Dynamic analysis of non-point source pollution in the Sanhekou Reservoir watershed: Implications for sustainable water management

Abstract

Exogenous pollution, especially non-point source pollution runoff during a flood season, is an important factor affecting the water quality of reservoirs. The Sanhekou Reservoir (Shaanxi, China) is a newly dammed water body, so its non-point source pollution characteristics are unknown. In this study, three major tributaries of the Sanhekou Reservoir watershed were sampled during five rainfall-runoff events in the 2022 flood season. This enabled study of the transport processes of nitrogen, phosphorus, and suspended particles in the runoff under different rainfall conditions. Using hysteresis and redundancy analyses, the sources and transport modes of pollutants are explored here, alongside analysis of rainfall and hydrological characteristics that affect pollutant concentrations, and exploration of land-use relationships. The results showed that (i) nitrate nitrogen and particulate nitrogen were the main forms of nitrogen output, and particulate phosphorus was the main form of phosphorus output. (ii) Total nitrogen, suspended particles, total phosphorus, and particulate phosphorus were significantly affected by maximum rainfall intensity, average rainfall intensity, and average flow rate, whereas nitrate nitrogen and ammonia nitrogen were significantly affected by rainfall duration, rainfall amount, and rainfall-runoff duration. (iii) If 70 % of barren land and cultivated land with slope >15° were converted to forests, total nitrogen, total phosphorus, and suspended particulate loads in the Sanhekou Reservoir would be reduced during the flood season by 10.37 %, 33.01 %, and 45.39 %, respectively. The factors influencing migration and transformation of pollutants during rainfall runoff are important for operational scheduling decisions of reservoirs and guaranteeing quality of the water supply.