Recharge and Groundwater Flow Within an Intracratonic Basin,Midwestern United States

The conservative nature of chloride (Cl^?) in groundwater and the abundance of geochemical data from various sources (both published and unpublished) provided a means of developing, for the first time, a representation of the hydrogeology of the Illinois Basin on a basin‐wide scale. The creation of Cl^? isocons superimposed on plan view maps of selected formations and on cross sections across the Illinois Basin yielded a conceptual model on a basin‐wide scale of recharge into, groundwater flow within and through the Illinois Basin. The maps and cross sections reveal the infiltration and movement of freshwater into the basin and dilution of brines within various geologic strata occurring at basin margins and along geologic structures. Cross‐formational movement of brines is also seen in the northern part of the basin. The maps and cross sections also show barriers to groundwater movement created by aquitards resulting in areas of apparent isolation/stagnation of concentrated brines within the basin. The distribution of Cl^? within the Illinois Basin suggests that the current chemical composition of groundwater and distribution of brines within the basin is dependent on five parameters: (1) presence of bedrock exposures along basin margins; (2) permeability of geologic strata and their distribution relative to one another; (3) presence or absence of major geologic structures; (4) intersection of major waterways with geologic structures, basin margins, and permeable bedrock exposures; and (5) isolation of brines within the basin due to aquitards, inhomogeneous permeability, and, in the case of the deepest part of the basin, brine density effects.     

Response of deep groundwater to land use change in desert basins of the Trans‐Pecos region,Texas, USA: Effects on infiltration,recharge, and nitrogen fluxes

Quantifying the effects of anthropogenic processes on groundwater in arid regions can be complicated by thick unsaturated zones with long transit times. Human activities can alter water and nutrient fluxes, but their impact on groundwater is not always clear. This study of basins in the Trans‐Pecos region of Texas links anthropogenic land use and vegetation change with alterations to unsaturated zone fluxes and regional increases in basin groundwater NO₃^? concentrations. Median increases in groundwater NO₃^? (by 0.7–0.9 mg‐N/l over periods ranging from 10 to 50+ years) occurred despite low precipitation (220–360 mm/year), high potential evapotranspiration (~1570 mm/year), and thick unsaturated zones (10–150+ m). Recent model simulations indicate net infiltration and groundwater recharge can occur beneath Trans‐Pecos basin floors, and may have increased due to irrigation and vegetation change. These processes were investigated further with chemical and isotopic data from groundwater and unsaturated zone cores. Some unsaturated zone solute profiles indicate flushing of natural salt accumulations has occurred. Results are consistent with human‐influenced flushing of naturally accumulated unsaturated zone nitrogen as an important source of NO₃^? to the groundwater. Regional mass balance calculations indicate the mass of natural unsaturated zone NO₃^? (122–910 kg‐N/ha) was sufficient to cause the observed groundwater NO₃^? increases, especially if augmented locally with the addition of fertilizer N. Groundwater NO₃^? trends can be explained by small volumes of high NO₃^? modern recharge mixed with larger volumes of older groundwater in wells. This study illustrates the importance of combining long‐term monitoring and targeted process studies to improve understanding of human impacts on recharge and nutrient cycling in arid regions, which are vulnerable to the effects of climate change and increasing human reliance on dryland ecosystems.     

Hydrogeological and hydrogeochemical control of groundwater salinity in an arid inland basin: Dunhuang Basin,northwestern China

High groundwater salinity has become a major concern in the arid alluvial plain of the Dunhuang Basin in northwestern China because it poses a significant challenge to water resource management. Isotopic and geochemical analyses were conducted on 55 water samples from springs, boreholes and surface water to identify potential sources of groundwater salinity and analyse the processes that control increasing salinity. The total dissolved solid (TDS) content in the groundwater ranged from 400 to 41 000 mg/l, and high TDS values were commonly associated with shallow water tables and flow‐through and discharge zones in unconfined aquifers. Various groundwater contributions from rainwater, agricultural irrigation, river water infiltration and lateral inflows from mountains were identified by major ions and δD and δ¹⁸O. In general, HCO₃^? and SO₄^2? were the dominant anions in groundwater with a salinity of <2500 mg/l, whereas Cl^? and SO₄^2? were the dominant anions in groundwater with a salinity of >2500 mg/l. The major ion concentrations indicated that mineral weathering, including carbonate and evaporite dissolution, primarily affected groundwater salinity in recharge areas. Evapotranspiration controlled the major ion concentration evolution and salinity distribution in the unconfined groundwaters in the flow‐through and discharge areas, although it had a limited effect on groundwater in the recharge areas and confined aquifers. Agricultural irrigation increased the water table and enhanced evapotranspiration in the oasis areas of the basin. TDS and Cl became more concentrated, but H and O isotopes were not enriched in the irrigation district, indicating that transpiration dominated the increasing salinity. For other places in the basin, as indicated by TDS, Cl, δD and δ¹⁸O characteristics, evaporation, transpiration and water–rock interactions dominated at different hydrogeological zones, depending on the plant coverage and hydrogeological conditions. Groundwater ages of ³H, and δD and δ¹⁸O compositions and distributions suggest that most of the groundwaters in Dunhuang Basin have a paleometeoric origin and experienced a long residence time. These results can contribute to groundwater management and future water allocation programmes in the Dunhuang Basin. Copyright © 2015 John Wiley & Sons, Ltd.     

Identification of groundwater recharge sources and processes in a heterogeneous alluvial aquifer: results from multi‐level monitoring of hydrochemistry and environmental isotopes in a riverside agricultural area in Korea

We evaluated sources and pathways of groundwater recharge for a heterogeneous alluvial aquifer beneath an agricultural field, based on multi‐level monitoring of hydrochemistry and environmental isotopes of a riverside groundwater system at Buyeo, Korea. Two distinct groundwater zones were identified with depth: (1) a shallow oxic groundwater zone, characterized by elevated concentrations of NO₃^? and (2) a deeper (>10–14 m from the ground surface) sub‐oxic groundwater zone with high concentrations of dissolved Fe, silica, and HCO₃^?, but little nitrate. The change of redox zones occurred at a depth where the aquifer sediments change from an upper sandy stratum to a silty stratum with mud caps. The δ¹⁸O and δ²H values of groundwater were also different between the two zones. Hydrochemical and δ¹⁸O? δ²H data of oxic groundwater are similar to those of soil water. This illustrates that recharge of oxic groundwater mainly occurs through direct infiltration of rain and irrigation water in the sandy soil area where vegetable cropping with abundant fertilizer use is predominant. Oxic groundwater is therefore severely contaminated by agrochemical pollutants such as nitrate. In contrast, deeper sub‐oxic groundwater contains only small amounts of dissolved oxygen (DO) and NO₃^?. The ³H contents and elevated silica concentrations in sub‐oxic groundwater indicate a somewhat longer mean residence time of groundwater within this part of the aquifer. Sub‐oxic groundwater was also characterized by higher δ¹⁸O and δ²H values and lower d‐excess values, indicating significant evaporation during recharge. We suggest that recharge of sub‐oxic groundwater occurs in the areas of paddy rice fields where standing irrigation and rain water are affected by strong evaporation, and that reducing conditions develop during subsequent sub‐surface infiltration. This study illustrates the existence of two groundwater bodies with different recharge processes within an alluvial aquifer. Copyright © 2009 John Wiley & Sons, Ltd.     

Insights into groundwater salinization from hydrogeochemical and isotopic evidence in an arid inland basin

In the Manas River basin (MRB), groundwater salinization has become a major concern, impeding groundwater use considerably. Isotopic and hydrogeochemical characteristics of 73 groundwater and 11 surface water samples from the basin were analysed to determine the salinization process and potential sources of salinity. Groundwater salinity ranged from 0.2 to 11.91 g/L, and high salinities were generally located in the discharge area, arable land irrigated by groundwater, and depression cone area. The quantitative contributions of the evaporation effect were calculated, and the various groundwater contributions of transpiration, mineral dissolution, and agricultural irrigation were identified using hydrogeochemical diagrams and δD and δ¹⁸O compositions of the groundwater and surface water samples. The average evaporation contribution ratios to salinity were 5.87% and 32.7% in groundwater and surface water, respectively. From the piedmont plain to the desert plain, the average groundwater loss by evaporation increased from 7% to 29%. However, the increases in salinity by evaporation were small according to the deuterium excess signals. Mineral dissolution, transpiration, and agricultural irrigation activities were the major causes of groundwater salinization. Isotopic information revealed that river leakage quickly infiltrated into aquifers in the piedmont area with weak evaporation effects. The recharge water interacted with the sediments and dissolved minerals and subsequently increased the salinity along the flow path. In the irrigation land, shallow groundwater salinity and Cl^? concentrations increased but not δ¹⁸O, suggesting that both the leaching of soil salts due to irrigation and transpiration effect dominated in controlling the hydrogeochemistry. Depleted δ¹⁸O and high Cl^? concentrations in the middle and deep groundwater revealed the combined effects of mixing with paleo‐water and mineral dissolution with a long residence time. These results could contribute to the management of groundwater sources and future utilization programs in the MRB and similar areas.     

Hydrological and isotopic characterization of river water,groundwater, and groundwater recharge in the Heihe River basin,northwestern China

We used hydrochemistry and environmental isotope data (δ¹⁸O, δD, tritium, and ¹⁴C) to investigate the characteristics of river water, groundwater, and groundwater recharge in China's Heihe River basin. The river water and groundwater could be characterized as Ca²⁺? Mg²⁺? HCO₃^?? SO₄^2? and Na⁺? Mg²⁺? SO₄^2?? Cl^? types, respectively. Hydrogeochemical modelling using PHREEQC software revealed that the main hydrogeochemical processes are dissolution (except for gypsum and anhydrite) along groundwater flow paths from the upper to middle Heihe reaches. Towards the lower reaches, dolomite and calcite tend to precipitate. The isotopic data for most of the river water and groundwater lie on the global meteoric water line (GMWL) or between the GMWL and the meteoric water line in northwestern China, indicating weak evaporation. No direct relationship existed between recharge and discharge of groundwater in the middle and lower reaches based on the isotope ratios, d‐excess, and ¹⁴C values. On the basis of tritium in precipitation and by adopting an exponential piston‐flow model, we evaluated the mean residence time of shallow groundwater with high tritium activities, which was around 50 years (a). Furthermore, based on the several popular models, it is calculated that the deep groundwaters in piedmont alluvial fan zone of the middle reaches and in southern part of the lower reaches are modern water, whereas the deep groundwaters in the edge of the middle reaches and around Juyan Lake in the lower reaches of Heihe river basin are old water. Copyright © 2010 John Wiley & Sons, Ltd.     

Groundwater discharge mechanism in semi‐arid regions and the role of evapotranspiration

The present study examined groundwater recharge/discharge mechanisms in the regional Central Sudan Rift Basins (CSRB). Aquifers in CSRB constitute poorly sorted silisiclastics of sand, clay and gravels deposited in closed hydrologic systems of the Cretaceous–Pleistocene fluviolacustrine environments. CSRB are bounded to the north by the highlands of the Central African Shear Zone (CAZS) that represents the surface and groundwater divides. Sporadic recharge in the peripheries of the basins along the CASZ occurs subsequent to decadal and centennial storm events. Inflow from the Nile into the aquifers represents an additional source of recharge. Thus, groundwater resources cannot be labelled fossil nor can they be readily recharged. Closed hydrologic troughs located adjacent to the influent Nile system mark areas of main groundwater discharge characterized by lower hydraulic heads. This study has examined mechanisms that derive the discharge of the groundwater in these closed basins and concluded that only evapotranspirative discharge can provide a plausible explanation. Groundwater abstraction is mainly through deep‐rooted trees and effective evaporation. The increase of TDS along the flow indicates local recharge at the peripheries of basins and shows the influence of evaporation and rock/water interaction. The decline in groundwater level along a flow path was calculated using Darcy's law to estimate average recharge and evapotranspirative discharge, which are equal under natural equilibrium and make the only fluxes in CSRB. Steady‐state 2D flow modelling has demonstrated that an average recharge of 4–8 mm yr^?1 and evapotranspirative discharge of 1–22 mm yr^?1 will maintain natural equilibrium in CSRB. Sporadic storms provide recharge in the highlands to preserve the current hydraulic gradient and maintain aquifer dynamics. Simulated recharge from the Nile totals about 17·5 mm yr^?1 and is therefore a significant contributor to the water balance. Copyright © 2007 John Wiley & Sons, Ltd.     

Chemical and isotopic methods for management of artificial recharge in Mazraha Station (Damascus Basin,Syria)

Artificially enhancing recharge rate into groundwater aquifer at specially designed facilities is an attractive option for increasing the storage capacity of potable water in arid and semi‐arid region such as Damascus basin (Syria). Two dug wells (I and II) for water injection and 24 wells for water extraction are available in Mazraha station for artificial recharge experiment. Chemical and stable isotopes (δ²H and δ¹⁸O) were used to evaluate artificial recharge efficiency. 400 to 500*10³ m³ of spring water were injected annually into the ambient shallow groundwater in Mazraha station, which is used later for drinking purpose. Ambient groundwater and injected spring water are calcium bicarbonate type with EC about 880 ± 60 μS/cm and 300 ± 50 μS/cm, respectively. The injected water is under saturated versus calcite and the ambient groundwater is over saturated, while the recovered water is near equilibrium. It was observed that the injection process formed a chemical dilution plume that improves the groundwater quality. Results demonstrate that the hydraulic conductivity of the aquifer is estimated around 6.8*10^?4 m/s. The effective diameter of artificial recharge is limited to about 250 m from the injection wells. Mixing rate of 30% is required in order to reduce nitrate concentration below 50 mg/l which is considered the maximum concentration limit for potable water. Deuterium and oxygen‐18 relationship demonstrates that mixing line between injected water and ambient groundwater has a slope of 6.1. Oxygen‐18 and Cl^? plot indicates that groundwater salinity origin is from mixing process, and no dissolution and evaporation were observed. These results demonstrate the efficiency of the artificial recharge experiments to restore groundwater storage capacity and to improve the water quality. Copyright © 2011 John Wiley & Sons, Ltd.     

Innovative Environmental Tracer Techniques for Evaluating Sources of Spring Discharge from a Carbonate Aquifer Bisected by a River

Littlefield Springs discharge about 1.6 m³/s along a 10‐km reach of the Virgin River in northwestern Arizona. Understanding their source is important for salinity control in the Colorado River Basin. Environmental tracers suggest that Littlefield Springs are a mixture of older groundwater from the regional Great Basin carbonate aquifer and modern (post‐1950s) seepage from the Virgin River. While corrected ¹⁴C apparent ages range from 1 to 9 ka, large amounts of nucleogenic ⁴He and low ³He/⁴He ratios suggest that the carbonate aquifer component is likely even older Pleistocene recharge. Modeled infiltration of precipitation, hydrogeologic cross sections, and hydraulic gradients all indicate recharge to the carbonate aquifer likely occurs in the Clover and Bull Valley Mountains along the northern part of the watershed, rather than in the nearby Virgin Mountains. This high‐altitude recharge is supported by relatively cool noble‐gas recharge temperatures and isotopically depleted δ²H and δ¹⁸O. Excess (crustal) SF₆ and ⁴He precluded dating of the modern component of water from Littlefield Springs using SF₆ and ³H/³He methods. Assuming a lumped‐parameter model with a binary mixture of two piston‐flow components, Cl^?/Br^?, Cl^?/F^?, δ²H, and CFCs indicate the mixture is about 60% Virgin River water and 40% groundwater from the carbonate aquifer, with an approximately 30‐year groundwater travel time for Virgin River seepage to re‐emerge at Littlefield Springs. This suggests that removal of high‐salinity sources upstream of the Virgin River Gorge would reduce the salinity of water discharging from Littlefield Springs into the Virgin River within a few decades.     

Michigan basin regional ground water flow discharge to three Great Lakes

Ground 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 50% 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 approximately 1.13 m3/sec ground water; the southern half of the Lake Michigan shoreline receives only approximately 2.83 m3/sec. In contrast, the northern half of the Lake Michigan shoreline receives more than 17 m3/sec from upland areas.     

Estimating groundwater residence time and recharge patterns in a saline coastal aquifer

A detailed study using environmental tracers such as chloride (Cl^?) and tritium (³H), deuterium (²H) and oxygen (¹⁸O) isotopes was performed in an alluvial coastal aquifer in two contrasting environments (urban and agricultural). These environmental tracers combined with a high‐resolution multi‐level sampling approach were used to estimate groundwater residence time and recharge patterns and to validate the hydrogeochemical conceptual model already proposed in previous studies. δ¹⁸O and δ²H combined with Cl^? data proved that the hypersaline groundwater present in the deepest part of the aquifer was sourced from the underlying hypersaline aquitard via an upward flux. Both chemical and isotopic data were employed to calibrate a density‐dependent numerical model based on SEAWAT 4.0, where ³H and Cl^? were helped quantifying solutes transport within the modelled aquifer. Model results highlighted the differences on estimated recharge in the two contrasting environments, with the urban one exhibiting concentrated recharge because of preferential infiltration associated to the storm water drains network, while scarce local recharge characterized the agriculture setting. In the urban field site, is still possible to recognize at 9 m b.g.l. the input of the atmospheric anthropogenic ³H generated by testing of thermonuclear weapons, while in the agricultural field site, the ³H peak has been washed out at 6 m b.g.l. because the groundwater circulation is restricted only to the upper fresh part of the aquifer, drained by the reclamation system. The presented approach that combined high‐resolution field monitoring, environmental tracers and numerical modelling, resulted effective in validating the conceptual model of the aquifer salinization. Copyright © 2016 John Wiley & Sons, Ltd.     

Hydrological flowpaths and nitrate removal rates within a riparian floodplain along a fourth‐order stream in Brittany (France)

Three main reservoirs were identified that contribute to the shallow subsurface flow regime of a valley drained by a fourth‐order stream in Brittany (western France). (i) An upland flow that supplied a wetland area, mainly during the high‐water period. It has high N‐NO₃^? and average Cl^? concentrations. (ii) A deep confined aquifer characterized by low nitrate and low chloride concentrations that supplied the floodplain via flow upwelling. (iii) An unconfined aquifer under the riparian zone with high Cl^? and low N‐NO₃^? concentrations where biological processes removed groundwater nitrate. This aquifer collected the upland flow and supplied a relict channel that controlled drainage from the whole riparian zone. Patterns of N‐NO₃^? and Cl^? concentrations along riparian transects, together with calculated high nitrate removal, indicate that removal occurred mainly at the hillslope–riparian zone interface (i.e. first few metres of wetland), whereas dilution occurred in lower parts of the transects, especially during low‐water periods and at the beginning of recharge periods. Stream flow was modelled as a mixture of water from the three reservoirs. An estimation of these contributions revealed that the deep aquifer contribution to stream flow averaged 37% throughout the study period, while the contribution of the unconfined reservoir below the riparian zone and hillslope flow was more variable (from ca 6 to 85%) relative to rainfall events and the level of the riparian water table. At the entire riparian zone scale, NO₃^? removal (probably from denitrification) appeared most effective in winter, despite higher estimated upland NO₃^? fluxes entering the riparian zone during this period. Copyright © 2003 John Wiley & Sons, Ltd.     

Groundwater–surface water interaction in Lake Nasser,Southern Egypt

A cross‐sectional model, based on the two dimensional groundwater flow equation of Edelman, was applied at seven transects distributed over four geological cross sections to estimate groundwater heads and recharge from/or groundwater discharge to Lake Nasser. The lake with a length of 500 km and an average width of 12 km was created over the period 1964–1970, the time for constructing the Aswan High Dam (AHD). The model, constrained by regional‐scale groundwater flow and groundwater head data in the vicinity of the lake, was successfully calibrated to timeseries of piezometeric heads collected at the cross sections in the period 1965–2004. Inverse modeling yielded high values for the horizontal hydraulic conductivity in the range of 6.0 to 31.1 m day^?1 and storage coefficient between 0.01 and 0.40. The results showed the existence of a strong vertical anisotropy of the aquifer. The calibrated horizontal permeability is systematically higher than the vertical permeability (≈1000:1). The calibrated model was used to explore the recharge from/or groundwater discharge to Lake Nasser at the seven transects for a 40‐year period, i.e. from 1965 to 2004. The analysis for the last 20‐year period, 1985–2004, revealed that recharge from Lake Nasser reduced by 37% compared to the estimates for the first 20‐year period, 1965–1984. In the period 1965–2004, seepage of Lake Nasser to the surrounding was estimated at 1.15 × 10⁹ m³ year^?1. This led to a significant rise of the groundwater table. Variance‐based sensitivity and uncertainty analysis on the Edelman results were conducted applying quasi‐Monte Carlo sequences (Latin Hypercube sampling). The maximum standard deviation of the total uncertainty on the groundwater table was 0.88 m at Toshka (west of the lake). The distance from the lake, followed by the storage coefficient and hydraulic conductivity, were identified as the most sensitive parameters. Copyright © 2012 John Wiley & Sons, Ltd.     

Use of Groundwater Levels with the PULSE Analytical Model

The PULSE analytical model, which calculates daily groundwater discharge on the basis of user‐specified recharge, was originally developed for calibration using streamflow data. This article describes a model application in which groundwater level data constitute the primary control on model input. As a test case, data were analyzed from a small basin in central Pennsylvania in which extensive groundwater level data are available. The timing and intensity of daily water‐level rises are used to ascertain temporal distribution of recharge, and the simulated groundwater discharge hydrograph has shape features that are similar to the streamflow hydrograph. This article does not include details about calibration, but some steps are illustrated and general procedures are described for calibration in specific hydrologic studies. The PULSE model can be used to assess results of fully automated base flow methods and can be used to define groundwater recharge and discharge at a relatively small time scale.     

Modelling the effects of land‐use change on water and salt delivery from a catchment affected by dryland salinity in south‐east Australia

A comprehensive framework for the assessment of water and salt balance for large catchments affected by dryland salinity is applied to the Boorowa River catchment (1550 km²), located in south‐eastern Australia. The framework comprised two models, each focusing on a different aspect and operating on a different scale. A quasi‐physical semi‐distributed model CATSALT was used to estimate runoff and salt fluxes from different source areas within the catchment. The effects of land use, climate, topography, soils and geology are included. A groundwater model FLOWTUBE was used to estimate the long‐term effects of land‐use change on groundwater discharge. Unlike conventional salinity studies that focus on groundwater alone, this study makes use of a new approach to explore surface and groundwater interactions with salt stores and the stream. Land‐use change scenarios based on increased perennial pasture and tree‐cover content of the vegetation, aimed at high leakage and saline discharge areas, are investigated. Likely downstream impacts of the reduction in flow and salt export are estimated. The water balance model was able to simulate both the daily observed stream flow and salt load at the catchment outlet for high and low flow conditions satisfactorily. Mean leakage rate of about 23·2 mm year^?1 under current land use for the Boorowa catchment was estimated. The corresponding mean runoff and salt export from the catchment were 89 382 ML year^?1 and 38 938 t year^?1, respectively. Investigation of various land‐use change scenarios indicates that changing annual pastures and cropping areas to perennial pastures is not likely to result in substantial improvement of water quality in the Boorowa River. A land‐use change of about 20% tree‐cover, specifically targeting high recharge and the saline discharge areas, would be needed to decrease stream salinity by 150 µS cm^?1 from its current level. Stream salinity reductions of about 20 µS cm^?1 in the main Lachlan River downstream of the confluence of the Boorowa River is predicted. The FLOWTUBE modelling within the Boorowa River catchment indicated that discharge areas under increased recharge conditions could re‐equilibrate in around 20 years for the catchment, and around 15 years for individual hillslopes. Copyright © 2004 John Wiley & Sons, Ltd.     

Characteristics of preferential flow and groundwater discharge to Shingobee Lake,Minnesota, USA

Small‐scale heterogeneities and large changes in hydraulic gradient over short distances can create preferential groundwater flow paths that discharge to lakes. A 170 m² grid within an area of springs and seeps along the shore of Shingobee Lake, Minnesota, was intensively instrumented to characterize groundwater‐lake interaction within underlying organic‐rich soil and sandy glacial sediments. Seepage meters in the lake and piezometer nests, installed at depths of 0·5 and 1·0 m below the ground surface and lakebed, were used to estimate groundwater flow. Statistical analysis of hydraulic conductivity estimated from slug tests indicated a range from 21 to 4·8 × 10^?3 m day^?1 and small spatial correlation. Although hydraulic gradients are overall upward and toward the lake, surface water that flows onto an area about 2 m onshore results in downward flow and localized recharge. Most flow occurred within 3 m of the shore through more permeable pathways. Seepage meter and Darcy law estimates of groundwater discharge agreed well within error limits. In the small area examined, discharge decreases irregularly with distance into the lake, indicating that sediment heterogeneity plays an important role in the distribution of groundwater discharge. Temperature gradients showed some relationship to discharge, but neither temperature profiles nor specific electrical conductance could provide a more convenient method to map groundwater–lake interaction. These results suggest that site‐specific data may be needed to evaluate local water budget and to protect the water quality and quantity of discharge‐dominated lakes. Copyright © 2002 John Wiley & Sons, Ltd.     

Patterns of groundwater hydrochemistry in Apan-Tochac sub-basin,Mexico

Abstract

On the basis of the degree of mineralization, the groundwater of Apan-Tochac sub-basin may be considered as fresh (TDS < 500 ppm). However, chlorination is necessary to make it fit for human consumption. Major ion analyses of over 235 water samples reveal a striking relationship between hydrochemical evolution and the groundwater flow system. A high content of total dissolved solids, and low values of the Ca:Mg ratio are present in wells located on the plain (discharge zone), whereas opposite conditions are associated with wells located in higher regions (recharge zone). Statistical data analysis using the method of principal components allowed to differentiation of two hydrochemical families: (a) low mineralization corresponding to the recharge zone, and (b) high mineralization corresponding to the discharge zone. Waters of the Ca + Mg + HCO₃, and Na + Mg + HCO₃ hydrochemical fades are present and the former is dominant. The water is slightly alkaline, having slight problems of salinity during the year owing mainly to Ca²⁺HCO₃ ^? and Na⁺Cl^? salts. The hydrochemistry of the groundwater reflects the pattern of local groundwater flow for this sub-basin.     

Groundwater–surface water interactions in a large semi‐arid floodplain: implications for salinity management

Flow regulation and water diversion for irrigation have considerably impacted the exchange of surface water between the Murray River and its floodplains. However, the way in which river regulation has impacted groundwater–surface water interactions is not completely understood, especially in regards to the salinization and accompanying vegetation dieback currently occurring in many of the floodplains. Groundwater–surface water interactions were studied over a 2 year period in the riparian area of a large floodplain (Hattah–Kulkyne, Victoria) using a combination of piezometric surface monitoring and environmental tracers (Cl⁻, δ²H, and δ¹⁸O). Despite being located in a local and regional groundwater discharge zone, the Murray River is a losing stream under low flow conditions at Hattah–Kulkyne. The discharge zone for local groundwater, regional groundwater and bank recharge is in the floodplain within ∼1 km of the river and is probably driven by high rates of transpiration by the riparian Eucalyptus camaldulensis woodland. Environmental tracers data suggest that the origin of groundwater is principally bank recharge in the riparian zone and a combination of diffuse rainfall recharge and localized floodwater recharge elsewhere in the floodplain. Although the Murray River was losing under low flows, bank discharge occurred during some flood recession periods. The way in which the water table responded to changes in river level was a function of the type of stream bank present, with point bars providing a better connection to the alluvial aquifer than the more common clay‐lined banks. Understanding the spatial variability in the hydraulic connection with the river channel and in vertical recharge following inundations will be critical to design effective salinity remediation strategies for large semi‐arid floodplains. Copyright © 2005 John Wiley & Sons, Ltd.     

Nitrate attenuation in soil and shallow groundwater under a bottomland hedgerow in a European farming landscape

In many agricultural areas, hedgerows give rise to strong expectations of reducing the inputs of excess nitrate to the groundwater and rivers. This study aims to analyse the spatial and seasonal influences of a hedgerow on nitrate dynamics in the soil and groundwater. Nitrate (NO₃^?) and chloride (Cl^?) concentrations were measured with spatially dense sampling in the unsaturated soil and in the groundwater along a transect intersecting a bottomland oak (Quercus rubor) hedgerow after the growing season and during the dormant season. We explain NO₃^? dynamics by using Cl^? as an index of tree‐root extension and water transfer. At the end of the growing season, NO₃^? is entirely absorbed by the trees over a large and deep volume corresponding to the rooting zone, where, in contrast Cl^? is highly concentrated due to root exclusion. However, these observed patterns in the soil have no influence on the deep groundwater composition at this season. During the dormant season, water transfer processes feeding the shallow groundwater layer are different upslope and downslope from the hedgerow in relation to the thickness of the unsaturated zone. Upslope, the shallow groundwater is fed by rainwater infiltration through the soil which favours Cl^? dilution. Right under the hedge and downslope, the rapid ascent of the groundwater near the ground surface prevents rainwater input and Cl^? dilution. Under the hedgerow the highest concentrations of Cl^? coincide with the absence of NO₃^? in the shallow groundwater layer and with high concentrations of dissolved organic carbon. The absence of NO₃^? during the dormant season seems to be due to denitrification in the hedgerow rooting zone when it is rapidly saturated by groundwater. Copyright © 2011 John Wiley & Sons, Ltd.     

Stable isotopic and geochemical identification of groundwater evolution and recharge sources in the arid Shule River Basin of Northwestern China

Stable isotopic (δD_VSMOW and δ¹⁸O_VSMOW) and geochemical signatures were employed to constrain the geochemical evolution and sources of groundwater recharge in the arid Shule River Basin, Northwestern China, where extensive groundwater extraction occurs for agricultural and domestic supply. Springs in the mountain front of the Qilian Mountains, the Yumen‐Tashi groundwater (YTG), and the Guazhou groundwater (GZG) were Ca‐HCO₃, Ca‐Mg‐HCO₃‐SO₄ and Na‐Mg‐SO₄‐Cl type waters, respectively. Total dissolved solids (TDS) and major ion (Mg²⁺, Na⁺, Ca²⁺, K⁺, SO₄^2?, Cl^? and NO₃^?) concentrations of groundwater gradually increase from the mountain front to the lower reaches of the Guazhou Basin. Geochemical evolution in groundwater was possibly due to a combination of mineral dissolution, mixing processes and evapotranspiration along groundwater flow paths. The isotopic and geochemical variations in melt water, springs, river water, YTG and GZG, together with the end‐member mixing analysis (EMMA) indicate that the springs in the mountain front mainly originate from precipitation, the infiltration of melt water and river in the upper reaches; the lateral groundwater from the mountain front and river water in the middle reaches are probably effective recharge sources for the YTG, while contribution of precipitation to YTG is extremely limited; the GZG is mainly recharged by lateral groundwater flow from the Yumen‐Tashi Basin and irrigation return flow. The general characteristics of groundwater in the Shule River Basin have been initially identified, and the results should facilitate integrated management of groundwater and surface water resources in the study area. Copyright © 2015 John Wiley & Sons, Ltd.