Exploring the effect of basin land degradation on lake and reservoir water quality in China

Abstract

Studying the trends and ecological impacts of basin land degradation is important to protect lake and reservoir water quality and for basin land-use planning. This study examined 12 lakes/reservoirs and their basins in China, and based on basin land-use and lake/reservoir water-quality indicator data (pH, dissolved oxygen (DO), permanganate index (CODMn), ammonia nitrogen (NH3-N), total nitrogen (TN), and total phosphorus (TP)) from 2005, 2010, and 2015, the land degradation trends of the basins and their relationships to lake/reservoir water quality were analyzed using Spearman correlation analysis, redundancy analysis (RDA), and geographic information system (GIS) techniques. The results showed that: (1) The proportion of ecological land (change rate: −0.06%) and cultivated land (change rate: −0.38%) showed a downward trend, and the proportion of degraded land showed a significant upward trend (change rate: +2.90%). The increase in built-up land was the fastest among all land types (change rate: +2.93%). (2) The proportion of degraded land (dominated by built-up land) and cultivated land (dominated by cropland) in the basins was significantly positively correlated with CODMn, NH3-N, TN, and TP but significantly negatively correlated with DO. Conversely, the proportion of ecological land (dominated by forest land) in the basins was significantly negatively correlated with CODMn, NH3-N, TN, and TP but significantly positively correlated with DO. This showed that basin land degradation had a significant adverse impact on lake/reservoir water quality. (3) RDA indicated that basin land degradation explained up to 58.6% of lake/reservoir water-quality changes. Degraded land had the highest RDA explanation rate (31.4%) for lake/reservoir water-quality changes, and within this category, built-up land had the highest explanation rate (built-up land: 27.9%; desertified land: 12.7%). Ecological land explained 29.2% of lake/reservoir water-quality changes, within which forest land had the highest explanation rate (forest land: 24.7%; grassland: 9.4%; wetland: 12.5%). Cultivated land explained 22.7% of lake/reservoir water-quality changes, within which cropland had the highest explanation rate (cropland: 19.7%; garden land: 4.9%). In conclusion, the land in the selected lake/reservoir basins showed a clear trend of degradation, and this degradation trend had a significant adverse impact on the changes in lake/reservoir water quality. The results of this study can support policymakers to contain basin land degradation, to protect lake/reservoir water quality and to improve the sustainability of basin land and water resources.