title: Identifying diffused nitrate sources in a stream in an agricultural field using a dual isotopic approach.
abstract: Nitrate (NO3(-)) pollution is a severe problem in aquatic systems in Taihu Lake Basin in China. A dual isotope approach (δ(15)NNO3(-) and δ(18)ONO3(-)) was applied to identify diffused NO3(-) inputs in a stream in an agricultural field at the basin in 2013. The site-specific isotopic characteristics of five NO3(-) sources (atmospheric deposition, AD; NO3(-) derived from soil organic matter nitrification, NS; NO3(-) derived from chemical fertilizer nitrification, NF; groundwater, GW; and manure and sewage, M&S) were identified. NO3(-) concentrations in the stream during the rainy season [mean±standard deviation (SD)=2.5±0.4mg/L] were lower than those during the dry season (mean±SD=4.0±0.5mg/L), whereas the δ(18)ONO3(-) values during the rainy season (mean±SD=+12.3±3.6‰) were higher than those during the dry season (mean±SD=+0.9±1.9‰). Both chemical and isotopic characteristics indicated that mixing with atmospheric NO3(-) resulted in the high δ(18)O values during the rainy season, whereas NS and M&S were the dominant NO3(-) sources during the dry season. A Bayesian model was used to determine the contribution of each NO3(-) source to total stream NO3(-). Results showed that reduced N nitrification in soil zones (including soil organic matter and fertilizer) was the main NO3(-) source throughout the year. M&S contributed more NO3(-) during the dry season (22.4%) than during the rainy season (17.8%). AD generated substantial amounts of NO3(-) in May (18.4%), June (29.8%), and July (24.5%). With the assessment of temporal variation of diffused NO3(-) sources in agricultural field, improved agricultural management practices can be implemented to protect the water resource and avoid further water quality deterioration in Taihu Lake Basin.
authors.affiliation: School of Environment, Beijing Normal University, Beijing 100875, China.
authors.forename: Jingtao
authors.initials: J
authors.lastname: Ding
authors.affiliation: Chinese Research Academy of Environmental Sciences, Beijing 100012, China. Electronic address: xbd100012@163.com.
authors.forename: Beidou
authors.initials: B
authors.lastname: Xi
authors.affiliation: Chinese Research Academy of Environmental Sciences, Beijing 100012, China.
authors.forename: Rutai
authors.initials: R
authors.lastname: Gao
authors.affiliation: Chinese Research Academy of Environmental Sciences, Beijing 100012, China.
authors.forename: Liansheng
authors.initials: L
authors.lastname: He
authors.affiliation: Chinese Research Academy of Environmental Sciences, Beijing 100012, China.
authors.forename: Hongliang
authors.initials: H
authors.lastname: Liu
authors.affiliation: Changzhou Environmental Monitoring Center, Jiangsu 213001, China.
authors.forename: Xuanli
authors.initials: X
authors.lastname: Dai
authors.affiliation: Changzhou Environmental Monitoring Center, Jiangsu 213001, China.
authors.forename: Yijun
authors.initials: Y
authors.lastname: Yu
mesh_terms: D000383:Agriculture; D001499:Bayes Theorem; D002681:China; D004784:Environmental Monitoring / Q000379:methods*; D005308:Fertilizers / Q000706:statistics & numerical data; D060587:Groundwater / Q000737:chemistry; D009566:Nitrates / Q000032:analysis*; D058465:Nitrification; D009587:Nitrogen Isotopes / Q000032:analysis; D010103:Oxygen Isotopes / Q000032:analysis; D045483:Rivers / Q000737:chemistry*; D012621:Seasons; D062065:Wastewater / Q000737:chemistry / Q000706:statistics & numerical data; D014874:Water Pollutants, Chemical / Q000032:analysis*; D014877:Water Pollution, Chemical / Q000706:statistics & numerical data*
chemical_list: D005308:Fertilizers; D009566:Nitrates; D009587:Nitrogen Isotopes; D010103:Oxygen Isotopes; D062065:Wastewater; D014874:Water Pollutants, Chemical
keywords: Dual isotope; Nitrate; SIAR; Source apportionment; Source identification