Lake acidification in Galloway: a palaeoecological test of competing hypotheses

Possible causes of lake acidification in Britain include acid precipitation, heathland regeneration, afforestation and post-glacial natural acidification (long-term change). In Galloway, south-west Scotland, several lakes with non-afforested catchments have been acidified by approximately 1pH unit since about 18401,2, which clearly precludes long-term change and afforestation as causes of the present acidity, but does not discriminate between the possible effects of heathland regeneration and acid precipitation; it could be argued that a decline in upland farming in this area led to an increase in acid heathland communities capable of promoting lake acidification during this period of time. Here we use pollen analysis to show that there is no evidence for an increase in Calluna vulgaris, the most important heathland species, over the past 200 yr or so, and we substantiate the acid precipitation hypothesis by demonstrating substantial increases of the heavy metals Pb, Cu and Zn in the sediment since about AD 1800.