Reservoir water-level operations to manage biogeochemical turnover

Abstract

Rapid decrease in temperature changes water stratification structure into an unstable state, reinforcing water convection and enhancing vertical biogeochemical fluxes, which might pose a threat to aquatic ecosystems, especially for drinking water use. At high latitudes, current research predominantly focuses on destratification systems to reduce the degradation of aquatic ecosystems. However, at low latitudes, the strategies of enhanced stratification through water level operation (WLO) provide a perspective for reservoir management. The present study integrates the analysis of thermocline motions with the WLO approach using a 3D hydrodynamic and particle tracking modeling based on in situ observations. The rate of thermocline downwelling (TDR) and reservoir depth were found to control turnover time and the migration of contaminants from the bottom to the surface. WLO extends the mixing time of the reservoir, avoiding thermal state transitions during cooling cycles and reducing water migration by up to 32%. A quantitative method based on particle tracking was applied to further calculate the suitable water depth range for WLO application in tropical and subtropical reservoirs in China. These findings emphasize the significance of the previously neglected operation strategies to mitigate reservoir turnover contaminants, which have different application effects depending on the reservoir depth and climatic conditions.