Seasonal hypoxia enhances sediment iron-bound phosphorus release in a subtropical river reservoir

Fenfang Wang; Jie Wang; Taotao Cao; Xiuwen Ji; Jing Yan; Shiming Ding; Nengwang Chen

doi:10.1016/j.scitotenv.2024.173261

Seasonal hypoxia enhances sediment iron-bound phosphorus release in a subtropical river reservoir

Sci Total Environ. 2024 Aug 1:936:173261. doi: 10.1016/j.scitotenv.2024.173261. Epub 2024 May 16.

Authors

Fenfang Wang¹, Jie Wang², Taotao Cao², Xiuwen Ji², Jing Yan², Shiming Ding³, Nengwang Chen⁴

Affiliations

¹ Fujian Provincial Key Laboratory for Coastal Ecology and Environmental Studies, College of the Environment and Ecology, Xiamen University, Xiamen 361102, China; State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen 361102, China.
² Fujian Provincial Key Laboratory for Coastal Ecology and Environmental Studies, College of the Environment and Ecology, Xiamen University, Xiamen 361102, China.
³ State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China.
⁴ Fujian Provincial Key Laboratory for Coastal Ecology and Environmental Studies, College of the Environment and Ecology, Xiamen University, Xiamen 361102, China; State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen 361102, China. Electronic address: nwchen@xmu.edu.cn.

PMID: 38761934
DOI: 10.1016/j.scitotenv.2024.173261

Abstract

Dams worldwide commonly accelerate the eutrophication of reservoirs. While the seasonal hypoxia in deep reservoirs is widely acknowledged, there is limited research on its impact on benthic phosphorus (P) cycling and P fraction release from the reservoir sediments. Here we show that seasonal hypoxia enhances sediment P release and P fluxes at the sediment-water interface (SWI) which might alter P dynamics in deep reservoirs. We conducted a detailed measurement of sediment P fractions through the SEDEX approach, combined with a labile P gradient analysis using the diffusive gradients in thin films (DGT) technique to understand P cycling patterns in sediments during the transition period from spring (oxic) to late summer (hypoxic) conditions. The sediment P pool was predominantly composed of iron-bound phosphorus (Fe-P, 76-80 %), primarily due to the widespread occurrence of lateritic red soil (rich in Fe₂O₃/MnO₂) in subtropical areas. More organic-P was observed in summer compared to spring. A significant increase in labile P occurred at the depth of 0-4 cm and 0-1 cm in spring and summer, respectively, where sediment P release was primarily governed by the reduction of Fe-P and the generation of S^2-. A higher apparent fluxes of phosphate across the SWI were observed in summer characterized by higher temperature and lower oxygen levels. The current results suggest that seasonal hypoxia was a crucial factor affecting P cycling and diffusion in deep reservoirs. These findings present important implications for the ecology and management of the watershed-coast ecosystem.

Keywords: DGT technique; Dam-reservoir; Eutrophication; Sediment-water interface.