Experimental Acidification of Lake 223, Experimental Lakes Area: Background Data and the First Three Years of Acidification

Abstract

Sulfuric acid was used to add 1.60 eq∙m−2 of hydrogen ion ([H+]) to Lake 223 over a 3-yr period from 1976 to 1978, to simulate the effects of acid precipitation on chemical and biological characteristics of the lake. The pH of epilimnion water was lowered from 6.7 to 7.0 in 1976, to 6.0–6.2 in 1977, and to 5.7–5.9 in 1978. The effectiveness of acid addition at depleting alkalinity from the water column in the first 2 yr was 31–38%. As a result, the pH of the lake did not decrease as much as predicted from theoretical calculations. The low efficiency of acidification appeared to be due to generation of dissolved inorganic carbon (DIC) by sulfate reduction in anoxic regions of the hypolimnion. Sulfate reduction increased as addition of sulfuric acid caused the concentration of sulfate in the lake to increase. Mobilization of iron from hypolimnion sediments during anoxic periods caused DIC respired by decomposers to be accumulated as HCO3− to balance the Fe+2 charge, buffering against acidification of the lake. Most of the reduced sulfur was precipitated from the lake as FeS. As a result, H2S in the hypolimnion was usually undetectable. Concentrations of ammonia, iron, manganese, zinc, and aluminum were higher in 1977 than in 1976. The transparency of the lake increased, although there was no apparent change in chlorophyll, dissolved color, dissolved organic carbon, or primary production.Key words: lake acidification, acid rain, mass balance, water chemistry, sulfur cycling