Effects of Land Use Types at Different Spatial Scales on Water Quality in Poyang Lake Wetland

Abstract

Water is a crucial environmental element that affects various ecological processes in wetlands. Poyang Lake is the largest freshwater lake in China, where seasonal variation in water level generates a unique landscape of wetland in the dry season-a critical habitat for Siberian migratory birds. Nevertheless, the water quality of the Poyang Lake wetland has not been systematically and rigorously studied. In this study, we analyzed the spatial pattern of water quality in the Poyang Lake wetland based on four key physicochemical parameters[i.e. chlorophyll-a (Chl-a), chemical oxygen demand using permanganate index, total nitrogen (TN), total phosphorus (TP)] at 30 randomly selected sample sites. 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 a 500 m buffer zone had the strongest explanatory power on the spatial variation of permanganate index, while those within a 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 a 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 percentage 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 the Poyang Lake wetland.