Discoloration of polyvinyl chloride (PVC) tape as a proxy for water-table depth in peatlands: validation and assessment of seasonal variability

USGS Publications Warehouse

Booth, Robert K.; Hotchkiss, Sara C.; Wilcox, Douglas A.

2005-01-01

Summary: 1. Discoloration of polyvinyl chloride (PVC) tape has been used in peatland ecological and hydrological studies as an inexpensive way to monitor changes in water-table depth and reducing conditions. 2. We investigated the relationship between depth of PVC tape discoloration and measured water-table depth at monthly time steps during the growing season within nine kettle peatlands of northern Wisconsin. Our specific objectives were to: (1) determine if PVC discoloration is an accurate method of inferring water-table depth in Sphagnum-dominated kettle peatlands of the region; (2) assess seasonal variability in the accuracy of the method; and (3) determine if systematic differences in accuracy occurred among microhabitats, PVC tape colour and peatlands. 3. Our results indicated that PVC tape discoloration can be used to describe gradients of water-table depth in kettle peatlands. However, accuracy differed among the peatlands studied, and was systematically biased in early spring and late summer/autumn. Regardless of the month when the tape was installed, the highest elevations of PVC tape discoloration showed the strongest correlation with midsummer (around July) water-table depth and average water-table depth during the growing season. 4. The PVC tape discoloration method should be used cautiously when precise estimates are needed of seasonal changes in the water-table.

Temporal changes in the configuration of the water table in the vicinity of the management systems evaluation area site, central Nebraska

USGS Publications Warehouse

Kilpatrick, John M.

1996-01-01

To improve understanding of the hydrologic characteristics of the shallow aquifer in the vicinity of the Management Systems Evaluation Area site near Shelton, Nebraska, water levels were measured in approximately 130 observation wells in both June and September 1991. Two water-table maps and a water-level-change map were drawn on the basis of these measurements. In addition, historical data from U.S. Geological Survey computer files and published reports were used to determine the approximate configuration of the water table in 1931 and to draw one short-term and two-long term water- level hydrographs. Comparison of the three water- table maps indicates general similarities. The average horizontal hydraulic gradient in the shallow aquifer is about 7.5 feet per mile, and the flow direction is to the east-northeast. The water table declined 2 to 10 feet between June and September 1991, with the greatest decline occurring in a wedge-shaped area south of the Wood River and north of the Platte River. The 1991 water-table configurations appear to indicate that the aquifer either was discharging to the Platte River in this reach or there was little flow between the river and the aquifer. Comparison of the 1931 and 1991 water-table maps indicates that, except for short-term variations, the water-table configuration changed little during this 61-year period. Two long-term water-level hydrographs confirm this conclusion, indicating that the shallow aquifer in this area has been in long-term, dynamic equilibrium.

NifH-Harboring Bacterial Community Composition across an Alaskan Permafrost Thaw Gradient

PubMed Central

Penton, C. Ryan; Yang, Caiyun; Wu, Liyou; Wang, Qiong; Zhang, Jin; Liu, Feifei; Qin, Yujia; Deng, Ye; Hemme, Christopher L.; Zheng, Tianling; Schuur, Edward A. G.; Tiedje, James; Zhou, Jizhong

2016-01-01

Since nitrogen (N) is often limiting in permafrost soils, we investigated the N2-fixing genetic potential and the inferred taxa harboring those genes by sequencing nifH gene fragments in samples taken along a permafrost thaw gradient in an Alaskan boreal soil. Samples from minimally, moderately and extensively thawed sites were taken to a depth of 79 cm to encompass zones above and below the depth of the water table. NifH reads were translated with frameshift correction and 112,476 sequences were clustered at 5% amino acid dissimilarity resulting in 1,631 OTUs. Sample depth in relation to water table depth was correlated to differences in the NifH sequence classes with those most closely related to group I nifH-harboring Alpha- and Beta-Proteobacteria in higher abundance above water table depth while those related to group III nifH-harboring Delta Proteobacteria more abundant below. The most dominant below water table depth NifH sequences, comprising 1/3 of the total, were distantly related to Verrucomicrobia-Opitutaceae. Overall, these results suggest that permafrost thaw alters the class-level composition of N2-fixing communities in the thawed soil layers and that this distinction corresponds to the depth of the water table. These nifH data were also compared to nifH sequences obtained from a study at an Alaskan taiga site, and to those of other geographically distant, non-permafrost sites. The two Alaska sites were differentiated largely by changes in relative abundances of the same OTUs, whereas the non-Alaska sites were differentiated by the lack of many Alaskan OTUs, and the presence of unique halophilic, sulfate- and iron-reducing taxa in the Alaska sites. PMID:27933054

NifH-Harboring Bacterial Community Composition across an Alaskan Permafrost Thaw Gradient

DOE PAGES

Penton, C. Ryan; Yang, Caiyun; Wu, Liyou; ...

2016-11-24

Since nitrogen (N) is often limiting in permafrost soils, we investigated the N 2-fixing genetic potential and the inferred taxa harboring those genes by sequencing nifH gene fragments in samples taken along a permafrost thaw gradient in an Alaskan boreal soil. Samples from minimally, moderately and extensively thawed sites were taken to a depth of 79 cm to encompass zones above and below the depth of the water table. NifH reads were translated with frameshift correction and 112,476 sequences were clustered at 5% amino acid dissimilarity resulting in 1,631 OTUs. Sample depth in relation to water table depth was correlatedmore » to differences in the NifH sequence classes with those most closely related to group I nifH-harboring Alpha- and Beta-Proteobacteria in higher abundance above water table depth while those related to group III nifH-harboring Delta Proteobacteria more abundant below. The most dominant below water table depth NifH sequences, comprising 1/3 of the total, were distantly related to Verrucomicrobia-Opitutaceae. Overall, these results suggest that permafrost thaw alters the class-level composition of N 2-fixing communities in the thawed soil layers and that this distinction corresponds to the depth of the water table. These nifH data were also compared to nifH sequences obtained from a study at an Alaskan taiga site, and to those of other geographically distant, non-permafrost sites. The two Alaska sites were differentiated largely by changes in relative abundances of the same OTUs, whereas the non-Alaska sites were differentiated by the lack of many Alaskan OTUs, and the presence of unique halophilic, sulfate- and iron-reducing taxa in the Alaska sites.« less

NifH-Harboring Bacterial Community Composition across an Alaskan Permafrost Thaw Gradient

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

Penton, C. Ryan; Yang, Caiyun; Wu, Liyou

Since nitrogen (N) is often limiting in permafrost soils, we investigated the N 2-fixing genetic potential and the inferred taxa harboring those genes by sequencing nifH gene fragments in samples taken along a permafrost thaw gradient in an Alaskan boreal soil. Samples from minimally, moderately and extensively thawed sites were taken to a depth of 79 cm to encompass zones above and below the depth of the water table. NifH reads were translated with frameshift correction and 112,476 sequences were clustered at 5% amino acid dissimilarity resulting in 1,631 OTUs. Sample depth in relation to water table depth was correlatedmore » to differences in the NifH sequence classes with those most closely related to group I nifH-harboring Alpha- and Beta-Proteobacteria in higher abundance above water table depth while those related to group III nifH-harboring Delta Proteobacteria more abundant below. The most dominant below water table depth NifH sequences, comprising 1/3 of the total, were distantly related to Verrucomicrobia-Opitutaceae. Overall, these results suggest that permafrost thaw alters the class-level composition of N 2-fixing communities in the thawed soil layers and that this distinction corresponds to the depth of the water table. These nifH data were also compared to nifH sequences obtained from a study at an Alaskan taiga site, and to those of other geographically distant, non-permafrost sites. The two Alaska sites were differentiated largely by changes in relative abundances of the same OTUs, whereas the non-Alaska sites were differentiated by the lack of many Alaskan OTUs, and the presence of unique halophilic, sulfate- and iron-reducing taxa in the Alaska sites.« less

[Effects of water table manipulation on leaf photosynthesis, morphology and growth of Phragmites australis and Imperata cylindrica in the reclaimed tidal wetland at Dongtan of Chongming Island, China].

PubMed

Zhong, Qi-Cheng; Wang, Jiang-Tao; Zhou, Jian-Hong; Ou, Qiang; Wang, Kai-Yun

2014-02-01

During the growing season of 2011, the leaf photosynthesis, morphological and growth traits of Phragmites australis and Imperata cylindrica were investigated along a gradient of water table (low, medium and high) in the reclaimed tidal wetland at the Dongtan of Chongming Island in the Yangtze Estuary of China. A series of soil factors, i. e., soil temperature, moisture, salinity and inorganic nitrogen content, were also measured. During the peak growing season, leaf photosynthetic capacity of P. australis in the wetland with high water table was significantly lower than those in the wetland with low and medium water tables, and no difference was observed in leaf photosynthetic capacity of I. cylindrica at the three water tables. During the entire growing season, at the shoot level, the morphological and growth traits of P. australis got the optimum in the wetland with medium water table, but most of the morphological and growth traits of I. cylindrica had no significant differences at the three water tables. At the population level, the shoot density, leaf area index and aboveground biomass per unit area were the highest in the wetland with high water table for P. australis, but all of the three traits were the highest in the wetland with low water table for I. cylindrica. At the early growing season, the rhizome biomass of P. australis in the 0-20 cm soil layer had no difference at the three water tables, and the rhizome biomass of I. cylindrica in the 0-20 cm soil layer in the wetland with high water table was significantly lower than those in the wetland with low and medium water table. As a native hygrophyte before the reclamation, the variations of performances of P. australis at the three water tables were probably attributed to the differences in the soil factors as well as the intensity of competition from I. cylindrica. To appropriately manipulate water table in the reclaimed tidal wetland may restrict the growth and propagation of the mesophyte I. cylindrica, and facilitate the restoration of P. australis-dominated marsh plant community.

Carbon cycling responses to a water table drawdown and decadal vegetation changes in a bog

NASA Astrophysics Data System (ADS)

Talbot, J.; Roulet, N. T.

2009-12-01

The quantity of carbon stored in peat depends on the imbalance between production and decomposition of organic matter. This imbalance is mainly controlled by the wetness of the peatland, usually described by the water table depth. However, long-term processes resulting from hydrological changes, such as vegetation succession, also play a major role in the biogeochemistry of peatlands. Previous studies have looked at the impact of a water table lowering on carbon fluxes in different types of peatlands. However, most of these studies were conducted within a time frame that did not allow the examination of vegetation changes due to the water table lowering. We conducted a study along a drainage gradient resulting from the digging of a drainage ditch 85 years ago in a portion of the Mer Bleue bog, located near Ottawa, Canada. According to water table reconstructions based on testate amoeba, the drainage dropped the water table by approximately 18 cm. On the upslope side of the ditch, the water table partly recovered and the vegetation changed only marginally. However, on the downslope side of the ditch, the water table stayed persistently lower and trees established (Larix and Betula). The importance of Sphagnum decreased with a lower water table, and evergreen shrubs were replaced by deciduous shrubs. The water table drop and subsequent vegetation changes had combined and individual effects on the carbon functioning of the peatland. Methane fluxes decreased because of the water table lowering, but were not affected by vegetation changes, whereas respiration and net ecosystem productivity were affected by both. The carbon storage of the system increased because of an increase in plant biomass, but the long-term carbon storage as peat decreased. The inclusion of the feedback effect that vegetation has on the carbon functioning of a peatland when a disturbance occurs is crucial to simulate the long-term carbon balance of this ecosystem.

Hydrologic relations between lakes and aquifer in a recharge area near Orlando, Florida

USGS Publications Warehouse

Lichtler, William F.; Hughes, G.H.; Pfischner, F.L.

1976-01-01

The three lakes investigated in Orange County, Florida, gain water from adjoining water-table aquifer and lose water to Floridan aquifer by downward leakage. Net seepage (net exchange of water between lake and aquifers) can be estimated by equation S = AX + BY, where S is net seepage, X represents hydraulic gradient between lake and water-table aquifer, A is lumped parameter representing effect of hydraulic conductivity and cross-sectional area of materials in flow section of water-table aquifer, Y is head difference between lake level and potentiometric surface of Floridan aquifer, and B is lumped parameter representing effect of hydraulic conductivity, area, and thickness of materials between lake bottom and Floridan aquifer. If values of S, X, and Y are available for two contrasting water-level conditions, coefficients A and B are determinable by solution of two simultaneous equations. If the relation between lake and ground-water level is the same on all sides of the lake--with regard to each aquifer--and if X and Y are truly representative of these relations, then X and Y terms of equation provide valid estimates of inflow to lake from water-table aquifer and outflow from lake to Floridan aquifer. (Woodard-USGS)

Methane emissions from boreal peatlands in a changing climate: Quantifying the sensitivity of methane fluxes to experimental manipulations of water table and soil temperature regimes in an Alaskan boreal fen

NASA Astrophysics Data System (ADS)

Treat, C. C.; Turetsky, M.; Harden, J.; McGuire, A.

2006-12-01

Peatlands cover only 3-5 % of the world's land surface but store 30 % of the world's soil carbon (C) pool. Peatlands currently are thought to function globally as a net sink for atmospheric CO2, sequestering approximately 76 Tg (1012 g) C yr-1. However, peatlands also function as a net source of atmospheric CH4. Approximately 25% of the 270 Tg CH4 yr-1 emitted from natural sources are emitted from northern wetlands. Methane production (methanogenesis) and consumption (methane oxidation) in peatlands are sensitive to both fluctuations in soil moisture and temperature. Boreal regions already are experiencing rapid changes in climate, including longer and drier growing seasons and the degradation of permafrost. Changes in peat environments in response to these climate changes could have significant implications for CH4 emissions to the atmosphere, and thus the radiative forcing of high latitude regions. In 2005, we initiated a large scale in situ climate experiment in a moderately rich fen near the Bonanza Creek LTER site in central Alaska (APEX: www.apex.msu.edu). The goal of our project is to understand vegetation and C cycling processes under altered water table and soil thermal regimes. We established three water table plots (control, raised, lowered), each about 120 m2 in area, using drainage ditches to lower the water table by 5-10 cm and solar powered pumps to raise the water table by about 5-15 cm. Within each water table plot, we constructed replicate open top chambers (OTCs) to passively increase surface temperatures by about 1 ° C. We used static chambers and gas chromatography to quantify methane fluxes at each water table x soil warming plot through the growing seasons of 2005 and 2006. Additionally, we quantified seasonal CH4 fluxes along an adjacent moisture gradient that included four distinct soil moisture and vegetation zones, including a moderately rich fen (APEX site), an emergent macrophyte marsh, a shrubby permafrost fen, and a black spruce permafrost forest. Our results thus far show that methane fluxes varied by a warming x water table interaction across our experimental treatments (Proc Mixed SAS Repeated Measures ANOVA; F2,8=4.07; p=0.05), with the largest methane fluxes in the warm, wet peatland plots and the lowest methane fluxes in the unwarmed, dry peatland plots. Sites along the moisture gradient transitioned from methane sources in the rich fen site (APEX plots) to small sinks of CH4 in the permafrost forest under drying soil moisture conditions. Our soil climate manipulations allow us to quantify interactions among biogeophysical variables that control CH4 emissions from peatlands. Our coupled experimental and gradient based measurements allow us to explore controls on microbial populations and methane emissions across a wider range of terrestrial boreal environments. This work so far shows that methane cycling in interior Alaskan ecosystems is extremely sensitive to soil climate conditions, and that the fate of methane emissions from high latitudes will be affected primarily by changes in precipitation and soil drainage that control water table position in peatlands and permafrost ecosystems.

Water-table decline in the south-central Great Basin during the Quaternary Period; implications for toxic-waste disposal

USGS Publications Warehouse

Winograd, I.J.; Szabo, B. J.

1986-01-01

The distribution of vein calcite, tufa, and other features indicative of paleo-groundwater discharge, indicates that during the early to middle Pleistocene, the water table at Ash Meadows, in the Amargosa Desert, Nevada, and at Furnace Creek Wash, in east-central Death Valley, California, was tens to hundreds of meters above the modern water table, and that groundwater discharge occurred up to 18 km up-the-hydraulic gradient from modern discharge areas. Uranium series dating of the calcitic veins permits calculation of rates of apparent water table decline; rates of 0.02 to 0.08 m/1000 yr are indicated for Ash meadows and 0.2 to 0.6 m/1000 yr for Furnace Creek Wash. The rates for Furnace Creek Wash closely match a published estimate of vertical crustal offset for this area, suggesting that tectonism is a major cause for the displacement observed. In general, displacements of the paleo-water table probably reflect a combination of: (a) tectonic uplift of vein calcite and tufa, unaccompanied by a change in water table altitude; (b) decline in water table altitude in response to tectonic depression of areas adjacent to dated veins and associated tufa; (c) decline in water table altitude in response to increasing aridity caused by major uplift of the Sierra Nevada and Transverse Ranges during the Quaternary; and (d) decline in water altitude in response to erosion triggered by increasing aridity and/or tectonism. A synthesis of geohydrologic, neotectonic, and paleoclimatologic information with the vein-calcite data permits the inference that the water table in the south-central Great Basin progressively lowered throughout the Quaternary. This inference is pertinent to an evaluation of the utility of thick (200-600 m) unsaturated zones of the region for isolating solidified radioactive wastes from the hydrosphere for hundreds of millenia. Wastes buried a few tens to perhaps 100 m above the modern water table--that is above possible water level rises due to future pluvial climates--are unlikely to be inundated by a rising water table in the foreseeable geologic future. (Author 's abstract)

Vertical Gradients in Water Chemistry and Age in the Southern High Plains Aquifer, Texas, 2002

USGS Publications Warehouse

McMahon, P.B.; Böhlke, J.K.; Lehman, T.M.

2004-01-01

The southern High Plains aquifer is the primary source of water used for domestic, industrial, and irrigation purposes in parts of New Mexico and Texas. Despite the aquifer's importance to the overall economy of the southern High Plains, fundamental ground-water characteristics, such as vertical gradients in water chemistry and age, remain poorly defined. As part of the U.S. Geological Survey's National Water-Quality Assessment Program, water samples from nested, short-screen monitoring wells installed in the southern High Plains aquifer at two locations (Castro and Hale Counties, Texas) were analyzed for field parameters, major ions, nutrients, trace elements, dissolved organic carbon, pesticides, stable and radioactive isotopes, and dissolved gases to evaluate vertical gradients in water chemistry and age in the aquifer. Tritium measurements indicate that recent (post-1953) recharge was present near the water table and that deeper water was recharged before 1953. Concentrations of dissolved oxygen were largest (2.6 to 5.6 milligrams per liter) at the water table and decreased with depth below the water table. The smallest concentrations were less than 0.5 milligram per liter. The largest major-ion concentrations generally were detected at the water table because of the effects of overlying agricultural activities, as indicated by postbomb tritium concentrations and elevated nitrate and pesticide concentrations at the water table. Below the zone of agricultural influence, major-ion concentrations exhibited small increases with depth and distance along flow paths because of rock/water interactions and mixing with water from the underlying aquifer in rocks of Cretaceous age. The concentration increases primarily were accounted for by dissolved sodium, bicarbonate, chloride, and sulfate. Nitrite plus nitrate concentrations at the water table were 2.0 to 6.1 milligrams per liter as nitrogen, and concentrations substantially decreased with depth in the aquifer to a maximum concentration of 0.55 milligram per liter as nitrogen. Dissolved-gas and nitrogen-isotope data from the deep wells in Castro County indicate that denitrification occurred in the aquifer, removing 74 to more than 97 percent of the nitrate originally present in recharge. There was no evidence of denitrification in the deep part of the aquifer in Hale County. After correcting for denitrification effects, the background concentration of nitrate in water recharged before 1953 ranged from 0.4 to 3.2 milligrams per liter as nitrogen, with an average of 1.6 milligrams per liter as nitrogen. The d15N composition of background nitrate at the time of recharge was estimated to range from 9.6 to 12.3 per mil. Mass-balance models indicate that the decreases in dissolved oxygen and nitrate concentrations and small increases in major-ion concentrations along flow paths can be accounted for by small amounts of silicate-mineral and calcite dissolution; SiO2, goethite, and clay-mineral precipitation; organic-carbon and pyrite oxidation; denitrification; and cation exchange. Mass-balance models for some wells also required mixing with water from the underlying aquifer in rocks of Cretaceous age to achieve mole and isotope balances. Carbon mass transfers identified in the models were used to adjust radiocarbon ages of water samples recharged before 1953. Adjusted radiocarbon ages ranged from less than 1,000 to 9,000 carbon-14 years before present. Radiocarbon ages were more sensitive to uncertainties in the carbon-14 content of recharge than uncertainties in carbon mass transfers, leading to 1-sigma uncertainties of about ?2,000 years in the adjusted ages. Despite these relatively large uncertainties in adjusted radiocarbon ages, it appears that deep water in the aquifer was considerably older (at least 1,000 years) than water near the water table. There was essentially no change in ground-water age with depth in deeper parts of the aquifer, indicating that water in that

Analytical estimation show low depth-independent water loss due to vapor flux from deep aquifers

NASA Astrophysics Data System (ADS)

Selker, John S.

2017-06-01

Recent articles have provided estimates of evaporative flux from water tables in deserts that span 5 orders of magnitude. In this paper, we present an analytical calculation that indicates aquifer vapor flux to be limited to 0.01 mm/yr for sites where there is negligible recharge and the water table is well over 20 m below the surface. This value arises from the geothermal gradient, and therefore, is nearly independent of the actual depth of the aquifer. The value is in agreement with several numerical studies, but is 500 times lower than recently reported experimental values, and 100 times larger than an earlier analytical estimate.

Geology and hydrogeology of Naval Air Station Chase Field and Naval Auxiliary Landing Field Goliad, Bee and Goliad counties, Texas

USGS Publications Warehouse

Snyder, G.L.

1995-01-01

Large vertical hydraulic-head gradients are present between the unconfined Evangeline aquifer and confined Fleming aquifers at Naval Air Station Chase Field and Naval Auxiliary Landing Field Goliad. These gradients, together with the results of the aquifer test at Naval Air Station Chase Field and assumed characteristics of the confining units, indicate that downward flow of ground water probably occurs from the water-table aquifer to the underlying aquifers. The rate of downward flow between the two confined Fleming aquifers (from A-sand to B-sand) can be approximated using an estimate of vertical hydraulic conductivity of the intervening confining unit obtained from assumed storage characteristics and data from the aquifer test. Under the relatively high vertical hydraulic-head gradient induced by the aquifer test, ground-water movement from the A-sand aquifer to the B-sand aquifer could require about 490 years; and about 730 years under the natural gradient. Future increases in ground-water withdrawals from the B-sand aquifer might increase downward flow in the aquifer system of the study area.

Geophysical and hydrogeological characterisation of the impacts of on-site wastewater treatment discharge to groundwater in a poorly productive bedrock aquifer.

PubMed

Donohue, Shane; McCarthy, Valerie; Rafferty, Patrick; Orr, Alison; Flynn, Raymond

2015-08-01

Contaminants discharging from on-site wastewater treatment systems (OSWTSs) can impact groundwater quality, threatening human health and surface water ecosystems. Risk of negative impacts becomes elevated in areas of extreme vulnerability with high water tables, where thin unsaturated intervals limit vadose zone attenuation. A combined geophysical/hydrogeological investigation into the effects of an OSWTS, located over a poorly productive aquifer (PPA) with thin subsoil cover, aimed to characterise effluent impacts on groundwater. Groundwater, sampled from piezometers down-gradient of the OSWTS percolation area displayed spatially erratic, yet temporally consistent, contaminant distributions. Electrical resistivity tomography identified an area of gross groundwater contamination close to the percolation area and, when combined with seismic refraction and water quality data, indicated that infiltrating effluent reaching the water table discharged to a deeper more permeable zone of weathered shale resting on more competent bedrock. Subsurface structure, defined by geophysics, indicated that elevated chemical and microbiological contaminant levels encountered in groundwater samples collected from piezometers, down-gradient of sampling points with lower contaminant levels, corresponded to those locations where piezometers were screened close to the weathered shale/competent rock interface; those immediately up-gradient were too shallow to intercept this interval, and thus the more impacted zone of the contaminant plume. Intermittent occurrence of faecal indicator bacteria more than 100m down gradient of the percolation area suggested relatively short travel times. Study findings highlight the utility of geophysics as part of multidisciplinary investigations for OSWTS contaminant plume characterisation, while also demonstrating the capacity of effluent discharging to PPAs to impact groundwater quality at distance. Comparable geophysical responses observed in similar settings across Ireland suggest the phenomena observed in this study are more widespread than previously suspected. Copyright © 2015 Elsevier B.V. All rights reserved.

A Regional Guidebook for Applying the Hydrogeomorphic Approach to Assessing Functions of Forested Wetlands in the Delta Region of Arkansas, Lower Mississippi River Alluvial Valley, Version 2.0

DTIC Science & Technology

2011-09-01

ERDC/EL TR-11-12 7 Table 1. Hydrogeomorphic Wetland Classes. HGM Wetland Class Definition Depression Depressional wetlands occur in topographic... depressions (i.e., closed elevation contours) that allow the accumulation of surface water. Depressional wetlands may have any combination of inlets...Riverine, Low-gradient Riverine Backwater, Low-gradient Riverine Overbank, Headwater Depression , Isolated Depression , and Connected Depression . For

Seasonal changes in Sphagnum peatland testate amoeba communities along a hydrological gradient.

PubMed

Marcisz, Katarzyna; Lamentowicz, Lukasz; Słowińska, Sandra; Słowiński, Michał; Muszak, Witold; Lamentowicz, Mariusz

2014-10-01

Testate amoebae are an abundant and functionally important group of protists in peatlands, but little is known about the seasonal patterns of their communities. We investigated the relationships between testate amoeba diversity and community structure and water table depth and light conditions (shading vs. insolation) in a Sphagnum peatland in Northern Poland (Linje mire) in spring and summer 2010. We monitored the water table at five sites across the peatland and collected Sphagnum samples in lawn and hummock micro-sites around each piezometer, in spring (3 May) and mid-summer (6 August) 2010. Water table differed significantly between micro-sites and seasons (Kruskal-Wallis test, p=0.001). The community structure of testate amoebae differed significantly between spring and summer in both hummock and lawn micro-sites. We recorded a small, but significant drop in Shannon diversity, between spring and summer (1.76 vs. 1.72). Strongest correlations were found between testate amoeba communities and water table lowering and light conditions. The relative abundance of mixotrophic species Hyalosphenia papilio, Archerella flavum and of Euglypha ciliata was higher in the summer. Copyright © 2014 Elsevier GmbH. All rights reserved.

New Mexico Geothermal Play Fairway Analysis from LANL

DOE Data Explorer

Rick Kelley

2015-10-27

This submission contains geospatial (GIS) data on water table gradient and depth, subcrop gravity and magnetic, propsectivity, heat flow, physiographic, boron and BHT for the Southwest New Mexico Geothermal Play Fairway Analysis by LANL Earth & Environmental Sciences. GIS data is in ArcGIS map package format.

Depth dependent microbial carbon use efficiency in the capillary fringe as affected by water table fluctuations in a column incubation experiment

NASA Astrophysics Data System (ADS)

Pronk, G. J.; Mellage, A.; Milojevic, T.; Smeaton, C. M.; Rezanezhad, F.; Van Cappellen, P.

2017-12-01

Microbial growth and turnover of soil organic carbon (SOC) depend on the availability of electron donors and acceptors. The steep geochemical gradients in the capillary fringe between the saturated and unsaturated zones provide hotspots of soil microbial activity. Water table fluctuations and the associated drying and wetting cycles within these zones have been observed to lead to enhanced turnover of SOC and adaptation of the local microbial communities. To improve our understanding of SOC degradation under changing moisture conditions, we carried out an automated soil column experiment with integrated of hydro-bio-geophysical monitoring under both constant and oscillating water table conditions. An artificial soil mixture composed of quartz sand, montmorillonite, goethite and humus was used to provide a well-defined system. This material was inoculated with a microbial community extracted from a forested riparian zone. The soils were packed into 6 columns (60 cm length and 7.5 cm inner diameter) to a height of 45 cm; and three replicate columns were incubated under constant water table while another three were saturated and drained monthly. The initial soil development, carbon cycling and microbial community development were then characterized during 10 months of incubation. This system provides an ideal artificial gradient from the saturated to the unsaturated zone to study soil development from initially homogeneous materials and the same microbial community composition under controlled conditions. Depth profiles of SOC and microbial biomass after 329 days of incubation showed a depletion of carbon in the transition drying and wetting zone that was not associated with higher accumulation of microbial biomass, indicating a lower carbon use efficiency of the microbial community established within the water table fluctuation zone. This was supported by a higher ATP to microbial biomass carbon ratio within the same zone. The findings from this study highlight the importance of considering the effects of transient soil moisture and oxygen availability on microbial mediated SOC transformations. The effects of these changes in carbon use efficiency need to be included in soil models in order to accurately predict SOC turnover.

Magnetic susceptibility as a proxy for the hydrobiogeochemical cycling of iron within the water table fluctuation zone at hydrocarbon contaminated sites

NASA Astrophysics Data System (ADS)

Atekwana, E. A.; Enright, A.; Atekwana, E. A.; Beaver, C. L.; Rossbach, S.; Slater, L. D.; Ntarlagiannis, D.

2016-12-01

Sharp redox gradients are indicative of enhanced biogeochemical activity and occur at or near the water table. Hydrologic forcing drives changes in redox state and oxygen levels, enhancing the elemental cycling of metals, and coupling different biogeochemical cycles. These coupled hydrobiogeochemical cycles are often difficult to study in the field using geochemical and microbial proxies because of direct sampling limitations, the costs associated with these techniques, and because the dynamic nature of these processes complicates the interpretation of single time point measurements, which may not give accurate representations of prevailing conditions. Geophysical techniques can provide both the spatial and temporal resolution needed to elucidate these processes. Here we investigated the use of magnetic susceptibility (c) as a viable proxy for understanding the biogeochemical cycling of iron at several hydrocarbon contaminated sites where active intrinsic bioremediation is occurring. We performed borehole c logging using a Bartington c probe in the field as well as made c measurements on core samples retrieved from the field sites. Our results show the following: (1) in both sulfate-rich and sulfate-poor aquifers, excursions in c are coincident with zones of free product contamination and are limited to the water table fluctuation (smear) zone; (2) c values within the free product plume and contamination source zones are higher compared to values within the dissolved product plume; (3) high c coincides with zones of elevated Fe (II) and Fe (III) concentrations extracted from aquifer solids; and (4) the mixed valence magnetite and greigite were the dominant magnetic minerals. The c excursions are limited to the water table fluctuation zones because fluctuating water level conditions are hot beds for microbial activity due to the steep hydrocarbon and nutrients and consequently redox gradients. High water levels during periods of recharge favor anaerobic conditions enhancing iron reduction, while low water conditions during drought periods favor iron oxidation due to increased oxygen penetration. Such conditions favor mixed valent iron minerals such as magnetite and greigite. We conclude that c measurements are a low cost, rapid monitoring tool for assessing the elemental cycling of iron.

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Isobaric groundwater well

DOEpatents

Hubbell, Joel M.; Sisson, James B.

1999-01-01

A method of measuring a parameter in a well, under isobaric conditions, including such parameters as hydraulic gradient, pressure, water level, soil moisture content and/or aquifer properties the method as presented comprising providing a casing having first and second opposite ends, and a length between the ends, the casing supporting a transducer having a reference port; placing the casing lengthwise into the well, second end first, with the reference port vented above the water table in the well; and sealing the first end. A system is presented for measuring a parameter in a well, the system comprising a casing having first and second opposite ends, and a length between the ends and being configured to be placed lengthwise into a well second end first; a transducer, the transducer having a reference port, the reference port being vented in the well above the water table, the casing being screened across and above the water table; and a sealing member sealing the first end. In one embodiment, the transducer is a tensiometer transducer and in other described embodiments, another type transducer is used in addition to a tensiometer.

Moisture drives surface decomposition in thawing tundra

NASA Astrophysics Data System (ADS)

Hicks Pries, Caitlin E.; Schuur, E. A. G.; Vogel, Jason G.; Natali, Susan M.

2013-07-01

Permafrost thaw can affect decomposition rates by changing environmental conditions and litter quality. As permafrost thaws, soils warm and thermokarst (ground subsidence) features form, causing some areas to become wetter while other areas become drier. We used a common substrate to measure how permafrost thaw affects decomposition rates in the surface soil in a natural permafrost thaw gradient and a warming experiment in Healy, Alaska. Permafrost thaw also changes plant community composition. We decomposed 12 plant litters in a common garden to test how changing plant litter inputs would affect decomposition. We combined species' tissue-specific decomposition rates with species and tissue-level estimates of aboveground net primary productivity to calculate community-weighted decomposition constants at both the thaw gradient and warming experiment. Moisture, specifically growing season precipitation and water table depth, was the most significant driver of decomposition. At the gradient, an increase in growing season precipitation from 200 to 300 mm increased mass loss of the common substrate by 100%. At the warming experiment, a decrease in the depth to the water table from 30 to 15 cm increased mass loss by 100%. At the gradient, community-weighted decomposition was 21% faster in extensive than in minimal thaw, but was similar when moss production was included. Overall, the effect of climate change and permafrost thaw on surface soil decomposition are driven more by precipitation and soil environment than by changes to plant communities. Increasing soil moisture is thereby another mechanism by which permafrost thaw can become a positive feedback to climate change.

Conductivity gradients as inferred by electromagnetic-induction meter (EM38) readings within a salt-affected wetland in Saskatchewan, Canada

NASA Astrophysics Data System (ADS)

Mirck, Jaconette; Schroeder, William

2018-01-01

The change from deep-rooted grass and shrub vegetation to annual-cropping dryland farming has contributed to serious soil salinization challenges on the semi-arid North American Great Plains. In some cases, cultivation of the Great Plains has increased the availability of water, causing dominant sulfate salts to travel from the uphill areas to depressions where it will surface when water evaporates at the soil surface. A potential solution could include the replanting of the native deep-rooted vegetation, which requires knowledge of the spatial distribution of soil salinity. This study tested the soil factors influencing electromagnetic-induction meter (EM38) readings of soil salinity distribution around wetlands. The objectives were to: (1) predict growth and survival of Salix dasyclados Wimm. (cv. `India') along a salinity gradient in a small wetland, and (2) investigate whether newly established willows affected water-table fluctuations, which would indicate their phreatophytic nature or their ability to obtain their water supply from the zone of saturation. Results indicated significantly lower salinity values for sampling points with EM38 readings above 175 and 250 mS m-1 for height and survival, respectively. In addition, diurnal fluxes of the water table in areas of good willow growth and lower salinity indicated that cultivar `India' was phreatophytic in these areas and therefore has great potential for being used to combat saline seeps.

Conductivity gradients as inferred by electromagnetic-induction meter (EM38) readings within a salt-affected wetland in Saskatchewan, Canada

NASA Astrophysics Data System (ADS)

Mirck, Jaconette; Schroeder, William

2018-06-01

The change from deep-rooted grass and shrub vegetation to annual-cropping dryland farming has contributed to serious soil salinization challenges on the semi-arid North American Great Plains. In some cases, cultivation of the Great Plains has increased the availability of water, causing dominant sulfate salts to travel from the uphill areas to depressions where it will surface when water evaporates at the soil surface. A potential solution could include the replanting of the native deep-rooted vegetation, which requires knowledge of the spatial distribution of soil salinity. This study tested the soil factors influencing electromagnetic-induction meter (EM38) readings of soil salinity distribution around wetlands. The objectives were to: (1) predict growth and survival of Salix dasyclados Wimm. (cv. `India') along a salinity gradient in a small wetland, and (2) investigate whether newly established willows affected water-table fluctuations, which would indicate their phreatophytic nature or their ability to obtain their water supply from the zone of saturation. Results indicated significantly lower salinity values for sampling points with EM38 readings above 175 and 250 mS m-1 for height and survival, respectively. In addition, diurnal fluxes of the water table in areas of good willow growth and lower salinity indicated that cultivar `India' was phreatophytic in these areas and therefore has great potential for being used to combat saline seeps.

Water table and overbank flow frequency changes due to suburbanization-induced channel incision, Virginia Coastal Plain, USA

NASA Astrophysics Data System (ADS)

Hancock, G.; Mattell, N.; Christianson, E.; Wacksman, J.

2004-12-01

Channel incision is a widely observed response to increased flow in urbanized watersheds, but the effects of channel lowering on riparian water tables is not well documented. In a rapidly incising suburban stream in the Virginia Coastal Plain, we hypothesize that incision has lowered floodplain water tables and decreased the overbank flow frequency, and suggest these changes impact vegetation distribution in a diverse, protected riparian habitat. The monitored stream is a tributary to the James River draining 1.3 km2, of which 15% is impervious cover. Incision has occurred largely through upstream migration of a one m high knickpoint at a rate of 1-2 m/yr, primarily during high flow events. We installed 33 wells in six floodplain transects to assess water table elevations beneath the floodplain adjacent to the incising stream. To document the impacts of incision, two transects are located 30 and 50 m upstream of the knickpoint in unincised floodplain, and the remainder are 5, 30, 70, and 100 m downstream of the knickpoint in incised floodplain. In one transect above and two below, pressure transducers attached to dataloggers provide a high-resolution record of water table response to storm events. Significant differences have been observed in the water table above and below the knickpoint. Above the knickpoint, the water table is relatively flat and is 0.2-0.4 m below the floodplain surface. Water table response to precipitation events is nearly immediate, with the water table rising to the floodplain surface in significant rainfall events. In the transect immediately downstream of the knickpoint, the water table possesses a steep gradient, rising from ~1 m below the floodplain at the stream to 0.3 m below the surface within 20 m. In the most downstream transects, the water table is relatively flat, but is one m below the floodplain surface, equivalent to the depth of incision generated by knickpoint passage. Upstream of the knickpoint, overbank flooding occurs frequently, while below the knickpoint the majority of storm flow is contained within the incised channel and occupation of the floodplain is rare. Plant diversity surveys reveal differences in the total density of herbaceous growth and species distribution between the floodplain above and below the knickpoint. Results from >100 plots show that there is more leaf litter, less exposed ground, and a decrease in floodplain species cover in the incised portion of the floodplain. The changes in flood frequency and water table elevation appear to have allowed one invasive species, Japanese stilt grass (Microstegium vimineum), to become dominant in the floodplain understory, displacing native wetland species.

LONG-TERM TRENDS IN GROWTH OF PINUS PALUSTRIS AND PINUS ELLIOTTII GROWING ALONG A HYDROLOGICAL GRADIENT IN CENTRAL FLORIDA

EPA Science Inventory

Land-use change and urbanization has led to changes in the hydrologic regime in wet central Florida, with a trend toward lowered water table levels. These hydrologic changes are having environmental consequences in wetlands, where shifts in species composition and fire frequency...

Optimality and inference in hydrology from entropy production considerations: synthetic hillslope numerical experiments

NASA Astrophysics Data System (ADS)

Kollet, S. J.

2015-05-01

In this study, entropy production optimization and inference principles are applied to a synthetic semi-arid hillslope in high-resolution, physics-based simulations. The results suggest that entropy or power is indeed maximized, because of the strong nonlinearity of variably saturated flow and competing processes related to soil moisture fluxes, the depletion of gradients, and the movement of a free water table. Thus, it appears that the maximum entropy production (MEP) principle may indeed be applicable to hydrologic systems. In the application to hydrologic system, the free water table constitutes an important degree of freedom in the optimization of entropy production and may also relate the theory to actual observations. In an ensuing analysis, an attempt is made to transfer the complex, "microscopic" hillslope model into a macroscopic model of reduced complexity using the MEP principle as an interference tool to obtain effective conductance coefficients and forces/gradients. The results demonstrate a new approach for the application of MEP to hydrologic systems and may form the basis for fruitful discussions and research in future.

Map showing the altitude and configuration of the water level in the shallow aquifer, January 1975, Roswell Basin, Chaves and Eddy counties, New Mexico

USGS Publications Warehouse

Welder, G.E.

1977-01-01

The altitude and gradient of the water table in the ' shallow aquifer ' of the Roswell basin in Chaves and Eddy Counties, New Mexico, for January 1975 is shown on a map, scale of 1/2-inch per mile. The map was prepared by the U.S. Geological Survey in cooperation with the New Mexico State Engineer Office. (Woodard-USGS)

Map showing the altitude and configuration of the water level in the shallow aquifer, January 1964, Roswell Basin, Chaves and Eddy counties, New Mexico

USGS Publications Warehouse

Welder, G.E.

1977-01-01

The altitude and gradient of the water table in the ' shallow aquifer ' of the Roswell basin in Chaves and Eddy Counties, New Mexico, for January 1964 is shown on a map, scale of 1/2-inch per mile. The map was prepared by the U.S. Geological Survey in cooperation with the New Mexico State Engineer Office. (Woodard-USGS)

Viability of karezes (ancient water supply systems in Afghanistan) in a changing world

NASA Astrophysics Data System (ADS)

Macpherson, G. L.; Johnson, W. C.; Liu, Huan

2017-07-01

The Afghanistan population living far from rivers relies upon groundwater delivered from karezes (sub-horizontal tunnels). Karezes exploit unconfined groundwater in alluvial fans recharged largely by snowmelt from the Hindu Kush, the central mountain range of the country. Since the multi-year drought that began in 1998, many karezes have stopped flowing. This study characterizes the hydraulics of a kariz, the potential for reduced groundwater recharge because of climate change, and the impact of increasing population on kariz water production. A typical kariz in Afghanistan is 1-2 km long with a cross-section of 1-2 m2 and gradient of 1 m km-1. MODFLOW simulations show that water delivery from a kariz can be modeled by imposing a high ratio of kariz hydraulic conductivity to aquifer hydraulic conductivity on the cells representing the kariz. The model is sensitive to hydraulic conductivity, kariz gradient, and length of the kariz in contact with the water table. Precipitation data are scarce in Afghanistan, but regional data show a long-term trend of decreased snow cover, and therefore strong likelihood of decreased aquifer recharge. Population in Afghanistan has increased at a rate of about 2.2 % over the past several decades. An assessment of a six-district region within Kandahar Province where karezes are the most likely source of water indicates that water demand could have caused water tables to decline by 0.8-5.6 m, more than enough to cause karezes to stop flowing. These results suggest that kariz water production is not sustainable under current climate- and population-growth trends.

River stage influences on uranium transport in a hydrologically dynamic groundwater-surface water transition zone

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

Zachara, John M.; Chen, Xingyuan; Murray, Chris

In this study, a well-field within a uranium (U) plume in the groundwater-surface water transition zone was monitored for a 3 year period for water table elevation and dissolved solutes. The plume discharges to the Columbia River, which displays a dramatic spring stage surge resulting from snowmelt. Groundwater exhibits a low hydrologic gradient and chemical differences with river water. River water intrudes the site in spring. Specific aims were to assess the impacts of river intrusion on dissolved uranium (U aq), specific conductance (SpC), and other solutes, and to discriminate between transport, geochemical, and source term heterogeneity effects. Time seriesmore » trends for U aq and SpC were complex and displayed large temporal and well-to-well variability as a result of water table elevation fluctuations, river water intrusion, and changes in groundwater flow directions. The wells were clustered into subsets exhibiting common behaviors resulting from the intrusion dynamics of river water and the location of source terms. Hot-spots in U aq varied in location with increasing water table elevation through the combined effects of advection and source term location. Heuristic reactive transport modeling with PFLOTRAN demonstrated that mobilized U aq was transported between wells and source terms in complex trajectories, and was diluted as river water entered and exited the groundwater system. While U aq time-series concentration trends varied significantly from year-to-year as a result of climate-caused differences in the spring hydrograph, common and partly predictable response patterns were observed that were driven by water table elevation, and the extent and duration of river water intrusion.« less

River stage influences on uranium transport in a hydrologically dynamic groundwater-surface water transition zone

DOE PAGES

Zachara, John M.; Chen, Xingyuan; Murray, Chris; ...

2016-03-04

In this study, a well-field within a uranium (U) plume in the groundwater-surface water transition zone was monitored for a 3 year period for water table elevation and dissolved solutes. The plume discharges to the Columbia River, which displays a dramatic spring stage surge resulting from snowmelt. Groundwater exhibits a low hydrologic gradient and chemical differences with river water. River water intrudes the site in spring. Specific aims were to assess the impacts of river intrusion on dissolved uranium (U aq), specific conductance (SpC), and other solutes, and to discriminate between transport, geochemical, and source term heterogeneity effects. Time seriesmore » trends for U aq and SpC were complex and displayed large temporal and well-to-well variability as a result of water table elevation fluctuations, river water intrusion, and changes in groundwater flow directions. The wells were clustered into subsets exhibiting common behaviors resulting from the intrusion dynamics of river water and the location of source terms. Hot-spots in U aq varied in location with increasing water table elevation through the combined effects of advection and source term location. Heuristic reactive transport modeling with PFLOTRAN demonstrated that mobilized U aq was transported between wells and source terms in complex trajectories, and was diluted as river water entered and exited the groundwater system. While U aq time-series concentration trends varied significantly from year-to-year as a result of climate-caused differences in the spring hydrograph, common and partly predictable response patterns were observed that were driven by water table elevation, and the extent and duration of river water intrusion.« less

Upland-wetland connectivity provides a significant nexus between isolated wetlands and downstream water bodies

NASA Astrophysics Data System (ADS)

Mclaughlin, D. L.; Kaplan, D. A.; Cohen, M. J.

2013-12-01

Recent rulings by the U.S. Supreme Court have limited federal protection over isolated wetlands, requiring documentation of a 'significant nexus' to a navigable water body to ensure federal jurisdiction. Despite geographic isolation, isolated wetlands influence the surficial aquifer dynamics that regulate baseflow to surface water systems. Due to differences in specific yield (Sy) between upland soils and inundated wetlands, responses of the upland water table to atmospheric fluxes (precipitation, P, and evapotranspiration, ET) are amplified relative to wetland water levels, leading to reversals in the hydraulic gradient between the two systems. As such, wetlands act as a water sink during wet cycles (via wetland exfiltration) and a source (via infiltration) during drier times, regulating both the surficial aquifer and its baseflow to downstream systems. To explore the importance of this wetland function at the landscape scale, we integrated models of soil moisture, upland water table, and wetland stage to simulate the hydrology of a low-relief, depressional landscape. We quantified the hydrologic buffering effect of wetlands by calculating the relative change in the standard deviation (SD) of water table elevation between model runs with and without wetlands. Using this model we explored the effects wetland area and spatial distribution over a range of climatic drivers (P and ET) and soil types. Increasing wetland cumulative area and/or density reduced water table variability relative to landscapes without wetlands, supporting the idea that wetlands stabilize regional hydrologic variation, but also increased mean water table depth because of sustained high ET rates in wetlands during dry periods. Maintaining high cumulative wetland area, but with fewer wetlands, markedly reduced the effect of wetland area, highlighting the importance of small, distributed wetlands on water table regulation. Simulating a range of climate scenarios suggested that the capacity of wetlands to buffer water table variation is most pronounced along a 'sweet spot' where P and ET are relatively balanced. High P and low ET yielded consistently high water tables with wetlands acting predominantly as sinks (i.e., little switching behavior), while low P and high ET scenarios limited wetland inundation. On the other hand, when both P and ET were moderate, the SD of the regional water table was reduced by nearly 50% for landscapes with 30% wetland area distributed over ~1 ha watersheds. Additionally, we found these buffering effects to be stronger in coarser soils compared with finer soils. Considering the strong influence of regional water table on downstream surface water systems, loss of isolated wetland area or mitigation of this loss at the expense of wetland density (i.e., large mitigation banks to replace small distributed systems) has the potential to significantly impact downstream water bodies. Isolated wetlands buffer surficial aquifer dynamics by providing water storage capacitance at the landscape scale and ultimately exert hydraulic regulation of regional surface waters through an indirect, but significant nexus.

Relation between ground water and surface water in Brandywine Creek basin, Pennsylvania

USGS Publications Warehouse

Olmsted, F.H.; Hely, A.G.

1962-01-01

The relation between ground water and surface water was studied in Brandywine Creek basin, an area of 287 square miles in the Piedmont physiographic province in southeastern Pennsylvania. Most of the basin is underlain by crystalline rocks that yield only small to moderate supplies of water to wells, but the creek has an unusually well-sustained base flow. Streamflow records for the Chadds Ford, Pa., gaging station were analyzed; base flow recession curves and hydrographs of base flow were defined for the calendar years 1928-31 and 1952-53. Water budgets calculated for these two periods indicate that about two-thirds of the runoff of Brandywine Creek is base flow--a significantly higher proportion of base flow than in streams draining most other types of consolidated rocks in the region and almost as high as in streams in sandy parts of the Coastal Plain province in New Jersey and Delaware. Ground-water levels in 16 observation wells were compared with the base flow of the creek for 1952-53. The wells are assumed to provide a reasonably good sample of average fluctuations of the water table and its depth below the land surface. Three of the wells having the most suitable records were selected as index wells to use in a more detailed analysis. A direct, linear relation between the monthly average ground-water stage in the index wells and the base flow of the creek in winter months was found. The average ground-water discharge in the basin for 1952-53 was 489 cfs (316 mgd), of which slightly less than one-fourth was estimated to be loss by evapotranspiration. However, the estimated evapotranspiration from ground water, and consequently the estimated total ground-water discharge, may be somewhat high. The average gravity yield (short-term coefficient of storage) of the zone of water-table fluctuation was calculated by two methods. The first method, based on the ratio of change in ground-water storage as calculated from a witner base-flow recession curve is seasonal change in ground-water stage in the observation wells, gave values of about 7 percent using 16 wells) and 7 1/2 percent (using 3 index wells). The second method, in which the change in ground water storage is based on a hypothetical base-flow recession curve (derived from the observed linear relation between ground-water stage in the index wells and base flow), gave a value of about 10 1/2 percent. The most probable value of gravity yield is between 7 1/2 and 10 percent, but this estimate may require modification when more information on the average magnitude of water-table fluctuation and the sources of base flow of the creek become available. Rough estimates were made of the average coefficient of transmissibility of the rocks in the basin by use of the estimated total ground-water discharge for the period 1952-53, approximate values of length of discharge areas, and average water-table gradients adjacent to the discharge areas. The estimated average coefficient of transmissibility for 1952-53 is roughly 1,000 gpd per foot. The transmissibility is variable, decreasing with decreasing ground-water stage. The seeming inconsistency between the small to moderate ground-water yield to wells and the high yield to streams is explained in terms of the deep permeable soils, the relatively high gravity yield of the zone of water-table fluctuation, the steep water-table gradients toward the streams, the relatively low transmissibility of the rocks, and the rapid decreases in gravity yield below the lower limit of water-table fluctuation. It is concluded that no simple relation exists between the amount of natural ground-water discharge in an area and all the proportion of this discharge that can be diverted to wells.

Ground-water flow in the shallow aquifer system at the Naval Weapons Station Yorktown, Virginia

USGS Publications Warehouse

Smith, Barry S.

2001-01-01

The Environmental Directorate of the Naval Weapons Station Yorktown, Virginia, is concerned about possible contamination of ground water at the Station. Ground water at the Station flows through a shallow system of layered aquifers and leaky confining units. The units of the shallow aquifer system are the Columbia aquifer, the Cornwallis Cave confining unit, the Cornwallis Cave aquifer, the Yorktown confining unit, and the Yorktown-Eastover aquifer. The Eastover-Calvert confining unit separates the shallow aquifer system from deeper confined aquifers beneath the Station. A three-dimensional, finite-difference, ground-water flow model was used to simulate steady-state ground-water flow of the shallow aquifer system in and around the Station. The model simulated ground-water flow from the peninsular drainage divide that runs across the Lackey Plain near the southern end of the Station north to King Creek and the York River and south to Skiffes Creek and the James River. The model was calibrated by minimizing the root mean square error between 4 7 measured and corresponding simulated water levels. The calibrated model was used to determine the ground-water budget and general directions of ground-water flow. A particle-tracking routine was used with the calibrated model to estimate groundwater flow paths, flow rates, and traveltimes from selected sites at the Station. Simulated ground-water flow velocities of the Station-area model were small beneath the interstream areas of the Lackey Plain and Croaker Flat, but increased outward toward the streams and rivers where the hydraulic gradients are larger. If contaminants from the land surface entered the water table at or near the interstream areas of the Station, where hydraulic gradients are smaller, they would migrate more slowly than if they entered closer to the streams or the shores of the rivers where gradients commonly are larger. The ground-water flow simulations indicate that some ground water leaks downward from the water table to the Yorktown confining unit and, where the confining unit is absent, to the Yorktown-Eastover aquifer. The velocities of advective-driven contaminants would decrease considerably when entering the Yorktown confining unit because the hydraulic conductivity of the confining unit is small compared to that of the aquifers. Any contaminants that moved with advective ground-water flow near the groundwater divide of the Lackey Plain would move relatively slowly because the hydraulic gradients are small there. The direction in which the contaminants would move, however, would be determined by precisely where the contaminants entered the water table. The model was not designed to accurately simulate ground-water flow paths through local karst features. Beneath Croaker Flat, ground water flows downward through the Columbia aquifer and the Yorktown confining unit into the Yorktown-Eastover aquifer. Analyses of the movement of simulated particles from two adjacent sites at Croaker Flat indicated that ground-water flow paths were similar at first but diverged and discharged to different tributaries of Indian Field Creek or to the York River. These simulations indicate that complex and possibly divergent flow paths and traveltimes are possible at the Station. Although the Station-area model is not detailed enough to simulate ground-water flow at the scales commonly used to track and remediate contaminants at specific sites, general concepts about possible contaminant migration at the Station can be inferred from the simulations.

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

Friedrichs, D.R.; Cole, C.R.; Arnett, R.C.

The Hanford Pathline Calculational Program (HPCP) is a numerical model developed to predict the movement of fluid particles from one location to another within the Hanford or similar groundwater systems. As such it can be considered a simple transport model wherein only advective changes are considered. Application of the numerical HPCP to test cases for which semianalytical results are obtainable showed that with reasonable time steps and the grid spacing requirements HPCP give good agreement with the semianalytical solution. The accuracy of the HPCP results is most sensitive in areas near steep or rapidly changing potential gradients and may requiremore » finer grid spacing in those areas than for the groundwater system as a whole. Initial applications of HPCP to the Hanford groundwater flow regime show that significant differences (improvements) in the predictions of fluid particle movement are obtainable with the pathline approach (changing groundwater potential or water table surface) as opposed to the streamline approach (unchanging potential or water table surface) used in past Hanford groundwater analyses. This report documents capability developed for estimating groundwater travel times from the Hanford high-level waste areas to the Columbia River at different water table levels.« less

Aquifer-scale controls on the distribution of nitrate and ammonium in ground water near La Pine, Oregon, USA

USGS Publications Warehouse

Hinkle, S.R.; Böhlke, J.K.; Duff, J.H.; Morgan, D.S.; Weick, R.J.

2007-01-01

Geochemical and isotopic tools were applied at aquifer, transect, and subtransect scales to provide a framework for understanding sources, transport, and fate of dissolved inorganic N in a sandy aquifer near La Pine, Oregon. NO3 is a common contaminant in shallow ground water in this area, whereas high concentrations of NH4-N (up to 39 mg/L) are present in deep ground water. N concentrations, N/Cl ratios, tracer-based apparent ground-water ages, N isotope data, and hydraulic gradients indicate that septic tank effluent is the primary source of NO3. N isotope data, N/Cl and N/C relations, 3H data, and hydraulic considerations point to a natural, sedimentary organic matter source for the high concentrations of NH4, and are inconsistent with an origin as septic tank N. Low recharge rates and flow velocities have largely restricted anthropogenic NO3 to isolated plumes within several meters of the water table. A variety of geochemical and isotopic data indicate that denitrification also affects NO3 gradients in the aquifer. Ground water in the La Pine aquifer evolves from oxic to increasingly reduced conditions. Suboxic conditions are achieved after about 15-30 y of transport below the water table. NO3 is denitrified near the oxic/suboxic boundary. Denitrification in the La Pine aquifer is characterized well at the aquifer scale with a redox boundary approach that inherently captures spatial variability in the distribution of electron donors. ?? 2006 Elsevier B.V. All rights reserved.

Assessment of ground-water contamination near Lantana landfill, Southeast Florida

USGS Publications Warehouse

Russell, G.M.; Higer, A.L.

1988-01-01

The Lantana landfill located in Palm Beach County rises 40 to 50 feet above normal ground level and consists of about 250 acres of compacted garbage and trash, some below the water table. Surface-resistivity measurements and water-quality analyses indicate a contaminant plume along the eastern perimeter of the landfill that has migrated about 300 feet eastward toward an adjacent lake. Concentrations of chloride, ammonia, and nitrate were elevated within the plume. The surficial aquifer consists primarily of sand from 0 to about 68 feet, and sand interbedded with sandstone and limestone from 68 to 220 feet. A slight hydraulic gradient exists, indicating ground-water movement from the landfill toward a lake to the east. Analyses of geoelectric, lithologic, and water-quality data indicate that surface geophysical techniques were successful in determining the areal and vertical extent of leachate migration at this location.The Lantana landfill located in Palm Beach County rises 40 to 50 feet above normal ground level and consists of about 250 acres of compacted garbage and trash, some below the water table. Surface-resistivity measurements and water-quality analyses indicate a contaminant plume along the eastern perimeter of the landfill that has migrated about 300 feet eastward toward an adjacent lake. Concentrations of chloride, ammonia, and nitrate were elevated within the plume. The surficial aquifer consists primarily of sand from 0 to about 68 feet, and sand interbedded with sandstone and limestone from 68 to 220 feet. A slight hydraulic gradient exists, indicating ground-water movement from the landfill toward a lake to the east. Analyses of geoelectric, lithologic, and water-quality data indicate that surface geophysical techniques were successful in determining the areal and vertical extent of leachate migration at this location.

A Hydraulic Nexus between Geographically Isolated Wetlands and Downstream Water Bodies

NASA Astrophysics Data System (ADS)

Mclaughlin, D. L.; Kaplan, D. A.; Cohen, M. J.

2014-12-01

Geographic isolation does not imply hydrological isolation; indeed, local groundwater exchange between geographically isolated wetlands (GIWs) and surrounding uplands may yield important controls on regional hydrology. Differences in specific yield (Sy) between aquifers and inundated GIWs drive differences in water level responses to atmospheric fluxes, leading to frequent reversals in hydraulic gradients that cause GIWs to act as both groundwater sinks and sources. When distributed across the landscape, these reversals in local groundwater fluxes are predicted to collectively buffer the surficial aquifer and its regulation of baseflow delivery, a process we refer to as landscape hydrologic capacitance. To test this hypothesis, we integrated models of daily soil moisture, upland water table, and wetland stage dynamics to simulate hydrology of a low-relief landscape with GIWs. Simulations explored the influences of cumulative wetland area, individual wetland size, climate, and soil texture on water table and baseflow variation. Increasing cumulative wetland area and decreasing individual wetland size reduced water table variation and the frequency of extremely shallow and deep water tables. This buffering effect extended to baseflow deliveries, decreasing the standard deviation of daily baseflow by as much as 50%. For the same total wetland area, landscapes with fewer (i.e., larger) wetlands exhibited markedly lower hydrologic capacitance than those with more (i.e., smaller) wetlands, highlighting the important role of small GIWs in regulating regional hydrology. Recent U.S. Supreme Court rulings have limited federal protections for GIWs except where a "significant nexus" to a navigable water body is demonstrated. Our results suggest that GIWs regulate downstream baseflow, even where water in GIWs may never physically reach downstream systems, providing a significant "hydraulic" nexus to distant water bodies.

Temporal Hyporheic Zone Response to Water Table Fluctuations.

PubMed

Malzone, Jonathan M; Anseeuw, Sierra K; Lowry, Christopher S; Allen-King, Richelle

2016-03-01

Expansion and contraction of the hyporheic zone due to temporal hydrologic changes between stream and riparian aquifer influence the biogeochemical cycling capacity of streams. Theoretical studies have quantified the control of groundwater discharge on the depth of the hyporheic zone; however, observations of temporal groundwater controls are limited. In this study, we develop the concept of groundwater-dominated differential hyporheic zone expansion to explain the temporal control of groundwater discharge on the hyporheic zone in a third-order stream reach flowing through glacially derived terrain typical of the Great Lakes region. We define groundwater-dominated differential expansion of the hyporheic zone as: differing rates and magnitudes of hyporheic zone expansion in response to seasonal vs. storm-related water table fluctuation. Specific conductance and vertical hydraulic gradient measurements were used to map changes in the hyporheic zone during seasonal water table decline and storm events. Planar and riffle beds were monitored in order to distinguish the cause of increasing hyporheic zone depth. Planar bed seasonal expansion of the hyporheic zone was of a greater magnitude and longer in duration (weeks to months) than storm event expansion (hours to days). In contrast, the hyporheic zone beneath the riffle bed exhibited minimal expansion in response to seasonal groundwater decline compared to storm related expansion. Results indicated that fluctuation in the riparian water table controlled seasonal expansion of the hyporheic zone along the planar bed. This groundwater induced hyporheic zone expansion could increase the potential for biogeochemical cycling and natural attenuation. © 2015, National Ground Water Association.

Linking soil moisture balance and source-responsive models to estimate diffuse and preferential components of groundwater recharge

USGS Publications Warehouse

Cuthbert, M.O.; Mackay, R.; Nimmo, J.R.

2012-01-01

Results are presented of a detailed study into the vadose zone and shallow water table hydrodynamics of a field site in Shropshire, UK. A conceptual model is developed and tested using a range of numerical models, including a modified soil moisture balance model (SMBM) for estimating groundwater recharge in the presence of both diffuse and preferential flow components. Tensiometry reveals that the loamy sand topsoil wets up via macropore flow and subsequent redistribution of moisture into the soil matrix. Recharge does not occur until near-positive pressures are achieved at the top of the sandy glaciofluvial outwash material that underlies the topsoil, about 1 m above the water table. Once this occurs, very rapid water table rises follow. This threshold behaviour is attributed to the vertical discontinuity in the macropore system due to seasonal ploughing of the topsoil, and a lower permeability plough/iron pan restricting matrix flow between the topsoil and the lower outwash deposits. Although the wetting process in the topsoil is complex, a SMBM is shown to be effective in predicting the initiation of preferential flow from the base of the topsoil into the lower outwash horizon. The rapidity of the response at the water table and a water table rise during the summer period while flow gradients in the unsaturated profile were upward suggest that preferential flow is also occurring within the outwash deposits below the topsoil. A variation of the source-responsive model proposed by Nimmo (2010) is shown to reproduce the observed water table dynamics well in the lower outwash horizon when linked to a SMBM that quantifies the potential recharge from the topsoil. The results reveal new insights into preferential flow processes in cultivated soils and provide a useful and practical approach to accounting for preferential flow in studies of groundwater recharge estimation.

Examining the spatial and temporal variation of groundwater inflows to a valley-to-floodplain river using 222Rn, geochemistry and river discharge: the Ovens River, southeast Australia

NASA Astrophysics Data System (ADS)

Yu, M. C. L.; Cartwright, I.; Braden, J. L.; de Bree, S. T.

2013-12-01

Radon (222Rn) and major ion geochemistry were used to define and quantify the catchment-scale groundwater-surface water interactions along the Ovens River in the southeast Murray-Darling Basin, Victoria, Australia, between September 2009 and October 2011. The Ovens River is characterized by the transition from a single channel within a mountain valley in the upper catchment to a multi-channel meandering river on flat alluvial plains in the lower catchment. Overall, the Ovens River is dominated by gaining reaches, receiving groundwater from both alluvial and basement aquifers. The distribution of gaining and losing reaches is governed by catchment morphology and lithology. In the upper catchment, rapid groundwater recharge through the permeable aquifers increases the water table. The rising water table, referred to as hydraulic loading, increases the hydraulic head gradient toward the river and hence causes high baseflow to the river during wet (high flow) periods. In the lower catchment, lower rainfall and finer-gained sediments reduce the magnitude and variability of hydraulic gradient between the aquifer and the river, producing lower but more constant groundwater inflows. The water table in the lower reaches has a shallow gradient, and small changes in river height or groundwater level can result in fluctuating gaining and losing behaviour. The middle catchment represents a transition in river-aquifer interactions from the upper to the lower catchment. High baseflow in some parts of the middle and lower catchments is caused by groundwater flowing over basement highs. Mass balance calculations based on 222Rn activities indicate that groundwater inflows are 2 to 17% of total flow with higher inflows occurring during high flow periods. In comparison to 222Rn activities, estimates of groundwater inflows from Cl concentrations are higher by up to 2000% in the upper and middle catchment but lower by 50 to 100% in the lower catchment. The high baseflow estimates using Cl concentrations may be due to the lack of sufficient difference between groundwater and surface water Cl concentrations. Both hydrograph separation and differential flow gauging yield far higher baseflow fluxes than 222Rn activities and Cl concentrations, probably indicating the input of other sources to the river in additional to regional groundwater, such as bank return flows.

Methane oxidation in a crude oil contaminated aquifer: Delineation of aerobic reactions at the plume fringes

USGS Publications Warehouse

Amos, R.T.; Bekins, B.A.; Delin, G.N.; Cozzarelli, I.M.; Blowes, D.W.; Kirshtein, J.D.

2011-01-01

High resolution direct-push profiling over short vertical distances was used to investigate CH4 attenuation in a petroleum contaminated aquifer near Bemidji, Minnesota. The contaminant plume was delineated using dissolved gases, redox sensitive components, major ions, carbon isotope ratios in CH4 and CO2, and the presence of methanotrophic bacteria. Sharp redox gradients were observed near the water table. Shifts in ??13CCH4 from an average of - 57.6??? (?? 1.7???) in the methanogenic zone to - 39.6??? (?? 8.7???) at 105 m downgradient, strongly suggest CH4 attenuation through microbially mediated degradation. In the downgradient zone the aerobic/anaerobic transition is up to 0.5 m below the water table suggesting that transport of O2 across the water table is leading to aerobic degradation of CH4 at this interface. Dissolved N2 concentrations that exceeded those expected for water in equilibrium with the atmosphere indicated bubble entrapment followed by preferential stripping of O2 through aerobic degradation of CH4 or other hydrocarbons. Multivariate and cluster analysis were used to distinguish between areas of significant bubble entrapment and areas where other processes such as the infiltration of O 2 rich recharge water were important O2 transport mechanisms. ?? 2011 Elsevier B.V. All rights reserved.

Effects of groundwater-flow paths on nitrate concentrations across two riparian forest corridors

USGS Publications Warehouse

Speiran, Gary K.

2010-01-01

Groundwater levels, apparent age, and chemistry from field sites and groundwater-flow modeling of hypothetical aquifers collectively indicate that groundwater-flow paths contribute to differences in nitrate concentrations across riparian corridors. At sites in Virginia (one coastal and one Piedmont), lowland forested wetlands separate upland fields from nearby surface waters (an estuary and a stream). At the coastal site, nitrate concentrations near the water table decreased from more than 10 mg/L beneath fields to 2 mg/L beneath a riparian forest buffer because recharge through the buffer forced water with concentrations greater than 5 mg/L to flow deeper beneath the buffer. Diurnal changes in groundwater levels up to 0.25 meters at the coastal site reflect flow from the water table into unsaturated soil where roots remove water and nitrate dissolved in it. Decreases in aquifer thickness caused by declines in the water table and decreases in horizontal hydraulic gradients from the uplands to the wetlands indicate that more than 95% of the groundwater discharged to the wetlands. Such discharge through organic soil can reduce nitrate concentrations by denitrification. Model simulations are consistent with field results, showing downward flow approaching toe slopes and surface waters to which groundwater discharges. These effects show the importance of buffer placement over use of fixed-width, streamside buffers to control nitrate concentrations.

Modeling hydrology and in-stream transport on drained forested lands in coastal Carolinas, U.S.A.

Treesearch

Devendra Amatya

2005-01-01

This study summarizes the successional development and testing of forest hydrologic models based on DRAINMOD that predicts the hydrology of low-gradient poorly drained watersheds as affected by land management and climatic variation. The field scale (DRAINLOB) and watershed-scale in-stream routing (DRAINWAT) models were successfully tested with water table and outflow...

Obliquity (41kyr) Paced SE Asian Monsoon Variability Following the Miocene Climate Transition

NASA Astrophysics Data System (ADS)

Heitmann, E. O.; Breecker, D.; Ji, S.; Nie, J.

2016-12-01

We investigated Asian monsoon variability during the Miocene, which may provide a good analog for the future given the lack of northern hemisphere ice sheets. In the Miocene Yanwan Section (Tianshui Basin, China) 25cm thick CaCO3-cemented horizons overprint siltstones every 1m. We suggest this rhythmic layering records variations in water availability influenced by the Asian monsoon. We interpret the siltstones as stacked soils that formed in a seasonal climate with a fluctuating water table, evidenced by roots, clay films, mottling, presence of CaCO3 nodules, and stacked carbonate nodule δ13C and δ18O profiles that mimic modern soils. We interpret the CaCO3-cemented horizons as capillary-fringe carbonates that formed in an arid climate with a steady water table and high potential evapotranspiration (PET), evidenced by sharp upper and basal contacts, micrite, sparite, and root-pore cements. The magnetostratigraphy-based age model indicates obliquity-pacing of the CaCO3-cemented horizons suggesting an orbital control on water availability, for which we propose two mechanisms: 1) summer monsoon strength, moderated by the control of obliquity on the cross-equatorial pressure gradient, and 2) PET, moderated by the control of precession on 35oN summer insolation. We use orbital configurations to predict lithology. Coincidence of obliquity minima and insolation maxima drives strong summer monsoons, seasonal variations in water table depth and soil formation. Coincidence of obliquity maxima and insolation minima drives weak summer monsoons, high PET, and carbonate accumulation above a deepened, stable water table. Coincidence of obliquity and insolation minima drives strong monsoons, low PET, and a high water table, explaining the evidence for aquatic plants previously observed in this section. Southern hemisphere control of summer monsoon variability in the Miocene may thus have resulted in large water availability variations in central China.

A significant nexus: Geographically isolated wetlands influence landscape hydrology

NASA Astrophysics Data System (ADS)

McLaughlin, Daniel L.; Kaplan, David A.; Cohen, Matthew J.

2014-09-01

Recent U.S. Supreme Court rulings have limited federal protections for geographically isolated wetlands (GIWs) except where a "significant nexus" to a navigable water body is demonstrated. Geographic isolation does not imply GIWs are hydrologically disconnected; indeed, wetland-groundwater interactions may yield important controls on regional hydrology. Differences in specific yield (Sy) between uplands and inundated GIWs drive differences in water level responses to precipitation and evapotranspiration, leading to frequent reversals in hydraulic gradients that cause GIWs to act as both groundwater sinks and sources. These reversals are predicted to buffer surficial aquifer dynamics and thus base flow delivery, a process we refer to as landscape hydrologic capacitance. To test this hypothesis, we connected models of soil moisture, upland water table, and wetland stage to simulate hydrology of a low-relief landscape with GIWs, and explored the influences of total wetland area, individual wetland size, climate, and soil texture on water table and base flow variation. Increasing total wetland area and decreasing individual wetland size substantially decreased water table and base flow variation (e.g., reducing base flow standard deviation by as much as 50%). GIWs also decreased the frequency of extremely high and low water tables and base flow deliveries. For the same total wetland area, landscapes with fewer (i.e., larger) wetlands exhibited markedly lower hydrologic capacitance than those with more (i.e., smaller) wetlands, highlighting the importance of small GIWs to regional hydrology. Our results suggest that GIWs buffer dynamics of the surficial aquifer and stream base flow, providing an indirect but significant nexus to the regional hydrologic system.

Influence of hydrological, biogeochemical and temperature transients on subsurface carbon fluxes in a flood plain environment

DOE PAGES

Arora, Bhavna; Spycher, Nicolas F.; Steefel, Carl I.; ...

2016-02-12

Flood plains play a potentially important role in the global carbon cycle. The accumulation of organic matter in flood plains often induces the formation of chemically reduced groundwater and sediments along riverbanks. In this study, our objective is to evaluate the cumulative impact of such reduced zones, water table fluctuations, and temperature gradients on subsurface carbon fluxes in a flood plain at Rifle, Colorado located along the Colorado River. 2-D coupled variably-saturated, non-isothermal flow and biogeochemical reactive transport modeling was applied to improve our understanding of the abiotic and microbially mediated reactions controlling carbon dynamics at the Rifle site. Modelmore » simulations considering only abiotic reactions (thus ignoring microbial reactions) underestimated CO 2 partial pressures observed in the unsaturated zone and severely underestimated inorganic (and overestimated organic) carbon fluxes to the river compared to simulations with biotic pathways. Both model simulations and field observations highlighted the need to include microbial contributions from chemolithoautotrophic processes (e.g., Fe +2 and S -2 oxidation) to match locally-observed high CO 2 concentrations above reduced zones. Observed seasonal variations in CO 2 concentrations in the unsaturated zone could not be reproduced without incorporating temperature gradients in the simulations. Incorporating temperature fluctuations resulted in an increase in the annual groundwater carbon fluxes to the river by 170 % to 3.3 g m -2 d -1, while including water table variations resulted in an overall decrease in the simulated fluxes. We thus conclude that spatial microbial and redox zonation as well as temporal fluctuations of temperature and water table depth contribute significantly to subsurface carbon fluxes in flood plains and need to be represented appropriately in model simulations.« less

Influence of hydrological, biogeochemical and temperature transients on subsurface carbon fluxes in a flood plain environment

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

Arora, Bhavna; Spycher, Nicolas F.; Steefel, Carl I.

2016-02-01

Flood plains play a potentially important role in the global carbon cycle. The accumulation of organic matter in flood plains often induces the formation of chemically reduced groundwater and sediments along riverbanks. In this study, our objective is to evaluate the cumulative impact of such reduced zones, water table fluctuations, and temperature gradients on subsurface carbon fluxes in a flood plain at Rifle, Colorado located along the Colorado River. 2-D coupled variably-saturated, non-isothermal flow and biogeochemical reactive transport modeling was applied to improve our understanding of the abiotic and microbially mediated reactions controlling carbon dynamics at the Rifle site. Modelmore » simulations considering only abiotic reactions (thus ignoring microbial reactions) underestimated CO2 partial pressures observed in the unsaturated zone and severely underestimated inorganic (and overestimated organic) carbon fluxes to the river compared to simulations with biotic pathways. Both model simulations and field observations highlighted the need to include microbial contributions from chemolithoautotrophic processes (e.g., Fe?2 and S-2 oxidation) to match locally-observed high CO2 concentrations above reduced zones. Observed seasonal variations in CO2 concentrations in the unsaturated zone could not be reproduced without incorporating temperature gradients in the simulations. Incorporating temperature fluctuations resulted in an increase in the annual groundwater carbon fluxes to the river by 170 % to 3.3 g m-2 d-1, while including water table variations resulted in an overall decrease in the simulated fluxes. We conclude that spatial microbial and redox zonation as well as temporal fluctuations of temperature and water table depth contribute significantly to subsurface carbon fluxes in flood plains and need to be represented appropriately in model simulations.« less

Response of Plant Height, Species Richness and Aboveground Biomass to Flooding Gradient along Vegetation Zones in Floodplain Wetlands, Northeast China.

PubMed

Lou, Yanjing; Pan, Yanwen; Gao, Chuanyu; Jiang, Ming; Lu, Xianguo; Xu, Y Jun

2016-01-01

Flooding regime changes resulting from natural and human activity have been projected to affect wetland plant community structures and functions. It is therefore important to conduct investigations across a range of flooding gradients to assess the impact of flooding depth on wetland vegetation. We conducted this study to identify the pattern of plant height, species richness and aboveground biomass variation along the flooding gradient in floodplain wetlands located in Northeast China. We found that the response of dominant species height to the flooding gradient depends on specific species, i.e., a quadratic response for Carex lasiocarpa, a negative correlation for Calamagrostis angustifolia, and no response for Carex appendiculata. Species richness showed an intermediate effect along the vegetation zone from marsh to wet meadow while aboveground biomass increased. When the communities were analysed separately, only the water table depth had significant impact on species richness for two Carex communities and no variable for C. angustifolia community, while height of dominant species influenced aboveground biomass. When the three above-mentioned communities were grouped together, variations in species richness were mainly determined by community type, water table depth and community mean height, while variations in aboveground biomass were driven by community type and the height of dominant species. These findings indicate that if habitat drying of these herbaceous wetlands in this region continues, then two Carex marshes would be replaced gradually by C. angustifolia wet meadow in the near future. This will lead to a reduction in biodiversity and an increase in productivity and carbon budget. Meanwhile, functional traits must be considered, and should be a focus of attention in future studies on the species diversity and ecosystem function in this region.

Response of Plant Height, Species Richness and Aboveground Biomass to Flooding Gradient along Vegetation Zones in Floodplain Wetlands, Northeast China

PubMed Central

Lou, Yanjing; Pan, Yanwen; Gao, Chuanyu; Jiang, Ming; Lu, Xianguo; Xu, Y. Jun

2016-01-01

Flooding regime changes resulting from natural and human activity have been projected to affect wetland plant community structures and functions. It is therefore important to conduct investigations across a range of flooding gradients to assess the impact of flooding depth on wetland vegetation. We conducted this study to identify the pattern of plant height, species richness and aboveground biomass variation along the flooding gradient in floodplain wetlands located in Northeast China. We found that the response of dominant species height to the flooding gradient depends on specific species, i.e., a quadratic response for Carex lasiocarpa, a negative correlation for Calamagrostis angustifolia, and no response for Carex appendiculata. Species richness showed an intermediate effect along the vegetation zone from marsh to wet meadow while aboveground biomass increased. When the communities were analysed separately, only the water table depth had significant impact on species richness for two Carex communities and no variable for C. angustifolia community, while height of dominant species influenced aboveground biomass. When the three above-mentioned communities were grouped together, variations in species richness were mainly determined by community type, water table depth and community mean height, while variations in aboveground biomass were driven by community type and the height of dominant species. These findings indicate that if habitat drying of these herbaceous wetlands in this region continues, then two Carex marshes would be replaced gradually by C. angustifolia wet meadow in the near future. This will lead to a reduction in biodiversity and an increase in productivity and carbon budget. Meanwhile, functional traits must be considered, and should be a focus of attention in future studies on the species diversity and ecosystem function in this region. PMID:27097325

Geothermal Exploration of the Winston Graben, Central New Mexico, USA

NASA Astrophysics Data System (ADS)

Sophy, M. J.; Kelley, S. A.

2011-12-01

We are assessing the geothermal potential of the Winston Graben of central New Mexico using borehole temperature logs and geophysical data. The Winston Graben is a late Cenozoic rift basin, part of the larger Rio Grande rift, which is 5 to 10 km wide and 56 km long with northern and southern termini occurring at accommodation zones that coincide with late Cenozoic volcanic lineaments. The graben is interpreted to be symmetric based on geologic mapping, with 2 km of stratigraphic offset on both the western and eastern margins. The graben is bordered by the Black Range to the west and is separated from the Rio Grande valley by the Sierra Cuchillo, a horst block made of Paleozoic rocks intruded by a laccolith. Geothermal and geophysical data, including water table measurements, well temperature logs, thermal conductivity samples, bottom hole temperatures, water chemistry, and gravity data have been extracted from the New Mexico Geothermal Database, part of the National Geothermal Database, and the Geonet Gravity and Magnetic Dataset Repository. Combined with existing geologic maps of the Winston Graben and surroundings, these data help to identify spatial relationships between geologic structures and groundwater parameters and distribution. Geothermal gradients from industry temperature-depth well profiles range from 20°C/km to 60°C/km with a spatial distribution of higher gradients located on the eastern side of the Sierra Cuchillo horst, which is where a mapped warm spring is located. Lower thermal gradients were observed to the west in the groundwater recharge area of the basin. Analysis of Bouguer gravity data indicate a gravity low coinciding with the center of the Winston Graben, which is attributed to be the deepest part of the basin, symetrically surrounded by gravity highs. Gravity highs coincide with the middle Cenozoic Morenci and Chise volcanic lineaments along the northern and southern ends of the graben. The mapped warm spring occurs at the intersection of basin bounding faults and the Chise lineament. Water table gradient information from phreatic aquifers less than 75 meters deep suggests both along axis and cross axis flow direction within the basin. Because the temperature anomalies trend east-west and water table gradients trend north-south, a two component hydrogeologic system may exist. The east-west trend may be the result of deep groundwater, heated along its flowpath beneath the basin and the Sierra Cuchillo, being forced to the surface at structural zones. Major rift bounding faults along the Sierra Cuchillo horst block serve as fluid pathways for the existing warm springs, and a low temperature geothermal resource may have formed as deep warm, and shallow cool waters interact. Planned work on this project includes collecting hydrogen and oxygen isotopic data of precipitation and groundwater which may show distinct water chemistries of a two component system, continued temperature logging of deeper wells in order to understand temperature distributions at depth, and an increased number of gravity measurements of the southern end of the Winston Graben to improve mapping of the southern accommodation zone relative to the hydrogeologic system.

Ant distribution in relation to ground water in north Florida pine flatwoods.

PubMed

Tschinkel, Walter R; Murdock, Tyler; King, Joshua R; Kwapich, Christina

2012-01-01

Longleaf pine savannas are one of the most threatened ecosystems in the world, yet are understudied. Ants are a functionally important and diverse group of insects in these ecosystems. It is largely unknown how local patterns of species diversity and composition are determined through the interaction of this dominant animal group with abiotic features of longleaf pine ecosystems. Here we describe how an important abiotic variable, depth to water table, relates to ant species distributions at local scales. Pitfall trapping studies across habitat gradients in the Florida coastal plains longleaf pine flatwoods showed that the ant community changed with mild differences in habitat. In this undulating landscape, elevation differences were less than 2 m, and the depth to the water table ranged from < 20 cm to 1.2 m. The plant species composing the ground cover were zoned in response to depth to water, and shading by canopy trees increased over deeper water tables. Of the 27 ant species that were analyzed, depending on the statistical test, seven or eight were significantly more abundant over a deep water table, eight to ten over a shallow one, and nine to eleven were not significantly patterned with respect to depth to water. Ant species preferring sites with shallow groundwater also preferred the shadier parts of the sites, while those preferring sites with deeper groundwater preferred the sunnier parts of the sites. This suggests that one group of species prefers hot-dry conditions, and the other cooler-moist. Factor analysis and abundance-weighted mean site characteristics generally confirmed these results. These results show that ant communities in this region respond to subtle differences in habitat, but whether these differences arise from founding preferences, survival, competition, or some combination of these is not known.

Ecohydrological controls over water budgets in floodplain meadows

NASA Astrophysics Data System (ADS)

Morris, Paul J.; Verhoef, Anne; Macdonald, David M. J.; Gardner, Cate M.; Punalekar, Suvarna M.; Tatarenko, Irina; Gowing, David

2013-04-01

Floodplain meadows are important ecosystems, characterised by high plant species richness including rare species. Fine-scale partitioning along soil hydrological gradients allows many species to co-exist. Concerns exist that even modest changes to soil hydrological regime as a result of changes in management or climate may endanger floodplain meadows communities. As such, understanding the interaction between biological and physical controls over floodplain meadow water budgets is important to understanding their likely vulnerability or resilience. Floodplain meadow plant communities are highly heterogeneous, leading to patchy landscapes with distinct vegetation. However, it is unclear whether this patchiness in plant distribution is likely to translate into heterogeneous soil-vegetation-atmosphere transfer (SVAT) rates of water and heat, or whether floodplain meadows can reasonably be treated as internally homogeneous in physical terms despite this patchy vegetation. We used a SVAT model, the Soil-Water-Atmosphere-Plants (SWAP) model by J.C. van Dam and co-workers, to explore the controls over the partitioning of water budgets in floodplain meadows. We conducted our research at Yarnton Mead on the River Thames in Oxfordshire, one of the UK's best remaining examples of a floodplain meadow, and which is still managed and farmed in a low-intensity mixed-use manner. We used soil and plant data from our site to parameterise SWAP; we drove the model using in-situ half-hourly meteorological data. We analysed the model's sensitivity to a range of soil and plant parameters - informed by our measurements - in order to assess the effects of different plant communities on SVAT fluxes. We used a novel method to simulate water-table dynamics at the site; the simulated water tables provide a lower boundary condition for SWAP's hydrological submodel. We adjusted the water-table model's parameters so as to represent areas of the mead with contrasting topography, and so different heights above the river level and different moisture and drainage regimes. The model was most sensitive to changes in the parameters that define the water-table model. Plant above-ground parameters, such as leaf area index and canopy height also had strong influences on simulated fluxes. The model exhibited low sensitivity to plant root parameters; this was particularly true during wet periods when the simulated plant communities were oxygen stressed. Changes in soil texture profile exhibited an intermediate level of control over SVAT fluxes. Our findings indicate that unlike in environments with deep water tables, such as drylands and headwater basins, high-quality water-table data with decimetre or even centimetre accuracy are important to accurate simulation of SVAT fluxes. Future studies that seek to simulate SVAT fluxes in shallow groundwater systems should either use high frequency, high-quality water-table observations as part of the driving data set, or should ensure that water-table dynamics and their interactions with surface processes can be simulated in a robust and physically meaningful manner. The low sensitivity of our model to plant root parameters reflects the proximity of the water table to the ground surface and the fact that the simulated plant community is rarely water-stressed, and again contrasts with findings from existing SVAT model research in environments with deep water tables.

Plant species distribution in relation to water-table depth and soil redox potential in montane riparian meadows

Treesearch

Kathleen A. Dwire; J. Boone Kauffman; John E. Baham

2006-01-01

The distribution of riparian plant species is largely driven by hydrologic and soil variables, and riparian plant communities frequently occur in relatively distinct zones along streamside elevational and soil textural gradients. In two montane meadows in northeast Oregon, USA, we examined plant species distribution in three riparian plant communities¡ªdefined as wet,...

Remedial Amendment Delivery near the Water Table Using Shear Thinning Fluids: Experiments and Numerical Simulations

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

Oostrom, Martinus; Truex, Michael J.; Vermeul, Vincent R.

2014-08-19

The use of shear thinning fluids (STFs) containing xanthan is a potential enhancement for emplacing a solute amendment near the water table and within the capillary fringe. Most research to date related to STF behavior has involved saturated and confined conditions. A series of flow cell experiments were conducted to investigate STF emplacement in variable saturated homogeneous and layered heterogeneous systems. Besides flow visualization using dyes, amendment concentrations and pressure data were obtained at several locations. The experiments showed that injection of STFs considerably improved the subsurface distribution near the water table by mitigating preferential flow through higher permeability zonesmore » compared to no-polymer injections. The phosphate amendment migrated with the xanthan SFT without retardation. Despite the high viscosity of the STF, no excessive mounding or preferential flow were observed in the unsaturated zone. The STOMP simulator was able to predict the experimentally observed fluid displacement and amendment concentrations reasonably well. Cross flow between layers could be interpreted as the main mechanism to transport STFs into lower permeability layers based on the observed pressure gradient and concentration data in layers of differing hydraulic conductivity.« less

Channel Incision Driven by Suburbanization: Impacts to Riparian Groundwater Flow and Overbank Flow Frequency

NASA Astrophysics Data System (ADS)

Bowles, C. J.; Lawrence, R. L.; Noll, C.; Hancock, G. S.

2005-12-01

Channel incision is a widely observed response to increased flow in urbanized watersheds, but the effects of channel lowering on riparian water tables is not well documented. In a rapidly incising suburban stream in the Virginia Coastal Plain, we hypothesize that stream incision has lowered floodplain water tables and decreased the overbank flow frequency. The monitored stream is a tributary to the James River draining 1.3 km2 of which 15% is impervious cover. Incision has occurred largely through upstream migration of a one meter high knickpoint at a rate of ~1.5 m/yr, primarily during high flow events. We installed 63 wells in six stream-perpendicular transects as well as a cluster of wells around the knickpoint to assess water table elevations beneath the floodplain adjacent to the incising stream. Two transects are located 30 and 50 m upstream of the knickpoint in the unincised floodplain, and the remainder are 5, 30, 70, and 100 m downstream in the incised floodplain. In one transect above and two below, pressure transducers attached to dataloggers provide a high-resolution record of water table changes. Erosion pins were installed and channel cross-sections surveyed to determine streambed stability. Significant differences are observed in bank morphology and groundwater flow above vs. below the knickpoint. Above the knickpoint, the banks are stable, ~3 m wide, and ~0.3 m deep, and widen and deepen slightly toward the knickpoint. The water table is relatively flat and is 0.2-0.4 m below the floodplain surface, and groundwater contours suggest flow is parallel to the stream direction. The water table responds immediately to precipitation events, and rises to the floodplain surface in significant rainfall events. Immediately downstream of the knickpoint, channel width increases by about a meter, and stream depth increases to ~1.5 meters. The water table immediately below the knickpoint possesses a steep gradient, and is up to one meter below the floodplain surface. Groundwater flow is redirected toward the stream. Moving downstream banks continue to widen, and the channel is up to 8 m wide and ~1.3 m deep ~100 m below the current knickpoint position. In the most downstream transects, the water table slopes gently toward the stream and remains ~1 m below the floodplain surface, equivalent to the depth of incision generated by knickpoint passage. Upstream of the knickpoint, overbank flooding occurs frequently, while below the knickpoint the majority of storm flow is contained within the incised channel and occupation of the floodplain is rare. The impact of incision to the riparian water table is dramatic, with a lowered water table and redirection of groundwater flow toward the stream. The incision is driven by suburbanization upstream of this riparian corridor, and has likely reduced the ability of this protected riparian system to improve the water quality of the suburban runoff that passes through it.

Vertical gradients in water chemistry in the central High Plains aquifer, southwestern Kansas and Oklahoma panhandle, 1999

USGS Publications Warehouse

McMahon, Peter B.

2001-01-01

The central High Plains aquifer is the primary source of water for domestic, industrial, and irrigation uses in parts of Colorado, Kansas, New Mexico, Oklahoma, and Texas. Water-level declines of more than 100 feet in some areas of the aquifer have increased the demand for water deeper in the aquifer. The maximum saturated thickness of the aquifer ranged from 500 to 600 feet in 1999. As the demand for deeper water increases, it becomes increasingly important for resource managers to understand how the quality of water in the aquifer changes with depth. In 1998?99, 18 monitoring wells at nine sites in southwestern Kansas and the Oklahoma Panhandle were completed at various depths in the central High Plains aquifer, and one monitoring well was completed in sediments of Permian age underlying the aquifer. Water samples were collected once from each well in 1999 to measure vertical gradients in water chemistry in the aquifer. Tritium concentrations measured in ground water indicate that water samples collected in the upper 30 feet of the aquifer were generally recharged within the last 50 years, whereas all of the water samples collected at depths more than 30 feet below the water table were recharged more than 50 years ago. Dissolved oxygen was present throughout the aquifer, with concentrations ranging from 1.7 to 8.4 mg/L. Water in the central High Plains aquifer was predominantly a calcium-bicarbonate type that exhibited little variability in concentrations of dissolved solids with depth (290 to 642 mg/L). Exceptions occurred in some areas where there had been upward movement of mineralized water from underlying sediments of Permian age and areas where there had been downward movement of mineralized Arkansas River water to the aquifer. Calcium-sulfate and sodium-chloride waters dominated and concentrations of dissolved solids were elevated (862 to 4,030 mg/L) near the base of the aquifer in the areas of upward leakage. Dissolution of gypsum or anhydrite and halite in sediments of Permian age by ground water was the likely source of calcium, sulfate, sodium, and chloride in those waters. Calcium-sodium-sulfate waters dominated, and concentrations of dissolved solids were as large as 4,916 mg/L near the water table in the area of downward leakage. Dissolution of minerals in sedimentary deposits of marine origin in upstream areas of the Arkansas River drainage were the likely sources of calcium, sodium, and sulfate in those waters. Nitrate was detected throughout the aquifer and the background concentration was estimated to be 2.45 mg/L as N. The largest nitrate concentrations (8.28, 22, and 54.4 mg/L as N) occurred in recently recharged water collected adjacent to irrigated fields. Three pesticides (atrazine, metolachlor, simazine) and five pesticide degradation products (alachlor ethanesulfonic acid, alachlor oxanilic acid, deethylatrazine, metolachlor ethanesulfonic acid, metolachlor oxanilic acid) were detected in recently recharged water from six water-table wells. Five of the six wells were adjacent to irrigated fields. These data indicate that concentrations of nitrate and pesticides increased over time in some areas of the aquifer as a result of agricultural activities. Results from this study indicate that vertical gradients in water chemistry existed in the central High Plains aquifer. The chemical gradients resulted from chemical inputs to the aquifer from underlying sediments of Permian age, from the Arkansas River, and from agricultural activities. In areas where those chemical inputs occurred, water quality in the aquifer was impaired and may not have been suitable for some intended uses.

Seasonal patterns and controls on net ecosystem CO2 exchange in a boreal peatland complex

NASA Astrophysics Data System (ADS)

Bubier, Jill L.; Crill, Patrick M.; Moore, Tim R.; Savage, Kathleen; Varner, Ruth K.

1998-12-01

We measured seasonal patterns of net ecosystem exchange (NEE) of CO2 in a diverse peatland complex underlain by discontinuous permafrost in northern Manitoba, Canada, as part of the Boreal Ecosystems Atmosphere Study (BOREAS). Study sites spanned the full range of peatland trophic and moisture gradients found in boreal environments from bog (pH 3.9) to rich fen (pH 7.2). During midseason (July-August, 1996), highest rates of NEE and respiration followed the trophic sequence of bog (5.4 to -3.9 μmol CO2 m-2 s-1) < poor fen (6.3 to -6.5 μmol CO2 m-2 s-1) < intermediate fen (10.5 to -7.8 μmol CO2 m-2 s-1) < rich fen (14.9 to -8.7 μmol CO2m-2 s-1). The sequence changed during spring (May-June) and fall (September-October) when ericaceous shrub (e.g., Chamaedaphne calyculata) bogs and sedge (Carex spp.) communities in poor to intermediate fens had higher maximum CO2 fixation rates than deciduous shrub-dominated (Salix spp. and Betula spp.) rich fens. Timing of snowmelt and differential rates of peat surface thaw in microtopographic hummocks and hollows controlled the onset of carbon uptake in spring. Maximum photosynthesis and respiration were closely correlated throughout the growing season with a ratio of approximately 1/3 ecosystem respiration to maximum carbon uptake at all sites across the trophic gradient. Soil temperatures above the water table and timing of surface thaw and freeze-up in the spring and fall were more important to net CO2 exchange than deep soil warming. This close coupling of maximum CO2 uptake and respiration to easily measurable variables, such as trophic status, peat temperature, and water table, will improve models of wetland carbon exchange. Although trophic status, aboveground net primary productivity, and surface temperatures were more important than water level in predicting respiration on a daily basis, the mean position of the water table was a good predictor (r2 = 0.63) of mean respiration rates across the range of plant community and moisture gradients. Q10 values ranged from 3.0 to 4.1 from bog to rich fen, but when normalized by above ground vascular plant biomass, the Q10 for all sites was 3.3.

An Examination of Potential Causes of the Persistent Capillary Fringe Extension Observed During a Pumping Test in an Unconfined Aquifer

NASA Astrophysics Data System (ADS)

Bunn, M. I.; Jones, J.; Endres, A. L.

2008-12-01

Hydrogeologists quantify the properties of unconfined aquifers by analyzing the data from pumping tests. The most appropriate method of incorporating flow contributions from the vadose zone into these analyses has been the subject of debate for decades. Recently, a highly detailed data set was collected during a seven- day pumping test at CFB Borden, Ontario (Bevan et al., 2005) which has allowed a close examination of the vadose zone response to pumping. Water table drawdown was monitored using pressure transducers in 11 monitoring wells, while moisture profiles were collected 19 times during the 7-day test using neutron logging. The Borden aquifer system is quite homogeneous, and numerical simulations using the variably saturated model InHM resulted in excellent reproduction of the observed hydraulic head drawdowns. Conversely, the simulated moisture profiles correlated poorly with neutron-logging-derived observed profiles. Specifically, the field results show delayed drawdown in the vadose zone, resulting in a persistent and significant extension of the capillary fringe, with the shape of the moisture profile remaining constant through the transition zone. Numerical simulations using various forms of the capillary pressure-saturation relationship with reasonable parameter sets were unable produce the extension. Neutron moisture profiles were selected from three locations (3, 5, and 15 m radial distance from the pumping well) at which an adjacent shallow deep piezometer pair could be used to accurately estimate water table location. Using this data in conjunction with the inverse modeling tool PEST, a set of van Genuchten capillary pressure-saturation parameters was generated to match each observed moisture profile. Horizontal and vertical hydraulic gradients and flow rates at the water table were generated using model output and compared to the fitted parameters. The van Genuchten parameter n was found to have significant scatter in both profile location and observation time when compared to any of the modeled results. The van Genuchten parameter alpha was found to vary linearly as a function of horizontal hydraulic gradient; further the results from all observation locations and times were found to follow the same linear relationship. The likely effects of consolidation, entrapped air, heterogeneity, and hydraulic gradients on the observed moisture profile were also evaluated. Results indicate a need for further investigation into the applicability of laboratory derived steady-state water retention curves for field scale simulations.

In-channel Restoration Structures and the Implications on Hyporheic Exchange: a Laboratory Experiment

NASA Astrophysics Data System (ADS)

Han, B.; Chu, H. H.; Endreny, T. A.

2014-12-01

In-channel structures, i.e. cross-vanes and J-hooks, are commonly installed in river restoration projects to modify the streambed morphology and stream water surface profile, and are known to change hyporhiec exchange flux and habitats for riverine animals. However, few studies have continuous and accurate pre- and post-treatment data to evaluate the impact of these structures on channel hydraulic gradients and morphology. To quantify the effects of in-channel structures, we developed a scaled physical model of a meandering stream with a cross-vane and 6 J-hooks on a mobile-bed river table. Close-range photogrammetry technique was applied to obtain 3-D water and ground surface profiles with sub-millimeter vertical accuracy and horizontal resolution. The experiment was compared with a control experiment without structures while maintaining the same initial conditions of river bed, floodplain and stream flow. Results indicated that the cross-vane caused an average local head loss that represented 16% of the total stream reach head loss, and a 74% increase in channel load in the entire stream reach. Most J-hooks can create stepwise patterns in stream longitudinal profile, and cross-vane can create even more significant ones. Hydraulic gradients across the intra-meander zone also increased with in-channel structures, i.e. from 2.5% to 3.5% at the meander neck. Scour pools developed downstream of the cross-vane, and mostly around the 4 meander apex J-hooks at their hooked tip. Backwater caused by the cross-vane steepened the local water table profile by an additional 4.2%, and was the primary driver of statistically significant hydraulic gradient increase. Reach scale water and streambed surface profiles from our study provided detailed data to improve the understanding of in-channel structure effects, and may serve as reliable data source in computational modeling of hyporheic exchange.

Reconnaissance of the ground-water, surface-water system in the Zekiah Swamp Run basin, Charles and Prince Georges Counties, Maryland

USGS Publications Warehouse

Hopkins, H.T.; Fisher, G.T.; McGreevy, L.J.

1986-01-01

The water table in the alluvium of the Zekiah Swamp Run valley in southern Maryland is above stream level during most of the year and the alluvial aquifer contributes water to the stream. During the summer, however, high evapotranspiration sometimes lowers the water table below the stream level. Water then moves from the stream to the alluvium and, at times, reaches of the stream become dry. Pumping from the confined aquifers has caused water levels to decline several tens of ft, which has increased the downward gradient between the water-table aquifer and the underlying confined aquifers. Three synoptic surveys of base flow show areal and temporal variations in stream discharge, pH, specific conductance, dissolved oxygen, and temperature. April 1984 base flows were high (141 cu ft/sec, at the Route 6 gage) because of high precipitation during March. July 1983 base flows were low (2.35 cu ft/sec at the Route 6 gage) and showed significant loss of streamflow because of high antecedent evapotranspiration. Estimates of inflow and outflow of the Zekiah Swamp Run basin above Route 6 during the 1984 water year include: Precipitation, 50.21 in; stream outflow, 20.10 in; shallow groundwater underflow, 0.1 in; stream outflow, 20.10 in; shallow groundwater underflow, 0.1 in; and evapotranspiration, 33 in. A streamflow budget of a 5.1 mi area of the valley of Zekiah Swamp Run between Routes 5 and 6, during the April 1984 survey and a loss of almost 5 cu ft during the July 1983 survey. (Author 's abstract)

Testate amoeba transfer function performance along localised hydrological gradients.

PubMed

Tsyganov, Andrey N; Mityaeva, Olga A; Mazei, Yuri A; Payne, Richard J

2016-09-01

Testate amoeba transfer functions are widely used for reconstruction of palaeo-hydrological regime in peatlands. However, the limitations of this approach have become apparent with increasing attention to validation and assessing sources of uncertainty. This paper investigates effects of peatland type and sampling depth on the performance of a transfer function using an independent test-set from four Sphagnum-dominated sites in European Russia (Penza Region). We focus on transfer function performance along localised hydrological gradients, which is a useful analogue for predictive ability through time. The performance of the transfer function with the independent test-set was generally weaker than for the leave-one-out or bootstrap cross-validations. However, the transfer function was robust for the reconstruction of relative changes in water-table depth, provided the presence of good modern analogues and overlap in water-table depth ranges. When applied to subsurface samples, the performance of the transfer function was reduced due to selective decomposition, the presence of deep-dwelling taxa or vertical transfer of shells. Our results stress the importance of thorough testing of transfer functions, and highlight the role of taphonomic processes in determining results. Further studies of stratification, taxonomy and taphonomy of testate amoebae will be needed to improve the robustness of transfer function output. Copyright © 2015 Elsevier GmbH. All rights reserved.

Ground water stratification and delivery of nitrate to an incised stream under varying flow conditions.

PubMed

Böhlke, J K; O'Connell, Michael E; Prestegaard, Karen L

2007-01-01

Ground water processes affecting seasonal variations of surface water nitrate concentrations were investigated in an incised first-order stream in an agricultural watershed with a riparian forest in the coastal plain of Maryland. Aquifer characteristics including sediment stratigraphy, geochemistry, and hydraulic properties were examined in combination with chemical and isotopic analyses of ground water, macropore discharge, and stream water. The ground water flow system exhibits vertical stratification of hydraulic properties and redox conditions, with sub-horizontal boundaries that extend beneath the field and adjacent riparian forest. Below the minimum water table position, ground water age gradients indicate low recharge rates (2-5 cm yr(-1)) and long residence times (years to decades), whereas the transient ground water wedge between the maximum and minimum water table positions has a relatively short residence time (months to years), partly because of an upward increase in hydraulic conductivity. Oxygen reduction and denitrification in recharging ground waters are coupled with pyrite oxidation near the minimum water table elevation in a mottled weathering zone in Tertiary marine glauconitic sediments. The incised stream had high nitrate concentrations during high flow conditions when much of the ground water was transmitted rapidly across the riparian zone in a shallow oxic aquifer wedge with abundant outflow macropores, and low nitrate concentrations during low flow conditions when the oxic wedge was smaller and stream discharge was dominated by upwelling from the deeper denitrified parts of the aquifer. Results from this and similar studies illustrate the importance of near-stream geomorphology and subsurface geology as controls of riparian zone function and delivery of nitrate to streams in agricultural watersheds.

Ground water stratification and delivery of nitrate to an incised stream under varying flow conditions

USGS Publications Warehouse

Böhlke, J.K.; O'Connell, M. E.; Prestegaard, K.L.

2007-01-01

Ground water processes affecting seasonal variations of surface water nitrate concentrations were investigated in an incised first-order stream in an agricultural watershed with a riparian forest in the coastal plain of Maryland. Aquifer characteristics including sediment stratigraphy, geochemistry, and hydraulic properties were examined in combination with chemical and isotopic analyses of ground water, macropore discharge, and stream water. The ground water flow system exhibits vertical stratification of hydraulic properties and redox conditions, with sub-horizontal boundaries that extend beneath the field and adjacent riparian forest. Below the minimum water table position, ground water age gradients indicate low recharge rates (2-5 cm yr-1) and long residence times (years to decades), whereas the transient ground water wedge between the maximum and minimum water table positions has a relatively short residence time (months to years), partly because of an upward increase in hydraulic conductivity. Oxygen reduction and denitrification in recharging ground waters are coupled with pyrite oxidation near the minimum water table elevation in a mottled weathering zone in Tertiary marine glauconitic sediments. The incised stream had high nitrate concentrations during high flow conditions when much of the ground water was transmitted rapidly across the riparian zone in a shallow oxic aquifer wedge with abundant outflow macropores, and low nitrate concentrations during low flow conditions when the oxic wedge was smaller and stream discharge was dominated by upwelling from the deeper denitrified parts of the aquifer. Results from this and similar studies illustrate the importance of near-stream geomorphology and subsurface geology as controls of riparian zone function and delivery of nitrate to streams in agricultural watersheds. ?? ASA, CSSA, SSSA.

River stage influences on uranium transport in a hydrologically dynamic groundwater-surface water transition zone: U TRANSPORT IN A GROUNDWATER-SURFACE WATER TRANSITION ZONE

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

Zachara, John M.; Chen, Xingyuan; Murray, Chris

A tightly spaced well-field within a groundwater uranium (U) plume in the groundwater-surface water transition zone was monitored for a three year period for groundwater elevation and dissolved solutes. The plume discharges to the Columbia River, which displays a dramatic spring stage surge resulting from mountain snowmelt. Groundwater exhibits a low hydrologic gradient and chemical differences with river water. River water intrudes the site in spring. Specific aims were to assess the impacts of river intrusion on dissolved uranium (Uaq), specific conductance (SpC), and other solutes, and to discriminate between transport, geochemical, and source term heterogeneity effects. Time series trendsmore » for Uaq and SpC were complex and displayed large temporal well-to well variability as a result of water table elevation fluctuations, river water intrusion, and changes in groundwater flow directions. The wells were clustered into subsets exhibiting common temporal behaviors resulting from the intrusion dynamics of river water and the location of source terms. Concentration hot spots were observed in groundwater that varied in location with increasing water table elevation. Heuristic reactive transport modeling with PFLOTRAN demonstrated that mobilized U was transported between wells and source terms in complex trajectories, and was diluted as river water entered and exited the groundwater system. While uranium time-series concentration trends varied significantly from year to year as a result of climate-caused differences in the spring hydrograph, common and partly predictable response patterns were observed that were driven by water table elevation, and the extent and duration of the river water intrusion event.« less

Fire activity and hydrological dynamics in the past 5700 years reconstructed from Sphagnum peatlands along the oceanic-continental climatic gradient in northern Poland

NASA Astrophysics Data System (ADS)

Marcisz, Katarzyna; Gałka, Mariusz; Pietrala, Patryk; Miotk-Szpiganowicz, Grażyna; Obremska, Milena; Tobolski, Kazimierz; Lamentowicz, Mariusz

2017-12-01

Fire is a critical component of many ecosystems and, as predicted by various climate models, fire activity may increase significantly in the following years due to climate change. Therefore, knowledge about the past fire activity of various ecosystems is highly important for future nature conservation purposes. We present results of high-resolution investigation of fire activity and hydrological changes in northern Poland. We analyzed microscopic charcoal from three Sphagnum-dominated peatlands located on the south of Baltic, on the oceanic-continental (west-east) climatic gradient, and reconstructed the history of fire in the last 5700 years. We hypothesize that air circulation patterns are highly important for local fire activity, and that fire activity is more intensive in peatlands influenced by continental air masses. We have found out that forest fires have been occurring regularly since the past millennia and were linked to climatic conditions. We show that fire activity (related to climate and fuel availability) was significantly higher in sites dominated by continental climate (northeastern Poland) than in the site located under oceanic conditions (northwestern Poland)-microscopic charcoal influx was 13.3 times higher in the eastern study site of the gradient, compared to the western study site. Recorded fire activity patterns were different between the sites in a long timescale. Moreover, most of the recorded charcoal peaks occurred during high water tables. Rising human pressure has caused droughts and water table instability, and substantial increase in fire activity in the last 400 years.

Ground-water contamination by crude oil at the Bemidji, Minnesota, research site; US Geological Survey Toxic Waste--ground-water contamination study

USGS Publications Warehouse

Hult, M.F.

1984-01-01

The project site is near Bemidji in northern Minnesota where an accidental spill of 10,500 barrels of crude oil occurred when a pipeline broke on August 20, 1979. Regulatory and remedial actions have been completed. The site is in a remote area with neither man-made hydraulic stresses nor other anthropogenic sources of the compounds of interest. The spill is in the recharge area of a local flow system that discharges to a small closed lake approximately 1,000 feet down the hydraulic gradient. The aquifer is pitted outwash dissected by younger glacial channels and is underlain by poorly permeable till at a depth of about 80 feet. Ground water dissolves oil floating on the water table under the spill site and moves toward the lake. At the water table, ground water enters the lake through lacustrine sediments; at depth, flow may be underneath the lake through the outwash. Contaminant transport has been as rapid as 4 feet per day based on the rate of movement of contaminants monitored through wells installed within a few days of the spill, but average rates are undoubtedly much less.

Surface water-ground water interactions along the lower Dungeness River and vertical hydraulic conductivity of streambed sediments, Clallam County, Washington, September 1999-July 2001

USGS Publications Warehouse

Simonds, F. William; Sinclair, Kirk A.

2002-01-01

The Dungeness River emerges from the Olympic Mountains and flows generally north toward the Strait of Juan De Fuca, crossing the broad, fertile alluvial fan of the Sequim-Dungeness peninsula in northeastern Clallam County, Washington. Increasing competition for the peninsula's ground-water resources, changing water-use patterns, and recent requirements to maintain minimum in-stream flows to enhance endangered salmon and trout populations have severely strained the peninsula's water resources and necessitated a better understanding of the interaction between surface water and groundwater. Three methods were used to characterize the interchange between surface water and groundwater along the lower 11.8 miles of the Dungeness River corridor between September 1999 and July 2001. In-stream mini-piezometers were used to measure vertical hydraulic gradients between the river and the water-table aquifer at 27 points along the river and helped to define the distribution of gaining and losing stream reaches. Seepage runs were used to quantify the net volume of water exchanged between the river and ground water within each of five river reaches, termed 'seepage reaches.' Continuous water-level and water-temperature monitoring at two off-stream well transects provided data on near-river horizontal hydraulic gradients and temporal patterns of water exchange for a representative gaining stream reach and a representative losing stream reach. Vertical hydraulic gradients in the mini-piezometers generally were negative between river miles 11.8 and 3.6, indicating loss of water from the river to ground water. Gradients decreased in the downstream direction from an average of -0.86 at river mile 10.3 to -0.23 at river mile 3.7. Small positive gradients (+0.01 to +0.02) indicating ground-water discharge occurred in three localized reaches below river mile 3.7. Data from the seepage runs and off-stream transect wells supported and were generally consistent with the mini-piezometer findings. An exception occurred between river miles 8.1 and 5.5 where seepage results showed a small gain and the mini-piezometers showed negative gradients. Vertical hydraulic conductivity of riverbed sediments was estimated using hydraulic gradients measured with the mini-piezometers and estimated seepage fluxes. The resulting conductivity values ranged from an average of 1 to 29 feet per day and are similar to values reported for similar river environments elsewhere. The results of this study will be used to calibrate a transient, three-dimensional ground-water flow model of the Sequim-Dungeness peninsula. The model will be used to assess the potential effects on ground-water levels and river flows that result from future water use and land-use changes on the peninsula.

An experimental test of fitness variation across a hydrologic gradient predicts willow and poplar species distributions.

PubMed

Wei, Xiaojing; Savage, Jessica A; Riggs, Charlotte E; Cavender-Bares, Jeannine

2017-05-01

Environmental filtering is an important community assembly process influencing species distributions. Contrasting species abundance patterns along environmental gradients are commonly used to provide evidence for environmental filtering. However, the same abundance patterns may result from alternative or concurrent assembly processes. Experimental tests are an important means to decipher whether species fitness varies with environment, in the absence of dispersal constraints and biotic interactions, and to draw conclusions about the importance of environmental filtering in community assembly. We performed an experimental test of environmental filtering in 14 closely related willow and poplar species (family Salicaceae) by transplanting cuttings of each species into 40 common gardens established along a natural hydrologic gradient in the field, where competition was minimized and herbivory was controlled. We analyzed species fitness responses to the hydrologic environment based on cumulative growth and survival over two years using aster fitness models. We also examined variation in nine drought and flooding tolerance traits expected to contribute to performance based on a priori understanding of plant function in relation to water availability and stress. We found substantial evidence that environmental filtering along the hydrologic gradient played a critical role in determining species distributions. Fitness variation of each species in the field experiment was used to model their water table depth optima. These optima predicted 68% of the variation in species realized hydrologic niches based on peak abundance in naturally assembled communities in the surrounding region. Multiple traits associated with water transport efficiency and water stress tolerance were correlated with species hydrologic niches, but they did not necessarily covary with each other. As a consequence, species occupying similar hydrologic niches had different combinations of trait values. Moreover, individual traits were less phylogenetically conserved than species hydrologic niches and integrated water stress tolerance as determined by multiple traits. We conclude that differential fitness among species along the hydrologic gradient was the consequence of multiple traits associated with water transport and water stress tolerance, expressed in different combinations by different species. Varying environmental tolerance, in turn, played a critical role in driving niche segregation among close relatives along the hydrologic gradient. © 2017 by the Ecological Society of America.

ORCHIDEE-PEAT (revision 4596), a model for northern peatland CO2, water, and energy fluxes on daily to annual scales

NASA Astrophysics Data System (ADS)

Qiu, Chunjing; Zhu, Dan; Ciais, Philippe; Guenet, Bertrand; Krinner, Gerhard; Peng, Shushi; Aurela, Mika; Bernhofer, Christian; Brümmer, Christian; Bret-Harte, Syndonia; Chu, Housen; Chen, Jiquan; Desai, Ankur R.; Dušek, Jiří; Euskirchen, Eugénie S.; Fortuniak, Krzysztof; Flanagan, Lawrence B.; Friborg, Thomas; Grygoruk, Mateusz; Gogo, Sébastien; Grünwald, Thomas; Hansen, Birger U.; Holl, David; Humphreys, Elyn; Hurkuck, Miriam; Kiely, Gerard; Klatt, Janina; Kutzbach, Lars; Largeron, Chloé; Laggoun-Défarge, Fatima; Lund, Magnus; Lafleur, Peter M.; Li, Xuefei; Mammarella, Ivan; Merbold, Lutz; Nilsson, Mats B.; Olejnik, Janusz; Ottosson-Löfvenius, Mikaell; Oechel, Walter; Parmentier, Frans-Jan W.; Peichl, Matthias; Pirk, Norbert; Peltola, Olli; Pawlak, Włodzimierz; Rasse, Daniel; Rinne, Janne; Shaver, Gaius; Schmid, Hans Peter; Sottocornola, Matteo; Steinbrecher, Rainer; Sachs, Torsten; Urbaniak, Marek; Zona, Donatella; Ziemblinska, Klaudia

2018-02-01

Peatlands store substantial amounts of carbon and are vulnerable to climate change. We present a modified version of the Organising Carbon and Hydrology In Dynamic Ecosystems (ORCHIDEE) land surface model for simulating the hydrology, surface energy, and CO2 fluxes of peatlands on daily to annual timescales. The model includes a separate soil tile in each 0.5° grid cell, defined from a global peatland map and identified with peat-specific soil hydraulic properties. Runoff from non-peat vegetation within a grid cell containing a fraction of peat is routed to this peat soil tile, which maintains shallow water tables. The water table position separates oxic from anoxic decomposition. The model was evaluated against eddy-covariance (EC) observations from 30 northern peatland sites, with the maximum rate of carboxylation (Vcmax) being optimized at each site. Regarding short-term day-to-day variations, the model performance was good for gross primary production (GPP) (r2 = 0.76; Nash-Sutcliffe modeling efficiency, MEF = 0.76) and ecosystem respiration (ER, r2 = 0.78, MEF = 0.75), with lesser accuracy for latent heat fluxes (LE, r2 = 0.42, MEF = 0.14) and and net ecosystem CO2 exchange (NEE, r2 = 0.38, MEF = 0.26). Seasonal variations in GPP, ER, NEE, and energy fluxes on monthly scales showed moderate to high r2 values (0.57-0.86). For spatial across-site gradients of annual mean GPP, ER, NEE, and LE, r2 values of 0.93, 0.89, 0.27, and 0.71 were achieved, respectively. Water table (WT) variation was not well predicted (r2 < 0.1), likely due to the uncertain water input to the peat from surrounding areas. However, the poor performance of WT simulation did not greatly affect predictions of ER and NEE. We found a significant relationship between optimized Vcmax and latitude (temperature), which better reflects the spatial gradients of annual NEE than using an average Vcmax value.

Regulation of Methane Oxidation in a Freshwater Wetland by Water Table Changes and Anoxia

NASA Technical Reports Server (NTRS)

Roslev, Peter; King, Gary M.

1996-01-01

The effects of water table fluctuations and anoxia on methane emission and methane oxidation were studied in a freshwater marsh. Seasonal aerobic methane oxidation rates varied between 15% and 76% of the potential diffusive methane flux (diffusive flux in the absence of aerobic oxidation). On an annual basis, approximately 43% of the methane diffusing into the oxic zone was oxidized before reaching the atmosphere. The highest methane oxidation was observed when the water table was below the peat surface. This was confirmed in laboratory experiments where short-term decreases in water table levels increased methane oxidation but also net methane emission. Although methane emission was generally not observed during the winter, stems of soft rush (Juncus effusus) emitted methane when the marsh was ice covered. Indigenous methanotrophic bacteria from the wetiand studied were relatively anoxia tolerant. Surface peat incubated under anoxic conditions maintained 30% of the initial methane oxidation capacity after 32 days of anoxia. Methanotrophs from anoxic peat initiated aerobic methane oxidation relatively quickly after oxygen addition (1-7 hours). These results were supported by culture experiments with the methanotroph Methylosinus trichosporium OB3b. This organism maintained a greater capacity for aerobic methane oxidation when starved under anoxic compared to oxic conditions. Anoxic incubation of M. trichosporium OB3b in the presence of sulfide (2 mM) and a low redox potential (-110 mV) did not decrease the capacity for methane oxidation relative to anoxic cultures incubated without sulfide. The results suggest that aerobic methane oxidation was a major regulator of seasonal methane emission front the investigated wetland. The observed water table fluctuations affected net methane oxidation presumably due to associated changes in oxygen gradients. However, changes from oxic to anoxic conditions in situ had relatively little effect on survival of the methanotrophic bacteria and thus on methane oxidation potential per se.

Effect of oil pollution on fresh groundwater in Kuwait

NASA Astrophysics Data System (ADS)

Al-Sulaimi, J.; Viswanathan, M. N.; Székely, F.

1993-11-01

Massive oil fires in Kuwait were the aftermath of the Gulf War. This resulted in the pollution of air, water, and soil, the magnitude of which is unparalleled in the history of mankind. Oil fires damaged several oil well heads, resulting in the flow of oil, forming large oil lakes. Products of combustion from oil well fires deposited over large areas. Infiltrating rainwater, leaching out contaminants from oil lakes and products of combustion at ground surface, can reach the water table and contaminate the groundwater. Field investigations, supported by laboratory studies and mathematical models, show that infiltration of oil from oil lakes will be limited to a depth of about 2 m from ground surface. Preliminary mathematical models showed that contaminated rainwater can infiltrate and reach the water table within a period of three to four days, particularly at the Raudhatain and Umm Al-Aish regions. These are the only regions in Kuwait where fresh groundwater exists. After reaching the water table, the lateral movement of contaminants is expected to be very slow under prevailing hydraulic gradients. Groundwater monitoring at the above regions during 1992 showed minor levels of vanadium, nickel, and total hydrocarbons at certain wells. Since average annual rainfall in the region is only 120 mm/yr, groundwater contamination due to the infiltration of contaminated rainwater is expected to be a long-term one.

Soil-Landscape Relations at Selected Sites Along Environmental Gradients in Northern Alaska.

DTIC Science & Technology

1981-05-01

conditions of a frigid humid climate, poor drainage, gleization and mechanical disturbance and thus were placed within the Zonal Soil Order. The...operating: (1) gleization , (2) congeliturbation, and (3) organic accretion. Manganese and iron occur in soil systems in both oxidized and/or reduced...yellowish-red mottles and in grey matrix, is referred to as gleying ( gleization ). In some gleyed soils the process is favored by a fluctuating water table

Variably-saturated groundwater modeling for optimizing managed aquifer recharge using trench infiltration

USGS Publications Warehouse

Heilweil, Victor M.; Benoit, Jerome; Healy, Richard W.

2015-01-01

Spreading-basin methods have resulted in more than 130 million cubic meters of recharge to the unconfined Navajo Sandstone of southern Utah in the past decade, but infiltration rates have slowed in recent years because of reduced hydraulic gradients and clogging. Trench infiltration is a promising alternative technique for increasing recharge and minimizing evaporation. This paper uses a variably saturated flow model to further investigate the relative importance of the following variables on rates of trench infiltration to unconfined aquifers: saturated hydraulic conductivity, trench spacing and dimensions, initial water-table depth, alternate wet/dry periods, and number of parallel trenches. Modeling results showed (1) increased infiltration with higher hydraulic conductivity, deeper initial water tables, and larger spacing between parallel trenches, (2) deeper or wider trenches do not substantially increase infiltration, (3) alternating wet/dry periods result in less overall infiltration than keeping the trenches continuously full, and (4) larger numbers of parallel trenches within a fixed area increases infiltration but with a diminishing effect as trench spacing becomes tighter. An empirical equation for estimating expected trench infiltration rates as a function of hydraulic conductivity and initial water-table depth was derived and can be used for evaluating feasibility of trench infiltration in other hydrogeologic settings

Assessing the magnitude and timing of anthropogenic warming of a shallow aquifer: example from Virginia Beach, USA

USGS Publications Warehouse

Eggleston, John R.; McCoy, Kurt J.

2015-01-01

Groundwater temperature measurements in a shallow coastal aquifer in Virginia Beach, Virginia, USA, suggest groundwater warming of +4.1 °C relative to deeper geothermal gradients. Observed warming is related to timing and depth of influence of two potential thermal drivers—atmospheric temperature increases and urbanization. Results indicate that up to 30 % of groundwater warming at the water table can be attributed to atmospheric warming while up to 70 % of warming can be attributed to urbanization. Groundwater temperature readings to 30-m depth correlate positively with percentage of impervious cover and negatively with percentage of tree canopy cover; thus, these two land-use metrics explain up to 70 % of warming at the water table. Analytical and numerical modeling results indicate that an average vertical groundwater temperature profile for the study area, constructed from repeat measurement at 11 locations over 15 months, is consistent with the timing of land-use change over the past century in Virginia Beach. The magnitude of human-induced warming at the water table (+4.1 °C) is twice the current seasonal temperature variation, indicating the potential for ecological impacts on wetlands and estuaries receiving groundwater discharge from shallow aquifers.

Modeling the effects of martian surface frost on ice table depth

NASA Astrophysics Data System (ADS)

Williams, K. E.; McKay, Christopher P.; Heldmann, J. L.

2015-11-01

Ground ice has been observed in small fresh craters in the vicinity of the Viking 2 lander site (48°N, 134°E). To explain these observations, current models for ground ice invoke levels of atmospheric water of 20 precipitable micrometers - higher than observations. However, surface frost has been observed at the Viking 2 site and surface water frost and snow have been shown to have a stabilizing effect on Antarctic subsurface ice. A snow or frost cover provides a source of humidity that should reduce the water vapor gradient and hence retard the sublimation loss from subsurface ice. We have modeled this effect for the Viking 2 landing site with combined ground ice and surface frost models. Our model is driven by atmospheric output fields from the NASA Ames Mars General Circulation Model (MGCM). Our modeling results show that the inclusion of a thin seasonal frost layer, present for a duration similar to that observed by the Viking Lander 2, produces ice table depths that are significantly shallower than a model that omits surface frost. When a maximum frost albedo of 0.35 was permitted, seasonal frost is present in our model from Ls = 182° to Ls = 16°, resulting in an ice table depth of 64 cm - which is 24 cm shallower than the frost-free scenario. The computed ice table depth is only slightly sensitive to the assumed maximum frost albedo or thickness in the model.

A modular finite-element model (MODFE) for areal and axisymmetric ground-water-flow problems, Part 1: Model Description and User's Manual

USGS Publications Warehouse

Torak, L.J.

1993-01-01

A MODular, Finite-Element digital-computer program (MODFE) was developed to simulate steady or unsteady-state, two-dimensional or axisymmetric ground-water flow. Geometric- and hydrologic-aquifer characteristics in two spatial dimensions are represented by triangular finite elements and linear basis functions; one-dimensional finite elements and linear basis functions represent time. Finite-element matrix equations are solved by the direct symmetric-Doolittle method or the iterative modified, incomplete-Cholesky, conjugate-gradient method. Physical processes that can be represented by the model include (1) confined flow, unconfined flow (using the Dupuit approximation), or a combination of both; (2) leakage through either rigid or elastic confining beds; (3) specified recharge or discharge at points, along lines, and over areas; (4) flow across specified-flow, specified-head, or bead-dependent boundaries; (5) decrease of aquifer thickness to zero under extreme water-table decline and increase of aquifer thickness from zero as the water table rises; and (6) head-dependent fluxes from springs, drainage wells, leakage across riverbeds or confining beds combined with aquifer dewatering, and evapotranspiration. The report describes procedures for applying MODFE to ground-water-flow problems, simulation capabilities, and data preparation. Guidelines for designing the finite-element mesh and for node numbering and determining band widths are given. Tables are given that reference simulation capabilities to specific versions of MODFE. Examples of data input and model output for different versions of MODFE are provided.

A modular finite-element model (MODFE) for areal and axisymmetric ground-water-flow problems; Part 1, Model description and user's manual

USGS Publications Warehouse

Torak, Lynn J.

1992-01-01

A MODular, Finite-Element digital-computer program (MODFE) was developed to simulate steady or unsteady-state, two-dimensional or axisymmetric ground-water flow. Geometric- and hydrologic-aquifer characteristics in two spatial dimensions are represented by triangular finite elements and linear basis functions; one-dimensional finite elements and linear basis functions represent time. Finite-element matrix equations are solved by the direct symmetric-Doolittle method or the iterative modified, incomplete-Cholesky, conjugate-gradient method. Physical processes that can be represented by the model include (1) confined flow, unconfined flow (using the Dupuit approximation), or a combination of both; (2) leakage through either rigid or elastic confining beds; (3) specified recharge or discharge at points, along lines, and over areas; (4) flow across specified-flow, specified-head, or head-dependent boundaries; (5) decrease of aquifer thickness to zero under extreme water-table decline and increase of aquifer thickness from zero as the water table rises; and (6) head-dependent fluxes from springs, drainage wells, leakage across riverbeds or confining beds combined with aquifer dewatering, and evapotranspiration.The report describes procedures for applying MODFE to ground-water-flow problems, simulation capabilities, and data preparation. Guidelines for designing the finite-element mesh and for node numbering and determining band widths are given. Tables are given that reference simulation capabilities to specific versions of MODFE. Examples of data input and model output for different versions of MODFE are provided.

BOREAS TGB-1/TGB-3 Water Table and Peat Temperature Data over the NSA

NASA Technical Reports Server (NTRS)

Bubier, Jill L.; Comer, Neil; Moore, Tim R.; Hall, Forrest G. (Editor); Conrad, Sara K. (Editor)

2000-01-01

The BOREAS TGB-1 and TGB-3 teams collected several data sets that contributed to understanding the measured trace gas fluxes over sites in the NSA. This data set contains continuous and manual measurements of water level and air and soil temperatures at the four subsites within the NSA Tower Fen site complex. The measurements were taken to understand the thermal and hydrological gradients associated with each plant community present in the fen. Measurements were taken from May to September 1994 and May to October 1996. The data are provided in tabular ASCII files.

Orbitally-paced variations of water availability in the SE Asian Monsoon region following the Miocene Climate Transition

NASA Astrophysics Data System (ADS)

Heitmann, Emma O.; Ji, Shunchuan; Nie, Junsheng; Breecker, Daniel O.

2017-09-01

Middle Miocene Earth had several boundary conditions similar to those predicted for future Earth including similar atmospheric pCO2 and substantial Antarctic ice cover but no northern hemisphere ice sheets. We describe a 12 m outcrop of the terrestrial Yanwan Section in the Tianshui Basin, Gansu, China, following the Miocene Climate Transition (13.9-13.7 Ma). It consists of ∼25 cm thick CaCO3-cemented horizons that overprint siltstones every ∼1 m. We suggest that stacked soils developed in siltstones under a seasonal climate with a fluctuating water table, evidenced by roots, clay films, mottling, presence of CaCO3 nodules, and stacked carbonate nodule δ13 C and δ18 O profiles that mimic modern soils. We suggest that the CaCO3-cemented horizons are capillary-fringe carbonates that formed in an arid climate with a steady water table and high potential evapotranspiration rates (PET), evidenced by sharp upper and basal contacts, micrite, sparite, and root-pore cements. The CaCO3 of the cemented horizons and the carbonate nodules have similar mean δ18 O and δ13 C values but the cements have significantly smaller variance in δ13 C and δ18 O values and a different δ18 O versus δ13 C slope, supporting the conclusion that these carbonates are from different populations. The magneto-stratigraphic age model indicates obliquity pacing of the arid conditions required to form the CaCO3-cemented horizons suggesting an orbital control on water availability. We suggest two possible drivers for the obliquity pacing of arid conditions: 1) variability in the cross-equatorial pressure gradient that controls summer monsoon (ASM) strength and is influenced by obliquity-paced variations of Antarctic ice volume and 2) variability in Western Pacific Ocean-East Asian continent pressure gradient controlled by the 25-45°N meridional insolation gradient. We also suggest that variations in aridity were influenced by variations in PET and sensible heating of the regional land surface which are both influenced by precession-controlled 35°N summer insolation. We then use orbital configurations to predict lithology. Coincidence of obliquity minima (strong ASM) and 35°N summer insolation maxima (strong ASM) drives strong ASM and high PET, resulting in soil formation in an environment with relatively large seasonal changes in water availability. Coincidence of obliquity maxima (weak ASM) and 35°N summer insolation maxima (strong ASM) moderates the ASM, results in high PET, and thus drives overprinting of soils by capillary fringe carbonates above a deepened and relatively stable water table. Coincidence of obliquity and insolation minima also moderates the ASM but results in low PET and thus a high water table, which explains the previously documented occurrence of aquatic plants in this section. This context allows us to assign an orbital configuration to atmospheric pCO2 determined from the paleosols. Our best estimate of pCO2 during the times of intermediate ice volume is 475 + 650 / - 230 ppmV (median value with error reported as 84th-16th percentile values). Southern hemisphere control of ASM variability during the Middle Miocene may have resulted in larger orbital scale water availability variations compared with the Pleistocene.

Potential effects of sea-level rise on the depth to saturated sediments of the Sagamore and Monomoy flow lenses on Cape Cod, Massachusetts

USGS Publications Warehouse

Walter, Donald A.; McCobb, Timothy D.; Masterson, John P.; Fienen, Michael N.

2016-05-25

In 2014, the U.S. Geological Survey, in cooperation with the Association to Preserve Cape Cod, the Cape Cod Commission, and the Massachusetts Environmental Trust, began an evaluation of the potential effects of sea-level rise on water table altitudes and depths to water on central and western Cape Cod, Massachusetts. Increases in atmospheric and oceanic temperatures arising, in part, from the release of greenhouse gases likely will result in higher sea levels globally. Increasing water table altitudes in shallow, unconfined coastal aquifer systems could adversely affect infrastructure—roads, utilities, basements, and septic systems—particularly in low-lying urbanized areas. The Sagamore and Monomoy flow lenses on Cape Cod are the largest and most populous of the six flow lenses that comprise the region’s aquifer system, the Cape Cod glacial aquifer. The potential effects of sea-level rise on water table altitude and depths to water were evaluated by use of numerical models of the region. The Sagamore and Monomoy flow lenses have a number of large surface water drainages that receive a substantial amount of groundwater discharge, 47 and 29 percent of the total, respectively. The median increase in the simulated water table altitude following a 6-foot sea-level rise across both flow lenses was 2.11 feet, or 35 percent when expressed as a percentage of the total sea-level rise. The response is nearly the same as the sea-level rise (6 feet) in some coastal areas and less than 0.1 foot near some large inland streams. Median water table responses differ substantially between the Sagamore and Monomoy flow lenses—at 29 and 49 percent, respectively—because larger surface water discharge on the Sagamore flow lens results in increased dampening of the water table response than in the Monomoy flow lens. Surface waters dampen water table altitude increases because streams are fixed-altitude boundaries that cause hydraulic gradients and streamflow to increase as sea-level rises, partially fixing the local water table altitude.The region has a generally thick vadose zone with a mean of about 38 feet; areas with depths to water of 5 feet or less, as estimated from light detection and ranging (lidar) data from 2011 and simulated water table altitudes, currently [2011] occur over about 24.9 square miles, or about 8.4 percent of the total land area of the Sagamore and Monomoy flow lenses, generally in low-lying coastal areas and inland near ponds and streams. Excluding potentially submerged areas, an additional 4.5, 9.8, and 15.9 square miles would have shallow depths to water (5 feet or less) for projected sea-level rises of 2, 4, and 6 feet above levels in 2011. The additional areas with shallow depths to water generally occur in the same areas as the areas with current [2011] depths to water of 5 feet or less: low-lying coastal areas and near inland surface water features. Additional areas with shallow depths to water for the largest sea-level rise prediction (6 feet) account for about 5.7 percent of the total land area, excluding areas likely to be inundated by seawater. The numerous surface water drainages will dampen the response of the water table to sea-level rise. This dampening, combined with the region’s thick vadose zone, likely will mitigate the potential for groundwater inundation in most areas. The potential does exist for groundwater inundation in some areas, but the effects of sea-level rise on depths to water and infrastructure likely will not be substantial on a regional level.

Resolving terrestrial ecosystem processes along a subgrid topographic gradient for an earth-system model

USGS Publications Warehouse

Subin, Z M; Milly, Paul C.D.; Sulman, B N; Malyshev, Sergey; Shevliakova, E

2014-01-01

Soil moisture is a crucial control on surface water and energy fluxes, vegetation, and soil carbon cycling. Earth-system models (ESMs) generally represent an areal-average soil-moisture state in gridcells at scales of 50–200 km and as a result are not able to capture the nonlinear effects of topographically-controlled subgrid heterogeneity in soil moisture, in particular where wetlands are present. We addressed this deficiency by building a subgrid representation of hillslope-scale topographic gradients, TiHy (Tiled-hillslope Hydrology), into the Geophysical Fluid Dynamics Laboratory (GFDL) land model (LM3). LM3-TiHy models one or more representative hillslope geometries for each gridcell by discretizing them into land model tiles hydrologically coupled along an upland-to-lowland gradient. Each tile has its own surface fluxes, vegetation, and vertically-resolved state variables for soil physics and biogeochemistry. LM3-TiHy simulates a gradient in soil moisture and water-table depth between uplands and lowlands in each gridcell. Three hillslope hydrological regimes appear in non-permafrost regions in the model: wet and poorly-drained, wet and well-drained, and dry; with large, small, and zero wetland area predicted, respectively. Compared to the untiled LM3 in stand-alone experiments, LM3-TiHy simulates similar surface energy and water fluxes in the gridcell-mean. However, in marginally wet regions around the globe, LM3-TiHy simulates shallow groundwater in lowlands, leading to higher evapotranspiration, lower surface temperature, and higher leaf area compared to uplands in the same gridcells. Moreover, more than four-fold larger soil carbon concentrations are simulated globally in lowlands as compared with uplands. We compared water-table depths to those simulated by a recent global model-observational synthesis, and we compared wetland and inundated areas diagnosed from the model to observational datasets. The comparisons demonstrate that LM3-TiHy has the capability to represent some of the controls of these hydrological variables, but also that improvement in parameterization and input datasets are needed for more realistic simulations. We found large sensitivity in model-diagnosed wetland and inundated area to the depth of conductive soil and the parameterization of macroporosity. With improved parameterization and inclusion of peatland biogeochemical processes, the model could provide a new approach to investigating the vulnerability of Boreal peatland carbon to climate change in ESMs.

Linking Water Table Dynamics to Carbon Cycling in Artificial Soil Column Incubations

NASA Astrophysics Data System (ADS)

Geertje, Pronk; Adrian, Mellage; Tatjana, Milojevic; Fereidoun, Rezanezhad; Cappellen Philippe, Van

2016-04-01

The biogeochemistry of wetlands soils is closely tied to their hydrology. Water table fluctuations that cause flooding and drying of these systems may lead to enhanced degradation of organic matter and release of greenhouse gasses (e.g. CO2, CH4) to the atmosphere. However, predicting the influence of water table fluctuations on the biogeochemical functioning of soils requires an understanding of the interactions of soil hydrology with biogeochemical and microbial processes. To determine the effects of water table dynamics on carbon cycling, we are carrying out state-of-the-art automated soil column experiments with fully integrated monitoring of hydro-bio-geophysical process variables under both constant and oscillating water table conditions. An artificial, homogeneous mixture consisting of minerals and organic matter is used to provide a well-defined starting material. The artificial soils are composed of quartz sand, montmorillonite, goethite and humus from a forested riparian zone, from which we also extracted the microbial inoculum added to the soil mixture. The artificial soils are packed into 60 cm high, 7.5 cm wide columns. In the currently ongoing experiment, three replicate columns are incubated while keeping the water table constant water at mid-depth, while another three columns alternate between drained and saturated conditions. Micro-sensors installed at different depths below the soil surface record time-series redox potentials (Eh) varying between oxidizing (~+700 mV) and reducing (~-200 mV) conditions. Continuous O2 levels throughout the soil columns are monitored using high-resolution, luminescence-based, Multi Fiber Optode (MuFO) microsensors. Pore waters are collected periodically with MicroRhizon samplers from different depths, and analyzed for pH, EC, dissolved inorganic and organic carbon and ion/cation compositions. These measurements allow us to track the changes in pore water geochemistry and relate them to differences in carbon cycling between the contrasting water table regimes. Particular attention is given to the mobilization and redistribution of iron from the initially homogeneously distributed goethite. In addition, small solid-phase samples are collected monthly from the saturated and unsaturated zones of the soil columns to characterize the microbial communities and changes in soil microstructure and organo-mineral associations. Headspace gas measurements are used to derive the effluxes of CO2 and CH4 during the experiment. Together, the experimental data will provide a comprehensive picture of the early development of the soil and the accompanying establishment of biogeochemical gradients under dynamic hydrological conditions. They will allow us to relate the degradation of soil organic matter and greenhouse gas emissions to the saturation conditions and redox chemistry under controlled conditions. The experiment is in progress with an expected total duration of 6 months.

Rumsey and Walker_AMT_2016_Table 2.xlsx

EPA Pesticide Factsheets

Table summarizes instrument precision assessed by collocating the two sample boxes. Precision is quantified as the standard deviation of the residuals of an orthogonal least squares regression of concentrations from the two sample boxes. This allows for an estimation of gradient precision and ultimately gradient and flux detection limits. This dataset is associated with the following publication:Rumsey, I. Application of an online ion chromatography-based instrument for gradient flux measurements of speciated nitrogen and sulfur. ENVIRONMENTAL SCIENCE & TECHNOLOGY. American Chemical Society, Washington, DC, USA, 9(6): 2581-2592, (2016).

Microform-related community patterns of methane-cycling microbes in boreal Sphagnum bogs are site specific.

PubMed

Juottonen, Heli; Kotiaho, Mirkka; Robinson, Devin; Merilä, Päivi; Fritze, Hannu; Tuittila, Eeva-Stiina

2015-09-01

Vegetation and water table are important regulators of methane emission in peatlands. Microform variation encompasses these factors in small-scale topographic gradients of dry hummocks, intermediate lawns and wet hollows. We examined methane production and oxidization among microforms in four boreal bogs that showed more variation of vegetation within a bog with microform than between the bogs. Potential methane production was low and differed among bogs but not consistently with microform. Methane oxidation followed water table position with microform, showing higher rates closer to surface in lawns and hollows than in hummocks. Methanogen community, analysed by mcrA terminal restriction fragment length polymorphism and dominated by Methanoregulaceae or 'Methanoflorentaceae', varied strongly with bog. The extent of microform-related variation of methanogens depended on the bog. Methanotrophs identified as Methylocystis spp. in pmoA denaturing gradient gel electrophoresis similarly showed effect of bog, and microform patterns were stronger within individual bogs. Our results suggest that methane-cycling microbes in boreal Sphagnum bogs with seemingly uniform environmental conditions may show strong site-dependent variation. The bog-intrinsic factor may be related to carbon availability but contrary to expectations appears to be unrelated to current surface vegetation, calling attention to the origin of carbon substrates for microbes in bogs. © FEMS 2015. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Vertical gradients in water chemistry and age in the Northern High Plains Aquifer, Nebraska, 2003

USGS Publications Warehouse

McMahon, P.B.; Böhlke, J.K.; Carney, C.P.

2007-01-01

The northern High Plains aquifer is the primary source of water used for domestic, industrial, and irrigation purposes in parts of Colorado, Kansas, Nebraska, South Dakota, and Wyoming. Despite the aquifer’s importance to the regional economy, fundamental ground-water characteristics, such as vertical gradients in water chemistry and age, remain poorly defined. As part of the U.S. Geological Survey’s National Water-Quality Assessment Program, water samples from nested, short-screen monitoring wells installed in the northern High Plains aquifer were analyzed for major ions, nutrients, trace elements, dissolved organic carbon, pesticides, stable and radioactive isotopes, dissolved gases, and other parameters to evaluate vertical gradients in water chemistry and age in the aquifer. Chemical data and tritium and radiocarbon ages show that water in the aquifer was chemically and temporally stratified in the study area, with a relatively thin zone of recently recharged water (less than 50 years) near the water table overlying a thicker zone of older water (1,800 to 15,600 radiocarbon years). In areas where irrigated agriculture was an important land use, the recently recharged ground water was characterized by elevated concentrations of major ions and nitrate and the detection of pesticide compounds. Below the zone of agricultural influence, major-ion concentrations exhibited small increases with depth and distance along flow paths because of rock/water interactions. The concentration increases were accounted for primarily by dissolved calcium, sodium, bicarbonate, sulfate, and silica. In general, the chemistry of ground water throughout the aquifer was of high quality. None of the approximately 90 chemical constituents analyzed in each sample exceeded primary drinking-water standards.Mass-balance models indicate that changes in groundwater chemistry along flow paths in the aquifer can be accounted for by small amounts of feldspar and calcite dissolution; goethite and clay-mineral precipitation; organic-carbon and pyrite oxidation; oxygen reduction and denitrification; and cation exchange. Mixing with surface water affected the chemistry of ground water in alluvial sediments of the Platte River Valley. Radiocarbon ages in the aquifer, adjusted for carbon mass transfers, ranged from 1,800 to 15,600 14C years before present. These results have important implications with respect to development of ground-water resources in the Sand Hills. Most of the water in the aquifer predates modern anthropogenic activity so excessive removal of water by pumping is not likely to be replenished by natural recharge in a meaningful timeframe. Vertical gradients in ground-water age were used to estimate long-term average recharge rates in the aquifer. In most areas, the recharge rates ranged from 0.02 to 0.05 foot per year. The recharge rate was 0.2 foot per year in one part of the aquifer characterized by large downward hydraulic gradients.Nitrite plus nitrate concentrations at the water table were 0.13 to 3.13 milligrams per liter as nitrogen, and concentrations substantially decreased with depth in the aquifer. Dissolved-gas and nitrogen-isotope data indicate that denitrification in the aquifer removed 0 to 97 percent (average = 50 percent) of the nitrate originally present in recharge. The average amount of nitrate removed by denitrification in the aquifer north of the Platte River (Sand Hills) was substantially greater than the amount removed south of the river (66 as opposed to 0 percent), and the extent of nitrate removal appears to be related to the presence of thick deposits of sediment on top of the Ogallala Group in the Sand Hills that contained electron donors, such as organic carbon and pyrite, to support denitrification.Apparent rates of dissolved-oxygen reduction and denitrification were estimated on the basis of decreases in dissolved-oxygen concentrations and increases in concentrations of excess nitrogen gas and ground-water ages along flow paths from the water table to deeper wells. Median rates of dissolved-oxygen reduction and denitrification south of the Platte River were at least 10 times smaller than the median rates north of the river in the Sand Hills. The relatively large denitrification rates in the Sand Hills indicate that the aquifer in that area may have a greater capacity to attenuate nitrate contamination than the aquifer south of the river, depending on rates of ground-water movement in the two areas. Small denitrification rates south of the river indicate that nitrate contamination in that part of the aquifer would likely persist for a longer period of time.

Spatial variability in plant species composition and peatland carbon exchange

NASA Astrophysics Data System (ADS)

Goud, E.; Moore, T. R.; Roulet, N. T.

2015-12-01

Plant species shifts in response to global change will have significant impacts on ecosystem carbon (C) exchange and storage arising from changes in hydrology. Spatial variation in peatland C fluxes have largely been attributed to the spatial distribution of microhabitats that arise from variation in surface topography and water table depth, but little is known about how plant species composition impacts peatland C cycling or how these impacts will be influenced by changing environmental conditions. We quantified the effect of species composition and environmental variables on carbon dioxide (CO2) and methane (CH4) fluxes over 2 years in a temperate peatland for four plant communities situated along a water table gradient from ombrotrophic bog to beaver pond. We hypothesized that (i) spatial heterogeneity in species composition would drive predictable spatial heterogeneity in C fluxes due to variation in plant traits and ecological tolerances, and (ii) increases in peat temperature would increase C fluxes. Species had different effects on C fluxes primarily due to differences in leaf traits. Differences in ecological tolerances among communities resulted in different rates of CO2 exchange in response to changes in water table depth. There was an overall reduction in ecosystem respiration (ER), gross primary productivity (GPP) and CH4 flux in response to colder peat temperatures in the second year, and the additive effects of a deeper water table in the bog margin and pond sites further reduced flux rates in these areas. These results demonstrate that different plant species can increase or decrease the flux of C into and out of peatlands based on differences in leaf traits and ecological tolerances, and that CO2 and CH4 fluxes are sensitive to changes in soil temperature, especially when coupled with changes in moisture availability.

Automated correction of improperly rotated diffusion gradient orientations in diffusion weighted MRI.

PubMed

Jeurissen, Ben; Leemans, Alexander; Sijbers, Jan

2014-10-01

Ensuring one is using the correct gradient orientations in a diffusion MRI study can be a challenging task. As different scanners, file formats and processing tools use different coordinate frame conventions, in practice, users can end up with improperly oriented gradient orientations. Using such wrongly oriented gradient orientations for subsequent diffusion parameter estimation will invalidate all rotationally variant parameters and fiber tractography results. While large misalignments can be detected by visual inspection, small rotations of the gradient table (e.g. due to angulation of the acquisition plane), are much more difficult to detect. In this work, we propose an automated method to align the coordinate frame of the gradient orientations with that of the corresponding diffusion weighted images, using a metric based on whole brain fiber tractography. By transforming the gradient table and measuring the average fiber trajectory length, we search for the transformation that results in the best global 'connectivity'. To ensure a fast calculation of the metric we included a range of algorithmic optimizations in our tractography routine. To make the optimization routine robust to spurious local maxima, we use a stochastic optimization routine that selects a random set of seed points on each evaluation. Using simulations, we show that our method can recover the correct gradient orientations with high accuracy and precision. In addition, we demonstrate that our technique can successfully recover rotated gradient tables on a wide range of clinically realistic data sets. As such, our method provides a practical and robust solution to an often overlooked pitfall in the processing of diffusion MRI. Copyright © 2014 Elsevier B.V. All rights reserved.

Hydrologic Regulation of Plant Rooting Depth and Vice Versa

NASA Astrophysics Data System (ADS)

Fan, Y.; Miguez-Macho, G.

2017-12-01

How deep plant roots go and why may hold the answer to several questions regarding the co-evolution of terrestrial life and its environment. In this talk we explore how plant rooting depth responds to the hydrologic plumbing system in the soil/regolith/bedrocks, and vice versa. Through analyzing 2200 root observations of >1000 species along biotic (life form, genus) and abiotic (precipitation, soil, drainage) gradients, we found strong sensitivities of rooting depth to local soil water profiles determined by precipitation infiltration depth from the top (reflecting climate and soil), and groundwater table depth from below (reflecting topography-driven land drainage). In well-drained uplands, rooting depth follows infiltration depth; in waterlogged lowlands, roots stay shallow avoiding oxygen stress below the water table; in between, high productivity and drought can send roots many meters down to groundwater capillary fringe. We explore the global significance of this framework using an inverse model, and the implications to the coevolution of deep roots and the CZ in the Early-Mid Devonian when plants colonized the upland environments.

Alluvial Mountain Meadow Source-Sink Dynamics: Land-Cover Effects on Water and Fluvial Carbon Export

NASA Astrophysics Data System (ADS)

Weiss, T.; Covino, T. P.; Wohl, E.; Rhoades, C.; Fegel, T.; Clow, D. W.

2017-12-01

Fluvial networks of historically glaciated mountain landscapes alternate between confined and unconfined valley segments. In low-gradient unconfined reaches, river-connected wet meadows commonly establish, and have been recognized as important locations of long-term water, carbon, and nutrient storage. Among connected meadow floodplains, sink-source behavior shifts as a function of flow state; storing water at high flows (snowmelt) and contributing toward higher late-season baseflows. Despite these benefits, historical and contemporary land-use practices often result in the simplification of wet meadow systems, leading to reduced river-floodplain connectivity, lower water-tables and reductions in hydrologic buffering capacity. In this study, we are exploring hydrologic-carbon relationships across a gradient of valley confinement and river-floodplain connectivity (connected, n=3; disconnected, n=4) within the Colorado Rockies. Our approach includes hydrologic analysis, fluorometric assays, water chemistry, instream metabolic measures, and land-cover assessment to examine patterns between land-form, carbon quantity and quality, and stream ecosystem productivity. Between different meadow types, preliminary results suggest differences between instream productivity, carbon qualities, and hydrologic-carbon sink-source dynamics across the season. These data and analyses will provide insight into water, carbon and nutrient flux dynamics as a function of land-cover in mountain headwaters.

Comment on “Reconciliation of the Devils Hole climate record with orbital forcing”

USGS Publications Warehouse

Coplen, Tyler B.

2016-01-01

Moseley et al.’s (Reports, 8 January 2016, p. 165) preferred-Termination-II age is subjective, as evidenced by variation in their Termination-II ages of 2500 years per meter. Termination-II-age bias decreases to zero at ~1.5 meters below the present-day water table, if one assumes linear variation with core-sample height. Maintaining the required gradient of thorium isotope 230Th over 3.6 meters for 1000 years, much less 10,000 years, seems exceedingly unlikely.

Comment on “Reconciliation of the Devils Hole climate record with orbital forcing”

NASA Astrophysics Data System (ADS)

Coplen, Tyler B.

2016-10-01

Moseley et al.’s (Reports, 8 January 2016, p. 165) preferred-Termination-II age is subjective, as evidenced by variation in their Termination-II ages of 2500 years per meter. Termination-II-age bias decreases to zero at ~1.5 meters below the present-day water table, if one assumes linear variation with core-sample height. Maintaining the required gradient of thorium isotope 230Th over 3.6 meters for 1000 years, much less 10,000 years, seems exceedingly unlikely.

Spokane Valley-Rathdrum Prairie aquifer, Washington and Idaho

USGS Publications Warehouse

Drost, B.W.; Seitz, Harold R.

1977-01-01

The Spokane Valley-Rathdrum Prairie aquifer is composed of unconsolidated Quaternary glaciofluvial deposits underlying an area of about 350 square miles. Transmissivities in the aquifer range from about 0.13 million to 11 million feet squared per day and ground-water velocities exceed 60 feet per day in some areas. The water-table gradient ranges from about 2 feet per mile to more than 60 feet per mile, and during a year the water table fluctuates on the order of 5 to 10 feet. For most of the aquifer the water table is between 40 and 400 feet below land surface. The aquifer is recharged and discharged at an average rate of about 1,320 cubic feet per second. Water is presently (1976) pumped from the aquifer at an average rate of about 239 cubic feet per second for domestic, industrial, and agricultural uses. Most of this is discharged to the Spokane River, lost to evapotranspiration, or applied to the land surface with little or no change in quality. However, about 34 cubic feet per second becomes waste water generated by domestic and industrial activities and is returned to the aquifer by percolation from cesspools and drain fields. The quality of water in the aquifer is generally good. Less than one-half of 1 percent of the 3,300 analyses available exceeded the maximum contaminant levels specified in the National Interim Primary (or Proposed Secondary) Drinking Water Regulations (U.S. Environmental Protection Agency, 1975) for constituents which may be hazardous to health. Of the 6,300 analyses for constituents considered detrimental to the esthetic quality of water, about 1.4 percent have yielded values which exceeded the recommended levels. Alternative water sources for the area supplied by the aquifer are the Spokane and Little Spokane Rivers, lakes adjacent to the aquifer, and other aquifers. All of these potential sources are less desirable than the Spokane Valley-Rathdrum Prairie aquifer because of insufficient supplies, poor water quality, and (or) remoteness from the areas of need.

Nutrient stoichiometry in Sphagnum along a nitrogen deposition gradient in highly polluted region of Central-East Europe.

PubMed

Jiroušek, Martin; Hájek, Michal; Bragazza, Luca

2011-02-01

We investigated the variation of N:P and N:K ratio in ombrotrophic Sphagnum plants along a gradient of atmospheric N deposition from 1 to 2.5 g m(-2) year(-1) in Central-East Europe. The N:P and N:K ratio in Sphagnum capitula increased significantly along the N deposition gradient. Sphagnum species from the Cuspidata section were characterised by significantly lower ratios at low N deposition. When we compared the observed N:P ratios in Sphagnum plants with the values reported in a previous European-wide study, we found a correspondence in nutrient stoichiometry only for a few bogs: higher P concentration in Sphagnum capitula caused a lower N:P ratio in most of the study bogs so that Sphagnum plants still seem N-limited despite their N saturation. Interaction between summer water table decrease and aerial liming of surrounding forests is proposed as an explanation for this discrepancy. Local forestry practice interacting with climate thus alter N:P stoichiometry of Sphagnum along the N deposition gradient. Copyright © 2010 Elsevier Ltd. All rights reserved.

DMS emissions from Sphagnum-dominated wetlands

NASA Technical Reports Server (NTRS)

Hines, Mark E.; Demello, William Zamboni; Bayley, Suzanne E.

1992-01-01

The role of terrestrial sources of biogenic S and their effect on atmospheric chemistry remain as major unanswered questions in our understanding of the natural S cycle. The role of northern wetlands as sources and sinks of gaseous S was investigated by measuring rates of S gas exchange as a function of season, hydrologic conditions, and gradients in trophic status. Experiments were conducted in wetlands in New Hampshire (NH), and in Mire 239, a poor fen at the Experimental Lakes Area (ELA) in Ontario. Emissions were determined using Teflon enclosures, gas cryotrapping methods, and GC with flame photometric detection. Emissions of DMS dominated fluxes. In NH, DMS fluxes were greater than 1.6 micromol/m(sup -2)d(sup -1) in early summer, 1989 when temperatures were warm and the water table was approximately 5 cm below the surface. These rates are several-fold faster than average oceanic rates of DMS emission. A rapid drop in the water table resulted in a 6-fold decrease in DMS emissions in late July. In 1990, a new beaver dam kept water levels above the surface and S emissions were much lower than during 1989. The elimination of the beaver and a drop in the water table in August produced a rapid increase in S gas emissions. Emissions of DMS were highest in the most oligotrophic areas. Mire 239 (ELA) was irrigated with sulfuric and nitric acids to simulate acid rain. S emissions were determined before and after an acidification event in control and experimental areas in both minerotrophic and oligotrophic regions. Emissions of DMS were higher in the acidified areas compared to unacidified controls. Emissions were also much higher in the oligotrophic regions compared to the minerotrophic ones. Despite the wide differences in S gas fluxes (20-fold), it was difficult to determine whether acidification or variations in trophic status was not responsible for differences in S gas emissions. DMS emitted into the atmosphere was not derived from the water table but originated in peat in the unsaturated zone.

A progress report on results of test drilling and ground-water investigations of the Snake Plain aquifer, southeastern Idaho: Part 1: Mud Lake Region, 1969-70 and Part 2: Observation Wells South of Arco and West of Aberdeen

USGS Publications Warehouse

Crosthwaite, E.G.

1973-01-01

The results of drilling test holes to depths of approximately 1,000 feet in the Mud Lake region show that a large part of the region is underlain by both sedimentary deposits and basalt flows. At some locations, predominantly sedimentary deposits were penetrated; at others, basalt flows predominated. The so-called Mud Lake-Market Lake barrier denotes a change in geology. From the vicinity of the barrier area, as described by Stearns, Crandall, and Steward (1938, p. 111), up the water-table gradient for at least a few tens of miles, the saturated geologic section consists predominantly of beds of sediments that are intercalated with numerous basalt flows. Downgradient from the barrier, sedimentary deposits are not common and practically all the water-bearing formations are basalt, at least to the depths explored so far. Thus, the barrier is a transition zone from a sedimentary-basaltic sequence to a basaltic sequence. The sedimentary-basaltic sequence forms a complex hydrologic system in which water occurs under water-table conditions in the upper few tens of feet of saturated material and under artesian conditions in the deeper material in the southwest part of the region. The well data indicate that southwest of the barrier, artesian pressures are not significant. Southwest of the barrier, few sedimentary deposits occur in the basalt section and, as described by Mundorff, Crosthwaite, and Kilburn (1964). ground water occurs in a manner typical of the Snake Plain aquifer. In several wells, artesian pressures are higher in the deeper formations than in the shallower ones, but the reverse was found in a few wells. The available data are not adequate to describe the water-bearing characteristics of the artesian aquifer nor the effects that pumping in one zone would have on adjacent zones. The water-table aquifer yields large quantities of water to irrigation wells.

Managed aquifer recharge of treated wastewater: water quality changes resulting from infiltration through the vadose zone.

PubMed

Bekele, Elise; Toze, Simon; Patterson, Bradley; Higginson, Simon

2011-11-01

Secondary treated wastewater was infiltrated through a 9 m-thick calcareous vadose zone during a 39 month managed aquifer recharge (MAR) field trial to determine potential improvements in the recycled water quality. The water quality improvements of the recycled water were based on changes in the chemistry and microbiology of (i) the recycled water prior to infiltration relative to (ii) groundwater immediately down-gradient from the infiltration gallery. Changes in the average concentrations of several constituents in the recycled water were identified with reductions of 30% for phosphorous, 66% for fluoride, 62% for iron and 51% for total organic carbon when the secondary treated wastewater was infiltrated at an applied rate of 17.5 L per minute with a residence time of approximately four days in the vadose zone and less than two days in the aquifer. Reductions were also noted for oxazepam and temazepam among the pharmaceuticals tested and for a range of microbial pathogens, but reductions were harder to quantify as their magnitudes varied over time. Total nitrogen and carbamazepine persisted in groundwater down-gradient from the infiltration galleries. Infiltration does potentially offer a range of water quality improvements over direct injection to the water table without passage through the unsaturated zone; however, additional treatment options for the non-potable water may still need to be considered, depending on the receiving environment or the end use of the recovered water. Crown Copyright © 2011. Published by Elsevier Ltd. All rights reserved.

Hydrologic processes in deep vadose zones in interdrainage arid environments

USGS Publications Warehouse

Walvoord, Michelle Ann; Scanlon, Bridget R.; Hogan, James F.; Phillips, Fred M.; Scanlon, Bridget R.

2004-01-01

A unifying theory for the hydrology of desert vadose zones is particularly timely considering the rising population and water stresses in arid and semiarid regions. Conventional models cannot reconcile the apparent discrepancy between upward flow indicated by hydraulic gradient data and downward flow suggested by environmental tracer data in deep vadose zone profiles. A conceptual model described here explains both hydraulic and tracer data remarkably well by incorporating the hydrologic role of desert plants that encroached former juniper woodland 10 to 15 thousand years ago in the southwestern United States. Vapor transport also plays an important role in redistributing moisture through deep soils, particularly in coarse-grained sediments. Application of the conceptual model to several interdrainage arid settings reproduces measured matric potentials and chloride accumulation by simulating the transition from downward flow to upward flow just below the root zone initiated by climate and vegetation change. Model results indicate a slow hydraulic drying response in deep vadose zones that enables matric potential profiles to be used to distinguish whether precipitation episodically percolated below the root zone or was completely removed via evapotranspiration during the majority of the Holocene. Recharge declined dramatically during the Holocene in interdrainage basin floor settings of arid and semiarid basins. Current flux estimates across the water table in these environmental settings, are on the order of 0.01 to 0.1 mm yr-1 and may be recharge (downward) or discharge (upward) depending on vadose zone characteristics, such as soil texture, geothermal gradient, and water table depth. In summary, diffuse recharge through the basin floor probably contributes only minimally to the total recharge in arid and semiarid basins.

Water Table Depth and Growth of Young Cottonwood

Treesearch

W. M. Broadfoot

1973-01-01

Planted cottonwood grew best when the water table was about 2 feet deep, whether the tree was planted on soil with a high water table or the water table was raised 1 year after planting. Growth over a 1- foot-deep water table was about the same as over no water table, but a surface water table restricted growth of cuttings planted in the water, and killed trees planted...

Experimental studies in natural groundwater-recharge dynamics: The analysis of observed recharge events

USGS Publications Warehouse

Sophocleous, M.; Perry, C.A.

1985-01-01

The amounts and time distribution of groundwater recharge from precipitation over an approximately 19-month period were investigated at two instrumented sites in south-central Kansas. Precipitation and evapotranspiration sequences, soil-moisture profiles and storage changes, water fluxes in the unsaturated zone and hydraulic gradients in the saturated zone at various depths, soil temperatures, water-table hydrographs, and water-level changes in nearby wells clearly depict the recharge process. Antecedent moisture conditions and the thickness and nature of the unsaturated zone were found to be the major factors affecting recharge. Although the two instrumented sites are located in sand-dune environments in areas characterized by shallow water table and subhumid continental climate, a significant difference was observed in the estimated effective recharge. The estimates ranged from less than 2.5 to approximately 154 mm at the two sites from February to June 1983. The main reasons for this large difference in recharge estimates were the greater thickness of the unsaturated zone and the lower moisture content in that zone resulting from lower precipitation and higher potential evapotranspiration for one of the sites. Effective recharge took place only during late winter and spring. No summer or fall recharge was observed at either site during the observation period of this study. ?? 1985.

Water movement through thick unsaturated zones overlying the central High Plains aquifer, southwestern Kansas, 2000-2001

USGS Publications Warehouse

McMahon, Peter B.; Dennehy, K.F.; Michel, R.L.; Sophocleous, M.A.; Ellett, K.M.; Hurlbut, D.B.

2003-01-01

The role of irrigation as a driving force for water and chemical movement to the central High Plains aquifer is uncertain because of the thick unsaturated zone overlying the aquifer. Water potentials and profiles of tritium, chloride, nitrate, and pesticide concentrations were used to evaluate water movement through thick unsaturated zones overlying the central High Plains aquifer at three sites in southwestern Kansas. One site was located in rangeland and two sites were located in areas dominated by irrigated agriculture. In 2000?2001, the depth to water at the rangeland site was 50 meters and the depth to water at the irrigated sites was about 45.4 meters. Irrigation at the study sites began in 1955?56. Measurements of matric potential and volumetric water content indicate wetter conditions existed in the deep unsaturated zone at the irrigated sites than at the rangeland site. Total water potentials in the unsaturated zone at the irrigated sites systematically decreased with depth to the water table, indicating a potential existed for downward water movement from the unsaturated zone to the water table at those sites. At the rangeland site, total water potentials in the deep unsaturated zone indicate small or no potential existed for downward water movement to the water table. Postbomb tritium was not detected below a depth of 1.9 meters in the unsaturated zone or in ground water at the rangeland site. In contrast, postbomb tritium was detected throughout most of the unsaturated zone and in ground water at both irrigated sites. These results indicate post-1953 water moved deeper in the unsaturated zone at the irrigated sites than at the rangeland site. The depth of the interface between prebomb and postbomb tritium and a tritium mass-balance method were used to estimate water fluxes in the unsaturated zone at each site. The average water fluxes at the rangeland site were 5.4 and 4.4 millimeters per year for the two methods, which are similar to the average water flux (5.1 millimeters per year) estimated using a chloride mass-balance method. Tritium profiles in the unsaturated zone at the irrigated sites were complicated by the presence of tritium-depleted intervals separating upper and lower zones containing postbomb tritium. If the interface between prebomb and postbomb tritium was at the top of the tritium-depleted interval and postbomb tritium detected beneath that interval was from the declining water table in the area, then the average water flux at the irrigated sites was estimated to be 21 to 54 millimeters per year. If postbomb tritium detected beneath the tritium-depleted interval was from bypass or preferential water movement through the local unsaturated zone instead of the declining water table, then the minimum water flux at the irrigated sites was estimated to be 106 to 116 millimeters per year. In either case, water fluxes at the irrigated sites were at least 4 to 12 times larger than the flux at the rangeland site, indicating irrigation was an important driving force for water movement through the unsaturated zone. The presence of postbomb tritium and large nitrate and total pesticide concentrations (24 milligrams per liter as nitrogen and 0.923 microgram per liter, respectively) in ground water at the irrigated sites indicates irrigation water also was an important driving force for chemical movement to the water table. The persistence of a downward hydraulic gradient from the deep unsaturated zone to the water table at the irrigated sites, in addition to large nitrate and atrazine concentrations in deep soil water (34 milligrams per liter as nitrogen and 0.79 microgram per liter, respectively), indicate that the deep unsaturated zone will be a source of nitrate and atrazine to the aquifer in the future.

Longleaf Pine Ground-Layer Vegetation in Francis Marion National Forest: Reintroduction, Restoration, and Vegetation Assembly

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

Glitzenstein, J.; Streng, D.; Wade, D.

2001-01-01

Study represents significant progress in understanding of compositional gradients in longleaf pine plant communities of Central South Carolina. Study shows the importance of water table depths as a controlling variable with vegetation patterns in the field and similar effects in a garden experiment. Grass planting study suggests that observed field distributions of dormant pine savannah grasses derive from complex interactive effects of fire history, hydrology and light environments. Use of regional longleaf data set to identify candidate species for introduction also appears to be a pioneering effort.

Analysis of Microbial Community Composition and Methane Production From Northern Peatlands Across a Climate Gradient

NASA Astrophysics Data System (ADS)

Sarno, A. F.; Humphreys, E.; Olefeldt, D.; Heffernan, L.; Roman, T. D.; Sebestyen, S.; Kolka, R.; Yavitt, J. B.; Finn, D.; Cadillo-Quiroz, H.

2017-12-01

Northern peatland ecosystems allow for the accumulation of a carbon (C) pool as the rate of photosynthesis exceeds the rate of organic carbon decomposition. Under current climate conditions, many northern peatlands act as a C sink; however, changes in climate and other environmental conditions, such as soil permafrost melting, are capable of changing the decomposition cascade. Here we take advantage of four peatlands situated along a climate gradient from tundra (Daring Lake, Canada) to boreal forest (Lutose, Canada) to temperate broadleaf and mixed forest (Bog Lake, MN and Chicago Bog, NY) biomes to assess how the relative abundance of microbial functional groups and substrate availability within the microbial community might impact the decomposition of soil organic matter to methane. The four peatlands had similar hydrology and geochemistry and were poor fen types. Soil, water and gas samples were collected at the water table level. Microbial community composition, derived from Illumina amplicon sequencing of the 16S rRNA gene, and geochemical and climate variables were analyzed with principal component regression analysis to determine major drivers of community variation. Mean annual temperature (r2=0.53), mean annual precipitation (r2=0.36), water table level (r2=0.43) and soil temperature (r2=0.49), were all statistically significant drivers of both general microbial and methanogen community composition (p value < 0.001). The relative abundance of Methanocella, Methanosarcina and Methanobacterium varied significantly across the climate gradient (p value < 0.05), however the majority of methanogen genera did not. Interestingly, dissolved methane (r2=0.24) was statistically significant at the general community level (p value < 0.001), but not significant when tested against only the methanogen community. The results demonstrate that environmental factors predicted to change over time due to climate change will have a significant impact on microbial community composition and C sinks within Northern peatlands. Further analyses of microbial processes that produce methanogenic substrates such as fermentation and syntrophic reactions, in tandem with the further identification and quantification of methanogens, will elucidate other drivers of methane production in Northern peatlands.

Slope instability in complex 3D topography promoted by convergent 3D groundwater flow

NASA Astrophysics Data System (ADS)

Reid, M. E.; Brien, D. L.

2012-12-01

Slope instability in complex topography is generally controlled by the interaction between gravitationally induced stresses, 3D strengths, and 3D pore-fluid pressure fields produced by flowing groundwater. As an example of this complexity, coastal bluffs sculpted by landsliding commonly exhibit a progression of undulating headlands and re-entrants. In this landscape, stresses differ between headlands and re-entrants and 3D groundwater flow varies from vertical rainfall infiltration to lateral groundwater flow on lower permeability layers with subsequent discharge at the curved bluff faces. In plan view, groundwater flow converges in the re-entrant regions. To investigate relative slope instability induced by undulating topography, we couple the USGS 3D limit-equilibrium slope-stability model, SCOOPS, with the USGS 3D groundwater flow model, MODFLOW. By rapidly analyzing the stability of millions of potential failures, the SCOOPS model can determine relative slope stability throughout the 3D domain underlying a digital elevation model (DEM), and it can utilize both fully 3D distributions of pore-water pressure and material strength. The two models are linked by first computing a groundwater-flow field in MODFLOW, and then computing stability in SCOOPS using the pore-pressure field derived from groundwater flow. Using these two models, our analyses of 60m high coastal bluffs in Seattle, Washington showed augmented instability in topographic re-entrants given recharge from a rainy season. Here, increased recharge led to elevated perched water tables with enhanced effects in the re-entrants owing to convergence of groundwater flow. Stability in these areas was reduced about 80% compared to equivalent dry conditions. To further isolate these effects, we examined groundwater flow and stability in hypothetical landscapes composed of uniform and equally spaced, oscillating headlands and re-entrants with differing amplitudes. The landscapes had a constant slope for both headlands and re-entrants to minimize slope effects on stability. Despite these equal slopes, our analyses, given dry conditions, illustrated that the headlands can be 5-7% less stable than the re-entrants, owing to the geometry of the 3D failure mass with the lowest stability. We then simulated groundwater flow in these landscapes; flow was caused by recharge perching on a horizontal low permeability layer with discharge at the bluff faces. By systematically varying recharge, hydraulic conductivity of the material, and conductance at the bluffs, we created different 3D pore-pressure fields. Recharge rates and hydraulic conductivities controlled the height of the water table, whereas bluff conductance influenced the gradient of the water table near the bluff face. Given elevated water tables with steep gradients, bluffs in the re-entrants became unstable where flow converged. Thus, with progressively stronger effects from water flow, overall instability evolved from relatively unstable headlands to more uniform stability to relatively unstable re-entrants. Larger re-entrants led to more 3D flow convergence and greater localized instability. One- or two-dimensional models cannot fully characterize slope instability in complex topography.

How well do testate amoebae transfer functions relate to high-resolution water-table records?

NASA Astrophysics Data System (ADS)

Holden, Joseph; Swindles, Graeme; Raby, Cassandra; Blundell, Antony

2014-05-01

Testate amoebae (TA) community composition records from peat cores are often used to infer past water-table conditions on peatland sites. However, one of the problems is that validation of water-table depths used in such work typically comes from a one-off water-table measurement or a few measurements of water-table depth from the testate amoebae sample extraction point. Furthermore, one value of water-table depth is produced by the transfer function reconstruction, with sample-specific errors generated through a statistical resampling approach. However, we know that water tables fluctuate in peatlands and are dynamic. Traditional TA water-table data may not adequately capture a mean value from a site, and may not account for water-table dynamics (e.g. seasonal or annual variability) that could influence the TA community composition. We analysed automatically logged (at least hourly, mainly 15-min) peatland water-table data from 72 different dipwells located across northern Sweden, Wales and the Pennine region of England. Each location had not been subject to recent management intervention. A suite of characteristics of water-table dynamics for each point were determined. At each point surface samples were extracted and the TA community composition was determined. Our results show that estimated water-table depth based on the TA community transfer functions poorly represents the real mean or median water tables for the study sites. The TA approach does, however, generally identify sites that have water tables that are closer to the surface for a greater proportion of the year compared to sites with deeper water tables for large proportions of the year. However, the traditional TA approach does not differentiate between sites with similar mean (or median) water-table depths yet which have quite different water table variability (e.g. interquartile range). We suggest some ways of improving water-table metrics for use in Holocene peatland hydrology reconstructions.

Wildfire effects on vadose zone hydrology in forested boreal peatland microforms

NASA Astrophysics Data System (ADS)

Thompson, Dan K.; Waddington, James M.

2013-04-01

SummaryPeatland vulnerability to wildfire disturbance has been shown to vary as a function of hummock and hollow microforms and vadose zone hydrology, with low-lying hollow microforms most susceptible to deep combustion of peat. To better understand how this microform induced pattern of burning alters vadose water storage, pore-water pressure, and water table relationships, we examined a paired burned and unburned peatland in the boreal plain region of north central Alberta. Water table response to rain events increased significantly after wildfire, resulting in a more variable unsaturated zone thickness that was more responsive to smaller rain events. Water storage losses in the vadose zone occurred primarily at depths greater than 15 cm. Large peat surface water loss occurred in hummock microforms in the early spring due to the presence of unsaturated frozen peat at depth, likely a result of a vapour gradient from the unfrozen peat into the frozen peat underneath. During this period, the loss of water storage in the vadose zone satisfied up to 25% of daily evaporative demand, compared to only 3-5% during ice-free periods. A similar but less severe drying was observed late in summer, with burned hummocks the most vulnerable with high pore-water pressures. The enhanced surface drying observed is a precursor to high pore-water pressure conditions that inhibit Sphagnum regeneration. Our observations point to a paradox where the hummocks, being most resistant to combustion, are themselves most prone to high pore-water pressures following wildfire. The harsher hummock environment may contribute to the observed delay in post-fire Sphagnum regeneration in hummocks compared to hollows.

Effect of permafrost thaw on the dynamics of lakes recharged by ice-jam floods: case study in Yukon Flats, Alaska

USGS Publications Warehouse

Steve M. Jepsen,; Walvoord, Michelle Ann; Voss, Clifford I.; Rover, Jennifer R.

2016-01-01

Large river floods are a key water source for many lakes in fluvial periglacial settings. Where permeable sediments occur, the distribution of permafrost may play an important role in the routing of floodwaters across a floodplain. This relationship is explored for lakes in the discontinuous permafrost of Yukon Flats, interior Alaska, using an analysis that integrates satellite-derived gradients in water surface elevation, knowledge of hydrogeology, and hydrologic modeling. We observed gradients in water surface elevation between neighboring lakes ranging from 0.001 to 0.004. These high gradients, despite a ubiquitous layer of continuous shallow gravel across the flats, are consistent with limited groundwater flow across lake basins resulting from the presence of permafrost. Permafrost impedes the propagation of floodwaters in the shallow subsurface and constrains transmission to “fill-and-spill” over topographic depressions (surface sills), as we observed for the Twelvemile-Buddy Lake pair following a May 2013 ice-jam flood on the Yukon River. Model results indicate that permafrost table deepening of 1–11 m in gravel, depending on watershed geometry and subsurface properties, could shift important routing of floodwater to lakes from overland flow (fill-and-spill) to shallow groundwater flow (“fill-and-seep”). Such a shift is possible in the next several hundred years of ground surface warming, and may bring about more synchronous water level changes between neighboring lakes following large flood events. This relationship offers a potentially useful tool, well-suited to remote sensing, for identifying long-term changes in shallow groundwater flow resulting from thawing of permafrost.

Measuring and computing natural ground-water recharge at sites in south-central Kansas

USGS Publications Warehouse

Sophocleous, M.A.; Perry, C.A.

1987-01-01

To measure the natural groundwater recharge process, two sites in south-central Kansas were instrumented with sensors and data microloggers. The atmospheric-boundary layer and the unsaturated and saturated soil zones were monitored as a single regime. Direct observations also were used to evaluate the measurements. Atmospheric sensors included an anemometer, a tipping-bucket rain gage, an air-temperature thermistor, a relative-humidity probe, a net radiometer, and a barometric-pressure transducer. Sensors in the unsaturated zone consisted of soil-temperature thermocouples, tensiometers coupled with pressure transducers and dial gages, gypsum blocks, and a neutron-moisture probe. The saturated-zone sensors consisted of a water-level pressure transducer, a conventional float gage connected to a variable potentiometer, soil thermocouples, and a number of multiple-depth piezometers. Evaluation of the operation of these sensors and recorders indicates that certain types of equipment, such as pressure transducers, are very sensitive to environmental conditions. A number of suggestions aimed at improving instrumentation of recharge investigations are outlined. Precipitation and evapotranspiration data, taken together with soil moisture profiles and storage changes, water fluxes in the unsaturated zone and hydraulic gradients in the saturated zone at various depths, soil temperature, water table hydrographs, and water level changes in nearby wells, describe the recharge process. Although the two instrumented sites are located in sand-dune environments in area characterized by a shallow water table and a sub-humid continental climate, a significant difference was observed in the estimated total recharge. The estimates ranged from less than 2.5 mm at the Zenith site to approximately 154 mm at the Burrton site from February to June 1983. The principal reasons that the Burrton site had more recharge than the Zenith site were more precipitation, less evapotranspiration, and a shallower depth to the water table. Effective recharge took place only during late winter and spring. No summer or fall recharge was observed at either site during the observation period of this study. (Author 's abstract)

The paleohydrology of unsaturated and saturated zones at Yucca Mountain, Nevada, and vicinity

USGS Publications Warehouse

Paces, James B.; Whelan, Joseph F.; Stuckless, John S.

2012-01-01

Surface, unsaturated-zone, and saturated-zone hydrologic conditions at Yucca Mountain responded to past climate variations and are at least partly preserved by sediment, fossil, and mineral records. Characterizing past hydrologic conditions in surface and subsurface environments helps to constrain hydrologic responses expected under future climate conditions and improve predictions of repository performance. Furthermore, these records provide a better understanding of hydrologic processes that operate at time scales not readily measured by other means. Pleistocene climates in southern Nevada were predominantly wetter and colder than the current interglacial period. Cyclic episodes of aggradation and incision in Fortymile Wash, which drains the eastern slope of Yucca Mountain, are closely linked to Pleistocene climate cycles. Formation of pedogenic cement is favored under wetter Pleistocene climates, consistent with increased soil moisture and vegetation, higher chemical solubility, and greater evapotranspiration relative to Holocene soil conditions. The distribution and geochemistry of secondary minerals in subsurface fractures and cavities reflect unsaturated-zone hydrologic conditions and the response of the hydrogeologic system to changes in temperature and percolation flux over the last 12.8 m.y. Physical and fluid-inclusion evidence indicates that secondary calcite and opal formed in air-filled cavities from fluids percolating downward through connected fracture pathways in the unsaturated zone. Oxygen, strontium, and carbon isotope data from calcite are consistent with a descending meteoric water source but also indicate that water compositions and temperatures evolved through time. Geochronological data indicate that secondary mineral growth rates are less than 1–5 mm/m.y., and have remained approximately uniform over the last 10 m.y. or longer. These data are interpreted as evidence for hydrological stability despite large differences in surface moisture caused by climate shifts between the Miocene and Pleistocene and between Pleistocene glacial-interglacial cycles. Secondary mineral distribution and δ18O profiles indicate that evaporation in the shallower welded tuffs reduces infiltration fluxes. Several near-surface and subsurface processes likely are responsible for diverting or dampening infiltration and percolation, resulting in buffering of percolation fluxes to the deeper unsaturated zone. Cooler and wetter Pleistocene climates resulted in increased recharge in upland areas and higher water tables at Yucca Mountain and throughout the region. Discharge deposits in the Amargosa Desert were active during glacial periods, but only in areas where the modern water table is within 7–30 m of the surface. Published groundwater models simulate water-table rises beneath Yucca Mountain of as much as 150 m during glacial climates. However, most evidence from Fortymile Canyon up gradient from Yucca Mountain limits water-table rises to 30 m or less, which is consistent with evidence from discharge sites in the Amargosa Desert. The isotopic compositions of uranium in tuffs spanning the water table in two Yucca Mountain boreholes indicate that Pleistocene water-table rises likely were restricted to 25–50 m above modern positions and are in approximate agreement with water-table rises estimated from zeolitic-to-vitric transitions in the Yucca Mountain tuffs (less than 60 m in the last 11.6 m.y.).

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

NASA Astrophysics Data System (ADS)

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

2011-12-01

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

Effect of Pumping on Groundwater Levels: A Case Study

NASA Astrophysics Data System (ADS)

Sindhu, G.; Vijayachandran, Lekshmi

2018-03-01

Groundwater is a major source for drinking and domestic purposes. Nowadays, extensive pumping has become a major issue of concern since pumping has led to rapid decline in the groundwater table, thus imposing landward gradient, leading to saline water intrusion especially in coastal areas. Groundwater pumping has seen its utmost effect on coastal aquifer systems, where the sea-ward gradient gets disturbed due to anthropogenic influences. Hence, a groundwater flow modelling of an aquifer system is essential for understanding the various hydro-geologic conditions, which can be used to study the responses of the aquifer system with regard to various pumping scenarios. Besides, a model helps to predict the water levels for the future period with respect to changing environment. In this study, a finite element groundwater flow model of a coastal aquifer system at Aakulam, Trivandrum district is developed, calibrated and simulated using the software Finite Element subsurface Flow system (FEFLOW 6.2).This simulated model is then used to predict the groundwater levels for a future 5 year period during pre monsoon and post monsoon season.

Effect of Pumping on Groundwater Levels: A Case Study

NASA Astrophysics Data System (ADS)

Sindhu, G.; Vijayachandran, Lekshmi

2018-06-01

Groundwater is a major source for drinking and domestic purposes. Nowadays, extensive pumping has become a major issue of concern since pumping has led to rapid decline in the groundwater table, thus imposing landward gradient, leading to saline water intrusion especially in coastal areas. Groundwater pumping has seen its utmost effect on coastal aquifer systems, where the sea-ward gradient gets disturbed due to anthropogenic influences. Hence, a groundwater flow modelling of an aquifer system is essential for understanding the various hydro-geologic conditions, which can be used to study the responses of the aquifer system with regard to various pumping scenarios. Besides, a model helps to predict the water levels for the future period with respect to changing environment. In this study, a finite element groundwater flow model of a coastal aquifer system at Aakulam, Trivandrum district is developed, calibrated and simulated using the software Finite Element subsurface Flow system (FEFLOW 6.2).This simulated model is then used to predict the groundwater levels for a future 5 year period during pre monsoon and post monsoon season.

Paleohydrology of the southern Great Basin, with special reference to water table fluctuations beneath the Nevada Test Site during the late(?) Pleistocene

USGS Publications Warehouse

Winograd, Isaac Judah; Doty, Gene C.

1980-01-01

Knowledge of the magnitude of water-table rise during Pleistocene pluvial climates, and of the resultant shortening of groundwater flow path and reduction in unsaturated zone thickness, is mandatory for a technical evaluation of the Nevada Test Site (NTS) or other arid zone sites as repositories for high-level or transuranic radioactive wastes. The distribution of calcitic veins filling fractures in alluvium, and of tufa deposits between the Ash Meadows spring discharge area and the Nevada Test Site indicates that discharge from the regional Paleozoic carbonate aquifer during the Late( ) Pleistocene pluvial periods may have occurred at an altitude about 50 meters higher than at present and 14 kilometers northeast of Ash Meadows. Use of the underflow equation (relating discharge to transmissivity, aquifer width, and hydraulic gradient), and various assumptions regarding pluvial recharge, transmissivity, and altitude of groundwater base level, suggest possible rises in potentiometric level in the carbonate aquifer of about -90 meters beneath central Frenchman Flat. During Wisconsin time the rise probably did not exceed 30 meters. Water-level rises beneath Frenchman Flat during future pluvials are unlikely to exceed 30 meters and might even be 10 meters lower than modern levels. Neither the cited rise in potentiometric level in the regional carbonate aquifer, nor the shortened flow path during the Late( ) Pleistocene preclude utilization of the NTS as a repository for high-level or transuranic-element radioactive wastes provided other requisite conditions are met as this site. Deep water tables, attendant thick (up to several hundred meter) unsaturated zones, and long groundwater flow paths characterized the region during the Wisconsin Stage and probably throughout the Pleistocene Epoch and are likely to so characterize it during future glacial periods. (USGS)

Modeling Vegetation Growth Impact on Groundwater Recharge

NASA Astrophysics Data System (ADS)

Anurag, H.; Ng, G. H. C.; Tipping, R.

2017-12-01

Vegetation growth is affected by variability in climate and land-cover / land-use over a range of temporal and spatial scales. Vegetation also modifies water budget through interception and evapotranspiration and thus has a significant impact on groundwater recharge. Most groundwater recharge assessments represent vegetation using specified, static parameter, such as for leaf-area-index, but this neglects the effect of vegetation dynamics on recharge estimates. Our study addresses this gap by including vegetation growth in model simulations of recharge. We use NCAR's Community Land Model v4.5 with its BGC module (BGC is the new CLM4.5 biogeochemistry). It integrates prognostic vegetation growth with land-surface and subsurface hydrological processes and can thus capture the effect of vegetation on groundwater. A challenge, however, is the need to resolve uncertainties in model inputs ranging from vegetation growth parameters all the way down to the water table. We have compiled diverse data spanning meteorological inputs to subsurface geology and use these to implement ensemble model simulations to evaluate the possible effects of dynamic vegetation growth (versus specified, static vegetation parameterizations) on estimating groundwater recharge. We present preliminary results for select data-intensive test locations throughout the state of Minnesota (USA), which has a sharp east-west precipitation gradient that makes it an apt testbed for examining ecohydrologic relationships across different temperate climatic settings and ecosystems. Using the ensemble simulations, we examine the effect of seasonal to interannual variability of vegetation growth on recharge and water table depths, which has implications for predicting the combined impact of climate, vegetation, and geology on groundwater resources. Future work will include distributed model simulations over the entire state, as well as conditioning uncertain vegetation and subsurface parameters on remote sensing data and statewide water table records using data assimilation.

Inverting Residual Self-Potential Data for Redox Potentials of Contaminant Plumes

NASA Astrophysics Data System (ADS)

Linde, N.; Revil, A.

2007-05-01

Self-potential (SP) data can be separated into a streaming potential component that is associated with pore water flow and a redox potential component, which is sensitive to differences in the redox potentials of organic-rich contaminant plumes and the surroundings. This work presents the first inversion method that uses residual SP (i.e., corrected for the streaming potential component) to invert for the redox potentials of contaminant plumes. We consider a two-layered electrical conductivity structure, where the boundary corresponds to the water table. We assume that the electrical dipole sources are associated with microbial breakdown of contaminants at the water table. This geobattery model is hypothesized to exist (1) because the water table is associated with a strong redox gradient between highly reducing conditions within the contaminated groundwater (due to biodegradation and oxygen depletion) and the oxidized vadose zone, and (2) because the microbial biofilms and precipitation of metallic particles can provide an electron conductor to complete the circuit required for the geobattery. The inverse method was applied to residual SP estimated from SP measurements collected at the ground surface in the vicinity of the Entressen landfill, South of France. The estimated redox potentials correlate well with in situ measurements (correlation coefficient is 0.93) and the estimated amplitudes of the redox potentials are similar to those measured in situ. A sensitivity analysis reveals that meaningful estimates of the redox potential can be derived even if the electrical conductivity structure is only known within an order of magnitude. These results provide further evidence that the SP method can be useful to monitor the spreading of contaminants around landfills and to evaluate the efficiency of remediation programs.

Validating a topographically driven model of peatland water table: Implications for understanding land cover controls on water table.

NASA Astrophysics Data System (ADS)

Evans, Martin; Allott, Tim; Worrall, Fred; Rowson, James; Maskill, Rachael

2014-05-01

Water table is arguably the dominant control on biogeochemical cycling in peatland systems. Local water tables are controlled by peat surface water balance and lateral transfer of water driven by slope can be a significant component of this balance. In particular, blanket peatlands typically have relatively high surface slope compared to other peatland types so that there is the potential for water table to be significantly contolled by topographic context. UK blanket peatlands are also significantly eroded so that there is the potential for additional topographic drainage of the peatland surface. This paper presents a topographically driven model of blanket peat water table. An initial model presented in Allott et al. (2009) has been refined and tested against further water table data collected across the Bleaklow and Kinderscout plateaux of the English Peak District. The water table model quantifies the impact of peat erosion on water table throughout this dramatically dissected landscape demonstrating that almost 50% of the landscape has suffered significant water table drawdown. The model calibrates the impact of slope and degree of dissection on local water tables but does not incorporate any effects of surface cover on water table conditions. Consequently significant outliers in the test data are potentially indicative of important impacts of surface cover on water table conditions. In the test data presented here sites associated with regular moorland burning are significant outliers. The data currently available do not allow us to draw conclusions around the impact of land cover but they indicate an important potential application of the validated model in controlling for topographic position in further testing of the impact of land cover on peatland water tables. Allott, T.E.H. & Evans, M.G., Lindsay, J.B., Agnew, C.T., Freer, J.E., Jones, A. & Parnell, M. Water tables in Peak District blanket peatlands. Moors for the Future Report No. 17. Moors for the Future Partnership, Edale, 47pp.

An approach for delineating drinking water wellhead protection areas at the Nile Delta, Egypt.

PubMed

Fadlelmawla, Amr A; Dawoud, Mohamed A

2006-04-01

In Egypt, production has a high priority. To this end protecting the quality of the groundwater, specifically when used for drinking water, and delineating protection areas around the drinking water wellheads for strict landuse restrictions is essential. The delineation methods are numerous; nonetheless, the uniqueness of the hydrogeological, institutional as well as social conditions in the Nile Delta region dictate a customized approach. The analysis of the hydrological conditions and land ownership at the Nile Delta indicates the need for an accurate methodology. On the other hand, attempting to calculate the wellhead protected areas around each of the drinking wells (more than 1500) requires data, human resources, and time that exceed the capabilities of the groundwater management agency. Accordingly, a combination of two methods (simplified variable shapes and numerical modeling) was adopted. Sensitivity analyses carried out using hypothetical modeling conditions have identified the pumping rate, clay thickness, hydraulic gradient, vertical conductivity of the clay, and the hydraulic conductivity as the most significant parameters in determining the dimensions of the wellhead protection areas (WHPAs). Tables of sets of WHPAs dimensions were calculated using synthetic modeling conditions representing the most common ranges of the significant parameters. Specific WHPA dimensions can be calculated by interpolation, utilizing the produced tables along with the operational and hydrogeological conditions for the well under consideration. In order to simplify the interpolation of the appropriate dimensions of the WHPAs from the calculated tables, an interactive computer program was written. The program accepts the real time data of the significant parameters as its input, and gives the appropriate WHPAs dimensions as its output.

Absorption of the Martian regolith: Specific surface area and missing CO(sub 2)

NASA Technical Reports Server (NTRS)

Zent, A. P.; Fanale, F. P.; Postawko, S. E.

1987-01-01

For most estimates of available regolith and initial degassed CO(sub 2) inventories, it appears that any initial inventory must have been lost to space or incorporated into carbonates. Most estimates of the total available degassed CO(sub 2) inventory are only marginally sufficient to allow for a major early greenhouse effect. It is suggested that the requirements for greenhouse warming to produce old dessicated terrain would be greatly lessened if groundwater brines rather than rainfall were involved and if a higher internal gradient were involved to raise the water (brine) table, leading to more frequent sapping.

Ground-water contamination by crude oil at the Bemidji, Minnesota, research site- An introduction: Chapter A in Ground-water contamination by crude oil at the Bemidji, Minnesota, research site; US Geological Survey Toxic Waste--ground-water contamination study

USGS Publications Warehouse

1984-01-01

The U.S. Geological Survey has begun a research project to improve understanding of the mobilization, transport, and fate of petroleum contaminants in the shallow subsurface and to use this understanding to develop predictive models of contaminant behavior. The project site is near Bemidji in northern Minnesota where an accidental spill of 10,500 barrels of crude oil occurred when a pipeline broke on August 20, 1979. Regulatory and remedial actions have been completed. The site is in a remote area with neither man-made hydraulic stresses nor other anthropogenic sources of the compounds of interest. The spill is in the recharge area of a local flow system that discharges to a small closed lake approximately 1,000 feet down the hydraulic gradient. The aquifer is pitted outwash dissected by younger glacial channels and is underlain by poorly permeable till at a depth of about 80 feet. Ground water dissolves oil floating on the water table under the spill site and moves toward the lake. At the water table, ground water enters the lake through lacustrine sediments; at depth, flow may be underneath the lake through the outwash. Contaminant transport has been as rapid as 4 feet per day based on the rate of movement of contaminants monitored through wells installed within a few days of the spill, but average rates are undoubtedly much less. 

Sustainable yields from large diameter wells in shallow weathered aquifers

NASA Astrophysics Data System (ADS)

Rushton, K. R.; de Silva, C. S.

2016-08-01

Large diameter wells in shallow weathered aquifers provide a valuable source of water for domestic and agricultural purposes in many locations including the Indian subcontinent. However, when used for irrigation, these wells often fail towards the end of the dry season. By considering two case studies in the dry and intermediate rainfall zones of Sri Lanka, reasons for the limited yield of these wells are identified. The first case study is concerned with a sloping catchment; a significant proportion of the precipitation during the rainy season either becomes runoff or passes down-gradient through the aquifer and is discharged at the ground surface. Furthermore, during the dry season, groundwater discharge continues. In the second case study the topography is generally flat but, even though the aquifer fills most years during the rainy season, there is often only sufficient water to irrigate about half of each farmer's holding. These investigations are based on field information and the development of conceptual and computational models. Of critical importance in assessing the long term yield of a well is the formation of a seepage face on the side of the well, with the water table a significant distance above the pumping water level. Consequently the water table may only be lowered to about half the depth of the well. The paper concludes with recommendations for the exploitation of groundwater from shallow weathered aquifers to minimise the risk of failure during the dry season.

Soil Water and Shallow Groundwater Relations in an Agricultural Hillslope

NASA Astrophysics Data System (ADS)

Logsdon, S. D.; Schilling, K. E.

2007-12-01

Shallow water tables contribute to soil water variations under rolling topography, and soil properties contribute to shallow water table fluctutations. Preferential flow through large soil pores can cause a rise in the water table with little increase in soil water except near the soil surface. Lateral groundwater flow can cause a large rise in water table at toeslope and depressional landscape positions. As plants transpire, water can move up into the root zone from the water table and wet soil below the root zone. Roots can utilize water in the capillary fringe. The purpose of this study was to interface automated measurements of soil water content and water table depth for determining the importance of drainage and upward movement. In 2006 soil water and water table depth were monitored at three positions: shoulder, backslope, and toeslope. Neutron access tubes were manually monitored to 2.3 m depth, and automated soil moisture was measured using CS616 probes installed at 0.3, 0.5, 0.7, and 0.9 m depth. Water table depths were monitored manually and automated, but the automated measurements failed during the season at two sites. In 2007, similar measurements were made at one toeslope position, but the CS616 probes were installed at nine depths and better quality automated well depth equipment was used. The 2006 data revealed little landscape position effect on daytime soil water loss on a wetter date; however, on a dry day just before a rain, daytime water loss was greatest for the toeslope positon and least for the shoulder position. After a period of intense rain, a rapid and significant water table rise occurred at the toeslope position but little water table rise occurred at the other landscape positions. The rapid toeslope water table rise was likely caused by lateral groundwater flow whereas minor water table rise at the other positions was likely due to preferential flow since the soil had not wet up below 0.6 m. Use of automated equipment has improved our understanding of the relations of soil water to water table fluctuations in an agricultural field.

Using hydraulic heads, geochemistry and 3H to understand river bank infiltration; an example from the Ovens Valley, southeast Australia

NASA Astrophysics Data System (ADS)

Yu, Matthew; Cartwright, Ian

2014-05-01

Defining the relationship between the river and its river bank is important in constraining baseflow to a river and enhancing our ability in protecting water resources and riparian ecology. Hydraulic heads, geochemistry and 3H were measured in river banks along the Ovens River, southeast Australia. The Ovens River is characterised by the transition from a single channel river residing within a mountain valley to a multi-channel meandering river on broad alluvial plains in the lower catchment. The 3H concentrations of most near-river groundwater (less than 10 m from river channel) and bank water (10 - 30 m from the river channel) in the valley range between 1.93 and 2.52 TU. They are similar to those of the river, which are between 2.37 and 2.24 TU. These groundwater also have a Na/Cl ratio of 2.7 - 4.7 and are close to the river Na/Cl ratios. These similarities suggest that most river banks in the valley are recharged by the river. The hydraulic heads and EC values indicate that some of these river banks are recharged throughout the year, while others are only recharged during high flow events. Some near-river groundwater and bank water in the valley have a much lower 3H concentration, ranging from 0.97 to 1.27 TU. They also have a lower Na/Cl ratio of 1.6 - 3.1. These differences imply that some of the river banks in the valley are rarely recharged by the river. The lack of infiltration is supported by the constant head gradient toward the river and the constant EC values in these river banks. The river banks with bank infiltration are located in the first few hundred kilometres in the valley and in the middle catchment where the valley is broaden. In the first few hundred kilometres in the valley, it has a relatively flat landscape and does not allow a high regional water table to form. The river thus is always above the water table and recharges the river banks and the valley aquifers. In the broader valley, the relatively low lateral hydraulic gradient is sometimes reversed during high flow events, causing river to infiltrate the river banks. The river banks with no infiltration are in a location where the river runs in the middle of valley with a relatively steep incised bank. Thus, a strong lateral heads gradient toward the river can from in the bank, preventing river water from infiltration, even during a high flow event.

The thermal impact of subsurface building structures on urban groundwater resources - A paradigmatic example.

PubMed

Epting, Jannis; Scheidler, Stefan; Affolter, Annette; Borer, Paul; Mueller, Matthias H; Egli, Lukas; García-Gil, Alejandro; Huggenberger, Peter

2017-10-15

Shallow subsurface thermal regimes in urban areas are increasingly impacted by anthropogenic activities, which include infrastructure development like underground traffic lines as well as industrial and residential subsurface buildings. In combination with the progressive use of shallow geothermal energy systems, this results in the so-called subsurface urban heat island effect. This article emphasizes the importance of considering the thermal impact of subsurface structures, which commonly is underestimated due to missing information and of reliable subsurface temperature data. Based on synthetic heat-transport models different settings of the urban environment were investigated, including: (1) hydraulic gradients and conductivities, which result in different groundwater flow velocities; (2) aquifer properties like groundwater thickness to aquitard and depth to water table; and (3) constructional features, such as building depths and thermal properties of building structures. Our results demonstrate that with rising groundwater flow velocities, the heat-load from building structures increase, whereas down-gradient groundwater temperatures decrease. Thermal impacts on subsurface resources therefore have to be related to the permeability of aquifers and hydraulic boundary conditions. In regard to the urban settings of Basel, Switzerland, flow velocities of around 1 md -1 delineate a marker where either down-gradient temperature deviations or heat-loads into the subsurface are more relevant. Furthermore, no direct thermal influence on groundwater resources should be expected for aquifers with groundwater thicknesses larger 10m and when the distance of the building structure to the groundwater table is higher than around 10m. We demonstrate that measuring temperature changes down-gradient of subsurface structures is insufficient overall to assess thermal impacts, particularly in urban areas. Moreover, in areas which are densely urbanized, and where groundwater flow velocities are low, appropriate measures for assessing thermal impacts should specifically include a quantification of heat-loads into the subsurface which result in a more diffuse thermal contamination of urban groundwater resources. Copyright © 2017 Elsevier B.V. All rights reserved.

Identifying Stream/Aquifer Exchange by Temperature Gradient in a Guarani Aquifer System Outcrop Zone

NASA Astrophysics Data System (ADS)

Wendland, E.; Rosa, D. M. S.; Anache, J. A. A.; Lowry, C.; Lin, Y. F. F.

2017-12-01

Recharge of the Guarani Aquifer System (GAS) in South America is supposed to occur mainly in the outcrop zones, where the GAS appears as an unconfined aquifer (10% of the 1.2 Million km2 aquifer extension). Previous evaluations of recharge are based essentially on water balance estimates for the whole aquifer area or water table fluctuations in monitoring wells. To gain a more detailed understanding of the recharge mechanisms the present work aimed to study the stream aquifer interaction in a watershed (Ribeirão da Onça) at an outcrop zone. Two Parshall flumes were installed 1.3 km apart for discharge measurement in the stream. Along this distance an optic fiber cable was deployed to identify stretches with gaining and losing behavior. In order to estimate groundwater discharge in specific locations, 8 temperature sticks were set up along the stream reach to measure continuously the vertical temperature gradient. A temperature probe with 4 thermistors was also used to map the shallow streambed temperature gradient manually along the whole distance. The obtained results show a discharge difference of 250 m3/h between both flumes. Since the last significant rainfall (15 mm) in the watershed occurred 3 months ago, this value can be interpreted as the base flow contribution to the stream during the dry season. Given the temperature difference between groundwater ( 24oC) and surface water ( 17oC) the fiber-optic distributed temperature sensing (FO-DTS) allowed the identification of stretches with gaining behavior. Temperature gradients observed at the streambed varied between 0.67 and 14.33 oC/m. The study demonstrated that heat may be used as natural tracer even in tropical conditions, where the groundwater temperature is higher than the surface water temperature during the winter. The obtained results show that the discharge difference between both flumes can not be extrapolated without detailed analysis. Gaining and loosing stretches have to be identified on order to estimate total base flow contribution of the watershed. This result is important to correct the water balance of the system.

Incorporating water table dynamics in climate modeling: 1. Water table observations and equilibrium water table simulations

NASA Astrophysics Data System (ADS)

Fan, Ying; Miguez-Macho, Gonzalo; Weaver, Christopher P.; Walko, Robert; Robock, Alan

2007-05-01

Soil moisture is a key participant in land-atmosphere interactions and an important determinant of terrestrial climate. In regions where the water table is shallow, soil moisture is coupled to the water table. This paper is the first of a two-part study to quantify this coupling and explore its implications in the context of climate modeling. We examine the observed water table depth in the lower 48 states of the United States in search of salient spatial and temporal features that are relevant to climate dynamics. As a means to interpolate and synthesize the scattered observations, we use a simple two-dimensional groundwater flow model to construct an equilibrium water table as a result of long-term climatic and geologic forcing. Model simulations suggest that the water table depth exhibits spatial organization at watershed, regional, and continental scales, which may have implications for the spatial organization of soil moisture at similar scales. The observations suggest that water table depth varies at diurnal, event, seasonal, and interannual scales, which may have implications for soil moisture memory at these scales.

Emulation of recharge and evapotranspiration processes in shallow groundwater systems

NASA Astrophysics Data System (ADS)

Doble, Rebecca C.; Pickett, Trevor; Crosbie, Russell S.; Morgan, Leanne K.; Turnadge, Chris; Davies, Phil J.

2017-12-01

In shallow groundwater systems, recharge and evapotranspiration are highly sensitive to changes in the depth to water table. To effectively model these fluxes, complex functions that include soil and vegetation properties are often required. Model emulation (surrogate modelling or meta-modelling) can provide a means of incorporating detailed conceptualisation of recharge and evapotranspiration processes, while maintaining the numerical tractability and computational performance required for regional scale groundwater models and uncertainty analysis. A method for emulating recharge and evapotranspiration processes in groundwater flow models was developed, and applied to the South East region of South Australia and western Victoria, which is characterised by shallow groundwater, wetlands and coastal lakes. The soil-vegetation-atmosphere transfer (SVAT) model WAVES was used to generate relationships between net recharge (diffuse recharge minus evapotranspiration from groundwater) and depth to water table for different combinations of climate, soil and land cover types. These relationships, which mimicked previously described soil, vegetation and groundwater behaviour, were combined into a net recharge lookup table. The segmented evapotranspiration package in MODFLOW was adapted to select values of net recharge from the lookup table depending on groundwater depth, and the climate, soil and land use characteristics of each cell. The model was found to be numerically robust in steady state testing, had no major increase in run time, and would be more efficient than tightly-coupled modelling approaches. It made reasonable predictions of net recharge and groundwater head compared with remotely sensed estimates of net recharge and a standard MODFLOW comparison model. In particular, the method was better able to predict net recharge and groundwater head in areas with steep hydraulic gradients.

40 CFR Appendix - Tables to Part 132

Code of Federal Regulations, 2010 CFR

2010-07-01

... Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) WATER PROGRAMS WATER QUALITY GUIDANCE FOR THE GREAT... Tables to Part 132 Table 1—Acute Water Quality Criteria for Protection of Aquatic Life in Ambient Water... FR 35286, June 2, 2000] Table 2—Chronic Water Quality Criteria for Protection of Aquatic Life in...

Study on hydraulic property models for water retention and unsaturated hydraulic conductivity in MATSIRO with representation of water table dynamics

NASA Astrophysics Data System (ADS)

Yoshida, N.; Oki, T.

2016-12-01

Appropriate initial condition of soil moisture and water table depth are important factors to reduce uncertainty in hydrological simulations. Approaches to determine the initial water table depth have been developed because of difficulty to get information on global water table depth and soil moisture distributions. However, how is equilibrium soil moisture determined by climate conditions? We try to discuss this issue by using land surface model with representation of water table dynamics (MAT-GW). First, the global pattern of water table depth at equilibrium soil moisture in MAT-GW was verified. The water table depth in MAT-GW was deeper than the previous one at fundamentally arid region because the negative recharge and continuous baseflow made water table depth deeper. It indicated that the hydraulic conductivity used for estimating recharge and baseflow need to be reassessed in MAT-GW. In soil physics field, it is revealed that proper hydraulic property models for water retention and unsaturated hydraulic conductivity should be selected for each soil type. So, the effect of selecting hydraulic property models on terrestrial soil moisture and water table depth were examined.Clapp and Hornburger equation(CH eq.) and Van Genuchten equation(VG eq.) were used as representative hydraulic property models. Those models were integrated on MAT-GW and equilibrium soil moisture and water table depth with using each model were compared. The water table depth and soil moisture at grids which reached equilibrium in both simulations were analyzed. The equilibrium water table depth were deeper in VG eq. than CH eq. in most grids due to shape of hydraulic property models. Then, total soil moisture were smaller in VG eq. than CH eq. at almost all grids which water table depth reached equilibrium. It is interesting that spatial patterns which water table depth reached equilibrium or not were basically similar in both simulations but reverse patterns were shown in east and west part of America. Selection of each hydraulic property model based on soil types may compensate characteristic of models in initialization.

Hydrogeologic investigation of the Malvern TCE Superfund Site, Chester County, Pennsylvania

USGS Publications Warehouse

Sloto, Ronald A.

1997-01-01

The Malvern TCE Superfund Site, a former solvent recycling facility that now stores and sells solvents, consists of a plant and disposal area, which are approximately 1,900 ft (feet) apart. The site is underlain by an unconfined carbonate bedrock aquifer in which permeability has been enhanced in places by solution. Water levels respond quickly to precipitation and show a similar seasonal variation, response to precipitation, and range of fluctuation. The altitude of water levels in wells at the disposal area is nearly identical because of the small hydraulic gradient. A comparison of water-table maps for 1983, 1993, and 1994 shows that the general shape of the water table and hydraulic gradients in the area have remained the same through time and for different climatic conditions.The plant area is underlain by dolomite of the Elbrook Formation. The dolomite at the plant area does not yield as much water as the dolomite at the disposal area because it is less fractured, and wells penetrate few water-bearing fractures. Yields of nine wells at the plant area range from 1 to 200 gal/min (gallons per minute); the median yield is 6 gal/min. Specific capacities range from 0.08 to 2 (gal/min)/ft (gallons per minute per foot). Aquifer tests were conducted in two wells; median transmissivities estimated from the aquifer-test data ranged from 528 to 839 feet squared per day. Maximum concentrations of volatile organic compounds (VOC's) in ground water at the plant area in 1996 were 53,900 ug/L (micrograms per liter) for trichloroethylene (TCE), 7,110 ug/L for tetrachloroethylene (PCE), and 17,700 ug/L for 1,1,1-trichloroethane (TCA).A ground-water divide is located between the plant area and the disposal area. Ground-water withdrawal for dewatering the Catanach quarry has caused a cone of depression in the water-table surface that reaches to the plant area. From the plant area, ground water flows 1.2 miles to the northeast and discharges to the Catanach quarry. The regional hydraulic gradient between the plant and the Catanach quarry is 0.019. Concentrations of VOC's in water from wells drilled northeast and donwgradient of the plant property boundary are one to two orders of magnitude less than concentrations in water from wells less than 100 ft away at the plant.A capture-zone analysis was performed for two wells at the plant area. The analysis showed that pumping well CC-19 at 20 gal/min would be sufficient to capture all ground-water flow from the plant area. Although water from other wells at the plant site contains higher concentrations of VOC's than water from well CC-19, pumping well CC-19 would induce the flow of water with higher concentrations of VOC's; however, pumping well CC-19 might causes VOC's to move lower into the aquifer.The disposal area is underlain by the Ledger Dolomite. The dolomite at the disposal area is much more fractured than the dolomite at the plant area. Although many of the fractures are filled or partially filled with clay, the dolomite at the disposal area yields more water than the dolomite at the plant area. Yields of eight wells at the disposal area range from 15 to more than 200 gal/min; the median yield is greater than 100 gal/min. Specific capacities range from 2 to 280 (gal/min)/ft. Aquifer tests were conducted in two wells; estimated transimissivities were 34,900 and 56,300 feet squared per day. Concentrations of VOC's in ground water are lower at the disposal area than at the plant area. Water samples collected from wells at the disposal area in 1996 had maximum concentrations of TCE of 768 ug/L, PCE of 111 ug/L, and TCA of 108 ug/L. These concentrations are lower than concentrations in water samples collected before cleanup of drums in the disposal area was completed in 1984.Ground water from the disposal area flows south-southeast toward Valley Creek. The hydraulic gradient between the disposal area and Valley Creek is 0.001. A well-defined plume of VOC’s in ground water extends downgradient from the disposal area toward Valley Creek. A comparison of data from 1995 to 1996 with data from 1981 to 1984 shows that concentrations of TCE, PCE, and TCA in water from most off-site wells have decreased and that water from fewer wells contains detectable concentrations of those compounds.A capture-zone analysis was performed for three wells at the disposal area. The analysis showed that pumping wells CC-16, CC-17, and CC-18 at a combined rate of 270 gal/min would form a capture zone ranging from approximately 443 to 477 ft wide at a distance 500 ft upgradient from the center of the pumping wells. Pumping wells CC-16 and CC-17 together at a combined rate of 172 gal/min would form a capture zone ranging from approximately 172 to 400 ft wide at a distance 500 ft upgradient from the center of the pumping wells.

Mapping a Pristine Glaciofluvial Aquifer on the Canadian Shield Using Ground-Penetrating Radar and Electrical Resistivity Tomography

NASA Astrophysics Data System (ADS)

Graves, L. W.; Shirokova, V.; Bank, C.

2013-12-01

Our study aims to construct a 3D structural model of an unconfined pristine aquifer in Laurentian Hills, Ontario, Canada. The stratigraphy of the study site, which covers about 5400 square meters, features reworked glaciofluvial sands and glacial till on top of Canadian Shield bedrock. A network of 25 existing piezometers provides ground-truth. We used two types of geophysical surveys to map the water table and the aquifer basin. Ground-penetrating radar (GPR) collected 40 profiles over distances up to 140 meters using 200MHz and 400MHz antennas with a survey wheel. The collected radargrams show a distinct reflective layer, which can be mapped to outcrops of glacial till within the area. This impermeable interface forms the aquitard. Depths of the subsurface features were calculated using hyperbolic fits on the radargrams in Matlab by determining wave velocity then converting measured two-way-time to depth. Electrical resistivity was used to determine the water table elevations because the unconfined water table did not reflect the radar waves. 20 resistivity profiles were collected in the same area using Wenner-Alpha and dipole-dipole arrays with both 24 and 48 electrodes and for 0.5, 0.75, 1.0 and 2.0 meter spacing. The inverted resistivity models show low resistivity values (<1000 Ohm.m) below 2 to 5 meter depths and higher resistivity values (2000-6000 Ohm.m) above 1 to 2 meter depths. These contrasting resistivity values correspond to saturated and wet sand (lower resistivity) to dry sand (higher resistivity); a correlation we could verify with several bore-hole logs. The water table is marked on the resistivity profiles as a steep resistivity gradient, and the depth can be added to the comprehensive 3D model. This model also incorporates hydrogeological characteristics and geochemical anomalies found within the aquifer. Ongoing seasonal and annual monitoring of the aquifer using geophysical methods will bring a fourth dimension to our understanding of this dynamic system. GPR Profile with Glacial Till Interface.

Estimated Depth to Ground Water and Configuration of the Water Table in the Portland, Oregon Area

USGS Publications Warehouse

Snyder, Daniel T.

2008-01-01

Reliable information on the configuration of the water table in the Portland metropolitan area is needed to address concerns about various water-resource issues, especially with regard to potential effects from stormwater injection systems such as UIC (underground injection control) systems that are either existing or planned. To help address these concerns, this report presents the estimated depth-to-water and water-table elevation maps for the Portland area, along with estimates of the relative uncertainty of the maps and seasonal water-table fluctuations. The method of analysis used to determine the water-table configuration in the Portland area relied on water-level data from shallow wells and surface-water features that are representative of the water table. However, the largest source of available well data is water-level measurements in reports filed by well constructors at the time of new well installation, but these data frequently were not representative of static water-level conditions. Depth-to-water measurements reported in well-construction records generally were shallower than measurements by the U.S. Geological Survey (USGS) in the same or nearby wells, although many depth-to-water measurements were substantially deeper than USGS measurements. Magnitudes of differences in depth-to-water measurements reported in well records and those measured by the USGS in the same or nearby wells ranged from -119 to 156 feet with a mean of the absolute value of the differences of 36 feet. One possible cause for the differences is that water levels in many wells reported in well records were not at equilibrium at the time of measurement. As a result, the analysis of the water-table configuration relied on water levels measured during the current study or used in previous USGS investigations in the Portland area. Because of the scarcity of well data in some areas, the locations of select surface-water features including major rivers, streams, lakes, wetlands, and springs representative of where the water table is at land surface were used to augment the analysis. Ground-water and surface-water data were combined for use in interpolation of the water-table configuration. Interpolation of the two representations typically used to define water-table position - depth to the water table below land surface and elevation of the water table above a datum - can produce substantially different results and may represent the end members of a spectrum of possible interpolations largely determined by the quantity of recharge and the hydraulic properties of the aquifer. Datasets of depth-to-water and water-table elevation for the current study were interpolated independently based on kriging as the method of interpolation with parameters determined through the use of semivariograms developed individually for each dataset. Resulting interpolations were then combined to create a single, averaged representation of the water-table configuration. Kriging analysis also was used to develop a map of relative uncertainty associated with the values of the water-table position. Accuracy of the depth-to-water and water-table elevation maps is dependent on various factors and assumptions pertaining to the data, the method of interpolation, and the hydrogeologic conditions of the surficial aquifers in the study area. Although the water-table configuration maps generally are representative of the conditions in the study area, the actual position of the water-table may differ from the estimated position at site-specific locations, and short-term, seasonal, and long-term variations in the differences also can be expected. The relative uncertainty map addresses some but not all possible errors associated with the analysis of the water-table configuration and does not depict all sources of uncertainty. Depth to water greater than 300 feet in the Portland area is limited to parts of the Tualatin Mountains, the foothills of the Cascade Range, and muc

Evaluating the Classical Versus an Emerging Conceptual Model of Peatland Methane Dynamics

NASA Astrophysics Data System (ADS)

Yang, Wendy H.; McNicol, Gavin; Teh, Yit Arn; Estera-Molina, Katerina; Wood, Tana E.; Silver, Whendee L.

2017-09-01

Methane (CH4) is a potent greenhouse gas that is both produced and consumed in soils by microbially mediated processes sensitive to soil redox. We evaluated the classical conceptual model of peatland CH4 dynamics—in which the water table position determines the vertical distribution of methanogenesis and methanotrophy—versus an emerging model in which methanogenesis and methanotrophy can both occur throughout the soil profile due to spatially heterogeneous redox and anaerobic CH4 oxidation. We simultaneously measured gross CH4 production and oxidation in situ across a microtopographical gradient in a drained temperate peatland and ex situ along the soil profile, giving us novel insight into the component fluxes of landscape-level net CH4 fluxes. Net CH4 fluxes varied among landforms (p < 0.001), ranging from 180.3 ± 81.2 mg C m-2 d-1 in drainage ditches to -0.7 ± 1.2 mg C m-2 d-1 in the highest landform. Contrary to prediction by the classical conceptual model, variability in methanogenesis alone drove the landscape-level net CH4 flux patterns. Consistent with the emerging model, freshly collected soils from above the water table produced CH4 within anaerobic microsites. Even in soil from beneath the water table, gross CH4 production was best predicted by the methanogenic fraction of carbon mineralization, an index of highly reducing microsites. We measured low rates of anaerobic CH4 oxidation, which may have been limited by relatively low in situ CH4 concentrations in the hummock/hollow soil profile. Our study revealed complex CH4 dynamics better represented by the emerging heterogeneous conceptual model than the classical model based on redox strata.

A computer program for predicting recharge with a master recession curve

USGS Publications Warehouse

Heppner, Christopher S.; Nimmo, John R.

2005-01-01

Water-table fluctuations occur in unconfined aquifers owing to ground-water recharge following precipitation and infiltration, and ground-water discharge to streams between storm events. Ground-water recharge can be estimated from well hydrograph data using the water-table fluctuation (WTF) principle, which states that recharge is equal to the product of the water-table rise and the specific yield of the subsurface porous medium. The water-table rise, however, must be expressed relative to the water level that would have occurred in the absence of recharge. This requires a means for estimating the recession pattern of the water-table at the site. For a given site there is often a characteristic relation between the water-table elevation and the water-table decline rate following a recharge event. A computer program was written which extracts the relation between decline rate and water-table elevation from well hydrograph data and uses it to construct a master recession curve (MRC). The MRC is a characteristic water-table recession hydrograph, representing the average behavior for a declining water-table at that site. The program then calculates recharge using the WTF method by comparing the measured well hydrograph with the hydrograph predicted by the MRC and multiplying the difference at each time step by the specific yield. This approach can be used to estimate recharge in a continuous fashion from long-term well records. Presented here is a description of the code including the WTF theory and instructions for running it to estimate recharge with continuous well hydrograph data.

Effect of Water-Table Fluctuations on Source Depletion and Dissolved-Plume Behavior of a Multi-Component Light Nonaqueous-Phase Liquid

NASA Astrophysics Data System (ADS)

Dobson, R.; Schroth, M. H.; Zeyer, J.

2006-12-01

Light nonaqueous-phase liquids (LNAPLs) such as gasoline and diesel are among the most common soil and groundwater contaminants. Dissolution and subsequent advective transport of LNAPL components can negatively impact downgradient water supplies, while biodegradation is commonly thought to be an important sink for this class of contaminants. Water-table fluctuations, either naturally occurring or intentionally induced, may affect LNAPL component transport and biodegradation in aquifers. We present a laboratory investigation of the effect of water-table fluctuations on the dissolution and biodegradation of a multi-component LNAPL in a pair of similar model aquifers, one of which was subjected to a water-table fluctuation. Water-table fluctuation resulted in LNAPL and air entrapment below the water table, an increase in the vertical extent of LNAPL contamination and an increase in the volume of water passing through the contaminated zone. Effluent concentrations of dissolved LNAPL components were higher and those of dissolved nitrate were lower in the aquifer model where a fluctuation had been induced. Thus, water table fluctuation led to enhanced LNAPL dissolution as well as enhanced biodegradation activity. The increase in biodegradation observed after fluctuation was of lesser magnitude than the increase in LNAPL dissolution, such that water-table fluctuations might be expected to result in increased exposure of downgradient receptors to dissolved LNAPL components. Conversely, the potential for free-phase LNAPL migration was reduced following a water-table fluctuation, as LNAPL entrapment by the rising water table reduced the amount of free phase LNAPL. Lateral migration of LNAPL following emplacement was observed in the model aquifer where no fluctuation occurred, but not in the model aquifer where a water-table fluctuation was induced.

A validation of the 3H/3He method for determining groundwater recharge

NASA Astrophysics Data System (ADS)

Solomon, D. K.; Schiff, S. L.; Poreda, R. J.; Clarke, W. B.

1993-09-01

Tritium and He isotopes have been measured at a site where groundwater flow is nearly vertical for a travel time of 100 years and where recharge rates are spatially variable. Because the mid-1960s 3H peak (arising from aboveground testing of thermonuclear devices) is well-defined, the vertical groundwater velocity is known with unusual accuracy at this site. Utilizing 3H and its stable daughter 3He to determine groundwater ages, we compute a recharge rate of 0.16 m/yr, which agrees to within about 5% of the value based on the depth of the 3H peak (measured both in 1986 and 1991) and two-dimensional modeling in an area of high recharge. Zero 3H/3He age occurs at a depth that is approximately equal to the average depth of the annual low water table, even though the capillary fringe extends to land surface during most of the year at the study site. In an area of low recharge (0.05 m/yr) where the 3H peak (and hence the vertical velocity) is also well-defined, the 3H/3He results could not be used to compute recharge because samples were not collected sufficiently far above the 3H peak; however, modeling indicates that the 3H/3He age gradient near the water table is an accurate measure of vertical velocities in the low-recharge area. Because 3H and 3He have different diffusion coefficients, and because the amount of mechanical mixing is different in the area of high recharge than in the low-recharge area, we have separated the dispersive effects of mechanical mixing from molecular diffusion. We estimate a longitudinal dispersivity of 0.07 m and effective diffusion coefficients for 3H (3HHO) and 3He of 2.4×10-5 and 1.3×10-4 m2/day, respectively. Although the 3H/3He age gradient is an excellent indicator of vertical groundwater velocities above the mid-1960s 3H peak, dispersive mixing and diffusive loss of 3He perturb the age gradient near and below the 3H peak.

Water table dynamics in undisturbed, drained and restored blanket peat

NASA Astrophysics Data System (ADS)

Holden, J.; Wallage, Z. E.; Lane, S. N.; McDonald, A. T.

2011-05-01

SummaryPeatland water table depth is an important control on runoff production, plant growth and carbon cycling. Many peatlands have been drained but are now subject to activities that might lead to their restoration including the damming of artificial drains. This paper investigates water table dynamics on intact, drained and restored peatland slopes in a blanket peat in northern England using transects of automated water table recorders. Long-term (18 month), seasonal and short-term (storm event) records are explored. The restored site had drains blocked 6 years prior to monitoring commencing. The spatially-weighted mean water table depths over an 18 month period were -5.8 cm, -8.9 cm and -11.5 cm at the intact, restored and drained sites respectively. Most components of water table behaviour at the restored site, including depth exceedance probability curves, seasonality of water table variability, and water table responses to individual rainfall events were intermediate between that of the drained and intact sites. Responses also depended on location with respect to the drains. The results show that restoration of drained blanket peat is difficult and the water table dynamics may not function in the same way as those in undisturbed blanket peat even many years after management intervention. Further measurement of hydrological processes and water table responses to peatland restoration are required to inform land managers of the hydrological success of those projects.

Hydrologic regulation of plant rooting depth

PubMed Central

Miguez-Macho, Gonzalo; Jobbágy, Esteban G.; Jackson, Robert B.; Otero-Casal, Carlos

2017-01-01

Plant rooting depth affects ecosystem resilience to environmental stress such as drought. Deep roots connect deep soil/groundwater to the atmosphere, thus influencing the hydrologic cycle and climate. Deep roots enhance bedrock weathering, thus regulating the long-term carbon cycle. However, we know little about how deep roots go and why. Here, we present a global synthesis of 2,200 root observations of >1,000 species along biotic (life form, genus) and abiotic (precipitation, soil, drainage) gradients. Results reveal strong sensitivities of rooting depth to local soil water profiles determined by precipitation infiltration depth from the top (reflecting climate and soil), and groundwater table depth from below (reflecting topography-driven land drainage). In well-drained uplands, rooting depth follows infiltration depth; in waterlogged lowlands, roots stay shallow, avoiding oxygen stress below the water table; in between, high productivity and drought can send roots many meters down to the groundwater capillary fringe. This framework explains the contrasting rooting depths observed under the same climate for the same species but at distinct topographic positions. We assess the global significance of these hydrologic mechanisms by estimating root water-uptake depths using an inverse model, based on observed productivity and atmosphere, at 30″ (∼1-km) global grids to capture the topography critical to soil hydrology. The resulting patterns of plant rooting depth bear a strong topographic and hydrologic signature at landscape to global scales. They underscore a fundamental plant–water feedback pathway that may be critical to understanding plant-mediated global change. PMID:28923923

Hydrologic regulation of plant rooting depth.

PubMed

Fan, Ying; Miguez-Macho, Gonzalo; Jobbágy, Esteban G; Jackson, Robert B; Otero-Casal, Carlos

2017-10-03

Plant rooting depth affects ecosystem resilience to environmental stress such as drought. Deep roots connect deep soil/groundwater to the atmosphere, thus influencing the hydrologic cycle and climate. Deep roots enhance bedrock weathering, thus regulating the long-term carbon cycle. However, we know little about how deep roots go and why. Here, we present a global synthesis of 2,200 root observations of >1,000 species along biotic (life form, genus) and abiotic (precipitation, soil, drainage) gradients. Results reveal strong sensitivities of rooting depth to local soil water profiles determined by precipitation infiltration depth from the top (reflecting climate and soil), and groundwater table depth from below (reflecting topography-driven land drainage). In well-drained uplands, rooting depth follows infiltration depth; in waterlogged lowlands, roots stay shallow, avoiding oxygen stress below the water table; in between, high productivity and drought can send roots many meters down to the groundwater capillary fringe. This framework explains the contrasting rooting depths observed under the same climate for the same species but at distinct topographic positions. We assess the global significance of these hydrologic mechanisms by estimating root water-uptake depths using an inverse model, based on observed productivity and atmosphere, at 30″ (∼1-km) global grids to capture the topography critical to soil hydrology. The resulting patterns of plant rooting depth bear a strong topographic and hydrologic signature at landscape to global scales. They underscore a fundamental plant-water feedback pathway that may be critical to understanding plant-mediated global change.

Hydrologic regulation of plant rooting depth

NASA Astrophysics Data System (ADS)

Fan, Ying; Miguez-Macho, Gonzalo; Jobbágy, Esteban G.; Jackson, Robert B.; Otero-Casal, Carlos

2017-10-01

Plant rooting depth affects ecosystem resilience to environmental stress such as drought. Deep roots connect deep soil/groundwater to the atmosphere, thus influencing the hydrologic cycle and climate. Deep roots enhance bedrock weathering, thus regulating the long-term carbon cycle. However, we know little about how deep roots go and why. Here, we present a global synthesis of 2,200 root observations of >1,000 species along biotic (life form, genus) and abiotic (precipitation, soil, drainage) gradients. Results reveal strong sensitivities of rooting depth to local soil water profiles determined by precipitation infiltration depth from the top (reflecting climate and soil), and groundwater table depth from below (reflecting topography-driven land drainage). In well-drained uplands, rooting depth follows infiltration depth; in waterlogged lowlands, roots stay shallow, avoiding oxygen stress below the water table; in between, high productivity and drought can send roots many meters down to the groundwater capillary fringe. This framework explains the contrasting rooting depths observed under the same climate for the same species but at distinct topographic positions. We assess the global significance of these hydrologic mechanisms by estimating root water-uptake depths using an inverse model, based on observed productivity and atmosphere, at 30″ (˜1-km) global grids to capture the topography critical to soil hydrology. The resulting patterns of plant rooting depth bear a strong topographic and hydrologic signature at landscape to global scales. They underscore a fundamental plant-water feedback pathway that may be critical to understanding plant-mediated global change.

Rumsey and Walker_AMT_2016_Table 1

EPA Pesticide Factsheets

Table summarizes instrument analytical detection limits, including liquid and equivalent air concentrations.This dataset is associated with the following publication:Rumsey, I. Application of an online ion chromatography-based instrument for gradient flux measurements of speciated nitrogen and sulfur. ENVIRONMENTAL SCIENCE & TECHNOLOGY. American Chemical Society, Washington, DC, USA, 9(6): 2581-2592, (2016).

The Dependence of Peat Soil Hydraulic Conductivity on Dominant Vegetation Type in Mountain Fens

NASA Astrophysics Data System (ADS)

Crockett, A. C.; Ronayne, M. J.; Cooper, D. J.

2014-12-01

The peat soil within fen wetlands provides water storage that can substantially influence the hydrology of mountain watersheds. In this study, we investigated the relationship between hydraulic conductivity and vegetation type for fens occurring in Rocky Mountain National Park (RMNP), Colorado, USA. Vegetation in RMNP fens can be dominated by woody plants and shrubs, such as willows; by mosses; or by herbaceous plants such as sedges. Fens dominated by each vegetation type were selected for study. Six fens were investigated, all of which are in the Colorado River watershed on the west side of RMNP. For each site, soil hydraulic conductivity was measured at multiple locations using a single-ring infiltrometer. As a result of the shallow water table in these fens (the water table was always within 10 cm of the surface), horizontal hydraulic gradients were produced during the field tests. The measured infiltration rates were analyzed using the numerical model HYDRUS. In order to determine the hydraulic conductivity, a parameter estimation problem was solved using HYDRUS as the forward simulator. Horizontal flow was explicitly accounted for in the model. This approach produced more accurate estimates of hydraulic conductivity than would be obtained using an analytical solution that assumes strictly vertical flow. Significant differences in hydraulic properties between fens appear to result at least in part from the effects of different dominant vegetation types on peat soil formation.

Ecohydrologic Separation of Plant Life Forms Across A Soil Moisture Gradient in a Montane Wetland

NASA Astrophysics Data System (ADS)

Mercer, J.; Millar, D.; Williams, D. G.

2016-12-01

Sources of water used by plants can differ from those that flow to groundwater and streams. Such ecohydrologic separation forms the basis for the "two water worlds hypothesis" that challenges commonly held notions of how water moves through terrestrial ecosystems. Yet, recent observations in a humid, low energy wetland environment did not support the presence of ecohydrologic separation. These contrasting results, in the context of general physical principles, suggest that energy gradients along the soil-plant-atmosphere continuum may play a role in defining the magnitude of ecohydrologic separation. We quantified ecohydrologic separation in a montane wetland with pronounced hummocks and hollows located in southeastern Wyoming. The rooting zone in this wetland is fully saturated during the spring, but is prone to water table draw-downs (> 1 m) during the summer, likely producing significant water potential differences between plant and soil water pools. We predict that wetland vegetation will express some degree of ecohydrologic separation, but such expression will differ based on microtopgraphic position and the rooting strategy of different plant life form (i.e., trees, shrubs, graminoids). For example, shallowly rooted graminoids on raised hummocks may use water that is distinctly different from that located in wetter hollows, with water in hollows being more isotopically similar to water leaving the wetland via surface water flows. We collected xylem water from dominant plant life forms in hummocks and hollows, free water (via piezometers) and bulk soil water at depths of 20 and 60 cm, as well as surface water and groundwater. Stable isotope ratios of H and O were determined from samples by either laser spectroscopy or isotope ratio mass spectrometry. Our expected results suggest that most of the water being used by wetland plants will be similar to that leaving the wetland via surface flow. In the context of their being two water worlds in the surrounding forested uplands, we suggest that mountain wetlands may play a more important role in provisioning streamflow than previously thought.

Integrated approach for demarcating subsurface pollution and saline water intrusion zones in SIPCOT area: a case study from Cuddalore in Southern India.

PubMed

Sankaran, S; Sonkamble, S; Krishnakumar, K; Mondal, N C

2012-08-01

This paper deals with a systematic hydrogeological, geophysical, and hydrochemical investigations carried out in SIPCOT area in Southern India to demarcate groundwater pollution and saline intrusion through Uppanar River, which flows parallel to sea coast with high salinity (average TDS 28, 870 mg/l) due to back waters as well as discharge of industrial and domestic effluents. Hydrogeological and geophysical investigations comprising topographic survey, self-potential, multi-electrode resistivity imaging, and water quality monitoring were found the extent of saline water intrusion in the south and pockets of subsurface pollution in the north of the study area. Since the area is beset with highly permeable unconfined quaternary alluvium forming potential aquifer at shallow depth, long-term excessive pumping and influence of the River have led to lowering of the water table and degradation of water quality through increased salinity there by generating reversal of hydraulic gradient in the south. The improper management of industrial wastes and left over chemicals by closed industries has led surface and subsurface pollution in the north of the study area.

A physical framework for evaluating net effects of wet meadow restoration on late summer streamflow

NASA Astrophysics Data System (ADS)

Grant, G.; Nash, C.; Selker, J. S.; Lewis, S.; Noël, P.

2017-12-01

Restoration of degraded wet meadows that develop on upland valley floors is intended to achieve a range of ecological benefits. A widely cited benefit is the potential for meadow restoration to augment late-season streamflow; however, there has been little field data demonstrating increased summer flows following restoration. Instead, the hydrologic consequences of restoration have typically been explored using coupled groundwater and surface water flow models at instrumented sites. The expected magnitude and direction of change provided by models has, however, been inconclusive. Here, we assess the streamflow benefit that can be obtained by wet meadow restoration using a parsimonious, physically-based approach. We use a one-dimensional linearized Boussinesq equation with a superimposed solution for changes in storage due to groundwater upwelling and and explicitly calculate evapotranspiration using the White Method. The model accurately predicts water table elevations from field data in the Middle Fork John Day watershed in Oregon, USA. The full solution shows that while raising channel beds can increase total water storage via increases in water table elevation in upland valley bottoms, the contributions of both lateral and longitudinal drainage from restored floodplains to late summer streamflow are undetectably small, while losses in streamflow due to greater transpiration, lower hydraulic gradients, and less drainable pore volume are substantial. Although late-summer streamflow increases should not be expected as a direct result of wet meadow restoration, these approaches offer benefits for improving the quality and health of riparian and meadow vegetation that would warrant considering such measures, even at the cost of increased water demand and reduced streamflow.

Effect of irrigation water salinity and sodicity and water table position on water table chemistry beneath Atriplex lentiformis and Hordeum marinum

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

Browning, L.S.; Bauder, J.W.; Phelps, S.D.

2006-04-15

Coal bed methane (CBM) extraction in Montana and Wyoming's Powder River Basin (PRB) produces large quantities of modestly saline-sodic water. This study assessed effects of irrigation water quality and water table position on water chemistry of closed columns, simulating a perched or a shallow water table. The experiment assessed the potential salt loading in areas where shallow or perched water tables prevent leaching or where artificial drainage is not possible. Water tables were established in sand filled PVC columns at 0.38, 0.76, and1.14 m below the surface, after which columns were planted to one of three species, two halophytic Atriplexmore » spp. and Hordeum marinum Huds. (maritime barley), a glycophyte. As results for the two Atriplex ssp. did not differ much, only results from Atriplex lentiformis (Torn) S. Wats. (big saltbush) and H. marinum are presented. Irrigation water representing one of two irrigation sources was used: Powder River (PR) (electrolytic conductivity (EC) = 0.19 Sm{sup -1}, sodium adsorption ratio (SAR) = 3.5) or CBM water (EC = 0.35 Sm-1, SAR = 10.5). Continuous irrigation with CBM and PR water led to salt loading over time, the extent being proportional to the salinity and sodicity of applied water. Water in columns planted to A. lentiformis with water tables maintained at 0.38 m depth had greater EC and SAR values than those with 0.76 and 1.14 m water table positions. Elevated EC and SAR values most likely reflect the shallow rooted nature of A. lentiformis, which resulted in enhanced ET with the water table close to the soil surface.« less

Direction of ground-water flow in the surficial aquifer in the vicinity of impact areas G-10 and K-2, Camp Lejeune Marine Corps Base, North Carolina, 2004

USGS Publications Warehouse

Harden, Stephen L.; Howe, Stephen S.; Terziotti, Silvia

2004-01-01

Marine Corps Base Camp Lejeune is located in Onslow County in the North Carolina Coastal Plain. In support of North Carolina Department of Environment and Natural Resource requirements, Camp Lejeune is developing a site closure plan for two Resource Conservation and Recovery Act (RCRA) regulated open burn/open detonation (OB/OD) facilities located within Impact Area K-2 and Impact Area G-10, respectively. Both Impact Areas are used for training activities involving live artillery fire. The two OB/OD facilities are used to treat RCRA regulated waste munitions. To provide Base officials with information needed for assessing the quality of ground water at these sites, hydrologic data were used to characterize groundwater flow directions and hydraulic gradients in the surficial aquifer underlying the Impact Areas. Water-level data in the unconfined surficial aquifer and potentiometric head data in the underlying Castle Hayne aquifer were compiled from existing and newly drilled wells. Water-table contour maps were developed for Impact Areas K-2 and G-10 to examine the direction of ground-water flow in the surficial aquifer. The primary directions of ground-water flow beneath K-2 are southward and eastward toward discharge zones along the New River and its tributaries. Beneath interior areas of G-10, water in the surficial aquifer flows outward in all directions toward discharge zones along local streams that drain westward to the New River or to streams that drain southward and eastward to the Intracoastal Waterway and the Atlantic Ocean. Long-term water-level data for the period October 1994 through September 2004 at selected Camp Lejeune well sites were used to examine trends in ground-water levels and vertical hydraulic gradients between the surficial and Castle Hayne aquifers. Evaluation of water-level data for three wells in the surficial aquifer indicated no significant trends for this period of record. The apparent water-level declines in two of the three Castle Hayne wells examined are likely the result of local pumping of the Castle Hayne aquifer. Vertical hydraulic gradients determined for two well cluster sites indicate a downward flow of water from the surficial aquifer into the underlying Castle Hayne aquifer.

TOPMODEL simulations of streamflow and depth to water table in Fishing Brook Watershed, New York, 2007-09

USGS Publications Warehouse

Nystrom, Elizabeth A.; Burns, Douglas A.

2011-01-01

TOPMODEL uses a topographic wetness index computed from surface-elevation data to simulate streamflow and subsurface-saturation state, represented by the saturation deficit. Depth to water table was computed from simulated saturation-deficit values using computed soil properties. In the Fishing Brook Watershed, TOPMODEL was calibrated to the natural logarithm of streamflow at the study area outlet and depth to water table at Sixmile Wetland using a combined multiple-objective function. Runoff and depth to water table responded differently to some of the model parameters, and the combined multiple-objective function balanced the goodness-of-fit of the model realizations with respect to these parameters. Results show that TOPMODEL reasonably simulated runoff and depth to water table during the study period. The simulated runoff had a Nash-Sutcliffe efficiency of 0.738, but the model underpredicted total runoff by 14 percent. Depth to water table computed from simulated saturation-deficit values matched observed water-table depth moderately well; the root mean squared error of absolute depth to water table was 91 millimeters (mm), compared to the mean observed depth to water table of 205 mm. The correlation coefficient for temporal depth-to-water-table fluctuations was 0.624. The variability of the TOPMODEL simulations was assessed using prediction intervals grouped using the combined multiple-objective function. The calibrated TOPMODEL results for the entire study area were applied to several subwatersheds within the study area using computed hydrogeomorphic properties of the subwatersheds.

Manipulative lowering of the water table during summer does not affect CO2 emissions and uptake in a fen in Germany.

PubMed

Muhr, Jan; Höhle, Juliane; Otieno, Dennis O; Borken, Werner

2011-03-01

We simulated the effect of prolonged dry summer periods by lowering the water table on three manipulation plots (D(1-3)) in a minerotrophic fen in southeastern Germany in three years (2006-2008). The water table at this site was lowered by drainage and by excluding precipitation; three nonmanipulated control plots (C(1-3)) served as a reference. We found no significant differences in soil respiration (R(Soil)), gross primary production (GPP), or aboveground respiration (R(AG)) between the C(1-3) and D(1-3) plots in any of the measurement years. The water table on the control plots was naturally low, with a median water table (2006-2008) of 8 cm below the surface, and even lower during summer when respiratory activity was highest, with median values (C(1-3)) between 11 and 19 cm below the surface. If it is assumed that oxygen availability in the uppermost 10 cm was not limited by the location of the water table, manipulative lowering of the water table most likely increased oxygen availability only in deeper peat layers where we expect R(Soil) to be limited by poor substrate quality rather than anoxia. This could explain the lack of a manipulation effect. In a second approach, we estimated the influence of the water table on R(Soil) irrespective of treatment. The results showed a significant correlation between R(Soil) and water table, but with R(Soil) decreasing at lower water tables rather than increasing. We thus conclude that decomposition in the litter layer is not limited by waterlogging in summer, and deeper peat layers bear no significant decomposition potential due to poor substrate quality. Consequently, we do not expect enhanced C losses from this site due to increasing frequency of dry summers. Assimilation and respiration of aboveground vegetation were not affected by water table fluctuations between 10 and >60 cm depth, indicating the lack of stress resulting from either anoxia (high water table) or drought (low water table).

Ground-water resources of the Ainsworth unit, Cherry and Brown Counties, Nebraska

USGS Publications Warehouse

Cronin, James G.; Newport, Thomas G.; Krieger, R.A.

1956-01-01

The Ainsworth unit, so named by the U. S. Bureau of Reclamation, is in north-central Nebraska and is in the drainage basin of the Niobrara River. It is an area of about 1,000 square miles in the east-central part of Cherry County and northern part of Brown County. The east-west length of the area is about 60 miles and the width ranges from 9 to 21 miles. About 80 percent of the area consists of grass-covered sandhills; the remainder is the Ainsworth tableland, which is flat to gently rolling farmland between Plum and Long Pine Creeks in the eastern part of the area. The average annual precipitation is about 23 inches. Although most of the C).ops are raised by dry-farming methods, some farmland is irrigated with water pumped from wells. The U. S. Bureau of Reclamation has proposed to irrigate much of the Ainsworth tableland with surface water to be stored in a reservoir on the Snake River at the west border of the Ainsworth unit. The rocks exposed in the Ainsworth unit range in age from Tertiary (Pliocene) to Quaternary (Recent). The Ogallala formation of Pliocene age is exposed along the lower part of the Snake River valley and underlies the entire Ainsworth unit. It is composed of silt, sand, and gravel, and contains layers of sandstone and conglomerate, much of which is cross bedded and cemented with lime; coarser sediments generally are more prominent in the lower part. Overlying the Ogallala formation are deposits of Pleistocene age consisting in part of layers of saturated sand and gravel which are the most important sources of ground water in the Ainsworth unit. Throughout most of the area the ground water is under watertable conditions, but locally it is confined by lenses of clay or silty clay. Some wells tap only the sand and gravel of Pleistocene age, some tap both the deposits of Pleistocene age and the underlying Ogallala formation, and some tap only the Ogallala formation; no wells are known to extend into rocks older than the Ogallala. Dune sand mantles the deposits of Pleistocene age in about 80 percent of the Ainsworth unit and a thin deposit of loess covers the surface elsewhere. Terrace deposits border the flood plain of the principal streams, and alluvium underlies the flood plain of most of the stream valleys in the area. Precipitation and underflow from the southwest are the principal sources of the ground water in the Ainsworth unit. As most of the precipitation in the sandhills evaporates, is utilized by growing plants, or penetrates to the zone of saturation, the overland runoff from this part of the area is small. In the vicinity of Ainsworth a minor amount of recharge probably is derived from the return of irrigation water pumped from wells. Where the water table is near the surface in the valleys of the sandhills, ground water is discharged directly from the zone of saturation to the atmosphere by evapotranspiration; and, as the surface of the lakes in the sandhills area is an extension of the water table, evaporation from the lake surface also constitutes ground-water discharge. In addition, ground water is discharged by the streams that are incised below the water table and by subsurface outflow. The yield of wells accounts for only a small part of the discharge of ground water from the area. In the Ainsworth unit the water table slopes northeastward from the region of favorable recharge, the sandhills, toward the Niobrara River and its principal tributaries. The average gradient of the water table is about 10 feet per mile. In the sandhills the water table is at or near the surface in the valleys and as much as 100 feet, or a little more, beneath the higher sandhills. In the vicinity of Ainsworth the water level in wells ranges from less than 1 foot to about 40 feet below the land surface, but nearer the Niobrara River and close to its deeply entrenched tributaries the depth to the water table is as much as, or a little more than, 200 feet. The coefficient of transmissibility of the gr

40 CFR Appendix - Tables to Part 132

Code of Federal Regulations, 2013 CFR

2013-07-01

... 40 Protection of Environment 23 2013-07-01 2013-07-01 false Tables to Part 132 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) WATER PROGRAMS WATER QUALITY GUIDANCE FOR THE GREAT LAKES SYSTEM Application of part 132 requirements in Great Lakes States and Tribes. Pt. 132, Tables Tables to Part 132 Table 1—Acute Water Quality...

Predicting water table response to rainfall events, central Florida.

PubMed

van Gaalen, J F; Kruse, S; Lafrenz, W B; Burroughs, S M

2013-01-01

A rise in water table in response to a rainfall event is a complex function of permeability, specific yield, antecedent soil-water conditions, water table level, evapotranspiration, vegetation, lateral groundwater flow, and rainfall volume and intensity. Predictions of water table response, however, commonly assume a linear relationship between response and rainfall based on cumulative analysis of water level and rainfall logs. By identifying individual rainfall events and responses, we examine how the response/rainfall ratio varies as a function of antecedent water table level (stage) and rainfall event size. For wells in wetlands and uplands in central Florida, incorporating stage and event size improves forecasting of water table rise by more than 30%, based on 10 years of data. At the 11 sites studied, the water table is generally least responsive to rainfall at smallest and largest rainfall event sizes and at lower stages. At most sites the minimum amount of rainfall required to induce a rise in water table is fairly uniform when the water table is within 50 to 100 cm of land surface. Below this depth, the minimum typically gradually increases with depth. These observations can be qualitatively explained by unsaturated zone flow processes. Overall, response/rainfall ratios are higher in wetlands and lower in uplands, presumably reflecting lower specific yields and greater lateral influx in wetland sites. Pronounced depth variations in rainfall/response ratios appear to correlate with soil layer boundaries, where corroborating data are available. © 2012, The Author(s). Groundwater © 2012, National Ground Water Association.

Ammonia Volatilization Losses from Paddy Fields under Controlled Irrigation with Different Drainage Treatments

PubMed Central

He, Yupu; Yang, Shihong; Wang, Yijiang

2014-01-01

The effect of controlled drainage (CD) on ammonia volatilization (AV) losses from paddy fields under controlled irrigation (CI) was investigated by managing water table control levels using a lysimeter. Three drainage treatments were implemented, namely, controlled water table depth 1 (CWT1), controlled water table depth 2 (CWT2), and controlled water table depth 3 (CWT3). As the water table control levels increased, irrigation water volumes in the CI paddy fields decreased. AV losses from paddy fields reduced due to the increases in water table control levels. Seasonal AV losses from CWT1, CWT2, and CWT3 were 59.8, 56.7, and 53.0 kg N ha−1, respectively. AV losses from CWT3 were 13.1% and 8.4% lower than those from CWT1 and CWT2, respectively. A significant difference in the seasonal AV losses was confirmed between CWT1 and CWT3. Less weekly AV losses followed by TF and PF were also observed as the water table control levels increased. The application of CD by increasing water table control levels to a suitable level could effectively reduce irrigation water volumes and AV losses from CI paddy fields. The combination of CI and CD may be a feasible water management method of reducing AV losses from paddy fields. PMID:24741349

Ammonia volatilization losses from paddy fields under controlled irrigation with different drainage treatments.

PubMed

He, Yupu; Yang, Shihong; Xu, Junzeng; Wang, Yijiang; Peng, Shizhang

2014-01-01

The effect of controlled drainage (CD) on ammonia volatilization (AV) losses from paddy fields under controlled irrigation (CI) was investigated by managing water table control levels using a lysimeter. Three drainage treatments were implemented, namely, controlled water table depth 1 (CWT1), controlled water table depth 2 (CWT2), and controlled water table depth 3 (CWT3). As the water table control levels increased, irrigation water volumes in the CI paddy fields decreased. AV losses from paddy fields reduced due to the increases in water table control levels. Seasonal AV losses from CWT1, CWT2, and CWT3 were 59.8, 56.7, and 53.0 kg N ha(-1), respectively. AV losses from CWT3 were 13.1% and 8.4% lower than those from CWT1 and CWT2, respectively. A significant difference in the seasonal AV losses was confirmed between CWT1 and CWT3. Less weekly AV losses followed by TF and PF were also observed as the water table control levels increased. The application of CD by increasing water table control levels to a suitable level could effectively reduce irrigation water volumes and AV losses from CI paddy fields. The combination of CI and CD may be a feasible water management method of reducing AV losses from paddy fields.

Impact of a prescribed groundwater table on the global water cycle in the IPSL land-atmosphere coupled model

NASA Astrophysics Data System (ADS)

Wang, Fuxing; Ducharne, Agnès; Cheruy, Frédérique; Lo, Min-Hui

2017-04-01

The main objective of the present work is to study the impacts of the water table depth on the global water cycle and the physical mechanisms responsible for it through analysis of land-atmosphere coupled numerical simulations. The analysis is performed with the LMDZ (standard physics) and ORCHIDEE models, which are the atmosphere-land components of the IPSL (Institut Pierre Simon Laplace) Climate Model. Results of sensitivity experiments with groundwater table (WT) prescribed at 1m (WTD1) and 2m (WTD2) are compared to the results of a reference simulation with free drainage from an unsaturated 2m soil (REF). The precipitation and evaporation are significantly impacted by WT with the largest difference found between REF and WTD1. Saturating the bottom half of the soil in WTD1 induces an increase of soil moisture. Evapotranspiration increases over water-limited regimes due to increased soil moisture, while it decreases over energy-limited regimes owing to the decrease of downwelling radiation and the increase of cloud cover. Consequently, the land-atmosphere coupling strength is weakened in WTD1 over the water-limited regimes. The tropical (25°S-25°N) and extratropical areas (25°N-60°N and 25°S-60°S) are significantly impacted by the WT with an increase of precipitation. This can be explained by more vigorous updrafts due to the uneven distributed change of evaporation, which transports more water vapor upward causing a positive precipitation change in the ascending branch. Transition zones like the Mediterranean area and central North America are also impacted, with strengthened convection resulting from increased evaporation (recycling). Over the West African Monsoon region, the rainfall belt moves northward. The more intense convection and the change of large scale dynamics (increased meridional temperature gradient) are responsible of this change. Despite the model dependence, these results with the ISPL climate model are consistent with the ample body of literature regarding the sensitivity of the simulated climate to soil moisture increase.

Changes in vegetative communities and water table dynamics following timber harvesting in small headwater streams

Treesearch

B. Choi; J.C. Dewey; J. A. Hatten; A.W. Ezell; Z. Fan

2012-01-01

In order to better understand the relationship between vegetation communities and water table in the uppermost portions (ephemeral–intermittent streams) of headwater systems, seasonal plot-based field characterizations of vegetation were used in conjunction with monthly water table measurements. Vegetation, soils, and water table data were examined to determine...

Three-dimensional semi-analytical solution to groundwater flow in confined and unconfined wedge-shaped aquifers

NASA Astrophysics Data System (ADS)

Sedghi, Mohammad Mahdi; Samani, Nozar; Sleep, Brent

2009-06-01

The Laplace domain solutions have been obtained for three-dimensional groundwater flow to a well in confined and unconfined wedge-shaped aquifers. The solutions take into account partial penetration effects, instantaneous drainage or delayed yield, vertical anisotropy and the water table boundary condition. As a basis, the Laplace domain solutions for drawdown created by a point source in uniform, anisotropic confined and unconfined wedge-shaped aquifers are first derived. Then, by the principle of superposition the point source solutions are extended to the cases of partially and fully penetrating wells. Unlike the previous solution for the confined aquifer that contains improper integrals arising from the Hankel transform [Yeh HD, Chang YC. New analytical solutions for groundwater flow in wedge-shaped aquifers with various topographic boundary conditions. Adv Water Resour 2006;26:471-80], numerical evaluation of our solution is relatively easy using well known numerical Laplace inversion methods. The effects of wedge angle, pumping well location and observation point location on drawdown and the effects of partial penetration, screen location and delay index on the wedge boundary hydraulic gradient in unconfined aquifers have also been investigated. The results are presented in the form of dimensionless drawdown-time and boundary gradient-time type curves. The curves are useful for parameter identification, calculation of stream depletion rates and the assessment of water budgets in river basins.

Selected Physical, Chemical, and Biological Data for 30 Urbanizing Streams in the North Carolina Piedmont Ecoregion, 2002-2003

USGS Publications Warehouse

Giddings, E.M.; Moorman, Michelle; Cuffney, Thomas F.; McMahon, Gerard; Harned, Douglas A.

2007-01-01

This report provides summarized physical, chemical, and biological data collected during a study of the effects of urbanization on stream ecosystems as part of the U.S. Geological Survey's National Water-Quality Assessment study. The purpose of this study was to examine differences in biological, chemical, and physical characteristics of streams across a gradient of urban intensity. Thirty sites were selected along an urbanization gradient that represents conditions in the North Carolina Piedmont ecoregion, including the cities of Raleigh, Durham, Cary, Greensboro, Winston-Salem, High Point, Asheboro, and Oxford. Data collected included streamflow variability, stream temperature, instream chemistry, instream aquatic habitat, and collections of the algal, macroinvertebrate, and fish communities. In addition, ancillary data describing land use, socioeconomic conditions, and urban infrastructure were compiled for each basin using a geographic information system analysis. All data were processed and summarized for analytical use and are presented in downloadable data tables, along with the methods of data collection and processing.

Tables Of Gaussian-Type Orbital Basis Functions

NASA Technical Reports Server (NTRS)

Partridge, Harry

1992-01-01

NASA technical memorandum contains tables of estimated Hartree-Fock wave functions for atoms lithium through neon and potassium through krypton. Sets contain optimized Gaussian-type orbital exponents and coefficients, and near Hartree-Fock quality. Orbital exponents optimized by minimizing restricted Hartree-Fock energy via scaled Newton-Raphson scheme in which Hessian evaluated numerically by use of analytically determined gradients.

Applying Hillslope Hydrology to Bridge between Ecosystem and Grid-Scale Processes within an Earth System Model

NASA Astrophysics Data System (ADS)

Subin, Z. M.; Sulman, B. N.; Malyshev, S.; Shevliakova, E.

2013-12-01

Soil moisture is a crucial control on surface energy fluxes, vegetation properties, and soil carbon cycling. Its interactions with ecosystem processes are highly nonlinear across a large range, as both drought stress and anoxia can impede vegetation and microbial growth. Earth System Models (ESMs) generally only represent an average soil-moisture state in grid cells at scales of 50-200 km, and as a result are not able to adequately represent the effects of subgrid heterogeneity in soil moisture, especially in regions with large wetland areas. We addressed this deficiency by developing the first ESM-coupled subgrid hillslope-hydrological model, TiHy (Tiled-hillslope Hydrology), embedded within the Geophysical Fluid Dynamics Laboratory (GFDL) land model. In each grid cell, one or more representative hillslope geometries are discretized into land model tiles along an upland-to-lowland gradient. These geometries represent ~1 km hillslope-scale hydrological features and allow for flexible representation of hillslope profile and plan shapes, in addition to variation of subsurface properties among or within hillslopes. Each tile (which may represent ~100 m along the hillslope) has its own surface fluxes, vegetation state, and vertically-resolved state variables for soil physics and biogeochemistry. Resolution of water state in deep layers (~200 m) down to bedrock allows for physical integration of groundwater transport with unsaturated overlying dynamics. Multiple tiles can also co-exist at the same vertical position along the hillslope, allowing the simulation of ecosystem heterogeneity due to disturbance. The hydrological model is coupled to the vertically-resolved Carbon, Organisms, Respiration, and Protection in the Soil Environment (CORPSE) model, which captures non-linearity resulting from interactions between vertically-heterogeneous soil carbon and water profiles. We present comparisons of simulated water table depth to observations. We examine sensitivities to alternative parameterizations of hillslope geometry, macroporosity, and surface runoff / inundation, and to the choice of global topographic dataset and groundwater hydraulic conductivity distribution. Simulated groundwater dynamics among hillslopes tend to cluster into three regimes of wet and well-drained, wet but poorly-drained, and dry. In the base model configuration, near-surface gridcell-mean water tables exist in an excessively large area compared to observations, including large areas of the Eastern U.S. and Northern Europe. However, in better-drained areas, the decrease in water table depth along the hillslope gradient allows for realistic increases in ecosystem water availability and soil carbon downslope. The inclusion of subgrid hydrology can increase the equilibrium 0-2 m global soil carbon stock by a large factor, due to the nonlinear effect of anoxia. We conclude that this innovative modeling framework allows for the inclusion of hillslope-scale processes and the potential for wetland dynamics in an ESM without need for a high-resolution 3-dimensional groundwater model. Future work will include investigating the potential for future changes in land carbon fluxes caused by the effects of changing hydrological regime, particularly in peatland-rich areas poorly treated by current ESMs.

Beaver Mediated Water Table Dynamics in Mountain Peatlands

NASA Astrophysics Data System (ADS)

Karran, D. J.; Westbrook, C.; Bedard-Haughn, A.

2016-12-01

Water table dynamics play an important role in the ecological and biogeochemical processes that regulate carbon and water storage in peatlands. Beaver are common in these habitats and the dams they build have been shown to raise water tables in other environments. However, the impact of beaver dams in peatlands, where water tables rest close to the surface, has yet to be determined. We monitored a network of 50 shallow wells in a Canadian Rocky Mountain peatland for 6 years. During this period, a beaver colony was maintaining a number of beaver ponds for four years until a flood event removed the colony from the area and breached some of the dams. Two more years of data were collected after the flood event to assess whether the dams enhanced groundwater storage. Beaver dams raised water tables just as they do in other environments. Furthermore, water tables within 100 meters of beaver dams were more stable than those further away and water table stability overall was greater before the flood event. Our results suggest the presence/absence of beaver in peatlands has implications for groundwater water storage and overall system function.

Dynamics of groundwater-surface water interactions in urban streams

NASA Astrophysics Data System (ADS)

Musolff, A.; Schmidt, C.; Fleckenstein, J. H.

2010-12-01

In industrialized countries the majority of streams and rivers have been subject to changes in the hydrological regime and alteration of the channel morphology. Urban streams are typically characterized by “flashier” hydrographs as a result of more direct runoff from impervious surfaces. Channel structure and complexity are often impaired compared to pristine streams. As a consequence the potential for bedform-driven water flow in the streambed is reduced. The downward transport of oxygen by advective flow in the streambed is known to be of great ecological importance for the hyporheic macro and micro fauna and facilitates nutrient cycling and the degradation of organic pollutants. We studied the dynamics of groundwater-surface water exchange of two anthropogenically impacted streams in urban areas to examine the effects of variable hydrologic boundary conditions on water flux and redox conditions in the streambed. The first stream is fed by groundwater as well as storm-water from a large industrial area. Here, we monitored the variability of vertical hydraulic gradients, streambed temperature and redox conditions in the streambed over the course of 5 months. The second stream is frequently polluted by combined sewer overflows (CSO) from an urban watershed. Here, we measured the vertical hydraulic gradients, streambed temperature and electrical conductivity (EC) in the stream, the streambed and in the adjacent aquifer. Both streams are characterized by strong variations in hydraulic gradients due to the dynamic hydrographs as well as the variations in total head in the shallow aquifer. Therefore, magnitude and direction of water flux through the streambed changed significantly over time. At the first site long-term variations of redox conditions in the shallow streambed (0.1 m) were related to the direction of water fluxes. Downward water flow resulted in increased redox potentials. However, the high short-term variability of redox conditions could not be directly attributed to changes in the hydraulic conditions. At the second site, increased EC in the shallow aquifer was related to seasonally losing conditions (associated with low water tables in summer) and the resulting groundwater recharge. Sudden increases in stream stage due to rain events and subsequent CSO resulted in altered streambed water fluxes, as evidenced by the disturbance of vertical streambed temperature profiles down to a depth of 0.3 m. Both, short-term and long-term variations in hydraulic gradients between the stream, the streambed and the groundwater were found to influence the magnitude and direction of water fluxes. Flashy flow events influence the water flux in the streambed very rapidly. However, changes in redox potential in the streambed require losing conditions over time scales longer than the duration of a typical high flow event. As a consequence, the complexity of water exchange in the streambed should be carefully monitored, both in space and time. Our results indicate that variable hydraulic gradients may induce intense exchange fluxes between the stream and streambed in urban streams and may compensate some of the negative consequences of degraded channels with limited bedform-driven flow.

A time series approach to inferring groundwater recharge using the water table fluctuation method

NASA Astrophysics Data System (ADS)

Crosbie, Russell S.; Binning, Philip; Kalma, Jetse D.

2005-01-01

The water table fluctuation method for determining recharge from precipitation and water table measurements was originally developed on an event basis. Here a new multievent time series approach is presented for inferring groundwater recharge from long-term water table and precipitation records. Additional new features are the incorporation of a variable specific yield based upon the soil moisture retention curve, proper accounting for the Lisse effect on the water table, and the incorporation of aquifer drainage so that recharge can be detected even if the water table does not rise. A methodology for filtering noise and non-rainfall-related water table fluctuations is also presented. The model has been applied to 2 years of field data collected in the Tomago sand beds near Newcastle, Australia. It is shown that gross recharge estimates are very sensitive to time step size and specific yield. Properly accounting for the Lisse effect is also important to determining recharge.

Implementation and testing of the on-the-fly thermal scattering Monte Carlo sampling method for graphite and light water in MCNP6

DOE PAGES

Pavlou, Andrew T.; Ji, Wei; Brown, Forrest B.

2016-01-23

Here, a proper treatment of thermal neutron scattering requires accounting for chemical binding through a scattering law S(α,β,T). Monte Carlo codes sample the secondary neutron energy and angle after a thermal scattering event from probability tables generated from S(α,β,T) tables at discrete temperatures, requiring a large amount of data for multiscale and multiphysics problems with detailed temperature gradients. We have previously developed a method to handle this temperature dependence on-the-fly during the Monte Carlo random walk using polynomial expansions in 1/T to directly sample the secondary energy and angle. In this paper, the on-the-fly method is implemented into MCNP6 andmore » tested in both graphite-moderated and light water-moderated systems. The on-the-fly method is compared with the thermal ACE libraries that come standard with MCNP6, yielding good agreement with integral reactor quantities like k-eigenvalue and differential quantities like single-scatter secondary energy and angle distributions. The simulation runtimes are comparable between the two methods (on the order of 5–15% difference for the problems tested) and the on-the-fly fit coefficients only require 5–15 MB of total data storage.« less

Incorporating Peatland Plant Communities into the Enzymic 'Latch' Hypothesis: Can Vegetation Influence Carbon Storage Mechanisms?

NASA Astrophysics Data System (ADS)

Romanowicz, K. J.; Daniels, A. L.; Potvin, L. R.; Kane, E. S.; Kolka, R. K.; Chimner, R. A.; Lilleskov, E. A.

2012-12-01

High water table conditions in peatland ecosystems are known to favor plant production over decomposition and carbon is stored. Dominant plant communities change in response to water table but little is know of how these changes affect belowground carbon storage. One hypothesis known as the enzymic 'latch' proposed by Freeman et al. suggests that oxygen limitations due to high water table conditions inhibit microorganisms from synthesizing specific extracellular enzymes essential for carbon and nutrient mineralization, allowing carbon to be stored as decomposition is reduced. Yet, this hypothesis excludes plant community interactions on carbon storage. We hypothesize that the dominant vascular plant communities, sedges and ericaceous shrubs, will have inherently different effects on peatland carbon storage, especially in response to declines in water table. Sedges greatly increase in abundance following water table decline and create extensive carbon oxidation and mineralization hotspots through the production of deep roots with aerenchyma (air channels in roots). Increased oxidation may enhance aerobic microbial activity including increased enzyme activity, leading to peat subsidence and carbon loss. In contrast, ericaceous shrubs utilize enzymatically active ericoid mycorrhizal fungi that suppress free-living heterotrophs, promoting decreased carbon mineralization by mediating changes in rhizosphere microbial communities and enzyme activity regardless of water table declines. Beginning May 2010, bog monoliths were harvested, housed in mesocosm chambers, and manipulated into three vegetation treatments: unmanipulated (+sedge, +Ericaceae), sedge (+sedge, -Ericaceae), and Ericaceae (-sedge, +Ericaceae). Following vegetation manipulations, two distinct water table manipulations targeting water table seasonal profiles were implemented: (low intra-seasonal variability, higher mean water table; high intra-seasonal variability, lower mean water table). In 2012, peat cores are being assayed monthly from June - October for two oxidase enzyme activities (phenol oxidase, peroxidase) and four hydrolase enzyme activities (β-glucosidase, chitinase, cellobiohydrolase, and acid-phosphatase). Early season assays (June and July) where water table treatments did not significantly vary showed trends of decreasing oxidase activities while hydrolase activities increased. These preliminary results show no significant differences between vegetation treatments but as the season progresses (August - October), water table levels between high and low treatments will continue to experience greater dissimilarities. These water table declines within sedge and ericaceous shrub communities may have opposing effects on rhizosphere extracellular enzyme activities indicating plant communities may significantly influence belowground carbon storage mechanisms in ways not previously considered in peatland ecosystems.

Improvements to a global-scale groundwater model to estimate the water table across New Zealand

NASA Astrophysics Data System (ADS)

Westerhoff, Rogier; Miguez-Macho, Gonzalo; White, Paul

2017-04-01

Groundwater models at the global scale have become increasingly important in recent years to assess the effects of climate change and groundwater depletion. However, these global-scale models are typically not used for studies at the catchment scale, because they are simplified and too spatially coarse. In this study, we improved the global-scale Equilibrium Water Table (EWT) model, so it could better assess water table depth and water table elevation at the national scale for New Zealand. The resulting National Water Table (NWT) model used improved input data (i.e., national input data of terrain, geology, and recharge) and model equations (e.g., a hydraulic conductivity - depth relation). The NWT model produced maps of the water table that identified the main alluvial aquifers with fine spatial detail. Two regional case studies at the catchment scale demonstrated excellent correlation between the water table elevation and observations of hydraulic head. The NWT water tables are an improved water table estimation over the EWT model. In two case studies the NWT model provided a better approximation to observed water table for deep aquifers and the improved resolution of the model provided the capability to fill the gaps in data-sparse areas. This national model calculated water table depth and elevation across regional jurisdictions. Therefore, the model is relevant where trans-boundary issues, such as source protection and catchment boundary definition, occur. The NWT model also has the potential to constrain the uncertainty of catchment-scale models, particularly where data are sparse. Shortcomings of the NWT model are caused by the inaccuracy of input data and the simplified model properties. Future research should focus on improved estimation of input data (e.g., hydraulic conductivity and terrain). However, more advanced catchment-scale groundwater models should be used where groundwater flow is dominated by confining layers and fractures.

Northern part, Ten Mile and Taunton River basins

USGS Publications Warehouse

Williams, John R.; Willey, Richard E.

1967-01-01

This report is one of two prepared by the Geological Survey for the Water Resources Commission. The principal purpose of this report is to make available the basic data on which the other, a map showing availability of ground water, is based. This basic-data report also can be used by engineers, planners, and others interested in or responsible for water-resources planning to determine the materials to be encountered (tables 3 and 4) and the yields which may be obtained from wells and test holes (tables 1 and 2) in the stratified sand and gravel that are the principal source of ground water and in bedrock. Partial and complete chemical analyses (tables 7 and 8) of these test holes and of some privately-owned wells provide information on the general quality of the water for domestic and other uses. A tabulation of existing municipal supplies, their capacity, production (table 5), and chemical quality of the water (table 6) may be used for regional planning purposes. Water-level measurements (figure 1) can be used to determine the annual fluctuations of the water table in certain types of materials. Seismic work (table 9) in the Canoe River valley, Norton, and test drilling with a power augur (tables 2 and 4) were done for the Geological Survey as  part of the investigation.

Using an implicitly-coupled hydrologic and river-operations models to investigate the trade-offs of artificial recharge in agricultural areas

NASA Astrophysics Data System (ADS)

Morway, E. D.; Niswonger, R. G.; Triana, E.

2016-12-01

In irrigated agricultural regions supplied by both surface-water and groundwater, increased reliance on groundwater during sustained drought leads to long-term water table drawdown and subsequent surface-water losses. This, in turn, may threaten the sustainability of the irrigation project. To help offset groundwater resource losses and restore water supply reliability, an alternative management strategy commonly referred to as managed aquifer recharge (MAR) in agricultural regions helps mitigate long-term aquifer drawdown and provides additional water for subsequent withdraw. Sources of MAR in this investigation are limited to late winter runoff in years with above average precipitation (i.e., above average snowpack). However, where winter MAR results in an elevated water table, non-beneficial consumptive use may increase from evapotranspiration in adjacent and down-gradient fallow and naturally vegetated lands. To rigorously explore this trade-off, the recently published MODSIM-MODFLOW model was applied to quantify both the benefits and unintended consequences of MAR. MODSIM-MODFLOW is a generalized modeling tool capable of exploring the effects of altered river operations within an integrated groundwater and surface-water (GW-SW) model. Thus, the MODSIM-MODFLOW model provides a modeling platform capable of simulating MAR in amounts and duration consistent with other senior water rights in the river system (e.g., minimum in-stream flow requirements). Increases in non-beneficial consumptive use resulting from winter MAR are evaluated for a hypothetical model patterned after alluvial aquifers common in arid and semi-arid areas of the western United States. Study results highlight (1) the benefit of an implicitly-coupled river operations and hydrologic modeling tool, (2) the balance between winter MAR and the potential increase in non-beneficial consumptive use, and (3) conditions where MAR may or may not be an appropriate management option, such as the availability of surface-water storage.

Self-potential investigations of a gravel bar in a restored river corridor

USGS Publications Warehouse

Linde, N.; Doetsch, J.; Jougnot, D.; Genoni, O.; Durst, Y.; Minsley, B.J.; Vogt, T.; Pasquale, N.; Luster, J.

2011-01-01

Self-potentials (SP) are sensitive to water fluxes and concentration gradients in both saturated and unsaturated geological media, but quantitative interpretations of SP field data may often be hindered by the superposition of different source contributions and time-varying electrode potentials. Self-potential mapping and close to two months of SP monitoring on a gravel bar were performed to investigate the origins of SP signals at a restored river section of the Thur River in northeastern Switzerland. The SP mapping and subsequent inversion of the data indicate that the SP sources are mainly located in the upper few meters in regions of soil cover rather than bare gravel. Wavelet analyses of the time-series indicate a strong, but non-linear influence of water table and water content variations, as well as rainfall intensity on the recorded SP signals. Modeling of the SP response with respect to an increase in the water table elevation and precipitation indicate that the distribution of soil properties in the vadose zone has a very strong influence. We conclude that the observed SP responses on the gravel bar are more complicated than previously proposed semi-empiric relationships between SP signals and hydraulic head or the thickness of the vadose zone. We suggest that future SP monitoring in restored river corridors should either focus on quantifying vadose zone processes by installing vertical profiles of closely spaced SP electrodes or by installing the electrodes within the river to avoid signals arising from vadose zone processes and time-varying electrochemical conditions in the vicinity of the electrodes. ?? 2011 Author(s).

Self-potential investigations of a gravel bar in a restored river corridor

USGS Publications Warehouse

Linde, N.; Doetsch, J.; Jougnot, D.; Genoni, O.; Durst, Y.; Minsley, Burke J.; Vogt, T.; Pasquale, N.; Luster, J.

2011-01-01

 Self-potentials (SP) are sensitive to water fluxes and concentration gradients in both saturated and unsaturated geological media, but quantitative interpretations of SP field data may often be hindered by the superposition of different source contributions and time-varying electrode potentials. Self-potential mapping and close to two months of SP monitoring on a gravel bar were performed to investigate the origins of SP signals at a restored river section of the Thur River in northeastern Switzerland. The SP mapping and subsequent inversion of the data indicate that the SP sources are mainly located in the upper few meters in regions of soil cover rather than bare gravel. Wavelet analyses of the time-series indicate a strong, but non-linear influence of water table and water content variations, as well as rainfall intensity on the recorded SP signals. Modeling of the SP response with respect to an increase in the water table elevation and precipitation indicate that the distribution of soil properties in the vadose zone has a very strong influence. We conclude that the observed SP responses on the gravel bar are more complicated than previously proposed semi-empiric relationships between SP signals and hydraulic head or the thickness of the vadose zone. We suggest that future SP monitoring in restored river corridors should either focus on quantifying vadose zone processes by installing vertical profiles of closely spaced SP electrodes or by installing the electrodes within the river to avoid signals arising from vadose zone processes and time-varying electrochemical conditions in the vicinity of the electrodes.

Water table variability and runoff generation in an eroded peatland, South Pennines, UK

NASA Astrophysics Data System (ADS)

Daniels, S. M.; Agnew, C. T.; Allott, T. E. H.; Evans, M. G.

2008-10-01

SummaryHydrological monitoring in an eroded South Pennine peatland shows that persistent and frequent water table drawdowns occur at gully edge locations, defining a deeper and thicker acrotelm than is observed in intact peatlands (an erosional acrotelm). Antecedent water table elevation is a key control on the hydrological response to precipitation events, in particular runoff percent, the timing of peak discharges and maximum water table elevations. Significant discharge is generated whilst water table elevations are relatively low at gully edge locations, and this has a strong influence on flow pathways. Four characteristics of runoff response are recognised: (i) the rapid development of macropore/pipe flow at the start of the storm; (ii) peat rewetting, water table elevation increase and continued macropore/pipe flow; (iii) maximum water table elevations and peak stream discharge with throughflow occurring within the erosional acrotelm and rapid flow through the subsurface macropore/pipe network; (iv) rapidly declining water table elevations and stream flow following the cessation of rainfall. Gully edge peats provide a key linkage between the hillslope hydrological system and channel flow so that their influence on the hydrological functioning of the peatlands is disproportionate to their aerial extent within the catchment. Future climate change may lead to further degradation of the bogs and a reinforcement of the importance of erosion gullies to runoff generation and water quality.

The design of a research water table

NASA Technical Reports Server (NTRS)

Fike, R. L.; Kinney, R. B.; Perkins, H. C.

1973-01-01

A complete design for a research water table is presented. Following a brief discussion of the analogy between water and compressible-gas flows (hydraulic analogy), the components of the water table and their function are described. The major design considerations are discussed, and the final design is presented.

A modular finite-element model (MODFE) for areal and axisymmetric ground-water-flow problems, Part 2: Derivation of finite-element equations and comparisons with analytical solutions

USGS Publications Warehouse

Cooley, Richard L.

1992-01-01

MODFE, a modular finite-element model for simulating steady- or unsteady-state, area1 or axisymmetric flow of ground water in a heterogeneous anisotropic aquifer is documented in a three-part series of reports. In this report, part 2, the finite-element equations are derived by minimizing a functional of the difference between the true and approximate hydraulic head, which produces equations that are equivalent to those obtained by either classical variational or Galerkin techniques. Spatial finite elements are triangular with linear basis functions, and temporal finite elements are one dimensional with linear basis functions. Physical processes that can be represented by the model include (1) confined flow, unconfined flow (using the Dupuit approximation), or a combination of both; (2) leakage through either rigid or elastic confining units; (3) specified recharge or discharge at points, along lines, or areally; (4) flow across specified-flow, specified-head, or head-dependent boundaries; (5) decrease of aquifer thickness to zero under extreme water-table decline and increase of aquifer thickness from zero as the water table rises; and (6) head-dependent fluxes from springs, drainage wells, leakage across riverbeds or confining units combined with aquifer dewatering, and evapotranspiration. The matrix equations produced by the finite-element method are solved by the direct symmetric-Doolittle method or the iterative modified incomplete-Cholesky conjugate-gradient method. The direct method can be efficient for small- to medium-sized problems (less than about 500 nodes), and the iterative method is generally more efficient for larger-sized problems. Comparison of finite-element solutions with analytical solutions for five example problems demonstrates that the finite-element model can yield accurate solutions to ground-water flow problems.

Dual permeability modeling of tile drain management influences on hydrologic and nutrient transport characteristics in macroporous soil

NASA Astrophysics Data System (ADS)

Frey, Steven K.; Hwang, Hyoun-Tae; Park, Young-Jin; Hussain, Syed I.; Gottschall, Natalie; Edwards, Mark; Lapen, David R.

2016-04-01

Tile drainage management is considered a beneficial management practice (BMP) for reducing nutrient loads in surface water. In this study, 2-dimensional dual permeability models were developed to simulate flow and transport following liquid swine manure and rhodamine WT (strongly sorbing) tracer application on macroporous clay loam soils under controlled (CD) and free drainage (FD) tile management. Dominant flow and transport characteristics were successfully replicated, including higher and more continuous tile discharge and lower peak rhodamine WT concentrations in FD tile effluent; in relation to CD, where discharge was intermittent, peak rhodamine concentrations higher, and mass exchange from macropores into the soil matrix greater. Explicit representation of preferential flow was essential, as macropores transmitted >98% of surface infiltration, tile flow, and tile solute loads for both FD and CD. Incorporating an active 3rd type lower boundary condition that facilitated groundwater interaction was imperative for simulating CD, as the higher (relative to FD) water table enhanced water and soluble nutrient movement from the soil profile into deeper groundwater. Scenario analysis revealed that in conditions where slight upwards hydraulic gradients exist beneath tiles, groundwater upwelling can influence the concentration of surface derived solutes in tile effluent under FD conditions; whereas the higher and flatter CD water table can restrict groundwater upwelling. Results show that while CD can reduce tile discharge, it can also lead to an increase in surface-application derived nutrient concentrations in tile effluent and hence surface water receptors, and it can promote NO3 loading into groundwater. This study demonstrates dual permeability modeling as a tool for increasing the conceptual understanding of tile drainage BMPs.

Hydrogeological characterization of flow system in a karstic aquifer, Seymareh dam, Iran

NASA Astrophysics Data System (ADS)

Behrouj Peely, Ahmad; Mohammadi, Zargham; Raeisi, Ezzatollah; Solgi, Khashayar; Mosavi, Mohammad J.; Kamali, Majid

2018-07-01

In order to determine the characteristics of the flow system in a karstic aquifer, an extensive hydrogeological study includes dye tracing test was conducted. The aquifer suited left abutment of Seymareh Dam, in Ravandi Anticline and discharges by more than 50 springs in the southern flank. Flow system in the aquifer is mainly controlled by the reservoir of Seymareh Dam. Time variations of the spring discharge and water table in the observation wells were highly correlated with the reservoir water level. The average groundwater velocity ranges from 0.2 to more than 14 m/h based on the dye tracing test. The probable flow paths were differentiated in two groups including the flow paths in the northern and southern flanks of Ravandi Anticline. Types of groundwater flow in the proposed flow paths are determined as diffuse or conduit flow type considering groundwater velocity and shape of the breakthrough curves. An index is proposed for differentiation of diffuse and conduit flow system based on relationship of groundwater velocity and hydraulic gradient. Dominant geometry of the flow routs (e.g., conduit diameter and fracture aperture) is estimated for the groundwater flow paths toward the springs. Based on velocity variations and variance coefficient of the water table and discharge of springs on map view a major karst conduit was probably developed in the aquifer. This research emphasizes applying of an extensive hydrogeological study for characterization of flow system in the karst aquifer.

Thermal-gradient migration of brine inclusions in salt crystals. [Synthetic single crystals of NaCl and KCl

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

Yagnik, S.K.

1982-09-01

It has been proposed that high-level nuclear waste be disposed in a geologic repository. Natural-salt deposits, which are being considered for this purpose, contain a small volume fraction of water in the form of brine inclusions distributed throughout the salt. Radioactive-decay heating of the nuclear wastes will impose a temperature gradient on the surrounding salt which mobilizes the brine inclusions. Inclusions filled completely with brine migrate up the temperature gradient and eventually accumulate brine near the buried waste forms. The brine may slowly corrode or degrade the waste forms which is undesirable. In this work, thermal gradient migration of bothmore » all-liquid and gas-liquid inclusions was experimentally studied in synthetic single crystals of NaCl and KCl using a hot-stage attachment to an optical microscope which was capable of imposing temperature gradients and axial compressive loads on the crystals. The migration velocities of the inclusions were found to be dependent on temperature, temperature gradient, and inclusion shape and size. The velocities were also dictated by the interfacial mass transfer resistance at brine/solid interface. This interfacial resistance depends on the dislocation density in the crystal, which in turn, depends on the axial compressive loading of the crystal. At low axial loads, the dependence between the velocity and temperature gradient is non-linear.At high axial loads, however, the interfacial resistance is reduced and the migration velocity depends linearly on the temperature gradient. All-liquid inclusions filled with mixed brines were also studied. For gas-liquid inclusions, three different gas phases (helium, air and argon) were compared. Migration studies were also conducted on single crystallites of natural salt as well as in polycrystalline natural salt samples. The behavior of the inclusions at large angle grain boundaries was observed. 35 figures, 3 tables.« less

A method for simulating transient ground-water recharge in deep water-table settings in central Florida by using a simple water-balance/transfer-function model

USGS Publications Warehouse

O'Reilly, Andrew M.

2004-01-01

A relatively simple method is needed that provides estimates of transient ground-water recharge in deep water-table settings that can be incorporated into other hydrologic models. Deep water-table settings are areas where the water table is below the reach of plant roots and virtually all water that is not lost to surface runoff, evaporation at land surface, or evapotranspiration in the root zone eventually becomes ground-water recharge. Areas in central Florida with a deep water table generally are high recharge areas; consequently, simulation of recharge in these areas is of particular interest to water-resource managers. Yet the complexities of meteorological variations and unsaturated flow processes make it difficult to estimate short-term recharge rates, thereby confounding calibration and predictive use of transient hydrologic models. A simple water-balance/transfer-function (WBTF) model was developed for simulating transient ground-water recharge in deep water-table settings. The WBTF model represents a one-dimensional column from the top of the vegetative canopy to the water table and consists of two components: (1) a water-balance module that simulates the water storage capacity of the vegetative canopy and root zone; and (2) a transfer-function module that simulates the traveltime of water as it percolates from the bottom of the root zone to the water table. Data requirements include two time series for the period of interest?precipitation (or precipitation minus surface runoff, if surface runoff is not negligible) and evapotranspiration?and values for five parameters that represent water storage capacity or soil-drainage characteristics. A limiting assumption of the WBTF model is that the percolation of water below the root zone is a linear process. That is, percolating water is assumed to have the same traveltime characteristics, experiencing the same delay and attenuation, as it moves through the unsaturated zone. This assumption is more accurate if the moisture content, and consequently the unsaturated hydraulic conductivity, below the root zone does not vary substantially with time. Results of the WBTF model were compared to those of the U.S. Geological Survey variably saturated flow model, VS2DT, and to field-based estimates of recharge to demonstrate the applicability of the WBTF model for a range of conditions relevant to deep water-table settings in central Florida. The WBTF model reproduced independently obtained estimates of recharge reasonably well for different soil types and water-table depths.

Redox potential characterization and soil greenhouse gas concentration across a hydrological gradient in a Gulf coast forest

USGS Publications Warehouse

Yu, K.; Faulkner, S.P.; Patrick, W.H.

2006-01-01

Soil redox potential (Eh), concentrations of oxygen (O2) and three greenhouse gases (CO2, CH4, and N2O) were measured in the soil profile of a coastal forest at ridge, transition, and swamp across a hydrological gradient. The results delineated a distinct boundary in soil Eh and O2 concentration between the ridge and swamp with essentially no overlap between the two locations. Critical soil Eh to initiate significant CH4 production under this field conditions was about +300 mV, much higher than in the homogenous soils (about -150 mV). The strength of CH4 source to the atmosphere was strong for the swamp, minor for the transition, and negligible or even negative (consumption) for the ridge. Maximum N2O concentration in the soils was found at about Eh +250 mV, and the soil N2O emission was estimated to account for less than 4% for the ridge and transition, and almost negligible for the swamp in the cumulative global warming potential (GWP) of these three gases. The dynamic nature of this study site in response to water table fluctuations across a hydrological gradient makes it an ideal model of impact of future sea level rise to coastal ecosystems. Soil carbon (C) sequestration potential due to increasing soil water content upon sea level rise and subsidence in this coastal forest was likely limited and temporal, and at the expense of increasing soil CH4 production and emission. ?? 2005 Elsevier Ltd. All rights reserved.

Water levels in observation wells in Nebraska during 1955

USGS Publications Warehouse

Keech, C.F.

1956-01-01

The objective of the dbservation-well program in Nebraska is to provide an evaluation of the status of the ground-water supplies. Many uses for water-.level data are known but not all potential uses can be forseen. Among the important uses are the following:To indicate the status of ground water in storage or in transit and the availability of supplies.To show the trend of ground-water supplies and the outlook for the future.To estimate or forcast the base flow of streams.To indicate areas in which the water level is approaching too close to the land surface (water-logging) or is receding toward economic limits of lift or tow rd impairment by water of poor quality.To provide long-term vidence for evaluating the effectiveness of land-management and water...0 nservation programs in relation to water conservation actually of ected, and for use in basin or "watershed" studies.To provide longterm ontinuous records to serve as a framework to which short-term records collected during intensive investigation may be related.The water level in an observation well functions as a gage to indicate the position of the water table o The water table is defined as the upper surface of the zone of saturation except where that surface is formed by overlying impermeable materials. The water table is also the boundary between the zone of saturation and the zone of aeration. It is not a level surface but is a sloping surface that has many irregularities, and it often conforms in a general way to the land surface. The irregularities are caused by several factors. In places where the recharge to the ground-water reservoir is exceptionally large, the water-table may rise to form a mound from which the water slowly spreads. Depressions or troughs in the water table indicate places where the ground water is discharging, as along streams that are below the normal level of the water table, or indicate places where water is being withdrawn by wells or vegetation.The several factors that influence the water table vary in fact and amount from time to time because of changes in weather and the water requirements of vegetation and man; thus, the water table is nearly always rising or falling.The fluctuations of the water table are shown by the changes in water levels in wells. Thus, the rate and amount of the fluctuation of the water table can be ascertained by observing the water levels in wells, and the magnitude of the several factors effecting the position of the water table can be interpreted by analyzing the water—level data.Water-level measurements are given, in this report, in feet below the land surface at the well site. Water levels that are above land surface are preceded by a plus (+) sign, whereas those below land surface have no sign but are understood to be minus (-). The words "land-surface datum" are abbreviated "lsd" in tables of this report.The altitude above mean sea level (msl) of the land surface at many of the well sites has been determined and is included in the tables of this report.Lower case letters which appear in the table of water level measurements indicate the following: 6', nearby well pumped recently; f, dry; g, measured by outside agency; and j, frozen.Twenty-.six observation wells in Nebraska are equipped with recording gages. Each recording gage produces a continuous graph of water-level fluctuations in the well. Only the lowest water level on the last day of record in each month, as recorded by the gage, is given in this report; the complete record is on file in the office of the U. S. Geological Survey in Lincoln, Nebr.

Factors controlling the concentration of methane and other volatiles in groundwater and soil-gas around a waste site

NASA Astrophysics Data System (ADS)

Barber, C.; Davis, G. B.; Briegel, D.; Ward, J. K.

1990-01-01

The concentration of methane in groundwater and soil-gas in the vicinity of a waste landfill on an unconfined sand aquifer has been investigated in detail. These data have been used to evaluate techniques which use volatile organic compounds in soil-gas as indicators of groundwater contamination. Simple one-dimensional models of gas advection and diffusion have been adapted for use in the study. Lateral advection of gas in the unsaturated sand was found to be seasonal and was most noticeable in winter when the profile was wet; a mean velocity of 1 m d - was measured from breakthrough of a helium tracer in an injection test. The effects of advection on trace concentrations of methane in soil-gas were limited to within 150-200m from the waste site and resulted from pressure gradients brought about by positive gas pressures in the landfill, and also as a result of ebullition (gas bubbling) from contaminated groundwater. The distribution of methane in soil-gas at shallow (2m) depth gave a general indication of the direction of movement of contaminants with groundwater in close proximity to the landfill. Outside this zone, diffusional transport of methane from groundwater to soil-gas occurred and methane in soil-gas sampled close to the water table was found to be a useful indicator of contaminated groundwater. Modelling the exchange of volatiles between aqueous and gas phases indicates that a wide range of organic compounds, particularly those with Henry's Law constants greater than 2.5 × 10 t-2 kPam 3mol -1, would have potential for use as indicators of pollution, if these were present in groundwater and they behaved relatively conservatively. In general, the principal factors controlling the concentration of these volatiles in soil-gas were the concentration gradient at the water table and capillary fringe and the ratio of diffusion coefficients in the saturated and unsaturated zones.

Ecosystem-groundwater interactions under changing land uses: Linking water, salts, and carbon across central Argentina

NASA Astrophysics Data System (ADS)

Jobbagy, E. G.; Nosetto, M. D.; Santoni, C. S.; Jackson, R. B.

2007-05-01

Although most ecosystems display a one-way connection with groundwater based on the regulation of deep water drainage (recharge), this link can become reciprocal when the saturated zone is shallow and plants take up groundwater (discharge). In what context is the reciprocal link most likely? How is it affected by land use changes? Has it consequences on salt and carbon cycling? We examine these questions across a precipitation gradient in the Pampas and Espinal of Argentina focusing on three vegetation change situations (mean annual rainfall): afforestation of humid (900-1300 mm) and subhumid grassland (700-900 mm/yr of rainfall), annual cultivation of subhumid grasslands (700-800 mm/yr), and annual cultivation of semiarid forests (500-700 mm). Humid and subhumid grasslands have shallow (< 5 m deep) groundwater tables that are poorly consumed by grasses but highly used by planted trees, as evidenced by satellite canopy temperatures, soil moisture and water table level records, and sapflow measurements. Groundwater contributions enhance carbon uptake in plantations compared to grasslands as suggested by aboveground biomass measurements and satellite vegetation indexes from sites with and without access to groundwater. Where rainfall is <1100 mm, grassland afforestation switches water fluxes to groundwater from positive (net recharge) to negative (net discharge) causing a salt accumulation process in soils and groundwater that is ultimately limited by the tolerance to salinity of tree species. Cultivation with corn and soybean can lead to groundwater consumption in the driest belt of subhumid grassland. Up to five-fold yield increases in lowlands vs. uplands during the driest years indicate a dramatic impact of groundwater use on carbon uptake and groundwater salinization suggests a recharge-to- discharge switch. In dry forests groundwater is not accessible (> 15 m deep) and recharge under natural conditions is null. The establishment of crops, however, triggers the onset of recharge, as evidenced by vadose zones getting wetter and leached of atmospheric chloride. Cropping may cause water table raises leading to a two-way coupling of ecosystems and groundwater in the future, as it has been documented for similar settings in Australia and the Sahel. In the Pampas land use change interacts with groundwater consumption leading to higher carbon uptake (humid and subhumid grasslands) and salt accumulation (subhumid grasslands). In the Espinal (semiarid forest) land use change currently involves a one-way effect on groundwater recharge that may switch to a reciprocal connection if regional water table raises occur. Neglecting the role of groundwater in flat sedimentary plains can obscure our understanding of carbon and salt cycling and curtail our attempts to sustain soil and water resources under changing land uses.

Influence of water table on carbon dioxide, carbon monoxide, and methane fluxes from taiga bog microcosms

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

Funk, D.W.; Pullmann, E.R.; Peterson, K.M.

1994-09-01

Hydrological changes, particularly alterations in water table level, may largely overshadow the more direct effects of global temperature increase upon carbon cycling in arctic and subarctic wetlands. Frozen cores (n=40) of intact soils and vegetation were collected from a bog near Fairbanks, Alaska, and fluxes of CO{sub 2}, CH{sub 4}, and Co in response to water table variation were studied under controlled conditions in the Duke University phytotron. Core microcosms thawed to a 20-cm depth over 30 days under a 20 hour photoperiod with a day/night temperature regime of 20/10{degrees}C. After 30 days the water table in 20 microcosms wasmore » decreased from the soil surface to -15 cm and maintained at the soil surface in 20 control cores. Outward fluxes of CO{sub 2} (9-16 g m{sup -2}d{sup -1}) and CO (3-4 mg m{sup -2}d{sup -1}) were greatest during early thaw and decreased to near zero for both gases before the water table treatment started. Lower water table tripled CO{sub 2} flux to the atmosphere when compared with control cores. Carbon monoxide was emitted at low rates from high water table cores and consumed by low water table cores. Methane fluxes were low (<1 mg m{sup -2}d{sup -1}) in all cores during thaw. High water table cores increased CH{sub 4} flux to 8-9 mg m{sup -2}d{sup -1} over 70 days and remained high relative to the low water table cores (<0.74 mg m{sup -2}d{sup -1}). Although drying of wetland taiga soils may decrease CH{sub 4} emissions to the atmosphere, the associated increase in CO{sub 2} due to aerobic respiration will likely increase the global warming potential of gas emissions from these soils. 43 refs., 4 figs.« less

Analysis of Evaporative Flux Over Irrigated and Unirrigated Pasture in the Wood River Basin

NASA Astrophysics Data System (ADS)

Cuenca, R. H.; Mahrt, L.; Hagimoto, Y.; Peterson, S.

2005-12-01

The reduction in evaporative fluxes due to withholding irrigation water for pasture in the Wood River subbasin of the Upper Klamath Basin was evaluated to estimate the potential benefit in subsequent streamflow. Two Campbell Scientific (CSI) Bowen ratio - energy balance systems were installed, one over a fully irrigated site and one over a non-irrigated site separated by approximately 11 km. The systems were comprised of an infrared gas analyzer for water vapor gradients, fine-wire thermocouples for temperature gradients, net radiometer and soil heat flux sensors. Additional micrometeorological sensors for precipitation, solar radiation, air temperature and relative humidity, wind speed and direction enabled calculation of a Penman-Monteith reference evapotranspiration. Both sites had uniform fetch conditions in excess of 1 km in the predominant upwind direction. Bowen ratio data were quality controlled using the Ohmura algorithm and energy balance components and fluxes computed every 20-min. Soil temperature and soil moisture profile sensors in six depth layers down to 80 cm were installed at the same sites and monitored every 15-min. High frequency (10-min) recording piezometers for water table monitoring were also installed. Both irrigated and unirrigated sites started the 2004 growing season with virtually the same soil moisture conditions due to over winter precipitation and melting of the snowpack. The evaporative flux rates from the two sites were nearly identical early in the season, and the repeatability of the diurnal fluxes at the two sites during this period is excellent. Towards the middle of the growing season, the evaporative flux rate at the irrigated site increased relative to the unirrigated site until at the end of the season there was approximately a 40 percent unbiased (dividing by the mean) difference between the two sites. The micrometeorological data indicate nearly uniform atmospheric conditions at the two sites due to turbulent mixing of the air mass within the valley. The persistence of the evaporative flux rate at the unirrigated site was probably due to contributions from the water table, as exhibited in the diurnal piezometer data. The difference in soil heat flux rates between the two sites after dry-down of the unirrigated site was relatively high and affected the difference in available energy (net radiation - soil heat flux). Initial application of LANDSAT data to integrate regional effects of unirrigated project lands over the basin is presented.

Response of plant community structure and primary productivity to experimental drought and flooding in an Alaskan fen

USGS Publications Warehouse

Churchill, A.C.; Turetsky, Merritt R.; McGuire, A. David; Hollingsworth, Teresa N.

2014-01-01

Northern peatlands represent a long-term net sink for atmospheric CO2, but these ecosystems can shift from net carbon (C) sinks to sources based on changing climate and environmental conditions. In particular, changes in water availability associated with climate control peatland vegetation and carbon uptake processes. We examined the influence of changing hydrology on plant species abundance and ecosystem primary production in an Alaskan fen by manipulating the water table in field treatments to mimic either sustained flooding (raised water table) or drought (lowered water table) conditions for 6 years. We found that water table treatments altered plant species abundance by increasing sedge and grass cover in the raised water table treatment and reducing moss cover while increasing vascular green area in the lowered water table treatment. Gross primary productivity was lower in the lowered treatment than in the other plots, although there were no differences in total biomass or vascular net primary productivity among the treatments. Overall, our results indicate that vegetation abundance was more sensitive to variation in water table than total biomass and vascular biomass accrual. Finally, in our experimental peatland, drought had stronger consequences for change in vegetation abundance and ecosystem function than sustained flooding.

Hydrogeology of the surficial aquifer in the vicinity of a former landfill, Naval Submarine Base Kings Bay, Camden County, Georgia

USGS Publications Warehouse

Leeth, David C.

1999-01-01

Neogene and Quaternary sediments constitute the surficial aquifer beneath the study area; in descending order from youngest to oldest these include-the Quaternary undifferentiated surficial sand and Satilla Formation; the Pliocene(?) Cypresshead Formation; and the middle Miocene Coosawhatchie Formation. Beneath the surficial aquifer, the upper Brunswick aquifer consists of part of the lower Miocene Marks Head Formation. The surficial aquifer is divided into three water-bearing zones on the basis of lithologic and geophysical properties of sediments, hydraulic-head differences between zones, and differences in ground-water chemistry. The shallowest zone-the water-table zone-consists of medium to fine sand and clayey sand and is present from land surface to a depth of about 77 feet. Below the water-table zone, the confined upper water-bearing zone consists of medium to very coarse sand and is present from a depth of about 110 to 132 feet. Beneath the upper water-bearing zone, the confined lower water-bearing zone consists of coarse sand and very fine gravel and is present from a depth of about 195 to 237 feet. Hydraulic separation is suggested by differences in water chemistry between the water-table zone and upper water-bearing zone. The sodium chloride type water in the water-table zone differs from the calcium bicarbonate type water in the upper water-bearing zone. Hydraulic separation also is indicated by hydraulic head differences of more than 6.5 feet between the water-table zone and the upper water-bearing zone. Continuous and synoptic water-level measurements in the water-table zone, from October 1995 to April 1997, indicate the presence of a water-table high beneath and adjacent to the former landfill-the surface of which varies about 5 feet with time because of recharge and discharge. Water-level data from clustered wells also suggest that restriction of vertical ground-water flow begins to occur at an altitude of about 5 to 10 feet below sea level (35 to 40 feet below land surface) in the water-table zone because of the increasing clay content of the Cypresshead Formation.

Heat flow vs. atmospheric greenhouse on early Mars

NASA Technical Reports Server (NTRS)

Fanale, F. P.; Postawko, S. E.

1991-01-01

Researchers derived a quantitative relationship between the effectiveness of an atmospheric greenhouse and internal heat flow in producing the morphological differences between earlier and later Martian terrains. The derivation is based on relationships previously derived by other researchers. The reasoning may be stated as follows: the CO2 mean residence time in the Martian atmosphere is almost certainly much shorter than the total time span over which early climate differences are thought to have been sustained. Therefore, recycling of previously degassed CO2 quickly becomes more important than the ongoing supply of juvenile CO2. If so, then the atmospheric CO2 pressure, and thereby the surface temperature, may be approximated mathematically as a function of the total degassed CO2 in the atmosphere plus buried material and the ratio of the atmospheric and regolith mean residence times. The latter ratio can also be expressed as a function of heat flow. Hence, it follows that the surface temperature may be expressed as a function of heat flow and the total amount of available CO2. However, the depth to the water table can simultaneously be expressed as a function of heat flow and the surface temperature (the boundary condition). Therefore, for any given values of total available CO2 and regolith conductivity, there exist coupled independent equations which relate heat flow, surface temperature, and the depth to the water table. This means we can now derive simultaneous values of surface temperature and the depth of the water table for any value of the heat flow. The derived relationship is used to evaluate the relative importance of the atmospheric greenhouse effect and the internal regolith thermal gradient in producing morphological changes for any value of the heat flow, and to assess the absolute importance of each of the values of the heat flow which are thought to be reasonable on independent geophysical grounds.

Can we distinguish autotrophic respiration from heterotrophic respiration in a field site using high temporal resolution CO2 flux measurements?

NASA Astrophysics Data System (ADS)

Biro, Beatrice; Berger, Sina; Praetzel, Leandra; Blodau, Christian

2016-04-01

The processes behind C-cycling in peatlands are important to understand for assessing the vulnerability of peatlands as carbon sinks under changing climate conditions. Especially boreal peatlands are likely to underlie strong alterations in the future. It is expected that C-pools that are directly influenced by vegetation and water table fluctuations can be easily destabilized. The CO2 efflux through respiration underlies autotrophic and heterotrophic processes that show different feedbacks on changing environmental conditions. In order to understand the respiration fluxes better for more accurate modelling and prognoses, the determination of the relative importance of different respiration sources is necessary. Earlier studies used e.g. exfoliation experiments, incubation experiments or modelling approaches to estimate the different respiration sources for the total ecosystem respiration (Reco). To further the understanding in this topic, I want to distinguish autotrophic and heterotrophic respiration using high temporal resolution measurements. The study site was selected along a hydrological gradient in a peatland in southern Ontario (Canada) and measurements were conducted from May to September 2015 once per month. Environmental controls (water table, soil temperature and soil moisture) that effect the respiration sources were recorded. In my study I used a Li-COR 6400XT and a Los Gatos greenhouse gas analyzer (GGA). Reco was determined by chamber flux measurements with the GGA, while simultaneously CO2 respiration measurements on different vegetation compartments like roots, leaves and mosses were conducted using the Li-COR 6400XT. The difference between Reco and autotrophic respiration equals heterotrophic respiration. After the measurements, the vegetation plots were harvested and separated for all compartments (leaves, roots, mosses, soil organic matter), dried and weighed. The weighted respiration rates from all vegetation compartments sum up to autotrophic respiration of the whole plot. I anticipate that heterotrophic processes contribute more to total Reco than the autotrophic ones and that they become more important with increasing water table.

Impact of groundwater levels on evaporation and water-vapor fluxes in highly saline soils

NASA Astrophysics Data System (ADS)

Munoz, J. F.; Hernández, M. F.; Braud, I.; Gironas, J. A.; Suarez, F. I.

2012-12-01

In aquifers of arid and hyper-arid zones, such as those occurring in the Chilean Andes high plateau, it is important to determine both the quantity and location of water discharges at the temporal scales of interest to close the basin's water budget and thus, to manage the water resource properly. In zones where shallow aquifers are the main source of water, overexploitation of the water resource changes the dynamics of water, heat and solute transport in the vadose zone. As aquifers are exploited, fluctuations in depth to groundwater are exacerbated. These fluctuations modify both soil structure and evaporation from the ground, which is typically the most important discharge from the water budget and is very difficult to estimate. Therefore, a correct quantification of evaporation from these soils is essential to improve the accuracy of the water balance estimation. The objective of this study was to investigate the evaporation processes and water-vapor fluxes in a soil column filled with a saline soil from the Salar del Huasco basin, Chile. Water content, electrical conductivity and temperature at different depths in the soil profile were monitored to determine the liquid and vapor fluxes within the soil column. The results showed that evaporation is negligible when the groundwater table is deeper than 1 m. For shallower groundwater levels, evaporation increases in an exponential fashion reaching a value of 3 mm/day when the groundwater table is near the surface of the ground. These evaporation rates are on the same order of magnitude than the field measurements, but slightly lower due to the controlled conditions maintained in the laboratory. Isothermal fluid fluxes were predominant over the non-isothermal fluid and water vapor fluxes. The net flux for all the phreatic levels tested in the laboratory showed different behaviors, with ascending or descending flows as a consequence of changes in water content and temperature distribution within the soil. It was found that evaporation from bare soils occurs as a consequence of vapor transport due to the thermal gradients. This vapor transport was also influences by the salinity of the soil.

Soil-water content characterisation in a modified Jarvis-Stewart model: A case study of a conifer forest on a shallow unconfined aquifer

NASA Astrophysics Data System (ADS)

Guyot, Adrien; Fan, Junliang; Oestergaard, Kasper T.; Whitley, Rhys; Gibbes, Badin; Arsac, Margaux; Lockington, David A.

2017-01-01

Groundwater-vegetation-atmosphere fluxes were monitored for a subtropical coastal conifer forest in South-East Queensland, Australia. Observations were used to quantify seasonal changes in transpiration rates with respect to temporal fluctuations of the local water table depth. The applicability of a Modified Jarvis-Stewart transpiration model (MJS), which requires soil-water content data, was assessed for this system. The influence of single depth values compared to use of vertically averaged soil-water content data on MJS-modelled transpiration was assessed over both a wet and a dry season, where the water table depth varied from the surface to a depth of 1.4 m below the surface. Data for tree transpiration rates relative to water table depth showed that trees transpire when the water table was above a threshold depth of 0.8 m below the ground surface (water availability is non-limiting). When the water table reached the ground surface (i.e., surface flooding) transpiration was found to be limited. When the water table is below this threshold depth, a linear relationship between water table depth and the transpiration rate was observed. MJS modelling results show that the influence of different choices for soil-water content on transpiration predictions was insignificant in the wet season. However, during the dry season, inclusion of deeper soil-water content data improved the model performance (except for days after isolated rainfall events, here a shallower soil-water representation was better). This study demonstrated that, to improve MJS simulation results, appropriate selection of soil water measurement depths based on the dynamic behaviour of soil water profiles through the root zone was required in a shallow unconfined aquifer system.

Estimated depth to the water table and estimated rate of recharge in outcrops of the Chicot and Evangeline aquifers near Houston, Texas

USGS Publications Warehouse

Noble, J.E.; Bush, P.W.; Kasmarek, M.C.; Barbie, D.L.

1996-01-01

In 1989, the U.S. Geological Survey, in cooperation with the Harris-Galveston Coastal Subsidence District, began a field study to determine the depth to the water table and to estimate the rate of recharge in outcrops of the Chicot and Evangeline aquifers near Houston, Texas. The study area comprises about 2,000 square miles of outcrops of the Chicot and Evangeline aquifers in northwest Harris County, Montgomery County, and southern Walker County. Because of the scarcity of measurable water-table wells, depth to the water table below land surface was estimated using a surface geophysical technique, seismic refraction. The water table in the study area generally ranges from about 10 to 30 foot below land surface and typically is deeper in areas of relatively high land-surface altitude than in areas of relatively low land- surface altitude. The water table has demonstrated no long-term trends since ground-water development began, with the probable exception of the water table in the Katy area: There the water table is more than 75 feet deep, probably due to ground-water pumpage from deeper zones. An estimated rate of recharge in the aquifer outcrops was computed using the interface method in which environmental tritium is a ground-water tracer. The estimated average total recharge rate in the study area is 6 inches per year. This rate is an upper bound on the average recharge rate during the 37 years 1953-90 because it is based on the deepest penetration (about 80 feet) of postnuclear-testing tritium concentrations. The rate, which represents one of several components of a complex regional hydrologic budget, is considered reasonable but is not definitive because of uncertainty regarding the assumptions and parameters used in its computation.

Links between climate change, water-table depth, and water chemistry in a mineralized mountain watershed

USGS Publications Warehouse

Manning, Andrew H.; Verplanck, Philip L.; Caine, Jonathan S.; Todd, Andrew S.

2013-01-01

Recent studies suggest that climate change is causing rising solute concentrations in mountain lakes and streams. These changes may be more pronounced in mineralized watersheds due to the sensitivity of sulfide weathering to changes in subsurface oxygen transport. Specific causal mechanisms linking climate change and accelerated weathering rates have been proposed, but in general remain entirely hypothetical. For mineralized watersheds, a favored hypothesis is that falling water tables caused by declining recharge rates allow an increasing volume of sulfide-bearing rock to become exposed to air, thus oxygen. Here, we test the hypothesis that falling water tables are the primary cause of an increase in metals and SO4 (100-400%) observed since 1980 in the Upper Snake River (USR), Colorado. The USR drains an alpine watershed geologically and climatologically representative of many others in mineralized areas of the western U.S. Hydrologic and chemical data collected from 2005 to 2011 in a deep monitoring well (WP1) at the top of the USR watershed are utilized. During this period, both water table depths and groundwater SO4 concentrations have generally increased in the well. A numerical model was constructed using TOUGHREACT that simulates pyrite oxidation near WP1, including groundwater flow and oxygen transport in both saturated and unsaturated zones. The modeling suggests that a falling water table could produce an increase in metals and SO4 of a magnitude similar to that observed in the USR (up to 300%). Future water table declines may produce limited increases in sulfide weathering high in the watershed because of the water table dropping below the depth of oxygen penetration, but may continue to enhance sulfide weathering lower in the watershed where water tables are shallower. Advective air (oxygen) transport in the unsaturated zone caused by seasonally variable recharge and associated water table fluctuations was found to have little influence on pyrite oxidation rates near WP1. However, this mechanism could be important in the case of a shallow dynamic water table and more abundant/reactive sulfides in the shallow subsurface. Data from WP1 and numerical modeling results are thus consistent with the falling water table hypothesis, and illustrate fundamental processes linking climate and sulfide weathering in mineralized watersheds.

Documentation of the Unsaturated-Zone Flow (UZF1) Package for modeling Unsaturated Flow Between the Land Surface and the Water Table with MODFLOW-2005

USGS Publications Warehouse

Niswonger, Richard G.; Prudic, David E.; Regan, R. Steven

2006-01-01

Percolation of precipitation through unsaturated zones is important for recharge of ground water. Rain and snowmelt at land surface are partitioned into different pathways including runoff, infiltration, evapotranspiration, unsaturated-zone storage, and recharge. A new package for MODFLOW-2005 called the Unsaturated-Zone Flow (UZF1) Package was developed to simulate water flow and storage in the unsaturated zone and to partition flow into evapotranspiration and recharge. The package also accounts for land surface runoff to streams and lakes. A kinematic wave approximation to Richards? equation is solved by the method of characteristics to simulate vertical unsaturated flow. The approach assumes that unsaturated flow occurs in response to gravity potential gradients only and ignores negative potential gradients; the approach further assumes uniform hydraulic properties in the unsaturated zone for each vertical column of model cells. The Brooks-Corey function is used to define the relation between unsaturated hydraulic conductivity and water content. Variables used by the UZF1 Package include initial and saturated water contents, saturated vertical hydraulic conductivity, and an exponent in the Brooks-Corey function. Residual water content is calculated internally by the UZF1 Package on the basis of the difference between saturated water content and specific yield. The UZF1 Package is a substitution for the Recharge and Evapotranspiration Packages of MODFLOW-2005. The UZF1 Package differs from the Recharge Package in that an infiltration rate is applied at land surface instead of a specified recharge rate directly to ground water. The applied infiltration rate is further limited by the saturated vertical hydraulic conductivity. The UZF1 Package differs from the Evapotranspiration Package in that evapotranspiration losses are first removed from the unsaturated zone above the evapotranspiration extinction depth, and if the demand is not met, water can be removed directly from ground water whenever the depth to ground water is less than the extinction depth. The UZF1 Package also differs from the Evapotranspiration Package in that water is discharged directly to land surface whenever the altitude of the water table exceeds land surface. Water that is discharged to land surface, as well as applied infiltration in excess of the saturated vertical hydraulic conductivity, may be routed directly as inflow to specified streams or lakes if these packages are active; otherwise, this water is removed from the model. The UZF1 Package was tested against the U.S. Geological Survey's Variably-Saturated Two-Dimensional Flow and Transport Model for a vertical unsaturated flow problem that includes evapotranspiration losses. This report also includes an example in which MODFLOW-2005 with the UZF1 Package was used to simulate a realistic surface-water/ground-water flow problem that includes time and space variable infiltration, evapotranspiration, runoff, and ground-water discharge to land surface and to streams. Another simpler problem is presented so that the user may use the input files as templates for new problems and to verify proper code installation.

WTAQ: A Computer Program for Calculating Drawdowns and Estimating Hydraulic Properties for Confined and Water-Table Aquifers

USGS Publications Warehouse

Barlow, Paul M.; Moench, Allen F.

1999-01-01

The computer program WTAQ calculates hydraulic-head drawdowns in a confined or water-table aquifer that result from pumping at a well of finite or infinitesimal diameter. The program is based on an analytical model of axial-symmetric ground-water flow in a homogeneous and anisotropic aquifer. The program allows for well-bore storage and well-bore skin at the pumped well and for delayed drawdown response at an observation well; by including these factors, it is possible to accurately evaluate the specific storage of a water-table aquifer from early-time drawdown data in observation wells and piezometers. For water-table aquifers, the program allows for either delayed or instantaneous drainage from the unsaturated zone. WTAQ calculates dimensionless or dimensional theoretical drawdowns that can be used with measured drawdowns at observation points to estimate the hydraulic properties of confined and water-table aquifers. Three sample problems illustrate use of WTAQ for estimating horizontal and vertical hydraulic conductivity, specific storage, and specific yield of a water-table aquifer by type-curve methods and by an automatic parameter-estimation method.

Ground-water quality beneath solid-waste disposal sites at anchorage, Alaska

USGS Publications Warehouse

Zenone, Chester; Donaldson, D.E.; Grunwaldt, J.J.

1975-01-01

Studies at three solid-waste disposal sites in the Anchorage area suggest that differences in local geohydrologic conditions influence ground-water quality. A leachate was detected in ground water within and beneath two sites where the water table is very near land surface and refuse is deposited either at or below the water table in some parts of the filled areas. No leachate was detected in ground water beneath a third site where waste disposal is well above the local water table.

Real-time 4D ERT monitoring of river water intrusion into a former nuclear disposal site using a transient warping-mesh water table boundary (Invited)

NASA Astrophysics Data System (ADS)

Johnson, T.; Hammond, G. E.; Versteeg, R. J.; Zachara, J. M.

2013-12-01

The Hanford 300 Area, located adjacent to the Columbia River in south-central Washington, USA, is the site of former research and uranium fuel rod fabrication facilities. Waste disposal practices at site included discharging between 33 and 59 metric tons of uranium over a 40 year period into shallow infiltration galleries, resulting in persistent uranium contamination within the vadose and saturated zones. Uranium transport from the vadose zone to the saturated zone is intimately linked with water table fluctuations and river water intrusion driven by upstream dam operations. As river stage increases, the water table rises into the vadose zone and mobilizes contaminated pore water. At the same time, river water moves inland into the aquifer, and river water chemistry facilitates further mobilization by enabling uranium desorption from contaminated sediments. As river stage decreases, flow moves toward the river, ultimately discharging contaminated water at the river bed. River water specific conductance at the 300 Area varies around 0.018 S/m whereas groundwater specific conductance varies around 0.043 S/m. This contrast provides the opportunity to monitor groundwater/river water interaction by imaging changes in bulk conductivity within the saturated zone using time-lapse electrical resistivity tomography. Previous efforts have demonstrated this capability, but have also shown that disconnecting regularization constraints at the water table is critical for obtaining meaningful time-lapse images. Because the water table moves with time, the regularization constraints must also be transient to accommodate the water table boundary. This was previously accomplished with 2D time-lapse ERT imaging by using a finely discretized computational mesh within the water table interval, enabling a relatively smooth water table to be defined without modifying the mesh. However, in 3D this approach requires a computational mesh with an untenable number of elements. In order to accommodate the water table boundary in 3D, we propose a time-lapse warping mesh inversion, whereby mesh elements that traverse the water table are modified to generate a smooth boundary at the known water table position, enabling regularization constraints to be accurately disconnected across the water table boundary at a given time. We demonstrate the approach using a surface ERT array installed adjacent to the Columbia River at the 300 Area, consisting of 352 electrodes and covering an area of approximately 350 m x 350 m. Using autonomous data collection, transmission, and filtering tools coupled with high performance computing resources, the 4D imaging process is automated and executed in real time. Each time lapse survey consists of approximately 40,000 measurements and 4 surveys are collected and processed per day from April 1st , 2013 to September 30th, 2013. The data are inverted on an unstructured tetrahedral mesh that honors LiDAR-based surface topography and is comprised of approximately 905,000 elements. Imaging results show the dynamic 4D extent of river water intrusion, and are validated with well-based fluid conductivity measurements at each monitoring well within the imaging domain.

Hydrology and model study of the proposed Prosperity Reservoir, Center Creek Basin, southwestern Missouri

USGS Publications Warehouse

Harvey, Edward Joseph; Emmett, Leo F.

1980-01-01

A dam and reservoir have been proposed for construction on Center Creek, Jasper County, in southwestern Missouri. Ground-water levels in the hills adjacent to the reservoir will rise when the impoundment is completed. One of the problems is that the proposed site of Prosperity Reservoir is a few miles upstream from the lead-zinc mining area known as the Oronogo-Duenweg belt. In this belt transmissivities are variable but appear to be higher than they are in the immediate area of the reservoir.Grove Creek lies down-gradient from the reservoir area and separates it from the mining belt. A model study indicates that inflow from the proposed reservoir to the water table could cause water level rises varying from about 20 feet near the reservoir to 0.5 to 1.0 foot in the southern part of Grove Creek drainage basin. These rises will cause significant changes to the natural ground-water flow system. Increased ground-water elevations in the reservoir area could result in increased ground-water gradients and discharge to Grove and Center Creeks. The increase in ground-water discharge to Grove Creek, and in turn Center Creek, will have the beneficial effect of diluting mine-water discharge from the Oronogo-Duenweg belt during periods of low flow.However, if Grove Creek does not act as an effective drain and if conduits extend beneath Grove Creek to transfer the increased water available to the Oronogo-Duenweg belt, the flow regimen could change in the mining belt west of Grove Creek increasing mine-water discharge to Center Creek downstream from the reservoir.Bedrock in the area is Mississippian limestone, the deeply solutioned formation that contained the ore deposits. The limestone in the mining district was greatly altered by solution prior to ore deposition while the limestone in the area of the reservoir was altered less. The extent of the alteration is related to the aquifer characteristics in that high and low values of transmissivity and storage coefficient correspond to greatly altered brecciated rocks in the mining district and less altered, less brecciated rocks in the reservoir area, respectively.The authors suggest that an ancestral east-flowing White River drained the area about Joplin in Late Mississippian time. This is based on the configuration of the contact between Meramecian and Osagean rocks of Mississippian age. A high topographic area existed in the region about Joplin in which the water table stood 200 feet below the land surface when sinkholes and caverns of that depth were formed. The large number of Pennsylvanian-filled sinkholes in the Joplin area and the smaller number to the east suggest a higher land surface to the west than that to the east. The distribution of paleokarst sinkholes supports the conclusion based on the configuration of the Meramecian-Osagean contact.

A Blind Hydrothermal System in an Ocean Island Environment: Humu'ula Saddle, Hawaii Island

NASA Astrophysics Data System (ADS)

Thomas, D. M.; Wallin, E.; Lautze, N. C.; Lienert, B. R.; Pierce, H. A.

2014-12-01

A recently drilled groundwater investigation borehole, drilled to a depth of 1760 m in the Humu'ula Saddle of Hawaii Island, encountered an unexpectedly high temperature gradient of more than 160 ̊C/km. Although prior MT surveys across the region identified conductive formations of modest extent in the region, there were few surface manifestations of geologic structures likely to host a geothermal system and no evidence of an active, extensive hydrothermal system. Cores recovered from the borehole showed the presence of intrusive formations and moderate hydrothermal alteration at depth with progressive infilling of fractures and vesicles with depth and temperature. Independent modeling of gravity data (Flinders et al., 2013) suggests the presence of a broad intrusive complex within the region that is consistent with the borehole's confirmation of a high-elevation (~1400 m amsl) regional water table. A subsequent MT survey covering much of the western Saddle region has confirmed the presence of highly conductive conditions, consistent with thermal activity, to depths of 4 km and greater. Light stable isotope data for the borehole fluids indicate that the regional water table is derived from recharge from the upper elevations of Mauna Kea; major element chemistry indicates that formation temperatures exceed 200 ̊C. A conceptual model of the hydrothermal system, along with isotopic and fluid chemistry of the thermal fluids will be presented.

Altitude of the water table in the alluvial and other shallow aquifers along the Colorado River near La Grange, Texas, December 1980

USGS Publications Warehouse

Rettman, Paul

1981-01-01

The delineation of the water table in the alluvium of the Colorado River is fairly well defined, and 10-feet contour intervals may be interpreted with confidence in the area called ' potential lignite-mining area. ' The water table in the bedrock aquifers is more difficult to delineate with the available data; therefore, the contours are only estimates of the position of the water table in the hilly bedrock area adjacent to the Colorado River alluvium. 

Hydrologic conditions, recharge, and baseline water quality of the surficial aquifer system at Jekyll Island, Georgia, 2012-13

USGS Publications Warehouse

Gordon, Debbie W.; Torak, Lynn J.

2016-03-08

Groundwater levels and specific-conductance measurements showed the dependence of freshwater resources on rainfall to recharge the water-table zone of the surficial aquifer system and to influence groundwater flow on Jekyll Island. The unseasonably dry conditions during November 2012 to April 2013 induced saline water infiltration to the water-table zone from the marshland separating the Jekyll River from the island. A strong correlation (R2 = 0.97) of specific conductance to chloride concentration in water samples from wells installed in the water-table zone provided support for the determination of seasonal directions of groundwater flow by confirming salinity changes in the water-table zone. Unseasonably wet conditions during the late spring to August caused groundwater-flow reversals in some areas. The high dependence of the water-table zone in the surficial aquifer system on precipitation to replenish the aquifer with freshwater underscored the importance of monitoring groundwater levels, water quality, and water use to identify aquifer-discharge conditions that have the potential to promote seawater encroachment and degrade freshwater resources on Jekyll Island.

Impact of a shallow groundwater table on the global water cycle in the IPSL land-atmosphere coupled model

NASA Astrophysics Data System (ADS)

Wang, Fuxing; Ducharne, Agnès; Cheruy, Frédérique; Lo, Min-Hui; Grandpeix, Jean-Yves

2017-07-01

The main objective of the present work is to study the impacts of water table depth on the near surface climate and the physical mechanisms responsible for these impacts through the analysis of land-atmosphere coupled numerical simulations. The analysis is performed with the LMDZ (standard physics) and ORCHIDEE models, which are the atmosphere-land components of the Institut Pierre Simon Laplace (IPSL) Climate Model. The results of sensitivity experiments with groundwater tables (WT) prescribed at depths of 1 m (WTD1) and 2 m (WTD2) are compared to the results of a reference simulation with free drainage from an unsaturated 2 m soil (REF). The response of the atmosphere to the prescribed WT is mostly concentrated over land, and the largest differences in precipitation and evaporation are found between REF and WTD1. Saturating the bottom half of the soil in WTD1 induces a systematic increase of soil moisture across the continents. Evapotranspiration (ET) increases over water-limited regimes due to increased soil moisture, but it decreases over energy-limited regimes due to the decrease in downwelling radiation and the increase in cloud cover. The tropical (25°S-25°N) and mid-latitude areas (25°N-60°N and 25°S-60°S) are significantly impacted by the WT, showing a decrease in air temperature (-0.5 K over mid-latitudes and -1 K over tropics) and an increase in precipitation. The latter can be explained by more vigorous updrafts due to an increased meridional temperature gradient between the equator and higher latitudes, which transports more water vapour upward, causing a positive precipitation change in the ascending branch. Over the West African Monsoon and Australian Monsoon regions, the precipitation changes in both intensity (increases) and location (poleward). The more intense convection and the change of the large-scale dynamics are responsible for this change. Transition zones, such as the Mediterranean area and central North America, are also impacted, with strengthened convection resulting from increased ET.

Hydrology and chemistry of groundwater and seasonal ponds in the Atlantic Coastal Plain in Delaware, USA

USGS Publications Warehouse

Phillips, P.J.; Shedlock, R.J.

1993-01-01

The hydrochemistry of small seasonal ponds was investigated by studying relations between ground-water and surface water in a forested Coastal Plain drainage basin. Observation of changes in the water table in a series of wells equipped with automatic water-level recorders showed that the relation between water-table configuration and basin topography changes seasonally, and particularly in response to spring recharge. Furthermore, in this study area the water table is not a subdued expression of the land surface topography, as is commonly assumed. During the summer and fall months, a water-table trough underlies sandy ridges separating the seasonal ponds, and maximum water-table altitudes prevail in the sediments beneath the dry pond bottoms. As the ponds fill with water during the winter, maximum water-table altitudes shift to the upland-margin zone adjacent to the seasonal ponds. Increases in pond stage are associated with the development of transient water-table mounds at the upland-margin wells during the spring. The importance of small local-flow systems adjacent to the seasonal ponds also is shown by the similarities in the chemistry of the shallow groundwater in the upland margin and water in the seasonal ponds. The upland margin and surface water samples have low pH (generally less than 5.0), and contain large concentrations of dissolved aluminum (generally more than 100 ??g 1-1), and low bicarbonate concentrations (2 mg l4 or less). In contrast, the parts of the surficial aquifer that do not experience transient mounding have higher pH and larger concentrations of bicarbonate. These results suggest that an understanding of the hydrochemistry of seasonally ponded wetlands requires intensive study of the adjacent shallow groundwater-flow system. ?? 1993.

The complex relationships between methane emissions and water table at an ombrotrophic bog

NASA Astrophysics Data System (ADS)

Humphreys, Elyn; Roulet, Nigel; Moore, Tim

2017-04-01

Broad spatial and temporal variations in methane emissions from peatlands have been related to many variables including water table position, temperature and vegetation characteristics and functioning. In general, wetter peatlands tend to have greater methane emissions. However, over shorter periods of time and space, the relationship between water table and methane emissions can reverse, show hysteresis or be absent entirely. These relationships are investigated at the Mer Bleue Bog, a temperate ombrotrophic bog near Ottawa, Canada. Six years of concurrent growing season eddy covariance and automated chamber fluxes reveal the expected broad patterns. During the wettest growing season, the water table remained within 40 cm of the bog's hummock surfaces. Methane emissions were upwards of 20 to 45 mg C m-2 d-1 and exceeded the emission rates from two drier growing seasons which saw periods where the water table dropped to nearly 80 cm below the hummock surface. In those periods, methane emission rates declined to about 5 mg C m-2 d-1 or less. Lawn plots with aerenchymatous Eriophorum vegetation and high water tables had greatest emissions (exceeding 200 mg C m-2 d-1) compared to hummock plots vegetated by ericaceous shrubs, which had emissions rates similar to those measured by eddy covariance. However, within a growing season, hysteresis and inverse relationships between water table and methane emissions were observed at both ecosystem and chamber plot scales. These included periods between rainfall events where methane emissions increased while the water table deepened. The potential roles of methane production, consumption, storage and transport processes on these patterns will be discussed.

Groundwater in the Boreal Plains: How Climate and Geology Interact to Control Water Table Configurations in a Sub-Humid, Low-Relief Region

NASA Astrophysics Data System (ADS)

Hokanson, K. J.; Devito, K.; Mendoza, C. A.

2017-12-01

The Boreal Plain (BP) region of Canada, a landscape characterized by low-relief, a sub-humid climate and heterogeneous glacial landforms, is experiencing unprecedented anthropogenic and natural disturbance, including climate change and oil & gas operations. Understanding the controls on and the natural variability of water table position, and subsequently predicting changes in water table position under varying physical and climatic scenarios will become important as water security becomes increasingly threatened. The BP is composed of a mosaic of forestland, wetland, and aquatic land covers that contrast in dominant vegetation cover, evapotranspiration, and soil storage that, in turn, influence water table configurations. Additionally, these land-covers overlie heterogeneous glacial landforms with large contrasts in storage and hydraulic properties which, when coupled with wet-dry climate cycles, result in complex water table distributions in time and space. Several forestland-wetland-pond complexes were selected at the Utikuma Research Study Area (URSA) over three distinct surficial geologic materials (glacial fluvial outwash, stagnant ice moraine, lacustrine clay plain) to explore the roles of climate (cumulative departure from the long term yearly mean precipitation), geology, topographic position, and land cover on water table configurations over 15 years (2002 - 2016). In the absence of large groundwater flow systems, local relief and shallow low conductivity substrates promote the formation of near-surface water tables that are less susceptible to climate variation, regardless of topography. Furthermore, in areas of increased storage, wet and dry climate conditions can result in appreciably different water table configurations over time, ranging from mounds to hydraulic depressions, depending on the arrangement of land-covers, dominant surficial geology, and substrate layering.

Transport of E. coli in a sandy soil as impacted by depth to water table.

PubMed

Stall, Christopher; Amoozegar, Aziz; Lindbo, David; Graves, Alexandria; Rashash, Diana

2014-01-01

Septic systems are considered a source of groundwater contamination. In the study described in this article, the fate of microbes applied to a sandy loam soil from North Carolina coastal plain as impacted by water table depth was studied. Soil materials were packed to a depth of 65 cm in 17 columns (15-cm diameter), and a water table was established at 30, 45, and 60 cm depths using five replications. Each day, 200 mL of an artificial septic tank effluent inoculated with E. coli were applied to the top of each column, a 100-mL sample was collected at the water table level and analyzed for E. coli, and 100 mL was drained from the bottom to maintain the water table. Two columns were used as control and received 200 mL/day of sterilized effluent. Neither 30 nor 45 cm of unsaturated soil was adequate to attenuate bacterial contamination, while 60 cm of separation appeared to be sufficient. Little bacterial contamination moved with the water table when it was lowered from 30 to 60 cm.

Secondary precious metal enrichment by steam-heated fluids in the Crofoot-Lewis hot spring gold-silver deposit and relation to paleoclimate

USGS Publications Warehouse

Ebert, S.W.; Rye, R.O.

1997-01-01

The Crofoot-Lewis deposit is an adularia-sericite-type (low-sulfidation) epithermal Au-Ag deposit, whose well-preserved paleosurface includes abundant opaline sinters, widespread and intense silicification, bedded hydrothermal eruption breccias, and a large zone of acid sulfate alteration. Radiogenic isotope ages indicate that the system was relatively long-lived, with hydrothermal activity starting around 4 Ma and extending, at least intermittently, for the next 3 m.y. Field evidence indicates that the surficial zone of acid sulfate alteration formed in a steam-heated environment within an active geothermal system. A drop in the water table enabled descending acid sulfate waters to leach Au and Ag from zones of low-grade disseminated mineralization, resulting in the redistribution and concentration of Au and Ag into ore-grade concentrations. These zones of secondary Au-Ag enrichment are associated with opal + alunite + kaolinite + montmorillonite ?? hematite and were deposited in open space fractures at, and within a few tens of meters below, the paleowater table. The stable isotope systematics of alunite and kaolinite in the steam-heated environment are relatively complex, due to variations in the residence time of aqueous SO4 that formed from the oxidation of H2S prior to precipitation of alunite, and the susceptibility of fine-grained kaolinites to hydrogen isotope exchange with later waters. Most of the alunites are enriched in 34S relative to early sulfide minerals, reflecting partial S isotope exchange between aqueous SO4 and H2S. About half of the alunites give reasonable calculated ??18OSO4-OH temperatures for a steam-heated environment indicating O isotope equilibrium between aqueous SO4 and water. The ??5DH2O values of the hydrothermal fluids varied by almost 60 per mil over the life of the meteoric water-dominated system, suggesting significant climate changes. Mineralization is believed to have resulted from large-scale convection of meteoric water controlled largely by basin and range fractures and a high geothermal gradient with H2S for Au complexing derived from organic matter in basin sediments. A wet climate resulted in the formation of a large inland lake which provided abundant recharge water for the hydrothermal system. A fluctuating water table controlled by changing climatic conditions enabled steam-heated acid sulfate fluids to overprint lower grade mineralization resulting in ore-grade precious metal enrichment.

Testate amoebae communities sensitive to surface moisture conditions in Patagonian peatlands

NASA Astrophysics Data System (ADS)

Loisel, J.; Booth, R.; Charman, D.; van Bellen, S.; Yu, Z.

2017-12-01

Here we examine moss surface samples that were collected during three field campaigns (2005, 2010, 2014) across southern Patagonian peatlands to assess the potential use of testate amoebae and 13C isotope data as proxy indicators of soil moisture. These proxies have been widely tested across North America, but their use as paleoecological tools remains sparse in the southern hemisphere. Samples were collected along a hydrological gradient spanning a range of water table depth from 0cm in wet hollows to over 85cm in dry hummocks. Moss moisture content was measured in the field. Over 25 taxa were identified, with many of them not found in North America. Ordinations indicate statistically significant and dominant effects of soil moisture and water table depth on testate assemblages, though interestingly 13C is even more strongly correlated with testates amoebae than direct soil conditions. It is possible that moss 13C signature constitutes a compound indicator that represents seasonal soil moisture better than opportunistic sampling during field campaigns. There is no significant effect of year or site across the dataset. In addition to providing a training set that translates testate amoebae moisture tolerance range into water tabel depth for Patagonian peatlands, we also compare our results with those from the North American training set to show that, despite 'novel' Patagonian taxa, the robustness of international training sets is probably sufficient to quantify most changes in soil moisture from any site around the world. We also identify key indicator species that are shown to be of universal value in peat-based hydrological reconstructions.

Fully integrated physically-based numerical modelling of impacts of groundwater extraction on surface and irrigation-induced groundwater interactions: case study Lower River Murray, Australia

NASA Astrophysics Data System (ADS)

Alaghmand, S.; Beecham, S.; Hassanli, A.

2013-07-01

Combination of reduction in the frequency, duration and magnitude of natural floods, rising saline water-table in floodplains and excessive evapotranspiration have led to an irrigation-induced groundwater mound forced the naturally saline groundwater onto the floodplain in the Lower River Murray. It is during the attenuation phase of floods that these large salt accumulations are likely to be mobilised and will discharge into the river. The Independent Audit Group for Salinity highlighted this as the most significant risk in the Murray-Darling Basin. South Australian government and catchment management authorities have developed salt interception schemes (SIS). This is to pump the highly saline groundwater from the floodplain aquifer to evaporation basins in order to reduce the hydraulic gradient that drives the regional saline groundwater towards the River Murray. This paper investigates the interactions between a river (River Murray in South Australia) and a saline semi-arid floodplain (Clarks Floodplain) significantly influenced by groundwater lowering (Bookpurnong SIS). Results confirm that groundwater extraction maintain a lower water-table and more fresh river water flux to the saline floodplain aquifer. In term of salinity, this may lead to less amount of solute stored in the floodplain aquifer. This occurs through two mechanisms; extracting some of the solute mass from the system and changing the floodplain groundwater regime from a losing to gaining one. Finally, it is shown that groundwater extraction is able to remove some amount of solute stored in the unsaturated zone and mitigate the floodplain salinity risk.

Effects of soil water table regime on tree community species richness and structure of alluvial forest fragments in Southeast Brazil.

PubMed

Silva, A C; Higuchi, P; van den Berg, E

2010-08-01

In order to determine the influence of soil water table fluctuation on tree species richness and structure of alluvial forest fragments, 24 plots were allocated in a point bar forest and 30 plots in five forest fragments located in a floodplain, in the municipality of São Sebastião da Bela Vista, Southeast Brazil, totalizing 54, 10 X 20 m, plots. The information recorded in each plot were the soil water table level, diameter at breast height (dbh), total height and botanical identity off all trees with dbh > 5 cm. The water table fluctuation was assessed through 1 m deep observation wells in each plot. Correlations analysis indicated that sites with shallower water table in the flooding plains had a low number of tree species and high tree density. Although the water table in the point bar remained below the wells during the study period, low tree species richness was observed. There are other events taking place within the point bar forest that assume a high ecological importance, such as the intensive water velocity during flooding and sedimentation processes.

Hyporheic Exchange Flows and Biogeochemical Patterns near a Meandering Stream: East Fork of the Jemez River, Valles Caldera National Preserve, New Mexico

NASA Astrophysics Data System (ADS)

Christensen, H.; Wooten, J. P.; Swanson, E.; Senison, J. J.; Myers, K. D.; Befus, K. M.; Warden, J.; Zamora, P. B.; Gomez, J. D.; Wilson, J. L.; Groffman, A.; Rearick, M. S.; Cardenas, M. B.

2012-12-01

A study by the 2012 Hydrogeology Field Methods class of the University of Texas at Austin implemented multiple approaches to evaluate and characterize local hyporheic zone flow and biogeochemical trends in a highly meandering reach of the of the East Fork of the Jemez River, a fourth order stream in northwestern New Mexico. This section of the Jemez River is strongly meandering and exhibits distinct riffle-pool morphology. The high stream sinuosity creates inter-meander hyporheic flow that is also largely influenced by local groundwater gradients. In this study, dozens of piezometers were used to map the water table and flow vectors were then calculated. Surface water and ground water samples were collected and preserved for later geochemical analysis by ICPMS and HPLC, and unstable parameters and alkalinity were measured on-site. Additionally, information was collected from thermal monitoring of the streambed, stream gauging, and from a series of electrical resistivity surveys forming a network across the site. Hyporheic flow paths are suggested by alternating gaining and losing sections of the stream as determined by stream gauging at multiple locations along the reach. Water table maps and calculated fluxes across the sediment-water interface also indicate hyporheic flow paths. We find variability in the distribution of biogeochemical constituents (oxidation-reduction potential, nitrate, ammonium, and phosphate) along interpreted flow paths which is partly consistent with hyporheic exchange. The variability and heterogeneity of reducing and oxidizing conditions is interpreted to be a result of groundwater-surface water interaction. Two-dimensional mapping of biogeochemical parameters show redox transitions along interpreted flow paths. Further analysis of various measured unstable chemical parameters results in observable trends strongly delineated along these preferential flow paths that are consistent with the direction of groundwater flow and the assumed direction of inter-meander hyporheic flow.

Event-Based Analysis of Rainfall-Runoff Response to Assess Wetland-Stream Interaction in the Prairie Pothole Region

NASA Astrophysics Data System (ADS)

Haque, M. A.; Ross, C.; Schmall, A.; Bansah, S.; Ali, G.

2016-12-01

Process-based understanding of wetland response to precipitation is needed to quantify the extent to which non-floodplain wetlands - such as Prairie potholes - generate flow and transmit that flow to nearby streams. While measuring wetland-stream (W-S) interaction is difficult, it is possible to infer it by examining hysteresis characteristics between wetland and stream stage during individual precipitation events. Hence, to evaluate W-S interaction, 10 intact and 10 altered/lost potholes were selected for study; they are located in Broughton's Creek Watershed (Manitoba, Canada) on both sides of a 5 km creek reach. Stilling wells (i.e., above ground wells) were deployed in the intact and altered wetlands to monitor surface water level fluctuations while water table wells were drilled below drainage ditches to a depth of 1 m to monitor shallow groundwater fluctuations. All stilling wells and water table wells were equipped with capacitance water level loggers to monitor fluctuations in surface water and shallow groundwater every 15 minutes. In 2013 (normal year) and 2014 (wet year), 15+ precipitation events were identified and scatter plots of wetland (x-axis) versus stream (y-axis) stage were built to identify W-S hysteretic dynamics. Initial data analysis reveals that in dry antecedent conditions, intact and altered wetlands show clockwise W-S relations, while drained wetlands show anticlockwise W-S hysteresis. However, in wetter antecedent conditions, all wetland types show anticlockwise hysteresis. Future analysis will target the identification of thresholds in antecedent moisture conditions that determine significant changes in event wetland response characteristics (e.g., the delay between the start of rainfall and stream stage, the maximum water level rise in each wetland during each event, the delay between the start of rainfall and peak wetland stage) as well as hysteresis properties (e.g., gradient and area of the hysteresis loop).

Estimating steady-state evaporation rates from bare soils under conditions of high water table

USGS Publications Warehouse

Ripple, C.D.; Rubin, J.; Van Hylckama, T. E. A.

1970-01-01

A procedure that combines meteorological and soil equations of water transfer makes it possible to estimate approximately the steady-state evaporation from bare soils under conditions of high water table. Field data required include soil-water retention curves, water table depth and a record of air temperature, air humidity and wind velocity at one elevation. The procedure takes into account the relevant atmospheric factors and the soil's capability to conduct 'water in liquid and vapor forms. It neglects the effects of thermal transfer (except in the vapor case) and of salt accumulation. Homogeneous as well as layered soils can be treated. Results obtained with the method demonstrate how the soil evaporation rates·depend on potential evaporation, water table depth, vapor transfer and certain soil parameters.

Evaluating hillslope and riparian contributions to dissolved nitrogen (N) export from a boreal forest catchment

NASA Astrophysics Data System (ADS)

Blackburn, M.; Ledesma, José L. J.; Näsholm, Torgny; Laudon, Hjalmar; Sponseller, Ryan A.

2017-02-01

Catchment science has long held that the chemistry of small streams reflects the landscapes they drain. However, understanding the contribution of different landscape units to stream chemistry remains a challenge which frequently limits our understanding of export dynamics. For limiting nutrients such as nitrogen (N), an implicit assumption is that the most spatially extensive landscape units (e.g., uplands) act as the primary sources to surface waters, while near-stream zones function more often as sinks. These assumptions, based largely on studies in high-gradient systems or in regions with elevated inputs of anthropogenic N, may not apply to low-gradient, nutrient-poor, and peat-rich catchments characteristic of many northern ecosystems. We quantified patterns of N mobilization along a hillslope transect in a northern boreal catchment to assess the extent to which organic matter-rich riparian soils regulate the flux of N to streams. Contrary to the prevailing view of riparian functioning, we found that near-stream, organic soils supported concentrations and fluxes of ammonium (NH4+) and dissolved organic nitrogen that were much higher than the contributing upslope forest soils. These results suggest that stream N chemistry is connected to N mobilization and mineralization within the riparian zone rather than the wider landscape. Results further suggest that water table fluctuation in near-surface riparian soils may promote elevated rates of net N mineralization in these landscapes.

An interoperability experiment for sharing hydrological rating tables

NASA Astrophysics Data System (ADS)

Lemon, D.; Taylor, P.; Sheahan, P.

2013-12-01

The increasing demand on freshwater resources is requiring authorities to produce more accurate and timely estimates of their available water. Calculation of continuous time-series of river discharge and storage volumes generally requires rating tables. These approximate relationships between two phenomena, such as river level and discharge, and allow us to produce continuous estimates of a phenomenon that may be impractical or impossible to measure directly. Standardised information models or access mechanisms for rating tables are required to support sharing and exchange of water flow data. An Interoperability Experiment (IE) is underway to test an information model that describes rating tables, the observations made to build these ratings, and river cross-section data. The IE is an initiative of the joint World Meteorological Organisation/Open Geospatial Consortium's Hydrology Domain Working Group (HydroDWG) and the model will be published as WaterML2.0 part 2. Interoperability Experiments (IEs) are low overhead, multiple member projects that are run under the OGC's interoperability program to test existing and emerging standards. The HydroDWG has previously run IEs to test early versions of OGC WaterML2.0 part 1 - timeseries. This IE is focussing on two key exchange scenarios: Sharing rating tables and gauging observations between water agencies. Through the use of standard OGC web services, rating tables and associated data will be made available from water agencies. The (Australian) Bureau of Meteorology will retrieve rating tables on-demand from water authorities, allowing the Bureau to run conversions of data within their own systems. Exposing rating tables and gaugings for online analysis and educational purposes. A web client will be developed to enable exploration and visualization of rating tables, gaugings and related metadata for monitoring points. The client gives a quick view into available rating tables, their periods of applicability and the standard deviation of observations against the relationship. An example of this client running can be seen at the link provided. The result of the IE will form the basis for the standardisation of WaterML2.0 part 2. The use of the standard will lead to increased transparency and accessibility of rating tables, while also improving general understanding of this important hydrological concept.

Reduction of hydraulic conductivity in column simulations of unconsolidated sediments by growth of in situ microflora

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

Bertetti, F.P.; Birnbaum, S.J.

1992-01-01

Laboratory experiments were employed to determine the effects of microbial growth upon the hydraulic conductivity (K) of unconsolidated sediments at Kelly Air Force Base, Texas. Indigenous microflora were isolated from sediment samples collected at sites contaminated with toxic organic compounds (e.g. dichlorobenzene) by plating on concentrated and dilute media. Plexiglas columns were packed with silica beads or Kelly AFB sediment and used to simulate ground water flow conditions. Grain sizes were selected to yield realistic K values (2.0 [times] 10[sup [minus]1] to 8.0 [times] 10[sup [minus]3] cm/sec) defined by field data from the contaminated sites. Both individual and mixed microbialmore » colonies, selected based on morphological characteristics individual and mixed microbial colonies, selected based on morphological characteristics deemed favorable for porosity obstruction, were injected into sterile, saturated columns. Growth was stimulated by adding sterile liquid nutrient media. Media flow rates were based upon field derived hydraulic conductivity values and water table gradients. Flow rates were controlled using a peristaltic pump. Growth of the microorganisms produced biomass which reduced the column hydraulic conductivity by up to 90% in 11 days. Reduction in K was accomplished via clogging of pore throats by cell attachment and accumulation on bead surfaces, and extracellular biofilm development. Sediment packed columns showed reduction in K values similar to that of bead packed columns of equivalent grain size. Porosity obstruction and corresponding reduction in K persisted in the columns even when subjected to hydraulic gradients significantly exceeding gradients measured in the field thereby demonstrating the robust nature of biological barrier to flow.« less

Numerical modeling of the destruction of steel plates with a gradient substrate

NASA Astrophysics Data System (ADS)

Orlov, M. Yu.; Glazyrin, V. P.; Orlov, Yu. N.

2017-10-01

The paper presents the results of numerical simulation of the shock loading process of steel barriers with a gradient substrate. In an elastic plastic axisymmetric statement, a shock is simulated along the normal in the range of initial velocities up to 300 m / s. A range of initial velocities was revealed, in which the presence of a substrate "saved" the obstacle from spallation. New tasks were announced to deepen scientific knowledge about the behavior of unidirectional gradient barriers at impact. The results of calculations are obtained in the form of graphs, calculated configurations of the "impact - barrier" and tables.

Natural groundwater recharge in an upland area of central North Dakota, U.S.A.

USGS Publications Warehouse

Rehm, B.W.; Moran, S.R.; Groenewold, G.H.

1982-01-01

The magnitude of groundwater recharge to coal aquifers in a 150-km2 area in west-central North Dakota was determined using three separate approaches: (1) the net water level rise in water-table wells; (2) calculations of the fluid flux between nested piezometers, using the Darcy equation and measured values of hydraulic conductivity and vertical gradients; and (3) evaluation of the inputs to and outputs from the coal aquifer, using a steady-state control volume approach in which the aquifer was divided into semi-rectangular cells bounded by equipotential lines and flow lines. Measurements of potential gradients and hydraulic conductivity permitted indirect determination of all components of flow into and out of the cell except the recharge input, which was determined by difference. All methods yielded consistent results on the order of 0.04-0.01 m yr.-1 These values, which represent 2-9% of the annual precipitation, are consistent with results of other studies on recharge throughout the prairies of North America. Evaluation of site hydrology and stable-isotope data indicates that recharge is restricted in both time and place. Most recharge occurs in late spring and in the fall following heavy rainfall events. During these seasons the ground is not frozen and vegetation is not transpiring large amounts of water. Some recharge may occur during very heavy localized summer storms, but it is not considered volumetrically significant. Major permanent depressions on the site are a source of significant recharge. In addition, the extensive area of ephemeral standing water bodies that result from snowmelt can produce significant amounts of infiltration over the entire site. ?? 1982.

Elk browsing increases aboveground growth of water-stressed willows by modifying plant architecture.

PubMed

Johnston, Danielle B; Cooper, David J; Hobbs, N Thompson

2007-12-01

In the northern elk wintering range of Yellowstone National Park, USA, wolf (Canis lupus) removal allowed elk (Cervus elaphus) to overbrowse riparian woody plants, leading to the exclusion of beaver (Castor canadensis) and a subsequent water table decline in many small stream valleys. Reduced elk browsing following wolf reintroduction may or may not facilitate willow (Salix sp.) recovery in these areas. To determine if the effect of elk browsing on willow interacts with that of beaver abandonment, we manipulated elk browsing and the water table in a factorial experiment. Under the condition of an ambient (low) water table, elk browsing increased shoot water potential (Psis), photosynthesis per unit leaf area (A), stomatal conductance per unit leaf area (gs), and aboveground current annual growth (CAG) by 50%. Elk browsing occurred entirely during dormancy and did not affect total plant leaf area (L). Improved water balance, photosynthetic rate, and annual aboveground productivity in browsed willows appeared to be due to morphological changes, such as increased shoot diameter and decreased branching, which typically increase plant hydraulic conductivity. An elevated water table increased Psis, A, gs, CAG, and L, and eliminated or lessened the positive effect of browsing on CAG for most species. Because low water tables create conditions whereby high willow productivity depends on the morphological effects of annual elk browsing, removing elk browsing in areas of water table decline is unlikely to result in vigorous willow stands. As large willow standing crops are required by beaver, a positive feedback between water-stressed willow and beaver absence may preclude the reestablishment of historical conditions. In areas with low water table, willow restoration may depend on actions to promote the re-establishment of beaver in addition to reducing elk browsing.

Response of anaerobic carbon cycling to water table manipulation in an Alaskan rich fen

Treesearch

E.S. Kane; M.R. Chivers; M.S. Turetsky; C.C. Treat; D.G. Petersen; M. Waldrop; J.W. Harden; A.D. McGuire

2013-01-01

To test the effects of altered hydrology on organic soil decomposition, we investigated CO2 and CH4 production potential of rich-fen peat (mean surface pH = 6.3) collected from a field water table manipulation experiment including control, raised and lowered water table treatments. Mean anaerobic CO2...

Peatland pines as a proxy for water table fluctuations: disentangling tree growth, hydrology and possible human influence.

PubMed

Smiljanić, Marko; Seo, Jeong-Wook; Läänelaid, Alar; van der Maaten-Theunissen, Marieke; Stajić, Branko; Wilmking, Martin

2014-12-01

Dendrochronological investigations of Scots pine (Pinus sylvestris L.) growing on Männikjärve peatland in central Estonia showed that annual tree growth of peatland pines can be used as a proxy for past variations of water table levels. Reconstruction of past water table levels can help us to better understand the dynamics of various ecological processes in peatlands, e.g. the formation of vegetation patterns or carbon and nitrogen cycling. Männikjärve bog has one of the longest water table records in the boreal zone, continuously monitored since 1956. Common uncertainties encountered while working with peatland trees (e.g. narrow, missing and wedging rings) were in our case exacerbated with difficulties related to the instability of the relationship between tree growth and peatland environment. We hypothesized that the instable relationship was mainly due to a significant change of the limiting factor, i.e. the rise of the water table level due to human activity. To test our hypothesis we had to use several novel methods of tree-ring chronology analysis as well as to test explicitly whether undetected missing rings biased our results. Since the hypothesis that the instable relationship between tree growth and environment was caused by a change in limiting factor could not be rejected, we proceeded to find possible significant changes of past water table levels using structural analysis of the tree-ring chronologies. Our main conclusions were that peatland pines can be proxies to water table levels and that there were several shifting periods of high and low water table levels in the past 200 years. Copyright © 2014 Elsevier B.V. All rights reserved.

Effect of vegetation removal and water table drawdown on the non-methane biogenic volatile organic compound emissions in boreal peatland microcosms

NASA Astrophysics Data System (ADS)

Faubert, Patrick; Tiiva, Päivi; Rinnan, Åsmund; Räty, Sanna; Holopainen, Jarmo K.; Holopainen, Toini; Rinnan, Riikka

2010-11-01

Biogenic volatile organic compound (BVOC) emissions are important in the global atmospheric chemistry and their feedbacks to global warming are uncertain. Global warming is expected to trigger vegetation changes and water table drawdown in boreal peatlands, such changes have only been investigated on isoprene emission but never on other BVOCs. We aimed at distinguishing the BVOCs released from vascular plants, mosses and peat in hummocks (dry microsites) and hollows (wet microsites) of boreal peatland microcosms maintained in growth chambers. We also assessed the effect of water table drawdown (-20 cm) on the BVOC emissions in hollow microcosms. BVOC emissions were measured from peat samples underneath the moss surface after the 7-week-long experiment to investigate whether the potential effects of vegetation and water table drawdown were shown. BVOCs were sampled using a conventional chamber method, collected on adsorbent and analyzed with GC-MS. In hummock microcosms, vascular plants increased the monoterpene emissions compared with the treatment where all above-ground vegetation was removed while no effect was detected on the sesquiterpenes, other reactive VOCs (ORVOCs) and other VOCs. Peat layer from underneath the surface with intact vegetation had the highest sesquiterpene emissions. In hollow microcosms, intact vegetation had the highest sesquiterpene emissions. Water table drawdown decreased monoterpene and other VOC emissions. Specific compounds could be closely associated to the natural/lowered water tables. Peat layer from underneath the surface of hollows with intact vegetation had the highest emissions of monoterpenes, sesquiterpenes and ORVOCs whereas water table drawdown decreased those emissions. The results suggest that global warming would change the BVOC emission mixtures from boreal peatlands following changes in vegetation composition and water table drawdown.

Health of native riparian vegetation and its relation to hydrologic conditions along the Mojave River, southern California

USGS Publications Warehouse

Lines, Gregory C.

1999-01-01

The health of native riparian vegetation and its relation to hydrologic conditions were studied along the Mojave River mainly during the growing seasons of 1997 and 1998. The study concentrated on cottonwood?willow woodlands (predominantly Populus fremontii and Salix gooddingii) and mesquite bosques (predominantly Prosopis glandulosa). Tree-growth characteristics were measured at 16 cottonwood?willow woodland sites and at 3 mesquite bosque sites. Density of live and dead trees, tree diameter and height, canopy density, live-crown volume, leaf-water potential, leaf-area index, mortality, and reproduction were measured or noted at each site. The sites included healthy and reproducing woodlands and bosques, stressed woodlands and bosques with no reproduction, and woodlands and bosques with high mortality. Tree roots were studied at seven sites to determine the vertical distribution of the root system and their relation to the water table at healthy, stressed, and high-mortality cottonwood?willow woodlands. In the six trenches that were dug for this study in May 1997, no cottonwood roots were observed that reached the water table. The root systems of healthy trees typically ended 1 to 2 feet above the water table. At sites with high mortality, the main root mass was commonly 7 to 8 feet above the water table. Water-table depth was monitored at each of the study sites. In addition, volumetric soil moisture and soil-water potential were monitored at varying depths at three cottonwood?willow woodland study sites and at two mesquite bosque sites. Ground, soil, river, lake, and plant (xylem sap) water were analyzed for concentrations of stable hydrogen and oxygen isotopes to determine the source of water used by the trees. On the basis of the root-distribution, soil- and leaf-water potential, and isotope data, it was concluded that cottonwood, willow, and mesquite trees mainly rely on ground water for their perennial sustained supply of water. The trees mainly utilize ground water that has moved upward from the water table into the capillary fringe and into unsaturated soil nearer to land surface. Most precipitation (average is 4 to 6 inches per year) is lost by evaporation and by transpiration of shallow-rooted xeric plants, and very little reaches the root zone of trees along the Mojave River. Water-table depth had no strong correlation to many individual tree-growth characteristics, such as density, diameter, height, and live-crown volume. However, leaf-area index (corrected for stem area) of both healthy and stressed cottonwood?willow woodlands had a highly significant statistical relation to water-table depth, and a curvilinear regression model was defined. As in cottonwood?willow woodlands, leaf-area index of mesquite bosques also decreased with increased water-table depth. However, because of the small number of sites, no significant statistical relation could be defined for mesquite bosques. Because it can be accurately measured repeatedly at the same locations, leaf-area index (corrected for stem area) is recommended as the primary growth characteristic that should be monitored. Future vegetation changes along the Mojave River can be quantified using the sites established for this study. Mortality was as high as 39 percent in healthy cottonwood?willow woodlands, but mortality of 50 to 100 percent was common where water-table depth was greater than about 7 feet or in areas where permanent water-table declines greater than about 5 feet had occurred. At a healthy mesquite bosque where the water-table depth ranged from about 8 to 11 feet, mortality was about 20 percent. Where the water table had been lowered an additional 10 to 25 feet by pumping, mortality of the mesquite was extremely high (80 to 99 percent). On the basis of observations of plant reproduction, it was concluded that established cottonwood?willow woodlands probably will reproduce, mainly by root sprouting of mature trees, if the water-t

Field data and numerical simulation of btex concentration trends under water table fluctuations: Example of a jet fuel-contaminated site in Brazil

NASA Astrophysics Data System (ADS)

Teramoto, Elias Hideo; Chang, Hung Kiang

2017-03-01

Mass transfer of light non-aqueous phase liquids (LNAPLs) trapped in porous media is a complex phenomenon. Water table fluctuations have been identified as responsible for generating significant variations in the concentration of dissolved hydrocarbons. Based on field evidence, this work presents a conceptual model and a numerical solution for mass transfer from entrapped LNAPL to groundwater controlled by both LNAPL saturation and seasonal water table fluctuations within the LNAPL smear zone. The numerical approach is capable of reproducing aqueous BTEX concentration trends under three different scenarios - water table fluctuating within smear zone, above the smear zone and partially within smear zone, resulting in in-phase, out-of-phase and alternating in-phase and out-of-phase BTEX concentration trend with respect to water table oscillation, respectively. The results demonstrate the model's applicability under observed field conditions and its ability to predict source zone depletion.

Importance of unsaturated zone flow for simulating recharge in a humid climate

USGS Publications Warehouse

Hunt, R.J.; Prudic, David E.; Walker, J.F.; Anderson, M.P.

2008-01-01

Transient recharge to the water table is often not well understood or quantified. Two approaches for simulating transient recharge in a ground water flow model were investigated using the Trout Lake watershed in north-central Wisconsin: (1) a traditional approach of adding recharge directly to the water table and (2) routing the same volume of water through an unsaturated zone column to the water table. Areas with thin (less than 1 m) unsaturated zones showed little difference in timing of recharge between the two approaches; when water was routed through the unsaturated zone, however, less recharge was delivered to the water table and more discharge occurred to the surface because recharge direction and magnitude changed when the water table rose to the land surface. Areas with a thick (15 to 26 m) unsaturated zone were characterized by multimonth lags between infiltration and recharge, and, in some cases, wetting fronts from precipitation events during the fall overtook and mixed with infiltration from the previous spring snowmelt. Thus, in thicker unsaturated zones, the volume of water infiltrated was properly simulated using the traditional approach, but the timing was different from simulations that included unsaturated zone flow. Routing of rejected recharge and ground water discharge at land surface to surface water features also provided a better simulation of the observed flow regime in a stream at the basin outlet. These results demonstrate that consideration of flow through the unsaturated zone may be important when simulating transient ground water flow in humid climates with shallow water tables.

Controls on Ecosystem and Root Respiration in an Alaskan Peatland

NASA Astrophysics Data System (ADS)

McConnell, N. A.; McGuire, A. D.; Harden, J. W.; Kane, E. S.; Turetsky, M. R.

2010-12-01

Boreal ecosystems cover 14% of the vegetated surface on earth and account for 25-30% of the world’s soil carbon (C), mainly due to large carbon stocks in deep peat and frozen soil layers. While peatlands have served as historical sinks of carbon, global climate change may trigger re-release of C to the atmosphere and may turn these ecosystems into net C sources. Rates of C release from a peatland are determined by regional climate and local biotic and abiotic factors such as vegetation cover, thaw depth, and peat thickness. Soil CO2 fluxes are driven by both autotrophic (plant) respiration and heterotrophic (microbial) respiration. Thus, changes in plant and microbial activity in the soil will impact CO2 emissions from peatlands. In this study, we explored environmental and vegetation controls on ecosystem respiration and root respiration in a variety of wetland sites. The study was conducted at the Alaskan Peatland Experiment (APEX; www.uoguelph.ca/APEX) sites in the Bonanza Creek Experimental Forest located 35 km southwest of Fairbanks Alaska. We measured ecosystem respiration, root respiration, and monitored a suite of environmental variables along a vegetation and soil moisture gradient including a black spruce stand with permafrost, a shrubby site with permafrost, a tussock grass site, and a herbaceous open rich fen. Within the rich fen, we have been conducting water table manipulations including a control, lowered, and raised water table treatment. In each of our sites, we measured total ecosystem respiration using static chambers and root respiration by harvesting roots from the uppermost 20 cm and placing them in a root cuvette to obtain a root flux. Ecosystem respiration (ER) on a μmol/m2/sec basis varied across sites. Water table was a significant predictor of ER at the lowered manipulation site and temperature was a strong predictor at the control site in the rich fen. Water table and temperature were both significant predictors of ER at the raised manipulation site. Root respiration fluxes on a ppm CO2/sec/g dry mass basis were highest for herbaceous species, which dominated the open rich fen sites. Root respiration flux was significantly lower in tree-dominated black spruce sites. It appears that the variation in root respiration explains the variation in ER between herbaceous and tree-dominated systems. Therefore an important next step is to partition ER into heterotrophic and autotrophic components across these ecosystems. This in turn will provide a better assessment of peatland C responses to global climate change.

Interactive effects of dissolved zinc and orthophosphate on phytoplankton from Coeur d'Alene Lake, Idaho

USGS Publications Warehouse

Kuwabara, James S.; Topping, Brent R.; Woods, Paul F.; Carter, James L.; Hager, Stephen W.

2006-01-01

Within the longitudinal chemical-concentration gradient in Coeur d'Alene Lake, generated by inputs from the St. Joe and Coeur d'Alene Rivers, two dominant algal species, Chlorella minutissima and Asterionella formosa, were isolated and cultured in chemically defined media to examine growth response to a range of dissolved orthophosphate concentrations and zinc-ion activities representative of the region within- and up-gradient of the Coeur d'Alene River inlet to the lake. Although zinc is an essential micronutrient, the toxicity of algal species to elevated concentrations of uncomplexed zinc has been demonstrated, and affects the metabolism of phosphorus (Kuwabara, 1985a; Kuwabara and others, 1986), the limiting nutrient in the lake. This interaction between solutes could be of management interest. As an extension of field work conducted in August, 1999 (Kuwabara and others, 2003b), the water column and benthos of Coeur d'Alene Lake were sampled in August 2001, June 2004 and June 2005 (Fig. 1; Table 1) to provide the biological characterization in terms of phytoplankton community composition, benthic macroinvertebrate community composition and benthic chlorophyll concentrations, as well as chemical characterizations at six sites (three depths per site) within the lake. This work, in support of the Idaho Department of Environmental Quality and regional tribal organizations, provides the first phytoplankton response models in a format that may be incorporated into a process-interdependent water-quality model like CAEDYM (Fig. 2; Brookes and others, 2004; Centre for Water Research, 2006) as a management tool for the lake. This study provides information in support of developing process-interdependent solute-transport models for the watershed (that is, models integrating physical, geochemical and biological processes), and hence in support of subsequent evaluation of remediation or load-allocation strategies. The following two questions are posed: Are dissolved zinc and orthophosphate concentrations interactively associated with growth parameters of dominant phytoplankton species within the longitudinal concentration gradient of Coeur d'Alene Lake? If so, can these interactions be quantitatively incorporated into a water-quality model for the lake?

Altitude and Configuration of the Potentiometric Surface in the Upper White Clay Creek and Lower West Branch Brandywine Creek Basins including Portions of Penn, London Grove, New Garden, Londonderry, West Marlborough, Highland, and East Fallowfield Townships and West Grove, Avondale, Modena, and South Coatesville boroughs, Chester County, Pennsylvania, May through July 2006

USGS Publications Warehouse

Hale, Lindsay B.

2007-01-01

INTRODUCTION Since 1984, the U.S. Geological Survey (USGS) has been mapping the altitude and configuration of the potentiometric surface in Chester County as part of an ongoing cooperative program to measure and describe the water resources of the county. These maps can be used to determine the general direction of ground-water flow and are frequently referenced by municipalities and developers to evaluate ground-water conditions for water supply and resource-protection requirements. For this study, the potentiometric surface was mapped for an area in south-central Chester County. The northern part of the map includes portions of Highland, East Fallowfield, Londonderry, and West Marlborough Townships and South Coatesville and Modena Boroughs. The southern part of the map includes portions of Londonderry, West Marlborough, Penn, London Grove, and New Garden Townships and West Grove and Avondale Boroughs. The study area is mostly underlain by metamorphic rocks of the Glenarm Supergroup including Peters Creek Schist, Octoraro Phyllite, Wissahickon Schist, Cockeysville Mrable, and Setters Quartzite; and by pegmatite, mafic gneiss, felsic gneiss, and diabase. Ground water is obtained from these bedrock formations by wells that intercept fractures. The altitude and configuration of the potentiometric surface was contoured from water levels measured on different dates in available wells during May through July 2006 and from the altitude of springs and perennial streams. Topography was used as a guide for contouring so that the altitude of the potentiometric surface was inferred nowhere to be higher than the land surface. The potentiometric surface shown on this map is an approximation of the water table. The altitude of the actual potentiometric surface may differ from the water table, especially in areas where wells are completed in a semi-confined zone or have long open intervals that reflect the composite hydraulic head of multiple water-yielding fractures. A composite head may differ from the potentiometric-surface altitude, particularly beneath hilltops and valleys where vertical hydraulic gradients are significant.

Developing Automatic Water Table Control System for Reducing Greenhouse Gas Emissions from Paddy Fields

NASA Astrophysics Data System (ADS)

Arif, C.; Fauzan, M. I.; Satyanto, K. S.; Budi, I. S.; Masaru, M.

2018-05-01

Water table in rice fields play important role to mitigate greenhouse gas (GHG) emissions from paddy fields. Continuous flooding by maintenance water table 2-5 cm above soil surface is not effective and release more GHG emissions. System of Rice Intensification (SRI) as alternative rice farming apply intermittent irrigation by maintaining lower water table is proven can reduce GHG emissions reducing productivity significantly. The objectives of this study were to develop automatic water table control system for SRI application and then evaluate the performances. The control system was developed based on fuzzy logic algorithms using the mini PC of Raspberry Pi. Based on laboratory and field tests, the developed system was working well as indicated by lower MAPE (mean absolute percentage error) values. MAPE values for simulation and field tests were 16.88% and 15.80%, respectively. This system can save irrigation water up to 42.54% without reducing productivity significantly when compared to manual irrigation systems.

Water tables constrain height recovery of willow on Yellowstone's northern range.

PubMed

Bilyeu, Danielle M; Cooper, David J; Hobbs, N Thompson

2008-01-01

Excessive levels of herbivory may disturb ecosystems in ways that persist even when herbivory is moderated. These persistent changes may complicate efforts to restore ecosystems affected by herbivores. Willow (Salix spp.) communities within the northern range in Yellowstone National Park have been eliminated or degraded in many riparian areas by excessive elk (Cervus elaphus L.) browsing. Elk browsing of riparian willows appears to have diminished following the reintroduction of wolves (Canis lupis L.), but it remains uncertain whether reduced herbivory will restore willow communities. The direct effects of elk browsing on willows have been accompanied by indirect effects from the loss of beaver (Castor canadensis Kuhl) activity, including incision of stream channels, erosion of fine sediments, and lower water tables near streams historically dammed by beaver. In areas where these changes have occurred, lowered water tables may suppress willow height even in the absence of elk browsing. We conducted a factorial field experiment to understand willow responses to browsing and to height of water tables. After four years of protection from elk browsing, willows with ambient water tables averaged only 106 cm in height, with negligible height gain in two of three study species during the last year of the experiment. Willows that were protected from browsing and had artificially elevated water tables averaged 147 cm in height and gained 19 cm in the last year of the experiment. In browsed plots, elevated water tables doubled height gain during a period of slightly reduced browsing pressure. We conclude that water availability mediates the rate of willow height gain and may determine whether willows grow tall enough to escape the browse zone of elk and gain resistance to future elk browsing. Consequently, in areas where long-term beaver absence has resulted in incised stream channels and low water tables, a reduction in elk browsing alone may not be sufficient for recovery of tall willow stands. Because tall willow stems are important elements of habitat for beaver, mitigating water table decline may be necessary in these areas to promote recovery of historical willow-beaver mutualisms.

Factors influencing impingement of fish by Lake Ontario power plants

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

Wyman, R.L.; Dischel, R.S.

1984-01-01

Fish impinged by two Lake Ontario power plants were examined to determine the causal factors. Fish were near shore because they resided there, migrated there to spawn or forage, or because the water mass in which they resided moved near shore. Once near shore, fish abundance in impingement collections was correlated with demersal or pelagic behavior. Periodic increases in diversity and abundance of impinged fish corresponded with times of upwelling and thermocline oscillations. These data suggest that some species were segregated along temperature gradients and were impinged when the thermocline passed near the intake. Comparisons of impingement catch between twomore » power plants, one withdrawing a constant volume of water and the other a varying volume, showed that responses of fish to an intake were of three kinds. Alosa pseudoharengus and Osmerus mordax were apparently attracted to water currents entering the intake. Morone americana, Morone chrysops, Dorosoma cepedianum, and Perca flavescens were not influenced by changes in flow rate, suggesting that their impingement was proportional to their density in nearshore water. Micropterus dolomieui avoided the intake at higher flow rates in part due to rheotactic behavior. 25 references, 4 figures, 3 table.« less

Raised Water Tables Affect Southern Hardwood Growth

Treesearch

W. M. Broadfoot

1973-01-01

In natural stands near Demopolis Lock and Dam Reservoir in Alabama, the average growth in tree radius increased about 50 percent in the 5 years after the water table was raised from an indefinite depth to within reach of the tree roots. In natural stands near the Jim Woodruff Reservoir in Florida, radial growth of trees also increased markedly after the water table was...

Recharge characteristics of an unconfined aquifer from the rainfall-water table relationship

NASA Astrophysics Data System (ADS)

Viswanathan, M. N.

1984-02-01

The determination of recharge levels of unconfined aquifers, recharged entirely by rainfall, is done by developing a model for the aquifer that estimates the water-table levels from the history of rainfall observations and past water-table levels. In the present analysis, the model parameters that influence the recharge were not only assumed to be time dependent but also to have varying dependence rates for various parameters. Such a model is solved by the use of a recursive least-squares method. The variable-rate parameter variation is incorporated using a random walk model. From the field tests conducted at Tomago Sandbeds, Newcastle, Australia, it was observed that the assumption of variable rates of time dependency of recharge parameters produced better estimates of water-table levels compared to that with constant-recharge parameters. It was observed that considerable recharge due to rainfall occurred on the very same day of rainfall. The increase in water-table level was insignificant for subsequent days of rainfall. The level of recharge very much depends upon the intensity and history of rainfall. Isolated rainfalls, even of the order of 25 mm day -1, had no significant effect on the water-table levels.

Database of well and areal data, South San Francisco Bay and Peninsula area, California

USGS Publications Warehouse

Leighton, D.A.; Fio, J.L.; Metzger, L.F.

1995-01-01

A database was developed to organize and manage data compiled for a regional assessment of geohydrologic and water-quality conditions in the south San Francisco Bay and Peninsula area in California. Available data provided by local, State, and Federal agencies and private consultants was utilized in the assessment. The database consists of geographicinformation system data layers and related tables and American Standard Code for Information Interchange files. Documentation of the database is necessary to avoid misinterpretation of the data and to make users aware of potential errors and limitations. Most of the data compiled were collected from wells and boreholes (collectively referred to as wells in this report). This point-specific data, including construction, water-level, waterquality, pumping test, and lithologic data, are contained in tables and files that are related to a geographic information system data layer that contains the locations of the wells. There are 1,014 wells in the data layer and the related tables contain 35,845 water-level measurements (from 293 of the wells) and 9,292 water-quality samples (from 394 of the wells). Calculation of hydraulic heads and gradients from the water levels can be affected adversely by errors in the determination of the altitude of land surface at the well. Cation and anion balance computations performed on 396 of the water-quality samples indicate high cation and anion balance errors for 51 (13 percent) of the samples. Well drillers' reports were interpreted for 762 of the wells, and digital representations of the lithology of the formations are contained in files following the American Standard Code for Information Interchange. The usefulness of drillers' descriptions of the formation lithology is affected by the detail and thoroughness of the drillers' descriptions, as well as the knowledge, experience, and vocabulary of the individual who described the drill cuttings. Additional data layers were created that contain political, geohydrologic, and other geographic data. These layers contain features represented by areas and lines rather than discrete points. The layers consist of data representing the thickness of alluvium, surficial geology, physiographic subareas, watershed boundaries, land use, water-supply districts, wastewater treatment districts, and recharge basins. The layers manually digitizing paper maps, acquisition of data already in digital form, or creation of new layers from available layers. The scale of the source data affects the accurate representation of real-world features with the data layer, and, therefore, the scale of the source data must be considered when the data are analyzed and plotted.

Enhancing Groundwater Cost Estimation with the Interpolation of Water Tables across the United States

NASA Astrophysics Data System (ADS)

Rosli, A. U. M.; Lall, U.; Josset, L.; Rising, J. A.; Russo, T. A.; Eisenhart, T.

2017-12-01

Analyzing the trends in water use and supply across the United States is fundamental to efforts in ensuring water sustainability. As part of this, estimating the costs of producing or obtaining water (water extraction) and the correlation with water use is an important aspect in understanding the underlying trends. This study estimates groundwater costs by interpolating the depth to water level across the US in each county. We use Ordinary and Universal Kriging, accounting for the differences between aquifers. Kriging generates a best linear unbiased estimate at each location and has been widely used to map ground-water surfaces (Alley, 1993).The spatial covariates included in the universal Kriging were land-surface elevation as well as aquifer information. The average water table is computed for each county using block kriging to obtain a national map of groundwater cost, which we compare with survey estimates of depth to the water table performed by the USDA. Groundwater extraction costs were then assumed to be proportional to water table depth. Beyond estimating the water cost, the approach can provide an indication of groundwater-stress by exploring the historical evolution of depth to the water table using time series information between 1960 and 2015. Despite data limitations, we hope to enable a more compelling and meaningful national-level analysis through the quantification of cost and stress for more economically efficient water management.

Water-level data from wells and test holes through 1991 and potentiometric contours as of 1991 for Yucca Flat, Nevada Test Site, Nye County, Nevada

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

Hale, G.S.; Trudeau, D.A.; Savard, C.S.

The underground nuclear testing program of the US Department of Energy (USDOE) takes place at the Nevada Test Site (NTS), about 65 mi north-west of Las Vegas, Nevada. Underground nuclear tests at Yucca Flat, one of the USDOE test areas at NTS, have affected hydrologic conditions, including groundwater levels. The purpose of this map report, prepared in cooperation with USDOE, is to present selected water-level data collected from wells and test holes through December 1991, and to show potentiometric contours representing 1991 water-table conditions in the Yucca Flat area. The more generic term, potentiometric contours, is used herein rather thanmore » ``water-table contours`` because the hydrologic units contributing water to wells and test holes may not accurately represent the water table. The water table is that surface in an unconfined water body at which the pressure is atmospheric. It is defined by the altitude at which non- perched ground water is first found in wells and test holes. Perched ground water is defined as unconfined ground water separated from an underlying body of ground water by an unsaturated zone. This map report updates information on water levels in some wells and test holes and the resulting water-table contours in rocks of Cenozoic and Paleozoic age shown by Doty and Thordarson for 1980 conditions.« less

Non-invasive water-table imaging with joint DC-resistivity/microgravity/hydrologic-model inversion

NASA Astrophysics Data System (ADS)

Kennedy, J.; Macy, J. P.

2017-12-01

The depth of the water table, and fluctuations thereof, is a primary concern in hydrology. In riparian areas, the water table controls when and where vegetation grows. Fluctuations in the water table depth indicate changes in aquifer storage and variation in ET, and may also be responsible for the transport and degradation of contaminants. In the latter case, installation of monitoring wells is problematic because of the potential to create preferential flow pathways. We present a novel method for non-invasive water table monitoring using combined DC resistivity and repeat microgravity data. Resistivity profiles provide spatial resolution, but a quantifiable relation between resistivity changes and aquifer-storage changes depends on a petrophysical relation (typically, Archie's Law), with additional parameters and therefore uncertainty. Conversely, repeat microgravity data provide a direct, quantifiable measurement of aquifer-storage change but lack depth resolution. We show how these two geophysical measurements, together with an unsaturated-zone flow model (Hydrogeosphere), effectively constrain the water table position and help identify groundwater-flow model parameters. A demonstration of the method is made using field data collected during the historic 2014 pulse flow in the Colorado River Delta, which shows that geophysical data can effectively constrain a coupled surface-water/groundwater model used to simulate the potential for riparian vegetation germination and recruitment.

Gradients of microhabitat and crappie (Pomoxis spp.) distributions in reservoir coves

USGS Publications Warehouse

Kaczka, Levi J.; Miranda, Leandro E.

2013-01-01

Embayments are among the most widespread littoral habitats found in Mississippi flood-control reservoirs. These macrohabitats represent commonly used nursery zones for age-0 crappies, Pomoxis spp., despite barren and eroded shorelines formed over 60–70 years of annual water level fluctuations. We tested if embayments displayed microhabitat gradients linked to the effect of water level fluctuations on riparian vegetation and if these gradients were paralleled by gradients in age-0 crappie distribution. Habitat composition changed longitudinally along the embayments with the most pronounced gradient representing a shift from nonvegetated mudflats near the mouth of embayments to herbaceous material upstream. The degree of habitat change depended on the water level. Similarly, catch rates of crappies increased upstream toward the rear of embayments, differing among water levels and reservoirs, but the longitudinal pattern persisted. Our results indicate that habitat composition gradients occur in embayments of northwest Mississippi flood-control reservoirs and that these gradients may influence a similar gradient in age-0 crappie distribution. While the biotic interactions behind the gradients may be less clear, we speculate that water level is the main factor influencing the observed gradients in habitat composition and fish. Management to benefit age-0 crappies may involve habitat improvement along embayment shorelines and water level regimes that foster growth of herbaceous plants.

Reference manual for data base on Nevada water-rights permits

USGS Publications Warehouse

Cartier, K.D.; Bauer, E.M.; Farnham, J.L.

1995-01-01

The U.S. Geological Survey and Nevada Division of Water Resources have cooperatively developed and implemented a data-base system for managing water-rights permit information for the State of Nevada. The Water-Rights Permit data base is part of an integrated system of computer data bases using the Ingres Relational Data-Base Manage-ment System, which allows efficient storage and access to water information from the State Engineer's office. The data base contains a main table, three ancillary tables, and five lookup tables, as well as a menu-driven system for entering, updating, and reporting on the data. This reference guide outlines the general functions of the system and provides a brief description of data tables and data-entry screens.

Interpolations of groundwater table elevation in dissected uplands.

PubMed

Chung, Jae-won; Rogers, J David

2012-01-01

The variable elevation of the groundwater table in the St. Louis area was estimated using multiple linear regression (MLR), ordinary kriging, and cokriging as part of a regional program seeking to assess liquefaction potential. Surface water features were used to determine the minimum water table for MLR and supplement the principal variables for ordinary kriging and cokriging. By evaluating the known depth to the water and the minimum water table elevation, the MLR analysis approximates the groundwater elevation for a contiguous hydrologic system. Ordinary kriging and cokriging estimate values in unsampled areas by calculating the spatial relationships between the unsampled and sampled locations. In this study, ordinary kriging did not incorporate topographic variations as an independent variable, while cokriging included topography as a supporting covariable. Cross validation suggests that cokriging provides a more reliable estimate at known data points with less uncertainty than the other methods. Profiles extending through the dissected uplands terrain suggest that: (1) the groundwater table generated by MLR mimics the ground surface and elicits a exaggerated interpolation of groundwater elevation; (2) the groundwater table estimated by ordinary kriging tends to ignore local topography and exhibits oversmoothing of the actual undulations in the water table; and (3) cokriging appears to give the realistic water surface, which rises and falls in proportion to the overlying topography. The authors concluded that cokriging provided the most realistic estimate of the groundwater surface, which is the key variable in assessing soil liquefaction potential in unconsolidated sediments. © 2011, The Author(s). Ground Water © 2011, National Ground Water Association.

Effect of hydrological conditions on nitrous oxide, methane, and carbon dioxide dynamics in a bottomland hardwood forest and its implication for soil carbon sequestration

USGS Publications Warehouse

Yu, K.; Faulkner, S.P.; Baldwin, M.J.

2008-01-01

This study was conducted at three locations in a bottomland hardwood forest with a distinct elevation and hydrological gradient: ridge (high, dry), transition, and swamp (low, wet). At each location, concentrations of soil greenhouse gases (N2O, CH4 , and CO2), their fluxes to the atmosphere, and soil redox potential (Eh) were measured bimonthly, while the water table was monitored every day. Results show that soil Eh was significantly (P transition > ridge location. The ratio CO2/CH4 production in soil is a critical factor for evaluating the overall benefit of soil C sequestration, which can be greatly offset by CH4 production and emission. ?? Journal compilation ?? 2008 Blackwell Publishing.

Evaluating the value of ENVISAT ASAR Data for the mapping and monitoring of peatland water table depths

NASA Astrophysics Data System (ADS)

Bechtold, Michel; Schlaffer, Stefan

2015-04-01

The Advanced Synthetic Aperture Radar (ASAR) onboard ENVISAT collected C-Band microwave backscatter data from 2005 to 2012. Backscatter in the C-Band depends to a large degree on the roughness and the moisture status of vegetation and soil surface with a penetration depth of ca. 3 cm. In wetlands with stable high water levels, the annual soil surface moisture dynamics are very distinct compared to the surrounding areas, which allows the monitoring of such environments with ASAR data (Reschke et al. 2012). Also in drained peatlands, moisture status of vegetation and soil surface strongly depends on water table depth due to high hydraulic conductivities of many peat soils in the low suction range (Dettmann et al. 2014). We hypothesize that this allows the characterization of water table depths with ASAR data. Here we analyze whether ASAR data can be used for the spatial and temporal estimation of water table depths in different peatlands (natural, near-natural, agriculturally-used and rewetted). Mapping and monitoring of water table depths is of crucial importance, e.g. for upscaling greenhouse gas emissions and evaluating the success of peatland rewetting projects. Here, ASAR data is analyzed with a new map of water table depths for the organic soils in Germany (Bechtold et al. 2014) as well as with a comprehensive data set of monitored peatland water levels from 1100 dip wells and 54 peatlands. ASAR time series from the years 2005-2012 with irregular temporal sampling intervals of 3-14 days were processed. Areas covered by snow were masked. Primary results about the accuracy of spatial estimates show significant correlations between long-term backscatter statistics and spatially-averaged water table depths extracted from the map at the resolution of the ASAR data. Backscatter also correlates with long-term averages of point-scale water table depth data of the monitoring wells. For the latter, correlation is highest between the dry reference backscatter values and summer mean water table depth. Using the boosted regression tree model of Bechtold et al., we evaluate whether the ASAR data can improve prediction accuracy and/or replace parts of ancillary data that is often not available in other countries. In the temporal domain primary results often show a better dependency between backscatter and water table depths compared to the spatial domain. For a variety of vegetation covers the temporal monitoring potential of ASAR data is evaluated at the level of annual water table depth statistics. Bechtold, M., Tiemeyer, B., Laggner, A., Leppelt, T., Frahm, E., and Belting, S., 2014. Large-scale regionalization of water table depth in peatlands optimized for greenhouse gas emission upscaling, Hydrol. Earth Syst. Sci., 18, 3319-3339. Dettmann, U., Bechtold, M., Frahm, E., Tiemeyer, B., 2014. On the applicability of unimodal and bimodal van Genuchten-Mualem based models to peat and other organic soils under evaporation conditions. Journal of Hydrology, 515, 103-115. Reschke, J., Bartsch, A., Schlaffer, S., Schepaschenko, D., 2012. Capability of C-Band SAR for Operational Wetland Monitoring at High Latitudes. Remote Sens. 4, 2923-2943.

Rapid Response of Hydrological Loss of DOC to Water Table Drawdown and Warming in Zoige Peatland: Results from a Mesocosm Experiment

PubMed Central

Lou, Xue-Dong; Zhai, Sheng-Qiang; Kang, Bing; Hu, Ya-Lin; Hu, Li-Le

2014-01-01

A large portion of the global carbon pool is stored in peatlands, which are sensitive to a changing environment conditions. The hydrological loss of dissolved organic carbon (DOC) is believed to play a key role in determining the carbon balance in peatlands. Zoige peatland, the largest peat store in China, is experiencing climatic warming and drying as well as experiencing severe artificial drainage. Using a fully crossed factorial design, we experimentally manipulated temperature and controlled the water tables in large mesocosms containing intact peat monoliths. Specifically, we determined the impact of warming and water table position on the hydrological loss of DOC, the exported amounts, concentrations and qualities of DOC, and the discharge volume in Zoige peatland. Our results revealed that of the water table position had a greater impact on DOC export than the warming treatment, which showed no interactive effects with the water table treatment. Both DOC concentration and discharge volume were significantly increased when water table drawdown, while only the DOC concentration was significantly promoted by warming treatment. Annual DOC export was increased by 69% and 102% when the water table, controlled at 0 cm, was experimentally lowered by −10 cm and −20 cm. Increases in colored and aromatic constituents of DOC (measured by Abs254 nm, SUVA254 nm, Abs400 nm, and SUVA400 nm) were observed under the lower water tables and at the higher peat temperature. Our results provide an indication of the potential impacts of climatic change and anthropogenic drainage on the carbon cycle and/or water storage in a peatland and simultaneously imply the likelihood of potential damage to downstream ecosystems. Furthermore, our results highlight the need for local protection and sustainable development, as well as suggest that more research is required to better understand the impacts of climatic change and artificial disturbances on peatland degradation. PMID:25369065

Rapid response of hydrological loss of DOC to water table drawdown and warming in Zoige peatland: results from a mesocosm experiment.

PubMed

Lou, Xue-Dong; Zhai, Sheng-Qiang; Kang, Bing; Hu, Ya-Lin; Hu, Li-Le

2014-01-01

A large portion of the global carbon pool is stored in peatlands, which are sensitive to a changing environment conditions. The hydrological loss of dissolved organic carbon (DOC) is believed to play a key role in determining the carbon balance in peatlands. Zoige peatland, the largest peat store in China, is experiencing climatic warming and drying as well as experiencing severe artificial drainage. Using a fully crossed factorial design, we experimentally manipulated temperature and controlled the water tables in large mesocosms containing intact peat monoliths. Specifically, we determined the impact of warming and water table position on the hydrological loss of DOC, the exported amounts, concentrations and qualities of DOC, and the discharge volume in Zoige peatland. Our results revealed that of the water table position had a greater impact on DOC export than the warming treatment, which showed no interactive effects with the water table treatment. Both DOC concentration and discharge volume were significantly increased when water table drawdown, while only the DOC concentration was significantly promoted by warming treatment. Annual DOC export was increased by 69% and 102% when the water table, controlled at 0 cm, was experimentally lowered by -10 cm and -20 cm. Increases in colored and aromatic constituents of DOC (measured by Abs(254 nm), SUVA(254 nm), Abs(400 nm), and SUVA(400 nm)) were observed under the lower water tables and at the higher peat temperature. Our results provide an indication of the potential impacts of climatic change and anthropogenic drainage on the carbon cycle and/or water storage in a peatland and simultaneously imply the likelihood of potential damage to downstream ecosystems. Furthermore, our results highlight the need for local protection and sustainable development, as well as suggest that more research is required to better understand the impacts of climatic change and artificial disturbances on peatland degradation.

Effect of water table dynamics on land surface hydrologic memory

NASA Astrophysics Data System (ADS)

Lo, Min-Hui; Famiglietti, James S.

2010-11-01

The representation of groundwater dynamics in land surface models has received considerable attention in recent years. Most studies have found that soil moisture increases after adding a groundwater component because of the additional supply of water to the root zone. However, the effect of groundwater on land surface hydrologic memory (persistence) has not been explored thoroughly. In this study we investigate the effect of water table dynamics on National Center for Atmospheric Research Community Land Model hydrologic simulations in terms of land surface hydrologic memory. Unlike soil water or evapotranspiration, results show that land surface hydrologic memory does not always increase after adding a groundwater component. In regions where the water table level is intermediate, land surface hydrologic memory can even decrease, which occurs when soil moisture and capillary rise from groundwater are not in phase with each other. Further, we explore the hypothesis that in addition to atmospheric forcing, groundwater variations may also play an important role in affecting land surface hydrologic memory. Analyses show that feedbacks of groundwater on land surface hydrologic memory can be positive, negative, or neutral, depending on water table dynamics. In regions where the water table is shallow, the damping process of soil moisture variations by groundwater is not significant, and soil moisture variations are mostly controlled by random noise from atmospheric forcing. In contrast, in regions where the water table is very deep, capillary fluxes from groundwater are small, having limited potential to affect soil moisture variations. Therefore, a positive feedback of groundwater to land surface hydrologic memory is observed in a transition zone between deep and shallow water tables, where capillary fluxes act as a buffer by reducing high-frequency soil moisture variations resulting in longer land surface hydrologic memory.

How Does Tree Density Affect Water Loss of Peatlands? A Mesocosm Experiment

PubMed Central

Limpens, Juul; Holmgren, Milena; Jacobs, Cor M. J.; Van der Zee, Sjoerd E. A. T. M.; Karofeld, Edgar; Berendse, Frank

2014-01-01

Raised bogs have accumulated more atmospheric carbon than any other terrestrial ecosystem on Earth. Climate-induced expansion of trees and shrubs may turn these ecosystems from net carbon sinks into sources when associated with reduced water tables. Increasing water loss through tree evapotranspiration could potentially deepen water tables, thus stimulating peat decomposition and carbon release. Bridging the gap between modelling and field studies, we conducted a three-year mesocosm experiment subjecting natural bog vegetation to three birch tree densities, and studied the changes in subsurface temperature, water balance components, leaf area index and vegetation composition. We found the deepest water table in mesocosms with low tree density. Mesocosms with high tree density remained wettest (i.e. highest water tables) whereas the control treatment without trees had intermediate water tables. These differences are attributed mostly to differences in evapotranspiration. Although our mesocosm results cannot be directly scaled up to ecosystem level, the systematic effect of tree density suggests that as bogs become colonized by trees, the effect of trees on ecosystem water loss changes with time, with tree transpiration effects of drying becoming increasingly offset by shading effects during the later phases of tree encroachment. These density-dependent effects of trees on water loss have important implications for the structure and functioning of peatbogs. PMID:24632565

Ground-water quality in the vicinity of landfill sites, southern Franklin County, Ohio

USGS Publications Warehouse

De Roche, J.T.; Razem, A.C.

1981-01-01

The hydrogeology and ground-water quality in the vicinity of five landfills in southern Franklin County, Ohio, were investigated by use of data obtained from 46 existing wells, 1 seep, 1 surface-water site, and 1 leachate-collection site. Interpretation was based on data from the wells, a potentiometric-surface map, and chemical analyses. Four of the five landfills are in abandoned sand and gravel pits. Pumping of water from a quarry near the landfills has modified the local ground-water flow pattern, increased the hydraulic gradient, and lowered the water table. Ground water unaffected by the landfills is a hard, calcium bicarbonate type with concentrations of dissolved iron and dissolved sulfate as great as 3.0 milligrams per liter and 200 milligrams per liter, respectively. Water sampled from wells downgradient from two landfills shows an increase in sodium, chloride, and other constituents. The change in water quality cannot be traced directly to the landfills, however, because of well location and the presence of other potential sources of contamination. Chemical analysis of leachate from a collection unit at one landfill shows significant amounts of zinc, chromium, copper, and nickel, in addition to high total organic carbon, biochemical oxygen demand, and organic nitrogen. Concentrations of chloride, iron, lead, manganese and phenolic compounds exceed Ohio Environmental Protection Agency Water Quality Standards for drinking water. Water from unaffected wells within the study area have relatively small amounts of these constituents. (USGS)

Diameter growth and phenology of trees on sites with high water tables

Treesearch

D.C. McClurkin

1965-01-01

On a site where the water table always was within the root zone, thinning had little effect on diameter growth of white ash or sweetgum but increased the growth of baldcypress. Thinning did not extend durating of growth into the fall, nor was growth related to seasonal fluctuations in the water table. In ash and sweetgum, growth initiation seemed related to soil...

Short-term response of methane fluxes and methanogen activity to water table and soil warming manipulations in an Alaskan peatland

Treesearch

M.R. Turetsky; C.C. Treat; M. Waldrop; J.M. Waddington; J.W. Harden; A.D. McGuire

2008-01-01

Growing season CH4 fluxes were monitored over a two year period following the start of ecosystem-scale manipulations of water table position and surface soil temperatures in a moderate rich fen in interior Alaska. The largest CH4 fluxes occurred in plots that received both flooding (raised water table position) and soil...

Sensitivity of stream flow and water table depth to potential climatic variability in a coastal forested watershed

Treesearch

Zhaohua Dai; Carl Trettin; Changsheng Li; Devendra M. Amatya; Ge Sun; Harbin Li

2010-01-01

A physically based distributed hydrological model, MIKE SHE, was used to evaluate the effects of altered temperature and precipitation regimes on the streamflow and water table in a forested watershed on the southeastern Atlantic coastal plain. The model calibration and validation against both streamflow and water table depth showed that the MIKE SHE was applicable for...

Effects of water table position and plant functional group on plant community, aboveground production, and peat properties in a peatland mesocosm experiment (PEATcosm)

Treesearch

Lynette R. Potvin; Evan S. Kane; Rodney A. Chimner; Randall K. Kolka; Erik A. Lilleskov

2015-01-01

Aims Our objective was to assess the impacts of water table position and plant functional type on peat structure, plant community composition and aboveground plant production. Methods We initiated a full factorial experiment with 2 water table (WT) treatments (high and low) and 3 plant functional groups (PFG: sedge, Ericaceae,...

Forecast model for a water table control system in cranberry production

NASA Astrophysics Data System (ADS)

Racine, Cintia; José Gumiere, Silvio; Paniconi, Claudio; Dupuis, Christian; Lafond, Jonathan; Scudeler, Carlotta; Camporese, Matteo

2017-04-01

Water table control is gaining popularity in cranberry production. Cranberry plants require specific soil moisture conditions to enhance crop yields. In fact, water table control systems installed in the fields allow the plants to respond efficiently to the daily demand for evapotranspiration by capillarity rise and also regulate the soil water excess in drainage conditions. The scope of this study is to develop a forecast hydrological model at the field scale, able to simulate water level for water table control operations. In this work, the finite element CATHY (CATchment Hydrology) model associated with sequential data assimilation with an ensemble Kalman filter (EnKF) method will be used to simulated the soil water dynamics and perform model calibration in real-time. The study is conducted in cranberry fields located in Québec, Canada. During the last five years, these fields were extensive characterized regarding hydrological, pedological, and geological processes. Data collected from LIDAR and Ground Penetrating Radar (GPR) surveys and in-situ soil sampling have been used to define the domain geometry and initial soil properties. First results are promising and in agreement the in-situ water table measurements.

40 CFR 230.25 - Salinity gradients.

Code of Federal Regulations, 2010 CFR

2010-07-01

... gradients form where salt water from the ocean meets and mixes with fresh water from land. (b) Possible loss... those organisms that are adapted to freshwater environments. It may also affect municipal water supplies... fresh or salt water may change existing salinity gradients. For example, partial blocking of the...

CO2 fluxes and ecosystem dynamics at five European treeless peatlands - merging data and process oriented modelling

NASA Astrophysics Data System (ADS)

Metzger, C.; Jansson, P.-E.; Lohila, A.; Aurela, M.; Eickenscheidt, T.; Belelli-Marchesini, L.; Dinsmore, K. J.; Drewer, J.; van Huissteden, J.; Drösler, M.

2014-06-01

The carbon dioxide (CO2) exchange of five different peatland systems across Europe with a wide gradient in landuse intensity, water table depth, soil fertility and climate was simulated with the process oriented CoupModel. The aim of the study was to find out to what extent CO2 fluxes measured at different sites, can be explained by common processes and parameters implemented in the model. The CoupModel was calibrated to fit measured CO2 fluxes, soil temperature, snow depth and leaf area index (LAI) and resulting differences in model parameters were analysed. Finding site independent model parameters would mean that differences in the measured fluxes could be explained solely by model input data: water table, meteorological data, management and soil inventory data. The model, utilizing a site independent configuration for most of the parameters, captured seasonal variability in the major fluxes well. Parameters that differed between sites included the rate of soil organic decomposition, photosynthetic efficiency, and regulation of the mobile carbon (C) pool from senescence to shooting in the next year. The largest difference between sites was the rate coefficient for heterotrophic respiration. Setting it to a common value would lead to underestimation of mean total respiration by a factor of 2.8 up to an overestimation by a factor of 4. Despite testing a wide range of different responses to soil water and temperature, heterotrophic respiration rates were consistently lowest on formerly drained sites and highest on the managed sites. Substrate decomposability, pH and vegetation characteristics are possible explanations for the differences in decomposition rates. Applying common parameter values for the timing of plant shooting and senescence, and a minimum temperature for photosynthesis, had only a minor effect on model performance, even though the gradient in site latitude ranged from 48° N (South-Germany) to 68° N (northern Finland). This was also true for common parameters defining the moisture and temperature response for decomposition. CoupModel is able to describe measured fluxes at different sites or under different conditions, providing that the rate of soil organic decomposition, photosynthetic efficiency, and the regulation of the mobile carbon (C) pool are estimated from available information on specific soil conditions, vegetation and management of the ecosystems.

Bibliography of In-House and Contract Reports. Supplement 16

DTIC Science & Technology

1989-10-01

Differences from ETL-71-CR-10 1971 Grav,t% and Gravity Gradients 54 TiLE REPORT NO. YEAR Determination of Level Sensitivity (Field ETL-RN-74-4 1974...Data Base Study, Phase II ETL-0360 1984 High Resolution Optical Power Spectrum Analyzer ETL-0127 1978 High Resolution Orthophoto Output Table (HIROOT...AD 856 731L 1969 High Resolution Orthophoto Output Table ETL-ETR-72-3 1972 High Speed Disc Memory and a Color Image AD 878 975L 1970 Display for a

Image Understanding Workshop. Proceedings of a Workshop Held in Los Angeles, California on 23-25 February 1987. Volume 2

DTIC Science & Technology

1987-02-25

Modellierung von Kanten bei unregel. Navigation within a building, to be published in IEEE mifliger Rasterung in Bildverarbeitun uand Muster...converted them into equivalent machine cycles in Table 3-1. We took into account of 100 nanosecond 0 - 0, machine cycle time of the MPP. In MPP, NON- VON ...We show the result for the conjugate gradient method in of NON- VON . We assumed that the instructions which carry Table 4-4. The computation of four

Determining the mean hydraulic gradient of ground water affected by tidal fluctuations

USGS Publications Warehouse

Serfes, Michael E.

1991-01-01

Tidal fluctuations in surface-water bodies produce progressive pressure waves in adjacent aquifers. As these pressure waves propagate inland, ground-water levels and hydraulic gradients continuously fluctuate, creating a situation where a single set of water-level measurements cannot be used to accurately characterize ground-water flow. For example, a time series of water levels measured in a confined aquifer in Atlantic City, New Jersey, showed that the hydraulic gradient ranged from .01 to .001 with a 22-degree change in direction during a tidal day of approximately 25 hours. At any point where ground water tidally fluctuates, the magnitude and direction of the hydraulic gradient fluctuates about the mean or regional hydraulic gradient. The net effect of these fluctuations on ground-water flow can be determined using the mean hydraulic gradient, which can be calculated by comparing mean ground- and surface-water elevations. Filtering methods traditionally used to determine daily mean sea level can be similarly applied to ground water to determine mean levels. Method (1) uses 71 consecutive hourly water-level observations to accurately determine the mean level. Method (2) approximates the mean level using only 25 consecutive hourly observations; however, there is a small error associated with this method.

Altitude of the water table in the alluvial and Wilcox aquifers in the vicinity of Richland and Tehuacana creeks and the Trinity River, Texas, December 1979

USGS Publications Warehouse

Garza, Sergio

1980-01-01

This map shows the altitude of the water table in the alluvial and Wilcox aquifers in the vicinity of Richland and Tehuacana Creeks and the Trinity River, Tex., in December 1979. The water-table contours were constructed on the basis of water-level control derived from an inventory of shallow wells in the area, topographic maps, and field locations of numerous small springs and seeps. (USGS)

Estimating Carbon Stocks and Atmospheric Exchange of Depressional Marshes on the Central Florida Landscape

NASA Astrophysics Data System (ADS)

Benscoter, B.; McClellan, M. D.; Benavides, V.; Harshbarger, D.; Comas, X.

2014-12-01

Depressional marshes are ubiquitous throughout central and south Florida. Often distributed within a matrix of sandy pine flatwoods and hammocks, these wetlands have a seasonally variable water table, alternating between inundation and complete drydown. Though these landforms are typically small individually, they comprise a substantial component of the landscape and provide vital habitat for an array of flora and fauna. Given their fluctuating hydrology, conditions for soil and plant carbon (C) exchange mechanisms can vary greatly both spatially and temporally. In this study, we are developing a C budget for depressional marsh landforms by assessing ecosystem carbon exchange along an ecotone gradient and quantifying belowground C stocks using non-invasive geophysical methods (ground penetrating radar, GPR) at the Disney Wilderness Preserve (DWP) in Kissimmee, FL, USA. Using a series of closed chambers transecting the marsh from the center outward into the surrounding flatwoods, we are quantifying the effects of seasonal water table change on the magnitude of C exchange. Three dimensional GPR surveys were used to quantify peat layer thickness, and were constrained with direct core sampling to verify subsurface lithology and to assess peat C content. Using the relationship between landform surface area and belowground C volume, we assessed the cumulative C storage in depressional marshes across the DWP landscape. In conjunction with a nearby eddy covariance tower and seasonal hydrologic data, these response functions will help to evaluate the contribution of these small but widespread landscape features on regional C cycling.

Microscopic and molecular studies of the diversity of free-living protozoa in meat-cutting plants.

PubMed

Vaerewijck, Mario J M; Sabbe, Koen; Baré, Julie; Houf, Kurt

2008-09-01

The diversity of free-living protozoa in five meat-cutting plants was determined. Light microscopy after enrichment culturing was combined with sequencing of PCR-amplified, denaturing gradient gel electrophoresis (DGGE)-separated 18S rRNA gene fragments, which was used as a fast screening method. The general results of the survey showed that a protozoan community of amoebae, ciliates, and flagellates was present in all of the plants. Protozoa were detected mainly in floor drains, in standing water on the floor, on soiled bars of cutting tables, on plastic pallets, and in out-of-use hot water knife sanitizers, but they were also detected on surfaces which come into direct contact with meat, such as conveyer belts, working surfaces of cutting tables, and needles of a meat tenderizer. After 7 days of incubation at refrigerator temperature, protozoa were detected in about one-half of the enrichment cultures. Based on microscopic observations, 61 morphospecies were found, and Bodo saltans, Bodo spp., Epistylis spp., Glaucoma scintillans, Petalomonas spp., Prodiscophrya collini, and Vannella sp. were the most frequently encountered identified organisms. Sequencing of DGGE bands resulted in identification of a total of 49 phylotypes, including representatives of the Amoebozoa, Chromalveolata, Excavata, Opisthokonta, and Rhizaria. Sequences of small heterotrophic flagellates were affiliated mainly with the Alveolata (Apicomplexa), Stramenopiles (Chrysophyceae), and Rhizaria (Cercozoa). This survey showed that there is high protozoan species richness in meat-cutting plants and that the species included species related to known hosts of food-borne pathogens.

The effect of water table fluctuation on soil respiration in a lower coastal plain forested wetland in the southeastern U.S.

NASA Astrophysics Data System (ADS)

Miao, Guofang; Noormets, Asko; Domec, Jean-Christophe; Trettin, Carl C.; McNulty, Steve G.; Sun, Ge; King, John S.

2013-12-01

and environmental pressures on wetland hydrology may trigger changes in carbon (C) cycling, potentially exposing vast amounts of soil C to rapid decomposition. We measured soil CO2 efflux (Rs) continuously from 2009 to 2010 in a lower coastal plain forested wetland in North Carolina, U.S., to characterize its main environmental drivers. To understand and quantify the spatial variation due to microtopography and associated differences in hydrology, measurements were conducted at three microsites along a microtopographic gradient. The seasonal hysteresis in Rs differed by microtopographic location and was caused by the transitions between flooded and nonflooded conditions. Because flooded Rs was small, we reported Rs dynamics mainly during nonflooded periods. A nested model, modified from conventional Q10 (temperature sensitivity) model with dynamic parameters, provided a significantly better simulation on the observed variation of Rs. The model performed better with daily data, indicating that soil temperature (Ts) and water table depth (WTD) were the primary drivers for seasonal variation. The diel variation of Rs was high and independent of Ts and WTD, which both had small diel variations, suggesting the likely association with plant activity. Overall, the site-average soil CO2 efflux was approximately 960-1103 g C m-2 yr-1 in 2010, of which 93% was released during nonflooded periods. Our study indicates that Rs is highly linked to hydroperiod and microtopography in forested wetlands and droughts in wetlands will accelerate soil C loss.

Data Tables - Environments and Contaminants - Drinking Water Contaminants

EPA Pesticide Factsheets

This document contains a table of the estimated percentage of children ages 0 to 17 years served by community water systems that did not meet all applicable health-based drinking water standards, 1993-2009.

Field data and numerical simulation of btex concentration trends under water table fluctuations: Example of a jet fuel-contaminated site in Brazil.

PubMed

Teramoto, Elias Hideo; Chang, Hung Kiang

2017-03-01

Mass transfer of light non-aqueous phase liquids (LNAPLs) trapped in porous media is a complex phenomenon. Water table fluctuations have been identified as responsible for generating significant variations in the concentration of dissolved hydrocarbons. Based on field evidence, this work presents a conceptual model and a numerical solution for mass transfer from entrapped LNAPL to groundwater controlled by both LNAPL saturation and seasonal water table fluctuations within the LNAPL smear zone. The numerical approach is capable of reproducing aqueous BTEX concentration trends under three different scenarios - water table fluctuating within smear zone, above the smear zone and partially within smear zone, resulting in in-phase, out-of-phase and alternating in-phase and out-of-phase BTEX concentration trend with respect to water table oscillation, respectively. The results demonstrate the model's applicability under observed field conditions and its ability to predict source zone depletion. Copyright © 2017 Elsevier B.V. All rights reserved.

Environmental factors controlling methane emissions from peatlands in northern Minnesota

NASA Technical Reports Server (NTRS)

Dise, Nancy B.; Gorham, Eville; Verry, Elon S.

1993-01-01

The environmental factors affecting the emission of methane from peatlands were investigated by correlating CH4 emission data for two years, obtained from five different peatland ecosystems in northern Minnesota, with peat temperature, water table position, and degree of peat humification. The relationship obtained between the CH4 flux and these factors was compared to results from a field manipulation experiment in which the water table was artificially raised in three experimental plots within the driest peatland. It was found that peat temperature, water table position, and degree of peat humification explained 91 percent of the variance in log CH4 flux, successfully predicted annual CH4 emission from individual wetlands, and predicted the change in flux due to the water table manipulation. Raising the water table in the bog corrals by an average of 6 cm in autumn 1989 and 10 cm in summer 1990 increased CH4 emission by 2.5 and 2.2 times, respectively.

Paleoclimatic Inferences from a 120,000-Yr Calcite Record of Water-Table Fluctuation in Browns Room of Devils Hole, Nevada

USGS Publications Warehouse

Szabo, B. J.; Kolesar, Peter T.; Riggs, A.C.; Winograd, I.J.; Ludwig, K. R.

1994-01-01

The petrographic and morphologic differences between calcite precipitated below, at, or above the present water table and uranium-series dating were used to reconstruct a chronology of water-table fluctuation for the past 120,000 yr in Browns Room, a subterranean air-filled chamber of Devils Hole fissure adjacent to the discharge area of the large Ash Meadows groundwater flow system in southern Nevada. The water table was more than 5 m above present level between about 116,000 and 53,000 yr ago, fluctuated between about +5 and +9 m during the period between about 44,000 and 20,000 yr ago, and declined rapidly from +9 to its present level during the past 20,000 yr. Because the Ash Meadows groundwater basin is greater than 12,000 km2 in extent, these documented water-table fluctuations are likely to be of regional significance. Although different in detail, water-level fluctuation recorded by Browns Room calcites generally correlate with other Great Basin proxy palcoclimatic data.

Basement flooding and foundation damage from water-table rise in the East New York section of Brooklyn, Long Island, New York

USGS Publications Warehouse

Soren, Julian

1976-01-01

A rising water table following cessation of public-supply pumping has been causing basement flooding and building-foundation damage in the East New York section of Brooklyn, Kings County, Long Island, N.Y., since 1975. The water table in the central part of the area rose from a low of about 12 feet (3.7 meters) below sea level in 1936 to about 8 to 10 feet (2.4 to 3 meters) above sea level in March 1976. Public-supply pumping in Brooklyn ceased in 1947 and ceased in 1974 in the adjacent Woodhaven section of Queens County. A further water-table rise of about 2 feet (0.6 meter) is anticipated in the next several years in the central part of the East New York area, and the ultimate water-table height could be as much as about 15 feet (4.6 meters) above sea level. Relief from the flooding by dewatering operations is complicated by problems with disposal of pumped-out ground water. (Woodard-USGS)

Quantifying the Benthic Source of Nutrients to the Water Column of Upper Klamath Lake, Oregon

USGS Publications Warehouse

Kuwabara, James S.; Lynch, Dennis D.; Topping, Brent R.; Murphy, Fred; Carter, James L.; Simon, Nancy S.; Parcheso, Francis; Wood, Tamara M.; Lindenberg, Mary K.; Wiese, Katryn; Avanzino, Ronald J.

2007-01-01

Executive Summary Five sampling trips were coordinated in April, May and August 2006, and May and July 2007 to sample the water column and benthos of Upper Klamath Lake, OR (Fig. 1; Table 1), before, during and after the annual cyanophyte bloom of Aphanizomenon flos-aquae (AFA). A pore-water profiler was designed and fabricated to obtain the first high-resolution (centimeter-scale) estimates of the vertical concentration gradients for diffusive-flux determinations. Estimates based on molecular diffusion may underestimate benthic flux because solute transport across the sediment-water interface can be enhanced by processes including bioturbation, bioirrigation and ground-water advection. Water-column and benthic samples were also collected to help interpret spatial and temporal trends in diffusive-flux estimates. Data from these samples complement geochemical analyses of bottom-sediments taken from Upper Klamath Lake (UKL) in 2005. This ongoing study provides information necessary for developing process-interdependent solute-transport models for the watershed (that is, models integrating physical, geochemical and biological processes), and supports efforts to evaluate remediation or load-allocation strategies. To augment studies funded by the U.S. Bureau of Reclamation (USBR), the Department of Interior supported an additional full deployment of pore-water profilers in July 2007, during the summer AFA bloom. Results from this recent field trip are not fully completed. Data not presented herein will be included in a subsequent publication, scheduled for March 2009.

Water and vapor transfer in vadose zone of Gobi desert and riparian in the hyper arid environment of Ejina, China

NASA Astrophysics Data System (ADS)

Du, C.; Yu, J.; Sun, F.; Liu, X.

2015-12-01

To reveal how water and vapor transfer in vadose zone affect evapotranspiration in Gobi desert and riparian in hyper arid region is important for understanding eco-hydrological process. Field studies and numerical simulations were imported to evaluate the water and vapor movement processes under non isothermal and lower water content conditions. The soil profiles (12 layers) in Gobi desert and riparian sites of Ejina were installed with sensors to monitor soil moisture and temperature for 1 year. The meteorological conditions and water table were measured by micro weather stations and mini-Divers respectively in the two sites. Soil properties, including particles composition, moisture, bulk density, water retention curve, and saturated hydraulic conductivity of two site soil profiles, was measured. The observations showed that soil temperatures for the two sites displayed large diurnal and seasonal fluctuations. Temperature gradients with depth resulted in a downward in summer and upward in winter and became driving force for thermal vapor movement. Soil moistures in Gobi desert site were very low and varied slowly with time. While the soil moistures in riparian site were complicated due to root distribution but water potentials remained uniform with time. The hydrus-1D was employed to simulate evapotranspiration processes. The simulation results showed the significant difference of evaporation rate in the Gobi desert and riparian sites.

Hydrologic data; North Canadian River from Lake Overholser to Lake Eufaula, central Oklahoma

USGS Publications Warehouse

Havens, J.S.

1984-01-01

The data contained in this report were gathered during the period 1982 to 1984 for use in constructing a digital model of the North Canadian River from Lake Overholser, in the western part of Oklahoma City, to Lake Eufaula, in eastern Oklahoma. Locations of test holes and sampling sites are show in figure 1. Information on well depths and water levels in table 1 was gathered in the summer of 1982. Some information in the table was reported by well owners. Field water-quality data for water temperatures, specific conductance, and pH were measured at the time the wells were inventoried in 1982 and appear in table 2. Forty-nine test holes were augered to provide more comprehensive lithologic and water-level data along the North Canadian River. Lithologic logs of these test holes appear in table 3. Thirty-eight of the test holes were completed as observations wells by placing perforated plastic casing in the holes. Water levels were measured in these observations wells from the time of completion in mid-1982 through mid-1984. Hydrographs of the observation wells are shown in figures 2 through 15. The data are presented graphically for clarity. Hydrographs of water-level fluctuations in two wells equipped with continuous water-level recorders and hydrographs of stage fluctuations on the North Canadian River at nearby gaging stations are shown in figures 16 and 17. Two sets of low-flow measurements for the North Canadian River showing gains and losses in flow between measuring sites in the reach from Lake Overholser to Lake Eufaula are given in table 4. Measurements of flow on tributary streams are also given in this table. Analyses of water-quality samples collected at the time of the low-flow measurements are given in table 5.

41. PATTERN STORAGE, GRIND STONE, WATER TANK, SHAFTING, AND TABLE ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

41. PATTERN STORAGE, GRIND STONE, WATER TANK, SHAFTING, AND TABLE SAW (L TO R)-LOOKING WEST. - W. A. Young & Sons Foundry & Machine Shop, On Water Street along Monongahela River, Rices Landing, Greene County, PA

Treatment of table olive washing water using trickling filters, constructed wetlands and electrooxidation.

PubMed

Tatoulis, Triantafyllos; Stefanakis, Alexandros; Frontistis, Zacharias; Akratos, Christos S; Tekerlekopoulou, Athanasia G; Mantzavinos, Dionissios; Vayenas, Dimitrios V

2017-01-01

The production of table olives is a significant economic activity in Mediterranean countries. Table olive processing generates large volumes of rinsing water that are characterized by high organic matter and phenol contents. Due to these characteristics, a combination of more than one technology is imperative to ensure efficient treatment with low operational cost. Previously, biological filters were combined with electrooxidation to treat table olive washing water. Although this combination was successful in reducing pollutant loads, its cost could be further reduced. Constructed wetlands could be an eligible treatment method for integrated table olive washing water treatment as they have proved tolerant to high organic matter and phenol loads. Two pilot-scale horizontal subsurface constructed wetlands, one planted and one unplanted, were combined with a biological filter and electrooxidation over a boron-doped diamond anode to treat table olive washing water. In the biological filter inlet, chemical oxygen demand (COD) concentrations ranged from 5500 to 15,000 mg/L, while mean COD influent concentration in the constructed wetlands was 2800 mg/L. The wetlands proved to be an efficient intermediate treatment stage, since COD removal levels for the planted unit reached 99 % (mean 70 %), while the unplanted unit presented removal rates of around 65 %. Moreover, the concentration of phenols in the effluent was typically below 100 mg/L. The integrated trickling filter-constructed wetland-electrooxidation treatment system examined here could mineralize and decolorize table olive washing water and fully remove its phenolic content.

Seasonal changes in ground-water levels in the shallow aquifer near Hagerman and the Pecos River, Chaves County, New Mexico

USGS Publications Warehouse

Garn, H.S.

1988-01-01

The Pecos River near Hagerman in Chaves County, New Mexico, historically has been a gaining stream. In 1938, the slope of the water table in the shallow alluvial aquifer near Hagerman was toward the Pecos River. By 1950, a large water-table depression had formed in the alluvial aquifer southwest of Hagerman. Continued enlargement of this depression could reverse the direction of groundwater flow to the Pecos River. Water levels were measured during 1981-85 in wells along a section extending from the Pecos River to a point within the depression. Although the water-table depression has not caused a perennial change in direction of groundwater flow, it has caused a seasonal reversal in the slope of the water table between the river and the depression during the growing season when pumpage from the shallow aquifer is the greatest. (USGS)

Excess growing-season water limits lowland black spruce productivity

NASA Astrophysics Data System (ADS)

Dymond, S.; Kolka, R. K.; Bolstad, P. V.; Gill, K.; Curzon, M.; D'Amato, A. W.

2015-12-01

The annual growth of many tree species is limited by water availability, with growth increasing as water becomes less scarce. In lowland bogs of northern Minnesota, however, black spruce (Picea mariana) is often exposed to excess water via high water table elevations. These trees grow in thick deposits of organic mucky peat and often have shallow rooting systems to avoid the complete submersion of roots in water. While it is generally believed that black spruce decrease growth rates with rising water table elevations, this hypothesis has not been tested in situ. We used a unique, 50-year record of daily bog water table elevations at the Marcell Experimental Forest (MEF) in northern Minnesota to investigate the relationship between climate and black spruce productivity. Nine 1/20th ha circular plots were established in five different bogs and tree height, diameter-at-breast-height (DBH), and crown class were recorded. Additionally, two perpendicular cores were collected on all trees greater than 10 cm diameter-at-breast-height. Tree cores were sanded, mounted, cross-dated, and de-trended according to standard dendrochronological procedures. Ring width measurements were correlated with precipitation, temperature, and water table elevation using package BootRes in R to determine the climatic variables most associated with stand level productivity. Across the different plots, we found that early growing season water table elevation (May and June) was negatively correlated with both individual and stand-level black spruce growth (p < 0.01), while growth was positively correlated with March temperatures (p < 0.01). No significant relationships existed between black spruce growth and monthly precipitation. If summer water table elevations in these peatland ecosystems rise as is anticipated with more extreme precipitation events due to climate change, we could see an overall decrease in the stand level productivity of black spruce.

Understanding High Temperature Gradients in the Buckman Well Field, Santa Fe County, New Mexico

NASA Astrophysics Data System (ADS)

Folsom, M.; Gulvin, C. J.; Tamakloe, F. M.; Yauk, K.; Kelley, S.; Frost, J.; Jiracek, G. R.

2014-12-01

We propose a conceptual model to explain elevated thermal gradients, localized laterally over a few 100 m, discovered during the SAGE program in 2013 and confirmed in 2014 at the Buckman water well field in the Española Basin of north central New Mexico. The anomalous gradients of temperature with depth, dT/dz, exceed 70 ºC/km and are found in three shallow (< 100 m-deep) USGS monitoring wells close to the Rio Grande. A temperature increase of only 3 - 4 ºC at ~100 m depth would elevate the regional temperature value enough to yield the anomalous dT/dz values in the upper ~100 m. The coincidence of a 25 km2 region of InSAR-confirmed subsidence with the locally anomalous dT/dz region suggests a way to achieve a higher temperature at ~ 100 m depth. The mechanism is an isothermal release of warmer water from ~ 200 m depth along a fissure or reactivated fault. A fourth well, 290 m away, has a temperature gradient of only 33ºC/km in the upper 100 m and a distinctly different geochemical profile, suggesting aquifer compartmentalization and possible faulting close to the anomaly. In 2001 a 800 m-long surface scarp with up to 0.2 m offset appeared 2 km to the east in response to over-pumping that depressed the groundwater table by over 100 m. Such drawdown is expected to have 2 - 5 m of compaction with attendant movement along faults or fissures. This could allow groundwater to be released upward isothermally until encountering an unbreached aquitard where it would establish an elevated thermal boundary. Besides the local thermal anomaly, we have temperature-logged deeper water wells in the area. These and other measurements have been used to construct cross-sections of isotherms across the Española Basin along the groundwater flow units (GFUs). This allows comparison of the local thermal anomaly with classic, regional, basin hydrological models. For example, the fully-screened Skillet well, 2.3 km from the anomaly, shows a classic concave down dT/dz form indicating upwelling water. This is consistent with the regional hydraulic head and historical accounts of artesian wells pre-dating Buckman pumping. We quantified the upwelling by Péclet number analysis to be 0.076 - 0.11 m/yr. Numerical modeling using the TOUGH2 computer code is proceeding to further understand regional and local subsurface groundwater flow patterns and dT/dz values.

Biodegradation of phenol, salicylic acid, benzenesulfonic acid, and iomeprol by Pseudomonas fluorescens in the capillary fringe

NASA Astrophysics Data System (ADS)

Hack, Norman; Reinwand, Christian; Abbt-Braun, Gudrun; Horn, Harald; Frimmel, Fritz H.

2015-12-01

Mass transfer and biological transformation phenomena in the capillary fringe were studied using phenol, salicylic acid, benzenesulfonic acid, and the iodinated X-ray contrast agent iomeprol as model organic compounds and the microorganism strain Pseudomonas fluorescens. Three experimental approaches were used: Batch experiments (uniform water saturation and transport by diffusion), in static columns (with a gradient of water saturation and advective transport in the capillaries) and in a flow-through cell (with a gradient of water saturation and transport by horizontal and vertical flow: 2-dimension flow-through microcosm). The reactors employed for the experiments were filled with quartz sand of defined particle size distribution (dp = 200…600 μm, porosity ε = 0.42). Batch experiments showed that phenol and salicylic acid have a high, whereas benzenesulfonic acid and iomeprol have a quite low potential for biodegradation under aerobic conditions and in a matrix nearly close to water saturation. Batch experiments under anoxic conditions with nitrate as electron acceptor revealed that the biodegradation of the model compounds was lower than under aerobic conditions. Nevertheless, the experiments showed that the moisture content was also responsible for an optimized transport in the liquid phase of a porous medium. Biodegradation in the capillary fringe was found to be influenced by both the moisture content and availability of the dissolved substrate, as seen in static column experiments. The gas-liquid mass transfer of oxygen also played an important role for the biological activity. In static column experiments under aerobic conditions, the highest biodegradation was found in the capillary fringe (e.g. βt/β0 (phenol) = 0 after t = 6 d) relative to the zone below the water table and unsaturated zone. The highest biodegradation occurred in the flow-through cell experiment where the height of the capillary fringe was largest.

Will the Arctic Land Surface become Wetter or Drier in Response to a Warming Climate

NASA Astrophysics Data System (ADS)

Hinzman, L. D.; Rawlins, M.; Serreze, M.; Vorosmarty, C. J.; Walsh, J. E.

2015-12-01

There is much concern about a potentially "accelerated" hydrologic cycle, with associated extremes in weather and climate-related phenomena. Whether this translates into wetter or drier conditions across arctic landscapes remains an open question. Arctic ecosystems differ substantially from those in temperate regions, largely due to the interactions of extremes in climate and land surface characteristics. Ice-rich permafrost prevents percolation of rainfall or snowmelt water, often maintaining a moist to saturated active layer where the permafrost table is shallow. Permafrost may also block the lateral movement of groundwater, and act as a confining unit for water in sub- or intra-permafrost aquifers. However, as permafrost degrades, profound changes in interactions between groundwater and surface water occur that affect the partitioning among the water balance components with subsequent impacts to the surface energy balance and essential ecosystem processes. Most simulations of arctic climate project sustained increases in temperature and gradual increases in precipitation over the 21st century. However, most climatic models do not correctly represent the essential controls that permafrost exerts on hydrological, ecological, and climatological processes. If warming continues as projected, we expect large-scale changes in surface hydrology as permafrost degrades. Where groundwater gradients are downward (i.e. surface water will infiltrate to subsurface groundwater), as in most cases, we may expect improved drainage and drier soils, which would result in reduced evaporation and transpiration (ET). In some special cases, where the groundwater gradient is upward (as in many wetlands or springs) surface soils may become wetter or inundated as permafrost degrades. Further, since soil moisture is a primary factor controlling ecosystem processes, interactions between ecosystems, GHG emissions, and high-latitude climate must also be considered highly uncertain. These inter-dependent processes will exert primary controls on several important feedback processes and vary across space and time in some as yet, unknown way.

Biodegradation of phenol, salicylic acid, benzenesulfonic acid, and iomeprol by Pseudomonas fluorescens in the capillary fringe.

PubMed

Hack, Norman; Reinwand, Christian; Abbt-Braun, Gudrun; Horn, Harald; Frimmel, Fritz H

2015-12-01

Mass transfer and biological transformation phenomena in the capillary fringe were studied using phenol, salicylic acid, benzenesulfonic acid, and the iodinated X-ray contrast agent iomeprol as model organic compounds and the microorganism strain Pseudomonas fluorescens. Three experimental approaches were used: Batch experiments (uniform water saturation and transport by diffusion), in static columns (with a gradient of water saturation and advective transport in the capillaries) and in a flow-through cell (with a gradient of water saturation and transport by horizontal and vertical flow: 2-dimension flow-through microcosm). The reactors employed for the experiments were filled with quartz sand of defined particle size distribution (dp=200...600 μm, porosity ε=0.42). Batch experiments showed that phenol and salicylic acid have a high, whereas benzenesulfonic acid and iomeprol have a quite low potential for biodegradation under aerobic conditions and in a matrix nearly close to water saturation. Batch experiments under anoxic conditions with nitrate as electron acceptor revealed that the biodegradation of the model compounds was lower than under aerobic conditions. Nevertheless, the experiments showed that the moisture content was also responsible for an optimized transport in the liquid phase of a porous medium. Biodegradation in the capillary fringe was found to be influenced by both the moisture content and availability of the dissolved substrate, as seen in static column experiments. The gas-liquid mass transfer of oxygen also played an important role for the biological activity. In static column experiments under aerobic conditions, the highest biodegradation was found in the capillary fringe (e.g. βt/β0 (phenol)=0 after t=6 d) relative to the zone below the water table and unsaturated zone. The highest biodegradation occurred in the flow-through cell experiment where the height of the capillary fringe was largest. Copyright © 2015 Elsevier B.V. All rights reserved.

Groundwater Monitoring Plan. Volume 2. Final Quality Assurance Project Plan

DTIC Science & Technology

1993-10-01

5 Table 4-2. US EPA Drinking Water MCLs ........................................ 4-6 Table 5-1. Sample Bottle Requirements, Preservation, and Holding... drinking water . " The types of quality control samples that will be collected during the Canal Creek groundwater monitoring program. ]- Jacobs...Revision No.: 0 Date: 10/27/93 Page: 6 of 9 Canal Creek Area, APG-EA, Maryland Groundwater Monitoring Plan, VOLUME I1 Table 4-2. US EPA Drinking Water

Water table tests of proposed heat transfer tunnels for small turbine vanes

NASA Technical Reports Server (NTRS)

Meitner, P. L.

1974-01-01

Water-table flow tests were conducted for proposed heat-transfer tunnels which were designed to provide uniform flow into their respective test sections of a single core engine turbine vane and a full annular ring of helicopter turbine vanes. Water-table tests were also performed for the single-vane test section of the core engine tunnel. The flow in the heat-transfer tunnels was shown to be acceptable.

The effects of groundwater depth on water uptake of Populus euphratica and Tamarix ramosissima in the hyperarid region of Northwestern China.

PubMed

Chen, Yapeng; Chen, Yaning; Xu, Changchun; Li, Weihong

2016-09-01

Knowledge of the water sources used by desert trees and shrubs is critical for understanding how they function and respond to groundwater decline and predicting the influence of water table changes on riparian plants. In this paper, we test whether increased depth to groundwater changed the water uptake pattern of desert riparian species and whether competition for water resources between trees and shrubs became more intense with a groundwater depth gradient. The water sources used by plants were calculated using the IsoSource model, and the results suggested differences in water uptake patterns with varying groundwater depths. At the river bank (groundwater depth = 1.8 m), Populus euphratica and Tamarix ramosissima both used a mixture of river water, groundwater, and deeper soil water (>75 cm). When groundwater depth was 3.8 m, trees and shrubs both depended predominantly on soil water stored at 150-375 cm depth. When the groundwater depth was 7.2 m, plant species switched to predominantly use both groundwater and deeper soil water (>375 cm). However, differences in water acquisition patterns between species were not found. The proportional similarity index (PSI) of proportional contribution to water uptake of different water resources between P. euphratica and T. ramosissima was calculated, and results showed that there was intense water resource competition between P. euphratica and T. ramosissima when grown at shallow groundwater depth (not more than 3.8 m), and the competition weakened when the groundwater depth increased to 7.2 m.

--No Title--

Science.gov Websites

| |----------|--------|----------------------------------------------------------| | | | | | GFSCLS1 | A60243 | TABLE A ENTRY - GFSMODEL MESSAGES | | | | | | HEADR | 362001 | TABLE D ENTRY - PROFILE COORDINATES | | PROFILE | 362002 | TABLE D ENTRY - PROFILE DATA | | CLS1 | 362003 | TABLE D ENTRY - SURFACE | TABLE B ENTRY - SNOW WATER EQUIVALENT | | LCLD | 020051 | TABLE B ENTRY - AMOUNT OF LOW CLOUD | | MCLD

40 CFR 132.3 - Adoption of criteria.

Code of Federal Regulations, 2014 CFR

2014-07-01

...) The acute water quality criteria for protection of aquatic life in Table 1 of this part, or a site... water quality criteria for protection of aquatic life in Table 2 of this part, or a site-specific....3 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) WATER PROGRAMS WATER QUALITY...

Installation Restoration Program. Preliminary Assessment: Record Search for the 110th Tactical Air Support Group, Michigan Air National Guard, W. K. Kellogg Regional Airport, Battle Creek, Michigan.

DTIC Science & Technology

1987-09-01

these wetlands. Because of the generally low relief at the Base, several manmade drainage ditches have been constructed to improve surface water ...northerly boundary (Hickock, 1985). Within the Marshall Formation, the water table or piezometric surface con- forms somewhat to the land surface. The...34hills" in the water table underlie hills seen on land. The " lows " in the water table coincide with low areas on land (Vanlier, 1966). Thus, the

Water table in rocks of Cenozoic and Paleozoic age, 1980, Yucca Flat, Nevada Test Site, Nevada

USGS Publications Warehouse

Doty, G.C.; Thordarson, William

1983-01-01

The water table at Yucca Flat, Nevada Test Site, Nevada, occurs in rocks of Paleozoic age and in tuffs and alluvium of Cenozoic age and ranges in altitude from about 2,425 feet to about 3,500 feet. The configuration of the water table is depicted by contours with intervals of 25 to 500 feet. Control for the map consists of water-level information from 61 drill holes, whose locations and age of geologic units penetrated are shown by symbols on the map. (USGS)

A study on the influence of tides on the water table conditions of the shallow coastal aquifers

NASA Astrophysics Data System (ADS)

Singaraja, C.; Chidambaram, S.; Jacob, Noble

2018-03-01

Tidal variation and water level in aquifer is an important function in the coastal environment, this study attempts to find the relationship between water table fluctuation and tides in the shallow coastal aquifers. The study was conducted by selecting three coastal sites and by monitoring the water level for every 2-h interval in 24 h of observation. The study was done during two periods of full moon and new moon along the Cuddalore coastal region of southern part of Tamil Nadu, India. The study shows the relationship between tidal variation, water table fluctuations, dissolved oxygen, and electrical conductivity. An attempt has also been made in this study to approximate the rate of flow of water. Anyhow, the differences are site specific and the angle of inclination of the water table shows a significant relation to the mean sea level, with respect to the distance of the point of observation from the sea and elevation above mean sea level.

Seasonal variability of near surface soil water and groundwater tables in Florida : phase II.

DOT National Transportation Integrated Search

2008-01-01

The seasonal high groundwater table (SHGWT) is a critical measure for design projects requiring : surface water permits including roadway design and detention or retention pond design. Accurately : measuring and, more importantly, predicting water ta...

Hydrologic processes governing near surface saturation of alpine wetlands in the Canadian Rockies

NASA Astrophysics Data System (ADS)

Westbrook, C.; Mercer, J.

2016-12-01

Alpine wetlands are vital for habitat, biodiversity, carbon cycling and water storage, but little is known about their hydrologic condition. Climate trends toward smaller mountain snowpacks that melt earlier are thought to pose a threat to the continued provision of alpine wetland ecological functions, and their existence, as it is believed they derive their water mainly from snowmelt. Our objective was to determine the hydrologic processes governing near surface saturation in alpine wetlands. We monitored the water table dynamics of three alpine wetlands in contrasting hydrogeomorphic landscape positions for two summers in Banff National Park, Canada. We concurrently monitored water balance components, and analyzed soil properties and source water geochemistry. Despite very different snow conditions between the two study years, water tables remained near the surface and relatively stable in both years, indicating wetlands are more hydrologically buffered from snowpack variations than expected. We did not find convincing evidence of hydrogeomorphic position influencing wetland water table dynamics. Instead, peat thickness seemed to be critical in regulating water table as the wetland with the thickest peat soil (>1 m) maintained water tables closest to the ground surface for the longest period of time. Thicker peat deposits may develop under convergent hydrologic flow path conditions. Our results indicate that alpine wetlands are more resilient to shifting environmental conditions than previously reported.

The Impact of Water Table Drawdown and Drying on Subterranean Aquatic Fauna in In-Vitro Experiments

PubMed Central

Stumpp, Christine; Hose, Grant C.

2013-01-01

The abstraction of groundwater is a global phenomenon that directly threatens groundwater ecosystems. Despite the global significance of this issue, the impact of groundwater abstraction and the lowering of groundwater tables on biota is poorly known. The aim of this study is to determine the impacts of groundwater drawdown in unconfined aquifers on the distribution of fauna close to the water table, and the tolerance of groundwater fauna to sediment drying once water levels have declined. A series of column experiments were conducted to investigate the depth distribution of different stygofauna (Syncarida and Copepoda) under saturated conditions and after fast and slow water table declines. Further, the survival of stygofauna under conditions of reduced sediment water content was tested. The distribution and response of stygofauna to water drawdown was taxon specific, but with the common response of some fauna being stranded by water level decline. So too, the survival of stygofauna under different levels of sediment saturation was variable. Syncarida were better able to tolerate drying conditions than the Copepoda, but mortality of all groups increased with decreasing sediment water content. The results of this work provide new understanding of the response of fauna to water table drawdown. Such improved understanding is necessary for sustainable use of groundwater, and allows for targeted strategies to better manage groundwater abstraction and maintain groundwater biodiversity. PMID:24278111

Estimating drain flow from measured water table depth in layered soils under free and controlled drainage

NASA Astrophysics Data System (ADS)

Saadat, Samaneh; Bowling, Laura; Frankenberger, Jane; Kladivko, Eileen

2018-01-01

Long records of continuous drain flow are important for quantifying annual and seasonal changes in the subsurface drainage flow from drained agricultural land. Missing data due to equipment malfunction and other challenges have limited conclusions that can be made about annual flow and thus nutrient loads from field studies, including assessments of the effect of controlled drainage. Water table depth data may be available during gaps in flow data, providing a basis for filling missing drain flow data; therefore, the overall goal of this study was to examine the potential to estimate drain flow using water table observations. The objectives were to evaluate how the shape of the relationship between drain flow and water table height above drain varies depending on the soil hydraulic conductivity profile, to quantify how well the Hooghoudt equation represented the water table-drain flow relationship in five years of measured data at the Davis Purdue Agricultural Center (DPAC), and to determine the impact of controlled drainage on drain flow using the filled dataset. The shape of the drain flow-water table height relationship was found to depend on the selected hydraulic conductivity profile. Estimated drain flow using the Hooghoudt equation with measured water table height for both free draining and controlled periods compared well to observed flow with Nash-Sutcliffe Efficiency values above 0.7 and 0.8 for calibration and validation periods, respectively. Using this method, together with linear regression for the remaining gaps, a long-term drain flow record for a controlled drainage experiment at the DPAC was used to evaluate the impacts of controlled drainage on drain flow. In the controlled drainage sites, annual flow was 14-49% lower than free drainage.

Controlling the Accumulation of Water at Oil-Solid Interfaces with Gradient Coating.

PubMed

Li, Yan; Yang, Qiaomu; Mei, Ran Andy; Cai, Meirong; Heng, Jerry Y Y; Yang, Zhongqiang

2017-07-13

In this work, we demonstrate a strategy to control the accumulation of water in the oil-solid interface using a gradient coating. Gradient chemistry on glass surface is created by vapor diffusion of organosilanes, leading to a range of contact angles from 110 to 20°. Hexadecane is placed on the gradient substrate as an oil layer, forming a "water/hexadecane/gradient solid substrate" sandwich structure. During incubation, water molecules spontaneously migrate through the micrometer-thick oil layer and result in the formation of micrometer-sized water droplets at the oil-solid interface. It turns out that water droplets at more hydrophobic regions tend to be closer to a regular spherical shape, which is attributed to their higher contact angle with the hydrophobic substrate. However, along the gradient from hydrophobic to hydrophilic, the water droplets gradually form more irregular shapes, as hydrophilic surfaces pin the edges of droplets to form a distorted morphology. It indicates that more hydrophilic surfaces containing more Si-OH groups lead to a higher electrostatic interaction with water and a higher growth rate of interfacial water droplets. This work provides further insights into the mechanism of spontaneous water accumulation at oil-solid interfaces and assists in the rational design for controlling such interfacial phenomenon.

Trajectories of water table recovery following the re-vegetation of bare peat

NASA Astrophysics Data System (ADS)

Shuttleworth, Emma; Evans, Martin; Allott, Tim; Maskill, Rachael; Pilkington, Michael; Walker, Jonathan

2016-04-01

The hydrological status of blanket peat influences a wide range of peatland functions, such as runoff generation, water quality, vegetation distribution, and rates of carbon sequestration. The UK supports 15% of the world's blanket peat cover, but much of this vital resource is significantly degraded, impacted by industrial pollution, overgrazing, wildfire, and climatic shifts. These pressures have produced a unique landscape characterised by severe gully erosion and extensive areas of bare peat. This in turn has led water tables to become substantially drawn down, impacting peatland function and limiting the resilience of these landscapes to future changes in climate. The restoration of eroding UK peatlands is a major conservation concern, and landscape-scale interventions through the re-vegetation of bare peat is becoming increasingly extensive in areas of upland Britain. Water table is the primary physical parameter considered in the monitoring of many peatland restoration projects, and there is a wealth of data on individual monitoring programmes which indicates that re-vegetation significantly raises water tables. This paper draws on data from multiple restoration projects carried out by the Moors for the Future Partnership in the Southern Pennines, UK, covering a range of stages in the erosion-restoration continuum, to assess the trajectories of water table recovery following re-vegetation. This will allow us to generate projections of future water table recovery, which will be of benefit to land managers and conservation organisations to inform future restoration initiatives.

Ground-water data, Sevier Desert, Utah

USGS Publications Warehouse

Mower, Reed W.; Feltis, Richard D.

1964-01-01

This report is intended to serve two purposes: (1) to make available to the public basic ground-water data useful in planning and studying development of water resources, and (2) to supplement an interpretive report that will be published later.Records were collected during the period 1935-64 by the U.S. Geological survey in cooperation with the Utah State Engineer as part of the investigation of ground-water conditions in the Sevier Desert, in Juab and Millard Counties, Utah. The interpretive material will be published in a companion report by R. W. Mower and R. D. Feltis.This report is most useful in predicting conditions likely to be found in areas that are being considered as well sites. The person considering the new well can spot the proposed site on plate 1 and examine the records of nearby wells as shown in the tables and figures. From table 1 he can note such things as depth, diameter, water level, yield, use of water, temperature of water, and depth of perforations. By comparing the depth of perforations with the drillers' logs in table 3 he can note the type of material that yields water to the wells. Table 2 and figure 2 show the historic fluctuations and trends of water levels in the vicinity. From table 4 he can note the chemical quality of the water from wells in the vicinity. Table 5 shows the amount of water discharged during 1951-63 from the pumped irrigation, public supply, and industrial wells. If the reader decides from his examination that conditions are favorable, he can place an application to drill a well with the state Engineer. If the State Engineer believes unappropriated water is available, the application may be approved after minimum statutory requirements have been satisfied.The report is also useful when planning large-scale developments of water supply. This and other uses of the report will be helped by use of the interpretive report upon its release.

Osmotic potential and projected drought tolerance of four phreatophytic shrub species in Owens Valley, California

USGS Publications Warehouse

Dileanis, Peter D.; Groeneveld, David P.

1989-01-01

A substantial quantity of the water used by plant communities growing on the floor of Owens Valley, California, is derived from a shallow unconfined aquifer. Fluctuations in the water table caused by ground-water withdrawal may result in periods when this water supply is not accessible to plants. The capacity of the plants to adapt to these periods of water loss depends on the availability of water stored in the soil and on physiological characteristics related to the ability of the plants to resist dehydration and wilting. Osmotic adjustment occurred in four phreatophytic shrub species at sites near Bishop, California, where the water table had been lowered by a system of pump-equipped wells installed in the vicinity of vegetation transects. The pressure-volume technique was used to determine osmotic potential and cell-wall elasticity between March 1985 and September 1986 for Atriplex torreyi, Chrysothamnus nauseosus , Sarcobatus verm iculatus , and Artemisia tridentata. Although not usually classified as a phreatophyte, Artemisia tridentata, where it grows on the valley floor, is apparently dependent on the depth to the water table. During late summer, osmotic potentials were 0.37 to 0.41 MPa (megapascal) lower in plants growing on the site where the water table had been lowered compared to an adjacent site where the water table remained at its natural levels. Measurements of soil matric potential at the two sites indicated that osmotic adjustment occurred in response to stress caused by lowering the water table. A theoretical lower limit of osmotic adjustment was determined by comparing initial cell osmotic potentials with initial xylem water potentials. These experimentally derived limits indicated that Atriplex torreyi and S. vermiculatus may maintain leaf cell turgor at significantly lower cell water potentials (about -4.5 MPa) than C. nauseosus or Artemisia tridentata (about -2.5 MPa), which allows them to function in drier soil environments.

Controls on ecosystem and root respiration across a permafrost and wetland gradient in interior Alaska

USGS Publications Warehouse

McConnell, Nicole A.; Turetsky, Merritt R.; McGuire, A. David; Kane, Evan S.; Waldrop, Mark P.; Harden, Jennifer W.

2013-01-01

Permafrost is common to many northern wetlands given the insulation of thick organic soil layers, although soil saturation in wetlands can lead to warmer soils and increased thaw depth. We analyzed five years of soil CO2 fluxes along a wetland gradient that varied in permafrost and soil moisture conditions. We predicted that communities with permafrost would have reduced ecosystem respiration (ER) but greater temperature sensitivity than communities without permafrost. These predictions were partially supported. The colder communities underlain by shallow permafrost had lower ecosystem respiration (ER) than communities with greater active layer thickness. However, the apparent Q10 of monthly averaged ER was similar in most of the vegetation communities except the rich fen, which had smaller Q10 values. Across the gradient there was a negative relationship between water table position and apparent Q10, showing that ER was more temperature sensitive under drier soil conditions. We explored whether root respiration could account for differences in ER between two adjacent communities (sedge marsh and rich fen), which corresponded to the highest and lowest ER, respectively. Despite differences in root respiration rates, roots contributed equally (~40%) to ER in both communities. Also, despite similar plant biomass, ER in the rich fen was positively related to root biomass, while ER in the sedge marsh appeared to be related more to vascular green area. Our results suggest that ER across this wetland gradient was temperature-limited, until conditions became so wet that respiration became oxygen-limited and influenced less by temperature. But even in sites with similar hydrology and thaw depth, ER varied significantly likely based on factors such as soil redox status and vegetation composition.

Contributions of algae to GPP and DOC production in an Alaskan fen: effects of historical water table manipulations on ecosystem responses to a natural flood.

PubMed

Wyatt, Kevin H; Turetsky, Merritt R; Rober, Allison R; Giroldo, Danilo; Kane, Evan S; Stevenson, R Jan

2012-07-01

The role of algae in the metabolism of northern peatlands is largely unknown, as is how algae will respond to the rapid climate change being experienced in this region. In this study, we examined patterns in algal productivity, nutrients, and dissolved organic carbon (DOC) during an uncharacteristically wet summer in an Alaskan rich fen. Our sampling was conducted in three large-scale experimental plots where water table position had been manipulated (including both drying and wetting plots and a control) for the previous 4 years. This study allowed us to explore how much ecosystem memory of the antecedent water table manipulations governed algal responses to natural flooding. Despite no differences in water table position between the manipulated plots at the time of sampling, algal primary productivity was consistently higher in the lowered water table plot compared to the control or raised water table plots. In all plots, algal productivity peaked immediately following seasonal maxima in nutrient concentrations. We found a positive relationship between algal productivity and water-column DOC concentrations (r (2) = 0.85, P < 0.001). Using these data, we estimate that algae released approximately 19% of fixed carbon into the water column. Algal exudates were extremely labile in biodegradability assays, decreasing by more than 55% within the first 24 h of incubation. We suggest that algae can be an important component of the photosynthetic community in boreal peatlands and may become increasingly important for energy flow in a more variable climate with more intense droughts and flooding.

Assessing field-scale biogeophysical signatures of bioremediation over a mature crude oil spill

USGS Publications Warehouse

Slater, Lee; Ntarlagiannis, Dimitrios; Atekwana, Estella; Mewafy, Farag; Revil, Andre; Skold, Magnus; Gorby, Yuri; Day-Lewis, Frederick D.; Lane, John W.; Trost, Jared J.; Werkema, Dale D.; Delin, Geoffrey N.; Herkelrath, William N.; Rectanus, H.V.; Sirabian, R.

2011-01-01

We conducted electrical geophysical measurements at the National Crude Oil Spill Fate and Natural Attenuation Research Site (Bemidji, MN). Borehole and surface self-potential measurements do not show evidence for the existence of a biogeobattery mechanism in response to the redox gradient resulting from biodegradation of oil. The relatively small self potentials recorded are instead consistent with an electrodiffusion mechanism driven by differences in the mobility of charge carriers associated with biodegradation byproducts. Complex resistivity measurements reveal elevated electrical conductivity and interfacial polarization at the water table where oil contamination is present, extending into the unsaturated zone. This finding implies that the effect of microbial cell growth/attachment, biofilm formation, and mineral weathering accompanying hydrocarbon biodegradation on complex interfacial conductivity imparts a sufficiently large electrical signal to be measured using field-scale geophysical techniques.

Spatial and temporal changes in microbial community structure associated with recharge-influenced chemical gradients in a contaminated aquifer

USGS Publications Warehouse

Haack, S.K.; Fogarty, L.R.; West, T.G.; Alm, E.W.; McGuire, J.T.; Long, D.T.; Hyndman, D.W.; Forney, L.J.

2004-01-01

In a contaminated water-table aquifer, we related microbial community structure on aquifer sediments to gradients in 24 geochemical and contaminant variables at five depths, under three recharge conditions. Community amplified ribsosomal DNA restriction analysis (ARDRA) using universal 16S rDNA primers and denaturing gradient gel electrophoresis (DGGE) using bacterial 16S rDNA primers indicated: (i) communities in the anoxic, contaminated central zone were similar regardless of recharge; (ii) after recharge, communities at greatest depth were similar to those in uncontaminated zones; and (iii) after extended lack of recharge, communities at upper and lower aquifer margins differed from communities at the same depths on other dates. General aquifer geochemistry was as important as contaminant or terminal electron accepting process (TEAP) chemistry in discriminant analysis of community groups. The Shannon index of diversity (H) and the evenness index (E), based on DGGE operational taxonomic units (OTUs), were statistically different across community groups and aquifer depths. Archaea or sulphate-reducing bacteria 16S rRNA abundance was not clearly correlated with TEAP chemistry indicative of methanogenesis or sulphate reduction. Eukarya rRNA abundance varied by depth and date from 0 to 13% of the microbial community. This contaminated aquifer is a dynamic ecosystem, with complex interactions between physical, chemical and biotic components, which should be considered in the interpretation of aquifer geochemistry and in the development of conceptual or predictive models for natural attenuation or remediation.

Patterned gradient surface for spontaneous droplet transportation and water collection: simulation and experiment

NASA Astrophysics Data System (ADS)

Tan, Xianhua; Zhu, Yiying; Shi, Tielin; Tang, Zirong; Liao, Guanglan

2016-11-01

We demonstrate spontaneous droplet transportation and water collection on wedge-shaped gradient surfaces consisting of alternating hydrophilic and hydrophobic regions. Droplets on the surfaces are modeled and simulated to analyze the Gibbs free energy and free energy gradient distributions. Big half-apex angle and great wettability difference result in considerable free energy gradient, corresponding to large driving force for spontaneous droplet transportation, thus causing the droplets to move towards the open end of the wedge-shaped hydrophilic regions, where the Gibbs free energy is low. Gradient surfaces are then fabricated and tested. Filmwise condensation begins on the hydrophilic regions, forming wedge-shaped tracks for water collection. Dropwise condensation occurs on the hydrophobic regions, where the droplet size distribution and departure diameters are controlled by the width of the regions. Condensate water from both the hydrophilic and hydrophobic regions are collected directionally to the open end of the wedge-shaped hydrophilic regions, agreeing with the simulations. Directional droplet transport and controllable departure diameters make the branched gradient surfaces more efficient than smooth surfaces for water collection, which proves that gradient surfaces are potential in water collection, microfluidic devices, anti-fogging and self-cleaning.

Representing Northern Peatland Hydrology and Biogeochemistry with ALM Land Surface Model

NASA Astrophysics Data System (ADS)

Shi, X.; Ricciuto, D. M.; Thornton, P. E.; Hanson, P. J.; Xu, X.; Mao, J.; Warren, J.; Yuan, F.; Norby, R. J.; Sebestyen, S.; Griffiths, N.; Weston, D. J.; Walker, A.

2017-12-01

Northern peatlands are likely to be important in future carbon cycle-climate feedbacks due to their large carbon pool and vulnerability to hydrological change. Predictive understanding of northern peatland hydrology is a necessary precursor to understanding the fate of massive carbon stores in these systems under the influence of present and future climate change. Current models have begun to address microtopographic controls on peatland hydrology, but none have included a prognostic calculation of peatland water table depth for a vegetated wetland, independent of prescribed regional water tables. Firstly, we introduce a new configuration of the land model (ALM) of Accelerated Climate model for Energy (ACME), which includes a fully prognostic water table calculation for a vegetated peatland. Secondly, we couple our new hydrology treatment with vertically structured soil organic matter pool, and the addition of components from methane biogeochemistry. Thirdly, we introduce a new PFT for mosses and implement the water content dynamics and physiology of mosses. We inform and test our model based on SPRUCE experiment to get the reasonable results for the seasonal dynamics water table depths, water content dynamics and physiology of mosses, and correct soil carbon profiles. Then, we use our new model structure to test the how the water table depth and CH4 emission will respond to elevated CO2 and different warming scenarios.

Technical Note: Interleaved Bipolar Acquisition and Low-rank Reconstruction for Water-Fat Separation in MRI.

PubMed

Cho, JaeJin; Park, HyunWook

2018-05-17

To acquire interleaved bipolar data and reconstruct the full data using low-rank property for water fat separation. Bipolar acquisition suffers from issues related to gradient switching, the opposite gradient polarities, and other system imperfections, which prevent accurate water-fat separation. In this study, an interleaved bipolar acquisition scheme and a low-rank reconstruction method were proposed to reduce issues from the bipolar gradients while achieving a short imaging time. The proposed interleaved bipolar acquisition scheme collects echo-time signals from both gradient polarities; however, the sequence increases the imaging time. To reduce the imaging time, the signals were subsampled at every dimension of k-space. The low-rank property of the bipolar acquisition was defined and exploited to estimate the full data from the acquired subsampled data. To eliminate the bipolar issues, in the proposed method, the water-fat separation was performed separately for each gradient polarity, and the results for the positive and negative gradient polarities were combined after the water-fat separation. A phantom study and in-vivo experiments were conducted on a 3T Siemens Verio system. The results for the proposed method were compared with the results of the fully sampled interleaved bipolar acquisition and Soliman's method, which was the previous water-fat separation approach for reducing the issues of bipolar gradients and accelerating the interleaved bipolar acquisition. The proposed method provided accurate water and fat images without the issues of bipolar gradients and demonstrated a better performance compared with the results of the previous methods. The water-fat separation using the bipolar acquisition has several benefits including a short echo-spacing time. However, it suffers from bipolar-gradient issues such as strong gradient switching, system imperfection, and eddy current effects. This study demonstrated that accurate water-fat separated images can be obtained using the proposed interleaved bipolar acquisition and low-rank reconstruction by using the benefits of the bipolar acquisition while reducing the bipolar-gradient issues with a short imaging time. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.

Stoichiometry, Metabolism and Nutrient Limitation Across the Periodic Table in Natural Flowing-Water Chemostats

NASA Astrophysics Data System (ADS)

Cohen, M. J.; Nifong, R. L.; Kurz, M. J.; Cropper, W. P.; Martin, J. B.

2014-12-01

Relative supplies of macro and micronutrients (C,N,P, various metals), along with light and water, controls ecosystem metabolism, trophic energy transfer and community structure. Here we test the hypothesis, using measurements from 41 spring-fed rivers in Florida, that tissue stoichiometry indicates autotroph nutrient limitation status. Low variation in discharge, temperature and chemical composition within springs, but large variation across springs creates an ideal setting to assess the relationship between limitation and resource supply. Molar N:P ranges from 0.4 to 90, subjecting autotrophs to dramatically different nutrient supply. Over this gradient, species-specific autotroph tissue C:N:P ratios are strictly homeostatic, and with no evidence that nutrient supply affects species composition. Expanding to include 19 metals and micronutrients revealed autotrophs are more plastic in response to micronutrient variation, particularly for iron and manganese whose supply fluxes are small compared to biotic demand. Using a Droop model modified to reflect springs conditions (benthic production, light limitation, high hydraulic turnover), we show that tissue stoichiometry transitions from homeostatic to plastic with the onset of nutrient limitation, providing a potentially powerful new tool for predicting nutrient limitation and thus eutrophication in flowing waters.

A simple microgravity table for the Orbiter or Space Station

NASA Technical Reports Server (NTRS)

Garriott, O. K.; Debra, D. B.

1985-01-01

Methods of limiting perturbations in microgravity experiments are proposed. An acceleration level below 10 to the -4th m/s-squared is necessary to maintain an undisturbed microgravity environment. Machinery vibrations, crew motion, and the firing of vernier thrusters produce acceleration levels greate than 10 to the -4th m/s-squared. The use of a weak spring system or simple electromagnets to isolate an experimental table from these factors is described. The manners in which crew motion and vernier firing are countered by the springs are examined. The steady acceleration caused by atmospheric drag, gravity gradient force, and steady rotation can be maintained below 10 to the -th m/s-squared; however, the springs can protect the table from these accelerations if required.

Mobility Analyses of Standard- and High-Mobility Tactical Support Vehicles (HIMO Study)

DTIC Science & Technology

1976-02-01

l, APPENDIX G: PARTICIPANTS IN SCENARIO EXERCISES ... ....... Gl I ?S LIST OF TABLES Table Page I Summary of Vehicle Caracteristics and Some...15 1 :1010 2 :1111 Organid silts and clays ( plastic ) >7-30 0 11212 1 1 1313Peat (nou plastic ) _._>_3_0 0 .1414 Li Groups with Different Materiai in 0...diameter LL = Liquid limit PI - Plasticity index Drainage potential classified by occurrence of water table as follows: Class 0 Water table occurs at

Osmotic potential and projected drought tolerance of four phreatophytic shrub species in Owens Valley, California

USGS Publications Warehouse

Dileanis, Peter D.; Groeneveld, D.P.

1988-01-01

A large part of the water used by plant communities growing on the floor of Owens Valley, California, is derived from a shallow unconfined aquifer. Fluctuations in the water table caused by groundwater withdrawal may result in periods when this water supply is not accessible to plants. The capacity of the plants to adapt to these periods of water loss depend on the availability of water stored in the soil and on physiological characteristics related to the ability of the plants to resist dehydration and wilting. Osmotic adjustment occurred in four phreatophytic shrub species at sites near bishop, California, where the water table had been lowered by a system of pump-equipped wells installed in the vicinity of vegetation transects. The pressure-volume techniques was used to determine osmotic potential and cell-wall elasticity between March 1985 and September 1986 for Atriplex torreyi, Chrysothamnus nauseosus , Sarcobatus vermiculatus, and Artemisia tridentata. Although not usually classified as a phreatophyte, Artemisia tridentata, where it grows on the valley floor, is apparently dependent on the depth to the water table. During late summer, osmotic potentials were 0.37 to 0.41 megapascal lower in plants growing on the site where the water table had been lowered compared to an adjacent site where the water table remained at its natural levels. Measurements of soil matric potential at the two sites indicated that osmotic adjustment occurred in response to stress caused by lowering the water table. A theoretical lower limit of osmotic adjustment was determined by comparing initial cell osmotic potentials with initial xylem water potentials. These experimentally derived limits indicated that A. torreyi and S. vermiculatus may maintain leaf cell turgor at significantly lower cell water potentials (about -4.5 megapascals) than C. nauseosus or A. tridentata (about -2.5 megapascals) and allows them to function in dryer soil environments. (Author 's abstract)

Human Health Benchmarks for Pesticides

EPA Pesticide Factsheets

Advanced testing methods now allow pesticides to be detected in water at very low levels. These small amounts of pesticides detected in drinking water or source water for drinking water do not necessarily indicate a health risk. The EPA has developed human health benchmarks for 363 pesticides to enable our partners to better determine whether the detection of a pesticide in drinking water or source waters for drinking water may indicate a potential health risk and to help them prioritize monitoring efforts.The table below includes benchmarks for acute (one-day) and chronic (lifetime) exposures for the most sensitive populations from exposure to pesticides that may be found in surface or ground water sources of drinking water. The table also includes benchmarks for 40 pesticides in drinking water that have the potential for cancer risk. The HHBP table includes pesticide active ingredients for which Health Advisories or enforceable National Primary Drinking Water Regulations (e.g., maximum contaminant levels) have not been developed.

Saline-water intrusion related to well construction in Lee County, Florida

USGS Publications Warehouse

Boggess, Durward Hoye; Missimer, T.M.; O'Donnell, T. H.

1977-01-01

Ground water is the principle source of water supply in Lee County, Florida where an estimated 30,000 wells have been drilled since 1990. These wells ranges in depth from about 10 to 1,240 feet and tap the water table aquifer or one or more of the artesian water-bearing units or zones in the Tamiami Formation, the upper part of the Hawthorn Formation, the lower part of the Hawthorn Formation and the Tampa Limestone and the Suwannee Limestone. Before 1968, nearly all wells were constructed with galvanized or black iron pipe. Many of these wells are sources of saline-water intrusion into freshwater-bearing zones. The water-bearing zones in the lower part of the Hawthorn Formation, Tampa Limestone, and Suwannee Limestone are artesian-they have higher water levels and usually contain water with a higher concentration of dissolved solids than do the aquifers occurring at shallower depths. The water from these deeper aquifers generally range in dissolved solids concentration from about 1,500 to 2,400 mg/L, and in chloride from about 500 to 1,00 mg/L. A maximum chloride concentration of 15,200 mg/L has been determined. Few of the 3,00 wells estimated to have been drilled to these zones contain sufficient casing to prevent upward flow into overlaying water-bearing zones. Because of water-level differentials, upward movement and lateral intrusion of saline water occurs principally into the upper part of the Hawthorn Formation where the chloride concentrations in water unaffected by saline-water intrusion ranges from about 80 to 150 mg/L. Where intrusion from deep artesian zones has occurred, the chloride concentration in water from the upper part of the Hawthorn Formation ranges from about 300 to more than 2,100 mg/L Surface discharges of the saline water from wells tapping the lower part of the Hawthorn Formation and the Suwannee Limestone also had affected the water-table aquifer which normally contains water with 10 to 50 mg/L of chloride. In one area, the chloride concentration in water from the water table aquifer ranged from 200 to 590 mg/L as a result of intrusion. In areas adjacent to tidal-water bodies, the water table aquifer contains water that is very saline, Where the wells in such areas have been constructed with metal casings, the metal corrodes when exposed to the saline water, and many ultimately develop holes. This permits saline water to leak into the well where the water level in the well is lower than the water table. The intrusion of saline water from the water-table aquifer into the upper part of the Hawthorn Formation is a major problem in parts of Cape Coral. Withdrawal of water from the upper part of the Hawthorn Formation has caused water levels to decline below the lowest annual position of the water table, so that downward leakage is perennial. In some coastal areas, wells that tap the upper part of the Hawthorn Formation contain water whose chloride concentration is as much as 9,500 mg/L. Upward leakage of saline water from the deep artesian aquifers and downward leakage of saline water from the water-table aquifer can be prevented by proper well construction.

Evaporation from bare ground with different water-table depths based on an in-situ experiment in Ordos Plateau, China

NASA Astrophysics Data System (ADS)

Zhang, Zaiyong; Wang, Wenke; Wang, Zhoufeng; Chen, Li; Gong, Chengcheng

2018-03-01

The dynamic processes of ground evaporation are complex and are related to a multitude of factors such as meteorological influences, water-table depth, and materials in the unsaturated zone. To investigate ground evaporation from a homogeneous unsaturated zone, an in-situ experiment was conducted in Ordos Plateau of China. Two water-table depths were chosen to explore the water movement in the unsaturated zone and ground evaporation. Based on the experimental and calculated results, it was revealed that (1) bare ground evaporation is an atmospheric-limited stage for the case of water-table depth being close to the capillary height; (2) the bare ground evaporation is a water-storage-limited stage for the case of water-table depth being beyond the capillary height; (3) groundwater has little effect on ground-surface evaporation when the water depth is larger than the capillary height; and (4) ground evaporation is greater at nighttime than that during the daytime; and (5) a liquid-vapor interaction zone at nearly 20 cm depth is found, in which there exists a downward vapor flux on sunny days, leading to an increasing trend of soil moisture between 09:00 to 17:00; the maximum value is reached at midday. The results of this investigation are useful to further understand the dynamic processes of ground evaporation in arid areas.

Environmental and Physiographic Controls on Inter-Growing Season Variability of Carbon Dioxide and Water Vapour Fluxes in a Minerotrophic Fen

NASA Astrophysics Data System (ADS)

van der Kamp, G.; Sonnentag, O.; Chen, J. M.; Barr, A.; Hedstrom, N.; Granger, R.

2008-12-01

The interaction of fens with groundwater is spatially and temporally highly variable in response to meteorological conditions, resulting in frequent changes of groundwater fluxes in both vertical and lateral directions (flow reversals) across the mineral soil-peat boundary. However, despite the importance of the topographic and hydrogeological setting of fens, no study has been reported in the literature that explores a fen's atmospheric CO2 and energy flux densities under contrasting meteorological conditions in response to its physiographic setting. In our contribution we report four years of growing season eddy covariance and supporting measurements from the Canada Fluxnet-BERMS fen (formerly BOREAS southern peatland) in Saskatchewan, Canada. We first analyze hydrological data along two piezometer transects across the mineral soil-peat boundary with the objective of assessing changes in water table configuration and thus hydraulic gradients, indicating flow reversals, in response to dry and wet meteorological conditions. Next we quantify and compare growing season totals and diurnal and daily variations in evapotranspiration (ET) and net ecosystem exchange (NEE) and its component fluxes gross ecosystem productivity (GPP) and terrestrial ecosystem respiration (TER) to identify their controls with a major focus on water table depth. While ET growing season totals were similar (~ 310 mm) under dry and wet meteorological conditions, the CO2 sink- source strength of Sandhill fen varied substantially from carbon neutral (NEE = -2 [+-7] g C m-2 per growing season) under dry meteorological condition (2003) to a moderate CO2- sink with NEE ranging between 157 [+- 10] and 190 [+- 11] g C m-2 per growing season under wet meteorological conditions (2004, 2005, and 2006). Using a process-oriented ecosystem model, BEPS-TerrainLab, we investigate how different canopy components at Sandhill contribute to total ET and GPP, and thus water use efficiency, under dry and wet meteorological conditions.

The Effects of Urbanization on Atmospheric Nitrogen Deposition and Nitrate Removal Capacity of Urban Wetlands

NASA Astrophysics Data System (ADS)

Stander, E. K.; Ehrenfeld, J. G.

2006-12-01

Wetlands are increasingly being used as management tools to combat the widespread problem of excess nitrogen in surface waters of the United States. This is particularly true in urban or urbanizing watersheds. However, due to hypothesized higher rates of atmospheric nitrogen deposition and altered hydrology in the urban context, urban wetlands may actually be acting as sources of nitrate to receiving bodies of water. Fourteen palustrine, forested wetlands in northeastern New Jersey, the most urban part of the state, were sampled for hydrology and rates of nitrogen cycling processes. One autowell in each site recorded water table measurements four times daily. In situ rates of net nitrogen mineralization and nitrification were measured monthly during the same time period using the static core technique. Denitrification rates were measured monthly in laboratory incubations using the acetylene block technique. Additionally, in nine of the 14 sites, which represent a gradient of urban intensity from very urban to less urban, we measured inorganic nitrogen in throughfall and leachate on a weekly basis. Throughfall collectors and lysimeters to 50cm depth were installed in three locations in each of the nine sites. Throughfall and leachate samples were analyzed for 15N and 18O isotopes to distinguish between atmospheric versus nitrification sources of nitrate in soil leachate. Hydrographs demonstrated that many sites have water table depths below 30 cm (i.e., below the biologically active zone) for long periods of time. Many wetlands display uncharacteristically flashy hydrographs. Wetlands with dry or flashy hydrographs had higher rates of nitrification and lower rates of denitrification than wetlands with more normal hydrology. Rates of atmospheric N deposition were higher in wetlands located in municipalities with higher population densities. Population density, however, was not a good predictor of nitrification or denitrification rates. Results from the isotopic analysis are forthcoming.

Response of anaerobic carbon cycling to water table manipulation in an Alaskan rich fen

USGS Publications Warehouse

Kane, E.S.; Chivers, M.R.; Turetsky, M.R.; Treat, C.C.; Petersen, D.G.; Waldrop, M.; Harden, J.W.; McGuire, A.D.

2013-01-01

To test the effects of altered hydrology on organic soil decomposition, we investigated CO2 and CH4 production potential of rich-fen peat (mean surface pH = 6.3) collected from a field water table manipulation experiment including control, raised and lowered water table treatments. Mean anaerobic CO2 production potential at 10 cm depth (14.1 ± 0.9 μmol C g−1 d−1) was as high as aerobic CO2 production potential (10.6 ± 1.5 μmol C g−1 d−1), while CH4 production was low (mean of 7.8 ± 1.5 nmol C g−1 d−1). Denitrification enzyme activity indicated a very high denitrification potential (197 ± 23 μg N g−1 d−1), but net NO-3 reduction suggested this was a relatively minor pathway for anaerobic CO2 production. Abundances of denitrifier genes (nirK and nosZ) did not change across water table treatments. SO2-4 reduction also did not appear to be an important pathway for anaerobic CO2 production. The net accumulation of acetate and formate as decomposition end products in the raised water table treatment suggested that fermentation was a significant pathway for carbon mineralization, even in the presence of NO-3. Dissolved organic carbon (DOC) concentrations were the strongest predictors of potential anaerobic and aerobic CO2 production. Across all water table treatments, the CO2:CH4 ratio increased with initial DOC leachate concentrations. While the field water table treatment did not have a significant effect on mean CO2 or CH4 production potential, the CO2:CH4 ratio was highest in shallow peat incubations from the drained treatment. These data suggest that with continued drying or with a more variable water table, anaerobic CO2 production may be favored over CH4 production in this rich fen. Future research examining the potential for dissolved organic substances to facilitate anaerobic respiration, or alternative redox processes that limit the effectiveness of organic acids as substrates in anaerobic metabolism, would help explain additional uncertainty concerning carbon mineralization in this system.

Effects of shallow water table, salinity and frequency of irrigation water on the date palm water use

NASA Astrophysics Data System (ADS)

Askri, Brahim; Ahmed, Abdelkader T.; Abichou, Tarek; Bouhlila, Rachida

2014-05-01

In southern Tunisia oases, waterlogging, salinity, and water shortage represent serious threats to the sustainability of irrigated agriculture. Understanding the interaction between these problems and their effects on root water uptake is fundamental for suggesting possible options of improving land and water productivity. In this study, HYDRUS-1D model was used in a plot of farmland located in the Fatnassa oasis to investigate the effects of waterlogging, salinity, and water shortage on the date palm water use. The model was calibrated and validated using experimental data of sap flow density of a date palm, soil hydraulic properties, water table depth, and amount of irrigation water. The comparison between predicted and observed data for date palm transpiration rates was acceptable indicating that the model could well estimate water consumption of this tree crop. Scenario simulations were performed with different water table depths, and salinities and frequencies of irrigation water. The results show that the impacts of water table depth and irrigation frequency vary according to the season. In summer, high irrigation frequency and shallow groundwater are needed to maintain high water content and low salinity of the root-zone and therefore to increase the date palm transpiration rates. However, these factors have no significant effect in winter. The results also reveal that irrigation water salinity has no significant effect under shallow saline groundwater.

Long-term Effects of Hydrologic Manipulations on Pore Water Dissolved Organic Carbon in an Alaskan Rich Fen

NASA Astrophysics Data System (ADS)

Rupp, D.; Kane, E. S.; Keller, J.; Turetsky, M. R.; Meingast, K. M.

2016-12-01

Boreal peatlands are experiencing rapid changes due to temperature and precipitation regime shifts in northern latitudes. In areas near Fairbanks, Alaska, thawing permafrost due to climatic changes alters peatland hydrology and thus the biogeochemical cycles within. Pore water chemistry reflects the biological and chemical processes occurring in boreal wetlands. The characterization of dissolved organic carbon (DOC) within pore water offers clues into the nature of microbially-driven biogeochemical shifts due to changing hydrology. There is mounting evidence that organic substances play an important role in oxidation-reduction (redox) reactivity of peat at northern latitudes, which is closely linked to carbon cycling. However, the redox dynamics of DOC are complex and have not been examined in depth in boreal peatlands. Here, we examine changes in organic substances and their influences on redox activity at the Alaska Peatland Experiment (APEX) site near Fairbanks, Alaska, where water table manipulation treatments have been in place since 2005 (control, raised water table, and lowered water table). With time, the altered hydrology has led to a shift in the plant community to favor sedge species in the raised water table treatment and more shrubs and non-aerenchymous plants in the lowered water table treatment. The litter from different plant functional types alters the character of the dissolved organic carbon, with more recalcitrant material containing lignin in the lowered water table plot due to the greater abundance of shrubs. A greater fraction of labile DOC in the raised treatment plot likely results from more easily decomposed sedge litter, root exudates at depth, and more frequently waterlogged conditions, which are antagonistic to aerobic microbial decomposition. We hypothesize that a greater fraction of phenolic carbon compounds supports higher redox activity. However, we note that not all "phenolic" compounds, as assayed by spectrophotometry, have the same redox activity. We report these results in the context of previous observations of higher methane fluxes from the raised water table plot. Taken together, these findings provide the mechanistic details needed to understand residual error in modeling efforts of anaerobic carbon evasion (methane and carbon dioxide) in boreal wetlands.

Water-table contours and depth to water in the southeastern part of the Sweetwater River basin, central Wyoming, 1982

USGS Publications Warehouse

Borchert, William B.

1987-01-01

This map describes the southeastern part of the Sweetwater River basin; the major aquifer consists of the upper part of the White River formations, all of Tertiary age, and to a small extent, the alluvium of the Quaternary age along the Sweetwater River. The saturated thickness of the aquifer in most of the area, but not including the alluvium ranges from 500 to 3000 ft. The maximum saturated thickness of the alluvium penetrated by test holes was 63 ft. The water-table contours and depths to water are based primarily on groundwater-level measurements made during 1982 in 104 wells, most of which are located south of the Sweetwater River. Land-surface altitudes of springs and water-surface altitudes along the Sweetwater River and perennial reaches of creeks flowing northward from the Green and Ferris Mountains also were used as control for mapping the water table. The perennial reaches shown on the map are assumed hydraulically connected with the water table. They were identified from streamflow gain-and-loss measurements made during April and May 1982. (Author 's abstract)

R-Area Reactor 1993 annual groundwater monitoring report

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

Not Available

1994-09-01

Groundwater was sampled and analyzed during 1993 from wells monitoring the following locations in R Area: Well cluster P20 east of R Area (one well each in the water table and the McBean formation), the R-Area Acid/Caustic Basin (the four water-table wells of the RAC series), the R-Area Ash Basin/Coal Pile (one well of the RCP series in the Congaree formation and one in the water table), the R-Area Disassembly Basin (the three water-table wells of the RDB series), the R-Area Burning/Rubble Pits (the four water-table wells of the RRP series), and the R-Area Seepage Basins (numerous water-table wells inmore » the RSA, RSB, RSC, RSD, RSE, and RSF series). Lead was the only constituent detected above its 50{mu}g/L standard in any but the seepage basin wells; it exceeded that level in one B well and in 23 of the seepage basin wells. Cadmium exceeded its drinking water standard (DWS) in 30 of the seepage basin wells, as did mercury in 10. Nitrate-nitrite was above DWS once each in two seepage basin wells. Tritium was above DWS in six seepage basin wells, as was gross alpha activity in 22. Nonvolatile beta exceeded its screening standard in 29 wells. Extensive radionuclide analyses were requested during 1993 for the RCP series and most of the seepage basin wells. Strontium-90 in eight wells was the only specific radionuclide other than tritium detected above DWS; it appeared about one-half of the nonvolatile beta activity in those wells.« less

3. DETAIL OF STONEWORK ON ARCH, WATER TABLE AND DENTILS ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

3. DETAIL OF STONEWORK ON ARCH, WATER TABLE AND DENTILS ON EAST ELEVATION LOOKING NORTHWEST. - Original Airport Entrance Overpass, Spanning original Airport Entrance Road at National Airport, Arlington, Arlington County, VA

Wetland tree transpiration modified by river-floodplain connectivity

USGS Publications Warehouse

Allen, Scott T.; Krauss, Ken W.; Cochran, J. Wesley; King, Sammy L.; Keim, Richard F.

2016-01-01

Hydrologic connectivity provisions water and nutrient subsidies to floodplain wetlands and may be particularly important in floodplains with seasonal water deficits through its effects on soil moisture. In this study, we measured sapflow in 26 trees of two dominant floodplain forest species (Celtis laevigata and Quercus lyrata) at two hydrologically distinct sites in the lower White River floodplain in Arkansas, USA. Our objective was to investigate how connectivity-driven water table variations affected water use, an indicator of tree function. Meteorological variables (photosynthetically active radiation and vapor pressure deficit) were the dominant controls over water use at both sites; however, water table variations explained some site differences. At the wetter site, highest sapflow rates were during a late-season overbank flooding event, and no flood stress was apparent. At the drier site, sapflow decreased as the water table receded. The late-season flood pulse that resulted in flooding at the wetter site did not affect the water table at the drier site; accordingly, higher water use was not observed at the drier site. The species generally associated with wetter conditions (Q. lyrata) was more positively responsive to the flood pulse. Flood water subsidy lengthened the effective growing season, demonstrating ecological implications of hydrologic connectivity for alleviating water deficits that otherwise reduce function in this humid floodplain wetland.

HCMM energy budget data as a model input for assessing regions of high potential ground-water pollution

NASA Technical Reports Server (NTRS)

Moore, D. G. (Principal Investigator); Heilman, J.; Tunheim, J.

1978-01-01

The author has identified the following significant results. Analysis of soil temperature and water table data indicated that shallow aquifers appear to produce a heat sink effect when the depth to water table is approximately four meters or less.

Delineation and Characterization of Furnace Brook Watershed in Marshfield, Massachusetts: A Study of Effects upon Conjunctive Water Use within a Watershed

NASA Astrophysics Data System (ADS)

Croll, E. D.; Enright, R.

2012-12-01

An understanding of conjunctive use between surface and ground water is essential to resource management both for sustained public use and watershed conservation practices. The Furnace Brook watershed in Marshfield, Massachusetts supplies a coastal community of 25,132 residents with nearly 50% of the town water supply. As with many other coastal communities, development pressure has increased creating a growing demand for freshwater extraction. It has been observed, however, that portions of the stream and Furnace Pond disappear entirely. This has created a conflict between protection of the designated wetland areas and meeting public pressure for water resources, even within what is traditionally viewed as a humid region. Questions have arisen as to whether the town water extraction is influencing this losing behavior by excessively lowering water-table elevations and potentially endangering the health of the stream. This study set out to initially characterize these behaviors and identify possible influences of anthropogenic and natural sources acting upon the watershed including stream flow obstructions, water extraction, and geologic conditions. The initial characterization was conducted utilizing simple, low-cost and minimally intrusive methods as outlined by Lee and Cherry (1978), Rosenberry and LaBaugh (2008) and others during a six week period. Five monitoring stations were established along a 3.0 mile reach of the basin consisting of mini-piezometers, seepage meters, survey elevation base-lines, and utilizing a Marsh-McBirney flow velocity meter. At each station stream discharge, seepage flux rates and hydraulic gradients were determined to develop trends of stream behavior. This methodology had the benefit of demonstrating the efficacy of an intrinsically low-expense, minimally intrusive initial approach to characterizing interactions between surface and ground water resources. The data was correlated with town pumping information, previous geologic surveys and meteorological data. Early data analysis indicated that the stream behaved in an anomalous manner decreasing in discharge with downstream flow despite normal precipitation inputs. The behavior within this particular watershed appeared to be influenced by four primary factors resulting in the stream "running dry" during the June-August period. These factors included: (1) A losing gradient induced by well pumping (2) Obstructions to stream flow reduced contribution from upper reaches to lower reaches (3) A highly anisotropic layer of lower conductivity material regulated infiltration rates and (4) Evapotranspiration effects are such that during this period the basin is in a deficit situation even without additional losses. Additionally, relationships between well pumping and decreasing discharge, seepage flux loss rates and hydraulic gradients have demonstrated that even within humid region watersheds it cannot be assumed aquifer recharge is sufficient to avoid conflict between surface water protection and ground water utilization. Timing of precipitation events combined with geological governance of aquifer recharge play critical roles in managing the conjunctive use of water resources and cannot be assumed to have a negligible effect, even within relatively humid regions.

Use of Ground Penetrating Radar to Study Gradient Media

NASA Astrophysics Data System (ADS)

Titov, A.

2016-12-01

Nowadays Ground Penetrating Radar (GPR) is often used to solve different problems of applied geophysics including the hydrological ones. This work was motivated by detection of weak reflections in the body of water observed during the surveys on the freshwater lakes using GPR. The same reflections were first analyzed by John Bradford in 2007. These reflections can arise from the thermal gradient layer or thermocline due to different dielectric permittivity of cold and warm water. We employed physical and mathematical modeling to identify the properties of such thermoclines. We have constructed a special GPR stand to study the gradient media in our laboratory. The stand consists of a water-filled plastic tank and plastic tubes, which gather the cold water under the warm water. Our stand allows for changing parameters of the gradient layer, such as limits of dielectric permittivity and the thickness of the gradient layer. GPR antenna was placed slightly under the water surface to remove the parasitic reflections. To visualize the thermal distribution, an infrared camera and thermal sensors were used. Analysis of the GPR traces after physical modeling, performed in the MATLAB environment, allows us to locate the weak reflection from the gradient layer. We observed that (i) the change of the gradient boundary values alters the amplitude of the signal, (ii) the arrival time of the impulse reflected from the gradient layer corresponds to the arrival time of the impulse reflected from the top boundary of this layer, and (iii) the shape of the signal reflected from the gradient layer coincides with the shape of the signal reflected from the non-gradient boundary between two bodies. The quantitative properties of thermocline can be determined using amplitude analysis of GPR signals. Finally, the developed methods were successfully applied to real field data.

Temporal and spatial variabilities in the surface moisture content of a fine-grained beach

NASA Astrophysics Data System (ADS)

Namikas, S. L.; Edwards, B. L.; Bitton, M. C. A.; Booth, J. L.; Zhu, Y.

2010-01-01

This study examined spatial and temporal variations in the surface moisture content of a fine-grained beach at Padre Island, Texas, USA. Surface moisture measurements were collected on a 27 × 24 m grid that extended from the dune toe to the upper foreshore. The grid was surveyed at 2 to 4 h intervals for two tidal cycles, generating 17 maps of the spatial distribution of surface moisture. Simultaneous measurements of air temperature and humidity, wind speed and direction, tidal elevation, and water table elevation were used to interpret observed changes in surface moisture. It was found that the spatial distribution of surface moisture was broadly characterized by a cross-shore gradient of high to low content moving landward from the swash zone. The distribution of surface moisture was conceptualized in terms of three zones: saturated (> 25%), intermediate or transitional (5-25%), and dry (< 5%). The position of the saturated zone corresponded to the uppermost swash zone and therefore shifted in accordance with tidal elevation. Moisture contents in the intermediate and dry zones were primarily related to variation in water table depth (which was in turn controlled by tidal elevation) and to a lesser extent by evaporation. Signals associated with atmospheric processes such as evaporation were muted by the minimal degree of variation in atmospheric parameters experienced during most of the study period, but were apparent for the last few hours. The observed spatial and temporal variations in moisture content correspond reasonably well with observations of key controlling processes, but more work is needed to fully characterize this process suite.

Predcition of Long term Water table Trends in Response to Groundwater Irrigation and Climate Change in an Indian Context

NASA Astrophysics Data System (ADS)

Thekkemeppilly Sivakumar, I.; Steenhuis, T. S.; Walter, M. F.; Ghosh, S.; Salvi, K. A.

2015-12-01

Intensified groundwater irrigation is a major factor that contributes to water table decline. This phenomenon has been documented in many parts of the world. This study investigates trends in water table in response to agriculture intensification to meet increasing food demand, water management practices and climate change. A shallow-aquifer model based on the extended Thornthwaite-Mather procedure is used to predict groundwater levels in response to precipitation, evapotranspiration, and groundwater pumping for irrigation. Krishna district in the state of Andhra Pradesh in southern India which has a sub-humid, monsoon climate and Calicut district of Kerala state with a wet tropical monsoon climate have been chosen as sites for this study. The effect of increasing food demand by a growing population is investigated by increasing the number of crops per year from one to three. We consider three climate scenarios and two water management practices in this study. The three climate scenarios are the ones those envisaged by the Intergovernmental Panel for Climate Change (IPCC). The two water management practices considered are the traditional flooded agriculture and the system of rice intensification method which does not use total flooding. The results show that single crop agriculture in Krishna district is sustainable for all climate scenarios and water management practices with a maximum depth to water table around 6 - 7 m at the end of dry season and the water table recovers to the surface most of the time. Increasing crop production with two or three crops per year with groundwater irrigation is unsustainable with the water table levels dropping potentially to 200 - 1000 m at the end of 21st century. We found that climate change and better irrigation water management practices affected ground water levels only minimally compared to the growing more than one crop per year. Our study leads to the conclusion that ground water irrigated rice can only be sustainable when crop evaporation is less then precipitation and in order to meet increasing food demands the rice yield per unit water should be improved.

Water flux through a semi-deciduous forest grove of the Orinoco savannas.

PubMed

San José, José J; Montes, Ruben A; Florentino, Adriana

1995-02-01

Water relations were analysed in a semi-deciduous forest grove occurring in the oxisols of the Orinoco savannas. This grove has a shallow unconsolidated ironstone cuirass, which is overlaid by a sandy loam layer (0.0-0.5 m) that contains more than 90% of the grove forest root phytomass. Evapotranspiration and through drainage were calculated by using data from the soil profile as related to physical characteristics of the site root zone, hydraulic conductivity, volumetric water content and potential hydraulic gradient. Mean annual evapotranspiration was 783 mm year -1 and annual through drainage below the root zone was 14% (162 mm year -1 ) of the gross rainfall. This drainage recharged the 42% of the annual saturation deficit of the water table. Similar mean annual evapotranspiration (770 mm year -1 ) was also calculated by using the water balance components. The mean daily coupling omega factor (Ω) between the grove canopy and the surrounding atmosphere indicated that a high degree of coupling (Ω=0.14±0.16) occurs in the grove and evapotranspiration was mainly controlled by surface conductance. As the dry season proceeded, the soil saturation deficit (δθ) increased rapidly resulting in a threshold surface conductance (0.030-0.005 m s -1 ) for δθ ranging from 0.05 to 0.10. Hypotheses to explain the omnipresence of perennial species in the wide range of physical conditions in neotropical savannas are discussed.

Structure of peat soils and implications for biogeochemical processes and hydrological flow

NASA Astrophysics Data System (ADS)

Rezanezhad, F.; McCarter, C. P. R.; Gharedaghloo, B.; Kleimeier, C.; Milojevic, T.; Liu, H.; Weber, T. K. D.; Price, J. S.; Quinton, W. L.; Lenartz, B.; Van Cappellen, P.

2017-12-01

Permafrost peatlands contain globally important amounts of soil organic carbon and play major roles in global water, nutrient and biogeochemical cycles. The structure of peatland soils (i.e., peat) are highly complex with unique physical and hydraulic properties; where significant, and only partially reversible, shrinkage occurs during dewatering (including water table fluctuations), compression and/or decomposition. These distinct physical and hydraulic properties controls water flow, which in turn affect reactive and non-reactive solute transport (such as, sorption or degradation) and biogeochemical functions. Additionally, peat further attenuates solute migration through molecular diffusion into the inactive pores of Sphagnum dominated peat. These slow, diffusion-limited solute exchanges between the pore regions may give rise to pore-scale chemical gradients and heterogeneous distributions of microbial habitats and activity in peat soils. Permafrost peat plateaus have the same essential subsurface characteristics as other widely organic soil-covered peatlands, where the hydraulic conductivity is related to the degree of decomposition and soil compression. Increasing levels of decomposition correspond with a reduction of effective pore diameter and consequently restrict water and solute flow (by several orders of magnitude in hydraulic conductivity between the ground surface and a depth of 50 cm). In this presentation, we present the current knowledge of key physical and hydraulic properties related to the structure of globally available peat soils and discuss their implications for water storage, flow and the migration of solutes.

Estimation of water table based on geomorphologic and geologic conditions using public database of geotechnical information over Japan

NASA Astrophysics Data System (ADS)

Koshigai, Masaru; Marui, Atsunao

Water table provides important information for the evaluation of groundwater resource. Recently, the estimation of water table in wide area is required for effective evaluation of groundwater resources. However, evaluation process is met with difficulties due to technical and economic constraints. Regression analysis for the prediction of groundwater levels based on geomorphologic and geologic conditions is considered as a reliable tool for the estimation of water table of wide area. Data of groundwater levels were extracted from the public database of geotechnical information. It was observed that changes in groundwater level depend on climate conditions. It was also observed and confirmed that there exist variations of groundwater levels according to geomorphologic and geologic conditions. The objective variable of the regression analysis was groundwater level. And the explanatory variables were elevation and the dummy variable consisting of group number. The constructed regression formula was significant according to the determination coefficients and analysis of the variance. Therefore, combining the regression formula and mesh map, the statistical method to estimate the water table based on geomorphologic and geologic condition for the whole country could be established.

Modeling the effects of hydrology on gross primary productivity and net ecosystem productivity at Mer Bleue bog

NASA Astrophysics Data System (ADS)

Dimitrov, Dimitre D.; Grant, Robert F.; Lafleur, Peter M.; Humphreys, Elyn R.

2011-12-01

The ecosys model was applied to investigate the effects of water table and subsurface hydrology changes on carbon dioxide exchange at the ombrotrophic Mer Bleue peatland, Ontario, Canada. It was hypothesized that (1) water table drawdown would not affect vascular canopy water potential, hence vascular productivity, because roots would penetrate deeper to compensate for near-surface dryness, (2) moss canopy water potential and productivity would be severely reduced because rhizoids occupy the uppermost peat that is subject to desiccation with water table decline, and (3) given that in a previous study of Mer Bleue, ecosystem respiration showed little sensitivity to water table drawdown, gross primary productivity would mainly determine the net ecosystem productivity through these vegetation-subsurface hydrology linkages. Model output was compared with literature reports and hourly eddy-covariance measurements during 2000-2004. Our findings suggest that late-summer water table drawdown in 2001 had only a minor impact on vascular canopy water potential but greatly impacted hummock moss water potential, where midday values declined to -250 MPa on average in the model. As a result, simulated moss productivity was reduced by half, which largely explained a reduction of 2-3 μmol CO2 m-2 s-1 in midday simulated and measurement-derived gross primary productivity and an equivalent reduction in simulated and measured net ecosystem productivity. The water content of the near-surface peat (top 5-10 cm) was found to be the most important driver of interannual variability of annual net ecosystem productivity through its effects on hummock moss productivity and on ecosystem respiration.

Implications of sea level rise scenarios on land use /land cover classes of the coastal zones of Cochin, India.

PubMed

Mani Murali, R; Dinesh Kumar, P K

2015-01-15

Physical responses of the coastal zones in the vicinity of Cochin, India due to sea level rise are investigated based on analysis of inundation scenarios. Quantification of potential habitat loss was made by merging the Land use/Land cover (LU/LC) prepared from the satellite imagery with the digital elevation model. Scenarios were generated for two different rates of sea level rise and responses of changes occurred were made to ascertain the vulnerability and loss in extent. LU/LC classes overlaid on 1 m and 2 m elevation showed that it was mostly covered by vegetation areas followed by water and urban zones. For the sea level rise scenarios of 1 m and 2 m, the total inundation zones were estimated to be 169.11 km(2) and 598.83 km(2) respectively using Geographic Information System (GIS). The losses of urban areas were estimated at 43 km(2) and 187 km(2) for the 1 m and 2 m sea level rise respectively which is alarming information for the most densely populated state of India. Quantitative comparison of other LU/LC classes showed significant changes under each of the inundation scenarios. The results obtained conclusively point that sea level rise scenarios will bring profound effects on the land use and land cover classes as well as on coastal landforms in the study region. Coastal inundation would leave ocean front and inland properties vulnerable. Increase in these water levels would alter the coastal drainage gradients. Reduction in these gradients would increase flooding attributable to rainstorms which could promote salt water intrusion into coastal aquifers and force water tables to rise. Changes in the coastal landforms associated with inundation generate concern in the background that the coastal region may continue to remain vulnerable in the coming decades due to population growth and development pressures. Copyright © 2014 Elsevier Ltd. All rights reserved.

Changes in Pore Water Quality After Peatland Restoration: Assessment of a Large-Scale, Replicated Before-After-Control-Impact Study in Finland

NASA Astrophysics Data System (ADS)

Menberu, Meseret Walle; Marttila, Hannu; Tahvanainen, Teemu; Kotiaho, Janne S.; Hokkanen, Reijo; Kløve, Bjørn; Ronkanen, Anna-Kaisa

2017-10-01

Drainage is known to affect peatland natural hydrology and water quality, but peatland restoration is considered to ameliorate peatland degradation. Using a replicated BACIPS (Before-After-Control-Impact Paired Series) design, we investigated 24 peatlands, all drained for forestry and subsequently restored, and 19 pristine control boreal peatlands with high temporal and spatial resolution data on hydroclimate and pore water quality. In drained conditions, total nitrogen (Ntot), total phosphorus (Ptot), and dissolved organic carbon (DOC) in pore water were several-fold higher than observed at pristine control sites, highlighting the impacts of long-term drainage on pore water quality. In general, pore water DOC and Ntot decreased after restoration measures but still remained significantly higher than at pristine control sites, indicating long time lags in restoration effects. Different peatland classes and trophic levels (vegetation gradient) responded differently to restoration, primarily due to altered hydrology and varying acidity levels. Sites that were hydrologically overrestored (inundated) showed higher Ptot, Ntot, and DOC than well-restored or insufficiently restored sites, indicating the need to optimize natural-like hydrological regimes when restoring peatlands drained for forestry. Rich fens (median pH 6.2-6.6) showed lower pore water Ptot, Ntot, and DOC than intermediate and poor peats (pH 4.0-4.6) both before and after restoration. Nutrients and DOC in pore water increased in the first year postrestoration but decreased thereafter. The most important variables related to pore water quality were trophic level, peatland class, water table level, and soil and air temperature.

Effect of sequential release of NAPLs on NAPL migration in porous media

NASA Astrophysics Data System (ADS)

Bang, Woohui; Yeo, In Wook

2016-04-01

NAPLs (Non-aqueous phase liquids) are common groundwater contaminants and are classified as LNAPLs (Light non-aqueous phase liquids) and DNAPLs (Dense non-aqueous phase liquids) according to relative density for water. Due to their low solubility in water, NAPLs remain for a long time in groundwater, and they pose a serious environmental problem. Therefore, understanding NAPLs migration in porous media is essential for effective NAPLs remediation. DNAPLs tend to move downward through the water table by gravity force because its density is higher than water. However, if DNAPLs do not have sufficient energy which breaks capillary force of porous media, they will just accumulate above capillary zone or water table. Mobile phase of LNAPLs rises and falls depending on fluctuation of water table, and it could change the wettability of porous media from hydrophilic to hydrophobic. This could impacts on the migration characteristics of subsequently-released DNAPLs. LNAPLs and DNAPLs are sometime disposed at the same place (for example, the Hill air force base, USA). Therefore, this study focuses on the effect of sequential release of NAPLs on NAPLs (in particular, DNAPL) migration in porous media. We have conducted laboratory experiments. Gasoline, which is known to change wettability of porous media from hydrophilic to intermediate, and TCE (Trichloroethylene) were used as LNAPL and DNAPL, respectively. Glass beads with the grain size of 1 mm and 2 mm were prepared for two sets of porous media. Gasoline and TCE was dyed for visualization. First, respective LNAPL and DNAPL of 10 ml were separately released into prepared porous media. For the grain size of 2 mm glass beads, LNAPL became buoyant above the water table, and DNAPL just moved downward through porous media. However, for the experiment with the grain size of 1 mm glass beads, NAPLs behaved very differently. DNAPL did not migrate downward below and just remained above the water table due to capillary pressure of porous media. To study the effect of subsequent release of NAPLs, as soon as LNAPL was released to porous medium with 1 mm of glass beads, being buoyant above water table, water table was lowered, which left residuals along the path of LNAPL. DNAPL was subsequently released. DNAPL was breaking through the water table now, which was opposed to only DNAPL release case. This study indicates that sequential release of NAPLs can leads to different migration characteristics of NAPLs, compared with the release of single phase NAPL into porous media.

Ground Water in the Southern Lihue Basin, Kauai, Hawaii

USGS Publications Warehouse

Izuka, Scot K.; Gingerich, Stephen B.

1998-01-01

A multi-phased study of ground-water resources, including well drilling, aquifer tests, analysis of ground-water discharge, and numerical ground-water modeling, indicates that the rocks of the southern Lihue Basin, Kauai, have permeabilities that are much lower than in most other areas of ground-water development in the Hawaiian islands. The regional hydraulic conductivity of the Koloa Volcanics, which dominates fresh ground-water flow in the basin, is about 0.275 foot per day. The Waimea Canyon Basalt which surrounds the basin and underlies the Koloa Volcanics within the basin is intruded by dikes that reduce the bulk hydraulic conductivity of the rocks to about 1.11 feet per day. The low permeabilities result in steeper head gradients compared with other areas in the Hawaiian islands, and a higher proportion of ground-water discharging to streams than to the ocean. Water levels rise from near sea level at the coast to several hundreds of feet above sea level at the center of the basin a few miles inland. The high inland water levels are part of a completely saturated ground-water system. Because of the low regional hydraulic conductivity and high influx of water from recharge in the southern Lihue Basin, the rocks become saturated nearly to the surface and a variably saturated/unsaturated (perched) condition is not likely to exist. Streams incising the upper part of the aquifer drain ground water and keep the water levels just below the surface in most places. Streams thus play an important role in shaping the water table in the southern Lihue Basin. At least 62 percent of the ground water discharging from the aquifer in the southern Lihue Basin seeps to streams; the remainder seeps directly to the ocean or is withdrawn by wells.

Holes in the Bathtub: Water Table Dependent Services and Threshold Behavior in an Economic Model of Groundwater Extraction

NASA Astrophysics Data System (ADS)

Kirk-lawlor, N. E.; Edwards, E. C.

2012-12-01

In many groundwater systems, the height of the water table must be above certain thresholds for some types of surface flow to exist. Examples of flows that depend on water table elevation include groundwater baseflow to river systems, groundwater flow to wetland systems, and flow to springs. Meeting many of the goals of sustainable water resource management requires maintaining these flows at certain rates. Water resource management decisions invariably involve weighing tradeoffs between different possible usage regimes and the economic consequences of potential management choices are an important factor in these tradeoffs. Policies based on sustainability may have a social cost from forgoing present income. This loss of income may be worth bearing, but should be well understood and carefully considered. Traditionally, the economic theory of groundwater exploitation has relied on the assumption of a single-cell or "bathtub" aquifer model, which offers a simple means to examine complex interactions between water user and hydrologic system behavior. However, such a model assumes a closed system and does not allow for the simulation of groundwater outflows that depend on water table elevation (e.g. baseflow, springs, wetlands), even though those outflows have value. We modify the traditional single-cell aquifer model by allowing for outflows when the water table is above certain threshold elevations. These thresholds behave similarly to holes in a bathtub, where the outflow is a positive function of the height of the water table above the threshold and the outflow is lost when the water table drops below the threshold. We find important economic consequences to this representation of the groundwater system. The economic value of services provided by threshold-dependent outflows (including non-market value), such as ecosystem services, can be incorporated. The value of services provided by these flows may warrant maintaining the water table at higher levels than would be the case if only the benefits and costs of groundwater extraction were considered. This hole-in-the-bathtub model can motivate managers to consider the costs of the loss of such flows, which may be very costly (in terms of loss of environmental services, loss of access to surface water, etc.). Alternatively, the decision to maintain the water table at an elevation that sustains a threshold-dependent outflow may cause income loss from the imposition of lower groundwater extraction rates. Weighing the benefits of maintaining threshold-dependent flows (including non-market benefits) with the net benefits of increased extraction is an important step in a prudent water management framework. To illustrate the usefulness of the modified model in a joint economic-hydrologic context, we provide a short case study of the Ojos de San Pedro area of the Rio Loa Basin in northern Chile. Evidence indicates that a wetland and lacustrine environment and a village dependent on that environment disappeared due to water extraction for industrial use. We demonstrate how the key features of the model provide important insight in understanding the tradeoffs that were made in this case.

A 5 Year Study of Carbon Fluxes from a Restored English Blanket Bog

NASA Astrophysics Data System (ADS)

Worrall, F.; Dixon, S.; Evans, M.

2014-12-01

This study aimed to measure the effects of ecological restoration on blanket peat water table depths, DOC concentrations and CO2 fluxes. In April 2003 the Bleaklow Plateau, an extensive area of deep blanket peat in the Peak District National Park, northern England, was devegetated by a wildfire. As a result the area was selected for large scale restoration. In this study we considered a 5-year study of four restored sites in comparison to both an unrestored, bare peat control and to vegetated control that did not require restoration. Results suggested that sites with revegetation alongside slope stabilisation had the highest rates of photosynthesis and were the largest net (daylight hours) sinks of CO2. Bare sites were the largest net sources of CO2 and had the deepest water table depths. Sites with gully wall stabilisation were between 5-8 times more likely to be net CO2 sinks than the bare sites. Revegetation without gully flow blocking using plastic dams did not have a large effect on water table depths in and around the gullies investigated whereas a blocked gully had water table depths comparable to a naturally revegetating gully. A ten centimetre lowering in water table depth decreased the probability of observing a net CO2 sink, on a given site, by up to 30%. With respect to DOC the study showed that the average soil porewater DOC concentration on the restored sites rose significantly over the 5 year study representing a 34% increase relative to the vegetated control and an 11% increase relative to the unrestored, bare control. Soil pore water concentrations were not significantly different from surface runoff DOC concentrations and therefore restoration as conducted by this study would have contributed to water quality deterioration in the catchment. The most important conclusion of this research was that restoration interventions were apparently effective at increasing the likelihood of net CO2 sink behaviour and raising water tables on degraded, climatically marginal blanket bog. However, had water table restoration been conducted alongside revegetation then a significant decline in DOC concentrations could have also been realised.

Geoarchaeological and paleohydrological evidence for a clovis-age drought in North America and its bearing on extinction

NASA Astrophysics Data System (ADS)

Haynes, C. Vance

1991-05-01

At the Murray Springs Clovis site in southeastern Arizona, stratigraphic and geomorphic evidence indicates that an abnormally low water table 10,900 yr B.P. was followed soon thereafter by a water-table rise accompanied by the deposition of an algal mat (the black mat) that buried mammoth tracks, Clovis artifacts, and a well. This water-table fluctuation correlates with pluvial lake fluctuations in the Great Basin during and immediately following Clovis occupation of that region. Many elements of Pleistocene megafauna in North America became extinct during the dry period. Oxygen isotope records show a marked decrease in δ18O correlated with the Younger Dryas cold-dry event of northern Europe which ended 10,750 yr B.P., essentially the same time as the water table began to rise in southeastern Arizona. Clovis hunters may have found large game animals easier prey when concentrated at water holes and under stress. If so, both climate and human predation contributed to Pleistocene extinction in America.

Groundwater flow, heat transport, and water table position within volcanic edifices: Implications for volcanic processes in the Cascade Range

USGS Publications Warehouse

Hurwitz, S.; Kipp, K.L.; Ingebritsen, S.E.; Reid, M.E.

2003-01-01

The position of the water table within a volcanic edifice has significant implications for volcano hazards, geothermal energy, and epithermal mineralization. We have modified the HYDROTHERM numerical simulator to allow for a free-surface (water table) upper boundary condition and a wide range of recharge rates, heat input rates, and thermodynamic conditions representative of continental volcano-hydrothermal systems. An extensive set of simulations was performed on a hypothetical stratovolcano system with unconfined groundwater flow. Simulation results suggest that the permeability structure of the volcanic edifice and underlying material is the dominant control on water table elevation and the distribution of pressures, temperatures, and fluid phases at depth. When permeabilities are isotropic, water table elevation decreases with increasing heat flux and increases with increasing recharge, but when permeabilities are anisotropic, these effects can be much less pronounced. Several conditions facilitate the ascent of a hydrothermal plume into a volcanic edifice: a sufficient source of heat and magmatic volatiles at depth, strong buoyancy forces, and a relatively weak topography-driven flow system. Further, the plume must be connected to a deep heat source through a pathway with a time-averaged effective permeability ???1 ?? 10-16 m2, which may be maintained by frequent seismicity. Topography-driven flow may be retarded by low permeability in the edifice and/or the lack of precipitation recharge; in the latter case, the water table may be relatively deep. Simulation results were compared with observations from the Quaternary stratovolcanoes along the Cascade Range of the western United States to infer hydrothermal processes within the edifices. Extensive ice caps on many Cascade Range stratovolcanoes may restrict recharge on the summits and uppermost flanks. Both the simulation results and limited observational data allow for the possibility that the water table beneath the stratovolcanoes is relatively deep.

Water Table and Soil Gas Emission Responses to Disturbance in Northern Forested Wetlands

NASA Astrophysics Data System (ADS)

Pypker, T. G.; Van Grinsven, M. J.; Bolton, N. W.; Shannon, J.; Davis, J.; Wagenbrenner, J. W.; Sebestyen, S. D.; Kolka, R. K.

2014-12-01

Exotic pest infestations are increasingly common throughout North American forests. In forested wetlands, disturbance events may alter nutrient, carbon, and hydrologic pathways. Recently, ash (Fraxinus spp.) forests in North Central and Eastern North America have been exposed to the exotic emerald ash borer (EAB) (Burprestidae: Agrilus planipennis), and the rapid and extensive expansion of EAB populations since 2001 may soon eliminate most existing ash stands. Limited research has focused on post-establishment ecosystem impacts of an EAB disturbance, and to our knowledge, there are no studies that have evaluated the coupled response of black ash (Fraxinus nigra) wetland water tables, soil temperatures, and soil gas emissions to an EAB infestation. We present preliminary results that detail those responses to a simulated EAB disturbance. Water table position, soil temperature, and soil gas emissions (CO2 and CH4) were monitored in nine black ash wetlands in the Upper Peninsula of Michigan for three years, including one year of pre-treatment and two years of post-treatment data-collection. An EAB disturbance was simulated by girdling (Girdle) or felling (Clearcut) all black ash trees with diameters of 2.5 cm or greater within the wetland, and each treatment was applied to three sites. The results indicate that wetland water tables were insensitive to treatment effects, soil temperatures were significantly higher in the Clearcut treatment, soil gas flux was significantly higher in the Clearcut treatment, and the rate of soil gas flux was strongly regulated by water table position and temperature. No significant treatment effects were detected in the Girdle treatment during the first post-treatment year. Because water tables were insensitive to treatment, we concluded that water tables did not independently generate a soil gas flux response despite their strong regulatory influence. Furthermore, we concluded that the response of soil temperature to disturbance was largely the reason why elevated soil gas flux rates were observed in the Clearcut treatment.

Geology, hydrogeology, and potential of intrinsic bioremediation at the National Park Service Dockside II site and adjacent areas, Charleston, South Carolina, 1993-94

USGS Publications Warehouse

Campbell, B.G.; Petkewich, M.D.; Landmeyer, J.E.; Chapelle, F.H.

1996-01-01

A long history of industrial and commercial use of the National Park Service property and adjacent properties located in downtown Charleston, South Carolina, has caused extensive contamination of the shallow subsurface soils and water-table aquifer. The National Park Service property is located adjacent to a former manufactured-gas plant site, which is the major source of the contamination. Contamination of this shallow water-table aquifer is of concern because shallow ground water discharges to the Cooper River and contains contaminants, which may affect adjacent wildlife or human populations. The geology of the National Park Service property above the Ashley Formation of the Cooper Group consists of two Quaternary lithostratigraphic marine units, the Wando Formation and Holocene deposits, overlain by artificial fill. The Wando Formation overlies the Ashley Formation, a sandy calcareous clay, and consists of soft, organic clay overlain by gray sand. The Holocene deposits are composed of clayey to silty sand and soft organic-rich clay. The artificial fill, which was placed at the site to create dry land where salt marsh existed previously, is composed of sand, silt, and various scrap materials. The shallow hydrogeology of the National Park Service property overlying the Ashley Formation can be subdivided into two sandy aquifers separated by a leaky, black, organic-rich clay. The unconfined upper surficial aquifer is primarily artificial fill. The lower surficial aquifer consists of the Wando sand unit and is confined by the leaky organic-rich clay. Aquifer tests performed on the wells screened in these aquifers resulted in hydraulic conductivities from 0.1 to 10 feet per day for the upper surficial aquifer, and 16 feet per day for the lower surficial aquifer. Vertical hydraulic gradients at the site are typically low. A downward gradient from the upper surficial aquifer to the lower surficial aquifer occurs throughout most of the year. A brick-lined storm-water-drainage archway located in the study area is a conduit for the overflow of seawater into the surficial aquifer during exceptionally high tides. The efficiency of intrinsic bioremediation to reduce contaminant migration in the upper surficial aquifer at the National Park Service site was assessed to determine if, and at what concentrations, contaminants are being transported to the Cooper River. This assessment required incorporating hydrologic, geochemical, microbiologic, and demographic information into a predictive solute-transport model to determine rates of contaminant transport to the Cooper River. The transport of toluene and naphthalene was modeled as a surrogate for the transport of aromatic and other hydrocarbon compounds at the study area. Laboratory estimates of the adsorption coefficients for sediments of the upper surficial aquifer suggest preferential adsorption of naphthalene over toluene. The adsorption coefficient of naphthalene is at least two orders of magnitude greater than that determined for toluene. Laboratory microbial-biodegradation experiments indicate that microorganisms present in the shallow aquifer have the potential to degrade toluene under anaerobic and aerobic conditions, and naphthalene primarily under aerobic conditions. Rates of microbial biodegradation are similar for both compounds under aerobic conditions. Flow-model calibration to the January 1994 water-table surface of the upper surficial aquifer was achieved by specifying appropriate hydrogeologic boundary conditions and using hydraulic conductivity values determined in the field. The brick-lined storm-water drainage archway located in the study area was modeled to account for ground-water discharge through this drain. An exploratory modeling approach was used to evaluate the range of possible solutions that approximate the transport of contaminants to the observed distributions. Approximate toluene solute-transport conditions for January 1994 were estimated using velocity dist

Methods to predict seasonal high water table (SHGWT) : final report.

DOT National Transportation Integrated Search

2017-04-03

The research study was sectioned into 5 separate tasks. Task 1 included defining the seasonal high ground water table (SHGWT); describing : methods and techniques used to determine SHGWTs; identify problems associated with estimating SHGWT conditions...

Thermal and hydrological observations near Twelvemile Lake in discontinuous permafrost, Yukon Flats, interior Alaska, September 2010-August 2011

USGS Publications Warehouse

Jepsen, Steven M.; Koch, Joshua C.; Rose, Joshua R.; Voss, Clifford I.; Walvoord, Michelle Ann

2012-01-01

A series of ground-based observations were made between September 2010 and August 2011 near Twelvemile Lake, 19 kilometers southwest of Fort Yukon, Alaska, for use in ongoing hydrological analyses of watersheds in this region of discontinuous permafrost. Measurements include depth to ground ice, depth to water table, soil texture, soil moisture, soil temperature, and water pressure above the permafrost table. In the drained basin of subsiding Twelvemile Lake, we generally find an absence of newly formed permafrost and an undetectable slope of the water table; however, a sloping water table was observed in the low-lying channels extending into and away from the lake watershed. Datasets for these observations are summarized in this report and can be accessed by clicking on the links in each section or from the Downloads folder of the report Web page.

Flow in a discrete slotted nozzle with massive injection. [water table tests

NASA Technical Reports Server (NTRS)

Perkins, H. C.

1974-01-01

An experimental investigation has been conducted to determine the effect of massive wall injection on the flow characteristics in a slotted nozzle. Some of the experiments were performed on a water table with a slotted-nozzle test section. This has 45 deg and 15 deg half angles of convergence and divergence, respectively, throat radius of 2.5 inches, and throat width of 3 inches. The hydraulic analogy was employed to qualitatively extend the results to a compressible gas flow through the nozzle. Experimental results from the water table include contours of constant Froude and Mach number with and without injection. Photographic results are also presented for the injection through slots of CO2 and Freon-12 into a main-stream air flow in a convergent-divergent nozzle in a wind tunnel. Schlieren photographs were used to visualize the flow, and qualititative agreement between the results from the gas tunnel and water table is good.

Modeling Subsurface Hydrology in Floodplains

NASA Astrophysics Data System (ADS)

Evans, Cristina M.; Dritschel, David G.; Singer, Michael B.

2018-03-01

Soil-moisture patterns in floodplains are highly dynamic, owing to the complex relationships between soil properties, climatic conditions at the surface, and the position of the water table. Given this complexity, along with climate change scenarios in many regions, there is a need for a model to investigate the implications of different conditions on water availability to riparian vegetation. We present a model, HaughFlow, which is able to predict coupled water movement in the vadose and phreatic zones of hydraulically connected floodplains. Model output was calibrated and evaluated at six sites in Australia to identify key patterns in subsurface hydrology. This study identifies the importance of the capillary fringe in vadose zone hydrology due to its water storage capacity and creation of conductive pathways. Following peaks in water table elevation, water can be stored in the capillary fringe for up to months (depending on the soil properties). This water can provide a critical resource for vegetation that is unable to access the water table. When water table peaks coincide with heavy rainfall events, the capillary fringe can support saturation of the entire soil profile. HaughFlow is used to investigate the water availability to riparian vegetation, producing daily output of water content in the soil over decadal time periods within different depth ranges. These outputs can be summarized to support scientific investigations of plant-water relations, as well as in management applications.

Relationships between water table and model simulated ET

Treesearch

Prem B. Parajuli; Gretchen F. Sassenrath; Ying Ouyang

2013-01-01

This research was conducted to develop relationships among evapotranspiration (ET), percolation (PERC), groundwater discharge to the stream (GWQ), and water table fluctuations through a modeling approach. The Soil and Water Assessment Tool (SWAT) hydrologic and crop models were applied in the Big Sunflower River watershed (BSRW; 7660 km2) within the Yazoo River Basin...

Soil property changes during loblolly pine production

Treesearch

R. Wayne Skaggs; Devendra M. Amatya; G.M. Chescheir; Christine D. Blanton

2006-01-01

Three watersheds, each approximately 25 ha, were instrumented to measure and record drainage rate, water table depth, rainfall and meteorological data. Data continuously collected on the site since 1988 include response of hydrologic and water quality variables for nearly all growth stages of a Loblolly pine plantation. Data for drainage outflow rates and water table...

Combining the Neuman and Boulton models for flow to a well in an unconfined aquifer

USGS Publications Warehouse

Moench, Allen F.

1995-01-01

A Laplace transform solution is presented for flow to a well in a homogeneous, water-table aquifer with noninstanta-neous drainage of water from the zone above the water table. The Boulton convolution integral is combined with Darcy's law and used as an upper boundary condition to replace the condition used by Neuman. Boulton's integral derives from the assumption that water drained from the unsaturated zone is released gradually in a manner that varies exponentially with time in response to a unit decline in hydraulic head, whereas the condition used by Newman assumes that the water is released instantaneously. The result is a solution that reduces to the solution obtained by Neuman as the rate of release of water from the zone above the water table increases. A dimensionless fitting parameter, γ, is introduced that incorporates vertical hydraulic conductivity, saturated thickness, specific yield, and an empirical constant α1, similar to Boulton's α. Results show that theoretical drawdown in water-table piezometers is amplified by noninstantaneous drainage from the unsaturated zone to a greater extent than drawdown in piezometers located at depth in the saturated zone. This difference provides a basis for evaluating γ by type-curve matching in addition to the other dimensionless parameters. Analysis of drawdown in selected piezometers from the published results of two aquifer tests conducted in relatively homogeneous glacial outwash deposits but with significantly different hydraulic conductivities reveals improved comparison between the theoretical type curves and the hydraulic head measured in water-table piezometers.

Terrestrial Responses to Variability in the Southern Westerlies Inferred from Deep Holocene Peat Archives

NASA Astrophysics Data System (ADS)

Hughes, P. D. M.; Mauquoy, D.; van Bellen, S.; Roland, T. P.; Loader, N.; Street-Perrott, F. A.; Daley, T.

2017-12-01

The deep ombrotrophic peat bogs of Chile are located throughout the latitudes dominated by the southern westerly wind belt. The domed surfaces of these peatlands make them sensitive to variability in summer atmospheric moisture balance and the near-continuous accumulation of deep peat strata throughout the Holocene to the present day means that these sites provide undisturbed archives of palaeoclimatic change. We have reconstructed late-Holocene bog water table depths - which can be related to changes in the regional balance of precipitation to evaporation (P-E) - from a suite of peat bogs located in three areas of Tierra del Feugo, Chile, under the main path of the SWWB. Water-table depths were reconstructed from sub-fossil testate amoebae assemblages using a conventional transfer function to infer past water-table depths, based on taxonomic classification of tests but also an innovative trait-based transfer function to infer the same parameter. Water table reconstructions derived from the two methods were consistent within sites. They show that mire water tables have been relatively stable in the last 2000 years across Tierra del Feugo. Higher water table levels, most probably indicating increased effective precipitation, were found between c. 1400 and 900 cal. BP., whereas a consistent drying trend was reconstructed across the region in the most recent peat strata. This shift may represent a pronounced regional decrease in precipitation and/or a change to warmer conditions linked to strengthening of the SWWB. However, other factors such as recent thinning of the ozone layer over Tierra del Fuego could have contributed to recent shifts in some testate amoebae species.

The effects of artificial recharge on groundwater levels and water quality in the west hydrogeologic unit of the Warren subbasin, San Bernardino County, California

USGS Publications Warehouse

Stamos, Christina L.; Martin, Peter; Everett, Rhett; Izbicki, John A.

2013-01-01

Between the late 1940s and 1994, groundwater levels in the Warren subbasin, California, declined by as much as 300 feet because pumping exceeded sparse natural recharge. In response, the local water district, Hi-Desert Water District, implemented an artificial-recharge program in early 1995 using imported water from the California State Water Project. Subsequently, the water table rose by as much as 250 feet; however, a study done by the U.S. Geological Survey found that the rising water table entrained high-nitrate septic effluent, which caused nitrate (as nitrogen) concentrations in some wells to increase to more than the U.S. Environmental Protection Agency maximum contaminant level of 10 milligrams per liter.. A new artificial-recharge site (site 3) was constructed in 2006 and this study, which started in 2004, was done to address concerns about the possible migration of nitrates in the unsaturated zone. The objectives of this study were to: (1) characterize the hydraulic, chemical, and microbiological properties of the unsaturated zone; (2) monitor changes in water levels and water quality in response to the artificial-recharge program at site 3; (3) determine if nitrates from septic effluent infiltrated through the unsaturated zone to the water table; (4) determine the potential for nitrates within the unsaturated zone to mobilize and contaminate the groundwater as the water table rises in response to artificial recharge; and (5) determine the presence and amount of dissolved organic carbon because of its potential to react with disinfection byproducts during the treatment of water for public use. Two monitoring sites were installed and instrumented with heat-dissipation probes, advanced tensiometers, suction-cup lysimeters, and wells so that the arrival and effects of recharging water from the State Water Project through the 250 to 425 foot-thick unsaturated zone and groundwater system could be closely observed. Monitoring site YVUZ-1 was located between two recharge ponds in the middle of site 3, and YVUZ-2 was located approximately 1,200 feet down-gradient and to the southeast in an area where septic systems have been in use since about 1960. Site YVUZ-3 only went to a depth of 42 feet and was used to sample the upper part of the unsaturated zone near a golf course. Prior to the start of artificial recharge at site 3, nitrate concentrations reported as nitrogen from the soil leachate below YVUZ-1 did not exceed 1.58 milligrams per kilogram. Nitrate-reducing bacteria concentrations of 4,300 most probable number were found at about 220 feet below land surface and at the top of the water table at YVUZ-1. Nitrate concentrations at YVUZ-2 reached a maximum concentration of about 25 milligrams per kilogram between about 100 and 121 feet below land surface; concentrations of nitrate-reducing or denitrifying bacteria were as high as 21,000 most probable number at 36 feet below land surface but did not exceed 40 most probable number below about 150 feet below land surface. Between June 2006 and September 2009, more than 9,800 acre feet of water from the State Water Project was released to site 3 ponds. The infiltration of the recharge water was predominantly vertical with limited lateral spreading to a depth of about 200 feet below land surface at YVUZ-1. Lateral spreading of the recharge water with depth was caused by geologic heterogeneities within the unsaturated zone, and resulted in varied arrival times of the recharge water to the instruments and slower rates of vertical movement with depth. No abrupt changes in soil moisture were observed at YVUZ-2, indicating that the recharge water had not reached that site by September 2009. Water levels from the monitoring wells at both sites and from five production wells nearby showed that the water table rose at a mean rate of about 0.08 feet per day between June 2006 and January 2009. The arrival of the water from the State Water Project caused relatively rapid changes in the stable-isotopic ratios from the lysimeters at YVUZ-1. The estimated average rate of infiltration of the recharge water through the unsaturated zone ranged from 3.7 to 25 feet per day. The recharge water arrived at the monitoring well below the recharge ponds between August 2007 and March 2008; the rate of vertical movement to the monitoring well was between 0.6 and 0.9 feet per day. By September 2008, a production well located 375 feet west of site 3 was producing almost 100 percent infiltrated recharge water. By contrast, the stable-isotope data from the lysimeters at YVUZ-2 showed that the recharge water had not reached this site by September 2009, but that septic effluent in the unsaturated zone likely had mixed with the native pore water to at least 154 feet below land surface. Assuming vertical infiltration, the minimum rate of infiltration of septic effluent since 1960 was about 3 feet per year. The isotopic data from the lysimeters at YVUZ-3 indicated two different sources of water to the upper 43 feet–irrigation-return flow and precipitation. Nitrate concentrations of the water from the State Water Project did not exceed 1 milligram per liter. Prior to artificial recharge, nitrate concentrations of the pore water at YVUZ-1 ranged between 6 to 18.2 milligrams per liter. After the arrival of the recharge water, the nitrate concentrations from the lysimeters and well at YVUZ-1 decreased to less than 1 milligram per liter, with the exception of samples collected at 205.5 feet, which did not exceed 4.12 milligrams per liter. The decrease in nitrate concentrations after artificial recharge indicated that the rising water table did not result in an increase of nitrates below YVUZ-1. At YVUZ-2, nitrate concentrations ranged between 12 to 479 milligrams per liter. The highest nitrate concentrations were at 92 feet below land surface and were almost seven times that of samples collected from a nearby septic tank. Nitrate concentrations from the lysimeter at 273 feet below land surface increased from 6 to almost 58 milligrams per liter after it was saturated by the rising water table in December 2007. These increases could be the result of the mobilization of high-nitrate water from regional sources of septic effluent after saturation, or the result of high-nitrate water present at the top of the water table that may be diluted deeper in the aquifer. Nitrate concentrations in groundwater from five nearby production wells and from both monitoring wells were less than 5 milligrams per liter before artificial recharge started. Nitrate concentrations decreased to less than 3 milligrams per liter in three of the production wells and the monitoring well below the recharge ponds after artificial recharge. Dissolved organic carbon concentrations were measured in the recharge water and groundwater because of the potential for dissolved organic carbon to react with chlorine to form trihalomethanes during the water-treatment process. The dissolved organic carbon concentrations of the recharge water were 3.1 milligrams per liter or less, and dissolved organic carbon concentrations of the groundwater were less than 1 milligram per liter. Even though recharge water was present in some of the wells by September 2008, the concentrations of both dissolved organic carbon and trihalomethane formation potential in the groundwater did not increase. Interpretation of these data suggests that the dissolved organic carbon from the recharge water is altered or metabolized in the unsaturated zone, either by absorption to the grain particles in the soil or by microbiological processes.

Physiological and morphological effects of high water tables on early growth of giant reed ( Arundo donax), elephant grass ( Pennisetum purpureum), energycane and sugarcane ( Saccharum spp.)

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

Jennewein, Stephen Peter

Here, an increasing demand for renewable energy sources has spurred interest in high-biomass crops used for energy production. Species potentially well-suited for biofuel production in the seasonally wet organic Everglades Agricultural Area (EAA) of Florida include giant reed ( Arundo donax), elephant grass ( Pennisetum Purpureum), energycane ( Saccharum spp.), and sugarcane ( Saccharum spp.). The objectives in this study were to evaluate the role of fluctuating water tables on the morphology, physiology, and early season growth of these four genotypes. The candidate genotypes were grown in a greenhouse under three water table depths, defined by distance of the watermore » table from the soil surface: two constant water tables (-16 cm and -40 cm) along with a flood cycle (2 weeks of flood to the soil level followed by 2 weeks at -40 cm from the soil level). The genotypes included CP 89-2143 (sugarcane), L 79-1002 (energycane), Merkeron (elephant grass), and wild type (giant reed). The experiment was repeated for plant cane, first ratoon, and successive plant cane crop cycles. Reductions in dry matter yield were observed among genotypes subjected to the -40 cm drained, periodically flooded (40F) water table relative to the -40 cm constant (40C) or -16 cm constant (16C). Plant cane dry weights were reduced by 37% in giant reed, 52% in elephant grass, 42% in energycane, and 34% in sugarcane in the 40F compared to 40C water table treatments. Similarly, in the first ratoon crop dry weights were reduced by 29% in giant reed, 42% in elephant grass, 27% in energycane, and 62% in sugarcane. In plant cane and successive plant cane, average total dry weight was greatest for elephant grass whereas ratoon total dry weight was greatest for energycane. Genotype had more pronounced effects on physiological attributes than water table including the highest stomatal conductance and SPAD values in giant reed, and the highest stalk populations in elephant grass and energycane. Aerenchyma presence and volume increased under higher water tables with elephant grass having the greatest aerenchyma production. Because of the high yields and stalk populations in energycane and elephant grass for all crop stages seen in this study, these two genotypes show potential for bioenergy production in the EAA, but field trials are recommended to confirm this.« less

Particle tracking for selected groundwater wells in the lower Yakima River Basin, Washington

USGS Publications Warehouse

Bachmann, Matthew P.

2015-10-21

Generalized groundwater-flow directions in unconsolidated basin-fill deposits were towards the Yakima River, which acts as a local sink for shallow groundwater, and roughly parallel to topographic gradients. Particles backtracked from more shallow aquifer locations traveled shorter distances before reaching the water table than particles from deeper locations. Flowpaths for particles starting at wells completed in the basalt units underlying the basin-fill deposits sometimes were different than for wells with similar lateral locations but more shallow depths. In cases where backtracking particles reached geologic structures simulated as flow barriers, abrupt changes in direction in some particle pathlines suggest significant changes in simulated hydraulic gradients that may not accurately reflect actual conditions. Most groundwater wells sampled had associated zones of contribution within the Toppenish/Benton subbasin between the well and the nearest subbasin margin, but interpretation of these results for any specific well is likely to be complicated by the assumptions and simplifications inherent in the model construction process. Delineated zones of contribution for individual wells are sensitive to the depths assigned to the screened interval of the well, resulting in simulated areal extents of the zones of contribution to a discharging well that are elongated in the direction of groundwater flow.

Water Relations and Foliar Isotopic Composition of Prosopis tamarugo Phil., an Endemic Tree of the Atacama Desert Growing at Three Levels of Water Table Depth.

PubMed

Garrido, Marco; Silva, Paola; Acevedo, Edmundo

2016-01-01

Prosopis tamarugo Phil. is a strict phreatophyte tree species endemic to the "Pampa del Tamarugal", Atacama Desert. The extraction of water for various uses has increased the depth of the water table in the Pampa aquifers threatening its conservation. This study aimed to determine the effect of the groundwater table depth on the water relations of P. tamarugo and to present thresholds of groundwater depth (GWD) that can be used in the groundwater management of the P. tamarugo ecosystem. Three levels of GWD, 11.2 ± 0.3 m, 10.3 ± 0.3 m, and 7.1 ± 0.1 m, (the last GWD being our reference) were selected and groups of four individuals per GWD were studied in the months of January and July of the years 2011 through 2014. When the water table depth exceeded 10 m, P. tamarugo had lower pre-dawn and mid-day water potential but no differences were observed in minimum leaf stomatal resistance when compared to the condition of 7.1 m GWD; the leaf tissue increased its δ(13)C and δ(18)O composition. Furthermore, a smaller green canopy fraction of the trees and increased foliage loss in winter with increasing water table depth was observed. The differences observed in the physiological behavior of P. tamarugo trees, attributable to the ground water depth; show that increasing the depth of the water table from 7 to 11 m significantly affects the water status of P. tamarugo. The results indicate that P. tamarugo has an anisohydric stomatal behavior and that given a reduction in water supply it regulates the water demand via foliage loss. The growth and leaf physiological activities are highly sensitive to GWD. The foliage loss appears to prevent the trees from reaching water potentials leading to complete loss of hydraulic functionality by cavitation. The balance achieved between water supply and demand was reflected in the low variation of the water potential and of the variables related to gas exchange over time for a given GWD. This acclimation capacity of P. tamarugo after experiencing increases in GWD has great value for the implementation of conservation strategies. The thresholds presented in this paper should prove useful for conservation purposes of this unique species.

Water Relations and Foliar Isotopic Composition of Prosopis tamarugo Phil., an Endemic Tree of the Atacama Desert Growing at Three Levels of Water Table Depth

PubMed Central

Garrido, Marco; Silva, Paola; Acevedo, Edmundo

2016-01-01

Prosopis tamarugo Phil. is a strict phreatophyte tree species endemic to the “Pampa del Tamarugal”, Atacama Desert. The extraction of water for various uses has increased the depth of the water table in the Pampa aquifers threatening its conservation. This study aimed to determine the effect of the groundwater table depth on the water relations of P. tamarugo and to present thresholds of groundwater depth (GWD) that can be used in the groundwater management of the P. tamarugo ecosystem. Three levels of GWD, 11.2 ± 0.3 m, 10.3 ± 0.3 m, and 7.1 ± 0.1 m, (the last GWD being our reference) were selected and groups of four individuals per GWD were studied in the months of January and July of the years 2011 through 2014. When the water table depth exceeded 10 m, P. tamarugo had lower pre-dawn and mid-day water potential but no differences were observed in minimum leaf stomatal resistance when compared to the condition of 7.1 m GWD; the leaf tissue increased its δ13C and δ18O composition. Furthermore, a smaller green canopy fraction of the trees and increased foliage loss in winter with increasing water table depth was observed. The differences observed in the physiological behavior of P. tamarugo trees, attributable to the ground water depth; show that increasing the depth of the water table from 7 to 11 m significantly affects the water status of P. tamarugo. The results indicate that P. tamarugo has an anisohydric stomatal behavior and that given a reduction in water supply it regulates the water demand via foliage loss. The growth and leaf physiological activities are highly sensitive to GWD. The foliage loss appears to prevent the trees from reaching water potentials leading to complete loss of hydraulic functionality by cavitation. The balance achieved between water supply and demand was reflected in the low variation of the water potential and of the variables related to gas exchange over time for a given GWD. This acclimation capacity of P. tamarugo after experiencing increases in GWD has great value for the implementation of conservation strategies. The thresholds presented in this paper should prove useful for conservation purposes of this unique species. PMID:27064665

Nutrient transport and transformation beneath an infiltration basin

USGS Publications Warehouse

Sumner, D.M.; Rolston, D.E.; Bradner, L.A.

1998-01-01

Field experiments were conducted to examine nutrient transport and transformation beneath an infiltration basin used for the disposal of treated wastewater. Removal of nitrogen from infiltrating water by denitrification was negligible beneath the basin, probably because of subsurface aeration as a result of daily interruptions in basin loading. Retention of organic nitrogen in the upper 4.6 m of the unsaturated zone (water table depth of approximately 11 m) during basin loading resulted in concentrations of nitrate as much as 10 times that of the applied treated wastewater, following basin 'rest' periods of several weeks, which allowed time for mineralization and nitrification. Approximately 90% of the phosphorus in treated wastewater was removed within the upper 4.6 m of the subsurface, primarily by adsorption reactions, with abundant iron and aluminum oxyhydroxides occurring as soil coatings. A reduction in the flow rate of infiltrating water arriving at the water table may explain the accumulation of relatively coarse (>0.45 ??m), organic forms of nitrogen and phosphorus slightly below the water table. Mineralization and nitrification reactions at this second location of organic nitrogen accumulation contributed to concentrations of nitrate as much as three times that of the applied treated wastewater. Phosphorus, which accumulated below the water table, was immobilized by adsorption or precipitation reactions during basin rest periods.Field experiments were conducted to examine nutrient transport and transformation beneath an infiltration basin used for the disposal of treated wastewater. Removal of nitrogen from infiltrating water by denitrification was negligible beneath the basin, probably because of subsurface aeration as a result of daily interruptions in basin loading. Retention of organic nitrogen in the upper 4.6 m of the unsaturated zone (water table depth of approximately 11 m) during basin loading resulted in concentrations of nitrate as much as 10 times that of the applied treated wastewater, following basin 'rest' periods of several weeks, which allowed time for mineralization and nitrification. Approximately 90% of the phosphorus in treated wastewater was removed within the upper 4.6 m of the subsurface, primarily by adsorption reactions, with abundant iron and aluminum oxyhydroxides occurring as soil coatings. A reduction in the flow rate of infiltrating water arriving at the water table may explain the accumulation of relatively coarse (>0.45 ??m), organic forms of nitrogen and phosphorus slightly below the water table. Mineralization and nitrification reactions at this second location of organic nitrogen accumulation contributed to concentrations of nitrate as much as three times that of the applied treated wastewater. Phosphorus, which accumulated below the water table, was immobilized by adsorption or precipitation reactions during basin rest periods.

Stratigraphy and hydrologic conditions at the Brookhaven National Laboratory and vicinity, Suffolk County, New York, 1994-97

USGS Publications Warehouse

Scorca, Michael P.; Dorsch, William R.; Paquette, Douglas E.

1999-01-01

Brookhaven National Laboratory (BNL) has installed many test borings as part of an effort to delineate the extent of ground-water contamination at the site. In 1994, the U.S. Geological Survey began a study in cooperation with BNL to define the stratigraphy in the 28-square-mile area encompassing BNL, and to monitor ground-water levels in the 300 squaremile area of central Suffolk County that surrounds BNL. The uppermost geologic units at BNL are of Pleistocene age. These sediments are underlain unconformably by the Matawan Group-Magothy Formation, undifferentiated (referred to as the Magothy Formation), of Cretaceous age, which typically consists of light- to dark-gray, variably sorted sand interbedded with light- to dark-gray clay layers; it also contains beds of grayish-brown to brownish-gray sand. Bed thicknesses differ substantially within each boring and tend to be laterally discontinuous as a result of their terrestrial deltaic depositional environment, although a prominent clay unit, referred to as the ?grayish-brown clay? in this report, was encountered at many borings. Pollen-sample analyses confirm that this unit is of Cretaceous age and is the uppermost unit of Cretaceous sediments in several parts of the study area. The upper surface of the Cretaceous deposits is irregular within the 28-square-mile study area and has relief of about 120 feet. Several prominent channels and ridges in the surface are aligned generally northwest-southeast. The Cretaceous surface beneath BNL is characterized more by local erosional features than by the regional cuesta shape that was suggested by previous authors. The overlying Pleistocene-aged units include (1) a sand layer overlain by the Gardiners Clay, (2) the Gardiners Clay, and (3) upper Pleistocene deposits, which include the Upton unit, glacial outwash, glaciolacustrine deposits, and terminal moraine deposits. The sand unit below the Gardiners Clay was the first Pleistocene unit to be deposited atop the irregular surface of the Cretaceous deposits in this area. The Gardiners Clay was deposited during a major rise in sea level as the sea encroached into parts of the present-day BNL study area. The shallow part of the upper Pleistocene deposits generally consists of light-brown sand and gravel but overlies green to grayish-green, variably sorted sand, silt, and clay at altitudes of 50 to 70 feet below sea level in some parts of the study area. This lower part of the upper Pleistocene deposits in the study area was referred to by previous investigators as the unidentified unit and has been designated as the Upton unit in this report. The discharge of ground water to the Peconic and Carmans Rivers locally affects the water-table configuration. The main ground-water divide on Long Island is about 0.5 miles north of the site; a secondary divide originates near the start of flow of the Peconic River and extends east-southeastward toward the South Fork. The water-table configuration on the BNL site is affected by pumping from supply wells and remediation wells, by infiltration of the water through recharge basins, by discharge from the sewage-treatment plant, and by local near-surface clay units. The horizontal hydraulic gradient at BNL typically is 0.001 foot per foot but can steepen near recharge basins and pumping wells. Vertical flow gradients within the upper Pleistocene deposits (upper glacial aquifer) were as large as 0.007 foot per foot (downward) in the northern part of BNL and were negligible in the southern part. Downward vertical gradients between the lower part of the upper glacial aquifer and the upper part of the Magothy Formation (Magothy aquifer) were about 0.018 foot per foot throughout the site.

Late quaternary history and uranium isotopic compositions of ground water discharge deposits, Crater Flat, Nevada

USGS Publications Warehouse

Paces, James B.; Taylor, Emily M.; Bush, Charles

1993-01-01

Three carbonate-rich spring deposits are present near the southern end of Crater Flat, NV, approximately 18 km southwest of the potential high-level waste repository at Yucca Mountain. We have analyzed five samples of carbonate-rich material from two of the deposits for U and Th isotopic compositions. Resulting U-series disequilibrium ages indicate that springs were active at 18 ?? 1, 30 ?? 3, 45 ?? 4 and >70 ka. These ages are consistent with a crude internal stratigraphy at one site. Identical ages for two samples at two separate sites suggest that springs were contemporaneous, at least in part, and were most likely part of the same hydrodynamic system. In addition, initial U isotopic compositions range from 2.8 to 3.8 and strongly suggest that ground water from the regional Tertiary-volcanic aquifer provided the source for these hydrogenic deposits. This interpretation, along with water level data from near-by wells suggest that the water table rose approximately 80 to 115 m above present levels during the late Quaternary and may have fluctuated repeatedly. Current data are insufficient to allow reconstruction of a detailed depositional history, however geochronological data are in good agreement with other paleoclimatic proxy records preserved throughout the region. Since these deposits are down gradient from the potential repository site, the possibility of higher ground water levels in the future dramatically shortens both vertical and lateral ground water pathways and reduces travel times of transported radionuclides to potential discharge sites.

A Mathematical View of Water Table Fluctuations in a Shallow Aquifer in Brazil.

PubMed

Neto, Dagmar C; Chang, Hung K; van Genuchten, Martinus Th

2016-01-01

Detailed monitoring of the groundwater table can provide important data about both short- and long-term aquifer processes, including information useful for estimating recharge and facilitating groundwater modeling and remediation efforts. In this paper, we presents results of 4 years (2002 to 2005) of monitoring groundwater water levels in the Rio Claro Aquifer using observation wells drilled at the Rio Claro campus of São Paulo State University in Brazil. The data were used to follow natural periodic fluctuations in the water table, specifically those resulting from earth tides and seasonal recharge cycles. Statistical analyses included methods of time-series analysis using Fourier analysis, cross-correlation, and R/S analysis. Relationships could be established between rainfall and well recovery, as well as the persistence and degree of autocorrelation of the water table variations. We further used numerical solutions of the Richards equation to obtain estimates of the recharge rate and seasonable groundwater fluctuations. Seasonable soil moisture transit times through the vadose zone obtained with the numerical solution were very close to those obtained with the cross-correlation analysis. We also employed a little-used deep drainage boundary condition to obtain estimates of seasonable water table fluctuations, which were found to be consistent with observed transient groundwater levels during the period of study. © 2015, National Ground Water Association.

Wetland Resiliency: How does multi-year water table level decline and recovery influence carbon dioxide and methane fluxes?

NASA Astrophysics Data System (ADS)

Pugh, C.; Reed, D. E.; Desai, A. R.; Sulman, B. N.

2016-12-01

Wetlands play a disproportionately large role in the global carbon budget, and individual wetlands can fluctuate between carbon sinks and sources depending on factors such as hydrology, biogeochemistry, and land use. Although much research has been done on wetland biogeochemical cycles, there is a lack of experimental evidence concerning how changes in wetland hydrology influence these cycles over interannual timescales. Over a seven-year period, Sulman et al. (2009) found that a drought-induced declining water table at a shrub wetland in northern Wisconsin coincided with increased ecosystem respiration (ER) and gross ecosystem productivity (GEP) (Sulman et al. 2009). Since then, however, the average water table level at this site has begun to increase, thus allowing a unique opportunity to explore how wetland carbon storage is impacted by water table recovery. With the addition of three more years of eddy covariance observations post recovery and new methane flux observations, we found that water table level no longer had a significant correlation with GEP, ER, or methane flux. Air temperature, however, had a strong correlation with all three. Average methane flux stayed relatively constant under 14 °C, before increasing an order of magnitude from 3.7 nmol m-2 s-1 in April to 36 nmol m-2 s-1 in July. These results suggest that, over decadal timescales, temperature, rather than water level, is a stronger limiting factor for both aerobic and anaerobic respiration in shrub fen wetlands. Wetlands play a disproportionately large role in the global carbon budget, and individual wetlands can fluctuate between carbon sinks and sources depending on factors such as hydrology, biogeochemistry, and land use. Although much research has been done on wetland biogeochemical cycles, there is a lack of experimental evidence concerning how changes in wetland hydrology influence these cycles over interannual timescales. Over a seven-year period, Sulman et al. (2009) found that a drought-induced declining water table at a shrub wetland in northern Wisconsin coincided with increased ecosystem respiration (ER) and gross ecosystem productivity (GEP) (Sulman et al. 2009). Since then, however, the average water table level at this site has begun to increase, thus allowing a unique opportunity to explore how wetland carbon storage is impacted by water table recovery. With the addition of three more years of eddy covariance observations post recovery and new methane flux observations, we found that water table level no longer had a significant correlation with GEP, ER, or methane flux. Air temperature, however, had a strong correlation with all three. Average methane flux stayed relatively constant under 14 °C, before increasing an order of magnitude from 3.7 nmol m-2 s-1 in April to 36 nmol m-2 s-1 in July. These results suggest that, over decadal timescales, temperature, rather than water level, is a stronger limiting factor for both aerobic and anaerobic respiration in shrub fen wetlands.

Application of the conjugate-gradient method to ground-water models

USGS Publications Warehouse

Manteuffel, T.A.; Grove, D.B.; Konikow, Leonard F.

1984-01-01

The conjugate-gradient method can solve efficiently and accurately finite-difference approximations to the ground-water flow equation. An aquifer-simulation model using the conjugate-gradient method was applied to a problem of ground-water flow in an alluvial aquifer at the Rocky Mountain Arsenal, Denver, Colorado. For this application, the accuracy and efficiency of the conjugate-gradient method compared favorably with other available methods for steady-state flow. However, its efficiency relative to other available methods depends on the nature of the specific problem. The main advantage of the conjugate-gradient method is that it does not require the use of iteration parameters, thereby eliminating this partly subjective procedure. (USGS)

Water-table and potentiometric-surface altitudes of the upper glacial, Magothy, and Lloyd aquifers on Long Island, New York, in March-April 2000, with a summary of hydrogeologic conditions

USGS Publications Warehouse

Busciolano, Ronald J.

2002-01-01

The three main water-bearing units on Long Island, New York--the upper glacial aquifer (water table) and the underlying Magothy and Lloyd aquifers--are the sole source of water supply for more than 3 million people. Water-table and potentiometric-surface altitudes were contoured from water-level measurements made at 394 observation, public-supply, and industrial-supply wells during March-April 2000. In general, water-level altitudes in the upper glacial, Magothy, and Lloyd aquifers were lower throughout most parts of Long Island than those measured during March-April 1997. Changes in altitude during this period ranged from an increase of about 6 feet in the Magothy aquifer in southwestern Nassau County to a decrease of more than 8 feet in the upper glacial aquifer in eastern Suffolk County.

Bathymetric maps and water-quality profiles of Table Rock and North Saluda Reservoirs, Greenville County, South Carolina

USGS Publications Warehouse

Clark, Jimmy M.; Journey, Celeste A.; Nagle, Doug D.; Lanier, Timothy H.

2014-01-01

Lakes and reservoirs are the water-supply source for many communities. As such, water-resource managers that oversee these water supplies require monitoring of the quantity and quality of the resource. Monitoring information can be used to assess the basic conditions within the reservoir and to establish a reliable estimate of storage capacity. In April and May 2013, a global navigation satellite system receiver and fathometer were used to collect bathymetric data, and an autonomous underwater vehicle was used to collect water-quality and bathymetric data at Table Rock Reservoir and North Saluda Reservoir in Greenville County, South Carolina. These bathymetric data were used to create a bathymetric contour map and stage-area and stage-volume relation tables for each reservoir. Additionally, statistical summaries of the water-quality data were used to provide a general description of water-quality conditions in the reservoirs.

A multi-method study of regional groundwater circulation in the Ordos Plateau, NW China

NASA Astrophysics Data System (ADS)

Jiang, Xiao-Wei; Wan, Li; Wang, Xu-Sheng; Wang, Dan; Wang, Heng; Wang, Jun-Zhi; Zhang, Hong; Zhang, Zhi-Yuan; Zhao, Ke-Yu

2018-01-01

The Ordos Basin is one of the most intensively studied groundwater basins in China. The Ordos Plateau, located in the north part of the Ordos Basin, is ideal to study the pattern of regional groundwater circulation induced by water-table undulations due to the wavy topography and the relatively simple aquifer systems with macroscopically homogeneous sandstone. In catchments located near the first-order divide, the water table is found to be a subdued replica of the topography, and the nonclosed water-table contours in topographic highs of a catchment are indicative of regional groundwater outflow to other catchments. In topographic lows, groundwater-fed lakes/rivers, topography-driven flowing wells, water-loving and/or salt-tolerant vegetation, and soap holes are all indicative of discharge areas. In discharge areas, although groundwater inflow from recharge areas is relatively stable, seasonal variations in groundwater recharge and evapotranspiration lead to significant seasonal fluctuations in the water table, which can be used to estimate groundwater inflow and evapotranspiration rates based on water balance at different stages of water-table change. In the lowest reaches of a complex basin, superposition of local flow systems on regional flow systems has been identified based on groundwater samples collected from wells with different depths and geophysical measurements of apparent resistivity, both of which can be used for characterizing groundwater flow systems. This study enhances understanding of the pattern of regional groundwater circulation in the Ordos Plateau, and also tests the effectiveness of methods for groundwater flow-system characterization.

Groundwater influence on soil moisture memory and land-atmosphere interactions over the Iberian Peninsula

NASA Astrophysics Data System (ADS)

Martinez-de la Torre, Alberto; Miguez-Macho, Gonzalo

2017-04-01

We investigate the memory introduced in soil moisture fields by groundwater long timescales of variation in the semi-arid regions of the Iberian Peninsula with the LEAFHYDRO soil-vegetation-hydrology model, which includes a dynamic water table fully coupled to soil moisture and river flow via 2-way fluxes. We select a 10-year period (1989-1998) with transitions from wet to dry to again wet long lasting conditions and we carry out simulations at 2.5 km spatial resolution forced by ERA-Interim and a high-resolution precipitation analysis over Spain and Portugal. The model produces a realistic water table that we validate with hundreds of water table depth observation time series (ranging from 4 to 10 years) over the Iberian Peninsula. Modeled river flow is also compared to observations. Over shallow water table regions, results highlight the groundwater buffering effect on soil moisture fields over dry spells and long-term droughts, as well as the slow recovery of pre-drought soil wetness once climatic conditions turn wetter. Groundwater sustains river flow during dry summer periods. The longer lasting wet conditions in the soil when groundwater is considered increase summer evapotranspiration, that is mostly water-limited. Our results suggest that groundwater interaction with soil moisture should be considered for climate seasonal forecasting and climate studies in general over water-limited regions where shallow water tables are significantly present and connected to land surface hydrology.

Toward a Periodic Table of Niches, or Exploring the Lizard Niche Hypervolume.

PubMed

Pianka, Eric R; Vitt, Laurie J; Pelegrin, Nicolás; Fitzgerald, Daniel B; Winemiller, Kirk O

2017-11-01

Widespread niche convergence suggests that species can be organized according to functional trait combinations to create a framework analogous to a periodic table. We compiled ecological data for lizards to examine patterns of global and regional niche diversification, and we used multivariate statistical approaches to develop the beginnings for a periodic table of niches. Data (50+ variables) for five major niche dimensions (habitat, diet, life history, metabolism, defense) were compiled for 134 species of lizards representing 24 of the 38 extant families. Principal coordinates analyses were performed on niche dimensional data sets, and species scores for the first three axes were used as input for a principal components analysis to ordinate species in continuous niche space and for a regression tree analysis to separate species into discrete niche categories. Three-dimensional models facilitate exploration of species positions in relation to major gradients within the niche hypervolume. The first gradient loads on body size, foraging mode, and clutch size. The second was influenced by metabolism and terrestrial versus arboreal microhabitat. The third was influenced by activity time, life history, and diet. Natural dichotomies are activity time, foraging mode, parity mode, and habitat. Regression tree analysis identified 103 cases of extreme niche conservatism within clades and 100 convergences between clades. Extending this approach to other taxa should lead to a wider understanding of niche evolution.

Ground-water resources of the North Beach Peninsula, Pacific County, Washington

USGS Publications Warehouse

Tracy, James V.

1977-01-01

The anticipated water demand of 425 million gallons per year for the North Brach Peninsula, Pacific County, Wash., can be met by properly developing the ground-water supplies of the area 's water-table aquifer. Of the approximately 77 inches of annual precipitation on the peninsula, an estimated 23 inches is lost to evapotranspiration, and approximately 36 inches is discharged by the water-table aquifer into the ocean and bay. The remaining water either runs off the surface or is leaked to a deeper aquifer that ultimately discharges to the ocean. At least 12 inches of the water that discharges naturally through the aquifer is available for additional development. This quantity of water is approximately equivalent to 860,000 gallons per day. Wells spaced at least 1,000 feet apart along the major axis of the peninsula and pumped at average rates of no more than 80 gallons per minute could ensure that water-level declines do not exceed 6 feet near the wells and 1 foot at the shoreline, thereby preventing seawater intrusion. Lowering of the water table may be beneficial in reducing waterlogging problems, but care must be taken not to lower the levels near cranberry bogs, which require a shallow water table. Treatment of the otherwise good quality water for iron may be required, as about 75 percent of the well water sampled from the aquifer had iron concentrations in excess of limits recommended by the U.S. Environmental Protection Agency. (Woodard-USGS)

Effects of high-rate wastewater spray disposal on the water-table aquifer, Hilton Head Island, South Carolina

USGS Publications Warehouse

Speiran, G.K.

1985-01-01

A study by the U.S. Geological Survey from April 1982 through December 1983 evaluated the effects of high-rate disposal of treated wastewater on the water table aquifer, Hilton Head Island, South Carolina. Flooding of topographically low areas resulted from the application of 10.8 inches of wastewater in 10 days in January 1983. The water table remained 2-1/2 to 5-1/2 feet below land surface when wastewater was applied at rates of 5 inches per week in August and December 1983. (USGS)

Investigation of remote sensing to detect near-surface groundwater on irrigated lands

NASA Technical Reports Server (NTRS)

Ryland, D. W.; Schmer, F. A.; Moore, D. G.

1975-01-01

The application of remote sensing techniques was studied for detecting areas with high water tables in irrigated agricultural lands. Aerial data were collected by the LANDSAT-1 satellite and aircraft over the Kansas/Bostwick Irrigation District in Republic and Jewell Counties, Kansas. LANDSAT-1 data for May 12 and August 10, 1973, and aircraft flights (midday and predawn) on August 10 and 11, 1973, and June 25 and 26, 1974, were obtained. Surface and water table contour maps and active observation well hydrographs were obtained from the Bureau of Reclamation for use in the analysis. Results of the study reveal that LANDSAT-1 data (May MSS band 6 and August MSS band 7) correlate significantly (0.01 level) with water table depth for 144 active observation wells located throughout the Kansas/Bostwick Irrigation District. However, a map of water table depths of less than 1.83 meters prepared from the LANDSAT-1 data did not compare favorably with a map of seeped lands of less than 1.22 m (4 feet) to the water table. Field evaluation of the map is necessary for a complete analysis. Analysis of three fields on a within or single-field basis for the 1973 LANDSAT-1 data also showed significant correlation results.

Mapping water table depth using geophysical and environmental variables.

PubMed

Buchanan, S; Triantafilis, J

2009-01-01

Despite its importance, accurate representation of the spatial distribution of water table depth remains one of the greatest deficiencies in many hydrological investigations. Historically, both inverse distance weighting (IDW) and ordinary kriging (OK) have been used to interpolate depths. These methods, however, have major limitations: namely they require large numbers of measurements to represent the spatial variability of water table depth and they do not represent the variation between measurement points. We address this issue by assessing the benefits of using stepwise multiple linear regression (MLR) with three different ancillary data sets to predict the water table depth at 100-m intervals. The ancillary data sets used are Electromagnetic (EM34 and EM38), gamma radiometric: potassium (K), uranium (eU), thorium (eTh), total count (TC), and morphometric data. Results show that MLR offers significant precision and accuracy benefits over OK and IDW. Inclusion of the morphometric data set yielded the greatest (16%) improvement in prediction accuracy compared with IDW, followed by the electromagnetic data set (5%). Use of the gamma radiometric data set showed no improvement. The greatest improvement, however, resulted when all data sets were combined (37% increase in prediction accuracy over IDW). Significantly, however, the use of MLR also allows for prediction in variations in water table depth between measurement points, which is crucial for land management.

The influence of irrigation-induced water table fluctuation on iron redistribution and arsenic immobilization within the unsaturation zone.

PubMed

Chi, Zeyong; Xie, Xianjun; Pi, Kunfu; Wang, Yanxin; Li, Junxia; Qian, Kun

2018-05-08

Given the long-term potential risk of arsenic (As)-contaminated agricultural soil to public health, the redistribution of iron (Fe) and immobilization of As within the unsaturation zone during irrigation and consequent water table fluctuations were studied via a column experiment and corresponding geochemical modeling. Experimental results show that As and Fe accumulated significantly at the top of the column during irrigation. A tremendous increase in As and Fe accumulation rates exists after water table recovery. It was deduced that Fe(II) and As(III) were oxidized directly by O 2 at the period of low water table. But the production of hydroxyl radical (OH) was promoted at the period of high water table due to the oxidation of adsorbed Fe(II). The generated OH further accelerate the oxidation of Fe(II) and As(III). Moreover, the combination of As and Fe is more stronger at the top of the column due to the transformation of combined states of As from surface complexation into surface precipitation with the growth of Fe(III) minerals. This study details the processes and mechanisms of As and Fe immobilization within the unsaturation zone during different irrigation periods and accordingly provides some insights to mitigate As accumulation in topsoil. Copyright © 2018 Elsevier B.V. All rights reserved.

40 CFR Table 3 to Subpart Ooo - Fugitive Emission Limits

Code of Federal Regulations, 2011 CFR

2011-07-01

... 40 Protection of Environment 6 2011-07-01 2011-07-01 false Fugitive Emission Limits 3 Table 3 to... Processing Plants Subpt. OOO, Table 3 Table 3 to Subpart OOO—Fugitive Emission Limits Table 3 to Subpart OOO...; andPeriodic inspections of water sprays according to § 60.674(b) and § 60.676(b); and A repeat...

40 CFR Table 3 to Subpart Ooo - Fugitive Emission Limits

Code of Federal Regulations, 2010 CFR

2010-07-01

... 40 Protection of Environment 6 2010-07-01 2010-07-01 false Fugitive Emission Limits 3 Table 3 to... Processing Plants Subpt. OOO, Table 3 Table 3 to Subpart OOO—Fugitive Emission Limits Table 3 to Subpart OOO...; andPeriodic inspections of water sprays according to § 60.674(b) and § 60.676(b); and A repeat...

MODELING TRANSPORT IN THE DOWN GRADIENT PORTION OF THE 200-PO-1 OPERABLE UNIT AT THE HANFORD SITE

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

MEHTA S; ALY AH; MILLER CW

2009-12-03

Remedial Investigations are underway for the 200-PO-l Operable Unit (OU) at the U.S. Department of Energy's Hanford Site in Washington State. To support the baseline risk assessment and evaluation of remedial alternatives, fate and transport modeling is being conducted to predict the future concentration of contaminants of potential concern in the 200-PO-1 OU. This study focuses on modeling the 'down gradient' transport of those contaminants that migrate beyond the 3-D model domain selected for performing detailed 'source area' modeling within the 200-PO-1 OU. The down gradient portion is defined as that region of the 200-PO-1 OU that is generally outsidemore » the 200 Area (considered 'source area') of the Hanford Site. A 1-D transport model is developed for performing down gradient contaminant fate and transport modeling. The 1-D transport model is deemed adequate based on the inferred transport pathway of tritium in the past and the observation that most of the contaminant mass remains at or near the water table within the unconfined aquifer of the Hanford Formation and the Cold-Creek/Pre-Missoula Gravel unit. The Pipe Pathway feature of the GoldSim software is used to perform the calculations. The Pipe Pathway uses a Laplace transform approach to provide analytical solutions to a broad range of advection-dominated mass transport systems involving one-dimensional advection, longitudinal dispersion, retardation, decay and ingrowth, and exchanges with immobile storage zones. Based on the historical concentration distribution data for the extensive tritium plume in this area, three Pipe Pathways are deemed adequate for modeling transport of contaminants. Each of these three Pipe Pathways is discretized into several zones, based on the saturated thickness variation in the unconfined aquifer and the location of monitoring wells used for risk assessment calculation. The mass fluxes of contaminants predicted to exit the source area model domain are used as an input to the down gradient model, while the flow velocities applied are based on the present-day hydraulic gradients and estimation of hydraulic conductivity in the unconfined aquifer. The results of the calculation indicate that the future concentrations of contaminants of potential concern in the down gradient portion of the 200-PO-1 OU declines with time and distance.« less

Lateral water flux in the unsaturated zone: A mechanism for the formation of spatial soil heterogeneity in a headwater catchment

Treesearch

John P. Gannon; Kevin J. McGuire; Scott W. Bailey; Rebecca R. Bourgault; Donald S. Ross

2017-01-01

Measurements of soil water potential and water table fluctuations suggest that morphologically distinct soils in a headwater catchment at the Hubbard Brook Experimental Forest in New Hampshire formed as a result of variations in saturated and unsaturated hydrologic fluxes in the mineral soil. Previous work showed that each group of these soils had distinct water table...

Results of ground-water tracer tests using tritiated water at Oak Ridge National Laboratory, Tennessee

USGS Publications Warehouse

Webster, D.A.

1996-01-01

Ground-water tracer test were conducted at two sites in the radioactive-waste disposal area of Oak Ridge National Laboratory from 1977 to 1982. The purpose of the tests was to determine if the regolith beds had weathered sufficiently to permit the substantial flow of water across them. About 50 curies of tritium dissolved in water were used as the tracer in one site, and about 100 curies at the other. Results demonstrated that ground water is able to flow through joints in the weathered bedding and that the direction of the water-table gradient is the primary factor governint flow direction. Nevertheless, the substantial lateral spread of the plume as it developed showed that bedding-plane openings can still exert a significant secondary influence on flow direction in weathered rock. About 3,500 water samples from the injection and observation wells were analyzed for tritium during the test period. Concentrations detected spanned 11 orders of magnitude. Measurable concentrations were still present in the two injection wells and most observation wells 5 years after the tracer was introduced. Matrix diffusion may have played a significant role in these tests. The process would account for the sustained concentrations of tritium at many of the observation wells, the long-term residual concentrations at the injection and observation wells, and the apparent slow movement of the centers of mass across the two well fields. The process also would have implications regarding aquifer remediation. Other tracer tests have been conducted in the regolith of the Conasauga Group. Results differ from the results described in this report.

Potential groundwater contribution to Amazon evapotranspiration

NASA Astrophysics Data System (ADS)

Fan, Y.; Miguez-Macho, G.

2010-07-01

Climate and land ecosystem models simulate a dry-season vegetation stress in the Amazon forest, but observations show enhanced growth in response to higher radiation under less cloudy skies, indicating an adequate water supply. Proposed mechanisms include larger soil water store and deeper roots in nature and the ability of roots to move water up and down (hydraulic redistribution). Here we assess the importance of the upward soil water flux from the groundwater driven by capillarity. We present a map of water table depth from observations and groundwater modeling, and a map of potential capillary flux these water table depths can sustain. The maps show that the water table beneath the Amazon can be quite shallow in lowlands and river valleys (<5 m in 36% and <10 m in 60% of Amazonia). The water table can potentially sustain a capillary flux of >2.1 mm day-1 to the land surface averaged over Amazonia, but varies from 0.6 to 3.7 mm day-1 across nine study sites. Current models simulate a large-scale reduction in dry-season photosynthesis under today's climate and a possible dieback under projected future climate with a longer dry season, converting the Amazon from a net carbon sink to a source and accelerating warming. The inclusion of groundwater and capillary flux may modify the model results.

Artificial recharge through a thick, heterogeneous unsaturated zone

USGS Publications Warehouse

Izbicki, J.A.; Flint, A.L.; Stamos, C.L.

2008-01-01

Thick, heterogeneous unsaturated zones away from large streams in desert areas have not previously been considered suitable for artificial recharge from ponds. To test the potential for recharge in these settings, 1.3 ?? 10 6 m3 of water was infiltrated through a 0.36-ha pond along Oro Grande Wash near Victorville, California, between October 2002 and January 2006. The pond overlies a regional pumping depression 117 m below land surface and is located where thickness and permeability of unsaturated deposits allowed infiltration and saturated alluvial deposits were sufficiently permeable to allow recovery of water. Because large changes in water levels caused by nearby pumping would obscure arrival of water at the water table, downward movement of water was measured using sensors in the unsaturated zone. The downward rate of water movement was initially as high as 6 m/d and decreased with depth to 0.07 m/d; the initial time to reach the water table was 3 years. After the unsaturated zone was wetted, water reached the water table in 1 year. Soluble salts and nitrate moved readily with the infiltrated water, whereas arsenic and chromium were less mobile. Numerical simulations done using the computer program TOUGH2 duplicated the downward rate of water movement, accumulation of water on perched zones, and its arrival at the water table. Assuming 10 ?? 10 6 m3 of recharge annually for 20 years, a regional ground water flow model predicted water level rises of 30 m beneath the ponds, and rises exceeding 3 m in most wells serving the nearby urban area.

Hydrogeologic characteristics and geospatial analysis of water-table changes in the alluvium of the lower Arkansas River Valley, southeastern Colorado, 2002, 2008, and 2015

USGS Publications Warehouse

Holmberg, Michael J.

2017-05-15

The U.S. Geological Survey in cooperation with the Lower Arkansas Valley Water Conservancy District measures groundwater levels periodically in about 100 wells completed in the alluvial material of the Arkansas River Valley in Pueblo, Crowley, Otero, Bent, and Prowers Counties in southeastern Colorado, of which 95 are used for the analysis in this report. The purpose of this report is to provide information to water-resource administrators, managers, planners, and users about groundwater characteristics in the alluvium of the lower Arkansas Valley extending roughly 150 miles between Pueblo Reservoir and the Colorado-Kansas State line. This report includes three map sheets showing (1) bedrock altitude at the base of the alluvium of the lower Arkansas Valley; (2) estimated spring-to-spring and fall-to-fall changes in water-table altitude between 2002, 2008, and 2015; and (3) estimated saturated thickness in the alluvium during spring and fall of 2002, 2008, and 2015, and thickness of the alluvium in the lower Arkansas Valley. Water-level changes were analyzed by geospatial interpolation methods.Available data included all water-level measurements made between January 1, 2001, and December 31, 2015; however, only data from fall and spring of 2002, 2008, and 2015 are mapped in this report. To account for the effect of John Martin Reservoir in Bent County, Colorado, lake levels at the reservoir were assigned to points along the approximate shoreline and were included in the water-level dataset. After combining the water-level measurements and lake levels, inverse distance weighting was used to interpolate between points and calculate the altitude of the water table for fall and spring of each year for comparisons. Saturated thickness was calculated by subtracting the bedrock surface from the water-table surface. Thickness of the alluvium was calculated by subtracting the bedrock surface from land surface using a digital elevation model.In order to analyze the response of the alluvium to varying environmental and anthropogenic conditions, the percentage of area of the lower Arkansas Valley showing an absolute change of 3 feet or less was calculated for each of the six water-table altitude change maps. For fall water-table altitude change maps, the periods between 2002 and 2008, 2008 and 2015, and 2002 and 2015 showed that 86.5 percent, 85.2 percent, and 66.3 percent of the study area, respectively, showed a net change of 3 feet or less. In the spring water-table altitude change maps these periods showed a net change of 3 feet or less in 94.4 percent, 96.1 percent, and 90.2 percent of the study area, respectively. While the estimated change in water-table altitude was slightly greater and more variable in fall-to-fall comparisons, these high percentages of area with relatively small net changes indicated that, at least in comparisons of the years presented, there was not a large amount of fluctuation in the altitude of the water table.The saturated thickness in the lower Arkansas Valley was between 25 and 50 feet in 34.4 to 35.9 percent of the study area, depending on the season and year. Between 30.2 and 35.6 percent of the area showed saturated thicknesses between 0 and 25 feet. Less than 1 percent of the area showed a saturated thickness greater than 200 feet in all mapped seasons and years.

Water flux through human aquaporin 1: inhibition by intracellular furosemide and maximal response with high osmotic gradients.

PubMed

Ozu, Marcelo; Dorr, Ricardo A; Teresa Politi, M; Parisi, Mario; Toriano, Roxana

2011-06-01

This work studies water permeability properties of human aquaporin 1 (hAQP1) expressed in Xenopus laevis oocyte membranes, applying a technique where cellular content is replaced with a known medium, with the possibility of measuring intracellular pressure. Consequences on water transport-produced by well-known anisotonic gradients and by the intracellular effect of probable aquaporin inhibitors-were tested. In this way, the specific intracellular inhibition of hAQP1 by the diuretic drug furosemide was demonstrated. In addition, experiments imposing anisotonic mannitol gradients with a constant ionic strength showed that the relationship between water flux and the applied mannitol gradient deflects from a perfect osmometer response when the gradient is higher than 150 mosmol kg (W) (-1) . These results would indicate that the passage of water molecules through hAQP1 may have a maximum rate. As a whole, this work demonstrates the technical advantage of controlling both intracellular pressure and medium composition in order to study biophysical properties of hAQP1, and contributes information on water channel behavior under osmotic challenges and the discovery of new inhibitors.

Study of hydro-saline characteristics of soils a palm grove in basin of Ouargla (Northern Algerian Sahara)

NASA Astrophysics Data System (ADS)

Rezagui, D.; Bouhoun, M. Daddi; Boutoutaou, D.; Djaghoubi, A.

2016-07-01

Saharan soils are often faced with several problems of development, taking account the hydro-edaphic constraints, mainly of hydric types by water table, mechanical by gypso-calcareous crusts and saline by irrigation waters and upwelling of water table. Our work consists in doing a soil characterization of a palm grove in Ouargla in order to study the constraints hydro-halomorphes. The results show that irrigation water by two plies of Senonian and Mioplcène had a high salinity with a value of 2.83 and 5.10 dS.m-1 respectively. The conduct of irrigation is traditional random of submersion type. The palm grove has a poor drainage with a level of water table 156.67±15.71 cm and salinity of 31.37±34.04 dS.m-1. The drains are open type and their maintenance is not regular. This situation of management of irrigation-drainage promotes the upwelling of water table and the waterlogging in soils. The study of soil profiles shows the existence of mechanical obstruction of gypso-calcareous crusts which limit the entrenchment of the date palms and the leaching of salts. Soil salinity is excessive in profiles with a range of 8.98 ± 4.58 dS.m-1. This accumulation of salts is due to the dynamic ascending and descending of salts respectively under the effect of upwelling of water table and leaching by irrigation. The salinization, the upwelling of water table and the presence of gypso-calcareous crusts recorded in Ouargla testify to a degradation hydro-halomorphe and mechanic of soil which constitute the major constraints in the management of system irrigation-drainage and sustainable agricultural development of the palm groves of the basin of Ouargla. Some hydro-agricultural planning are necessary to apply in the oasis to improve the hydro-mechanical properties of soils in order to reduce their degradation.

Representing northern peatland microtopography and hydrology within the Community Land Model

DOE PAGES

Shi, Xiaoying; Thornton, Peter E.; Ricciuto, Daniel M.; ...

2015-11-12

Predictive understanding of northern peatland hydrology is a necessary precursor to understanding the fate of massive carbon stores in these systems under the influence of present and future climate change. Current models have begun to address microtopographic controls on peatland hydrology, but none have included a prognostic calculation of peatland water table depth for a vegetated wetland, independent of prescribed regional water tables. We introduce here a new configuration of the Community Land Model (CLM) which includes a fully prognostic water table calculation for a vegetated peatland. Our structural and process changes to CLM focus on modifications needed to representmore » the hydrologic cycle of bogs environment with perched water tables, as well as distinct hydrologic dynamics and vegetation communities of the raised hummock and sunken hollow microtopography characteristic of peatland bogs. The modified model was parameterized and independently evaluated against observations from an ombrotrophic raised-dome bog in northern Minnesota (S1-Bog), the site for the Spruce and Peatland Responses Under Climatic and Environmental Change experiment (SPRUCE). Simulated water table levels compared well with site-level observations. The new model predicts hydrologic changes in response to planned warming at the SPRUCE site. At present, standing water is commonly observed in bog hollows after large rainfall events during the growing season, but simulations suggest a sharp decrease in water table levels due to increased evapotranspiration under the most extreme warming level, nearly eliminating the occurrence of standing water in the growing season. Simulated soil energy balance was strongly influenced by reduced winter snowpack under warming simulations, with the warming influence on soil temperature partly offset by the loss of insulating snowpack in early and late winter. Furthermore, the new model provides improved predictive capacity for seasonal hydrological dynamics in northern peatlands, and provides a useful foundation for investigation of northern peatland carbon exchange.« less

Representing northern peatland microtopography and hydrology within the Community Land Model

DOE PAGES

Shi, X.; Thornton, P. E.; Ricciuto, D. M.; ...

2015-02-20

Predictive understanding of northern peatland hydrology is a necessary precursor to understanding the fate of massive carbon stores in these systems under the influence of present and future climate change. Current models have begun to address microtopographic controls on peatland hydrology, but none have included a prognostic calculation of peatland water table depth for a vegetated wetland, independent of prescribed regional water tables. We introduce here a new configuration of the Community Land Model (CLM) which includes a fully prognostic water table calculation for a vegetated peatland. Our structural and process changes to CLM focus on modifications needed to representmore » the hydrologic cycle of bogs environment with perched water tables, as well as distinct hydrologic dynamics and vegetation communities of the raised hummock and sunken hollow microtopography characteristic of peatland bogs. The modified model was parameterized and independently evaluated against observations from an ombrotrophic raised-dome bog in northern Minnesota (S1-Bog), the site for the Spruce and Peatland Responses Under Climatic and Environmental Change experiment (SPRUCE). Simulated water table levels compared well with site-level observations. The new model predicts significant hydrologic changes in response to planned warming at the SPRUCE site. At present, standing water is commonly observed in bog hollows after large rainfall events during the growing season, but simulations suggest a sharp decrease in water table levels due to increased evapotranspiration under the most extreme warming level, nearly eliminating the occurrence of standing water in the growing season. Simulated soil energy balance was strongly influenced by reduced winter snowpack under warming simulations, with the warming influence on soil temperature partly offset by the loss of insulating snowpack in early and late winter. The new model provides improved predictive capacity for seasonal hydrological dynamics in northern peatlands, and provides a useful foundation for investigation of northern peatland carbon exchange.« less

Geochemical evolution of acidic ground water at a reclaimed surface coal mine in western Pennsylvania

USGS Publications Warehouse

Cravotta,, Charles A.

1991-01-01

Concentrations of dissolved sulfate and acidity in ground water increase downflow in mine spoil and underlying bedrock at a reclaimed surface coal mine in the bituminous field of western Pennsylvania. Elevated dissolved sulfate and negligible oxygen in ground water from bedrock about 100 feet below the water table suggest that pyritic sulfur is oxidized below the water table, in a system closed to oxygen. Geochemical models for the oxidation of pyrite (FeS2) and production of sulfate (SO42-) and acid (H+) are presented to explain the potential role of oxygen (O2) and ferric iron (Fe3+) as oxidants. Oxidation of pyrite by O2 and Fe3+ can occur under oxic conditions above the water table, whereas oxidation by Fe3+ also can occur under anoxic conditions below the water table. The hydrated ferric-sulfate minerals roemerite [Fe2+Fe43+(SO4)4·14H2O], copiapite [Fe2+Fe43+(SO4)6(OH)2·20H20], and coquimbite [Fe2(SO4)3·9H2O] were identified with FeS2 in coal samples, and form on the oxidizing surface of pyrite in an oxic system above the water table. These soluble ferric-sulfate 11 salts11 can dissolve with recharge waters or a rising water table releasing Fe3+, SO42-. and H+, which can be transported along closed-system ground-water flow paths to pyrite reaction sites where O2 may be absent. The Fe3+ transported to these sites can oxidize pyritic sulfur. The computer programs WATEQ4F and NEWBAL were used to compute chemical speciation and mass transfer, respectively, considering mineral dissolution and precipitation reactions plus mixing of waters from different upflow zones. Alternative mass-balance models indicate that (a) extremely large quantities of O2, over 100 times its aqueous solubility, can generate the observed concentrations of dissolved SO42- from FeS2, or (b) under anoxic conditions, Fe3+ from dissolved ferric-sulfate minerals can oxidize FeS2 along closed-system ground-water flow paths. In a system open to O2, such as in the unsaturated zone, the aqueous solubility of O2 is not limiting, and oxidation of pyrite by O2 and Fe3+ accounts for most SO42- and Fe2+ observed in acidic ground water. However, in a system closed to O2, such as in the saturated zone, O2 solubility is limiting; hence, ferric oxidation of pyrite is a reasonable explanation for the observed elevated SO42- with increasing depth below the water table.

Growth and nutrient status of black spruce seedlings as affected by water table depth

Treesearch

Miroslaw M. Czapowskyj; Robert V. Rourke; Walter J. Grant; Walter J. Grant

1986-01-01

The objective of this study was to determine the effect of different soil water table levels on growth, biomass production, and nutrient accumulation in black spruce seedlings growing under greenhouse conditions over three growing seasons after transplanting.

Directional solidification at ultra-high thermal gradient

NASA Technical Reports Server (NTRS)

Flemings, M. C.; Lee, D. S.; Neff, M. A.

1980-01-01

A high gradient controlled solidification (HGC) furnace was designed and operated at gradients up to 1800 C/cm to continuously produce aluminum alloys. Rubber '0' rings for the water cooling chamber were eliminated, while still maintaining water cooling directly onto the solidified metal. An HGC unit for high temperature ferrous alloys was also designed. Successful runs were made with cast iron, at thermal gradients up to 500 C/cm.

Optical Properties of Nanocellulose Dispersions in Water, Dimethylformamide and Poly(Methyl Methacrylate)

DTIC Science & Technology

2013-10-01

measurements for cellulose and PMMA thin- films . ..13  v List of Tables Table 1. Recorded optical data for nanocellulose in water...applications beyond thin films . In particular, the effects of nanocellulose fibers in higher concentrations, processed in different solvents, and...Optical Properties of Nanocellulose Dispersions in Water, Dimethylformamide and Poly(Methyl Methacrylate) by James F. Snyder, Joshua Steele

46 CFR 180.200 - Survival craft-general.

Code of Federal Regulations, 2014 CFR

2014-10-01

... in Table 180.200(c). Table 180.200(c) Route Survival craft requirements Oceans (a) cold water 1—100...(b). Coastwise (a) wood vsls in cold water. (i) 67% IBA—§ 180.204(a)(1). (ii) w/subdivision—100% LF... 20 miles from a harbor of safe refuge) (a) wood vsls in cold water.(i) 67% IBA—§ 180.205(a)(1). (ii...

Radionuclides in ground water of the Carson River Basin, western Nevada and eastern California, U.S.A.

USGS Publications Warehouse

Thomas, J.M.; Welch, A.H.; Lico, M.S.; Hughes, J.L.; Whitney, R.

1993-01-01

Ground water is the main source of domestic and public supply in the Carson River Basin. Ground water originates as precipitation primarily in the Sierra Nevada in the western part of Carson and Eagle Valleys, and flows down gradient in the direction of the Carson River through Dayton and Churchill Valleys to a terminal sink in the Carson Desert. Because radionuclides dissolved in ground water can pose a threat to human health, the distribution and sources of several naturally occurring radionuclides that contribute to gross-alpha and gross-beta activities in the study area were investigated. Generally, alpha and beta activities and U concentration increase from the up-gradient to down-gradient hydrographic areas of the Carson River Basin, whereas 222Rn concentration decreases. Both 226Ra and 228Ra concentrations are similar throughout the study area. Alpha and beta activities and U concentration commonly exceed 100 pCi/l in the Carson Desert at the distal end of the flow system. Radon-222 commonly exceeds 2,000 pCi/l in the western part of Carson and Eagle Valleys adjacent to the Sierra Nevada. Radium-226 and 228Ra concentrations are <5 pCi/l. Four ground water samples were analyzed for 210Po and one sample contained a high concentration of 21 pCi/l. Seven samples were analyzed for 210Pb; six contained <3 pCi/l and one contained 12 pCi/l. Thorium-230 was detected at concentrations of 0.15 and 0.20 pCi/l in two of four samples. Alpha-emitting radionuclides in the ground water originated from the dissolution of U-rich granitic rocks in the Sierra Nevada by CO2, oxygenated water. Dissolution of primary minerals, mainly titanite (sphene) in the granitic rocks, releases U to the water. Dissolved U is probably removed from the water by adsorption on Fe- and Mn-oxide coatings on fracture surfaces and fine-grained sediment, by adsorption on organic matter, and by coprecipitation with Fe and Mn oxides. These coated sediments are transported throughout the basin by fluvial processes. Thus, U is transported as dissolved and adsorbed species. A rise in the water table in the Carson Desert because of irrigation has resulted in the oxidation of U-rich organic matter and dissolution of U-bearing coatings on sediments, producing unusually high U concentration in the ground water. Alpha activity in the ground water is almost entirely from the decay of U dissolved in the water. Beta activity in ground water samples is primarily from the decay of 40K dissolved in the water and ingrowth of 238U progeny in the sample before analysis. Approximately one-half of the measured beta activity may not be present in ground water in the aquifer, but instead is produced in the sample after collection and before analysis. Potassium-40 is primarily from the dissolution of K-containing minerals, probably K-feldspar and biotite. Radon-222 is primarily from the decay of 226Ra in the aquifer materials. Radium in the ground water is thought to be mainly from alpha recoil associated with the decay of Th in the aquifer material. Some Ra may be from dissolution (or desorption) or Ra-rich coatings on sediments. ?? 1993.

Evaluation of a mechanistic algorithm to calculate the influence of a shallow water table on hydrology sediment and pesticide transport through vegetative filter strips

NASA Astrophysics Data System (ADS)

Lauvernet, C.; Munoz-Carpena, R.; Carluer, N.

2012-04-01

Natural or introduced areas of vegetation, also known as vegetative filter strips (VFS), are a common environmental control practice to protect surface water bodies from human influence. In Europe, VFS are placed along the water network to protect from agrochemical drift during applications, in addition to runoff control. Their bottomland placement next to the streams often implies the presence of a seasonal shallow water table which can have a profound impact on the efficiency of the buffer zone (Lacas et al. 2005). A physically-based algorithm describing ponded infiltration into soils bounded by a water table, proposed by Salvucci and Enthekabi (1995), was further developed to simulate VFS dynamics by making it explicit in time, account for unsteady rainfall conditions, and by coupling to a numerical overland flow and transport model (VFSMOD) (Munoz-Carpena et al., submitted). In this study, we evaluate the importance of the presence of a shallow water table on filter efficiency (reductions in runoff, sediment and pesticide mass), in the context of all other input factors used to describe the system. Global sensitivity analysis (GSA) was used to rank the important input factors and the presence of interactions, as well as the contribution of the important factors to the output variance. GSA of VSFMOD modified for shallow water table was implemented on 2 sites selected in France because they represent different agro-pedo-climatic conditions for which we can compare the role of the factors influencing the performance of grassed buffer strips for surface runoff, sediment and pesticide removal. The first site at Morcille watershed in the Beaujolais wineyard (Rhône-Alpes) contains a very permeable sandy-clay with water table depth varying with the season (very deep in summer and shallow in winter), with a high slope (20 to 30%), and subject to strong seasonal storms (semi-continental, Mediterranean climate). The second site at La Jailliere (Loire-Atlantique, ARVALIS-Institut du Végétal, mainly wheat and maize) is a poorly permeable medium loamy over clay soil, with possible local shallow water tables, slopes around 3% and mild and rainy winter while summer is cool and wet (temperate, oceanic climate). GSA allowed us to interpret the results from the multivariate Monte-Carlo uncertainty analysis and gain insights on the management and placement of the buffer systems.

Tafilalet OASIS System: Water Resources Management and Investigation by GIS and Groundwater Flow Model

NASA Astrophysics Data System (ADS)

Bouaamlat, I.; Larabi, A.; Faouzi, M.

2014-12-01

The geographical location of Tafilalet oasis system (TOS) in the south of the valley of Ziz (Morocco) offers him a particular advantage on the plane of water potential. The surface water which comes from humid regions of the High Atlas and intercepted by a dam then converged through the watercourse of Ziz towards the plain of the TOS, have created the conditions for the formation of a water table relatively rich with regard to the local climatic conditions (arid climate with recurrent drought). Given the role of the water table in the economic development of the region, a hydrogeological study was conducted to understand the impact of artificial recharge and recurrent droughts on the development of the groundwater reserves of TOS. In this study, a three-dimensional model of groundwater flow was developed for the TOS, to assist the decision makers as a "management tool" in order to assess alternative schemes for development and exploitation of groundwater resources based on the variation of artificial recharge and drought. The results from this numerical investigation of the TOS aquifer shows that the commissioning of the dam to control the flows of extreme flood and good management of water releases, has avoided the losses of irrigation water and consequently the non-overexploitation of the groundwater. So that with one or two water releases per year from the dam of flow rate more than 28 million m3/year it is possible to reconstruct the volume of water abstracted by wells. The idea of lowering water table by pumping wells is not exactly true, as well the development of groundwater abstraction has not prevented the wound of water table in these last years, the pumping wells accompanied more than it triggers the lowering of water table and it is mainly the succession of dry periods causing the decreases of the piezometric level. This situation confirms the important role that groundwater plays as a "buffer" during the drought periods.

A high-resolution land model coupled with groundwater lateral flow, human water regulation and the changes in soil freeze-thaw fronts

NASA Astrophysics Data System (ADS)

Xie, Z.; Zeng, Y.; Liu, S.; Gao, J.; Jia, B.; Qin, P.

2017-12-01

Both anthropogenic water regulation and groundwater lateral flow essentially affect groundwater table patterns. Their relationship is close because lateral flow recharges the groundwater depletion cone, which is induced by over-exploitation. And the movement of frost and thaw fronts (FTFs) affects soil water and thermal characteristics, as well as energy and water exchanges between land surface and the atmosphere. In this study, schemes describing groundwater lateral flow, human water regulation and the changes in soil freeze-thaw fronts were developed and incorporated into the Community Land Model 4.5. Then the model was applied in Heihe River Basin(HRB), an arid and semiarid region, northwest China. High resolution ( 1 km) numerical simulations showed that groundwater lateral flow driven by changes in water heads can essentially change the groundwater table pattern with the deeper water table appearing in the hillslope regions and shallower water table appearing in valley bottom regions and plains. Over the last decade, anthropogenic groundwater exploitation deepened the water table by approximately 2 m in the middle reaches of the HRB and rapidly reduced the terrestrial water storage, while irrigation increased soil moisture by approximately 0.1 m3 m-3. The water stored in the mainstream of the Heihe River was also reduced by human surface water withdrawal. The latent heat flux was increased by 30 W m-2 over the irrigated region, with an identical decrease in sensible heat flux. The simulated groundwater lateral flow was shown to effectively recharge the groundwater depletion cone caused by over-exploitation. The offset rate is higher in plains than mountainous regions. In addition, the simulated FTFs depth compared well with the observed data both in D66 station (permafrost) and Hulugou station (seasonally frozen ground). Over the HRB, the upstream area is permafrost region with maximum thawed depth at 2.5 m and lower region is seasonal frozen ground region with maximum frozen depth at 3 m.

Experimental Study on the Flow Regimes and Pressure Gradients of Air-Oil-Water Three-Phase Flow in Horizontal Pipes

PubMed Central

Al-Hadhrami, Luai M.; Shaahid, S. M.; Tunde, Lukman O.; Al-Sarkhi, A.

2014-01-01

An experimental investigation has been carried out to study the flow regimes and pressure gradients of air-oil-water three-phase flows in 2.25 ID horizontal pipe at different flow conditions. The effects of water cuts, liquid and gas velocities on flow patterns and pressure gradients have been studied. The experiments have been conducted at 20°C using low viscosity Safrasol D80 oil, tap water and air. Superficial water and oil velocities were varied from 0.3 m/s to 3 m/s and air velocity varied from 0.29 m/s to 52.5 m/s to cover wide range of flow patterns. The experiments were performed for 10% to 90% water cuts. The flow patterns were observed and recorded using high speed video camera while the pressure drops were measured using pressure transducers and U-tube manometers. The flow patterns show strong dependence on water fraction, gas velocities, and liquid velocities. The observed flow patterns are stratified (smooth and wavy), elongated bubble, slug, dispersed bubble, and annular flow patterns. The pressure gradients have been found to increase with the increase in gas flow rates. Also, for a given superficial gas velocity, the pressure gradients increased with the increase in the superficial liquid velocity. The pressure gradient first increases and then decreases with increasing water cut. In general, phase inversion was observed with increase in the water cut. The experimental results have been compared with the existing unified Model and a good agreement has been noticed. PMID:24523645

Experimental study on the flow regimes and pressure gradients of air-oil-water three-phase flow in horizontal pipes.

PubMed

Al-Hadhrami, Luai M; Shaahid, S M; Tunde, Lukman O; Al-Sarkhi, A

2014-01-01

An experimental investigation has been carried out to study the flow regimes and pressure gradients of air-oil-water three-phase flows in 2.25 ID horizontal pipe at different flow conditions. The effects of water cuts, liquid and gas velocities on flow patterns and pressure gradients have been studied. The experiments have been conducted at 20 °C using low viscosity Safrasol D80 oil, tap water and air. Superficial water and oil velocities were varied from 0.3 m/s to 3 m/s and air velocity varied from 0.29 m/s to 52.5 m/s to cover wide range of flow patterns. The experiments were performed for 10% to 90% water cuts. The flow patterns were observed and recorded using high speed video camera while the pressure drops were measured using pressure transducers and U-tube manometers. The flow patterns show strong dependence on water fraction, gas velocities, and liquid velocities. The observed flow patterns are stratified (smooth and wavy), elongated bubble, slug, dispersed bubble, and annular flow patterns. The pressure gradients have been found to increase with the increase in gas flow rates. Also, for a given superficial gas velocity, the pressure gradients increased with the increase in the superficial liquid velocity. The pressure gradient first increases and then decreases with increasing water cut. In general, phase inversion was observed with increase in the water cut. The experimental results have been compared with the existing unified Model and a good agreement has been noticed.

Water budgets for major streams in the Central Valley, California, 1961-77

USGS Publications Warehouse

Mullen, J.R.; Nady, Paul

1985-01-01

A compilation of annual streamflow data for 20 major stream systems in the central Valley of California, for water years 1961-77, is presented. The water-budget tables list gaged and ungaged inflow from tributaries and canals, diversions, and gaged outflow. Theoretical outflow and gain or loss in a reach are computed. A schematic diagram and explanation of the data are provided for each water-budget table. (USGS)

Water Table Depth Reconstruction in Ombrotrophic Peatlands Using Biomarker Abundance Ratios and Compound-Specific Hydrogen Isotope Composition

NASA Astrophysics Data System (ADS)

Nichols, J. E.; Jackson, S. T.; Booth, R. K.; Pendall, E. G.; Huang, Y.

2005-12-01

Sediment cores from ombrotrophic peat bogs provide sensitive records of changes in precipitation/evaporation (P/E) balance. Various proxies have been developed to reconstruct surface moisture conditions in peat bogs, including testate amoebae, plant macrofossils, and peat humification. Studying species composition of testate amoeba assemblages is time consuming and requires specialized training. Humification index can be influenced by environmental factors other than moisture balance. The plant macrofossil proxy is less quantitative and cannot be performed on highly decomposed samples. We demonstrate that the ratio of C23 alkane to C29 alkane abundance may provide a simple alternative or complementary means of tracking peatland water-table depth. Data for this proxy can be collected quickly using a small sample (100 mg dry). Water-table depth decreases during drought, and abundance of Sphagnum, the dominant peat-forming genus, decreases as vascular plants increase. Sphagnum moss produces mainly medium chain-length alkanes (C21-C25) while vascular plants (grasses and shrubs) produce primarily longer chain-length alkanes (C27-C31). Therefore, C23:C29 n-alkane ratios quantitatively track the water table depth fluctuations in peat bogs. We compared C23:C29 n-alkane ratios in a core from Minden Bog (southeastern Michigan) with water table depth reconstructions based on testate-amoeba assemblages and humification. The 184-cm core spans the past ~3kyr of continuous peat deposition in the bog. Our results indicate that the alkane ratios closely track the water table depth variations, with C29 most abundant during droughts. We also explored the use of D/H ratios in Sphagnum biomarkers as a water-table depth proxy. Compound-specific hydrogen isotope ratio analyses were performed on Sphagnum biomarkers: C23 and C25 alkane and C24 acid. Dry periods are represented in these records by an enrichment of deuterium in these Sphagnum-specific compounds. These events also correlate with drought events in the testate amoeba record and the alkane abundance ratio record. These biogeochemical proxies can be used in paleohydrological studies of ombrotrophic bogs and provide a new and complimentary source of data from these underutilized paleoclimate archives.

Angle-domain common imaging gather extraction via Kirchhoff prestack depth migration based on a traveltime table in transversely isotropic media

NASA Astrophysics Data System (ADS)

Liu, Shaoyong; Gu, Hanming; Tang, Yongjie; Bingkai, Han; Wang, Huazhong; Liu, Dingjin

2018-04-01

Angle-domain common image-point gathers (ADCIGs) can alleviate the limitations of common image-point gathers in an offset domain, and have been widely used for velocity inversion and amplitude variation with angle (AVA) analysis. We propose an effective algorithm for generating ADCIGs in transversely isotropic (TI) media based on the gradient of traveltime by Kirchhoff pre-stack depth migration (KPSDM), as the dynamic programming method for computing the traveltime in TI media would not suffer from the limitation of shadow zones and traveltime interpolation. Meanwhile, we present a specific implementation strategy for ADCIG extraction via KPSDM. Three major steps are included in the presented strategy: (1) traveltime computation using a dynamic programming approach in TI media; (2) slowness vector calculation by the gradient of a traveltime table calculated previously; (3) construction of illumination vectors and subsurface angles in the migration process. Numerical examples are included to demonstrate the effectiveness of our approach, which henceforce shows its potential application for subsequent tomographic velocity inversion and AVA.

Nitrogen Inputs and Transformations in a Boreal Wetland: Hypotheses and Preliminary Results From the Alaska Peatland Experiment (APEX)

NASA Astrophysics Data System (ADS)

Millar, N.; O'Donnell, J. A.; Turetsky, M. R.

2005-12-01

High latitudes are expected to experience some of the most dramatic effects of climate change in the near future. This is already evident from existing permafrost and air temperature records in Alaska. Peatlands are a major component of boreal landscapes and store massive reservoirs of soil organic carbon (C) and nitrogen (N), yet the vulnerability of these organic matter stocks to climate change is poorly understood. While some field studies have focused on N cycling in bogs, little is known about N inputs and transformations within boreal fens. We recently initiated a large scale manipulation of soil temperature and water table in a moderately rich fen situated near the Bonanza Creek LTER site, outside Fairbanks, Alaska (the Alaska Peatland Experiment or APEX; www.apex.msu.edu). As part of this experiment, we hypothesized that water table height regulates microbial reduction - oxidation (redox) reactions in organic soils. This may alter the potential for nitrification and denitrification, and therefore, concentrations of ammonium (NH4+), and nitrate (NO3-), and fluxes of nitrous oxide (N2O) in fen ecosystems. Denitrification however, may be limited by low NO3- concentrations in this fen, which is dominated by a mix of herbaceous species, brown mosses, and Sphagnum. We also hypothesized that warming would increase N transformation rates by stimulating heterotrophic microbial activity, leading to variation in N mineralization rates and N availability. We established three water table plots (control, raised, lowered), each about 120 m2 in area. Water table levels at the lowered and raised plots were manipulated using drainage ditches and solar powered pumping techniques, respectively, and were kept at between 5-10 cm below and at 5 cm above the control plot. At 3 of the 6 sub plots within each water table plot, we constructed replicate open top chambers (OTCs) to passively increase surface temperatures by about 1 ° C. In the first season of measurements at the APEX, our initial results suggest that higher water table levels increase atmospheric N2O concentrations above the soil surface (400 ± 3 and 380 ± 7 ppbv, at raised and lowered water table level, respectively). We also measured lower dissolved N2O concentrations in soil water (37 and 4 ppbv at raised and lowered water table level, respectively at 100 cm depth). Here, we will present interactions between thermal and moisture regimes in the experimental fen in relation to N balance, by quantifying concentrations of various N species (e.g., NH4+, NO3-, N2O, TDN, DON, DIN) in the soil, water and atmosphere. This work will help define the role of N availability and N transformations in boreal peatland ecosystems in feedbacks to global climate change.

Intrinsic diffusion sensitivity of the balanced steady-state free precession (bSSFP) imaging sequence.

PubMed

Bär, Sébastien; Weigel, Matthias; von Elverfeldt, Dominik; Hennig, Jürgen; Leupold, Jochen

2015-11-01

The purpose of this work was to analyze the intrinsic diffusion sensitivity of the balanced steady-state free precession (bSSFP) imaging sequence, meaning the observation of diffusion-induced attenuation of the bSSFP steady-state signal due to the imaging gradients. Although these diffusion effects are usually neglected for most clinical gradient systems, such strong gradient systems are employed for high resolution imaging of small animals or MR Microscopy. The impact on the bSSFP signal of the imaging gradients characterized by their b-values was analyzed with simulations and experiments at a 7T animal scanner using a gradient system with maximum gradient amplitude of approx. 700 mT/m. It was found that the readout gradients have a stronger impact on the attenuation than the phase encoding gradients. Also, as the PE gradients are varying with each repetition interval, the diffusion effects induce strong modulations of the bSSFP signal over the sequence repetition cycles depending on the phase encoding gradient table. It is shown that a signal gain can be obtained through a change of flip angle as a new optimal flip angle maximizing the signal can be defined. The dependency of the diffusion effects on relaxation times and b-values were explored with simulations. The attenuation increases with T2. In conclusion, diffusion attenuation of the bSSFP signal becomes significant for high resolution imaging voxel size (roughly < 100 μm) of long T2 substances. Copyright © 2015 John Wiley & Sons, Ltd.

Comparison of specific-yield estimates for calculating evapotranspiration from diurnal groundwater-level fluctuations

NASA Astrophysics Data System (ADS)

Gribovszki, Zoltán

2018-05-01

Methods that use diurnal groundwater-level fluctuations are commonly used for shallow water-table environments to estimate evapotranspiration (ET) and recharge. The key element needed to obtain reliable estimates is the specific yield (Sy), a soil-water storage parameter that depends on unsaturated soil-moisture and water-table fluxes, among others. Soil-moisture profile measurement down to the water table, along with water-table-depth measurements, can provide a good opportunity to calculate Sy values even on a sub-daily scale. These values were compared with Sy estimates derived by traditional techniques, and it was found that slug-test-based Sy values gave the most similar results in a sandy soil environment. Therefore, slug-test methods, which are relatively cheap and require little time, were most suited to estimate Sy using diurnal fluctuations. The reason for this is that the timeframe of the slug-test measurement is very similar to the dynamic of the diurnal signal. The dynamic characteristic of Sy was also analyzed on a sub-daily scale (depending mostly on the speed of drainage from the soil profile) and a remarkable difference was found in Sy with respect to the rate of change of the water table. When comparing constant and sub-daily (dynamic) Sy values for ET estimation, the sub-daily Sy application yielded higher correlation, but only a slightly smaller deviation from the control ET method, compared with the usage of constant Sy.

Geohydrology of the Unconsolidated Valley-Fill Aquifer in the Meads Creek Valley, Schuyler and Steuben Counties, New York

USGS Publications Warehouse

Miller, Todd S.; Bugliosi, Edward F.; Reddy, James E.

2008-01-01

The Meads Creek valley encompasses 70 square miles of predominantly forested uplands in the upper Susquehanna River drainage basin. The valley, which was listed as a Priority Waterbody by the New York State Department of Environmental Conservation in 2004, is prone to periodic flooding, mostly in its downstream end, where development is occurring most rapidly. Hydraulic characteristics of the unconsolidated valley-fill aquifer were evaluated, and seepage rates in losing and gaining tributaries were calculated or estimated, in an effort to delineate the aquifer geometry and identify the factors that contribute to flooding. Results indicated that (1) Meads Creek gained about 61 cubic feet of flow per second (about 6.0 cubic feet per second per mile of stream channel) from ground-water discharge and inflow from tributaries in its 10.2-mile reach between the northernmost and southernmost measurement sites; (2) major tributaries in the northern part of the valley are not significant sources of recharge to the aquifer; and (3) major tributaries in the central and southern part of the valley provide recharge to the aquifer. The ground-water portion of streamflow in Meads Creek (excluding tributary inflow) was 11.3 cubic feet per second (ft3/s) in the central part of the valley and 17.2 ft3/s in the southern part - a total of 28.5 ft3/s. Ground-water levels were measured in 29 wells finished in unconfined deposits for construction of a potentiometric-surface map to depict directions of ground-water flow within the valley. In general, ground water flows from the edges of the valley toward Meads Creek and ultimately discharges to it. The horizontal hydraulic gradient for the entire 12-mile-long aquifer averages about 30 feet per mile, whereas the gradient in the southern fourth of the valley averages about half that - about 17 feet per mile. A water budget for the aquifer indicated that 28 percent of recharge was derived from precipitation that falls on the aquifer, 32 percent was from losing reaches of tributaries, 38 percent was unchanneled flow from hillsides that slope toward the valley (this estimate includes runoff and shallow ground-water inflow from till and bedrock), and the remaining 2 percent was from deep ground-water inflow from till and bedrock to the sides and bottom of the aquifer. Nearly all (94 percent) of the water discharged from the aquifer is equivalent to the streamflow gain in Meads Creek; the remaining 6 percent discharges as deep outflow to unconsolidated deposits in the Cohocton River valley. Several characteristics of the Meads Creek valley may contribute to flooding in the downstream area: (1) the southward decrease in the ground-water gradient impedes the ability of the aquifer to transmit water southward and can cause water levels to rise, (2) a high water table, typically only 5 to 10 feet below land surface, results in little storage capacity to absorb water from large storms, (3) a downstream narrowing of the valley impedes the southward flow of ground water and can cause water levels to rapidly rise during periods of prolonged or heavy precipitation, and (4) the upland slopes (till-covered bedrock) produce rapid runoff that recharges the aquifer. The combined effect of these conditions limits the ability of the aquifer to transmit sudden, large increases in recharge from precipitation and thereby provides a high potential for flooding in the southern third of the valley.

Summer carbon dioxide and water vapor fluxes across a range of northern peatlands

NASA Astrophysics Data System (ADS)

Humphreys, Elyn R.; Lafleur, Peter M.; Flanagan, Lawrence B.; Hedstrom, Newell; Syed, Kamran H.; Glenn, Aaron J.; Granger, Raoul

2006-12-01

Northern peatlands are a diverse group of ecosystems varying along a continuum of hydrological, chemical, and vegetation gradients. These ecosystems contain about one third of the global soil carbon pool, but it is uncertain how carbon and water cycling processes and response to climate change differ among peatland types. This study examines midsummer CO2 and H2O fluxes measured using the eddy covariance technique above seven northern peatlands including a low-shrub bog, two open poor fens, two wooded moderately rich fens, and two open extreme-rich fens. Gross ecosystem production and ecosystem respiration correlated positively with vegetation indices and with each other. Consequently, 24-hour net ecosystem CO2 exchange was similar among most of the sites (an average net carbon sink of 1.5 ± 0.2 g C m-2 d-1) despite large differences in water table depth, water chemistry, and plant communities. Evapotranspiration was primarily radiatively driven at all sites but a decline in surface conductance with increasing water vapor deficit indicated physiological restrictions to transpiration, particularly at the peatlands with woody vegetation and less at the peatlands with 100% Sphagnum cover. Despite these differences, midday evapotranspiration ranged only from 0.21 to 0.34 mm h-1 owing to compensation among the factors controlling evapotranspiration. Water use efficiency varied among sites primarily as a result of differences in productivity and plant functional type. Although peatland classification includes a great variety of ecosystem characteristics, peatland type may not be an effective way to predict the magnitude and characteristics of midsummer CO2 and water vapor exchanges.

Mineralogy of fine-grained alluvium from borehole U11g, expl. 1, northern Frenchman Flat area, Nevada Test Site

USGS Publications Warehouse

Jones, B.F.

1982-01-01

The mineralogy of matrix fines in alluvium from borehole Ullg, expl. 1, north of Frenchman Flat, Nevada Test Site, has been examined for evidence of past variations in water table elevation. Although greater abundance of zeolite and slightly more expanded basal spacings in smectite clays suggest effects of increased hydration of material up to 50 m above the present water table, these differences might also be related to provenance of environment of deposition. The relative uniformity of clay hydration properties in the 50 meters above the current water table suggest long-term stability near the present level. (USGS)

Filling the gap: using non-invasive geophysical methods to monitor the processes leading to enhanced carbon turnover induced by periodic water table fluctuations

NASA Astrophysics Data System (ADS)

Mellage, A.; Pronk, G.; Atekwana, E. A.; Furman, A.; Rezanezhad, F.; Van Cappellen, P.

2017-12-01

Subsurface transition environments such as the capillary fringe are characterized by steep gradients in redox conditions. Spatial and temporal variations in electron acceptor and donor availability - driven by hydrological changes - may enhance carbon turnover, in some cases resulting in pulses of CO2-respiration. Filling the mechanistic knowledge gap between the hydrological driver and its biogeochemical effects hinges on our ability to monitor microbial activity and key geochemical markers at a high spatial and temporal resolution. However, direct access to subsurface biogeochemical processes is logistically difficult, invasive and usually expensive. In-line, non-invasive geophysical techniques - Spectral Induced Polarization (SIP) and Electrodic Potential (EP), specifically - offer a comparatively inexpensive alternative and can provide data with high spatial and temporal resolution. The challenge lies in linking electrical responses to specific changes in biogeochemical processes. We conducted SIP and EP measurements on a soil column experiment where an artificial soil mixture was subjected to monthly drainage and imbibition cycles. SIP responses showed a clear dependence on redox zonation and microbial abundance. Temporally variable responses exhibited no direct moisture dependence suggesting that the measured responses recorded changes in microbial activity and coincided with the depth interval over which enhanced carbon turnover was observed. EP measurements detected the onset of sulfate mineralization and mapped its depth zonation. SIP and EP signals thus detected enhanced microbial activity within the water table fluctuation zone as well as the timing of the development of specific reactive processes. These findings can be used to relate measured electrical signals to specific reaction pathways and help inform reactive transport models, increasing their predictive capabilities.

Simulation of hydrodynamics, temperature, and dissolved oxygen in Table Rock Lake, Missouri, 1996-1997

USGS Publications Warehouse

Green, W. Reed; Galloway, Joel M.; Richards, Joseph M.; Wesolowski, Edwin A.

2003-01-01

Outflow from Table Rock Lake and other White River reservoirs support a cold-water trout fishery of substantial economic yield in south-central Missouri and north-central Arkansas. The Missouri Department of Conservation has requested an increase in existing minimum flows through the Table Rock Lake Dam from the U.S. Army Corps of Engineers to increase the quality of fishable waters downstream in Lake Taneycomo. Information is needed to assess the effect of increased minimum flows on temperature and dissolved- oxygen concentrations of reservoir water and the outflow. A two-dimensional, laterally averaged, hydrodynamic, temperature, and dissolved-oxygen model, CE-QUAL-W2, was developed and calibrated for Table Rock Lake, located in Missouri, north of the Arkansas-Missouri State line. The model simulates water-surface elevation, heat transport, and dissolved-oxygen dynamics. The model was developed to assess the effects of proposed increases in minimum flow from about 4.4 cubic meters per second (the existing minimum flow) to 11.3 cubic meters per second (the increased minimum flow). Simulations included assessing the effect of (1) increased minimum flows and (2) increased minimum flows with increased water-surface elevations in Table Rock Lake, on outflow temperatures and dissolved-oxygen concentrations. In both minimum flow scenarios, water temperature appeared to stay the same or increase slightly (less than 0.37 ?C) and dissolved oxygen appeared to decrease slightly (less than 0.78 mg/L) in the outflow during the thermal stratification season. However, differences between the minimum flow scenarios for water temperature and dissolved- oxygen concentration and the calibrated model were similar to the differences between measured and simulated water-column profile values.

Evaluation and analysis of current compaction methods for FDOT pipe trench backfills in areas of high water tables

DOT National Transportation Integrated Search

1999-01-01

This research project was undertaken to examine the practicality and adequacy of the FDOT specifications regarding compaction methods for pipe trench backfills under high water table. Given the difficulty to determine density and to attain desired de...

Aquifer response to stream-stage and recharge variations. I. Analytical step-response functions

USGS Publications Warehouse

Moench, A.F.; Barlow, P.M.

2000-01-01

Laplace transform step-response functions are presented for various homogeneous confined and leaky aquifer types and for anisotropic, homogeneous unconfined aquifers interacting with perennial streams. Flow is one-dimensional, perpendicular to the stream in the confined and leaky aquifers, and two-dimensional in a plane perpendicular to the stream in the water-table aquifers. The stream is assumed to penetrate the full thickness of the aquifer. The aquifers may be semi-infinite or finite in width and may or may not be bounded at the stream by a semipervious streambank. The solutions are presented in a unified manner so that mathematical relations among the various aquifer configurations are clearly demonstrated. The Laplace transform solutions are inverted numerically to obtain the real-time step-response functions for use in the convolution (or superposition) integral. To maintain linearity in the case of unconfined aquifers, fluctuations in the elevation of the water table are assumed to be small relative to the saturated thickness, and vertical flow into or out of the zone above the water table is assumed to occur instantaneously. Effects of hysteresis in the moisture distribution above the water table are therefore neglected. Graphical comparisons of the new solutions are made with known closed-form solutions.Laplace transform step-response functions are presented for various homogeneous confined and leaky aquifer types and for anisotropic, homogeneous unconfined aquifers interacting with perennial streams. Flow is one-dimensional, perpendicular to the stream in the confined and leaky aquifers, and two-dimensional in a plane perpendicular to the stream in the water-table aquifers. The stream is assumed to penetrate the full thickness of the aquifer. The aquifers may be semi-infinite or finite in width and may or may not be bounded at the stream by a semipervious streambank. The solutions are presented in a unified manner so that mathematical relations among the various aquifer configurations are clearly demonstrated. The Laplace transform solutions are inverted numerically to obtain the real-time step-response functions for use in the convolution (or superposition) integral. To maintain linearity in the case of unconfined aquifers, fluctuations in the elevation of the water table are assumed to be small relative to the saturated thickness, and vertical flow into or out of the zone above the water table is assumed to occur instantaneously. Effects of hysteresis in the moisture distribution above the water table are therefore neglected. Graphical comparisons of the new solutions are made with known closed-form solutions.

A generalized groundwater fluctuation model based on precipitation for estimating water table levels of deep unconfined aquifers

NASA Astrophysics Data System (ADS)

Jeong, Jina; Park, Eungyu; Shik Han, Weon; Kim, Kue-Young; Suk, Heejun; Beom Jo, Si

2018-07-01

A generalized water table fluctuation model based on precipitation was developed using a statistical conceptualization of unsaturated infiltration fluxes. A gamma distribution function was adopted as a transfer function due to its versatility in representing recharge rates with temporally dispersed infiltration fluxes, and a Laplace transformation was used to obtain an analytical solution. To prove the general applicability of the model, convergences with previous water table fluctuation models were shown as special cases. For validation, a few hypothetical cases were developed, where the applicability of the model to a wide range of unsaturated zone conditions was confirmed. For further validation, the model was applied to water table level estimations of three monitoring wells with considerably thick unsaturated zones on Jeju Island. The results show that the developed model represented the pattern of hydrographs from the two monitoring wells fairly well. The lag times from precipitation to recharge estimated from the developed system transfer function were found to agree with those from a conventional cross-correlation analysis. The developed model has the potential to be adopted for the hydraulic characterization of both saturated and unsaturated zones by being calibrated to actual data when extraneous and exogenous causes of water table fluctuation are limited. In addition, as it provides reference estimates, the model can be adopted as a tool for surveilling groundwater resources under hydraulically stressed conditions.

Depth distribution of microbial production and oxidation of methane in northern boreal peatlands.

PubMed

Sundh, I; Nilsson, M; Granberg, G; Svensson, B H

1994-05-01

The depth distributions of anaerobic microbial methane production and potential aerobic microbial methane oxidation were assessed at several sites in both Sphagnum- and sedge-dominated boreal peatlands in Sweden, and compared with net methane emissions from the same sites. Production and oxidation of methane were measured in peat slurries, and emissions were measured with the closed-chamber technique. Over all eleven sites sampled, production was, on average, highest 12 cm below the depth of the average water table. On the other hand, highest potential oxidation of methane coincided with the depth of the average water table. The integrated production rate in the 0-60 cm interval ranged between 0.05 and 1.7 g CH4 m (-2) day(-) and was negatively correlated with the depth of the average water table (linear regression: r (2) = 0.50, P = 0.015). The depth-integrated potential CH4-oxidation rate ranged between 3.0 and 22.1 g CH4 m(-2) day(-1) and was unrelated to the depth of the average water table. A larger fraction of the methane was oxidized at sites with low average water tables; hence, our results show that low net emission rates in these environments are caused not only by lower methane production rates, but also by conditions more favorable for the development of CH4-oxidizing bacteria in these environments.

Geohydrology of the High Energy Laser System Test Facility site, White Sands Missile Range, Tularosa Basin, south-central New Mexico

USGS Publications Warehouse

Basabilvazo, G.T.; Nickerson, E.L.; Myers, R.G.

1994-01-01

The Yesum-HoHoman and Gypsum land (hummocky) soils at the High Energy Laser System Test Facility (HELSTF) represent wind deposits from recently desiccated lacustrine deposits and deposits from the ancestral Lake Otero. The upper 15-20 feet of the subsurface consists of varved gypsiferous clay and silt. Below these surfidai deposits the lithology consists of interbedded clay units, silty-clay units, and fine- to medium-grained quartz arenite units in continuous and discontinuous horizons. Clay horizons can cause perched water above the water table. Analyses of selected clay samples indicate that clay units are composed chiefly of kaolinire and mixed-layer illite/ smectite. The main aquifer is representative of a leaky-confined aquifer. Estimated aquifer properties are: transmissivity (T) = 780 feet squared per day, storage coefficient (S) = 3.1 x 10-3, and hydraulic conductivity (K) = 6.0 feet per day. Ground water flows south and southwest; the estimated hydraulic gradient is 5.3 feet per mile. Analyses of water samples indicate that ground water at the HELSTF site is brackish to slightly saline at the top of the main aquifer. Dissolved-solids concentration near the top of the main aquifer ranges from 5,940 to 11,800 milligrams per liter. Predominant ions are sodium and sulfate. At 815 feet below land surface, the largest dissolved-solids concentration measured is 111,000 milligrams per liter, which indicates increasing salinity with depth. Predominant ions are sodium and chloride.

Treatment of Chlorinated Aliphatic Contamination of Groundwater by Horizontal Recirculation Wells and by Constructed Vertical Flow Wetlands

DTIC Science & Technology

2002-03-01

groundwater laden with contaminants. Once the contaminated water is at the surface, it must be treated for contaminant destruction, generally by...treatment walls only work under very specific hydrogeologic conditions (relatively shallow water table, no seasonal fluctuations in groundwater flow...GCWs Elevation Schematic Water Table Contaminated Groundwater Contaminated Groundwater Treated Groundwater Treated Groundwater Reactive Porous Medium

Forest gradient response in Sierran landscapes: the physical template

USGS Publications Warehouse

Urban, Dean L.; Miller, Carol; Halpin, Patrick N.; Stephenson, Nathan L.

2000-01-01

Vegetation pattern on landscapes is the manifestation of physical gradients, biotic response to these gradients, and disturbances. Here we focus on the physical template as it governs the distribution of mixed-conifer forests in California's Sierra Nevada. We extended a forest simulation model to examine montane environmental gradients, emphasizing factors affecting the water balance in these summer-dry landscapes. The model simulates the soil moisture regime in terms of the interaction of water supply and demand: supply depends on precipitation and water storage, while evapotranspirational demand varies with solar radiation and temperature. The forest cover itself can affect the water balance via canopy interception and evapotranspiration. We simulated Sierran forests as slope facets, defined as gridded stands of homogeneous topographic exposure, and verified simulated gradient response against sample quadrats distributed across Sequoia National Park. We then performed a modified sensitivity analysis of abiotic factors governing the physical gradient. Importantly, the model's sensitivity to temperature, precipitation, and soil depth varies considerably over the physical template, particularly relative to elevation. The physical drivers of the water balance have characteristic spatial scales that differ by orders of magnitude. Across large spatial extents, temperature and precipitation as defined by elevation primarily govern the location of the mixed conifer zone. If the analysis is constrained to elevations within the mixed-conifer zone, local topography comes into play as it influences drainage. Soil depth varies considerably at all measured scales, and is especially dominant at fine (within-stand) scales. Physical site variables can influence soil moisture deficit either by affecting water supply or water demand; these effects have qualitatively different implications for forest response. These results have clear implications about purely inferential approaches to gradient analysis, and bear strongly on our ability to use correlative approaches in assessing the potential responses of montane forests to anthropogenic climatic change.

Pumping strategies for management of a shallow water table: The value of the simulation-optimization approach

USGS Publications Warehouse

Barlow, P.M.; Wagner, B.J.; Belitz, K.

1996-01-01

The simulation-optimization approach is used to identify ground-water pumping strategies for control of the shallow water table in the western San Joaquin Valley, California, where shallow ground water threatens continued agricultural productivity. The approach combines the use of ground-water flow simulation with optimization techniques to build on and refine pumping strategies identified in previous research that used flow simulation alone. Use of the combined simulation-optimization model resulted in a 20 percent reduction in the area subject to a shallow water table over that identified by use of the simulation model alone. The simulation-optimization model identifies increasingly more effective pumping strategies for control of the water table as the complexity of the problem increases; that is, as the number of subareas in which pumping is to be managed increases, the simulation-optimization model is better able to discriminate areally among subareas to determine optimal pumping locations. The simulation-optimization approach provides an improved understanding of controls on the ground-water flow system and management alternatives that can be implemented in the valley. In particular, results of the simulation-optimization model indicate that optimal pumping strategies are constrained by the existing distribution of wells between the semiconfined and confined zones of the aquifer, by the distribution of sediment types (and associated hydraulic conductivities) in the western valley, and by the historical distribution of pumping throughout the western valley.

SU-F-I-24: Feasibility of Magnetic Susceptibility to Relative Electron Density Conversion Method for Radiation Therapy

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

Ito, K; Kadoya, N; Chiba, M

2016-06-15

Purpose: The aim of this study is to develop radiation treatment planning using magnetic susceptibility obtained from quantitative susceptibility mapping (QSM) via MR imaging. This study demonstrates the feasibility of a method for generating a substitute for a CT image from an MRI. Methods: The head of a healthy volunteer was scanned using a CT scanner and a 3.0 T MRI scanner. The CT imaging was performed with a slice thickness of 2.5 mm at 80 and 120 kV (dual-energy scan). These CT images were converted to relative electron density (rED) using the CT-rED conversion table generated by a previousmore » dual-energy CT scan. The CT-rED conversion table was generated using the conversion of the energy-subtracted CT number to rED via a single linear relationship. One T2 star-weighted 3D gradient echo-based sequence with four different echo times images was acquired using the MRI scanner. These T2 star-weighted images were used to estimate the phase data. To estimate the local field map, a Laplacian unwrapping of the phase and background field removal algorithm were implemented to process phase data. To generate a magnetic susceptibility map from the local field map, we used morphology enabled dipole inversion method. The rED map was resampled to the same resolution as magnetic susceptibility, and the magnetic susceptibility-rED conversion table was obtained via voxel-by-voxel mapping between the magnetic susceptibility and rED maps. Results: A correlation between magnetic susceptibility and rED is not observed through our method. Conclusion: Our results show that the correlation between magnetic susceptibility and rED is not observed. As the next step, we assume that the voxel of the magnetic susceptibility map comprises two materials, such as water (0 ppm) and bone (-2.2 ppm) or water and marrow (0.81ppm). The elements of each voxel were estimated from the ratio of the two materials.« less

18 CFR Table 1 to Part 301 - Functionalization and Escalation Codes

Code of Federal Regulations, 2010 CFR

2010-04-01

... 18 Conservation of Power and Water Resources 1 2010-04-01 2010-04-01 false Functionalization and Escalation Codes 1 Table 1 to Part 301 Conservation of Power and Water Resources FEDERAL ENERGY REGULATORY COMMISSION, DEPARTMENT OF ENERGY REGULATIONS FOR FEDERAL POWER MARKETING ADMINISTRATIONS AVERAGE SYSTEM COST...

18 CFR Table 1 to Part 301 - Functionalization and Escalation Codes

Code of Federal Regulations, 2012 CFR

2012-04-01

... 18 Conservation of Power and Water Resources 1 2012-04-01 2012-04-01 false Functionalization and Escalation Codes 1 Table 1 to Part 301 Conservation of Power and Water Resources FEDERAL ENERGY REGULATORY COMMISSION, DEPARTMENT OF ENERGY REGULATIONS FOR FEDERAL POWER MARKETING ADMINISTRATIONS AVERAGE SYSTEM COST...

18 CFR Table 1 to Part 301 - Functionalization and Escalation Codes

Code of Federal Regulations, 2013 CFR

2013-04-01

... 18 Conservation of Power and Water Resources 1 2013-04-01 2013-04-01 false Functionalization and Escalation Codes 1 Table 1 to Part 301 Conservation of Power and Water Resources FEDERAL ENERGY REGULATORY COMMISSION, DEPARTMENT OF ENERGY REGULATIONS FOR FEDERAL POWER MARKETING ADMINISTRATIONS AVERAGE SYSTEM COST...

18 CFR Table 1 to Part 301 - Functionalization and Escalation Codes

Code of Federal Regulations, 2014 CFR

2014-04-01

... 18 Conservation of Power and Water Resources 1 2014-04-01 2014-04-01 false Functionalization and Escalation Codes 1 Table 1 to Part 301 Conservation of Power and Water Resources FEDERAL ENERGY REGULATORY COMMISSION, DEPARTMENT OF ENERGY REGULATIONS FOR FEDERAL POWER MARKETING ADMINISTRATIONS AVERAGE SYSTEM COST...

Denitrification and gas emissions from organic soils under different water-table and flooding management

USDA-ARS?s Scientific Manuscript database

Draining the Florida Everglades for agricultural use has led to land subsidence and increase phosphorus loads to the southern Everglades, environmental concerns which can be limited by controlling water table depth. The resulting anaerobic conditions in saturated soils may lead to increased denitrif...

18 CFR Table 1 to Part 301 - Functionalization and Escalation Codes

Code of Federal Regulations, 2011 CFR

2011-04-01

... 18 Conservation of Power and Water Resources 1 2011-04-01 2011-04-01 false Functionalization and Escalation Codes 1 Table 1 to Part 301 Conservation of Power and Water Resources FEDERAL ENERGY REGULATORY COMMISSION, DEPARTMENT OF ENERGY REGULATIONS FOR FEDERAL POWER MARKETING ADMINISTRATIONS AVERAGE SYSTEM COST...

Controlled laboratory experiments and modeling of vegetative filter strips with shallow water tables

NASA Astrophysics Data System (ADS)

Fox, Garey A.; Muñoz-Carpena, Rafael; Purvis, Rebecca A.

2018-01-01

Natural or planted vegetation at the edge of fields or adjacent to streams, also known as vegetative filter strips (VFS), are commonly used as an environmental mitigation practice for runoff pollution and agrochemical spray drift. The VFS position in lowlands near water bodies often implies the presence of a seasonal shallow water table (WT). In spite of its potential importance, there is limited experimental work that systematically studies the effect of shallow WTs on VFS efficacy. Previous research recently coupled a new physically based algorithm describing infiltration into soils bounded by a water table into the VFS numerical overland flow and transport model, VFSMOD, to simulate VFS dynamics under shallow WT conditions. In this study, we tested the performance of the model against laboratory mesoscale data under controlled conditions. A laboratory soil box (1.0 m wide, 2.0 m long, and 0.7 m deep) was used to simulate a VFS and quantify the influence of shallow WTs on runoff. Experiments included planted Bermuda grass on repacked silt loam and sandy loam soils. A series of experiments were performed including a free drainage case (no WT) and a static shallow water table (0.3-0.4 m below ground surface). For each soil type, this research first calibrated VFSMOD to the observed outflow hydrograph for the free drainage experiments to parameterize the soil hydraulic and vegetation parameters, and then evaluated the model based on outflow hydrographs for the shallow WT experiments. This research used several statistical metrics and a new approach based on hypothesis testing of the Nash-Sutcliffe model efficiency coefficient (NSE) to evaluate model performance. The new VFSMOD routines successfully simulated the outflow hydrographs under both free drainage and shallow WT conditions. Statistical metrics considered the model performance valid with greater than 99.5% probability across all scenarios. This research also simulated the shallow water table experiments with both free drainage and various water table depths to quantify the effect of assuming the former boundary condition. For these two soil types, shallow WTs within 1.0-1.2 m below the soil surface influenced infiltration. Existing models will suggest a more protective vegetative filter strip than what actually exists if shallow water table conditions are not considered.

Controlling Directional Liquid Motion on Micro- and Nanocrystalline Diamond/β-SiC Composite Gradient Films.

PubMed

Wang, Tao; Handschuh-Wang, Stephan; Huang, Lei; Zhang, Lei; Jiang, Xin; Kong, Tiantian; Zhang, Wenjun; Lee, Chun-Sing; Zhou, Xuechang; Tang, Yongbing

2018-01-30

In this Article, we report the synthesis of micro- and nanocrystalline diamond/β-SiC composite gradient films, using a hot filament chemical vapor deposition (HFCVD) technique and its application as a robust and chemically inert means to actuate water and hazardous liquids. As revealed by scanning electron microscopy, the composition of the surface changed gradually from pure nanocrystalline diamond (hydrophobic) to a nanocrystalline β-SiC surface (hydrophilic). Transmission electron microscopy and Raman spectroscopy were employed to determine the presence of diamond, graphite, and β-SiC phases. The as-prepared gradient films were evaluated for their ability to actuate water. Indeed, water was transported via the gradient from the hydrophobic (hydrogen-terminated diamond) to the hydrophilic side (hydroxyl-terminated β-SiC) of the gradient surface. The driving distance and velocity of water is pivotally influenced by the surface roughness. The nanogradient surface showed significant promise as the lower roughness combined with the longer gradient yields in transport distances of up to 3.7 mm, with a maximum droplet velocity of nearly 250 mm/s measured by a high-speed camera. As diamond and β-SiC are chemically inert, the gradient surfaces can be used to drive hazardous liquids and reactive mixtures, which was signified by the actuation of hydrochloric acid and sodium hydroxide solution. We envision that the diamond/β-SiC gradient surface has high potential as an actuator for water transport in microfluidic devices, DNA sensors, and implants, which induce guided cell growth.

Transformations of fluxes and forces describing the simultaneous transport of water and heat in unsaturated porous media

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

Raats, P.A.C.

1975-12-01

Balances of mass for the water in N distinct phases and a balance of heat for the medium as a whole were formulated. Following Philip and de Vries, it was assumed that the flux of water in each phase is proportional to the gradient of the pressure in that phase and that the diffusive component of the flux of heat is proportional to the gradient of the temperature. Clapeyron equations were used to express the gradient of the pressure in any phase in terms of the gradient of the pressure in a reference state and of the temperature. The referencemore » state may be the water in one of the phases or the water in some measuring device such as a tensiometer or a psychrometer. Expressions for the total flux of water and for the diffusive flux of heat plus the convective flux of heat associated with the conversion from any phase to the reference state were shown to satisfy the onsager reciprocal relations. A theorem due to Meixner was used to delineate the class of fluxes and forces that preserves these relations. In particular, it was shown that if the gradients of water content and temperature are used as the driving forces, the onsager relations are no longer satisfied.« less

Dynamic chemistry in the perched groundwater flowing through weathered bedrock underling a steep forested hillslope, north California

NASA Astrophysics Data System (ADS)

Kim, H.; Rempe, D. M.; Bishop, J. K.; Dietrich, W.; Fung, I.; Wood, T. J.

2012-12-01

The spatial and temporal pattern of groundwater chemistry in the seasonally perched groundwater systems that develop in the weathered bedrock zone under hillslopes have rarely been documented, yet chemical evolution of water here dictates the runoff chemistry to streams in many places. Here we exploit an intensively instrumented hillslope to document water well chemistry at three wells and adjacent stream. We have been sampling groundwater at daily frequency since October 2008 on a forested hillslope, "Rivendell", at the Angelo Coast Range Reserve located at the headwaters of the Eel River, California. The site is typical of California's coastal Mediterranean climate. The groundwater samples have been collected from a depth near the boundary between the weathered and fresh bedrock at three locations along the hillslope: Well 1 (bottom of hillslope), Well 3 (mid-slope), and Well 10 (near the ridge). Bulk rainwater and throughfall samples were collected at a meadow across the hillslope and at the middle of the slope, respectively, as well. Near the ridge (Well 10), during the first significant rainstorms of 2009 (133mm/42.5hours) and 2010 (220mm/42hours), when the water table changed only 0.32m and 0.66m, respectively, the concentration of Ca, Mg, and Na started to increase rapidly compared to the dry season (e.g. 2-6 μM vs 0.02-0.2μM [Mg]/day). However, during these same storms, K concentration sharply increased to 50-60 μM and decreased to 20-30μM, synchronizing with the water table responses. Throughfalls of these storms had at least 10 fold lower Ca, Mg, and Na concentrations than the well water while they had 10 fold higher K compared to the pre-event groundwater values. When the total seasonal cumulative rainfall exceeds 600 mm, the Well 10 solute concentration was diluted nearly 3 fold (e.g. [Mg] 0.3 mM vs. 0.1 mM) and the water table was raised significantly (2-6 meters). Throughout the rainy season, Well10 retained its diluted chemistry signature and on average the water table remained elevated as subsequent rainstorms repeatedly recharged the system. Well10 solute concentration slowly increased at the end of the rainy season when the water table fell. In contrast, at the foot of the hill slope, even though the water table was responsive to each rainfall event, its water chemistry developed a strong dilution signatures only during the intense rainstorms (total rainfall > 70mm); the solute concentration decreased (e.g. [Mg] = 0.1mM) during the rising limb of the well hydrograph and recovered back to its pre-event value (e.g. [Mg] = 0.3mM) during the falling limb of the well hydrograph. During small storms, the solute concentration of Well 1 either did not change or slightly increased. Mid-slope showed similar behavior to Well 1. The Well 3 solute concentration was diluted about 3 fold (e.g. [Mg] 0.3mM to 0.1mM) as the water table rose and increased as the water table receded. However unlike Well 1, the water chemistry of Well 3 did not recover to its pre-event composition at any point during the rainy season and the recovery rate was slower than that of Well 1. These water chemistry observations provide insight into the dynamics of water movement within the fractured, weathered bedrock zone, and point to both vertical and lateral mixing processes that influence the chemical evolution of waters.

Biomass production, forage quality, and cation uptake of Quail bush, four-wing saltbush, and seaside barley irrigated with moderately saline-sodic water

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

Bauder, J.W.; Browning, L.S.; Phelps, S.D.

2008-07-01

The study reported here investigated capacity of Atriplex lentiformis (Torr.) S. Wats. (Quail bush), Atriplex X aptera A. Nels. (pro sp.) (Wytana four-wing saltbush), and Hordeum marinum Huds. (seaside barley) to produce biomass and crude protein and take up cations when irrigated with moderately saline-sodic water, in the presence of a shallow water table. Water tables were established at 0.38, 0.76, and 1.14m below the surface in sand-filled columns. The columns were then planted to the study species. Study plants were irrigated for 224 days; irrigation water was supplied every 7 days equal to water lost to evapotranspiration (ET) plusmore » 100mL (the volume of water removed in the most previous soil solution sampling). Water representing one of two irrigation sources was used: Powder River (PR) or coalbed natural gas (CBNG) wastewater. Biomass production did not differ significantly between water quality treatments but did differ significantly among species and water table depth within species. Averaged across water quality treatments, Hordeum marinum produced 79% more biomass than A. lentiformis and 122% more biomass than Atriplex X aptera, but contained only 11% crude protein compared to 16% crude protein in A. lentiformis and 14% crude protein in Atriplex X aptera. Atriplex spp. grown in columns with the water table at 0.38m depth produced more biomass, took up less calcium on a percentage basis, and took up more sodium on a percentage basis than when grown with the water table at a deeper depth. Uptake of cations by Atriplex lentiformis was approximately twice the uptake of cations by Atriplex X aptera and three times that of H. marinum. After 224 days of irrigation, crop growth, and cation uptake, followed by biomass harvest, EC and SAR of shallow groundwater in columns planted to A. lentiformis were less than EC and SAR of shallow ground water in columns planted to either of the other species.« less

Stemflow-induced processes of soil water storage

NASA Astrophysics Data System (ADS)

Germer, Sonja

2013-04-01

Compared to stemflow production studies only few studies deal with the fate of stemflow at the near-stem soil. To investigate stemflow contribution to the root zone soil moisture by young and adult babassu palms (Attalea speciosa Mart.), I studied stemflow generation, subsequent soil water percolation and root distributions. Rainfall, stemflow and perched water tables were monitored on an event basis. Perched water tables were monitored next to adult palms at two depths and three stem distances. Dye tracer experiments monitored stemflow-induced preferential flow paths. Root distributions of fine and coarse roots were related to soil water redistribution. Average rainfall-collecting area per adult palm was 6.4 m², but variability between them was high. Funneling ratios ranged between 16-71 and 4-55 for adult and young palms, respectively. Nonetheless, even very small rainfall events of 1 mm can generate stemflow. On average, 9 liters of adult palm stemflow were intercepted and stemflow tended to decrease for-high intensity rainfall events. Young babassu palms funneled rainfall via their fronds, directly to their subterranean stems. The funneling of rainfall towards adult palm stems, in contrast, led to great stemflow fluxes down to the soil and induced initial horizontal water flows through the soil, leading to perched water tables next to palms, even after small rainfall events. The perched water tables extended, however, only a few decimeters from palm stems. After perched water tables became established, vertical percolation through the soil dominated. To my knowledge, this process has not been described before, and it can be seen as an addition to the two previously described stemflow-induced processes of Horton overland flow and fast, deep percolation along roots. This study has demonstrated that Babassu palms funnel water to their stems and subsequently store it in the soil next to their stems in areas where coarse root length density is very high. This might partly explain the competitive position of babassu palms on pastures or secondary forests.

Predicting Seawater Intrusion in Coastal Groundwater Boreholes Using Self-Potential Data

NASA Astrophysics Data System (ADS)

Graham, M.; MacAllister, D. J.; Jackson, M.; Vinogradov, J.; Butler, A. P.

2017-12-01

Many coastal groundwater abstraction wells are under threat from seawater intrusion: this is exacerbated in summer by low water tables and increased abstraction. Existing hydrochemistry or geophysical techniques often fail to predict the timing of intrusion events. We investigate whether the presence and transport of seawater can influence self-potentials (SPs) measured within groundwater boreholes, with the aim of using SP monitoring to provide early warning of saline intrusion. SP data collection: SP data were collected from a coastal groundwater borehole and an inland borehole (> 60 km from the coast) in the Seaford Chalk of southern England. The SP gradient in the inland borehole was approximately 0.05 mV/m, while that in the coastal borehole varied from 0.16-0.26 mV/m throughout the monitoring period. Spectral analysis showed that semi-diurnal fluctuations in the SP gradient were several orders of magnitude higher at the coast than inland, indicating a strong influence from oceanic tides. A characteristic decrease in the gradient, or precursor, was observed in the coastal borehole several days prior to seawater intrusion. Modelling results: Hydrodynamic transport and geoelectric modelling suggest that observed pressure changes (associated with the streaming potential) are insufficient to explain either the magnitude of the coastal SP gradient or the semi-diurnal SP fluctuations. By contrast, a model of the exclusion-diffusion potential closely matches these observations and produces a precursor similar to that observed in the field. Sensitivity analysis suggests that both a sharp saline front and spatial variations in the exclusion efficiency arising from aquifer heterogeneities are necessary to explain the SP gradient observed in the coastal borehole. The presence of the precursor in the model depends also on the presence and depth of fractures near the base of the borehole. Conclusions: Our results indicate that SP monitoring, combined with hydrodynamic transport and geoelectric modelling, holds considerable promise as an early warning device for seawater intrusion. We now aim to refine our understanding of the technique by applying it to a range of aquifer types.

Geohydrologic framework of the Roswell ground-water basin, Chaves and Eddy Counties, New Mexico

USGS Publications Warehouse

Welder, G.E.

1983-01-01

This report describes the geohydrology of the Roswell ground-water basin and shows the long-term hydrostatic-head changes in the aquifers. The Roswell ground-water basin consists of a carbonate artesian aquifer overlain by a leaky confining bed, which, in turn is overlain by an alluvial water-table aquifer. The water-table aquifer is hydraulically connected to the Pecos River. Ground-water pumpage from about 1,500 wells in the basin was about 378,000 acre-feet in 1978. Irrigation use on about 122,000 acres accounted for 95 percent of that pumpage.

Water resources of Washington Parish, Louisiana

USGS Publications Warehouse

White, Vincent E.; Prakken, Lawrence B.

2016-06-13

In 2010, about 34.55 million gallons per day (Mgal/d) of water were withdrawn in Washington Parish, including about 28.10 Mgal/d from groundwater sources and 6.44 Mgal/d from surface-water sources1 (table 1). Withdrawals for industrial use accounted for about 52 percent (17.80 Mgal/d) of the total water withdrawn (table 2). Other categories of use included public supply, rural domestic, irrigation, and livestock. Water-use data collected at 5-year intervals from 1960 to 2010 (fig. 2) indicated that water withdrawals peaked in 1975 at about 51.9 Mgal/d.

Modelling stream aquifer seepage in an alluvial aquifer: an improved loosing-stream package for MODFLOW

NASA Astrophysics Data System (ADS)

Osman, Yassin Z.; Bruen, Michael P.

2002-07-01

Seepage from a stream, which partially penetrates an unconfined alluvial aquifer, is studied for the case when the water table falls below the streambed level. Inadequacies are identified in current modelling approaches to this situation. A simple and improved method of incorporating such seepage into groundwater models is presented. This considers the effect on seepage flow of suction in the unsaturated part of the aquifer below a disconnected stream and allows for the variation of seepage with water table fluctuations. The suggested technique is incorporated into the saturated code MODFLOW and is tested by comparing its predictions with those of a widely used variably saturated model, SWMS_2D simulating water flow and solute transport in two-dimensional variably saturated media. Comparisons are made of both seepage flows and local mounding of the water table. The suggested technique compares very well with the results of variably saturated model simulations. Most currently used approaches are shown to underestimate the seepage and associated local water table mounding, sometimes substantially. The proposed method is simple, easy to implement and requires only a small amount of additional data about the aquifer hydraulic properties.

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.

Hydrogeological characterization of shallow-depth zone for CO2 injection and leak test at a CO2 environmental monitoring site in Korea

NASA Astrophysics Data System (ADS)

Lee, S. S.; Kim, T. W.; Kim, H. H.; Ha, S. W.; Jeon, W. T.; Lee, K. K.

2015-12-01

The main goal of the this study is to evaluate the importance of heterogeneities in controlling the field-scale transport of CO2 are originated from the CO2 injected at saturated zone below the water table for monitoring and prediction of CO2 leakage from a reservoir. Hydrogeological and geophysical data are collected to characterize the site, prior to conducting CO2 injection experiment at the CO2 environmental monitoring site at Eumseong, Korea. The geophysical data were acquired from borehole electromagnetic flowmeter tests, while the hydraulic data were obtained from pumping tests, slug tests, and falling head permeability tests. Total of 13 wells to perform hydraulic and geophysical test are established along groundwater flow direction in regular sequence, revealed by the results of borehole electromagnetic flowmeter test. The results of geophysical tests indicated that hydraulic gradient is not identical with the topographic gradient. Groundwater flows toward the uphill direction in the study area. Then, the hydraulic tests were conducted to identify the hydraulic properties of the study site. According to the results of pumping and slug tests at the study site, the hydraulic conductivity values show ranges between 4.75 x 10-5 cm/day and 9.74 x 10-5 cm/day. In addition, a portable multi-level sampling and monitoring packer device which remains inflated condition for a long period developed and used to isolate designated depths to identify vertical distribution of hydrogeological characteristics. Hydrogeological information obtained from this study will be used to decide the injection test interval of CO2-infused water and gaseous CO2. Acknowledgement: Financial support was provided by "R&D Project on Environmental Mangement of Geologic CO2 Storage" from the KEITI (Project Number: 2014001810003).

Performance of deep-rooted phreatophytic trees at a site containing total petroleum hydrocarbons.

PubMed

Ferro, Ari M; Adham, Tareq; Berra, Brett; Tsao, David

2013-01-01

Poplar and willow tree stands were installed in 2003 at a site in Raleigh, North Carolina containing total petroleum hydrocarbon - contaminated groundwater. The objective was groundwater uptake and plume control. The water table was 5 to 6 m below ground surface (bgs) and therefore methods were used to encourage deep root development. Growth rates, rooting depth and sap flow were measured for trees in Plot A located in the center of the plume and in Plot B peripheral to the plume. The trees were initially sub-irrigated with vertically installed drip-lines and by 2005 had roots 4 to 5 m bgs. Water balance calculations suggested groundwater uptake. In 2007, the average sap flow was higher for Plot B (approximately 59 L per day per tree) than for Plot A (approximately 23 L per day per tree), probably as a result of TPH-induced stress in Plot A. Nevertheless, the estimated rate of groundwater uptake for Plot A was sufficient, relative to the calculated rate of groundwater flux beneath the stand, that a high level of plume control was achieved based on MODFLOW modeling results. Down-gradient groundwater monitoring wells installed in late 2011 should provide quantitative data for plume control.

Preliminary Water-Table Map and Water-Quality Data for Part of the Matanuska-Susitna Valley, Alaska, 2005

USGS Publications Warehouse

Moran, Edward H.; Solin, Gary L.

2006-01-01

The Matanuska-Susitna Valley is in the northeastern part of the Cook Inlet Basin, Alaska, an area experiencing rapid population growth and development proximal to many lakes. Here water commonly flows between lakes and ground water, indicating interrelation between water quantity and quality. Thus concerns exist that poorer quality ground water may degrade local lake ecosystems. This concern has led to water-quality sampling in cooperation with the Alaska Department of Environmental Conservation and the Matanuska-Susitna Borough. A map showing the estimated altitude of the water table illustrates potential ground-water flow directions and areas where ground- and surface-water exchanges and interactions might occur. Water quality measured in selected wells and lakes indicates some differences between ground water and surface water. 'The temporal and spatial scarcity of ground-water-level and water-quality data limits the analysis of flow direction and water quality. Regionally, the water-table map indicates that ground water in the eastern and southern parts of the study area flows southerly. In the northcentral area, ground water flows predominately westerly then southerly. Although ground and surface water in most areas of the Matanuska-Susitna Valley are interconnected, they are chemically different. Analyses of the few water-quality samples collected in the area indicate that dissolved nitrite plus nitrate and orthophosphorus concentrations are higher in ground water than in surface water.'

Effects of unsaturated zone on ground-water mounding

USGS Publications Warehouse

Sumner, D.M.; Rolston, D.E.; Marino, M.A.

1999-01-01

The design of infiltration basins used to dispose of treated wastewater or for aquifer recharge often requires estimation of ground-water mounding beneath the basin. However, the effect that the unsaturated zone has on water-table response to basin infiltration often has been overlooked in this estimation. A comparison was made between two methods used to estimate ground-water mounding-an analytical approach that is limited to the saturated zone and a numerical approach that incorporates both the saturated and the unsaturated zones. Results indicate that the error that is introduced by a method that ignores the effects of the unsaturated zone on ground-water mounding increases as the basin-loading period is shortened; as the depth to the water table increases, with increasing subsurface anisotropy; and with the inclusion of fine-textured strata. Additionally, such a method cannot accommodate the dynamic nature of basin infiltration, the finite transmission time of the infiltration front to the water table, or the interception of the basin floor by the capillary fringe.The design of infiltration basins used to dispose of treated wastewater or for aquifer recharge often requires estimation of ground-water mounding beneath the basin. However, the effect that the unsaturated zone has on water-table response to basin infiltration often has been overlooked in this estimation. A comparison was made between two methods used to estimate ground-water mounding - an analytical approach that is limited to the saturated zone and a numerical approach that incorporates both the saturated and the unsaturated zones. Results indicate that the error that is introduced by a method that ignores the effects of the unsaturated zone on ground-water mounding increases as the basin-loading period is shortened; as the depth to the water table increases, with increasing subsurface anisotropy; and with the inclusion of fine-textured strata. Additionally, such a method cannot accommodate the dynamic nature of basin infiltration, the finite transmission time of the infiltration front to the water, or the interception of the basin floor by the capillary fringe.

40 CFR Table 3 to Subpart Ooo of... - Fugitive Emission Limits

Code of Federal Regulations, 2014 CFR

2014-07-01

... 40 Protection of Environment 7 2014-07-01 2014-07-01 false Fugitive Emission Limits 3 Table 3 to... Mineral Processing Plants Pt. 60, Subpt. OOO, Table 3 Table 3 to Subpart OOO of Part 60—Fugitive Emission...; andPeriodic inspections of water sprays according to § 60.674(b) and § 60.676(b); and A repeat...

40 CFR Table 3 to Subpart Ooo of... - Fugitive Emission Limits

Code of Federal Regulations, 2013 CFR

2013-07-01

... 40 Protection of Environment 7 2013-07-01 2013-07-01 false Fugitive Emission Limits 3 Table 3 to... Mineral Processing Plants Pt. 60, Subpt. OOO, Table 3 Table 3 to Subpart OOO of Part 60—Fugitive Emission...; andPeriodic inspections of water sprays according to § 60.674(b) and § 60.676(b); and A repeat...

40 CFR Table 2 to Subpart II of... - Volatile Organic HAP (VOHAP) Limits for Marine Coatings

Code of Federal Regulations, 2013 CFR

2013-07-01

... for Marine Coatings 2 Table 2 to Subpart II of Part 63 Protection of Environment ENVIRONMENTAL... (Surface Coating) Pt. 63, Subpt. II, Table 2 Table 2 to Subpart II of Part 63—Volatile Organic HAP (VOHAP) Limits for Marine Coatings Coating category VOHAP limits a,b,c Grams/liter coating (minus water and...

40 CFR Table 2 to Subpart II of... - Volatile Organic HAP (VOHAP) Limits for Marine Coatings

Code of Federal Regulations, 2012 CFR

2012-07-01

... for Marine Coatings 2 Table 2 to Subpart II of Part 63 Protection of Environment ENVIRONMENTAL... (Surface Coating) Pt. 63, Subpt. II, Table 2 Table 2 to Subpart II of Part 63—Volatile Organic HAP (VOHAP) Limits for Marine Coatings Coating category VOHAP limits a,b,c Grams/liter coating (minus water and...

40 CFR Table 2 to Subpart II of... - Volatile Organic HAP (VOHAP) Limits for Marine Coatings

Code of Federal Regulations, 2014 CFR

2014-07-01

... for Marine Coatings 2 Table 2 to Subpart II of Part 63 Protection of Environment ENVIRONMENTAL... (Surface Coating) Pt. 63, Subpt. II, Table 2 Table 2 to Subpart II of Part 63—Volatile Organic HAP (VOHAP) Limits for Marine Coatings Coating category VOHAP limits a b c Grams/liter coating (minus water and...

40 CFR Table 2 to Subpart II of... - Volatile Organic HAP (VOHAP) Limits for Marine Coatings

Code of Federal Regulations, 2010 CFR

2010-07-01

... for Marine Coatings 2 Table 2 to Subpart II of Part 63 Protection of Environment ENVIRONMENTAL... (Surface Coating) Pt. 63, Subpt. II, Table 2 Table 2 to Subpart II of Part 63—Volatile Organic HAP (VOHAP) Limits for Marine Coatings Coating category VOHAP limits a,b,c Grams/liter coating (minus water and...

40 CFR Table 2 to Subpart II of... - Volatile Organic HAP (VOHAP) Limits for Marine Coatings

Code of Federal Regulations, 2011 CFR

2011-07-01

... for Marine Coatings 2 Table 2 to Subpart II of Part 63 Protection of Environment ENVIRONMENTAL... (Surface Coating) Pt. 63, Subpt. II, Table 2 Table 2 to Subpart II of Part 63—Volatile Organic HAP (VOHAP) Limits for Marine Coatings Coating category VOHAP limits a,b,c Grams/liter coating (minus water and...

Use of geospatial technology for delineating groundwater potential zones with an emphasis on water-table analysis in Dwarka River basin, Birbhum, India

NASA Astrophysics Data System (ADS)

Thapa, Raju; Gupta, Srimanta; Gupta, Arindam; Reddy, D. V.; Kaur, Harjeet

2018-05-01

Dwarka River basin in Birbhum, West Bengal (India), is an agriculture-dominated area where groundwater plays a crucial role. The basin experiences seasonal water stress conditions with a scarcity of surface water. In the presented study, delineation of groundwater potential zones (GWPZs) is carried out using a geospatial multi-influencing factor technique. Geology, geomorphology, soil type, land use/land cover, rainfall, lineament and fault density, drainage density, slope, and elevation of the study area were considered for the delineation of GWPZs in the study area. About 9.3, 71.9 and 18.8% of the study area falls within good, moderate and poor groundwater potential zones, respectively. The potential groundwater yield data corroborate the outcome of the model, with maximum yield in the older floodplain and minimum yield in the hard-rock terrains in the western and south-western regions. Validation of the GWPZs using the yield of 148 wells shows very high accuracy of the model prediction, i.e., 89.1% on superimposition and 85.1 and 81.3% on success and prediction rates, respectively. Measurement of the seasonal water-table fluctuation with a multiplicative model of time series for predicting the short-term trend of the water table, followed by chi-square analysis between the predicted and observed water-table depth, indicates a trend of falling groundwater levels, with a 5% level of significance and a p-value of 0.233. The rainfall pattern for the last 3 years of the study shows a moderately positive correlation ( R 2 = 0.308) with the average water-table depth in the study area.

An efficient and guaranteed stable numerical method for continuous modeling of infiltration and redistribution with a shallow dynamic water table

NASA Astrophysics Data System (ADS)

Lai, Wencong; Ogden, Fred L.; Steinke, Robert C.; Talbot, Cary A.

2015-03-01

We have developed a one-dimensional numerical method to simulate infiltration and redistribution in the presence of a shallow dynamic water table. This method builds upon the Green-Ampt infiltration with Redistribution (GAR) model and incorporates features from the Talbot-Ogden (T-O) infiltration and redistribution method in a discretized moisture content domain. The redistribution scheme is more physically meaningful than the capillary weighted redistribution scheme in the T-O method. Groundwater dynamics are considered in this new method instead of hydrostatic groundwater front. It is also computationally more efficient than the T-O method. Motion of water in the vadose zone due to infiltration, redistribution, and interactions with capillary groundwater are described by ordinary differential equations. Numerical solutions to these equations are computationally less expensive than solutions of the highly nonlinear Richards' (1931) partial differential equation. We present results from numerical tests on 11 soil types using multiple rain pulses with different boundary conditions, with and without a shallow water table and compare against the numerical solution of Richards' equation (RE). Results from the new method are in satisfactory agreement with RE solutions in term of ponding time, deponding time, infiltration rate, and cumulative infiltrated depth. The new method, which we call "GARTO" can be used as an alternative to the RE for 1-D coupled surface and groundwater models in general situations with homogeneous soils with dynamic water table. The GARTO method represents a significant advance in simulating groundwater surface water interactions because it very closely matches the RE solution while being computationally efficient, with guaranteed mass conservation, and no stability limitations that can affect RE solvers in the case of a near-surface water table.

Statistics of chemical gradients in heterogeneous porous media

NASA Astrophysics Data System (ADS)

Le Borgne, T.; Huck, P. D.; Dentz, M.; Villermaux, E.

2017-12-01

As they create chemical disequilibrium and drive mixing fluxes, spatial gradients in solute concentrations exert a strong control on mixing and biogeochemical reactions in the subsurface. Large concentration gradients may develop in particular at interfaces between surface water and groundwater bodies, such as hyporheic zones, sea water - surface water interfaces or recharge areas. They also develop around contaminant plumes and fluids injected in subsurface operations. While macrodispersion theories predict smooth gradients, decaying in time due to dispersive dissipation, we show that concentration gradients are sustained by flow heterogeneity and have broadly distributed values. We present a general theory predicting the statistics of concentration gradients from the flow heterogeneity (Le Borgne et al., 2017). Analytical predictions are validated from high resolution simulations of transport in heterogeneous Darcy fields ranging from low to high permeability variances and low to high Peclet numbers. This modelling framework hence opens new perspectives for quantifying the dynamics of chemical gradients and the kinetics of associated biogeochemical reactions in heterogeneous subsurface environments.Reference:Le Borgne T., P.D. Huck, M. Dentz and E. Villermaux (2017) Scalar gradients in stirred mixtures and the deconstruction of random fields, J. of Fluid Mech. vol. 812, pp. 578-610 doi:10.1017/jfm.2016.799

SU-E-T-548: How To Decrease Spine Dose In Patients Who Underwent Sterotactic Spine Radiosurgery?

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

Acar, H; Altinok, A; Kucukmorkoc, E

2014-06-01

Purpose: Stereotactic radiosurgery for spine metastases involves irradiation using a single high dose fraction. The purpose of this study was to dosimetrically compare stereotactic spine radiosurgery(SRS) plans using a recently new volumetric modulated arc therapy(VMAT) technique against fix-field intensity-modulated radiotherapy(IMRT). Plans were evaluated for target conformity and spinal cord sparing. Methods: Fifteen previously treated patients were replanned using the Eclipse 10.1 TPS AAA calculation algorithm. IMRT plans with 7 fields were generated. The arc plans used 2 full arc configurations. Arc and IMRT plans were normalized and prescribed to deliver 16.0 Gy in a single fraction to 90% of themore » planning target volume(PTV). PTVs consisted of the vertebral body expanded by 3mm, excluding the PRV-cord, where the cord was expanded by 2mm.RTOG 0631 recommendations were applied for treatment planning. Partial spinal cord volume was defined as 5mm above and below the radiosurgery target volume. Plans were compared for conformity and gradient index as well as spinal cord sparing. Results: The conformity index values of fifteen patients for two different treatment planning techniques were shown in table 1. Conformity index values for 2 full arc planning (average CI=0.84) were higher than that of IMRT planning (average CI=0.79). The gradient index values of fifteen patients for two different treatment planning techniques were shown in table 2. Gradient index values for 2 full arc planning (average GI=3.58) were higher than that of IMRT planning (average GI=2.82).The spinal cord doses of fifteen patients for two different treatment planning techniques were shown in table 3. D0.35cc, D0.03cc and partial spinal cord D10% values in 2 full arc plannings (average D0.35cc=819.3cGy, D0.03cc=965.4cGy, 10%partial spinal=718.1cGy) were lower than IMRT plannings (average D0.35cc=877.4cGy, D0.03c=1071.4cGy, 10%partial spinal=805.1cGy). Conclusions: The two arc VMAT technique is superior to 7 field IMRT technique in terms of both spinal cord sparing and better conformity and gradient indexes.« less

Water Table Uncertainties due to Uncertainties in Structure and Properties of an Unconfined Aquifer.

PubMed

Hauser, Juerg; Wellmann, Florian; Trefry, Mike

2018-03-01

We consider two sources of geology-related uncertainty in making predictions of the steady-state water table elevation for an unconfined aquifer. That is the uncertainty in the depth to base of the aquifer and in the hydraulic conductivity distribution within the aquifer. Stochastic approaches to hydrological modeling commonly use geostatistical techniques to account for hydraulic conductivity uncertainty within the aquifer. In the absence of well data allowing derivation of a relationship between geophysical and hydrological parameters, the use of geophysical data is often limited to constraining the structural boundaries. If we recover the base of an unconfined aquifer from an analysis of geophysical data, then the associated uncertainties are a consequence of the geophysical inversion process. In this study, we illustrate this by quantifying water table uncertainties for the unconfined aquifer formed by the paleochannel network around the Kintyre Uranium deposit in Western Australia. The focus of the Bayesian parametric bootstrap approach employed for the inversion of the available airborne electromagnetic data is the recovery of the base of the paleochannel network and the associated uncertainties. This allows us to then quantify the associated influences on the water table in a conceptualized groundwater usage scenario and compare the resulting uncertainties with uncertainties due to an uncertain hydraulic conductivity distribution within the aquifer. Our modeling shows that neither uncertainties in the depth to the base of the aquifer nor hydraulic conductivity uncertainties alone can capture the patterns of uncertainty in the water table that emerge when the two are combined. © 2017, National Ground Water Association.

Spatial patterns and temporal variability in water quality from City of Albuquerque drinking-water supply wells and piezometer nests, with implications for the ground-water flow system

USGS Publications Warehouse

Bexfield, Laura M.; Anderholm, Scott K.

2002-01-01

Water-quality data for 93 City of Albuquerque drinking-water supply wells, 7 deep piezometer nests, and selected additional wells were examined to improve understanding of the regional ground-water system and its response to pumpage. Plots of median values of several major parameters showed discernible water-quality differences both areally and with depth in the aquifer. Areal differences were sufficiently large to enable delineation of five regions of generally distinct water quality, which are consistent with areas of separate recharge defined by previous investigators. Data for deep piezometer nests indicate that water quality generally degrades somewhat with depth, except in areas where local recharge influenced by evapotranspiration or contamination could be affecting shallow water. The orientations of the five water-quality regions indicate that the direction of ground-water flow has historically been primarily north to south. This is generally consistent with maps of predevelopment hydraulic heads, although some areas lack consistency, possibly because of differences in time scales or depths represented by water quality as opposed to hydraulic head. The primary sources of recharge to ground water in the study area appear to be mountain-front recharge along the Sandia Mountains to the east and the Jemez Mountains to the north, seepage from the Rio Grande, and infiltration through Tijeras Arroyo. Elevated concentrations of many chemical constituents in part of the study area appear to be associated with a source of water having large dissolved solids, possibly moving upward from depth. Hydraulic-head data for deep piezometer nests indicate that vertical head gradients differ in direction and magnitude across the study area. Hydraulic-head gradients are downward in the central and western parts of the study area and upward across much of the eastern part, except at the mountain front. Water-quality data for the piezometers indicate that the ground water is not well mixed, even in areas of large vertical gradients. Water levels in most piezometers respond to short-term variations in ground-water withdrawals and to the cumulative effect of long-term withdrawals throughout the area. In most piezometers screened below the water table, water levels respond clearly to seasonal variations in ground-water withdrawals. Water levels decline from about April through July and rise from about September through January. Water levels seem to be declining in most piezometers at a rate less than 1 foot per year. Water-quality data for unfiltered samples collected over a 10-year period from 93 City of Albuquerque drinking-water supply wells were examined for variability and temporal trends in 10 selected parameters. Variability generally was found to be greatest in the Western and Northeast water-quality regions of the study area. For the 10 parameters investigated, temporal trends were found in 5 to 57 wells. Dissolved-solids, sodium, sulfate, chloride, and silica concentrations showed more increasing than decreasing trends; calcium, bicarbonate, and arsenic concentrations, field pH, and water temperature showed more decreasing than increasing trends. The median magnitudes of most of these trends over a 1-year period were not particularly large (generally less than 1.0 milligram per liter), although the magnitudes for a few individual wells were significant. For the 10 parameters investigated, correlations with monthly pumpage volumes were found in 10 to 32 wells. Calcium and sulfate concentrations, field pH, and water temperature showed more positive than negative correlations with monthly pumpage; dissolved-solids, sodium, bicarbonate, chloride, silica, and arsenic concentrations showed more negative than positive correlations. An increase in pumpage in an individual well appears to increase the contribution

Factors influencing CO2 and CH4 emissions from coastal wetlands in the Liaohe Delta, Northeast China

NASA Astrophysics Data System (ADS)

Olsson, L.; Ye, S.; Yu, X.; Wei, M.; Krauss, K. W.; Brix, H.

2015-08-01

Many factors are known to influence greenhouse gas emissions from coastal wetlands, but it is still unclear which factors are most important under field conditions when they are all acting simultaneously. The objective of this study was to assess the effects of water table, salinity, soil temperature and vegetation on CH4 emissions and ecosystem respiration (Reco) from five coastal wetlands in the Liaohe Delta, Northeast China: two Phragmites australis (common reed) wetlands, two Suaeda salsa (sea blite) marshes and a rice (Oryza sativa) paddy. Throughout the growing season, the Suaeda wetlands were net CH4 sinks whereas the Phragmites wetlands and the rice paddy were net CH4 sources emitting 1.2-6.1 g CH4 m-2 yr-1. The Phragmites wetlands emitted the most CH4 per unit area and the most CH4 relative to CO2. The main controlling factors for the CH4 emissions were water table, temperature, soil organic carbon and salinity. The CH4 emission was accelerated at high and constant (or managed) water tables and decreased at water tables below the soil surface. High temperatures enhanced CH4 emissions, and emission rates were consistently low (< 1 mg CH4 m-2 h-1) at soil temperatures < 18 °C. At salinity levels > 18 ppt, the CH4 emission rates were always low (< 1 mg CH4 m-2 h-1) probably because methanogens were out-competed by sulphate-reducing bacteria. Saline Phragmites wetlands can, however, emit significant amounts of CH4 as CH4 produced in deep soil layers are transported through the air-space tissue of the plants to the atmosphere. The CH4 emission from coastal wetlands can be reduced by creating fluctuating water tables, including water tables below the soil surface, as well as by occasional flooding by high-salinity water. The effects of water management schemes on the biological communities in the wetlands must, however, be carefully studied prior to the management in order to avoid undesirable effects on the wetland communities.

Factors influencing CO2 and CH4 emissions from coastal wetlands in the Liaohe Delta, Northeast China

NASA Astrophysics Data System (ADS)

Olsson, L.; Ye, S.; Yu, X.; Wei, M.; Krauss, K. W.; Brix, H.

2015-02-01

Many factors are known to influence greenhouse gas emissions from coastal wetlands, but it is still unclear which factors are most important under field conditions when they are all acting simultaneously. The objective of this study was to assess the effects of water table, salinity, soil temperature and vegetation on CH4 emissions and ecosystem respiration (Reco) from five coastal wetlands in the Liaohe Delta, northeast China: two Phragmites australis (common reed) wetlands, two Suaeda salsa (sea blite) marshes and a rice (Oryza sativa) paddy. Throughout the growing season, the Suaeda wetlands were net CH4 sinks whereas the Phragmites wetlands and the rice paddy were net CH4 sources emitting 1.2-6.1 g CH4 m-2 y-1. The Phragmites wetlands emitted the most CH4 per unit area and the most CH4 relative to CO2. The main controlling factors for the CH4 emissions were water table, temperature and salinity. The CH4 emission was accelerated at high and constant (or managed) water tables and decreased at water tables below the soil surface. High temperatures enhanced CH4 emissions, and emission rates were consistently low (< 1 mg CH4 m-2 h) at soil temperatures <18 °C. At salinity levels > 18 ppt, the CH4 emission rates were always low (< 1 mg CH4 m-2 h-1) probably because methanogens were outcompeted by sulphate reducing bacteria. Saline Phragmites wetlands can, however, emit significant amounts of CH4 as CH4 produced in deep soil layers are transported through the air-space tissue of the plants to the atmosphere. The CH4 emission from coastal wetlands can be reduced by creating fluctuating water tables, including water tables below the soil surface, as well as by occasional flooding by high-salinity water. The effects of water management schemes on the biological communities in the wetlands must, however, be carefully studied prior to the management in order to avoid undesirable effects on the wetland communities.

The role of groundwater in hydrological processes and memory

NASA Astrophysics Data System (ADS)

Lo, Min-Hui

The interactions between soil moisture and groundwater play important roles in controlling Earth's climate, by changing the terrestrial water cycle. However, most contemporary land surface models (LSMs) used for climate modeling lack any representation of groundwater aquifers. In this dissertation, the effects of water table dynamics on the National Center for Atmospheric Research (NCAR) Community Land Model (CLM) and Community Atmosphere Model (CAM) hydrology and land-atmosphere simulations are investigated. First, a simple, lumped unconfined aquifer model is incorporated into the CLM, in which the water table is interactively coupled to the soil moisture through groundwater recharge fluxes. The recent availability of GRACE water storage data provides a unique opportunity to constrain LSMs simulations of terrestrial hydrology. A multi-objective calibration framework using GRACE and streamflow data is developed. This approach improves parameter estimation and reduces the uncertainty of water table simulations in the CLM. Next, experiments are conducted with the off-line CLM to explore the effects of groundwater on land surface memory. Results show that feedbacks of groundwater on land surface memory can be positive, negative, or neutral depending on water table dynamics. The CAM-CLM is further utilized to investigate the effects of water table dynamics on spatial-temporal variations of precipitation. Results indicate that groundwater can increase short-term (seasonal) and long-term (interannual) memory of precipitation for some regions with suitable groundwater table depth. Finally, lower tropospheric water vapor is increased due to the presence of groundwater in the model. However, the impact of groundwater on the spatial distribution of precipitation is not globally homogeneous. In the boreal summer, tropical land regions show a positive (negative) anomaly over the Northern (Southern) Hemisphere. The increased tropical precipitation follows the climatology of the convective zone rather than that of evapotranspiration. In contrast, evapotranspiration is the major contribution to the increased precipitation in the transition climatic zone (e.g., Central North America), where the land and atmosphere are strongly coupled. This dissertation reveals the highly nonlinear responses of precipitation and soil moisture to the groundwater representation in the model, and also underscores the importance of subsurface hydrological memory processes in the climate system.

Geology, hydrology, and ground-water quality at the Byron Superfund site near Byron, Illinois

USGS Publications Warehouse

Kay, Robert T.; Yeskis, Douglas J.; Bolen, William J.; Rauman, James R.; Prinos, Scott T.

1997-01-01

A study was conducted by the U.S. Geological Survey and the U.S. Environmental Protection Agency to define the geohydrology and contaminant distribution at a Superfund site near Byron, Illinois. Geologic units of interest beneath the site are the St. Peter Sandstone; the shale, dolomite and sandstone of the Glenwood Formation; the dolomite of the Platteville and Galena Groups; and sands, gravels, tills and loess of Quaternary age. The hydrologic units of interest are the unconsolidated aquifer, Galena-Platteville aquifer, Harmony Hill Shale semiconfining unit, and the St. Peter aquifer. Ground-water flow generally is from the upland areas northwest and southwest toward the Rock River. Water levels indicate the potential for downward ground-water flow in most of the area except near the Rock River. The Galena-Platteville aquifer can be subdivided into four zones characterized by differing water-table altitudes, hydraulic gradients, and vertical and horizontal permeabilities. Geophysical, hydraulic, and aquifer-test data indicate that lithology, stratigraphy, and tectonic structures affect the distribution of primary and secondary porosity of dolomite in the Galena and Platteville Groups, which affects the permeability distribution in the Galena-Platteville aquifer. The distribution of cyanide, chlorinated aliphatic hydrocarbons, and aromatic hydrocarbons in ground water indicates that these contaminants are derived from multiple sources in the study area. Contaminants in the northern part of this area migrate northwest to the Rock River. Contaminants in the central and southern parts of this area appear to migrate to the southwest in the general direction of the Rock River.

Non-linear osmosis

PubMed Central

Diamond, Jared M.

1966-01-01

1. The relation between osmotic gradient and rate of osmotic water flow has been measured in rabbit gall-bladder by a gravimetric procedure and by a rapid method based on streaming potentials. Streaming potentials were directly proportional to gravimetrically measured water fluxes. 2. As in many other tissues, water flow was found to vary with gradient in a markedly non-linear fashion. There was no consistent relation between the water permeability and either the direction or the rate of water flow. 3. Water flow in response to a given gradient decreased at higher osmolarities. The resistance to water flow increased linearly with osmolarity over the range 186-825 m-osM. 4. The resistance to water flow was the same when the gall-bladder separated any two bathing solutions with the same average osmolarity, regardless of the magnitude of the gradient. In other words, the rate of water flow is given by the expression (Om — Os)/[Ro′ + ½k′ (Om + Os)], where Ro′ and k′ are constants and Om and Os are the bathing solution osmolarities. 5. Of the theories advanced to explain non-linear osmosis in other tissues, flow-induced membrane deformations, unstirred layers, asymmetrical series-membrane effects, and non-osmotic effects of solutes could not explain the results. However, experimental measurements of water permeability as a function of osmolarity permitted quantitative reconstruction of the observed water flow—osmotic gradient curves. Hence non-linear osmosis in rabbit gall-bladder is due to a decrease in water permeability with increasing osmolarity. 6. The results suggest that aqueous channels in the cell membrane behave as osmometers, shrinking in concentrated solutions of impermeant molecules and thereby increasing membrane resistance to water flow. A mathematical formulation of such a membrane structure is offered. PMID:5945254

Balancing practicality and hydrologic realism: a parsimonious approach for simulating rapid groundwater recharge via unsaturated-zone preferential flow

USGS Publications Warehouse

Mirus, Benjamin B.; Nimmo, J.R.

2013-01-01

The impact of preferential flow on recharge and contaminant transport poses a considerable challenge to water-resources management. Typical hydrologic models require extensive site characterization, but can underestimate fluxes when preferential flow is significant. A recently developed source-responsive model incorporates film-flow theory with conservation of mass to estimate unsaturated-zone preferential fluxes with readily available data. The term source-responsive describes the sensitivity of preferential flow in response to water availability at the source of input. We present the first rigorous tests of a parsimonious formulation for simulating water table fluctuations using two case studies, both in arid regions with thick unsaturated zones of fractured volcanic rock. Diffuse flow theory cannot adequately capture the observed water table responses at both sites; the source-responsive model is a viable alternative. We treat the active area fraction of preferential flow paths as a scaled function of water inputs at the land surface then calibrate the macropore density to fit observed water table rises. Unlike previous applications, we allow the characteristic film-flow velocity to vary, reflecting the lag time between source and deep water table responses. Analysis of model performance and parameter sensitivity for the two case studies underscores the importance of identifying thresholds for initiation of film flow in unsaturated rocks, and suggests that this parsimonious approach is potentially of great practical value.

Chemical character of ground water in the shallow water-table aquifer at selected localities in the Memphis area, Tennessee

USGS Publications Warehouse

Parks, William Scott; Graham, D.D.; Lowery, J.F.

1981-01-01

Eight deep wells are being monitored in the Memphis, Tenn., area to detect any changes in the chemical character of water moving through the Memphis Sand towards major pumping centers. These wells are strategically located so as to intercept groundwater enroute through the Memphis Sand from the outcrop-recharge area. Although water quality analyses are available for many wells in the shallow water-table aquifer, no specific investigation has been made to characterize the quality of the water in this aquifer from which the Memphis Sand also receives part of its recharge. This investigation is to determine the chemical character of groundwater in the shallow water-table aquifer at selected localities in the Memphis area. Methods used to install eight shallow wells at abandoned dump sites containing chemical and/or industrial waste are described. Water samples from the eight shallow wells and two deep wells in the Memphis Sand were collected and analyzed. Results of the analysis are presented and the locations of the wells and dumps are shown on maps. (USGS)

Four-dimensional electrical conductivity monitoring of stage-driven river water intrusion: Accounting for water table effects using a transient mesh boundary and conditional inversion constraints

DOE PAGES

Johnson, Tim; Versteeg, Roelof; Thomle, Jon; ...

2015-08-01

Our paper describes and demonstrates two methods of providing a priori information to the surface-based time-lapse three-dimensional electrical resistivity tomography (ERT) problem for monitoring stage-driven or tide-driven surface water intrusion into aquifers. First, a mesh boundary is implemented that conforms to the known location of the water table through time, thereby enabling the inversion to place a sharp bulk conductivity contrast at that boundary without penalty. Moreover, a nonlinear inequality constraint is used to allow only positive or negative transient changes in EC to occur within the saturated zone, dependent on the relative contrast in fluid electrical conductivity between surfacemore » water and groundwater. A 3-D field experiment demonstrates that time-lapse imaging results using traditional smoothness constraints are unable to delineate river water intrusion. The water table and inequality constraints provide the inversion with the additional information necessary to resolve the spatial extent of river water intrusion through time.« less

Four-dimensional electrical conductivity monitoring of stage-driven river water intrusion: Accounting for water table effects using a transient mesh boundary and conditional inversion constraints

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

Johnson, Tim; Versteeg, Roelof; Thomle, Jon

Our paper describes and demonstrates two methods of providing a priori information to the surface-based time-lapse three-dimensional electrical resistivity tomography (ERT) problem for monitoring stage-driven or tide-driven surface water intrusion into aquifers. First, a mesh boundary is implemented that conforms to the known location of the water table through time, thereby enabling the inversion to place a sharp bulk conductivity contrast at that boundary without penalty. Moreover, a nonlinear inequality constraint is used to allow only positive or negative transient changes in EC to occur within the saturated zone, dependent on the relative contrast in fluid electrical conductivity between surfacemore » water and groundwater. A 3-D field experiment demonstrates that time-lapse imaging results using traditional smoothness constraints are unable to delineate river water intrusion. The water table and inequality constraints provide the inversion with the additional information necessary to resolve the spatial extent of river water intrusion through time.« less

Selected techniques for monitoring water movement through unsaturated alluvium during managed aquifer recharge

USGS Publications Warehouse

Nawikas, Joseph M.; O'Leary, David R.; Izbicki, John A.; Burgess, Matthew K.

2016-10-21

Managed aquifer recharge is used to augment natural recharge to aquifers. It can be used to replenish aquifers depleted by pumping or to store water during wetter years for withdrawal during drier years. Infiltration from ponds is a commonly used, inexpensive approach for managed aquifer recharge.At some managed aquifer-recharge sites, the time when infiltrated water arrives at the water table is not always clearly shown by water-level data. As part of site characterization and operation, it can be desirable to track downward movement of infiltrated water through the unsaturated zone to identify when it arrives at the water table.

30 CFR 75.501-1 - Coal seams above the water table.

Code of Federal Regulations, 2011 CFR

2011-07-01

... 30 Mineral Resources 1 2011-07-01 2011-07-01 false Coal seams above the water table. 75.501-1 Section 75.501-1 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR COAL MINE SAFETY AND HEALTH MANDATORY SAFETY STANDARDS-UNDERGROUND COAL MINES Electrical Equipment-General § 75.501...

30 CFR 75.501 - Permissible electric face equipment; coal seams above water table.

Code of Federal Regulations, 2014 CFR

2014-07-01

... 30 Mineral Resources 1 2014-07-01 2014-07-01 false Permissible electric face equipment; coal seams..., DEPARTMENT OF LABOR COAL MINE SAFETY AND HEALTH MANDATORY SAFETY STANDARDS-UNDERGROUND COAL MINES Electrical Equipment-General § 75.501 Permissible electric face equipment; coal seams above water table. [Statutory...

30 CFR 75.501-1 - Coal seams above the water table.

Code of Federal Regulations, 2012 CFR

2012-07-01

... 30 Mineral Resources 1 2012-07-01 2012-07-01 false Coal seams above the water table. 75.501-1 Section 75.501-1 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR COAL MINE SAFETY AND HEALTH MANDATORY SAFETY STANDARDS-UNDERGROUND COAL MINES Electrical Equipment-General § 75.501...

30 CFR 75.501-1 - Coal seams above the water table.

Code of Federal Regulations, 2014 CFR

2014-07-01

... 30 Mineral Resources 1 2014-07-01 2014-07-01 false Coal seams above the water table. 75.501-1 Section 75.501-1 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR COAL MINE SAFETY AND HEALTH MANDATORY SAFETY STANDARDS-UNDERGROUND COAL MINES Electrical Equipment-General § 75.501...

30 CFR 75.501-1 - Coal seams above the water table.

Code of Federal Regulations, 2010 CFR

2010-07-01

... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Coal seams above the water table. 75.501-1 Section 75.501-1 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR COAL MINE SAFETY AND HEALTH MANDATORY SAFETY STANDARDS-UNDERGROUND COAL MINES Electrical Equipment-General § 75.501...

30 CFR 75.501 - Permissible electric face equipment; coal seams above water table.

Code of Federal Regulations, 2010 CFR

2010-07-01

... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Permissible electric face equipment; coal seams..., DEPARTMENT OF LABOR COAL MINE SAFETY AND HEALTH MANDATORY SAFETY STANDARDS-UNDERGROUND COAL MINES Electrical Equipment-General § 75.501 Permissible electric face equipment; coal seams above water table. [Statutory...

30 CFR 75.501-1 - Coal seams above the water table.

Code of Federal Regulations, 2013 CFR

2013-07-01

... 30 Mineral Resources 1 2013-07-01 2013-07-01 false Coal seams above the water table. 75.501-1 Section 75.501-1 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR COAL MINE SAFETY AND HEALTH MANDATORY SAFETY STANDARDS-UNDERGROUND COAL MINES Electrical Equipment-General § 75.501...

30 CFR 75.501 - Permissible electric face equipment; coal seams above water table.

Code of Federal Regulations, 2012 CFR

2012-07-01

... 30 Mineral Resources 1 2012-07-01 2012-07-01 false Permissible electric face equipment; coal seams..., DEPARTMENT OF LABOR COAL MINE SAFETY AND HEALTH MANDATORY SAFETY STANDARDS-UNDERGROUND COAL MINES Electrical Equipment-General § 75.501 Permissible electric face equipment; coal seams above water table. [Statutory...

30 CFR 75.501 - Permissible electric face equipment; coal seams above water table.

Code of Federal Regulations, 2011 CFR

2011-07-01

... 30 Mineral Resources 1 2011-07-01 2011-07-01 false Permissible electric face equipment; coal seams..., DEPARTMENT OF LABOR COAL MINE SAFETY AND HEALTH MANDATORY SAFETY STANDARDS-UNDERGROUND COAL MINES Electrical Equipment-General § 75.501 Permissible electric face equipment; coal seams above water table. [Statutory...

Sugarcane Responses to Water-Table Depth and Periodic Flood

USDA-ARS?s Scientific Manuscript database

Sugarcane (Saccharum spp.) is routinely exposed to periodic floods and shallow water tables in Florida’s Everglades Agricultural Area (EAA). The purpose of this study was to examine the yields and juice quality of four sugarcane cultivars (CP 88-1762, CP 89-2143, CP 89-2376, and CP 96-1252) maintain...

30 CFR 75.501 - Permissible electric face equipment; coal seams above water table.

Code of Federal Regulations, 2013 CFR

2013-07-01

... 30 Mineral Resources 1 2013-07-01 2013-07-01 false Permissible electric face equipment; coal seams... Equipment-General § 75.501 Permissible electric face equipment; coal seams above water table. [Statutory Provision] On and after March 30, 1974, all electric face equipment, other than equipment referred to in...

29 CFR 1910.110 - Storage and handling of liquefied petroleum gases.

Code of Federal Regulations, 2011 CFR

2011-07-01

.... (i) Containers used with systems embodied in paragraphs (d), (e), (g), and (h) of this section... unit of weight for containers with a water capacity of 300 pounds or less. (h) With marking indicating... Table H-23. Table H-23 Water capacity per container Minimum distances Containers Underground Aboveground...

29 CFR 1910.110 - Storage and handling of liquefied petroleum gases.

Code of Federal Regulations, 2010 CFR

2010-07-01

.... (i) Containers used with systems embodied in paragraphs (d), (e), (g), and (h) of this section... unit of weight for containers with a water capacity of 300 pounds or less. (h) With marking indicating... Table H-23. Table H-23 Water capacity per container Minimum distances Containers Underground Aboveground...

Effects of nearshore recharge on groundwater interactions with a lake in mantled karst terrain

USGS Publications Warehouse

Lee, Terrie M.

2000-01-01

The recharge and discharge of groundwater were investigated for a lake basin in the mantled karst terrain of central Florida to determine the relative importance of transient groundwater inflow to the lake water budget. Variably saturated groundwater flow modeling simulated water table responses observed beneath two hillsides radiating outward from the groundwater flow‐through lake. Modeling results indicated that transient water table mounding and groundwater flow reversals in the nearshore region following large daily rainfall events generated most of the net groundwater inflow to the lake. Simulated daily groundwater inflow was greatest following water table mounding near the lake, not following subsequent peaks in the water level of upper basin wells. Transient mounding generated net groundwater inflow to the lake, that is, groundwater inflow in excess of the outflow occurring through the deeper lake bottom. The timing of the modeled net groundwater inflow agreed with an independent lake water budget; however, the quantity was considerably less than the budget‐derived value.

Physiological and morphological response patterns of Populus deltoides to alluvial groundwater

USGS Publications Warehouse

Cooper, D.J.; D'Amico, D.R.; Scott, M.L.

2003-01-01

We examined the physiological and morphological response patterns of plains cottonwood [Populus deltoides subsp. monilifera (Aiton) Eck.] to acute water stress imposed by groundwater pumping. Between 3 and 27 July 1996, four large pumps were used to withdraw alluvial groundwater from a cottonwood forest along the South Platte River, near Denver, Colorado, USA. The study was designed as a stand-level, split-plot experiment with factorial treatments including two soil types (a gravel soil and a loam topsoil over gravel), two water table drawdown depths (∼0.5 m and >1.0 m), and one water table control (no drawdown) per soil type. Measurements of water table depth, soil water potential (Ψs), predawn and midday shoot water potential (Ψpd and Ψmd), and D/H (deuterium/hydrogen) ratios of different water sources were made in each of six 600-m2 plots prior to, during, and immediately following pumping. Two additional plots were established and measured to examine the extent to which surface irrigation could be used to mitigate the effects of deep drawdown on P. deltoides for each soil type. Recovery of tree water status following pumping was evaluated by measuring stomatal conductance (gs) and xylem water potential (Ψxp) on approximately hourly time steps from before dawn to mid-afternoon on 11 August 1996 in watered and unwatered, deep-drawdown plots on gravel soils. P. deltoides responded to abrupt alluvial water table decline with decreased shoot water potential followed by leaf mortality. Ψpd and percent leaf loss were significantly related to the magnitude of water table declines. The onset and course of these responses were influenced by short-term variability in surface and ground water levels, acting in concert with physiological and morphological adjustments. Decreases in Ψpd corresponded with increases in Ψmd, suggesting shoot water status improved in response to stomatal closure and crown dieback. Crown dieback caused by xylem cavitation likely occurred when Ψpd reached −0.4 to −0.8 MPa. The application of surface irrigation allowed trees to maintain favorable water status with little or no apparent cavitation, even in deep-drawdown plots. Two weeks after the partial canopy dieback and cessation of pumping, gs and Ψxp measurements indicated that water stress persisted in unwatered P. deltoides in deep-drawdown plots.

Patterns in Soil Electrical Resistivity Across Land Uses in the Calhoun Critical Zone Observatory Landscape

NASA Astrophysics Data System (ADS)

Markewitz, D.; Sutter, L.; Richter, D. D., Jr.

2017-12-01

Soil Electrical Resistivity Tomography (ERT) was measured across the Calhoun Critical Zone Observatory in relation to land use cover. ERT can help identify patterns in soil and saprolite physical attributes and moisture content through multiple meters. ERT data were generated with an AGI Supersting R8 with a 28 probe dipole-dipole array on a 1.5 meter spacing providing information through the upper 9 m. In Nov/Dec 2016 ten soil pits were dug to 3m depth in agricultural fields, pine forests, and hardwood forests across the CCZO and ERT measures were taken centered on these pits. ERT values ranged from 200 to 2500 Ohm-m. ERT patterns in the agricultural field demonstrated a limited resistivity gradient (200-700 Ohm-m) appearing moist throughout. In contrast, research areas under pine and hardwood forest had stronger resistivity gradients reflecting both moisture and physical attributes (i.e., texture or rock content). For example, research area 2 under pine had an area of higher resistivity that correlated with a band of saprolite that was readily visible in the exposed profile. In research area 7 and 8 that included both pine and hardwood forest resistivity gradients had contradictory patterns of high to low resistivity from top to bottom. In research area 7 resistivity was highest at the surface and decreased with depth, a common pattern when water table is at depth. In research area 8 the inverse was observed with low resistivity above and resistivity increasing with depth, a pattern observed in upper landscape positions on ridges with moist clay above dry saprolite. ERT patterns did reflect a large difference in the measured agricultural fields compared to forest while other difference appeared to reflect landscape position.

Bistability of mangrove forests and competition with freshwater plants

USGS Publications Warehouse

Jiang, Jiang; Fuller, Douglas O; Teh, Su Yean; Zhai, Lu; Koh, Hock Lye; DeAngelis, Donald L.; Sternberg, L.D.S.L.

2015-01-01

Halophytic communities such as mangrove forests and buttonwood hammocks tend to border freshwater plant communities as sharp ecotones. Most studies attribute this purely to underlying physical templates, such as groundwater salinity gradients caused by tidal flux and topography. However, a few recent studies hypothesize that self-reinforcing feedback between vegetation and vadose zone salinity are also involved and create a bistable situation in which either halophytic dominated habitat or freshwater plant communities may dominate as alternative stable states. Here, we revisit the bistability hypothesis and demonstrate the mechanisms that result in bistability. We demonstrate with remote sensing imagery the sharp boundaries between freshwater hardwood hammock communities in southern Florida and halophytic communities such as buttonwood hammocks and mangroves. We further document from the literature how transpiration of mangroves and freshwater plants respond differently to vadose zone salinity, thus altering the salinity through feedback. Using mathematical models, we show how the self-reinforcing feedback, together with physical template, controls the ecotones between halophytic and freshwater communities. Regions of bistability along environmental gradients of salinity have the potential for large-scale vegetation shifts following pulse disturbances such as hurricane tidal surges in Florida, or tsunamis in other regions. The size of the region of bistability can be large for low-lying coastal habitat due to the saline water table, which extends inland due to salinity intrusion. We suggest coupling ecological and hydrologic processes as a framework for future studies.

"How low can it go?" - Scenarios for the future of water tables and groundwater irrigated agriculture in India

NASA Astrophysics Data System (ADS)

Modi, V.; Fishman, R.

2010-12-01

Groundwater irrigation, while critical for food production and rural livelihood in many developing countries, is often unsustainable. India, the world’s largest consumer of groundwater, mostly for irrigation, is a prime example: data suggests water tables are falling in the most of its productive regions. Because of the long-term consequences for the viability and efficiency of agriculture, it is important to know how far water tables might fall and what will eventually stabilize them: will it be a reduction in water use and increases in water use efficiency (a sustainable path) or more pessimistically, an energy ‘crunch’ or the hydrological ‘bottom’. Using national-level data, we document an alarming trend of non-decreasing water withdrawals supported by increasing energy use and little, if any, improvement in efficiency. We also study in detail a particular hot spot of advanced depletion that presents a grave warning signal of how far things can go if allowed to proceed on their present course. In our study area, water tables have been falling rapidly for three decades now and reach as much as 200m, with the astounding consequence that energy use for pumping, subsidized by the state, is now worth more than the income farmers generate from its use. Despite this, the large potential for water savings in agriculture there is still unexploited. We discuss policy measures that can prevent other parts of the country from following the same disastrous trajectory.

The impact of long-term changes in water table height on carbon cycling in sub-boreal peatlands

NASA Astrophysics Data System (ADS)

Pypker, T. G.; Moore, P. A.; Waddington, J. M.; Hribljan, J. A.; Ballantyne, D.; Chimner, R. A.

2011-12-01

Peatlands are a critical component in the global carbon (C) cycle because they have been slowly sequestering atmospheric greenhouse gases as peat since the last glaciation. Today, soil C stocks in peatlands are estimated to represent 224 to 455 Pg, equal to 12-30% of the global soil C pool. At present, peatlands are estimated to sequester 76 Tg C yr-1. The flux of C to and from peatlands is likely to respond to climate change, thereby influencing atmospheric C concentrations. Peatland C budgets are tightly linked to their hydrology, hence, it is critical we understand how changes in hydrology will affect the C budgets of peatlands. The main objective of the project was to determine how long-term changes in water table height affect CO2 and CH4 fluxes from three adjacent peatlands. This study took place in the Seney National Wildlife Refuge (SNWR) in the Upper Peninsula of Michigan. SNWR is home to the largest wetland drainage project in Michigan. In 1912, ditches and dikes were created in an effort to convert approximately 20,000 ha of peatland to agriculture. The ditches and dikes were unsuccessful in creating agricultural land, but they are still in place. The manipulation of water table heights provides an opportunity to research how long-term peat drying or wetting alters C cycling in peatlands. From May to November in 2009, 2010 and 2011, we monitored CO2 fluxes using eddy covariance and chamber techniques in three adjacent peatlands with lowered, relatively unaltered ("control") and raised water table heights. In 2011, we installed CH4 analyzers to continuously monitor CH4 fluxes at the sites with high and relatively unaltered water table heights. The results are compared across sites to determine how changes in water table height might affect C fluxes sub-boreal peatlands.

Topographic Controls on Hillslope-Riparian Water Table Continuity in a set of Nested Catchments, Northern Rocky Mountains, Montana

NASA Astrophysics Data System (ADS)

Jencso, K. G.; McGlynn, B. L.; Gooseff, M. N.; Wondzell, S. M.; Bencala, K. E.; Payn, R. A.

2007-12-01

Understanding how hillslope and riparian water table dynamics influence catchment scale hydrologic response remains a challenge. In steep headwater catchments with shallow soils, topographic convergence and divergence (upslope accumulated area-UAA) is a hypothesized first-order control on the distribution of soil water and groundwater. To test the relationship between UAA and the longevity of hillslope-riparian-stream shallow groundwater connectivity, we quantified water table continuity based on 80+ recording wells distributed across 24 hillslope-riparian-stream cross-sections. Cross-section upstream catchment areas ranged in size from 0.41 to 17.2 km2, within the Tenderfoot Creek Experimental Forest (U.S. Forest Service), northern Rocky Mountains, Montana, USA. We quantified toe-slope UAA and the topographic index (TI = ln a/tanβ) with a Multiple-D- Infinity (area routing in multiple infinite downslope directions) flow accumulation algorithm analysis of 1, 3, 10, and 30m ALSM derived DEMs. Indices derived from the 10m DEM best characterized subsurface flow accumulation, highlighting the balance between the process of interest, topographic complexity, and optimal grid scale representation. Across the 24 transects, toe-slope UAA ranged from 600-40,000 m2, the TI ranged from 5-16, and riparian widths were between 0-60m. Patterns in shallow groundwater table fluctuations suggest hydrologic dynamics reflective of hillslope-riparian landscape setting. Specifically, correlations were observed between longevity of hillslope-riparian water table continuity and the size of the UAA (r2=0.84) and its topographic index (r2=.86). These observations highlight the temporal component of topographic-hydrologic relationships important for understanding threshold mediated hydrologic variables. We are working to quantify the characteristics and spatial distribution of hillslope-riparian sequences and their water table dynamics to temporally link runoff source areas to whole catchment hydrologic response.

Stochastic analysis of unsaturated steady flows above the water table

NASA Astrophysics Data System (ADS)

Severino, Gerardo; Scarfato, Maddalena; Comegna, Alessandro

2017-08-01

Steady flow takes place into a three-dimensional partially saturated porous medium where, due to their spatial variability, the saturated conductivity Ks, and the relative conductivity Kr are modeled as random space functions (RSF)s. As a consequence, the flow variables (FVs), i.e., pressure-head and specific flux, are also RSFs. The focus of the present paper consists into quantifying the uncertainty of the FVs above the water table. The simple expressions (most of which in closed form) of the second-order moments pertaining to the FVs allow one to follow the transitional behavior from the zone close to the water table (where the FVs are nonstationary), till to their far-field limit (where the FVs become stationary RSFs). In particular, it is shown how the stationary limits (and the distance from the water table at which stationarity is attained) depend upon the statistical structure of the RSFs Ks, Kr, and the infiltrating rate. The mean pressure head ><Ψ>> has been also computed, and it is expressed as <Ψ>=Ψ0>(1+ψ>), being ψ a characteristic heterogeneity function which modifies the zero-order approximation Ψ0 of the pressure head (valid for a vadose zone of uniform soil properties) to account for the spatial variability of Ks and Kr. Two asymptotic limits, i.e., close (near field) and away (far field) from the water table, are derived into a very general manner, whereas the transitional behavior of ψ between the near/far field can be determined after specifying the shape of the various input soil properties. Besides the theoretical interest, results of the present paper are useful for practical purposes, as well. Indeed, the model is tested against to real data, and in particular it is shown how it is possible for the specific case study to grasp the behavior of the FVs within an environment (i.e., the vadose zone close to the water table) which is generally very difficult to access by direct inspection.

Land Retirement as a Habitat Restoration Tool

NASA Astrophysics Data System (ADS)

Singh, P. N.; Wallender, W. W.

2007-12-01

Use of intensive irrigation in arid and semi-arid areas usually leads to gradual salination of the soil leading to crop yield decline. The salination problem is mitigated by applying irrigation in excess of crop requirements, which leaches the excess salt load to the groundwater. Insufficient natural or man made drainage to dispose off this saline recharge to the groundwater leads to a gradual rise in the water table and eventual encroachment upon the root zone. This may ultimately make the land unfit for any economically productive activity. The abandoned land may even lead to desertification with adverse environmental consequences. In drainage basins with no surface outflow (sometimes called closed basins), land retirement has been proposed as a management tool to address this problem. Land retirement essentially entails intentionally discontinuing irrigation of selected farmlands with the expectation that the shallow water table beneath those lands should drop and the root zone salinity level should decrease. In the San Joaquin Valley of California, intensive irrigation in conjunction with a shallow underlying layer of clay, known as the Corcoran clay layer and absence of a drainage system caused the root zone to become highly saline and the shallow water table to rise. Land retirement would remove from production those farmlands contributing the poorest quality subsurface drain water. Based on numerical models results, it was expected that with land retirement of substantial irrigated lands with poor drainage characteristics, beneath which lies shallow groundwater with high salt load, the shallow water table beneath those lands should drop. A part of the retired lands could also be used for wildlife habitat. A potential negative side of the land retirement option that has to be considered is that in certain enabling evapotranspiration, soil and water table conditions, water will be drawn upwards and evaporated, leaving a deposit of salts on the surface and in the root zone. Salt on the surface may then be wind blown to adjacent areas creating a potential environmental hazard. Using field results from the U.S. Department of the Interior Land Retirement Demonstration Project at the Tranquillity site located in western Fresno County, principles of mass balance in a fixed control volume, the HYDRUS-1D Software Package for Simulating the One-Dimensional Movement of Water, Heat, and Multiple Solutes in Variably-Saturated Media, and PEST, a model-independent parameter optimizer, we have investigated the processes of soil water and salinity movement in the root zone and the deep vadose zone. Various combinations of evapotranspiration, soil water retention properties, water table condition and top and bottom boundary condition were tested. We show that certain Land Retirement scenarios decrease shallow water table and soil water salinity and enhance development of native plants as a means to facilitate habitat restoration for certain combination of soil and bottom boundary condition. Other combinations are not sustainable.

Design and Verification of an Inexpensive Ultrasonic Water Depth Sensor Using Arduino

NASA Astrophysics Data System (ADS)

Mihevc, T. M.; Rajagopal, S.

2012-12-01

A system that combines the arduino micro-controller, a Parallax PING Ultrasonic distance sensor and a secure digital card to log the data is developed to help monitor water table depths in multiple settings. Traditional methods of monitoring water table depths involve the use of a pressure transducer and expensive data loggers that cost upward of 1000. The present system is built for less than 100, with the caveat that the accuracy of the measurements is 1cm. In this laboratory study, we first build the arduino based system to monitor water table depths in a piezometer and compare these measurements to those made by a pressure transducer. Initial results show that the depth measurements are accurate in comparison to actual tape measurements. Results from this benchmarking experiment will be presented at the meeting.

Flow to a well in a water-table aquifer: An improved laplace transform solution

USGS Publications Warehouse

Moench, A.F.

1996-01-01

An alternative Laplace transform solution for the problem, originally solved by Neuman, of constant discharge from a partially penetrating well in a water-table aquifer was obtained. The solution differs from existing solutions in that it is simpler in form and can be numerically inverted without the need for time-consuming numerical integration. The derivation invloves the use of the Laplace transform and a finite Fourier cosine series and avoids the Hankel transform used in prior derivations. The solution allows for water in the overlying unsaturated zone to be released either instantaneously in response to a declining water table as assumed by Neuman, or gradually as approximated by Boulton's convolution integral. Numerical evaluation yields results identical with results obtained by previously published methods with the advantage, under most well-aquifer configurations, of much reduced computation time.

Long-distance abscisic acid signalling under different vertical soil moisture gradients depends on bulk root water potential and average soil water content in the root zone.

PubMed

Puértolas, Jaime; Alcobendas, Rosalía; Alarcón, Juan J; Dodd, Ian C

2013-08-01

To determine how root-to-shoot abscisic acid (ABA) signalling is regulated by vertical soil moisture gradients, root ABA concentration ([ABA](root)), the fraction of root water uptake from, and root water potential of different parts of the root zone, along with bulk root water potential, were measured to test various predictive models of root xylem ABA concentration [RX-ABA](sap). Beans (Phaseolus vulgaris L. cv. Nassau) were grown in soil columns and received different irrigation treatments (top and basal watering, and withholding water for varying lengths of time) to induce different vertical soil moisture gradients. Root water uptake was measured at four positions within the column by continuously recording volumetric soil water content (θv). Average θv was inversely related to bulk root water potential (Ψ(root)). In turn, Ψ(root) was correlated with both average [ABA](root) and [RX-ABA](sap). Despite large gradients in θv, [ABA](root) and root water potential was homogenous within the root zone. Consequently, unlike some split-root studies, root water uptake fraction from layers with different soil moisture did not influence xylem sap (ABA). This suggests two different patterns of ABA signalling, depending on how soil moisture heterogeneity is distributed within the root zone, which might have implications for implementing water-saving irrigation techniques. © 2013 John Wiley & Sons Ltd.

The Stream Table in Physical Geography Instruction.

ERIC Educational Resources Information Center

Wikle, Thomas A.; Lightfoot, Dale R.

1997-01-01

Outlines a number of activities to be conducted with a stream table (large wooden box filled with sediment and designed for water to pass through) in class. Activities illustrate such fluvial processes as stream meandering, erosion, transportation, and deposition. Includes a diagram for constructing a stream table. (MJP)

Use of water by bottom-land vegetation in lower Safford Valley, Arizona

USGS Publications Warehouse

Gatewood, Joseph S.; Robinson, T.W.; Colby, B.R.; Hem, J.D.; Halpenny, L.C.

1950-01-01

Lower Safford Valley, Graham County, Ariz., is an alluvial lowland plain 1 to 3 measurements, and the rate of ground-water inflow to the bottom-land area was determined on the basis of the hydraulic gradient, of the water table at. the time of each set of seepage measurements, the transmissibility of the aquifer, and the length of the reach. Although the methods differed greatly, the figure for use of ground water computed by each method was within 20 percent of the mean determined by averaging the results of all six methods. As a part of the investigation, the quality of the waters of lower Safford Valley was studied in detail. The quality-of-water studies included more than 5,000 analyses of surface and ground waters. These analyses showed that surface waters of the area contain 250 to about 6,000 parts per million of dissolved solids and that ground waters contain 200 to more than 10,000 parts per million. The waters of low dissolved-solids concentration contain mostly sodium or calcium and bicarbonate. Highly mineralized waters contain mostly sodium and chloride. Based on the results obtained by the six methods, the total use of water by vegetation during the 12-month period ending September 30, 1944, was 28,000 acre-feet in a total of 9,303 acres in the 46-mile reach of Gila River from Thatcher to Calva. As precipitation and runoff were subnormal in most of the period of the investigation, it is possible that the total use of water in other years may exceed 28,000 acre-feet. Of the total water used, 23,000 acre-feet was derived frown the ground-water reservoir, and the remainder was derived from precipitation on the area. Of the 23,000 acre-feet, more than 75 percent was used by saltcedar.

Reference manual for data base on Nevada well logs

USGS Publications Warehouse

Bauer, E.M.; Cartier, K.D.

1995-01-01

The U.S. Geological Survey and Nevada Division of Water Resources are cooperatively using a data base for are cooperatively using a data base for managing well-log information for the State of Nevada. The Well-Log Data Base is part of an integrated system of computer data bases using the Ingres Relational Data-Base Management System, which allows efficient storage and access to water information from the State Engineer's office. The data base contains a main table, two ancillary tables, and nine lookup tables, as well as a menu-driven system for entering, updating, and reporting on the data. This reference guide outlines the general functions of the system and provides a brief description of data tables and data-entry screens.

Selected hydrologic data from a wastewater spray disposal site on Hilton Head Island, South Carolina

USGS Publications Warehouse

Speiran, G.K.; Belval, D.L.

1985-01-01

This study presents data collected during a study of the effects on the water table aquifer from wastewater application at rates of up to 5 inches per week on a wastewater spray disposal site on Hilton Head Island, South Carolina. The study was conducted from April 1982 through December 1983. The disposal site covers approximately 14 acres. Water level and water quality data from organic, inorganic, and nutrient analyses from the water table aquifer to a depth of 30 ft and similar water quality data from the wastewater treatment plant are included. (USGS)

Annual safe groundwater yield in a semiarid basin using combination of water balance equation and water table fluctuation

NASA Astrophysics Data System (ADS)

Rezaei, Abolfazl; Mohammadi, Zargham

2017-10-01

The safe groundwater yield plays a major role in the appropriate management of groundwater systems, particularly in (semi-)arid areas like Iran. This study incorporates both the water balance equation and the water table fluctuation to estimate the annual safe yield of the unconfined aquifer in the eastern part of the Kaftar Lake, an Iranian semiarid region. Firstly, the water balance year 2002-03, owing same water table elevation at the beginning and year-end, was chosen from the monthly representative groundwater hydrograph of the aquifer to be taken into account as a basic water year for determining the safe yield. Then the ratio of the total groundwater pumping to the annual groundwater recharge in the selected water balance year together with the quantity of total recharge occurred in the wet period (October to May) of the year of interest were applied to evaluate the annual safe yield at the initiation of the dry period (June to September) of the year of interest. Knowing the annual safe groundwater withdrawal rate at the initiation of each dry period could be helpful to decision makers in managing groundwater resources conservation. Analysis results indicate that to develop a safe management strategy in the aquifer; the ratio of the annual groundwater withdrawal to the annually recharged volume should not exceed 0.69. In the water year 2003-04 where the ratio is equal to 0.52, the water table raised up (about 0.48 m) while the groundwater level significantly declined (about 1.54 m) over the water year 2007-08 where the ratio of the annual groundwater withdrawal to the annually recharged volume (i.e., 2.76) is larger than 0.69.

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

Buddemeier, R.W.; Oberdorfer, J.A.

A wide variety of forces can produce head gradients that drive the flow and advective mixing of internal coral reef pore waters. Oscillatory gradients that produce mixing result from wave and tide action. Sustained gradients result from wave and tide-induced setup and ponding, from currents impinging on the reef structure, from groundwater heads, and from density differenced (temperature or salinity gradients). These gradients and the permeabilities and porosities of reef sediments are such that most macropore environments are dominated by advection rather than diffusion. The various driving forces must be analyzed to determine the individual and combined magnitudes of theirmore » effects on a specific reef pore-water system. Pore-water movement controls sediment diagenesis, the exchange of nutrients between sediments and benthos, and coastal/island groundwater resources. Because of the complexity of forcing functions, their interactions with specific local reef environments, experimental studies require careful incorporation of these considerations into their design and interpretation. 8 refs., 3 figs., 1 tab.« less