Livestock Breeding Dominates Nitrogen and Phosphorus Loads in a Typical Agricultural Basin: Targeted Control Strategies for Critical Source Areas

The Shaying River Basin, a major tributary of the Huai River, confronts severe agricultural non-point source pollution (ANPSP). Current management strategies are hindered by broad-scale assessments that fail to identify the dominant pollution sources and precise locations for intervention. This study aims to quantify nitrogen (TN) and phosphorus (TP) loads at a county scale and pinpoint Critical Source Areas (CSAs) to enable targeted pollution control. We employed an export coefficient model to estimate annual TN and TP loads from various sources, including land use, livestock and poultry breeding, and rural domestic sewage, across 60 counties in the Henan section of the basin. K-means clustering was applied to classify pollution levels and identify CSAs. The estimated annual TN and TP loads were 340,659.24 t and 45,779.95 t, respectively, displaying a distinct spatial pattern of lower loads in the western mountains and higher loads in the eastern plains. A pivotal finding was that livestock and poultry breeding was the overwhelming dominant source , contributing 60.63% of TN and 78.81% of TP—far exceeding contributions from cultivated land. We identified 14 counties/districts as CSAs, where the contribution from livestock was particularly pronounced. This study demonstrates that managing livestock breeding is the most critical leverage point for mitigating ANPSP in the Shaying River Basin, a finding that challenges conventional focus on cultivated land. The CSAs map and detailed source apportionment provide a scientific foundation for implementing cost-effective, targeted pollution control measures, advocating a essential shift from diffuse management to precise targeting.