Studies On Community Structure Of Zoobenthos In Five Water Source Reservoris In Liaoning Province

Zoobenthos is one of the important aquatic taxa in water ecosystems,and plays an important role in material cycling and energy flow in the ecosystem as a natural bait for fish.In this study,the zoobenthos of five reservoirs in Liaoning Province were sampled eight times by season from 2018 to 2021,including Guanyinge Reservoir,Baishi Reservoir,Chaihe Reservoir,Qinghe Reservoir,and Tanghe Reservoir.Then the characteristics of community structure of the five reservoirs and their spatial and temporal changes were analyzed,the zoobenthos data and physicochemical indicators of the water bodies were integrated,their driving factors were analyzed against environmental characteristics.The biomass was used to estimate the fish production potential,and to provide a basis for the development of water conservation fisheries in the five reservoirs.The results were outlined below.1.A total of 76 species of zoobenthos were detected from the five reservoirs detected,which belonged to 3 phyla.The manily species were aquatic insects and oligochaetes.The maily aquatic insects were chironomid larvae and the mainly oligochaetes were Tubifex and Naididae.Only 4 species of mollusks were collected,including Radix swinhoei which from Guanyinge Reservoir and Tanghe Reservoir,Cipangopaludina cathayensis and Bellamya purificata which from Guanyinge Reservoir,and Cristaria plicata which from Baishi Reservoir.Tanghe Reservoir has the largest number of species,with 40 species,including 32 species of arthropods,7 species of oligochaetes,and 1 mollusk species.Secondly,38 species were detected from Guanyinge Reservoir,including 26 species of arthropods,9 species of oligochaetes and3 species of mollusks.There are 30 species detected from Qinghe Reservoir,including23 species of arthropods,and 7 species of oligochaetes.And 26 species were detected from Baishi Reservoir,including 16 species of arthropods,9 species of oligochaetes,and 1 species of mollusks.What’s more,there also 26 species were detected from Chaihe Reservoir,including 17 species of arthropods,and 9 species of oligochaetes.2.Chaihe and Tanghe reservoirs had the highest number of dominant species with8 species,followed by Qinghe Reservoir with 7 species,Guanyinge and Baishi reservoirs with the least with 6 species.The dominant species of zoobenthos in the five reservoirs were composed of chironomid larvae and oligochaetes.In the Guanyinge Reservoir and Chaihe Reservoir,the higher dominant species were oligochaetes.There were 5 species of oligochaetes and 1 species of chironomid larvae in Guanyinge Reservoir.And 5 species of oligochaetes and 3 species of chironomid larvae in Chaihe Reservoir.The number of oligochaetes and chironomid larvae of the dominant species composition in other reservoirs was similar.The common dominant species of the five reservoirs were Limnodrilus hoffmeisteri and Tubifex sinicus.Limnodrilus hoffmeisteri was the first dominant species in Guanyinge Reservoir,Chaihe Reservoir and Qinghe Reservoir.The first dominant species in Baishi Reservoir and Tanghe Reservoir were Tanypus punctipennis and Propsilocerus akamusi,respectively.3.Baishi Reservoir has the highest average annual density during 2018 to 2021with 2144.86 ind·m^-2,followed by Guanyinge Reservoir with 1148.79 ind·m^-2,Chaihe Reservoir with 1066.64 ind·m^-2,Qinghe Reservoir with 782.38 ind·m^-2,and Tanghe Reservoir with the lowest with 681.01 ind·m^-2.The biomass was the highest in Guanyinge Reservoir with 20.07 g·m^-2,followed by Baishi Reservoir with 10.68 g·m^-2,Tanghe Reservoir with 6.31 g·m^-2,Chaihe Reservoir with 4.19 g·m^-2,and Qinghe Reservoir was the lowest with 2.87 g·m^-2.In Guanyinge Reservoir,the highest percentage of density was oligochaete,accounting for 86.80%.The highest proportion of biomass in Guanyinge Reservoir was mollusks,accounting for 82.35%.The dominate species of density and biomass in Chaihe Reservoir both were oligochaetes,accounting for 87.64%and 71.74%,respectively.Aquatic insects was the highest proportion of species in Baishi Reservoir,Qinghe Reservoir and Tanghe Reservoir,accounting for 54.25%,51.05%and 69.72%of the density,66.79%,60.44%and 83.63%of the biomass,respectively.The mainly densities and biomass of aquatic insect in the five reservoirs were chironomid larvae,while oligochaetes were dominated by tubifex.4.The density and biomass in the five reservoirs were highest in spring and lowest in summer,while autumn was season that the lowest value of density and biomass in Guanyinge Reservoir.In the spring of 2021,the density of each reservoir was highest,which was significantly elevated compared to other seasons.The peak biomass was not entirely consistent with density,as it were occurred in the spring of 2021 in Guanyinge Reservoir,Baishi Reservoir and Chaihe Reservoir,while Qinghe Reservoir and Chaihe Reservoir were in spring 2019.The density and biomass of aquatic insects exhibited higher levels in spring and winter,while lower levels in summer and autumn,the oligochaetes were higher in spring and autumn,and lower in summer.In terms of horizontal distribution,Chaihe Reservoir,Qinghe Reservoir,and Tanghe Reservoir showed the highest density and biomass in the downstream and the lowest in the reservoir entrance,While the highest density and biomass values in Guanyinge Reservoir were in the midstream and upstream of the reservoir respectively,and the lowest values both in front of the dam.The highest biomass values of Baishi Reservoir was in the midstream and lowest values was in the upper-middle reaches of the reservoir.5.The mean value of Shannon.Wiener index in Tanghe Reservoir was the highest with 1.84,followed by Chaihe Reservoir with 1.46 and the lowest value was in Guanyinge Reservoir with 1.24.The mean value of Pielou index in Chaihe Reservoir was the highest with 0.77,followed by Tanghe Reservoir with 0.72 and the lowest value was in Guanyinge Reservoir with 0.59.The highest mean value of Marglef index was from Tanghe Reservoir with 1.48,followed by 0.98 in Chaihe Reservoir and the lowest of 0.91 in Qinghe Reservoir.The highest Shannon-Wiener index of the five reservoirs appeared in spring,summer,autumn and winter,and the lowest index both appeared in summer,while only in Guanyinge Reservoir was in autumn.Pielou index and Marglef index showed opposite seasonal trends.Pielou index was higher in summer and autumn,and lower in spring and winter,while Marglef index was higher in spring and winter,and lower in summer and autumn.6.The results of Pearson correlation analysis and canonical correspondence analysis（CCA）showed that the response of zoobenthos to environmental factors differed in five reservoirs.In the results of Pearson correlation analysis,showed that benthic animal density in Guanyinge Reservoir was significantly correlated with water depth and dissolved oxygen,Baishi Reservoir was total nitrogen,ammonia nitrogen and chlorophyll-a,Chaihe Reservoir was total phosphorus,dissolved oxygen and p H,Qinghe Reservoir was water depth,water temperature,and dissolved oxygen,Tanghe Reservoir was chlorophyll-a.The species and composition of zoobenthos were significantly affected by nitrogen and phosphorus content.Baishi Reservoir had the highest TN,TP,and NH⁴⁺-N,showing the least number of species and high dominance of water filarial worms,while TN,TP,and NH⁴⁺-N in Tanghe Reservoir were the lowest,showing the most species and high dominance of chironomid larvae.The results of CCA analysis show that water depth,ammonia nitrogen,dissolved oxygen,chlorophyll-a,total nitrogen,p H were the key environmental factors which had a significant correlation with zoobenthos in the five reservoirs.7.Based on the biomass of zoobenthos,the fish production potential of the five reservoirs was estimated to be the highest in Baishi Reservoir with 51.42kg·hm².Tanghe Reservoir,Guanyinge Reservoir and Chaihe Reservoir had similar fish production potential with 28.36 kg·hm²,26.72 kg·hm² and 25.75 kg·hm²,respectively.Qinghe Reservoir was the lowest fish production potential with 14.87 kg·hm².The fishery potential of Guanyinge Reservoir,Chaihe Reservoir and Qinghe Reservoir were higher in the contribution of oligochaetes,while in Baishi Reservoir and Tanghe Reservoir were dominated by aquatic insects.The five reservoirs should develop reasonable stocking and fishing programs for demersal fishes according to the results of fish production potential estimation.In this way,nitrogen,phosphorus and other nutrient salts from water would be transferred,it also brings economic benefits and guarantees the sustainable development of water conservation fisheries.