Land-use change and lake acidification: Iron Age de-settlement in northern Sweden as a pre-industrial analogue

Abstract

Iron Age de-settlement in Halsingland, Northern Sweden, can be regarded as a good analogue for the possible effects of land-use and vegetational changes on lake acidification without the effect of contemporary atmospheric pollution. Pollen analyses were used to identify vegetational change associated with a de-settlement period ca . 500 A. D. and diatom analyses to assess if there was any associated change in lake-water pH. A clear settlement horizon was found in the two lakes studied, indicating catchment disturbance associated with Iron Age agriculture. There was no change, however, in diatom reconstructed pH after de-settlement, during vegetation regeneration, when it has been postulated that the build up of raw humus and change of ion-exchange conditions would result in acidification. Importantly, one of the lakes began to acidify, before liming, under contemporary levels of acid deposition.