The significance of atmospheric deposition of heavy metals in four Danish lakes

Abstract

The atmospheric deposition rate of heavy metals was determined throughout a seventeen month period at four lakes and a control station across Mid-Jutland, Denmark, and its significance was assessed in relation to the concentrations of Zn, Cu, Pb, and Cd in water, sediment and aquatic macrophytes ( Phragmites australis (Cav.) Trin, Littorella uniflora (L.) Ashers., Isoetes lacustris L. and Juncus bulbosus L.) from Lake Hampen, Lake Meldgaard, Lake Sortesø, and Lake Gødstrup. Mean annual deposition rates of 1.81–2.77 mg Cu m −2, 4.09–8.73 mg Pb m −2, and 0.21–0.37 mg Cd m −2 were determined. For Zn a mean deposition rate of 15 mg Zn m −2 year −1 was used (Hovmand, 1979). The atmospheric deposition per m 2 of Zn and Cu amounts to 0.2–37%, 0.05–4.3% and 3.4–107% of the contents present in the water column of the lakes, the upper 10 cm of the littoral sediment and in dense vegetation of aquatic macrophytes, respectively. Equivalent figures for Pb and Cd are 1.8–649%, 0.8–30.6%, and 16.8–951%. In the profundal sediments of the oligotrophic Lake Hampen, post-war atmospheric deposition has increased the heavy metal concentration and content up to 180 times. The Pb concentrations in sediments from different depths were significantly correlated with the post-war consumption of gasoline in Denmark. It is concluded that atmospheric deposition of heavy metals results in a significant contamination of lakes, especially oligotrophic lakes for which aerial fallout is the major source. It is further concluded that lake sediments uncontaminated with heavy metals are probably no longer found in Denmark.