Effects of Soil Acidification on Forest Land Snails

The objectives of our investigation were to determine whether on-going acidification in Sweden affects forest land snail populations and to study the relationships between snail density and the complex of chemical parameters related to calcium. We approached the problems through: i) re-inventories of snail populations in localities originally investigated some decades earlier, ii) experimental liming in forests, and iii) examination of elemental composition in snail shells from different environmental situations. The re-inventories were made at 57 forest sites in southern and central Sweden, originally sampled between 14 and 46 yr earlier. In general, snail density clearly decreased over the 14-46 yr periods, particularly at localities with low base saturation and low pH. In some oligotrophic coniferous forest sites in southern Sweden the snail fauna even seemed to have died out. Parallel to this a decrease in calcium concentration in litter has occurred. According to rarefraction analyses the number of species had decreased significantly only at six sites in SW Sweden. Experimental liming in beech forests resulted in an increase of snail density by a factor of 10-90, indicating that liming can counteract depauperization of snail populations caused by soil acidification. Analysis of the results from the retrospective studies and liming experiments showed highly significant correlations between snail density and calcium concentration, pH, base saturation and base cation concentration of the litter. These abiotic factors were strongly inter-correlated. Analyses by instrumental neutron activation and other methods of shell elemental composition indicated that concentrations of certain elements were dependent on acidity in the environment in which the snails lived. This suggests that shells from different localities and time periods can be used as bio-indicators and environmental archives.