Sediment cores were collected from two remote subalphine lakes: the rather shallow (1.5m) Little Ghost Lake at 2040 , elevation and the deep Great Ghost Lake (35m) at 2150 m elevation. The distributions of metal/Al (in bulk samples) and acid-leached metal in the sediments of the Little Ghost Lake suggest that the surface enrichments of Cd and Pb (probably also Cr and Zn) are caused mainly by anthropogenic inputs. The distributions of leached Pb and Pb-206/Pb-207 ratios indicate a large anthropogenic input since about 1940, as based on Pb-210 and C-14 dating.
A natural process driven by the Fe redox cycle caused surface enrich men of acid-leached Fe, Ni, Zn and part of Pb in the Great Ghost Lake. The Pb-206/Pb-207 ratios con rm the anthropogenic Pb input in surface sediments here. According to C-14 dating, the onset of the large anthropogenic Pb increase occurred in around 1945, suggesting that such large increases in these two subalpine lakes are due to widespread lead emissions from automobiles.
The Fe oxides produced during winter overturn in the Great Ghost Lake play a major role in removing the aeolian anthropogenic metals, particularly Pb, from the water column. In the Little Ghost Lake, the aeolian anthropogenic metals may be directly removed with the sinking of aeolian particulates and/or by aquatic organisms.