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1.
A vegetable- and meat-canning facility located in the karst of southeastern Minnesota disposes ≈2.85×105 m3 yr?1 of wastewater by spray irrigation of an 83.7-ha field located atop the local groundwater divide. Cannery effluent contains high levels of chloride and nitrogen (organic and ammonia), in excess of 7000 mg/l and 400 mg/l, respectively. Nitrate-nitrogen concentrations are generally < 5 mg/l. Agricultural, domestic, and municipal sources of chloride and nitrate are common in the region, and water supplies frequently exceed the drinking-water limit for nitrate-nitrogen of 10 mg/l. Fifty-two area wells and thirteen surface-water locations were sampled and analyzed for five ionic species, including: chloride (Cl), nitrate-nitrogen (NO3-N), sulfate (SO4), nitrite-nitrogen (NO2-N), and phosphate (PO4). Two distinct chloride plumes flowing outward from the groundwater divide were identified, and 65% of the wells sampled had nitrate-nitrogen concentrations in excess of 10 mg/l. The data were divided into two groups: one group of samples from wells located near the canning facility and another group from outside that area. A correlation coefficient of R2= 0.004 for Cl vs. NO3-N in the vicinity of the irrigation fields indicates essentially no relationship between the source of Cl and NO3. In areas of agricultural and domestic activities located away from the cannery, an R2 of 0.54 suggests that Cl and NO3 have common sources in these areas. 相似文献
2.
《Applied Geochemistry》1995,10(4):391-405
Extensive NO3− contamination of groundwater in the Abbotsford aquifer to levels above drinking water limits is a major problem in the Fraser Lowlands of southwestern British Columbia, Canada. Nitrate concentrations in the aquifer ranged from 0 to 151 mg/l NO3−, with a median concentration of 46 mg/l NO3−. Of 117 wells sampled, 54% had NO3− concentrations exceeding the drinking water limit of 45 mg/1. Approximately 80% of the study area had groundwater NO3− concentrations exceeding 40 mg/1 NO3−. Potential NO3− source materials were poultry manure N and synthetic NH4 based fertilizers. Theδ15N of solid poultry manure samples ranged between + 7.9 and + 8.6‰ (AIR). Four brands of synthetic fertilizers commonly used hadδ15N values between −1.5 and −0.6‰. Ammonia volatilization caused theδ15N of groundwater NO3− produced from poultry manure N to range between +8 and +16‰. Theδ18O values of groundwater NO3−, by contrast, mostly ranged between +2 and +5‰ (SMOW). This narrow range ofδ18O values fell within the expected range of NO3− produced by nitrification of reduced N forms such as poultry manure N and NH4 fertilizers, and had a similar range ofδ18O values as NO3− in the upper part of the unsaturated zone below raspberry fields and beneath former manure piles. Theδ15N-NO3− andδ18O-NO3− data confirmed that NO3− in the aquifer was predominantly derived from poultry manure and to a lesser extent from synthetic fertilizers. Theδ18O-NO3− data further suggested the nitrification process occurred mainly in the summer months, with the soil NO3− produced subsequently flushed into the aquifer during fall recharge. Theδ15N-NO3−andδ18O-NO3− data conclusively indicated that no significant bacterial denitrification is taking place in the Abbotsford aquifer. 相似文献
3.
Dugin Kaown Eun-Hee Koh Bernhard Mayer Heejung Kim Dong Kyu Park Byeong-Hak Park Kang-Kun Lee 《Hydrogeology Journal》2018,26(6):2009-2020
The extent of denitrification in a small agricultural area near a river in Yangpyeong, South Korea, was determined using multiple isotopes, groundwater age, and physicochemical data for groundwater. The shallow groundwater at one monitoring site had high concentrations of NO3-N (74–83 mg L?1). The δ15N-NO3 values for groundwater in the study area ranged between +9.1 and +24.6‰ in June 2014 and +12.2 to +21.6‰ in October 2014. High δ15N-NO3 values (+10.7 to +12.5‰) in both sampling periods indicated that the high concentrations of nitrate in the groundwater originated from application of organic fertilizers and manure. In the northern part of the study area, some groundwater samples showed elevated δ15N-NO3 and δ18O-NO3 values, which suggest that nitrate was removed from the groundwater via denitrification, with N isotope enrichment factors ranging between ?4.8 and ?7.9‰ and O isotope enrichment factors varying between ?3.8 and ?4.9‰. Similar δD and δ18O values of the surface water and groundwater in the south appear to indicate that groundwater in that area was affected by surface-water infiltration. The mean residence times (MRTs) of groundwater showed younger ages in the south (10–20 years) than in the north (20–30 years). Hence, it was concluded that denitrification processes under anaerobic conditions with longer groundwater MRT in the northern part of the study area removed considerable amounts of nitrate. This study demonstrates that multi-isotope data combined with physicochemical data and age-dating information can be effectively applied to characterize nitrate contaminant sources and attenuation processes. 相似文献
4.
The Silurian bedrock aquifer constitutes a major aquifer system for groundwater supply across the Ontario province in Canada. The application of natural and industrial fertilizers near urban centers has led to groundwater NO3−-N concentrations that sometimes have exceeded the drinking water limit, posing a threat to the usage of groundwater for the human consumption. Therefore, there is a growing interest and concern about how nitrate is being leached, transported and potentially attenuated in bedrock aquifers. This study assesses the local distribution of groundwater NO3− in the up-gradient area of two historically impacted municipal wells, called Carter Wells, in the City of Guelph, Canada, in order to evaluate the potential nitrate attenuation mechanisms, using both groundwater geochemical and isotopic analysis (3H, δ15N-NO3, δ18O-NO3, δ18O-SO4, δ34S-SO4) and a detailed vertical hydrogeological and geochemical bedrock characterization. The results indicate that probably the main source of nitrate to the Carter Wells is the up-gradient Arkell Research Station (ARS), an agricultural research facility where manure has been historically applied. The overburden and bedrock groundwater with high NO3 concentrations at the ARS exhibits a manure-related δ15N and δ18O signature, isotopically similar to the high nitrate in the down-gradient groundwater from domestic wells and from the Carter Wells. The nitrate spatial distribution appears to be influenced and controlled by the geology, in which more permeable rock is found in the Guelph Formation which in turn is related to most of the high NO3− groundwater. The presence of an underlying low permeability Eramosa Formation favors the development of oxygen-depleted conditions, a key factor for the occurrence of denitrification. Groundwater with low NO3−-N concentrations associated with more oxygen-limited conditions and coincident with high SO42− concentrations are related to more enriched δ15N and δ18O values in NO3− and to more depleted δ34S and δ18O values in SO42−, suggesting that denitrification coupled with pyrite oxidation is taking place. The presence of macro crystalized and disseminated pyrite especially in the Eramosa Formation, can support the occurrence of this attenuation process. Moreover, based on tritium analysis, some denitrification can occur in shallow bedrock and within relatively short residence times, associated with less permeable conditions in depth which facilitates oxygen consumption through sulfide oxidation. The role of denitrification mediated by organic carbon cannot be discarded at the study site. This study suggests that the geological configuration and particularly the presence of low permeability Eramosa Formation can play an important role on nitrate natural attenuation, which may serve as a decision factor on defining the bedrock water supply system for both domestic and municipal purposes. 相似文献
5.
Nitrate contamination of groundwater in an agroecosystem in Zhangye Oasis,Northwest China 总被引:5,自引:2,他引:3
In order to assess the extent of groundwater contamination by nitrate (NO3
−–N) and to provide information about the deterioration of the groundwater quality in Zhangye Oasis, Northwest China, a study
was conducted in this area. The mean value of NO3
−–N concentrations in groundwater samples was 10.66 ± 0.19 mg l−1. NO3
−–N concentrations exceeding 10 mg l−1 (the threshold for drinking water set by the World Health Organization) were found in 32.4% of 71 wells, and were 13, 33.3,
52.4 and 50.0% in the groundwater samples from drinking wells, irrigation wells, hand-pumping wells and groundwater table
observation wells, respectively. The result showed that the groundwater samples that had NO3
−–N concentrations exceeding the threshold for drinking water were mostly collected from a depth of less than 20 m. Groundwater
NO3
−–N concentrations in areas used for the cultivation of vegetables, seed maize and intercropped maize were significantly higher
than those in urban or paddy areas. NO3
−–N contamination of groundwater in areas with sandy soil was more severe than in those with loam soil. 相似文献
6.
Matthew K. Landon Christopher T. Green Kenneth Belitz Michael J. Singleton Bradley K. Esser 《Hydrogeology Journal》2011,19(6):1203-1224
In a 2,700-km2 area in the eastern San Joaquin Valley, California (USA), data from multiple sources were used to determine interrelations among hydrogeologic factors, reduction-oxidation (redox) conditions, and temporal and spatial distributions of nitrate (NO3), a widely detected groundwater contaminant. Groundwater is predominantly modern, or mixtures of modern water, with detectable NO3 and oxic redox conditions, but some zones have anoxic or mixed redox conditions. Anoxic conditions were associated with long residence times that occurred near the valley trough and in areas of historical groundwater discharge with shallow depth to water. Anoxic conditions also were associated with interactions of shallow, modern groundwater with soils. NO3 concentrations were significantly lower in anoxic than oxic or mixed redox groundwater, primarily because residence times of anoxic waters exceed the duration of increased pumping and fertilizer use associated with modern agriculture. Effects of redox reactions on NO3 concentrations were relatively minor. Dissolved N2 gas data indicated that denitrification has eliminated >5 mg/L NO3–N in about 10% of 39 wells. Increasing NO3 concentrations over time were slightly less prevalent in anoxic than oxic or mixed redox groundwater. Spatial and temporal trends of NO3 are primarily controlled by water and NO3 fluxes of modern land use. 相似文献
7.
Interactive effect of nitrogen fertilizer and hydrocarbon pollution on soil biological indicators 总被引:2,自引:1,他引:1
Somayeh Emami Ahmad Ali Pourbabaei Hossein Ali Alikhani 《Environmental Earth Sciences》2014,72(9):3513-3519
The investigation of the impact of different forms of nitrogen fertilizer (NO3-N and NH4-N) on microbial parameters, enzyme activities and phytotoxicity in a petroleum-contaminated soil was evaluated by an incubation study. The tested enzymes, microbial activity and seed germination index showed different patterns in response to both petroleum and nitrogen fertilizer addition and time of incubation. The results apparently showed that the contamination of soil with petroleum has a negative effect on soil ecosystem. Nitrogen fertilizer could improve inhibition of petroleum hydrocarbons in soil. Nevertheless, nitrogen fertilizer had no significant effect on urease activity in the petroleum-contaminated soil. As compared to NO3-N, the addition of NH4-N to the soil resulted in a greater impact on soil performance as attested by the recovery of the soil germination capability and higher values of the respiration. The application of nitrogen fertilizer may be suggested as a good strategy for restoring soils in regions affected by the same problem. 相似文献
8.
Eun-Hee Koh Seung Hyun Lee Dugin Kaown Hee Sun Moon Eunhee Lee Kang-Kun Lee Bong-Rae Kang 《Environmental Earth Sciences》2017,76(4):176
Impacts of land use changes and groundwater management actions on groundwater quality were evaluated at the island scale with spatiotemporal trends of NO3-N and Cl concentrations in groundwater of Jeju Island, Korea. The temporal trends from 1993 to 2012 in the concentrations of NO3-N and Cl from more than 3900 wells were estimated using the Mann–Kendall trend test and Sen’s slope analysis and compared with the land use change trend for the period 1995–2009. The results indicate that the upward trends in NO3-N were associated with the expansion of agricultural lands, whereas Cl trends were considered to be affected by other factors in addition to the land use changes. In the mid-mountainous region, the deterioration in the groundwater quality by the both NO3-N and Cl was expected due to the continuous expansion of agricultural lands. In the lowland area, the NO3-N and Cl components showed different trends depending on the regions. In the eastern area, increasing trends in NO3-N were observed due to the development of new agricultural areas, while the Cl concentration was observed to decrease as a result of the regulation on groundwater extraction to reduce seawater intrusion. Our study highlights that a comprehensive interpretation of trends in NO3-N and Cl and land use changes for long-term periods can provide useful insights to prepare for suitable groundwater management plans in the whole island perspective. 相似文献
9.
Dingjiang Chen Hailong Wang Gerty Gielen Yena Shen Songchao Chen Jiawei Chen Jun Lu 《Environmental Earth Sciences》2014,72(1):21-33
A comparative experiment was conducted in two cross sections with sandy and sandy loam sediment textures along an agricultural drainage stream in eastern China to address the effects of sediment texture on in-stream nitrogen uptake efficiency. Using dimerous chambers for in situ incubations, NO3-N and NH4-N uptake metrics (i.e., areal uptake rate and uptake velocity) and associated hydrochemical variables in the enclosed sediment–water column system were measured for 8 days and two nights across April–July in 2011 and March–June in 2012. For the investigated sites, in-stream uptake accounted for 2–45 and 9–36 % of the initial NH4-N and NO3-N within the enclosed water column, respectively. Although similar daytime, diel and day-to-day (daytime) variation patterns of NO3-N or NH4-N uptake metrics were observed for the two sites, the sandy loam sediments had average net NO3-N and NH4-N uptake efficiency ~50 % higher and ~40 % lower than for the sandy sediments, respectively. As NO3-N was the dominant nitrogen form in the studied water columns (typical of agricultural drainage rivers), the sandy loam sediment site had an average of about 47 % higher net uptake efficiency for dissolved inorganic nitrogen (i.e., NO3-N + NH4-N). This study demonstrates that sediment texture has a considerable effect on spatial variation of nitrogen uptake along the river system. Changing sediment texture due to anthropogenic modifications on catchment land use and stream channels has the potential to change stream nitrogen cycling as well as altering nitrogen inputs and forms to downstream aquatic ecosystems. 相似文献
10.
Impacts of a large Sahelian city on groundwater hydrodynamics and quality: example of Niamey (Niger)
Aïssata B. Hassane Christian Leduc Guillaume Favreau Barbara A. Bekins Thomas Margueron 《Hydrogeology Journal》2016,24(2):407-423
The management of groundwater resources is very important in the semiarid Sahel region, which is experiencing rapid urban development. Impacts of urbanization on groundwater resources were investigated in the unconfined aquifer of the Continental Terminal beneath the city of Niamey, Niger, using water level and chemical data. Hydrodynamic and chemical changes are best described by a combination of factors including the historical development of the city, current land use, water-table depth and topography. Seasonal groundwater recharge occurs with high spatial variability, as indicated by water-level monitoring in all wells, but there was no interannual trend over the 5-year study period. Groundwater salinity shows high spatial variability and a minor rising trend. The highest salinity is in the old city centre, with Na–NO3 dominant, and it increases seasonally with recharge. Salinity is much lower and more variable in the suburbs (Ca–HCO3, Ca–NO3, and Na–NO3 dominant). Nitrate is the main ionic contaminant and is seasonally or permanently above the international guidelines for drinking water quality in 36 % of sampled wells, with a peak value of 112 mg L?1 NO3–N (8 meq L?1). Comparison of urban and rural sites indicates a long-term increase in groundwater recharge and nitrate enrichment in the urban area with serious implications for groundwater management in the region. 相似文献
11.
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
12.
Taher Farhadinejad Ahmad Khakzad Mohamadreza Jafari Ziaodin Shoaee Khosro Khosrotehrani Rasol Nobari Vahid Shahrokhi 《Arabian Journal of Geosciences》2014,7(1):221-229
One of the important indicators to show the quality of water for drinking and irrigation is nitrate values in water and soil. Nitrate enters surface water and groundwater through degradation and decomposition of human and animal wastes, industrial productions, and agricultural runoff. The present paper focuses on the concentration of nitrite (NO2 ?1) and nitrate (NO3 ?1) of the groundwater in Taft region, Central Iran. Sixty-one samples of the region’s aqueducts, wells, and springs were collected in September 2008 and May 2009 and analyzed by ICP-MS method. However, distribution maps of nitrate and nitrite and their frequency diagram in the pertinent samples have been generated. Then, they were compared to the US Environmental Protection Agency (EPA) and WHO international standards. The mean of nitrate content measured in the samples was 18.52 mg/l, maximum was 115 mg/l which is higher than the EPA standard (i.e., 10 mg/l), and the mean of nitrite content was about 0.06 mg/l. According to the distribution maps, concentration of these anions is high in the downstream of settlements and farmlands of Taft region. With respect to the penetration of agricultural wastes, flooding irrigation, thin layer of alluvium, sandy texture, and the amount of fertilizer consumed in the region, and also absence of any natural source for these anions and absence of the major industrial activities in the region to produce sewage, it seems that nitrate and nitrite originated from the agricultural sewage and human waste. As the content of nitrate in drinking water in the region is higher than WHO and EPA standards, so there is the risk of methemoglobinemia disease in infants. In addition, nitrate content within the stomach and lungs interacts with amine and nitrosamines are made up which are potentially the initial cause of all cancers in human. 相似文献
13.
《Applied Geochemistry》2006,21(6):1016-1029
Nitrate concentrations approaching and greater than the maximum contaminant level are impairing the viability of many groundwater basins as drinking water sources. Nitrate isotope data are effective in determining contaminant sources, especially when combined with other isotopic tracers such as stable isotopes of water and 3H–He ages to give insight into the routes and timing of NO3 inputs to the flow system. This combination of techniques is demonstrated in Livermore, CA, where it is determined that low NO3 reclaimed wastewater predominates in the NW, while two flowpaths with distinct NO3 sources originate in the SE. Along the eastern flowpath, δ15N values greater than 10‰ indicate that animal waste is the primary source. Diminishing concentrations over time suggest that contamination results from historical land use practices. The other flowpath begins in an area where rapid recharge, primarily of low-NO3 imported water (identified by stable isotopes of water and a 3H–He residence time of <1 year), mobilizes a significant local NO3 source, bringing groundwater concentrations up to 53 mg NO3 L−1. In this area, artificial recharge of imported water via local arroyos increases the flux of NO3 to the regional aquifer. The low δ15N value (3.1‰) in this location implicates synthetic fertilizer. In addition to these anthropogenic sources, natural NO3 background levels between 15 and 20 mg NO3 L−1 are found in deep wells with residence times greater than 50 a. 相似文献
14.
《Applied Geochemistry》2004,19(5):709-719
The potential for exploitation of urban aquifers is partly dependent on understanding the distribution and fate of urban N sources, such as sewage and fertilisers, that can limit the use of groundwater for public supplies. To investigate the application of the dual-isotope approach to understanding the N hydrochemistry of urban groundwater, this paper presents δ15N–NO3− and δ18O–NO3− data collected from two multi-level piezometers in the Sherwood sandstone aquifer beneath Nottingham in the English Midlands, UK. At one multi-level piezometer (Old Basford), depth sample measurements of δ15N–NO3− in the range +9.2 to +11.4 ‰ and δ18O–NO3− in the range +8.2 to +10.9‰, together with NO3− nitrate concentrations from 31.7 to 66.7 mg/l, are evidence for nitrification of sewage-derived inputs. In contrast, at the other multi-level piezometer (the Meadows), isotopically enriched samples (δ15N–NO3− in the range +24.3 to +42.2 ‰ and δ18O–NO3− in the range +20.5 to +29.4‰) are evidence for denitrification, although the compositional range of δ15N–NO3− does not identify the N source without corroborating data. For the Meadows location, a cross-plot of δ15N–NO3− versus δ18O–NO3− gave an enrichment of the 15N isotope relative to the 18O isotope by a factor of 1.9, within the range of 1.3–2.1 reported for denitrification in other studies. This study has shown that the dual-isotope approach provides improved understanding of N sources and fate in the urban environment but further work is required to identify nitrification pathways to provide more confidence in the application and interpretation of δ18O–NO3− measurements. 相似文献
15.
Tatsuhiro Nishikiori Takejiro Takamatsu Ayato Kohzu Yasuhiro Nakajima Mirai Watanabe 《Environmental Earth Sciences》2012,67(5):1531-1545
Geological and geographical parameters including land use, stratigraphic structure, groundwater quality, and N- and O-isotopic compositions of nitrate in groundwater were investigated to elucidate the mechanism of groundwater pollution by NO3 ? in the agricultural area of Katori, Chiba, Japan. An aquitard distributed in the western part of the study area has produced two unconfined aquifers. The average concentrations of NO3 ? and dissolved oxygen (DO) were high in the aquifer above the aquitard (7.5 and 7.6 mg/L, respectively) and in the aquifer of the eastern part of the study area that was not influenced by the aquitard (11.9 and 7.8 mg/L, respectively); however, the levels in the aquifer under the aquitard were relatively low (2.2 and 3.7 mg/L, respectively). The δ15N and δ18O values of NO3 ? generally increased exponentially in the groundwater that flowed into the aquifer under the aquitard as the concentration of NO3 ? decreased, although this decrease in NO3 ? also occasionally occurred without isotopic changes. These results indicated that the aquitard prevented the penetration of NO3 ?, DO, and gaseous O2. Under the aquitard, denitrification and dilution with unpolluted water that entered from natural forested areas reduced the NO3 ? concentrations in the groundwater. The major sources of NO3 ? in groundwater in the study area were estimated to be NH4-chemical fertilizer, livestock waste, and manure. 相似文献
16.
The study area is in the southeastern part of the city of Elaz between 38°17–38°43 latitudes and 38°36–39°07 longitudes. Formations of Paleozoic, Mesozoic and Cenozoic age comprise confined and unconfined aquifers. Unconfined aquifers are represented by Na-Cl and Na-HCO3 type waters while confined aquifers are characterized by Ca-HCO3, Mg-HCO3 and Na-HCO3 type waters. Due to sodium pollution, as a result of irrigation from waters of Hazar lake in the plain, as well as intense use of artificial fertilizer and improper storage of animal fertilizers, NH4-N, NO3-N and total PO4-P pollution are detected in waters of the unconfined aquifer. Organic material contents in waters of well nos. S27, S29 and S32 completed in the unconfined aquifer are above 3.5 mg/l of Turkish Standard Institute (TSE), (266) standard. In confined aquifers, total PO4-P pollution in four wells and NH4-N pollution in three wells were observed to be above the TSE (266) standard. 相似文献
17.
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
18.
《Applied Geochemistry》2004,19(11):1655-1686
Water samples from short-screen monitoring wells installed along a 90-km transect in southwestern Kansas were analyzed for major ions, trace elements, isotopes (H, B, C, N, O, S, Sr), and dissolved gases (He, Ne, N2, Ar, O2, CH4) to evaluate the geochemistry, radiocarbon ages, and paleorecharge conditions in the unconfined central High Plains aquifer. The primary reactions controlling water chemistry were dedolomitization, cation exchange, feldspar weathering, and O2 reduction and denitrification. Radiocarbon ages adjusted for C mass transfers ranged from <2.6 ka (14C) B.P. near the water table to 12.8 ± 0.9 ka (14C) B.P. at the base of the aquifer, indicating the unconfined central High Plains aquifer contained a stratified sequence of ground water spanning Holocene time. A cross-sectional model of steady-state ground-water flow, calibrated using radiocarbon ages, is consistent with recharge rates ranging from 0.8 mm/a in areas overlain by loess to 8 mm/a in areas overlain by dune sand. Paleorecharge temperatures ranged from an average of 15.2 ± 0.7 °C for the most recently recharged waters to 11.6 ± 0.4 °C for the oldest waters. The temperature difference between Early and Late Holocene recharge was estimated to be 2.4 ± 0.7 °C, after taking into account variable recharge elevations. Nitrogen isotope data indicate NO3 in paleorecharge (average concentration=193 μM) was derived from a relatively uniform source such as soil N, whereas NO3 in recent recharge (average concentration=885 μM) contained N from varying proportions of fertilizer, manure, and soil N. Deep water samples contained components of N2 derived from atmospheric, denitrification, and deep natural gas sources. Denitrification rates in the aquifer were slow (5 ± 2× 10−3 μmol N L−1 a−1), indicating this process would require >10 ka to reduce the average NO3 concentration in recent recharge to the Holocene background concentration. 相似文献
19.
Meiliang Bay and Gonghu Bay, in the north of Taihu Lake, are important water sources for the city of Wuxi, and increased eutrophication now threatens the safety of drinking water. The distribution of nitrogen (N) speciation and source of N in the surface waters in the north of Taihu Lake is studied, which was an important first step in controlling N pollution. The result shows that the average concentration of ammonia (NH4 +) and nitrate (NO3 ?) of surface water in Meiliang Bay was 0.32 and 0.35 mg/L, while 0.21 and 0.74 mg/L of Gonghu Bay, in which both bays had serious nitrate pollution. The concentrations of NH4 + and NO3 ? in the surface water of the two bays had a trend of gradual decrease from north to south. The maximum concentrations of NH4 + and NO3 ? of two bays were observed near the inflowing rivers, and the maximum concentrations of NH4 + in surface water of two bays were 0.49 and 0.61, and 0.77 and 1.38 mg/L of NO3 ?. The concentration of NH4 + in the interstitial water of the two bays had a trend of gradual decrease from west to east, but NO3 ? had the opposite tendency. The maximum concentrations of NH4 + in the interstitial water of the two bays were 5.88 and 4.64, and 3.58 and 7.18 mg/L of NO3 ?. The exchangeable NH4 + content in the sediment of Meiliang Bay had a trend of gradual decrease from north to south, but Gonghu Bay showed the reverse. The exchangeable NO3 ? content in the sediment of Meiliang Bay had a trend of gradual decrease from east to west, but a decreasing trend from north to south was observed in Gonghu Bay. The maximum concentrations of exchangeable NH4 + were determined, and the values were 96.25 and 74.90 mg/kg, as well as NO3 ? with the values of 12.06 and 7.08 mg/kg. Chemical fertilizer and domestic sewage were the major sources of nitrate in surface water of Gonghu Bay, contributing 39.16 and 47.79%, respectively. Domestic sewage was the major source of nitrate in Meiliang Bay, contributing 84.79%. The denitrification process in Gonghu Bay was more apparent than in Meiliang Bay. Mixing and dilution processes had important effects on changing the concentration of nitrate transportation in the two bays. 相似文献
20.
Irrigated agriculture allows for the increase of agrarian yields and stability in food supply and raw materials, being, at the same time, responsible for the reduction of water resources availability and for the pollution by salts and nitrate. This work aims to analyze the impact of changes in irrigation management (establishment of an on-demand flood irrigated system, assignment of irrigation allowances and water payment for surface and irrigation water consumption) in a traditional irrigated land on drainage flow, electrical conductivity and nitrate concentration in irrigation return flows between the year 2001 and the period 2005–2008. Changes in water management significantly modified quantity (lower drainage) and quality (electrical conductivity and nitrate) of irrigation return flows, keeping similar evolution paths during the year with water ameliorants in summer due to the use of good irrigation water quality. Salinity in irrigation return flows is not a current problem in the area as electrical conductivity values in water did not exceed the limit established for water used in irrigation or intended for human consumption. Despite the fact that changes in irrigation management and crop distribution have reduced nitrate concentrations in irrigation return flows by 43 %, the water still presents nitrate values exceeding the 50 mg NO3 ?/l. Thus, nitrate remains as the main agro-environmental problem in this irrigation area. However, the nitrate concentration trends detected in this work mark the possibility of reaching nitrate values below 50 mg NO3 ?/l in the case of maintenance of the conditions in this agricultural system. 相似文献