Groundwater Nitrate Research Articles

Sources and transformation of nitrate in an agricultural riverine reservoir watershed of the Sichuan Basin

Elucidating the origins and transformations of nitrate in groundwater and surface water within agricultural regions is imperative for effectively managing watershed contamination and environmental improvement. This study conducted a comprehensive geochemical investigation using multiple stable isotopes (δD-H2O and δ18O–H2O, δ15N–NO3- and δ18O–NO3-, and δ15N–NH4+) and hydrogeochemical characteristics to explore the potential sources and transformation of nitrate in groundwater and reservoir water within an agricultural riverine reservoir watershed. The results indicated that nitrate pollution in groundwater exhibited a higher severity compared to the reservoir water within this watershed, thereby posing potential risks to the quality of the reservoir water through hydraulic connection. The integration of δ15N–NH4+ and dual-isotopes of nitrate, combined with hydrogeochemical analyses, revealed that the presence of NO3− in groundwater and reservoir water primarily originated from manure/sewage sources. Moreover, intricate biogeochemical processes containing denitrification, nitrification, and DNRA were identified within this watershed. The findings of the Bayesian stable isotope mixing model (SIAR) further corroborated the conclusion that manure/sewage was the primary source of nitrate. It revealed that manure/sewage accounted for an average of 46 % of groundwater NO3− concentration, followed by atmospheric precipitation (25 %), soil nitrogen (18 %), and chemical fertilizer (11 %). There were no distinct differences in nitrate source contributions between groundwater and reservoir water. For reservoir water, manure or sewage (45 % on average) > atmospheric precipitation (28 %) > soil nitrogen (16 %) > chemical fertilizer (11 %). This study demonstrates the effectiveness of incorporating δ15N–NH4+ with dual isotopes of nitrate and hydrogeochemical analyses, serving as a reliable methodology that yields valuable insights into the origins and transformations of NO3− in an agricultural reservoir watershed, with potential applicability to other regions.

Mapping specific groundwater nitrate concentrations from spatial data using machine learning: A case study of chongqing, China

Groundwater resources is not only important essential water resources but also imperative connectors within the intricate framework of the ecological environment. High nitrate concentrations in groundwater can exerting adverse impacts on human health. It is imperative to accurately delineate the distribution characteristics of groundwater nitrate concentrations. Four different machine learning models (Gradient Boosting Regression (GB), Random Forest Regression (RF), Extreme Gradient Boosting Regression (XG) and Adaptive Boosting Regression (AD)) which combine spatial environmental data and different radius contributing area was developed to predict the distribution of nitrate concentration in groundwater. The models use 595 groundwater samples and included topography, remote sensing, hydrogeological and hydrological, climate, nitrate input, and socio-economic predictor. Gradient Boosting Regression model outperforms the other models (R2 = 0.627, MAE = 0.529, RMSE = 0.705, PICP = 0.924 for test dataset) under 500 m radius contributing area. A high-resolution (1 km) groundwater nitrate concentration distribution map reveal in the majority of the study area, groundwater nitrate concentrations are below 1 mg/L and high nitrate concentration (>10 mg/L) proportion in southeast, northeast and central main urban area karst valley regions is 1.89%, 0.91%, and 0.38% respectively. In study area, hydrogeological conditions, soil parameters, nitrogen input factors, and percentage of arable land are among the most influential explanatory factors. This work, serving as the inaugural application of utilizing effective spatial methods for predicting groundwater nitrate concentrations in Chongqing city, furnish decision-making support for the prevention and control of groundwater pollution, particularly in areas primarily dependent on groundwater for water supply and holds profound significance as a milestone achievement.

Groundwater Contamination with Nitrate and Human Health Risk Assessment of North East Alluvial Plains of Bihar, India

Groundwater is natural resources which supplies almost half of all drinking water in the world and plays a key role in food production. Consuming water containing high nitrate concentration have immediate effect on infant and could cause the risk of diseases Methemoglobinemia in which blood lacks the ability to carry sufficient oxygen to the individual body cells. As difference in nitrate concentration in water, made it important to study the undesirable effect of it. In rural areas, groundwater contamination is a problem related to the excessive use of chemical fertilizers by local farmers. Shallow groundwater plays a vital role in water use and the yield of Maize. Nitrogen application significantly affects crop uptake and utilization of water from irrigation, but little is known about groundwater use. Farmers are applying nitrogen on an average 278 kg/ha in Kharif maize, which is about 131.72% more than the RDN of Kharif maize i.e. 120 KgN/ha. The mean value of N application by farmers ranges from 251-323 kg/ha. The Maximum rate of N application was observed in Khagaria (323 kg N/ha) followed by Madhepura (275.08 kg N/ha) and minimum in case of Saharsa district (251.16 kg N/ha). The application rate of nitrogenous fertilizer, varying from 109.25% to 169.16% over the RDN, resulting in NO3- leaching. The groundwater and surfacewater from 12 villages was collected and various quality parameters were analysed. The nitrate in ground water varied (1.87- 6.19 mg/L) and surface water (1.87 – 3.84 mg/L) being maximum concentration of nitrate in Madhepura district. The present study on nitrate leaching in soil, its level of contamination in ground water and human health risk assessment by chronic daily intake of nitrate and Hazard Quotient (H.Q) values in the study area of Khagaria, Saharsa, Madhepura and Supaul has been carried out in the eastern alluvial region of Bihar.

Identification of groundwater nitrate sources in an urban aquifer (Alborz Province, Iran) using a multi-parameter approach.

High concentrations of NO3̄ in water resources are detrimental to both human health and aquatic ecosystems. Identification of NO3̄ sources and biogeochemical processes is a crucial step in managing and controlling NO3̄ pollution. In this study, land use, hydrochemical data, dual stable isotopic ratios and Bayesian Stable Isotope Mixing Models (BSIMM) were integrated to identify NO3̄ sources and estimate their proportional contributions to the contamination of the Karaj Urban Aquifer (Iran). Elevated NO3̄ concentrations indicated a severe NO3̄ pollution, with 39 and 52% of groundwater (GW) samples displaying the concentrations of NO3̄ in exceedance of the World Health Organization (WHO) standard of 50 mg NO3̄ L-1 in the rainy and dry seasons, respectively. Dual stable isotopes inferred that urban sewage is the main NO3̄ source in the Karaj Plain. The diagram of NO3̄/Cl‾ versus Cl‾ confirmed that municipal sewage is the major source of NO3̄. Results also showed that biogeochemical nitrogen dynamics are mainly influenced by nitrification, while denitrification is minimal. The BSIMM model suggested that NO3̄ originated predominantly from urban sewage (78.2%), followed by soil organic nitrogen (12.2%), and chemical fertilizer (9.5%) in the dry season. In the wet season, the relative contributions of urban sewage, soil nitrogen and chemical fertilizer were 87.5, 6.7, and 5.5%, respectively. The sensitivity analysis for the BSIMM modeling indicates that the isotopic signatures of sewage had the major impact on the overall GW NO3̄ source apportionment. The findings provide important insights for local authorities to support effective and sustainable GW resources management in the Karaj Urban Aquifer. It also demonstrates that employing Bayesian models combined with multi-parameters can improve the accuracy of NO3̄ source identification.

Modeling canopy water content in the assessment for rainfall induced surface and groundwater nitrate contamination: The Bilate cropland sub watershed

Nitrate contamination in surface and groundwater remains a widespread problem in agricultural watersheds is primarily associated to high levels of percolation or leakage from fertilized soil, which allows easy infiltration from soil into groundwater. This study was aimed to predict canopy water content to determine the nitrate contamination index resulting from nitrogen fertilizer loss in surface and groundwater. The study used Geographically Weighted Regression (GWR) model using MODIS 006 MOD13Q1-EVI Earth observation data, crop information and rainfall data. Satellite data collection was synchronized with regional crop calendars and calibrated to plant biomass. The average plant biomass during observed plant growth stages was between 0.19 kg/m2 at the minimum and 0.57 kg/m2 at the maximum. These values are based on the growth stages of crops and provide a solid basis for monitoring and validating crop water productivity data. The simulation results were validated with a high correlation coefficient (R2 = 0.996, P < 0.0005) for the observed rainfall in the growing zone compared to the predicted canopy water content. The nitrate contamination index assessment was conducted in 2004, 2008, 2009, 2010, 2011, 2013, 2014, 2015, 2018 and 2020. Canopy water content and root zone seasonal water content were measured in (%) per portion as indicators of the NO−3-N-nitrate contamination index in these years (0.391, 0.316, 0.298, 0.389, 0.380, 0.339, 0.242, 0.342 and 0.356).

Source identification and potential health risks from elevated groundwater nitrate contamination in Sundarbans coastal aquifers, India

In recent years groundwater contamination through nitrate contamination has increased rapidly in the managementof water research. In our study, fourteen nitrate conditioning factors were used, and multi-collinearity analysis is done. Among all variables, pH is crucial and ranked one, with a value of 0.77, which controls the nitrate concentration in the coastal aquifer in South 24 Parganas. The second important factor is Cl−, the value of which is 0.71. Other factors like—As, F−, EC and Mg2+ ranked third, fourth and fifth position, and their value are 0.69, 0.69, 0.67 and 0.55, respectively. Due to contaminated water, people of this district are suffering from several diseases like kidney damage (around 60%), liver (about 40%), low pressure due to salinity, fever, and headache. The applied method is for other regions to determine the nitrate concentration predictions and for the justifiable alterationof some management strategies.

Coping with groundwater pollution in high-nitrate leaching areas: The efficacy of denitrification

The Ningxia Yellow River irrigation area, characterized by an arid climate and high leaching of NO3--N, exhibits complex and unique groundwater nitrate (NO3--N) pollution, with denitrification serving as the principal mechanism for NO3--N removal. The characteristics of N leaching from paddy fields and NO3--N removal by groundwater denitrification were investigated through a two-year field observation. The leaching losses of total nitrogen (TN) and NO3--N accounted for 10.81–27.34% and 7.59–12.74%, respectively, of the N input. The linear relationship between NO3--N leaching and N input indicated that the fertilizer-induced emission factor (EF) of NO3--N leaching in direct dry seeding and seedling-raising and transplanting paddy fields was 8.2% (2021, R2 = 0.992) and 6.7% (2022, R2 = 0.994), respectively. The study highlighted that the quadratic relationship between the NO3--N leaching loss and N input (R2 = 0.999) significantly outperformed the linear relationship. Groundwater denitrification capacity was characterized by monitoring the concentrations of dinitrogen (N2) and nitrous oxide (N2O). The results revealed substantial seasonal fluctuations in excess N2 and N2O concentrations in groundwater, particularly following fertilization and irrigation events. The removal efficiency of NO3--N via groundwater denitrification ranged from 42.70% to 74.38%, varying with depth. Groundwater denitrification capacity appeared to be linked to dissolved organic carbon (DOC) concentration, redox conditions, fertilization, irrigation, and soil texture. The anthropogenic-alluvial soil with limited water retention accelerated the leaching of NO3--N into groundwater during irrigation. This process enhances the groundwater recharge capacity and alters the redox conditions of groundwater, consequently impacting groundwater denitrification activity. The DOC concentration emerged as the primary constraint on the groundwater denitrification capacity in this region. Hence, increasing carbon source concentration and enhancing soil water retention capacity are vital for improving the groundwater denitrification capacity and NO3--N removal efficiency. This study provides practical insights for managing groundwater NO3--N pollution in agricultural areas, optimizing fertilization strategies and improving groundwater quality.

Spatial distribution pattern and health risk of groundwater contamination by cadmium, manganese, lead and nitrate in groundwater of an arid area.

Combining the results of base models to create a meta-model is one of the ensemble approaches known as stacking. In this study, stacking of five base learners, including eXtreme gradient boosting, random forest, feed-forward neural networks, generalized linear models with Lasso or Elastic Net regularization, and support vector machines, was used to study the spatial variation of Mn, Cd, Pb, and nitrate in Qom-Kahak Aquifers, Iran. The stacking strategy proved to be an effective substitute predictor for existing machine learning approaches due to its high accuracy and stability when compared to individual learners. Contrarily, there was not any best-performing base model for all of the involved parameters. For instance, in the case of cadmium, random forest produced the best results, with adjusted R2 and RMSE of 0.108 and 0.014, as opposed to 0.337 and 0.013 obtained by the stacking method. The Mn and Cd showed a tight link with phosphate by the redundancy analysis (RDA). This demonstrates the effect of phosphate fertilizers on agricultural operations. In order to analyze the causes of groundwater pollution, spatial methodologies can be used with multivariate analytic techniques, such as RDA, to help uncover hidden sources of contamination that would otherwise go undetected. Lead has a larger health risk than nitrate, according to the probabilistic health risk assessment, which found that 34.4% and 6.3% of the simulated values for children and adults, respectively, were higher than HQ = 1. Furthermore, cadmium exposure risk affected 84% of children and 47% of adults in the research area.

Distribusi spasial nitrat air tanah di Kecamatan Nanggulan, Kulon Progo, Yogyakarta

Residential areas in Nanggulan sub-district are mainly adjacent to irrigated rice fields. Groundwater in settlements close to irrigated rice fields has the potential to be contaminated with nitrates. Studies on the spatial distribution of groundwater nitrate around irrigated rice fields have never been conducted in Nanggulan District, Kulon Progo Regency. The study was conducted to determine the spatial distribution of nitrates in groundwater in Nanggulan District, Kulon Progo Regency. Nitrate data were collected through groundwater sample testing. The location of groundwater samples is determined using a systematic random sampling. The data was analyzed by spatial interpolation method through Arc GIS 10.6 software. The results showed variations in the spatial distribution of nitrates in the study area. Most of the study area had nitrate levels of 5-10 mg / L distributed in the south. Nitrates exceeding ten mg/L were distributed in the northern part of the study area. Based on research that has been conducted, it is known that 41% of groundwater in the study area is contaminated with nitrates, while 59% of groundwater is not contaminated with nitrates. Spatially, nitrate-contaminated groundwater is found in parts of Tanjungharo Village, some Wijimulyo Village, some Donomulyo Village, some Jatisarono Village, and some Kembang Villages. Groundwater not contaminated with nitrates is found in Banyuroto Village and most areas of Donomulyo Village. Factors that cause nitrate-contaminated groundwater are the location of excavated wells close to intensively fertilized irrigated rice fields, groundwater contained in geological formations of young Merapi volcano deposits, and groundwater depth of less than 5 meters.

Nitrate dynamics in the streamwater-groundwater interaction system: Sources, fate, and controls

Nitrate (NO3−) pollution has attracted widespread attention as a threat to human health and aquatic ecosystems; however, elucidating the controlling factors behind nitrate dynamics under the context of changeable hydrological processes, particularly the interactions between streamwater and groundwater (SW-GW), presents significant challenges. A multi-tracer approach, integrating physicochemical and isotopic tracers (Cl−, δ2H-H2O, δ18O-H2O, δ15N-NO3− and δ18O-NO3−), was employed to identify the response of nitrate dynamics to SW-GW interaction in the Fen River Basin. The streamwater and groundwater NO3− concentrations varied greatly with space and time. Sewage and manure (28 %–73 %), fertilizer (14 %–36 %) and soil organic nitrogen (12 %–28 %) were the main NO3− sources in water bodies. Despite the control of land use type on streamwater nitrate dynamics in losing sections, SW-GW interactions drove NO3− dynamics in both streamwater and groundwater under most circumstances. In gaining streams, streamwater nitrate dynamics were influenced either by groundwater dilution or microbial nitrification, depending on whether groundwater discharge ratios exceeded or fell below 25 %, respectively. In losing streams, groundwater nitrate content increased with streamwater infiltration time, but the influence was mainly limited within 3 km from the river channel. This study provides a scientific basis for the effective management of water nitrate pollution at the watershed scale.

Linking Transpiration to Reef Nitrogen Supply on a Tropical Coral Island

AbstractCoral reef islands are biodiversity hotspots with high conservation value, but we have a poor understanding of how island vegetation, through transpiration, influences groundwater nutrient supply to adjacent reef systems. Here we combine stable isotope tracing, geophysical surveys, and satellite analysis to unravel the links between transpiration and the discharge of groundwater nitrate to the waters surrounding a coral reef island (Lady Elliot Island in the Great Barrier Reef). Over a 2‐year study period (2020–2021) there was a net loss of freshwater from the island, that is, evapotranspiration (ET) exceeded rainfall, largely caused by high rates of transpiration (73% of ET). Transpiration was higher in forested areas, and groundwater salinity appeared to be higher there. By tracing the nitrogen stable isotope signature of groundwater nitrate into reef organism tissue we were able to map groundwater nitrogen discharge spatially and temporally. Groundwater nitrogen discharge was focussed on one side of the island and did not vary seasonally as expected, despite reduced rainfall and seabird guano inputs over the austral winter/spring. Based on our results, we propose that transpiration by island vegetation slows groundwater flow and concentrates nitrate in the groundwater being released to the surrounding reef system. High concentrations of nitrate in groundwater (up to 27 mmol L−) were observed on Lady Elliot Island and these seem to have increased since 2014, but further work is required to understand if this is a normal scenario for tropical coral islands or the result of the islands' revegetation program.

Climate Change Impacts on Nitrate Leaching and Groundwater Nitrate Dynamics Using a Holistic Approach and Med-CORDEX Climatic Models

This study presents the projected future evolution of water resource balance and nitrate pollution under various climate change scenarios and climatic models using a holistic approach. The study area is Almyros Basin and its aquifer system, located in Central Greece, Thessaly, Greece. Almyros Basin is a coastal agricultural basin and faces the exacerbation of water deficit and groundwater nitrate pollution. Using an Integrated Modeling System (IMS), which consists of the surface hydrology model (UTHBAL), the nitrate leachate model (REPIC, an R-ArcGIS-based EPIC model), the groundwater hydrology model (MODFLOW), and the nitrates’ advection, dispersion, and transport model (MT3MDS), the projected values of the variables of water quantity and quality are simulated. Nineteen climatic models from the Med-CORDEX database were bias-corrected with the Quantile Empirical Mapping method and employed to capture the variability in the simulated surface and groundwater water balance and nitrate dynamics. The findings indicate that future precipitation, runoff, and groundwater recharge will decrease while temperature and potential evapotranspiration will increase. Climate change will lead to reduced nitrogen leaching, lower groundwater levels, and persistent nitrate pollution; however, it will be accompanied by high variability and uncertainty, as simulations of IMS under multiple climatic models indicate.

Sources and seasonal variations of nitrate in the coastal multiple-aquifer groundwater of Beihai, southern China

Elevated nitrate (NO3−) loadings in groundwater may cause health effects in drinking water and nutrient enrichment of aquatic ecosystems. To reveal the sources and seasonal variations of NO3− in the coastal groundwater of Beihai, southern China, we carried out hydrochemical and isotopic (δ15N-δ18O in NO3−) investigations in the summer and winter, respectively, concerning multiple-aquifer groundwater, rainwater, seawater, and surface water. The sources of the main elements present in the waters were interpreted by ionic ratios. NO3− sources were identified by combined use of the δ15N values and δ18O values or NO3−/Na+ molar ratios, with estimations of the proportional contribution by the Bayesian stable isotope mixing model. Denitrification was interpreted along the flow paths. The results show groundwater main elements are originated primarily from silicate weathering, and secondarily from anthropogenic inputs and carbonate dissolution. Its qualities are largely affected by seawater intrusion along the coastline. Because of difference in the predominant minerals within the aquifers and in scale and extent of seawater intrusion, the groundwater displays distinct ionic ratio characters. NO3− concentrations are up to 33.9 mg/L, with higher loadings in the plains relative to along the coastline. Soil N, domestic sewage, rainwater, chemical fertilizers, and algae are NO3− sources, with average proportional contributions of 0.255, 0.221, 0.207, 0.202, and 0.116, respectively. In relation to the winter, higher production of NO3− from nitrification of soil N- and algae-derived ammonium induced by higher temperatures in the summer accounts for increases in groundwater NO3− loadings. In the rural areas, elevated loadings of NO3− in the winter may be due to larger infiltration fractions of sewage. Seasonal variations of atmospheric NO3− deposition and farming may also cause the dynamics. Our results improve the understanding of sources and seasonal dynamics of NO3− in coastal groundwater.

Appropriate stoichiometric ratios of dissolved organic carbon and nitrate can trigger a transition in nitrate removal in groundwater around plateau lakes, Southwest China

Increasing dissolved organic carbon (DOC) in groundwater as a carbon source for microorganisms that stimulate nitrate attenuation is considered a sustainable strategy to mitigate nitrate pollution in groundwater. However, little is known on the stoichiometric ratio of DOC and nitrate required in groundwater nitrate reduction processes, which has become an obstacle for evaluating the current status of DOC limitations on nitrate reduction. Here, the NO3—-N and DOC concentrations in groundwater around 8 plateau lakes were investigated, and a microcosm experiment was performed to elucidate the effects of different DOC:NO3—-N levels in groundwater on NO3—-N reduction, and the current status of DOC limitations on groundwater NO3—-N reduction around 8 lakes was further evaluated. The results indicated that nearly 41 % of the groundwater NO3—-N concentrations exceeded the WHO threshold for drinking water (11.3 mg L−1) and 79 % of the groundwater DOC concentrations exceeded 5 mg L−1. The differences in groundwater NO3—-N and DOC concentrations among the 8 lakes were controlled by the intensity of agricultural and human activities and hydrogeological background. The stoichiometric ratio of DOC:NO3—-N regulated the NO3—-N reduction process, and groundwater NO3—-N accumulation rate appeared to become limited and sharply decreased when the DOC concentration was approximately 10 mg L−1 or when the DOC:NO3—-N ratio was close to 1:1, and the DOC:NO3—-N ratio threshold for limiting the NO3—-N reduction process was approximately 2.25. Based on this threshold, >33 %–86 % of the groundwater samples around the 8 plateau lakes were strongly limited in the reduction of groundwater NO3—-N due to a lack of sufficient DOC provides energy for heterotrophic microorganisms. Additionally, we highlight that the sustainable strategy of increasing DOC to stimulate groundwater NO3— attenuation should be combined with short-term strategies to jointly coordinate and control groundwater NO3— pollution.

Identifying the nitrate transport and transformations under apple orchards in the loess depositusing stable isotopes of water and nitrate

Understanding the behavior of nitrate in the unsaturated zone is critical for predicting groundwater nitrate pollution. Although this issue has been intensively investigated for shallow soil profiles, it remains poorly understood in deep soils. We collected soil samples up to 20 m depth under farmland and apple orchards with trees that were 16 and 22 years old (A16 and A22). We then determined soil-water content, stable isotopes (δ2H and δ18O) and nitrate content under two land use types. The stable isotopes of nitrate under two apple orchards were measured to a depth of 16 m. The mean nitrate contents in the shallow soils (0–6 m) under apple orchards (78.8 ± 87.8 mg kg−1 for A16, 180 ± 155 mg kg−1 for A22) were significantly higher than that of farmland (2.40 ± 1.56 mg kg−1) (p < 0.01), whereas the nitrate contents in the deep soils (6–20 m) were almost similar between apple orchards and farmland. Ammonium or urea-based nitrogen (N) fertilizers (30–61%) were the predominant contributors to nitrate in the shallow soil layers, followed by soil organic N and manure & sewage, whereas the soil organic N (mean 34%) was the primary source of nitrate in deep soils. Isotopic data revealed that the N transformation was controlled by nitrification, and denitrification was not apparent throughout the soil profiles. The downward transport of nitrate lagged behind soil-water. Nitrate was leached by piston flow in the vadose zone, and the nitrate from N application since the 1980 s has only infiltrated to 6 m depth. The difficulty in recharging deep soils mitigates the transport of nitrate to lower depths. The combination of water-nitrate stable isotopes provides new insights for identifying nitrate sources, transformation, and transport in the thick unsaturated zone.

Coupled hydrogeological modeling and nitrate transport modeling in an anthropized valley, a case study of the lower Soummam valley (Bejaïa Northeast of Algeria)

Anthropogenic activities, including wastewater discharges and fertilizer use, were identified as the primary factors influencing nitrate concentrations in the lower Soummam Valley in the North-East of Algeria. This study aimed to investigate nitrogen pollution and simulate nitrate mass transport coupled with a numerical flow model. Hydrogeochemical findings revealed significant seasonal variations between the high-water period (May 2019 and 2021) and the low-water period (September 2019 to November 2020 and 2021). During the low-water period, both temperature and electrical conductivity increased. However, pH, dissolved oxygen, and nitrate levels decreased in the high-water period. Nitrites and ammonium exhibited irregular fluctuations. The numerical flow model was developed using PMWIN and coupled with a solute transport model simulated with the Model Transport 3 Dimensions (MT3D). Calibration was conducted under steady-state conditions from 2011 to 2021 and was validated by comparing piezometric heads and nitrate concentrations measured in May 2021. Three scenarios were devised to simulate transient conditions from 2011 to 2050, considering variations in both groundwater levels and nitrate concentrations. The simulation revealed that river and dependent head boundaries are the primary sources of groundwater recharge. These boundaries contributed to approximately 87% of the total inflow. The model also depicted the water exchange between the aquifer and the river. However, the constant head boundary represented the main outflow, accounting for 85.7% of the total. The nitrate model illustrated an increase in nitrate concentrations, reaching 3.8 mg/L in 27 out of the 29 simulated wells. Both the river and groundwater head boundaries were identified as the key factors governing the hydrodynamic aquifer system and nitrate transport in the alluvial aquifer of the lower Soummam Valley.

Review of Groundwater Nitrate Pollution from Municipal Landfill Leachates: Implications for Environmental and Human Health and Leachate Treatment Technologies

Review of Groundwater Nitrate Pollution from Municipal Landfill Leachates: Implications for Environmental and Human Health and Leachate Treatment Technologies

New insights into the effect of EDTA on pyrite oxidation and N2O emission during pyrite autotrophic denitrification

Pyrite autotrophic denitrification (PAD) is crucial for removing nitrate in groundwater and advanced wastewater treatment. While disulfide is typically seen as the electron donor, the role of iron in pyrite oxidation is often ignored. In this study, Ethylene Diamine Tetraacetic Acid (EDTA) had been proven to have the potential to facilitate pyrite oxidation by promoting the solubility of iron in solution, thereby enhancing the kinetics of pyrite autotrophic denitrification. Firstly, EDTA could improve PAD performance, i.e. the nitrate removal rate at EDTA addition of 5 mM was 0.69 mg N/L•h and twice that of the control. However, high concentrations of EDTA inhibited the activity of the nitrous oxide reductase, resulting in the maximum accumulation of N2O reaching 13.26 mg N/L with an EDTA concentration of 15 mM. Furthermore, the X-ray Photoelectron Spectroscopy (XPS) result indicated that the EDTA addition promoted the production of bioavailable sulfur, with the concentration of S0 at 15 mM EDTA being more than twice higher than that of the control. Transmission electron microscopy (TEM) analysis indicated that EDTA could relieve the damage of iron encrustation on cell activity because it was difficult for EDTA-chelated ferrous iron to penetrate the cell membrane. Microbial community analyses showed an increase abundance of iron oxidizing bacteria, suggesting that EDTA addition promoted the bioavailability of iron for Fe(II) autotrophic denitrification. Overall, this study will provide insights into the understanding of oxidation mechanism of PAD process and the practical application for efficient nitrogen removal and N2O mitigation.

Human health risk assessment of nitrate and heavy metals in urban groundwater in Southeast Nigeria

Groundwater contamination by nitrate and heavy metals is a growing global concern due to its detrimental effects on human health through ingestion and dermal exposure. This study aimed to assess the concentrations of nitrate and heavy metals (Pb, Cu, Cd, and Fe) in groundwater and evaluate the associated health risks among different age groups (females, males, and children) in the Nnewi and Awka regions of southeast Nigeria. Standard methods were followed. Ten groundwater samples were collected from each study locality, and their physicochemical parameters were analyzed. The evaluation of heavy metal levels in groundwater was conducted using the risks of cancer and health hazard index as indicators of public health impact. The results showed that while nitrate levels were within acceptable limits, heavy metal concentrations exceeded permissible levels in all samples. Carcinogenic risk (CR) analysis revealed that approximately 40% of Nnewi samples and 80% of Awka samples exceeded the permitted range of ≤1 × 10 −6–1 × 10 −4. In the Nnewi region, the order of heavy metal toxicity was Cd > Pb > Cu > Fe, while in Awka, it was Pb > Cd > Cu > Fe, resulting in severe non-carcinogenic health hazards for users. Cd and Pb were identified as the most significant contaminants impacting water quality in both regions. Children exhibited greater vulnerability to health risks compared to adults in both areas. These findings contribute to our understanding of localized nitrate and heavy metal contamination, highlight the vulnerability of children, and emphasize the importance of regular monitoring and management practices.

Potential health risk assessment of nitrate in groundwater of Tonk district in Rajasthan, north western India

ABSTRACT Anthropogenic activities like adding synthetic nitrogenous fertilisers in agriculture fields, animal and human waste are the main factors responsible for the increase in nitrate concentration in groundwater of any area. Groundwater is the main source of not only irrigation but also dependency for drinking which has increased on it with decreasing surface sources. Today, increase in such anthropogenic activities has resulted in upsurge of the natural nitrate concentration to the extent of crossing its acceptable limit in drinking water. The Bureau of Indian Standard (BIS, 2012) 1 has prescribed the limit of 45 mg/L, whereas for WHO (2011) 2 the limit of nitrate is 50 mg/L. The goal of this present study is to assess the natural and anthropogenic NO3 concentrations in groundwater in a semi arid area of Rajasthan in Tonk District and its related risks to human health in the different groups of ages, such as children, males, and females. Being immune adults has little less effect on its continuous exposure than children. Even though these risks are non-carcinogenic, incessant exposure can create several health issues. In juveniles, it is known to cause methemoglobinemia, in adults it causes gastric and other stomach issues on prolonged consumption as well as dermal contact. The results show that the oral exposure of nitrate was very high compared to dermal contact. On the basis of non-carcinogenic health risk, the total Hazard Index (HITotal) values of groundwater nitrate were an average of 1.16 for males, 1.37 for females, and 1.58 for children. The nitrate health risk assessment shows that about 39%, 44%, and 51% of the samples constitute the non-carcinogenic health risk to males, females, and children, respectively.