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

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Title: Seasonal variations and hydrological management regulate nutrient transport in cascade damming: Insights from carbon and nitrogen isotopes.
Authors: Yang, Yujing1,2 (AUTHOR), Wang, Wanfa1,2 (AUTHOR) wfwang@gzu.edu.cn, Yu, Shengde3 (AUTHOR), Yi, Yuanbi4 (AUTHOR), Xu, Sen5 (AUTHOR), Yao, Yuanzhi6 (AUTHOR), Zhong, Jun5 (AUTHOR), Shi, Wenhong1,2 (AUTHOR), Chen, Sainan5 (AUTHOR), Wu, Qixin1,2 (AUTHOR), Ou, Zuhong7 (AUTHOR), Ding, Hu5 (AUTHOR), Li, Si-Liang5 (AUTHOR)
Source: Water Research. Mar2025, Vol. 271, pN.PAG-N.PAG. 1p.
Subjects: Water management, Nitrogen isotopes, Spring, Autumn, Carbon isotopes
Abstract: • Seasonal variation of nutrient concentrations in cascade reservoirs can be significantly regulated by dam operations. • The HJD reservoir acts as a nutrient sink during the wet season, yet alternates to a nutrient source during the dry season. • Hydrological management of cascade reservoirs magnifies the differences in nutrient fluxes from upstream to downstream. 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-NO 3 -) 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 (SiO 2) 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 SiO 2 , indicating substantial nutrient consumption in the cascading reservoirs. Conversely, during the DS, the *RET f values for TN, TP, and SiO 2 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. [Display omitted] [ABSTRACT FROM AUTHOR]
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Database: Engineering Source
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Abstract:• Seasonal variation of nutrient concentrations in cascade reservoirs can be significantly regulated by dam operations. • The HJD reservoir acts as a nutrient sink during the wet season, yet alternates to a nutrient source during the dry season. • Hydrological management of cascade reservoirs magnifies the differences in nutrient fluxes from upstream to downstream. 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-NO 3 -) 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 (SiO 2) 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 SiO 2 , indicating substantial nutrient consumption in the cascading reservoirs. Conversely, during the DS, the *RET f values for TN, TP, and SiO 2 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. [Display omitted] [ABSTRACT FROM AUTHOR]
ISSN:00431354
DOI:10.1016/j.watres.2024.122894