a system where the pelagic biomass dominates. Among resources that MPB and phytoplankton have to share, light seems to trigger the MPB bloom as soon as maximum bottom PAR is reached, i.e. one month earlier than the phytoplankton bloom in the water column. With regard to nutrients, the lack of phosphorus can be put forward to explain the decline of MPB biomass at the beginning of April, whereas the phytoplankton decline in the first week of May coincides to silicic acid deficiency. Dissolved inorganic nitrogen then becomes potentially limiting in the water column until the end of October. Competition with macroalgae at the bottom and grazing were also considered as being possible factors for the disparate course of phytoplankton and MPB dynamics. Further investigations are needed to give a more detailed picture on the interactions and feedback loops between MPB and phytoplankton. However, although benthic-pelagic relationships are complex, this study indicates the need to integrate such fundamental coupling to a thorough understanding of ecosystem dynamics and functions.

  11. Impact of urbanization on natural ecosystem service values: a comparative study.

    PubMed

    Zang, Shuying; Wu, Changshan; Liu, Hang; Na, Xiaodong

    2011-08-01

    With rapid population growth and rural to-urban migration in many Chinese cities, a large amount of natural lands have been converted to urban and agricultural lands recently. During this process of land conversion, economic development and quality of life improvement are considered as major goals, and their influences on ecological systems have often been neglected. The degradation of natural ecological systems due to land use change, however, has become severe,and may require immediate attentions from urban planners and local governments. Taking HaDaQi industrial corridor, Heilongjiang Province, China,as a case study area, this paper examined the trend of land use changes during 1990–2005, and quantified their influences on natural eco system service values. In particular, this study applied two major valuation methods, and examined whether different valuation methods generate significantly different results. Analysis of results suggests that human dominated land uses (e.g., urban and agriculture)have expanded rapidly at the cost of natural lands (e.g., wetlands and forest). Due to these land use changes, the total ecosystem service value decreased 29% (2.26% annually) from 1990 to 2005 when the first method was applied, and this rate is estimated to be 15.7% (1.13% annually)with the second approach. Moreover, the annual rate of ecosystem service value decline during 2000–2005 is about four times higher than that in 1990–2000 with both methods, suggesting much more severe ecosystem degradation during 2000–2005.

  12. Comparative behavior of three long-lived radionuclides in forest ecosystems

    SciTech Connect

    Auerbach, S.I.

    1986-01-01

    This paper deals with studies in three forest ecosystems in eastern Tennessee, an area of rich temperate deciduous forests, sometimes referred to as mixed mesophytic forests. Two of these forest ecosystems were contaminated as a result of waste disposal operations. The third was experimentally tagged with millicurie quantities of /sup 137/Cs. One of these ecosystems is a floodplain forest that is typical of this region. This forest has been growing on alluvial soils since 1944. Prior to that time the area was a temporary holding pond within White Oak Creek which received radioactive effluents from ORNL. Radiocesium was deposited in the pond sediments as were /sup 90/Sr, /sup 239/Pu, /sup 241/Am, and other radionuclides. The dam which created the pond failed in late 1944, and the area was allowed to revert to natural conditions. The result was the development of a floodplain forest consisting of three different forest communities. The soils are fertile alluvials representative of bottomlands. The overstory tree species are principally ash, sycamore, boxelder, willow, and sweetgum (Fraxinus americana L., Plantanus occidentalis L., Acer negundo L., Salix nigra Marsh, and Liquidambar styraciflua L., respectively).

  13. The Seasonal Cycle of Satellite Chlorophyll Fluorescence Observations and its Relationship to Vegetation Phenology and Ecosystem Atmosphere Carbon Exchange

    NASA Technical Reports Server (NTRS)

    Joiner, J.; Yoshida, Y.; Vasilkov, A. P.; Schaefer, K.; Jung, M.; Guanter, L.; Zhang, Y; Garrity, S.; Middleton, E. M.; Huemmrich, K. F.; Gu, L.; Marchesini, L. Belelli

    2014-01-01

    Mapping of terrestrial chlorophyll uorescence from space has shown potentialfor providing global measurements related to gross primary productivity(GPP). In particular, space-based fluorescence may provide information onthe length of the carbon uptake period that can be of use for global carboncycle modeling. Here, we examine the seasonal cycle of photosynthesis asestimated from satellite fluorescence retrievals at wavelengths surroundingthe 740nm emission feature. These retrievals are from the Global OzoneMonitoring Experiment 2 (GOME-2) flying on the MetOp A satellite. Wecompare the fluorescence seasonal cycle with that of GPP as estimated froma diverse set of North American tower gas exchange measurements. Because the GOME-2 has a large ground footprint (40 x 80km2) as compared with that of the flux towers and requires averaging to reduce random errors, we additionally compare with seasonal cycles of upscaled GPP in the satellite averaging area surrounding the tower locations estimated from the Max Planck Institute for Biogeochemistry (MPI-BGC) machine learning algorithm. We also examine the seasonality of absorbed photosynthetically-active radiation(APAR) derived with reflectances from the MODerate-resolution Imaging Spectroradiometer (MODIS). Finally, we examine seasonal cycles of GPP as produced from an ensemble of vegetation models. Several of the data-driven models rely on satellite reflectance-based vegetation parameters to derive estimates of APAR that are used to compute GPP. For forested sites(particularly deciduous broadleaf and mixed forests), the GOME-2 fluorescence captures the spring onset and autumn shutoff of photosynthesis as delineated by the tower-based GPP estimates. In contrast, the reflectance-based indicators and many of the models tend to overestimate the length of the photosynthetically-active period for these and other biomes as has been noted previously in the literature. Satellite fluorescence measurements therefore show potential for

  14. Net ecosystem exchange from five land-use transitions to bioenergy crops from four locations across the UK - The Ecosystem Land Use Modelling & Soil Carbon GHG Flux Trial (ELUM) project.

    NASA Astrophysics Data System (ADS)

    Xenakis, Georgios; Perks, Mike; Harris, Zoe M.; McCalmont, Jon; Rylett, Daniel; Brooks, Milo; Evans, Jonathan G.; Finch, Jon; Rowe, Rebecca; Morrison, Ross; Alberti, Giorgio; Donnison, Ian; Siebicke, Lukas; Morison, James; Taylor, Gail; McNamara, Niall P.

    2016-04-01

    A major part of international agreements on combating climate change is the conversion from a fossil fuel economy to a low carbon economy. Bioenergy crops have been proposed as a way to improve energy security while reducing CO2 emissions to help mitigate the effects of climate change. However, the impact of land-use change from a traditional land use (e.g., arable and grassland) to bioenergy cropping systems on greenhouse gas balance (GHG) and carbon stocks are poorly quantified at this time. The Ecosystem Land Use Modelling & Soil Carbon GHG Flux Trial (ELUM) project was commissioned and funded by the Energy Technologies Institute (ETI) to provide scientific evidence within the UK on a range of land-use conversions (LUC) to bioenergy crops. The ELUM network consists of seven partners investigating five LUCs in four locations including Scotland, Wales, North and South England. Transitions included grasslands to short rotation forestry (SRF), to short rotation coppice willow (SRC) and to Miscanthus and arable to SRC and Miscanthus Measurements of net ecosystem exchange (NEE) along with continuous measurements of meteorological conditions were made at seven sub-sites over a two-year period. Results showed that, over two years, two of the land-uses, a grassland in South England and a grassland conversion to Miscanthus in Wales were net sources of carbon. The greatest carbon sink was into the SRF site in Scotland followed by the SRC willow in South England. The annual terrestrial ecosystem respiration (TER) for the SRC willow in North and South Sussex sites were similar, but the annual GPP at the South England site was about 27% higher than that the North England site. Establishing a long term network will allow us to continue monitoring the effects of land use change on whole ecosystem carbon balance, providing an insight into which types of LUC are suitable for bioenergy cropping in the UK.

  15. The Seasonal and Diurnal Patterns of net Ecosystem CO2 Exchange in a Subtropical Montane Cloud Forest.

    NASA Astrophysics Data System (ADS)

    Chu, H.; Lai, C.; Wu, C.; Hsia, Y.

    2008-12-01

    CO2 fluxes were measured by an open/closed path eddy covariance system at a natural regenerated 50-years-old yellow cypress (Chamaecyparis obtusa var. formosana) forest at Chi-Lan Mountain site (CLM site, 24°35'N, 121°25'E, 1650 m elevation), north-eastern Taiwan. CLM site is located at a relative uniform south-eastern-facing valley slope (15°) characterized with year round fog occurrence and diurnal mountain-valley wind and can be classified as subtropical montane cloud forest. Based on measurement from July 2007 to June 2008, seasonal and diurnal patterns of CO2 fluxes were described and patterns under different cloudiness and foggy conditions were presented. Comparing with other cypress forests in temperate region, there is only a weak seasonal pattern of the CO2 fluxes at CLM site. Throughout the year, average incident photosynthetically active radiation in summer was almost the double of that in winter, whereas the difference of mean daytime CO2 fluxes among seasons was much less than the seasonal light difference. During summer when light intensity was higher, mean daytime CO2 fluxes reached -7.5 μmol/m2/s in July and -8.8 μmol/m2/s in August. As heavy fog accounted for 64% and 67% of the time in November and February, mean daytime CO2 fluxes dropped to -6.9 and -6.1 μmol/m2/s respectively. With comparable higher incident radiation intensity (>1000 μmol/m2/s), the CO2 fluxes were higher in overcast days than in clear days. In July 2007, clear days accounted for 30% of the month, light intensity reached its peak at midday, and however, CO2 fluxes didn't reach its highest value in the meanwhile. Canopy conductance calculated from the Penman-Monteith equation and measured latent heat fluxes both showed a midday depression at clear days, which indicated the regulation of transpiration by plant physiological mechanism. With comparable lower incident radiation intensity (<1000 μmol/m2/s), the CO2 fluxes were higher in overcast days than in foggy days. The

  16. Effects of hemoperfusion adsorption and/or plasma exchange in treatment of severe viral hepatitis: A comparative study

    PubMed Central

    He, Nian-Hai; Wang, Ying-Jie; Wang, Ze-Wen; Liu, Jun; Li, Jia-Jia; Liu, Guo-Dong; Wang, Yu-Ming

    2004-01-01

    AIM: Non-bioartificial liver has been applied to clinic for quite a long time, but the reported efficacy has been very different. The aim of this study was to compare the efficacy and safety of hemoperfusion adsorption, plasma exchange and plasma exchange plus hemoperfusion adsorption in treatment of severe viral hepatitis. METHODS: Seventy-five patients with severe viral hepatitis were treated with hemoperfusion adsorption therapy (24 cases), plasma exchange therapy (17 cases) and plasma exchange plus hemoperfusion adsorption therapy (34 cases). The data of liver function, renal function, blood routine test, prothrombin time (PT) and prothrombin activity (PTa) pre-and post-therapy were analyzed. RESULTS: Clinical symptoms of patients improved after treatment. The levels of aminotransferase, total bilirubin, direct bilirubin decreased significantly after 3 therapies (P < 0.05 or P < 0.01). PT, the level of total serum protein decreased significantly and PTa increased significantly after plasma exchange therapy and plasma exchange plus hemoperfusion adsorption therapy (P < 0.05 or P < 0.01). The side effects were few and mild in all patients. CONCLUSION: Three therapies were effective in the treatment of severe viral hepatitis. Plasma exchange therapy and plasma exchange plus hemoperfusion adsorption therapy are better than hemoperfusion adsorption therapy. PMID:15069730

  17. Comparing intra- and inter-specific effects on litter decomposition in an old-field ecosystem

    SciTech Connect

    Crutsinger, Greg; Sanders, Dr. Nathan James; Classen, Aimee T

    2009-09-01

    Plant species can differ in the quantity and quality of leaf litter they produce, and many studies have examined whether plant species diversity affects leaf-litter decomposition and nutrient release. A growing number of studies have indicated that intra-specific variation within plant species can also affect key ecosystem processes. However, the relative importance of intra- versus inter-specific variation for the functioning of ecosystems remains poorly known. Here, we investigate the effects of intra-specific variation in a dominant old-field plant species, tall goldenrod (Solidago altissima), and inter-specific variation among goldenrod species on litter quality, decomposition, and nitrogen (N) release. We found that the nutrient concentration of leaf litter varied among genotypes, which translated into 50% difference in decomposition rates. Variation among other goldenrod species in decomposition rate was more than twice that of genetic variation within S. altissima. Furthermore, by manipulating litterbags to contain 1, 3, 6, or 9 genotypes, we found that S. altissima genotype identity had much stronger effects than did genotypic diversity on leaf-litter quality, decomposition, and N release. Taken together, these results suggest that the order of ecological importance for controlling leaf-litter decomposition and N release dynamics is plant species identitygenotype identity>genotypic diversity.

  18. Comparative Ecology of H2 Cycling in Organotrophic and Phototrophic Ecosystems

    NASA Technical Reports Server (NTRS)

    Hoehler, Tori M.; Alperin, Marc J.; Albert, Daniel B.; Bebout, Brad M.; Martens, Christopher S.; DesMarais, David J.; DeVincenzi, Don (Technical Monitor)

    2001-01-01

    The simple biochemistry of H2 is critical to a large number of microbial processes, affecting the interaction of organisms with each other and with the environment. The sensitivity of these many processes to H2 can be described quantitatively, at a basic thermodynamic level. This shared dependence on H2 may provide a means for interpreting the ecology and system-level biogeochemistry of widely variant microbial ecosystems on a common (and quantitative) level. Understanding the factors that control H2 itself is a critical prerequisite. Here, we examine two ecosystems that vary widely with respect to H2 cycling. In anoxic, 'organotrophic' sediments from Cape Lookout Bight (North Carolina, USA), H2 partial pressures are strictly maintained at low, steady-state levels by H2-consuming organisms, in a fashion that can be quantitatively predicted by simple thermodynamic calculations. In phototrophic microbial mats from Baja, Mexico, H2 partial pressures are instead controlled by the activity of light-sensitive H2-producing organisms. In consequence, H2 partial pressures within the system fluctuate by orders of magnitude on hour-long time scales. The differences in H2 cycling subsequently impact H2-sensitive microbial processes, such as methanogenesis. For example, the presence of sulfate in the organotrophic system always yielded low levels of H2 that were inhibitory to methanogenesis; however, the elevated levels of H2 in the phototrophic system favored methane production at significant levels, even in the presence of high sulfate concentrations. The myriad of other H2-sensitive microbial processes are expected to exhibit similar behavior.

  19. Modelling Effects of Water Table Depth Variations on Net Ecosystem CO2 Exchange of a Western Canadian Peatland

    NASA Astrophysics Data System (ADS)

    Mezbahuddin, S.; Grant, R. F.; Flanagan, L. B.

    2014-12-01

    Water table depth (WTD) is one of the key drivers affecting aggradation and degradation of peatlands. Variations in WTD can alter the balance between gross primary productivity (GPP) and ecosystem respiration (Re) and so cause a peatland to change between a sink and a source of carbon. Process based mathematical modelling can provide insights on WTD-net ecosystem productivity (NEP) interactions over peatlands. We deployed a process-based ecosystem model ecosys to examine the WTD effects on variations in NEP of a fen peatland in Alberta, Canada. Our modelled results showed that a growing season (May-August) WTD drawdown of ~0.3m from 2004-2007 caused more rapid decomposition in deeper peat layers so that Re increased by ~180 g C m-2 growing season -1. However, similar increase in GPP (~ 170 g C m-2 growing season -1) under deeper WTD condition due to more rapid microbial and root growth, and hence more rapid mineralization and nutrient uptake, left no net effect of WTD drawdown on NEP. The modelled ecosystem was overall a large sink of C (~ 100 g C m-2 yr-1) over the study period of 2004-2009. However, gradually diminishing GPP by ~ 70 g C m-2 growing season -1 with progressively deeper WTD during 2008-2009 indicated that further drawdown of WTD could alter the source sink status of these peatlands. These modelled results were corroborated against hourly eddy covariance (EC) net CO2 fluxes, latent heat and sensible heat fluxes (R2~0.75, a→0, b→1); and annual estimates of EC-gap filled NEP and partitioned GPP and Re over the site from 2004-2009. Our findings indicated the needs for coupling of soil-plant-atmosphere schemes for gases, water, energy, carbon and nutrients in models to adequately simulate WTD effects on peatland C stocks.

  20. Marine ecosystem health status assessment through integrative biomarker indices: a comparative study after the Prestige oil spill "Mussel Watch".

    PubMed

    Marigómez, Ionan; Garmendia, Larraitz; Soto, Manu; Orbea, Amaia; Izagirre, Urtzi; Cajaraville, Miren P

    2013-04-01

    Five integrative biomarker indices are compared: Bioeffects Assessment Index (BAI), Health Status Index (HSI), integrated biological response (IBR), ecosystem health condition chart (EHCC) and Integrative Biomarker Index (IBI). They were calculated on the basis of selected biomarker data collected in the framework of the Prestige oil spill (POS) Mussel Watch monitoring (2003-2006) carried out in Galicia and the Bay of Biscay. According to the BAI, the health status of mussels was severely affected by POS and signals of recovery were evidenced in Galicia after April-04 and in Biscay Bay after April-05. The HSI (computed by an expert system) revealed high levels of environmental stress in 2003 and a recovery trend from April-04 to April-05. In July-05, the health status of mussels worsened but in October-05 and April-06 healthy condition was again recorded in almost all localities. IBR/n and IBI indicated that mussel health was severely affected in 2003 and improved from 2004 onwards. EHCC reflected a deleterious environmental condition in 2003 and a recovery trend after April-04, although a healthy ecosystem condition was not achieved in April-06 yet. Whereas BAI and HSI provide a basic indication of the ecosystem health status, star plots accompanying IBR/n and IBI provide complementary information concerning the mechanisms of biological response to environmental insult. Overall, although the integrative indices based on biomarkers show different sensitivity, resolution and informative output, all of them provide coherent information, useful to simplify the interpretation of biological effects of pollution in marine pollution monitoring. Each others' advantages, disadvantages and applicability for ecosystem health assessment are discussed.

  1. Exotic Spartina alterniflora invasion alters ecosystem-atmosphere exchange of CH4 and N2O and carbon sequestration in a coastal salt marsh in China.

    PubMed

    Yuan, Junji; Ding, Weixin; Liu, Deyan; Kang, Hojeong; Freeman, Chris; Xiang, Jian; Lin, Yongxin

    2015-04-01

    Coastal salt marshes are sensitive to global climate change and may play an important role in mitigating global warming. To evaluate the impacts of Spartina alterniflora invasion on global warming potential (GWP) in Chinese coastal areas, we measured CH4 and N2O fluxes and soil organic carbon sequestration rates along a transect of coastal wetlands in Jiangsu province, China, including open water; bare tidal flat; and invasive S. alterniflora, native Suaeda salsa, and Phragmites australis marshes. Annual CH4 emissions were estimated as 2.81, 4.16, 4.88, 10.79, and 16.98 kg CH4 ha(-1) for open water, bare tidal flat, and P. australis, S. salsa, and S. alterniflora marshes, respectively, indicating that S. alterniflora invasion increased CH4 emissions by 57-505%. In contrast, negative N2O fluxes were found to be significantly and negatively correlated (P < 0.001) with net ecosystem CO2 exchange during the growing season in S. alterniflora and P. australis marshes. Annual N2O emissions were 0.24, 0.38, and 0.56 kg N2O ha(-1) in open water, bare tidal flat and S. salsa marsh, respectively, compared with -0.51 kg N2O ha(-1) for S. alterniflora marsh and -0.25 kg N2O ha(-1) for P. australis marsh. The carbon sequestration rate of S. alterniflora marsh amounted to 3.16 Mg C ha(-1) yr(-1) in the top 100 cm soil profile, a value that was 2.63- to 8.78-fold higher than in native plant marshes. The estimated GWP was 1.78, -0.60, -4.09, and -1.14 Mg CO2 eq ha(-1) yr(-1) in open water, bare tidal flat, P. australis marsh and S. salsa marsh, respectively, but dropped to -11.30 Mg CO2 eq ha(-1) yr(-1) in S. alterniflora marsh. Our results indicate that although S. alterniflora invasion stimulates CH4 emissions, it can efficiently mitigate increases in atmospheric CO2 and N2O along the coast of China.

  2. Exotic Spartina alterniflora invasion alters ecosystem-atmosphere exchange of CH4 and N2O and carbon sequestration in a coastal salt marsh in China.

    PubMed

    Yuan, Junji; Ding, Weixin; Liu, Deyan; Kang, Hojeong; Freeman, Chris; Xiang, Jian; Lin, Yongxin

    2015-04-01

    Coastal salt marshes are sensitive to global climate change and may play an important role in mitigating global warming. To evaluate the impacts of Spartina alterniflora invasion on global warming potential (GWP) in Chinese coastal areas, we measured CH4 and N2O fluxes and soil organic carbon sequestration rates along a transect of coastal wetlands in Jiangsu province, China, including open water; bare tidal flat; and invasive S. alterniflora, native Suaeda salsa, and Phragmites australis marshes. Annual CH4 emissions were estimated as 2.81, 4.16, 4.88, 10.79, and 16.98 kg CH4 ha(-1) for open water, bare tidal flat, and P. australis, S. salsa, and S. alterniflora marshes, respectively, indicating that S. alterniflora invasion increased CH4 emissions by 57-505%. In contrast, negative N2O fluxes were found to be significantly and negatively correlated (P < 0.001) with net ecosystem CO2 exchange during the growing season in S. alterniflora and P. australis marshes. Annual N2O emissions were 0.24, 0.38, and 0.56 kg N2O ha(-1) in open water, bare tidal flat and S. salsa marsh, respectively, compared with -0.51 kg N2O ha(-1) for S. alterniflora marsh and -0.25 kg N2O ha(-1) for P. australis marsh. The carbon sequestration rate of S. alterniflora marsh amounted to 3.16 Mg C ha(-1) yr(-1) in the top 100 cm soil profile, a value that was 2.63- to 8.78-fold higher than in native plant marshes. The estimated GWP was 1.78, -0.60, -4.09, and -1.14 Mg CO2 eq ha(-1) yr(-1) in open water, bare tidal flat, P. australis marsh and S. salsa marsh, respectively, but dropped to -11.30 Mg CO2 eq ha(-1) yr(-1) in S. alterniflora marsh. Our results indicate that although S. alterniflora invasion stimulates CH4 emissions, it can efficiently mitigate increases in atmospheric CO2 and N2O along the coast of China. PMID:25367159

  3. Comparing the impact of the 2003 and 2010 heatwaves on Net Ecosystem Production in Europe

    NASA Astrophysics Data System (ADS)

    Bastos, A. F.; Gouveia, C. M.; Trigo, R. M.

    2012-12-01

    Climate variability is known to influence primary productivity on land ecosystems (Nemani et al., 2003). In particular, extreme climatic events such as major droughts and heatwaves are known to have severe impact on primary productivity and, therefore, to affect significantly the carbon dioxide uptake by land ecosystems at regional (Ciais et al., 2005) or even global scale (Zhao and Running, 2010). In the last decade, Europe was struck by two outstanding heatwaves, the 2003 event in Western Europe and the recent 2010 episode over Eastern Europe. Both were characterised by record breaking temperatures at the daily, weekly, monthly and seasonal scales, although the amplitude and spatial extent of the 2010 mega-heatwave surpassed the 2003 event (Barriopedro et al., 2011). This work aims to assess the influence of both mega-heatwaves on seasonal and yearly Net Ecosystem Production (NEP). The work relies on monthly NEP data derived from satellite imagery obtained from MODIS (Moderate Resolution Imaging Spectroradiometer) sensor at 1km spatial resolution. Data were selected for the period between 2000 and 2011 over a region extending from 34.6 oN to 73.5 oN and 12.1 oW to 46.8 oE, covering Eurasia. In 2010 very low NEP anomalies are observed over a very large area in Eastern Europe, at the monthly, seasonal and yearly scale. In western Russia, yearly NEP anomalies fall below 50% of average cumulative NEP. These widespread negative anomalous values of NEP fields over the western Russia region match the patterns of very high temperature values combined with below-average precipitation, at the seasonal (summer) scale. Moreover, the impact of the heatwave is not only evident at the regional level but also at the wider continental (European) scale and is significantly more extensive and intense than the corresponding heatwave of 2003 in Western Europe (Ciais et al., 2005). References: Barriopedro, D., E. M. Fischer, J. Luterbacher, R. M. Trigo, and R. Garcia-Herrera (2011

  4. Comparative ecology of H2 cycling in sedimentary and phototrophic ecosystems

    NASA Technical Reports Server (NTRS)

    Hoehler, Tori M.; Albert, Daniel B.; Alperin, Marc J.; Bebout, Brad M.; Martens, Christopher S.; Des Marais, David J.

    2002-01-01

    The simple biochemistry of H2 is critical to a large number of microbial processes, affecting the interaction of organisms with each other and with the environment. The sensitivity of each of these processes to H2 can be described collectively, through the quantitative language of thermodynamics. A necessary prerequisite is to understand the factors that, in turn, control H2 partial pressures. These factors are assessed for two distinctly different ecosystems. In anoxic sediments from Cape Lookout Bight (North Carolina, USA), H2 partial pressures are strictly maintained at low, steady-state levels by H2-consuming organisms, in a fashion that can be quantitatively predicted by simple thermodynamic calculations. In phototrophic microbial mats from Baja California (Mexico), H2 partial pressures are controlled by the activity of light-sensitive H2-producing organisms, and consequently fluctuate over orders of magnitude on a daily basis. The differences in H2 cycling can subsequently impact any of the H2-sensitive microbial processes in these systems. In one example, methanogenesis in Cape Lookout Bight sediments is completely suppressed through the efficient consumption of H2 by sulfate-reducing bacteria; in contrast, elevated levels of H2 prevail in the producer-controlled phototrophic system, and methanogenesis occurs readily in the presence of 40 mM sulfate.

  5. Ecosystem structure and fishing impacts in the northwestern Mediterranean Sea using a food web model within a comparative approach

    NASA Astrophysics Data System (ADS)

    Corrales, Xavier; Coll, Marta; Tecchio, Samuele; Bellido, José María; Fernández, Ángel Mario; Palomera, Isabel

    2015-08-01

    We developed an ecological model to characterize the structure and functioning of the marine continental shelf and slope area of the northwestern Mediterranean Sea, from Toulon to Cape La Nao (NWM model), in the early 2000s. The model included previously modeled areas in the NW Mediterranean (the Gulf of Lions and the Southern Catalan Sea) and expanded their ranges, covering 45,547 km2, with depths from 0 to 1000 m. The study area was chosen to specifically account for the connectivity between the areas and shared fish stocks and fleets. Input data were based on local scientific surveys and fishing statistics, published data on stomach content analyses, and the application of empirical equations to estimate consumption and production rates. The model was composed of 54 functional groups, from primary producers to top predators, and Spanish and French fishing fleets were considered. Results were analyzed using ecological indicators and compared with outputs from ecosystem models developed in the Mediterranean Sea and the Gulf of Cadiz prior to this study. Results showed that the main trophic flows were associated with detritus, phytoplankton, zooplankton and benthic invertebrates. Several high trophic level organisms (such as dolphins, benthopelagic cephalopods, large demersal fishes from the continental shelf, and other large pelagic fishes), and the herbivorous salema fish, were identified as keystone groups within the ecosystem. Results confirmed that fishing impact was high and widespread throughout the food web. The comparative approach highlighted that, despite productivity differences, the ecosystems shared common features in structure and functioning traits such as the important role of detritus, the dominance of the pelagic fraction in terms of flows and the importance of benthic-pelagic coupling.

  6. Respiratory and hemodynamic outcomes following exchange extubation with laryngeal mask airway as compared to traditional awake extubation

    PubMed Central

    Suppiah, Ramanathan Kannan; Rajan, Sunil; Paul, Jerry; Kumar, Lakshmi

    2016-01-01

    Background: Traditional awake extubation leads to respiratory complications and hemodynamic response which are detrimental in neurosurgery, ENT surgery and patients with comorbidities. Aims: The primary objective was to compare the respiratory complications and hemodynamic stress response between traditional awake extubation of a endotracheal tube (ETT) and that following exchange extubation of ETT by using a laryngeal mask airway (LMA). Settings and Design: This prospective randomized study was conducted in a Tertiary Care Centre in 60 American Society of Anesthesiologists I and II patients coming for general surgery. Materials and Methods: Patients were randomized by permuted blocks into traditional awake extubation group and exchange extubation group. At the end of surgery in traditional group, awake extubation of ETT was done. In exchange group, 0.3 mg/kg propofol was administered, and the ETT was exchanged for a LMA. Awake extubation of LMA was then performed. Respiratory complications such as bucking, coughing, desaturation and the need for airway maneuvers and hemodynamic response were noted in both groups. Analysis Tools: Chi-square test, independent sample t- and paired t-tests were used as applicable. Results: Incidence of respiratory complication was 93.3% in traditional extubation while it was only 36.7% in exchange extubation group (P < 0.001). Hemodynamic response measured immediately at extubation in terms of heart rate, systolic blood pressure (BP), diastolic BP, mean arterial pressure, and rate pressure product were all significantly lesser in exchange group when compared to traditional extubation. Conclusion: Exchange extubation with LMA decreases respiratory complications and hemodynamic stress response when compared to traditional awake extubation. PMID:27212749

  7. Calorie-counting compared to exchange system diets in the treatment of overweight patients with type II diabetes.

    PubMed

    Wing, R R; Nowalk, M P; Epstein, L H; Koeske, R

    1986-01-01

    Patients with diabetes are usually placed on exchange system diets to ensure a nutritionally adequate intake. However, there have been few studies which have actually compared the nutritional adequacy of diets selected by patients on exchange system diets, with that selected by patients on the calorie-counting diets typically used in behavioral weight control programs. This study compared the nutritional adequacy of the diets selected by overweight patients with Type II diabetes who had been randomly assigned to either an exchange system diet or a calorie-counting diet. Three-day food diaries were completed by all patients at the start and end of a 16-week weight control program. No significant differences were observed between patients on the calorie-counting diet compared to those on the exchange system diet with respect to nutrient intake, macronutrient distribution, or percent of the RDA obtained. Patients on both types of diet reported decreases in the proportion of calories from fat. The average intake exceeded 100% of the RDA for all nutrients except calcium. This study suggests that patients are able to improve the nutritional adequacy of their intake while following either a calorie-counting or an exchange system diet. PMID:3739801

  8. Biophysical controls on interannual variability in ecosystem-scale CO2 and CH4 exchange in a California rice paddy

    NASA Astrophysics Data System (ADS)

    Knox, Sara Helen; Matthes, Jaclyn Hatala; Sturtevant, Cove; Oikawa, Patricia Y.; Verfaillie, Joseph; Baldocchi, Dennis

    2016-03-01

    We present 6.5 years of eddy covariance measurements of fluxes of methane (FCH4) and carbon dioxide (FCO2) from a flooded rice paddy in Northern California, USA. A pronounced warming trend throughout the study associated with drought and record high temperatures strongly influenced carbon (C) budgets and provided insights into biophysical controls of FCO2 and FCH4. Wavelet analysis indicated that photosynthesis (gross ecosystem production, GEP) induced the diel pattern in FCH4, but soil temperature (Ts) modulated its amplitude. Forward stepwise linear models and neural networking modeling were used to assess the variables regulating seasonal FCH4. As expected due to their competence in modeling nonlinear relationships, neural network models explained considerably more of the variance in daily average FCH4 than linear models. During the growing season, GEP and water levels typically explained most of the variance in daily average FCH4. However, Ts explained much of the interannual variability in annual and growing season CH4 sums. Higher Ts also increased the annual and growing season ratio of FCH4 to GEP. The observation that the FCH4 to GEP ratio scales predictably with Ts may help improve global estimates of FCH4 from rice agriculture. Additionally, Ts strongly influenced ecosystem respiration, resulting in large interannual variability in the net C budget at the paddy, emphasizing the need for long-term measurements particularly under changing climatic conditions.

  9. Peatland wetness and the inter-annual variability of net ecosystem exchange: comparison of multi-year records from two different types of northern peatlands

    NASA Astrophysics Data System (ADS)

    Roulet, N. T.; Nilsson, M. B.; Humphreys, E. R.

    2012-04-01

    Two continental northern peatlands have had the net ecosystem exchange (NEE) measured continuously for over a decade: Mer Bleue (MB) is a raised bog in the cool-temperate ecoclimatic region of central Canada and Degerö Stormyr (DS) is a minerogenic oligotrophic 'poor' fen in northern Sweden. The published multi-year net ecosystem carbon balance for each of these peatlands is approximately - 20 to 30 g C m-2 yr-1 based on measurements of all the major carbon exchanges, and is remarkably similar to other published balances and to the original analysis E. Gorham published for peatlands in 1991. However, while the NECB are similar the net ecosystem exchange (NEE) is very different between MB and DS. Most of the annual variance comes from the growing season - May to October. The growing season accumulated NEE for MB and DS for the period of measurements (10 years for MB and 9 years for DS) was -129.4 and -78.8 g C m-2 t-1, respectively, and the standard deviation and range around the mean at MB was 50.8 and 135.7 versus at 30.0 and 108.5 g C m-2 t-1 at DS. Both peatlands are nutrient poor. MB has a continuous cover of Sphagnum with a near complete cover of ericaceous shrubs. DS is covered by Eriophorum, shrubs, and sedges, and Sphagnum where the water table is below the surface. The main difference between these two peatlands is in the variation of moisture storage. MB has a much lower mean growing season water table depth (WTD) than DS, -42.3 versus -14.4 cm and the growing season range and standard deviation are greater at MB than DS (16.2 and 5.7 versus 13.4 and 4.8 cm). Further, the WTD is fairly normally distributed at DS but at MB on about half the years there is a longer tail towards WTDs > -50 cm. These growing seasons correspond to lower cumulative NEEs. At MB there is a significant inverse relationship between cumulative growing season NEE and mean WTD (r2 = 0.42) but not at DS. However, at DS a weak significant relationship arises if one anomalously large

  10. [Effects of drip irrigation with plastic mulching on the net primary productivity, soil heterotrophic respiration, and net CO2 exchange flux of cotton field ecosystem in Xinjiang, Northwest China].

    PubMed

    Li, Zhi-Guo; Zhang, Run-Hua; Lai, Dong-Mei; Yan, Zheng-Yue; Jiang, Li; Tian, Chang-Yan

    2012-04-01

    In April-October, 2009, a field experiment was conducted to study the effects of drip irrigation with plastic mulching (MD) on the net primary productivity (NPP), soil heterotrophic respiration (Rh) , and net CO2 exchange flux (NEF(CO2)) of cotton field ecosystem in Xinjiang, taking the traditional flood irrigation with no mulching (NF) as the control. With the increasing time, the NPP, Rh, and NEF(CO2) in treatments MD and NF all presented a trend of increasing first and decreased then. As compared with NF, MD increased the aboveground and belowground biomass and the NPP of cotton, and decreased the Rh. Over the whole growth period, the Rh in treatment MD (214 g C x m(-2)) was smaller than that in treatment NF (317 g C x m(-2)), but the NEF(CO2) in treatment MD (1030 g C x m(-2)) was higher than that in treatment NF (649 g C x m(-2)). Treatment MD could fix the atmospheric CO2 approximately 479 g C x m(-2) higher than treatment NF. Drip irrigation with plastic mulching could promote crop productivity while decreasing soil CO2 emission, being an important agricultural measure for the carbon sequestration and emission reduction of cropland ecosystems in arid area.

  11. A comparative study of resource allocation in Pteridium in different Brazilian ecosystems and its relationship with European studies.

    PubMed

    Silva Matos, D M; Xavier, R O; Tiberio, F C S; Marrs, R H

    2014-02-01

    Pteridium is a cosmopolitan genus that acts as an invasive species in many parts of the world. Most research on this genus has occurred in Europe, and there is a lack of data on it from South America, in spite of causing considerable conservation problems. We compared the biomass allocation of P. esculentum subsp. arachnoideum in two ecosystems in Brazil - Atlantic forest and Brazilian savanna. We measured the biomass of fronds, rhizomes and above-ground litter. We also compared the density, length and biomass of fronds from this Brazilian study with similar data of P. esculentum subsp. arachnoideum derived from Venezuela and P. aquilinum from Europe. P. esculentum subsp. arachnoideum showed a wide response range. We found a negative relationship between frond and necromass, indicating a negative feedback effect, while a positive relationship was observed between frond and rhizome biomass. The continental comparison of relationships showed that Pteridium responds in a different way in both Brazil and Europe, and that in Brazil fronds tend to be longer and heavier, presumably as a result of the continuous growing season in South America while is shortened in Europe by frost. The paper shows the ability of Pteridium to adapt to different ecosystems.

  12. A comparative study of resource allocation in Pteridium in different Brazilian ecosystems and its relationship with European studies.

    PubMed

    Silva Matos, D M; Xavier, R O; Tiberio, F C S; Marrs, R H

    2014-02-01

    Pteridium is a cosmopolitan genus that acts as an invasive species in many parts of the world. Most research on this genus has occurred in Europe, and there is a lack of data on it from South America, in spite of causing considerable conservation problems. We compared the biomass allocation of P. esculentum subsp. arachnoideum in two ecosystems in Brazil - Atlantic forest and Brazilian savanna. We measured the biomass of fronds, rhizomes and above-ground litter. We also compared the density, length and biomass of fronds from this Brazilian study with similar data of P. esculentum subsp. arachnoideum derived from Venezuela and P. aquilinum from Europe. P. esculentum subsp. arachnoideum showed a wide response range. We found a negative relationship between frond and necromass, indicating a negative feedback effect, while a positive relationship was observed between frond and rhizome biomass. The continental comparison of relationships showed that Pteridium responds in a different way in both Brazil and Europe, and that in Brazil fronds tend to be longer and heavier, presumably as a result of the continuous growing season in South America while is shortened in Europe by frost. The paper shows the ability of Pteridium to adapt to different ecosystems. PMID:25055097

  13. Reconciling estimates of the contemporary North American carbon balance among terrestrial biosphere models, atmospheric inversions, and a new approach for estimating net ecosystem exchange from inventory-based data

    USGS Publications Warehouse

    Hayes, Daniel J.; Turner, David P.; Stinson, Graham; McGuire, A. David; Wei, Yaxing; West, Tristram O.; Heath, Linda S.; de Jong, Bernardus; McConkey, Brian G.; Birdsey, Richard A.; Kurz, Werner A.; Jacobson, Andrew R.; Huntzinger, Deborah N.; Pan, Yude; Post, W. Mac; Cook, Robert B.

    2012-01-01

    We develop an approach for estimating net ecosystem exchange (NEE) using inventory-based information over North America (NA) for a recent 7-year period (ca. 2000–2006). The approach notably retains information on the spatial distribution of NEE, or the vertical exchange between land and atmosphere of all non-fossil fuel sources and sinks of CO2, while accounting for lateral transfers of forest and crop products as well as their eventual emissions. The total NEE estimate of a -327 ± 252 TgC yr-1 sink for NA was driven primarily by CO2 uptake in the Forest Lands sector (-248 TgC yr-1), largely in the Northwest and Southeast regions of the US, and in the Crop Lands sector (-297 TgC yr-1), predominantly in the Midwest US states. These sinks are counteracted by the carbon source estimated for the Other Lands sector (+218 TgC yr-1), where much of the forest and crop products are assumed to be returned to the atmosphere (through livestock and human consumption). The ecosystems of Mexico are estimated to be a small net source (+18 TgC yr-1) due to land use change between 1993 and 2002. We compare these inventory-based estimates with results from a suite of terrestrial biosphere and atmospheric inversion models, where the mean continental-scale NEE estimate for each ensemble is -511 TgC yr-1 and -931 TgC yr-1, respectively. In the modeling approaches, all sectors, including Other Lands, were generally estimated to be a carbon sink, driven in part by assumed CO2 fertilization and/or lack of consideration of carbon sources from disturbances and product emissions. Additional fluxes not measured by the inventories, although highly uncertain, could add an additional -239 TgC yr-1 to the inventory-based NA sink estimate, thus suggesting some convergence with the modeling approaches.

  14. Reconciling estimates of the contemporary North American carbon balance among terrestrial biosphere models, atmospheric inversions and a new approach for estimating net ecosystem exchange from inventory-based data

    SciTech Connect

    Hayes, Daniel J; Turner, David P; Stinson, Graham; Mcguire, David; Wei, Yaxing; West, Tristram O.; Heath, Linda S.; De Jong, Bernardus; McConkey, Brian G.; Birdsey, Richard A.; Kurz, Werner; Jacobson, Andrew; Huntzinger, Deborah; Pan, Yude; Post, Wilfred M; Cook, Robert B

    2012-01-01

    We develop an approach for estimating net ecosystem exchange (NEE) using inventory-based information over North America (NA) for a recent 7-year period (ca. 2000 2006). The approach notably retains information on the spatial distribution of NEE, or the vertical exchange between land and atmosphere of all non-fossil fuel sources and sinks of CO2, while accounting for lateral transfers of forest and crop products as well as their eventual emissions. The total NEE estimate of a 327 252 TgC yr1 sink for NA was driven primarily by CO2 uptake in the Forest Lands sector (248 TgC yr1), largely in the Northwest and Southeast regions of the US, and in the Crop Lands sector (297 TgC yr1), predominantly in the Midwest US states. These sinks are counteracted by the carbon source estimated for the Other Lands sector (+218 TgC yr1), where much of the forest and crop products are assumed to be returned to the atmosphere (through livestock and human consumption). The ecosystems of Mexico are estimated tobe a small net source (+18 TgC yr1) due to land use change between 1993 and 2002. We compare these inventorybased estimates with results from a suite of terrestrial biosphere and atmospheric inversion models, where the mean continental-scale NEE estimate for each ensemble is 511 TgC yr1 and 931 TgC yr1, respectively. In the modeling approaches, all sectors, including Other Lands, were generally estimated to be a carbon sink, driven in part by assumed CO2 fertilization and/or lack of consideration of carbon sources from disturbances and product emissions. Additional fluxes not measured by the inventories, although highly uncertain, could add an additional 239 TgC yr1 to the inventory-based NA sink estimate, thus suggesting some convergence with the modeling approaches.

  15. Soil carbon sensitivity to temperature and carbon use efficiency compared across microbial-ecosystem models of varying complexity

    SciTech Connect

    Li, Jianwei; Wang, Gangsheng; Allison, Steven D.; Mayes, Melanie; Luo, Yiqi

    2014-01-01

    Global ecosystem models may require microbial components to accurately predict feedbacks between climate warming and soil decomposition, but it is unclear what parameters and levels of complexity are ideal for scaling up to the globe. Here we conducted a model comparison using a conventional model with first-order decay and three microbial models of increasing complexity that simulate short- to long-term soil carbon dynamics. We focused on soil carbon responses to microbial carbon use efficiency (CUE) and temperature. Three scenarios were implemented in all models: constant CUE (held at 0.31), varied CUE ( 0.016 C 1), and 50 % acclimated CUE ( 0.008 C 1). Whereas the conventional model always showed soil carbon losses with increasing temperature, the microbial models each predicted a temperature threshold above which warming led to soil carbon gain. The location of this threshold depended on CUE scenario, with higher temperature thresholds under the acclimated and constant scenarios. This result suggests that the temperature sensitivity of CUE and the structure of the soil carbon model together regulate the long-term soil carbon response to warming. Equilibrium soil carbon stocks predicted by the microbial models were much less sensitive to changing inputs compared to the conventional model. Although many soil carbon dynamics were similar across microbial models, the most complex model showed less pronounced oscillations. Thus, adding model complexity (i.e. including enzyme pools) could improve the mechanistic representation of soil carbon dynamics during the transient phase in certain ecosystems. This study suggests that model structure and CUE parameterization should be carefully evaluated when scaling up microbial models to ecosystems and the globe.

  16. Eddy covariance flux measurements of net ecosystem carbon dioxide exchange from a lowland peatland flux tower network in England and Wales

    NASA Astrophysics Data System (ADS)

    Morrison, Ross; Balzter, Heiko; Burden, Annette; Callaghan, Nathan; Cumming, Alenander; Dixon, Simon; Evans, Jonathan; Kaduk, Joerg; Page, Susan; Pan, Gong; Rayment, Mark; Ridley, Luke; Rylett, Daniel; Worrall, Fred; Evans, Christopher

    2016-04-01

    Peatlands store disproportionately large amounts of soil carbon relative to other terrestrial ecosystems. Over recent decades, the large amount of carbon stored as peat has proved vulnerable to a range of land use pressures as well as the increasing impacts of climate change. In temperate Europe and elsewhere, large tracts of lowland peatland have been drained and converted to agricultural land use. Such changes have resulted in widespread losses of lowland peatland habitat, land subsidence across extensive areas and the transfer of historically accumulated soil carbon to the atmosphere as carbon dioxide (CO2). More recently, there has been growth in activities aiming to reduce these impacts through improved land management and peatland restoration. Despite a long history of productive land use and management, the magnitude and controls on greenhouse gas emissions from lowland peatland environments remain poorly quantified. Here, results of surface-atmosphere measurements of net ecosystem CO2 exchange (NEE) from a network of seven eddy covariance (EC) flux towers located at a range of lowland peatland ecosystems across the United Kingdom (UK) are presented. This spatially-dense peatland flux tower network forms part of a wider observation programme aiming to quantify carbon, water and greenhouse gas balances for lowland peatlands across the UK. EC measurements totalling over seventeen site years were obtained at sites exhibiting large differences in vegetation cover, hydrological functioning and land management. The sites in the network show remarkable spatial and temporal variability in NEE. Across sites, annual NEE ranged from a net sink of -194 ±38 g CO2-C m-2 yr-1 to a net source of 784±70 g CO2-C m-2 yr-1. The results suggest that semi-natural sites remain net sinks for atmospheric CO2. Sites that are drained for intensive agricultural production range from a small net sink to the largest observed source for atmospheric CO2 within the flux tower network

  17. Comparative Efficacy of the Picture Exchange Communication System (PECS) versus a Speech-Generating Device: Effects on Requesting Skills

    ERIC Educational Resources Information Center

    Boesch, Miriam C.; Wendt, Oliver; Subramanian, Anu; Hsu, Ning

    2013-01-01

    An experimental, single-subject research study investigated the comparative efficacy of the Picture Exchange Communication System (PECS) versus a speech-generating device (SGD) in developing requesting skills for three elementary-age children with severe autism and little to no functional speech. Results demonstrated increases in requesting…

  18. Fundamental structural aspects and features in the bioengineering of the gas exchangers: comparative perspectives.

    PubMed

    Maina, J N

    2002-01-01

    Over its life, an organism's survival and success are determined by the inventory of vital adaptations that its progenitors have creatively appropriated, devised and harnessed along the evolutionary pathway. Such conserved attributes provide the armamentarium necessary for withstanding the adverse effects of natural selection. Refinements of the designs of the respiratory organs have been critical for survival and phylogenetic advancement of animal life. Gas exchangers have changed in direct response to the respiratory needs of whole organisms in different environmental states and conditions. Nowhere else is the dictum that in biology 'there are no rules but only necessities' more manifest than in the evolutionary biology of the gas exchangers. The constructions have been continually fashioned and refined to meet specific needs. Solutions to common respiratory needs have been typified by profound structural convergence. Over the evolutionary continuum, as shifts in environmental situations occurred, infinitely many designs should theoretically have emerged. Moreover, without specific selective pressures and preference for certain designs, considering that there are only two naturally occurring respirable fluid media (air and water), air-lungs, water-lungs, air-gills and water-gills would have formed to similar extents. Factors such as body size, phylogenetic level of development, respiratory medium utilized and habitats occupied have permutatively prescribed the design of the gas exchangers. The construction of the modern gas exchangers has eventuated through painstaking cost-benefit analysis. Trade-offs and compromises have decreed only a limited number of structurally feasible and functionally competent outcomes. The morphological congruity (analogy) of the gas exchangers indicates that similar selective pressures have compelled the designs. Solutions to metabolic demands for molecular O2 have only differed in details. Passive physical diffusion, for example, is

  19. Partitioning net ecosystem carbon exchange into net assimilation and respiration using 13CO2 measurements: A cost-effective sampling strategy

    NASA Astrophysics Data System (ADS)

    OgéE, J.; Peylin, P.; Ciais, P.; Bariac, T.; Brunet, Y.; Berbigier, P.; Roche, C.; Richard, P.; Bardoux, G.; Bonnefond, J.-M.

    2003-06-01

    The current emphasis on global climate studies has led the scientific community to set up a number of sites for measuring the long-term biosphere-atmosphere net CO2 exchange (net ecosystem exchange, NEE). Partitioning this flux into its elementary components, net assimilation (FA), and respiration (FR), remains necessary in order to get a better understanding of biosphere functioning and design better surface exchange models. Noting that FR and FA have different isotopic signatures, we evaluate the potential of isotopic 13CO2 measurements in the air (combined with CO2 flux and concentration measurements) to partition NEE into FR and FA on a routine basis. The study is conducted at a temperate coniferous forest where intensive isotopic measurements in air, soil, and biomass were performed in summer 1997. The multilayer soil-vegetation-atmosphere transfer model MuSICA is adapted to compute 13CO2 flux and concentration profiles. Using MuSICA as a "perfect" simulator and taking advantage of the very dense spatiotemporal resolution of the isotopic data set (341 flasks over a 24-hour period) enable us to test each hypothesis and estimate the performance of the method. The partitioning works better in midafternoon when isotopic disequilibrium is strong. With only 15 flasks, i.e., two 13CO2 nighttime profiles (to estimate the isotopic signature of FR) and five daytime measurements (to perform the partitioning) we get mean daily estimates of FR and FA that agree with the model within 15-20%. However, knowledge of the mesophyll conductance seems crucial and may be a limitation to the method.

  20. Material exchange and food web of seagrass beds in the Sylt-Rømø Bight: how significant are community changes at the ecosystem level?

    NASA Astrophysics Data System (ADS)

    Asmus, H.; Asmus, R.

    2000-07-01

    Material exchange, biodiversity and trophic transfer within the food web were investigated in two different types of intertidal seagrass beds: a sheltered, dense Zostera marina bed and a more exposed, sparse Z. noltii bed, in the Northern Wadden Sea. Both types of Zostera beds show a seasonal development of above-ground biomass, and therefore measurements were carried out during the vegetation period in summer. The exchange of particles and nutrients between seagrass beds and the overlying water was measured directly using an in situ flume. Particle sedimentation [carbon (C), nitrogen (N) and phosphorus (P) constituents] from the water column prevailed in dense seagrass beds. In the sheltered, dense seagrass bed, a net particle uptake was found even on windy days (7-8 Beaufort). Dissolved inorganic N and orthophosphate were mainly taken up by the dense seagrass bed. At times of strong winds, nutrients were released from the benthic community to tidal waters. In a budget calculation of total N and total P, the dense seagrass beds were characterised as a material sink. The seagrass beds with sparse Z. noltii were a source of particles even during calm weather. The uptake of dissolved inorganic N in the sparse seagrass bed was low but significant, while the uptake of inorganic phosphate and silicate by seagrasses and their epiphytes was exceeded by release processes from the sediment into the overlying water. Estimates at the ecosystem level showed that material fluxes of seagrass beds in the Sylt-Rømø Bight are dominated by the dense type of Zostera beds. Therefore, seagrass beds act as a sink for particles and for dissolved inorganic nutrients. During storms, seagrass beds are distinct sources for inorganic nutrients. The total intertidal area of the Sylt-Rømø Bight could be described as a sink for particles and a source for dissolved nutrients. This balance of the material budget was estimated by either including or excluding seagrass beds. Including the

  1. The Net Exchange Between Terrestrial Ecosystems and the Atmosphere as a Result of Changes in Land Use

    NASA Technical Reports Server (NTRS)

    Houghton, R. A.

    1998-01-01

    The general purpose of this research was to improve and update (to 1990) estimates of the net flux of carbon between the world's terrestrial ecosystems and the atmosphere from changes in land use (e.g., deforestation and reforestation). The estimates are important for understanding the global carbon cycle, and for predicting future concentrations of atmospheric CO2 that will result from emissions. The emphasis of the first year's research was on the northern temperate zone and boreal forests, where the greatest discrepancy exists between estimates of flux. Forest inventories suggest net sinks of 0.6 PgC/yr; inversion analyses based on atmospheric data and models suggest much larger sinks 2-3.6 PgC/yr (e.g., Tans et al. 1990, Ciais et al. 1995). The work carried out with this grant calculated the flux attributable to changes in land use. The estimated flux was somewhat smaller than the flux calculated from inventory data suggesting that environmental changes have led to a small accumulation of carbon in forests that exceeds the accumulation expected from past rates of harvest. Two publications have described these results (Houghton 1996, 1998). The large difference between these estimates and those obtained with atmospheric data and models remains unexplained. The recent estimate of a 1.7 PgC/yr sink in North America, alone (Fan et al. 1998), is particularly difficult to explain. That part of the sink attributable to land-use change, however, is defined as a result of this grant.

  2. Comparing heat exchangers of thermacoustic prime movers with a Van der Pol model

    NASA Astrophysics Data System (ADS)

    Cox, I.; Jorgensen, M.; Andersen, B.

    2010-10-01

    A thermoacoustic standing-wave prime mover is a self-sustained oscillator whose initial growth of acoustic pressure into amplitude saturation can be modeled by the Van der Pol equation. The nonlinear Van der Pol equation is calculated computationally, using 4^th order Runge-Kutta. The Van der Pol model gives quantitative loss and gain parameters, when using a best-fit with experimental data. The engines tested in this study have an average frequency of 2700 Hz, which suggests that the first second of oscillations when using the Van der Pol model can reveal information about the steady-state performance of the device. This model is applied to studying the effect of different heat exchanger sizes. All sixteen possible permutations were tested using different copper wire mesh dimensions: 24X24, 40X40, 60X60, and 80X80 for the hot and cold heat exchangers (where ##X## indicates wires per inch). Plotting the steady-state acoustic pressure as a function of the gain term divided by the loss term shows roughly, a linear relationship. The engine with the highest gain term and smallest loss term was using 80X80 for the hot heat exchanger combined with the 24X24 for the cold heat exchanger and is consistent with the highest steady-state pressure achieved. The modeling process has been very successful and fits the Van der Pol equation.

  3. Research on Study Abroad, Mobility, and Student Exchange in Comparative Education Scholarship

    ERIC Educational Resources Information Center

    Streitwieser, Bernhard T.; Le, Emily; Rust, Val

    2012-01-01

    For many years there has been research on study abroad, student mobility and international student exchange; however in the last two decades the volume and scope of this work has increased significantly. There are now specific academic journals, a host of new books each year, expansive reports by international research organizations, and an…

  4. Comparing Acquisition of Exchange-Based and Signed Mands with Children with Autism

    ERIC Educational Resources Information Center

    Barlow, Kathryn E.; Tiger, Jeffrey H.; Slocum, Sarah K.; Miller, Sarah J.

    2013-01-01

    Therapists and educators frequently teach alternative-communication systems, such as picture exchanges or manual signs, to individuals with developmental disabilities who present with expressive language deficits. Michael (1985) recommended a taxonomy for alternative communication systems that differentiated between selection-based systems in…

  5. Utilizing continuous measurements of delta^{13}C_r, delta18O_r, and net ecosystem exchange of CO_2 and H_2O to understand the effects of inter-annual variability in drought on ecosystem functioning

    NASA Astrophysics Data System (ADS)

    Osuna, J. L.; McDowell, N. G.; Shim, J. H.; Rahn, T.; Pockman, W.

    2011-12-01

    In the semi-arid Southwestern US, seasonal drought has strengthened in recent years due to both a decrease in winter precipitation and delayed onset of the summer monsoon. A process-based understanding of ecosystem response to increased drought stress is vital to predicting the long-term stability of semi-arid biomes. To understand the processes responsible for inter-annual and seasonal variability in net ecosystem carbon and water fluxes, we compared nearly continuous measurements of ecosystem scale respiration (R_e) from an eddy covariance system with the stable carbon and oxygen isotope signals in ecosystem respired CO_2 (delta^{13}C_r and delta^{18}O_r) measured continuously by a tunable diode laser spectrometer (TDL) sampling at various canopy heights at the same site. The study site, at Los Alamos National Laboratory, converted from pitilde{n}on juniper woodland to juniper woodland after over 90% of pitilde{n}ons died in 2002-2003 following multiple years of enhanced drought leaving a high necromass at the site. We analyzed the relationships between the Bowen ratio, delta^{18}O_r, daily and annual accumulated NEE, and delta^{13}C_r to understand the (de)coupling between the response of transpiration and respiration under varying degrees of drought stress. Additionally, we explored the variability in the lag and intensity of ecosystem response to precipitation pulses depending on antecedent conditions. The response of delta^{18}O_r was more consistent across years and seasons whereas variability in the contribution of autotrophic versus heterotrophic respiration appeared to cause differing responses of delta^{13}C_r to drought stress and precipitation pulses. This result was supported by the diurnal CO_2 and H_2O fluxes indicating nearly immediate transpirational water loss initiated by most precipitation pulses. Annual accumulated precipitation (versus pulse size) was a better indicator of delta^{13}C_ r response (i.e. relative contributions of autotrophic

  6. Effect of non-homogeneity in flux footprint on the interpretation of seasonal, annual, and interannual ecosystem carbon exchange

    NASA Astrophysics Data System (ADS)

    Griebel, A.; Bennett, L. T.; Metzen, D.; Cleverly, J. R.; Burba, G. G.; Arndt, S. K.

    2015-12-01

    Carbon flux measurements using the eddy covariance method rely on several assumptions, including reasonably uniform terrain and homogenous vegetation. These are not always possible in complex terrain, structurally variable native vegetation or in disturbed ecosystems. Consequently, an increasing number of flux sites are located over not fully homogeneous areas. This implies that observed year-to-year variations in CO2 budgets may not always be related only to changes in the key driving factors such as weather, canopy state and physiology, but may also be affected by differences in the flux footprints between years. This may bias budget estimates over many locations, since a large number of flux sites are affected by wind channelling, contrasting climatic conditions with wind direction (e.g. maritime sites) and by variations of continental-scale climate patterns that modify prevailing wind directions. We tested the effects of a non-homogeneous footprint on annual carbon estimates for an evergreen forest, where the combination of terrain, weather and anthropogenic management shaped the local forest structure. Interactions among these factors caused the key drivers regulating carbon fluxes (such as LAI, temperature, VPD and turbulence) to vary significantly with wind direction, and their combinations resulted in pronounced carbon sequestration 'hotspots' that impacted instantaneous fluxes. These were most distinctive during the summer months, and they varied in extent and magnitude depending on prevailing weather. Consequently, interannual variations in footprints affected up to 18.9% of seasonal estimates during the summer months, and up to 23.1% of annual carbon budget estimates. The footprint-related bias was largest at 48.7% under 'ideal' uptake conditions (clear sky, mid-day during summer). We further present a procedure to recognise and quantify the apparent interannual variations in carbon estimates attributable to year-to-year variations in flux footprint.

  7. Hyporheic exchange and fulvic acid redox reactions in an alpine stream/wetland ecosystem, Colorado front range

    USGS Publications Warehouse

    Miller, M.P.; McKnight, Diane M.; Cory, R.M.; Williams, M.W.; Runkel, R.L.

    2006-01-01

    The influence of hyporheic zone interactions on the redox state of fulvic acids and other redox active species was investigated in an alpine stream and adjacent wetland, which is a more reducing environment. A tracer injection experiment using bromide (Br-) was conducted in the stream system. Simulations with a transport model showed that rates of exchange between the stream and hyporheic zone were rapid (?? ??? 10-3 s -1). Parallel factor analysis of fluorescence spectra was used to quantify the redox state of dissolved fulvic acids. The rate coefficient for oxidation of reduced fulvic acids (?? = 6.5 ?? 10-3 s -1) in the stream indicates that electron-transfer reactions occur over short time scales. The rate coefficients for decay of ammonium (?? = 1.2 ?? 10-3 s-1) and production of nitrate (?? = -1.0 ?? 10-3 s-1) were opposite in sign but almost equal in magnitude. Our results suggest that fulvic acids are involved in rapid electron-transfer processes in and near the stream channel and may be important in determining ecological energy flow at the catchment scale. ?? 2006 American Chemical Society.

  8. Process coupling and control over the response of net ecosystem CO2 exchange to climate variability and insect disturbance in subalpine forests of the Western US

    NASA Astrophysics Data System (ADS)

    Monson, R. K.; Moore, D. J.; Trahan, N. A.; Scott-Denton, L.; Burns, S. P.; Hu, J.; Bowling, D. R.

    2011-12-01

    Following ten years of studies in subalpine forest ecosystems of the Western US, we have concluded that the tight coupling between gross primary productivity (GPP) and the autotrophic component of soil respiration (Ra) drives responses of net ecosystem CO2 exchange (NEE) to climate variability and insect disturbance. This insight has been gained through long-term eddy flux observations, manipulative plot experiments, analyses of dynamics in the stable isotope compositions of CO2 and H2O, and chamber gas-exchange measurements. Using past observations from these studies, we deployed model-data assimilation techniques and forecast weather/climate modeling to estimate how the coupling between GPP and Ra is likely to affect future (Year 2100) dynamics in NEE. The amount of winter snow and its melting dynamics in the spring represents the dominant control over interannual variation in GPP. Using the SIPNET ecosystem process model, combined with knowledge about the stable isotope content of different water sources, we estimated that approximately 75% of growing season GPP is coupled to the use of snowmelt water, whereas approximately 25% is coupled to summer rain. The tight coupling between GPP and winter snow pack drives a similar tight coupling between soil respiration (Rs) and winter snow pack. Manipulation of snow pack on forest plots has shown that Rs increases with increased snow pack, and this effect disappears when trees are girdled, which stops the transfer of GPP to roots and the soil rhizosphere. Higher-than-normal winter snowpacks cause the carbon isotope ratios of soil-respired CO2 to be depleted in 13C, reflecting a signal of lower photosynthetic water-use efficiency in the GPP that is transferred to the soil rhizosphere. Large-scale forest disturbance due to catastrophic tree mortality from mountain pine beetle attack causes an initial (2-3 year) reduction in Rs, which is attributable to the loss of GPP and its effect on Ra. This near-term reduction in Rs

  9. Evaluating stomatal ozone fluxes in WRF-Chem: Comparing ozone uptake in Mediterranean ecosystems

    NASA Astrophysics Data System (ADS)

    Rydsaa, J. H.; Stordal, F.; Gerosa, G.; Finco, A.; Hodnebrog, Ø.

    2016-10-01

    The development of modelling tools for estimating stomatal uptake of surface ozone in vegetation is important for the assessment of potential damage induced due to both current and future near surface ozone concentrations. In this study, we investigate the skill in estimating ozone uptake in plants by the Weather Research and Forecasting model coupled with chemistry (WRF-Chem) V3.6.1, with the Wesely dry deposition scheme. To validate the stomatal uptake of ozone, the model simulations were compared with field measurements of three types of Mediterranean vegetation, over seven different periods representing various meteorological conditions. Some systematic biases in modelled ozone fluxes are revealed; the lack of an explicit and time varying dependency on plants' water availability results in overestimated daytime ozone stomatal fluxes particularly in dry periods. The optimal temperature in the temperature response function is likely too low for the woody species tested here. Also, too low nighttime stomatal conductance leads to underestimation of ozone uptake during night. We demonstrate that modelled stomatal ozone flux is improved by accounting for vapor pressure deficit in the ambient air. Based on the results of the overall comparison to measured fluxes, we propose that additional improvements to the stomatal conductance parameterization should be implemented before applying the modelling system for estimating ozone doses and potential damage to vegetation.

  10. On the difference in the net ecosystem exchange of CO2 between deciduous and evergreen forests in the southeastern United States.

    PubMed

    Novick, Kimberly A; Oishi, A Christopher; Ward, Eric J; Siqueira, Mario B S; Juang, Jehn-Yih; Stoy, Paul C

    2015-02-01

    The southeastern United States is experiencing a rapid regional increase in the ratio of pine to deciduous forest ecosystems at the same time it is experiencing changes in climate. This study is focused on exploring how these shifts will affect the carbon sink capacity of southeastern US forests, which we show here are among the strongest carbon sinks in the continental United States. Using eight-year-long eddy covariance records collected above a hardwood deciduous forest (HW) and a pine plantation (PP) co-located in North Carolina, USA, we show that the net ecosystem exchange of CO2 (NEE) was more variable in PP, contributing to variability in the difference in NEE between the two sites (ΔNEE) at a range of timescales, including the interannual timescale. Because the variability in evapotranspiration (ET) was nearly identical across the two sites over a range of timescales, the factors that determined the variability in ΔNEE were dominated by those that tend to decouple NEE from ET. One such factor was water use efficiency, which changed dramatically in response to drought and also tended to increase monotonically in nondrought years (P < 0.001 in PP). Factors that vary over seasonal timescales were strong determinants of the NEE in the HW site; however, seasonality was less important in the PP site, where significant amounts of carbon were assimilated outside of the active season, representing an important advantage of evergreen trees in warm, temperate climates. Additional variability in the fluxes at long-time scales may be attributable to slowly evolving factors, including canopy structure and increases in dormant season air temperature. Taken together, study results suggest that the carbon sink in the southeastern United States may become more variable in the future, owing to a predicted increase in drought frequency and an increase in the fractional cover of southern pines. PMID:25168968

  11. On the difference in the net ecosystem exchange of CO2 between deciduous and evergreen forests in the southeastern United States.

    PubMed

    Novick, Kimberly A; Oishi, A Christopher; Ward, Eric J; Siqueira, Mario B S; Juang, Jehn-Yih; Stoy, Paul C

    2015-02-01

    The southeastern United States is experiencing a rapid regional increase in the ratio of pine to deciduous forest ecosystems at the same time it is experiencing changes in climate. This study is focused on exploring how these shifts will affect the carbon sink capacity of southeastern US forests, which we show here are among the strongest carbon sinks in the continental United States. Using eight-year-long eddy covariance records collected above a hardwood deciduous forest (HW) and a pine plantation (PP) co-located in North Carolina, USA, we show that the net ecosystem exchange of CO2 (NEE) was more variable in PP, contributing to variability in the difference in NEE between the two sites (ΔNEE) at a range of timescales, including the interannual timescale. Because the variability in evapotranspiration (ET) was nearly identical across the two sites over a range of timescales, the factors that determined the variability in ΔNEE were dominated by those that tend to decouple NEE from ET. One such factor was water use efficiency, which changed dramatically in response to drought and also tended to increase monotonically in nondrought years (P < 0.001 in PP). Factors that vary over seasonal timescales were strong determinants of the NEE in the HW site; however, seasonality was less important in the PP site, where significant amounts of carbon were assimilated outside of the active season, representing an important advantage of evergreen trees in warm, temperate climates. Additional variability in the fluxes at long-time scales may be attributable to slowly evolving factors, including canopy structure and increases in dormant season air temperature. Taken together, study results suggest that the carbon sink in the southeastern United States may become more variable in the future, owing to a predicted increase in drought frequency and an increase in the fractional cover of southern pines.

  12. Strong Links Between Teleconnections and Ecosystem Exchange Found at a Pacific Northwest Old-Growth Forest from Flux Tower and MODIS EVI Data

    SciTech Connect

    Wharton, S; Chasmer, L; Falk, M; Paw U, K T

    2009-03-12

    Variability in three Pacific teleconnection patterns are examined to see if net carbon exchange at a low-elevation, old-growth forest is affected by climatic changes associated with these periodicities. Examined are the Pacific Decadal Oscillation (PDO), Pacific/North American Oscillation (PNA) and El Nino-Southern Oscillation (ENSO). We use nine years of eddy covariance CO{sub 2}, H{sub 2}O and energy fluxes measured at the Wind River AmeriFlux site, Washington, USA and eight years of tower-pixel remote sensing data from the Moderate Resolution Imaging Spectroradiometer (MODIS) to address this question. We compute a new Composite Climate Index (CCI) based on the three Pacific Oscillations to divide the measurement period into positive- (2003 and 2005), negative- (1999 and 2000) and neutral-phase climate years (2001, 2002, 2004, 2006 and 2007). The forest transitioned from an annual net carbon sink (NEP = + 217 g C m{sup -2} year{sup -1}, 1999) to a source (NEP = - 100 g C m{sup -2} year{sup -1}, 2003) during two dominant teleconnection patterns. Net ecosystem productivity (NEP), water use efficiency (WUE) and light use efficiency (LUE) were significantly different (P < 0.01) during positive (NEP = -0.27 g C m{sup -2} day{sup -1}, WUE = 4.1 mg C/g H{sub 2}O, LUE = 0.94 g C MJ{sup -1}) and negative (NEP = +0.37 g C m{sup -2} day{sup -1}, WUE = 3.4 mg C/g H{sub 2}O, LUE = 0.83 g C MJ{sup -1}) climate phases. The CCI was linked to variability in the MODIS Enhanced Vegetation Index (EVI) but not to MODIS Fraction of absorbed Photosynthetically Active Radiation (FPAR). EVI was highest during negative climate phases (1999 and 2000) and was positively correlated with NEP and showed potential for using MODIS to estimate teleconnection-driven anomalies in ecosystem CO{sub 2} exchange in old-growth forests. This work suggests that any increase in the strength or frequency of ENSO coinciding with in-phase, low frequency Pacific oscillations (PDO and PNA) will likely increase

  13. Early Season Goose Grazing Has a Greater Effect Than Advancement of the Growing Season on Net Ecosystem Exchange in a Sub-Arctic Coastal Wetland of Western Alaska

    NASA Astrophysics Data System (ADS)

    Leffler, A. J.; Choi, R. T.; Beard, K. H.; Schmutz, J. A.; Welker, J. M.

    2014-12-01

    The wetlands of the Yukon-Kuskokwim Delta in western Alaska are important breeding areas for geese and are experiencing rapid climate change. Growing seasons now begin earlier but geese have not advanced their breeding enough to match the advancement of spring. Consequently, geese enter a greener system that may be less nutritious than in the past because grasses and sedges have highest nutrient density shortly following emergence. One consequence of this changing phenology is that vegetation consumed by geese and returned as feces may have a different carbon to nitrogen ratio than in the past, which may influence net ecosystem exchange (NEE). We examine the effect of the advancement of the growing season and different arrival times by Brant Geese on NEE. Our study consists of six experimental blocks, each with nine plots. Half of the plots are warmed to advance the growing season. Two plots each receive early, mid, and late season grazing; the remaining two plots are not grazed and there is one control plot. In one block, we monitor NEE hourly with an automatic gas exchange system. In the other blocks, survey measurements of NEE and ecosystem respiration (ER) are made periodically with a portable system. Geese remove considerable vegetation from the system and maintain "grazing lawns" <1 cm tall of high quality forage. Plots grazed in the early summer were net sources of C to the atmosphere, releasing ca. 2-4 g m-2 d-1. Non-grazed plots were C sinks of similar magnitude. Grazing had little effect on ER but an advanced growing season enhanced ER in the plots by ca. 0.5 μmol m-2 s-1. We observed a similar advanced growing season effect on NEE that we attribute to enhanced ER. Consequently, the larger influence on NEE in the system is grazing and this influence is through removal of photosynthetic tissue. Grazing by Brant Geese shifts large areas of this coastal wetland to a C source while advanced growing season only reduces the strength of the C sink.

  14. Comparative daily dynamics of mycorrhizal fungal hyphae across differing ecosystems using an automated minirhizotron and sensor network

    NASA Astrophysics Data System (ADS)

    Allen, M. F.

    2013-05-01

    allow us to undertake comparative analyses of soil organisms, such as fungi, on time scale at which the respond to changing weather events and to track individual hyphae to determine turnover, the crucial missing datapoint in carbon modeling. They also tell us that each different ecosystem responds differently, and non-linearly to changes in T and SM, with dramatic shifts in C fluxes. If we are to obtain a mechanistic understanding of global carbon dynamics, we need to understand how soil organisms respond to both fine-scale and coarse scale shifts in different ecosystems.

  15. Hydrogen Exchange Mass Spectrometry of Related Proteins with Divergent Sequences: A Comparative Study of HIV-1 Nef Allelic Variants

    NASA Astrophysics Data System (ADS)

    Wales, Thomas E.; Poe, Jerrod A.; Emert-Sedlak, Lori; Morgan, Christopher R.; Smithgall, Thomas E.; Engen, John R.

    2016-06-01

    Hydrogen exchange mass spectrometry can be used to compare the conformation and dynamics of proteins that are similar in tertiary structure. If relative deuterium levels are measured, differences in sequence, deuterium forward- and back-exchange, peptide retention time, and protease digestion patterns all complicate the data analysis. We illustrate what can be learned from such data sets by analyzing five variants (Consensus G2E, SF2, NL4-3, ELI, and LTNP4) of the HIV-1 Nef protein, both alone and when bound to the human Hck SH3 domain. Regions with similar sequence could be compared between variants. Although much of the hydrogen exchange features were preserved across the five proteins, the kinetics of Nef binding to Hck SH3 were not the same. These observations may be related to biological function, particularly for ELI Nef where we also observed an impaired ability to downregulate CD4 surface presentation. The data illustrate some of the caveats that must be considered for comparison experiments and provide a framework for investigations of other protein relatives, families, and superfamilies with HX MS.

  16. Comparative Calculation of Heat Exchange with the Ground in Residential Building Including Periodes of Heat Waves

    NASA Astrophysics Data System (ADS)

    Staszczuk, Anna; Kuczyński, Tadeusz; Wojciech, Magdalena; Ziembicki, Piotr

    2016-06-01

    The paper provides verification of 3D transient ground-coupled model to calculation of heat exchange between ground and typical one-storey, passive residential building. The model was performed with computer software WUFI®plus and carried out to estimate the indoor air temperatures during extending hot weather periods. For verifying the results of calculations performed by the WUFI®plus software, the most recent version of EnergyPlus software version was used. Comparison analysis of calculation results obtained with the two above mentioned calculation method was made for two scenarios of slab on ground constructions: without thermal insulation and with thermal insulation under the whole slab area. Comprehensive statistical analysis was done including time series analysis and descriptive statistics parameters.

  17. Assessment of Metal Toxicity in Marine Ecosystems: Comparative Toxicity Potentials for Nine Cationic Metals in Coastal Seawater.

    PubMed

    Dong, Yan; Rosenbaum, Ralph K; Hauschild, Michael Z

    2016-01-01

    This study is a first attempt to develop globally applicable and spatially differentiated marine comparative toxicity potentials (CTPs) or ecotoxicity characterization factors for metals in coastal seawater for use in life cycle assessment. The toxicity potentials are based exclusively on marine ecotoxicity data and take account of metal speciation and bioavailability. CTPs were developed for nine cationic metals (Cd, Cr(III), Co, Cu(II), Fe(III), Mn, Ni, Pb, and Zn) in 64 large marine ecosystems (LMEs) covering all coastal waters in the world. The results showed that the CTP of a specific metal varies 3-4 orders of magnitude across LMEs, largely due to different seawater residence times. Therefore, the highest toxicity potential for metals was found in the LMEs with the longest seawater residence times. Across metals, the highest CTPs were observed for Cd, Pb, and Zn. At the concentration levels occurring in coastal seawaters, Fe acts not as a toxic agent but as an essential nutrient and thus has CTPs of zero.

  18. Comparative Genomics Analysis of Streptococcus Isolates from the Human Small Intestine Reveals their Adaptation to a Highly Dynamic Ecosystem

    PubMed Central

    Van den Bogert, Bartholomeus; Boekhorst, Jos; Herrmann, Ruth; Smid, Eddy J.; Zoetendal, Erwin G.; Kleerebezem, Michiel

    2013-01-01

    The human small-intestinal microbiota is characterised by relatively large and dynamic Streptococcus populations. In this study, genome sequences of small-intestinal streptococci from S. mitis, S. bovis, and S. salivarius species-groups were determined and compared with those from 58 Streptococcus strains in public databases. The Streptococcus pangenome consists of 12,403 orthologous groups of which 574 are shared among all sequenced streptococci and are defined as the Streptococcus core genome. Genome mining of the small-intestinal streptococci focused on functions playing an important role in the interaction of these streptococci in the small-intestinal ecosystem, including natural competence and nutrient-transport and metabolism. Analysis of the small-intestinal Streptococcus genomes predicts a high capacity to synthesize amino acids and various vitamins as well as substantial divergence in their carbohydrate transport and metabolic capacities, which is in agreement with observed physiological differences between these Streptococcus strains. Gene-specific PCR-strategies enabled evaluation of conservation of Streptococcus populations in intestinal samples from different human individuals, revealing that the S. salivarius strains were frequently detected in the small-intestine microbiota, supporting the representative value of the genomes provided in this study. Finally, the Streptococcus genomes allow prediction of the effect of dietary substances on Streptococcus population dynamics in the human small-intestine. PMID:24386196

  19. Comparative genomics analysis of Streptococcus isolates from the human small intestine reveals their adaptation to a highly dynamic ecosystem.

    PubMed

    Van den Bogert, Bartholomeus; Boekhorst, Jos; Herrmann, Ruth; Smid, Eddy J; Zoetendal, Erwin G; Kleerebezem, Michiel

    2013-01-01

    The human small-intestinal microbiota is characterised by relatively large and dynamic Streptococcus populations. In this study, genome sequences of small-intestinal streptococci from S. mitis, S. bovis, and S. salivarius species-groups were determined and compared with those from 58 Streptococcus strains in public databases. The Streptococcus pangenome consists of 12,403 orthologous groups of which 574 are shared among all sequenced streptococci and are defined as the Streptococcus core genome. Genome mining of the small-intestinal streptococci focused on functions playing an important role in the interaction of these streptococci in the small-intestinal ecosystem, including natural competence and nutrient-transport and metabolism. Analysis of the small-intestinal Streptococcus genomes predicts a high capacity to synthesize amino acids and various vitamins as well as substantial divergence in their carbohydrate transport and metabolic capacities, which is in agreement with observed physiological differences between these Streptococcus strains. Gene-specific PCR-strategies enabled evaluation of conservation of Streptococcus populations in intestinal samples from different human individuals, revealing that the S. salivarius strains were frequently detected in the small-intestine microbiota, supporting the representative value of the genomes provided in this study. Finally, the Streptococcus genomes allow prediction of the effect of dietary substances on Streptococcus population dynamics in the human small-intestine.

  20. Using a Regional Cluster of AmeriFlux Sites in Central California to Advance Our Knowledge on Decadal-Scale Ecosystem-Atmosphere Carbon Dioxide Exchange

    SciTech Connect

    Baldocchi, Dennis

    2015-03-24

    Continuous eddy convariance measurements of carbon dioxide, water vapor and heat were measured continuously between an oak savanna and an annual grassland in California over a 4 year period. These systems serve as representative sites for biomes in Mediterranean climates and experience much seasonal and inter-annual variability in temperature and precipitation. These sites hence serve as natural laboratories for how whole ecosystem will respond to warmer and drier conditions. The savanna proved to be a moderate sink of carbon, taking up about 150 gC m-2y-1 compared to the annual grassland, which tended to be carbon neutral and often a source during drier years. But this carbon sink by the savanna came at a cost. This ecosystem used about 100 mm more water per year than the grassland. And because the savanna was darker and rougher its air temperature was about 0.5 C warmer. In addition to our flux measurements, we collected vast amounts of ancillary data to interpret the site and fluxes, making this site a key site for model validation and parameterization. Datasets consist of terrestrial and airborne lidar for determining canopy structure, ground penetrating radar data on root distribution, phenology cameras monitoring leaf area index and its seasonality, predawn water potential, soil moisture, stem diameter and physiological capacity of photosynthesis.

  1. The CROSTVOC project - an integrated approach to study the effect of stress on BVOC exchange between agricultural crops and grassland ecosystems and the atmosphere

    NASA Astrophysics Data System (ADS)

    Amelynck, Crist; Heinesch, Bernard; Aubinet, Marc; Bachy, Aurélie; Delaplace, Pierre; Digrado, Anthony; du Jardin, Patrick; Fauconnier, Marie-Laure; Mozaffar, Ahsan; Schoon, Niels

    2015-04-01

    Global changes in atmospheric composition and climate are expected to affect BVOC exchange between terrestrial vegetation and the atmosphere through changes in the drivers of constitutive BVOC emissions and by increases in frequency and intensity of biotic or abiotic stress episodes. Indeed, several studies indicate changes in the emission patterns of constitutive BVOCs and emission of stress-induced BVOCs following heat, drought and oxidative stress, amongst others. Relating changes in BVOC emissions to the occurrence of one or multiple stressors in natural environmental conditions is not straightforward and only few field studies have dealt with it, especially for agricultural crop and grassland ecosystems. The CROSTVOC project aims to contribute in filling this knowledge gap in three ways. Firstly, it aims at performing long-term BVOC emission field measurements from maize (Zea mays L.) and wheat (Triticum aestivum L.), two important crop species on the global scale, and from grassland. This should lead to a better characterization of (mainly oxygenated) BVOC emissions from these understudied ecosystems, allowing a better representation of those emissions in air quality and atmospheric chemistry and transport models. BVOC fluxes are obtained by the Disjunct Eddy Covariance by mass scanning (DEC-MS) technique, using a hs-PTR-MS instrument for BVOC analysis. Secondly, the eddy covariance BVOC flux measurements (especially at the grassland site) will be accompanied by ozone flux, chlorophyll fluorescence, photosynthesis and soil moisture measurements, amongst others, to allow linking alterations in BVOC emissions to stress episodes. Simultaneously, automated dynamic enclosures will be deployed in order to detect specific abiotic and biotic stress markers by PTR-MS and identify them unambiguously by GC-MS. Thirdly, the field measurements will be accompanied by laboratory BVOC flux measurements in an environmental chamber in order to better disentangle the responses

  2. The Grammar of Exchange: A Comparative Study of Reciprocal Constructions Across Languages

    PubMed Central

    Majid, Asifa; Evans, Nicholas; Gaby, Alice; Levinson, Stephen C.

    2010-01-01

    Cultures are built on social exchange. Most languages have dedicated grammatical machinery for expressing this. To demonstrate that statistical methods can also be applied to grammatical meaning, we here ask whether the underlying meanings of these grammatical constructions are based on shared common concepts. To explore this, we designed video stimuli of reciprocated actions (e.g., “giving to each other”) and symmetrical states (e.g., “sitting next to each other”), and with the help of a team of linguists collected responses from 20 languages around the world. Statistical analyses revealed that many languages do, in fact, share a common conceptual core for reciprocal meanings but that this is not a universally expressed concept. The recurrent pattern of conceptual packaging found across languages is compatible with the view that there is a shared non-linguistic understanding of reciprocation. But, nevertheless, there are considerable differences between languages in the exact extensional patterns, highlighting that even in the domain of grammar semantics is highly language-specific. PMID:21713188

  3. A prospective randomized control study comparing classic laryngeal mask airway with Guedel's airway for tracheal tube exchange and smooth extubation

    PubMed Central

    Jain, Shruti; Nazir, Nazia; Khan, Rashid M.; Ahmed, Syed M.

    2016-01-01

    Introduction: Extubation in deep plane of anesthesia followed by Guedel's oropharyngeal airway (OPA™) insertion is a routine method to avoid hemodynamic changes associated with tracheal extubation. Exchange of endotracheal tube (ETT) with Classic laryngeal mask airway (LMA™) prior to emergence from anesthesia also serves similar purpose. We had compared the hemodynamic changes involved during this ETT/LMA™ and ETT/OPA™ exchange technique. Material and Methods: This was a randomized prospective study on ASA I and 2 patients undergoing elective surgery under general anesthesia. These patients were randomly divided into two groups i.e. OPA group and LMA group of 50 patients each. Hemodynamic parameters i.e. systolic blood pressure (SBP) and heart rate (HR) were recorded during exchange of ETT with OPA™ or LMA™. Coughing / bucking during removal of OPA™ and LMA™, and presence of post operative sore throat for both the groups were also graded and recorded. Data within the groups have been analyzed using paired “t” test while those between the groups were analyzed using unpaired “t” test. Chi square test was used to analyze grades of coughing and post operative sore throat. Results: In both groups, hemodynamic parameters rose significantly as OPA™/LMA™ was placed (P < 0.05) and then started declining. Hemodynamic parameters continued to fall in LMA group after extubation. However in OPA group, hemodynamic parameters continued to rise even after extubation and declined only when OPA™ was removed. There was no statistical significant difference between the LMA and OPA group in respect to coughing and post operative sore throat. Conclusion: LMA™ is superior to OPA™ for exchange of ETT as it provides greater hemodynamic stability. PMID:27746550

  4. Spatial and temporal CO2 exchanges measured by Eddy Correlation over a temperate intertidal flat and their relationships to net ecosystem production

    NASA Astrophysics Data System (ADS)

    Polsenaere, P.; Lamaud, E.; Lafon, V.; Bonnefond, J.-M.; Bretel, P.; Delille, B.; Deborde, J.; Loustau, D.; Abril, G.

    2011-06-01

    Measurements of carbon dioxide fluxes were performed over a temperate intertidal mudflat in southwestern France using the micrometeorological Eddy Correlation (EC) technique. EC measurements were carried out in two contrasting sites of the Arcachon lagoon during four periods and in three different seasons (autumn 2007, summer 2008, autumn 2008 and spring 2009). In this paper, spatial and temporal variations in vertical CO2 exchanges at the diurnal, tidal and seasonal scales are presented and discussed. In addition, satellite images of the tidal flat at low tide were used to link the net ecosystem exchange (NEE) with the occupation of the mudflat by primary producers, particularly by Zostera noltii meadows. CO2 fluxes during the four deployments showed important spatial and temporal variations, with the lagoon rapidly shifting from a sink to a source of CO2. CO2 fluxes showed generally low negative (influx) and positive (efflux) values and ranged from -13 to 19 μmol m-2 s-1 at maximum. Low tide and daytime conditions were always characterised by an uptake of atmospheric CO2. In contrast, during immersion and during low tide at night, CO2 fluxes where positive, negative or close to zero, depending on the season and the site. During the autumn of 2007, at the innermost station with a patchy Zostera noltii bed (cover of 22 ± 14 % in the wind direction of measurements), CO2 influx was -1.7 ± 1.7 μmol m-2 s-1 at low tide during the day, and the efflux was 2.7 ± 3.7 μmol m-2 s-1 at low tide during the night. A gross primary production (GPP) of 4.4 μmol m-2 s-1 during emersion could be attributed mostly to microphytobenthic communities. During immersion, the water was a source of CO2 to the atmosphere, suggesting strong heterotrophy or resuspension of microphytobenthic cells. During the summer and autumn of 2008, at the central station with a dense eelgrass bed (92 ± 10 %), CO2 uptakes at low tide during the day were -1.5 ± 1.2 and -0.9 ± 1.7 μmol m-2 s-1

  5. Ecosystem CO2 and CH4 Exchange in a Mixed Tundra and a Fen Within an Arctic Landscape: Modeled Impacts of Climate Change

    NASA Astrophysics Data System (ADS)

    Grant, R. F.

    2015-12-01

    Climate change will have important effects on arctic productivity and greenhouse gas exchange. These changes were projected by the model ecosys under an SRES A2 scenario over the 21st century for a landscape including an upland tundra and a lowland fen at Daring Lake, NWT. Rising temperatures and precipitation caused increases in active layer depths (ALD) and eventual formation of taliks, particularly in the fen, which were attributed to heat advection from warmer and more intense precipitation and downslope flow. These changes raised net primary productivity from more rapid N mineralization and uptake, driven by more rapid heterotrophic respiration and increasing deciduous vs. evergreen plant functional types. Consequently gains in net ecosystem productivity (NEP) of 29 and 10 g C m-2 y-1 were modelled in the tundra and fen after 90 years. However CH4 emissions modelled from the fen rose sharply from direct effects of increasing soil temperatures and greater ALD on fermenter and methanogenic populations, and from indirect effects of increasing sedge growth which hastened transfer of CH4 through porous roots to the atmosphere. After 90 years, landscape CH4 emissions increased from 1.1 to 5.2 g C m-2 y-1 while landscape NEP increased from 34 to 46 g C m-2 y-1. Positive feedback to radiative forcing from increases in CH4 emissions more than offset negative feedback from increases in NEP. This feedback was largely attributed to rises in CH4 emission caused by heat advection from increasing precipitation, the impacts of which require greater attention in arctic climate change studies.

  6. Ecosystem CO2 and CH4 exchange in a mixed tundra and a fen within a hydrologically diverse Arctic landscape: 2. Modeled impacts of climate change

    NASA Astrophysics Data System (ADS)

    Grant, R. F.

    2015-07-01

    Climate change will have important effects on arctic productivity and greenhouse gas exchange. These changes were projected by the model ecosys under an Special Report on Emissions Scenarios (SRES) A2 scenario over the 21st century for a landscape including an upland tundra and a lowland fen at Daring Lake, NWT. Rising temperatures and precipitation caused increases in active layer depths (ALD) and eventual formation of taliks, particularly in the fen, which were attributed to heat advection from warmer and more intense precipitation and downslope flow. These changes raised net primary productivity from more rapid N mineralization and uptake, driven by more rapid heterotrophic respiration and increasing deciduous versus evergreen plant functional types. Consequently, gains in net ecosystem productivity (NEP) of 29 and 10 g C m-2 yr-1 were modeled in the tundra and fen after 90 years. However, CH4 emissions modeled from the fen rose sharply from direct effects of increasing soil temperatures and greater ALD on fermenter and methanogenic populations and from indirect effects of increasing sedge growth, which hastened transfer of CH4 through porous roots to the atmosphere. After 90 years, landscape CH4 emissions increased from 1.1 to 5.2 g C m-2 yr-1 while landscape NEP increased from 34 to 46 g C m-2 yr-1. Positive feedback to radiative forcing from increases in CH4 emissions more than offset negative feedback from increases in NEP. This feedback was largely attributed to rises in CH4 emission caused by heat advection from increasing precipitation, the impacts of which require greater attention in arctic climate change studies.

  7. Ecosystem CO2 and CH4 exchange in a mixed tundra and a fen within a hydrologically diverse Arctic landscape: 1. Modeling versus measurements

    NASA Astrophysics Data System (ADS)

    Grant, R. F.; Humphreys, E. R.; Lafleur, P. M.

    2015-07-01

    CO2 and CH4 exchange are strongly affected by hydrology in landscapes underlain by permafrost. Hypotheses for these effects in the model ecosys were tested by comparing modeled CO2 and CH4 exchange with CO2 fluxes measured by eddy covariance from 2006 to 2009, and with CH4 fluxes measured with surface chambers in 2008, along a topographic gradient at Daring Lake, NWT. In an upland tundra, rises in net CO2 uptake in warmer years were constrained by declines in CO2 influxes when vapor pressure deficits (D) exceeded 1.5 kPa and by rises in CO2 effluxes with greater active layer depth. Consequently, net CO2 uptake rose little with warming. In a lowland fen, CO2 influxes declined less with D and CO2 effluxes rose less with warming, so that rises in net CO2 uptake were greater than those in the tundra. Greater declines in CO2 influxes with warming in the tundra were modeled from greater soil-plant-atmosphere water potential gradients that developed under higher D in drained upland soil, and smaller rises in CO2 effluxes with warming in the fen were modeled from O2 constraints to heterotrophic and belowground autotrophic respiration from a shallow water table in poorly drained lowland soil. CH4 exchange modeled during July and August indicated very small influxes in the tundra and larger effluxes characterized by afternoon emission events caused by degassing of warming soil in the fen. Emissions of CH4 modeled from degassing during soil freezing in October-November contributed about one third of the annual total.

  8. Comparing patterns of ecosystem service consumption and perceptions of range management between ethnic herders in Inner Mongolia and Mongolia

    NASA Astrophysics Data System (ADS)

    Zhen, L.; Ochirbat, B.; Lv, Y.; Wei, Y. J.; Liu, X. L.; Chen, J. Q.; Yao, Z. J.; Li, F.

    2010-01-01

    Ecosystems in the Central Asian Plateau, which includes the Mongolian Plateau, are becoming increasingly sensitive to human interventions, leading to deterioration of already fragile ecosystems. The goal of this paper is to illustrate human dependence on an ecosystem by identifying patterns of resource consumption in this region and investigating the knowledge and perceptions of herders living in these ecosystems. Data on consumption in the two regions were collected using structured questionnaires delivered to a total of 252 herders from Mongolia and China's Inner Mongolia. Meat and other animal products remain the dominant food items for most households, accompanied by various vegetables and cereals. This unbalanced diet leads to excessive consumption of protein and fat from animal sources. The major energy sources used by herders are fuelwood, animal dung, crop residues, and dry grass, but consumption patterns differed between the two areas. Mongolian herders rely more heavily on livestock for meeting their consumption needs than herders in Inner Mongolia. Herder knowledge and perceptions of ecosystem conditions and consumption of resources differed between Mongolia and Inner Mongolia, reflecting the influence of different state policies. The data reported and the conclusions drawn are relevant for developing resource management policies for the Mongolian Plateau, but also provide useful insights for any region where livestock production dominates the use of rangeland resources.

  9. Spatial and temporal CO2 exchanges measured by Eddy Covariance over a temperate intertidal flat and their relationships to net ecosystem production

    NASA Astrophysics Data System (ADS)

    Polsenaere, P.; Lamaud, E.; Lafon, V.; Bonnefond, J.-M.; Bretel, P.; Delille, B.; Deborde, J.; Loustau, D.; Abril, G.

    2012-01-01

    Measurements of carbon dioxide fluxes were performed over a temperate intertidal mudflat in southwestern France using the micrometeorological Eddy Covariance (EC) technique. EC measurements were carried out in two contrasting sites of the Arcachon flat during four periods and in three different seasons (autumn 2007, summer 2008, autumn 2008 and spring 2009). In addition, satellite images of the tidal flat at low tide were used to link the net ecosystem CO2 exchange (NEE) with the occupation of the mudflat by primary producers, particularly by Zostera noltii meadows. CO2 fluxes during the four deployments showed important spatial and temporal variations, with the flat rapidly shifting from sink to source with the tide. Absolute CO2 fluxes showed generally small negative (influx) and positive (efflux) values, with larger values up to -13 μmol m-2 s-1 for influxes and 19 μmol m-2 s-1 for effluxes. Low tide during the day was mostly associated with a net uptake of atmospheric CO2. In contrast, during immersion and during low tide at night, CO2 fluxes where positive, negative or close to zero, depending on the season and the site. During the autumn of 2007, at the innermost station with a patchy Zostera noltii bed (cover of 22 ± 14% in the wind direction of measurements), CO2 influx was -1.7 ± 1.7 μmol m-2 s-1 at low tide during the day, and the efflux was 2.7 ± 3.7 μmol m-2 s-1 at low tide during the night. A gross primary production (GPP) of 4.4 ± 4.1 μmol m-2 s-1 during emersion could be attributed to microphytobenthic communities. During the summer and autumn of 2008, at the central station with a dense eelgrass bed (92 ± 10%), CO2 uptakes at low tide during the day were -1.5 ± 1.2 and -0.9 ± 1.7 μmol m-2 s-1, respectively. Night time effluxes of CO2 were 1.0 ± 0.9 and 0.2 ± 1.1 μmol m-2 s-1 in summer and autumn, respectively, resulting in a GPP during emersion of 2.5 ± 1.5 and 1.1 ± 2.0 μmol m-2 s-1, respectively, attributed primarily to the

  10. Do inverse ecosystem models accurately reconstruct plankton trophic flows? Comparing two solution methods using field data from the California Current

    NASA Astrophysics Data System (ADS)

    Stukel, Michael R.; Landry, Michael R.; Ohman, Mark D.; Goericke, Ralf; Samo, Ty; Benitez-Nelson, Claudia R.

    2012-03-01

    Despite the increasing use of linear inverse modeling techniques to elucidate fluxes in undersampled marine ecosystems, the accuracy with which they estimate food web flows has not been resolved. New Markov Chain Monte Carlo (MCMC) solution methods have also called into question the biases of the commonly used L2 minimum norm (L 2MN) solution technique. Here, we test the abilities of MCMC and L 2MN methods to recover field-measured ecosystem rates that are sequentially excluded from the model input. For data, we use experimental measurements from process cruises of the California Current Ecosystem (CCE-LTER) Program that include rate estimates of phytoplankton and bacterial production, micro- and mesozooplankton grazing, and carbon export from eight study sites varying from rich coastal upwelling to offshore oligotrophic conditions. Both the MCMC and L 2MN methods predicted well-constrained rates of protozoan and mesozooplankton grazing with reasonable accuracy, but the MCMC method overestimated primary production. The MCMC method more accurately predicted the poorly constrained rate of vertical carbon export than the L 2MN method, which consistently overestimated export. Results involving DOC and bacterial production were equivocal. Overall, when primary production is provided as model input, the MCMC method gives a robust depiction of ecosystem processes. Uncertainty in inverse ecosystem models is large and arises primarily from solution under-determinacy. We thus suggest that experimental programs focusing on food web fluxes expand the range of experimental measurements to include the nature and fate of detrital pools, which play large roles in the model.

  11. Trace metal biogeochemistry in mangrove ecosystems: a comparative assessment of acidified (by acid sulfate soils) and non-acidified sites.

    PubMed

    Nath, Bibhash; Birch, Gavin; Chaudhuri, Punarbasu

    2013-10-01

    The generation of acidity and subsequent mobilization of toxic metals induced by acid sulfate soils (ASSs) are known to cause severe environmental damage to many coastal wetlands and estuaries of Australia and worldwide. Mangrove ecosystems serve to protect coastal environments, but are increasingly threatened from such ASS-induced acidification due to variable hydrological conditions (i.e., inundation-desiccation cycles). However, the impact of such behaviors on trace metal distribution, bio-availability and accumulation in mangrove tissues, i.e., leaves and pneumatophores, are largely unknown. In this study, we examined how ASS-induced acidifications controlled trace metal distribution and bio-availability in gray mangrove (Avicennia marina) soils and in tissues in the Kooragang wetland, New South Wales, Australia. We collected mangrove soils, leaves and pneumatophores from a part of the wetland acidified from ASS (i.e., an affected site) for detailed biogeochemical studies. The results were compared with samples collected from a natural intertidal mangrove forest (i.e., a control site) located within the same wetland. Soil pH (mean: 5.90) indicated acidic conditions in the affected site, whereas pH was near-neutral (mean: 7.17) in the control site. The results did not show statistically significant differences in near-total and bio-available metal concentrations, except for Fe and Mn, between affected and control sites. Iron concentrations were significantly (p values≤0.001) greater in the affected site, whereas Mn concentrations were significantly (p values≤0.001) greater in the control site. However, large proportions of near-total metals were potentially bio-available in control sites. Concentrations of Fe and Ni were significantly (p values≤0.001) greater in leaves and pneumatophores of the affected sites, whereas Mn, Cu, Pb and Zn were greater in control sites. The degree of metal bio-accumulation in leaves and pneumatophores suggest contrasting

  12. Trace metal biogeochemistry in mangrove ecosystems: a comparative assessment of acidified (by acid sulfate soils) and non-acidified sites.

    PubMed

    Nath, Bibhash; Birch, Gavin; Chaudhuri, Punarbasu

    2013-10-01

    The generation of acidity and subsequent mobilization of toxic metals induced by acid sulfate soils (ASSs) are known to cause severe environmental damage to many coastal wetlands and estuaries of Australia and worldwide. Mangrove ecosystems serve to protect coastal environments, but are increasingly threatened from such ASS-induced acidification due to variable hydrological conditions (i.e., inundation-desiccation cycles). However, the impact of such behaviors on trace metal distribution, bio-availability and accumulation in mangrove tissues, i.e., leaves and pneumatophores, are largely unknown. In this study, we examined how ASS-induced acidifications controlled trace metal distribution and bio-availability in gray mangrove (Avicennia marina) soils and in tissues in the Kooragang wetland, New South Wales, Australia. We collected mangrove soils, leaves and pneumatophores from a part of the wetland acidified from ASS (i.e., an affected site) for detailed biogeochemical studies. The results were compared with samples collected from a natural intertidal mangrove forest (i.e., a control site) located within the same wetland. Soil pH (mean: 5.90) indicated acidic conditions in the affected site, whereas pH was near-neutral (mean: 7.17) in the control site. The results did not show statistically significant differences in near-total and bio-available metal concentrations, except for Fe and Mn, between affected and control sites. Iron concentrations were significantly (p values≤0.001) greater in the affected site, whereas Mn concentrations were significantly (p values≤0.001) greater in the control site. However, large proportions of near-total metals were potentially bio-available in control sites. Concentrations of Fe and Ni were significantly (p values≤0.001) greater in leaves and pneumatophores of the affected sites, whereas Mn, Cu, Pb and Zn were greater in control sites. The degree of metal bio-accumulation in leaves and pneumatophores suggest contrasting

  13. Comparative analysis and validation of remotely sensed estimation of actual evapotranspiration in cotton ecosystems of Middle Asia

    NASA Astrophysics Data System (ADS)

    Knoefel, P.; Falk, U.; Conrad, C.; Dech, S.

    2012-04-01

    Detailed knowledge of land surface fluxes, especially latent and sensible components, is important for monitoring the climate and land surface, and for agriculture applications such as irrigation scheduling and water management. Accurate estimation of evapotranspiration (ET) plays an important role in quantification of the water balance at the watershed, basin, and regional scale for better planning and managing water resources. The growing interest in quantifying regional actual ET for water resource and irrigation management led to the development of numerous methods to estimate ET from remote sensing data. The objective of this study was to compare the performance of the established surface energy balance algorithm for land (SEBAL) approach for estimating the energy balance using input data with different temporal and spatial resolution (Landsat/MODIS). Input data to the model are basically surface reflectance, land use classification and meteorological data of the years 2009 and 2010. The study is primarily concerned with the irrigation farming of cotton ecosystems in Middle Asia, in particular with the situation within Khorezm Oblast in Uzbekistan. Regional problems of Khorezm Oblast are e.g. high groundwater levels, soil salinity, and non sustainable use of land and water. Cotton is the major crop in Khorezm region. About 46% of the agricultural area was covered with cotton in 2009 and 2010, among the other main crops winter wheat (30%) and rice (5%). Due to the low level of precipitation (<100 mm p.a.) irrigation is the only available water source for the crops. The water for irrigation is taken from the Amu Darya River and then canalled to the agricultural fields. The available water in Khorezm depends on the water demand in the upstream regions. Because of this variation and the historical annual shortage of available irrigation water a sustainable use of water is highly important for the regional water management in Khorezm. Input parameters and

  14. Comparing Tehran STOCK Exchange as AN Emerging Market with a Mature Market by Random Matrix Approach

    NASA Astrophysics Data System (ADS)

    Namaki, A.; Raei, R.; Jafari, G. R.

    We analyze cross-correlation between return fluctuations of stocks of an emerging market by using random matrix theory (RMT). We test the statistics of eigenvalues of cross-correlation (C) between stocks of the Tehran Price Index (TEPIX) as an emerging market and compare these with a mature market (US market). According to the "null hypothesis," a random correlation matrix constructed from mutually uncorrelated time series, the deviation from the Gaussian orthogonal ensemble of RTM is a good criterion. We find that a majority of the eigenvalues of C fall within the bulk (RMT bounds between λ+ and λ-) for the eigenvalues of the random correlation matrices. Further, we find that the distribution of eigenvector components for the eigenvectors corresponding to the largest deviating eigenvalues, display systematic deviations from the RMT prediction. Analyzing the components of the deviating eigenvectors by Inverse Participation Ratio, leads us to know that the largest eigenvalue corresponds to an influence common to the whole market. Our analysis of the other deviating eigenvectors shows distinct industries, whose identities corresponds to the structure of the Iran business environment.

  15. Strong cation exchange chiral stationary phase--a comparative study in high-performance liquid chromatography and subcritical fluid chromatography.

    PubMed

    Wolrab, Denise; Macíková, Pavla; Boras, Mario; Kohout, Michal; Lindner, Wolfgang

    2013-11-22

    The performance of a strong cation exchange-type (SCX) chiral stationary phase (CSP) was evaluated with subcritical fluid chromatography (subFC) and high performance liquid chromatography (HPLC). The chromatographic conditions in subFC were optimized by changing the amount of polar organic modifier, concentration of a basic additive in the modifier, system pressure and temperature. In this way the concentration of in situ formed transient ionic species could be varied. The gradual change of the concentration of the transient buffer, i.e. gradient elution conditions in subFC, was found beneficial for separation of a mixture of racemic compounds. The strength and amount of the in situ formed buffer was estimated on the basis of comparative experiments in subSFC and HPLC.

  16. Comparative study of glycated hemoglobin by ion exchange chromatography and affinity binding nycocard reader in type 2 diabetes mellitus.

    PubMed

    Gautam, N; Dubey, R K; Jayan, A; Nepaune, Y; Padmavathi, P; Chaudhary, S; Jha, S K; Sinha, A K

    2014-12-01

    The aim of this study was to compare the level of glycated hemoglobin (HbA1c) in type 2 Diabetes Mellitus (DM) patients by two different methods namely Ion Exchange Chromatography and Affinity Binding Nycocard Reader. This is a cross-sectional study conducted on confirmed type 2 diabetes mellitus patients (n = 100) who visited Out Patients Department of the Universal College of Medical Sciences Teaching hospital, Bhairahawa, Nepal from November 2012 to March 2013. The diagnosis of diabetes mellitus was done on the basis of their fasting (164.46 ± 45.33 mg/dl) and random (187.93 ± 78.02 mg/dl) serum glucose level along with clinical history highly suggestive of type 2 DM. The HbA1c values of (7.8 ± 1.9%) and (8.0 ± 2.2%) were found in DM patients as estimated by those two different methods respectively. The highest frequency was observed in HbA1c > 8.0% indicating maximum cases were under very poor glycemic control. However, there were no significant differences observed in HbA1c value showing both methods are comparable in nature and can be used in lab for ease of estimation. The significant raised in HbA1c indicates complications associated with DM and monitoring of therapy become hard for those patients. Despite having standard reference method for HbA1c determination, the availability of report at the time of the patient visit can be made easy by using Nycocard Reader and Ion Exchange Chromatography techniques without any delay in communicating glycemic control, clinical decision-making and changes in treatment regimen.

  17. Coupled cryoconite ecosystem structure-function relationships are revealed by comparing bacterial communities in alpine and Arctic glaciers.

    PubMed

    Edwards, Arwyn; Mur, Luis A J; Girdwood, Susan E; Anesio, Alexandre M; Stibal, Marek; Rassner, Sara M E; Hell, Katherina; Pachebat, Justin A; Post, Barbara; Bussell, Jennifer S; Cameron, Simon J S; Griffith, Gareth Wyn; Hodson, Andrew J; Sattler, Birgit

    2014-08-01

    Cryoconite holes are known as foci of microbial diversity and activity on polar glacier surfaces, but are virtually unexplored microbial habitats in alpine regions. In addition, whether cryoconite community structure reflects ecosystem functionality is poorly understood. Terminal restriction fragment length polymorphism and Fourier transform infrared metabolite fingerprinting of cryoconite from glaciers in Austria, Greenland and Svalbard demonstrated cryoconite bacterial communities are closely correlated with cognate metabolite fingerprints. The influence of bacterial-associated fatty acids and polysaccharides was inferred, underlining the importance of bacterial community structure in the properties of cryoconite. Thus, combined application of T-RFLP and FT-IR metabolite fingerprinting promises high throughput, and hence, rapid assessment of community structure-function relationships. Pyrosequencing revealed Proteobacteria were particularly abundant, with Cyanobacteria likely acting as ecosystem engineers in both alpine and Arctic cryoconite communities. However, despite these generalities, significant differences in bacterial community structures, compositions and metabolomes are found between alpine and Arctic cryoconite habitats, reflecting the impact of local and regional conditions on the challenges of thriving in glacial ecosystems.

  18. Comparing projections of future changes in runoff and water resources from hydrological and ecosystem models in ISI-MIP

    NASA Astrophysics Data System (ADS)

    Davie, J. C. S.; Falloon, P. D.; Kahana, R.; Dankers, R.; Betts, R.; Portmann, F. T.; Clark, D. B.; Itoh, A.; Masaki, Y.; Nishina, K.; Fekete, B.; Tessler, Z.; Liu, X.; Tang, Q.; Hagemann, S.; Stacke, T.; Pavlick, R.; Schaphoff, S.; Gosling, S. N.; Franssen, W.; Arnell, N.

    2013-02-01

    Projections of future changes in runoff can have important implications for water resources and flooding. In this study, runoff projections from ISI-MIP (Inter-sectoral Impact Model Intercomparison Project) simulations forced with HadGEM2-ES bias-corrected climate data under the Representative Concentration Pathway 8.5 have been analysed. Projections of change from the baseline period (1981-2010) to the future (2070-2099) from a number of different ecosystems and hydrological models were studied. The differences between projections from the two types of model were looked at globally and regionally. Typically, across different regions the ecosystem models tended to project larger increases and smaller decreases in runoff than the hydrological models. However, the differences varied both regionally and seasonally. Sensitivity experiments were also used to investigate the contributions of varying CO2 and allowing vegetation distribution to evolve on projected changes in runoff. In two out of four models which had data available from CO2 sensitivity experiments, allowing CO2 to vary was found to increase runoff more than keeping CO2 constant, while in two models runoff decreased. This suggests more uncertainty in runoff responses to elevated CO2 than previously considered. As CO2 effects on evapotranspiration via stomatal conductance and leaf-area index are more commonly included in ecosystems models than in hydrological models, this may partially explain some of the difference between model types. Keeping the vegetation distribution static in JULES runs had much less effect on runoff projections than varying CO2, but this may be more pronounced if looked at over a longer timescale as vegetation changes may take longer to reach a new state.

  19. Northern Watershed Ecosystem Response to Climate Change (North-Watch) - Towards a comparative ecohydrology of northern catchments.

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

    In few places will the changes and challenges associated with climatic change be greater than in the circumpolar mid-high latitudes of the northern hemisphere. Slight temperature differences determine whether precipitation falls as rain or snow, and the degree to which winter snow packs accumulate and the rate at which they subsequently melt. This has implications for stream flow regimes, water quality and in-stream hydroecology. The Northern Watershed Ecosystem Response to Climate Change (North-Watch) programme is an international interdisciplinary inter-site comparison project spanning a transect of hydro-climatic zones in Scotland, the USA, Canada and Scandinavia. The overall aim is to better understand the integrated consequences of climate change on the physical, chemical and biological characteristics of water resources across northern regions. Here, we present initial findings from these analyses. The way in which hydroclimatic drivers interact with catchment characteristics are examined to show how the synchroneity, resistance and resilience of input-output responses varies spatially and temporally across sites. The dominant influence is the nature of the snowmelt period and how strongly this influences the hydrological regime. Linked to this is the variable nature of the threshold response of input - streamflow dynamics and how this changes for rainfall and snowmelt events. The ways in which these hydrological controls regulate Carbon fluxes from different catchments are also explored, and the implications for in-stream ecosystem response assessed. As the hydroclimatic drivers influencing the catchments are changing in a warming climate, vegetation and soil are also likely to change. This in turn will affect patterns of partitioning, storage and release of water with associated changes in streamflow dynamics. Budyko Curves are used to examine the current differences between the North-Watch catchments in terms of water and energy limitations, and likely

  20. [Energy and mass transfer and the productivity of the main ecosystems of Siberia (according to the results of measurements by the method of turbulent pulsations). 2. Carbon exchange and productivity].

    PubMed

    Chebakova, N M; Vygodskaia, N N; Arnet, A; Belelli Markezini, L; Kurbatova, Iu A; Parfenova, E I; Valentini, R; Verkhovets, S V; Vaganov, E A; Schulze, E - D

    2014-01-01

    Using direct measurements of CO2 fluxes by the method of turbulent pulsations, it was shown that the studied middle-taiga pine forest, raised bog, true steppe, and southern tundra along the Yenisei meridian (approximately 90 degrees E) are stocks of carbon of different capacity in the annual output. The tundra starts to function as a stock of carbon from June; the forest and bog, from May; and the steppe, from the end of April. In the transitional seasons and winter, the ecosystems are a weak source of carbon: the tundra already in September; the forest and bog, from October; and the steppe, from November. The photosynthetic productivity of the forest and steppe ecosys- tems (480-530 g C/(m x year) exceeds 2-2.5 times the productivity ofbogs and tundras (200-220 g C/(m x year). The relationships between the thermal balance structure and CO2 exchange are shown. Possible feedbacks between the carbon exchange between the ecosystems and the atmosphere as a result of climate warming in the region are assessed.

  1. An assessment of the trophic structure of the Bay of Biscay continental shelf food web: Comparing estimates derived from an ecosystem model and isotopic data

    NASA Astrophysics Data System (ADS)

    Lassalle, G.; Chouvelon, T.; Bustamante, P.; Niquil, N.

    2014-01-01

    Comparing outputs of ecosystem models with estimates derived from experimental and observational approaches is important in creating valuable feedback for model construction, analyses and validation. Stable isotopes and mass-balanced trophic models are well-known and widely used as approximations to describe the structure of food webs, but their consistency has not been properly established as attempts to compare these methods remain scarce. Model construction is a data-consuming step, meaning independent sets for validation are rare. Trophic linkages in the French continental shelf of the Bay of Biscay food webs were recently investigated using both methodologies. Trophic levels for mono-specific compartments representing small pelagic fish and marine mammals and multi-species functional groups corresponding to demersal fish and cephalopods, derived from modelling, were compared with trophic levels calculated from independent carbon and nitrogen isotope ratios. Estimates of the trophic niche width of those species, or groups of species, were compared between these two approaches as well. A significant and close-to-one positive (rSpearman2 = 0.72 , n = 16, p < 0.0001) correlation was found between trophic levels estimated by Ecopath modelling and those derived from isotopic signatures. Differences between estimates were particularly low for mono-specific compartments. No clear relationship existed between indices of trophic niche width derived from both methods. Given the wide recognition of trophic levels as a useful concept in ecosystem-based fisheries management, propositions were made to further combine these two approaches.

  2. Comparing the Influence of Wildfire and Prescribed Burns on Watershed Nitrogen Biogeochemistry Using 15N Natural Abundance in Terrestrial and Aquatic Ecosystem Components

    PubMed Central

    Stephan, Kirsten; Kavanagh, Kathleen L.; Koyama, Akihiro

    2015-01-01

    We evaluated differences in the effects of three low-severity spring prescribed burns and four wildfires on nitrogen (N) biogeochemistry in Rocky Mountain headwater watersheds. We compared paired (burned/unburned) watersheds of four wildfires and three spring prescribed burns for three growing seasons post-fire. To better understand fire effects on the entire watershed ecosystem, we measured N concentrations and δ15N in both the terrestrial and aquatic ecosystems components, i.e., soil, understory plants in upland and riparian areas, streamwater, and in-stream moss. In addition, we measured nitrate reductase activity in foliage of Spiraea betulifolia, a dominant understory species. We found increases of δ15N and N concentrations in both terrestrial and aquatic ecosystem N pools after wildfire, but responses were limited to terrestrial N pools after prescribed burns indicating that N transfer from terrestrial to aquatic ecosystem components did not occur in low-severity prescribed burns. Foliar δ15N differed between wildfire and prescribed burn sites; the δ15N of foliage of upland plants was enriched by 2.9 ‰ (difference between burned and unburned watersheds) in the first two years after wildfire, but only 1.3 ‰ after prescribed burns. In-stream moss δ15N in wildfire-burned watersheds was enriched by 1.3 ‰, but there was no response by moss in prescription-burned watersheds, mirroring patterns of streamwater nitrate concentrations. S. betulifolia showed significantly higher nitrate reductase activity two years after wildfires relative to corresponding unburned watersheds, but no such difference was found after prescribed burns. These responses are consistent with less altered N biogeochemistry after prescribed burns relative to wildfire. We concluded that δ15N values in terrestrial and aquatic plants and streamwater nitrate concentrations after fire can be useful indicators of the magnitude and duration of fire effects and the fate of post

  3. Comparing the influence of wildfire and prescribed burns on watershed nitrogen biogeochemistry using 15N natural abundance in terrestrial and aquatic ecosystem components.

    PubMed

    Stephan, Kirsten; Kavanagh, Kathleen L; Koyama, Akihiro

    2015-01-01

    We evaluated differences in the effects of three low-severity spring prescribed burns and four wildfires on nitrogen (N) biogeochemistry in Rocky Mountain headwater watersheds. We compared paired (burned/unburned) watersheds of four wildfires and three spring prescribed burns for three growing seasons post-fire. To better understand fire effects on the entire watershed ecosystem, we measured N concentrations and δ15N in both the terrestrial and aquatic ecosystems components, i.e., soil, understory plants in upland and riparian areas, streamwater, and in-stream moss. In addition, we measured nitrate reductase activity in foliage of Spiraea betulifolia, a dominant understory species. We found increases of δ15N and N concentrations in both terrestrial and aquatic ecosystem N pools after wildfire, but responses were limited to terrestrial N pools after prescribed burns indicating that N transfer from terrestrial to aquatic ecosystem components did not occur in low-severity prescribed burns. Foliar δ15N differed between wildfire and prescribed burn sites; the δ15N of foliage of upland plants was enriched by 2.9 ‰ (difference between burned and unburned watersheds) in the first two years after wildfire, but only 1.3 ‰ after prescribed burns. In-stream moss δ15N in wildfire-burned watersheds was enriched by 1.3 ‰, but there was no response by moss in prescription-burned watersheds, mirroring patterns of streamwater nitrate concentrations. S. betulifolia showed significantly higher nitrate reductase activity two years after wildfires relative to corresponding unburned watersheds, but no such difference was found after prescribed burns. These responses are consistent with less altered N biogeochemistry after prescribed burns relative to wildfire. We concluded that δ15N values in terrestrial and aquatic plants and streamwater nitrate concentrations after fire can be useful indicators of the magnitude and duration of fire effects and the fate of post

  4. Comparing the influence of wildfire and prescribed burns on watershed nitrogen biogeochemistry using 15N natural abundance in terrestrial and aquatic ecosystem components.

    PubMed

    Stephan, Kirsten; Kavanagh, Kathleen L; Koyama, Akihiro

    2015-01-01

    We evaluated differences in the effects of three low-severity spring prescribed burns and four wildfires on nitrogen (N) biogeochemistry in Rocky Mountain headwater watersheds. We compared paired (burned/unburned) watersheds of four wildfires and three spring prescribed burns for three growing seasons post-fire. To better understand fire effects on the entire watershed ecosystem, we measured N concentrations and δ15N in both the terrestrial and aquatic ecosystems components, i.e., soil, understory plants in upland and riparian areas, streamwater, and in-stream moss. In addition, we measured nitrate reductase activity in foliage of Spiraea betulifolia, a dominant understory species. We found increases of δ15N and N concentrations in both terrestrial and aquatic ecosystem N pools after wildfire, but responses were limited to terrestrial N pools after prescribed burns indicating that N transfer from terrestrial to aquatic ecosystem components did not occur in low-severity prescribed burns. Foliar δ15N differed between wildfire and prescribed burn sites; the δ15N of foliage of upland plants was enriched by 2.9 ‰ (difference between burned and unburned watersheds) in the first two years after wildfire, but only 1.3 ‰ after prescribed burns. In-stream moss δ15N in wildfire-burned watersheds was enriched by 1.3 ‰, but there was no response by moss in prescription-burned watersheds, mirroring patterns of streamwater nitrate concentrations. S. betulifolia showed significantly higher nitrate reductase activity two years after wildfires relative to corresponding unburned watersheds, but no such difference was found after prescribed burns. These responses are consistent with less altered N biogeochemistry after prescribed burns relative to wildfire. We concluded that δ15N values in terrestrial and aquatic plants and streamwater nitrate concentrations after fire can be useful indicators of the magnitude and duration of fire effects and the fate of post

  5. Water use and carbon exchange of red oak- and eastern hemlock-dominated forests in the northeastern USA: implications for ecosystem-level effects of hemlock woolly adelgid.

    PubMed

    Hadley, Julian L; Kuzeja, Paul S; Daley, Michael J; Phillips, Nathan G; Mulcahy, Thomas; Singh, Safina

    2008-04-01

    Water use and carbon exchange of a red oak-dominated (Quercus rubra L.) forest and an eastern hemlock-dominated (Tsuga canadensis L.) forest, each located within the Harvard Forest in north-central Massachusetts, were measured for 2 years by the eddy flux method. Water use by the red oak forest reached 4 mm day(-1), compared to a maximum of 2 mm day(-1) by the eastern hemlock forest. Maximal carbon (C) uptake rate was also higher in the red oak forest than in the eastern hemlock forest (about 25 versus 15 micromol m(-2) s(-1)). Sap flux measurements indicated that transpiration of red oak, and also of black birch (Betula lenta L.), which frequently replaces eastern hemlock killed by hemlock woolly adelgid (Adelges tsugae Annand.), were almost twice that of eastern hemlock. Despite the difference between species in maximum summertime C assimilation rate, annual C storage of the eastern hemlock forest almost equaled that of the red oak forest because of net C uptake by eastern hemlock during unusually warm fall and spring weather, and a near-zero C balance during the winter. Thus, the effect on C storage of replacing eastern hemlock forest with a forest dominated by deciduous species is unclear. Carbon storage by eastern hemlock forests during fall, winter and spring is likely to increase in the event of climate warming, although this may be offset by C loss during hotter summers. Our results indicate that, although forest water use will decrease immediately following eastern hemlock mortality due to the hemlock woolly adelgid, the replacement of eastern hemlock by deciduous species such as red oak will likely increase summertime water use over current rates in areas where hemlock is a major forest species.

  6. Comparative analysis of crossover exchanges and chiasmata in Allium cepa x fistulosum after genomic in situ hybridization (GISH).

    PubMed

    Stevenson, M; Armstrong, S J; Ford-Lloyd, B V; Jones, G H

    1998-11-01

    Genomic in situ hybridization (GISH) successfully differentiated homoeologous genomes in the inter-specific hybrid Allium cepa x fistulosum, thus allowing the detection of reciprocal crossover events as label exchanges in separating anaphase I chromosomes. Three of the eight chromosome pairs were positively identified by fluorescence in situ hybridization (FISH) to rDNA sequences. There was a general similarity of the GISH-based label exchange frequencies and metaphase I chiasma frequencies, but with a 20% deficit of chiasmata. Reasons for this apparent deficit are discussed. The locations of chiasmata and label exchanges are in broad agreement. PMID:9886776

  7. Climatic influences on net ecosystem CO2 exchange during the transition from wintertime carbon source to springtime carbon sink in a high-elevation, subalpine forest.

    PubMed

    Monson, Russell K; Sparks, Jed P; Rosenstiel, Todd N; Scott-Denton, Laura E; Huxman, Travis E; Harley, Peter C; Turnipseed, Andrew A; Burns, Sean P; Backlund, Brant; Hu, Jia

    2005-11-01

    The transition between wintertime net carbon loss and springtime net carbon assimilation has an important role in controlling the annual rate of carbon uptake in coniferous forest ecosystems. We studied the contributions of springtime carbon assimilation to the total annual rate of carbon uptake and the processes involved in the winter-to-spring transition across a range of scales from ecosystem CO2 fluxes to chloroplast photochemistry in a coniferous, subalpine forest. We observed numerous initiations and reversals in the recovery of photosynthetic CO2 uptake during the initial phase of springtime recovery in response to the passage of alternating warm- and cold-weather systems. Full recovery of ecosystem carbon uptake, whereby the 24-h cumulative sum of NEE (NEEdaily) was consistently negative, did not occur until 3-4 weeks after the first signs of photosynthetic recovery. A key event that preceded full recovery was the occurrence of isothermality in the vertical profile of snow temperature across the snow pack; thus, providing consistent daytime percolation of melted snow water through the snow pack. Interannual variation in the cumulative annual NEE (NEEannual) was mostly explained by variation in NEE during the snow-melt period (NEEsnow-melt), not variation in NEE during the snow-free part of the growing season (NEEsnow-free). NEEsnow-melt was highest in those years when the snow melt occurred later in the spring, leading us to conclude that in this ecosystem, years with earlier springs are characterized by lower rates of NEEannual, a conclusion that contrasts with those from past studies in deciduous forest ecosystems. Using studies on isolated branches we showed that the recovery of photosynthesis occurred through a series of coordinated physiological and biochemical events. Increasing air temperatures initiated recovery through the upregulation of PSII electron transport caused in part by disengagement of thermal energy dissipation by the carotenoid

  8. Climatic influences on net ecosystem CO2 exchange during the transition from wintertime carbon source to springtime carbon sink in a high-elevation, subalpine forest.

    PubMed

    Monson, Russell K; Sparks, Jed P; Rosenstiel, Todd N; Scott-Denton, Laura E; Huxman, Travis E; Harley, Peter C; Turnipseed, Andrew A; Burns, Sean P; Backlund, Brant; Hu, Jia

    2005-11-01

    The transition between wintertime net carbon loss and springtime net carbon assimilation has an important role in controlling the annual rate of carbon uptake in coniferous forest ecosystems. We studied the contributions of springtime carbon assimilation to the total annual rate of carbon uptake and the processes involved in the winter-to-spring transition across a range of scales from ecosystem CO2 fluxes to chloroplast photochemistry in a coniferous, subalpine forest. We observed numerous initiations and reversals in the recovery of photosynthetic CO2 uptake during the initial phase of springtime recovery in response to the passage of alternating warm- and cold-weather systems. Full recovery of ecosystem carbon uptake, whereby the 24-h cumulative sum of NEE (NEEdaily) was consistently negative, did not occur until 3-4 weeks after the first signs of photosynthetic recovery. A key event that preceded full recovery was the occurrence of isothermality in the vertical profile of snow temperature across the snow pack; thus, providing consistent daytime percolation of melted snow water through the snow pack. Interannual variation in the cumulative annual NEE (NEEannual) was mostly explained by variation in NEE during the snow-melt period (NEEsnow-melt), not variation in NEE during the snow-free part of the growing season (NEEsnow-free). NEEsnow-melt was highest in those years when the snow melt occurred later in the spring, leading us to conclude that in this ecosystem, years with earlier springs are characterized by lower rates of NEEannual, a conclusion that contrasts with those from past studies in deciduous forest ecosystems. Using studies on isolated branches we showed that the recovery of photosynthesis occurred through a series of coordinated physiological and biochemical events. Increasing air temperatures initiated recovery through the upregulation of PSII electron transport caused in part by disengagement of thermal energy dissipation by the carotenoid

  9. Cost-effectiveness of heat and moisture exchangers compared to usual care for pulmonary rehabilitation after total laryngectomy in Poland.

    PubMed

    Retèl, Valesca P; van den Boer, Cindy; Steuten, Lotte M G; Okła, Sławomir; Hilgers, Frans J; van den Brekel, Michiel W

    2015-09-01

    The beneficial physical and psychosocial effects of heat and moisture exchangers (HMEs) for pulmonary rehabilitation of laryngectomy patients are well evidenced. However, cost-effectiveness in terms of costs per additional quality-adjusted life years (QALYs) has not yet been investigated. Therefore, a model-based cost-effectiveness analysis of using HMEs versus usual care (UC) (including stoma covers, suction system and/or external humidifier) for patients after laryngectomy was performed. Primary outcomes were costs, QALYs and incremental cost-effectiveness ratio (ICER). Secondary outcomes were pulmonary infections, and sleeping problems. The analysis was performed from a health care perspective of Poland, using a time horizon of 10 years and cycle length of 1 year. Transition probabilities were derived from various sources, amongst others a Polish randomized clinical trial. Quality of life data was derived from an Italian study on similar patients. Data on frequencies and mortality-related tracheobronchitis and/or pneumonia were derived from a Europe-wide survey amongst head and neck cancer experts. Substantial differences in quality-adjusted survival between the use of HMEs (3.63 QALYs) versus UC (2.95 QALYs) were observed. Total health care costs/patient were 39,553 PLN (9465 Euro) for the HME strategy and 4889 PLN (1168 Euro) for the UC strategy. HME use resulted in fewer pulmonary infections, and less sleeping problems. We could conclude that given the Polish threshold of 99,000 PLN/QALY, using HMEs is cost-effective compared to UC, resulting in 51,326 PLN/QALY (12,264 Euro/QALY) gained for patients after total laryngectomy. For the hospital period alone (2 weeks), HMEs were cost-saving: less costly and more effective.

  10. [Energy and mass exchange and the productivity of the main ecosystems of Siberia (from eddy covariance measurements). 1. Heat balance structure in the vegetation season].

    PubMed

    Chebakova, N M; Vygodskaia, N N; Arnet, A; Belelli Markezini, L; Kolle, O; Kurbatova, Iu A; Parfenova, E I; Valentini, R; Vaganov, E A; Shul'tse, E D

    2013-01-01

    Direct measurements of heat balance (turbulent heat transfer and evaporation heat consumption) by the method of turbulent pulsations in 1998-2000 and 2002-2004 were used to obtain information on the daily, seasonal, and annual dynamics of energy fluxes and mass transfer between the atmosphere and the typical ecosystems of Siberia (middle-taiga pine forest and raised bog, true four-grass steppe, with the use of data for typical tundra) along the Yenisei meridian (90 degrees E).

  11. [Energy and mass exchange and the productivity of the main ecosystems of Siberia (from eddy covariance measurements). 1. Heat balance structure in the vegetation season].

    PubMed

    Chebakova, N M; Vygodskaia, N N; Arnet, A; Belelli Markezini, L; Kolle, O; Kurbatova, Iu A; Parfenova, E I; Valentini, R; Vaganov, E A; Shul'tse, E D

    2013-01-01

    Direct measurements of heat balance (turbulent heat transfer and evaporation heat consumption) by the method of turbulent pulsations in 1998-2000 and 2002-2004 were used to obtain information on the daily, seasonal, and annual dynamics of energy fluxes and mass transfer between the atmosphere and the typical ecosystems of Siberia (middle-taiga pine forest and raised bog, true four-grass steppe, with the use of data for typical tundra) along the Yenisei meridian (90 degrees E). PMID:25518559

  12. Comparative Use of a Caribbean Mesophotic Coral Ecosystem and Association with Fish Spawning Aggregations by Three Species of Shark.

    PubMed

    Pickard, Alexandria E; Vaudo, Jeremy J; Wetherbee, Bradley M; Nemeth, Richard S; Blondeau, Jeremiah B; Kadison, Elizabeth A; Shivji, Mahmood S

    2016-01-01

    Understanding of species interactions within mesophotic coral ecosystems (MCEs; ~ 30-150 m) lags well behind that for shallow coral reefs. MCEs are often sites of fish spawning aggregations (FSAs) for a variety of species, including many groupers. Such reproductive fish aggregations represent temporal concentrations of potential prey that may be drivers of habitat use by predatory species, including sharks. We investigated movements of three species of sharks within a MCE and in relation to FSAs located on the shelf edge south of St. Thomas, United States Virgin Islands. Movements of 17 tiger (Galeocerdo cuvier), seven lemon (Negaprion brevirostris), and six Caribbean reef (Carcharhinus perezi) sharks tagged with acoustic transmitters were monitored within the MCE using an array of acoustic receivers spanning an area of 1,060 km2 over a five year period. Receivers were concentrated around prominent grouper FSAs to monitor movements of sharks in relation to these temporally transient aggregations. Over 130,000 detections of telemetered sharks were recorded, with four sharks tracked in excess of 3 years. All three shark species were present within the MCE over long periods of time and detected frequently at FSAs, but patterns of MCE use and orientation towards FSAs varied both spatially and temporally among species. Lemon sharks moved over a large expanse of the MCE, but concentrated their activities around FSAs during grouper spawning and were present within the MCE significantly more during grouper spawning season. Caribbean reef sharks were present within a restricted portion of the MCE for prolonged periods of time, but were also absent for long periods. Tiger sharks were detected throughout the extent of the acoustic array, with the MCE representing only portion of their habitat use, although a high degree of individual variation was observed. Our findings indicate that although patterns of use varied, all three species of sharks repeatedly utilized the MCE and

  13. Comparative Analysis of Reproductive Traits in Black-Chinned Tilapia Females from Various Coastal Marine, Estuarine and Freshwater Ecosystems

    PubMed Central

    Kantoussan, Justin; Ndiaye, Papa; Thiaw, Omar Thiom; Albaret, Jean-Jacques

    2012-01-01

    The black-chinned tilapia Sarotherodon melanotheron is a marine teleost characterised by an extreme euryhalinity. However, beyond a certain threshold at very high salinity, the species exhibits impaired growth and precocious reproduction. In this study, the relationships between reproductive parameters, environmental salinity and condition factor were investigated in wild populations of this species that were sampled in two consecutive years (2003 and 2004) from three locations in Senegal with different salinities: Guiers lake (freshwater, 0 psu), Hann bay (seawater, 37 psu) and Saloum estuary (hypersaline water, 66–127 psu). The highest absolute fecundity and spawning weight were recorded in seawater by comparison to either freshwater or hypersaline water whereas the poorest condition factors were observed in the most saline sampling site. These results reflect higher resource allocation to the reproduction due to the lowest costs of adaptation to salinity in seawater (the natural environment of this species) rather than differences in food resources at sites and/or efficiency at foraging and prey availability. Fecundities, oocyte size as well as spawning weight were consistent from year to year. However, the relative fecundity in the Saloum estuary varied significantly between the dry and rainy raisons with higher values in the wet season, which seems to reflect seasonal variations in environmental salinity. Such a reproductive tactic of producing large amounts of eggs in the rainy season when the salinity in the estuary was lower, would give the fry a better chance at survival and therefore assures a high larval recruitment. An inverse correlation was found between relative fecundity and oocyte size at the two extreme salinity locations, indicating that S. melanotheron has different reproductive strategies in these ecosystems. The adaptive significance of these two reproductive modes is discussed in regard to the heavy osmotic constraint imposed by extreme

  14. Comparable hydrogen isotopic fractionation of plant leaf wax n-alkanoic acids in arid and humid subtropical ecosystems

    NASA Astrophysics Data System (ADS)

    Gao, Li; Zheng, Mei; Fraser, Matthew; Huang, Yongsong

    2014-02-01

    Leaf wax hydrogen isotope proxies have been widely used to reconstruct past hydrological changes. However, published reconstructions have given little consideration for the potentially variable hydrogen isotopic fractionation relative to precipitation (ɛwax-p) under different climate and environmental settings. Chief among various potential factors controlling fractionation is relative humidity, which is known to strongly affect oxygen isotopic ratios of plant cellulose, but its effect on hydrogen isotopic fractionation of leaf waxes is still ambiguous. Analyses of lake surface sediments and individual modern plants have provided valuable information on the variability of ɛwax-p, but both approaches have significant limitations. Here, we present an alternative method to obtain the integrated, time-resolved ecosystem-level ɛwax-p values, by analyzing modern aerosol samples collected weekly from arid (Arizona lowlands) and humid subtropical (Atlanta, Georgia) environments during the main growth season. Because aerosol samples mainly reflect regional leaf wax resources, the extreme contrast in the hydroclimate and associated vegetation assemblages between our study sites allows us to rigorously assess the impact of relative humidity and associated vegetation assemblages on leaf wax hydrogen isotopic fractionation. We show there is only minor difference (mostly <10‰) in the mean ɛwax-p values in the two end-member environments. One possible explanation is that the positive isotopic effects of low relative humidity are offset by progressive replacement of trees with grasses that have a more negative apparent fractionation. Our results represent an important step toward quantitative interpretation of leaf wax hydrogen isotopic records.

  15. A Screening-Level Approach for Comparing Risks Affecting Aquatic Ecosystem Services over Socio-Environmental Gradients

    NASA Astrophysics Data System (ADS)

    Harmon, T. C.; Conde, D.; Villamizar, S. R.; Reid, B.; Escobar, J.; Rusak, J.; Hoyos, N.; Scordo, F.; Perillo, G. M.; Piccolo, M. C.; Zilio, M.; Velez, M.

    2015-12-01

    Assessing risks to aquatic ecosystems services (ES) is challenging and time-consuming, and effective strategies for prioritizing more detailed assessment efforts are needed. We propose a screening-level risk analysis (SRA) approach that scales ES risk using socioeconomic and environmental indices to capture anthropic and climatic pressures, as well as the capacity for institutional responses to those pressures. The method considers ES within a watershed context, and uses expert input to prioritize key services and the associated pressures that threaten them. The SRA approach focuses on estimating ES risk affect factors, which are the sum of the intensity factors for all hazards or pressures affecting the ES. We estimate the pressure intensity factors in a novel manner, basing them on the nation's (i) human development (proxied by Inequality-adjusted Human Development Index, IHDI), (ii) environmental regulatory and monitoring state (Environmental Performance Index, EPI) and (iii) the current level of water stress in the watershed (baseline water stress, BWS). Anthropic intensity factors for future conditions are derived from the baseline values based on the nation's 10-year trend in IHDI and EPI; ES risks in nations with stronger records of change are rewarded more/penalized less in estimates for good/poor future management scenarios. Future climatic intensity factors are tied to water stress estimates based on two general circulation model (GCM) outcomes. We demonstrate the method for an international array of six sites representing a wide range of socio-environmental settings. The outcomes illustrate novel consequences of the scaling scheme. Risk affect factors may be greater in a highly developed region under intense climatic pressure, or in less well-developed regions due to human factors (e.g., poor environmental records). As a screening-level tool, the SRA approach offers considerable promise for ES risk comparisons among watersheds and regions so that

  16. Comparative Use of a Caribbean Mesophotic Coral Ecosystem and Association with Fish Spawning Aggregations by Three Species of Shark

    PubMed Central

    Pickard, Alexandria E.; Vaudo, Jeremy J.; Wetherbee, Bradley M.; Nemeth, Richard S.; Blondeau, Jeremiah B.; Kadison, Elizabeth A.; Shivji, Mahmood S.

    2016-01-01

    Understanding of species interactions within mesophotic coral ecosystems (MCEs; ~ 30–150 m) lags well behind that for shallow coral reefs. MCEs are often sites of fish spawning aggregations (FSAs) for a variety of species, including many groupers. Such reproductive fish aggregations represent temporal concentrations of potential prey that may be drivers of habitat use by predatory species, including sharks. We investigated movements of three species of sharks within a MCE and in relation to FSAs located on the shelf edge south of St. Thomas, United States Virgin Islands. Movements of 17 tiger (Galeocerdo cuvier), seven lemon (Negaprion brevirostris), and six Caribbean reef (Carcharhinus perezi) sharks tagged with acoustic transmitters were monitored within the MCE using an array of acoustic receivers spanning an area of 1,060 km2 over a five year period. Receivers were concentrated around prominent grouper FSAs to monitor movements of sharks in relation to these temporally transient aggregations. Over 130,000 detections of telemetered sharks were recorded, with four sharks tracked in excess of 3 years. All three shark species were present within the MCE over long periods of time and detected frequently at FSAs, but patterns of MCE use and orientation towards FSAs varied both spatially and temporally among species. Lemon sharks moved over a large expanse of the MCE, but concentrated their activities around FSAs during grouper spawning and were present within the MCE significantly more during grouper spawning season. Caribbean reef sharks were present within a restricted portion of the MCE for prolonged periods of time, but were also absent for long periods. Tiger sharks were detected throughout the extent of the acoustic array, with the MCE representing only portion of their habitat use, although a high degree of individual variation was observed. Our findings indicate that although patterns of use varied, all three species of sharks repeatedly utilized the MCE

  17. The comparative effects of gamma radiation and in situ alpha particles on five strong-base anion exchange resins

    SciTech Connect

    Marsh, S.F.

    1991-01-01

    The effects of external gamma radiation and in situ alpha particles were measured on a recently available, macroporous, strong-base polyvinylpyridine resin and on four strong-base polystyrene anion exchange resins. Each resin was irradiated in 7 M nitric acid to 1--10 megaGray of gamma radiation from external {sup 60}Co, or to 5--14 megaGray of alpha particles from sorbed {sup 238}Pu. Each irradiated resin was measured for changes in dry weight, wet volume, weak-base and strong-base chloride exchange capacities, and exchange capacities for Pu(4) from nitric acid. Alpha-induced resin damage was significantly less than that caused by an equivalent dose of gamma radiation. The polyvinylpyridine resin offers the greatest resistance to damage from gamma radiation and from alpha particles. 5 refs., 1 figs. 5 tabs.

  18. A comparative interregional analysis of selected data from LANDSAT-1 and EREP for the inventory and monitoring of natural ecosystems

    NASA Technical Reports Server (NTRS)

    Poulton, C. E.

    1975-01-01

    Comparative statistics were presented on the capability of LANDSAT-1 and three of the Skylab remote sensing systems (S-190A, S-190B, S-192) for the recognition and inventory of analogous natural vegetations and landscape features important in resource allocation and management. Two analogous regions presenting vegetational zonation from salt desert to alpine conditions above the timberline were observed, emphasizing the visual interpretation mode in the investigation. An hierarchical legend system was used as the basic classification of all land surface features. Comparative tests were run on image identifiability with the different sensor systems, and mapping and interpretation tests were made both in monocular and stereo interpretation with all systems except the S-192. Significant advantage was found in the use of stereo from space when image analysis is by visual or visual-machine-aided interactive systems. Some cost factors in mapping from space are identified. The various image types are compared and an operational system is postulated.

  19. Mercury vapor air-surface exchange measured by collocated micrometeorological and enclosure methods - Part I: Data comparability and method characteristics

    NASA Astrophysics Data System (ADS)

    Zhu, W.; Sommar, J.; Lin, C.-J.; Feng, X.

    2015-01-01

    Reliable quantification of air-biosphere exchange flux of elemental mercury vapor (Hg0) is crucial for understanding the global biogeochemical cycle of mercury. However, there has not been a standard analytical protocol for flux quantification, and little attention has been devoted to characterize the temporal variability and comparability of fluxes measured by different methods. In this study, we deployed a collocated set of micrometeorological (MM) and dynamic flux chamber (DFC) measurement systems to quantify Hg0 flux over bare soil and low standing crop in an agricultural field. The techniques include relaxed eddy accumulation (REA), modified Bowen ratio (MBR), aerodynamic gradient (AGM) as well as dynamic flux chambers of traditional (TDFC) and novel (NDFC) designs. The five systems and their measured fluxes were cross-examined with respect to magnitude, temporal trend and correlation with environmental variables. Fluxes measured by the MM and DFC methods showed distinct temporal trends. The former exhibited a highly dynamic temporal variability while the latter had much more gradual temporal features. The diurnal characteristics reflected the difference in the fundamental processes driving the measurements. The correlations between NDFC and TDFC fluxes and between MBR and AGM fluxes were significant (R>0.8, p<0.05), but the correlation between DFC and MM fluxes were from weak to moderate (R=0.1-0.5). Statistical analysis indicated that the median of turbulent fluxes estimated by the three independent MM techniques were not significantly different. Cumulative flux measured by TDFC is considerably lower (42% of AGM and 31% of MBR fluxes) while those measured by NDFC, AGM and MBR were similar (<10% difference). This suggests that incorporating an atmospheric turbulence property such as friction velocity for correcting the DFC-measured flux effectively bridged the gap between the Hg0 fluxes measured by enclosure and MM techniques. Cumulated flux measured by REA

  20. No effect of seed source on multiple aspects of ecosystem functioning during ecological restoration: cultivars compared to local ecotypes of dominant grasses.

    PubMed

    Baer, Sara G; Gibson, David J; Gustafson, Danny J; Benscoter, Allison M; Reed, Lewis K; Campbell, Ryan E; Klopf, Ryan P; Willand, Jason E; Wodika, Ben R

    2014-02-01

    Genetic principles underlie recommendations to use local seed, but a paucity of information exists on the genetic distinction and ecological consequences of using different seed sources in restorations. We established a field experiment to test whether cultivars and local ecotypes of dominant prairie grasses were genetically distinct and differentially influenced ecosystem functioning. Whole plots were assigned to cultivar and local ecotype grass sources. Three subplots within each whole plot were seeded to unique pools of subordinate species. The cultivar of the increasingly dominant grass, Sorghastrum nutans, was genetically different than the local ecotype, but genetic diversity was similar between the two sources. There were no differences in aboveground net primary production, soil carbon accrual, and net nitrogen mineralization rate in soil between the grass sources. Comparable productivity of the grass sources among the species pools for four years shows functional equivalence in terms of biomass production. Subordinate species comprised over half the aboveground productivity, which may have diluted the potential for documented trait differences between the grass sources to influence ecosystem processes. Regionally developed cultivars may be a suitable alternative to local ecotypes for restoration in fragmented landscapes with limited gene flow between natural and restored prairie and negligible recruitment by seed. PMID:24567751

  1. No effect of seed source on multiple aspects of ecosystem functioning during ecological restoration: cultivars compared to local ecotypes of dominant grasses

    PubMed Central

    Baer, Sara G; Gibson, David J; Gustafson, Danny J; Benscoter, Allison M; Reed, Lewis K; Campbell, Ryan E; Klopf, Ryan P; Willand, Jason E; Wodika, Ben R

    2014-01-01

    Genetic principles underlie recommendations to use local seed, but a paucity of information exists on the genetic distinction and ecological consequences of using different seed sources in restorations. We established a field experiment to test whether cultivars and local ecotypes of dominant prairie grasses were genetically distinct and differentially influenced ecosystem functioning. Whole plots were assigned to cultivar and local ecotype grass sources. Three subplots within each whole plot were seeded to unique pools of subordinate species. The cultivar of the increasingly dominant grass, Sorghastrum nutans, was genetically different than the local ecotype, but genetic diversity was similar between the two sources. There were no differences in aboveground net primary production, soil carbon accrual, and net nitrogen mineralization rate in soil between the grass sources. Comparable productivity of the grass sources among the species pools for four years shows functional equivalence in terms of biomass production. Subordinate species comprised over half the aboveground productivity, which may have diluted the potential for documented trait differences between the grass sources to influence ecosystem processes. Regionally developed cultivars may be a suitable alternative to local ecotypes for restoration in fragmented landscapes with limited gene flow between natural and restored prairie and negligible recruitment by seed. PMID:24567751

  2. Developing and Applications of a Gap-filling Model for Eddy covariance CO2 Flux: Evaluating the Net Ecosystem Exchange of a Subtropical Evergreen Forest after a Server Environmental Disturbance

    NASA Astrophysics Data System (ADS)

    Li, M.; CHEN, Y.

    2013-12-01

    Successful eddy covariance (EC) applications often challenged by several difficulties, including non-ideal micrometeorological conditions, instrument failures, measurement limitations, and lacking consistent footprint area. Consequently, the resultant gaps in the time series of EC measurements limit the use of these dataset and cause the uncertainty in a range of 1 to 2 ton C/ha/yr for evaluating net ecosystem exchange (NEE) after different CO2 gap-filling procedures (Saigusa et al., 2013). It is crucial to develop a suitable gap-filling model for EC CO2 flux observations to provide reliable long-term surface fluxes for numerous applications. In this study, a gap-filling model was developed for EC CO2 flux by linking the gap-filled water vapor fluxes estimated by Chen et al. (2012) and the optimal nearest QC/QA passed CO2 fluxes for interpolating CO2 flux gaps. Considering the atmosphere characteristics and controlling mechanisms of CO2 fluxes, measured hydrometerological and flux data at the Lien-Hua-Chih (LHC) experimental watershed were separated into clear sky and cloudy/nighttime conditions. The successful applications of our gap-filling approaches were examined with various sizes of artificial CO2 gaps. Without any significant environmental disturbance in 2012, the annual NEE of this subtropical evergreen forest was estimated around 6.7 ton C/ha/yr as the amount of terrestrial CO2 sequestration. The effect of sever Typhoon Soulik (11-13, July, 2013) invasion on several ecosystem variables, such as changes of intrinsic water use efficiency, leaf area index, and canopy storage capacity, will be investigated to propose indicators for estimating NEE variations in association with environmental disturbances at this forest ecosystem.

  3. Beyond the Big Leaf: Quantifying Interactions between Canopy Structure and Canopy Photosynthesis Using Isotopic Partitioning of Net Ecosystem-Atmosphere Exchange of CO2 in a Temperate Forest

    NASA Astrophysics Data System (ADS)

    Asirwatham, J.; Wehr, R. A.; Saleska, S. R.

    2014-12-01

    Measurements of the forest-atmosphere exchange of carbon isotopes can be used to partition the net total carbon exchange (measured by standard eddy covariance) into its photosynthetic and respiratory components. This partitioning requires an estimate of the isotopic signature of canopy-scale photosynthesis, which has been obtained to date by assuming that the canopy behaves like a single 'big leaf'. This assumption neglects the heterogeneity of the canopy both vertically and with respect to leaf angles: leaves at various heights and angles experience different sunlight, temperature, and wind, and are physiologically different as well. In order to explore errors associated with the big leaf assumption, we applied a big leaf isotopic partitioning algorithm to canopy-scale net fluxes of 13CO2, 12CO2, heat, and water generated by a multi-leaf isotopic canopy simulation. The simulation included micro-environmental heterogeneity produced by the canopy geometry (leaf angles and arrangement) as well as physiological variation among leaves, invoking leaf-level energy balance to determine leaf temperatures. Leaf behavior in the simulation was parameterized by leaf-level gas-exchange measurements of the relevant characteristics of a range of leaves in the canopy (e.g. limiting photosynthetic rates, stomatal conductance, daytime respiration). These measurements indicated that photosynthetic capacity increased with height in the canopy, but that within a given canopy layer, leaf behavior showed surprisingly little variability. They also indicated that stomatal conductance did not relate quasi-linearly to light or photosynthetic rate, but was instead roughly constant with light at all photosynthetic photon flux densities above 100 μE m-2 s-1. The multi-leaf simulation incorporating these leaf behaviors suggested that the big leaf assumption is valid under diffuse light conditions but can lead to significant errors under clear sky conditions.

  4. A Southern Washington Chronosequence Study: The Impact of Interannual Climate Variability on Ecosystem Exchange of Carbon, Water, and Energy in a Newly Established and Old-Growth Coniferous Forest

    NASA Astrophysics Data System (ADS)

    Wharton, S.; Schroeder, M.; Falk, M.; Paw U, K.

    2005-12-01

    The T.T. Munger Research Natural Area of southern Washington provides a unique opportunity to study carbon exchange between coniferous forests and the atmosphere in a region that experiences a significant amount of forest harvesting disturbance and interannual climate variability. Here we present initial biometeorological measurements of carbon and water exchange at a 10 year old Douglas-fir stand with the goal of gaining information on how regional climate change will affect the carbon and hydrological budgets of a newly established forest. The young forest is 1.25 km from the Wind River Canopy Crane Research Facility, an AMERIFLUX site that has been continuously measuring carbon, water, and energy fluxes at an old-growth forest since 1998. Though still in its infancy, data from this chronosequence study will be used to quantify how sensitive net ecosystem exchange (NEE) of carbon is to interannual climate variability at different aged stands of the Washington western Cascades. Because the young stand is in close proximity to the old-growth forest, the climates at both forests will be identical, though the microclimates will not. The response in NEE at the young stand during the seasonal drought may be very different from that at the old-growth forest due to dissimilar canopy understory composition, which will lead to site differences in soil moisture and soil temperature. How this affects respiration rates and photosynthetic rates at both stands is one of the questions that will be addressed by this study. As the chronosequence study progresses, we hope to show any sensitivities that a newly established forest has to climate variability and in conjuncture with data from the old-growth stand, give the global carbon community important information on the forest carbon sequestration potential of the Pacific Northwest.

  5. Comparative ecotoxicity of interstitial waters in littoral ecosystems using Microtox{reg_sign} and the rotifer Brachionus plicatilis

    SciTech Connect

    Valls, T.A. Del; Forja, J.M.; Lubian, L.M.; Gomez-Parra, A.

    1997-11-01

    The toxic effects of sediment interstitial waters collected from seven littoral sites in the Gulf of Cadiz were tested with the Microtox assay and a 7-d Brachionus plicatilis (Rotifera) decline test. Dissolved organic carbon (DOC), nutrients (ammonia, phosphate, nitrate, nitrite, and silicate), the heavy metals (Fe, Mn, Zn, Cu, Pb, Cr, and Cd), and the linear alkylbenzensulfonate (LAS) concentrations in the interstitial water were measured. The results of assays were compared in a dose-response relationship between sites. This comparison has demonstrated a general agreement between toxicity values determined by Brachionus plicatilis and Photobacterium phosphoreum, except in the case of interstitial water toxicity from mixtures of heavy metals. Data derived from interstitial water chemistry and bioassays were assembled by multivariate statistical techniques (principal components analysis). Positive prevalence of these components in cases studied was used to establish those ranges in chemical concentrations associated with adverse effects. The interstitial water guidelines, in terms of concentrations at or below which biological effects have been shown to be minimal (mg/L), are: DOC, 12.8; phosphate, 0.28; LAS, 80.4; ammonia, 12.1: chromium, 0.0045.

  6. Ecosystem Journalism

    ERIC Educational Resources Information Center

    Robertson, Amy; Mahlin, Kathryn

    2005-01-01

    If the organisms in a prairie ecosystem created a newspaper, what would it look like? What important news topics of the ecosystem would the organisms want to discuss? Imaginative and enthusiastic third-grade students were busy pondering these questions as they tried their hands at "ecosystem journalism." The class had recently completed a study of…

  7. Ecosystem Jenga!

    ERIC Educational Resources Information Center

    Umphlett, Natalie; Brosius, Tierney; Laungani, Ramesh; Rousseau, Joe; Leslie-Pelecky, Diandra L.

    2009-01-01

    To give students a tangible model of an ecosystem and have them experience what could happen if a component of that ecosystem were removed; the authors developed a hands-on, inquiry-based activity that visually demonstrates the concept of a delicately balanced ecosystem through a modification of the popular game Jenga. This activity can be…

  8. Natural ecosystems

    USGS Publications Warehouse

    Fleishman, Erica; Belnap, Jayne; Cobb, Neil; Enquist, Carolyn A.F.; Ford, Karl; MacDonald, Glen; Pellant, Mike; Schoennagel, Tania; Schmit, Lara M.; Schwartz, Mark; van Drunick, Suzanne; Westerling, Anthony LeRoy; Keyser, Alisa; Lucas, Ryan

    2013-01-01

    Natural Ecosystems analyzes the association of observed changes in climate with changes in the geographic distributions and phenology (the timing of blossoms or migrations of birds) for Southwestern ecosystems and their species, portraying ecosystem disturbances—such as wildfires and outbreaks of forest pathogens—and carbon storage and release, in relation to climate change.

  9. Methylotrophic bacteria symbiosis with the higher plants as means of minimization of the lower hydrocarbons concentration during artificial ecosystem gas exchange

    NASA Astrophysics Data System (ADS)

    Berkovich, Yuliy; Smolyanina, Svetlana; Moukhamedieva, Lana; Mardanov, Robert; Doronina, Nina; Ivanova, Ekaterina

    Plant growth unit should be included in the LSS for the space vehicles for vitamin greens supply and psychological support of cosmonauts during long-term missions. The lower hydrocarbons such as methane, methanol, methylated sulfuric compounds and methylated amines, ethylene and so on, are the natural products of human and plant metabolism and usually considered as the air pollutions. It is shown, that one way to decrease the lower hydrocarbons concentration in the artificial ecosystems could be colonization of the plants by methylotrophic bacteria. The aerobic methylotrophic bacteria possess unique ability to use methane and its oxidized or replaced derivatives without food damage and human, animals or plants infection. We have found that methylotrophic bacteria are the phyto-symbiotic bacteria: they stimulate growth and development of the colonized plants because of synthesizing cytokinins and auxins, and vitamin B12.Two collection strains of the obligate methylotrophic bacteria - Methylovorus mays C and Methylomonas metanica S - were chosen because of their high activity to assimilate the lower hydrocarbons due to functioning of methanoldehydrogenase, methanmonooxigenase and ribulose monophosphate cycle enzymes system.Colonization of the leaf cabbage Brassica chinensis L. by these strains led to approximately 30 % reduce of methanol and methane concentration in the air inside phytotron. Experimental estimations of the influence of methylotrophic bacteria on leafy greens growth and development are obtained.

  10. Carbon exchange between the mantle and the crust and its effect upon the atmosphere: Today compared to Archean time

    NASA Technical Reports Server (NTRS)

    Desmarais, D.

    1986-01-01

    Paleobiologists now recognize that the Earth's biosphere has been profoundly affected by geologic processes. One very important process is the dissipation of heat which has been generated by radioactivity and/or stored within the earth. Heat flow is responsible for crustal movements and therefore it is the principal architect for constructing the environments (e.g. shallow marine, continental, etc.) wherein life developed and flourished. Heat flow has also influenced the movements of volatile elements (e.g. C, N, H, S, rare gases, etc.) both within the Earth's crust and between the crust and mantle. The inventory of these elements in the Earth's crust is important, not just because some of them constitute the building blocks of organic matter, but also because they influence the biosphere's climate. The purpose of this work is to evaluate how the decline of heat flow over the course of the Earth's history has influenced the carbon inventory in the Earth's crust. Such an evaluation must first consider whether the rate at which carbon is presently being exchanged between the mantle and crust is sufficient to play an important role in controlling the crustal inventory. Secondly, this exchange of carbon must be reevaluated in the context of the Precambrian Earth's environment. One very important consideration is that the upper mantle was perhaps 300 C hotter 3 b.y. ago than it is today.

  11. Foliar retention of 15N tracers: implications for net canopy exchange in low- and high-elevation forest ecosystems

    SciTech Connect

    Garten Jr, Charles T; Schwab, Alison; Shirshac, Terri

    1998-04-01

    Nitrogen-15 ({sup 15}N) labelled ammonium and nitrate were applied to understory saplings in a low-elevation deciduous forest and a high-elevation coniferous forest during the 1993 growing season to estimate the minimum retention of inorganic N from wet deposition. Tissue samples were collected at both sites before and after the tracer applications to determine the initial and the final {sup 15}N content. The fraction of the tracer application retained by deciduous leaves or by current-year leaves and stems on conifers was calculated from measurements of {sup 15}N and total N content. At both study sites, tracer applications significantly increased the {sup 15}N content of sapling tissues, although there was no significant difference between the fractional retention of ammonium and nitrate. The results support earlier studies indicating that the foliar retention of {sup 15}N applied in simulated wet deposition is small. Our estimates of annual N uptake from wet deposition by the forest canopy at the low- and high-elevation study sites were only 14 and 7%, respectively. This study, along with prior studies of the different chemical forms of N deposition, indicates that canopy uptake of dry N deposition is a major contributor to the net canopy exchange of N in both forests.

  12. Knowledge-based systems as decision support tools in an ecosystem approach to fisheries: Comparing a fuzzy-logic and a rule-based approach

    NASA Astrophysics Data System (ADS)

    Jarre, Astrid; Paterson, Barbara; Moloney, Coleen L.; Miller, David C. M.; Field, John G.; Starfield, Anthony M.

    2008-10-01

    In an ecosystem approach to fisheries (EAF), management must draw on information of widely different types, and information addressing various scales. Knowledge-based systems assist in the decision-making process by summarising this information in a logical, transparent and reproducible way. Both rule-based Boolean and fuzzy-logic models have been used successfully as knowledge-based decision support tools. This study compares two such systems relevant to fisheries management in an EAF developed for the southern Benguela. The first is a rule-based system for the prediction of anchovy recruitment and the second is a fuzzy-logic tool to monitor implementation of an EAF in the sardine fishery. We construct a fuzzy-logic counterpart to the rule-based model, and a rule-based counterpart to the fuzzy-logic model, compare their results, and include feedback from potential users of these two decision support tools in our evaluation of the two approaches. With respect to the model objectives, no method clearly outperformed the other. The advantages of numerically processing continuous variables, and interpreting the final output, as in fuzzy-logic models, can be weighed up against the advantages of using a few, qualitative, easy-to-understand categories as in rule-based models. The natural language used in rule-based implementations is easily understood by, and communicated among, users of these systems. Users unfamiliar with fuzzy-set theory must “trust” the logic of the model. Graphical visualization of intermediate and end results is an important advantage of any system. Applying the two approaches in parallel improved our understanding of the model as well as of the underlying problems. Even for complex problems, small knowledge-based systems such as the ones explored here are worth developing and using. Their strengths lie in (i) synthesis of the problem in a logical and transparent framework, (ii) helping scientists to deliberate how to apply their science to

  13. Ecosystem experiments

    SciTech Connect

    Mooney, H.A.; Medina, E.; Schindler, D.W.; Schulze, E.D.; Walker, B.H.

    1991-01-01

    Large scale, human-induced modifications to terrestrial and hydrological systems have been a major factor in contributing to global change. The objective of this book is to explore the potential of ecosystem experimentation as a tool to understanding and predicting more precisely the consequences of our changing biosphere. The papers in this book are the result of two SCOPE workshops to evaluated understanding of the response of ecosystems to large scale perturbations and to design ecosystem experiments to study the impace of increased atmospheric carbon dioxide concentrations on ecosystem processes. The general topics addressed include the following: how changes in driving variables affect different biotic interactions within ecosystems; the human role in modifying forest structure and the resulting ecosystem processes; the role of ecosystem experiments in the study of controlling factors such as hydrological controls, temperature, and biotic controlles; analysis of ecosystem dynamics as a complex and chaotic system; role of ecosystem experiments in the study of the impact of acid deposition; role of ecosystem experimentation in the study of global change impace on the biosphere and the biospheric feedbacks to global environmental change.

  14. Controls of Net Ecosystem Exchange at an Old Field, a Pine Plantation, and a Hardwood Forest under Identical Climatic and Edaphic Conditions-Isotopic Studies

    SciTech Connect

    Chanton, J. P.; Mortazavi, B.

    2004-11-04

    During the past year we have submitted two manuscripts. 1. Mortazavi, B., J. Chanton, J.L. Prater, A.C. Oishi, R. Oren and G. Katul. Temporal variability in 13C of respired CO2 in a pine and a hardwood forest subject to similar climatic conditions (in Press). Oecologia 2. Mortazavi, B. and J. P. Chanton. Use of Keeling plots for determining sources of dissolved organic carbon in nearshore and open ocean systems (Published in Limnology and Oceanography (2004) Vol 49 pages 102-108). 3. Mortazavi, B., J. L. Prater, and J. P. Chanton (2004). A field-based method for simultaneous measurements of the 18O and 13C of soil CO2 efflux. Biogeosciences Vol 1:1-16 Most recent products delivered: Mortazavi, B. and J. P. Chanton. Abiotic and biotic controls on the 13C of respired CO2 in the southeastern US forest mosaics and a new technique for measuring the of soil CO2 efflux. Joint Biosphere Stable Isotope Network (US) and Stable Isotopes in Biosphere Atmosphere Exchange (EU) 2004 Meeting, Interlaken, Switzerland, March 31-April 4, 2004. Mortazavi, B., J. Chanton, J.L. Prater, A.C. Oishi, R. Oren and G. Katul. Temporal variability in 13C of respired CO2 in a pine and a hardwood forest subject to similar climatic conditions. American Geophysical Union Fall Meeting, San Francisco, USA, December 8-12, 2003. Prater, J., Mortazavi, B. and J. P. Chanton. Measurement of discrimination against 13C during photosynthesis and quantification of the short-term variability of 13C over a diurnal cycle. American Geophysical Union Fall Meeting, San Francisco, USA, December 8-12, 2003.

  15. Soil-atmospheric exchange of CO2, CH4, and N2O in three subtropical forest ecosystems in southern China

    USGS Publications Warehouse

    Tang, X.; Liu, S.; Zhou, G.; Zhang, Dongxiao; Zhou, C.

    2006-01-01

    The magnitude, temporal, and spatial patterns of soil-atmospheric greenhouse gas (hereafter referred to as GHG) exchanges in forests near the Tropic of Cancer are still highly uncertain. To contribute towards an improvement of actual estimates, soil-atmospheric CO2, CH4, and N2O fluxes were measured in three successional subtropical forests at the Dinghushan Nature Reserve (hereafter referred to as DNR) in southern China. Soils in DNR forests behaved as N2O sources and CH4 sinks. Annual mean CO2, N2O, and CH4 fluxes (mean ?? SD) were 7.7 ?? 4.6MgCO2-Cha-1 yr-1, 3.2 ?? 1.2 kg N2ONha-1 yr-1, and 3.4 ?? 0.9 kgCH4-Cha-1 yr-1, respectively. The climate was warm and wet from April through September 2003 (the hot-humid season) and became cool and dry from October 2003 through March 2004 (the cool-dry season). The seasonality of soil CO2 emission coincided with the seasonal climate pattern, with high CO2 emission rates in the hot-humid season and low rates in the cool-dry season. In contrast, seasonal patterns of CH4 and N2O fluxes were not clear, although higher CH4 uptake rates were often observed in the cool-dry season and higher N2O emission rates were often observed in the hot-humid season. GHG fluxes measured at these three sites showed a clear increasing trend with the progressive succession. If this trend is representative at the regional scale, CO2 and N2O emissions and CH4 uptake in southern China may increase in the future in light of the projected change in forest age structure. Removal of surface litter reduced soil CO2 effluxes by 17-44% in the three forests but had no significant effect on CH4 absorption and N2O emission rates. This suggests that microbial CH4 uptake and N2O production was mainly related to the mineral soil rather than in the surface litter layer. ?? 2006 Blackwell Publishing Ltd.

  16. Obscuring ecosystem function with application of the ecosystem services concept.

    PubMed

    Peterson, Markus J; Hall, Damon M; Feldpausch-Parker, Andrea M; Peterson, Tarla Rai

    2010-02-01

    Conservationists commonly have framed ecological concerns in economic terms to garner political support for conservation and to increase public interest in preserving global biodiversity. Beginning in the early 1980s, conservation biologists adapted neoliberal economics to reframe ecosystem functions and related biodiversity as ecosystem services to humanity. Despite the economic success of programs such as the Catskill/Delaware watershed management plan in the United States and the creation of global carbon exchanges, today's marketplace often fails to adequately protect biodiversity. We used a Marxist critique to explain one reason for this failure and to suggest a possible, if partial, response. Reframing ecosystem functions as economic services does not address the political problem of commodification. Just as it obscures the labor of human workers, commodification obscures the importance of the biota (ecosystem workers) and related abiotic factors that contribute to ecosystem functions. This erasure of work done by ecosystems impedes public understanding of biodiversity. Odum and Odum's radical suggestion to use the language of ecosystems (i.e., emergy or energy memory) to describe economies, rather than using the language of economics (i.e., services) to describe ecosystems, reverses this erasure of the ecosystem worker. Considering the current dominance of economic forces, however, implementing such solutions would require social changes similar in magnitude to those that occurred during the 1960s. Niklas Luhmann argues that such substantive, yet rapid, social change requires synergy among multiple societal function systems (i.e., economy, education, law, politics, religion, science), rather than reliance on a single social sphere, such as the economy. Explicitly presenting ecosystem services as discreet and incomplete aspects of ecosystem functions not only allows potential economic and environmental benefits associated with ecosystem services, but also

  17. A COMPARATIVE ANALYSIS OF NUTRIENT LOADING, NUTRIENT RETENTION AND NET ECOSYSTEM METABOLISM IN THREE TIDAL RIVER ESTUARIES DIFFERING PREDOMINATELY BY THEIR WATERSHED LAND USE TYPES.

    EPA Science Inventory

    Abstract and oral presentation for the Estuarine Research Federation Conference.

    Estuarine retention of watershed nutrient loads, system-wide nutrient biogeochemical fluxes, and net ecosystem metabolism (NEM) were determined in three estuaries exhibiting differing magnitud...

  18. Visiting Scholar Exchange Reports.

    ERIC Educational Resources Information Center

    Rubin, Kyna, Ed.

    1986-01-01

    Provides reports of four United States scholars who visited China as part of the Visiting Scholar Exchange Program. The titles of the reports are (1) "China Journey: A Political Scientist's Look at Yan'an," (2) "The Social Consequences of Land Reclamation in Chinese Coastal Ecosystems," (3) "Anthropology Lectures in South China," and (4) "The Use…

  19. AQUATIC ECOSYSTEMS,

    EPA Science Inventory

    Aquatic ecosystems are a vital part of the urban water cycle (and of urban areas more broadly), and, if healthy, provide a range of goods and services valued by humans (Meyer 1997). For example, aquatic ecosystems (e.g., rivers, lakes, wetlands) provide potable water, food resou...

  20. Driving terrestrial ecosystem models from space

    NASA Technical Reports Server (NTRS)

    Waring, R. H.

    1993-01-01

    Regional air pollution, land-use conversion, and projected climate change all affect ecosystem processes at large scales. Changes in vegetation cover and growth dynamics can impact the functioning of ecosystems, carbon fluxes, and climate. As a result, there is a need to assess and monitor vegetation structure and function comprehensively at regional to global scales. To provide a test of our present understanding of how ecosystems operate at large scales we can compare model predictions of CO2, O2, and methane exchange with the atmosphere against regional measurements of interannual variation in the atmospheric concentration of these gases. Recent advances in remote sensing of the Earth's surface are beginning to provide methods for estimating important ecosystem variables at large scales. Ecologists attempting to generalize across landscapes have made extensive use of models and remote sensing technology. The success of such ventures is dependent on merging insights and expertise from two distinct fields. Ecologists must provide the understanding of how well models emulate important biological variables and their interactions; experts in remote sensing must provide the biophysical interpretation of complex optical reflectance and radar backscatter data.

  1. Managing riverine landscapes as meta-ecosystems

    NASA Astrophysics Data System (ADS)

    Tockner, K.

    2014-12-01

    Aquatic and terrestrial ecosystems are tightly linked through energy, material, information, and organism flows. At the landscape scale, these reciprocal flows are controlled by the composition, configuration, boundary conditions and linkage of individual ecosystem types, thereby forming so-called meta-ecosystems. The relative importance of individual ecosystem types depends on the intrinsic properties (so-called "ecosystem traits"), the setting within the landscape, and the characteristics of interfaces that control cross-system fluxes. For example, the juxtaposition of particular ecosystem types (i.e. their composition and configuration) may alter the magnitude of landscape processes as well as the directions of flow among ecosystem types. Therefore, the meta-ecosystem concept provides a framework to quantify ecosystem diversity, a neglected component of biodiversity, and to test its effects on genetic and species diversity as well as the functional performance in coupled ecosystems. Given their topographic position at the lowest point in the landscape, aquatic ecosystems are particularly susceptible to influences exerted by their surrounding terrestrial environment, both the immediately adjacent riparian zones and the entire catchment that they drain. Questions that need to be tackled may include: What are the consequences of exchange pulses between aquatic and terrestrial ecosystems on the functional performance of individual ecosystems? What are the mechanisms and processes underlying structural and functional biodiversity at aquatic-terrestrial interfaces? In this respect, the meta-ecosystem concept might be very helpful in landscape management and in ecosystem design and engineering.

  2. A comparative meta-analysis of maximal aerobic metabolism of vertebrates: implications for respiratory and cardiovascular limits to gas exchange.

    PubMed

    Hillman, Stanley S; Hancock, Thomas V; Hedrick, Michael S

    2013-02-01

    Maximal aerobic metabolic rates (MMR) in vertebrates are supported by increased conductive and diffusive fluxes of O(2) from the environment to the mitochondria necessitating concomitant increases in CO(2) efflux. A question that has received much attention has been which step, respiratory or cardiovascular, provides the principal rate limitation to gas flux at MMR? Limitation analyses have principally focused on O(2) fluxes, though the excess capacity of the lung for O(2) ventilation and diffusion remains unexplained except as a safety factor. Analyses of MMR normally rely upon allometry and temperature to define these factors, but cannot account for much of the variation and often have narrow phylogenetic breadth. The unique aspect of our comparative approach was to use an interclass meta-analysis to examine cardio-respiratory variables during the increase from resting metabolic rate to MMR among vertebrates from fish to mammals, independent of allometry and phylogeny. Common patterns at MMR indicate universal principles governing O(2) and CO(2) transport in vertebrate cardiovascular and respiratory systems, despite the varied modes of activities (swimming, running, flying), different cardio-respiratory architecture, and vastly different rates of metabolism (endothermy vs. ectothermy). Our meta-analysis supports previous studies indicating a cardiovascular limit to maximal O(2) transport and also implicates a respiratory system limit to maximal CO(2) efflux, especially in ectotherms. Thus, natural selection would operate on the respiratory system to enhance maximal CO(2) excretion and the cardiovascular system to enhance maximal O(2) uptake. This provides a possible evolutionary explanation for the conundrum of why the respiratory system appears functionally over-designed from an O(2) perspective, a unique insight from previous work focused solely on O(2) fluxes. The results suggest a common gas transport blueprint, or Bauplan, in the vertebrate clade. PMID

  3. A comparative meta-analysis of maximal aerobic metabolism of vertebrates: implications for respiratory and cardiovascular limits to gas exchange.

    PubMed

    Hillman, Stanley S; Hancock, Thomas V; Hedrick, Michael S

    2013-02-01

    Maximal aerobic metabolic rates (MMR) in vertebrates are supported by increased conductive and diffusive fluxes of O(2) from the environment to the mitochondria necessitating concomitant increases in CO(2) efflux. A question that has received much attention has been which step, respiratory or cardiovascular, provides the principal rate limitation to gas flux at MMR? Limitation analyses have principally focused on O(2) fluxes, though the excess capacity of the lung for O(2) ventilation and diffusion remains unexplained except as a safety factor. Analyses of MMR normally rely upon allometry and temperature to define these factors, but cannot account for much of the variation and often have narrow phylogenetic breadth. The unique aspect of our comparative approach was to use an interclass meta-analysis to examine cardio-respiratory variables during the increase from resting metabolic rate to MMR among vertebrates from fish to mammals, independent of allometry and phylogeny. Common patterns at MMR indicate universal principles governing O(2) and CO(2) transport in vertebrate cardiovascular and respiratory systems, despite the varied modes of activities (swimming, running, flying), different cardio-respiratory architecture, and vastly different rates of metabolism (endothermy vs. ectothermy). Our meta-analysis supports previous studies indicating a cardiovascular limit to maximal O(2) transport and also implicates a respiratory system limit to maximal CO(2) efflux, especially in ectotherms. Thus, natural selection would operate on the respiratory system to enhance maximal CO(2) excretion and the cardiovascular system to enhance maximal O(2) uptake. This provides a possible evolutionary explanation for the conundrum of why the respiratory system appears functionally over-designed from an O(2) perspective, a unique insight from previous work focused solely on O(2) fluxes. The results suggest a common gas transport blueprint, or Bauplan, in the vertebrate clade.

  4. Comparative effects of climate on ecosystem nitrogen and soil biogeochemistry in U.S. national parks. FY 2001 Annual Report (Res. Rept. No. 94)

    USGS Publications Warehouse

    Stottlemyer, R.; Edmonds, R.; Scherbarth, L.; Urbanczyk, K.; Van Miegroet, H.; Zak, J.

    2002-01-01

    In 1998, the USGS Global Change program funded research for a network of Long-Term Reference Ecosystems initially established in national parks and funded by the National Park Service. The network included Noland Divide, Great Smoky Mountains National Park, Tennessee; Pine Canyon, Big Ben National park, Texas; West Twin Creek, Olympic National Park, Washingtona?? Wallace Lake, Isle Royale National Park, Michigan; and the Asik watershed, Noatak National Preserve, Alaska. The watershed ecosystem model was used since this approach permits additional statistical power in detection of trends among variables, and the watershed in increasingly a land unit used in resource management and planning. The ecosystems represent a major fraction of lands administered by the National Park Service, and were chosen generally for the contrasts among sites. For example, tow of the site, Noland and West Twin, are characterized by high precipitation amounts, but Noland receives some of the highest atmospheric nitrogen (N) inputs in North America. In contrast, Pine Canyon and Asik are warm and cold desert sites respectively. The Asik watershed receives <1% the atmospheric N inputs Noland receives. The Asik site is at the northern extent (treeline) of the boreal biome in the North America while Wallace is at the southern ecotone between boreal and northern hardwoods. The research goal for these sites is to gain a basic understanding of ecosystem structure and function, and the response to global change especially atmospheric inputs and climate.

  5. Comparative efficacy of the picture exchange communication system (PECS) versus a speech-generating device: effects on social-communicative skills and speech development.

    PubMed

    Boesch, Miriam C; Wendt, Oliver; Subramanian, Anu; Hsu, Ning

    2013-09-01

    The Picture Exchange Communication System (PECS) and a speech-generating device (SGD) were compared in a study with a multiple baseline, alternating treatment design. The effectiveness of these methods in increasing social-communicative behavior and natural speech production were assessed with three elementary school-aged children with severe autism who demonstrated extremely limited functional communication skills. Results for social-communicative behavior were mixed for all participants in both treatment conditions. Relatively little difference was observed between PECS and SGD conditions. Although findings were inconclusive, data patterns suggest that Phase II of the PECS training protocol is conducive to encouraging social-communicative behavior. Data for speech outcomes did not reveal any increases across participants, and no differences between treatment conditions were observed.

  6. Commonalities of carbon dioxide exchange in semiarid regions with monsoon and Mediterranean climates

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Semiarid ecosystems with monsoon climates receive precipitation during the warm season while Mediterranean systems are characteristically wet in the cool season and dry in the summer. Comparing biosphere-atmosphere carbon exchange across these two climate regimes can yield information about the int...

  7. Latent heat exchange in the boreal and arctic biomes.

    PubMed

    Kasurinen, Ville; Alfredsen, Knut; Kolari, Pasi; Mammarella, Ivan; Alekseychik, Pavel; Rinne, Janne; Vesala, Timo; Bernier, Pierre; Boike, Julia; Langer, Moritz; Belelli Marchesini, Luca; van Huissteden, Ko; Dolman, Han; Sachs, Torsten; Ohta, Takeshi; Varlagin, Andrej; Rocha, Adrian; Arain, Altaf; Oechel, Walter; Lund, Magnus; Grelle, Achim; Lindroth, Anders; Black, Andy; Aurela, Mika; Laurila, Tuomas; Lohila, Annalea; Berninger, Frank

    2014-11-01

    In this study latent heat flux (λE) measurements made at 65 boreal and arctic eddy-covariance (EC) sites were analyses by using the Penman-Monteith equation. Sites were stratified into nine different ecosystem types: harvested and burnt forest areas, pine forests, spruce or fir forests, Douglas-fir forests, broadleaf deciduous forests, larch forests, wetlands, tundra and natural grasslands. The Penman-Monteith equation was calibrated with variable surface resistances against half-hourly eddy-covariance data and clear differences between ecosystem types were observed. Based on the modeled behavior of surface and aerodynamic resistances, surface resistance tightly control λE in most mature forests, while it had less importance in ecosystems having shorter vegetation like young or recently harvested forests, grasslands, wetlands and tundra. The parameters of the Penman-Monteith equation were clearly different for winter and summer conditions, indicating that phenological effects on surface resistance are important. We also compared the simulated λE of different ecosystem types under meteorological conditions at one site. Values of λE varied between 15% and 38% of the net radiation in the simulations with mean ecosystem parameters. In general, the simulations suggest that λE is higher from forested ecosystems than from grasslands, wetlands or tundra-type ecosystems. Forests showed usually a tighter stomatal control of λE as indicated by a pronounced sensitivity of surface resistance to atmospheric vapor pressure deficit. Nevertheless, the surface resistance of forests was lower than for open vegetation types including wetlands. Tundra and wetlands had higher surface resistances, which were less sensitive to vapor pressure deficits. The results indicate that the variation in surface resistance within and between different vegetation types might play a significant role in energy exchange between terrestrial ecosystems and atmosphere. These results suggest the need

  8. RESOLUTION AND ERROR IN MEASURING LAND-COVER CHANGE: EFFECTS ON ESTIMATING NET CARBON RELEASE FROM MEXICAN TERRESTRIAL ECOSYSTEMS

    EPA Science Inventory

    Reliable estimates of carbon exchange between terrestrial ecosystems and the atmosphere due to land-use change have become increasingly important. One source of land-use changes estimates comes from comparing multi-date remote sensing imagery, though the effect of land-cover clas...

  9. Non-use Economic Values for Little-Known Aquatic Species at Risk: Comparing Choice Experiment Results from Surveys Focused on Species, Guilds, and Ecosystems

    NASA Astrophysics Data System (ADS)

    Rudd, Murray A.; Andres, Sheri; Kilfoil, Mary

    2016-09-01

    Accounting for non-market economic values of biological diversity is important to fully assess the benefits of environmental policies and regulations. This study used three choice experiments (species-, guild-, and ecosystem-based surveys) in parallel to quantify non-use values for little-known aquatic species at risk in southern Ontario. Mean willingness-to-pay (WTP) ranged from 9.45 to 21.41 per listing status increment under Canada's Species at Risk Act for both named and unnamed little-known species. Given the broad range of valuable ecosystem services likely to accrue to residents from substantial increases in water quality and the rehabilitation of coastal wetlands, the difference in WTP between species- and ecosystem-based surveys seemed implausibly small. It appeared that naming species—the `iconization' of species in two of the three surveys—had an important effect on WTP. The results suggest that reasonable annual household-level WTP values for little-known aquatic species may be 10 to 25 per species or 10 to 20 per listing status increment. The results highlighted the utility of using parallel surveys to triangulate on non-use economic values for little-known species at risk.

  10. Non-use Economic Values for Little-Known Aquatic Species at Risk: Comparing Choice Experiment Results from Surveys Focused on Species, Guilds, and Ecosystems.

    PubMed

    Rudd, Murray A; Andres, Sheri; Kilfoil, Mary

    2016-09-01

    Accounting for non-market economic values of biological diversity is important to fully assess the benefits of environmental policies and regulations. This study used three choice experiments (species-, guild-, and ecosystem-based surveys) in parallel to quantify non-use values for little-known aquatic species at risk in southern Ontario. Mean willingness-to-pay (WTP) ranged from $9.45 to $21.41 per listing status increment under Canada's Species at Risk Act for both named and unnamed little-known species. Given the broad range of valuable ecosystem services likely to accrue to residents from substantial increases in water quality and the rehabilitation of coastal wetlands, the difference in WTP between species- and ecosystem-based surveys seemed implausibly small. It appeared that naming species-the 'iconization' of species in two of the three surveys-had an important effect on WTP. The results suggest that reasonable annual household-level WTP values for little-known aquatic species may be $10 to $25 per species or $10 to $20 per listing status increment. The results highlighted the utility of using parallel surveys to triangulate on non-use economic values for little-known species at risk. PMID:27294723

  11. Non-use Economic Values for Little-Known Aquatic Species at Risk: Comparing Choice Experiment Results from Surveys Focused on Species, Guilds, and Ecosystems.

    PubMed

    Rudd, Murray A; Andres, Sheri; Kilfoil, Mary

    2016-09-01

    Accounting for non-market economic values of biological diversity is important to fully assess the benefits of environmental policies and regulations. This study used three choice experiments (species-, guild-, and ecosystem-based surveys) in parallel to quantify non-use values for little-known aquatic species at risk in southern Ontario. Mean willingness-to-pay (WTP) ranged from $9.45 to $21.41 per listing status increment under Canada's Species at Risk Act for both named and unnamed little-known species. Given the broad range of valuable ecosystem services likely to accrue to residents from substantial increases in water quality and the rehabilitation of coastal wetlands, the difference in WTP between species- and ecosystem-based surveys seemed implausibly small. It appeared that naming species-the 'iconization' of species in two of the three surveys-had an important effect on WTP. The results suggest that reasonable annual household-level WTP values for little-known aquatic species may be $10 to $25 per species or $10 to $20 per listing status increment. The results highlighted the utility of using parallel surveys to triangulate on non-use economic values for little-known species at risk.

  12. Steppe to forest steppe ecosystems during the last glacial period in S Italy - evidence from sediment-paleosol sequences, compared to lacustrine archives and marine data

    NASA Astrophysics Data System (ADS)

    Sauer, Daniela; Zwanzig, Lisa; Scarciglia, Fabio; Kadereit, Annette; Brauer, Achim; Al-Sharif, Riyad; Brückner, Helmut

    2013-04-01

    During fieldwork on marine terraces near Lazzaro (Calabria, Southern Italy) in 2010 we discovered an alluvial fan overlying the MIS 5.5 terrace. Due to strong tectonic uplift (1.3 m ka-1) the alluvial fan was dissected by the same creek which previously had built it up. Thus, the internal structure of the fan was exposed, exhibiting a detailed sediment-paleosol sequence. The paleosols are mainly characterized by accumulation of soil organic matter (SOM), bioturbation and secondary carbonates. They represent Chernozem- and Phaeozem-like soils that very likely formed in steppe to forest steppe ecosystems. Strong carbonate accumulations occur in the lowermost part of the profile, between 513 and 693 cm depth. Their thickness and in parts massive character suggest that slope water contributed to the carbonate accumulations. Similar environmental conditions as reflected in the Lazzaro paleosols were reconstructed from the pollen record of Lago Grande di Monticchio, which indicates from 87.98 to 82.73 ka (MIS5b-a) a temperate deciduous forest (St. Germain 2); from 82.73 to 59.00 ka (MIS5a-4) first frequent vegetation fluctuations then Artemisia steppe, from 59.00 to 25.90 ka (MIS3) alternation between open steppe (stadials) and wooded steppe (interstadials); and from 25.90 to 14.30 ka (MIS2) again open steppe (Last Glacial Maximum). SOM of the two uppermost Lazzaro paleosols was 14C-dated to 26.8-28.8 cal ka BP and 28.9-30.3 cal ka BP, respectively. Thus, the formation of these soils falls into the period for which the lacustrine record indicates an alternation between open and wooded steppe. It is still an open question whether the sedimentation that interrupted the ecologically stable times of soil formation was triggered by fluctuations in climate and vegetation cover or by tectonics. The observation that the ages of the paleosols match a period of frequent environmental oscillations suggests that the phases of sedimentation are to a certain degree driven by

  13. Comparing three stochastic search algorithms for computational protein design: Monte Carlo, replica exchange Monte Carlo, and a multistart, steepest-descent heuristic.

    PubMed

    Mignon, David; Simonson, Thomas

    2016-07-15

    Computational protein design depends on an energy function and an algorithm to search the sequence/conformation space. We compare three stochastic search algorithms: a heuristic, Monte Carlo (MC), and a Replica Exchange Monte Carlo method (REMC). The heuristic performs a steepest-descent minimization starting from thousands of random starting points. The methods are applied to nine test proteins from three structural families, with a fixed backbone structure, a molecular mechanics energy function, and with 1, 5, 10, 20, 30, or all amino acids allowed to mutate. Results are compared to an exact, "Cost Function Network" method that identifies the global minimum energy conformation (GMEC) in favorable cases. The designed sequences accurately reproduce experimental sequences in the hydrophobic core. The heuristic and REMC agree closely and reproduce the GMEC when it is known, with a few exceptions. Plain MC performs well for most cases, occasionally departing from the GMEC by 3-4 kcal/mol. With REMC, the diversity of the sequences sampled agrees with exact enumeration where the latter is possible: up to 2 kcal/mol above the GMEC. Beyond, room temperature replicas sample sequences up to 10 kcal/mol above the GMEC, providing thermal averages and a solution to the inverse protein folding problem. © 2016 Wiley Periodicals, Inc. PMID:27197555

  14. Comparing three stochastic search algorithms for computational protein design: Monte Carlo, replica exchange Monte Carlo, and a multistart, steepest-descent heuristic.

    PubMed

    Mignon, David; Simonson, Thomas

    2016-07-15

    Computational protein design depends on an energy function and an algorithm to search the sequence/conformation space. We compare three stochastic search algorithms: a heuristic, Monte Carlo (MC), and a Replica Exchange Monte Carlo method (REMC). The heuristic performs a steepest-descent minimization starting from thousands of random starting points. The methods are applied to nine test proteins from three structural families, with a fixed backbone structure, a molecular mechanics energy function, and with 1, 5, 10, 20, 30, or all amino acids allowed to mutate. Results are compared to an exact, "Cost Function Network" method that identifies the global minimum energy conformation (GMEC) in favorable cases. The designed sequences accurately reproduce experimental sequences in the hydrophobic core. The heuristic and REMC agree closely and reproduce the GMEC when it is known, with a few exceptions. Plain MC performs well for most cases, occasionally departing from the GMEC by 3-4 kcal/mol. With REMC, the diversity of the sequences sampled agrees with exact enumeration where the latter is possible: up to 2 kcal/mol above the GMEC. Beyond, room temperature replicas sample sequences up to 10 kcal/mol above the GMEC, providing thermal averages and a solution to the inverse protein folding problem. © 2016 Wiley Periodicals, Inc.

  15. Status of whitebarkpine in the Greater Yellowstone Ecosystem: A step-trend analysis comparing 2004-2007 to 2008-2011

    USGS Publications Warehouse

    Shanahan, Erin; Irvine, Kathryn M.; Roberts, Dave; Litt, Andrea R.; Legg, Kristin; Daley, Rob; Chambers, Nina

    2014-01-01

    Whitebark pine (Pinus albicaulis) is a foundation and keystone species in upper subalpine environments of the northern Rocky Mountains that strongly influences the biodiversity and productivity of high-elevation ecosystems (Tomback et al. 2001, Ellison et al. 2005). Throughout its historic range, whitebark pine has decreased significantly as a major component of high-elevation forests. As a result, it is critical to understand the challenges to whitebark pine—not only at the tree and stand level, but also as these factors influence the distribution of whitebark pine across the Greater Yellowstone Ecosystem (GYE). In 2003, the National Park Service (NPS) Greater Yellowstone Inventory & Monitoring Network identified whitebark pine as one of twelve significant natural resource indicators or vital signs to monitor (Jean et al. 2005, Fancy et al. 2009) and initiated a long-term, collaborative monitoring program. Partners in this effort include the U.S. Geological Survey, U.S. Forest Service, and Montana State University with representatives from each comprising the Greater Yellowstone Whitebark Pine Monitoring Working Group. The objectives of the monitoring program are to assess trends in (1) the proportion of live, whitebark pine trees (>1.4-m tall) infected with white pine blister rust (blister rust); (2) to document blister rust infection severity by the occurrence and location of persisting and new infections; (3) to determine mortality of whitebark pine trees and describe potential factors contributing to the death of trees; and (4) to assess the multiple components of the recruitment of understory whitebark pine into the reproductive population. In this report we summarize the past eight years (2004-2011) of whitebark pine status and trend monitoring in the GYE. Our study area encompasses six national forests (NF), two national parks (NP), as well as state and private lands in portions of Wyoming, Montana, and Idaho; this area is collectively described as the

  16. [Variation characteristics of CO2 flux in Phyllostachys edulis forest ecosystem in subtropical region of China].

    PubMed

    Sun, Cheng; Jiang, Hong; Zhou, Guo-Mo; Yang, Shuang; Chen, Yun-Fei

    2013-10-01

    By using eddy covariance technique, this paper studied the CO2 flux in a Phyllostachys edulis forest ecosystem with high-efficiency management in Zhejiang Province of China from December, 2010 to November, 2011, and analyzed the variations of net ecosystem exchange (NEE), ecosystem respiration (RE), and gross ecosystem exchange (GEE). During the study period, the monthly NEE was always negative, with the maximum (-99.33 g C x m(-2)) in July and the minimum (-23.49 g C x m(-2)) in November, and the seasonal change showed a bimodal shape. The average diurnal change of the monthly CO2 flux varied greatly from -0.30 g CO2 x m(-2) x s(-1) (January) to -0.60 g CO2 x m(-2) x s(-1) (September). The NEE at the time point of positive and negative conversion had obvious seasonal characteristics. The yearly RE changed in unimodal shape, with the maximum in summer and the minimum in winter. The RE at nighttime had significant negative correlation with soil temperature. The yearly NEE, RE, and GEE were -668.40, 932.55, and -1600.95 g C x m(-2) x a(-1), respectively, among which, the NEE occupied 41.8% of the GEE. As compared with other ecosystems, P. edulis forest ecosystem had a strong capability in carbon sequestration. PMID:24483062

  17. Experimental Ecosystems Sealed in Glass

    NASA Technical Reports Server (NTRS)

    Hanson, J. A.

    1985-01-01

    Report describes investigation of dynamics of microbial ecosystems sealed in 1-liter flasks and exposed to Sunlight or artifical light for extended periods. Many organisms survived more than 15 years. Such systems have primary productivity and quantum efficiencies comparable to estimates for Earth's ecosystems.

  18. Unravelling the carbon and sulphur metabolism in coastal soil ecosystems using comparative cultivation-independent genome-level characterisation of microbial communities.

    PubMed

    Yousuf, Basit; Kumar, Raghawendra; Mishra, Avinash; Jha, Bhavanath

    2014-01-01

    Bacterial autotrophy contributes significantly to the overall carbon balance, which stabilises atmospheric CO2 concentration and decelerates global warming. Little attention has been paid to different modes of carbon/sulphur metabolism mediated by autotrophic bacterial communities in terrestrial soil ecosystems. We studied these pathways by analysing the distribution and abundance of the diagnostic metabolic marker genes cbbM, apsA and soxB, which encode for ribulose-1,5-bisphosphate carboxylase/oxygenase, adenosine phosphosulphate reductase and sulphate thiohydrolase, respectively, among different contrasting soil types. Additionally, the abundance of community members was assessed by quantifying the gene copy numbers for 16S rRNA, cbbL, cbbM, apsA and soxB. Distinct compositional differences were observed among the clone libraries, which revealed a dominance of phylotypes associated with carbon and sulphur cycling, such as Gammaproteobacteria (Thiohalomonas, Allochromatium, Chromatium, Thiomicrospira) and Alphaproteobacteria (Rhodopseudomonas, Rhodovulum, Paracoccus). The rhizosphere soil was devoid of sulphur metabolism, as the soxB and apsA genes were not observed in the rhizosphere metagenome, which suggests the absence or inadequate representation of sulphur-oxidising bacteria. We hypothesise that the novel Gammaproteobacteria sulphur oxidisers might be actively involved in sulphur oxidation and inorganic carbon fixation, particularly in barren saline soil ecosystems, suggesting their significant putative ecological role and contribution to the soil carbon pool.

  19. Ecosystem Service Valuation Assessments for Protected Area Management: A Case Study Comparing Methods Using Different Land Cover Classification and Valuation Approaches.

    PubMed

    Whitham, Charlotte E L; Shi, Kun; Riordan, Philip

    2015-01-01

    Accurate and spatially-appropriate ecosystem service valuations are vital for decision-makers and land managers. Many approaches for estimating ecosystem service value (ESV) exist, but their appropriateness under specific conditions or logistical limitations is not uniform. The most accurate techniques are therefore not always adopted. Six different assessment approaches were used to estimate ESV for a National Nature Reserve in southwest China, across different management zones. These approaches incorporated two different land-use land cover (LULC) maps and development of three economic valuation techniques, using globally or locally-derived data. The differences in ESV across management zones for the six approaches were largely influenced by the classifications of forest and farmland and how they corresponded with valuation coefficients. With realistic limits on access to time, data, skills and resources, and using acquired estimates from globally-relevant sources, the Buffer zone was estimated as the most valuable (2.494 million ± 1.371 million CNY yr(-1) km(-2)) and the Non-protected zone as the least valuable (770,000 ± 4,600 CNY yr(-1) km(-2)). However, for both LULC maps, when using the locally-based and more time and skill-intensive valuation approaches, this pattern was generally reversed. This paper provides a detailed practical example of how ESV can differ widely depending on the availability and appropriateness of LULC maps and valuation approaches used, highlighting pitfalls for the managers of protected areas.

  20. Ecosystem Service Valuation Assessments for Protected Area Management: A Case Study Comparing Methods Using Different Land Cover Classification and Valuation Approaches

    PubMed Central

    Whitham, Charlotte E. L.

    2015-01-01

    Accurate and spatially-appropriate ecosystem service valuations are vital for decision-makers and land managers. Many approaches for estimating ecosystem service value (ESV) exist, but their appropriateness under specific conditions or logistical limitations is not uniform. The most accurate techniques are therefore not always adopted. Six different assessment approaches were used to estimate ESV for a National Nature Reserve in southwest China, across different management zones. These approaches incorporated two different land-use land cover (LULC) maps and development of three economic valuation techniques, using globally or locally-derived data. The differences in ESV across management zones for the six approaches were largely influenced by the classifications of forest and farmland and how they corresponded with valuation coefficients. With realistic limits on access to time, data, skills and resources, and using acquired estimates from globally-relevant sources, the Buffer zone was estimated as the most valuable (2.494 million ± 1.371 million CNY yr-1 km-2) and the Non-protected zone as the least valuable (770,000 ± 4,600 CNY yr-1 km-2). However, for both LULC maps, when using the locally-based and more time and skill-intensive valuation approaches, this pattern was generally reversed. This paper provides a detailed practical example of how ESV can differ widely depending on the availability and appropriateness of LULC maps and valuation approaches used, highlighting pitfalls for the managers of protected areas. PMID:26086191

  1. Ecosystem Service Valuation Assessments for Protected Area Management: A Case Study Comparing Methods Using Different Land Cover Classification and Valuation Approaches.

    PubMed

    Whitham, Charlotte E L; Shi, Kun; Riordan, Philip

    2015-01-01

    Accurate and spatially-appropriate ecosystem service valuations are vital for decision-makers and land managers. Many approaches for estimating ecosystem service value (ESV) exist, but their appropriateness under specific conditions or logistical limitations is not uniform. The most accurate techniques are therefore not always adopted. Six different assessment approaches were used to estimate ESV for a National Nature Reserve in southwest China, across different management zones. These approaches incorporated two different land-use land cover (LULC) maps and development of three economic valuation techniques, using globally or locally-derived data. The differences in ESV across management zones for the six approaches were largely influenced by the classifications of forest and farmland and how they corresponded with valuation coefficients. With realistic limits on access to time, data, skills and resources, and using acquired estimates from globally-relevant sources, the Buffer zone was estimated as the most valuable (2.494 million ± 1.371 million CNY yr(-1) km(-2)) and the Non-protected zone as the least valuable (770,000 ± 4,600 CNY yr(-1) km(-2)). However, for both LULC maps, when using the locally-based and more time and skill-intensive valuation approaches, this pattern was generally reversed. This paper provides a detailed practical example of how ESV can differ widely depending on the availability and appropriateness of LULC maps and valuation approaches used, highlighting pitfalls for the managers of protected areas. PMID:26086191

  2. Electronic and magnetic properties of X2YZ and XYZ Heusler compounds: a comparative study of density functional theory with different exchange-correlation potentials

    NASA Astrophysics Data System (ADS)

    Rai, D. P.; Sandeep; Shankar, A.; Pradhan Sakhya, Anup; Sinha, T. P.; Khenata, R.; Ghimire, M. P.; Thapa, R. K.

    2016-07-01

    The electronic and magnetic properties of Heusler compounds X2YZ and XYZ (X = Co, Ni, Pt, Fe; Y = Mn, Cr, Vi; Z = Al, Sb, Ga) are investigated by using the density functional theory with generalized gradient approximation (GGA), GGA plus U (LSDA+U), and modified Becke-Johnson (mBJ) exchange potential. It is found that the half-metallic gaps are generally widened reasonably by LSDA+U and mBJ as compared to the conventional GGA. For the Co-based Heusler compounds the inclusion of U in GGA leads to a larger minority band gap while it is destroyed for Fe2VAl and NiMnSb. The magnetic properties of Co2VSi and Co2VSn are well defined within LSDA+U and mBJ with an exact integer value of magnetic moment. The band gaps of Fe2VAl and CoMnSb given by mBJ are in good agreement with the available experimental data of x-ray absorption spectroscopy. Except for the reasonably larger band gap, the mBJ band structure is almost same as that of GGA but is remarkably different from that of LSDA+U.

  3. Electronic and magnetic properties of X2YZ and XYZ Heusler compounds: a comparative study of density functional theory with different exchange-correlation potentials

    NASA Astrophysics Data System (ADS)

    Rai, D. P.; Sandeep; Shankar, A.; Pradhan Sakhya, Anup; Sinha, T. P.; Khenata, R.; Ghimire, M. P.; Thapa, R. K.

    2016-07-01

    The electronic and magnetic properties of Heusler compounds X2YZ and XYZ (X = Co, Ni, Pt, Fe; Y = Mn, Cr, Vi; Z = Al, Sb, Ga) are investigated by using the density functional theory with generalized gradient approximation (GGA), GGA plus U (LSDA+U), and modified Becke‑Johnson (mBJ) exchange potential. It is found that the half-metallic gaps are generally widened reasonably by LSDA+U and mBJ as compared to the conventional GGA. For the Co-based Heusler compounds the inclusion of U in GGA leads to a larger minority band gap while it is destroyed for Fe2VAl and NiMnSb. The magnetic properties of Co2VSi and Co2VSn are well defined within LSDA+U and mBJ with an exact integer value of magnetic moment. The band gaps of Fe2VAl and CoMnSb given by mBJ are in good agreement with the available experimental data of x-ray absorption spectroscopy. Except for the reasonably larger band gap, the mBJ band structure is almost same as that of GGA but is remarkably different from that of LSDA+U.

  4. Ecosystem services provided by bats.

    PubMed

    Kunz, Thomas H; Braun de Torrez, Elizabeth; Bauer, Dana; Lobova, Tatyana; Fleming, Theodore H

    2011-03-01

    Ecosystem services are the benefits obtained from the environment that increase human well-being. Economic valuation is conducted by measuring the human welfare gains or losses that result from changes in the provision of ecosystem services. Bats have long been postulated to play important roles in arthropod suppression, seed dispersal, and pollination; however, only recently have these ecosystem services begun to be thoroughly evaluated. Here, we review the available literature on the ecological and economic impact of ecosystem services provided by bats. We describe dietary preferences, foraging behaviors, adaptations, and phylogenetic histories of insectivorous, frugivorous, and nectarivorous bats worldwide in the context of their respective ecosystem services. For each trophic ensemble, we discuss the consequences of these ecological interactions on both natural and agricultural systems. Throughout this review, we highlight the research needed to fully determine the ecosystem services in question. Finally, we provide a comprehensive overview of economic valuation of ecosystem services. Unfortunately, few studies estimating the economic value of ecosystem services provided by bats have been conducted to date; however, we outline a framework that could be used in future studies to more fully address this question. Consumptive goods provided by bats, such as food and guano, are often exchanged in markets where the market price indicates an economic value. Nonmarket valuation methods can be used to estimate the economic value of nonconsumptive services, including inputs to agricultural production and recreational activities. Information on the ecological and economic value of ecosystem services provided by bats can be used to inform decisions regarding where and when to protect or restore bat populations and associated habitats, as well as to improve public perception of bats.

  5. Terrestrial ecosystems and climatic change

    SciTech Connect

    Emanuel, W.R. ); Schimel, D.S. . Natural Resources Ecology Lab.)

    1990-01-01

    The structure and function of terrestrial ecosystems depend on climate, and in turn, ecosystems influence atmospheric composition and climate. A comprehensive, global model of terrestrial ecosystem dynamics is needed. A hierarchical approach appears advisable given currently available concepts, data, and formalisms. The organization of models can be based on the temporal scales involved. A rapidly responding model describes the processes associated with photosynthesis, including carbon, moisture, and heat exchange with the atmosphere. An intermediate model handles subannual variations that are closely associated with allocation and seasonal changes in productivity and decomposition. A slow response model describes plant growth and succession with associated element cycling over decades and centuries. These three levels of terrestrial models are linked through common specifications of environmental conditions and constrain each other. 58 refs.

  6. Effect of environmental variables and stand structure on ecosystem respiration components in a Mediterranean beech forest.

    PubMed

    Guidolotti, Gabriele; Rey, Ana; D'Andrea, Ettore; Matteucci, Giorgio; De Angelis, Paolo

    2013-09-01

    The temporal variability of ecosystem respiration (RECO) has been reported to have important effects on the temporal variability of net ecosystem exchange, the net amount of carbon exchanged between an ecosystem and the atmosphere. However, our understanding of ecosystem respiration is rather limited compared with photosynthesis or gross primary productivity, particularly in Mediterranean montane ecosystems. In order to investigate how environmental variables and forest structure (tree classes) affect different respiration components and RECO in a Mediterranean beech forest, we measured soil, stem and leaf CO2 efflux rates with dynamic chambers and RECO by the eddy-covariance technique over 1 year (2007-2008). Ecosystem respiration showed marked seasonal variation, with the highest rates in spring and autumn and the lowest in summer. We found that the soil respiration (SR) was mainly controlled by soil water content below a threshold value of 0.2 m(3) m(-3), above which the soil temperature explained temporal variation in SR. Stem CO2 effluxes were influenced by air temperature and difference between tree classes with higher rates measured in dominant trees than in co-dominant ones. Leaf respiration (LR) varied significantly between the two canopy layers considered. Non-structural carbohydrates were a very good predictor of LR variability. We used these measurements to scale up respiration components to ecosystem respiration for the whole canopy and obtained cumulative amounts of carbon losses over the year. Based on the up-scaled chamber measurements, the relative contributions of soil, stem and leaves to the total annual CO2 efflux were: 56, 8 and 36%, respectively. These results confirm that SR is the main contributor of ecosystem respiration and provided an insight on the driving factors of respiration in Mediterranean montane beech forests. PMID:24044943

  7. [Comparative morpho-functional characteristics of the organs of the reproductive system of small mammals under conditions of anthropogenic transformation of Southern Ural steppe ecosystems].

    PubMed

    Shevliuk, N N; Blinova, E V; Bokov, D A; Demina, L L; Elina, E E; Meshkova, O A; Ryskulov, M F

    2013-01-01

    The morpho-functional characteristics of reproductive organs of small mammals--striped field mouse (Apodemus agrarius Pallas, 1771), house mouse (Mus musculus Linnaeus, 1758), wood mouse (Sylvaemus uralensis Pallas, 1811), common vole (Microtus arvalis Pallas, 1778), bank vole (Clethrionomys glareolus Schreber, 1780), steppe lemming (Lagurus lagurus Pallas, 1773), little suslik (Spermophilus pygmaeus Pallas, 1778), and red-heeked suslik (Spermophilus major Pallas, 1779)--belonging to the populations inhabiting anthropogenically modified steppe landscapes (zones influenced by the ferrous metallurgy plants and gas processing plant, as well as the territory of the large city) were studied using histological, electron microscopic, immunocytochemical and morphometric methods. In animals studied, inhabiting technologically modified ecosystems, in contrast to those from ecologically safe regions, the testis demonstrated the increased destruction of spermatogenic epithelium. In the ovaries, the accelerated exhaustion of follicular reserve was detected. The increased embryonic death rate was also observed. The portion of the animals participating in reproduction was enlarged, the female fecundity was increased, while the age at puberty was decreased. Among the animal species studied, the variable degree of stability against the effect of the negative factors was demonstrated.

  8. Soil and litter exchange of reactive trace gases

    EPA Science Inventory

    The soil and litter play an important role in the exchange of trace gases between terrestrial ecosystems and the atmosphere. - The exchange of ammonia between vegetation and the atmosphere is highly influenced by soil and litter emissions especially in managed ecosystems (grassla...

  9. Air-surface exchange of Hg0 measured by collocated micrometeorological and enclosure methods - Part 1: Data comparability and method characteristics

    NASA Astrophysics Data System (ADS)

    Zhu, W.; Sommar, J.; Lin, C.-J.; Feng, X.

    2014-09-01

    Reliable quantification of air-biosphere exchange flux of elemental mercury vapor (Hg0) is crucial for understanding global biogeochemical cycle of mercury. However, there has not been a standard analytical protocol for flux quantification, and little attention has been devoted to characterize the temporal variability and comparability of fluxes measured by different methods. In this study, we deployed a collocated set of micro-meteorological (MM) and enclosure measurement systems to quantify Hg0 flux over bare soil and low standing crop in an agricultural field. The techniques include relaxed eddy accumulation (REA), modified Bowen-ratio (MBR), aerodynamic gradient (AGM) as well as dynamic flux chambers of traditional (TDFC) and novel (NDFC) designs. The five systems and their measured fluxes were cross-examined with respect to magnitude, temporal trend and sensitivity to environmental variables. Fluxes measured by the MM and DFC methods showed distinct temporal trends. The former exhibited a highly dynamic temporal variability while the latter had much gradual temporal features. The diurnal characteristics reflected the difference in the fundamental processes driving the measurements. The correlations between NDFC and TDFC fluxes and between MBR and AGM fluxes were significant (R > 0.8, p < 0.05), but the correlation between DFC and MM instantaneous fluxes were from weak to moderate (R = 0.1-0.5). Statistical analysis indicated that the median of turbulent fluxes estimated by the three independent MM-techniques were not significantly different. Cumulative flux measured by TDFC is considerably lower (42% of AGM and 31% of MBR fluxes) while those measured by NDFC, AGM and MBR were similar (< 10% difference). This implicates that the NDFC technique, which accounts for internal friction velocity, effectively bridged the gap in measured Hg0 flux compared to MM techniques. Cumulated flux measured by REA was ~60% higher than the gradient-based fluxes. Environmental

  10. Multiple colonizations lead to cryptic biodiversity in an island ecosystem: comparative phylogeography of anchialine shrimp species in the Ryukyu Archipelago, Japan.

    PubMed

    Weese, David A; Fujita, Yoshihisa; Santos, Scott R

    2013-09-01

    Archipelagos of the Indo-West Pacific are considered to be among the richest in the world in biodiversity, and phylogeographic studies generally support either the center of origin or the center of accumulation hypothesis to explain this pattern. To differentiate between these competing hypotheses for organisms from the Indo-West Pacific anchialine ecosystem, defined as coastal bodies of mixohaline water fluctuating with the tides but having no direct oceanic connections, we investigated the genetic variation, population structure, and evolutionary history of three caridean shrimp species (Antecaridina lauensis, Halocaridinides trigonophthalma, and Metabetaeus minutus) in the Ryukyu Archipelago, Japan. We used two mitochondrial genes--cytochrome c oxidase subunit I (COI) and large ribosomal subunit (16S-rDNA)--complemented with genetic examination of available specimens from the same or closely related species from the Indian and Pacific Oceans. In the Ryukyus, each species encompassed 2-3 divergent (9.52%-19.2% COI p-distance) lineages, each having significant population structure and varying geographic distributions. Phylogenetically, the A. lauensis and M. minutus lineages in the Ryukyus were more closely related to ones from outside the archipelago than to one another. These results, when interpreted in the context of Pacific oceanographic currents and geologic history of the Ryukyus, imply multiple colonizations of the archipelago by the three species, consistent with the center of accumulation hypothesis. While this study contributes toward understanding the biodiversity, ecology, and evolution of organisms in the Ryukyus and the Indo-West Pacific, it also has potential utility in establishing conservation strategies for anchialine fauna of the Pacific Basin in general. PMID:24088794

  11. Biophysical regulation of carbon fluxes over an alpine meadow ecosystem in the eastern Tibetan Plateau

    NASA Astrophysics Data System (ADS)

    Wang, Shaoying; Zhang, Yu; Lü, Shihua; Su, Peixi; Shang, Lunyu; Li, Zhaoguo

    2016-06-01

    The eddy covariance method was used to measure net ecosystem CO2 exchange (NEE) between atmosphere and an alpine meadow ecosystem in the eastern Tibetan Plateau of China in 2010. Our results show that photosynthesis was reduced under low air temperature ( T a), high vapor pressure deficit (VPD), and medium soil water content (SWC) conditions, when compared to that under other T a (i.e., medium and high), VPD (i.e., low and medium), and SWC (i.e., low and high) conditions. The apparent temperature sensitivity of ecosystem respiration ( Q 10) declined with progressing phenology during the growing season and decreased with an increase of soil temperature ( T s) during the non-growing season. Increased ecosystem respiration ( R eco) was measured during spring soil thawing. By the path analysis, T a, T s, and VPD were the main control factors of CO2 exchange at 30-min scale in this alpine meadow. Integrated NEE, gross primary production (GPP), and R eco over the measured year were -156.4, 1164.3, and 1007.9 g C m-2, respectively. Zoige alpine meadow was a medium carbon sink based on published data for grassland ecosystems.

  12. Greenhouse gas exchange over grazed systems

    NASA Astrophysics Data System (ADS)

    Felber, R.; Ammann, C.; Neftel, A.

    2012-04-01

    Grasslands act as sinks and sources of greenhouse gases (GHG) and are, in conjunction with livestock production systems, responsible for a large share of GHG emissions. Whereas ecosystem scale flux measurements (eddy covariance) are commonly used to investigate CO2 exchange (and is becoming state-of-the-art for other GHGs, too), GHG emissions from agricultural animals are usually investigated on the scale of individual animals. Therefore eddy covariance technique has to be tested for combined systems (i.e. grazed systems). Our project investigates the ability of field scale flux measurements to reliably quantify the contribution of grazing dairy cows to the net exchange of CO2 and CH4. To quantify the contribution of the animals to the net flux the position, movement, and grazing/rumination activity of each cow are recorded. In combination with a detailed footprint analysis of the eddy covariance fluxes, the animal related CO2 and CH4 emissions are derived and compared to standard emission values derived from respiration chambers. The aim of the project is to test the assumption whether field scale CO2 flux measurements adequately include the respiration of grazing cows and to identify potential errors in ecosystem Greenhouse gas budgets.

  13. Comparing the Picture Exchange Communication System and the iPad™ for Communication of Students with Autism Spectrum Disorder and Developmental Delay

    ERIC Educational Resources Information Center

    Hill, Doris Adams; Flores, Margaret M.

    2014-01-01

    Both picture exchange, a low-tech picturebased communication system, and technologybased interventions, such as the iPad™ with communication application, are emerging treatments for students with autism spectrum disorder (ASD), according to the National Autism Center (2009). Recently, investigations regarding the use of the Apple iPad™ to…

  14. Climate change and viticulture in Mediterranean climates: the complex response of socio-ecosystems. A comparative case study from France and Australia (1955-2040)

    NASA Astrophysics Data System (ADS)

    Lereboullet, A.-L.; Beltrando, G.; Bardsley, D. K.

    2012-04-01

    The wine industry is very sensitive to extreme weather events, especially to temperatures above 35°C and drought. In a context of global climate change, Mediterranean climate regions are predicted to experience higher variability in rainfall and temperatures and an increased occurrence of extreme weather events. Some viticultural systems could be particularly at risk in those regions, considering their marginal position in the growth climatic range of Vitis vinifera, the long commercial lifespan of a vineyard, the high added-value of wine and the volatile nature of global markets. The wine industry, like other agricultural systems, is inserted in complex networks of climatic and non-climatic (other physical, economical, social and legislative) components, with constant feedbacks. We use a socio-ecosystem approach to analyse the adaptation of two Mediterranean viticultural systems to recent and future increase of extreme weather events. The present analysis focuses on two wine regions with a hot-summer Mediterranean climate (CSb type in the Köppen classification): Côtes-du-Roussillon in southern France and McLaren Vale in southern Australia. Using climate data from two synoptic weather stations, Perpignan (France) and Adelaide (Australia), with time series running from 1955 to 2010, we highlight changes in rainfall patterns and an increase in the number of days with Tx >35°c since the last three decades in both regions. Climate models (DRIAS project data for France and CSIRO Mk3.5 for Australia) project similar trends in the future. To date, very few projects have focused on an international comparison of the adaptive capacity of viticultural systems to climate change with a holistic approach. Here, the analysis of climate data was complemented by twenty in-depth semi-structured interviews with key actors of the two regional wine industries, in order to analyse adaptation strategies put in place regarding recent climate evolution. This mixed-methods approach

  15. Carbon monoxide exchange and partitioning of a managed mountain meadow

    NASA Astrophysics Data System (ADS)

    Wohlfahrt, G.; Hammerle, A.; Kitz, F.; Spielmann, F.

    2015-12-01

    With an average mole fraction of 100 ppb carbon monoxide (CO) plays a critical role in atmospheric chemistry and thus has an indirect global warming potential. While sources/sinks of CO on land at least partially cancel out each other, the magnitude of CO sources and sinks is highly uncertain. Even if direct CO fluxes from/to land ecosystems are very much likely clearly lower in magnitude compared to anthropogenic emissions, biomass burning, emissions from chemical precursors and the OH sink, it may be premature to neglect any direct contributions of land ecosystems to the CO budget. In addition, changes in global climate and resulting changes in global productivity may require re-evaluating older data and assumptions. One major reason for the large uncertainty is a general scarcity of empirical data. An additional factor contributing to the uncertainty is the lack of ecosystem-scale CO exchange measurements, i.e. CO flux data that encompass all sources and sinks within an ecosystem. Here we present data on continuous eddy covariance measurements of CO-fluxes above a managed mountain grassland in combination with soil chamber flux measurements, within- and above-canopy concentration profiles and an inverse Lagrangian analysis to disentangle sinks and sources of CO. Preliminary results show the grassland ecosystem to be a net source for CO during daytime, with increasing flux rates at higher solar radiation. At night, if at all, the meadow is a slight sink for CO. The same holds true for soil flux measurements.

  16. When vegetation change alters ecosystem water availability.

    PubMed

    Scott, Russell L; Huxman, Travis E; Barron-Gafford, Greg A; Darrel Jenerette, G; Young, Jessica M; Hamerlynck, Erik P

    2014-07-01

    The combined effects of vegetation and climate change on biosphere-atmosphere water vapor (H2 O) and carbon dioxide (CO2 ) exchanges are expected to vary depending, in part, on how biotic activity is controlled by and alters water availability. This is particularly important when a change in ecosystem composition alters the fractional covers of bare soil, grass, and woody plants so as to influence the accessibility of shallower vs. deeper soil water pools. To study this, we compared 5 years of eddy covariance measurements of H2 O and CO2 fluxes over a riparian grassland, shrubland, and woodland. In comparison with the surrounding upland region, groundwater access at the riparian sites increased net carbon uptake (NEP) and evapotranspiration (ET), which were sustained over more of the year. Among the sites, the grassland used less of the stable groundwater resource, and increasing woody plant density decoupled NEP and ET from incident precipitation (P), resulting in greater exchange rates that were less variable year to year. Despite similar gross patterns, how groundwater accessibility affected NEP was more complex than ET. The grassland had higher respiration (Reco ) costs. Thus, while it had similar ET and gross carbon uptake (GEP) to the shrubland, grassland NEP was substantially less. Also, grassland carbon fluxes were more variable due to occasional flooding at the site, which both stimulated and inhibited NEP depending upon phenology. Woodland NEP was large, but surprisingly similar to the less mature, sparse shrubland, even while having much greater GEP. Woodland Reco was greater than the shrubland and responded strongly and positively to P, which resulted in a surprising negative NEP response to P. This is likely due to the large accumulation of carbon aboveground and in the surface soil. These long-term observations support the strong role that water accessibility can play when determining the consequences of ecosystem vegetation change. PMID:24777485

  17. Astronomical Ecosystems

    NASA Astrophysics Data System (ADS)

    Neuenschwander, D. E.; Finkenbinder, L. R.

    2004-05-01

    Just as quetzals and jaguars require specific ecological habitats to survive, so too must planets occupy a tightly constrained astronomical habitat to support life as we know it. With this theme in mind we relate the transferable features of our elementary astronomy course, "The Astronomical Basis of Life on Earth." Over the last five years, in a team-taught course that features a spring break field trip to Costa Rica, we have introduced astronomy through "astronomical ecosystems," emphasizing astronomical constraints on the prospects for life on Earth. Life requires energy, chemical elements, and long timescales, and we emphasize how cosmological, astrophysical, and geological realities, through stabilities and catastrophes, create and eliminate niches for biological life. The linkage between astronomy and biology gets immediate and personal: for example, studies in solar energy production are followed by hikes in the forest to examine the light-gathering strategies of photosynthetic organisms; a lesson on tides is conducted while standing up to our necks in one on a Pacific beach. Further linkages between astronomy and the human timescale concerns of biological diversity, cultural diversity, and environmental sustainability are natural and direct. Our experience of teaching "astronomy as habitat" strongly influences our "Astronomy 101" course in Oklahoma as well. This "inverted astrobiology" seems to transform our student's outlook, from the universe being something "out there" into something "we're in!" We thank the SNU Science Alumni support group "The Catalysts," and the SNU Quetzal Education and Research Center, San Gerardo de Dota, Costa Rica, for their support.

  18. Comparative rates of exchange behind reflected shock waves. 2. /sup 15/No + C/sup 18/O vs. /sup 15/NO + N/sub 2/

    SciTech Connect

    Bopp, A.F.; Kern, R.D.; Niki, T.; Stack, G.M.

    1980-10-02

    The rates of isotopic exchange of nitric oxide with nitrogen and carbon monoxide were studied over the temperature range 2700-3800 K by analyzing the gas from the reflected shock zone at 20-..mu..s intervals with a time-of-flight mass spectrometer. Two mixtures containing 4% /sup 15/NO-4% N/sub 2/ in one and 4% /sup 15/NO-4% C/sup 18/O in the other were each diluted with a mixture of inert gases (Ne-Ar-Kr). The reacting gases were sampled dynamically in order to determine the time dependence of the products; i.e., m/e 29 and 30 for the first mixture and m/e 28 and 33 for the second mixture. The exchange of nitric oxide and carbon monoxide took place readily over the range investigated. The reaction profiles displayed nonlinear growth of the products with respect to reaction time. Computer simulation of the product profiles assuming an atomic mechanism revealed reasonable agreement with the experimental data. In contrast to /sup 15/NO + C/sup 18/O, the exchange of /sup 15/NO + N/sub 2/ did not occur to any measurable extent in accordance with the predictions of an atomic mechanism.

  19. Understanding the Adsorption of PFOA on MIL-101(Cr)-Based Anionic-Exchange Metal-Organic Frameworks: Comparing DFT Calculations with Aqueous Sorption Experiments.

    PubMed

    Liu, Kai; Zhang, Siyu; Hu, Xiyue; Zhang, Kunyang; Roy, Ajay; Yu, Gang

    2015-07-21

    To examine the effects of different functionalization methods on adsorption behavior, anionic-exchange MIL-101(Cr) metal-organic frameworks (MOFs) were synthesized using preassembled modification (PAM) and postsynthetic modification (PSM) methods. Perfluorooctanoic acid (PFOA) adsorption results indicated that the maximum PFOA adsorption capacity was 1.19 and 1.89 mmol g(-1) for anionic-exchange MIL-101(Cr) prepared by PAM and PSM, respectively. The sorption equilibrium was rapidly reached within 60 min. Our results indicated that PSM is a better modification technique for introducing functional groups onto MOFs for adsorptive removal because PAM places functional groups onto the aperture of the nanopore, which hinders the entrance of organic contaminants. Our experimental results and the results of complementary density functional theory calculations revealed that in addition to the anion-exchange mechanism, the major PFOA adsorption mechanism is a combination of Lewis acid/base complexation between PFOA and Cr(III) and electrostatic interaction between PFOA and the protonated carboxyl groups of the bdc (terephthalic acid) linker. PMID:26066631

  20. Understanding the Adsorption of PFOA on MIL-101(Cr)-Based Anionic-Exchange Metal-Organic Frameworks: Comparing DFT Calculations with Aqueous Sorption Experiments.

    PubMed

    Liu, Kai; Zhang, Siyu; Hu, Xiyue; Zhang, Kunyang; Roy, Ajay; Yu, Gang

    2015-07-21

    To examine the effects of different functionalization methods on adsorption behavior, anionic-exchange MIL-101(Cr) metal-organic frameworks (MOFs) were synthesized using preassembled modification (PAM) and postsynthetic modification (PSM) methods. Perfluorooctanoic acid (PFOA) adsorption results indicated that the maximum PFOA adsorption capacity was 1.19 and 1.89 mmol g(-1) for anionic-exchange MIL-101(Cr) prepared by PAM and PSM, respectively. The sorption equilibrium was rapidly reached within 60 min. Our results indicated that PSM is a better modification technique for introducing functional groups onto MOFs for adsorptive removal because PAM places functional groups onto the aperture of the nanopore, which hinders the entrance of organic contaminants. Our experimental results and the results of complementary density functional theory calculations revealed that in addition to the anion-exchange mechanism, the major PFOA adsorption mechanism is a combination of Lewis acid/base complexation between PFOA and Cr(III) and electrostatic interaction between PFOA and the protonated carboxyl groups of the bdc (terephthalic acid) linker.

  1. Ecoregion Framework Facilitating Synthesis and Up-scaling of Tower CO2 Exchange Measurements

    NASA Astrophysics Data System (ADS)

    Gilmanov, T. G.; Wylie, B. K.; Howard, D. M.; Zhang, L.

    2015-12-01

    As the flux-tower studies of terrestrial CO2 exchange are currently approaching the stage of generalization and up-scaling, there is a growing need for an effective framework for these efforts facilitating comparative analysis and synthesis of flux tower data. Developed in the 1980s to denote a region with recurring patterns of ecosystems with similar climatic, vegetation, soil, and relief conditions, during the past decades the ecoregion concept was widely used as a tool combining modeling, GIS and remote sensing techniques in environmental and nature conservation project at the national and international scale. We describe application of the ecoregion approach to synthesis and up-scaling of the tower CO2 exchange measurements in the three major ecoregions of the Great Plains: Shortgrass steppe (SGS), Mixed prairie (MP), and Tallgrass prairie (TP). Original data of tower CO2 exchange (NEE) measurements during the 1996-2013 period covering 23 years at 6 sites in SGS, 86 years at 21 sites in MP, and 80 years at 24 sites in TP were partitioned into the gross photosynthesis (Pg) and ecosystem respiration (Re) components using the light-soil temperature-VPD response method. We present ecoregion-specific multivariate models relating gross photosynthesis, ecosystem respiration and major ecosystem-scale ecophysiological parameters (photosynthetic capacity, apparent quantum yield, light-use efficiency, daytime respiration intensity) to on-site (climatic, plant, soil) and remotely sensed (NDVI) drivers of CO2 exchange. Superposition of these models on GIS layers of appropriate drivers was used to describe geographic patterns (maps) of photosynthesis, respiration, net CO2 exchange and ecophysiological parameters across the Great Plains. The source-sink activity at the ecoregion-scale was quantified by calculating spatial integrals of CO2 exchange characteristic over GIS pixels represented by the tower measurements.

  2. Effects of experimental water table and temperature manipulations on ecosystem CO2 fluxes in an Alaskan rich fen

    USGS Publications Warehouse

    Chivers, M.R.; Turetsky, M.R.; Waddington, J.M.; Harden, J.W.; McGuire, A.D.

    2009-01-01

    Peatlands store 30% of the world's terrestrial soil carbon (C) and those located at northern latitudes are expected to experience rapid climate warming. We monitored growing season carbon dioxide (CO2) fluxes across a factorial design of in situ water table (control, drought, and flooded plots) and soil warming (control vs. warming via open top chambers) treatments for 2 years in a rich fen located just outside the Bonanza Creek Experimental Forest in interior Alaska. The drought (lowered water table position) treatment was a weak sink or small source of atmospheric CO2 compared to the moderate atmospheric CO2 sink at our control. This change in net ecosystem exchange was due to lower gross primary production and light-saturated photosynthesis rather than increased ecosystem respiration. The flooded (raised water table position) treatment was a greater CO2 sink in 2006 due largely to increased early season gross primary production and higher light-saturated photosynthesis. Although flooding did not have substantial effects on rates of ecosystem respiration, this water table treatment had lower maximum respiration rates and a higher temperature sensitivity of ecosystem respiration than the control plot. Surface soil warming increased both ecosystem respiration and gross primary production by approximately 16% compared to control (ambient temperature) plots, with no net effect on net ecosystem exchange. Results from this rich fen manipulation suggest that fast responses to drought will include reduced ecosystem C storage driven by plant stress, whereas inundation will increase ecosystem C storage by stimulating plant growth. ?? 2009 Springer Science+Business Media, LLC.

  3. Ecosystem service valuations of mangrove ecosystems to inform decision making and future valuation exercises.

    PubMed

    Mukherjee, Nibedita; Sutherland, William J; Dicks, Lynn; Hugé, Jean; Koedam, Nico; Dahdouh-Guebas, Farid

    2014-01-01

    The valuation of ecosystem services is a complex process as it includes several dimensions (ecological, socio-cultural and economic) and not all of these can be quantified in monetary units. The aim of this paper is to conduct an ecosystem services valuation study for mangroves ecosystems, the results of which can be used to inform governance and management of mangroves. We used an expert-based participatory approach (the Delphi technique) to identify, categorize and rank the various ecosystem services provided by mangrove ecosystems at a global scale. Subsequently we looked for evidence in the existing ecosystem services literature for monetary valuations of these ecosystem service categories throughout the biogeographic distribution of mangroves. We then compared the relative ranking of ecosystem service categories between the monetary valuations and the expert based analysis. The experts identified 16 ecosystem service categories, six of which are not adequately represented in the literature. There was no significant correlation between the expert based valuation (the Delphi technique) and the economic valuation, indicating that the scope of valuation of ecosystem services needs to be broadened. Acknowledging this diversity in different valuation approaches, and developing methodological frameworks that foster the pluralism of values in ecosystem services research, are crucial for maintaining the credibility of ecosystem services valuation. To conclude, we use the findings of our dual approach to valuation to make recommendations on how to assess and manage the ecosystem services provided by mangrove ecosystems.

  4. Ecosystem service valuations of mangrove ecosystems to inform decision making and future valuation exercises.

    PubMed

    Mukherjee, Nibedita; Sutherland, William J; Dicks, Lynn; Hugé, Jean; Koedam, Nico; Dahdouh-Guebas, Farid

    2014-01-01

    The valuation of ecosystem services is a complex process as it includes several dimensions (ecological, socio-cultural and economic) and not all of these can be quantified in monetary units. The aim of this paper is to conduct an ecosystem services valuation study for mangroves ecosystems, the results of which can be used to inform governance and management of mangroves. We used an expert-based participatory approach (the Delphi technique) to identify, categorize and rank the various ecosystem services provided by mangrove ecosystems at a global scale. Subsequently we looked for evidence in the existing ecosystem services literature for monetary valuations of these ecosystem service categories throughout the biogeographic distribution of mangroves. We then compared the relative ranking of ecosystem service categories between the monetary valuations and the expert based analysis. The experts identified 16 ecosystem service categories, six of which are not adequately represented in the literature. There was no significant correlation between the expert based valuation (the Delphi technique) and the economic valuation, indicating that the scope of valuation of ecosystem services needs to be broadened. Acknowledging this diversity in different valuation approaches, and developing methodological frameworks that foster the pluralism of values in ecosystem services research, are crucial for maintaining the credibility of ecosystem services valuation. To conclude, we use the findings of our dual approach to valuation to make recommendations on how to assess and manage the ecosystem services provided by mangrove ecosystems. PMID:25243852

  5. Ecosystem Service Valuations of Mangrove Ecosystems to Inform Decision Making and Future Valuation Exercises

    PubMed Central

    Mukherjee, Nibedita; Sutherland, William J.; Dicks, Lynn; Hugé, Jean; Koedam, Nico; Dahdouh-Guebas, Farid

    2014-01-01

    The valuation of ecosystem services is a complex process as it includes several dimensions (ecological, socio-cultural and economic) and not all of these can be quantified in monetary units. The aim of this paper is to conduct an ecosystem services valuation study for mangroves ecosystems, the results of which can be used to inform governance and management of mangroves. We used an expert-based participatory approach (the Delphi technique) to identify, categorize and rank the various ecosystem services provided by mangrove ecosystems at a global scale. Subsequently we looked for evidence in the existing ecosystem services literature for monetary valuations of these ecosystem service categories throughout the biogeographic distribution of mangroves. We then compared the relative ranking of ecosystem service categories between the monetary valuations and the expert based analysis. The experts identified 16 ecosystem service categories, six of which are not adequately represented in the literature. There was no significant correlation between the expert based valuation (the Delphi technique) and the economic valuation, indicating that the scope of valuation of ecosystem services needs to be broadened. Acknowledging this diversity in different valuation approaches, and developing methodological frameworks that foster the pluralism of values in ecosystem services research, are crucial for maintaining the credibility of ecosystem services valuation. To conclude, we use the findings of our dual approach to valuation to make recommendations on how to assess and manage the ecosystem services provided by mangrove ecosystems. PMID:25243852

  6. Complete genome sequence and comparative analysis of Acetobacter pasteurianus 386B, a strain well-adapted to the cocoa bean fermentation ecosystem

    PubMed Central

    2013-01-01

    Background Acetobacter pasteurianus 386B, an acetic acid bacterium originating from a spontaneous cocoa bean heap fermentation, proved to be an ideal functional starter culture for coca bean fermentations. It is able to dominate the fermentation process, thereby resisting high acetic acid concentrations and temperatures. However, the molecular mechanisms underlying its metabolic capabilities and niche adaptations are unknown. In this study, whole-genome sequencing and comparative genome analysis was used to investigate this strain’s mechanisms to dominate the cocoa bean fermentation process. Results The genome sequence of A. pasteurianus 386B is composed of a 2.8-Mb chromosome and seven plasmids. The annotation of 2875 protein-coding sequences revealed important characteristics, including several metabolic pathways, the occurrence of strain-specific genes such as an endopolygalacturonase, and the presence of mechanisms involved in tolerance towards various stress conditions. Furthermore, the low number of transposases in the genome and the absence of complete phage genomes indicate that this strain might be more genetically stable compared with other A. pasteurianus strains, which is an important advantage for the use of this strain as a functional starter culture. Comparative genome analysis with other members of the Acetobacteraceae confirmed the functional properties of A. pasteurianus 386B, such as its thermotolerant nature and unique genetic composition. Conclusions Genome analysis of A. pasteurianus 386B provided detailed insights into the underlying mechanisms of its metabolic features, niche adaptations, and tolerance towards stress conditions. Combination of these data with previous experimental knowledge enabled an integrated, global overview of the functional characteristics of this strain. This knowledge will enable improved fermentation strategies and selection of appropriate acetic acid bacteria strains as functional starter culture for cocoa bean

  7. Optimization of Heat Exchangers

    SciTech Connect

    Ivan Catton

    2010-10-01

    The objective of this research is to develop tools to design and optimize heat exchangers (HE) and compact heat exchangers (CHE) for intermediate loop heat transport systems found in the very high temperature reator (VHTR) and other Generation IV designs by addressing heat transfer surface augmentation and conjugate modeling. To optimize heat exchanger, a fast running model must be created that will allow for multiple designs to be compared quickly. To model a heat exchanger, volume averaging theory, VAT, is used. VAT allows for the conservation of mass, momentum and energy to be solved for point by point in a 3 dimensional computer model of a heat exchanger. The end product of this project is a computer code that can predict an optimal configuration for a heat exchanger given only a few constraints (input fluids, size, cost, etc.). As VAT computer code can be used to model characteristics )pumping power, temperatures, and cost) of heat exchangers more quickly than traditional CFD or experiment, optimization of every geometric parameter simultaneously can be made. Using design of experiment, DOE and genetric algorithms, GE, to optimize the results of the computer code will improve heat exchanger disign.

  8. Comparative Intradermal Tuberculin Testing of Free-Ranging African Buffaloes (Syncerus caffer) Captured for Ex Situ Conservation in the Kafue Basin Ecosystem in Zambia.

    PubMed

    Munang'andu, Hetron Mweemba; Siamudaala, Victor; Matandiko, Wigganson; Nambota, Andrew; Muma, John Bwalya; Mweene, Aaron Simanyengwe; Munyeme, Musso

    2011-01-01

    Bovine tuberculosis (BTB) is endemic in African buffaloes (Syncerus caffer) in some National Parks in Southern Africa, whilst no studies have been conducted on BTB on buffalo populations in Zambia. The increased demand for ecotourism and conservation of the African buffalo on private owned game ranches has prompted the Zambian Wildlife Authority (ZAWA) and private sector in Zambia to generate a herd of "BTB-free buffaloes" for ex situ conservation. In the present study, 86 African buffaloes from four different herds comprising a total of 530 animals were investigated for the presence of BTB for the purpose of generating "BTB free" buffalo for ex-situ conservation. Using the comparative intradermal tuberculin test (CIDT) the BTB status at both individual animal and herd level was estimated to be 0.0% by the CIDT technique. Compared to Avian reactors only, a prevalence of 5.8% was determined whilst for Bovine-only reactors a prevalence of 0.0% was determined. These results suggest the likelihood of buffalo herds in the Kafue National Park being free of BTB.

  9. Sustaining the Landscape: A Method for Comparing Current and Desired Future Conditions of Forest Ecosystems in the North Cumberland Plateau and Mountains

    SciTech Connect

    Druckenbrod, D.L.

    2004-12-22

    This project initiates an integrated-landscape conservation approach within the Northern Cumberlands Project Area in Tennessee and Kentucky. The mixed mesophytic forests within the Cumberland Plateau and Mountains are among the most diverse in North America; however, these forests have been impacted by and remain threatened from changes in land use across this landscape. The integrated-landscape conservation approach presented in this report outlines a sequence of six conservation steps. This report considers the first three of these steps in two, successive stages. Stage 1 compares desired future conditions (DFCs) and current prevailing conditions (CPCs) at the landscape-scale utilizing remote sensing imagery, remnant forests, and descriptions of historical forest types within the Cumberland Plateau. Subsequently, Stage 2 compares DFCs and CPCs for at-risk forest types identified in Stage 1 utilizing structural, compositional, or functional attributes from USFS Forest Inventory and Analysis data. Ecological indicators will be developed from each stage that express the gaps between these two realizations of the landscape. The results from these first three steps will directly contribute to the final three steps of the integrated-landscape conservation approach by providing guidance for the generation of new conservation strategies in the Northern Cumberland Plateau and Mountains.

  10. When vegetation change alters ecosystem water availability

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The combined effects of vegetation and climate change on biosphere-atmosphere water vapor (H2O) and carbon dioxide (CO2) exchanges are expected to vary depending, in part, on how biotic activity is controlled by and alters water availability. This is particularly important when a change in ecosystem...

  11. Microtube strip heat exchanger

    SciTech Connect

    Doty, F.D.

    1991-10-16

    This progress report is for the September--October 1991 quarter. We have demonstrated feasibility of higher specific conductance by a factor of five than any other work in high-temperature gas-to-gas exchangers. These laminar-flow, microtube exchangers exhibit extremely low pressure drop compared to alternative compact designs under similar conditions because of their much shorter flow length and larger total flow area for lower flow velocities. The design appears to be amenable to mass production techniques, but considerable process development remains. The reduction in materials usage and the improved heat exchanger performance promise to be of enormous significance in advanced engine designs and in cryogenics.

  12. Improving policy and practice to promote equity and social justice - a qualitative comparative analysis building on key learnings from a twinning exchange between England and the US.

    PubMed

    Blanchard, Claire; Narle, Ginder; Gibbs, Martin; Ruddock, Charmaine; Grady, Michael; Brookes, Chris; Hopkins, Trevor; Norwood, Jayne

    2013-12-01

    Community health promotion interventions, targeted at marginalised populations and focusing on addressing the social determinants of health (SDH) to reduce health inequalities and addressing the processes of exclusion, are an important strategy to prevent and control non-communicable diseases (NCDs) and promote the health of underprivileged and under-resourced groups. This article builds on key lessons learnt from a learning exchange between Communities for Health in England and the Racial and Ethnic Approaches to Community Health across the US (REACH US) communities that are tackling health inequities. It presents a qualitative analysis further capturing information about specific community interventions involved in the exchange and identifying lessons learnt. This exchange was led by a partnership between the US Centers for Disease Control and Prevention, the International Union for Health Promotion and Education, the Department of Health of England, Health Action Partnership International, and Learning for Public Health West Midlands. These efforts provide interesting insights for further research, priority areas of action for policy and practice to address the SDH and to promote and sustain equity and social justice globally. The article highlights some key lessons about the use of data, assets-based community interventions and the importance of good leadership in times of crisis and adversity. Whilst complex and time-consuming to arrange, such programmes have the potential to offer other countries including the global south new insights and perspectives that will in turn contribute to the SDH field and provide concrete strategies and actions that effectively reduce inequities and promote the health of our societies. The key learnings have the potential to contribute to the global community and growing documentation on evidence of effective efforts in the reduction of health inequities. PMID:24722742

  13. Improving policy and practice to promote equity and social justice - a qualitative comparative analysis building on key learnings from a twinning exchange between England and the US.

    PubMed

    Blanchard, Claire; Narle, Ginder; Gibbs, Martin; Ruddock, Charmaine; Grady, Michael; Brookes, Chris; Hopkins, Trevor; Norwood, Jayne

    2013-12-01

    Community health promotion interventions, targeted at marginalised populations and focusing on addressing the social determinants of health (SDH) to reduce health inequalities and addressing the processes of exclusion, are an important strategy to prevent and control non-communicable diseases (NCDs) and promote the health of underprivileged and under-resourced groups. This article builds on key lessons learnt from a learning exchange between Communities for Health in England and the Racial and Ethnic Approaches to Community Health across the US (REACH US) communities that are tackling health inequities. It presents a qualitative analysis further capturing information about specific community interventions involved in the exchange and identifying lessons learnt. This exchange was led by a partnership between the US Centers for Disease Control and Prevention, the International Union for Health Promotion and Education, the Department of Health of England, Health Action Partnership International, and Learning for Public Health West Midlands. These efforts provide interesting insights for further research, priority areas of action for policy and practice to address the SDH and to promote and sustain equity and social justice globally. The article highlights some key lessons about the use of data, assets-based community interventions and the importance of good leadership in times of crisis and adversity. Whilst complex and time-consuming to arrange, such programmes have the potential to offer other countries including the global south new insights and perspectives that will in turn contribute to the SDH field and provide concrete strategies and actions that effectively reduce inequities and promote the health of our societies. The key learnings have the potential to contribute to the global community and growing documentation on evidence of effective efforts in the reduction of health inequities.

  14. Sensitivity of mesquite shrubland CO2 exchange to precipitation in contrasting physiographic settings 1871

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Life-history characteristics and functional traits of dominant organisms may interact with abiotic factors to shape ecosystem processes such as net primary productivity. For example, in terrestrial environments, physiographic position may interact with plant ontogeny to constrain ecosystem exchanges...

  15. Air-water oxygen exchange in a large whitewater river

    USGS Publications Warehouse

    Hall, Robert O.; Kennedy, Theodore A.; Rosi-Marshall, Emma J.

    2012-01-01

    Air-water gas exchange governs fluxes of gas into and out of aquatic ecosystems. Knowing this flux is necessary to calculate gas budgets (i.e., O2) to estimate whole-ecosystem metabolism and basin-scale carbon budgets. Empirical data on rates of gas exchange for streams, estuaries, and oceans are readily available. However, there are few data from large rivers and no data from whitewater rapids. We measured gas transfer velocity in the Colorado River, Grand Canyon, as decline in O2 saturation deficit, 7 times in a 28-km segment spanning 7 rapids. The O2 saturation deficit exists because of hypolimnetic discharge from Glen Canyon Dam, located 25 km upriver from Lees Ferry. Gas transfer velocity (k600) increased with slope of the immediate reach. k600 was -1 in flat reaches, while k600 for the steepest rapid ranged 3600-7700 cm h-1, an extremely high value of k600. Using the rate of gas exchange per unit length of water surface elevation (Kdrop, m-1), segment-integrated k600 varied between 74 and 101 cm h-1. Using Kdrop we scaled k600 to the remainder of the Colorado River in Grand Canyon. At the scale corresponding to the segment length where 80% of the O2 exchanged with the atmosphere (mean length = 26.1 km), k600 varied 4.5-fold between 56 and 272 cm h-1 with a mean of 113 cm h-1. Gas transfer velocity for the Colorado River was higher than those from other aquatic ecosystems because of large rapids. Our approach of scaling k600 based on Kdrop allows comparing gas transfer velocity across rivers with spatially heterogeneous morphology.

  16. Molecular comparative assessment of the microbial ecosystem in rumen and faeces of goats fed alfalfa hay alone or combined with oats.

    PubMed

    Mohammadzadeh, Hamid; Yáñez-Ruiz, David R; Martínez-Fernandez, Gonzalo; Abecia, Leticia

    2014-10-01

    The objective of this work was to compare the biomass and community structure of bacteria, protozoa and archaea communities in samples of rumen and faeces of goats and to what extent the diet (alfalfa hay with or without supplemented oats) offered to them exert an influence. Four cannulated adult goats fistulated in the rumen were used in a cross over design experiment in two experimental periods of 26 days, consisting in 14 days of adaptation, 7 days of sampling rumen contents and 5 days of digestibility measurement. Bacterial, protozoa and archaeal biomass and the communities' structure was assessed by real time PCR (qPCR) and denaturing gradient gel electrophoresis (DGGE), respectively. The numbers of archaea and bacteria in both rumen and faeces were higher and lower, respectively, in animals fed AH diet (P < 0.005). Contrary, protozoal numbers were not affected by the diet but were lower (P < 0.001) in faeces than in rumen. The analysis of the community structure revealed a consistently different population in structure in rumen and faeces for the three studied microbial groups and that supplementing alfalfa hay with oats led to a decrease in the similarity between sites in the rumen and faeces: similarity indexes for bacteria (57 and 27%), archaea (26 and 9%) and protozoa (62 and 22%) in animals fed AH and AHO diets, respectively.

  17. Molecular comparative assessment of the microbial ecosystem in rumen and faeces of goats fed alfalfa hay alone or combined with oats.

    PubMed

    Mohammadzadeh, Hamid; Yáñez-Ruiz, David R; Martínez-Fernandez, Gonzalo; Abecia, Leticia

    2014-10-01

    The objective of this work was to compare the biomass and community structure of bacteria, protozoa and archaea communities in samples of rumen and faeces of goats and to what extent the diet (alfalfa hay with or without supplemented oats) offered to them exert an influence. Four cannulated adult goats fistulated in the rumen were used in a cross over design experiment in two experimental periods of 26 days, consisting in 14 days of adaptation, 7 days of sampling rumen contents and 5 days of digestibility measurement. Bacterial, protozoa and archaeal biomass and the communities' structure was assessed by real time PCR (qPCR) and denaturing gradient gel electrophoresis (DGGE), respectively. The numbers of archaea and bacteria in both rumen and faeces were higher and lower, respectively, in animals fed AH diet (P < 0.005). Contrary, protozoal numbers were not affected by the diet but were lower (P < 0.001) in faeces than in rumen. The analysis of the community structure revealed a consistently different population in structure in rumen and faeces for the three studied microbial groups and that supplementing alfalfa hay with oats led to a decrease in the similarity between sites in the rumen and faeces: similarity indexes for bacteria (57 and 27%), archaea (26 and 9%) and protozoa (62 and 22%) in animals fed AH and AHO diets, respectively. PMID:24333680

  18. Can Volunteers Collect Data that are Comparable to Professional Scientists? A Study of Variables Used in Monitoring the Outcomes of Ecosystem Rehabilitation

    NASA Astrophysics Data System (ADS)

    Gollan, John; de Bruyn, Lisa Lobry; Reid, Nick; Wilkie, Lance

    2012-11-01

    Having volunteers collect data can be a cost-effective strategy to complement or replace those collected by scientists. The quality of these data is essential where field-collected data are used to monitor progress against predetermined standards because they provide decision makers with confidence that choices they make will not cause more harm than good. The integrity of volunteer-collected data is often doubted. In this study, we made estimates of seven vegetation attributes and a composite measure of six of those seven, to simulate benchmark values. These attributes are routinely recorded as part of rehabilitation projects in Australia and elsewhere in the world. The degree of agreement in data collected by volunteers was compared with those recorded by professional scientists. Combined results showed that scientists collected data that was in closer agreement with benchmarks than those of volunteers, but when data collected by individuals were analyzed, some volunteers collected data that were in similar or closer agreement, than scientists. Both groups' estimates were in closer agreement for particular attributes than others, suggesting that some attributes are more difficult to estimate than others, or that some are more subjective than others. There are a number of ways in which higher degrees of agreement could be achieved and introducing these will no doubt result in better, more effective programs, to monitor rehabilitation activities. Alternatively, less subjective measures should be sought when developing monitoring protocols. Quality assurance should be part of developing monitoring methods and explicitly budgeted for in project planning to prevent misleading declarations of rehabilitation success.

  19. Estimating agro-ecosystem carbon balance of northern Japan, and comparing the change in carbon stock by soil inventory and net biome productivity.

    PubMed

    Li, Xi; Toma, Yo; Yeluripati, Jagadeesh; Iwasaki, Shinya; Bellingrath-Kimura, Sonoko D; Jones, Edward O; Hatano, Ryusuke

    2016-06-01

    Soil C sequestration in croplands is deemed to be one of the most promising greenhouse gas mitigation options for agriculture. We have used crop-level yields, modeled heterotrophic respiration (Rh) and land use data to estimate spatio-temporal changes in regional scale net primary productivity (NPP), plant C inputs, and net biome productivity (NBP) in northern Japan's arable croplands and grasslands for the period of 1959-2011. We compared the changes in C stocks derived from estimated NBP and using repeated inventory datasets for each individual land use type from 2005 to 2011. For the entire study region of 2193 ha, overall annual plant C inputs to the soil constituted 37% of total region NPP. Plant C inputs in upland areas (excluding bush/fallow) could be predicted by climate variables. Overall NBP for all land use types increased from -1.26MgCha(-1)yr(-1) in 1959-0.26 Mg Cha(-1)yr(-1) in 2011. However, upland and paddy fields showed a decreased in NBP over the period of 1959-2011, under the current C input scenario. From 1988, an increase in agricultural abandonment (bush/fallow) and grassland cover caused a slow increase in the regional C pools. The comparison of carbon budgets using the NBP estimation method and the soil inventory method indicated no significant difference between the two methods. Our results showed C loss in upland crops, paddy fields and sites that underwent land use change from paddy field to upland sites. We also show C gain in grassland from 2005 to 2011. An underestimation of NBP or an overestimation of repeated C inventories cannot be excluded, but either method may be suitable for tracking absolute changes in soil C, considering the uncertainty associated with these methods.

  20. Estimating agro-ecosystem carbon balance of northern Japan, and comparing the change in carbon stock by soil inventory and net biome productivity.

    PubMed

    Li, Xi; Toma, Yo; Yeluripati, Jagadeesh; Iwasaki, Shinya; Bellingrath-Kimura, Sonoko D; Jones, Edward O; Hatano, Ryusuke

    2016-06-01

    Soil C sequestration in croplands is deemed to be one of the most promising greenhouse gas mitigation options for agriculture. We have used crop-level yields, mode