Regional Relative Risk Ranking of Diffuse Pollution Sources in an Urban Environment, Gothenburg (Sweden)

Magazine article, 2012

Complex urban environments are not easily described in terms of ecological risks. Relative regional risk ranking (developed by W.G. Landis) summarizes the impact of multiple parameters within a region considering their source and distribution. As part of the EU Interreg project (DiPol; homepage http://www.tu-harburg.de/iue/dipol.html), the regional relative risk ranking analysis in Gothenburg evaluates several diffuse pollution sources including agriculture, industry, forestry, recreation, surface water runoff, waste water treatment plants, and maritime shipping in the area in regards to geographical distribution and perceived risk and impact. The model combines sources, stressors, habitats, and indicators and allows the user to rank the relationships between these. The model output can help determine the highest at-risk regions within an area as well as the significant sources of diffuse pollution in order to prioritize remediation or mitigation measures. Our analysis focuses on the rivers and streams in Gothenburg, specifically looking at the Göta älv River, and the tributary streams Säve ån, Mölndals ån, Kvillebäcken, as well as the estuary at the mouth of Göta älv River. The highest risk to the indicators (bathing water quality, environmental water quality, and sediment quality) is suggested to be largely dependent on which region one looked at, but the highest relative risk is associated with surface water runoff, industry, and agriculture. However, the estuary is more highly affected by discharges from the city waste water treatment plant. As a decision-making tool, these results need to be evaluated with cost benefit and stakeholder concerns. In this project, a system analysis (“Sensitivity model”) was carried out to make these connections and to highlight the possible mitigation alternatives. In addition, GIS models for contaminant fluxes and site-specific loading along the urban waterways are used to complement the conclusions from relative risk ranking to balance, for instance, the use of local infiltration, treatment and direct discharge of surface runoff, one of the main sources of diffuse pollution. These models and quantitative assessments illustrate an integration of scientific and end-user perspectives, especially important for complex urban systems.