Integrated water quality monitoring and modeling in the Three Gorges Reservoir, China

摘要

Increasing eutrophication and algal bloom events in the Yangtze River Three Gorges Reservoir are widely discussed in relation to hydrodynamics and nutrient transport and distribution processes. Insights into water exchange and interaction dynamics between water masses related to large scale water level fluctuations in the reservoir are crucial to understand water quality and eutrophication dynamics. Therefore, confluence zones of tributaries with the Yangtze River main stream are dedicated key interfaces. In this study, water quality data recorded in-situ and on-line with the MINIBAT towed underwater multi-sensor system is integrated with data obtained from simulations done with TELEMAC hydrodynamic 2D numerical modeling. Key scenario for the current study was a discharge peak and corresponding rising water level in the Yangtze River at its confluence zone with the Daning River following a heavy precipitation event in August 2011. Water quality data obtained from MINIBAT measurements during this specific period suggest that Yangtze River main stream water flowed upstream into the Daning River. Hydrodynamic 2D numerical modeling supports that hypothesis and enables to specify water and substance origins. Observed algal blooming can only be partly explained by the 2D modeling approach. 3D effects like the stabilization of thermal stratification at the water surface forming good conditions for algal blooming cannot be simulated but were measured with the MINIBAT. However, input of higher nutrient loads from Yangtze River water and from waste water discharges into the Wushan Lake are supported by the model and the field measurements and may have played a key role for the observed algal bloom formation.