Effect of rainfall characteristics on the transport of trace metals in suspended particles during rainfall events

Abstract

Stormwater carries significant loads of pollutants into watersheds, deteriorating water quality. The load depends on numerous factors, such as land use and rainfall characteristics. The objective was to quantify the load of metals in suspended particles and the effect of rainfall characteristics on the wash-off pollutants. A quality-quantitative approach was applied to monitor rainfall characteristics, discharge, and water quality parameters. Fourteen parameters were measured, including turbidity, dissolved oxygen (OD), temperature, total suspended solids (TSS), particle size diameter, Co, Cd, Cr, Cu, Ni, Pb, Zn, Mn, and Fe . Multivariate analyses were used to verify the correlation between parameters. The rainfall events were classified using a Euclidean clustering method according to selected rainfall characteristics. Rainfall with moderate to heavy rainfall depth (RD) and intense peaks (RImax) showed the highest loads of metals and TSS. The load of TSS carried during the rain events ranged from 1.4 to 680.2 tons. Particulate metals concentration following order Fe > Zn > Mn > Cr > Cu > Ni > Co > Pb. Emphasis to mean concentration in mg/kg of Zn (13073.7 ± 27513.5), Mn (575.8 ± 516.2), Cr (190.70 ± 84.01), Cu (88.24 ± 44.97), and Ni (45.63 ± 31.20). The RImax, RD, and maximum flow (Qmax) were the variables that most influenced metals and TSS loads in the runoff. Except for Zn, all the trace metals had a strong correlation to TSS and rainfall characteristics. The particle size of < 40 µm was predominant in 60 % of the runoff events. Knowledge of the distribution of the pollutant throughout the rainfall and the variables that may interfere is essential to improving containment strategies, such as retention at the source, and preserving the quality of aquatic systems.