Tempo-spatial Variation Of Plankton And Its Influencing Factors In Lake Taihu, China

We conducted a large-scaled and monthly survey from2008to2010of Lake Taihu, and investigated phytoplankton, crustacean zooplankton, TN, NH4-N, NO3-N, NO2-N, TP, PO4-P, pH, water temperature (T), dissolved oxygen (DO), Secchi depth (SD) and conductivity. To research plankton communities and their relations to environmental factors, we analyzed following two aspects:(1) controlling factors of cyanobacteria blooms in Lake Taihu;(2) the influence of Microcystis blooms on crustacean zooplankton community.In the large sized of Lake Taihu trophic status showed high spatial variability, higher concentrations of nutrients were found in nothern bay and west coast, while lower values were found in Eastern Taihu and east coast. A total of87species belonging to8phylum of phytoplankton were identified during our study period. Species of Chlorophytaphyta were most abundant, followed by Bacillariophyta and Cyanophyta. Phytoplankton were dominated by Microcystis, Anabaena, Cyclotella, Synedra, Chroomonas and Cryptomonas. The biomass of phytoplankton was mainly composed of four abundant algal groups namely Cyanobacteria, Bacillariophyta, Cryptophyta and Chlorophytaphyta. Phytoplankton exhibited significant temporal variation; Cyanobacteria dominated the phytoplankton community from June to November2009, Bacillariophyta, Cryptophyta and Chlorophytaphyta jointly prevailed over the other groups in the rest seasons. Phytoplankton community in Eastern Taihu and east coast was characterized by more Bacillariophyta, and was substantially different from the other regions of the lake where Cryptophyta was dominant.The results of Redundancy Analyses showed the6significant independent variables (cladocera, COD, DO, T, TP and NO3-N) explained42.9%of variance in the phytoplankton data. Cyanophyta displayed clear positive correlations with cladocera, COD, T, TP and NO3-N, but inversely correlation with DO.During the two-year study, crustacean zooplankton community of the whole lake was characterized by high abundance and low diversity. We identified a total of30taxa in the study lake:cladocerans and copepods were represented by19and11taxa, respectively. The most abundant cladocera species were Bosmina coregoni and Ceriodaphnia cornuta, copepod was dominated by Sinocalanus dorrii and Limnoithona sinensis. Crustacean zooplankton presented a similar temporal pattern of high abundance from late spring to autumn with Microcystis. Copepod dominated the crustacean zooplankton community in December2008and from November2009to April2010, and cladocera prevailed in the rest seasons. Spatial distribution of plankton community revealed that coincident with the occurrence of massive Microcystis bloom, cladocerans dominated crustacean zooplankton community in the northern and western regions. Copepods accounted for a relatively large portion in the eastern region where blooms were rare.Multiple regression analysis found that cladoceran%was correlated with3environmental variables. Microcystis accounted for the most variation in cladoceran%, followed by conductivity and SD. A clear positive relationship was observed between Microcystis biomass and biomass of cladocerans (r2=0.73, P<0.001). Separating the cladocerans into species likewise revealed highly positive responses for all dominant species of cladocerans (Bosmina coregoni; r2=0.69, P<0.001, Ceriodaphnia cornuta; r2=0.52, P<0.001). However, the relationship between biomass of copepods and Microcystis was relatively weak (r2=0.44, P<0.001). Our study suggested that cyanobacterial blooms may change competitive relations of small-sized cladoceraand copepoda, favoring small cladocera.