Studies On The Effects Of Cladocerans On Eutrophication And Cyanobacteria

The occurrence of cyanobacterial blooms in eutrophic lakes, reservoirs, and recreational waters has become one of the most important and difficult worldwide enviromental problems since the 20th century. How to control the algae bloom, purify the water and remove excessive nitrogen and phosphorus has been a difficult problem throughout the world. Preliminary study on the application of biomanipulation to restore water quality and control the algae blooms has been conducted, that is, water quality is improved through adjusting the structure and function of ecosystem.In this paper, by analyzing the purification and filtering capacities of five cladocerans in the inside and outside experiments, the suitable kind of cladocerans was determined and their purification abilities were evaluated. The main results and conclusions are as follows:1.The mixture algae water of Microcystis aeruginosa and Chlorella sp. could supply enough nourishment for the growth and reproduction of the cladocerans. In the experiments, the number of cladocerans increased significantly with the number of D.longispina changing from 50 to 2000 and reaching the number of 200 in the end. And at the same time, the gender ratio of D.longispina changed greatly from 50:1 to 1:1 and ended with 2:5 (male to female).2.The purification and filtering abilities of cladocerans could be influenced by the kind of cladocerans. It might be the reason that different kinds of cladocerans had diffenent size of grazing food. So the D.longispina among the four cladocerans selected for experiments showed the strongest ability to filter the algae water and the P.aduncus took the second place.3.The outside conditions such as the density of algae cells could also influence the filtering ability of cladocerans. When the algae cells had high density, all of the four cladocerans showed distinct ability to graze the blue algae. But when the numbers of algae cells fell, only the D.longispina could still effectively control the growing of the algae and purify the water as well. It could control the OD of the algae water under 0.100.4 . Temperature is another important factor. During the experiment, cladocerans showed stronger purifying ability in the 16℃compared to the other two temperatures 10℃and 22℃.5.The water volume could not affect the purifying ability of caldoceras. The middle-size-experiment proved that the D.longispina and P.aduncus could keep high purificating efficiency in the larger water. The OD of the D.longispina and P.aduncus group fell down evidently against to control group. When the experiment ended, their OD were 0.115 and 0.200 to 1.160.6.The outdoor experiment showed that the D.longispina could effectively remove the T-P, T-N form the euthophic water, reduced the number of algae cells and improved the grade of transparency. After the experiment, the transparency of the experimental pool was as 2.08 times as the control group-Yunlong River and the romoval ratio of T-P and T-N were 33.06% and 11.28%.