Effects of heavy rain on the concentrations and forms of carbon, nitrogen and phosphorus in urban rivers of northern China

Abstract

Non-point source pollution caused by rainfall runoff is an important pollution source for river water. To explore the impact of heavy rain on urban river water environments, this paper studied the changes in carbon, nitrogen, and phosphorus levels, composition, and structure in the river water of Kaifeng, China, during the heavy rain in July 2021. The results showed that the concentrations of different forms of carbon, nitrogen, and phosphorus all increased under the effect of the heavy rain. The increase of phosphorus in the river was the largest, and that of carbon was the smallest. The most significant pollution from carbon, nitrogen, and phosphorus occurred in the HJ River. Colored dissolved organic matter (CDOM) was present in the form of macromolecules after the rain, and the degree of humification was deeper compared with before the rain. But heavy rain did not affect the CDOM composition in urban rivers. The spectral slope (S_R) and the absorption coefficient at 240 nm to 420 nm (E₂/E₄) values showed that the CDOM was dominated by exogenous input after the rain, with endogenous pollution again becoming the main factor one week after the rain.

Keywords: Carbon; Heavy rain; Nitrogen; Phosphorus; Urban river.