Comprehensive Evaluation Of The Structure Of Aquatic Organisms Community And Optimal Submerged Plant Coverage In Shihoudian Sub-lake In Summer And Autumn

Baiyangdian Lake is the largest shallow lake in the North China Plain.It consists of more than 140 lakes and is called the“the Pearl of North China”.In recent years,due to the effects of human interference,the structure and function of the Baiyangdian aquatic ecosystem have undergone tremendous changes.Some submerged plants completely degenerated or died out in the lake,algae multiplied in large numbers,and the lake presented serious eutrophication.Other lakes are facing severe swamping due to the explosive reproduction of submerged plants.As the main primary producer of shallow lakes,submerged plants play an important role in shaping the structure and function of aquatic ecosystems.Therefore,it is necessary to systematically study the dynamics of aquatic communities under different submerged vegetation coverage,so as to evaluate the optimal submerged vegetation coverage needed to maintain the health of baiyangdian aquatic ecosystem.At present,there are few reports about the optimal coverage of submerged plants in shallow lakes.This study chose Baiyangdian lake-Shihoudian lake as the research site.The selected vegetation coverage was 0%?C-0?,25%?C-25?,50%?C-50?,and 75%.?C-75?and 90%?C-90?.Field surveys of water quality,phytoplankton,zooplankton and zoobenthos were conducted in summer and autumn,and combined with indoor simulation tests,a preliminary evaluation of the optimal submerged plant coverage was conducted.The main results obtained are as follows:1. The effect of different submerged plant coverage on water quality.Two-way ANOVA shows that the coverage has a significant impact on all physical and chemical indexes of the water body;the season has no significant impact on DO and TP,but has a significant impact on other indexes;the interactive effect of coverage and season has no significant effect on TN and TP,but having significant interaction effects on the remaining indexes.The results of indoor simulation experiments show that compared with the control group,the nutrient of the water body is significantly reduced when submerged plants are present.The removal rate of TN by submerged plants were 84.32%,88.28%,90.98%and 76.43%in C-90,C-75,C-50 and C-25 groups,respectively.TP removal rates were 79%,87.76%,88.48%and 85.15%,respectively.Comprehensive analysis believes that the best water quality condition is when the coverage of Myriophyllum spicatum and Potamogeton pectinatus is maintained at about 50%.2. Changes of phytoplankton community structure under different submerged plant coverage.A total of 112 species of phytoplankton were identified,among which Chlorophyta were the most numerous,followed by Cyanophyta and Diatom.The number of species is 73,64,76,76 and 65 in C-90,C-75,C-50,C-25and C-0 group,respectively.Two-way ANOVA showed that the coverage had a significant effect on the number,density and biomass of phytoplankton;with the increase of the coverage,density and biomass of phytoplankton showed a gradual decrease trend.Season has significant effects on three indexes of phytoplankton.RDA results show that TDS,SPC,COD_Mnand SD have significant effects on the spatial distribution of phytoplankton in both seasons,p H,DO and TN only have a significant effect on a single season.3. Changes of zooplankton community structure under different submerged plant coverafes.A total of 129 zooplankton species were identified,including 43,64,10 and 12 species of protozoa,rotifers,cladocerans and copepods.Under five different coverages,the number of zooplankton were 78,73,73,68 and 63 in C-90,C-75,C-50,C-25 and C-0 groups,respectively.In the summer and autumn seasons,the zooplankton community mainly consists of rotifers and protozoa in Shihoudian sub-lake.Two-way ANOVA showed that coverage only has significant effects on zooplankton biomass,while seasons had significant effects on species number,density,and biomass.The interaction between coverages and seasons have no significant effects on the three indicators.RDA results show that TP,COD_Mnand SD are the main environmental factors that affect the distribution of four zooplankton groups in summer,and TP,TN,p H and TDS are the main factors in autumn.4. Changes of zoobenthos community structure under different submerged plant coverage.A total of 23 species of zoobenthos were identified,belonging to 3phyla,4 classes and 23 genera.Among them,a species number of aquatic insects,gastropods,leechidae and oligochaetes 14,4,and 5,respectively.The C-90,C-75,C-50,C-25 and C-0 groups have 11,9,12,10,and 4 zoobenthos species,respectively.Aquatic insects are the main dominant species under different coverages in the two seasons,and oligochaetes have a greater advantage in the C-0 group in summer.Two-way ANOVA showed that the coverage,season,and their interaction effects have significant effects on the density and biomass of zoobenthos.RDA shows that COD_Mn,SD,TDS,and SPC are the main environmental factors that affect the distribution of zoobenthos in summer;SD,p H,SPC,DO,and TN are the main environmental factors that affect the zoobenthos distribution in autumn.5. Comprehensive evaluation of the submerged plant optimal coverage.Based on the water bodies physical and chemical indexes of field investigations and indoor simulation experiments,the structure of aquatic organisms were evaluated for the optimal coverages to be maintained in Shihoudian sub-lake in summer and autumn.The results showed that the C-50 group was better in summer and autumn.In summary,too high or too low submerged plant coverage may be detrimental to the health of the ecosystem.It is recommended that the optimal submerged plant coverage be maintained at 50%in summer and autumn.The main innovation of this paper is the first evaluation of the most optimal submerged plant coverage.