The Recent Palaeolimnology of Acid Lakes in Galloway, South-West Scotland: Diatom Analysis, pH Trends, and the Role of Afforestation

Abstract

(1) To test the hypothesis that catchment afforestation is an important cause of lake acidification in Galloway, south-west Scotland, we carried out 2Pb dating and diatom analysis of sediment cores from six lakes with both unafforested and afforested catchments. (2) Major, post-eighteenth century changes in diatom communities have occurred in all six lakes. At the unafforested sites (Round Loch of Glenhead, Loch Enoch, and Loch Valley) and the afforested site (Loch Grannoch), acidobiontic Tabellaria quadriseptata and T. binalis, have become dominant whilst those taxa indicating less acid conditions, e.g. Anomoeoneis vitrea and Fragilaria virescens, have decreased in abundance. At the afforested sites (Loch Dee and Loch Skirrow), the most significant change is loss of the diatom phytoplankton in the late nineteenth century. (3) Recent histories of pH change reconstructed from the sediment core diatoms show that five of the six sites have been acidified by between 0 5 and 1 2 pH units within the past 140 years. The two lakes least acidified, Loch Dee and Loch Skirrow, have significalnt portions of their catchments in non-granitic areas. (4) At least within the Loch Doon granite area the degree of lake acidification seems to be closely linked with altitude, which is presumably linked with rainfall, but the timing of acidification appears to be controlled by catchment factors. (5) Acidification of the afforested sites (Loch Dee and Loch Grannoch) occurred prior to forest planting. (6) Acid deposition is the most probable cause of acidification at these sites.