Improved export coefficients enhanced export coefficient model's accuracy in assessing agricultural non-point pollution: a Jialing River Basin study

The export coefficient model (ECM) represents a well-developed and widely utilized approach for estimating agricultural non-point source pollution loads. Ensuring appropriate export coefficients of pollutants, such as total nitrogen (TN) and total phosphorus (TP) sourced from livestock and poultry is essential for precise model simulation, an aspect often neglected in previous studies. This study focuses on determining improved export coefficients (IEC) related to livestock and poultry for TN and TP losses along the Jialing River, considering regional and farming method variations. The results support the hypothesis that IEC enhances the ECM accuracy. Notably, the model's relative error (Re) significantly decreases when using IEC compared with the original exported coefficients [extensive mode exported coefficients (EMEC) and intensive mode exported coefficients (IMEC)]. Specifically, the Re for TP reduces from 11.59% (EMEC) and 16.78% (IMEC) to 5.80% with IEC. For TN, the Re decreases from 20.17% (EMEC) and 32.69% (IMEC) to 7.41% with IEC. These findings demonstrate that IEC improves the ECM's accuracy and enables the more accurate assessment of various agricultural non-point sources' contributions to TN and TP loads in the Jialing River Basin on a county scale. This enhanced understanding will aid in managing and controlling agricultural pollution in large-scale catchments.