In urban catchments, pollutants, like nutrients and metals, transported by rainfall as stormwater, can severely degrade water quality and the ecological state of receiving waters. Excessive quantities of nutrients can lead to eutrophication and cyanobacterial blooms in these systems; whereas excessive quantities of metals can have a myriad of toxic effects on aquatic organisms. To effectively manage urban catchments to reduce stormwater pollution, defining the many pollution sources is vital.
In urban catchments, assessing the pollution contribution of point sources is relatively straight forward. However, defining the pollution contribution from diffuse sources is more difficult. The wide range of different surface types that contribute to diffuse urban pollution can be broadly categorised by their functional use in an urban catchment. Examples of these ‘urban functional units’ (UFUs) are roofs, roads, footpaths and sports fields. Many studies attempt to infer correlations between the percentage cover of different UFUs and catchment level pollution exports. However, this can be made very difficult by the complex hydraulic connections and pollution generation processes of different UFUs.
While there is a reasonable body of empirical data on metal pollution from different UFUs in urban catchments, there is significantly less for nutrient pollution. Additionally, less common UFUs, like driveways, and footpaths have seen limited research.
To help define the relative pollutant contributions from different UFUs, rainfall runoff sampling was undertaken from roofs, roads, driveways, carparks, footpaths, desire paths, sealed areas and sports fields in Canberra, Australia. The collected water samples were analysed for concentrations of total and dissolved nutrients, metals, carbon, and total suspended solids.
Ordination analyses were used to characterise the pollutant signature from each UFU. Preliminary results suggest that runoff from different UFUs display distinctly different pollutant signatures. These findings have applications for pollution source apportionment, and redefining major diffuse pollution sources in urban catchments.