The Spatiotemporal Dynamic Changes in Net Anthropogenic Phosphorus Input (NAPI) in Quzhou City from 2003 to 2022

The Qujiang River Basin was a vital water source for Quzhou City and Zhejiang Province. Increasing human activities were found to significantly disrupt the phosphorus cycle in Quzhou, leading to frequent phosphorus pollution. To address this, the net anthropogenic phosphorus input (NAPI) model was used to estimate Quzhou′s phosphorus input from 2003 to 2022, and its spatiotemporal patterns, component changes, and influencing factors were analyzed. Results showed that Quzhou′s average NAPI over 20 years was 2,204 kg/(km2·a), which peaked at 2,983 kg/(km2·a) in 2012 before declining. Spatially, NAPI was observed to be higher in the east and lower in the west, closely linked to land use and significantly correlated with river total phosphorus (TP) levels (P=0.01860 kg/(km2·a), respectively, totaling 487 kg/(km2·a), achieving a relatively low national level.