Regional Aquifer Research Articles

Unveiling nitrate origins in semiarid aquifers: A comparative analysis of Bayesian isotope mixing models using nitrate and boron isotopes and a Positive Matrix Factorization model

Nitrate contamination of groundwater is a pressing global concern, affecting over 80 million people worldwide, with agricultural activities being the primary contributor to nitrogen inputs into aquifers. The primary objective of this study was to identify the predominant sources of nitrate pollution and biogeochemical transformations in the semiarid region of the Meoqui-Delicias aquifer, Mexico. In this region, the uncontrolled use of chemical fertilizers and manure leads to excessive nutrient input, which accelerates the deterioration of groundwater quality. This study introduces an innovative dual-model approach (δ15NNO3 vs. δ11B) to compare the Bayesian Isotope Mixing Model (BIMM) with Positive Matrix Factorization (PMF) for nuanced source apportionment. This approach enhanced the differentiation between manure and sewage as nitrate sources. Results from the δ15NNO3 vs. δ11B model revealed that manure (52.4%) was the most significant source of nitrate pollution in the aquifer, followed by soil (37.4%), chemical fertilizers (5.5%), and sewage (4.7%). The PMF model corroborated this finding and indicated that 60.2% of the NO3–-N pollution in the aquifer was attributed to manure and sewage, confirming the superior performance of the proposed BIMM in source differentiation. Our findings enhance the understanding of nitrate dynamics in semi-arid regions and can serve as a scientific evidence base for targeted interventions in nutrient management in the study area and elsewhere.

SEG Summer Field Camp: Multigeophysical imaging of an aquifer in the Astara region of Azerbaijan

Groundwater faces growing pressure due to human activities and the impacts of global climate change. Therefore, it is imperative to characterize near-surface aquifers, especially those that are unconfined because they are particularly vulnerable to these challenges. In Azerbaijan, alluvial plain aquifers represent a critical facet of the nation's water resources, yet they remain largely understudied. The objective of our study is to employ a multigeophysical survey (including electrical resistivity, seismic refraction, and ground-penetrating radar) to describe the subsurface attributes of an unconfined alluvial aquifer situated within an agricultural field in Astara, Azerbaijan. These data were acquired during the 2023 SEG Summer Field Camp by global students and specialists. Based on our general knowledge of the area, we interpret our findings as a subsurface with four distinct layers. The first is an initial 1 m thick soil layer covering the second layer, which is a more permeable unconfined aquifer likely consisting of a mixture of sand, pebbles, and gravel with a silty matrix (3 m thick). The third is a potential confining layer that is possibly clayey. The fourth layer is a presumed confined aquifer at a depth of 10 m. These results shed light on previously unstudied alluvial plain aquifers and contribute to comprehension of the hydrogeologic conditions at the local scale. To provide a broader understanding at the regional scale, the survey area should be extended and linked to borehole data to improve the interpretation of the geophysical results.

Assessment and Modeling of the Vulnerability of Regional Aquifers to Anthropogenic Perturbations

Assessment and Modeling of the Vulnerability of Regional Aquifers to Anthropogenic Perturbations

A multi-method approach for assessing groundwater vulnerability of shallow aquifers in the Marchfeld region (Austria)

Study regionMarchfeld region (Austria) Study focusA multi-method and multi-scale assessment of the intrinsic groundwater vulnerability to generic pollutants was carried out. At the regional scale, a parametric method, to assess the intrinsic groundwater vulnerability, and a transfer function model, to assess the travel time of a generic and non-reactive pollutant through the unsaturated zone, were applied. At the site-specific scale, the travel time of the peak concentration was evaluated by using a physically-based hydrological model. The comparison of results of different approaches allowed mutual validation and advanced the knowledge about the assessment of groundwater vulnerability. New hydrogeological insights for the regionTo assess the groundwater vulnerability, a detailed hydrogeological map of the study area was reconstructed. A large variability of hydrogeological, morphological and anthropic conditions was recognized. Alluvial aquifers formed by high-permeability deposits hosting shallow groundwater circulation are characterized by the highest groundwater vulnerability. Contrarily, lower groundwater vulnerability was recognized for aquifers formed by low-permeability deposits, favoring a reduction of infiltration processes and a major attenuation of pollutants’ potential effects. The presented multi-method approach revealed how comparing the results of a DRASTIC-like method and two process-based models can deliver hints regarding their suitability, different spatial densities and quality of required inputs, and effectiveness. Finally, the potential strong impact of some agricultural practices was confirmed.

Extended Aquifer System Pressure Behavior under Carbon Storage

Summary Most reported carbon storage projects have involved inexpensive carbon dioxide (CO2) capture from gas processing plants or ethanol refineries. However, widespread carbon capture and storage (CCS) application must avoid any risk that high capital investment cost for carbon capture from stationary point sources leads to unanticipated issues related to the aquifer storage. This paper reviews successful and unsuccessful carbon storage projects and explains simple extended aquifer system fundamentals that must be considered in selecting a storage aquifer. This study begins by evaluating reported carbon storage projects in the context of an extended aquifer system with specific attention to initial formation pore pressure and potential or known hydraulic vertical or lateral communication with hydrocarbon accumulations and/or fresh water. Further study focuses on how the contrast between injection well and aquifer pressure evolution enables understanding of the overall aquifer material balance. Finally, we consider implications of brine migration during and after long-term CO2 injection in unconfined aquifers. Experience in the petroleum industry with aquifer behavior includes presence or lack of water influx and production from hydrocarbon reservoirs that share a common aquifer. Of particular importance is the observation that hydrostatic initial formation pressure indicates the possibility that a petroleum system, or an extended aquifer system without hydrocarbon accumulation(s), connects to atmospheric pressure through an unconfined aquifer. In such cases, indefinite injection will never increase the regional aquifer pressure. Furthermore, initial formation pressure that exceeds hydrostatic pressure implies a petroleum system or an extended aquifer system that is volumetrically limited. In such cases, injection will increase the system pressure, and pressure monitoring can detect leakage from the system. Finally, CO2 injection into an aquifer will displace brine in the direction of lower pressure that could relate to distant production from the same aquifer or from hydrocarbon reservoirs with which it communicates. Reasons for known carbon storage project interruptions have included unexpected lateral plume migration or aquifer pressure increase during CO2 injection that might have been anticipated with attention to straightforward consideration of aquifer-enabled hydraulic communication. Such extended aquifer dynamics must be included in long-term models for permanent CO2 storage during and after injection.

The U.S. Midwest and High Plains Aquifer-fed croplands are previously unrealized hotspots of extreme evaporative demand exposure

Total evaporative demand or atmospheric thirst is a primary determinant of agroecosystems’ water use and an indispensable input to scientifically based irrigation design and management. However, despite its extensive use to represent agricultural environments, it has not been assessed for its extreme behavior. Prolonged exposure to extreme evaporative demand conditions a.k.a thirstwaves can be especially stressful for agricultural output, water use, and management, but remain uninvestigated owing to lack of meaningful metrics for quantifying and reporting ‘extreme thirst exposure’. In this letter, I present spatial (county-level) and temporal (1981–2021) changes in exposure to extreme thirst during the agricultural growing season across the conterminous U.S. (CONUS). Using a fully physical metric of evaporative demand, i.e., standardized short crop reference evapotranspiration (ETo), I define two novel measures: cumulative extreme thirst exposure (thirstcum) and average extreme thirst anomaly (thirstanom) to represent the seasonal-level severity of thirstwaves. Both metrics showed significant spatiotemporal variation with long-term averages of 12 mm (thirstcum) and 0.66 mm d−1 (thirstanom) for CONUS. Distinct spatial patterns were revealed for extreme thirst exposure that had little in common with those observed for total ETo. Spatially, hotspots of high extreme thirst exposure were co-located with the Midwest and High Plains aquifer regions, that account for 64% of total acreage and 28% of irrigated acreage nationally, respectively. Critical for food and water security, these regions have experienced the highest extreme thirst exposure nationally, hence necessitating reevaluation of regional disparities in water stress. While thirstcum and thirstanom have increased by 5.6 mm and 0.21 mm d−1 on an average in CONUS, worsening of extreme thirst exposure is especially concerning for the High Plains aquifer region (12.6 mm and 0.54 mm d−1, respectively). The emergence of previously unrealized hotspots in regions critical for water security uncover potential pitfalls for planning and adaptation that may result from overlooking extreme measures of evaporative demand.

Geochemical tracers associated with methane in aquifers overlying a coal seam gas reservoir

Understanding inter-aquifer connectivity or leakage of greenhouse gases and groundwater to aquifers overlying gas reservoirs is important for environmental protection and social licence to operate. Australia's Great Artesian Basin (GAB) is the largest artesian groundwater system in the world with groundwater extracted for agriculture, livestock, mines, energy, private or town water supply. Microbial coal seam gas (CSG) and production water are also extracted from the GAB. Here a range of groundwater tracers is used to investigate the potential for gas and groundwater connectivity between the CSG reservoir and aquifers.The GAB aquifer and alluvium contained a range of methane concentrations (0.001 to 2100 mg/L) that exhibit an increase with depth and δ13C-CH4. Aquifer and alluvium groundwater 87Sr/86Sr were in the range 0.7042 to 0.7082. CSG production waters however had non-radiogenic, distinctive 87Sr/86Sr signatures <0.7036, indicating a lack of significant groundwater leakage. One gassy aquifer bore with 160 mg/L methane conversely has 87Sr/86Sr, δ13C-CH4, δ2H-CH4 and δ13C-DIC values overlapping the CSG waters. In several aquifers δ34S-SO4 and δ18O-SO4 are sourced from windblown surface salts of inland Australian playa lakes in recharge waters. Bacterial sulphate reduction is additionally occurring in a regional aquifer. Cosmogenic isotopes and tritium show recent recharge and mixing with older groundwaters in several shallow aquifers.Groundwater and gas signatures indicate that leakage of groundwater and methane from the CSG reservoir was not occurring in the majority of areas investigated here. Methane was consistent with in situ generation in shallow GAB aquifers by primary microbial CO2 reduction or acetate fermentation. Connectivity of one alluvial bore and the underlying GAB aquifer could not be completely ruled out. Separately, one gassy Springbok GAB aquifer bore is either connected to the underlying CSG gas reservoir, or has in situ secondary microbial CO2 reduction producing methane from interbedded coal within the aquifer. This study is relevant to other basins in Australia and internationally where gas is observed in aquifers that overly conventional, unconventional or coal seam gas reservoirs.

Numerical Simulation of the Solute Migration Regulated by Vertical Cutoff Wall based on FEFLOW

Cutoff wall has been widely used in desalination of coastal aquifers in many coastal regions and remediation of industrial waste water pollution. In recent years, the excessive exploitation of resources in the coastal brine distribution area leads to the salinization of deep soil. At the same time, the mine water pollution caused by improper discharge of industrial waste water into the abandoned mining area is a new form of pollution in Shandong, China. However, due to the complex geological conditions of abandoned mining areas, loose collapse of overlying strata in roadway and gob layer, it is difficult to prevent and control groundwater pollution in deep gob layer. It is a major difficulty in practical engineering to evaluate the cutoff interception performance of vertical cutoff wall on the pollution of gob layer in such mining areas and optimize cutoff interception measures. In this paper, a typical polluted abandoned mining area in Shandong, China is taken as an example, and COD is used as the main simulation factor for numerical simulation. The numerical simulation results show that in the process of groundwater pollution control, the cutoff wall with appropriate thickness and hydraulic conductivity can effectively block the diffusion of solute. The horizontal transport of solute can be significantly weakened when the thickness of the cutoff wall is 90 cm and the hydraulic conductivity is 1.0×10-4 m/d. Compared with increasing the thickness, reducing the hydraulic conductivity of the cutoff wall is more effective in controlling the migration of solute in the site. When the hydraulic conductivity is reduced by an order of magnitude, the diffusion range of solute is reduced by 19.74% compared to before. Therefore, priority should be given to reducing the hydraulic conductivity of the cutoff wall in order to optimize its influence on pollutant migration.

The dominance and growth of shallow groundwater resources in continuous permafrost environments

Water is a limited resource in Arctic watersheds with continuous permafrost because freezing conditions in winter and the impermeability of permafrost limit storage and connectivity between surface water and deep groundwater. However, groundwater can still be an important source of surface water in such settings, feeding springs and large aufeis fields that are abundant in cold regions and generating runoff when precipitation is rare. Whether groundwater is sourced from suprapermafrost taliks or deeper regional aquifers will impact water availability as the Arctic continues to warm and thaw. Previous research is ambiguous about the role of deep groundwater, leading to uncertainty regarding Arctic water availability and changing water resources. We analyzed chemistry and residence times of spring, stream, and river waters in the continuous permafrost zone of Alaska, spanning the mountains to the coastal plain. Water chemistry and age tracers show that surface waters are predominately sourced from recent precipitation and have short (<50 y) subsurface residence times. Remote sensing indicates trends in the areal extent of aufeis over the last 37 y, and correlations between aufeis extent and previous year summer temperature. Together, these data indicate that surface waters in continuous permafrost regions may be impacted by short flow paths and shallow suprapermafrost aquifers that are highly sensitive to climatic and hydrologic change over annual timescales. Despite the lack of connection to regional aquifers, continued warming and permafrost thaw may promote deepening of the shallow subsurface aquifers and creation of shallow taliks, providing some resilience to Arctic freshwater ecosystems.

Delineation of aquifer storage potential in response to regional groundwater development

Developing aquifers as part of sustainability efforts toward groundwater development is a tactical approach to meeting water demand and management objectives. Delineation of aquifer storage potential (ASP) and longitudinal conductance (SL\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${S}_{L}$$\\end{document}) is a good approach to protect and manage groundwater resources. A Schlumberger configuration was applied to delineate fifteen (15) vertical electrical sounding (VES) stations alongside a 2D electrical resistivity imagery (ERI) profile and regional borehole data to characterize the regional ASP. The results of the study show that the layer resistivity and thickness values of the regional aquifer unit range from 39.9–105 Ωm and 15–44 m, respectively, while the overburden thickness overlays the regional aquifer unit varied between 5–10 m corresponding to the regional borehole data. The weathered/fractured basemen, which constitute the regional aquifer unit were delineated, which consists of shallow, moderate, and deep aquifer zones. The deep aquifer zones fall within the depth of 30–44 m and are considered suitable for groundwater prospective. The weathered layer with appreciably low resistivity values with thick aquifer regolith has also been identified as most suitable for borehole siting. The weathered/fractured encountered within thick aquifer regolith were mapped as the region with a high ASP for groundwater development. In addition, the values of longitudinal conductance, SL\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${S}_{L}$$\\end{document} and transverse resistance, RT\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${R}_{T}$$\\end{document} estimated from aquifer parameters vary between 0.21-0.85Ω-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$0.21-0.85 \\,{\\Omega }^{-1}$$\\end{document} and 1695-3124Ωm2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$1695-3124\\, {\\Omega m}^{2}$$\\end{document}, respectively. The SL\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${S}_{L}$$\\end{document} values show that the study area falls within moderate (0.20-0.69Ω-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$0.20-0.69 \\,{\\Omega }^{-1}$$\\end{document}) and good (0.7-4.9Ω-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$0.7-4.9 \\,{\\Omega }^{-1}$$\\end{document}), which invariably determined the regional aquifer protective capacity. Thus, the DC geoelectrical approach has been successfully employed in a lateritic-based environment to delineate aquifer-promising zones for regional groundwater development.

Groundwater composition and stable isotopes as proxies to investigate paleoclimate change in permafrost thawing regions

The paleoclimate since the late Pleistocene has gained substantial attention due to its profound effects on hydrology, ecosystems, and landforms, particularly in regions experiencing permafrost thawing. Northeast China is acknowledged for exhibiting distinctive yet contentious paleoclimate, which has been elucidated through various proxies. In this case, we emphasize the significance of stable isotopes within the northern Songnen Plain as complementary proxies for paleoclimate interpretation, bolstered by radiocarbon dating. The Cretaceous sandstone confined aquifer (CSA) is designated as the reference aquifer, based on the hydrogeochemical and isotopic characteristics. The 14C results indicate that the CSA preserves groundwater from the late Pleistocene to the modern. These findings, in conjunction with isotope variations, delineate specific climate events, which are aligning with results derived from conventional proxies. The late Pleistocene-early Holocene showed a climate shift from cold to warm. The middle Holocene was warm and humid. Then the late Holocene entered the Neoglacial, which characterized by a cold climate environment. Our analysis also reveals fluctuations in the age and TDS concentration along the groundwater runoff. The paleo groundwater exhibits simultaneous lower TDS concentration, maximum δ18O depletion and minimum recharge temperature. Neither latitude nor altitude effects could account for the sufficient isotopic depletion, instead, we found that the humid climate and permafrost meltwater also contributed to the isotope depletion. Simultaneously, the paleoclimatic environment such as freeze-thaw cycles of permafrost exerts a significant influence on the groundwater. The formation of permafrost hinders groundwater recharge, while its thawing dilutes the solute content of groundwater. Additionally, the recharge gaps also potentially result from arid climate, inadequate samples, and the effects of mixing water. The study substantiates the reliability of confined aquifers in permafrost thawing regions as robust paleoclimatic archives and emphasizes the utility of stable isotopes in combination with radiocarbon dating as ideal climate proxies.

Investigating the Morphometry and Hydrometeorological Variability of a Fragile Tropical Karstic Lake of the Yucatán Peninsula: Bacalar Lagoon

Comprehensive morphometric and hydrometeorological studies on Bacalar Lagoon, Mexico’s largest tropical karstic lake and a significant aquatic system of the Yucatán Peninsula, are lacking. This study provides a detailed analysis of its bathymetry, morphometry, and hydrometeorological characteristics. The lake’s main basin stretches more than 52.7 km in length, with widths varying from 0.18 km to 2.28 km. It has a volume of 554.4 million cubic meters, with an average depth of 8.85 m, reaching depths of up to 26 m in the north and featuring sub-lacustrine dolines in the south, with depths of 38 m, 48.5 m, and 63.6 m. The study reveals seasonal variations in surface water temperature, closely linked to air temperature (r = 0.89), and immediate responses of water levels to hydrometeorological events. Water level fluctuations also exhibit seasonal patterns that are correlated with regional aquifer conditions, with a lag of 2 months after seasonal rainfall. Interannual variability in rainfall and water levels was observed. From 2010 to 2012, rainfall consistently remained below its mean climatic value, due to a prolonged La Niña event, while the exceptionally wet conditions in 2020 were also associated with La Niña. Extreme and anomalous hydrometeorological events, such as those following tropical storm Cristobal in 2020, revealed the fragility of Bacalar Lagoon, causing a notable transformation in lake color and transparency, shifting it from its typical oligotrophic state to eutrophic conditions that lasted longer than a year. These color changes raise questions about the factors impacting ecological health in tropical karstic regions. Additional factors affecting water quality in the BL in 2020, such as deforestation, coastline changes, and urban growth, warrant further investigation. Our study can serve as a starting landmark.

An integrated study of Atopobathynella (Parabathynellidae, Bathynellacea) species reveals restricted distributions in a complex hydrogeological setting: two new species from the Pilbara (Australia)

Abstract The Pilbara bioregion (Western Australia) has become a hotspot for subterranean fauna as a consequence of many surveys conducted to comply with Western Australian environmental regulation requirements. In this bioregion, mining developments can have major implications for subterranean fauna and their conservation. However the diversity and species distributions of most taxa are still poorly known, including the crustacean family Parabathynellidae. Recent studies on a widespread genus of this family (Atopobathynella) from the Pilbara highlighted several undescribed taxa with interesting patterns of distribution. In the Gudai Darri locality, the northern flank of the Hamersley Range occurs as a stepped escarpment intersected by dykes and gullies, with groundwater occurring within fractured rocks abutting the Fortescue River valley, where a separate regional aquifer occurs. This investigation aimed to observe whether stygofauna species distributions (1) reflected the separation between the two major aquifers within the Hamersley Range and the Fortescue Valley; and (2) were influenced by the presence of dykes. We examined the Atopobathynella species occurring in the study area using morphological and molecular data. The results reflected the hydrogeological complexity of the study area with six new lineages of Atopobathynella, recorded mainly in different gullies, that do not share a most recent common ancestor. Two species are described here A. pagetae sp. nov. and A. lythei sp. nov., and four additional species are delineated through preliminary morphological analyses and molecular data. This study will improve future environmental impact assessments and the understanding of Parabathynellidae taxa distribution in hydrogeological complex areas.

Multidisciplinary approach to understand the salinization of fractured crystalline aquifers in semi-arid region

Multidisciplinary approach to understand the salinization of fractured crystalline aquifers in semi-arid region

Basin‐scale responses of groundwater‐resource quality to drought and recovery, San Joaquin Valley, California

AbstractGroundwater‐resource quality is assumed to be less responsive to drought compared to that of surface water due to relatively long transit times of recharge to drinking‐supply wells. Here, we evidence dynamic perturbations in aquifer pressure dynamics during drought and subsequent recovery periods cause dramatic shifts in groundwater quality on a basin scale. We used a novel application of time‐series clustering on annual nitrate anomalies at &gt;450 public‐supply wells (PSWs) across California's San Joaquin Valley during 2000–22 to group sub‐populations of wells with similar water‐quality responses to drought. Additionally, we statistically evaluated the direction and magnitude of multi‐constituent water‐quality changes across the San Joaquin Valley using a broader dataset of &gt;3000 PSWs with data during two select hydrologic stress periods representing an extreme drought (2012–16) and subsequent recovery (2016–19). Results of time‐series clustering and stress‐period change analyses corroborate a predominant regional response to pumping stress characterized by increased concentrations of anthropogenic constituents (nitrate, total dissolved solids) and decreased concentrations of geogenic constituents (arsenic, fluoride), which largely reversed during recovery. Cluster analysis also identified a secondary, less commonly occurring group of PSWs where nitrate decreased during drought, but explanatory factor analysis was not able to discern hydrogeologic drivers for these two divergent response patterns. Long‐term tracer data support the hypothesis that the predominant regional signal of nitrate increase during drought is caused by enhanced capture of modern‐aged groundwater by PSWs during periods of pumping stress, which can drive rapid changes in water quality on seasonal and multiannual timescales. Pumping‐induced migration of modern, oxic groundwater to depth during drought may affect geochemical conditions in deeper portions of regional aquifers controlling the mobility of geogenic contaminants over the long term.

Integrated approach to understand the multiple natural and anthropogenic stresses on intensively irrigated coastal aquifer in the Mediterranean region

Understanding the major factors influencing groundwater chemistry and its evolution in irrigation areas is crucial for efficient irrigation management. Major ions and isotopes (δD-H2O together with δ18O–H2O) were used to identify the natural and anthropogenic factors contributing to groundwater salinization in the shallow aquifer of the Wadi Guenniche Plain (WGP) in the Mediterranean region of Tunisia. A comprehensive geochemical investigation of groundwater was conducted during both the low irrigation season (L-IR) and the high irrigation season (H-IR). The results show that the variation range and average concentrations of almost all the ions in both the L-IR and H-IR seasons are high. The groundwater in both seasons is characterized by high electrical conductivity and CaMgCl/SO4 and NaCl types. The dissolution of halite and gypsum, the precipitation of calcite and dolomite, and Na–Ca exchange are the main chemical reactions in the geochemical evolution of groundwater in the Wadi Guenniche Shallow Aquifer (WGSA). Stable isotopes of hydrogen and oxygen (δ18O–H2O and δD-H2O) indicate that groundwater in WGSA originated from local precipitation. In the H-IR season, the δ18O–H2O and δD-H2O values indicate that the groundwater experienced noticeable evaporation. The enriched isotopic signatures reveal that the WGSA's groundwater was influenced by irrigation return flow and seawater intrusion. The proportions of mixing with seawater were found to vary between 0.12% and 5.95%, and between 0.13% and 8.42% during the L-IR and H-IR seasons, respectively. Irrigation return flow and the associated evaporation increase the dissolved solids content in groundwater during the irrigation season. The long-term human activities (fertilization, irrigation, and septic waste infiltration) are the main drives of the high nitrate-N concentrations in groundwater. In coastal irrigation areas suffering from water scarcity, these results can help planners and policy makers understand the complexities of groundwater salinization to enable more sustainable management and development.

Cover crops and irrigation impacts on corn production and economic returns

Increases in irrigated crop acreage and frequent droughts during the growing season have caused continual groundwater decline of the Mississippi River Valley Alluvial Aquifer in the Mississippi Delta region. A field experiment was conducted from 2019 to 2021 to determine if combinations of irrigation scheduling thresholds and cover crops (CCs) could improve corn (Zea mays L.) production, water productivity (WP), irrigation water use efficiency (IWUE), and net returns. The irrigation thresholds used for irrigation scheduling were a wet threshold (−40 kPa), a dry threshold (−90 kPa), and no irrigation. The CC treatments were cereal rye (Secale cereale L.), hairy vetch (Vicia villosa R.), wheat (Triticum aestivum L.)-radish (Raphanus sativus L.)-turnip (Brassica rapa L.) mix, and no cover crop. In 2020, CCs reduced corn yield by 9–26% compared to no cover crop. In 2021, wet irrigation threshold treatments had 8% and 9% higher corn yield than no irrigation and dry irrigation threshold treatments, respectively. No irrigation treatments showed higher WP than dry and wet irrigation thresholds, while hairy vetch had higher in WP among CC treatments in year two of this study. Hairy vetch under the dry irrigation threshold had higher IWUE than all other treatments. The no-CC treatments generated $167, $340, and $58 ha−1 more under the wet, dry, and no irrigation treatments, respectively, when averaged over both years. Water conservation was affected by CC selection and irrigation management.

Comparative study for coastal aquifer vulnerability assessment using deep learning and metaheuristic algorithms.

Coastal aquifer vulnerability assessment (CAVA) studies are essential for mitigating the effects of seawater intrusion (SWI) worldwide. In this research, the vulnerability of the coastal aquifer in the Lahijan region of northwest Iran was investigated. A vulnerability map (VM) was created applying hydrogeological parameters derived from the original GALDIT model (OGM). The significance of OGM parameters was assessed using the mean decrease accuracy (MDA)method, with the current state of SWI emerging as the most crucial factor for evaluating vulnerability. To optimize GALDIT weights, we introduced the biogeography-based optimization (BBO) and gray wolf optimization (GWO) techniques to obtain to hybrid OGM-BBO and OGM-GWO models, respectively. Despite considerable research focused on enhancing CAVA models, efforts to modify the weights and rates of OGM parameters by incorporating deep learning algorithms remain scarce. Hence, a convolutional neural network (CNN) algorithm was applied to produce the VM. The area under the receiver-operating characteristic curves for OGM-BBO, OGM-GWO, and VMCNN were 0.794, 0.835, and 0.982, respectively. According to the CNN-based VM, 41% of the aquifer displayed very high and high vulnerability to SWI, concentrated primarily along the coastline. Additionally, 32% of the aquifer exhibited very low and low vulnerability to SWI, predominantly in the southern and southwestern regions. The proposed model can be extended to evaluate the vulnerability of various coastal aquifers to SWI, thereby assisting land use planers and policymakers in identifying at-risk areas. Moreover, deep-learning-based approaches can help clarify the associations between aquifer vulnerability and contamination resulting from SWI.

Validation of the intrinsic vulnerability to pollution of fractured siliciclastic aquifers using natural background levels

Aquifers are important water reserves in water-scarce areas. However, uncontrolled human activities and lack of knowledge of aquifer characteristics increase their vulnerability to pollution. Assessing intrinsic vulnerability is essential for improving groundwater management. However, traditional tools, such as DRASTIC, ignore relevant parameters that, in particular contexts, lead to underestimating vulnerability. This work assesses the intrinsic vulnerability to pollution of a siliciclastic aquifer system (Shallow and Upper) by comparing the DRASTIC and modified DRASTIC methods. Modified DRASTIC included parameters such as Land Use and fracturing patterns relevant in populated areas where hydrogeological configurations involve highly cemented and fractured siliciclastic rocks with secondary porosity that define the main pathways for transporting contaminants from the surface. The intrinsic vulnerability was validated using Natural Background Levels (NBLs) of contaminant indicator ions (NO3−, PO43− and SO₄2-) to identify areas where the concentration of these indicators surpassed the NBLs. These areas were compared with the vulnerability classes from DRASTIC methods. NBLs were: 2.12 mg/l, 0.05 mg/L and 26.77 mg/L (Shallow aquifer), and 3.17 mg/L, 0.17 mg/L and 5.06 ml/L (Upper aquifer) for the ions of NO3−, PO43− and SO₄2-, respectively. The ion concentrations surpassing NBLs were spatially distributed, being more notable in the dry season and showing a greater coincidence with the high vulnerability class of the Modified DRASTIC. Thus, the modified DRASTIC better represented the high vulnerability of the aquifer system to pollution and the negative effect of anthropic activities. Additionally, Pearson's coefficients were calculated between the concentrations of contaminant indicator ions and intrinsic vulnerability indices of DRASTIC methods. However, the coefficients lack statistical significance. These results support the relevance of adding land use and fracturing patterns to assess the intrinsic vulnerability of fractured, siliciclastic aquifers in populated regions and show NBLs as a better validation method than Pearson's coefficients in data-scarce contexts.

Communicating About Water in the Floridan Aquifer Region: Part 6—Stakeholders’ Mental Models of Regional Water Challenges

If we could look into the minds of agricultural producers and environmentalists to see how they think about regional water challenges, we may be better able to help stakeholders understand each other’s perspectives and resolve perceived conflicts. A 2017–2018 study provides visual maps of producers’ and environmentalists’ conceptions of the relationship between water and the regional economy. The maps reveal that the groups think about the topic in fundamentally different ways. While surveyed producers possess an agricultural, operational-level view of the water-economic system that includes the protective actions taken by individual farmers and ranchers, environmentalists possess a watershed-level view of the water-economic system that highlights the detrimental collective impacts of the agricultural industry as a whole. The findings suggest steps that water communicators can take to reduce perceived conflict between the groups.