Temporal And Spatial Variation Of Planktonic Carapace Functional Groups And Their Influencing Factors In Lake Chaohu

In order to study the spatial and temporal variation of crustacean functional groups in eutrophic lake-Chaohu Lake and its main influencing factors,a total of 20 sampling points were set up in the main estuary area and pelagic area of Chaohu Lake.The spatial and temporal variation characteristics of crustacean functional groups in Chaohu Lake were analyzed and discussed through the investigation of community structure and environmental factors of crustacean in Chaohu Lake for four quarters.The effects of water quality on the community structure and functional groups of crustaceans were also discussed.Theoretical guidance for the eutrophication and algal control of Chaohu Lake was proposed.During the sampling period,the water temperature of the whole lake varied from 7.4℃ to 30.9℃,the transparency varied from 15.0 cm-60.0 cm,the dissolved oxygen varied from 1.49 mg/L-12.70 mg/L,and the average p H value of the whole year was 7.88,showing a weak alkaline water body.Different seasons and different sampling water environmental physical and chemical indexes were different.From the average size,except NH⁴⁺-N,the other five nutrient indexes showed that the estuary area was larger than the pelagic area.The water temperature,TN,NO₃^--N,NO₂^--N,TP and COD_Mnin the estuary area were significantly higher than those in the pelagic area.The water temperature showed obvious difference in each season,and the other indicators showed no obvious difference between seasons.In the 20 sampling sites of Chaohu Lake,a total of 39 species were identified in 22genera,including 22 species of cladicornis in 10 genera and 17 species of copepods in 12genera.Cladicornis accounted for 56.41%of the total species.There were 21 species of cladoceras in 10 genera and 16 species of copepods in 11 genera from 8 sampling sites in the estuary.18 species and 13 species of copepods in 12 genera were identified from 12sites in the pelagic area.On the whole,the zooplankton species composition in Chaohu estuary area is richer than that in pelagic area,but the difference in spatial distribution is not obvious.The average density of crustaceans in Chaohu estuary and pelagic area was530.77 ind/L and 506.23 ind/L,and the average biomass was 14.71 mg/L and 21.52 mg/L,respectively.Shannon-Wiener index showed that the estuary area and pelagic area were moderately polluted.The estuary area wasα-medium polluted in autumn and summer,β-medium polluted in spring and winter,and the pelagic area wasα-medium polluted only in summer andβ-medium polluted in other seasons.The Margalef index showed that both the estuary area and the pelagic area were heavily polluted only in summer and moderately polluted in other seasons.Chaohu crustaceans were divided into five functional groups according to their body size and feeding habits,which were SCF（small copepods and claocera filter feeders）,MCF（medium copepods and claocera filter）,MCC（middle copepods and claocera carnivora）,LCF（large copepods and claocera filter feeders）and LCC（large copepods and claocera carnivora）.LCC functional groups did not appear only in winter.The biomass of each functional group in the estuary and pelagic area had obvious seasonal changes,and the proportion of each functional group was different in different seasons.The dominant functional groups in the estuary area in summer were SCF functional groups.The dominant functional groups in autumn,winter and spring were SCF and LCF functional groups.Although SCF functional groups still dominated,the proportion of LCF functional groups gradually increased.The dominant function group of pelagic area in summer is SCF function group,which is higher than that of estuary area.In autumn,the dominant function group was SCF and MCC;In winter,SCF and LCF function group;The spring and summer functional groups are the same,both of which are SCF and MCF functional groups.SCF functional groups in summer,autumn and spring all account for more than half of the total number of functional groups.The proportions of SCF functional groups and LCF functional groups in autumn are 30.61%and 29.64%,which are relatively close.Through Pearson correlation analysis and RDA analysis between functional groups of crustaceans and environmental factors,the results showed that environmental factor WT（water temperature）was an environmental factor that jointly affected functional groups of crustaceans in estuary and pelagic area.The LCF functional groups of crustaceans in pelagic area can significantly affect the functional groups of SCF,MCC and LCC.This is due to the existence of interspecific competition and predation,which makes the correlation between functional groups exist.In addition to the correlation between functional groups,the correlation between functional groups and water environmental factors also showed varying degrees of correlation,among which temperature had the greatest influence.N,P,etc.,also had a non-negligible influence on the structure and distribution of functional groups of crustaceans.The results show that the pollution level of Chaohu estuary area is higher than that of pelagic area.Secondly,the eutrophication level of Chaohu Lake can be better represented by the functional groups of crustaceans.The eutrophication control and algal bloom control in the pelagic area of Chaohu Lake can be achieved by adjusting the structure of zooplankton functional groups and rebuilding the aquatic ecosystem.