Climate-driven decline in water level causes earlier onset of hypoxia in a subtropical reservoir

Huihuang Chen; Anqi Luo; Chenxi Mi; Yifan Lu; Yuanyuan Xue; Lei Jin; Hongteng Zhang; Jun Yang

doi:10.1016/j.watres.2024.122445

Climate-driven decline in water level causes earlier onset of hypoxia in a subtropical reservoir

Water Res. 2024 Sep 14:267:122445. doi: 10.1016/j.watres.2024.122445. Online ahead of print.

Authors

Huihuang Chen¹, Anqi Luo¹, Chenxi Mi², Yifan Lu¹, Yuanyuan Xue³, Lei Jin⁴, Hongteng Zhang³, Jun Yang⁵

Affiliations

¹ Aquatic EcoHealth Group, Key Laboratory of Urban Environment and Health, Fujian Key Laboratory of Watershed Ecology, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China; University of Chinese Academy of Sciences, Beijing 100049, China.
² Helmholtz Centre for Environmental Research, Department of Lake Research, Magdeburg 39114, Germany.
³ Aquatic EcoHealth Group, Key Laboratory of Urban Environment and Health, Fujian Key Laboratory of Watershed Ecology, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China.
⁴ Aquatic EcoHealth Group, Key Laboratory of Urban Environment and Health, Fujian Key Laboratory of Watershed Ecology, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China; College of Life Sciences, Hebei University, Baoding 071002, China.
⁵ Aquatic EcoHealth Group, Key Laboratory of Urban Environment and Health, Fujian Key Laboratory of Watershed Ecology, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China. Electronic address: jyang@iue.ac.cn.

PMID: 39316965
DOI: 10.1016/j.watres.2024.122445

Abstract

Hypoxia, especially in the bottom water, is occurring in deep and stratified reservoirs worldwide, threatening aquatic biodiversity, ecosystem functions and services. However, little is known about the timing of onset and ending of hypoxia, especially in subtropical reservoirs. Based on five-year (from April 2015 to January 2020) sampling of a subtropical monomictic deep reservoir (Tingxi Reservoir) in southeast China, we found the evidence of about 40 days earlier onset of hypolimnion hypoxia during low water level periods in dry years compared to wetter high water level years. We explored the effects of stratification and mixing conditions on hypoxia, cyanobacterial biomass, and nutrient dynamics; and revealed the physical and biochemical conditions that drove hypoxia. The results indicated that 1) The decline in water level increased the intensity of thermal stratification, resulting in 40 days earlier onset of hypolimnion hypoxia in dry years than in wet years; 2) The decline in water level expanded the extent of hypoxia by promoting nutrient accumulation and phytoplankton biomass growth; 3) Warmer climate and less precipitation (drought) significantly promoted the risk of hypoxic expansion and endogenous phosphorus release in subtropical reservoirs. We suggest that more attention needs to be paid to the early onset of hypoxia and its consequences on water quality in subtropical stratified reservoirs during low water level periods in a changing climate.

Keywords: Climate change; Mixing; Monomictic reservoir; Phytoplankton; Thermal stratification.