Temporal variation in discharge coefficients of non-point source pollution and its determinants in river-network areas in a plain

Abstract

【Objective】 Discharge coefficient is a coefficient describing the discharge of non-point source pollution to water bodies. It is affected by many biotic and abiotic factors. In this paper, we analyze its variation in typical drylands in river network areas in a plain. 【Method】 The studied area is located at the Chongming Island, Shanghai. A hydrology-water quality collaborative monitoring system was constructed in the island, which can accurately calculate the discharge coefficient of non-point source pollution, identify its temporal variation, and analyze the underlying influencing factors. 【Result】 ① Daily discharge coefficient of total nitrogen (TN) and total phosphorus (TP) is 2.2-9 843.9 and 0.08-667.0 g/(hm2·d), respectively; monthly discharge coefficients of TN and TP is 0.02-17.2 and 0.001-1.04 kg/(hm2·m) respectively. ② The total nitrogen discharge coefficient during precipitation runoff period is significantly positively correlated with duration of the precipitation, while the TP discharge coefficient is significantly positively correlated with the total precipitation, average precipitation intensity, and maximum hourly precipitation intensity. ③ Following fertilization, the daily discharge coefficient of TN increases rapidly, while the daily discharge coefficient of TP remains almost unchanged. ④ At different time scales, there is no notable correlation between TN discharge coefficient and surface runoff, whereas the TP discharge coefficient exhibits a significant positive correlation with surface runoff. 【Conclusion】 The discharge coefficients of nitrogen and phosphorus vary with time scales, with significant differences observed between daily and monthly discharge coefficients. TN discharge coefficient is primarily influenced by fertilization, whereas TP discharge coefficient is more sensitive to precipitation and surface runoff.

Keywords

• plain river-network
• dryland
• non-point source pollution
• collaborative monitoring
• discharge coefficient