Influence of pollution and acidification on metal concentrations in Finnish Lapland lake sediments

Fifteen Finnish Lapland lakes have been investigated to study pollution levels and possible acidification effects on nickel (Ni), copper (Cu), cobalt (Go), zinc (Zn), cadmium (Cd), lead eb), manganese (Mn), iron (Fe), potassium (K), sodium (Na), calcium (Ca), magnesium (Mg) and aluminium (Al) concentrations in sediments. Four lakes have average water pH lower than 6.0 and alkalinity lower than 0.050 meq/l. Contamination factor (C-f, ratio of metal concentrations in the uppermost to the deepest layers for a given lake sediment core) of Pb is high, particularly for acidic and acidifying lakes (C-f=5.2-10.4). Ni, Cu, Co, Zn and Cd concentrations increase insignificantly towards sediment surface of some lakes (with a neutral pH) with the rare exception. The influence of possible lake acidification consists of decreasing Cu, Cd, Al, Zn concentrations and organic material contents (loss on ignition) towards the sediment surface. The buffer capacity index (BCD, determined as the ratio of the sum of alkaline and alkaline-earth metals (K, Na, Ca, Mg) to Al, is lower for acidic lakes (from 0.12 to 0.36), whereas for the other lakes the BCI values are higher (from 0.42 to 1.34). Thus, BCI-values, decreased contents of Al, Cd, Zn and Cu, as well as organic matter contents (OMC) in the upper lake sediment suggest acidification of freshwater environments.