Abstract

Surface-water includes different kinds of pollutants from traffic and roads. To prevent these pollutants to reach nearby lakes one can construct surface-water ponds on locations with heavy traffic. At Bergviks shopping centre in Karlstad, two ponds, one smaller and one bigger has been constructed in order to decrease the pollutant pressure from the receiving waters of Kattfjorden. Several heavy metals are essential for plants and animals in low concentration but when they occur in higher concentrations, they become toxic to the organism. The larger pond at Bergviks shopping centre has a sedimentation function so the heavy metals sink to the bottom thereby not releasing directly in to Kattfjorden. In this specific pond, plants such as reed, reed mace and broad-leafed pondweeds are the most common plants. Several studies show that plants have the ability to accumulate and store heavy metals. Reed, reed mace and broad-leafed pondweeds in the surface-water pond at Bergviks shopping centre all contains arsenic, lead, cadmium, chrome, cobalt, copper, nickel and zinc. The results in this study show a significant difference between these three plants in their heavy metals concentration. Broad-leafed pondweed had significantly higher concentrations of chrome, cobalt, copper, nickel, vanadium and zinc than reed and reed mace. Cadmium, copper and zinc also occurred in higher concentrations in broad-leafed pondweeds than in the sediment of the pond. Broad-leafed pondweed has the ability to accumulate heavy metals directly from the water while reed and reed mace only accumulate heavy metals with their roots. This could help explain the higher concentration in broad-leafed pondweed, in comparison to reed and reed mace. Due to the high metal concentration in the broad-leafed pondweed, it is appropriate to put this plant in surface-water ponds, in order to elute the water from heavy metals. Regular harvesting of the broad-leafed pondweed from the surface-water pond, together with regular cleaning of the sediment may reduce the occurrence of heavy metals in the recipient of Kattfjorden.