Insight into the mechanisms of denitrification and sulfate reduction coexistence in cascade reservoirs of the Jialing River: Evidence from a multi-isotope approach

Gaoyang Cui; Xiao-Dong Li; Mengdi Yang; Shiyuan Ding; Qin-Kai Li; Yiyao Wang; Zhou Yang; Hu Ding

doi:10.1016/j.scitotenv.2020.141682

Insight into the mechanisms of denitrification and sulfate reduction coexistence in cascade reservoirs of the Jialing River: Evidence from a multi-isotope approach

Sci Total Environ. 2020 Dec 20:749:141682. doi: 10.1016/j.scitotenv.2020.141682. Epub 2020 Aug 12.

Authors

Gaoyang Cui¹, Xiao-Dong Li², Mengdi Yang¹, Shiyuan Ding¹, Qin-Kai Li¹, Yiyao Wang¹, Zhou Yang³, Hu Ding¹

Affiliations

¹ Institute of Surface-Earth System Science, School of Earth System Science, Tianjin University, Tianjin 300072, China.
² Institute of Surface-Earth System Science, School of Earth System Science, Tianjin University, Tianjin 300072, China. Electronic address: xiaodong.li@tju.edu.cn.
³ Tongren University, Tongren 554300, China.

PMID: 33370886
DOI: 10.1016/j.scitotenv.2020.141682

Abstract

The coexistence of denitrification and bacterial sulfate reduction (BSR) processes is commonly observed in natural water systems. However, its formation mechanism remains unclear at a basin scale due to the difficulty of precise identification of these processes. To address this issue, we investigated the spatial-temporal variations in water chemistry and isotopic compositions (e.g., δ¹³C_DIC, δ¹⁵N_NO3, δ¹⁸O_NO3, δ³⁴S_SO4, and δ¹⁸O_SO4) in cascade reservoirs (artificial dam lakes) of the Jialing River, SW China in 2016. The results showed that the denitrification and BSR processes coexisted in the studied reservoirs, which was supported by the positive correlation between δ¹⁵N_NO3 and δ¹⁸O_NO3 and between δ³⁴S_SO4 and δ¹⁸O_SO4, and by the decreasing concentrations of NO₃^- and SO₄^2-. Moreover, covariation of Δ¹³C_DIC, Δ¹⁵N_NO3, and Δ³⁴S_SO4 indicated the dominance of heterotrophic denitrification (HD) in the reservoir waters along with the occurrence of bacterial sulfide oxidation (BSO). In addition to SO₄^2- and NO₃^-, the coexistence of HD and BSR processes were also controlled by the dissolved organic carbon (DOC) in winter and dissolved oxygen (DO) contents in other seasons. Overall, the cumulative effect of cascade reservoirs caused δ¹⁵N_NO3 and δ³⁴S_SO4 to display an upward trend from upstream to downstream in the Jialing River, while δ¹³C_DIC showed an opposite downward trend, which implying that cascade reservoirs may be in favor of the coexistence of the HD and BSR processes. This study therefore concludes that the multi-isotope approach could be a useful technique to ascertain the coexistence mechanism of HD and BSR processes in reservoir water systems.

Keywords: Coexistence mechanisms; Denitrification; Multi-isotope tracers; Reservoirs; Sulfate reduction.