Studies On The Zoobenthic Community Structure And Environmental Quality Assessment In Donghu Lake, Wuhan After Cutting Off Sewerage

According to the investigation on zoobenthos of Donghu Lake in 2003, this paper deals with calculating whole zoobenthic standing crop, and analyzing the standing crop of 6 dominant species and their distributive patterns, and evaluating environmental quality using bio-index. Linking to past investigative results, it deals with studying successive regularization of zoobenthos, the change process of water environment and its effects on zoobenthos, too. The results show as follows:1. In 2003, there is total density of 759.2 ind./m2and total biomass of 463.40 g/m2in Donghu Lake. The standing crop of mollusk in subarea of Guozheng Lake, both aquatic oligochaete and aquatic insect in subarea of Shuiguo Lake was maximal. Generally, the changes of total zoobenthic density was affected by the changes of aquatic oligochaete density, and the changes of total zoobenthic biomass was affected by the changes of mollusk bio-mass in Donghu Lake.2. The seasonal changes of zoobenthic standing stock were very distinct. In 2003, to compare maximal biomass in October and the minimal bio-mass in January, the times that the bio-mass in subarea of Shuiguo Lake, Guozheng Lake and Tanglin Lake went up were 5.2, 3.9, and 2.1, respectively.3. Due to the constant development of eutrophication, the reduced tendency of thezoobenthic species of in Donghu Lake is quite obvious. Of which, Mollusca had disappeared in subarea of Shuiguo Lake, and Branchiura sowerbyi should die out from part subarea, impossibly.4. For the annual changes, the proportion that the aquatic oligochaete density went down was 76.2% from 1981 to 2003, but its percentage in total zoobenthic density reached 71.9% in 2003. The proportion that the mollusk density went down was 59.6% from 1980 to 2003, and the proportion that the aquatic insect density went down was 95.9% from 1981 to 2003. The bio-mass dominance of mollusk have been being absolute. Its minimum percentage in total benthic bio-mass reached 73.1% in 1999, and the percentage reached 99.5% in 2003.5. The dominant species of zoobenthos in Donghu Lake were continuous, and they were mainly Branchiura sowerbyi, Limnodrilus hoffmeisteri of Aquatic Oligochaeta, Bellamya aeruginosa, Parafossarulus striatulus of Mollusca, and Clinotanypus sugiyamai, Tokunagayusurika akamusi, Chironomus plumosus of Aquatic Insecta. But the dominance of Parafossarulus striatulus had died out since 1999. The percentage of all dominant species density in zoobenthic density was from 67.5% to 95.3%, and it was 81.7% in 2003. The percentage of the bio-mass was from 71.0% to 98.6%, and it was 98.6% in 2003.The distribution patterns of them, both Gastropod and Aquatic Oligochaeta and Insecta, were always a definite patchiness.6. The results of environment assessment show that water quality in subarea of Shuiguo Lake had been being on the down grade, and had made the level of heavy pollution. The water quality in subarea of Guozheng Lake and Tanglin Lake had reached the level of middle pollution.