bluuebunny/crossref_metadata_2025_split huggingface dataset:
An Assessment of a Mesocosm Approach to the Study of Microbial Respiration in a Sandy Unsaturated Zone
Authors: Hendry M.J. , Mendoza C.A. , Kirkland R. , Lawrence J.R. 
Published: December 2005

AbstractMicrobial respiration rates were determined through a 3.2 m thick, sandy unsaturated zone in a 2.4 m diameter X 4.6 m high mesocosm. The mesocosm was maintained under near constant temperature (18° to 23°C) and reached steady moisture content conditions after several hundred days. Soil‐gas CO2 concentrations in the mesocosm ranged from 0.09% to 3.31% and increased with depth. Respiration rates within the mesocosm were quantified over a 342–day period using measured CO2 concentrations and a transient, one‐dimensional finite‐element model. Microbial respiration rates were 2 × 10–1μg C·g−1·d−1 throughout most of the system, but decreased to 10–4 to 10–3μg C·g−1·d−1 within the capillary fringe. Microbial respiration rates were also determined in minicosms (500 g sample mass) over a range in temperatures (4° to 30°C) and volumetric moisture contents (0.044 to 0.37). The functional dependence of CO2 production on temperature and soil‐moisture content was similar for the two scales of laboratory observation. Respiration rates in the minicosms, for temperatures and moisture contents in the mesocosm, were up to an order of magnitude greater than those determined for the mesocosm. The higher respiration rates in the minicosms, compared to the mesocosm, were attributed to greater disturbance of the samples and to shorter acclimation time in the minicosms. Extrapolating the laboratory respiration rates to field conditions yielded rates that were two to three orders of magnitude greater than rates previously determined in situ for C‐horizon material. Results show that in situ microbial reaction rates determined using disturbed samples in minicosms and mesocosms yielded respiration rates that greatly exceeded field conditions. Mesocosms can, however, provide a useful environment for conducting process‐related research in unsaturated environments.
Arsenic in Glacial Drift Aquifers and the Implication for Drinking Water—Lower Illinois River Basin
Authors: Warner Kelly L. 
Published: December 2005

AbstractThe lower Illinois River Basin (LIRB) covers 47,000 km2 of central and western Illinois. In the LIRB, 90% of the ground water supplies are from the deep and shallow glacial drift aquifers. The deep glacial drift aquifer (DGDA) is below 152 m altitude, a sand and gravel deposit that fills the Mahomet Buried Bedrock Valley, and overlain by more than 30.5 m of clayey till. The LIRB is part of the USGS National Water Quality Assessment program, which has an objective to describe the status and trends of surface and ground water quality.In the DGDA, 55% of the wells used for public drinking‐water supply and 43% of the wells used for domestic drinking water supply have arsenic concentrations above 10 μg/L (a new U.S. EPA drinking water standard). Arsenic concentrations greater than 25 μg/L in ground water are mostly in the form of arsenite (AsIII). The proportion of arsenate (AsV) to arsenite does not change along the flowpath of the DGDA. Because of the limited number of arsenic species analyses, no clear relations between species and other trace elements, major ions, or physical parameters could be established. Arsenic and barium concentrations increase from east to west in the DGDA and are positively correlated. Chloride and arsenic are positively correlated and provide evidence that arsenic may be derived locally from underlying bedrock.Solid phase geochemical analysis of the till, sand and gravel, and bedrock show the highest presence of arsenic in the underlying organic‐rich carbonate bedrock. The black shale or coal within the organic‐rich carbonate bedrock is a potential source of arsenic. Most high arsenic concentrations found in the DGDA are west and downgradient of the bedrock structural features. Geologic structures in the bedrock are potential pathways for recharge to the DGDA from surrounding bedrock.
Trace Metal Concentrations in Shallow Ground Water
Authors: Zelewski Linda M. , Krabbenhoft David P. , Armstrong David E. 
Published: December 2005

AbstractTrace metal clean sampling and analysis techniques were used to examine the temporal patterns of Hg, Cu, and Zn concentrations in shallow ground water, and the relationships between metal concentrations in ground water and in a hydrologically connected river. Hg, Cu, and Zn concentrations in ground water ranged from 0.07 to 4.6 ng L−1, 0.07 to 3.10 μg L−1, and 0.17 to 2.18 μg L−1, respectively. There was no apparent seasonal pattern in any of the metal concentrations. Filtrable Hg, Cu, and Zn concentrations in the North Branch of the Milwaukee River ranged from below the detection limit to 2.65 ng Hg L−1,0.51 to 4.30 μg Cu L−1, and 0.34 to 2.33 μg Zn L−1. Thus, metal concentrations in ground water were sufficiently high to account for a substantial fraction of the filtrable trace metal concentration in the river. Metal concentrations in the soil ranged from 8 to 86 ng Hg g−1, 10 to 39 μg Cu g−1, and 15 to 84 μg Zn g−1. Distribution coefficients, KD, in the aquifer were 7900,22,000, and 23,000 L kg−1 for Hg, Cu, and Zn, respectively. These values were three to 40 times smaller than KD values observed in the Milwaukee River for suspended particulate matter.
The Steady‐State Dipole‐Flow Test for Characterization of Hydraulic Conductivity Statistics in a Highly Permeable Aquifer: Horkheimer Insel Site, Germany
Authors: Zlotnik Vitaly A. , Zurbuchen Brian R. , Ptak Thomas 
Published: December 2005

AbstractOver the last decade the dipole‐flow test (DFT) evolved from the general idea of using recirculatory flow to evaluate aquifer properties, to the development of prototype instrumentation and feasibility studies, to a reliable tool for characterization of aquifer heterogeneity. The DFT involves the interpretation of head in recirculatory flow between injection and extraction sections (chambers) in a single well isolated from each other by a multipacker system. In this study, the steady‐state dipole flow test (DFT) has been used to characterize the statistics of horizontal hydraulic conductivity (Kr) of the highly permeable, heterogeneous, and thin aquifer at the Horkheimer Insel site, Germany. In previous studies, Kr estimates were based on the steady‐state head difference between chambers. A new by‐chamber interpretation is proposed that is based on drawdown within each individual chamber. This interpretation yields more detailed information on structure of heterogeneity of the aquifer without introducing complexity into the analysis. The DFT results indicate that Kr ranges from 49 to 6000 m/day (mean In Kr [(m/s)]∼—4, and variance of In Kr [(m/s)] ∼ 1–2). Descriptive statistics from the DFT compare well with those from previous field and laboratory tests (pumping, borehole flowmeter, and permeameter tests and grain‐size analysis) at this site. It is shown that the role of confining boundaries in the DFT interpretation is negligible even in this case of a thin (< 4 m thick) aquifer. This study demonstrates the flexibility of the DFT and expands the potential application of this method to a wide range of hydrogeologic settings.
Effect of Natural Gas Exsolution on Specific Storage in a Confined Aquifer Undergoing Water Level Decline
Authors: Yager Richard M. , Fountain John C. 
Published: December 2005

AbstractThe specific storage of a porous medium, a function of the compressibility of the aquifer material and the fluid within it, is essentially constant under normal hydrologic conditions. Gases dissolved in ground water can increase the effective specific storage of a confined aquifer, however, during water level declines. This causes a reduction in pore pressure that lowers the gas solubility and results in exsolution. The exsolved gas then displaces water from storage, and the specific storage increases because gas compressibility is typically much greater than that of water or aquifer material.This work describes the effective specific storage of a confined aquifer exsolving dissolved gas as a function of hydraulic head and the dimensionless Henry's law constant for the gas. This relation is applied in a transient simulation of ground water discharge from a confined aquifer system to a collapsed salt mine in the Genesee Valley in western New York. Results indicate that exsolution of gas significantly increased the effective specific storage in the aquifer system, thereby decreasing the water level drawdown.
Ground Water/Surface Water Interactions in Lake Naivasha, Kenya, Using δ18O, δD, and 3H/3He Age‐Dating
Authors: Ojiambo Bwire S. , Poreda Robert J. , Lyons W. Berry 
Published: December 2005

AbstractWe have analyzed a series of ground water samples from the Lake Naivasha region, Kenya, for their helium isotopic composition. Lake Naivasha is unique among the East Africa Rift Valley lakes in that it is fresh. It has long been thought that the low salinity of this lake is due, in part, to rapid water loss from the lake into the local ground water system. Our results show that the Olkaria geothermal waters, south of the lake, are devoid of tritium and, thus, are more than 50 years old. An important implication of these results is that even if Olkaria geothermal reservoir water originated from Lake Naivasha, it has been underground for a long time, (>50 years) and is not derived from present‐day Lake Naivasha water. This flow time is of the same order of magnitude as conservative major solutes, such as chloride, as determined through residence time calculations. On the north side of Lake Naivasha, deep wells (91 m) have water ∼ 20 years old. Water from these wells has stable isotopic values resembling those of nearby rivers, and high‐elevation eastern Rift water. This indicates that this water recharges from rains from high eastern Rift Valley escarpments. Many of the shallow wells on the south side of the lake have 3H/3He ages between four and 17 years. The young ages and the δ18 O‐enriched signature of the water from these wells indicate that they are recharged by a mixture of water from the lake, Rift flanks, and water from deep pumping wells that is recharged during irrigation. Water mixing ratio calculations using δ18O and δD isotopes show that about 50% to 70% of the southern ground water system is derived from the lake, while the Olkaria geothermal reservoir water shows that 40% to 50% of this water is originally lake water. Calculated mean recharge rates range from 0.10 to 1.59 m/yr with a mean of 0.52±0.40 m/yr. Estimated horizontal velocity from 3H/3He age dating between Lake Naivasha and a well about 3 km to the south is 75 m/yr, giving average horizontal hydraulic conductivity of 6 m/day.
Introduction of Wavelet Analyses to Rainfall/Runoffs Relationship for a Karstic Basin: The Case of Licq‐Atherey Karstic System (France)
Authors: Labat David , Ababou Rachid , Mangin Alain 
Published: December 2005

AbstractKarstic systems are highly heterogeneous geological formations characterized by a multiscale temporal and spatial hydrologic behavior with more or less localized temporal and spatial structures. Classical correlation and spectral analyses cannot take into account these properties. Therefore, it is proposed to introduce a new kind of transformation: the wavelet transform. Here we focus particularly on the use of wavelets to study temporal behavior of local precipitation and watershed runoffs from a part of the karstic system. In the first part of the paper, a brief mathematical overview of the continuous Morlet wavelet transform and of the multiresolution analysis is presented. An analogy with spectral analyses allows the introduction of concepts such as wavelet spectrum and cross‐spectrum. In the second part, classical methods (spectral and correlation analyses) and wavelet transforms are applied and compared for daily rainfall rates and runoffs measured on a French karstic watershed (Pyrenees) over a period of 30 years.Different characteristic time scales of the rainfall and runoff processes are determined. These time scales are typically on the order of a few days for floods, but they also include significant half‐year and one‐year components and multi‐annual components. The multiresolution cross‐analysis also provides a new interpretation of the impulse response of the system. To conclude, wavelet transforms provide a valuable amount of information, which may be now taken into account in both temporal and spatially distributed karst modeling of precipitation and runoff.
Evaluation of Recharge in a Small Temperate Catchment Using Natural and Applied δ18O Profiles in the Unsaturated Zone
Authors: McConville C. , Kalin R.M. , Johnston H. , McNeill G.W. 
Published: December 2005

AbstractA water balance study was used for determining recharge rate and mechanisms in the Enler Catchment, Northern Ireland. Here spatially limited data for the water balance resulted in varied calculation of the annual and monthly net infiltration rate. This paper outlines a method whereby high‐resolution soil profiles (1 to 2 cm) were obtained from field cores in the upper 2 m of the unsaturated zone using δ18O of water. These profiles show changes in isotopic composition that range from individual rainfall events to annually integrated cycles of rainfall. Recharge rates were calculated from stable isotope profiles for each of the four main soil types in the study catchment and summed over each area resulting in an average recharge in the range 55 to 70 mm/a, which is comparable with previous findings. Applied isotopic tracer tests were also conducted to evaluate the extent of preferential flow through the two main soil types in the catchment. Rates of water movement found from these experiments show good agreement with natural isotopic profiles; however, evidence suggests that preferential flow is not the dominant process controlling water movement in this catchment. This type of data provides valuable information about recharge rates and mechanisms and may facilitate better prediction of contaminant transport pathways in the vadose zone.
Delineating a Recharge Area for a Spring Using Numerical Modeling, Monte Carlo Techniques, and Geochemical Investigation
Authors: Hunt Randall J. , Steuer Jeffery J. , Mansor M. Teresa C. , Bullen Thomas D. 
Published: December 2005

AbstractRecharge areas of spring systems can be hard to identify, but they can be critically important for protection of a spring resource. A recharge area for a spring complex in southern Wisconsin was delineated using a variety of complementary techniques. A telescopic mesh refinement (TMR) model was constructed from an existing regional‐scale ground water flow model. This TMR model was formally optimized using parameter estimation techniques; the optimized “best fit” to measured heads and fluxes was obtained by using a horizontal hydraulic conductivity 200% larger than the original regional model for the upper bedrock aquifer and 80% smaller for the lower bedrock aquifer. The uncertainty in hydraulic conductivity was formally considered using a stochastic Monte Carlo approach. Two‐hundred model runs used uniformly distributed, randomly sampled, horizontal hydraulic conductivity values within the range given by the TMR optimized values and the previously constructed regional model. A probability distribution of particles captured by the spring, or a “probabilistic capture zone,” was calculated from the realistic Monte Carlo results (136 runs of 200). In addition to portions of the local surface watershed, the capture zone encompassed areas outside of the watershed—demonstrating that the ground watershed and surface watershed do not coincide. Analysis of water collected from the site identified relatively large contrasts in chemistry, even for springs within 15 m of one another. The differences showed a distinct gradation from Ordovician‐carbonate‐dominated water in western spring vents to Cambrian‐sandstone‐influenced water in eastern spring vents. The difference in chemistry was attributed to distinctive bedrock geology as demonstrated by overlaying the capture zone derived from numerical modeling over a bedrock geology map for the area. This finding gives additional confidence to the capture zone calculated by modeling.
Migration of Induced‐Infiltrated Stream Water into Nearby Aquifers Due to Seasonal Ground Water Withdrawal
Authors: Chen Xunhong 
Published: December 2005

AbstractAnalysis of stream‐aquifer interaction due to ground water extraction has traditionally focused on the determination of the amount of water depleted in the stream. Less attention has been paid to the movement of infiltrated stream water inside aquifer, particularly for agricultural areas. This paper presents a method of using particle‐tracking techniques to evaluate the transport of the leaked stream water in the nearby aquifers. Simple stream‐aquifer conditions are used to demonstrate the usefulness of the analysis. Travel times, pathlines, and influence zones of stream water were determined between a stream and nearby pumping wells for seasonal ground water extraction areas. When water quantity is a concern, the analyses provide additional information about stream depletion; when water quality is an issue, they offer information for wellhead protection. Analyses were conducted for transient conditions, and both pumping and nonpumping periods were considered. According to the results from the simulation examples, migration of infiltrated stream water into the nearby aquifers is generally slow and most infiltrated stream water does not arrive at the pumping well at the end of a 90‐day irrigation season. Infiltrated stream water may remain in the aquifer for several years before arriving at the pumping well. For aquifers with a regional hydraulic gradient toward streams, part of the infiltrated stream water may discharge back to streams during a recovery period.
Application of a Nonlinear Slug Test Model
Authors: McElwee CD. 
Published: December 2005

AbstractKnowledge of the hydraulic conductivity distribution is of utmost importance in understanding the dynamics of an aquifer and in planning the consequences of any action taken upon that aquifer. Slug tests have been used extensively to measure hydraulic conductivity in the last 50 years since Hvorslev's (1951) work. A general nonlinear model based on the Navier‐Stokes equation, nonlinear frictional loss, non‐Darcian flow, acceleration effects, radius changes in the wellbore, and a Hvorslev model for the aquifer has been implemented in this work. The nonlinear model has three parameters: β, which is related primarily to radius changes in the water column; A, which is related to the nonlinear head losses; and K, the hydraulic conductivity. An additional parameter has been added representing the initial velocity of the water column at slug initiation and is incorporated into an analytical solution to generate the first time step before a sequential numerical solution generates the remainder of the time solution. Corrections are made to the model output for acceleration before it is compared to the experimental data. Sensitivity analysis and least squares fitting are used to estimate the aquifer parameters and produce some diagnostic results, which indicate the accuracy of the fit. Finally, an example of field data has been presented to illustrate the application of the model to data sets that exhibit nonlinear behavior. Multiple slug tests should be taken at a given location to test for nonlinear effects and to determine repeatability.
Subsurface Transfer of Chloride After a Lake Retreat in the Central Andes
Authors: Coudrain Anne , Talbi Amal , Ledoux Emmanuel , Loubet Michel , Vacher Jean , Ramirez Edson 
Published: December 2005

AbstractThe area under study covers 3500 km2 in the upstream part of the closed catchment basin of the salt crust of Uyuni. This crust is a remnant of the saline Lake Tauca, which covered the area about 15,000 years ago. In the downstream part of the aquifer, the Cl concentration of ground water and Cl content in the unsaturated zone exceed 20 meq/L and 18 kg/m2, respectively. With the present hydrological conditions under semiarid conditions, the ground water residence time in the study area exceeds 3000 years. Transient simulations over 11,000 years were made using initial conditions as the retreat of Lake Tauca and taking into account a low recharge during the arid mid‐Holocene period. The modeling simulates ground water flow, Cl transport, and ground water residence time. It includes the evaporation from the aquifer that leads to the accumulation of chloride in the unsaturated zone. Results of the modeling are consistent with the observations if it is assumed that the Cl previously accumulated in the unsaturated zone was flushed back into the aquifer around 2000 years B.P., contemporaneously with the end of the arid period.
Characterization and Origin of Dissolved Organic Carbon in Yegua Ground Water in Brazos County, Texas
Authors: Routh Joyanto , Grossman Ethan L. , Murphy Ellyn M. , Benner Ronald 
Published: December 2005

AbstractDissolved organic carbon (DOC) concentrations in five shallow (< 20 m) and three deeper wells (27 to 30 m) in the Eocene Yegua Formation (Brazos County in east‐central Texas) ranged from 92 to 500 μm. Characterization of high, intermediate, and low molecular weight DOC fractions (HMW > 3000 amu, IMW 1000 to 3000 amu, and LMW 500 to 1000 amu) and combined neutral sugar analyses provide information on organic matter sources in the Yegua aquifers. Combined neutral sugars ranged in concentration from 0.6 to 2.7 μmol/L and comprised 0.8% to 6.7% of DOC in ground water. Glucose was the most abundant neutral sugar, followed by xylose and galactose, arabinose, mannose, rhamnose, and fucose. These combined neutral sugars were more diagenetically altered in shallow, oxic ground water as indicated by high mole % fucose + rhamnose and low neutral sugar yield. The precursors for neutral sugars are most probably angiosperm leaves, which show a similar distribution pattern of neutral sugars. Ground water DOC was depleted in 13C relative to soil‐zone organic matter (OM) (−16‰ to −19‰). The δ13C values of bulk DOC and HMW DOC ranged from −24‰ to –32‰, whereas LMW and IMW DOC ranged from −32‰ to −34‰ and ‰16‰ to ‰28‰, respectively. This variability in δ13C values is probably related to microbial processes and selective preservation of OM. Carbon isotope analyses in bulk and different molecular weight DOC fractions imply a predominantly C3 OM source and a low contribution of soil‐zone OM to DOC.
Estimating Recharge Distribution by Incorporating Runoff from Mountainous Areas in an Alluvial Basin in the Great Basin Region of the Southwestern United States
Authors: Stone Dan B. , Moomaw Cynthia L. , Davis Andy 
Published: December 2005

AbstractA method is described to estimate the distribution of ground water recharge within hydrographic basins in the Great Basin region of the southwestern United States on the basis of estimated runoff from high mountainous areas and subsequent infiltration in alluvial fans surrounding the intermontane basins. The procedure involves a combination of Geographic Information System (GIS) analysis, empirical surface‐runoff modeling, and water‐balance calculations. The method addresses the need to develop and incorporate constraints on the distribution of recharge in regional‐scale ground water flow modeling of arid and semiarid environments. The conceptual approach and methodology were developed for Crescent Valley, Nevada. However, the concept and method are generally applicable to any region where excess precipitation in upland areas is conveyed to lower elevations before it infiltrates to recharge the ground water system. Application of the procedure to a ground water flow model of Crescent Valley appears both qualitatively and quantitatively to result in a more accurate representation of actual recharge conditions than might otherwise have been prescribed.