bluuebunny/crossref_metadata_2025_split huggingface dataset:
Modeling the Effect of Chemical Fertilizers on Ground Water Quality in the Nile Valley Aquifer, Egypt
Authors: Shamrukh Mohamed , Corapcioglu M. Yavuz , Hassona Fayek A.A. 
Published: December 2005

AbstractChemical fertilizer use in Egypt has increased significantly since the construction of the Aswan High Dam in 1968. Increased applications of chemical fertilizers in irrigated lands are likely to create nonpoint contamination sources of chemical fertilizer species. This study was conducted to investigate the contamination of ground water by nitrogen and phosphorus chemical fertilizers, as well as the availability of ground water for irrigation and public water supply for the next century. Future concentrations of NO3, and PO3‐ in shallow and deep ground water in the Nile Valley were assessed under realizable rates of fertilizer application. A ground water modeling system (GMS) was used to simulate the three‐dimensional ground water flow and contaminant transport in the Tahta region of the Nile Valley Aquifer, and to predict the future concentrations of chemical fertilizer species. Results of the transport simulation predict the occurrence of ground water contamination at shallow depths (30 m) due to the high rate and method of chemical fertilizer applications. Best management practices should be employed to control and reduce the nitrate leaching and future impact of phosphorus and potassium fertilizer applications. At the same time, new deeper wells should be constructed. In addition, the use of hand pumps, in zones close to croplands (15 m depth) must be avoided due to susceptibility to fertilizer contamination. Ground water from existing deep wells can be used as an alternative water supply. Furthermore, a ground water quality monitoring system should be established for early detection of ground water contamination and to determine progress of the fertilizer contaminant plume. A properly designed system should monitor nitrate and phosphate composition in observation and water supply wells.
Relating Nitrogen Sources and Aquifer Susceptibility to Nitrate in Shallow Ground Waters of the United States
Authors: Nolan Bernard T. 
Published: December 2005

AbstractCharacteristics of nitrogen loading and aquifer susceptibility to contamination were evaluated to determine their influence on contamination of shallow ground water by nitrate. A set of 13 explanatory variables was derived from these characteristics, and variables that have a significant influence were identified using logistic regression (LR). Multivariate LR models based on more than 900 sampled wells predicted the probability of exceeding 4 mg/L of nitrate in ground water. The final LR model consists of the following variables: (1) nitrogen fertilizer loading (p‐value = 0.012); (2) percent cropland‐pasture (p < 0.001); (3) natural log of population density (p < 0.001); (4) percent well‐drained soils (p = 0.002); (5) depth to the seasonally high water table (p = 0.001); and (6) presence or absence of a fracture zone within an aquifer (p = 0.002). Variables 1–3 were compiled within circular, 500 m radius areas surrounding sampled wells, and variables 4–6 were compiled within larger areas representing targeted land use and aquifers of interest. Fitting criteria indicate that the full logistic‐regression model is highly significant (p < 0.001), compared with an intercept‐only model that contains none of the explanatory variables. A goodness‐of‐fit test indicates that the model fits the data well, and observed and predicted probabilities of exceeding 4 mg/L nitrate in ground water are strongly correlated (r2= 0.971). Based on the multivariate LR model, vulnerability of ground water to contamination by nitrate depends not on any single factor but on the combined, simultaneous influence of factors representing nitrogen loading sources and aquifer susceptibility characteristics.
Use of NADP Archive Samples to Determine the Isotope Composition of Precipitation: Characterizing the Meteoric Input Function for Use in Ground Water Studies
Authors: Harvey F. Edwin 
Published: December 2005

AbstractStable oxygen and hydrogen isotopes have been used in ground water studies to investigate recharge, mixing, ground water/surface water interaction, advective‐diffusive transport, paleohydrogeologic interactions and to estimate ground water ages. Such studies require that the isotopic composition of precipitation be known, as precipitation is a major input to ground water and surface water systems. As oxygen‐18 and deuterium data for precipitation are lacking across much of the United States, there is need to establish additional local meteoric water lines as isotope input functions across the region, as well as to develop better understanding of the isotopic climate linkages that control oxygen and hydrogen isotope ratios in precipitation. In the absence of long‐term monitoring stations, one possible solution to this problem is to determine the δ18O and δ2H values of precipitation using archive samples collected at monitoring stations managed by the National Atmospheric Deposition Program (NADP). This study describes and interprets the seasonal δ18O and δ2H composition of archived precipitation samples collected in eastern Nebraska near the town of Mead during the years 1992–1994. Values for δ18O range from ‐23.6 to ‐0.7%o. Values for δ2H range from ‐172 to 0 %o Yearly arithmetic mean δ18O and 82H values for the Mead station are ‐8.1 %c and ‐53 %o, respectively. Weighted yearly means for δ18O and δ2H were ‐7.4 %c and ‐48 %c, respectively. Mead values show a strong isotopic enrichment between winter and summer precipitation, and a strong δ18O‐T correlation (r2= 0.91) for mean monthly values of about 0.5 %o per degree Celsius. The local meteoric water line for the Mead site is δ2H = 7.40 δ18O + 7.32. Deuterium excess values suggest that most of the moisture across the region is derived primarily from a Gulf of Mexico source. The results of this study demonstrate that in the absence of long‐term monitoring stations such as those operated globally by the International Atomic Energy Association, NADP archive samples can be used to determine the isotopic composition of precipitation, to characterize the local meteoric water line and establish the various climatic relationships, and define the meteoric input function for use in ground water studies.
Delineating Ground Water Recharge from Leaking Irrigation Canals Using Water Chemistry and Isotopes
Authors: Harvey F. Edwin , Sibray Steven S. 
Published: December 2005

AbstractAcross the Great Plains irrigation canals are used to transport water to cropland. Many of these canals are unlined, and leakage from them has been the focus of an ongoing legal, economic, and philosophical debate as to whether this lost water should be considered waste or be viewed as a beneficial and reasonable use since it contributes to regional ground water recharge. While historically there has been much speculation about the impact of canal leakage on local ground water, actual data are scarce. This study was launched to investigate the impact of leakage from the Interstate Canal, in the western panhandle of Nebraska, on the hydrology and water quality of the local aquifer using water chemistry and environmental isotopes. Numerous monitoring wells were installed in and around a small wetland area adjacent to the canal, and ground water levels were monitored from June 1992 until January 1995. Using the water level data, the seepage loss from the canal was estimated. In addition, the canal, the monitoring wells, and several nearby stock and irrigation wells were sampled for inorganic and environmental isotope analysis to assess water quality changes, and to determine the extent of recharge resulting from canal leakage. The results of water level monitoring within study wells indicates a rise in local ground water levels occurs seasonally as a result of leakage during periods when the canal is filled. This rise redirects local ground water flow and provides water to nearby wetland ecosystems during the summer months. Chemical and isotopic results were used to delineate canal, surface, and ground water and indicate that leaking canal water recharges both the surface alluvial aquifer and upper portions of the underlying Brule Aquifer. The results of this study indicate that lining the Interstate Canal could lower ground water levels adjacent to the canal, and could adversely impact the local aquifer.
Storage Coefficient Revisited: Is Purely Vertical Strain a Good Assumption?
Authors: Burbey Thomas J. 
Published: December 2005

AbstractThe storage coefficient that Is used ubiquitously today was first defined by the analytical work of Theis and Jacob over a half‐century ago. Inherent within this definition is the restriction of purely vertical compression of the aquifer during a reduction in pressure. The assumption is revisited and quantitatively evaluated by comparing numerical results using both one‐ and three‐dimensional strain models in the presence of three‐dimensional flow. Results indicate that (1) calculated hydraulic head values are nearly identical for both models; (2) the release of water from storage in terms of volume strain is nearly identical for both models and that the location of maximum production moves outward from the well as a function of time; (3) the vertical strain components are markedly different with at least 50% of the total volume of water pumped originating from horizontal strain (and Increasing to as much as 70%); and (4) for the one‐dimensional strain model to yield the necessary quantity of water to the pumped well, the resulting vertical compaction (land subsidence) is as much as four times greater and vertical strain Is as much as 60% greater than the three‐dimensional strain model. Results indicate that small changes in porosity resulting from horizontal strain can yield extremely large quantities of water to the pumping well. This study suggests that the assumption of purely vertical strain used In the definition of the storage coefficient is not valid.
Exploitation of High‐Yields in Hard‐Rock Aquifers: Downscaling Methodology Combining GIS and Multicriteria Analysis to Delineate Field Prospecting Zones
Authors: Lachassagne Patrick , Wyns R. , Bérard Pierre , Bruel Thierry , Chéry Laurence , Coutand Thierry , Desprats Jean‐François , Le Strat Paul 
Published: December 2005

AbstractBased on research work in the Truyàre River catchment of the Massif Central (Lozàre Department, France), a methodology has been developed for delineating favorable prospecting zones of a few square kilometers within basement areas of several hundred, if not thousand, square kilometers for the purpose of siting high‐yield water wells. The methodology adopts a functional approach to hard‐rock aquifers using a conceptual model of the aquifer structure and of the functioning of the main aquifer compartments: the alterites (weathered and decayed rock), the underlying weathered‐fissured zone, and the fractured bedrock. It involves an economically feasible method of mapping the thickness and spatial distribution of the alterites and the weathered‐fissured zone, on which the long‐term exploitation of the water resource chiefly depends. This method is used for the first time in hydrogeology.The potential ground water resources were mapped by GIS multicriteria analysis using parameters characterizing the structure and functioning of the aquifer, i.e., lithology and hydrogeological properties of the substratum, nature and thickness of the alterites and weathered‐fissured zone, depth of the water table, slope, fracture networks and present‐day tectonic stresses, and forecasted ground water quality.The methodology involves a coherent process of downscaling that, through applying methods that are increasingly precise but also increasingly costly, enables the selection of sites with diminishing surface areas as the work advances. The resulting documents are used for ground water exploration, although they can also be applied to the broader domain of land‐use management.
Drawdown and Stream Depletion Produced by Pumping in the Vicinity of a Partially Penetrating Stream
Authors: Butler James J. , Zlotnik Vitaly A. , Tsou Ming‐Shu 
Published: December 2005

AbstractCommonly used analytical approaches for estimation of pumping‐induced drawdown and stream depletion are based on a series of idealistic assumptions about the stream‐aquifer system. A new solution has been developed for estimation of drawdown and stream depletion under conditions that are more representative of those in natural systems (finite width stream of shallow penetration adjoining an aquifer of limited lateral extent). This solution shows that the conventional assumption of a fully penetrating stream will lead to a significant overestimation of stream depletion (> 100%) in many practical applications. The degree of overestimation will depend on the value of the stream leakance parameter and the distance from the pumping well to the stream. Although leakance will increase with stream width, a very wide stream will not necessarily be well represented by a model of a fully penetrating stream. The impact of lateral boundaries depends upon the distance from the pumping well to the stream and the stream leakance parameter. In most cases, aquifer width must be on the order of hundreds of stream widths before the assumption of a laterally infinite aquifer is appropriate for stream‐depletion calculations. An important assumption underlying this solution is that stream‐channel penetration is negligible relative to aquifer thickness. However, an approximate extension to the case of nonnegligible penetration provides reasonable results for the range of relative penetrations found in most natural systems (up to 85%). Since this solution allows consideration of a much wider range of conditions than existing analytical approaches, it could prove to be a valuable new tool for water management design and water rights adjudication purposes.
Explaining the Thinness of the Fresh Water Lens in the Pleistocene Carbonate Aquifer on Andros Island, Bahamas
Authors: Ritzi Robert W. , Bukowski John M. , Carney Cindy K. , Boardman Mark R. 
Published: December 2005

AbstractTwo hypotheses are explored to explain the thinness of the fresh water lens on Andros Island, Bahamas. The lens is an order of magnitude thinner than predicted by the Ghyben‐Herzberg theory. One hypothesis previously posed in the literature is that the base of the lens is governed by the contact between the Lucayan Formation and the pre‐Lucayan limestones. An alternate hypothesis, posed here, is that thinning is caused by the hydraulic influence of low‐permeability paleosols in the Lucayan Formation. These hypotheses were explored, along with the influence of recharge and other factors, using a numerical model for variable‐density flow and salt transport. In the layered system of grainstones/packstones and paleosols within the Lucayan Formation itself, the velocity vectors are nearly horizontal in the grainstones/packstones, and they are nearly vertical in the paleosols. These strata above the pre‐Lucayan, all lower than it in permeability, draw the base of the lens upward to a position well above the contact by significantly reducing pressure within and below the strata relative to hydrostatic pressure. It is the loss of pressure across the paleosols that dramatically thins the fresh water lens, and thus the predominant hydraulic control on lens thickness arises from the existence of paleosols.
Determination of Specific Yield for the Biscayne Aquifer with a Canal‐Drawdown Test
Authors: Bolster Carl H. , Genereux David P. , Saiers James E. 
Published: December 2005

AbstractData from a large‐scale canal‐drawdown test were used to estimate the specific yield (s) of the Biscayne Aquifer, an uncon‐fined limestone aquifer in southeast Florida. The drawdown test involved dropping the water level in a canal by about 30 cm and monitoring the response of hydraulic head in the surrounding aquifer. Specific yield was determined by analyzing data from the unsteady portion of the drawdown test using an analytical stream‐aquifer interaction model (Zlotnik and Huang 1999). Specific yield values computed from drawdown at individual piezometers ranged from 0.050 to 0.57, most likely indicating heterogeneity of specific yield within the aquifer (small‐scale variation in hydraulic conductivity may also have contributed to the differences in sy among piezometers). A value of 0.15 (our best estimate) was computed based on all drawdown data from all piezometers.We incorporated our best estimate of specific yield into a large‐scale two‐dimensional numerical MODFLOW‐based ground water flow model and made predictions of head during a 183–day period at four wells located 337 to 2546 m from the canal. We found good agreement between observed and predicted heads, indicating our estimate of specific yield is representative of the large portion of the Biscayne Aquifer studied here. This work represents a practical and novel approach to the determination of a key hydrogeological parameter (the storage parameter needed for simulation and calculation of transient unconfined ground water flow), at a large spatial scale (a common scale for water resource modeling), for a highly transmissive limestone aquifer (in which execution of a traditional pump test would be impractical and would likely yield ambiguous results). Accurate estimates of specific yield and other hydrogeological parameters are critical for management of water supply, Everglades environmental restoration, flood control, and other issues related to the ground water hydrology of the Biscayne Aquifer.
Numerical Examination of the Factors Controlling DNAPL Migration Through a Single Fracture
Authors: Reynolds D.A. , Kueper B.H. 
Published: December 2005

AbstractThe migration of five dense nonaqueous phase liquids (DNAPLs) through a single fracture in a clay aquitard was numerically simulated with the use of a compositional simulator. The effects of fracture aperture, fracture dip, matrix porosity, and matrix organic carbon content on the migration of chlorobenzene, 1,2‐dichloroethylene, trichloroethyiene, tetrachloroethylene, and 1,2‐dibromoethane were examined. Boundary conditions were chosen such that DNAPL entry into the system was allowed to vary according to the stresses applied. The aperture is the most important factor of those studied controlling the migration rate of DNAPL through a single fracture embedded in a clay matrix. Loss of mass to the matrix through diffusion does not significantly retard the migration rate of the DNAPL, particularly in larger aperture fractures (e.g., 50 urn). With time, the ratio of diffusive loss to the matrix to DNAPL flux into the fracture approaches an asymptotic value lower than unity. The implication is that matrix diffusion cannot arrest the migration of DNAPL in a single fracture. The complex relationships between density, viscosity, and solubility that, to some extent, govern the migration of DNAPL through these systems prevent accurate predictions without the use of numerical models. The contamination potential of the migrating DNAPL is significantly increased through the transfer of mass to the matrix. The occurrence of opposite concentration gradients within the matrix can cause dissolved phase contamination to exist in the system for more than 1000 years after the DNAPL has been completely removed from the fracture.
Methods to Determine Storativity of Infinite Confined Aquifers from a Recovery Test
Authors: Chenaf Djaouida , Chapuis Robert P. 
Published: December 2005

AbstractStarting from the equations of Theis and Cooper‐Jacob, two new mathematical methods are proposed for interpreting the residual drawdown data for an infinite confined aquifer. Under Theis' assumptions and using the Cooper‐Jacob approximation, the principal aquifer characteristics of transmissivity, pumping storativity, and recovery storativity are expressed without any correction or additional assumption. An actual case is used for illustration and confirms the validity of proposed equations and methods.
Michigan Basin Regional Ground Water Flow Discharge to Three Great Lakes
Authors: Hoaglund John Robert , Huffman Gary Cecil , Grannemann Norman Guy 
Published: December 2005

AbstractGround water discharge to the Great Lakes around the Lower Peninsula of Michigan is primarily from recharge in riparian basins and proximal upland areas that are especially important to the northern half of the Lake Michigan shoreline. A steady‐state finite‐difference model was developed to simulate ground water flow in four regional aquifers in Michigan's Lower Peninsula: the Glaciofluvial, Saginaw, Parma‐Bayport, and Marshall aquifers interlayered with the Till/“red beds,” Saginaw, and Michigan confining units, respectively. The model domain was laterally bound by a continuous specified‐head boundary, formed from lakes Michigan, Huron, St. Clair, and Erie, with the St. Clair and Detroit River connecting channels.The model was developed to quantify regional ground water flow in the aquifer systems using independently determined recharge estimates. According to the flow model, local stream stages and discharges account for 95% of the overall model water budget; only 5% enters the lakes directly from the ground water system. Direct ground water discharge to the Great Lakes' shorelines was calculated at 36 m3/sec, accounting for 5% of the overall model water budget. Lowland areas contribute far less ground water discharge to the Great Lakes than upland areas. The model indicates that Saginaw Bay receives only ∼1.13 m3/sec ground water; the southern half of the Lake Michigan shoreline receives only ∼2.83 m3/sec. In contrast, the northern half of the Lake Michigan shoreline receives more than 17 m3/sec from upland areas.
Localized Thermal Anomalies in Haloclines of Coastal Yucatan Sinkholes
Authors: Stoessell Ronald K. , Coke James G. , Easley Dale H. 
Published: December 2005

AbstractA temperature spike is reported in the haloclines of three Yucatan sinkholes along a 1 km NW‐SE transect from 5 to 4 km inland from the Caribbean coast. The temperature spike decreases in magnitude from ∼ 3.5°C to 0.2°C, approaching the coast. The anomaly does not vary diurnally and does not extend down into the underlying sea water. These conditions are inconsistent with explanations such as radiation absorption within the halocline, in situ microbially mediated sulfate reduction within the halocline and the underlying sea water, and sulfide oxidation by photosynthetic purple and green bacteria within the halocline.One explanation consistent with the shape and halocline location of the temperature spike involves a localized sea water convection cell operating near the coast. Cold sea water from the Caribbean Sea enters the coastal limestone at depths of a few hundred meters and heats up because of the geothermal gradient, buoyantly rising in vertical fractures within the unconfined aquifer. Blocked by the less dense fresh water, the movement stops in the halocline where the warm sea water mixes with brackish water. The convection cycle would be completed by the coastward movement of cooling brackish water. The observed temperature anomalies could possibly be snapshots of this warm layer moving coastward.