Isotopic Composition of the Ogallala-high Plains Aquifer Andvadose Zone

AbstractThe Ogallala-High Plains aquifer is an important resource for irrigated agriculture in a semi-arid region of the United States. Steep declines in groundwater levels are putting increasing strain on the viability of the aquifer for irrigation, necessitating improved estimates of recharge rates and sources to the aquifer. This study uses a combined approach to obtain high resolution geochemical and isotopic composition of the vadose zone and aquifer pore fluids to better understand recharge dynamics to the aquifer. Significant differences between the shallow, intermediate and deep vadose zone and shallow and deep aquifer indicate modern precipitation is not providing a significant source of recharge to the aquifer across a large area (diffuse recharge). Rather, recharge to the aquifer is a result of either focused recharge or long-term, delayed drainage from the portion of the vadose zone which was saturated before irrigation development

Hydrogeology, chemical and microbial activity measurement through deep permafrost

Little is known about hydrogeochemical conditions beneath thick permafrost, particularly in fractured crystalline rock, due to difficulty in accessing this environment. The purpose of this investigation was to develop methods to obtain physical, chemical, and microbial information about the subpermafrost environment from a surface-drilled borehole. Using a U-tube, gas and water samples were collected, along with temperature, pressure, and hydraulic conductivity measurements, 420 m below ground surface, within a 535 m long, angled borehole at High Lake, Nunavut, Canada, in an area with 460-m-thick permafrost. Piezometric head was well above the base of the permafrost, near land surface. Initial water samples were contaminated with drill fluid, with later samples <40% drill fluid. The salinity of the non-drill fluid component was <20,000 mg/L, had a Ca/Na ratio above 1, with {delta}{sup 18}O values {approx}5{per_thousand} lower than the local surface water. The fluid isotopic composition was affected by the permafrost-formation process. Nonbacteriogenic CH{sub 4} was present and the sample location was within methane hydrate stability field. Sampling lines froze before uncontaminated samples from the subpermafrost environment could be obtained, yet the available time to obtain water samples was extended compared to previous studies. Temperature measurements collected from a distributed temperature sensor indicated that this issue can be overcome easily in the future. The lack of methanogenic CH{sub 4} is consistent with the high sulfate concentrations observed in cores. The combined surface-drilled borehole/U-tube approach can provide a large amount of physical, chemical, and microbial data from the subpermafrost environment with few, controllable, sources of contamination

Stable Bromine Isotopic Composition of Coal Bed Methane (CBM) Produced Water, the Occurrence of Enriched 81Br, and Implications for Fluid Flow in the Midcontinent, USA

This study characterizes the δ37Cl, δ81Br, and 87Sr/86Sr of coal bed methane produced fluids from Pennsylvanian Cherokee Group coals of the Cherokee Basin in southeast Kansas, USA. The δ37Cl, δ81Br, and 87Sr/86Sr values range between −0.81 and +0.68‰ (SMOC), −0.63 and +3.17‰ (SMOB), and 0.70880 and 0.71109, respectively. A large percentage of samples have δ81Br above +2.00‰. Two fluid groups were identified on the basis of K/Br, Br/Cl, and Ca/Mg ratios, temperature, He content, δ2H, δ18O, δ81Br, and 87Sr/86Sr. Both fluid groups have geochemical similarities to fluids in Cambrian, Ordovician, and Mississippian units. Lower salinity and higher temperature fluids from deeper units are leaking up into the Cherokee Group and mixing with a higher salinity fluid with higher δ81Br and more radiogenic 87Sr/86Sr. Variation in δ37Cl indicates an unknown process other than mixing is affecting the salinity. This process does not appear to be related to evaporation, evaporite dissolution, or diffusion. Insufficient data are available to evaluate halide–gas or water–rock interaction, but halide–gas interactions are not likely a significant contributor to high δ81Br. Rather, interactions with organically bound bromine and soluble chloride within the coal could have the strongest effect on δ37Cl and δ81Br values

Flux and stable isotope fractionation of CO2 in a mesic prairie headwater stream

The carbon dioxide (CO2) fluxes from headwater streams are not well quantified and could be a source of significant carbon, particularly in systems underlain by carbonate lithology. Also, the sensitivity of carbonate systems to changes in temperature will make these fluxes even more significant as climate changes. This study quantifies small-scale CO2 efflux and estimates annual CO2 emission from a headwater stream at the Konza Prairie Long-Term Ecological Research Site and Biological Station (Konza), in a complex terrain of horizontal, alternating limestones and shales with small-scale karst features. CO2 effluxes ranged from 2.2 to 214 g CO2 m−2 day−1 (mean: 20.9 CO2 m−2 day−1). Downstream of point groundwater discharge sources, CO2 efflux decreased, over 2 m, to 3–40% of the point-source flux, while δ13C-CO2 increased, ranging from −9.8 ‰ to −23.2 ‰ V-PDB. The δ13C-CO2 increase was not strictly proportional to the CO2 flux but related to the origin of vadose zone CO2. The high spatial and temporal variability of CO2 efflux from this headwater stream informs those doing similar measurements and those working on upscaling stream data, that local variability should be assessed to estimate the impact of headwater stream CO2 efflux on the global carbon cycle. HIGHLIGHTS An intermittent stream in merokarst terrain has highly variable efflux both spatially and temporally.; CO2 efflux was rapid: 2 m downstream of the point of groundwater discharge flux was 3–40% of the point-source flux.; δ13C-CO2 correlated negatively with CO2 fluxes except for two high-flux values, suggesting δ13C-CO2 is not a reliable indicator of CO2 flux.

A combined laboratory and field-based experimental approach to characterize the heterogeneity of granular aquifers

Effective groundwater resource management requires appropriate conceptualization of aquifer heterogeneity, which is challenging for pro-deltaic systems. This study focuses on heterogeneity within the Valin River paleodelta (Canada), a complex granular aquifer constituting a system that is a regional water supply source. This study integrates laboratory and field-based experimental measurements of various hydrogeological properties and classifies the sediments using diverse statistical techniques. It demonstrates the advantage of diversified characterization for a better understanding of aquifer heterogeneity. The hydrogeological properties—i.e., hydraulic conductivity (K) and porosity (n)—of 27 lithofacies identified in nine sandpits were estimated and assigned a range of values. The identified lithofacies were grouped into four operative-lithofacies before being assigned to three primary hydrofacies that were used to define the aquifer heterogeneity. The importance of integrated sediment and hydraulic properties assessment is that the techniques allow an understanding of the heterogeneity within a complex prodeltaic aquifer type. Two scales of heterogeneity are defined: (1) lithofacial scale wherein small differences in sediment texture (grain size properties), in sedimentary structures, and in other sediment features of lithofacies (mean grain diameter, sorting, skewness, and kurtosis) cause significant changes in K and n, (2) hydrofacial scale wherein specific lithology units define larger-scale aquifer flow and potential solute movement. The multi-methodology approach used for characterizing the aquifer heterogeneity is a prerequisite to complete necessary information for developing more accurate and complex hydrogeological models. Une gestion efficace de la ressource en eau souterraine requiert une formalisation appropriée de l’hétérogénéité de l’aquifère, ce qui est difficile pour les systèmes pro-deltaïques. La présente étude porte sur l’hétérogénéité au sein du paléo-delta de la Rivière Valin (Canada), un aquifère granulaire complexe constituant un système qui est une source régionale d’alimentation en eau. Cette étude intègre la mesure expérimentale, au laboratoire et sur le terrain, de diverses propriétés hydrogéologiques et classe les sédiments selon diverses techniques statistiques. Elle démontre l’avantage d’une caractérisation diversifiée visant une meilleure compréhension de l’hétérogénéité d’un aquifère. Les propriétés hydrogéologiques (c’est à dire la conductivité hydraulique [K] et la porosité [n]) de 27 litho-faciès identifiés dans neuf sablières ont été estimées et assignées à une gamme de valeurs. Les litho-faciès identifiés ont été regroupés en quatre litho-faciès opératoires avant d’être affectés à trois hydro-faciès primaires utilisés pour définir l’hétérogénéité. L’importance de l’évaluation intégrée des propriétés sédimentaires et hydrauliques réside dans le fait que les techniques apportent une compréhension de l’hétérogénéité au sein d’un type d’aquifère pro-deltaïque complexe. .Deux échelles d’hétérogénéité sont définies: (1) une échelle de litho-faciès dans laquelle de petites différences dans la texture des sédiments (propriétés granulométriques ), les structures sédimentaires et les autres caractéristiques sédimentaires des litho-faciès (diamètre moyen du grain, classement, aplatissement, asymétrie) causent des variations significatives de K et n, (2) une échelle d’hydro-faciès dans laquelle des unités lithologiques spécifiques définissent à plus grande échelle l’écoulement dans l’aquifère et le mouvement potentiel des solutés. L’approche multi-méthode utilisée pour caractériser l’hétérogénéité de l’aquifère est un prérequis pour compléter l’information nécessaire au développement de modèles hydrogéologiques plus précis et plus complexes

Chloride-salinity as indicator of the chemical composition of groundwater: empirical predictive model based on aquifers in Southern Quebec, Canada

The present study first describes the variations in concentrations of 12 chemical elements in groundwater relative to salinity levels in Southern Quebec (Canada) groundwater systems, and then uses this data to develop an empirical predictive model for evaluating groundwater chemical composition relative to salinity levels. Data is drawn from a large groundwater chemistry database containing 2608 samples. Eight salinity classes were established from lowest to highest chloride (Cl) concentrations. Graphical analyses were applied to describe variations in major, minor, and trace element concentrations relative to salinity levels. Results show that the major elements were found to be dominant in the lower salinity classes, whereas Cl becomes dominant at the highest salinity classes. For each of the major elements, a transitional state was identified between domination of the major elements and domination of Cl. This transition occurred at a different level of salinity for each of the major elements. Except for Si, the minor elements Ba, B, and Sr generally increase relative to the increase of Cl. The highest Mn concentrations were found to be associated with only the highest levels of Cl, whereas F was observed to be more abundant than Mn. Based on this analysis of the data, a correlation table was established between salinity level and concentrations of the chemical constituents. We thus propose a predictive empirical model, identifying a profile of the chemical composition of groundwater relative to salinity levels, to help homeowners and groundwater managers evaluate groundwater quality before resorting to laborious and costly laboratory analyses

Vadose zone water stable isotope profiles for assessing groundwater recharge: Sensitivity to seasonal soil sampling

Groundwater recharge is widely recognized as being the most important parameter for the sustainable management of water resources. In semiarid environments, groundwater recharge can be quantified using the piston displacement method (PDM). From a single soil sampling campaign, the PDM relies on linking the deeper vadose zone soil pore water stable isotope composition (δ2HH2O and δ18OH2O) to the local meteoric water line (LMWL). However, the isotopic composition of precipitation changes seasonally, influencing the water isotope composition of the vadose zone over time. Thus, it is important to test whether the PDM is sensitive to seasonal soil sampling and whether the assessed recharge rate is independent of the time of sampling. This study investigates the effect of seasonal soil sampling on the distribution of vadose zone stable isotope composition to determine whether the sampling time influences the estimate of recharge rate from PDM. Soil samples were obtained along vertical profiles through the vadose zone in a semiarid region during the spring, summer, and autumn seasons. Specifically, the δ2HH2O and δ18OH2O of the soil pore water were determined along vertical profiles, and the PDM was applied to quantify the annual recharge. The δ2HH2O and δ18OH2O values range from −7.3 to −3.5 ‰ and from −54.4 to +7.41 ‰, respectively, and plot along a continuum with a slope less than the LMWL. Samples from deeper in the vadose zone profile had distinct ranges in isotopic composition between the three soil sampling campaigns, with isotopic composition of spring sampling dominated by lower values and those from autumn with higher values. Despite these differences, the resulting annual recharge rates from the different sampling campaigns are comparable (1.5 to 2 % of annual precipitation). Even though the pore water isotopic composition changed over time, the shift between the deeper vadose zone isotopic compositions and the LMWL remained relatively constant, leading to a similar recharge estimate over time. Therefore, the PDM-based recharge assessment in the tested semiarid environment is independent of the sampling time, which indicates that sampling for assessing groundwater recharge can be undertaken during any season

Nitrate sources and transformation processes in groundwater of a coastal area experiencing various environmental stressors

In coastal salinized groundwater systems, contamination from various nitrate (NO3) inputs combined with complex hydrogeochemical processes make it difficult to distinguish NO3 sources and identify potential NO3 transformtation processes. Effective field-based NO3 studies in coastal areas are needed to improve the understanding of NO3 contamination dynamics in groundwater of such complex coastal systems. This study focuses on a typical Mediterranean coastal agricultural area, located in Tunisia, experiencing substantial NO3 contamination from multiple anthropogenic sources. Here, multiple isotopic tracers (δ18OH2O, δ2HH2O, δ15NNO3, δ18ONO3, and δ11B) combined with a Bayesian isotope MixSIAR model are used (i) to identify the major NO3 sources and their contributions, and (ii) to describe the potential NO3 transformation processes. The measured NO3 concentrations in groundwater are above the natural baseline threshold, suggesting anthropogenic influence. The measured isotopic composition of NO3 indicates that manure, soil organic matter, and sewage are the potential sources of NO3, while δ11B values constrain the NO3 contamination to manure; a finding that is supported by the results of MixSIAR model revealing that manure-derived NO3 dominates over other likely sources. Nitrate derived from manure in the study area is attributed to organic fertilizers used to promote crop growth, and livestock that deposit manure directly on the ground surface. Evidence for ongoing denitrification in groundwaters of the study area is supported by an enrichment in both 15N and 18O in the remaining NO3, although isotopic mass balances between the measured and the theoretical δ18ONO3 values also suggest the occurrence of nitrification. The simultaneous occurrence of these biogeochemical processes with heterogeneous distribution across the study area reflect the complexity of interactions within the investigated coastal aquifer. The multiple isotopic tracer approach used here can identify the effect of multiple NO3 anthropogenic activities in coastal environments, which is fundamental for sustainable groundwater resources management

Combined effects of seawater intrusion and nitrate contamination on groundwater in coastal agricultural areas: A case from the Plain of the El-Nil River (North-Eastern Algeria)

This study focuses on coastal aquifers subject to uncontrolled land use development by investigating the combined effects of seawater intrusion and nitrate contamination. The research is undertaken in a Mediterranean coastal agricultural area (Plain of the El-Nil River, Algeria), where water resources are heavily impacted by anthropogenic activities. A multi-tracer approach, integrating hydrogeochemical and isotopic tracers (δ2HH2O, δ18OH2O, δ15NNO3 and δ18ONO3), is combined with a hydrochemical facies evolution diagram, and a Bayesian isotope mixing model (MixSIAR) to assess seawater contamination with its inland intrusion, and distinguish the nitrate sources and their apportionment. Results show that seawater intrusion is circumscribed to the sector neighboring the Mediterranean Sea, with two influencing functions including classic inland intrusion through the aquifer, and upstream seawater impact through the river mouth connected to the Mediterranean Sea. Groundwater and surface water samples reveal nitrate concentrations above the natural baseline threshold, suggesting anthropogenic influence. Results from nitrate isotopic composition, NO3 and Cl concentrations, and the MixSIAR model show that nitrate concentrations chiefly originate from sewage and manure sources. Nitrate derived from the sewage is related to wastewater discharge, whereas nitrate derived from the manure is attributed to an excessive use of animal manure to fertilise agricultural areas. The dual negative impact of seawater intrusion and nitrate contamination degrades water quality over a large proportion of the study area. The outcomes of this study are expected to contribute to effective and sustainable water resources management in the Mediterranean coastal area. Furthermore, this study may improve scientists' ability to predict the combined effect of various anthropogenic stressors on coastal environments and help decision-makers elsewhere to prepare suitable environmental strategies for other regions currently undergoing an early stage of water resources deterioration

Combined effects of seawater intrusion and nitrate contamination on groundwater in coastal agricultural areas: A case from the Plain of the El-Nil River (North-Eastern Algeria)

This study focuses on coastal aquifers subject to uncontrolled land use development by investigating the combined effects of seawater intrusion and nitrate contamination. The research is undertaken in a Mediterranean coastal agricultural area (Plain of the El-Nil River, Algeria), where water resources are heavily impacted by anthropogenic activities. A multi-tracer approach, integrating hydrogeochemical and isotopic tracers (δ2HH2O, δ18OH2O, δ15NNO3 and δ18ONO3), is combined with a hydrochemical facies evolution diagram, and a Bayesian isotope mixing model (MixSIAR) to assess seawater contamination with its inland intrusion, and distinguish the nitrate sources and their apportionment. Results show that seawater intrusion is circumscribed to the sector neighboring the Mediterranean Sea, with two influencing functions including classic inland intrusion through the aquifer, and upstream seawater impact through the river mouth connected to the Mediterranean Sea. Groundwater and surface water samples reveal nitrate concentrations above the natural baseline threshold, suggesting anthropogenic influence. Results from nitrate isotopic composition, NO3 and Cl concentrations, and the MixSIAR model show that nitrate concentrations chiefly originate from sewage and manure sources. Nitrate derived from the sewage is related to wastewater discharge, whereas nitrate derived from the manure is attributed to an excessive use of animal manure to fertilise agricultural areas. The dual negative impact of seawater intrusion and nitrate contamination degrades water quality over a large proportion of the study area. The outcomes of this study are expected to contribute to effective and sustainable water resources management in the Mediterranean coastal area. Furthermore, this study may improve scientists' ability to predict the combined effect of various anthropogenic stressors on coastal environments and help decision-makers elsewhere to prepare suitable environmental strategies for other regions currently undergoing an early stage of water resources deterioration