Evaluation Of Water Quality From The Perspective Of Eutrophication In Poyang Lake Wetland And Its Relationship With Land Use Patterns

The Poyang Lake wetland has important ecological functions.However,Poyang Lake wetland has suffered from intensive human disturbances in the past decades,and the water quality has declined significantly due to the pollution from agriculture and industry,which leads to the deterioration of wetland environment.The research on the water quality assessment of Poyang Lake wetland and its impact on land use pattern can provide a scientific basis for the improvement and protection of Poyang Lake wetland water quality and the planning and management of wetland.The main contents and conclusions of the article are as follows:Evaluation of water eutrophication can help acquire eutrophication status of the water body,and can also provide critical information for the protection and management of water resources.Five key water quality parameters for Poyang Lake wetland,i.e.chlorophyll-a（Chl-a）,Secchi disk depth（SD）,biochemical oxygen demand in manganese(COD_Mn),total nitrogen（TN）,total phosphorus（TP）,were measured at 30 randomly selected sample sites and selected as the factors for eutrophication assessment.In this study,evaluation results of the cloud model were compared with those of comprehensive trophic level index（TLI）method.It was showed that although there were differences between the two methods,both of them demonstrated that the water body of Poyang Lake wetland reached the extent of eutrophication on the whole,and the main pollutants were TN and TP.The cloud model developed in this study can provide important methods for monitoring water eutrophication in Poyang Lake wetland.We also investigated the relationships between water quality parameters and land use types at different spatial scales.We found that water quality at the sample sites varied from level III（fair）to level V（very poor）,with an average of level IV（poor）.TN and TP were the main pollutants in the water of Poyang Lake wetland,while Chl-a content and permanganate index were comparatively low.There were significant correlations between water quality parameters and land use types at different spatial scales.Land use types within 500 m buffer zone had the strongest explanatory power on the spatial variation of permanganate index while those within 1 km buffer zone had the strongest relationships with Chl-a,TN,TP and the overall water quality.Land use types in buffer zones exhibited stronger explanatory power than those at watershed scales.Built-up land was positively correlated with all water quality parameters,while farmland had positive relationships with TN and TP.Rivers within 200 m buffer zone were positively correlated with TN and TP,indicating that the river input might be an important source of nitrogen and phosphorus in Poyang Lake.The percent of lake area had negative relationships with Chl-a,TN and TP,suggesting that wetland was a source of pollutants compared with the main region of Poyang Lake.Our study shows that controlling the land use patterns within small spatial scales（≤1 km）,especially minimizing the area of built-up land and farmland,is important for the protection of water resources in Poyang Lake wetland.