Riverine organic pollution source and yield from the whole Changjiang river network: Effects of urbanization under changing hydrology

Organic pollution in river systems is a key indicator of river water quality. Identifying organic pollution sources and quantifying source contributions are important in improving water quality planning and management. However, basin-scale patterns in riverine organic pollution sources and yields to predict water quality remain poorly understood. Here, we propose an Urban Disturbed Index (UDI) coupled with riverine hydrology to quantify the current and potential impacts of urbanization on riverine organic pollution at the basin scale. We identified the source contribution from urban point sources and non-point sources by using monthly riverine discharge and monthly monitored data in chemical oxygen demand (COD) and biological oxygen demand (BOD) concentrations from 2016 to 2018. There were significant spatial differences in the river CODMn and BOD5 fields across the whole basin, and the urban point-source contribution of CODMn and BOD5 increased from 19% to 79% and from 18% to 76%, respectively, from the river source area to the river mouth. The urban point-source yields of CODMn and BOD5 increased as the UDI increased. Our study suggests that basin-scale UDI together with riverine discharge determine the river organic pollution source and yield in the entire Changjiang River network. Our results are useful for riverine water quality planning and management.

Automated summary

This study proposes an Urban Disturbed Index (UDI) combined with riverine hydrology to quantify the current and potential impacts of urbanization on riverine organic pollution at the basin scale. The results show significant differences in the contribution of CODMn and BOD5 from urban point sources across the basin, which increase with the UDI. These findings are valuable for riverine water quality planning and management.