EFFECT OF PH ON THE GROWTH AND ACTIVITY OF HETEROTROPHIC SEDIMENT MICROORGANISMS

Low pH markedly reduced heterotrophic microbial activity in sediment-lake water systems. A marked reduction in both the rate and the total amount of O2 consumed occurred as pH decreased. Low pH and low temperature (0.degree. C) resulted in longer turnover times (Tn) and also smaller Vmax values when the kinetics of 14C-glucose, 14C-glycine and 14C-glutamic acid utilization were examined. When the response of the microorganisms to heavy metals was examined, Hg was generally more toxic than Pb over the pH range 4.5-7.5 but both metals were more toxic at pH 4.5 than at higher pH levels. Hg also inhibited O2 utilization and 14C-glucose mineralization more than Pb at all pH levels. Bisulfite reduced microbial activity at all pH levels although it was always more toxic to the sediment microorganisms at pH values of 4 and 5 than at pH 7.