Will agricultural land scale management aggravate non-point source pollution?-Chaohu Lake Basin, China as a case study

In this study, we investigated the relationship between scale management and non-point source (NPS) total phosphorus (TP) load in Chaohu Lake Basin. We used agricultural point of interest (POI) density to characterize scale management and employed the Soil and Water Assessment Tool (SWAT) model for simulations. Our findings in 2018 showed that there was a segmented relationship between agricultural POI density and TP load in townships. Significant negative correlations between POI density and TP load were observed in medium-density (0.076 < POI<0.172) and high-density (POI>0.172) scale management townships, but not in low-density (POI<0.076) townships. The slope coefficient for high-density townships was approximately one-tenth of that for medium-density townships, indicating the prevalence of agricultural land scale management at only a certain density can effectively inhibit NPS TP emissions, and this inhibitory effect has a marginal diminishing effect. These observations also applied to vegetable, fruit, and flower nurseries bases. Notably, low-density scale management of farms still had a significant inhibitory effect on TP load. However, scale management of forest farms and tea plantations did not inhibit TP loads due to the influence of high natural background phosphorus content, low hills with large gradients, and low POI density.