Nitrate In Shallow Groundwater Research Articles

Sources and Transformation of Nitrate in Shallow Groundwater in the Three Gorges Reservoir Area: Hydrogeochemistry and Isotopes

Nitrate is among the most widely occurring contaminants in groundwater on a global scale, posing a serious threat to drinking water supplies. With the advancement of urbanization and mountainous agriculture, the nitrate in the groundwater of Wanzhou District in the Three Gorges Reservoir Area has formed a complex combination of pollution sources. To more accurately identify the sources of nitrate in groundwater, this study integrates hydrochemical methods and environmental isotope techniques to analyze the sources and transformation processes in shallow groundwater nitrate under different land-use types. Furthermore, the Bayesian isotope mixing model (MixSAIR) is employed to calculate the contribution rates in various nitrate sources. The results indicate that nitrate is the primary form of inorganic nitrogen in shallow groundwater within the study area, with nitrate concentrations in cultivated groundwater generally higher than those in construction land and forest land. The transformation process of nitrate is predominantly nitrification, with little to no denitrification observed. In cultivated shallow groundwater, nitrate mainly originates from chemical fertilizers (36.3%), sewage and manure (35.4%), and soil organic nitrogen (24.7%); in forested areas, nitrate primarily comes from atmospheric precipitation (35.3%), chemical fertilizers (31.3%), and soil organic nitrogen (22.1%); while in constructed areas, nitrate mainly derives from chemical fertilizers (46.0%) and sewage and manure (32.2%). These results establish a scientific foundation for formulating groundwater pollution control and management strategies in the region and serve as a reference for identifying nitrate sources in groundwater in regions with comparable hydrogeological features and pollution profiles.

Assessing impacts of land use/land cover patterns to shallow groundwater nitrate pollution in an agricultural-dominant area in northwest China using random forest

Assessing impacts of land use/land cover patterns to shallow groundwater nitrate pollution in an agricultural-dominant area in northwest China using random forest

Evaluation of nitrate in shallow groundwater at Pasirkoja of Bandung City, Indonesia, using the pollution index and the nitrate pollution index methods

Pasirkoja is an old residential area in Bandung City currently densely populated. Some people in Pasirkoja use shallow groundwater for washing and bathing, and some for cooking. Pollutants very easily pollute shallow groundwater, and nitrate is one of the pollutants found in shallow groundwater in residential areas. The water quality status was determined using the pollution index (PI) method based on a Decree of the Minister of Environment Number 115 of 2003 and the nitrate pollution index (NPI) to ascertain the shallow groundwater quality in Pasirkoja of Bandung City, Indonesia. The variables used in the PI method were pH, turbidity, total dissolved solids (TDS), nitrate, and nitrite, while the NPI method used the nitrate parameter. Shallow groundwater samples were taken during the rainy season and dry season. Based on the PI method, the results showed that the quality status of shallow groundwater at the research location is mostly lightly polluted in the rainy and dry seasons. Meanwhile, based on the NPI method, most are clean (not polluted). Differences in the quality status of shallow groundwater depend on the environmental conditions around which shallow groundwater samples were taken. The research results also showed that, based on the PI method, nitrate is not the main parameter that determines pollution at the research location.

Identification of critical effect factors for prediction of spatial and intra-annual variability of shallow groundwater nitrate in agricultural areas

Shallow groundwater nitrate nitrogen (NO3−-N) concentrations in agricultural areas usually show high spatial and intra-annual variability. It is hard to predict such concentrations due to the complexity of influencing factors (e.g., different forms of N in soil, vadose zone characteristics, and groundwater physiochemical conditions). Here, a large number of groundwater and soil samples were collected monthly over two years at 14 sites to analyze the soil and groundwater physiochemical properties and the stable isotopes of δ15N and δ18O of groundwater NO3−-N in agricultural areas. Based on field observations, a random forest (RF) model was used to predict the groundwater NO3−-N concentrations and reveal the importance of effect factors. The results show that there are large spatiotemporal variations in NO3−-N, δ15N-NO3−, and δ18O-NO3− in groundwater. NO3−-N is the major dominant specie of inorganic N in groundwater, and the groundwater NO3−-N concentration in 24 % of the samples failed to meet the drinking water standard of the WHO (10 mg L−1). The RF model satisfactorily predicted groundwater NO3−-N concentrations with R2 of 0.90–0.94, RMSE of 4.54–5.07, and MAE of 2.17–3.38. Groundwater nitrite and ammonium are the most important factors related to NO3−-N consumption and production, respectively, in groundwater. Denitrification and nitrification were further identified by the relationships among δ15N-NO3−, δ18O-NO3−, and NO3−-N, and by the ranges of δ15N-NO3−, δ18O-NO3−, temperature, pH, DO, and ORP in groundwater. Soil-soluble organic nitrogen (S-SON) and the depth of groundwater table were identified as vital factors related to N sourcing and leaching. Overall, as a first approach to adopting a RF model for high spatiotemporal-resolution prediction of groundwater NO3−-N variations, the findings of this study enable a better understanding of groundwater N pollution in agricultural areas. Optimizing management of irrigation and N inputs is anticipated to reduce S-SON accumulation and mitigate the threat to groundwater quality in agricultural areas.

Nitrate in shallow groundwater after more than four decades of manure application

Over-application of manure to agricultural fields can leach nitrogen below the root zone and contaminate groundwater. The goal of this study was to evaluate the factors affecting the spatial and temporal distribution of nitrate in shallow groundwater following 44 years of manure application to irrigated and non-irrigated long-term test plots. Sampling of 26 wells over an 18-month period revealed high spatial variability of groundwater nitrate concentrations, ranging from <0.1 mg-N/L to 1350 mg-N/L (mean = 118 mg-N/L). The highest concentrations were associated with the highest manure nitrogen loads, longer durations of manure application, and were generally located beneath irrigated land use. Regression modeling confirmed that cumulative manure loading had the greatest control on the spatial distribution of groundwater nitrate. A significant decreasing temporal trend was observed in selected wells downgradient of plots where manure application ceased more than a decade earlier. Isotopic analysis of 15N-NO3 and 18O-NO3 showed that denitrification occurred at 16 well locations, with evidence for dissolved organic carbon as the electron donor. The groundwater nitrate trends observed in this long-term study demonstrate that historical nutrient and water management practices will affect groundwater quality for many decades to come.

Isotopic tracing of nitrogen source and interaction between surface water and groundwater of a small valley plain in the Zhangxi watershed

Identifying the mechanism for circulation of nutrient elements in the hydrological cycle is crucial for protection of water resource quality. In this study, 72 surface water and 21 groundwater samples were collected in three seasons for hydrochemical and multiple isotopic (δD-H2O, δ18O–H2O, δ15N–NO3−, and δ18O–NO3−) analysis in the Zhangxi watershed, a small valley plain in the southeastern Yangtze River Delta. The hydrochemical type in surface water and shallow groundwater was Ca–HCO3, and the δD and δ18O isotope values were similar. Thus, the hydraulic connection and its material interaction were similar. Quantitative evaluation of the mass balance model showed that shallow groundwater accounted for more than 90% of surface water in the dry season but only 33.0% in the wet season. On the average, nitrate in shallow groundwater was mainly derived from organic fertilizer, whereas nitrate in surface water was mainly sourced from soil nitrogen and chemical fertilizer carried by surface runoff. At the time scale, the nitrogen sources of surface water showed seasonal variation owing to the interaction between surface water and groundwater. The contribution of organic fertilizer in the wet season was approximately 16.2%, but in the dry season increased to 32.3% and exceeded that of chemical fertilizer (24.6%). Shallow groundwater contributed more to surface water in the dry season, and transferred more nitrogen from organic fertilizer to surface water, so that they had similar nitrate sources. At the space scale, nitrate sources of surface water differed significantly with the land use types. The NO3− and δ15N–NO3− concentrations of the surface water in the mid-valley plain and downstream were significantly higher than in the natural forest area upstream, indicating the increased contribution of organic fertilizer. Agricultural activities and the interaction between surface water and groundwater in the valley plain area have a significant impact on nitrogen pollution. Reduction in nitrogen fertilizer use and establishment of a riparian protection zone are crucial to protect the water resource quality.

Shifts in the sources and fates of nitrate in shallow groundwater caused by agricultural intensification intensity: Revealed by hydrochemistry, stable isotopic composition and source contribution

Groundwater nitrogen (N) pollution in intensive agricultural regions is increasing globally, and understanding the effects of increasing agricultural intensity on the sources and fates of N is critical for the effective control of groundwater pollution. Using multiple stable isotopes (δ15N-NO3—, δ18O-NO3—, δ18O-H2O, δD-H2O), hydrochemistry and the Bayesian stable isotope mixing model, the sources and fates of N were expounded, and their contributions were quantified in shallow groundwater (SG, n = 325) from an intensive agricultural region, a facility agricultural region and a cropland fallow region. We found that NO3— accounted for 60% of total N, and 52% of SG samples exceeded the WHO NO3— drinking water threshold (10 mg N L−1). Each N form concentrations and NO3— exceeding the standard rate in the intensive and facility agricultural regions were significantly higher than those in the cropland fallow region. Soil N, N fertilizer and manure and sewage were the dominant NO3— contributors in the SG of intensive agricultural regions, contributing to 66%, 21% and 10% of NO3—, respectively. The highest contributions of manure and sewage occurred in the cropland fallow region (46%), followed by the soil N (33%) and N fertilizer (13%), while the N sources in the SG from the facility agricultural region were dominated by manure and sewage (35%), soil N (31%) and N fertilizer (25%). Denitrification was the primary N biogeochemical cycle process in SG from the intensive and facility agricultural regions, whereas nitrification mainly occurred in the cropland fallow region. These results indicated that the shifts in the sources and fates of N in SG were controlled by agricultural intensification intensity, and soil N and manure and sewage, rather than N fertilizer, may become the most dominant N sources in SG in intensive agricultural regions. The N contamination control in SG should pay attention to improving septic tanks and sewage pipelines, the scientific and reasonable stacking of manure, and reducing the soil N pool in intensive agricultural regions.

Identification and apportionment of shallow groundwater nitrate pollution in Weining Plain, northwest China, using hydrochemical indices, nitrate stable isotopes, and the new Bayesian stable isotope mixing model (MixSIAR)

Groundwater nitrate (NO3−) pollution is a worldwide environmental problem. Therefore, identification and partitioning of its potential sources are of great importance for effective control of groundwater quality. The current study was carried out to identify the potential sources of groundwater NO3− pollution and determine their apportionment in different land use/land cover (LULC) types in a traditional agricultural area, Weining Plain, in Northwest China. Multiple hydrochemical indices, as well as dual NO3− isotopes (δ15N–NO3 and δ18O–NO3), were used to investigate the groundwater quality and its influencing factors. LULC patterns of the study area were first determined by interpreting remote sensing image data collected from the Sentinel-2 satellite, then the Bayesian stable isotope mixing model (MixSIAR) was used to estimate proportional contributions of the potential sources to groundwater NO3− concentrations. Groundwater quality in the study area was influenced by both natural and anthropogenic factors, with anthropological impact being more important. The results of LULC revealed that the irrigated land is the dominant LULC type in the plain, covering an area of 576.6 km2 (57.18% of the total surface study area of the plain). On the other hand, the results of the NO3− isotopes suggested that manure and sewage (M&S), as well as soil nitrogen (SN), were the major contributors to groundwater NO3−. Moreover, the results obtained from the MixSIAR model showed that the mean proportional contributions of M&S to groundwater NO3− were 55.5, 43.4, 21.4, and 78.7% in the forest, irrigated, paddy, and urban lands, respectively. While SN showed mean proportional contributions of 29.9, 43.4, 61.5, and 12.7% in the forest, irrigated, paddy, and urban lands, respectively. The current study provides valuable information for local authorities to support sustainable groundwater management in the study region.

Predictive modeling of groundwater nitrate pollution and evaluating its main impact factors using random forest

Groundwater quality in plains and basins of arid and semi-arid regions with increased agriculture and urbanization development faces severe nitrate pollution, which is affected by both climate and anthropogenic activities. Here, shallow groundwater nitrate concentrations in the Yinchuan Region in central Yinchuan Plain were modeled during 2000, 2005, 2010, and 2015 using random forest. Multiple spatial environment factors were taken as predictor variables. The relative importance of these factors was also calculated using the constructed model. Remote sensing and GIS methods were used to compile various environmental factors to generate training and test sets for training and validation of the random forest model. Mean absolute error (MAE), root mean square error (RMSE), and coefficient of determination (R2) between the observed and predicted groundwater nitrate concentrations were used to measure the model performance. As indicated by these metrics, the random forest model for groundwater nitrate prediction was performed well. The relative importance of the predictor variables computed by the model indicated groundwater nitrate was mainly affected by the distance to the Yellow River, meteorological elements (precipitation, evaporation, and mean air temperature), and water level elevation. Additionally, urban and arable land were the two land use/land cover types that mainly influenced groundwater nitrate concentration in the Yinchuan Region, of which urban land was more influential than arable land as a result of intense expansion of urban land from 2000 to 2015. Overall, the current study provides an approach to integrate multiple environmental factors for groundwater quality study and is also significant for sustainable groundwater management in the Yinchuan Region.

Applications of a UV optical nitrate sensor in a surface water/groundwater quality field study.

Examples of the utility of UV optical nitrate sensors are provided for two field applications, investigating nitrate pollution in a lowland, peri-urban catchment. In one application, rapid, in-stream longitudinal nitrate surveys were made in summer and winter, by fixing an optical nitrate sensor operating in continuous measurement mode to a kayak that was paddled along 10km of the mainstem of the low-order stream in under 4h. Nitrate concentrations ranged between 3.45 and 6.39mg NO3-N/L. Nitrate hot-spots and cool-spots were mapped and found to relate to point discharges from spring-fed tributaries and land drains. Effective nitrate removal (dN/dx = - 0.08mgN/L/km), inferred to be from assimilation reactions, was evident in the summer dataset, but not the winter nitrate dataset. In a second application, the optical sensor was configured with appropriate technology to establish an autonomous and fully automated nitrate monitoring station. The station makes daily nitrate measurements of surface water, and groundwater, sampled from a cluster of four multi-level wells. Quarterly maintenance of the nitrate sensor has proven sufficient to keep measurement errors under 5%. Most nitrate variation has been recorded at or near the water table where concentrations have ranged between 3.47 and 5.88mg NO3-N/L, and annual maxima have occurred in late winter/spring, which coincides with when most nitrate leaching occurs from agricultural land. Seasonal nitrate patterns are not evident in groundwater sampled from 8-m depth, or deeper. High-frequency monitoring has revealed that some infra-season, short-term variability also occurs in shallow groundwater nitrate, driven by storm events, and which on occasion results in a temporary inversion of the groundwater nitrate-depth profile.

Characteristics of nitrogen pollution for shallow groundwater in typical urban planning area in Taihu Lake Basin

In order to verify the nitrogen pollution status of shallow groundwater in typical city of Taihu Lake Basin, urban planning area of Suzhou city was selected as the study area, and 14 sampling sites representing different land use types were selected to carry out water quality analysis. The status, temporal variability of nitrogen pollution and composition characteristics of various forms of nitrogen for shallow groundwater were analyzed. The results show that the nitrogen pollution of shallow groundwater in study area is relatively serious. The average contents of total nitrogen, dissolved inorganic nitrogen, total organic nitrogen, ammonia nitrogen, nitrite nitrogen and nitrate nitrogen are 8.23, 5.45, 2.77, 2.53, 0.12 and 2.81 mg/L, respectively. The variation coefficients of various forms of nitrogen are large and the spatial differentiation is significant. The contents of ammonia, nitrite and nitrate in shallow groundwater show an obvious spatial distribution characteristics. Nitrogen pollution in old urban areas is much more serious than other types of areas, especially ammonia nitrogen pollution is particularly prominent. Inorganic nitrogen is the main form of nitrogen in groundwater, while ammonia nitrogen is the main form of inorganic nitrogen.

Comparing riparian buffer design classification data among watersheds representing Iowa landscapes

AbstractRiparian buffers can improve water quality, but watershed‐scale evaluations of riparian buffering opportunities are rare. A landscape discretization tool called riparian catchments, part of the Agricultural Conservation Planning Framework (ACPF) version 3, was applied to evaluate functional riparian settings for 32 headwater watersheds representing three major land resource areas (MLRAs) in Iowa. Riparian settings of 250‐m length were classified based on height above channel and upslope contributing area to show where to place buffers primarily designed to intercept runoff, treat nitrate in shallow groundwater, and/or protect streambanks. Riparian zones found below small riparian catchments were common, typically occupying &gt;50% of streambank lengths in MLRA 103 (northern Iowa) and MLRA 108 (southeast Iowa). In these settings, narrow (6–10 m wide) buffers provide a buffer/contributing area ratio of &gt;0.02 to filter surface runoff, while providing streambank protection. This similarity occurred despite these two MLRAs having contrasting landscapes. Whereas the narrow buffers suggested are associated with ditches and flat terrain in MLRA 103, they occur below short slopes along streams that have well dissected the watersheds in MLRA 108. In MLRA 104 of east‐central Iowa, headwater alluvial streams often had broad low‐lying riparian zones, where wide buffers (&gt;25 m) may be placed to help mitigate nitrate transport in shallow groundwater. The ACPF riparian catchments approach enabled cross‐watershed analyses of riparian settings, while providing spatial data to inform watershed‐scale riparian planning efforts.

Multi-scaled response of groundwater nitrate contamination to integrated anthropogenic activities in a rapidly urbanizing agricultural catchment.

Anthropogenic activities have a significant contribution to groundwater nitrate contamination at multiple spatial scales in urbanizing agricultural catchments, while how to derive the optimal researching scale and explore the relative importance among anthropogenic activities for groundwater nitrate contamination still remains challenging. In this study, 165 perched groundwater and 120 shallow groundwater samples were collected in two urbanizing agricultural catchments, to explore anthropogenic activity effects on groundwater nitrate contamination crossing multiple spatial scales, integrating the probability kriging, multi-scale comparison at spatial scales of 100 to 1900 m with an increment of 200 m at the block scales, and variance partitioning analysis. Probability of perched and shallow groundwater nitrate concentration > 3 mg L-1 exhibited strong spatial autocorrelation, with effective ranges of 1091 m and 3743 m from semivariogram, respectively. Relationships between perched and shallow groundwater nitrate concentrations were more significant and robust (r = 0.30-0.52, p < 0.001) at the block scale from 300 to 1100 m, indicating that perched groundwater nitrate closely related to shallow groundwater nitrate. The responses of groundwater nitrate contamination on anthropogenic drivers presented strongly scaling correlation and had the highest correlation at the spatial scale of 1100 m, suggesting the optimal scale for exploring anthropogenic activity effects on groundwater nitrate contamination. The three categories of anthropogenic drivers (urbanization, agriculture intensification, and demographic driver) contributed to 31.0-84.0% part of the total variations in groundwater nitrate contamination at the spatial scale of 1100 m. Particularly, agriculture intensification was the most influential driver for groundwater nitrate contamination, while the urbanizing process and population growth played important roles surrounding urban cores. Our findings highlighted the importance of incorporating multi-scale comparisons on regional groundwater quality evaluation, and provided technical support to the groundwater resource management strategy development in urbanizing agricultural regions.

Effect of hydrogeological conditions and surface loads on shallow groundwater nitrate pollution in the Shaying River Basin: Based on least squares surface fitting model

Nitrate pollution in groundwater has become a widespread problem worldwide, but understanding of the factors influencing groundwater nitrate pollution remains limited. Numerous studies have attributed nitrate pollution mostly to surface conditions and have neglected the role of hydrogeology. Therefore, this study used the Shaying River Basin as the study area and developed a least squares surface fitting (LSSF) model to systematically analyze the effect of hydrogeological conditions and surface pollution loads on groundwater nitrate pollution. Intrinsic vulnerability and total soil nitrogen (TSN) were used to represent hydrogeological conditions and surface pollution loads, respectively. The results showed that the concentrations of NO3–N in shallow groundwater ranged from 0.002 to 256.29 mg/L (with an average of 14.38 mg/L). The concentration had an overall decreasing trend along the flow path. The water chemistry tended to change from HCO3–Ca to HCO3·Cl–Ca as the NO3–N concentration increased. Groundwater nitrate pollution was simultaneously controlled by intrinsic vulnerability and TSN, and the LSSF model explained 83.5% of the result within a 95% confidence interval. These findings explained the phenomenon by which some areas had high surface loads but no serious groundwater nitrate pollution and some areas had nitrate pollution but no high surface loads. Nitrate accumulated in high levels in areas with a high intrinsic vulnerability due to hydrogeological conditions. TSN, which was the main source of NO3–N in groundwater, came mainly from agricultural nitrogen fertilizer inputs and livestock manure. These findings provide helpful information for those tasked with managing and controlling groundwater quality.

Modeling shallow groundwater nitrate concentrations by direct coupling of the vadose and the saturated zone

In many aquifers in plains and valley basins, water movement and solute fate in the vadose zone is described without considering the actual depth of the groundwater table. However, for shallow groundwater conditions (i.e., when the water table is few meters below the ground surface), there is a feedback from the groundwater table on the soil moisture content which influences plant growth and evapotranspiration. Thus, an interactive coupling between vadose zone and groundwater processes is needed. In this research the implementation of a time step-based (direct) coupling between the soil water movement and nitrogen fate model SIMWASER/STOTRASIM and the groundwater flow and solute transport model FEFLOW is shown and applied to a part of an aquifer in southeast Austria. At the aquifer scale, areas with time step-based coupling are combined with areas of sequential coupling to account for shallow groundwater levels. To speed up the computation of vadose zone processes, a clustering approach is developed by grouping elements of similar groundwater level and nitrate concentrations time series together. Through the comparison between direct and sequential coupling results, it is demonstrated that including the feedback in the coupling reduces simulated nitrate concentrations by about 10%. Thus, if shallow groundwater conditions exist, the time step-based approach allows considering the interaction between vadose and saturated processes, which may lead to improved compromises between agricultural land use and groundwater protection.

Specific vulnerability assessment of nitrate in shallow groundwater with an improved DRSTIC-LE model

Datong basin is one of the most important agriculture zone of Shanxi Province, China, where intensive fertilizer and pesticide applications cause the groundwater contamination. Hence, it is necessary to carry out groundwater specific vulnerability assessment of nitrate. The prediction accuracy of conventional DRASTIC model for groundwater vulnerability assessment is severely limited by the inherent subjectivity in determining main parameters, rating scales and weighting coefficients. This paper attempts to overcome these problems by changing the evaluation parameters, parameters rating and weight calculation method. Based on the hydrogeological conditions and nitrate pollution characteristics of Datong Basin, the traditional groundwater vulnerability model DRASTIC was improved, called DRSTIC-LE model to assess the specific vulnerability of nitrate, which involves Depth of water table (D), Net recharge (R), Soil media (S), Topography (T), Impact of the vadose zone (I), hydraulic Conductivity (C), land use type (L), and groundwater exploitation (E) as evaluation parameters. And the theoretical weight of each parameter were determined with the aid of the improved weights determination method by the effective combination of the entropy weight method and analytic hierarchy process. Moreover, single-parameter sensitivity analysis was performed to evaluate the effect of each parameter on the groundwater specific vulnerability. According to the results of groundwater specific vulnerability map, very high and high vulnerability mainly situated in central, northern and northeastern portion of study area, with 6.25%, 17.93% of total area, respectively. Also, single-parameter sensitivity analysis represented that I and D are the main parameter which impacts groundwater to pollution while C contributes least to pollution in the Datong basin. The model is validated with the measured nitrate concentration and results have shown better correlation between SVI and nitrate concentration. Additionally, by comparing the correlation between the effective weights and the theoretical weights calculated by the three methods (EW, AHP and EW-AHP method), we can see that prediction accuracy of the EW-AHP method is higher than other methods. The research established the efficacy of EW-AHP method as a method of determining weights and provided a basis for regional control of groundwater nitrate pollution.

The characteristics and performance of sustainable-releasing compound carbon source material applied on groundwater nitrate in-situ remediation

Recently, reductant and carbon source were frequently used in groundwater nitrate remediation worldwide. Agricultural waste as a promising organic carbon source, has been paid much attention but the problem of sustainability, bioavailability and secondary pollution remained unsolved. This study was conducted to depict the characteristic and performance of developed sustainable-releasing compound carbon source material (SCCM) applied on the in-situ remediation of nitrate in shallow groundwater. Results showed the SCCM based on agricultural waste and zero valent-iron (ZVI) has a stable carbon releasing rate, which is suitable for stimulating the low microbial active environment in groundwater continuously, and capable of avoiding rapid TOC releasing in the early stage. The released carbon sources in SCCM leachate were mainly small molecular alcohols and acids with high microbial availability. As in-situ permeable reactive barrier (PRB) filling material, SCCM can form an optimal carbon source radiation range of 20 cm, with a maximum efficient carbon source radius of 1 m, which can reach an extended active zone. A positive correlation between the ZVI content and nitrate removal rate was found. The chemical and microbiological evidence both indicated that the expected chemical reduction and biological denitrification was gradually established. Additionally, the absorption of ammonia and chroma by attapulgite effectively avoided the secondary pollution. In conclusion, the application of SCCM in groundwater nitrate in-situ remediation optimized the nitrate removal efficiency and provided theoretical basis for engineer carbon sources development from straw-type agricultural waste.

Human health risk assessment and sources analysis of nitrate in shallow groundwater of the Liujiang basin, China

ABSTRACTHigh levels of nitrates in groundwater pose a risk to human health. Hence, groundwater-human health risk assessment and sources analysis are essential. The article aims to assess risk level and identify sources of nitrate in shallow groundwater of the Liujiang basin by using a human health risk assessment (HHRA) model, Factor analysis (FA) and GIS spatial analysis. The results indicated that the most serious pollution was distributed in southern region of the basin; about 60% of the samples exceeded the recommended limit of nitrate as per the World Health Organization limit. Moreover, ingants' health risk were greater than those of adults and children, and about 56% of the groundwater samples will put the infants at risk of health. FA was used to identify various underlying natural and anthropogenic processes that created these distinct risk levels. The FA results can be categorized by two major factors: (1) Organic fertilizers and sewage discharge contamination in central region. (2) Blocking effect of granite and redox conditions in southern parts. This study demonstrates that the great variation of nitrate risk levels in the basin should be attributed to both natural and anthropogenic processes.

ESTIMATION, REALITY AND TREND OF GROUNDWATER NITRATE CONCENTRATION UNDER UNSEWERED AREA OF YOGYAKARTA CITY – INDONESIA

In the last two decades, urbanization has transformed Yogyakarta City expanding beyond its administrative area with about one million inhabitants. The City sited on shallow unconfined aquifer has rapidly changed without appropriate access to sanitation and piped water supply. Until now, only 9% of the urban population is served by sewers system and less than 30% of urban population have access to clean water which supplied by the local public water-work. Most of the urban population depend on shallow groundwater for much of their water supply. Regards to the massive used of on-site sanitation systems in the city, contamination of nitrate in shallow groundwater is predicted to occur and surveys of domestic dug wells have revealed a widespread nitrate contamination of the groundwater. Comparison of groundwater nitrate and chloride concentration from several old data and the latest data shows clearly an evidence of the increasing of nitrate concentration and nitrate leaching in the shallow groundwater under Yogyakarta City overtime. Considering the trend, it is no doubt that most of nitrate concentration under urbanized area in the Yogyakarta City will be greater than 50 mg/L in the next several years, if appropriate management action to deal with the on-site sanitation system is not conducted.

Response of Ammonium-Oxidizing (amoA) and Nitrate-Reducing (narG) Gene Abundances in Groundwater to Land Use Change

This study examines the effects of land use change on nitrate concentration and the abundances of ammonia-oxidizing archaea (AOA), ammonia-oxidizing bacteria (AOB), and narG-containing denitrifiers in shallow groundwater. The results reveal a general increase of nitrate in shallow groundwater following the change of land use from paddy fields to vegetable patches. Furthermore, a significant relationship between NO3−-N concentrations was observed both in groundwater and in soil at soil depths of 0–20, 20–40, 40–60, 60–80, and 80–100 cm. With regard to gene abundance in groundwater, the AOB amoA gene was most abundant and the AOA amoA gene copy numbers were lowest from the field with long-term paddy cultivation compared with the field under vegetable cultivation. The narG gene copy numbers were higher from the field under short-term vegetable cultivation compared with fields under long-term vegetable cultivation. The NO3−-N concentrations in groundwater correlated positively with AOA amoA gene copy numbers, negatively with the AOB amoA gene, but with no significant relationship with the narG gene. In conclusion, land use change from paddy fields to vegetable patches increases nitrate in groundwater, which is correlated significantly with nitrate in soil and the abundance of the amoA gene, but is not related to the narG gene in groundwater. This study also suggests that the removal of groundwater nitrate pollution is not feasible through biological denitrification without additional denitrifiers and that it might even become more aggravated because of the AOA.