Multi-perspective analysis on the characteristics of composite non-point source pollution in typical hilly and plain...

Urban composite non-point source (UCNPS) pollution has emerged as a critical bottleneck in improving watershed water quality. Currently, the understanding of its pollution characteristics in different type of urban still not comprehensive. This study systematically analyzed the pollution characteristics of UCNPS in typical hilly and plain urban aeras across three perspectives: pollutant concentration, particles composition, and dissolved organic matter (DOM) composition. The results revealed that: (1) Exponential wash-off model and functional data analysis can effectively quantify the first flush intensity of surface runoff, identifying that the first flush intensity in hilly urban was generally stronger than that in plain urban; (2) the improved exponential model can effectively identify the catchments with high UCNPS loads; (3) the particles in surface runoff and first-flush rainwater (FFR) from separate systems were primarily in the 4-63 μm range. The particles size distribution of combined sewer overflow (CSO) effluent was influenced by pipe flow velocity, with notable regional differences. Surface runoff was the primary source of particles in pipe runoff, while its own particles mainly originated from vehicle exhaust (6 %-56 %), soil (8 %-68 %), and brake wear (14 %-22 %); (4) DOM in surface runoff was predominantly composed of humic-like acids (26.29 %), while FFR and CSO were dominated by tryptophan-like components (26.85 % and 24.93 %). Multi-perspective analysis of UCNPS pollution characteristics can support to control it efficiently.