Nitrate Contamination Of Groundwater Research Articles

Nitrate and Ammonia Contamination in Groundwater and their Effect on Microbial Community in Apulia Region

Nitrate and Ammonia Contamination in Groundwater and their Effect on Microbial Community in Apulia Region

Evaluating the seasonal effects of whole orchard recycling on water movement and nitrogen retention for a newly established almond orchard: Simulation using HYDRUS-1D

Whole orchard recycling (WOR) is an emerging practice in perennial cropping systems and is an alternative to open or cogeneration burning. It is an orchard removal practice that incorporates large amounts of woody biomass back into the soil system. In this study, we utilized a soil hydrological model (HYDRUS-1D) to evaluate the seasonal effects of WOR on water movement and nitrogen (N) retention for a newly established almond orchard on a typical sandy loam soil in the Central Valley of California. Soil moisture and N content were monitored across the first five growing seasons from 2018 to 2022. The model was able to track seasonal moisture fluctuation nicely compared to observed data. Additionally, an increase in soil moisture was measured in the WOR treatments in surface soil (i.e., 0- to 15-cm depths) where biomass was incorporated, and N leaching was reduced when compared to the unamended control. Simulations suggest that with WOR, irrigation can be reduced by up to 20 % during the tree establishment stage with minimal effect on root water uptake. This reduction in applied water can increase farm water use efficiency and reduce operational expenses, e.g., cost of water and pumping. Likewise, the reduction in N leaching observed in both predicted results and laboratory analysis can further cut farm capital costs, e.g., fertilization, and lessen orchard environmental impacts. Overall, results from our simulation show a positive effect of WOR on soil ecosystem services and can potentially be a profitable strategy for orchard turnover. The results have important implications in reducing groundwater nitrate contamination in irrigated agriculture in the Central Valley of California and applicable to most parts of Southwestern United States.

Nitrate contamination in groundwater and its health risk assessment: a case study of Quanzhou, a typical coastal city in Southeast China

Nitrate contamination in groundwater and its health risk assessment: a case study of Quanzhou, a typical coastal city in Southeast China

Emerging nitrate contamination in groundwater: Changing phase in a fast-growing state of India

The consumption of nitrate-contaminated groundwater is often associated with potential health risks, particularly in children. This study aimed to assess the hydrochemistry and nitrate contamination in groundwater of Kerala state, India for the years 2010 and 2018 and evaluate the potential human health risks due to nitrate exposure in adults, and children through oral ingestion and dermal contact pathways. Nitrate-contaminated zones were identified by spatial mapping of nitrate concentration based on groundwater quality data of 324 wells. Groundwater is typically acidic to slightly alkaline, and the electrical conductivity (EC) varied from 33 to 1180 μS/cm in 2010 and 34.6–2500 mg/L in 2018 indicating a noticeable increase over the years. Most samples fall within low salt enrichment category. The nitrate concentration in groundwater varied from 0 to 173 mg/L with a mean of 15.4 mg/L during 2010 and 0 to 244 with a mean of 20.3 mg/L during 2018. Though nitrate concentrations show uneven spatial distributions due to both natural and anthropogenic sources, the spatial clustering of higher concentrations remains almost same in both periods. In 2010, non-carcinogenic risk, as measured by Health Index Total (HITotal) values in groundwater for the investigated region, ranged from 0.005 to 4.170 (mean of 0.349) for males, 0.005 to 4.928 (mean of 0.413) for females, and 0.008 to 7.243 (mean of 0.607) for children, while in 2018, the corresponding values varied from 0.001 to 5.881 (mean of 0.501) for males, 0.002 to 6.950 (mean of 0.592) for females, and 0.003 to 10.215 (mean of 0.870) for children, indicating a substantial increase in risk, for females and children. Greater health risk is observed in children during both the periods. The findings emphasize the need for proper water quality management, especially in regions with higher vulnerability to nitrate pollution, to safeguard human health and well-being.

Assessing Nitrate Leaching and Runoff Coefficients in the Dynamic Interplay of Seasonal Crop Biomass: A Study of Surface and Groundwater Nitrate Contamination in the Bilate Cropland Watershed

Effective water resource management and sustainable agricultural practices are contingent upon a thorough understanding of nitrate dynamics. This study investigates the utilization of seasonal average cropland runoff observations to improve the prediction accuracy of nitrate runoff loads to surface water originating from cropping zones. By integrating data from various sources, including seasonal rainfall/runoff observations and cropland parameters, the study explores the complex relationship between crop biomass growth, nitrogen fertilizer application, and seasonal rainfall over cropland. Monthly average observations of cropping zone rainfall/runoff in the cropping zone are analyzed to understand the response of seasonal crop biomass to nitrogen fertilizer application and seasonally calibrated rainfall/runoff in the cropland watershed. The study demonstrates the prototypical runoff observation from cultivated areas and statistically estimates seasonal runoff at downstream stream outlets. This shows a strong correlation with an R² of 0.9742 with a p-value less than 0.001 for seasonal rainfall climate parameters. Seasonal cropland runoff observations from EWX lite are presented for model calibration at downstream outlets, based on regional crop calendars, facilitating the estimation of nitrate loading to surface water and nitrate contamination from cropping zones. The findings reveal distinct cropping zones, particularly zones 5, 6, 11, and 13, which significantly contribute, each exceeding 50 mg/l of leaching load to groundwater. Moreover, more than ten zones surpass the threshold of 50mg/l in nitrate loading to surface water. These quantitative insights provide valuable spatial information regarding nitrate runoff relationships within the watershed, enabling the identification of specific zones with heightened nitrate contributions and offering actionable solutions for promoting sustainable agriculture and refining water resource management strategies.

Driving mechanism of different nutrient conditions on microbial mediated nitrate reduction in magnetite-present river infiltration zone

Significant research is focused on the ability of riparian zones to reduce groundwater nitrate contamination. Owing to the extremely high redox activity of nitrate, naturally existing electron donors, such as organic matter and iron minerals, are crucial in facilitating nitrate reduction in the riparian zone. Here, we examined the coexistence of magnetite, an iron mineral, and nitrate, a frequently observed coexisting system in sediments, to investigate nitrate reduction features at various C/N ratios and evaluate the response of microbial communities to these settings. Additionally, we aimed to use this information as a foundation for examining the effect of nutritional conditions on the nitrate reduction process in magnetite-present environments. These results emphasise the significance of organic matter in enabling dissimilatory nitrate reduction to ammonium (DNRA) and enhancing the connection between nitrate reduction and iron in sedimentary environments. In the later phases of nitrate reduction, nitrogen fixation was the prevailing process in low-carbon environments, whereas high-carbon environments tended to facilitate the breakdown of organic nitrogen. High-throughput sequencing analysis revealed a robust association between C/N ratios and alterations in microbial community composition, providing insights into notable modifications in essential functioning microorganisms. The nitrogen-fixing bacterium Ralstonia is more abundant in ecosystems with scarce organic matter. In contrast, in settings rich in organic matter, microorganisms, such as Acinetobacter and Clostridia, which may produce ammonia, play crucial roles. Moreover, the population of iron bacteria grows in such an environment. Hence, this study proposes that C/N ratios can influence Fe(II)/Fe(III) conversions and simultaneously affect the process of nitrate reduction by shaping the composition of specific microbial communities.

Spatial distribution, sources, and human health risk assessment of elevated nitrate levels in groundwater of an agriculture-dominant coastal area in Hainan Island, China

In order to comprehend the groundwater nitrate contamination in Hainan Island, which is recognized as China's sole “tropical agricultural production base,” the distribution characteristics of nitrate in different aquifers and land-use types were elucidated through hydrochemical and geostatistical analysis methods. Principal component analysis (PCA), hierarchical cluster analysis (HCA), and absolute principal component score-multiple linear regression (APCS-MLR) were employed for qualitative and quantitative analysis of the nitrate source. The results showed that NO3−-high (>88.57 mg/L) groundwater accounted for about 10 % of the total distribution area of the western coastal area in Hainan Island. Moreover, the proportions of NO3−-high groundwater in pore water and fissure water were 10 % and 7 %, respectively. The order of groundwater nitrate concentration in different land-use types was as follows: bare land, cultivated land, construction land, grassland, and woodland. The main sources of elevated nitrate concentrations in pore water were animal feces and nitrogen/potassium fertilizers, accounting for 45.4 % of the overall contribution. These substances infiltrated through the vadose zone, leaching out and mobilizing selenium within this zone, ultimately leading to the characteristic enrichment patterns observed in pore water, including nitrate, arsenic, potassium, and selenium. Furthermore, the occurrence of high nitrate in fissure water was mainly attributed to the leaching of cultured manure, septic tank leakage, and infiltration of domestic sewage, accounting for a contribution rate of 32.9 %. Simultaneously, under oxidizing conditions, selenium became activated and entered groundwater through water flow, thereby exhibiting common enrichment characteristics with nitrate and potassium in fissure water. In addition, the assessment of human health risks revealed that 16 % and 40 % of groundwater samples posed unacceptable non-carcinogenic risks to adults and children respectively, with a higher risk for local children. The study recommends the reasonable application of chemical fertilizers, as well as the strengthening of sewage treatment capacity and standardized disposal of manure and feces, to reduce nitrate contamination of groundwater at source and ensure the safety of drinking water.

Nitrate contamination in groundwater and its evaluation of non-carcinogenic health hazards from Arjunanadi River basin, south India

Nitrate (NO3-) contamination of groundwater is increasingly getting common in many places across India. Here, we present new data about nitrate pollution and the associated health consequences for infant, children, and adult population by evaluating 94 groundwater samples from the Madurai and Virudhunagar regions within the Arjunanadi River basin, situated at the southern region of India. Nitrate (9–221 mg/L) remained surpassed the WHO's recommended limit (>45 mg/L) in 34% samples. The piper diagram results specified that 75% of the samples fall in Mixed CaMgCl type. The correlation of nitrate results showed that groundwater of the region degraded by agricultural and industrial activities. The Nitrate Pollution Index (NPI) results of samples revealed significant pollution class, n = 18 (19%) and very significant pollution class, n = 26 (28%) in the study region. Its spatial distribution covered an area of 456.3 km2 in the risk zone with more than permissible nitrate. Among the shallow aquifers, about 16% of whole samples were in the high risk and 9% in very high-risk. Similarly, about 6% samples from deep aquifers were also in the category of high risk. The Water Quality Index (WQI) of groundwater samples indicateed 39% as good, 48% as poor and 9% as very poor to unsuitable. The health risk assessment from intake (HQintake) and skin contact (HQdermal) suggested 64%, 45% and 32% of samples with THI >1 pose hazard for infant, children, and adult population, respectively. The health risks and assessing groundwater quality indicated the necessity of regular groundwater quality monitoring for better long-term health management in this region.

Seasonal nitrate variations, risks, and sources in groundwater under different land use types in a thousand-year-cultivated region, northwestern China

The global public health concern of nitrate (NO3−) contamination in groundwater is particularly pronounced in irrigated agricultural regions. This paper aims to analyze the spatial distribution of groundwater NO3−, assess potential health risks for local residents, and quantitatively identify nitrate sources during different seasons and land use types in the Jinghuiqu Irrigation District, a region in northwestern China with a longstanding agricultural history. The investigation utilizes hydrochemical parameters, dual isotopic data, and the Bayesian stable isotope mixing model (MixSIAR). The findings underscore significant seasonal variations in the average concentrations of NO3−, with values of 87.72 mg/L and 101.87 mg/L during the wet and dry seasons, respectively. Furthermore, distinct fluctuations in nitrate concentration were observed across different land use types, whereby vegetable lands manifested the maximum concentration. Prolonged exposure to elevated nitrate concentrations may pose potential health risks to residents, especially in the dry season when the non-carcinogenic groundwater nitrate risk surges past its wet season counterpart. The MixSIAR analysis revealed that chemical fertilizers accounted for the majority of nitrate pollution in vegetable lands, both during the dry season (49.6%) and wet season (41.2%). In contrast, manure and sewage contributed significantly to NO3−concentrations in residential land during the wet (74.9%) and dry seasons (67.6%). For croplands, soil nitrogen emerged as a dominant source during the wet season (42.2%), while chemical fertilizers prevailed in the dry season (38.7%). In addition to source variations, the nitrate concentration of groundwater is further affected by hydrogeological conditions, with more permeable aquifers tending to display higher nitrate concentrations. Thus, targeted measures were proposed to modify or impede the nitrogen migration pathway, taking into consideration hydrogeological conditions and incorporating domestic sewage, organic fertilizer, and agricultural management practices.

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.

Nitrate concentrations tracking from multi-aquifer groundwater vulnerability zones: Insight from machine learning and spatial mapping

Nitrate contamination in groundwater is a significant environmental concern that poses risks to human health and ecosystems. Several goals and targets of Sustainable Development Goals (SDGs) are related to water quality, pollution, and sustainable management of water resources, which can encompass nitrate contamination. This study conducted real fieldwork of groundwater samples at several locations in Al-Hassa, Saudi Arabia. Subsequently, experimental based on chromatography (IC) and inductively coupled plasma mass spectrometry (ICP-MS) to analyze several groundwater hydro-geochemical elements. The study aimed to employ spatial mapping and advanced standalone optimization learning, including Elman Neural Network (ELNN), Gaussian Process Regression (GPR) models as nonparametric kernel-based probabilistic, and Random Forests (RFs) for tracking and modelling the nitrate (NO3) (mg/L) concentration. The outcomes were validated using several performance indicators and 2D-graphical methods. The resultant NO3 concentration in Al-Hassa was 77.9 mg/L, and the lowest was 9.8 mg/L. Despite marginal accuracy being obtained for most model combinations, GPR-C2 proved merit and reliable for modelling NO3 concentration with Wolffman Index (WI)=0.99 and PBAIS=−0.0001. The finding indicated that Al-Hassa regions are highly prone to NO3 pollution, further confirmed by spatial mapping. The outcomes provide insight into crucial information and decision-making for groundwater pollution risk at Al-Hassa, Saudi Arabia.

Hydrogeochemical characterization and non-carcinogenic health risk assessment of fluoride and nitrate-affected groundwater in northern parts of Tumkur district, Karnataka, India

Groundwater contamination from geogenic and anthropogenic sources is a significant concern for the public health across the globe. In India, fluoride and nitrate contamination are the most prevalent contaminants in the groundwater. This study evaluated groundwater quality in four over-exploited sub-districts of Tumkur district in Karnataka by collecting 143 samples from post and pre-monsoon seasons and using different hydrogeochemical, statistical and bivariate graphical approaches. Comparison with Drinking Water Standard guidelines revealed elevated levels of fluoride, nitrate, and total dissolved solids (TDS), rendering the groundwater unsuitable for drinking. According to Chadha’s diagram, the predominant groundwater type is Na-Cl, and Gibbs diagram suggested the influence of rock dissolution and weathering. Bivariate plots indicated that hydrogeochemical characteristics were primarily influenced by silicate weathering of minerals, cation ion exchange processes, and anthropogenic factors. A non-carcinogenic health risk assessment was conducted using two different hazard index (HI) approaches from United States Environmental Protection Agency (USEPA) and Agency for Toxic Substances and Disease Registry (ATSDR). It was found that health risk associated with fluoride is more significant than the health risk from nitrate, with children being the most affected, followed by adolescents and adults. A holistic approach to assess cumulative health risks from fluoride and nitrate contamination in groundwater, as demonstrated in this study, promotes the synergistic advancement of SDG 3: Good health and well-being and SDG 6: Clean water and sanitation.

Combining artificial neural networks and genetic algorithms to model nitrate contamination in groundwater

Combining artificial neural networks and genetic algorithms to model nitrate contamination in groundwater

Genome-Resolved Metagenomics and Denitrifying Strain Isolation Reveal New Insights into Microbial Denitrification in the Deep Vadose Zone.

The heavy use of nitrogen fertilizer in intensive agricultural areas often leads to nitrate accumulation in subsurface soil and nitrate contamination in groundwater, which poses a serious risk to public health. Denitrifying microorganisms in the subsoil convert nitrate to gaseous forms of nitrogen, thereby mitigating the leaching of nitrate into groundwater. Here, we investigated denitrifying microorganisms in the deep vadose zone of a typical intensive agricultural area in China through microcosm enrichment, genome-resolved metagenomic analysis, and denitrifying bacteria isolation. A total of 1000 metagenome-assembled genomes (MAGs) were reconstructed, resulting in 98 high-quality, dereplicated MAGs that contained denitrification genes. Among them, 32 MAGs could not be taxonomically classified at the genus or species level, indicating that a broader spectrum of taxonomic groups is involved in subsoil denitrification than previously recognized. A denitrifier isolate library was constructed by using a strategy combining high-throughput and conventional cultivation techniques. Assessment of the denitrification characteristics of both the MAGs and isolates demonstrated the dominance of truncated denitrification. Functional screening revealed the highest denitrification activity in two complete denitrifiers belonging to the genus Pseudomonas. These findings greatly expand the current knowledge of the composition and function of denitrifying microorganisms in subsoils. The constructed isolate library provided the first pool of subsoil-denitrifying microorganisms that could facilitate the development of microbe-based technologies for nitrate attenuation in groundwater.

Assessing nitrate contamination in groundwater for public supply: A study in a small Brazilian town

Monitoring groundwater quality is essential for drinking water, avoiding risks to human health, and making it possible to identify and prevent environmental contamination. In Tupã, west of São Paulo-Brazil, the drinking water supply is carried out exclusively by underground water through the public service or alternative solutions using private tubular wells. In this context, this study evaluated the quality of drinking water from 25 private tubular wells in all areas of Tupã. Of these wells evaluated, 12% were contaminated with E. coli and 44% with total coliforms, indicating that the sanitary quality of the water is inadequate and may be directly associated with waterborne diarrheal diseases. The results of the physical-chemical analyses referring to water potability parameters, such as apparent color, turbidity, total dissolved solids, hardness, iron, ammonia, nitrite, chloride, and fluorine, met the requirements of Brazilian legislation. However, all samples showed NO3− contamination, whose concentrations ranged from 1.9 to 23.2 mg L−1NO3−-N, where 32% of the wells exceeded the maximum allowable limit of 10 mg L−1NO3−-N. The consumption of water contaminated with high concentrations of NO3− can cause health risks, especially to children due to their low body weight, causing methemoglobinemia or blue baby syndrome. In the study of the evolution of urban growth, the city's central area exhibited the most significant NO3− contamination because it is an older area with leakage problems and insufficient sewage system maintenance. The non-carcinogenic health risk associated with NO3− contamination was assessed using the Environmental Protection Agency (USEPA) methodology applied to oral ingestion and dermal contact in children and adults. The results revealed negligible risks from dermal contact. However, the assessment highlighted the susceptibility of children to nitrate contamination through oral ingestion, mainly from water from wells in the city's central area. This study emphasizes the importance of monitoring groundwater in Tupã, identifies potential sources of contamination, and provides information to improve water resources management. Implementing appropriate measures based on these findings can mitigate waterborne diseases, safeguard consumer health, and protect the environment.

Balancing food security and environmental safety: rethinking modern agricultural practices

Agriculture has played an important role in human life, both for sustaining life and livelihood. The population explosion has necessitated huge agricultural production. Consequently, there has been modernisation of agriculture not only in farming practices, but also in introducing improved agricultural implements, irrigation, chemical fertilisers, synthetic pesticides, and high-yielding seeds. Agricultural intensification and monoculture make it possible to increase crop production, to a large extent gaining food security, but paying no or little attention to environmental well-being. Intensive tillage leads to soil erosion, nutrient loss, and soil organic carbon loss, which affects the soil biota. Extraction of underground water for irrigation causes groundwater levels to drop and hinders aquifer recharge. Monoculture and the cultivation of high-yielding crops lead to the loss of many indigenous crop varieties and the prevalence of pests and pathogens. Extensive chemical fertiliser application can cause soil acidification, eutrophication, and nitrate contamination in groundwater through leaching. Indiscriminate use of pesticides is a potential threat for non-target organisms, including humans. The agriculture sector contributes a considerable portion of greenhouse gases to the atmosphere. Therefore, the only way to protect our mother earth and create a healthy environment is through sustainable agriculture to ensure food safety and security.

An Integrated Framework to Assess the Environmental and Economic Impact of Fertilizer Restrictions in a Nitrate-Contaminated Aquifer

Groundwater nitrate contamination caused by the excessive use of nitrogen-based fertilizers has been widely recognized as an issue of significant concern in numerous rural areas worldwide. To mitigate nitrate contamination, corrective management practices, such as regulations on fertilizer usage, should be implemented. However, these measures often entail economic consequences that impact farmers’ income, and thus should be properly assessed. Within this context, an integrated framework combining the environmental and economic assessment of fertilization restrictions through multi-criteria decision analysis is presented in an effort to efficiently manage groundwater nitrate contamination in rural areas. For this task, various scenarios involving reductions (10%, 20%, 30%, 40% and 50%) in fertilizer application were investigated, evaluated and ranked in order to determine the most suitable option. The environmental assessment considered occurrences of nitrates in groundwater, with a specific emphasis on nitrate concentrations in water-supply wells, as obtained by a nitrate fate and transport model, while the economic analysis focused on the losses experienced by farmers due to the reduced fertilizer usage. Our case-study implementation showed that a 30% reduction in fertilization is the most appropriate option for the area being studied, highlighting the importance of adopting such an approach when confronted with conflicting outcomes among alternatives.

Nitrate Contamination of Groundwater in Selected Industrial and Non Industrial Sites, Coimbatore District, Tamil Nadu: Exposure and Health Risk Assessment

Groundwater resources are essential for sustaining human health, agricultural productivity, and industrial growth. In recent years, anthropogenic influences have caused a sharp decline in ground water quality, which is also having an impact on human health in many parts of India. It is crucial to analyze the risk of contamination to human health and the quality of the water supply. Coimbatore is one of the rapidly growing industrial areas in South India. The industrial areas of ground water have a significant impact on ground water quality due to anthropogenic activities such as discharge of Industrial waste, chemicals and pollutants into the ground which make water unsuitable for human and industrial use. Nitrate is the emerging contaminant which can cause a deadly disease methehemoglobinemia. Hence the present study is focused to analyze the ground water of selected industrial and non industrial sites of Coimbatore city. Nitrate concentration ranged from 32.90 to 88.13 mg/l in the samples industrial and non-industrial sites, and over 37% of both the sites had nitrate levels that above the Bureau of Indian Standards’ and WHO’s acceptable limits (45 mg/l and 50 mg/l, respectively). The USEPA human health risk assessment tool was used to examine the potential health hazards of increased nitrate intake for both adults and children.

Sampling methods may drive short-term groundwater nitrate variability in an irrigated watershed connected to a coastal lagoon (Campo de Cartagena-Mar Menor, SE Spain)

This study highlights concerns regarding the reliability of groundwater nitrate data used in official surveys, such as within the EU-mandated Water Framework Directive (WFD). The focus is on the Campo de Cartagena - Mar Menor hydrosystem in Spain, a region known for its intensively irrigated watershed and eutrophicated lagoon, where monitoring the evolution of nitrate contamination in surface and groundwater is crucial but challenging due to the risk of inconsistent characterization leading to erratic remediation measures. The study employed an experimental approach in private wells that belong to a longstanding official nitrate survey network marked by irregular sampling practices. Importantly, these wells lacked comprehensive design documentation and were frequently used by farmers. The study aimed to evaluate the representativity of dissolved nitrate measurements in such an emblematic case, while investigating the source of the water using geochemical and isotope tracers. This assessment considered the effects of different sampling techniques (bailer or pumping) and sampling parameters (depth and time), acknowledging actual practices. The research highlights several key findings. Firstly, the bailer sampling method proved to account for a substantial portion of the observed variation in nitrate content. Secondly, in some cases, pumping introduced contributions from different water horizons, complicating the interpretation of nitrate data. Thirdly, alterations in the sampling protocol had a notable impact on the resulting nitrate measurements. Furthermore, the study emphasized a critical issue: the lack of analytical uncertainty estimation in official surveys introduces significant bias in result interpretation, with discrepancies exceeding 100 mg/L in four of the six wells analyzed. This underscores the pressing need for improved sampling protocols, dedicated borehole infrastructure and precise data interpretation. Given the potential unreliability of some official groundwater nitrate data shared under EU or other regulations, with corresponding economic and environmental impacts, the study recommends meticulous verification before transmitting data.