Seed Bank In Aquaculture Area Of Lake Honghu And The Strategy Of Aqutatic Vegetation Restoration

Lake Honghu is the largest lake in Hubei Province and once had the same water level cycle with the Yangtze River. But now it has been changed into the shallow lake because of the artificial control of water level. It has great changes between the inter-annuals and within one year. Lake Honghu has the good name of land of fish and rice, which has an important role in economy. However, Lake Honghu has begun to have large-scale aquaculture since 1990. It has caused serious damage to water ecology. The water quality has a trend of serious eutrophication and fish stocks are depleted.In order to protect the ecology of Lake Honghu and study of aquatic vegetation restoration strategies, we have chosen a typical farming region to have the conventional survey of aquatic vegetation, water quality survey, zooplankton survey, seed bank survey, natural recovery test.The results as follows:(1) There are seldom water-submerged plants in experimental region of aquaculture, only have an extremely small number of water plants like reeds, wild rice grass and some floating-leaved lotus, hardly to find other large type plants. (2) Water quality is the III degree on experimental site, trophication level is mild, and trophication level of transparency reaches to moderate. Water quality has a significant difference of experimental site one between 2007 and 2008.(3) The number of zooplankton is the peak of the year from May to October, the quantity is 93ind / L ~ 2607ind / L, and the amount of zooplankton has a significant difference during two periods.(4) Sediment seed banks have 14 kinds of aquatic plants with an average density of 467±345 ind/m~2.(5) Natural recovery tests have 5 and 14 kinds of aquatic plants restoration , the coverage reaches to 100% and 30% respectively.Study shows that:(1) density of herbivorous fish is so large that aquatic vegetation, especially submerged vegetation begins succession to disappearance; density of filter-feeding fish is so large that it directly causes the decline of the total number of zooplanktons, smaller individuals, the reduction of types; density of amount of fish is so large that it directly causes the decline transparency of shallow water, deterioration of water quality. (2) Over-breeding is the main factor for the degradation of aquatic vegetation and main limiting factor for recovery, and if we change the types and amount of fish under the conditions of the existing water quality, the aquatic vegetation can be recovered.