Heavy metal pollution and lake acidity changes caused by one thousand years of copper mining at Falun, central Sweden

One thousand years of mining of sulfurous ores at the Falun copper mine, ce ntral Sweden, and the resulting atmospheric emissions of metals and sulfur dioxide, gives a unique opportunity to study long-term responses to acid de position. Copper production peaked in the 17(th) century, when Falun suppli ed 2/3 of the world's copper production. Thereafter production and associat ed emissions have declined, and the mine was closed in the 1990's. Sediment cores from 14 lakes situated between 3-27 km from the mine have been analy zed for Cu, Pb, Zn, Cd, S and Pb-206/Pb-207 isotope ratios to study the his torical and geographical distribution of airborne pollutants. Diatoms have been analyzed to infer past lake acidity and to assess whether lake acidifi cation has occurred and, if so, whether any recovery from acidification has occurred following the reduction in sulfur emissions. Eight of the fourtee n lakes have acidified, beginning as early as the late 17(t)h century, when the estimated annual emissions of SO2 amounted to 40,000 tons. This is per haps the earliest known record of anthropogenic lake acidification. Despite the large historical deposition of sulfur, the pH has only decreased by 0. 4-0.8 units, with the lowest diatom-inferred pH being 5.8. Effects of agric ulture and forestry following the expanding mining industry may have counte racted acidification. Despite the 300 yrs of lowered emissions the diatom r ecord shows no recovery in pH. There are still large amounts of sulfur accu mulated in the soils in the area that may delay recovery from lake acidific ation. Afforestation in the area over the last 100 yrs may also play an imp ortant role in delaying the recovery process.