Zooplankton Community Structure And Its Relation To Environmental Factors In The Lower Reaches Of The Yangtze River

This paper systematically investigated the distribution pattern of zooplankton in the mainstream of the lower reaches of the Yangtze River.At the same time,it analyzed the differences between the mainstream,the tributaries,and the external water bodies,and then explored the relationship between zooplankton and environmental factors.This provides basic data for zooplankton biodiversity in the mainstream of the lower reaches of the Yangtze River and provides scientific basis for the protection of the Yangtze River water ecosystem.The main findings are as follows:1.From 2016.10 to 2017.08 four surveys,a total of 129 species of zooplankton were identified in the lower reaches of the Yangtze River,including 2 classes,3 orders,20 families,31 genera,104 species of rotifers,7 branches,19 genera,7 families,and5 families of 4 families of copepods.Species,respectively,the proportion of the total species of 80%,15%,5%.For the first time,29 species of zooplankton were reported in the Yangtze River,including 25 species of rotifers and 4 species of branches.There are 11 main dominant species in the mainstream of the lower reaches of the Yangtze River,and there are slight differences in the combination of dominant species in each section of the Yangtze River.Among them,the dominant species in the lower reaches of the Yangtze River are: Polyarthra sp.,Copepoda nauplii,and Bosmina sp.In addition,the dominant species changed significantly during the season.The average biomass of zooplankton in the lower reaches of the Yangtze River was 76 ind/L,including 63 ind/L of rotifers,3 ind/L of branches,and 10 ind/L of copepods.The amount of zooplankton biomass in each river varied.It is 41-128 ind/L.The seasonal biomass of zooplankton varied from 61 to 115 ind/L in each season.The seasonal variation of zooplankton biomass was summer(114.9 ind/L)> autumn(79.4ind/L)> spring(64.4 ind/L)> Winter(61.4 ind/L).The average biomass of zooplankton in the lower reaches of the Yangtze River was 0.268 mg/L,including 0.037 mg/L of rotifer,0.084 mg/L of Cladocera,and 0.146mg/L of Copepoda.The zooplankton weight biomass varied by 0.091 mg/L.The zooplankton weight biomass varied from 0.075 to 0.477 mg/L in each season,and the seasonal variation trend of zooplankton weight biomass was summer(0.477 mg/L)>autumn(0.276 mg/L)> spring(0.242 mg/L)> Winter(0.075 mg/L).The average Shannon-Wiener index of zooplankton in the lower reaches of the Yangtze River was 2.45.The spatial range of each river section varies from 2.11 to2.67,and varies from 1.93 to 2.71 in each season.The rotifer diversity index was the highest,and was consistent with the spatial-temporal change trend of the zooplankton diversity index.The Shannon-Wiener index of copepods and Cladocera was low,and the seasonal changes of each river segment were not obvious.2.Because of the influx of tributaries,the community structure of the mainstream zooplankton will be affected.The total number of trunks is smaller than the species of zooplankton in the river mouth of the corresponding river section,the amount of biomass is low,and the weight biomass is low.The inflow of zooplankton to the main stream from the branch into the estuary was significantly different and statistically significant(p<0.05).In addition,the total number of trunks was smaller than the corresponding species of zooplankton in the peripheral waters of the corresponding section,and the amount of biomass was low and the weight of biomass was low.The difference between the main stream of the Anqing River and the surrounding water was significant,which was statistically significant(p<0.05).3.Pearson correlation analysis showed that water temperature,dissolved oxygen,total nitrogen,total phosphorus,salinity,and total dissolved solids were closely related to the zooplankton community structure in the mainstream of the lower reaches of the Yangtze River.Redundancy analysis(RDA)showed that the environmental factors affecting the spatial distribution of zooplankton in the lower reaches of the Yangtze River are water temperature,followed by total phosphorus and pH.The environmental factors affecting the spatial distribution of zooplankton in the lower reaches of the Yangtze River in the summer were water temperature.The Canonical Correspondence Analysis(CCA)shows that the environmental factors affecting the spatial distribution of zooplankton in the lower reaches of the Yangtze River in the winter are total nitrogen,water temperature,and total phosphorus.The environmental factors affecting the spatial distribution of zooplankton in the lower reaches of the Yangtze River in the spring are salinity,pH and total nitrogen.