A 12600 Year Perspective of the Acidification of Lilla Oresjon, Southwest Sweden

The pH history of Lilla Oresjon was studied by using diatom analyses of a 3.5 m long sediment core (700 contiguous 0.5 cm samples). Four pH periods were distinguished; (i) an alkaline period (12600-7800 BP) following deglaciation, (ii) a naturally acidic period (7800-2300 BP) when pH decreased from 6.0 to 5.2, (iii) a period with higher pH (greater than 6) (2300 BP-1900 A.D.), which started at the same time as agriculture expanded, and (iv) the recent acidification period that began with a deterioration phase around 1900 A.D. and developed into an acute acidification phase during the 1960s (pH 4.5). This post-1960 phase has no similarity with any of the previous periods identified.