Mechanism Study On The Response Of Freshwater Plankton Community To Environment In River And Lake

Rivers and lakes are important components of terrestrial water ecosystems and play a vital role in the material circulation and energy flow.As the health of aquatic ecosystems deteriorates,research on the conservation and restoration of river and lake ecosystems has received increasing attention.Plankton is the primary consumer and producer of freshwater ecosystems,and sensitive to environmental changes in the water.Therefore,it is great significance to explore the distribution characteristics of plankton community and its response mechanism to environment in rivers and lakes.This paper takes Balihe Lake and Wulihu River in the Huaihe River Basin as the research object.From April 2017 to January 2018,environmental factors and samples of plankton were collected or measured in different seasons.The spatial and temporal patterns of environmental factors,planktonic species richness,density and biomass in rivers and lakes were analyzed.On this basis,the Planktonic Index of Biotic Integrity(P-IBI)was calculated,the water ecosystem health assessment was carried out in the study area and the patterns of planktonic biotic integrity in river and lake were depicted.Application of canonical correspondence analysis(CCA)and locally weighted regression scatterplot smoother(LOWESS)explored the response mechanism of river and lake plankton to environmental factors.The main conclusions are as follows:(1)There were 7 phylum 59 species of phytoplankton and 3 phylum 28 species of zooplankton in Balihe Lake.The annual phytoplankton density in Balihe Lake varied from 2.20×105ind./L to 1.38×106ind./L,and the biomass distribution was between 0.12 mg/L and 0.66 mg/L.The density and biomass of plankton had significantly different in time and space scale,but the pattern of phytoplankton was similar.The significant change of protozoa density was the reason for the inconsistency of zooplankton density and biomass distribution pattern.The main influencing parameters of P-IBI value of Balihe Lake were Cladocera&Copepoda/Total zooplankton density ratio and Zooplankton average weight.For the seasonal variations,the P-IBI values and therefore the health levels can be ranked as Winter>Autumn>Spring>Summer.On space scale,the planktonic biotic integrity was found increased along the water flow direction.Pollutants from upper reaches,aquatic vegetation and human activities were the main factors affecting the local planktonic biotic integrity.The CCA results showed that ammonia nitrogen(NH4+-N),water temperature(WT),dissolved oxygen(DO)and secchi depth(SD)had significant effects on plankton species in Balihe Lake.The LOWESS fitting of P-IBI and environmental factors in Balihe Lake showed that the planktonic biotic integrity protection thresholds of NH4+-N,SD and DO were 0.46 mg/L,63 cm and 6.84 mg/L respectively.(2)There were 7 phylum 55 species of phytoplankton and 3 phylum 26 species of zooplankton in Wulihu River.The annual phytoplankton density in Wulihu River varied from 2.15×105ind./L to 3.41×106ind./L,and the biomass distribution was between 0.13 mg/L and 1.53 mg/L.The seasonal distribution of phytoplankton density was same as that of biomass in Wulihu River.The zooplankton density in summer was much higher than other seasons.Protozoa was the most dominant species of zooplankton in Wulihu River.The main influencing parameters of P-IBI value of Wulihu River was Cryptophyta abundance.For the seasonal variations,the P-IBI values and therefore the health levels can be ranked as autumn>winter>spring>summer On space scale,the planktonic integrity increased from upstream to downstream and then decreased in Wulihu River.The inflow of tributary pollutants and aquatic vegetation were the main factors affecting the planktonic integrity in Wulihu River.The CCA results showed that total nitrogen(TN),NH4+-N,total phosphorus(TP)and DO had significant effects on plankton species in Wulihu River.The LOWESS fitting of P-IBI and environmental factors in Wulihu River showed that three planktonic biotic integrity protection thresholds,including 1.33 mg/L for NH4+-N,15.6? for water temperature,12.34 mg/L for DO and 6.96 cm/s for v.The significance of this study is helpful to understand the mechanism study on the response of plankton community to environment in different freshwater ecological system and provide some enlightenment for the establishment of the P-IBI evaluation system.In the application,it can provide theoretical basis for ecological restoration and biological integrity protection of freshwater rivers and lakes.