Research article Environmental Geology 39 (7) May 2000 7 Q Springer-Verlag 723 Received: 19 February 1999 7 Accepted: 17 April 1999 S. Rognerud (Y) Norwegian Institute for Water Research, Sandvikaveien 41, N-2312 Ottestad, Norway D. Hongve National Institute of Public Health, P.O. Box 4404 Torshov, 0403 Oslo, Norway E. Fjeld Norwegian Institute for Water Research, P.O. Box 173, N-0411, Oslo, Norway R.T. Ottesen Geological Survey of Norway, P.O. Box 3006, N-7004, Trondheim, Norway Trace metal concentrations in lake and overbank sediments in southern Norway S. Rognerud 7 D. Hongve 7 E. Fjeld 7 R.T. Ottesen Abstract As, Be, Cd, Co, Cr, Cu, Hg, Ni, Pb, V, Se and Zn concentrations were determined and com- pared in lake and overbank sediments from 33 catchments without local pollution sources in southern Norway. There were no significant differ- ences in concentrations of Be, Co, Cr, Cu, Ni, and V in overbank and pre-industrial lake sediments. In areas with shallow overburden, and significant in- fluence from long-range atmospheric pollution, concentrations of As, Cd, Hg, Pb, Se, and Zn in overbank sediments were probably modified by vertical percolating water. In such areas, we suggest using lake sediments as a better sampling medium for mapping pre-industrial concentrations. Pre-in- dustrial lake sediments yield natural concentrations of Hg and Se, which consist of both geogenic and natural atmospheric deposition. Important covaria- bles like organic carbon content, Fe oxides, and fine mineral fraction were generally higher in pre- industrial lake sediments as compared to overbank sediments. By adjusting for such differences over- bank sediments could be used as an alternative in mapping background concentrations of trace metals in regions with few lakes. Key words Trace metals 7 Lake sediments 7 Overbank sediments 7 Geochemical mapping Introduction Natural background concentrations of metals in the envi- ronment vary widely both regionally and locally. In some areas, trace metals may reach levels that are harmful to ecosystems (Painter and others 1994). The natural distri- bution of metals should therefore be included into assess- ments of the critical loads of metal pollutants to terres- trial and aquatic ecosystems. Geological maps offer little information on the abundance and spatial distribution of trace metals. (Ottesen and others 1989; Davenport 1990). During weathering, mineral constituents are released to natural waters. Some trace metals are adsorbed on sur- faces of suspended material or may be incorporated in the lattice of minerals such as Fe and Mn oxides or in or- ganic matter. Particles originating in catchments are de- posited in lakes, river banks, and flood plains. Lake sedi- ments have been used to display spatial variation pat- terns of trace elements in the Canadian shield area (Cok- er and others 1979; Garrett and others 1990; Kerr and Davenport 1990), and Scandinavia (Johansson 1985; Rog- nerud and Fjeld 1993), indicating that lake sediments are a useful medium in evaluating the background concentra- tion of metals (Painter and others 1994). Overbank sedi- ments, sediments deposited from suspension on flood- plains in stages of overbank flow, have been used as a sampling medium in geochemical mapping in Fennoscan- dia and China (Ottesen and others 1989; Bølviken and others 1990; Shen and Yan 1995; Langedal 1997). Many factors influence natural background concentrations in drainage sediments. Concentrations in pre-industrial lake sediments may be modified by authigenic processes oc- curring in lake waters and by diagenetic processes within sediments. Pre-industrial overbank sediments may be in- fluenced by percolation of soil water and by terrestrial organic matter buried during floods. Recent monitoring of acid atmospheric deposition in Norway show obvious trends from low values in the north to high values in the southern and southwestern regions (Tørseth and Semb 1995). Precipitation monitor- ing also provides evidence of the long-range transport from continental Europe and Great Britain of various in- dustrial pollutants, including trace metals (Berg and oth- ers 1994). Steinnes and Njåstad (1995) and Berg and Steinnes (1997) have inferred enrichment of metals in mosses and the organic surface layer of natural soils in the southernmost Norway to be results of atmospheric