Effect of Acid Precipitation on Microbial Decomposition Processes in Sediment From Streams in the Turkey Lakes Watershed

Abstract

The effect of simulated acid precipitation (pHs between 3.5 and 5.9) on the breakdown of organic matter in streams was examined under laboratory conditions using two different sediment types from streams. Decomposition processes were measured using 14C-labelled glucose, leaf leachate, and leached leaf material. The data indicated that penetration of acid into settled sediment is small. Therefore, little effect of pH on organic matter breakdown could be perceived. During suspended conditions, however, a marked decrease in breakdown rates was noted. It appeared that under these conditions a slight stimulation in decomposition rates caused by the sulphate and nitrate present in the acid precipitation occurred. The effect of pH on the rate of organic matter breakdown depended on the type of substrate used in the experiment. Glucose decomposition was least inhibited by pH, followed by leaf leachate, and leached leaf material breakdown was the most inhibited. Sediment with higher organic matter was more sensitive under conditions of suspension, but less sensitive than the sediment with less organic matter under settled conditions. This appeared to be a result of the lower penetration of acid in the settled organic sediment.