Agricultural Return Flow Research Articles

Water quantity and quality challenges from Elephant Butte to Amistad

Management of the Rio Grande between Elephant Butte and Amistad Reservoirs involves a number of distinct water quantity and quality challenges. These challenges arise from both “natural” stressors, such as climate variability and geologic sources of salinization, and “human” stressors, such as bacterial and nutrient contamination from urban storm water, agricultural return flows, and wastewater treatment plants (WWTPs), altered hydrology, and increasing/changing water demands. The discussion does not argue for a single approach to surface water “sustainability” as these decisions are properly made by elected officials and decisions makers. Rather it provides an overview of the surface water system contrasting the pre‐development system with the present day to help inform how the stressors mentioned above impact this resource. Current efforts to address these issues are also discussed.

Salinity limits of vegetation in Cienega de Santa Clara, an oligotrophic marsh in the delta of the Colorado River, Mexico: Implications for an increase in salinity

Greenhouse and field trials were conducted to determine the salinity limits for main vegetation types in Cienega de Santa Clara, an oligohaline marsh in the delta of the Colorado River in Mexico. The Cienega is the largest brackish marsh in the Sonoran Desert and supports numerous bird, mammal and invertebrate species, including threatened or endangered marsh birds. It is supported by brackish agricultural return flows from the USA and Mexico, and operation of the Yuma Desalting Plant (YDP) could reduce the volume and increase the salinity of inflows. Current inflows average 4m3s−1 at 2.8gL−1 Total Dissolved Solids (TDS), and the dominant vegetation type is Typha domingensis, with subdominant stands of Schoenoplectus americanus and other emergent species distributed amidst the Typha stands. A greenhouse experiment showed that under flooded-soil conditions, T. domingensis had a linear reduction in relative growth rate based on biomass production (RGRBiomass) with salinity, with zero RGRBiomass at 8.3gL−1 TDS and a 50% reduction at 4.0gL−1 TDS. S. americanus was about twice as salt-tolerant, with zero RGRBiomass at 12.5gL−1 TDS and 50% RGRBiomass at 9gL−1 TDS. The results are consistent with other studies that show a mean reduction in RGRBiomass of 13.3% per g L−1 TDS for Typha spp. and 4.3% per g L−1 TDS for Schoenoplectus spp. Field surveys showed that T. domingensis stands were restricted to salinities of 6.5gL−1 TDS or less, and that annual biomass production was reduced by 85% in a stand at 5.9gL−1 TDS compared to a stand at 3.0gL−1 TDS. Normalized Difference Vegetation Index (NDVI) values of T. domingensis stands from satellite imagery showed a linear decline with increasing salinity in the marsh. It was concluded that 6gL−1 TDS is the approximate upper limit for vigorous stands of T. domingensis, and that replacement by S. americanus is a possibility if salinities increase. Implications for marsh vegetation structure and habitat value are discussed under different possible operating scenarios for the YDP.

Identification of groundwater contamination zones and its sources by using multivariate statistical approach in Thirumanimuthar sub-basin, Tamil Nadu, India

Hydrogeochemical studies have been made in the study area by using multivariate statistical analysis, which is mainly helpful for interpretation of complex data matrices to better understand the geochemical evolution of the area and it allows identifying the possible factors/ sources that influence water systems. The spatial distribu- tion of electrical conductivity reveals that an untreated industrial effluents, landfill and anthropogenic activities affecting their groundwater quality in its vicinity and the surrounding area. The dominance of ions was in the order of Na ? ( Ca 2? ( Mg 2? ( K ? = Cl - ( HCO3 - ( SO4 2- ( NO3 - and Ca 2? ( Mg 2? ( Na ? ( K ? = HCO3 - ( Cl - ( NO3 - ( SO4 2- during pre monsoon (PRM) and post monsoon (POM), respectively. The statistical results reveals that the groundwater chemistry gets altered by silicate weathering, ion exchange, leaching, anthropogenic input from agricultural return flow and longer distance of migrating groundwater. The hydrogeochemical regimes are distributed along the upstream side, northwestern, western and eastern parts of the study area. The study highlights the descriptive capabilities of conventional and multivariate techniques as effective tools in groundwater evaluation.

The response of microalgal biomass and community composition to environmental factors in the Sundays Estuary

The Sundays Estuary is permanently open to the sea and experiences regular freshwater inflow in the form of agricultural return flows with large supplies of nutrients. The objectives of this study were to measure microalgal biomass and community composition and relate these to freshwater inflow, water quality and other environmental variables. These data can then be used in setting the ecological water requirements of the estuary. Surveys in August 2006, March 2007, February, June and August 2008 showed that salinity less than 10, expressed in practical salinity units, mostly occurred from 12.5 km from the mouth in the middle reaches of the estuary, which was also where the highest water column chlorophyll a (>20 ƒEgE.-1) was found. The study showed that different groups of microalgae formed phytoplankton blooms during individual sampling sessions. These included blooms of green algae (August 2006), flagellates (March 2007), dinoflagellates (June 2008) and diatom species (February and August 2008). The estuary was then sampled over 5 consecutive weeks from March to April 2009 to identify environmental factors that support different microalgal bloom species. Phytoplankton blooms were found during Weeks 1, 4 and 5 from the middle to the upper reaches of the estuary. It was shown that diatoms occurred in blooms during warm, calm conditions whereas wind-mixing and reduced temperature, as a result of a cold front during 17 to 19 March 2009, promoted the dominance of flagellates throughout the estuary although they were present at all times. Dominant diatom species (Cylindrotheca closterium, Cyclotella atomus and Cyclostephanus dubius) indicated brackish, nutrient-rich water. Nanoplankton (2.7 - 20 ƒEm) was dominant during each week sampled and contributed 55 - 79% to the phytoplankton biomass. Maximum benthic chlorophyll a was found 12.5 km from the mouth. This study is the first to show successive chlorophyll a blooms consisting of different phytoplankton groups in an estuary, an indication of the eutrophic state of the system.

Major ion chemistry and identification of hydrogeochemical processes controlling groundwater in and around Neyveli Lignite Mines, Tamil Nadu, South India

Groundwater geochemistry was studied in and around the Neyveli lignite mining region of Tamil Nadu, India. Representative groundwater samples (168) were collected from bore wells during June 2004, October 2004, January 2005, and March 2005 to broadly cover seasonal variation. Higher electrical conductivity values were observed in the southeastern and southwestern part of the study area. During the southwest monsoon (June) and postmonsoon (January) seasons, bicarbonate + chloride dominated the anions, with few representations for sulphate. Sodium + potassium were the dominant cations in all the seasons except in summer (March). The data reveals that the region is a complex hydrogeochemical system with proportional interplay of ions from leaching of ions, ion exchange, agricultural return flow, and stagnant waters. The influence of mine waters and weathering of minerals varies according to the season and spatial distribution of the sources. The water quality can be used for drinking and irrigation, except in a few locations.

River water quality in the northern sugarcane-producing regions of South Africa and implications for irrigation: A scoping study

Sustainable cultivation of crops under irrigation requires water of appropriate quality, especially with regards to salinity and sodicity. Agriculture can impact negatively on water quality, often through the export of nutrients (particularly nitrogen (N) and phosphorus (P)) from the root zone, resulting in eutrophication of surface water and pollution of groundwater. Sugarcane is the major irrigated crop with regards to area cultivated in the Crocodile, Komati-Lomati and Pongola River catchments. Increasing demand for and use of water resources in these catchments has led to concerns about deterioration in water quality. In this study, chemical water quality data obtained from the South African Department of Water Affairs was used to assess the quality of river water in the above catchments. Electrical conductivity (EC) data show an increase in salt concentration along the river course as a result of various anthropogenic activities in the catchment. Irrigators located further downstream will therefore generally have to pay more attention to the quality of their irrigation water and on-farm salinity management. For the lower parts of the Komati-Lomati and Pongola River catchments, hazards due to sodicity will also need attention. Interestingly, acidifying effects of mine water drainage are potentially being countered by high salt input from agricultural return flow. Nutrient enrichment was evident at many of the river sampling points. Increasing salt, sodicity, N and P over time for most of the rivers studied is also a concern that requires action to ensure the sustainability of irrigation activities in these catchments. More intensive monitoring, including measurement of organic N and P fractions, is recommended to improve understanding of the contribution of different anthropogenic activities to river water pollution and to develop effective mitigation strategies.

Vulnerability of Groundwater System in Central Jordan Valley/Pollution Indicators and Decontamination Process

More than 60% of the water demand in Jordan is covered by groundwater. Due to the accelerated population growth and development in all sectors including agriculture, more water has been pumped and more fertilizers have been supplied to the natural system. In the Jordan Valley; Agriculture is practiced along the year according to the agro climatic conditions as well intensive patterns of farming are carried out to satisfy the growing food demand in Jordan. Thus, Groundwater quality analysis proved that groundwater quality is relatively polluted with respect to NO﹣3 and salinity. The pollution hot spots are mapped to be the vulnerable areas according to the considered variables (Geology, topography, land use …etc). Within this work groundwater quality was evaluated according to the global standards to be moderately polluted and not drinkable in more than 50% of the analyzed samples. The groundwater vulnerability map indicates that the pollution sources in the study area are mainly due to the agricultural return flow. To assure safe water supply for rural farmers a solar still was designed and implemented in the area for two months. The discharged water from the still proved to be suitable for drinking with no NO﹣3 content and economically it can be handled by locals.

Heavy metal pollution in water and sediments in the Kabini River, Karnataka, India

The River Kabini in Karnataka, India carries natural and anthropogenic pollutants, mainly heavy metal concentrations of Cr, Cu, Fe, Mn, Ni, Pb and Zn which are released from industrial effluents, agricultural return flows and domestic sewage. Kabini, which is a tributary of the Cauvery, drains through the industrial area at Nanjangud, Karnataka, India. Heavy metals were determined in waters and sediment (2 μm) of Kabini River. In the present investigation, chemical partitioning studies was carried out to know the association of base metals with various sedimentary phases. The concentrations of heavy metals are higher in loosely bonded fraction than the other studied fractions. Furthermore, the degree of sediment contamination was assessed by geochemical index. It should be pointed out that Cu and Cr show the highest pollution intensity. Cluster analysis was used to know about the inter correlation amongst the studied metals. It is evident that higher concentrations of metals are found in the vicinity of industrial effluents. The concentrations of Cr followed by Zn and Ni are rather higher than the maximum background values in the Kabini River sediment. This is especially true at the influx of paper mill effluents into the River.

Heavy Metal Pollution in Kabini River Sediments

The river Kabini which is tributary of Cauvery drains through industrial area at Nanjangud, Karnataka. Out of the sediment load carried by the river, 2micron the clay fraction was analyzed for total heavy metal contents and advanced statistical techniques such as cluster analysis and correlation matrix were applied in order to investigate the source of heavy metal concentration in the sediments. The river carries natural and anthropogenic pollutants, mainly heavy metal concentration of Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn which are released from industrial effluents, agricultural return flows and domestic sewage. The heavy metals find their residence in the colloidal form in water and in 2micron clay fraction in the river bed sediments. Systematic sampling of the river bed sediments at predefined locations has revealed that the metal accumulation is very close to normal and also beyond threshold limits. Compared with the maximum background values in Kabini river sediment, Pb was the highest in terms of contamination level, especially at point of influx of paper mill effluents, followed by Zn and Cu.

Efficacy of constructed wetlands for removal of bacterial contamination from agricultural return flows

Abstract Water quality degradation from bacterial pathogens is one of the leading causes of surface water impairment in California agricultural watersheds. In the San Joaquin Valley, approximately 50 and 100% of water samples collected from three different irrigation return flows exceeded the Escherichia coli standard of 126 cfu 100 mL−1 and the enterococci standard of 33 cfu 100 mL−1, respectively, as required for water discharge into state waterways. These results show that runoff from irrigated crops can contribute a significant load of bacteria indicators and potentially pathogenic microorganisms to waterways. Constructed wetlands are gaining recognition as a management practice for use in irrigated agriculture to reduce bacterial loads and a wide variety of water quality contaminants in agricultural return flows prior to discharge into waterways. Based on input–output sampling of four wetlands, 66–91% of E. coli concentrations and 86–94% of enterococci concentrations were retained in the wetlands. Removal efficiencies in terms of bacteria load were even higher, 80–87% and 88–97% for E. coli and enterococci, respectively, due to water losses (seepage and evapotranspiration) within the wetland. Of all the parameters considered, hydraulic residence time (HRT) appeared to be the factor having the greatest effect on the efficiency of bacteria indicator removal. Remarkably, a HRT of less than a day can achieve considerable bacteria indicator retention (∼70%), which allows for relatively small wetland areas being able to treat runoff from large agricultural areas (up to 360:1 in this study).

Impact of Metals on Macroinvertebrate Assemblages in the Forgotten Stretch of the Rio Grande

The objective of this study was to examine how changes in the benthic macroinvertebrate community structure and a variety of abiotic variables, such as conductivity and sediment metal concentrations, are modified along the Forgotten River stretch of the Rio Grande. This stretch receives industrial effluent, raw sewage, and agricultural return flow from the El Paso (TX, USA)-Ciudad Juárez (CHI, Mexico) metroplex and then flows relatively undisturbed for 320 km before its next significant input. The high degree of use, followed by the 320-km undisturbed stretch, makes the Forgotten River a unique study site to examine downstream attenuation of contaminants and other abiotic variables to determine their potential effects on macroinvertebrates. Five different sites along the Forgotten Stretch were sampled over a 2-year period. Metal concentrations were low throughout the stretch and were predominantly correlated to percent sediment organic matter rather than explained spatially. Several sensitive invertebrate species, such as Leptophlebiidae, increased in relative abundance downstream, whereas the percentage of tolerant invertebrates decreased. Nonmetric multidimensional scaling separated the macroinvertebrate communities upstream from those downstream, with the more sensitive species being found predominantly downstream and more tolerant taxa associated upstream. Additionally, there was a distinct seasonal gradient to the community. The most important drivers of the community assemblage appear to be distance downstream and seasonality, as well as water conductivity and concentrations of sediment cadmium, which was the only metal that exceeded protective criteria. This study did not provide evidence of the downstream attenuation of heavy metals in the sediments in the Forgotten Stretch; however, downstream changes in macroinvertebrates toward more sensitive taxa suggests that other, unmeasured contaminants might be affecting biological communities in this isolated stretch of an international waterway.

Synthesis of ground and remote sensing data for monitoring ecosystem functions in the Colorado River Delta, Mexico

The delta of the Colorado River in Mexico supports a rich mix of estuarine, wetland and riparian ecosystems that provide habitat for over 350 species of birds as well as fish, marine mammals, and other wildlife. An important part of the delta ecosystem is the riparian corridor, which is supported by agricultural return flows and waste spills of water originating in the U.S. and Mexico. These flows may be curtailed in the future due to climate change and changing land use practices (out-of-basin water transfers, increased agricultural efficiency, and more optimal management of dams) in the U.S. and Mexico, and resource managers need to monitor the effects of their water management practices on these ecosystems. We developed ground-validated, remote sensing methods to monitor the vegetation status, habitat value, and water use of wetland and riparian ecosystems using multi-temporal, multi-resolution images. The integrated methodology allowed us to project species composition, leaf area index, fractional cover, habitat value, and evapotranspiration over seasons and years throughout the delta, in response to variable water flows from the U.S. to Mexico. Waste spills of water from the U.S. have regenerated native cottonwood and willow trees in the riparian corridor and created backwater and marsh areas that support birds and other wildlife. However, the main source of water supporting the riparian vegetation is the regional aquifer recharged by underflow from U.S. and Mexico irrigation districts. Native trees have a short half-life in the riparian zone due to human-set fires and harvesting for timber. Active management, monitoring, and restoration programs are needed to maintain the habitat value of this ecosystem for the future.

Effect of constructed wetlands receiving agricultural return flows on disinfection byproduct precursors

The effects of wetland treatment on disinfection byproduct precursors were evaluated for six constructed wetlands receiving agricultural return flows in the Central Valley of California. Wetlands varied in size, age, vegetation, hydrologic residence time (0.9–20 days) and water management (continuous flow vs. flood pulse). The effects of wetland treatment were determined by analyzing input and outflow waters for dissolved organic carbon concentration and quality, bromide concentration, and formation potentials for nine disinfection byproduct species, including trihalomethanes, haloacetronitriles, chloral hydrate, and haloketones. We hypothesized that hydraulic residence time was a key factor governing differences in disinfection byproduct precursors. Small wetlands (<3 ha) with short hydraulic residence times (<2 days) did not produce significant changes in disinfection byproduct precursor concentrations with respect to the agricultural return flows input to the wetlands. In these wetlands hydraulic residence times were not long enough to promote processes that adversely affect dissolved organic carbon and bromide quantity, such as evapoconcentration and leaching from vegetation. Thus, less negative effects were associated with disinfection byproduct formation. In contrast, larger wetlands (>100 ha) with long hydraulic residence times (>10 days) resulted in higher dissolved organic carbon and bromide levels, increasing disinfection byproduct formation by factors ranging between 1.7 and 10.2 compared to agricultural return flows. Results from this study provide important information for optimizing the design and management of constructed wetlands to effectively combine control of disinfection byproduct precursors with other water quality parameters.

Application of multiple isotopic and geochemical tracers for investigation of recharge, salinization, and residence time of water in the Souss–Massa aquifer, southwest of Morocco

Summary Groundwater and surface water in Souss–Massa basin in the west-southern part of Morocco is characterized by a large variation in salinity, up to levels of 37 g L −1 . The high salinity coupled with groundwater level decline pose serious problems for current irrigation and domestic water supplies as well as future exploitation. A combined hydrogeologic and isotopic investigation using several chemical and isotopic tracers such as Br/Cl, δ 18 O, δ 2 H, 3 H, 87 Sr/ 86 Sr, δ 11 B, and 14 C was carried out in order to determine the sources of water recharge to the aquifer, the origin of salinity, and the residence time of water. Stable isotope, 3 H and 14 C data indicate that the high Atlas mountains in the northern margin of the Souss–Massa basin with high rainfall and low δ 18 O and δ 2 H values (−6 to −8‰ and −36 to −50‰) is currently constitute the major source of recharge to the Souss–Massa shallow aquifer, particularly along the eastern part of the basin. Localized stable isotope enrichments offset meteoric isotopic signature and are associated with high nitrate concentrations, which infer water recycling via water agricultural return flows. The 3 H and 14 C data suggest that the residence time of water in the western part of the basin is in the order of several thousands of years; hence old water is mined, particularly in the coastal areas. The multiple isotope analyses and chemical tracing of groundwater from the basin reveal that seawater intrusion is just one of multiple salinity sources that affect the quality of groundwater in the Souss–Massa aquifer. We differentiate between modern seawater intrusion, salinization by remnants of seawater entrapped in the middle Souss plains, recharge of nitrate-rich agricultural return flow, and dissolution of evaporate rocks (gypsum and halite minerals) along the outcrops of the high Atlas mountains. The data generated in this study provide the framework for a comprehensive management plan in which water exploitation should shift toward the eastern part of the basin where current recharge occurs with young and high quality groundwater. In contrast, we argued that the heavily exploited aquifer along the coastal areas is more vulnerable given the relatively longer residence time of the water and salinization processes in this part of the aquifer.

Hydrochemical appraisal of groundwater and its suitability in the intensive agricultural area of Muzaffarnagar district, Uttar Pradesh, India

Muzaffarnagar is an economically rich district situated in the most fertile plains of two great rivers Ganga and Yamuna in the Indo-gangetic plains, with agricultural land irrigated by both surface water as well as groundwater. An investigation has been carried out to understand the hydrochemistry of the groundwater and its suitability for irrigation uses. Groundwater in the study area is neutral to moderately alkaline in nature. Chemistry of groundwater suggests that alkaline earths (Ca+Mg) significantly exceed the alkalis (Na+K) and weak acids exceed the strong acids (Cl+SO4), suggesting the dominance of carbonate weathering followed by silicate weathering. Majority of the groundwater samples (62%) posses Ca–Mg–HCO3 type of hydrochemical species, followed by Ca–Na–Mg–HCO3, Na–Ca–Mg–HCO3, Ca–Mg–Na–HCO3–Cl and Na–Ca–HCO3–SO4 types. A positive high correlation (r2=0.928) between Na and Cl suggests that the salinity of groundwater is due to intermixing of two or more groundwater bodies with different hydrochemical compositions. Barring a few locations, most of the groundwater samples are suitable for irrigation uses. Chemical fertilizers, sugar factories and anthropogenic activities are contributing to the sulphate and chloride concentrations in the groundwater of the study area. Overexploitation of aquifers induced multi componential mixing of groundwater with agricultural return flow waters is responsible for generating groundwater of various compositions in its lateral extent.

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Nitrogen Sources and Sinks Within the Middle Rio Grande, New Mexico1

Abstract: Relationships between discharge, land use, and nitrogen sources and sinks were developed using 5 years of synoptic sampling along a 300 km reach of the Rio Grande in central New Mexico. Average river discharge was higher during 2001 and 2005 “wet years” (15 m3/s) than during the drought years of 2002‐04 “dry years” (8.9 m3/s), but there were no differences in nitrogen loading from wastewater treatment plants (WWTPs) which were the largest and most consistent source of nitrogen to the river (1,330 kg/day). Average total dissolved nitrogen (TDN) concentrations remained elevated for 180 km downstream of the Albuquerque WWTP averaging 1.2 mg/l in wet years and 0.52 mg/l in dry years. Possible explanations for the constant elevated TDN concentrations downstream of the major point source include reduced nitrogen retention capacity, minimal contact with riparian or channel vegetation, large suspended sediment loads, and low algal biomass. Somewhat surprisingly, agricultural return flows had lower average nitrogen concentrations than river water originally diverted to agriculture in both wet (0.81 mg/l) and dry years (0.19 mg/l), indicating that the agricultural system is a sink for nitrogen. Lower average nitrogen concentrations in the river during the dry years can be explained by the input of agricultural returns which comprise the majority of river flow in dry years.

Riparian vegetation dynamics and evapotranspiration in the riparian corridor in the delta of the Colorado River, Mexico

Like other great desert rivers, the Colorado River in the United States and Mexico is highly regulated to provide water for human use. No water is officially allotted to support the natural ecosystems in the delta of the river in Mexico. However, precipitation is inherently variable in this watershed, and from 1981–2004, 15% of the mean annual flow of the Lower Colorado River has entered the riparian corridor below the last diversion point for water in Mexico. These flows include flood releases from US dams and much smaller administrative spills released back to the river from irrigators in the US and Mexico. These flows have germinated new cohorts of native cottonwood and willow trees and have established an active aquatic ecosystem in the riparian corridor in Mexico. We used ground and remote-sensing methods to determine the composition and fractional cover of the vegetation in the riparian corridor, its annual water consumption, and the sources of water that support the ecosystem. The study covered the period 2000–2004, a flood year followed by 4 dry years. The riparian corridor occupies 30,000 ha between flood control levees in Mexico. Annual evapotranspiration (ET), estimated by Moderate Resolution Imaging Spectrometer (MODIS) satellite imagery calibrated against moisture flux tower data, was about 1.1 m yr −1 and was fairly constant throughout the study period despite a paucity of surface flows 2001–2004. Total ET averaged 3.4×10 8 m 3 yr −1, about 15% of Colorado River water entering Mexico from the US Surface flows could have played only a small part in supporting these high ET losses. We conclude that the riparian ET is supported mainly by the shallow regional aquifer, derived from agricultural return flows, that approaches the surface in the riparian zone. Nevertheless, surface flows are important in germinating cohorts of native trees, in washing salts from the soil and aquifer, and in providing aquatic habitat, thereby enriching the habitat value of the riparian corridor for birds and other wildlife. Conservation and water management strategies to enhance the delta habitats are discussed in light of the findings.

The geochemistry of groundwater resources in the Jordan Valley: The impact of the Rift Valley brines

The chemical composition of groundwater in the Jordan Valley, along the section between the Sea of Galilee and the Dead Sea, is investigated in order to evaluate the origin of the groundwater resources and, in particular, to elucidate the role of deep brines on the chemical composition of the regional groundwater resources in the Jordan Valley. Samples were collected from shallow groundwater in research boreholes on two sites in the northern and southern parts of the Jordan Valley, adjacent to the Jordan River. Data is also compiled from previous published studies. Geochemical data (e.g., Br/Cl, Na/Cl and SO 4/Cl ratios) and B, O, Sr and S isotopic compositions are used to define groundwater groups, to map their distribution in the Jordan valley, and to evaluate their origin. The combined geochemical tools enabled the delineation of three major sources of solutes that differentially affect the quality of groundwater in the Jordan Valley: (1) flow and mixing with hypersaline brines with high Br/Cl (>2 × 10 −3) and low Na/Cl (<0.8) ratios; (2) dissolution of highly soluble salts (e.g., halite, gypsum) in the host sediments resulting in typically lower Br/Cl signal (<2 × 10 −3); and (3) recharge of anthropogenic effluents, primarily derived from evaporated agricultural return flow that has interacted (e.g., base-exchange reactions) with the overlying soil. It is shown that shallow saline groundwaters influenced by brine mixing exhibit a north–south variation in their Br/Cl and Na/Cl ratios. This chemical trend was observed also in hypersaline brines in the Jordan valley, which suggests a local mixing process between the water bodies.

Tracing nitrates and sulphates in river basins using isotope techniques

The objective of this paper is to outline how stable isotope techniques can contribute to the elucidation of the sources and the fate of riverine nitrate and sulphate in watershed studies. The example used is the Oldman River Basin (OMRB), located in southern Alberta (Canada). Increasing sulphate concentrations and decreasing delta(34)S values along the flowpath of the Oldman River indicate that oxidation of pyrite in tills is a major source of riverine sulphate in the agriculturally used portion of the OMRB. Chemical and isotopic data showed that manure-derived nitrogen contributes significantly to the increase in nitrate concentrations in the Oldman River and its tributaries draining agricultural land. It is suggested that hydrological conditions control agricultural return flows to the surface water bodies in southern Alberta and impart significant seasonal variations on concentrations and isotopic compositions of riverine nitrate. Combining isotopic, chemical, and hydrometric data permitted us to estimate the relative contribution of major sources to the total solute fluxes. Hence, we submit that isotopic measurements can make an important contribution to the identification of nutrient and pollutant sources and to river basin management.