Comprehensive Assessment Of Aquatic Ecosystem Health Of Yuanhe River

River ecosystem is one of the most complex ecosystems in the world. Ecosystem health assessment is one of the most active fields in river ecology. How to assess river ecosystem state is becoming a hot spot and one of the most ground-breaking fields in the domain of river ecosystem. Moreover, the water environment management mode in China will gradually switch from water quality management to water ecosystem health management. Scientific assessment of river ecosystem health is the solid base of water ecosystem health management. This paper has assessed the water quality condition of Yuanhe River, a large tributary of Ganjiang River, through biodiversity index of phytoplankton. And the integral status of river ecosystem has also been assessed through the fish index of biotic integrity (F-IBI). Finally, the river ecosystem health has been evaluated through the comprehensive assessment index (CAI) in Yuanhe River. The results are the solid base of understanding the damaged situation and grasping the trend of structure and function changes in aquatic ecosystem of Yuanhe River. In addition, the results can be considered as the basis of ecological restoration, reasonable development and utilization of water resources, decision-making of ecological, economic and social sustainable development and management for the final aim of water quality control in this river basin. The main results and findings of this dissertation are as follows:(1) In the present study, phytoplankton abundance and community structure were investigated and analyzed in Yuanhe River. The results showed that 109 species of phytoplankton were identified, belonging to 61 genera of 6 phyla, among which the species mainly belonged to Chlorophyta, Bacillariophyta and Cyanophyta. Cyanophyta was the dominant phylum in both high-water period and low-water period, while Bacillariophyta dominated in the normal-water period. The dominant species of phytoplankton were the saprobic indicators, Fragilaria capucina, Phormidium tenue, Chroomonas caudate, Synedra amphicephala and Cyclotella meneghiniana. Furthermore, methods of modified bio-indicator community and biodiversity index were applied to biologically assess the water pollution, and the both methods came to the similar results, showing that the Yuanhe River was in the status ofα-βmoderate pollution.(2) Totally,46 species of fish were identified in Yuanhe River, belonging to 61 families of 6 orders, among which the species were mainly Cyprinidae fishes and also the native species. The constructive species of fish community were Carassius auratus, Cyprinus carpio, Hypophthalmichthys molitrix, Aristichthys nobili, Squalidus argentatus, Squaliobarbus curriculus and Peheobagrus fulvidraco. For the fish trophic guilds, the fish species of this river were mainly the subprime consumers, the omnivores and the detritivores, while the fish species number of primary consumers and top consumers was relatively less. As to the fish tolerance or intolerance, the tolerant species of fish were the dominant ones, and the intolerant and the intermediate were secondary, while the very intolerant and the very tolerant were rare. All the fish sampled in the investigation were health, and the freak fish and fish infected by the pathogenic bacteria were not found. This paper assessed the health status of river ecosystem through fish index of biotic integrity (F-IBI), and found that F-IBI scores were in the poor to fair status in Yuanhe River.(3) The method of the comprehensive assessment index (CAI), containing the information of fish and algae communities found, was developed to evaluate the river ecosystem health in Yuanhe River. The CAI system included five matrixes: river hydrology, physical morphology, riverside zone, water quality parameters and community construction of aquatic organisms. Results showed that the river ecosystem health of Yuanhe River was in sub-health.