Correlating Land Use Changes with Drinking Water Source Quality in Pearl River Delta Reservoirs

Reservoir-type drinking water sources in the Pearl River Delta ensure a safe urban water supply; thus, land-use changes are important factors affecting these aquatic environments. In this study, we investigated the water source areas of medium and large reservoirs in the Pearl River Delta to determine the contributions and trends of land-use changes within reservoir drinking water source areas to the reservoir water quality. First, we analyzed dynamic land-use changes in reservoir-type water sources in the Pearl River Delta region from 1980 to 2020. We then used the gray relational analysis method to determine the relationship between land use and water quality changes. We analyzed changes in the main water quality factors in the Dajingshan Reservoir (Zhuhai) and determined the relationship between changes in land use and the reservoir water quality index over the past 20 years using correlation and redundancy analyses. The results indicate that paddy fields, dry land, forest land, and water areas were the main land-use types around reservoir-type drinking water sources in the Pearl River Delta. Although construction land and water areas expanded, paddy fields, dry land, and forest land areas decreased. The land transfer trend was mainly from forest and cultivated land to production and living land (e.g.1980-2020), construction land) and water areas. With the implementation of the policy, the aforementioned land-use transformation began to slow. Regionally, the risk sources of non-point source pollution in the study area gradually decreased, but still accounted for 9.48% of total land use in 2020. The water quality of reservoir sources in the Pearl River Delta improved; however, nitrogen pollution remains problematic. Gray relational analysis indicates that land-use changes and water quality were correlated (in order of decreasing strength): construction land > agricultural land > forest land. Non-point source pollution caused by land use remains an important influencing factor. The Dajingshan Reservoir water quality is seriously polluted, as the total nitrogen exceeded the standard during several months, and nitrogen and phosphorus pollution gradually increased over time. Nitrogen and phosphorus were the main pollutants in the reservoir. Big mountain reservoir redundancy, correlation, and partial least squares regression analyses indicate that the land use type and water quality index were correlated, forest land and the nitrogen/phosphorus water quality index were negatively correlated, and construction and agricultural land were significantly positively correlated, which had a positive effect on the total nitrogen concentration. The influence of land-use patterns on non-point source pollution remains an uncontrollable factor. The specific effects of land-use changes on water quality are complex; therefore, further modeling should investigate the mechanism by which the water supply quality is influenced to improve reservoir water quality, ensure the safety of the regional water supply, and provide support for ecological restoration measures in protected areas.