Journal
ECOTOXICOLOGY AND ENVIRONMENTAL SAFETY
Volume 231, Issue -, Pages -Publisher
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.ecoenv.2022.113205
Keywords
Nitrate source; Stable isotope; MixSIAR model; Karst water; Intensive agriculture
Categories
Funding
- Guangxi Sci-ence and Technology Planning Project [GuiKe-AB18050026]
- Key Pro-gram for Hebei Education Department [ZD20180202]
- Science and Technology Research Project for Hebei Province University [QN2021052]
- China Geological Survey Project [DD20160302, DD20190825]
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This study used chemical variables and stable isotopes to analyze the sources and transformations of NO3- pollution in surface water and groundwater in the Huixian karst wetland. The results showed that long-term application of synthetic NH4(+) fertilizer and soil organic nitrogen were the main contributors to NO3- pollution. Additionally, agricultural activities had a significant impact on NO3- concentration.
Karst water as the vital water supply source is generally suffered from NO(3)(- )contamination in intensive agricultural areas worldwide. Identifying NO3- sources and transformations is the key for understanding nitrogen pathways, and also for effectively controlling diffuse NO3- pollution. In this study, chemical variables and stable isotopes (delta H-2-H2O, delta O-18-H2O, delta N-15-NO3- and delta O-18-NO3-) were measured in 10 surface water (SW) samples and 13 groundwater (GW) samples collected from the Huixian karst wetland, with the application of a Bayesian stable isotope mixing model (MixSIAR) to identified NO3- sources and biogeochemical transformations. The results showed that the NO3- concentrations ranged from the below detection limit to 117 mg/L, with 30.8% of GW samples obtained from the north central part of the study area exceeding the maximum permissible limit for drinking water, and posing significant non-carcinogenic health risks for native people through drinking water pathway. Moreover, based on characteristics of the hydrochemistry and stable isotopes, different biogeochemical fates were evaluated in SW and GW: nitrification process was a dominant factor in GW, as a result of high NO3- levels, and this microbial process was unlikely occurred in SW associated with relatively anaerobic condition and low NO(3)(-)levels; however, the denitrification might not be a main process of degradation NO(3)(-)levels throughout the study area. The MixSIAR outputs revealed that the long-term application of synthetic NH4(+) fertilizer (36.6%) and soil organic nitrogen (28.0%) were the main contributors to NO3- pollution, followed by synthetic NO3- fertilizer (16.8%) and domestic sewage and manure (15.1%), whereas NO3- in precipitation (3.44%) played a less important role. Additionally, NO3- concentration was significantly influenced by agricultural activities rather than NO(3)(- )source's contribution between SW and GW. This work suggests that synthetic NH4(+) fertilizer should be the primary target for control to prevent further NO(3)(- )pollution of the karst groundwater.
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