Evaluation Of Ecological Effects Of Different Concentrations Of Hexavalent Chromium,total Phosphorus And Sulfate Using The Mesocosm Experiment System

The widespread water pollution problem poses a serious threat to people’s life and safety,and has become an important factor hindering the sustainable development of human health,economy and society.It is urgent to improve water environment management and control water pollution.Water quality standards play an important role in the management and protection of water environment in China,and the ecological effects of pollutants are crucial to the formulation of water quality standards,assessment and management of water quality.Traditional pollutant assessment methods are mainly based on the experimental data of individual level,lacking the macro-level effect assessment of pollutants in population,community and ecosystem,which is difficult to meet the current needs of water environment protection.In addition,the ecological effects of pollutants will be different in different geographical areas due to differences in climate and species composition.Therefore,on the regional or watershed scale,examining the ecological effects of pollutants from the level of population and community is a useful supplement to the existing assessment methods,and is of great significance to the management of water ecosystems in specific watershed areas.In this study,ecological effects of three typical pollutants in Poyang Lake basin,namely hexavalent chromium(Cr⁶⁺),total phosphorus（TP）and sulfate(SO₄^2-),were examined in population and community levels in mesocosm experiments.The mesocosms included local benthos,plankton,submerged macrophytes and fish and the target concentrations of pollutants in mesocosms were referring to the literatures,which reported the three pollutants quality standards and concentrations in Poyang Lake Basin.The main results are as follows:（1）Hexavalent chromium(Cr⁶⁺)at 228.4μg/L concentration was lethal to Bellamya aeruginosa.The growth of juvenile snails was inhibited and the phytoplankton community changed from dominated by Cyanophyta to dominated by Chlorophyta when the Cr⁶⁺was at the concentration of 22.84μg/L.At the concentration of 10.35μg/L,there was no significant difference in each index between the treatment and the control group,indicating that Cr⁶⁺concentration below 10.35μg/L was relatively safe for Poyang Lake Basin.（2）Total phosphorus at the concentration of 0.20 mg/L,the mean concentration of chlorophyll a was high（65.57±64.85μg/L）,and the algae bloom occurred in this treatment during the experiment.The chlorophyll a concentration（52.45±58.60μg/L）at the concentration of 0.08 mg/L was significantly higher than that of 0.04 mg/L（28.53±29.74μg/L）and the control group（6.09±3.37μg/L）.With the increase of total phosphorus concentration,the biomass of Bellamya aeruginosa,Vallisneria natans and Carassius auratus all increased.At 0.04 mg/L,there was no significant difference between the chlorophyll a concentration and the control group.These results indicated that the total phosphorus concentration of 0.04 mg/L was relatively safe for Poyang Lake Basin.（3）The proportion of Pyrrophyta in phytoplankton community increased with the sulfate concentration increasing when the sulfate concentration higher than 20 mg/L.But the sulfate addition had no significant effects on the abundance of Bellamya aeruginosa,Vallisneria natans and Carassius auratus.At the concentration of 20 mg/L,there was no significant difference in each index between the treatment and the control group,indicating that sulfate concentration below 20 mg/L had little influence on Poyang Lake Basin.