Pollutants in storm runoff in the city of Kristiansand and pollution accounting for the Eastern harbour (Østre havn)

Summary

The Kristiansand fjord receives pollutants from many and diverse sources. The chemical status based on concentrations of EU priority substances in sediments and biota has been characterized as bad according to environmental quality standards (EQS) in the water regulations. Measures must be established to achieve good ecological and chemical status. More data on pollutant sources and their respective contributions is needed, however, to ensure that the most cost-efficient measures are selected. In this project, sampling for analyses of heavy metals and polycyclic aromatic hydrocarbons (PAH) was performed three times during each of four storm flow events. The sites were runoff from an undisturbed, but potentially polluted, forested catchment (Baneheia) and in the city stormwater pipes of three city streets. The sampling strategy was chosen in order to calculate mean event concentrations and mean site concentrations at these four sites. The mean concentrations would also represent runoff from the whole city center Kvadraturen, and thus was also used to calculate the impact in the three surrounding water bodies. The idea was also that effects of measures could be documented by adapting the same measuring strategy. We measured total fractions of heavy metals, whereas the EQS of the water regulations are for dissolved and in some cases (nickel and lead) biologically available fractions. Runoff from Baneheia was low in suspended solids, metal concentrations were independent on particle concentrations, but the water is acid (pH 5,1) and humic (10,4 mg TOC/L). A fraction of the heavy metals could be associated to the dissolved organic matter. Several of the mean site concentrations for heavy metals were close to the EQS-values for annual mean concentrations (AA-EQS), however, and we recommend to document the distribution among the heavy metal fractions. We recommend to reduce the particle concentration in the urban runoff in order to not violate the quality standards for PAH and to reduce present-day transport of Cu and Zn to the Eastern Harbor. We also recommend further documentation and work with the pollution accounting to improve the basis for cost-efficient measures.