As urbanisation rates continue to increase across the globe, so too do the issues around urban stormwater pollution. Pollutants transported by rainfall in urbanised catchments can severely degrade water quality and ecological state of receiving waters. Excessive quantities of pollutants, like nitrogen and phosphorus, can lead to eutrophication and cyanobacterial blooms in these systems.
Current approaches to identifying urban sources of nutrient pollution are insufficient to effectively assess the nutrient contributions of different urban impervious surfaces. These approaches generally involve inferring correlations between land use practices and catchment level nutrient concentrations. Impervious areas in urban catchments are comprised of a variety of surface types like roads, roofs, carparks, driveways, footpaths and bike paths. So, accurately assessing individual urban nutrient pollution sources requires separately defining these pollution sources.
To fill some of these knowledge gaps, rainfall runoff sampling from individual urban impervious surfaces was undertaken. Using this sampling approach, the runoff from roads, roofs, carparks, driveways, footpaths and bike paths were characterised by their total and dissolved nutrient concentrations.
The results of this study confirm that rainfall runoff from different urban impervious surfaces have different concentrations of total and dissolved nutrients. The surfaces with highest median total and dissolved nutrient concentrations were footpaths, driveways and roads. The results also show a positive correlation between total nutrient and suspended solids concentrations in runoff, suggesting sediment as a transport pathway. However, dissolved nutrients did not follow this same pattern. Rainfall parameters also showed distinct relationships with total and dissolved nutrient concentrations in runoff. Additionally, runoff samples taken from largely unresearched urban impervious surfaces, like footpaths and driveways, has highlighted them as potentially meaningful contributors to urban nutrient pollution.
These findings have implications for urban stormwater management, assisting in managing Australia’s valuable water resources in an increasingly variable climate.