PROGRESS IN STUDIES ON WATER ECOLOGY IN TIAN’E ZHOU OXBOW

In the early 1990s, the Tian’e Zhou Oxbow in Yangtze River in Hubei Province had good water quality and rich fish resources, which was considered to be an ideal location for the establishment of semi-natural reserve for Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis) and germplasm ecological reservoir for four major Chinese carps. Consequently, water ecology researches on Tian’e Zhou Oxbow from the environmental factor of water quality and sediments, the biological factor of phytoplankton, zooplankton, zoobenthos and aquatic macrophytes, as well as the resource factor of primary productivity, fish potential production and fish resource have made great progress with the successful implementation of the ex-situ conservation for Yangtze finless porpoise. The water quality in Tian’e Zhou Oxbow showed a trend of deterioration. The number of phytoplankton increased by two orders of magnitude, and the form of phytoplankton changed from single-celled individuals to multicellular colony, and cyanobacteria with gelatinous envelope displayed an absolute predominance in species and densities. The dominant species of zooplankton showed a trend of miniaturization. The density of zoobenthos decreased dramatically. Aquatic macrophytes displayed a trend of gradual recession. Fish resources showed a downward trend. The chemical evaluation and biological assessment of water quality and human activities on Tian’e Zhou Oxbow indicated that disconnection between Oxbow lake and Yangtze River, fishery activity and environmental pollution were the main factors impacting water ecology of Tian’e Zhou Oxbow, which affected the sustainability of Yangtze finless porpoise through water quality, bait resources and habitat. Five suggestions were proposed to protect water environment quality and water ecological health, and then maintain the sustainable survival of Yangtze finless porpoise. First, the connecting engineering between Tian’e Zhou Oxbow and Yangtze River should be implemented to restore the water ecological characteristics and improve the heterogeneity of physicochemical environment. Second, nutrient loading from internal and external source should be controlled to improve the water quality of Tian’e Zhou Oxbow. Third, the condition of water quality, sediments and aquatic organisms should be monitored continuously to establish the database of water ecology. Fourth, ecological restoration project should be implemented to improve the biodiversity of aquatic organism in Tian’e Zhou Oxbow. Finally, fishery activity should be regulated to optimize fishery resources.