Alluvial Groundwater Research Articles

The comprehensive evaluation of nitrate origin and transformation pathways in the oxic alluvial aquifer in Serbia.

Accurate pollution source identification is essential for establishing adequate water management strategies, particularly in groundwater with slow flow and prolonged recharge process allowing long-term pollution retention. An integrated study based on hydrogeochemical, dual isotopic (δ15NNO3 and δ18ONO3), and microbiological approaches (DN, IRB, and SRB BART tests) along with the statistical data processing was conducted to determine nitrate origin and fate in oxic alluvial groundwater source Ključ in Serbia. The findings from a comprehensive investigation, encompassing 20 groundwater sampling locations during the period 2010-2019, delineated three distinct zones - the hinterland (anthropogenic impact area-untreated sewage inflow), the middle zone (area of mixed influence from fertilizer application, accompanied by a mitigated anthropogenic impact), and the zone of riparian denitrification. Significant linear relationship between anthropogenic impact parameters (Na, Cl, B, NO3-, NH4+, and electrical conductivity) along with the isotopic signatures (δ15N-NO3- ranking from + 10.01 to + 11.18‰ and δ18O-NO3- ranking from + 1.15 to + 6.24‰) and grouped sampling objects by cluster analysis indicated that hinterland is burdened by the nitrates originating from anthropogenic impact. The cross-section of groundwater flow data, concurrent increase of NH4+, and pH levels, along with the highest values of δ15N-NO3- (+ 12.90‰) and δ18O-NO3- (+ 9.70‰), indicated area of fertilizers (urea) impact. BART test results, pH increase, and low oxygen concentration, along with the groundwater flow data in riparian zone, indicated the unfolding of denitrification process. Presented research emphasizes the importance, necessities, and advantages of simultaneous and complementary use of hydrogeochemical, microbiological, and isotopic data.

Metallic groundwater contamination assessment using the heavy metal pollution index: a case study of the Guelma plain alluvial groundwater, Northeast of Algeria

Metallic groundwater contamination assessment using the heavy metal pollution index: a case study of the Guelma plain alluvial groundwater, Northeast of Algeria

Estudo da influência das águas residuais da região de Tebessa na qualidade hidroquímica das águas subterrâneas do aquífero aluvial de Tebessa-Ain Chabro (Nordeste da Argélia)

ABSTRACT Along the Algerian-Tunisian border in northeastern Algeria, groundwater is regarded as the primary source of agricultural and drinking water for the local community. This situation is the result of low rainfall and limited surface water. Finding out how wastewater discharges affect the physicochemical and bacteriological quality of alluvial groundwater is the objective of this research paper. Thirty-six wells and boreholes were targeted to collect water samples. The analysis results show that the waters ranged from acidic to neutral (6.46 ≤ pH ≤ 8.3), and moderately to highly mineralized (754 μS/cm < C.E < 11680 μS/cm). The main water types, according to the Piper diagram, are calcic bicarbonate (HCO3- Ca2+) and calcic chloride (Cl- Ca2+). Total coliforms and Escherichia Coli were detected in 60 and 100% of the water samples analyzed, respectively. The geospatial data shows that the chemical and bacteriological pollution progresses from upstream to downstream, from Oued El Kebir river in the South East to Oued Chabro River in the North West. The multivariable statistical analysis (Principal Component Analysis and Closer Analysis) highlighted that water mineralization is controlled by three major phenomena, which are water-rock hydrolysis interaction, leaching of geological formations, and influence of anthropogenic activities.

Spatial variability of nitrate leaching and risk assessment of nitrate contamination in the Ghiss-Nekor alluvial aquifer system (Northeastern Morocco) through Disjunctive Kriging

In this study, groundwater nitrate monitoring data from water supply and water management organizations were processed in a GIS environment to evaluate spatial patterns of nitrate occurrence and explore its correlation with the corresponding land uses in Ghiss-Nekor alluvial groundwater (northeastern Morocco). Land-use/Land Cover within the Ghiss-Nekor plain incorporated rangeland, built area, crop fields, water bodies, dense vegetation, and bare ground categories, encompassing respectively about 39.06 %, 36.69 %, 17.57 %, 4.63 %, 1.24 %, and 0.81 % of the total area. According to the World Health Organization (WHO), the selected thresholds are an acceptable concentration of nitrate for potable water (50 mg/L) and a human affected value (13 mg/L). Simple Kriging and Disjunctive Kriging (D.K.) geostatistical methods were compared with a deterministic interpolation method (GPI) to identify the convenient approach to predict nitrate concentrations at unsampled sites. D.K. provided more accurate predictive performance and highlighted that nitrate contamination is higher in wells in the southern half of the study area, where nitrate concentrations exceeded 50 mg/L in 29.2 % (33,3 km²) of the study area. Areas occupying 21.28 % of the total surface, with nitrate contents exceeding the human-affected value, are located near small industrial sites, residential septic tanks, and agricultural areas. No significant correlation was found between the nitrate concentrations and the depth of the wells. The probability of nitrate content exceeding the thresholds of 13 and 50 mg/L is respectively less than 0.5 in 61.35 % (69.94 km²) and 77.63 % (88.4 km²) of the total study area, whereas the maximum likelihood of nitrate contamination is found along uncontrolled urban discharges located within highly permeable deposits. The assessment also demonstrated that areas showing high predicted probabilities of nitrate contamination diminish with increasing threshold value. The present study shed light on the necessity of depicting the extent of polluted areas, particularly in vulnerable alluvial aquifers, where exposure to higher levels of drinking water contaminants threatens human health.

Qualitative evaluation of groundwater in terms of its suitability for drinking and irrigation. The case study of Sidi-Bel-Abbes alluvial aquifer (NW Algeria)

Sidi-Bel-Abbes province is a semi-arid area mainly used for agricultural activity in northwestern Algeria. Its groundwater resources are characterized by high salinity varying from one area to another. This work aims at improving our understanding of these waters, through hydrochemical classification, to define their chemical facies and monitor their spatial evolution. In addition, this groundwater’s quality is assessed regarding their suitability for drinking and irrigation. The obtained results showed that the groundwater of the Sidi-Bel-Abbes area is dominated by chlorides, particularly the chloride calcium and sodium facies. Indeed, the spatial distribution of the different chemical facies confirmed the contribution of adjacent hydrogeological units and the interaction between the groundwater and the Mekerra Wadi. In terms of suitability for drinking, the maximum chemical element concentration accepted by the Algerian legislation is exceeded in most samples, especially for nitrates, chlorides, sodium and calcium. The interpretation of Riverside and Wilcox diagram revealed that the alluvial groundwater of Sidi-Bel-Abbes is generally characterized by a high salinity with a low to medium alkalinity danger. Therefore, the quality of this water is medium to poor, suitable for irrigation, but under certain conditions. Also, the groundwater is unsuitable for sensitive plants because of its high chloride (Cl) ion content. Moreover, the results obtained indicate that the use of these waters in irrigation presents low sodium risks, and therefore are not likely to modify the structure of the soils in the Sidi-Bel-Abbes plain or reduce their permeability.

Mercury transport and methylmercury production in the lower Cedar River (Iowa) floodplain

Scant attention has been paid to cycling of total mercury (THg) and methylmercury (MeHg) in agriculturally intensive watersheds. Monitoring of Hg and MeHg in river basins provides valuable information on the efficacy of environmental policy and the impacts of land use and climate change on Hg fluxes and biogeochemistry. We report on Hg and MeHg yields in the Cedar River (Iowa), a major tributary of the Upper Mississippi River, and on Hg biogeochemistry in a floodplain of the lower Cedar River, with emphasis on Hg cycling in groundwater and wetland ponds. For the period 2016 to 2018, total Hg yields for the 21,000 km2 Cedar River watershed ranged from 2.6 to 6.9 μg m−2 yr−1, or 25% to 70% of estimated wet deposition, and MeHg yields ranged from 0.09 to 0.18 μg m−2 yr−1. High watershed transfer efficiencies for THg are driven by soil erosion and suspended sediment delivery. Policies and land management practices targeting soil conservation are thus likely to have significant impacts on downstream transport of Hg. Within alluvial groundwaters, Hg and MeHg concentrations were highly spatiotemporally variable, ranging from 0.5 to 2.0 ng/L for THg and 0.03–1.50 ng/L for MeHg. Microtopography exerted strong control on groundwater geochemistry and Hg biogeochemical cycling, with groundwater sampled from lower lying swales exhibiting less dissolved oxygen (DO), higher conductivity, higher dissolved organic carbon (DOC), and higher THg and MeHg. The alluvial aquifer exhibits high hydrologic connectivity with the river and groundwater THg and MeHg concentrations responded rapidly to hydrologic events, with MeHg concentrations increasing with a rising water table. Concentrations of THg and MeHg in wetland ponds were elevated compared to groundwater and most strongly correlated with DOC and UV-absorbance. Methylation potentials in pond sediments were among the highest reported for freshwater sediments, up to 0.15 d−1, which we hypothesize to be linked to high primary productivity associated with nutrient enrichment. Floodplain groundwaters and wetlands constitute important ecosystem control points for downstream MeHg delivery, the magnitude of which is sensitive to changing hydroclimate, especially flood frequency.

Main water pathways in cultivated clayey calcisols in molassic hills in southwestern France: Toward spatialization of soil waterlogging

AbstractLocal waterlogging often occurs on the steep slopes of clayey–calcareous soils in southwestern France, causing nutrients and pollutants transfer to the river bodies and reduced ecosystems services. These soils developed in the Miocene molassic hill formation and are generally impermeable with abundant traces of hydromorphy and heterogenous spatial distribution. This article aims to describe the hydrological functioning of these soils, based on a cross analysis of pedological, hydrological, and geophysical characterizations. Our experimental site is the catchment area located in Auradé (southwestern France). Here, we analyze the flows at the outlet of the studied watershed together with piezometric and climatic monitoring from September 2020 to September 2021. We show that the hydrological year is divided into three phases: first, a soil recharge phase with an effective rainfall of about 100 mm; second, a saturation phase, when 80% of the effective precipitation is drained mostly by runoff and hypodermic flows; third, a drying phase. Soil waterlogging events usually occur during the saturation phase. They are due to several forms of flow: surface runoff associated with return flow, hypodermic flow caused by the presence of soil layers with lower hydraulic conductivity in the subsurface (swelling clays and plowing sole) and groundwater flow with intermittent connection of the soil water table in the hillside to the alluvial groundwater table. We also conducted independent seismic refraction tomography analyses that validate localized waterlogging patterns along the catchment and open the way to spatializing areas with high waterlogging potential at the scale of the study plot.

The effects of floods, droughts and elephants on riparian tree mortality in a semi-arid savanna

Riparian forests have declined around the world over the past century. This is mostly attributed to alteration of river flow regimes and abstraction of alluvial groundwater, although in Africa damage from elephants is often considered the primary cause. Large stands of riparian forest along the Limpopo River in Mapungubwe National Park (South Africa) were transformed to woodland between 1990 and 2005, and water stress resulting from reduced river flows and abstraction, an extreme flood and canopy infestation by climbing plants were identified as contributing causes. Recent recolonization of the area by elephant has created an additional potential driver of mortality. To determine if tree losses have continued and gain further insights into the causes - particularly the relative importance of water stress versus debarking by elephant - tagged trees were surveyed annually from 2011 to 2022. Rates of mortality were higher than in the previous decade for four of the five dominant tree species. Bank erosion from flooding remained a cause but accounted for far less mortality than in the past. For individuals not lost to floods, survival analysis indicated that low rainfall was the primary driver of mortality. Canopy infestation by climbers did not decrease survival, and while elephant damage was common for all species and most likely killed some individuals, it had far less effect than our measures of water availability. Isotopic analysis of xylem, soil, river and groundwater revealed few differences in source water use between species, and marginal contributions from the alluvial aquifer. All species relied on deep soil water, illustrating a key linkage between rainfall and survival under the current hydrological regime. Persistence of the remaining large trees at this site is highly unlikely, considering the altered flow regime of the river and likelihood that future climate change will exacerbate water stress. Given the degree of ecosystem change over the past four decades, future conservation should shift focus to the recruitment and establishment of other large tree species, particularly those tolerant of water stress and elephant browsing.

Hydro‐economic modeling of managed aquifer recharge in the lower Mississippi

AbstractThe Mississippi Embayment aquifer is one of the largest alluvial groundwater aquifers in the United States. It is being excessively used, located along the lower Mississippi River covering approximately 202,019 km2 (78,000 square miles). Annual average groundwater depletion in the aquifer has been estimated at 5.18 billion cubic meters (Gm3) (4.2 million acre‐feet) in 1981–2000. However, since 2000, annual groundwater depletion has increased abruptly to 8 Gm3 (2001–2008). In recent years, multi‐state efforts have been initiated to improve the Mississippi Embayment aquifer sustainability. One management strategy of interest for preserving groundwater resources is managed aquifer recharge (MAR). In this study, we evaluate the impact of different MAR scenarios on land and water use decisions and the overall groundwater system using an economic model able to assess profitability of crop and land use decisions coupled to the Mississippi Embayment Regional Aquifer Study (MERAS) hydrogeologic model. We run the coupled model for 60 years by considering the hydrologic conditions from the MERAS model for the years 2002–2007 and repeating them 10 times. We find MAR is not economically attractive when the water cost is greater than $0.05/m3. Groundwater storage is unlikely to improve when relying solely on MAR as groundwater management strategy but rather should be implemented jointly with other groundwater conservation policies.

May a Former Municipal Landfill Contaminate Groundwater in Microplastics? First Investigations from the “Prairie de Mauves Site” (Nantes, France)

Municipal landfills receive a high amount of plastic waste and due to the occurring physical and biochemical degradation processes, could be significant sources of microplastics (MP). Evaluating the threat to groundwater through the transfer of MP via landfill leachates require more research. The former “Prairie de Mauves” landfill, operated from 1963 to 1987 by the municipality of Nantes (France), and located above the alluvial groundwater of the Loire River, represents a good candidate for such investigations. Leachates and groundwater were sampled along a transect line from upstream to downstream of the landfill, in March and June 2022. MP (>25 µm) were quantified and characterized using µFTIR imaging in transmission mode. MP were observed in every sample with concentrations ranging from 0.71 to 106.7 MP/L. Concentrations in the leachates and the alluvial groundwater illustrate a migration of MP. Twelve polymers were identified and polyethylene (PE) and polypropylene (PP) were predominant. After a conventional rainfall event (14.3 mm), higher concentrations, diversity, and size ranges of MP were observed. Water infiltration through the heterogeneous geological substratum therefore enhanced the migration of larger MP towards the alluvial groundwater of the Loire River.

Increasing contribution of alluvial groundwater to riparian cottonwood forest water use through warm and dry summers

In semi-arid regions, riparian forests access alluvial groundwater to supplement the limited local precipitation. Understanding the sensitivity of riparian forests to variations in weather and climate, and water resources management is essential for guiding riparian conservation measures, especially on rivers impacted by dams and water withdrawal. We anticipated a seasonal trade-off in ecosystem water sources, with increasing relative groundwater use through the summer to compensate for the reduced availability of the shallow soil moisture. To test this hypothesis, we assessed the temporal patterns of alluvial groundwater uptake by a riparian cottonwood (Populus species) forest along a regulated river in southern Alberta, Canada over a three-year interval with relatively warm and dry weather, and low river flows. In support of our hypothesis, groundwater evapotranspiration, as calculated from diurnal fluctuations in the alluvial water table, displayed relative seasonal consistency until the autumnal leaf senescence period. In contrast, the ecosystem-scale evapotranspiration, measured by eddy covariance, gradually receded through the summer as precipitation inputs that fed the shallow soil layers became limited. The consistent uptake rate of alluvial groundwater by cottonwoods enables riparian forests to maintain high rates of water use and productivity in this semi-arid prairie region. We conclude the consistent groundwater use through the warm and dry summer reflected: (1) perennial river flow that replenished the floodplain aquifer; (2) adaptations of cottonwoods to the riparian hydrology and the semi-arid climate; and (3) environmental flow operations that maintained the minimum river and alluvial groundwater levels. Our study provides information on the riparian forest water sources and water use patterns that could help water managers effectively regulate river flows to support healthy downstream riparian ecosystems.

Are riparian vegetation flow response guilds transferable between rivers?

Abstract Understanding the current distribution of riparian plant species is essential for predicting their expansions or contractions in response to flow alterations due to climate changes or direct human actions. Riparian vegetation flow response guilds are assemblages of species that have common functional traits and are hypothesised to respond similarly to fluvial disturbance and water availability along rivers. Species distribution models using guilds may be useful within and across catchments, regions, and continents where floristic composition differs. We examined the distribution of riparian vegetation guilds along gradients of depth to groundwater and inundation exceedance probability (EP) on three rivers in the Colorado River basin and modelled the response of each guild to simulated changes in river flows and alluvial groundwater depth. Groundwater guild distribution models were transferable for the tall tree and flood‐tolerant shrub guilds, but groundwater depth and EP thresholds differed between reaches. Optimal groundwater levels for tall trees and flood‐tolerant shrubs were shallower in Colorado due to higher floodplain groundwater levels and more gentle sub‐surface groundwater gradients. Riparian vegetation guilds were better predicted by groundwater depth than EP while generalist upland guilds were excluded from areas frequently inundated. Presence of the tall tree guild (e.g., Populus fremontii) was predicted by depth to groundwater at all free‐flowing reaches but was not predicted at the one reach where flows are regulated by an upstream dam. In higher elevation reaches, models predicted riparian vegetation guild occurrences with less accuracy, suggesting the influence of other factors such as competition or water contributions from surrounding hillslopes. Scenarios that imposed a groundwater decline indicated that extinctions of both tall trees and flood‐tolerant shrubs (e.g., Salix exigua) could occur in some reaches, depending on future groundwater contributions from hillslopes and the river. Our study demonstrates that river reaches with different plant species composition can have similar guild compositions and the occurrences of these guilds are predicted by hydrologic conditions. Depth to groundwater had a stronger magnitude effect on guild occurrence, highlighting the importance of this less frequently quantified variable in river studies. Our results suggest that the relationship between riparian flow response guild occurrence and hydrologic conditions are transferable between river reaches with differing flow regime, elevation, and climate for some, but not all guilds. Although guilds may respond in similar ways to groundwater depth and flooding, they are not all well predicted by hydrologic condition alone. Guild distributions may be transferable between river systems, but prediction accuracy increases when models are grouped based on reach‐scale hillslope groundwater contributions, elevation, and valley setting.

A Proposed Approach towards Quantifying the Resilience of Water Systems to the Potential Climate Change in the Lali Region, Southwest Iran

Computing the resilience of water resources, especially groundwater, has hitherto presented difficulties. This study highlights the calculation of the resilience of water resources in the small-scale Lali region, southwest Iran, to potential climate change in the base (1961–1990) and future (2021–2050) time periods under two Representative Concentration Pathways, i.e., RCP4.5 and RCP8.5. The Lali region is eminently suitable for comparing the resilience of alluvial groundwater (Pali aquifer), karst groundwater (Bibitarkhoun spring and the observation wells W1, W2 and W3) and surface water (Taraz-Harkesh stream). The log-normal distribution of the mean annual groundwater level and discharge rate of the water resources was initially calculated. Subsequently, different conditions from extremely dry to extremely wet were assigned to the different years for every water system. Finally, the resilience values of the water systems were quantified as a number between zero and one, such that they can be explicitly compared. The Pali alluvial aquifer demonstrated the maximum resilience, i.e., 1, to the future climate change. The Taraz-Harkesh stream, which is fed by the alluvial aquifer and the Bibitarkhoun karst spring, which is the largest spring of the Lali region, depicted average resilience of 0.79 and 0.59, respectively. Regarding the karstic observation wells, W1 being located in the recharge zone had the lowest resilience (i.e., 0.52), W3 being located in the discharge zone had the most resilience (i.e., 1) and W2 being located between W1 and W3 had an intermediate resilience (i.e., 0.60) to future climate change.

A Potential Approach of Reporting Risk to Baseflow from Increased Groundwater Extraction in the Murray-Darling Basin, South-Eastern Australia

An approach of reporting long-term trends in groundwater extraction and baseflow impacts in the Murray-Darling Basin (MDB) in south-eastern Australia was developed and tested. The principal aim of the framework was to provide early warning of any potential adverse impacts from groundwater extraction on environmental releases of surface water for baseflow, support adaptive management of these impacts, and highlight those areas which may benefit from conjunctive water management. The analysis showed that there is no current decadal trend in the annual aggregate groundwater extraction volumes or stream impact across the non-Victorian MDB, with much of the interannual variability being related to rainfall. Despite this, increasing volumes of environmental releases of water for baseflows in some river valleys are being required to replace the stream depletion caused by historical patterns of groundwater extraction established before 2003. Two valleys were identified for which there may be insufficient surface water storage to release water to substitute stream losses to groundwater and still support ecosystems during dry periods. The increasing trend in extraction since 2003 in one of the units has significantly increased the risk in that valley. The reporting framework was shown to be effective for alluvial groundwater systems connected to regulated rivers.

Microbial diversity and geochemistry of groundwater impacted by steel slag leachates

To understand long-term impacts of steel slag material on aquifer geochemistry and microbial communities, we conducted four sampling campaigns in the Gier alluvial groundwater (Loire, France). In its northern part, the aquifer flows under a 200,000 m3 steel slag exhibiting high levels of chromium and molybdenum. Geochemical analyses of the water table revealed the existence of water masses with different chemical signatures. They allowed us to identify an area particularly contaminated by leachates from the slag heap, whatever the sampling period. Water samples from this area were compared to non-contaminated samples, with geochemical characteristics similar to the river samples. To follow changes in microbial communities, the V3-V4 region of 16 s rRNA gene was sequenced. Overall, we observed lower diversity indices in contaminated areas, with higher relative abundances of Verrucomicrobiota and Myxococcota phyla, while several Proteobacteria orders exhibited lower relative abundances. In particular, one single genus among the Verrucomicrobiota, Candidatus Omnitrophus, represented up to 36 % of total taxon abundance in areas affected by steel slag leachates. A large proportion of taxa identified in groundwater were also detected in the upstream river, indicating strong river-groundwater interactions. Our findings pave the way for future research work on C. Omnitrophus remediation capacities.

Hydrochemistry and Nitrate Pollution of Groundwater in the Alluvial Aquifer of the Eastern Mitidja (Algeria)

The study carried out in the eastern Mitidja (Algeria) using groundwater chemistry data is aimed at clarifying the geochemical behavior of the alluvial groundwater as well as assessing the degree of nitrate contamination. The aquifer is characterized by a heterogeneous lithology marked by alternating levels of alluvium, gravel, sand and clay. The chemical facies encountered are: Na - Cl type with 52.7%, Mixed Ca - Mg - Cl type with 29.1%, Mixed Ca - Na - HCO3 type with 9.1% and Ca – HCO3 type with 9.1%. The interpretation of the analytical data shows that water mineralization is controlled by many ions Na+, SO42-, Cl-, Ca2+ and HCO3-. The Gibbs diagram suggests that weathering rock is the determining factor in the current chemical composition of groundwater. Agricultural activity is the main source of groundwater contamination by nitrates. Most of the water points tested have NO3 values very close to the critical threshold of 50 mg/l, the world health organization (WHO) drinking water reference value. By comparing this with the "human affected value" of 13 mg/l, 95% of the analyzed waters are considered contaminated. This water degradation is linked to the widespread use of nitrogen fertilizers, agricultural practices and increasing urbanization.

Geochemical and isotope tracing of groundwater salinity in the coastal Gujarat alluvial plain, India

This study attempts to learn the groundwater salinization mechanism in the large and well-populated coastal Gujarat alluvial plain under growing anthropogenic pressures. For this purpose, geochemical compositions and 87Sr/86Sr were analyzed in 53 groundwater samples collected in the three different seasons during 2016–2017. Additionally, surface water samples collected in each season from two nearby large rivers (Narmada and Tapi) and urban sewage discharge of Surat city were also analyzed. Excluding a few salinity hotspots (EC >8–18 mS/cm), the seasonal average of EC (~2.3–2.5 mS/cm) in groundwater shows little fluctuations negating evaporation as the major salinization process. Localized anthropogenic inputs as traced using NO3 also fail to explain the widespread groundwater salinity. A strong marine influence on the groundwater salinity is revealed by an average Cl/Br of ~655 ± 104 mol/mol in groundwater (except a few outliers) falling close to the seawater composition. The lateral seawater intrusion at shallow depths is generally not supported by the freshening of coastal groundwater samples and generally seaward movements of shallow groundwater as indicated by regional piezometric heads. However, few (Ca)-Mg-Cl type groundwaters collected from north of the Narmada River fall in the piezometric depressions and hint at seawater intrusion and/or upconing of deep saline aquifers. The Sr isotope budget in most of the alluvial groundwater samples is controlled by the seepage groundwater–seawater mixing. Exceptional 87Sr/86Sr values owing to Sr inputs from different age terrains are found in the northeastern groundwater and a few groundwater samples collected downslope of ancient deposits in the central alluvium. The upconing of salty waters having marine signatures partly altered by aquifer–water interactions primarily governs the regional groundwater salinity, which makes the study area vulnerable to continued salinization by excessive groundwater extraction.

Mesilla/Conejos-Médanos Basin: U.S.-Mexico Transboundary Water Resources

Synthesizing binational data to characterize shared water resources is critical to informing binational management. This work uses binational hydrogeology and water resource data in the Mesilla/Conejos-Médanos Basin (Basin) to describe the hydrologic conceptual model and identify potential research that could help inform sustainable management. The Basin aquifer is primarily composed of continuous basin-fill Santa Fe Group sediments, allowing for transboundary throughflow. Groundwater flow, however, may be partially or fully restricted by intrabasin uplifts and limited recharge. The shallow groundwater in the Rio Grande alluvium receives recharge from the Rio Grande and responds to changes in water supply and demand. About 11% of Rio Grande alluvial groundwater volume is recharged annually, an amount that is less than recent withdrawals. Potentially recoverable fresh to slightly brackish groundwater was estimated at 82,600 cubic hectometers in the U.S. portion of the Basin and 69,100 cubic hectometers in the Mexican portion. Alluvial groundwater geochemistry is governed by the evaporative concentration of the Rio Grande and agricultural diversions, whereas deeper groundwater geochemistry is governed by mixing and geochemical processes. Continued refinements to storage estimates, the water budget, and deep groundwater extent and geochemistry can improve estimates of sustainable use and inform alternative water sources.

Characterizing land use effect on shallow groundwater contamination by using self-organizing map and buffer zone

Nitrate–nitrogen (NO3–N) contamination in groundwater is a major problem of drinking and domestic waters in rural areas. This study revealed the influence of land use type on shallow alluvial groundwaters in a typical rural area in South Korea by applying a self-organizing map (SOM), principal component analysis (PCA), and hierarchical cluster analysis (HCA). The uncertainty of spatial information on land use was improved by using a buffer zone of the average influence radius of 32.65 m surrounding wells. Two major land-use types, forests (44.9%) and rice fields (28.8%), occupied a total of 73.7% of the rural area. The higher concentrations of NO3–N in public facilities and livestock areas were demonstrated to directly recharge groundwater pollutants. NO3–N contamination in rice paddies, which also contained chlorine (Cl) and sulfate (SO4), was assessed according to the nutrients and residual salt in the soil. In addition, different NO3–N concentrations for the same land use indicate various biochemical reactions and NO3–N recharge types into the groundwater system. The shallow groundwaters in the study area were classified into three clusters according to their chemical constituents and land–use properties, especially NO3–N concentration, including pH, Cl, and SO4, using a SOM, PCA, and HCA. Unlike existing studies, we applied a buffer zone based on the Cooper–Jacob equation to obtain an improved SOM model prediction accuracy approximately 10% greater than that using the original dataset.

Assessment of groundwater quantitative vulnerability to climate change in Slovenia

Assessment ofthe potential impact of climate change on groundwater recharge and availability of groundwater resources is as essential in Slovenia as it is elsewhere. Adaptive planning is of immense importance when aiming for reduction of negative impacts, even more so in areas with the highest groundwater exploitation levels and the lowest adaptive capacity. We have assessed quantitative groundwater vulnerability to climate change through potential impact and adaptive capacity indicators for all groundwater bodies in Slovenia. High and moderatly high quantitative groundwater vulnerability can be observed in merely 9 % of Slovenian territory. The highest quantitative vulnerability was accounted to shallow alluvial groundwater bodies in the northeastern part of the country, where the annual change in groundwater recharge due to climate change until the middle of this century is expected to represent more than a quarter of the current average annual groundwater extraction.