Status quo and the succession of the biological resources in Lake Gucheng

Based on the survey of the biological resources in Lake Gucheng in 1999 and the survey data in 1981 and 1988,comparison was conducted to analyze dynamics of biological resources in the lake.It was found that within almost 20 years from 1981 to 1999 the population of phytoplanktons increased by 44.8 times in abundance and the biomass by 40.6 times,but the biodiversity reduced.The population of zooplanktons decreased by 50% as compared with that in the 1980s,while the biomass was higher than that in the early 1980s but lower than that in the late 1980s.The biomass of zoobenthos decreased,especially lamellibranch and mollusca,while that of freshwater oligochaeta and chironomidae larvae increased remarkably.The succession of hydrophyte community in Lake Gucheng was drastic and its structure changed greatly with Potamogoton maackianus and Potamogeton crispus communities replacing Vallisneria and Hydrilla verticillata communities,thus resulting in the fall of its fishery value.Every year large volumes of float grasses rotted and accumulated in the bottom,deteriorating the water quality of the lake.There are some indicator species that are contamination-tolerant,for instance,Bellamya purificata (heude),Parafossarulus striatulus (benson),Branchiura sowerbyi (beddard) and so on.The water quality showed a declining trend in the recent 20 years.The key to protection of the lake environment is to intensify regulation and to reasonably exploit the biological resources of the lake.