|Other Abstract||As an important ecological group in freshwater ecosystems, macrozoobenthos play an important role in material cycling and energy flow, and are widely used in environmental monitoring. Previous evaluation criteria of biological indexes of water quality was based on the studies of streams, little has been established for mid-lower Yangtze lakes. Hence, systematical investigations of lakes in Wuhan City and its vicinities were carried out during 2007-2008. First, species composition, standing crops, functional feeding groups of macrozoobenthos in these lakes were studied. Secondly, we assessed water quality of 24 Yangtze lakes using four candidate metrics, and selected the optimum biological indicatoras a general indictor of the whole catchment. The main results are as follows:
1. Assemblage characteristics of macrozoobenthos in different lakes have been systematically analyzed. Altogether 37, 15, 24 and 50 taxa of macrozoobenthos were identified in Lake Baoanhu, Lake Niushanhu, Lake Nanbeizui and Lake Donghu District, respectively. The average densities and biomasses were 549 ind/m2, 49.2 g/m2; 181 ind/m2, 35.5 g/m2; 194 ind/m2, 21.6 g/m2; 3673 ind/m2, 14.2 g/m2. The standing crop of macrozoobenthos in Lake Baoankou was the highest on the four regions of Lake Baoanhu. The predominant group was aquatic insects which have large body size in Baoankou. In the other three regions, the density of macrozoobenthos in Lake Xiaosihai was the lowest and biomass of macrozoobenthos in Biandantang was the lowest. The epiphytic gastropods such as Alocinma longicornis and Parafossarulus striatulus were predominant in density and biomass in Lake Niushanhu and Lake Nanbeizui due to the rich aquatic plants. The water quality of Lake Yandonghu which have many taxa preferring clear water was the best in Lake Donghu District. There are many lotic taxa in the channel of Qingshangang due to its freely connection with the Yangtze River.
2. The suitable biological index for environmental monitoring has been selected and the evaluation criteria have been established. On the basis of macrozoobenthos data of 24 lakes of the mid-lower Yangtze lakes investigated during 2002-2008, we used four candidate metrics to evaluate the water quality. Results indicate that the Biotic Index is the most suitable. So, we recommend Biotic Index as an optimum index of biological evaluation of the mid-lower Yangtze lakes. Using a sample of sites from the entire population, the 5th percentile of the BI from the population of sites was determined. Any values below the 5th percentile were considered as “excellent”, and values above the 5th percentile was quadrisected for different water quality ratings. Criteria of BI for the mid-lower Yangtze lakes was also preliminary determined, < 5.48, excellent; 5.48-6.46, good; 6.461-7.44, good-fair; 7.441-8.42, fair; > 8.42, poor.
3. The biotic index has been used to evaluate the water quality of Lake Donghu District. Results show that the water quality of Lake Yandonghu is good; Lake Tanglinhu, Lake Yanxihu and Qingshangang are good-fair; Lake Miaohu, Lake Beihu and Lake Shahu are poor; the rest are fair.|