[Analysis of Rainwater Runoff Pollution Characteristics of Various Typical Underlying Surfaces in Ningbo]

The pollution of rainwater runoff in urban areas can cause nutrient enrichment and eutrophication in receiving waters. To explore the pollution characteristics of rainwater runoff in Ningbo, eight sampling campaigns were carried out during rainfall events from 2009 to 2019. Samples of rainwater runoff were collected from underlying surfaces of roofs, squares, grassland, main roads, and the roads in commercial streets and residential districts. The concentrations of runoff pollutants, their sources and correlations, and first flush effects were studied using frequency statistical analysis and correlation analysis. The average event mean concentrations of the chemical oxygen demand (COD), ammonia nitrogen, total nitrogen, total phosphorus, and total suspended solids (TSS) in the rainwater runoff in Ningbo were in the ranges of 23.88-102.31, 0.40-1.69, 3.41-8.71, 0.09-0.50, and 37.6-323.4 mg·L^-1, respectively. Apart from the square surfaces, the COD and total nitrogen pollution of the underlying surfaces was severe. The ammonia nitrogen concentrations from the roof, commercial street, and residential district surfaces were significantly higher (P<0.05) than those from the square, grassland, and main road surfaces. The concentrations of total phosphorus from the commercial street, main road, and grassland surfaces were significantly higher (P<0.05) than those of the other underlying surfaces. The correlations of TSS with COD, ammonia nitrogen, and total phosphorus showed that the pollutants and TSS have the same original sources in roof, square, main road, and commercial street runoff, while ammonia nitrogen and total nitrogen have the same original sources in runoff from grassland and residential areas. Under the meteorological conditions of light and moderate rain, the first flush effects of ammonia nitrogen in the runoff of roofs and grassland were observed clearly, whereas this was not the same for the pollutants of total nitrogen and total phosphorus in the residential area, main road, and square runoff.