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1.
This paper is the result of a study which was carried out in order to verify if the traditional methods to evaluate the intrinsic vulnerability or vulnerability related parameters, are able to clarify the problem of nitrate pollution in groundwater. In particular, the aim was to evaluate limitations and problems connected to aquifer vulnerability methods applied to nitrate contamination prevision in groundwater. The investigation was carried out by comparing NO3 − concentrations, measured in March and November 2004 in the shallow aquifer, and the vulnerability classes, obtained by using GOD and TOT methods. Moreover, it deals with a comparison between NO3 − concentrations and single parameters (depth to water table, land use and nitrogen input). The study area is the plain sector of Piemonte (Northern Italy), where an unconfined aquifer nitrate contamination exists. In this area the anthropogenic presence is remarkable and the input of N-fertilizers and zootechnical effluents to the soil cause a growing amount of nitrates in groundwater. This approach, used in a large area (about 10,000 km2) and in several monitoring wells (about 500), allowed to compare the efficiency of different vulnerability methods and to verify the importance of every parameter on the nitrate concentrations in the aquifer. Furthermore it allowed to obtain interesting correlations in different hydrogeological situations. Correlations between depth to water table, land use and nitrogen input to the soil with nitrate concentrations in groundwater show unclear situations: in fact these comparisons describe the phenomenon trend and highlight the maximum nitrate concentrations for each circumstance but often show wide ranges of possible nitrate concentrations. The same situation could be observed by comparing vulnerability indexes and nitrate concentrations in groundwater. These results suggest that neither single parameters nor vulnerability methods (GOD and TOT) are able to describe individually the complex phenomena affecting nitrate concentrations in soil, subsoil and groundwater. In particular, the traditional methods for vulnerability analysis do not analyze physical processes in aquifers, such as denitrification and nitrate dilution. According to a recent study in the shallow unconfined aquifer of the Piemonte plain, dilution can be considered as the main cause for nitrate attenuation in groundwater.  相似文献   

2.
High nitrate concentrations, above the WHO guideline of 50 mg l−1, were observed in samples of shallow wells reaching the Yeumbeul suburb (Senegal) area groundwater. This groundwater is exploited by 7000 houses and therefore there are health implications. Correlations between parameters such as nitrate content (NO3−) in the groundwater and soil water, the distance between shallow wells and family latrines, and soil water chloride (Cl−) and colon bacillus content led to two possible sources of groundwater pollution: first, contamination by non impervious and shallow latrines; and second, the leaching of soil NO3− from waste organic matter carried in groundwater.  相似文献   

3.
Twenty private wells and ten stream locations were sampled to assess the source and fate of dissolved nitrate in the Cedar River watershed of Iowa, USA. The average levels of nitrate in groundwater decreased from 39.5 mg/L in May, to 38 mg/L in July, to 30 mg/L in September. Although several surface water samples exceeded MCL in May, most values dropped to below 20 mg/L by July and September. The decreasing N levels were attributed to the gradual uptake of nitrate by growing crops as well as the cyanobacterial growth in the aquatic systems. The δ15N values of dissolved nitrate in groundwater ranged from +0.45 to +5.35‰, whereas those in surface water ranged from +1.48 to +5.16‰. The results suggested that commercial fertilizers and soil organic nitrogen were probably mixed up in their transport pathways. A fertilizer-only source would provide much lower delta values, whereas soil nitrogen would provide higher than observed delta values. Denitrification was considered unlikely because of the low δ15N values, high nitrate concentrations, and moderately high DO content in groundwater. Animal wastes were not found as a possible source of nitrate in the water. This is supported by the low chloride concentrations and lower than 10‰ delta values in the water samples. The study demonstrates that nitrogen isotope data in coordination with the dissolved nitrate levels and land use can be effectively used in nitrogen source identification and its transformation studies.  相似文献   

4.
The causes and nature of nitrate pollution of wells in a village within Kotagede, a subdistrict of the city of Yogyakarta, Indonesia, were investigated in a detailed hydrological study. Nitrate concentrations in groundwater frequently exceeded the WHO recommended limit of 50 mg L − 1. Groundwater nitrate concentrations were measured over a 19-month period in monitoring wells and in piezometers placed strategically in relation to sewage tanks within the village. Results indicate that the tanks are major sources of nitrate in the groundwater and that the input is markedly dependent on rainfall, resulting in a surge of nitrate into the groundwater at the beginning of each wet season. That the tanks are a major source was confirmed by measuring nitrate in soil cores obtained by augering close to selected tanks. Washrooms, where people wash themselves, are not significant sources of nitrate. Faecal coliform counts in groundwater from a random selection of wells are very high. The results have implications for the siting of wells and toilets within villages in Indonesia. Received, January 1999/Revised, August 1999/Accepted, August 1999  相似文献   

5.
Water quality data from 56 wells, aquifer characteristics, soil types and land use in the city suburb of Dakar were compared to assess the effects of land use on the Thiaroye groundwater quality. The study area encompassed an unsewered densely populated zone, agricultural land, low density villages, and undeveloped land located in the sand dunes. A method similar to GIS technologies was applied to evaluate the degree of vulnerability of the different parts of the aquifer in relation to urban development, land use and aquifer characteristics. The aquifer parameters (hydraulic conductivity, groundwater level depth, recharge, soil type) were re-evaluated qualitatively into three class rankings (high, moderate and low), depending on the likelihood for contaminants reaching the water table, then combined using the two matrix Boolean logic based approaches to identify the nine classes of vulnerability assessed in the aquifer domain. An attempt was made to explain the distribution of nitrate concentration with the assessed vulnerability. In the area assessed, in the densely populated zone running from Pikine, to Thiaroye and Yeumbeul, very high nitrate concentrations correspond with the highest vulnerability index (H1). Nitrate contamination in this area is a consequence of point-source seepage from individual septic systems improperly built in this area. In the eastern part of the aquifer, high nitrate concentrations at Deni B. Ndao, Mbawane and Golam localities coincide with a moderate vulnerability assessment. The major source of nitrate in these areas is induced by agricultural activities.  相似文献   

6.
Understanding the linkage between temporal climate variability and groundwater nitrate concentration variability in monitoring well records is key to interpreting the impacts of changes in land-use practices and assessing groundwater quality trends. This study explores the coupling of climate variability and groundwater nitrate concentration variability in the Abbotsford-Sumas aquifer. Over the period of 1992–2009, the average groundwater nitrate concentration in the aquifer remained fairly steady at approximately 15 mg/L nitrate-N. Normalized nitrate data for 19 individual monitoring wells were assessed for a range of intrinsic factors including precipitation, depth to water table, depth below water table, and apparent groundwater age. At a broad scale, there is a negative correlation between nitrate concentration and apparent groundwater age. Each dedicated monitoring well shows unique, non-uniform cyclical variability in nitrate concentrations that appears to correspond with seasonal (1 year) cycles in precipitation as well as longer-period cycles (~5 years), possibly due to ENSO (El Niño Southern Oscillation) or the Pacific North American (PNA) pattern. These precipitation cycles appear to influence nitrate concentrations by approximately ±30 % of the critical concentration (10 mg/L NO3–N). Not all wells show direct correlation due to many complex local-scale factors that influence nitrate leaching including spatially and temporally variable nutrient management practices and soil/crop nitrogen dynamics (anthropogenic and agronomic factors).  相似文献   

7.
Analyses of groundwater samples collected from several locations in a small watershed of the Deccan Trap Hydrologic Province, indicated anomalously higher values of nitrate than the background. However, the NO3 concentrations in water from dug wells under pastureland where the subsurface material consisted of stony waste were minimum. The maximum values were reported for water from dug wells where the principal land use was agricultural. Lowering of NO3 values under shallow water-table conditions suggests denitrification. Higher concentrations of nitrate determined for samples collected from the wells with a deeper water-table indicate that denitrification process is inactive. The high values of nitrate coinciding with agricultural land use indicate fertilizers as the main source of nitrate pollution of ground-water. Decrease in Cl/NO3 ratio for agricultural land use confirms this inference.  相似文献   

8.
Spatial relations between land use and groundwater quality in the watershed adjacent to Assateague Island National Seashore, Maryland and Virginia, USA were analyzed by the use of two spatial models. One model used a logit analysis and the other was based on geostatistics. The models were developed and compared on the basis of existing concentrations of nitrate as nitrogen in samples from 529 domestic wells. The models were applied to produce spatial probability maps that show areas in the watershed where concentrations of nitrate in groundwater are likely to exceed a predetermined management threshold value. Maps of the watershed generated by logistic regression and probability kriging analysis showing where the probability of nitrate concentrations would exceed 3 mg/L (>0.50) compared favorably. Logistic regression was less dependent on the spatial distribution of sampled wells, and identified an additional high probability area within the watershed that was missed by probability kriging. The spatial probability maps could be used to determine the natural or anthropogenic factors that best explain the occurrence and distribution of elevated concentrations of nitrate (or other constituents) in shallow groundwater. This information can be used by local land-use planners, ecologists, and managers to protect water supplies and identify land-use planning solutions and monitoring programs in vulnerable areas.  相似文献   

9.
The purpose of this study is to develop statistical models for groundwater quality assessment in urban areas using Geographic Information Systems (GIS). To develop the models, the concentrations of nitrate (expressed as nitrogen, NO3-N), which are different according to the type of land use, well depth and distribution of rainfall, were analyzed in the Seoul (the capital of South Korea) area. Data such as land use, location of wells and groundwater quality data for nitrate contamination were collected and a database constructed within GIS. The distribution of NO3-N concentrations is not normal, and the results of the Mann-Whitney U-test analysis show the difference of NO3-N concentration by well depth and by distribution of rainfall. In both the shallow and deep wells, the radius of influence is 200 m in the dry season and 250 m in the rainy season, showing the tendency to increase in the rainy season. The results of correlation and regression analysis indicate that mixed residential and business areas and cropped field areas are likely to be the major contributor of increasing NO3-N concentration. Land uses are better correlated with NO3-N in deep wells than in shallow wells.  相似文献   

10.
In agricultural areas, fertilizer application is the main source of nitrate contamination of groundwater. To develop fertilizer management strategies to combat this problem, arable land in Hokkaido, Japan was evaluated using geographic information system techniques for intrinsic groundwater vulnerability to nitrate contamination. The DRASTIC method was modified to adapt it to the Hokkaido environment and used for the evaluation. Of the seven original DRASTIC factors, the depth to water (D), net recharge (R), soil media (S), topography (T), and impact of vadose zone media (I) were selected and used to explain the vertical movement of contaminants to the aquifer. The rating for the net recharge factor was also modified to a dilution factor for contaminants, rather than as a transporter. The frequency of wells with nitrate concentrations exceeding the Japanese environmental standard (10 mg/L) was reasonably explained by vulnerability evaluation results (GLM: logit-link, quasi-binomial distribution, Y = [1 + exp(6.873765 − 0.045988 × X)]−1, p < 0.001). However, in the paddy fields and pastures, vulnerability did not exhibit a clear relationship with the frequency of wells exceeding the standard. This suggests that the modified DRASTIC method is applicable for fertilizer application management in upland fields. In addition, under the ongoing policy for acreage allotment for rice production, this method will be useful for deciding the arrangement of arable land and crop rotation taking into consideration the potential risk of fertilizer-induced nitrate contamination of groundwater.  相似文献   

11.
Differences in the degree of confinement, redox conditions, and dissolved organic carbon (DOC) are the main factors that control the persistence of nitrate and pesticides in the Upper Floridan aquifer (UFA) and overlying surficial aquifer beneath two agricultural areas in the southeastern US. Groundwater samples were collected multiple times from 66 wells during 1993–2007 in a study area in southwestern Georgia (ACFB) and from 48 wells in 1997–98 and 2007–08 in a study area in South Carolina (SANT) as part of the US Geological Survey National Water-Quality Assessment Program. In the ACFB study area, where karst features are prevalent, elevated nitrate-N concentrations in the oxic unconfined UFA (median 2.5 mg/L) were significantly (p = 0.03) higher than those in the overlying oxic surficial aquifer (median 1.5 mg/L). Concentrations of atrazine and deethylatrazine (DEA; the most frequently detected pesticide and degradate) were higher in more recent groundwater samples from the ACFB study area than in samples collected prior to 2000. Conversely, in the SANT study area, nitrate-N concentrations in the UFA were mostly <0.06 mg/L, resulting from anoxic conditions and elevated DOC concentrations that favored denitrification. Although most parts of the partially confined UFA in the SANT study area were anoxic or had mixed redox conditions, water from 28 % of the sampled wells was oxic and had low DOC concentrations. Based on the groundwater age information, nitrate concentrations reflect historic fertilizer N usage in both the study areas, but with a lag time of about 15–20 years. Simulated responses to future management scenarios of fertilizer N inputs indicated that elevated nitrate-N concentrations would likely persist in oxic parts of the surficial aquifer and UFA for decades even with substantial decreases in fertilizer N inputs over the next 40 years.  相似文献   

12.
 A large amount of the water requirement (municipal, industrial, etc.) of Eskişehir city, Turkey, is supplied from groundwater via wells in the urban area. The groundwater in the Eskişehir Plain alluvium has been polluted by municipal and industrial wastewater, and agricultural activities. The nitrate concentrations at nine sampling points on Porsuk River, the main water course in the plain, ranged from 1.5 to 63.3 mg/l during the period from July 1986 to August 1988. In the same period, the nitrate concentrations measured in water from 51 wells ranged between 2.2–257.0 mg/l. The nitrate content of the groundwater samples was 34.2% above 45 mg/l, the upper limit for nitrate in drinking water standards. High nitrate levels were observed in water from wells in the central and eastern parts of the urban area. The nitrate content of the well water is subject to seasonal fluctuation. In general, low nitrate concentrations were observed in wet seasons, and high ones in dry seasons. Received: 16 April 1996 · Accepted: 2 October 1996  相似文献   

13.
High contents of nitrate in groundwater, ranging up to 1,500 mg/l, have been found. High concentrations are more common in village wells than in irrigation wells situated in the fields. The losses of nitrogen from the soil zone through deep leaching into the groundwater are small (260 kg N/km2); however, due to a small net infiltration (29 mm/year), the median content in groundwater still approaches the permissible limit of 50 mg/l NO 3 ? . In villages about 10–20% of the nitrogen from excreta are leached into the groundwater. Mineralization of soil nitrogen during a dry period, followed by heavy rains, caused extremely high contents of nitrate in groundwater.  相似文献   

14.
The subject of this paper is the detailed hydrological simulation of two playa lakes located in southern Spain from January 2011 to March 2012 on a daily basis. These playas are placed over a 400-km 2 shallow aquifer, which is exposed to an increasing stress caused by agricultural activities, mainly olive grove plantations. The objective of the paper is to elaborate a detailed numeric model that simulates the water regime of each playa lake on a daily scale. The simulation is compared to measured water level (WL) data of the playas in order to characterize the groundwater–surface interactions. The ultimate objective of this paper is to assess the environmental impact of the increasing anthropogenic water consumption within the area of research. The results of the GW–surface interaction were very consistent with previous works. One of the playa lakes is groundwater-dependent and the other one is presumably a perched playa lake. The GW discharge of the former playa (214 mm) during the research period stands in sharp contrast to no regional GW discharge in the latter. Water level data prove that the hydrological year (2011–2012) had a very negative water budget. The evapotranspiration estimation was almost as high as double the sum of the precipitation, the run-off, and the groundwater discharge. The simulation of an anthropologically altered water regime proves that water retrieval has a harmful impact on the WL of the playa lakes as well as on the aquifer.  相似文献   

15.
Considering the importance of groundwater resources in water-supply demands in arid and semiarid areas such as Iran, it is essential to investigate the risk of groundwater pollution. Nitrate is one of the main pollutants that penetrate into the groundwater from various sources such as chemical fertilizers, pesticides, and domestic and industrial sewage. Unfortunately currently, nitrate contamination of the aquifers is a serious problem in Iran. The Karaj aquifer is not exempted, and the nitrate pollution zone, with concentrations far beyond the permitted limit (50 mg/L), expands fast. In this paper, the long-term groundwater-quality data (from 2000 to 2013) collected from Alborz Province Water and Wastewater Company were analyzed using ArcGIS10 and statistical software, and the spatial and temporal patterns of nitrate pollution in drinking-water wells in the Karaj plain and effective parameters (such as depth to groundwater level, hydraulic gradient, land use, precipitation, and urban, agricultural and industrial wastewater) were investigated. The authors also investigated the status of nitrate concentration variation using the concepts of geostatistics, based on determinations from 62 to 194 surveyed wells with a suitable distribution across the plain. With respect to the relationship between quality parameters, hydrogeological status of the aquifer and land usage, causes of the increase in the concentration of nitrate in the water and its trend were investigated as well. Results revealed that the nitrate levels in the northern portion of the study area were the highest with maximum concentrations of 181.7 mg/L from 2000 to 2013. Based on nitrate concentration distribution maps, the levels of nitrate increased from 2006 onwards to 26–100 mg/L. Unfortunately from 2008 to 2012, a pollution zone with a nitrate water concentration of 101–150 mg/L has been observed and even a concentration of 180 mg/L has been determined. In 2000, the entire aquifer area has been drinkable but with the increase in nitrate concentration, the area with undrinkable water has expanded to 21% in 2003, 24% in 2005, 33% in 2007, 39% in 2009, 43% in 2011 and 44% in 2013. The results of this study could provide valuable information with on the status of nitrate water concentrations in the Karaj plain which demands proper strategies and qualitative approaches in the future.  相似文献   

16.
The aquifer Westliches Leibnitzer Feld, Austria, is a significant resource for regional and supraregional drinking water supply for more than 100,000 inhabitants, but the region also provides excellent agricultural conditions. This dual use implicates conflicts (e.g., non-point source groundwater pollution by nitrogen leaching), which have to be harmonized for a sustainable coexistence. At the aquifer scale, numerical models are state-of-the-art tools to simulate the behavior of groundwater quantity and quality and serve as decision support system for implementing groundwater protecting measures. While fully and iteratively coupled simulation models consider feedback between the saturated and unsaturated zone, sandy soil conditions and groundwater depths beneath the root zone allow the use of a unidirectional sequential coupling of the unsaturated water flow and nitrate transport model SIMWASER/STOTRASIM with FEFLOW for the investigation area. Considering separated inputs of water and nitrogen into groundwater out of surface water bodies, agricultural, residential and forested areas, first simulation results match observed groundwater tables, but underestimate nitrate concentrations in general. Thus, multiple scenarios assuming higher nitrogen inputs at the surface are simulated to converge with measured nitrate concentrations. Preliminary results indicate that N-input into the groundwater is strongly dominated by contributions of agricultural land.  相似文献   

17.
Geologic and geochemical variations across a 4200 km2 area of south-central Wisconsin (USA) were used to examine their relationship to phosphorus concentrations in groundwater from more than four hundred private water supply wells. Surficial geology in the study area ranged from Cambrian sandstones to Ordovician dolomites. Groundwater phosphorus concentrations were higher in aquifers of older Cambrian age compared to the concentrations in aquifers of younger Cambrian and Ordovician age. Because iron concentrations were relatively low in these waters and agricultural land use was similar in all geologic regions, we propose that the differences in bedrock phosphorus and anthropogenic geochemical impacts explain the differences in phosphorus concentrations between aquifers. Within the older Cambrian aquifers, groundwater phosphorus concentrations were elevated in groundwater with higher nitrate-nitrogen concentrations. This finding is consistent with the presence of phosphorus within sediment in these strata and geologic conditions that weakly buffered pH reduction from anthropogenic acidification. In contrast, groundwater phosphorus concentrations in younger Cambrian and Ordovician aquifers were not elevated in samples with higher nitrate. Anthropogenic acidification in these carbonate-rich aquifers was neutralized through increased carbonate weathering, which led to higher groundwater calcium and alkalinity and would limit the dissolution of phosphate-rich minerals, such as apatite, where present. Low iron concentrations observed in most samples suggest that the phosphorus release in the Cambrian strata occurs beyond the zone of secondary mineral retention in the soil. These results have important implications for the eutrophication of inland surface waters in areas with bedrock phosphorus and anthropogenic acidity that is not neutralized before it contacts phosphatic rock.  相似文献   

18.
In recent years, nitrate contamination of groundwater has become a growing concern for people in rural areas in North China Plain (NCP) where groundwater is used as drinking water. The objective of this study was to simulate agriculture derived groundwater nitrate pollution patterns with artificial neural network (ANN), which has been proved to be an effective tool for prediction in many branches of hydrology when data are not sufficient to understand the physical process of the systems but relative accurate predictions is needed. In our study, a back propagation neural network (BPNN) was developed to simulate spatial distribution of NO3-N concentrations in groundwater with land use information and site-specific hydrogeological properties in Huantai County, a typical agriculture dominated region of NCP. Geographic information system (GIS) tools were used in preparing and processing input–output vectors data for the BPNN. The circular buffer zones centered on the sampling wells were designated so as to consider the nitrate contamination of groundwater due to neighboring field. The result showed that the GIS-based BPNN simulated groundwater NO3-N concentration efficiently and captured the general trend of groundwater nitrate pollution patterns. The optimal result was obtained with a learning rate of 0.02, a 4-7-1 architecture and a buffer zone radius of 400 m. Nitrogen budget combined with GIS-based BPNN can serve as a cost-effective tool for prediction and management of groundwater nitrate pollution in an agriculture dominated regions in North China Plain.  相似文献   

19.
 The nitrate concentration in 12 water-supply wells were monitored for the period April 1992 to March 1993. Each water-supply well was sampled once a month. The nitrate concentrations in the 12 wells ranged from 7 to 156 mg/l. Two water-supply wells (Chacsinkin and Peto) showed concentrations that reached 3.5 times the maximum permissible limit for the Drinking Water Standard (45 mg/l). A third water-supply well (Akil) exceeds the norm for 7 out of 12 months. The use of nitrogen-rich fertilizers are responsible for high nitrate concentrations in groundwater in the southern part of Yucatan, Mexico where intensive agricultural practices exist. Received: 14 December 1999 · Accepted: 2 May 2000  相似文献   

20.
Groundwater plays a key role in arid regions as the majority of water is supplied by it. Groundwater pollution is a major issue, because it is susceptible to contamination from land use and other anthropogenic impacts. A study was carried out to build a vulnerability map for the Ordos Plateau using the DRASTIC model in a GIS environment. The map was designed to show the areas of the highest potential for groundwater pollution based on hydrogeological conditions. Seven environmental parameters, such as depth to water table, net recharge, aquifer media, soil media, topography, impact of the vadose zone media, and hydraulic conductivity of the aquifer, were incorporated into the DRASTIC model and GIS was used to create a groundwater vulnerability map by overlaying the available data. The results of this study show that 24.8 % of the study area has high pollution potential, 24.2 % has moderate pollution potential, 19.7 % has low pollution potential, and the remaining 31.3 % of the area has no risk of groundwater pollution. The regional distribution of nitrate is well correlated with the DRASTIC vulnerability index. In contrast to this, although the DRASTIC model indicated that the western part had no risk, nitrate concentrations were higher in some of these areas. In particular, higher nitrate concentrations were recorded along river valleys and around lakes, such as the Mulin River valley. This is mainly caused by the intensive agricultural development and favorable conditions for recharge along river valleys.  相似文献   

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