Quantitative Identification of Nitrate Sources in a Coastal Peri-Urban Watershed Using Hydrogeochemical Indicators and Dual Isot
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Chemosphere 243 (2020) 125364 Contents lists available at ScienceDirect Chemosphere journal homepage: www.elsevier.com/locate/chemosphere Quantitative identification of nitrate sources in a coastal peri-urban watershed using hydrogeochemical indicators and dual isotopes together with the statistical approaches * Zhaofeng Guo a, b, Changzhou Yan a, , Zaosheng Wang a, Feifei Xu a, Fan Yang a a Key Laboratory of Urban Environment and Health, Fujian Key Laboratory of Watershed Ecology, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen, 361021, China b University of Chinese Academy of Sciences, Beijing, 100049, China highlights graphical abstract MixSIAR model revealed no signifi- À cant seasonal difference in NO3 pollution. Reveal the degree and difference of water pollution by using PCA in peri- urban area. Relationships between lower d15N values and nutrients implied nitrifi- cation occurred. Manure and sewage were the main À NO3 sources of Jimei Lake. article info abstract Article history: Surplus nutrient load and complex migration and transformation processes are the challenges for water Received 2 June 2019 quality management in the peri-urban coastal watershed, leading to increasing concerns worldwide. We Received in revised form investigated the spatio-temporal variation of hydrogeochemical parameters in surface water of Jimei 11 October 2019 À Lake watershed, and distinguished the sources and transformation of nitrate-N (NO3 -N) using dual Accepted 12 November 2019 À isotopes of nitrate (d15N and d18OinNO) with hydrogeochemical indicators. Principal component Available online 16 November 2019 3 analysis (PCA) on hydrogeochemical parameters demonstrated that surface water was seriously polluted Handling Editor: Hyunook Kim by nutrients, especially in the southeast of the downstream. There were signs of seawater intrusion and increased wastewater discharge in the mid-lower reaches with high ammonium concentrations. Nitri- 15 18 À Keywords: fication occurred throughout the monitoring period with lower d N and d O values and NO3 derived À Nitrate isotope from mixed pollution sources. Results of Bayesian model showed that dominant NO3 input originated Spatio-temporal variations from manure and sewage (M&S, 71% and 76% in the wet and dry season, respectively) and atmospheric Multivariate statistical analysis deposition (22% and 16%, respectively). This result implied that the controls and treatment of M&S Bayesian model À discharges are essential to alleviate of NO3 pollution. The proposed method is helpful to understand the Source apportionment À origins of NO3 and may be suitable to develop measures for the reducing of nitrogen loadings in the peri- urban watershed. © 2019 Elsevier Ltd. All rights reserved. 1. Introduction * Corresponding author. As main input channels of nutrients and chemicals, coastal E-mail address: [email protected] (C. Yan). https://doi.org/10.1016/j.chemosphere.2019.125364 0045-6535/© 2019 Elsevier Ltd. All rights reserved. 2 Z. Guo et al. / Chemosphere 243 (2020) 125364 À watersheds have an important influence on the water quality of fertilizers and possible sources of atmospheric NO3 and human/ À coastal sea area, and are vulnerable to land use and population animal waste based on NO3 isotopes and chemical indicators (e.g., change. According to statistics, 27% of the coastal watersheds in chloride, sodium, fluoride, sulfate, atrazine). To better evaluate the China did not meet the Class IV water quality standards (Environ- contamination contribution of each nitrogen source, source mental Quality Standards for Surface Water of China, GB3838- apportionment models such as IsoSource, mass-balance mixing 2002), and the main pollutant exceeding the standard was inor- model, and Bayesian model have been applied (Deutsch et al., ganic nitrogen, resulting in over 51% of the sea areas in various 2006; Hale et al., 2014; Nie et al., 2012; Yang and Toor, 2017). degrees of eutrophication (Bulletin on China’s Marine Ecological Compared with other models, MixSIAR model, which applied À Environment in 2018). NO3 pollution in coastal environment is Marchain Monte Carlo method to estimate the probability distri- mainly caused by intensive anthropogenic activities (e.g., sewage bution, can be better considered the uncertainties (seasonal vari- discharge from production and living, synthetic fertilizers and ation of isotopes, multiple sources > 3, and isotope fractionation) manure use, and excess nitrogen deposition due to the air pollu- (Parnell et al., 2010). tion) and continuous in-depth change in land use, which has Jimei Lake watershed in southeast China is an important coastal become a widespread environmental issue (Kaushal et al., 2011; area with municipal water supply, landscape water, agricultural À Zhang et al., 2015). Elevated NO3 concentrations in water bodies, irrigation and flood control functions. As a typical peri-urban area, especially in coastal and marine environments, cause eutrophica- Jimei Lake watershed is disturbed by intensive human activities. As tion, harmful algal blooms, and hypoxia, ultimately resulting in a a result, Jimei Lake is beset by serious eutrophication. The security series of harmful knock-on effects (Dai et al., 2008; Gutierrez et al., guarantee of water environment in studied areas is causing great À 2018). Consequently, to ensure the safety of water quality, it is public concern. Source apportionment of NO3 pollution and nu- essential to take effective measures to reduce inputs of excessive trients discharge is the primary attention for integrative gover- À nitrogen. The accurate identification of the main NO3 contributors nance actions. Due to the complex land-use types in peri-urban and its transformations are critical prerequisite for efficient water areas, the source apportionment remains challenging with the quality management. diversification of pollution sources. Locally, the most important À To date, existing investigations have frequently been done about contribution of NO3 may be from the production and domestic À identification of NO3 sources in groundwater or surface water ac- wastewater, because of the increasing urbanization rate. In addi- 15 18 À À cording to the typical d N and d O values of NO3 sources (Hale tion, the monthly average of NO3 concentrations in rainwater À et al., 2014; Johannsen et al., 2008; Kreitler and Browning, 1983; collected from Xiamen reached 1.84 mg L 1 (Wu et al., 2018), which Pasten-Zapata et al., 2014; Wassenaar, 1995). The successful appli- suggested that nitrogen deposition from the atmospheric system is cation of the isotopic technique for identification of contamination also a major source of nitrogen pollution in Xiamen’s water envi- À sources is due to the fact that some NO3 sources exhibit distinctive ronment. In recent years, although the use of agricultural chemical isotopic compositions. Yet, the initial isotope abundance can be fertilizers under the government control has reduced by nearly half greatly altered by isotopic fractionation during biogeochemical since 2010 (Website: http://www.xm.gov.cn/zwgk/tqjj/xmjjtqnj/), transformation (Kendall et al., 2007). Thus, in addition to deter- the amount of nitrogen fertilizer (e.g., ammonium bicarbonate, À mining the origins, recently, the transformation pathways of NO3 urea and nitrate fertilizer), phosphate fertilizer (e.g., calcium su- such as denitrification, nitrification, assimilation and mineraliza- perphosphate and calcium magnesium phosphate), potassium tion have been differentiated through the dual isotope model fertilizer, and compound fertilizer still reached 2905, 1396, 2407, À (Adebowale et al., 2019; Einsiedl and Mayer, 2006; Mayer and and 5669 tons respectively in 2017. Besides, NO3 pollution caused Wassenaar, 2012; Yi et al., 2017). by organic fertilizer, such as poultry manure, used in agriculture A more bothersome challenge is the overlapping source isotope and aquaculture cannot be neglected. The contribution of other compositions in complex systems, making it difficult to provide nitrogen sources to this watershed remains to be further examined. À specific sources using NO3 isotopes. Recent researches have already Here, we conducted an integrated research to investigate the À argued that the integration of stable isotopes with hydro- spatio-temporal patterns and source apportionment of NO3 geochemical parameters is regarded as an effective and screening pollution in Jimei Lake watershed by coupling hydrogeochemical À tool to reduce the uncertainties in tracing sources of NO3 in water. indicators and dual isotopes together with the statistical ap- Source identification with hydrogeochemistry is of interest proaches. Firstly, the spatio-temporal variations of hydro- À considering that besides NO3 , relevant nitrogen sources contain geochemical parameters were evaluated in the study watershed. other characteristic components, which will inevitably change the Secondly, combining principal component analysis (PCA) and content of these components in the environment and have an multiple hydrogeochemical indicators provided preliminary infor- À impact on the water quality. In particular, nitrogen sources and mation on potential NO3 sources. Then, the spatio-temporal vari- À À transformation of NO3 as well as equilibrium fractionations of ations of NO3 sources and related transformations were further isotopic fractionation (Fenech et al., 2012) were closely associated distinguished by combining land-use type and dual stable isotopes. with land use and physicochemical