Nitrate Concentrations In Shallow Groundwater Research Articles

Identification of high nitrate concentration in shallow groundwater of an arid region: a case study of South Kuwait's Bay.

Coastal aquifer is a fragile environment due to the interaction of groundwater with seawater, especially in arid environments. Groundwater along Kuwait's Bay is polluted due to discharge of waste from desalination plants, power plants, and other anthropogenic activities. Earlier studies on submarine groundwater discharge in Kuwait's Bay region have reported the transfer of nutrient flux from the groundwater to Kuwait's Bay. The current study focused on nitrate sources and processes governing their distribution in groundwater samples collected from the southern part of Kuwait's Bay. The concentration of nitrate in the samples ranged from 22.7 to 803.9mg/L. Higher values were noted in the samples collected inland and a few samples adjacent to the Bay. Spearman's correlation analysis of the data indicated that NO3- has a strong positive correlation with SO42- and moderate positive correlation with Na + , TDS/EC. The PCA analysis and factor scores revealed the different sources for groundwater nitrate contamination as follows: leakage of sewer lines in the urban region has led to the infiltration of contaminated sewage, high saline environment due to seawater intrusion, chemical weathering, and influence of denitrifying bacteria. The health risk has resulted due to the NO3- concentration being above the standard limit for adults. Furthermore, the nitrate concentration was higher in the region adjoining the landfills. In addition, the discharge of groundwater with higher nitrate to the adjacent open water in the Bay may lead to eutrophication. Hence, proper management strategies are to be adopted to control the nitrate pollution in groundwater.

Influence of redox gradients on nitrate transport from the landscape to groundwater and streams

Increases in nitrogen applications to the land surface since the 1950s have led to a cascade of negative environmental impacts, including degradation of drinking water supplies, nutrient enrichment of aquatic ecosystems and contributions to global climate change. In this study, groundwater, streambed porewater, and stream sampling were used to establish trends in nitrate concentrations and how redox gradients influence nitrate transport across diverse glacial terranes. Decadal sampling has found that elevated nitrate concentrations in shallow groundwater beneath cropland have been sustained for decades. Redox gradients established in the saturated zone using dissolved O2, iron, nitrate and excess N2 from denitrification suggest that nitrate-bearing zones are thin in glacial terranes dominated by fine materials. These thin nitrate-bearing zones lead to suboxic, low nitrate streambed porewater and limit the contributions of nitrate to streams from slow-flow groundwater. In contrast, thick oxic zones in more coarse-grained glacial terranes allow nitrate to reach deeper groundwater, resulting in streambed porewater with elevated nitrate concentrations and causing a large portion of stream nitrate to be derived from slow-flow groundwater. Groundwater age tracer data indicate that denitrification occurs more quickly in the terrane dominated by fine material than in the more coarse-grained terrane. The quicker depletion of nitrate in the more fine-grained terrane suggests that the thinner oxic zone in this terrane is due, in part, to the greater availability and reactivity of electron donors in this terrane than in the more coarse-grained terrane. Groundwater age tracer data and hydrograph separation analysis suggest that saturated zone lag times between when changes in land use practices occur and when changes in stream water are fully observed may vary widely across hydrogeologic settings.

Electrical conductivity and dissolved oxygen as predictors of nitrate concentrations in shallow groundwater in Erhai Lake region

Elevated nitrogen (N) concentration in shallow groundwater is becoming increasingly problematic, putting water resources under pressure. For more effective management of such a resource, more precise predictors of N level in groundwater using smart monitoring networks are needed. However, external factors such as land use type, rainfall, and N loads from multiple sources (residential and agricultural) make it difficult to accurately predict the spatial and temporal variations of N concentration. In order to identify the key factors affecting spatial and temporal N concentration in shallow groundwater and develop a predictive model, 635 groundwater samples from drinking wells in residential areas and agricultural wells in croplands of a typical agricultural watershed in the Erhai Lake Basin, southwest China, in the period from 2018 to 2020, were collected and analyzed. The results showed that the type of land use and seasonal variations significantly affected the N forms and their concentrations in the shallow groundwater, as the ratios of ON and NO3−-N to TN were 30%–39% and 52%–59% for the two land uses and 25%–44% and 46%–66% for seasonal changes. Their variations were reflected by electrical conductivity (EC) and redox environment. EC and dissolved oxygen (DO) had a positive non-linear relationship with the concentrations of total nitrogen (TN) and nitrate (NO3−-N). The fitted non-linear quantitative models were established separately to predict TN and NO3−-N concentrations in groundwater using easily available indictors (EC and DO). The high accuracy and performance of the models were investigated and approved by rRMSE, MAE, and 1:1 line. These findings can provide technical support for the rapid prediction and evaluation of N pollution in shallow groundwater through easily available indicators.

Monitoring of nitrate contamination in groundwater: case study of the campus of UNESP, Rio Claro/SP

This study presents the results of the monitoring of nitrate concentrations in shallow groundwater at the UNESP Campus of Rio Claro/SP assumed to be sourced by septic tank leakage, which were discontinued in October 2014. The distribution of nitrate concentrations provides support to a conceptual model of contamination by multiple sources, since the concentration gradients are not observed along the flowpaths. The results of the monitoring indicate that in some monitored wells, the nitrate concentrations remain stable, while in other wells minor to strong fall trends were observed. These results provide support to the presence of other active sources, such as sewage leakage in the external and internal area of the campus. This scenario perfect fit with the maintenance of recorded high nitrate concentrations over the time. Despite the nitrate concentrations are below potability limit, additional investigations will be conducted to identify sources of contamination to ensure water quality in the future.

Distribution of Nitrate Household Waste and Groundwater Flow Direction around Code River, Yogyakarta, Indonesia

The nitrate concentrations in shallow groundwater of the Yogyakarta City and its surroundings has increased to about twenty times in the period 1985-2018. The objective of this study was to analyse the distribution of nitrate concentrations in water well around the Code River, Yogyakarta. Flownets mapping was performed to find out the distribution and direction of potential groundwater pollution. Nitrate concentration was analysed by taking 18 groundwater samples scattered in the upstream, midstream and downstream areas of the Code River. The results of this study indicate that nitrate concentrations in the water well of upstream and downstream areas could still be used as a source of drinking water and recreation-irrigation-livestock. Meanwhile, the nitrate concentration in water well of the midstream area of the Code River, Yogyakarta City, mostly (80% of the sample) did not meet all classes of water quality standards. Human activities in the densely populated settlements were the main factors that influence nitrate pollution. Furthermore, groundwater flow in the study area leads from north to south and towards the Code River. This condition indicates that the nitrate concentrations in the groundwater can be a source of a pollutant for the Code River.

A statistical learning framework for groundwater nitrate models of the Central Valley, California, USA

Summary We used a statistical learning framework to evaluate the ability of three machine-learning methods to predict nitrate concentration in shallow groundwater of the Central Valley, California: boosted regression trees (BRT), artificial neural networks (ANN), and Bayesian networks (BN). Machine learning methods can learn complex patterns in the data but because of overfitting may not generalize well to new data. The statistical learning framework involves cross-validation (CV) training and testing data and a separate hold-out data set for model evaluation, with the goal of optimizing predictive performance by controlling for model overfit. The order of prediction performance according to both CV testing R2 and that for the hold-out data set was BRT > BN > ANN. For each method we identified two models based on CV testing results: that with maximum testing R2 and a version with R2 within one standard error of the maximum (the 1SE model). The former yielded CV training R2 values of 0.94–1.0. Cross-validation testing R2 values indicate predictive performance, and these were 0.22–0.39 for the maximum R2 models and 0.19–0.36 for the 1SE models. Evaluation with hold-out data suggested that the 1SE BRT and ANN models predicted better for an independent data set compared with the maximum R2 versions, which is relevant to extrapolation by mapping. Scatterplots of predicted vs. observed hold-out data obtained for final models helped identify prediction bias, which was fairly pronounced for ANN and BN. Lastly, the models were compared with multiple linear regression (MLR) and a previous random forest regression (RFR) model. Whereas BRT results were comparable to RFR, MLR had low hold-out R2 (0.07) and explained less than half the variation in the training data. Spatial patterns of predictions by the final, 1SE BRT model agreed reasonably well with previously observed patterns of nitrate occurrence in groundwater of the Central Valley.

Nitrate in shallow groundwater in typical agricultural and forest ecosystems in China, 2004–2010

The nitrate-nitrogen (NO3−-N) concentrations from shallow groundwater wells situated in 29 of the Chinese Ecosystem Research Network field stations, representing typical agro- and forest ecosystems, were assessed using monitoring data collected between 2004 and 2010. Results from this assessment permit a national scale assessment of nitrate concentrations in shallow groundwater, and allow linkages between nitrate concentrations in groundwater and broad land use categories to be made. Results indicated that most of the NO3−-N concentrations in groundwater from the agro- and forest ecosystems were below the Class 3 drinking water standard stated in the Chinese National Standard: Quality Standard for Ground Water (≤ 20 mg/L). Over the study period, the average NO3−-N concentrations were significantly higher in agro-ecosystems (4.1 ± 0.33 mg/L) than in forest ecosystems (0.5 ± 0.04 mg/L). NO3−-N concentrations were relatively higher (> 10 mg N/L) in 10 of the 43 wells sampled in the agricultural ecosystems. These elevated concentrations occurred mainly in the Ansai, Yucheng, Linze, Fukang, Akesu, and Cele field sites, which were located in arid and semi-arid areas where irrigation rates are high. We suggest that improvements in N fertilizer application and irrigation management practices in the arid and semi-arid agricultural ecosystems of China are the key to managing groundwater nitrate concentrations.

Denitrifying bacteria and hydrogeochemistry in a natural wetland adjacent to farmlands in Chiba, Japan

AbstractThis study combined bacterial incubation and hydrogeochemical methods to investigate denitrification in the surface water, top soil (0–20 cm), and shallow groundwater of the Ochi wetland in Japan. Surface water was rich in nitrate (40 mg/l) and denitrifying bacteria (700 per ml). Three functional zones in the wetland were identified in the top soil and shallow groundwater. In the upstream portion of the wetland (Zone I), the counts of denitrifying bacteria in top soil increased from 5200 to 14 970 per ml and nitrate decreased from 25·4 to 1·8 mg/l. Organic carbon concentrations decreased as sulfate increased from 4·0 to 9·6 mg/l in this zone. In the middle‐stream of the wetland (Zone II), all concentrations of major anions, iron, organic carbon, and total nitrogen content in top soil were relatively constant, but the counts of denitrifying bacteria increased up to 70 200 per ml. In the downstream portion of the wetland (Zone III), complete removal of nitrate resulted in sharp reduction of counts of denitrifying bacteria. Correspondingly, dissolved oxygen (DO), organic carbon, and total nitrogen increased in this zone. Counts of denitrifying bacteria were lower in shallow groundwater than in top soil; nitrate concentrations in shallow groundwater were also very low in this zone. DO and the oxidation/reduction potential data suggest that groundwater flows to the surface along an extended flow path, thus providing nitrate for the denitrifying community. Copyright © 2011 John Wiley & Sons, Ltd.

Multiscale Effects of Management, Environmental Conditions, and Land Use on Nitrate Leaching in Dairy Farms

Nitrate leaching in intensive grassland- and silage maize-based dairy farming systems on sandy soil is a main environmental concern. Here, statistical relationships are presented between management practices and environmental conditions and nitrate concentration in shallow groundwater (0.8 m depth) at farm, field, and point scales in The Netherlands, based on data collected in a participatory approach over a 7-yr period at one experimental and eight pilot commercial dairy farms on sandy soil. Farm milk production ranged from 10 to 24 Mg ha(-1). Soil and hydrological characteristics were derived from surveys and weather conditions from meteorological stations. Statistical analyses were performed with multiple regression models. Mean nitrate concentration at farm scale decreased from 79 mg L(-1) in 1999 to 63 in 2006, with average nitrate concentration in groundwater decreasing under grassland but increasing under maize land over the monitoring period. The effects of management practices on nitrate concentration varied with spatial scale. At farm scale, nitrogen surplus, grazing intensity, and the relative areas of grassland and maize land significantly contributed to explaining the variance in nitrate concentration in groundwater. Mean nitrate concentration was negatively correlated to the concentration of dissolved organic carbon in the shallow groundwater. At field scale, management practices and soil, hydrological, and climatic conditions significantly contributed to explaining the variance in nitrate concentration in groundwater under grassland and maize land. We conclude that, on these intensive dairy farms, additional measures are needed to comply with the European Union water quality standard in groundwater of 50 mg nitrate L(-1). The most promising measures are omitting fertilization of catch crops and reducing fertilization levels of first-year maize in the rotation.

Weather-induced temporal variations in nitrate concentrations in shallow groundwater

Summary For the evaluation of policy action programs to improve groundwater quality, research institutes and governments intensively monitor nitrate concentrations in shallow or near surface groundwater. However, trend detection is often hampered by the large seasonal and multi-annual temporal variability in nitrate concentrations, especially in shallow groundwater within 0–5 m below the surface in relatively humid regions. This variability is mainly caused by variations in precipitation excess (precipitation minus evapotranspiration) that results in strong variability in groundwater recharge. The objective of this study was to understand and quantify this weather-induced variability in shallow groundwater nitrate concentrations. We present an example of measured weather related variations in shallow groundwater nitrate concentrations from De Marke, an intensively monitored experimental farm in The Netherlands. For the quantification of the weather-induced variability, concentration-indices were calculated using a 1D model for water and solute transport. The results indicate that nitrate concentrations in the upper meter of groundwater at De Marke vary between 55% and 153% of the average concentration due to meteorological variability. The concentration-index quantification method was successfully used to distinguish weather related variability from human-induced trends in the nitrate concentration monitoring data from De Marke. Our model simulations also shows that sampling from fixed monitoring wells produces less short term variability than measuring from open boreholes. In addition, using larger screen depths and longer screens filters out short term temporal variability at the cost of a more delayed detection of trends in groundwater quality.

Stochastic uncertainties and sensitivities of a regional-scale transport model of nitrate in groundwater

Groundwater quality management relies more and more on models in recent years. These models are used to predict the risk of groundwater contamination for various land uses. This paper presents an assessment of uncertainties and sensitivities to input parameters for a regional model. The model had been set up to improve and facilitate the decision-making process between stakeholders and in a groundwater quality conflict. The stochastic uncertainty and sensitivity analysis comprised a Monte Carlo simulation technique in combination with a Latin hypercube sampling procedure. The uncertainty of the calculated concentrations of nitrate leached into groundwater was assessed for the various combinations of land use, soil type, and depth of the groundwater table in a vulnerable, sandy region in The Netherlands. The uncertainties in the shallow groundwater were used to assess the uncertainty of the nitrate concentration in the abstracted groundwater. The confidence intervals of the calculated nitrate concentrations in shallow groundwater for agricultural land use functions did not overlap with those of non-agricultural land use such as nature, indicating significantly different nitrate leaching in these areas. The model results were sensitive for almost all input parameters analyzed. However, the NSS is considered pretty robust because no shifts in uncertainty between factors occurred between factors towards systematic changes in fertilizer and manure inputs of the scenarios. In view of these results, there is no need to collect more data to allow science based decision-making in this planning process. © 2008 Elsevier B.V. All rights reserved.

Numerical simulation of a fine-grained denitrification layer for removing septic system nitrate from shallow groundwater

One of the most common methods to dispose of domestic wastewater involves the release of septic effluent from drains located in the unsaturated zone. Nitrogen from such systems is currently of concern because of nitrate contamination of drinking water supplies and eutrophication of coastal waters. It has been proposed that adding labile carbon sources to septic distribution fields could enhance heterotrophic denitrification and thus reduce nitrate concentrations in shallow groundwater. In this study, a numerical model which solves for variably saturated flow and reactive transport of multiple species is employed to investigate the performance of a drain field design that incorporates a fine-grained denitrification layer. The hydrogeological scenario simulated is an unconfined sand aquifer. The model results suggest that the denitrification layer, supplemented with labile organic carbon, may be an effective means to eliminate nitrogen loading to shallow groundwater. It is also shown that in noncalcareous aquifers, the denitrification reaction may provide sufficient buffering capacity to maintain near neutral pH conditions beneath and down gradient of the drain field. Leaching of excess dissolved organic carbon (DOC) from the denitrification layer is problematic, and causes an anaerobic plume to develop in simulations where the water table is less than 5–6 m below ground surface; this anaerobic plume may lead to other down gradient changes in groundwater quality. A drain field and denitrification layer of smaller dimensions is shown to be just as effective for reducing nitrate, but has the benefit of reducing the excess DOC leached from the layer. This configuration will minimize the impact of wastewater disposal in areas where the water table is as shallow as 3.5 m.

Nitrogen monitoring in groundwater in the sandy regions of the Netherlands

The Nitrate Directive of the European Communities sets goals for preventing pollution and reducing existing nitrate concentrations in groundwater. Establishment of an action program is one of the obligations Member States have, to ensure the reduction of nitrate leaching and runoff. The effectiveness of the action program by Member States must be determined by regular monitoring of such items as groundwater quality. The study documented here regarding the Dutch effort within this action program, was aimed at quantifying both the nitrate concentration in shallow groundwater of the sandy regions of the Netherlands and the land area where the EC limit value is exceeded. Since shallow groundwater quality is influenced by variation in precipitation, nitrate concentrations were adjusted to be representative for average precipitation. Using monitoring results and geographical information, we calculated that the EC limit value (LV) of 50 mg l −1 for nitrate in groundwater was exceeded in 77–85% of the land area in the Netherlands' sandy regions. The LV was found to be exceeded in a calculated agricultural area of 890,000–940,000 ha (94–99% of total agricultural area), and a forest and heath area of 60,000–86,000 ha (21–30% of total forest and heath areas).

Nitrate in Groundwater and Water Sources used by Riparian Trees in an Agricultural Watershed: A Chemical and Isotopic Investigation in Southern Minnesota

This study evaluates processes that affect nitrate concentrations in groundwater beneath riparian zones in an agricultural watershed. Nitrate pathways in the upper 2 m of groundwater were investigated beneath wooded and grass‐shrub riparian zones next to cultivated fields. Because trees can be important components of the overall nitrate pathway in wooded riparian zones, water sources used by riparian trees and possible effects of trees on nitrate concentrations in groundwater were also investigated. Average nitrate concentrations in shallow groundwater beneath the cultivated fields were 5.5 mg/L upgradient of the wooded riparian zone and 3.5 mg/L upgradient of the grass‐shrub zone. Shallow groundwater beneath the fields passed through the riparian zones and discharged into streams that had average nitrate concentrations of 8.5 mg/L (as N). Lateral variations of δD values in groundwater showed that mixing among different water sources occurred beneath the riparian zones. In the wooded riparian zone, nitrate concentrations in shallow groundwater were diluted by upwelling, nitrate‐poor, deep groundwater. Upwelling deep groundwater contained ammonium with a δ15N of 5‰ that upon nitrification and mixing with nitrate in shallow groundwater caused nitrate δ15N values in shallow groundwater to decrease by as much as 19.5‰. Stream water penetrated laterally beneath the wooded riparian zone as far as 19 m from the stream's edge and beneath the grass‐shrub zone as far as 27 m from the stream's edge. Nitrate concentrations in shallow groundwater immediately upgradient of where it mixed with stream water averaged 0.4 mg/L in the wooded riparian zone and 0.8 mg/L near the grass‐shrub riparian zone. Nitrate concentrations increased toward the streams because of mixing with nitrate‐rich stream water. Because nitrate concentrations were larger in stream water than shallow groundwater, concentrated nitrate in the streams cannot have come from shallow groundwater at these sites. Water sources of riparian trees were identified by comparing δD values of sap water, soil water, groundwater, and stream water. Soil water was the main water source for trees in the outer 4 to 6 m of one part of the wooded riparian zone and outer 10 m of another part. Groundwater was a significant water source for trees closer to the streams where the water table was less than about 2.1 to 2.7 m below the surface. No evidence was found in the nitrate concentration profiles that trees close to the streams that took up groundwater through their roots also took up nitrate from groundwater. The lack of such evidence is attributed to the nitrate concentration profiles being insufficiently sensitive indicators of nitrate removal by trees.

NITRATE TRANSPORT ON A SANDY COASTAL PLAIN SOIL UNDERLAIN BY PLINTHITE

ABSTRACT Transport of nitrate (NO3-N) by surface runoff, shallow subsurface flow, and leaching during 1988-89 was determined on a sandy Coastal Plain soil having plinthic subsoil materials. The study was conducted on a small (0.34 ha) instrumented watershed. Nitrate concentrations were measured in surface runoff, shallow subsurface flow, soil samples collected from the upper 30 cm of the root zone, and water samples collected from shallow and deep wells. The study showed that most of the NO3-N leached from the upper 30 cm of the root zone within 1.5 months after N application, given a total rainfall of 200 mm or more. Surface runoff NO3-N concentrations and loads were small, with monthly loads not exceeding 0.3 kg/ha. Nitrate concentrations in shallow groundwater (0.9 to 1.8 m) during the sweet com growing season reflected applied N, with values ranging from 11 to 19 mg/L. Applied N was also reflected in shallow subsurface flow during the spring months. Mean NO3-N concentrations in subsurface flow ranged from 3.9 to 14.1 mg/L, while monthly loads ranged from 0.1 to 9.2 kg/ha. The study indicated that some NO3-N is being lost by vertical water movement in plinthic Coastal Plain soils towards deeper groundwater, and that this loss pathway should be of environmental concem.

Seventy five years of arthritis research at the Strangeways Research Laboratory: 1912-87.

<h3>ABSTRACT:</h3> Nitrate contamination of shallow groundwater has been widely documented in association with agriculture in the Coastal Plain region of the Chesapeake Bay watershed. Elevated groundwater nitrate levels limit the use of shallow groundwater for human consumption and also result in elevated nonpoint source nitrogen (N) loads to Chesapeake Bay via elevated stream base-flow nitrate concentrations. This study investigated the effects of cereal grain winter cover crops on nitrate leaching rates, profile nitrate storage, and nitrate concentrations in shallow groundwater in two field-scale watersheds planted continuously in corn (Zea mays L) from 1984 through 1996. Winter-fallow conditions were maintained following the 1984 through 1987 growing seasons and cereal rye (Secale cereale L.) as a cover crop was planted immediately after grain harvest from 1988 through 1996. Cover crop effects on nitrate leaching rates also were evaluated in continuous no-till corn plots from 1990 through 1995. Nitrate leaching losses from the root zone and recharge of ‘shallow aquifers occurred primarily during winter months under conditions of law evapotranspiration’. The potential for nitrate leaching losses was determined primarily by the availability of nitrate in the root zone at the onset of the winter groundwater recharge period. Rye winter cover crops planted after corn harvest consistently reduced nitrate-N concentrations in root zone leachate to less than 1 mg/L during most of the groundwater recharge period, and reduced annual nitrate leaching losses by approximately 80% relative to winter-fallow treatments. Shallow groundwater nitrate-N concentrations under long-term continuous corn production decreased from the 10 to 20 mg/L range to less than 5 mg/L after seven years of cover crop use. Cover crops appeared to increase corn yields under adverse growing season conditions, but limited residual nitrate availability during the growing season relative to winter-fallow settings. Cover crop growth was generally N limited, suggesting that increased N inputs would have little effect on nitrate leaching, but would increase cover crop contributions to soil carbon pools.