Cascade dams affect river health in plateau regions： a case of Huangshui River

Impact of cascade dams on the health of plateau rivers, such as Huangshui River in Qinghai, was analyzed with an index of 12 indicators at the level of hydrology, aquatic ecology, and water ecology．With natural rivers as reference for evaluation criteria, the fuzzy comprehensive health evaluation model was used．Cascade dams were found to drastically change hydrological and water quality characteristics in the damming river section．After damming, river flow velocity and DO decreased by an average of 75% and 12%, respectively, but water depth and water temperature increased by an average of 67% and 50%．COD_Mn and BOD indicators in continuous damming areas were found to have decreased by 28% and 21%, respectively．Average TN, TP and TOC increases in water sediments were found to be 40%, 23% and 64%．Changes in hydrology and water quality led to changes in the growth environment of plankton in damming rivers, population structure of phytoplankton and zooplankton underwent significant changes．Types, density and biomass of plankton were found to have increased by 1.7 times, 71 times and 12 times on average．Effect of cascade dams on rivers in dry seasons was found to be 78% higher than in normal and high water periods．Impact on upper dam area was 56% higher than downstream dam area．Small cascade dams were found to have greater impact．We suggest that long-term monitoring and systematic evaluation are urgently needed．