Eutrophication caused by inputs of excess nitrogen(N) has become a serious environmental problem in Hangzhou Bay(China),but the sources of this nitrogen are not well understood.In this study,the August 2019 distributi...Eutrophication caused by inputs of excess nitrogen(N) has become a serious environmental problem in Hangzhou Bay(China),but the sources of this nitrogen are not well understood.In this study,the August 2019 distributions of salinity,nutrients [nitrate(NO_(3)^(-)),nitrite,ammonium,and phosphate],and the stable isotopic composition of NO_(3)^(-)(δ^(15)N and δ^(18)O) were used to investigate sources of dissolved inorganic nitrogen(DIN) to Hangzhou B ay.Spatial distributions of nitrate,salinity,and nitrate δ^(18)O indicate that the Qiantang River,the Changjiang River,and nearshore coastal waters may all contribute nitrate to the bay.Based on the isotopic compositions of nitrate in these potential source waters and conservative mixing of nitrate in our study area,we suggest that the NO_(3)^(- )in Hangzhou B ay was likely derived mainly from soils,synthetic N fertilizer,and manure and sewage.End-member modeling indicates that in the upper half of the bay,the Qiantang River was a very important DIN source,possibly contributing more than 50% of DIN in the bay head area.In the lower half of the bay,DIN was sourced mainly from strongly intruding coastal water.DIN coming directly from the Changjiang River made a relatively small contribution to Hangzhou Bay DIN in August 2019.展开更多
China is experiencing rapid urbanization that has changed the water quality of rivers, especially nutrient loads. In this study, a typical urban river located in a karst area, Chengguan River, was chosen to explore th...China is experiencing rapid urbanization that has changed the water quality of rivers, especially nutrient loads. In this study, a typical urban river located in a karst area, Chengguan River, was chosen to explore the influence of urbanization on river ecosystems based on nutrient concentration and nitrate isotopes. The results show monthly variability of water chemistry and nutrient concentration. Nutrient concentration in two tributaries and the mainstem showed significant spatial variability, with heavy N and P pollution in one tributary near a suburban area,indicating a response to different levels of urbanization.Measurements of nitrate dual isotopes suggest thatvolatilization, assimilation, nitrification, and denitrification all occur in the polluted river. Water chemistry and nitrate isotopes show that major nitrogen sources included domestic waste and agricultural input, such as chemical fertilizer and manure. The results suggest that urbanization increases nutrient concentrations and accelerates the riverine nitrogen dynamic, and point to the need to manage point sources of sewage effluents to improve the water quality of urban rivers in southwestern China.展开更多
In recent years,emergent pollutant’s accidents have occurred frequently in China,causing serious harm to the ecological environment.In this study,the impact of an accidental fire and explosion at Tianjin Port in 2015...In recent years,emergent pollutant’s accidents have occurred frequently in China,causing serious harm to the ecological environment.In this study,the impact of an accidental fire and explosion at Tianjin Port in 2015 on the atmosphere over the Bohai Sea was explored.Results showed sharp increases in the concentrations of several important components of fine particulate matter(e.g.NO3−,SO42−,NH4+,organic carbon,elemental carbon)over Beihuangcheng Island after the explosion.Among them,NO3−was most affected(about 10 days),with a maximum concentration of 16.45μg m−3.Theδ15N-NO3−ranged from−1.58‰to+8.74‰,with an average of+2.79‰±3.32‰.Influenced by the explosion,δ15N-NO3−decreased significantly,which was in accordance with the industrial processes of explosives.Theδ18O-NO3−varied between+49.40‰and+69.52‰,and showed a marked increase(+66.62‰±3.92‰)in the explosion-affected period.Using Monte Carlo simulation,the•OH pathway for NO3−formation was 51.79%±10.94%at that time—much lower than in the regular period.The elevated dry deposition of NO3−caused by the explosion was 266.08μmol N m−2 d−1 over the Bohai Sea—again,much higher than in the regular period.With the dry nitrogen deposition of NH4+(42.41μmol N m−2 d−1),the total nitrogen deposition increased by 308.49μmol N m−2 d−1,leading to severe ecological risk.Through the inverse computation of the dry deposition flux of NO3−,the affected area over the Bohai Sea was less than 1.42×104 km2,which is about 20%of the total area.展开更多
The dual isotopes(N and O)of nitrate were measured using a denitrifier bacterial method in the western South China Sea(WSCS)during September 2015 to elucidate key information during N transformation in the lower eupho...The dual isotopes(N and O)of nitrate were measured using a denitrifier bacterial method in the western South China Sea(WSCS)during September 2015 to elucidate key information during N transformation in the lower euphotic zone(LEZ)-upper mesopelagic zone(UMZ,down to 500 m in this study)continuum,which is a vital sub-environment for marine N cycle and sequestration of atmospheric CO_(2)as well.The N isotopic composition(δ^(15)N)of nitrate generally decreased from 500 m toward the base of the euphotic zone(∼100 m),reaching a value of∼4.6‰(vs.air N_(2))at the base of the LEZ,suggesting the imprint of remineralization(nitrification)of isotopically light N from atmospheric source.Theδ^(15)N andδ18O of nitrate only generally conform to a 1:1 line at 50 m and 75 m,suggesting that nitrate assimilation is a dominant process to shape nitrate isotope signature in this light-limited and relatively N-replete lower part of the euphotic zone.The fractionation factors of N and O isotopes during nitrate fractionation(15εASSIM,18εASSIM)using a steady-state model were estimated to be 4.0‰±0.3‰and 5.4‰±0.3‰,respectively.The occurrence of nitrification at the base of the LEZ and most of the UMZ is corroborated by the decoupling ofδ^(15)N and the oxygen isotopic composition(δ18O)of nitrate.Our results will provide insights for better understanding N cycle in the South China Sea from a perspective of present and past.展开更多
The Turpan-Hami Basin in eastern Xinjiang is one of the driest regions on Earth and a premier environment to form and preserve nitrate.A large nitrate ore field in this basin was found recently.It is estimated there a...The Turpan-Hami Basin in eastern Xinjiang is one of the driest regions on Earth and a premier environment to form and preserve nitrate.A large nitrate ore field in this basin was found recently.It is estimated there are about 2.5 billion tons of resources of nitrate,and the amount is as much as the Atacama Desert super-scale nitrate deposit in Chile.Nitrate is one of a few minerals with mass-independent fractionation（MIF）,and the oxygen isotope MIF is an effective method to determine the source of nitrate.Theδ^（17）O,δ^（18）O of nitrate were measured by fluorination and thermal decomposition method.The date indicated that this is the first time that oxygen isotope MIF has been located in inland nitrate minerals.The results obtained by two methods are similar,⊿^（17）=δ^（17）O-0.52×δ^（18）O=12‰-17‰.The experiment and observation data proved that oxygen isotope MIF of nitrate are the result of photochemical reactions in the troposphere and stratosphere.Thus, evidence from MIF oxygen isotopic compositions indicate that long term atmospheric deposition of nitrate aerosol particles produced by photochemical reactions is the source of the deposits.展开更多
The Changjiang Estuary has been considered as one of the most polluted estuaries in the world due to high nitrate （NO3） input, especially in spring and summer. In this study, 6~5N and t^180 of NO3, along with other ...The Changjiang Estuary has been considered as one of the most polluted estuaries in the world due to high nitrate （NO3） input, especially in spring and summer. In this study, 6~5N and t^180 of NO3, along with other chemical parameters in this area, were measured in spring to evaluate NO3 biogeochemical processes. A simple two end-members mixing model was used to examine the relative contribution of the Changjiang River Diluted Water and marine water to NO~ sources in the Changjiang Estuary and the adjacent East Chi- na Sea. The isotopic signals show that NO3 behaved relatively and conservatively in Transect F and Transect P where assimilation was weak possibly due to vertical mixing, while active assimilation and weak nitrifi- cation occurred in Transect D. Spatial difference in assimilation was indicated by the ~ 1：1 enrichment of S 15N and 6180 in the three transects, while spatial difference in nitrification was reflected by deviations of 15N and 6180 from assimilation line. Our results suggest that the input of the Changjiang River Diluted Wa- ter promoted NO3 assimilation possibly by stratifying the water column which favored the phytoplankton growth.展开更多
Groundwater vulnerability for nitrate pollution of groundwater in the Brussel’s Capital Region was modelled using data-driven modelling approaches. The land use in the study area is heterogeneous. The South South-Eas...Groundwater vulnerability for nitrate pollution of groundwater in the Brussel’s Capital Region was modelled using data-driven modelling approaches. The land use in the study area is heterogeneous. The South South-Eastern part of the region is forested, while the remaining part is urbanised. Groundwater nitrate concentration data were determined at 48 measurement stations distributed over the study area. In addition, oxygen and nitrogen isotope concentration of the nitrates were determined. The data show that the groundwater body is degraded, particularly in the urbanised part of the study area. The contamination with nitrates at degraded stations is slightly decreasing, while the opposite is true for the nitrate contamination at the less degraded stations. We modelled the contamination and trends of nitrate contamination using linear and non-linear statistical modelling techniques. In total, we defined 23 spatially distributed proxy variables that could explain nitrate contamination of the groundwater body. These proxy variables were defined at the grid size of 10 m, and averaged over the influence zone of each measurement station. The influence zones were identified using a simplified particle tracking algorithm from the groundwater piezometric map. The calculated influence zones were consistent with results obtained from a detailed numerical groundwater flow and transport model. Stepwise regression allowed explaining 56% of the observed variability of nitrate contaminations, while non-linear artificial neural network modelling allows explaining nearly 60% of the variability. The dominant explaining variables are the percentage of impermeable surface, the percentage of the sewage system that is in a degradation state, the number of urban infrastructure construction permits with a high pollution risk, the size of the influence zone, and the depth of the groundwater sampling. These results illustrate the important role of urban infrastructure on groundwater degradation and are consistent with the isotopic signature of nitrates determined on the sampling stations. The overlay of the nitrate contamination data with the DRASTIC vulnerability model shows that this latter conceptual model captures partially the spatial signature of the observed contamination.展开更多
A metropolitan city such as Los Angeles (LA) is an ideal study site with a very high population density, and it houses at least 3 treatment plants where sewage is treated preliminarily and then progressing to tertiary...A metropolitan city such as Los Angeles (LA) is an ideal study site with a very high population density, and it houses at least 3 treatment plants where sewage is treated preliminarily and then progressing to tertiary treatment before discharging into the LA River. We will gain a better understanding of the water quality in the LA River and the nitrate load in the watershed system by examining the influence of waste water treatment plants (WWTPs). The goal of this study is to pinpoint the exact source of nitrate in the LA River using the isotope signatures. We have selected sampling locations both upstream and downstream of the WWTP. This serves to monitor nitrate levels, aiding in the assessment of treatment plant effectiveness, pinpointing nitrate pollution sources, and ensuring compliance with environmental regulations. The research explores the isotopic composition of NO3 in relation to atmospheric nitrogen and Vienna Standard Mean Ocean Water, shedding light on the contributions from various sources such as manure, sewage, soil organic nitrogen, and nitrogen fertilizers. Specifically, there is a change in the δ15NAir value between the dry and wet seasons. The isotope values in the Tillman WWTP sample changed between dry and wet seasons. Notably, the presence of nitrate originating from manure and sewage is consistent across seasons, emphasizing the significant impact of anthropogenic and agricultural activities on water quality. This investigation contributes to the broader understanding of nitrogen cycling in urban water bodies, particularly in the context of wastewater effluent discharge. The findings hold implications for water quality management and highlight the need for targeted interventions to mitigate the impact of nitrogen-containing compounds on aquatic ecosystems. Overall, the study provides a valuable framework for future research and environmental stewardship efforts aimed at preserving the health and sustainability of urban water resources. This data informs decisions regarding additional treatment or mitigation actions to safeguard downstream water quality and ecosystem health.展开更多
To explain the presence and spatial distribution of NO_(3)^(−)and N-NH_(3)in the Aquifer of the Metropolitan Area of Mexico City(AMAMC),a hydrogeochemical and isotopic analysis using^(13)C DIC(as well as the stable is...To explain the presence and spatial distribution of NO_(3)^(−)and N-NH_(3)in the Aquifer of the Metropolitan Area of Mexico City(AMAMC),a hydrogeochemical and isotopic analysis using^(13)C DIC(as well as the stable isotopes^(18)O and^(2)H)in groundwater was conducted.This aquifer is located in an old closed lacustrine volcano-sedimentary basin;some wells hosted in the semi-confined zone contain high N-NH_(3)concentrations,while others present NO_(3)^(−)contents in the recharge zones(hosted in an oxidizing environment).In this study,a change in the isotopic signature(primarily in^(18)O and^(2)H)was observed from the recharge zones to the basin center in some of the wells with high NO_(3)^(−)concentrations,this behavior can be attributed to evaporation during the incorporation of recently infiltrated water.In addition,the results for^(13)C(along with ^(2) H)in wells with the highest N-NH_(3)concentrations exhibited an atypically broad range of values.Results indicated the occurrence of hydrogeochemical and/or biochemical processes in the aquifer(in an oxidizing or reducing environment),such as organic degradation,bacterial decomposition(primarily in the ancient Lake Texcoco and which acts as a natural sink for carbon,nitrogen,sulfur,and phosphorus),besides rock weathering and dissolution,which may be responsible for a very marked isotopic modification of the^(13)C(and,to a lesser extent,2 H).Methanotrophic bacterial activity and methanogenic activity may be related to N-NH_(3)removal processes by oxidation and residual water incorporation respectively,whereas the increase in the NO_(3)^(−)content in some wells is due to the recent contribution of poor-quality water due to contamination.展开更多
The recently discovered nitrate ore field in the Turpan-Hami Basin of western China represents an estimated resource of 2.5 billion tons, and is comparable in scale to the Atacama Desert super-scale nitrate deposit in...The recently discovered nitrate ore field in the Turpan-Hami Basin of western China represents an estimated resource of 2.5 billion tons, and is comparable in scale to the Atacama Desert super-scale nitrate deposit in Chile. The research on this area is rarely carried out, and the origin of the deposits remains uncertain. In this study, new methods were used to systematically analyze N and O isotopes in nitrate minerals collected from the Kumutage, Xiaocaohu, Wuzongbulak, Dawadi, Tuyugou, and Shaer ore deposits in the Turpan-Hami Basin. The data showed that the δ15NAir value ranges from 0.7‰ to 27.6‰, but mostly between 2‰ and 6‰, which was similar to atmospheric NO3-. The 18O was highly enriched with δ18OV-SMOW varying from 30.2‰ to 46.7‰. This differs from levels in deposits derived from microbial nitrogen fixation, but is similar to those in atmospheric nitrates. N and O isotopes data indicated that nitrate deposits in Turpan-Hami Basin must be the result of deposition of atmospheric nitrate particles. Although atmospheric nitrate particles are common, the nitrate deposits could form only under the condition of long-term extreme drought climate and very limited biological activity. This paper summarized the ore-forming mechanism of different types nitrate deposits based on their geological setting.展开更多
A multi-isotope approach and mixing model were combined to identify spatial and seasonal variations of sources,and their proportional contribution to nitrate in the Hutuo River alluvial-pluvial fan region.The results ...A multi-isotope approach and mixing model were combined to identify spatial and seasonal variations of sources,and their proportional contribution to nitrate in the Hutuo River alluvial-pluvial fan region.The results showed that the NO3- concentration was significantly higher in the Hutuo River valley plain(178.7 mg/L) region than that in the upper and central pluvial fans of the Hutuo River(82.1 mg/L and 71.0 mg/L,respectively)and in the river(17.0 mg/L).Different land use types had no significant effect on the groundwater nitrate concentration.Based on a multi-isotope approach,we confirmed that the main sources of groundwater nitrate in different land use areas were domestic sewage and manure,followed by soil nitrogen,ammonia fertilizer,nitrate fertilizer and rainwater,and there were no significant spatial or seasonal variations.Combining δ^15N-NO3,δ^18O-NO3- and δ^37Cl results can increase the accuracy of traceability.Nitrification could be the most important nitrogen migration and transformation process,and denitrification did not significantly affected the isotopic composition of the nitrate.The SIAR model outputs revealed that the main nitrate pollution sources in groundwater and river water were domestic sewage and manure,accounting for 55.9%-61.0% and 22.6%(dry season),50.3%-60.4% and 34.1%(transition season),42.7%-47.6% and 35.6%(wet season 2016) and 45.9%-46.7% and 38.4%(wet season 2017),respectively.This work suggests that the random discharge and disposal of domestic sewage and manure should be the first target for control in order to prevent further nitrate contamination of the water environment.展开更多
基金The Zhejiang Provincial Natural Science Foundation of China under contract No.LZ22D060002the Key R&D Program of Zhejiang under contract No.2022C03044the National Key Research and Development Program of China under contract No.2021YFC3101702。
文摘Eutrophication caused by inputs of excess nitrogen(N) has become a serious environmental problem in Hangzhou Bay(China),but the sources of this nitrogen are not well understood.In this study,the August 2019 distributions of salinity,nutrients [nitrate(NO_(3)^(-)),nitrite,ammonium,and phosphate],and the stable isotopic composition of NO_(3)^(-)(δ^(15)N and δ^(18)O) were used to investigate sources of dissolved inorganic nitrogen(DIN) to Hangzhou B ay.Spatial distributions of nitrate,salinity,and nitrate δ^(18)O indicate that the Qiantang River,the Changjiang River,and nearshore coastal waters may all contribute nitrate to the bay.Based on the isotopic compositions of nitrate in these potential source waters and conservative mixing of nitrate in our study area,we suggest that the NO_(3)^(- )in Hangzhou B ay was likely derived mainly from soils,synthetic N fertilizer,and manure and sewage.End-member modeling indicates that in the upper half of the bay,the Qiantang River was a very important DIN source,possibly contributing more than 50% of DIN in the bay head area.In the lower half of the bay,DIN was sourced mainly from strongly intruding coastal water.DIN coming directly from the Changjiang River made a relatively small contribution to Hangzhou Bay DIN in August 2019.
基金financially supported by National Natural Science Foundation of China(Grant Nos.41571130072 and41130536)the Ministry of Science and Technology of China through Grant Nos.2016YFA0601000 and 2013CB956700
文摘China is experiencing rapid urbanization that has changed the water quality of rivers, especially nutrient loads. In this study, a typical urban river located in a karst area, Chengguan River, was chosen to explore the influence of urbanization on river ecosystems based on nutrient concentration and nitrate isotopes. The results show monthly variability of water chemistry and nutrient concentration. Nutrient concentration in two tributaries and the mainstem showed significant spatial variability, with heavy N and P pollution in one tributary near a suburban area,indicating a response to different levels of urbanization.Measurements of nitrate dual isotopes suggest thatvolatilization, assimilation, nitrification, and denitrification all occur in the polluted river. Water chemistry and nitrate isotopes show that major nitrogen sources included domestic waste and agricultural input, such as chemical fertilizer and manure. The results suggest that urbanization increases nutrient concentrations and accelerates the riverine nitrogen dynamic, and point to the need to manage point sources of sewage effluents to improve the water quality of urban rivers in southwestern China.
基金This research was financially supported by a project funded by the China Postdoctoral Science Foundation[grant numbers 2017LH020 and 2017M622815]the National Natural Science Foundation of China[grant numbers 41977190 and 41907198].
文摘In recent years,emergent pollutant’s accidents have occurred frequently in China,causing serious harm to the ecological environment.In this study,the impact of an accidental fire and explosion at Tianjin Port in 2015 on the atmosphere over the Bohai Sea was explored.Results showed sharp increases in the concentrations of several important components of fine particulate matter(e.g.NO3−,SO42−,NH4+,organic carbon,elemental carbon)over Beihuangcheng Island after the explosion.Among them,NO3−was most affected(about 10 days),with a maximum concentration of 16.45μg m−3.Theδ15N-NO3−ranged from−1.58‰to+8.74‰,with an average of+2.79‰±3.32‰.Influenced by the explosion,δ15N-NO3−decreased significantly,which was in accordance with the industrial processes of explosives.Theδ18O-NO3−varied between+49.40‰and+69.52‰,and showed a marked increase(+66.62‰±3.92‰)in the explosion-affected period.Using Monte Carlo simulation,the•OH pathway for NO3−formation was 51.79%±10.94%at that time—much lower than in the regular period.The elevated dry deposition of NO3−caused by the explosion was 266.08μmol N m−2 d−1 over the Bohai Sea—again,much higher than in the regular period.With the dry nitrogen deposition of NH4+(42.41μmol N m−2 d−1),the total nitrogen deposition increased by 308.49μmol N m−2 d−1,leading to severe ecological risk.Through the inverse computation of the dry deposition flux of NO3−,the affected area over the Bohai Sea was less than 1.42×104 km2,which is about 20%of the total area.
基金The National Natural Science Foundation of China under contract Nos 42076042 and 41721005the Science and Technology Basic Resources Investigation Program of China under contract No.2017FY201403.
文摘The dual isotopes(N and O)of nitrate were measured using a denitrifier bacterial method in the western South China Sea(WSCS)during September 2015 to elucidate key information during N transformation in the lower euphotic zone(LEZ)-upper mesopelagic zone(UMZ,down to 500 m in this study)continuum,which is a vital sub-environment for marine N cycle and sequestration of atmospheric CO_(2)as well.The N isotopic composition(δ^(15)N)of nitrate generally decreased from 500 m toward the base of the euphotic zone(∼100 m),reaching a value of∼4.6‰(vs.air N_(2))at the base of the LEZ,suggesting the imprint of remineralization(nitrification)of isotopically light N from atmospheric source.Theδ^(15)N andδ18O of nitrate only generally conform to a 1:1 line at 50 m and 75 m,suggesting that nitrate assimilation is a dominant process to shape nitrate isotope signature in this light-limited and relatively N-replete lower part of the euphotic zone.The fractionation factors of N and O isotopes during nitrate fractionation(15εASSIM,18εASSIM)using a steady-state model were estimated to be 4.0‰±0.3‰and 5.4‰±0.3‰,respectively.The occurrence of nitrification at the base of the LEZ and most of the UMZ is corroborated by the decoupling ofδ^(15)N and the oxygen isotopic composition(δ18O)of nitrate.Our results will provide insights for better understanding N cycle in the South China Sea from a perspective of present and past.
基金supported by the National Science Foundation of China(No:40543013, 40873003)and Key Laboratory of Isotope Geology, Ministry of Land and Resources
文摘The Turpan-Hami Basin in eastern Xinjiang is one of the driest regions on Earth and a premier environment to form and preserve nitrate.A large nitrate ore field in this basin was found recently.It is estimated there are about 2.5 billion tons of resources of nitrate,and the amount is as much as the Atacama Desert super-scale nitrate deposit in Chile.Nitrate is one of a few minerals with mass-independent fractionation（MIF）,and the oxygen isotope MIF is an effective method to determine the source of nitrate.Theδ^（17）O,δ^（18）O of nitrate were measured by fluorination and thermal decomposition method.The date indicated that this is the first time that oxygen isotope MIF has been located in inland nitrate minerals.The results obtained by two methods are similar,⊿^（17）=δ^（17）O-0.52×δ^（18）O=12‰-17‰.The experiment and observation data proved that oxygen isotope MIF of nitrate are the result of photochemical reactions in the troposphere and stratosphere.Thus, evidence from MIF oxygen isotopic compositions indicate that long term atmospheric deposition of nitrate aerosol particles produced by photochemical reactions is the source of the deposits.
基金The National Basic Research Program of China (973Program) under contract No.2010CB428903the National Natural Science Foundation of China under contract Nos 41006045 and 91128212+2 种基金National Science and Technology Pillar Program under contract No.2008BAC42B01China Postdoctoral Science Foundation under contract No.20100471690SIOSOA Project under contract Nos JT0707 and GCMAC1103
文摘The Changjiang Estuary has been considered as one of the most polluted estuaries in the world due to high nitrate （NO3） input, especially in spring and summer. In this study, 6~5N and t^180 of NO3, along with other chemical parameters in this area, were measured in spring to evaluate NO3 biogeochemical processes. A simple two end-members mixing model was used to examine the relative contribution of the Changjiang River Diluted Water and marine water to NO~ sources in the Changjiang Estuary and the adjacent East Chi- na Sea. The isotopic signals show that NO3 behaved relatively and conservatively in Transect F and Transect P where assimilation was weak possibly due to vertical mixing, while active assimilation and weak nitrifi- cation occurred in Transect D. Spatial difference in assimilation was indicated by the ~ 1：1 enrichment of S 15N and 6180 in the three transects, while spatial difference in nitrification was reflected by deviations of 15N and 6180 from assimilation line. Our results suggest that the input of the Changjiang River Diluted Wa- ter promoted NO3 assimilation possibly by stratifying the water column which favored the phytoplankton growth.
文摘Groundwater vulnerability for nitrate pollution of groundwater in the Brussel’s Capital Region was modelled using data-driven modelling approaches. The land use in the study area is heterogeneous. The South South-Eastern part of the region is forested, while the remaining part is urbanised. Groundwater nitrate concentration data were determined at 48 measurement stations distributed over the study area. In addition, oxygen and nitrogen isotope concentration of the nitrates were determined. The data show that the groundwater body is degraded, particularly in the urbanised part of the study area. The contamination with nitrates at degraded stations is slightly decreasing, while the opposite is true for the nitrate contamination at the less degraded stations. We modelled the contamination and trends of nitrate contamination using linear and non-linear statistical modelling techniques. In total, we defined 23 spatially distributed proxy variables that could explain nitrate contamination of the groundwater body. These proxy variables were defined at the grid size of 10 m, and averaged over the influence zone of each measurement station. The influence zones were identified using a simplified particle tracking algorithm from the groundwater piezometric map. The calculated influence zones were consistent with results obtained from a detailed numerical groundwater flow and transport model. Stepwise regression allowed explaining 56% of the observed variability of nitrate contaminations, while non-linear artificial neural network modelling allows explaining nearly 60% of the variability. The dominant explaining variables are the percentage of impermeable surface, the percentage of the sewage system that is in a degradation state, the number of urban infrastructure construction permits with a high pollution risk, the size of the influence zone, and the depth of the groundwater sampling. These results illustrate the important role of urban infrastructure on groundwater degradation and are consistent with the isotopic signature of nitrates determined on the sampling stations. The overlay of the nitrate contamination data with the DRASTIC vulnerability model shows that this latter conceptual model captures partially the spatial signature of the observed contamination.
文摘A metropolitan city such as Los Angeles (LA) is an ideal study site with a very high population density, and it houses at least 3 treatment plants where sewage is treated preliminarily and then progressing to tertiary treatment before discharging into the LA River. We will gain a better understanding of the water quality in the LA River and the nitrate load in the watershed system by examining the influence of waste water treatment plants (WWTPs). The goal of this study is to pinpoint the exact source of nitrate in the LA River using the isotope signatures. We have selected sampling locations both upstream and downstream of the WWTP. This serves to monitor nitrate levels, aiding in the assessment of treatment plant effectiveness, pinpointing nitrate pollution sources, and ensuring compliance with environmental regulations. The research explores the isotopic composition of NO3 in relation to atmospheric nitrogen and Vienna Standard Mean Ocean Water, shedding light on the contributions from various sources such as manure, sewage, soil organic nitrogen, and nitrogen fertilizers. Specifically, there is a change in the δ15NAir value between the dry and wet seasons. The isotope values in the Tillman WWTP sample changed between dry and wet seasons. Notably, the presence of nitrate originating from manure and sewage is consistent across seasons, emphasizing the significant impact of anthropogenic and agricultural activities on water quality. This investigation contributes to the broader understanding of nitrogen cycling in urban water bodies, particularly in the context of wastewater effluent discharge. The findings hold implications for water quality management and highlight the need for targeted interventions to mitigate the impact of nitrogen-containing compounds on aquatic ecosystems. Overall, the study provides a valuable framework for future research and environmental stewardship efforts aimed at preserving the health and sustainability of urban water resources. This data informs decisions regarding additional treatment or mitigation actions to safeguard downstream water quality and ecosystem health.
基金support granted to carry out the research,and for the funding,Dr.Graciela Herrera Zamarron,responsible for the project with Contract number 0266-1O-ED-F-DGAT-UNAM-2-19-1928.
文摘To explain the presence and spatial distribution of NO_(3)^(−)and N-NH_(3)in the Aquifer of the Metropolitan Area of Mexico City(AMAMC),a hydrogeochemical and isotopic analysis using^(13)C DIC(as well as the stable isotopes^(18)O and^(2)H)in groundwater was conducted.This aquifer is located in an old closed lacustrine volcano-sedimentary basin;some wells hosted in the semi-confined zone contain high N-NH_(3)concentrations,while others present NO_(3)^(−)contents in the recharge zones(hosted in an oxidizing environment).In this study,a change in the isotopic signature(primarily in^(18)O and^(2)H)was observed from the recharge zones to the basin center in some of the wells with high NO_(3)^(−)concentrations,this behavior can be attributed to evaporation during the incorporation of recently infiltrated water.In addition,the results for^(13)C(along with ^(2) H)in wells with the highest N-NH_(3)concentrations exhibited an atypically broad range of values.Results indicated the occurrence of hydrogeochemical and/or biochemical processes in the aquifer(in an oxidizing or reducing environment),such as organic degradation,bacterial decomposition(primarily in the ancient Lake Texcoco and which acts as a natural sink for carbon,nitrogen,sulfur,and phosphorus),besides rock weathering and dissolution,which may be responsible for a very marked isotopic modification of the^(13)C(and,to a lesser extent,2 H).Methanotrophic bacterial activity and methanogenic activity may be related to N-NH_(3)removal processes by oxidation and residual water incorporation respectively,whereas the increase in the NO_(3)^(−)content in some wells is due to the recent contribution of poor-quality water due to contamination.
基金supported by Basic Scientific Research Operation Cost of State-Leveled Public Welfare Scientific Research Courtyard (Grant No. K0926)National Natural Science Foundation of China (Grant Nos. 40543013, 40873003)Key Laboratory of Isotope Geology, Ministry of Land and Resources
文摘The recently discovered nitrate ore field in the Turpan-Hami Basin of western China represents an estimated resource of 2.5 billion tons, and is comparable in scale to the Atacama Desert super-scale nitrate deposit in Chile. The research on this area is rarely carried out, and the origin of the deposits remains uncertain. In this study, new methods were used to systematically analyze N and O isotopes in nitrate minerals collected from the Kumutage, Xiaocaohu, Wuzongbulak, Dawadi, Tuyugou, and Shaer ore deposits in the Turpan-Hami Basin. The data showed that the δ15NAir value ranges from 0.7‰ to 27.6‰, but mostly between 2‰ and 6‰, which was similar to atmospheric NO3-. The 18O was highly enriched with δ18OV-SMOW varying from 30.2‰ to 46.7‰. This differs from levels in deposits derived from microbial nitrogen fixation, but is similar to those in atmospheric nitrates. N and O isotopes data indicated that nitrate deposits in Turpan-Hami Basin must be the result of deposition of atmospheric nitrate particles. Although atmospheric nitrate particles are common, the nitrate deposits could form only under the condition of long-term extreme drought climate and very limited biological activity. This paper summarized the ore-forming mechanism of different types nitrate deposits based on their geological setting.
基金supported by the Natural Science Foundation of Hebei Province of China,China (No.D2015504008)the Fundamental Research Funds for the Institute of Hydrogeology and Environmental Geology,Chinese Academy of Geological Sciences,China (No.SK201707)Projects of China Geological Survey,China (No.DD20190331).
文摘A multi-isotope approach and mixing model were combined to identify spatial and seasonal variations of sources,and their proportional contribution to nitrate in the Hutuo River alluvial-pluvial fan region.The results showed that the NO3- concentration was significantly higher in the Hutuo River valley plain(178.7 mg/L) region than that in the upper and central pluvial fans of the Hutuo River(82.1 mg/L and 71.0 mg/L,respectively)and in the river(17.0 mg/L).Different land use types had no significant effect on the groundwater nitrate concentration.Based on a multi-isotope approach,we confirmed that the main sources of groundwater nitrate in different land use areas were domestic sewage and manure,followed by soil nitrogen,ammonia fertilizer,nitrate fertilizer and rainwater,and there were no significant spatial or seasonal variations.Combining δ^15N-NO3,δ^18O-NO3- and δ^37Cl results can increase the accuracy of traceability.Nitrification could be the most important nitrogen migration and transformation process,and denitrification did not significantly affected the isotopic composition of the nitrate.The SIAR model outputs revealed that the main nitrate pollution sources in groundwater and river water were domestic sewage and manure,accounting for 55.9%-61.0% and 22.6%(dry season),50.3%-60.4% and 34.1%(transition season),42.7%-47.6% and 35.6%(wet season 2016) and 45.9%-46.7% and 38.4%(wet season 2017),respectively.This work suggests that the random discharge and disposal of domestic sewage and manure should be the first target for control in order to prevent further nitrate contamination of the water environment.
