Aquifer Water Quality Research Articles

Statistical approach to the monitoring of groundwater quality for drinking in Northern Algeria

The scarcity of surface water during prolonged droughts makes the Mitidja quaternary aquifer in north-central Algeria essential for drinking water supply. This study aims to improve understanding of the hydrochemical behavior of this aquifer using multivariate statistical analysis. The main objective is to identify the factors influencing the chemical composition of the water and determine its suitability for domestic use. To this end, water samples were taken from 20 boreholes and analyzed for electrical conductivity, pH, and significant ions during the dry and wet seasons. The results showed significant spatial variations in salinity, particularly in the plain's extreme eastern and western regions, where several parameters exceeded WHO standards. Chemical quality was higher in the western and central boreholes than in those to the east, which were deemed unsuitable for human consumption. Various chemical facies result from the dissolution of dolomitic and evaporitic formations, leading to increased mineralization. In addition, human activity has affected water quality, notably through the excessive use of chemical fertilizers and the discharge of untreated wastewater. This study underlines the need for sustainable environmental management to preserve water quality in the Mitidja quaternary aquifer, which is essential for guaranteeing local communities' drinking water access.

Identification of Groundwater Table Depth as A Source of Raw Water in Elelim District, Yalimo Regency

Clean water is a fundamental need for communities, sourced from both surface water (e.g., rivers, streams, springs) and groundwater (surface and deep aquifers). Groundwater dynamics are influenced by natural factors, including geology and geomorphology, which determine aquifer characteristics such as type, depth, thickness, and permeability. Geological structures influence groundwater flow direction, while lithology affects aquifer ion concentration and water quality. Surface morphology impacts groundwater table depth and movement patterns, with morphogenesis influencing permeability, porosity, and infiltration rates. This research investigates groundwater potential in Yalimo Regency, Mountainous Papua Province. The research aims to evaluate aquifer characteristics using regional geological and geomorphological assessments complemented by advanced mapping technology. The methodology integrates field mapping with geospatial analysis to identify and delineate groundwater resources. Results provide a detailed understanding of aquifer distribution, capacity, and potential for sustainable utilization. Conclusions emphasize the importance of combining traditional and technological approaches for accurate groundwater resource assessment, offering insights for effective water management in the region.

Best Management Practices to Mitigate Contamination of Karstic Aquifers from Emergency Fire-Control Runoff

We propose best management practices to increase karstic aquifer drinking water supplies’ resilience to potential hazardous material impacts where first responders and public safety officials suspect emergency firefighting runoff has entered the subsurface in the aquifer recharge zone. Karstic aquifers are unique because of their direct openings to the land’s surface, which allows contaminants in runoff or other surface waters to rapidly enter the subsurface and impact aquifer water quality. In the United States, 20% of the land surface is karst, and about a third of the groundwater used for drinking comes from karstic aquifers. Proposed best management practices emphasize on-site, real-time evaluation of the transport and fate of HAZMAT that may enter the subsurface and focus on water quality sampling, runoff and groundwater flow modeling, nontoxic dye tracing, and related studies for use in planning before and during an event and after emergency response has ended. We recommend best management practices for evidence-based screening of high-risk sites to facilitate placement of hazardous material sampling devices and emergency responder deployment. The best management practices, tools, curricula, and training described combine with earlier work by the authors to provide a comprehensive menu of actions to (1) help first responders prevent or limit flushing of hazardous material into a karstic aquifer; (2) help emergency management officials understand the consequences of contamination and issue data-driven geographically focused health and safety risk communications; and (3) help provide health and safety officials with relevant science- and data-based information that can help mitigate human and environmental health risks.

Reducing wastewater nitrogen loading by >90% with carbon-amended septic systems: A field demonstration in Barnstable (Cape Cod), Massachusetts

Onsite wastewater treatment systems (OWTS) are a major source of excess nutrients and co-pollutants in watersheds across the United States. In Barnstable County (Cape Cod), Massachusetts, effluent from septic systems and cesspools contributes approximately 80% of the controllable reactive nitrogen (N) load to numerous impaired estuaries and degrades water quality in the region's sole source aquifer, streams and ponds. In unsewered areas, wastewater N loads could be reduced substantially by Innovative/Alternative (I/A) septic systems designed for enhanced removal. Use, however, has been partly limited by the availability of high performing, cost effective options, while conventional septic systems continue to be installed in watersheds with well documented N impairments. This paper describes the strategic replacement of residential OWTS with two I/A models that incorporate woodchip bioreactors to enhance N removal. Systems were installed at 14 neighboring homes in Barnstable, MA, and monitored for field performance. Influent and effluent were sampled monthly and analyzed for N and phosphorus (P), among other water quality indicators. Flow to each system was continuously metered to estimate nutrient loads. Results from the first 25 months of monitoring for 13 systems with at least a full year of data are presented in terms of 1) reductions in nutrient concentrations and mass loads and 2) reliability of the systems for meeting a performance goal of total N (TN) < 10 mg/L. Discussion supports consideration of where and how these technologies may be successfully used to manage excess N in sensitive watersheds.

Monitoring and Evaluation of Water Quality in Underground Aquifers Using (GIS) and (IWQI): Western Karbala’a as a Case Study

Abstract: This study aims to provide an assessment of the current state of groundwater quality and to provide a combination of water quality criteria that may be utilized to develop the irrigation water quality index (IWQI), a suitable technique for classifying irrigation water. Seven wells’ worth of water were collected in the region under evaluation, and their physical and chemical characteristics, such as cation and anion concentrations, were examined. An interpolation method called “Inverse Distance Weighted, IDW” was employed in a geographic information system (GIS) to analyze the data obtained. The water may be labelled as “severe restriction, SR” because the projected values of the irrigation water quality index (IWQI) were more than zero but less than 40. Throughout the six-year period (2017, 2018, 2019, 2020, 2021, and 2022), water samples from seven wells in the study area have been analyzed for their major and minor components. The finding shows that the irrigation water quality indexes (IWQIs) for 2017 and 2018 had measured values above zero but below 55, whereas IWQIs for the other years had calculated values below 40. Therefore, the water can be identified as “High Restriction, HR,” in the early years and as “severe restriction, SR,” in the latter years. As a consequence, this water cannot be utilized for irrigation, and it is abundantly evident that there will be a shortfall in the value of IWQI for a number of years in a row.

Quantifying recharge mechanisms in low-hilly areas of a loess region: Implications for the quantity and quality of groundwater

Groundwater plays a crucial role in sustaining water supply and irrigation in arid regions with thick vadose zones; however, the recharge mechanisms and their impact on water quality remain contentious. For flood-irrigated areas, irrigation water amount is not well known to evaluate the effect of irrigation on the recharge. In this study, we employed multiple tracers to investigate recharge mechanisms in a low-hilly region with some flood-irrigated areas, where irrigation water recharge was estimated by the chloride mass balance method combined with the tritium peak method. Deep soil samples from irrigated lands in vadose zone and groundwater from unconfined aquifers were collected to determine the contents of the water isotopes (2H, 18O, and 3H), chlorides (Cl-), and nitrates (NO3−). The findings revealed unique tritium peaks preserved in the loess vadose zone, where the recharge rate under the non-irrigated site was estimated to be only 8.6 mm yr−1, 2.4 % of the average annual precipitation. According to the estimated irrigated recharge rates, irrigation water dominates the potential diffuse recharge in vadose zone. For the aquifer recharge, we then quantified diffuse recharge (62.2 ± 4.7 %, piston flow) and focused recharge (37.8 ± 4.7 %, preferential flow) via the line-conditioned excess (lc-excess) balance method. Focused recharge occurred in low depressions, where surface runoff carrying sediments with high solutes converged in large rainfall events during wet season. Subsequently, focused mode rapidly recharges groundwater with NO3− and Cl- elevated, deteriorating water quality of phreatic aquifer. Finally, we concluded focused recharge does not dominate aquifer recharge, but significantly affects groundwater quality. These findings underscore the implications for the sustainability of agricultural water and soil resources management, emphasizing the potential impacts of soil conservation on groundwater quality in low-hilly regions.

Water Quality of Unconfined Aquifer in Universitas Negeri Malang Following the Drinking Water Quality Standard of Indonesian Ministry of Health

The quality of groundwater is naturally determined by water-bearing rock characteristics. However, the progression of civilian activities also negatively affects the groundwater quality. Therefore, this study aims to assess the physical, chemical, and biological characteristics of groundwater in the Universitas Negeri Malang (UM) campus area in Indonesia and evaluate its compliance with drinking water quality standards, particularly the Class A standard. A comparative descriptive strategy was utilized in the study by involving groundwater in the campus area of UM. The focus of the research is water quality in unconfined aquifer. Through purposive sampling, 12 wells were selected to ensure appropriate spatial dispersion. Water samples were collected in sample bottles and tested for physical, biological, and chemical properties. These water quality tests were carried out in the Perum Jasa Tirta I Malang. Water quality data were analyzed qualitatively, descriptively, and comparatively. This study concludes that (1) the groundwater on the UM campus generally meets the physical criteria for drinking water quality standards; (2) the chemical quality of the groundwater on the UM campus still satisfies the drinking water quality standards; and (3) biologically, the free groundwater on the UM campus fails to meet drinking water quality standards. The novelty of this research is that the biggest threat to the quality of free groundwater in the campus area is bacterial contamination from sanitation activities. Accordingly, it is recommended that groundwater is boiled before being utilized for drinking water purposes to neutralize the E. coli bacteria present in all well water samples.Keywords: Water Quality; Unconfined Aquifer; The Drinking Water; Quality Standard

Geospatial insights into groundwater contamination from urban and industrial effluents in Faisalabad

Groundwater remains the most dependable resource for various essential uses such as drinking, cleansing, agricultural irrigation, and industrial applications. In urban areas, the dependency on groundwater to meet water demands is significant. However, this resource faces threats from overuse and poor management, leading to a degradation in quality primarily due to the unchecked release of industrial and household wastes. The escalation of industrial activities and rapid urban growth have amplified the volume of wastewater, adversely affecting the purity of freshwater sources within aquifers. This investigation focuses on evaluating the impact of industrial and urban effluents on groundwater quality in the city of Faisalabad. The main contributors to groundwater pollution include the indiscriminate disposal of industrial and urban effluents through unlined drains and the extensive application of chemical agents in agriculture, such as fertilizers, and pesticides. To understand the physiochemical properties of both, drain and groundwater, samples were collected at various distances 50 m, 100 m, and 150 m from drain outlets. This study utilized Geographic Information Systems (GIS) to accurately map and analyze the distribution and impact of contaminants. Parameters such as pH, electrical conductivity (EC), total dissolved solids (TDS), total hardness, bicarbonates, calcium and magnesium hardness, and chloride levels were examined. The findings indicated that contaminant levels were highest in drain water and increased in concentration the closer they were to the drainage sources, with the exception of pH levels. All samples exceeded the World Health Organization's (WHO) safe limits, deeming them unfit for use. This finding indicates widespread contamination, posing significant public health risks and highlighting the urgent need for improved waste management and water treatment practices in Faisalabad. It underscores the critical importance of implementing effective pollution control measures to safeguard public health and ensure water security in the region. However, a notable correlation was observed between the concentration of pollutants in drain water and key indicators such as EC, TDS, total hardness, and magnesium hardness, highlighting their role in deteriorating aquifer water quality. Moreover, groundwater samples collected 50 m from drains exhibited the highest pollutant concentrations compared to those taken further away, at 100 m and 150 m distances.

The Hydraulic Evolution of Groundwater-Fed Pit Lakes After Mine Closure.

Open pit mining frequently requires regional water tables to be lowered to access ore deposits. When mines close, dewatering ceases allowing the water table to recover. In arid and semi-arid mining regions, the developing pit lakes are predominantly fed by groundwater during this recovery phase and pit lakes develop first into "terminal sinks" for the surrounding groundwater system. With time, the re-establishment of regional hydraulic gradients can cause pit lakes to develop into throughflow systems, in which pit lake water outflows into adjacent aquifers. In this study, we use numerical groundwater modeling to aid process understanding of how regional hydraulic gradients, aquifer properties, net evaporation rates, and pit geometry determine the hydraulic evolution of groundwater-fed pit lakes. We find that before the recovery of the regional water table to its new equilibrium, pit lakes frequently transition to throughflow systems. Throughflow from pit lakes to downstream aquifers can develop within two decades following cessation of dewatering even under low hydraulic gradients (e.g., 5 × 10-4) or high net evaporation rates (e.g., 2.5 m/year). Pit lakes remain terminal sinks only under suitable combinations of high evaporation rates, low hydraulic gradients, and low hydraulic conductivities. In addition, we develop an approximate analytical solution for a rapid assessment of the hydraulic status of pit lakes under steady-state conditions. Understanding whether pit lakes remain terminal sinks or transition into throughflow systems largely determines the long-term water quality of pit lakes and downstream aquifers. This knowledge is fundamental for mine closure and planning post-mining land use.

An advanced hybrid deep learning model for predicting total dissolved solids and electrical conductivity (EC) in coastal aquifers

For more than one billion people living in coastal regions, coastal aquifers provide a water resource. In coastal regions, monitoring water quality is an important issue for policymakers. Many studies mentioned that most of the conventional models were not accurate for predicting total dissolved solids (TDS) and electrical conductivity (EC) in coastal aquifers. Therefore, it is crucial to develop an accurate model for forecasting TDS and EC as two main parameters for water quality. Hence, in this study, a new hybrid deep learning model is presented based on Convolutional Neural Networks (CNNE), Long Short-Term Memory Neural Networks (LOST), and Gaussian Process Regression (GPRE) models. The objective of this study will contribute to the sustainable development goal (SDG) 6 of the united nation program which aims to guarantee universal access to clean water and proper sanitation. The new model can obtain point and interval predictions simultaneously. Additionally, features of data points can be extracted automatically. In the first step, the CNNE model automatically extracted features. Afterward, the outputs of CNNE were flattened. The LOST used flattened arrays for the point prediction. Finally, the outputs of the GPRE model receives the outputs of the LOST model to obtain the interval prediction. The model parameters were adjusted using the rat swarm optimization algorithm (ROSA). This study used PH, Ca + + , Mg2 + , Na + , K + , HCO3, SO4, and Cl− to predict EC and TDS in a coastal aquifer. For predicting EC, the CNNE-LOST-GPRE, LOST-GPRE, CNNE-GPRE, CNNE-LOST, LOST, and CNNE models achieved NSE values of 0.96, 0.95, 0.92, 0.91, 0.90, and 0.87, respectively. Sodium adsorption ratio, EC, magnesium hazard ratio, sodium percentage, and total hardness indices were used to evaluate the quality of GWL. These indices indicated poor groundwater quality in the aquifer. This study shows that the CNNE-LOST-GPRE is a reliable model for predicting complex phenomena. Therefore, the current developed hybrid model could be used by private and public water sectors for predicting TDS and EC for enhancing water quality in coastal aquifers.

Groundwater Quality Monitoring in Response to Marine Intrusion: A Case Study in Northern Morocco

Water stress, resulting from a demand for water exceeding the available quantity, is a major global challenge. Groundwater usage is a commonly adopted strategy to address this situation, but it often leads to marine intrusion, threatening the quality of water in coastal aquifers. This phenomenon typically stems from overexploitation of aquifers, declining water table levels, and rising sea levels due to climate change. Our study aims to monitor the quality of groundwater intended for human consumption and provide a detailed assessment of its current state. We identified several physicochemical parameters, such as temperature, pH, and bicarbonates, with maximum electrical conductivity values reaching 2810 µs/cm, a total hardness of 21 meq/L, sulfate levels of 689 mg/L, and chloride levels of 628 mg/L, from six boreholes and one well located along the coastal area of the Al Hoceima region. These samples were also subjected to Principal component analysis (PCA) of the chemical parameters, revealing two factors that represent approximately 62.15% of the total variance in the groundwater quality dataset. Simulation results indicate signs of seawater intrusion in several areas, particularly near the coast, emphasizing the urgency of protecting groundwater resources and developing sustainable management strategies to ensure a safe and reliable supply of drinking water in the region.

Hydrogeological characterization of Settat Ben Ahmed plateau aquifer (Central Morocco)

This study aims to determine groundwater dynamic and hydrochemistry for a better understanding of a hydrogeological unity of sedimentary rock to learn about chemical processes and water quality of Settat Ben Ahmed plateau aquifer. The findings reveal the chemical facies change according to the depth and geological nature of the aquifer captured. Samples of deeper point captured upstream and from Cenomano-Turonien limestones are HCO3-Ca-Mg type and account for lowest electric conductivity (EC) values. However, samples of shallow points and downstream are Cl-SO4-Ca with important EC values.

Evaluating groundwater quality using health risk assessment and irrigation indexes: Saveh Aquifer, Iran

Abstract The aim of the study was to assess water quality in the Saveh aquifer for drinking, public health, and agricultural uses. The heavy metal pollution index (HPI), hazard index (HI) using non-carcinogenic health risk assessment, sodium percentage, sodium adsorption ratio (SAR), irrigation water quality index (IWQI), and a Piper diagram were used. The HPI exceeded 3,300, much higher than the WHO critical value, which is 100. The aquifer is severely contaminated with heavy metals and unsuitable for drinking. The heavy metal concentrations also caused the water to have cumulative HI &amp;gt; 1 in 54 and 77% of sampling wells, respectively, for adults and children. For agriculture, both %NA and IWQI were stricter than SAR. Most of the aquifer was deemed suitable for irrigation using SAR, while %Na showed most parts unreliable, and IWQI represented almost all areas unsuitable for irrigation. The Piper diagram showed that the dominant water type was N–Cl, followed by Na–HCO3 and Ca–HCO3, indicating high aquifer salinity. Generally, the Saveh aquifer is saline and heavily polluted with heavy metals, so its use for drinking and/or irrigation carries many risks.

Coastal aquifer water quality for domestic supply of small communities in the semiarid Potiguar - Brazilian Northeast

This study analyzed groundwater quality used to supply small communities in the coastal zone of the Brazilian Northeast, identifying the risks from domestic use of water, and potential contaminants from domestic effluents. We realized analyses of 24 chemical and physical parameters in 15 samples of water from shallow wells. The data was processed through quality modeling, descriptive statistics, principal component analysis, and geoespacialization through kriging. The groundwater used by communities showed some limitations to domestic use. Parameters of Br, hardness, Na+, NO3−, Cl−, SO4−, and turbidity exceed the allowed for Brazilian Health Minister (Ministerial Order n. 888/2021). Furthermore, TDS values present low water quality, predominantly brackish and saltwater, most salinity waters are related to depth and sea proximity. Depth of saturated zone probably is a determinant in nitrate concentrations, comparing the study areas. Water self-supply is considered a risk by health because inferior natural quality of water used and contaminations from domestic sewage determine concentrations of some parameters above of legislation.

Urban green spaces and their relationship with groundwater quality: the case of a shallow aquifer in the south of Mexico City

Water supply security is a top priority for decision-makers in cities. Urban population growth increases water demand from aquifers, while urban expansion reduces water infiltration and boosts water pollution sources. Urban green spaces are a few of the remaining infiltration areas. Therefore, they are essential for water supply and urban hydric resilience. The urban dynamic directly influences shallow aquifers, but they usually are unappreciated. This work illustrates the relationship between urban green spaces and city water quality by evaluating the influence of urban green space, Reserva Ecológica del Pedregal de San Angel (REPSA), on a shallow aquifer in Mexico City. Five springs were sampled: two upstream of REPSA, a spring within REPSA, and two downstream. Because the study area is mainly residential but with an industrial history, water quality was tested based on microbiological pathogens, nutrients, pharmaceutical drugs, and heavy metals. Results showed an enhancement of water quality of the shallow aquifer in the sampling points downstream of REPSA for some of the pollutants. These results illustrate how urban green spaces can help to dilute pollutants present in the water of shallow aquifers, increasing water quality in cities.

Effect of seawater intrusion on water quality of coastal aquifer of Bagerhat district, Bangladesh

Effect of seawater intrusion on water quality of coastal aquifer of Bagerhat district, Bangladesh

The Characterization of Groundwater Quality for Safe Drinking Water Wells via Disinfection and Sterilization in Jordan: A Case Study

This work aims to evaluate the quality of drinking water in the Disi aquifer in Jordan. Several water quality parameters are included in the mathematical equation to evaluate the average water quality and establish the suitability of water for drinking purposes. Water sampling zones from three wells were used to calculate the water quality indices (WQI). The water samples were analyzed for several physicochemical parameters, including pH, turbidity, total dissolved solids, Na+, Ca2+, Mg2+, Na+, K+, HCO3−, SO42−, Cl−, NO3−, total hardness, electrical conductivity (EC) and other elements (Fe2+, Zn2+, Mn2+, Cd2+, As2−, Pb4+ and Cu2+), in the groundwater wells. Biological parameters, such as faecal coliform, were also tested. The Weighted Arithmetic WQI indicated that most of the wells were of good to excellent quality. These determined indices support decision making and are beneficial to monitoring the groundwater quality in the Disi aquifer. The relative weight is specific to each parameter and ranges from 1 to 5; it establishes the importance of the water quality parameters for domestic purposes. The WQI analysis rates the water quality between 75 to 65 from good to medium. The water quality of the Disi aquifer for potable drinking water was compared with the guidelines of the World Health Organization (2011) and the Jordan Drinking Standard (JS286); the results indicated that water in the Disi aquifer was of high quality and was fit for drinking.

Fluoride and nitrate enrichment in coastal aquifers of the Eastern Province, Saudi Arabia: The influencing factors, toxicity, and human health risks

Fluoride and nitrate contamination of groundwater is a major environmental issue in the world's arid and semiarid regions. This issue is severe in both developed and developing countries. This study aimed at assessing the concentration levels, contamination mechanisms, toxicity, and human health risks of NO3− and F− in the groundwater within the coastal aquifers of the eastern part of Saudi Arabia using a standard integrated approach. Most of the tested physicochemical properties of the groundwater exceeded their standard limits. The water quality index and synthetic pollution index evaluated the suitability of the groundwater and showed that all the samples have poor and unsuitable quality for drinking. The toxicity of F− was estimated to be higher than NO3−. Also, the health risk assessment revealed higher risks due to F− than NO3−. Younger populations had higher risks than elderly populations. For both F− and NO3−, the order of health risk was Infants > Children > Adults. Most of the samples posed medium to high chronic risks due to F− and NO3− ingestion. However, negligible health risks were obtained for potential dermal absorption of NO3−. Na–Cl and Ca–Mg–Cl water types predominate in the area. Pearson's correlation analysis, principal component analysis, regression models, and graphical plots were used to determine the possible sources of the water contaminants and their enrichment mechanisms. Geogenic and geochemical processes had greater impact he groundwater chemistry than anthropogenic activities. For the first time, these findings provide public knowledge on the overall water quality of the coastal aquifers and could help the inhabitants, water management authorities, and researchers to identify the groundwater sources that are most desirable for consumption and the human populations that are vulnerable to non-carcinogenic health risks.

Simulation of water drainage and nitrate leaching at an irrigated maize (Zea mays L.) oasis cropland with a shallow groundwater table

Nitrogen pollution is a serious threat to water resources worldwide, and it poses a particular threat to groundwater in desert oases where the water table is shallow. Leaching loss of nitrogen fertilizer means economic loss and threatens the water quality of phreatic aquifer with a thinner vadose zone thickness, especially in the Hailiutu River catchment, China, where phreatic aquifer is a unique source of local domestic water. The objective of this study was to quantify N leaching for irrigated maize with different fertilizer and irrigation management practices, as well as fluctuating groundwater tables, and to recommend the best management practices for maize. A field experiment was conducted in such a locale for two consecutive years. Maize was grown where nitrogen was introduced at increasing rates (from 38 to 438 kg N ha−1, at intervals of 100 kg N ha−1). The 338 kg N ha−1 represented the conventional fertilization practice (N338), and served as a reference. Unlike the conventional 70 mm irrigation depth applied at each water application, water conserving irrigation was performed by applying only 20 mm at each irrigation — six times in 2017 and four in 2018. The HYDRUS-1D model was first calibrated against measured soil moisture and nitrate in soil water across all soil layers, then independently validated and finally repeatedly run to simulate NO3N leaching under the following simulation conditions: a) increasing N fertilization rate, but fixed 20 mm individual irrigation depth; b) increasing individual irrigation depth (from 10 to 70 mm), but only considering the reference N fertilization rate (N338). In both cases, five different shifts in water table depth were assumed, + 0.10, 0, − 0.10, − 0.20, or − 0.30 m of groundwater table change, respectively. The simulation results suggest that conventional fertilization practices result in nitrogen losses of over 100 kg ha−1, and 238 kg N ha−1 N fertilization, accompanying by a depth of 20 mm for each irrigation is the best combination of management practices. The NO3−N leaching loss was more influenced by the depth of irrigation than the fertilizer application rate. A shallower water table resulted in the greater loss of NO3N by leaching. Such results can help develop improved irrigation and nitrogen fertilization management for desert oasis cropping systems.

Impact of Gravel Pits on Water Quality in Alluvial Aquifers

Gravel pits are considered potentially hazardous in terms of groundwater quality protection as they represent an open part of the aquifer system, increasing the aquifer’s vulnerability to contamination from the surface. The aim of this research was to determine the biogeochemical processes in gravel pits that have a positive effect on the groundwater quality in the alluvial aquifer in NW Croatia. The aquifer is situated below developed agricultural land, with high groundwater nitrate concentrations having been recorded over the last decades. The differences between two gravel pits and the surrounding groundwater were studied using in situ, hydrochemical, and isotopic parameters (δ15N-NO3 and δ18O-NO3), together with existing microbial data. The analyses of nitrogen species indicated that nitrate attenuation processes take place in gravel pits. Bacterial denitrification and nitrate uptake by algae were responsible for significant decreases in nitrate concentration. These processes were more effective in the inactive gravel pit, which has a longer water residence time and during warm periods, when microbial biomass, abundance, and activity were high. The seasonally variable microbial activity also affected trace metals, removing them from groundwater, possibly through the biosorption of metal ions. The presented research shows that the observed biogeochemical processes are associated with seasonal changes that affect the types and number of microbial communities and the chemical composition of water, resulting in gravel pits being groundwater remediation points.