Abstract
A high concentration of nitrate (NO3−) in surface water threatens aquatic systems and human health. Revealing nitrate characteristics and identifying its sources are fundamental to making effective water management strategies. However, nitrate sources in multi-tributaries and mix land use watersheds remain unclear. In this study, based on 20 surface water sampling sites for more than two years’ monitoring from April 2012 to December 2014, water chemical and dual isotopic approaches (δ15N-NO3− and δ18O-NO3−) were integrated for the first time to evaluate nitrate characteristics and sources in the Huashan watershed, Jianghuai hilly region, China. Nitrate-nitrogen concentrations (ranging from 0.02 to 8.57 mg/L) were spatially heterogeneous that were influenced by hydrogeological and land use conditions. Proportional contributions of five potential nitrate sources (i.e., precipitation; manure and sewage, M & S; soil nitrogen, NS; nitrate fertilizer; nitrate derived from ammonia fertilizer and rainfall) were estimated by using a Bayesian isotope mixing model. The results showed that nitrate sources contributions varied significantly among different rainfall conditions and land use types. As for the whole watershed, M & S (manure and sewage) and NS (soil nitrogen) were major nitrate sources in both wet and dry seasons (from 28% to 36% for manure and sewage and from 24% to 27% for soil nitrogen, respectively). Overall, combining a dual isotopes method with a Bayesian isotope mixing model offered a useful and practical way to qualitatively analyze nitrate sources and transformations as well as quantitatively estimate the contributions of potential nitrate sources in drinking water source watersheds, Jianghuai hilly region, eastern China.
Highlights
Nitrate is essential for the growth and survival of plants, animals, and humans
Five potential nitrate sources (NO3 − in precipitation, NP; manure and sewage, M & S; soil N, NS; NO3 − fertilizer, NF; and NO3 − nitrified from NH4 + in fertilizer and rainfall, NFA) were integrated by the Stable Isotope Analysis in R (SIAR) for different watersheds (ESW, middle sub-watershed sub‐watershed (MSW), watershed sub‐watershed (WSW), Zhuyuangou sub-watershed sub‐watershed (ZSW) and whole watershed (WW)) during different temporal periods
Multi-tributaries with different land uses perplexed nitrate sources identification in the Huashan watershed located in the upper stream of drink water source of Chuzhou city, China
Summary
Nitrate is essential for the growth and survival of plants, animals, and humans. a high concentration of nitrate in surface and ground water brings risks to aquatic systems (e.g., eutrophication and hypoxia) and human health (e.g., reducing oxygen supply of red blood cells) [1]. The basic mass balance mixing model can solve three sources using dual isotopes of δ15 N-NO3 − and δ18 O-NO3 − [3] This method cannot calculate contribution proportions of nitrate from different sources when there are more than three sources, and the temporal and spatial variability of δ15 N-NO3 − and δ18 O-NO3 − in sources is not incorporated [18]. Bayesian framework isotope mixing models provide a way to simulate proportional contribution from multiple sources along with probability estimations. A Bayesian stable isotope mixing model was developed in R statistical computing programs, which is referred to as Stable Isotope Analysis in R (SIAR) [3,18,20] This model estimates proportions in mixtures with more than three sources and takes into account the uncertainties in tempo-spatial variabilities as well as isotopic fractionations. Different nitrate sources based on a Bayesian isotope mixing model
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