Assessment Of Eutrophication And Ecological Risk Of Microcystin-LR In The Upstream Section Of Mainstream Of Haihe River

Eutrophication of surface water bodies has been the main problem in water quality management in recent decades,and the MC-LR,a secondary metabolity produced by cyanobacteria,has drawn more attention.Therefore,this paper aims at studying on the assessment of eutrophication and ecological risk of MC-LR in the upstream section of mainstream of Haihe River.This study was implemented based on the mechanisms of eutrophication assessment,ecological risk assessment,correlation analysis and so on.Firstly,the water quality parameters were determined according to the eutrophication assessment method and environmental factors that affect the production of MC-LR.And the total nitrogen(TN),total phosphorus(TP),CODMn,chlorophyll a(Chla),secchi depth(SD),dissolved oxygen(DO),pH and water temperature were investigated by this study.The comprehensive eutrophication state index was used to evaluate the eutrophication state.Secondly,seven indexes including endpoint,exposure duration,medium,and test location and so on were used as search criteria to collect toxicity aquatic data of MC-LR.Log-logistic was selected to fit the species sensitivity distribution(SSD)curve for MC-LR for all aquatic organisms.Then the hazardous concentration for 5% of species(HC5)and the predicted no effect concentration(PNEC)were calculated based on the SSD curve constructed.And the risk quotient(RQ)was used to determine the ecological risk level.Finally,the relationship between MC-LR production and the environmental conditions was investigated through correlation analysis.Therfore,the significant environmental factors that strongly influence the variation in the MC-LR concentrations were identified,which was in favour of the management of cyanobacterial blooms.The results showed that the comprehensive eutrophication state index from the upstream section of mainstream of Haihe River during the summer of 2015 ranged from 55.21 to 67.71,suggesting the river was eutrophic or meso-eutrophic during this period.The hazardous concentration for 5% of species(HC5)was 15.43 ?g/L while the predicted no effect concentration(PNEC)was 5.14 ?g/L.The mean value of RQ ranged from 0.13 to 6.27 suggesting that the risk level of MC-LR to aquatic organisms in the river was medium or high during the study period.The MC-LR concentrations were positively correlated with the eutrophication status and significantly affected by TP,water temperature and pH.