Nitrate source apportionment in groundwater using Bayesian isotope mixing model based on nitrogen isotope fractionation

Lu Yu; Tianyuan Zheng; Xilai Zheng; Yujie Hao; Ruyu Yuan

doi:10.1016/j.scitotenv.2020.137242

Nitrate source apportionment in groundwater using Bayesian isotope mixing model based on nitrogen isotope fractionation

Sci Total Environ. 2020 May 20:718:137242. doi: 10.1016/j.scitotenv.2020.137242. Epub 2020 Feb 10.

Authors

Lu Yu¹, Tianyuan Zheng², Xilai Zheng³, Yujie Hao¹, Ruyu Yuan¹

Affiliations

¹ College of Environmental Science and Engineering, Ocean University of China, Qingdao 266100, China; Key Lab of Marine Environmental Science and Ecology, Ministry of Education, Ocean University of China, Qingdao 266100, China.
² College of Engineering, Ocean University of China, Qingdao 266100, China. Electronic address: zhengtianyuan@ouc.edu.cn.
³ College of Environmental Science and Engineering, Ocean University of China, Qingdao 266100, China; Key Lab of Marine Environmental Science and Ecology, Ministry of Education, Ocean University of China, Qingdao 266100, China. Electronic address: zhxilai@ouc.edu.cn.

PMID: 32105927
DOI: 10.1016/j.scitotenv.2020.137242

Abstract

Accurate identification of nitrate (NO₃^-) sources is critical to address the issue of groundwater pollution. The nitrogen (N) isotopic enrichment factor (ɛ_p/s) is an important parameter to explain the N cycle and determine the proportional contribution of NO₃^- sources. Considering the isotopic fractionation effects in N transformation processes, this study quantitatively analyzed the NO₃^- sources in groundwater using stable isotopes (δ¹⁵N-NO₃^- and δ¹⁸O-NO₃^-) and the Bayesian isotope mixing model (SIAR). For the first time, the ɛ_p/s values (0.0‰, -8.7‰, -8.7‰, and 14.7‰) of atmospheric deposition (AD), soil nitrogen (SN), chemical fertilizers (CF), and manure and sewage (M&S) were calculated to determine the NO₃^- source apportionment in groundwater. It was proved that the isotopic fractionation effect could produce a more accurate NO₃^- source apportionment. We also found that the NO₃^- source contributions were closely related to the cropping system. In the vegetable cultivation area, CF (54.32%) and SN (37.75%) were the dominant NO₃^- source, while in the grain cultivation area, NO₃^- pollution was largely influenced by SN (33.67%), CF (33.27%), and M&S (30.16%). According to this study, the isotope fractionation is strongly recommended for NO₃^- source apportionment in groundwater system.

Keywords: Bayesian isotope mixing model; Isotope fractionation; Nitrate source; Nitrogen transformation.