The Application Study Of Fish Biomanipulation In Improving Aquatic Environment Of Suzhou

The biomanipulation of fish was to effect nutritious substance in rivers to improve water quality by changing the composition of fish which lied in the tope of food web. With the help of the integrated demonstrational project of the improvement of the aquatic environment quality in Suzhou, the biomanipulation effect of fish was studied to find biologic controlling technology to improve the aquatic environment quality in city and solve the endogenous pollution of water. According to the investigation, the water characteristics of Miaojia River was low DO, high organic suspensoid conten and the breaking out of alga blooms in summer. According to the characteristics of aquatic environment, laboratory experiment and field test was processed by releasing Xenocypri Davidi Bleeke,Silver Carp,Bighead. The results indicated that suspensoid conten in water was removed and vicous reproduction of alga was inhibited by the biomanipulation function of fish.1, Simulative Experiment in Laboratory(1) The results indicated: the the Xenocypri Davidi Bleeker had inhibitory effect on alga and can improve the transparency of water by ingesting a great deal of organic suspensoid conten when the biomass released was about 40g/m3. At this point, the removal of organic debris is 134mg/g ? d, and the removal rate of alga can reach 32.9%.(2) Silver Carp and Bighead had good inhibitory effect on alga and their biomanipulation function was distinct at the proper releasing density. The removal rate of alga was 26.9% when Silver Carp was released solely. The removal rate of alga was 21.1% when Bighead was released solely. The removal rate of alga was 28.5% when Silver Carp and Bighead were mixed.2, Dynamic Test in Field(1) The results indicated: Xenocypri Davidi Bleeker can endure the low dissolved oxygen in polluted water. They can ingest when the concentration of DO reached the point of suffocation (0.25mg/L). The ingesting rate reached about 53% every day in the ordinary course. After the releasing of Xenocypri Davidi Bleeker, the concentration of DO in water improved, the category and quantity of plankton were increased and the biodiversity of river ecosystem was improved.(2) According to the field test, Silver Carp and Bighead can not survive when the concentration of DO was less than 2mg/L. It was not appropriate to use Silver Carp and Bighead to purify the water in the river which was polluted seriously.