A whole-basin study of sediment accumulation using stable lead isotopes and flyash particles in an acidified lake, Sweden

Using analyses of lead concentrations, lead isotopes (Pb-206/Pb-207), and s pheroidal carbonaceous flyash particles (SCP), we studied sediment accumula tion patterns in the acidified lake Harsvatten in southwest Sweden. After d etermining the natural background Pb-206/Pb-207 ratio (1.5) in deeper sedim ents in long sediment cores from three basins in the lake, we applied an is otope mixing model to quantify pollution Pb accumulation in 46 gravity core s. The mean pollution Pb inventory in the cores was 2.6 g m(-2) (range, 0.3 -11 g m(-2)). Although some variation in Pb concentrations can be explained by loss on ignition (LOI) and water depth (together, R-adj(2) = 0.33), the re is no relationship between pollution Pb inventories and these variables. Contrary to the traditional model of sediment focusing, where higher accum ulations of pollutants are expected in deeper waters, the highest inventori es for pollution Pb and SCP are generally found at shallow sites (<4 m wate r depth) and not in the three deep basins of the lake (10, 12, and 24 m dee p). Furthermore, the model for sediment focusing, which may be appropriate for describing the physical building of sediments in a lake basin, may be i nappropriate for describing the specific processes controlling the distribu tion of pollutants in a lake basin of this type.