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Although diatom has been widely used in biological or ecological monitoring of rivers,there is little information on diatom communities in most of Chinese rivers.In this study,we reported periphytic diatoms on artificial substrata(tile)in the Huizhou section of the Dongjiang River.We analyzed seasonal variations of the species composition and the relationship between the relative abundance and seasonal environmental factors at five sampling stations in 2010.A total of 153 periphytic diatom species,belonging to 40 genera,were identified.Dominant genera included Achnanthidium,Gomphonema,Melosira,Navicula,Nitzschia and Synedra.Gomphonema parvulum and Nitzschia palea were the common species in all the sampling sites with relative abundance1%.However,the relative abundance of the two species varied largely in seasons.Chl.a concentrations of the periphytic algae were positively correlated with the temperature.Redundancy analysis showed that water temperature,DO,NH+4-N,PO3-4-P,conductivity and pH were the major factors influencing the community structure of periphytic diatoms.Furthermore,hydrographic condition was crucial to some mobile species such as Nitzschia palea,whose relative abundance was low in summer mainly due to flushing in flood season.

Rotifers were sampled monthly from February to November in 2009 in Lake Erhai,Yunnan Province,China,in order to study their diversity and seasonal dynamics.Lake Erhai has a rotifer composition with tropical-subtropical characteristics: 68 species belonging to 25 genera of 17 families were identified,the majority of which were eurythermal or mesophilic.The genera of Trichocerca,Lecane and Brachionus were more abundant than others,accounting for 37% of the total community.Lecane arcuata and Trichocera inermis are new records in China.Biomass of the rotifer communities in Lake Erhai exhibited a bimodal seasonal cycle.An increase occurred during spring from low winter levels to an annual maximum in the mid fishing moratorium and a second increase in the early fishing season.In the mid fishing moratorium,the rotifer biomass was dominated by Asplanchna priodonta;while in the early fishing season,it was dominated by the small-sized Keratella cochlearis and Polyarthra vulgaris,then by A.priodonta again.The seasonal fishing moratorium affected not only the predation pressure on rotifers,but also competitive pressure on rotifer through influencing the community structure of Cladocera.Through the influence of predation and competition,rotifers were dominated by large omnivorous A.priodonta,which showed a bimodal seasonal distribution pattern.