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[equivalent].cntdot.m-2 of [H+] to Lake 223 over a 3 yr period from 1976-1978, to simulate the effects of acid precipitation on chemical and biological characteristics of the lake. The pH of epilimnion water was lowered from 6.7-7.0 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 may be due to generation of dissolved inorganic C (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 Fe 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 S was precipitated from the lake as FeS. H2S in the hypolimnion was usually undetectable. Concentrations of NH3, Fe, Mn, Zn and Al 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 C or primary production.