Causes of lake acidification in Galloway, South-West Scotland: a palaeoecological evaluation of the relative roles of atmospheric contamination and catchment change for two acidified sites with non-afforested catchments

(1) Pollen, geochemical and carbonaceous particle analyses of the sediments of two lakes with moorland catchments in Galloway, Scotland are used to evaluate the relative importance of acid deposition and catchment change as alternative causes of lake acidification. (2) Both sites are very acid (pH 4.5-4.7) and have been acidified since about AD 1850. They lie on granite. Local soils are peaty podsols or deep peats and vegetation is dominated by Molina caerulea and Calluna vulgaris. The catchment of the lower altitude site (The Round Loch of Glenhead) is regularly burnt for sheep grazing. (3) The Calluna: Gramineae pollen ratio and the Calluna pollen accumulation rate have declined over recent centuries, probably because of continued burning. These trends are inconsistent with soil acidification. (4) Higher concentrations of Pb, Zn and Cu in the upper sediments of Loch Enoch cannot be explained by increased flux from the catchment, but are consistent with progressive atmospheric pollution since about AD 1800. Analyses of the complete post-glacial record from the Round Loch of Glenhead indicate that increased concentrations of Pb, Zn and Cu have occurred only over the last 200 years. (5) Concentrations of spherical carbonaceous particles derived from fossil fuel combustion increase rapidly in post-1930 sediments at both sites. (6) The record of atmospheric contamination in the sediments of these two lakes is consistent both in timing and in trends with acid deposition. Because catchment management in this area has, if anything, countered acidification, it is concluded that lake acidification in this area is entirely due to acid deposition.