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

<p indent="0mm">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 <sc>20 years</sc> was <sc>2,204 kg/(km</sc> ²·a), which peaked at <sc>2,983 kg/(km</sc> ²·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=0.018&lt;0.05). NAPI composition was found on average 58%–75% from food/feed, 19%–33% from fertilizer, and 7%–11% from non-food sources. From 2003 to 2022, changes in NAPI were primarily driven by food/feed input, followed by fertilizer, with non-food sources having minimal impact. To reduce NAPI, key measures were proposed, including controlling fertilizer use and aligning standards with advanced agricultural countries, regulating livestock farming based on local needs, and promoting phosphate-free detergents. These steps were expected to cut NAPI by 180, 247, and <sc>60 kg/(km</sc> ²·a), respectively, totaling <sc>487 kg/(km</sc> ²·a), achieving a relatively low national level.