Metal burdens in surface sediments of limed and nonlimed lakes

Abstract

Acidification has been shown to increase the concentrations of many metals in lake water as a result of increased mobility at lower pH, whereas liming has been found to decrease lake water metal concentrations. We hypothesise that increased sedimentation as a result of liming increases the metal burdens in the sediments of limed lakes, but especially those that have been treated directly on the lake surface. We also hypothesise that acidification results in decreased metal burdens in the sediments, whereas near neutral reference lakes and lakes where the lime has been applied on wetlands or upstream have intermediate metal burdens in the sediments. In order to test the hypothesis, we statistically compare the areal metal and P burdens in the sediments of four groups of lakes: (1) Mainly surface limed lakes, (2) Mainly upstream/wetland limed lakes, (3) Near neutral reference lakes and, (4) Acidified reference lakes. The statistical analysis reveals that the surface limed group have significantly higher areal burdens of As, Cd, Co and Zn in the sediment compared to the acidified reference group, despite large variations within the groups. The investigation indicates that surface liming increases the areal burdens in the sediments of Cd and Pb, probably of As, Ca and Mn and possibly Co and Zn, whereas acidification decreases the areal burdens in sediments of Cd, Fe, Mn and possibly Co, P and Zn. The results of the study confirm the hypothesis.