Structure Of Phytoplankton Community And Its Relationship With The Environmental Factors In Dali-nor Lake

Dali-Nor Lake(Dali Lake),located in Chifeng city of Inner Mongolia Autonomous Region,is the second largest freshwater lake and serves as an important fishery production base.Phytoplankton is an important primary productivity and the food for zooplankton and fish in the ecological system.At present,there is little research on the relevant aspects of the lake.In order to explore the phytoplankton community structure and its relationship with the water quality of Dali Lake,the physical and chemical indicators and phytoplankton community structure were monitored monthly at nine sampling points in the lake.Correlation analysis and canonical correspondence analysis were used to determine the effects of environmental factors on the distribution of phytoplankton.The trophic state index and ecological index were used to evaluate the water quality.The main results are as follows:(1)During the investigationin,7 phylum 51 genera and 130 species(including varietas and metatype)were identified.The dominant phytoplankton species are 3 genera 19 genera and 31 species,Oocystis lacustris and Oocystis solitaria are the main species,the dominant species are Chlorophyta Cyanophyta diatom.(2)The average number of species is 60,the number of species in July up to the maximum,the number of types at B4 is the maximum number in space,and the number of species is the maximum at the depth of 0.5m under the water.The abundance and biomass of phytoplankton are decreased with water depth.There is a decreasing trend in the upper and middle parts of the water body and from the periphery of the lake to the center.There is a descending trend at the lower part of water body from northeast to southwest.(3)As for the horizontal distribution of the Shannon-Wiener diversity index and Margalef richness index,they are higher than at the north part of the lake and the centre of lake that of the South lake.In the vertical distribution,the maximum value is at 1.5m below the water surface.The horizontal distribution of Pielou evenness index is more uniform,and it increases with the increase of water depth.(4)The average transparency(SD)of the lake is smaller.The difference at of the electrical conductivity(EC)and water temperature(T)is smaller,the change of the values in time is that of autumn>summer>winter.It is alkaline water,and it has the highest value in January.Dissolved oxygen(DO)is large in January.Salinity(SAT)is the lowest in January,and the values at site A7 and B6 were significantly smaller in July.(5)The total nitrogen(TN)and total phosphorus(TP)in the lake were higher in winter than that of in summer and autumn;the difference between the sites is obvious.The dissolved total phosphorus(DTP)in winter was lower than that of in summer and autumn.The concentration of orthophosphate(DIP)was higher in winter,and the difference was significant.Chemical oxygen demand(CODcr)in winter is about 2.5 times of the value in summer.Chlorophyll a(Chl-a)was the largest in August,and the difference was significant.(6)Correlation analysis showed that Phytoplankton abundance was positively correlated with water temperature(T),total nitrogen(TN),total phosphorus(TP),chlorophyll a(Chl-a),transparency(SD)and dissolved oxygen(DO).There was a negative correlation between pH and chemical oxygen demand(CODcr).Canonical correspondence analysis showed that the main factors affecting the structural characteristics of phytoplankton in the lake are temperature(T),transparency(SD),chlorophyll a(Chl-a),chemical oxygen demand(CODcr)and salinity(SAT).The nutritional status of water body was evaluated,and the results shown that the eutrophication level is medium to high.The evaluation of phytoplankton community index was shown that the lake is polluted at all the sites from light to moderat.