Sources Of Nitrate In Groundwater Research Articles

Nitrate Source and Transformation in Groundwater under Urban and Agricultural Arid Environment in the Southeastern Nile Delta, Egypt

With the intensification of human activities, nitrate pollutants in groundwater are receiving increasing attention worldwide. Especially in the arid Nile Delta of Egypt, groundwater is one of the most valuable water resources in the region. Identifying the source of nitrate in groundwater with strong human disturbances is important to effective water resource management. This paper examined the stable isotopes (δ15N/δ18O-NO3 and δ2H/δ18O-H2O) and the hydrogeochemical parameters of the shallow groundwaters in the arid southeast of the Nile Delta to assess the potential sources and transformation processes of nitrate under severe urban and agricultural activities. The results revealed that the groundwaters were recharged by the Nile River. Meanwhile, the infiltration of irrigation water occurred in the west, while the mixing with the deep groundwater occurred in the east regions of the study area. The TDS, SO42−, NO3−, and Mn2+ concentrations of groundwaters (n = 55) exceeded the WHO permissible limit with 34.6%, 23.6%, 23.6%, and 65.5%, respectively. The NO3− concentrations in the shallow groundwaters ranged from 0.42 mg/L to 652 mg/L, and the higher levels were observed in the middle region of the study area where the unconfined condition prevailed. It extended to the deep groundwater and eastward of the study area in the groundwater flow direction. The δ15N-NO3 and δ18O-NO3 values suggested that the groundwater NO3− in the west and east regions of semi-confined condition were largely from the nitrification of soil organic nitrogen (SON) and chemical fertilizer (CF). In contrast, wastewater input (e.g., domestic sewage and unlined drains) and prevalent denitrification were identified in the middle region. The denitrification might be tightly coupled with the biogeochemical cycling of manganese. This study provides the first report on the groundwater NO3− dynamics in the Nile Delta, which generated valuable clues for effective water resource management in the arid region.

Geochemistry, stable isotopes and statistic tools to estimate threshold and source of nitrate in groundwater (Sardinia, Italy)

In the European Union, nitrate vulnerable zone (NVZ) should be designed for the mitigation of nitrate (NO3−) contamination caused by agricultural practices. Before establishing new NVZ, the sources of NO3− must be recognized. A geochemical and multiple stable isotopes approach (hydrogen, oxygen, nitrogen, sulfur and boron) and statistical tools were applied to define the geochemical characteristics of groundwater (60 samples), calculate the local NO3− threshold and assess potential sources of NO3− contamination in two study areas (hereafter Northern and Southern), located in a Mediterranean environment (Sardinia, Italy). Results of the integrated approach applied to two case study, permits to highlight the strengths of integrating geochemical and statistical methods to provide nitrate source identification as a reference by decision makers to remediate and mitigate nitrate contamination in groundwater.Hydrogeochemical features in the two study areas were similar: near neutral to slightly alkaline pH, electrical conductivity in the range of 0.3 to 3.9 mS/cm, and chemical composition ranging from Ca-HCO3− at low salinity to Na-Cl− at high salinity. Concentrations of NO3− in groundwater were in the range of 1 to 165 mg/L, whereas the nitrogen reduced species were negligible, except few samples having NH4+ up to 2 mg/L. Threshold values in the studied groundwater samples were between 4.3 and 6.6 mg/L NO3−, which was in agreement with previous estimates in Sardinian groundwater.Values of δ34S and δ18OSO4 of SO42− in groundwater samples indicated different sources of SO42−. Sulfur isotopic features attributed to marine SO42− were consistent with groundwater circulation in marine-derived sediments. Other source of SO42− were recognize due to the oxidation of sulfide minerals, to fertilizers, manure, sewage fields, and SO42− derived from a mix of different sources.Values of δ15N and δ18ONO3 of NO3− in groundwater samples indicated different biogeochemical processes and NO3− sources. Nitrification and volatilization processes might have occurred at very few sites, and denitrification was likely to occur at specific sites. Mixing among various NO3− sources in different proportions might account for the observed NO3− concentrations and the nitrogen isotopic compositions. The SIAR modeling results showed a prevalent NO3− source from sewage/manure. The δ11B signatures in groundwater indicated the manure to be the predominant NO3− source, whereas NO3− from sewage was recognized at few sites. Geographic areas showing either a predominant process or a defined NO3− source where not recognize in the studied groundwater. Results indicate widespread contamination of NO3− in the cultivated plain of both areas. Point sources of contamination, due to agricultural practices and/or inadequate management of livestock and urban wastes, were likely to occur at specific sites.

Watershed-Scale Shallow Groundwater Anthropogenic Nitrate Source, Loading, and Contamination Assessment in a Typical Wheat Production Region: Case Study in Yiluo River Watershed, Middle of China

Nitrate pollution in groundwater has become a global concern for agriculture and regional ecology. However, tracing the spatiotemporal groundwater nitrate pollution sources, calculating the total nitrogen loading, and assessing contamination at the watershed scale have not been well documented. In this study, 20 groundwater samplings from 2020 to 2021 (in dry and wet seasons) on the Yiluo River watershed in middle China were collected. Tracing groundwater nitrate pollution sources, calculating total nitrogen loading, and assessing contamination using dual isotopes (18ONO3 and 15NNO3), conservation of mass, and the nitrate pollution index (NPI), respectively. The results indicated that there were three nitrate sources in groundwater: (1) manure and sewage waste input (MSWI), (2) sediment nitrogen input (SNI), and (3) agriculture chemical fertilizer input (ACFI) in the Yiluo River watershed. ACFI and SNI were the main groundwater nitrogen pollution sources. The average nitrogen loading percentages of ACFI, SNI, and MSWI in the whole watershed were 94.7%, 4.34%, and 0.96%, respectively. The total nitrogen loading in the Yiluo River watershed was 7,256,835.99 kg/year, 4,084,870.09 kg/year in downstream areas, 2,121,938.93 kg/year in midstream areas, and 1,050,026.95 kg/year in upstream areas. Sixty percent of groundwater in the Yiluo River watershed has been polluted by nitrate. Nitrate pollution in midstream areas is more severe. Nitrite pollution was more serious in the wet season than in the dry season. The results of this study can provide useful information for watershed-scale groundwater nitrogen pollution control and treatment.

Identification of nitrogen pollution sources and transport transformation processes in groundwater of different landforms using C, H, N, and O isotope techniques: an example from the lower Weihe River.

Nitrogen pollution in groundwater is an environmental issue of global concern. Identifying nitrogen pollution sources and determining migration and transformation processes are the major ways to prevent and control nitrogen pollution in the groundwater on a regional scale. In this study, groundwater in the lower Wei River was investigated by combining multi-isotope tracing techniques with the SIAR hybrid model (source resolution) to trace the nitrate sources and their contribution rate to nitrogen pollution in groundwater of different geomorphological units, considering types of geomorphology as the units. The multi-isotope tracing technique allows dynamic analysis of nitrate sources, and the combination of this technology can improve the accuracy of nitrogen source traceability. The results indicated that the pH of the water bodies in the study area ranged from 6.83 to 8.01, which is neutral and weakly alkaline. The nitrogen pollution was mainly due to nitrates. The significant factors affecting nitrogen migration in groundwater are the geomorphological type, the chemical characteristics of the groundwater, and the age of the groundwater. Nitrogen migration and transformation processes in the study area were dominated by nitrification, and sources of nitrate pollution were mainly animal manure and domestic sewage (32.6%), followed by atmospheric deposition (26.8%), soil nitrogen (20.9%), and chemical fertilizer (19.7%). The main sources of nitrate in groundwater from river flats, alluvial plains, and loess tableland were animal manure and domestic sewage (43.7%), animal manure and domestic sewage (59.1%), and atmospheric deposition (55.5%), respectively. The result is mainly related to the different structural characteristics of various geomorphic units and the intensity of human activities. This study can provide a theoretical basis for the relevant agencies to develop plans to combat groundwater pollution.

PREDICTION OF NITRATE CONCENTRATION IN GROUNDWATER USING MLR AND AGRICULTURAL INDICATORS

Environmental pollution results in the degradation of all segments of nature. Groundwater, as one of thesignificant sources of drinking water at the global level, is increasingly exposed to various types of pollutants thatare mainly the result of anthropogenic action. Nitrate are one of the pollutants that can persist for a long time ingroundwater and their concentrations can reach high levels. Namely, the fact that groundwater is used for variouspurposes such as: irrigation, food production, drinking, special attention is focused on monitoring the concentrationof nitrate in groundwater. In this sense, EU legislation also prescribed a standard for drinking water in terms ofnitrate concentration in order to avoid possible threats to human health. The main sources of nitrate in groundwaterare agricultural activities, which primarily involve the use of chemical fertilizer, animal farms, waste water fromindustries that produce chemical fertilizer. In this paper, the prediction of average annual concentrations of nitrate ingroundwater at the national level was performed. Bearing in mind the mentioned sources of nitrate in groundwater, atotal of seven agricultural indicators were selected in this paper, which were assumed to contribute to higher nitrateconcentrations, namely: the area used for agriculture, meat production on farms, the balance of indicators - whichrepresents the total potential environmental risk caused by excess or deficit of N and P in agricultural soils, areaused for organic agricultural production, consumption of chemical fertilizer, sale of pesticides and percentage ofpopulation associated with at least secondary wastewater treatment. The prediction was made using multiple linearregression, where agricultural indicators were used as input parameters, i.e. independent variables, a total of seven,while the dependent variable was the average annual concentration of nitrate in groundwater at the national level. Inthis paper, five EU countries were selected for nitrate prediction: Belgium, Bulgaria, the Czech Republic, Germanyand France. For the development of the MLR (Multiple linear regression) model, available data from 2011 to 2015were used for all eight variables. Before developing the model, a correlation analysis was first performed todetermine whether the selected independent variables were correlated with the dependent variable. The results of thecorrelation analysis showed that there is a significant correlation between the independent and dependent variables.The developed MLR model showed good prediction results with a value of coefficient of determination R2 - 0.96.The results of the one year prediction by the MLR model showed satisfactory results, the biggest deviations betweenthe measured and model predicted values are in the case of Germany and France. Based on the obtained results, itcan be concluded that the MLR model can be applied as one of the alternatives in the assessment of nitrateconcentration in groundwater.

Source identification and apportionment of the nitrogen in groundwater based on isotope methods in the Beilin region of Suihua basin, northeastern China.

Multi-isotope method was used to analyze the migration and transformation characteristics of nitrogen in groundwater in the center of a typical confined water basin, and a simplified isotope mixing model was established to quantify the contribution of potential nitrate sources in the center of the basin. Based on the water quality monitoring results, the contour map of nitrate concentration in groundwater in the center of the basin was drawn. The results showed that the nitrate concentration in groundwater in the center of the basin increased gradually from upstream to downstream. The high value area of nitrate concentration in phreatic water is mainly affected by agricultural activities and infiltration of sewage discharge from upstream urban areas. The high value area of nitrate concentration in confined water is mainly due to the water level depression funnel caused by large exploitation of confined water. The quantitative results of N-O isotope mixing model for potential nitrate sources show that the main recharge sources of groundwater in the center of the basin are atmospheric precipitation, agricultural irrigation water, and the lateral inflow of upstream groundwater. Agricultural irrigation water has the highest contribution rate of 67.01%. The main recharge sources of confined aquifer in the center of the basin are phreatic water leakage and lateral inflow of upstream confined water. The contribution rate of upstream confined water is between 45.55% and 56.35%, which is basically maintained at about 50%. Compared with the calculation results of D-O isotope mixing model, the accuracy of the established N-O isotope mixing model meets the basic requirements. The results of this study can provide technical reference and theoretical support for the identification and quantitative research of potential nitrate sources in groundwater under the same type of hydrogeological conditions. PRACTITIONER POINTS: Multiple isotope fingerprint comparison to identify nitrate source contribution ratio. Migration and transformation of nitrogen in the center of a typical confined water basin Simplified the traditional isotope mixing model to quickly quantify the source of contamination.

Using PCA-APCS-MLR model and SIAR model combined with multiple isotopes to quantify the nitrate sources in groundwater of Zhuji, East China

Rapid urbanization intensifies nitrate (NO3−) pollution in groundwater. Based on hydrochemical analysis and stable isotopes (δD-H2O, δ18O–H2O, δ15N–NO3- and δ18O–NO3-, a principal component analysis-absolute principal component score-multiple linear regression (PCA-APCS-MLR) model and a Bayesian isotopic mixing model (SIAR model) were used to quantify groundwater pollution sources, especially NO3− sources, in Zhuji, East China. The results showed that the main chemical types in Zhuji were HCO3–Ca in shallow groundwater, HCO3–Ca and HCO3–Ca·Na in deep groundwater. The δD-H2O and δ18O–H2O values in groundwater ranged from −43.4‰ to −32.1% and from −7.0‰ to −4.8%, respectively, and atmospheric precipitation was the main recharge source of groundwater. The calculation of the PAC-APCS-MLR model showed that the potential pollution sources in shallow and deep groundwater were hydrogeological conditions, agricultural activities and domestic sewage/manure, with the total contributions of 77.62% and 71.90%, respectively. The contributions from agricultural activities and sewage/manure to TN, NO3− and NH4+ in shallow groundwater (>82.00%) were higher than those in deep groundwater (>74.00%). The δ15N–NO3-(6.0‰–33.0‰) and δ18O–NO3-(7‰–29.9‰) values of groundwater indicated the existence of clear denitrification in groundwater in Zhuji. The results highlighted that an accurate isotopic fractionation enrichment factor could improve NO3− source apportionment by the SIAR model. When the denitrification isotopic fractionation enrichment factors were εN = −5.3‰ to −8.7‰ and εO = −8.0‰ in the SIAR model, the NO3− contributions from sewage/manure accounted for 51.7%–40.9% in shallow groundwater and 49.3%–40.3% in deep groundwater. The NO3− contributions from soil nitrogen and chemical fertilizer were relatively low, those in shallow groundwater were 25.6%–28.4% and 22.7%–30.7%, respectively; and those in deep groundwater were 27.2%–29.8% and 23.5%–29.9%, respectively. It was demonstrated that PAC-APCS-MLR model coupled with SIAR model was an effective method for source identification and apportionment in groundwater.

Geochemical evolution of groundwater under the influence of human activities： A case study in the southwest of Poyang Lake Basin

Groundwater quality continues to be threatened globally by anthropogenic activities including excessive use of chemical fertilizers and sewage discharge. However, few studies on the evolution of groundwater chemistry have systematically characterized human and natural effects, while which is of great importance for sustainable water resources management. In this study, hydrochemical data and multiple tracers (δ15N–NO3-, δ18O–NO3-, and 87Sr/86Sr) were employed to elucidate the geochemical evolution of groundwater in an intensive human activity area - the southwest of Poyang Lake Basin where is characterized by the highly complex hydrogeological environment with the diversity of aquifer types and lithology. Combining fuzzy c-means (FCM) clustering with natural background levels (NBLs) analyses, groundwater was divided into four groups with hydrological and statistical significance: groundwater in recharge zones (group 2-1 and group 3), transition zones (group 2-2) and discharge zones (group 1). Using the ions relations and 87Sr/86Sr, we found that the dissolved components of groundwater in recharge zones were controlled by natural processes (water-rock interactions and groundwater runoff conditions), and human activities have altered the natural geochemical evolution of groundwater in transition zones and discharge zones. Multi-tracer approach (δ15N–NO3-, δ18O–NO3-, and 87Sr/86Sr) were used to analyze the sources of nitrate in groundwater. The results showed that the high nitrate load in groundwater was predominately from sewage, and the groundwater quality in local areas was also influenced by NH4+ fertilizer and manure. In addition, nitrate in groundwater was controlled by land use types that groundwater flows through, depending on hydrogeological conditions and soil properties. Inverse geochemical models were developed and constrained to evaluate the relative contributions of natural and anthropogenic sources and to establish a conceptual model of groundwater geochemical evolution in the study area. This study provides a way to evaluate the relative contributions of natural and anthropogenic sources on groundwater quality and explore the geochemical evolution of groundwater in human activity areas.

Determining hydrogeological and anthropogenic controls on N pollution in groundwater beneath piedmont alluvial fans using multi-isotope data

Piedmont alluvial fans have, for a long time, supported clean groundwater for human development worldwide. Rapid urbanization in China has over-exploited groundwater and resulted in severe groundwater nitrate pollution in piedmont alluvial fans, which has led to both human health concerns and clean water shortages, especially in rural residential areas where drinking water is mainly derived from shallow groundwater. However, sources of nitrate in groundwater and their pathways are still unclear. In this study, we hypothesized that untreated manure and domestic sewage are the primary nitrate sources in a residential area, and that an unconfined aquifer would be more vulnerable to nitrate pollution than a confined aquifer due to nitrate infiltration via the vadose zone. To verify this hypothesis, groundwater nitrate pollution in a well-characterized piedmont alluvial fan was studied through hydrochemical composition and multi-isotope (δ15NNO3, δ34SSO4, δ18OSO4, δ13CDIC) data over four seasons. Seasonal variations for both NO3− concentrations and δ15NNO3 values in unconfined groundwater (UGW) and confined groundwater (CGW) were observed. Mixing of nitrate sourced from manure/sewage, precipitation, soil nitrogen, and synthetic fertilizer controlled the groundwater nitrate level, and manure/sewage contributed 52.4%, 32.4%, and 33.7% nitrate to UGW, CGW, and surface water (SFW), respectively, based on Stable Isotope Mixing Models in R (SIMMR) analysis. Denitrification had a minor effect on groundwater nitrate levels in a residential area, and nitrate pollution in CGW was partly due to nitrate migration through geological faults and fracture zones in a piedmont alluvial fan. Nitrate pollution sources and pathways in residential areas were confirmed through multiple isotopes (δ15NNO3, δ13CDIC, δ34SSO4, and δ18OSO4). Collectively, these results highlight the roles of the hydrogeological setting and anthropogenic activities in groundwater N pollution beneath piedmont alluvial fans.

Identifying anthropogenic sources of groundwater contamination by natural background levels and stable isotope application in Pinggu basin, China

The assessment of natural background levels (NBLs) in groundwater is considered as an efficient way to distinguish the geogenic compound from anthropogenic pollution of groundwater—a basic issue in groundwater environmental management. At present, most studies only assess NBLs of single parameters in groundwater. Such method, however, ignored the complex components and interaction in the groundwater, which leads to the inaccuracy of the assessment. In this study, 51 groundwater samples were investigated in November 2018 in Pinggu basin—one of the most important emergency groundwater supply sources of Beijing. Hierarchical cluster analysis (HCA) was used firstly to divide the study area into four zones. By combining single-parameter NBLs assessment and comprehensive NBLs assessment, the possible anthropogenic impact on groundwater quality in different zones could be determined with the use of land use map. For single-parameter NBLs assessment, iterative Grubbs’ test was used to assess NBLs of the data following Gaussian distribution, and the median plus/minus twofold the median of the absolute deviations from the median (median ± 2MAD) method was used to assess NBLs of the data for the non-Gaussian distribution. For comprehensive NBLs assessment, Mahalanobis distances of scatters in scatter plots which express the hydrogeological evolution processes were involved. In addition, δ15N-NO3− and δ18O-NO3− were used to analyze the sources of nitrate in groundwater. The results showed that the groundwater was affected by industrial activities, agricultural activities, urban domestic sewage and landfills. And the groundwater quality in the east of the study area was better than that in the west. Nitrate in the groundwater of study area mainly came from nitrification, and denitrification occurred in the groundwater near the landfills. This study provides a way to assess the NBLs of groundwater quality, and to determine sources and transformation of nitrate in the groundwater, which contributes to the identification of anthropogenic pollution in groundwater.

Hydrochemical evolution, geospatial groundwater quality and potential health risks associated with intake of nitrate via drinking water: case of Gboko agricultural district, central Nigeria

Elevated nitrate concentration in groundwater used for domestic purposes can pose a health hazard to humans. This study is aimed at determining the hydrochemical characteristics, and evaluating nitrate contamination, and assessment of nitrate health risk in Gboko district, Nigeria. A total of 50 groundwater samples were collected from shallow wells and analyzed for various physicochemical parameters. Nitrate concentration ranged from 0.02 to 156.85 mg/l and a mean value of 26.50 mg/l, and 26% of the groundwater samples have concentration above the guideline value (50 mg/l) for drinking water. Nitrate sources in groundwater of the area included application of nitrogen-based fertilizer, sanitary facility, and sewage. Hazard quotient via oral ingestion (HQoral) for adult and children has mean values of 0.43 and 0.83 respectively while the hazard quotient via dermal exposure (HQdermal) has mean values of 0.002 and 0.0031 for adults and children respectively. Hazard index (HI) for adults ranged from 0.0003 to 2.4317 with a mean of 0.4419, and HI for children ranged from 0.0006 to 4.592 with a mean value of 0.8344. The results showed that children are at more risk than adults in consuming nitrate contaminated groundwater. Proper groundwater planning, development, and management are required to ensure the supply of potable groundwater.

Shift of nitrate sources in groundwater due to intensive livestock farming on Jeju Island, South Korea: With emphasis on legacy effects on water management

Time lags between anthropogenic nitrogen inputs and their impacts to nitrate levels cause a misunderstanding for sources and subsequently misguide the groundwater management.We investigated the hydrochemical data of groundwater samples (n = 172 from 49 wells) with chlorofluorocarbons (CFCs)-based groundwater age dating and stable N (δ15N) and O isotopes (δ18O) of nitrate to assess the legacy effect of livestock farming to groundwater in an agricultural area where intensive livestock farming started in the 1970s and illegal dumping of manure wastewater in a lava cave was revealed in 2015. Approximately 90% of the groundwater samples had nitrate concentrations exceeding the natural threshold (5.5 mg/L NO3−) for nitrate contamination and 34% exceeded the World Health Organization's guideline for drinking water quality (44.3 mg/L), indicating severe nitrate contamination. The δ15NNO3 values (5.5 to 24.3‰) in groundwater exceeding the threshold of nitrate showed that livestock manure was a major nitrate source, while ammonium fertilizer also seemed influential given the δ15NNO3 values in the overlapping fields of N sources. Factor analysis of hydrochemical data also supported nitrate contamination by manure as well as by plant farming in the study area. Based on the spatial distribution of nitrate levels and δ15NNO3, livestock farming affected nitrate contamination by illegal manure dumping in the leakage cave. According to a Bayesian mixing model, the contribution of manure wastewater was 33.5 to 81.8% as of 2015–2018, with the rest from fertilizers. Meanwhile, the groundwater ages showed negative correlations with both nitrate levels (r = –0.90) and δ15NNO3 values (r = –0.74) on a log scale, consistent with the increasing N release from livestock farming since the 1960s. In particular, the median value of δ15NNO3 rapidly increased to 9.2‰ in groundwater recharged between the late 1970s and early 1990s when N production exponentially increased, implying a significant effect of livestock farming after the 1980s. Groundwater quality is expected to deteriorate over the next several decades based on the groundwater ages (> 23.5 years), the increased N production from livestock farming, and the legacy effect of N. Long-term groundwater management plans (> 25 years) are required to decrease N loads in the study area, because it takes time for management practices to take effect. The study results are a good reference for groundwater management in regions with a source shift to livestock farming under intensive livestock production systems. Moreover, the chronological study using historical N production, groundwater age data, and dual nitrate isotopes can be applied to other regions with multiple N sources and their shifting for identifying sources and estimating time lags.

An investigation into the hydrochemistry, quality and risk to human health of groundwater in the central region of Shandong Province, North China

This study aimed to characterize the hydrochemistry and risk to human health of groundwater in the central region of Shandong Province (CRSP) as well as to investigate the factors controlling groundwater quality. Methods applied included traditional hydrochemical analysis methods, the water quality index (WQI) and a health risk model. The results showed that groundwater of the CRSP is weakly alkaline, with average concentrations of total dissolved solids (TDS) over the wet and dry seasons of 666.2 mg·L−1 and 653.9 mg·L−1, respectively. The southeast part of the study region and Laiwu, Xintai and Taian showed higher concentrations of TDS and NO3−. The dominant hydrochemical types of groundwater in the CRSP were identified to be HCO3–Ca·Mg and SO4·Cl–Ca·Mg. The main factors influencing the hydrochemical composition of groundwater in CRSP were identified to include rock weathering, cation exchange and anthropogenic inputs, and the main source of nitrate in groundwater was identified as agricultural activities. The results of the water quality evaluation showed that most groundwater samples of the CRSP were suitable for drinking and agricultural irrigation. However, the non-carcinogenic risk index (HQ) values calculated for groundwater of the CRSP over both the dry and wet seasons indicated unacceptable risk to the health of both children and adults. The contradicting results between the water quality evaluation and health risk assessment were due to differences in the water quality standard limits used. It is suggested that permissible limits of water quality variables be adjusted according to local conditions and that a water quality evaluation system be established that is suitable for Chinese residents, so as to ensure the sustainable management of groundwater and the safety of drinking water.

Source and Quality of Groundwater Surrounding the Qinghai Lake, NE Qinghai‐Tibet Plateau

Comprehensive studies on the spatial distribution, water quality, recharge source, and hydrochemical evolution of regional groundwater form the foundation of rational utilization of groundwater resources. In this study, we investigated the water levels, hydrochemistry, and stable isotope composition of groundwater in the vicinity of the Qinghai Lake in China to reveal its recharge sources, hydrochemical evolution, and water quality. The level of groundwater relative to the level of water in the Qinghai Lake ranged from -1.27 to 122.91 m, indicating most of the groundwater to be flowing into the lake. The local evaporation line (LEL) of groundwater was simulated as δ2 H=6.08 δ18 O-3.01. The groundwater surrounding the Qinghai Lake was primarily recharged through local precipitation at different altitudes. The hydrochemical type of most of the groundwater samples was Ca-Mg-HCO3 ; the hydrochemistry was primarily controlled by carbonate dissolution during runoff. At several locations, the ionic concentrations in groundwater exceeded the current drinking water standards making it unsuitable for drinking. The main source of nitrate in groundwater surrounding the Qinghai Lake was animal feces and sewage, suggesting that groundwater pollution should be mitigated in areas practicing animal husbandry in the Qinghai-Tibet Plateau, regardless of industrial and urbanization rates being relatively low in the region. The scientific planning, engineering, and management of livestock manure and wastewater discharge from animal husbandry practices is a crucial and is urgently required in the Tibetan Plateau.

Identifying Nitrate Sources in a Typical Karst Underground River Basin

Underground rivers are an important source of groundwater in karst area. Recently, nitrate pollution of underground rivers has become a serious issue. To identify the sources of nitrate in Guancun typical karst underground river basin, stable isotope techniques (δ15N-NO3-, δ18O-NO3-, and δ18O-H2O) were applied in this study. The contribution rates of different nitrate sources in groundwater were quantitatively identified based on the stable isotope analysis in R (SIAR) model, and the influence of land use type on nitrate distribution and source in watershed water was clarified. The results showed that ① nitrate mainly came from fertilizers, soil organic nitrogen, and manure/sewage based to the isotopic composition of nitrate nitrogen and oxygen isotopes. It was revealed that non-point sources significantly contributed to nitrate in waters of the Guancun underground river basin. ② Nitrification dominated the formation process of nitrate in groundwater, and the initial values of nitrogen and oxygen isotopes were not affected by fractionation. ③ Based on SIAR, the contribution of different sources to nitrate in water in the basin varied seasonally, and the contributions of fertilizer, soil organic nitrogen, and manure/sewage to nitrate were 57.07%, 34.06%, and 8.87% in the wet season and 34.14%, 33.02%, and 32.84% in the dry season, respectively. Overall, the present study quantitatively evaluated the temporal variations of nitrate sources in a typical karst groundwater river basin and provided a theoretical foundation for prevention and control management of non-point source pollution and watershed management in karst areas.

Geochemical Assessment of Potential Sources for Nitrate in the Wasia Aquifer, Al Kharj Area, Central Saudi Arabia

Nitrate (NO3−) represents one of the major groundwater constituents with increasing distribution and concentration in the Kingdom of Saudi Arabia. This study aimed to determine potential sources of nitrate in the Early to Late Cretaceous Wasia aquifer system at the Al Kharj area (Central Saudi Arabia) by an integrative approach using groundwater geochemistry, nitrate isotopes (15N–NO3 and 18O–NO3), and tritium (3H) measurements. The lowest saline groundwater samples (TDS = 1400–2000 mg/L) from the peripheral zone were representative for pristine groundwater from the Wasia aquifer with nitrate concentrations below 20 mg/L and low 18O–NO3 ratios (8.7–20.6‰) but enriched 15N–NO3 values (up to 10.8‰). In contrast, 11 out of 34 analyzed water samples from irrigation wells and cattle watering wells exceeded the World Health Organization (WHO) drinking water guideline value for nitrate of 50 mg/L with maximum concentrations of up to 395 mg/L. Nitrate fertilizers and atmospheric deposition are the main sources of nitrate in groundwater in the eastern and northern sections of the study area. The combination of elevated salinities (4940–7330 mg/L), NO3 (111–395 mg/L), boron (516–1430 μg/L), and enriched 18O–NO3 (21.7–25.8‰) ratios with depleted 15N–NO3 (5.7–7.6‰) confirm the local influx of evaporated irrigation water with remnants of dissolved fertilizer into the Wasia groundwater system. There was no evidence for the influx of animal or human wastes from adjacent dairy, poultry, and housing infrastructures. Tritium concentrations below the detection limit of 0.8 TU for most borehole samples implied the absence of recent natural recharge. The estimated annual average N influx of 3.34 to 6.67 kg/ha to the Wasia aquifer requires a combination of atmospheric deposition and anthropogenic sources (mainly nitrate fertilizers) to increase the nitrogen content of the Wasia aquifer.

Origin, implications and management strategies for nitrate pollution in surface and ground waters of Anthemountas basin based on a δ15N-NO3− and δ18O-NO3− isotope approach

Nitrate pollution of surface and groundwater resources is a major worldwide environmental problem. In this study nitrogen isotopes of water, soil, fertilizer and manure were analyzed to determine the pollution sources of nitrate in the groundwater and surface waters of Anthemountas basin. The SIAR model and multivariate statistical analysis were used to determine and quantify the contribution of different NO3̄ sources in groundwater and surface water. Additionally, a detailed literature overview was carried out to identify the origin of nitrate pollution in surface and ground waters based on ΝΟ3− isotopes. The Piper diagram identified the dominant water types as Mg-Ca-HCO3 and Ca-Mg-HCO3. Nitrate concentrations reached 162.0 mg/L in groundwater and 39.0 mg/L in surface waters. The main source of nitrate in groundwater was mainly nitrified ammonium-based synthetic urea and less nitrate-based synthetic fertilizers. The correlation of SIAR results with other trace elements revealed a negative correlation between hexavalent chromium and a) nitrate-based synthetic fertilizers, and b) nitrification of urea synthetic fertilizers. However, a positive correlation was observed between hexavalent chromium and anthropogenic organic matter. The literature overview provided the basis to design a novel management protocol for nitrate pollution that includes three steps: a) fundamental research, b) management tools, c) monitoring and preservation actions. However, an integrated management protocol for nitrate pollution requires a deeper understanding of the hydro-system and the full participation of local farmers and stakeholders.

The Importance of Incorporating Denitrification in the Assessment of Groundwater Vulnerability

Human activities are deeply connected with groundwater reservoirs, so protecting them from pollution has become a priority in many regions of the world. Nitrate is considered the main groundwater pollutant since it is directly linked to many human activities. Agricultural activities and domestic wastewater have been identified as the main sources of nitrate in groundwater. Nevertheless, there are some natural processes that can mitigate nitrate pollution. Together with dilution processes, the degradation of nitrate through denitrification has been acknowledge as a process that can potentially reduce nitrogen loads, in both deep and shallow aquifers. Usually these processes were not properly quantified in vulnerability assessment methods, until the introduction of LOS indices. In this study, the application of the LOS indices on 4 agricultural areas is discussed, highlighting how the LOS indices can identify portions of the landscape with higher potential denitrification and how they directly enhance the groundwater vulnerability assessment. Previous studies have shown that LOS indices are a valuable tool for proper vulnerability assessment to nitrate, however they need to be coupled with other parameters that also describe nitrate behavior in groundwater. The SINTACS-SVN and DRASTIC-PA methods that include the LOS indices, were applied for the first time in the Epanomi coastal area to evaluate the reliably of the assessment and, despite the different classes range and the weights applied, similar groundwater vulnerability assessment maps were obtained. The nitrate vulnerability maps were comparable with the observed nitrate concentrations and were found to be highly comparable with original LOS maps. Nevertheless, it should be kept in mind that vulnerability methods are only screening tools and groundwater quality observations are pivotal information for environmental management.

Groundwater quality appraisal for non-carcinogenic human health risks and irrigation purposes in a part of Yamuna sub-basin, India

In this study, groundwater quality in part of Yamuna sub-basin, comprising of Panipat district of Haryana, India, impacted by agricultural and industrial activities, was evaluated for the non-carcinogenic human health risks associated with drinking water quality. The hazard quotient (HQ) associated with the occurrence of fluoride and nitrate in groundwater was calculated for the adults and children. Hazard index (HI) induced by the fluoride and nitrate in groundwater of the study area indicated that the children were more prone to non-carcinogenic human health risk than the adults. The Eastern half of the study area had better WQI than the Western half where the value of WQI was greater than 100 and cannot be recommended for drinking purposes. The correlation plot for groundwater quality exhibited that the alkaline conditions and presence of Na+ and HCO3- favored the high fluoride content, and the source of nitrate in groundwater was mainly anthropogenic in nature. Further, suitability of groundwater samples for irrigational purposes was evaluated by comparing several irrigational indices. Approximately 80% groundwater samples were found suitable for irrigation purposes except for some locations where adequate sub-surface drainage system has to be developed.

Source Analysis of Nitrate Nitrogen in Groundwater Based on Different Modes of Land use

Background: The study area is located in the Hebei province Luanxian section along the Luanhe River. The right of Luanhe River is arranged with 3 monitoring sections and is laid with 5 wells in the A-A section and B-B section and 1 well on the floodplain (inside the dike), the distance from the river level is about 10m. The distance between the 4 wells outside the dike is 20m, 50m, 200m and 1500m respectively. 2 wells are arranged on the C-C section, so there are 13 observation wells in the study area. 3# wells and 11# wells have used existing monitoring wells, so 11 wells have been set up actually. The monitoring wells are designed to monitor groundwater level, groundwater quality and isotope analysis. Methods: In the upstream of Luanhe’s A-A section of the No. 4 well near the edge of the woods and downstream of the B-B section of the No. 8 well near the edge of farmland (wheat), each point of soil is sampled to determine the content of nitrate nitrogen and 15N isotope ratio in soil profile. The depth of soil is sampled from surface to groundwater level, the total depth is about 2.5m. Taking about 1kg soil samples at 20cm every time from the ground surface and collect and seal in plastic bags and number. The sampling time was November 2015, March 2016, May 2016 and July 2016, taking 4 times. Results: The analysis showed that higher nitrate content in soil is within 0-60cm, and is same as the depth of fertilizing the crops (including animal manure), so when estimating the proportion of groundwater in nitrate, nitrate content in 0-60cm is assumed as the initial value; which is close to the underground water level in the soil and is regarded as the final value of 60cm, that is, the final value of nitrate into the groundwater, which can estimate the soil nitrate into groundwater ratio. Conclusion: The sources of nitrate in groundwater are complex and related to many factors, such as river water, soil and so on. According to the content of nitrogen and oxygen isotopes, it determines the main source of nitrate nitrogen:soil and Luanhe River. The results showed that the ratio of nitrate to groundwater in the forest soil was 20%~80.8%, and the average value was 56.3%. The proportion of nitrate in the soil in the wheat field was 6.8%~98.2%, with an average value of 48.3%. Nitrate nitrogen from water in proportion of large changes with the seasons, the upper reaches of the Luanhe River (near No. 2 wells) for 0~19.6%; the Luanhe River (near No. 7 wells) for 0~31.5%.