The Response Of Phytoplankton Assemblages To Ecological Restoration In Huizhou West Lake, A Tropical Lake

Fish removal and macrophyte restoration can impose a significant impact on lake restoration In order to improve water quality,fish removal was carried out in June to August 2007 in Huizhou West Lake,southern China.Present study investigated the changes in phytoplankton communities after fish removal.The results showed that there was a significant change in algal cell densities and biomass.The cell densities and biomass of cyanobacteria,green algae and diatoms increased during fish removal.The present study suggests that fish affect significantly phytoplankton community,but fish revomal is not able to reduce phytoplankton biomass in tropical shallow lakes.Shallow lake restoration in tropical region has to include other measures such as macrophyte restoration.After taking the measure of macrophyte restoration,water quality and eutrophication have been a remarkably improvement from the analysis of phytoplankton.The totall cell densities have sharply descresed,from 4.51×10~7 cell/L before the restoration to 8.65×10~6 cell/L after the restoration,the average is 8.65×10~6 cell/L,and the lowest is 2.48×10~5 cell/L on Feb.2008. During the phase of restoration,cell densities have rapidly increased to 1.06×10~9 cell/L,which is 23.5 times more than that before restoration.Before the restoration the totall biomass is 7.49 mg/L,and during the restoration phase,it rapidly increases to 29.57 mg/L,which is four times than before.From Sep.,2007 to Dec.,2008, the average of biomass is 2.69 mg/L,the lowest is 0.64 mg/L in Mar.,2008.However,there were many Cryptomona eiosa and Chroomonas acuta in Feb.,2008,which have bigger biomass,so the biomass is not the lowest.From aspects of phytoplankton species composition,species diversity has been a number of growths.Especially the poor species in nutrition,such as Bacillariophyta,Euglenophyta et al.. Dominant species have changed from Merismopedia spp.,Dactylococcopsis sp,,Scenedesmus spp.,kistrodesmus acicularis et al.into Fragilaria sp.,Cocconeis placentula,Cryptomona eiosa, Chroomonas acuta,Phacus sp.Euglena sp.etc.Besides,Coelastrum sp.,Mallomonas sp. Cocconeis placentula etc.have appeared,which are the indicator species of clear water.