Seasonal variations and hydrological management regulate nutrient transport in cascade damming: Insights from carbon and nitrogen isotopes

Yujing Yang; Wanfa Wang; Shengde Yu; Yuanbi Yi; Sen Xu; Yuanzhi Yao; Jun Zhong; Wenhong Shi; Sainan Chen; Qixin Wu; Zuhong Ou; Hu Ding; Si-Liang Li

doi:10.1016/j.watres.2024.122894

Seasonal variations and hydrological management regulate nutrient transport in cascade damming: Insights from carbon and nitrogen isotopes

Water Res. 2024 Nov 30:271:122894. doi: 10.1016/j.watres.2024.122894. Online ahead of print.

Authors

Yujing Yang¹, Wanfa Wang², Shengde Yu³, Yuanbi Yi⁴, Sen Xu⁵, Yuanzhi Yao⁶, Jun Zhong⁵, Wenhong Shi¹, Sainan Chen⁵, Qixin Wu¹, Zuhong Ou⁷, Hu Ding⁵, Si-Liang Li⁵

Affiliations

¹ Key Laboratory of Karst Georesources and Environment, Ministry of Education, Guizhou University, Guiyang 550025, PR China; College of Resources and Environmental Engineering, Guizhou Karst Environmental Ecosystems Observation and Research Station, Ministry of Education, Guiyang 550025, PR China.
² Key Laboratory of Karst Georesources and Environment, Ministry of Education, Guizhou University, Guiyang 550025, PR China; College of Resources and Environmental Engineering, Guizhou Karst Environmental Ecosystems Observation and Research Station, Ministry of Education, Guiyang 550025, PR China. Electronic address: wfwang@gzu.edu.cn.
³ Ecohydrology Research Group, Department of Earth and Environmental Sciences, University of Waterloo, 200 University Avenue West, Waterloo N2L 3G1, Ontario, Canada.
⁴ Department of Ocean Science and the Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), The Hong Kong University of Science and Technology, Hong Kong 999077, PR China.
⁵ Institute of Surface-Earth System Science, School of Earth System Science, Tianjin University, Tianjin 300072, PR China.
⁶ School of Geographic Sciences, East China Normal University, Shanghai 201210, PR China.
⁷ Power China GuiYang Engineering Corporation Limited, Guiyang 550081, PR China.

PMID: 39631157
DOI: 10.1016/j.watres.2024.122894

Abstract

Reservoirs around the world have significantly altered the natural transport of nutrients in rivers. However, the specific effects of the cascade damming on the migration, transformation, and environmental consequences of these nutrients remain unclear. To address this knowledge gap, we analyzed spatiotemporal variations in water chemistry, nutrient concentrations, stable isotope of dissolved inorganic carbon (δ¹³C_DIC) and nitrate isotope (δ¹⁵N-NO₃^-) in seven cascade reservoirs along the Wujiang River, each characterized by different regulatory regimes. Our findings reveal that the average absolute changes in concentrations of total nitrogen (TN), total phosphorus (TP), and silicon dioxide (SiO₂) during the wet season (WS, spring and summer) were 2.4, 1.4, and 1.1 times higher than those observed in the dry season (DS, autumn and winter). During the WS, the average apparent retention efficiency (*RET_f) values in the Hongjiadu reservoir were 97 % for TN, 98 % for TP, and 95 % for SiO₂, indicating substantial nutrient consumption in the cascading reservoirs. Conversely, during the DS, the *RET_f values for TN, TP, and SiO₂ were negative, suggesting notable nutrient accumulation within the reservoirs. The nutrient fluxes released downstream from the cascade reservoirs in the Wujiang River were significantly greater than the upstream inflow fluxes. These findings help demonstrate how downstream discharge across cascade reservoirs amplifies nutrient flux disparities due to dam construction. Our study enhances the understanding of how cascade dam construction impacts nutrient dynamics, supporting the optimization of reservoir operation models and advancing scientific water resource management and conservation efforts.

Keywords: Cascade reservoirs; Dual isotopes; Hydrological management; Nutrient dynamics; Seasonal variations.