Determination of NPS Pollutant Unit Loads from Different Landuses

This study aimed to estimate pollutant unit loads for different landuses and pollutants that reflected long-term runoff characteristics of nonpoint source (NPS) pollutants and recent environmental changes. During 2008-2014, 2026 rainfall events were monitored. The average values of antecedent dry days, total rainfall, rainfall intensity, rainfall duration, runoff duration, and runoff coefficient for each landuse were 3.8-5.9 d, 35.2-65.0 mm, 2.9-4.1 mm/h, 12.5-20.4 h, 12.4-27.9 h, and 0.24-0.45, respectively. Uplands (UL) exhibited high suspended solids (SS, 606.2 mg/L), total nitrogen (TN, 7.38 mg/L), and total phosphorous (TP, 2.27 mg/L) levels, whereas the runoff coefficient was high in the building sites (BS), with a high impervious surface ratio. The event mean concentration (EMC) for biological oxygen demand (BOD) was the highest in BS (8.0 mg/L), while the EMC was the highest in BS (in the rainfall range <10 mm) and UL and forest land (in the rainfall range >50 mm). The unit loads for BOD (1.49-17.76 kg/km(2)center dot d), TN (1.462-10.147 kg/km(2)center dot d), TP (0.094-1.435 kg/km(2)center dot d), and SS (15.20-327.70 kg/km(2)center dot d) were calculated. The findings can be used to manage NPS pollutants and watershed environments and implement relevant associated management systems.