Study On Plankton Community Structure And Food Web Structure In Wushan Lake Of Hubei Province

Wushan Lake is located in the northern suburb of Wuxue City,Hubei Province.Wushan Lake belongs to one of the medium-sized shallow lakes and connects to the Yangtze River by ditches.The water area is about 15.2 km².The fish catches were about1,500 tons per year in the last three years,of which about 21%was the silver carp（Hypophthalmcihthys molitix）and about 70%was bighead carp（Aristichthys nobilis）.The submerged macrophytes were abundance and water transparency were high in Wushan Lake before 1980s.However,the water state shifted from a clear water macrophyte-dominated state to a turbid phytoplankton-dominated state because of industrial and agricultural pollution and large-scale bait farming since 1980s.After the establishment of the Wushan Lake National Wetland Park by the State Forestry Administration in December 2011,protection and restoration have been carried out in recent years.The cultured pearls and cultured fish farming by bait have been fully forbidden.However,recent monitoring results indicated that the water quality was still Inferior V.In the present study,we sought to elucidate the effects of fish structure dominated by the silver carp and bighead carp.To test this effect,we conducted a field survey and food web analysis during September 2017 to August 2018 using plankton community analysis,a ¹³C and ¹⁵N stable isotope approach and Ecopath model.The main results are as follows:（1）The water quality is inferior to V（Chinese surface water environmental quality standards）.Trophic status indices showed the water quality was between mesotrophy and severe eutrophication.The main pollutants are total phosphorus（TP）and total nitrogen（TN）.（2）The dominant species of phytoplankton are cyanobacteria,diatoms,green algae and cyanobacteria in autumn,winter,spring and summer,respectively.Redundancy analyses indicated that TP and water temperature（WT）were the key drivers behind this difference of the phytoplankton abundance.（3）The dominant species of zooplankton are mainly rotifers and protozoa.The dominant species of zooplankton are rotifers in autumn,spring and summer,and copepods in winter.Redundancy analyses indicated that TP,water and permanganate index（CODMn）were the key drivers behind this difference of the zooplankton abundance.（4）Cluster analysis indicated that fish catches,seasonal changes and domestic sewage discharge had significant effects on the phytoplankton and zooplankton community structure.Combined with the fishing and stocking period,the stocking of silver carp and bighead carp may be the main reason for the miniaturization of phytoplankton and zooplankton.（5）The total system throughput was about 54509.82 t?km^-2?year^-1,the total transfer efficiency was about 8.24%.The ratio of total primary production to total respiratory volume is 2.064.The connectance index and system omnivory index were 0.254 and0.098,respectively.Finn’s cycling index and Finn’s mean path length were 28.65%and6.044,respectively.Low internal linkage complexity,high energy conversion efficiency and high liquidity that indicated large biomass in Wushan Lake.The ecosystem is close to saturation.MTI mixed trophic analysis indicated that silver carp can decrease phytoplankton abundance,while bighead carp cannot.