To help us control pollution caused by urban runoff, we need to understand how particulate matter in storm runoff contributes to the total pollutant load. In this study, we collected samples from ten sites along on the banks of an urban river during five rainfall events. We determined the grain size and phosphorus (P) forms in the particulate matter to assess how much P there was in storm runoff. The results showed that the particles were mostly medium-sized, and particles with a diameter of less than 850 μm but greater than 150 μm accounted for 50% of the total particulate matter. The average particulate P concentration, at 298.7 mg/kg, was high and was mostly organic P (Po), which had an average concentration of 134.64 mg/kg. The concentrations of the different P forms varied with particle size. The main fraction in the large-sized grains was acid-extractable inorganic P (Pi), while Po and alkalinity-extractable Pi dominated in medium- and small-sized particles. Overall, our results illustrate that, by enhancing the control of particulate matter in storm runoff, P, and in particular Po, inputs to urban rivers can be reduced.
Keywords: Grain size; Organic phosphorus; Particulate matter; Stormwater; Urban river.