A bottom-up model for quantifying anthropogenic phosphorus cycles in watersheds

Aiming at tracing the sources of anthropogenic phosphorus flowing into watercourses, this study develops a static model for analyzing the phosphorus flows within a socioeconomic ecosystem. This model consists of four major subsystems: phosphorus ore mining/processing, phosphorous-containing product manufacturing, phosphorus-containing product use and phosphorus-containing waste/wastewater management. Furthermore, based on the principle of mass balance, we provided formulas for calculating phosphorus flows of the ecosystem. Then, we quantified the anthropogenic phosphorus flows using the bottom-up approach for the Chaohu watershed in 2008. The data and parameters are mainly obtained from field surveys, the literature, industrial experts, and official statistics. The results show that approximately 36 thousand tons of phosphorous flowed into watercourses in the Chaohu watershed in 2008, of which 99% came from phosphorus-containing product use (55% from crop farming, 34% from large-scale breeding, 7% from rural consumption, 2% from urban consumption, and 1% from domestic breeding). Therefore, we provided suggestions on mitigating phosphorus loss into watercourses. The study provides a method (model and the calculation formulas) to quantify anthropogenic phosphorus flows at a watershed level, which helps to understand the relationship between human activities and eutrophication.