Diverse responses of hydrodynamics, nutrients and algal biomass to water diversion in a eutrophic shallow lake

Water diversion has been increasingly applied to accelerate lake water exchange and alleviate urgent water crisis. However, effects of water diversion on water exchange and water quality for eutrophic lakes remain controversial. In this study, a three-dimensional hydrodynamic-water quality-sediment diagenesis model has been developed to assess effects of water diversion on hydrodynamics and water quality in eutrophic shallow Lake Wanghu. Results suggested that water diversion could dramatically promote water exchange and reduce residence time in most lake regions but its influence on water quality was diverse. A water transferring flow rate of 20–30 m3/s could reduce water age to 40–58 days during regular water diversion operation, whereas a high transferring flow rate of 100 m3/s was the best for emergency operation in late spring before the wet season. Moreover, nutrients and Chlorophyll-a exhibited notable spatial heterogeneity in improvement efficiency. Nutrients level in the donating system was a prerequisite to the relationship among water transport time scales, nutrients, and algal biomass in this eutrophic lake. During a clean water diversion, nutrients and algal biomass were positively associated with water age. However, when the donating system contained high level of nutrients, accumulated nutrients in the lake may still trigger algal bloom after a temporary relief due to flushing effect. Therefore, these water diversion strategies could be applied to guide a sustainable management of eutrophic Lake Wanghu in terms of transferring flow rate, wind fields, water quality in the donating system, transferring operation, and water diversion route.