Survey Of Molluscs Resources In Datong Lake And Effect Of Fish-polyculture On The Community Structure Of Plankton

Datong Lake has had more than 20 years of history of intensive farming to enter the middle eutrophication stage.However,compared with other nutrient-rich water bodies,Datong Lake has the most unique three characteristics: high concentrations of nutrients,lower density of phytoplankton,and rich benthic mollusc resources.Over the past decade,fertilization and investment a series of production activities,such as bait,have also exerted tremendous pressure on the aquaculture environment while improving their production performance.At present,common species in the purification of benthic molluscs have strong ability to resist fouling and strong filtration,and can effectively absorb N,P and heavy metal components in the water.After the comprehensive treatment,the content of nitrogen and phosphorus in Datong Lake decreased significantly,and the density of phytoplankton was relatively low.It is still unclear how the huge mollusk resources are regulated in Datong Lake water quality.Research at home and abroad has also found that using a variety of aquatic higher plants,aquatic vegetation and mollusks to form artificial composite ecosystems has unique advantages in the management of eutrophication of water bodies.This study was based on the previous research work of the research group and was based on the domestic aquaculture waters in China.Widely distributed mollusks are the subject of research on the regulatory mechanisms of molluscs on aquaculture waters.On the one hand,through field investigations,the temporal and spatial changes of the Datong Molluscs were emphatically analyzed,and scientific evaluation methods were used to explore its role in the nitrogen and phosphorus cycle of Datong Lake.On the other hand,the enclosure experiments were conducted to verify the presence of Daphnia carp and mollusks in Datong Lake.Ecological function reveals its specific function in improving water quality and inhibiting algae growth.The main findings are as follows:1)Datong Lake has rich mollusk resources all year round,and its distribution has obvious time heterogeneity and spatial heterogeneity.There is a significant difference between mollusk density and biomass in Datong Lake in different years,and fishing intensity may be one of the biggest factors affecting mollusk density and biomass.There are two reasons that lead to a significant reduction in the existing amount of ticks in Datong Lake.The first is that small shellfish such as mussels have a relatively rapid growth rate,and small individuals are significantly larger than large individuals.The second reason for the quicker replenishment is the nature of the sampling tool.The implementation of the Datong Lake Ecological Environment Protection Project not only resulted in a significant increase in mollusk density and biomass,but also resulted in a wider and more uniform distribution of molluscs.2)The capture volume of about 16,940 tons does not have much impact on the storage of zoobenthos in Datong Lake.Absolute limitation The zooplankton fishing in Datong Lake is not the best way to control and improve the eutrophication of Datong Lake.It strictly prohibits the feeding of feedstuffs and fertilizers,rationally develops mollusks,moderately rears filter-feeding fish,and focuses on the restoration of aquatic vegetation.It is the most effective and best measure for ecological environmental protection in Datong Lake.3)In the enclosure experiment,the effects of different treatment groups on the transparency of the facies water body were significantly different(p < 0.05).The feeding effects of C.crispus and carp could significantly reduce the transparency of the water body.The differences in stocking densities,stocking conditions and other experimental conditions may be the main reasons that different treatment groups have no significant effect on the water quality of the grid.After all,only the enclosure experiments fully understand the ecological habits and specific functions of the species in the ecosystem.The mode of action is unrealistic and impossible.A total of 128 species of 7 phylums and 77 genres of phytoplankton were detected,including 20 species of 14 genus Cyanophyta,3 species of 2 genus of Cyanophyta,31 species of 17 genus of diatoms,3 species of 1 genus of Cryptophyta,1 genus of 1 There are 8 species of 5 genera in Euglena,and 64 species of 37 species in Chlorophyta.The change of chlorophyll a concentration was consistent with the change of phytoplankton abundance.The results showed that the control effects of different treatment groups on phytoplankton growth were: T3> T2> T1.Both crested crested cockroach and squid significantly reduced the species and quantity of phytoplankton in cultured waters.Although the pleated crown has a certain effect on the growth of phytoplankton,it does not change the general trend of phytoplankton growth.However,the T2 and T3 groups that added squid can fundamentally reduce phytoplankton in the cultured water.Total amount.And the carp has a certain degree of selectivity to food,its main ingestion objects are the macroalgae such as Anabaena,A.punctiformis,and it has a small size and single cell.In the enclosure experiment,a total of 40 species of zooplankton were detected,including 11 species in 10 genera of protozoa,23 species in 16 genera of rotifer,2 species in 2 genus of branches,2 species in 2 species of copepods,and 2 species of planktonic larvae.The study found that the crested cocoon group had little effect on the density of zooplankton in the aquaculture water,and the cod polyculture group could significantly reduce the density of zooplankton in the aquaculture water.There were no obvious rules for the effect of different treatment groups on the zooplankton community structure.