PARTICULATE TRACE-ELEMENT CONCENTRATIONS AND LOADINGS ASSOCIATED WITH EROSION OF PERVIOUS URBAN LAND

The dynamics of particulate elemental (Mn, V, Al) concentrations and loadings associated with erosion of pervious urban surfaces were examined in the context of a potency factor approach to modelling contributions to stormwater runoff. The accuracy of a potency factor approach in estimating elemental loadings depends on the ability to determine "representative" elemental concentrations and the accuracy of sediment transport modelling. Particulate element concentration variability was observed throughout sampled events at different pervious surfaces and may be related to factors including variable source-area inputs, transported particle size and environmental conditions. However, event mean concentrations at the sites often were not significantly different. The mean concentrations were used as the representative concentrations in the potency factor-type modelling for two of the sample sites; a grassed playing field and an aggregate parking area. Sediment transport was modelled using a modified version of CREAMS (Chemicals, Runoff and Erosion from Agricultural Management Systems). The average (absolute) prediction errors of Mn, V and Al loadings for events at the grassed site were 25%, 32% and 29%, respectively; and for events at the aggregate parking area were 33%, 30% and 33%, respectively. The results suggest that a potency factor approach can be a useful planning level tool to estimate elemental loadings from pervious urban surfaces. Finally, it was found that Mn, V and Al yields (gm) for sampled events at an aggregate parking area were three to four times greater than for adjacent suburban land with ten times the area. Aggregate surfaces therefore may be an important pollutant source to the sewer system in some areas.