土地利用类型对渭河流域关中段地表水硝酸盐污染的影响
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摘要
地表水硝酸盐(NO~-_3)污染会造成水生态环境损害,引起水生态系统发生退化。通过溯源研究能够及时发现隐患和危害的源头,对保障水生态环境安全具有重要的意义。本研究选取渭河流域关中段13个子流域为研究对象,运用同位素方法结合水化学研究土地利用类型与地表水NO~-_3含量的关系,准确识别NO~-_3的主要污染来源。研究结果表明,整个流域NO~-_3含量范围为4.2—150.1 mg/L,平均含量38.2 mg/L。约有35.3%的样品NO~-_3含量超过《地表水环境质量标准》(GB 3838—2002)中硝酸盐的含量。渭河干流污染较支流严重,南岸支流较北岸支流污染严重。渭河干流、支流的源头及上游区域NO~-_3浓度普遍较低,说明受人类活动影响较小,沿着河流流向,NO~-_3浓度逐渐升高。耕地和城乡/工矿/居民用地面积与地表水NO~-_3浓度呈显著正相关(P<0.05),相关系数分别为0.627和0.830。而草地和林地与NO~-_3浓度呈显著负相关(P<0.05),相关系数分别为-0.775和-0.695。流域内,NO~-_3污染来源主要为动物排泄物及生活污水和工业废水的排放。农业活动中化肥的施用也是NO~-_3升高的一个重要原因。根据流域污染溯源结果,建议规范建设用地,加强污水排放和畜禽粪便的管理,同时提高化肥的使用效率,以达到减少水生态环境损害的目的。
Land-use patterns changes dramatically have effects on the river water quality by altering the natural appearance, material circulation, and energy distribution of landscapes within watershed ecosystems. Nitrogen pollution is due to alteration of runoff, non-point source pollution production, and nutrient transportation driven by land-use changes. Nitrate pollution in rivers is becoming a serious problem,and excessively high levels of nitrate in rivers could lead to more virulent diseases and cause environmental and ecological problems. The pollution sources of river nitrate can be identified by the nitrogen isotopic composition of nitrate. In this study, thirteen subwatersheds are selected with surface water samples collected from Guanzhong area in the Weihe River basin in January 2016. Hydrochemical assessment and nitrogen isotopic measurement are made to determine the pollution levels of nitrate, investigate the effects of land-use types on river nitrogen pollution, and identify the principal sources of nitrate pollution in surface water. For the whole watershed, the nitrate concentration of surface water ranges from 4.2 mg/L to 150.1 mg/L, with the mean value of 38.2 mg/L. Approximately 35.3% of the surface water samples exceed the maximum contaminant level(MCL) of nitrate for the environmental quality standards for surface water. The nitrate concentration of the Weihe River main stream, northern tributaries, and southern tributaries range from 9.6 mg/L to 82.5 mg/L, 4.2 mg/L to 86.4 mg/L, and 8.0 mg/L to 150.1 mg/L, with the average nitrate concentration of 47.9 mg/L, 33.1 mg/L, and 43.8 mg/L, respectively. About 40%, 33.3%, and 33.3% of surface water samples from the Weihe River main stream, northern tributaries, and southern tributaries, respectively, exceed the MCL. Nitrate content in the main stream is obviously greater than that in the tributaries. Nitrate pollution in the surface water around the mountainous areas was much less than that in other areas. The proportions of land-use types differ greatly among the subwatersheds, and the proportion of cropland is the largest, with the average value of 47.5%. The proportion of build-up land increases from upstream to downstream With rivers receiving municipal sewage along the flow directions. A correlation analysis shows that four land-use types(build-up land, cropland, forestland, and grassland) correlate well with nitrate variables, with the correlation coefficients of 0.830, 0.627,-0.695, and-0.775, respectively, an indication that farmland and built-up land uses have positive contribution to river nitrate pollution, whereas grassland and forestland use types have negative contribution to river nitrate pollution in the surface water. There is no significant effect of denitrification on the shift in N isotopic values. The δ~(15)N composition ranges from 0.7‰ to 19.1‰, with the average value of 10.3‰. Analyses of hydrochemistry and nitrogen isotopic composition indicate that the nitrate pollution in the Weihe River basin is significantly affected by human activities. Manure and sewage are considered to be the dominant sources of NO~-_3 pollution of surface water in the whole basin, especially in the lower reaches(Xianyang, Xi′an, and Weinan sections). Chemical fertilizer is the other important nitrate contributor to rivers in the agricultural areas. It is suggested by this research that regulating build-up land uses, strengthening the management of manure and sewage, and improving the application rate of fertilizer should be the effective methods for controlling river nitrogen.
Land-use patterns changes dramatically have effects on the river water quality by altering the natural appearance, material circulation, and energy distribution of landscapes within watershed ecosystems. Nitrogen pollution is due to alteration of runoff, non-point source pollution production, and nutrient transportation driven by land-use changes. Nitrate pollution in rivers is becoming a serious problem,and excessively high levels of nitrate in rivers could lead to more virulent diseases and cause environmental and ecological problems. The pollution sources of river nitrate can be identified by the nitrogen isotopic composition of nitrate. In this study, thirteen subwatersheds are selected with surface water samples collected from Guanzhong area in the Weihe River basin in January 2016. Hydrochemical assessment and nitrogen isotopic measurement are made to determine the pollution levels of nitrate, investigate the effects of land-use types on river nitrogen pollution, and identify the principal sources of nitrate pollution in surface water. For the whole watershed, the nitrate concentration of surface water ranges from 4.2 mg/L to 150.1 mg/L, with the mean value of 38.2 mg/L. Approximately 35.3% of the surface water samples exceed the maximum contaminant level(MCL) of nitrate for the environmental quality standards for surface water. The nitrate concentration of the Weihe River main stream, northern tributaries, and southern tributaries range from 9.6 mg/L to 82.5 mg/L, 4.2 mg/L to 86.4 mg/L, and 8.0 mg/L to 150.1 mg/L, with the average nitrate concentration of 47.9 mg/L, 33.1 mg/L, and 43.8 mg/L, respectively. About 40%, 33.3%, and 33.3% of surface water samples from the Weihe River main stream, northern tributaries, and southern tributaries, respectively, exceed the MCL. Nitrate content in the main stream is obviously greater than that in the tributaries. Nitrate pollution in the surface water around the mountainous areas was much less than that in other areas. The proportions of land-use types differ greatly among the subwatersheds, and the proportion of cropland is the largest, with the average value of 47.5%. The proportion of build-up land increases from upstream to downstream With rivers receiving municipal sewage along the flow directions. A correlation analysis shows that four land-use types(build-up land, cropland, forestland, and grassland) correlate well with nitrate variables, with the correlation coefficients of 0.830, 0.627,-0.695, and-0.775, respectively, an indication that farmland and built-up land uses have positive contribution to river nitrate pollution, whereas grassland and forestland use types have negative contribution to river nitrate pollution in the surface water. There is no significant effect of denitrification on the shift in N isotopic values. The δ~(15)N composition ranges from 0.7‰ to 19.1‰, with the average value of 10.3‰. Analyses of hydrochemistry and nitrogen isotopic composition indicate that the nitrate pollution in the Weihe River basin is significantly affected by human activities. Manure and sewage are considered to be the dominant sources of NO~-_3 pollution of surface water in the whole basin, especially in the lower reaches(Xianyang, Xi′an, and Weinan sections). Chemical fertilizer is the other important nitrate contributor to rivers in the agricultural areas. It is suggested by this research that regulating build-up land uses, strengthening the management of manure and sewage, and improving the application rate of fertilizer should be the effective methods for controlling river nitrogen.
引文
[1] Li S L,Liu C Q,Li J,Xue Z C,Guan J,Liang Y C,Ding H,Li H B.Evaluation of nitrate source in surface water of southwestern China based on stable isotopes.Environmental Earth Sciences,2013,68(1):219-228.
[2] Domangue R J,Mortazavi B.Nitrate reduction pathways in the presence of excess nitrogen in a shallow eutrophic estuary.Environmental Pollution,2018,238:599-606.
[3] 丁京涛,席北斗,许其功,高如泰,卢义,黄健,刘鸿亮.稳定同位素技术在地表水硝酸盐污染研究中的应用.湖泊科学,2013,25(5):617-627.
[4] Zhang Y,Shi P,Li F D,Wei A L,Song J X,Ma J J.Quantification of nitrate sources and fates in rivers in an irrigated agricultural area using environmental isotopes and a Bayesian isotope mixing model.Chemosphere,2018,208:493-501.
[5] 刘相超,祖波,宋献方,夏军,唐常源,张依章.三峡库区梁滩河流域水化学与硝酸盐污染.地理研究,2010,29(4):629-639.
[6] Zhang Y,Li F D,Zhang Q Y,Li J,Liu Q.Tracing nitrate pollution sources and transformation in surface- and ground-waters using environmental isotopes.Science of the Total Environment,2014,490:213-222.
[7] Yue F J,Liu X L,Li J,Zhu Z Z,Wang Z L.Using nitrogen isotopic approach to identify nitrate sources in waters of Tianjin,China.Bulletin of Environmental Contamination and Toxicology,2010,85(6):562-567.
[8] Li S L,Liu C Q,Li J,Liu X L,Chetelat B,Wang B L,Wang F S.Assessment of the sources of nitrate in the Changjiang River,China using a nitrogen and oxygen isotopic approach.Environmental Science & Technology,2010,44(5):1573-1578.
[9] Marconi D,Weigand M A,Rafter P A,McIlvin M R,Forbes M,Casciotti K L,Sigman D M.Nitrate isotope distributions on the US GEOTRACES North Atlantic cross-basin section:Signals of polar nitrate sources and low latitude nitrogen cycling.Marine Chemistry,2015,177:143-156.
[10] Yang Y Y,Toor G S.Sources and mechanisms of nitrate and orthophosphate transport in urban stormwater runoff from residential catchments.Water Research,2017,112:176-184.
[11] 张东,杨伟,赵建立.氮同位素控制下黄河及其主要支流硝酸盐来源分析.生态与农村环境学报,2012,28(6):622-627.
[12] 郭巍.水质水量结合评价渭河干流(陕西段)水资源变化.水资源与水工程学报,2011,22(5):115-120,125-125.
[13] 董雯,张振文,孙长顺,李怀恩.1996-2009年渭河干流氮素污染特征.水土保持通报,2014,34(5):114-117.
[14] Xing M,Liu W G.Using dual isotopes to identify sources and transformations of nitrogen in water catchments with different land uses,Loess Plateau of China.Environmental Science and Pollution Research,2016,23(1):388-401.
[15] 邢萌,刘卫国.西安浐河、灞河硝酸盐氮同位素特征及污染源示踪探讨.地球学报,2008,29(6):783-789.
[16] 邢萌,刘卫国.浐河、灞河硝酸盐端元贡献比例—基于硝酸盐氮、氧同位素研究.地球环境学报,2016,7(1):27-36.
[17] 邢萌,刘卫国,胡婧.泸河、涝河河水硝酸盐氮污染来源的氮同位素示踪.环境科学,2010,31(10):2305-2310.
[18] Bu H M,Zhang Y,Meng W,Song X F.Effects of land-use patterns on in-stream nitrogen in a highly-polluted river basin in Northeast China.Science of the Total Environment,2016,553:232-242.
[19] 张蓉珍,张幸.渭河流域陕西段近50年生态环境演变.干旱区资源与环境,2008,22(2):37-42.
[20] 张丽梅,赵广举,穆兴民,高鹏,孙文义.基于Budyko假设的渭河径流变化归因识别.生态学报,2018,38(21):7607-7617.
[21] Silva S R,Ging P B,Lee R W,Ebbert J C,Tesoriero A J,Inkpen E L.Forensic applications of nitrogen and oxygen isotopes in tracing nitrate sources in urban environments.Environmental Forensics,2002,3(2):125-130.
[22] Piňa-Ochoa E,álvarez-Cobelas M.Denitrification in aquatic environments:A cross-system analysis.Biogeochemistry,2006,81(1):111-130.
[23] 孙占超,钱会,孟祥仪.渭河陕西段氨氮污染物时空特征分析.华北水利水电大学学报:自然科学版,2015,36(5):81-83.
[24] 陈成龙,高明,倪九派,谢德体,邓华.三峡库区小流域不同土地利用类型对氮素流失影响.环境科学,2016,37(5):1707-1716.
[25] Lee K S,Bong Y S,Lee D,Kim Y,Kim K.Tracing the sources of nitrate in the Han River watershed in Korea,using δ15N-NO3- and δ18O-NO3 values.Science of the Total Environment,2008,395(2/3):117-124.
[26] 项颂,庞燕,窦嘉顺,吕兴菊,薛力强,储昭升.不同时空尺度下土地利用对洱海入湖河流水质的影响.生态学报,2018,38(3):876-885.
[27] Piatek K B,Christopher S F,Mitchell M J.Spatial and temporal dynamics of stream chemistry in a forested watershed.Hydrology and Earth System Sciences,2009,13(3):423-439.
[28] Liu W G,Xing M.Isotopic indicators of carbon and nitrogen cycles in river catchments during soil erosion in the arid Loess Plateau of China.Chemical Geology,2012,296-297:66-72.
[29] 陕西省统计局.陕西统计年鉴2015.北京:中国统计出版社,2015.
[30] Xue Y,Song J X,Zhang Y,Kong F H,Wen M,Zhang G T.Nitrate pollution and preliminary source identification of surface water in a semi-arid river basin,using isotopic and hydrochemical approaches.Water,2016,8(8):328.
[2] Domangue R J,Mortazavi B.Nitrate reduction pathways in the presence of excess nitrogen in a shallow eutrophic estuary.Environmental Pollution,2018,238:599-606.
[3] 丁京涛,席北斗,许其功,高如泰,卢义,黄健,刘鸿亮.稳定同位素技术在地表水硝酸盐污染研究中的应用.湖泊科学,2013,25(5):617-627.
[4] Zhang Y,Shi P,Li F D,Wei A L,Song J X,Ma J J.Quantification of nitrate sources and fates in rivers in an irrigated agricultural area using environmental isotopes and a Bayesian isotope mixing model.Chemosphere,2018,208:493-501.
[5] 刘相超,祖波,宋献方,夏军,唐常源,张依章.三峡库区梁滩河流域水化学与硝酸盐污染.地理研究,2010,29(4):629-639.
[6] Zhang Y,Li F D,Zhang Q Y,Li J,Liu Q.Tracing nitrate pollution sources and transformation in surface- and ground-waters using environmental isotopes.Science of the Total Environment,2014,490:213-222.
[7] Yue F J,Liu X L,Li J,Zhu Z Z,Wang Z L.Using nitrogen isotopic approach to identify nitrate sources in waters of Tianjin,China.Bulletin of Environmental Contamination and Toxicology,2010,85(6):562-567.
[8] Li S L,Liu C Q,Li J,Liu X L,Chetelat B,Wang B L,Wang F S.Assessment of the sources of nitrate in the Changjiang River,China using a nitrogen and oxygen isotopic approach.Environmental Science & Technology,2010,44(5):1573-1578.
[9] Marconi D,Weigand M A,Rafter P A,McIlvin M R,Forbes M,Casciotti K L,Sigman D M.Nitrate isotope distributions on the US GEOTRACES North Atlantic cross-basin section:Signals of polar nitrate sources and low latitude nitrogen cycling.Marine Chemistry,2015,177:143-156.
[10] Yang Y Y,Toor G S.Sources and mechanisms of nitrate and orthophosphate transport in urban stormwater runoff from residential catchments.Water Research,2017,112:176-184.
[11] 张东,杨伟,赵建立.氮同位素控制下黄河及其主要支流硝酸盐来源分析.生态与农村环境学报,2012,28(6):622-627.
[12] 郭巍.水质水量结合评价渭河干流(陕西段)水资源变化.水资源与水工程学报,2011,22(5):115-120,125-125.
[13] 董雯,张振文,孙长顺,李怀恩.1996-2009年渭河干流氮素污染特征.水土保持通报,2014,34(5):114-117.
[14] Xing M,Liu W G.Using dual isotopes to identify sources and transformations of nitrogen in water catchments with different land uses,Loess Plateau of China.Environmental Science and Pollution Research,2016,23(1):388-401.
[15] 邢萌,刘卫国.西安浐河、灞河硝酸盐氮同位素特征及污染源示踪探讨.地球学报,2008,29(6):783-789.
[16] 邢萌,刘卫国.浐河、灞河硝酸盐端元贡献比例—基于硝酸盐氮、氧同位素研究.地球环境学报,2016,7(1):27-36.
[17] 邢萌,刘卫国,胡婧.泸河、涝河河水硝酸盐氮污染来源的氮同位素示踪.环境科学,2010,31(10):2305-2310.
[18] Bu H M,Zhang Y,Meng W,Song X F.Effects of land-use patterns on in-stream nitrogen in a highly-polluted river basin in Northeast China.Science of the Total Environment,2016,553:232-242.
[19] 张蓉珍,张幸.渭河流域陕西段近50年生态环境演变.干旱区资源与环境,2008,22(2):37-42.
[20] 张丽梅,赵广举,穆兴民,高鹏,孙文义.基于Budyko假设的渭河径流变化归因识别.生态学报,2018,38(21):7607-7617.
[21] Silva S R,Ging P B,Lee R W,Ebbert J C,Tesoriero A J,Inkpen E L.Forensic applications of nitrogen and oxygen isotopes in tracing nitrate sources in urban environments.Environmental Forensics,2002,3(2):125-130.
[22] Piňa-Ochoa E,álvarez-Cobelas M.Denitrification in aquatic environments:A cross-system analysis.Biogeochemistry,2006,81(1):111-130.
[23] 孙占超,钱会,孟祥仪.渭河陕西段氨氮污染物时空特征分析.华北水利水电大学学报:自然科学版,2015,36(5):81-83.
[24] 陈成龙,高明,倪九派,谢德体,邓华.三峡库区小流域不同土地利用类型对氮素流失影响.环境科学,2016,37(5):1707-1716.
[25] Lee K S,Bong Y S,Lee D,Kim Y,Kim K.Tracing the sources of nitrate in the Han River watershed in Korea,using δ15N-NO3- and δ18O-NO3 values.Science of the Total Environment,2008,395(2/3):117-124.
[26] 项颂,庞燕,窦嘉顺,吕兴菊,薛力强,储昭升.不同时空尺度下土地利用对洱海入湖河流水质的影响.生态学报,2018,38(3):876-885.
[27] Piatek K B,Christopher S F,Mitchell M J.Spatial and temporal dynamics of stream chemistry in a forested watershed.Hydrology and Earth System Sciences,2009,13(3):423-439.
[28] Liu W G,Xing M.Isotopic indicators of carbon and nitrogen cycles in river catchments during soil erosion in the arid Loess Plateau of China.Chemical Geology,2012,296-297:66-72.
[29] 陕西省统计局.陕西统计年鉴2015.北京:中国统计出版社,2015.
[30] Xue Y,Song J X,Zhang Y,Kong F H,Wen M,Zhang G T.Nitrate pollution and preliminary source identification of surface water in a semi-arid river basin,using isotopic and hydrochemical approaches.Water,2016,8(8):328.
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