Influential factors detection for surface water quality with geographical detectors in China

Surface water quality is a matter of serious concern in China. This study quantitatively analyzes the spatial-temporal characteristics of surface water quality among 100 monitoring stations in China during 2015. A geographical detector was used to detect the influential annual and seasonal factors. Surface water quality is primarily controlled by the content of nutrient pollutants and organic pollutants. Natural factors (precipitation, temperature, soil erosion, and terrain) and anthropogenic factors [land use type, population density, and per capita gross domestic product (GDP-per-capita)] were selected as geographical proxies to be tested for their explanatory power for surface water quality. Results indicated that the top three factors influencing the annual mean of nutrient pollutants were the population density, terrain, and precipitation, the explanatory power of which was 0.82, 0.35, and 0.24, respectively. The interactive explanatory power for population density and terrain was 0.88 and for population density and precipitation was 0.87, both exhibiting enhanced interaction relationships. The top three factors influencing the annual mean of organic pollutants were population density, temperature, and basin, the explanatory power of which was 0.46, 0.29, and 0.27, respectively. The interactive explanatory power for population density and basin was 0.80 and for terrain and precipitation was 0.82, both demonstrating a nonlinear enhanced interaction relationship. For seasonal changes, the nutrient pollutants and organic pollutants were both affected by agricultural runoff due to seasonal farming. This study revealed that anthropogenic factors influenced surface water quality two to three times more than natural factors.