Tracing sulfate origin and transformation in an area with multiple sources of pollution in northern China by using environmental isotopes and Bayesian isotope mixing model

摘要

Sulfate (SO42-) contamination in groundwater and surface water is an environmental problem of wide-spread concern. In this study, we combined stable isotope analyses of SO42- (delta S-34 and delta O-18) and water (delta H-2 and delta O-18) with a Bayesian mixing model (SIAR), for the first time, to identify sources and transformation of SO42- in an area of northern China with multiple potential sources of pollution. The overall values of delta S-34 and delta O-18-SO42- ranged from 1.3 parts per thousand to 16.3 parts per thousand and -3.8 parts per thousand-8.8 parts per thousand in groundwater, and from -1.1 parts per thousand to 9.3 parts per thousand and 2.7 parts per thousand-9.2 parts per thousand in surface waters, respectively. Analyses of SO42- isotopes and water chemistry indicated that SO42- in groundwater and surface water mainly originated from mixing of oxidation of sulfate, sewage, chemical fertilizers, dissolution of evaporite and precipitation. There was no significant correlation between delta S-34 and delta O-18 and SO42- concentration in groundwater, indicating that bacterial sulfate reduction did not affect the SO42- isotopic composition. SIAR model showed the main sources of SO42- in groundwater and surface water comprised oxidation of sulfide minerals and sewage. In groundwater, oxidation of sulfide minerals and sewage accounted for 37.5-44.5% and 35.5-42.7% of SO42-, respectively. In regard to surface waters, the contribution of oxidation of sulfide minerals to SO42- was higher in the wet season (31.8 +/- 9.9%) than in the intermediate (22.4 +/- 7.8%) and dry (20.9 +/- 8.2%) seasons, but the contribution proportion of sewage was slightly lower in the wet season (19.9 +/- 8.5%) than in the intermediate (23.8 +/- 8.7%) and dry (24.2 +/- 8.5%) seasons. This study indicates that it is necessary for local government to improve the treatment infrastructure for domestic sewage and optimize methods of agricultural fertilization and irrigation to prevent SO42- contamination of groundwater and surface water. (C) 2020 Elsevier Ltd. All rights reserved.