Nutritional characteristics and aquatic ecosystem health assessment in cascade reservoirs of Wuxijiang

Extensive cascading hydropower dam exploitation may profoundly affect the river ecosystem health. The nutritional characteristics and community structure of phytoplankton in upstream Hunanzhen reservoir and downstream Huangtankou reservoir in Wuxijiang cascade reservoirs from June 2017 to November 2017 were investigated, and the assessment of the reservoir aquatic ecosystem health was performed by Index of Biological Integrity (IBI) method. The results indicated that nitrogen, phosphorus and organic matter contents of Wuxijiang cascade reservoirs were low, the nutritional level was poor. The 152 taxa of phytoplankton belonging to 8 phyla were identified, the densities of cyanobacteria and chlorophyte were high, and the phytoplankton density in downstream Huangtankou reservoir was lower than that in upstream Hunanzhen reservoir. The IBI assessment result showed that Wuxijiang cascade reservoirs were in relatively high biological integrity, and at normal to sub-health level. The IBI index was significantly affected by the water temperature, suggesting that the good health level was found in Huangtankou reservoir with low water temperature, but in Hunanzhen reservoir with high water temperature.