Study on Eutrophication of Water Bodies Caused by Yangqu Reservoir Impoundment

Yangqu Reservoir is a very important project in the construction of cascade hydropower stations in the upper reaches of the Yellow River. After the reservoir was built and put into operation, the rise of the water level in the upstream river caused an increase in the area of the water surface in the river, submerging the vegetation on both sides and reducing the self-purification capacity of the water body. The concentrations of COD, NH3-N and TN in the reservoir were simulated and predicted using the HD and AD models in MIKE21. The results showed that the concentrations of COD, NH3-N and TN in the reservoir had increased significantly. After the reservoir was built, on the one hand, due to the rise of the water level in the upstream river, the shedding and death of some submerged plants would cause local pollution concentration to exceed the standard, resulting in eutrophication of the water body. On the other hand, the hydraulic retention time increased, the degradation time of pollutants increased, and the change in environmental self-purification capacity was limited. To address the water quality issues of the reservoir, the spatial configuration (vertical and horizontal) and restoration design of vegetation communities were proposed to minimize the impact on vegetation communities caused by the construction of the reservoir, while also better playing multiple functions such as conserving soil and water, purifying water and maintaining biodiversity.