Improvement Of Different Food Chains On Eutrophic Water

Baiyangdian lake is the most typical lake and wetland in the North China Plain, the eutrophi cation is a serious problem there. Although physical and chemical methods are used to restore Baiyangdian lake, the water quality has not been ideal. At present, biological method is applied in water ecological restoration. The biological method has been successfully used in China’s East Lake, Chaohu, Dianchi, Qiandao Lake and other places, but has not been applied in region of Baiyangdian Lake. This paper mainly focused on the application of biological control for the water ecological restoration of Baiyangdian lake. Based on survey data of the fish in Baiyangdian Lake, the food web of fish was constructed. After the suitable chains were fitted, the improvement on water quality was assessed due to enclosure experiment, providing a basical theory for restoration of Baiyangdian lake.1、Based on the survey of8typical sampling sites in Baiyangdian lake from2009to2010, the paper described the feeding habit, the trophic level and the food web characteristics of25species of fish in Baiyangdian lake, and the energy flow path of the fish food web, the current status and the historical changes were analyzed. The results showed that the fish resources in Baiyandian lake was destroyed seriously, the medium predatory fish species became few, skipping trophic level occured, and the structure of food web was becoming simple and incomplete.2、During August31,2010to September28th2010, situ enclosures (9m2each) were constructed in Baiyangdian Lake, and mainly used for investigating effects of Myriophyllum spicatum and Ceratophyllum demersum on the phytoplankton community in eutrophic water body. The situ enclosures were selected for Myriophyllum spicatum and Ceratophyllum demersum being planted with different density,20and10ind./m3, respectively. Due to five-week observation, the biomass of phytoplankton decreased, the SD increased in enclosures, and the eutrophi cation level reduced. improvement on the water quality of Myriophyllum spicatum was better than Ceratophyllum demersumn.The phytoplankton composition was closely related with nutrient concentration by determination of physical and chemical index. The index of Shannon-Weaver diversity, Margalef and Pielou changed insignificantly which suggested that the single index could not be used to evaluate water quality of enclosures.3、 Using situ enclosures in Baiyangdian Lake from July15th to August19th,2011, further research to investigate the effect of different food chains on phytoplankton community and water quality was conducted. The result showed that SD in test enclosures changed a little, but that of control decreased obviously. In the enclosure which has Hypophthalmichthys molitrix, SD and DO were lower than the enclosures of benthos. Under the same conditions, DO in test enclosures planted Myriophyllum spicatum was higher than the enclosures planted Ceratophyllum demersum. The test enclosures’s CODmii were lower than the others. CODmn of bentho’s enclosures was lower than the enclosures of Hypophtlmlmichthys molitrix. CODmn of Myriophyllum spicatum enclosures was lower than Ceratophyllum demersum enclosures. The chla of four test encloures had been in a steady state. And the results suggested that nonclassical biomanipulation had very good effect on water body of Baiyangdian lake, filter-feeding fish could effectively control the cyanobacterial water bloom, but can not reduce the total content of phytoplankton.