Four nonhumic lakes in northern Michigan, ranging in pH from 4.0 to 8.0, were selected to assess the effects of pH on leaf decay rates, leaf-associated macroinvertebrate assemblages, and the relative importance of microbes and shredders to the leaf decay process. Except for pH (and covariates of pH) these lakes were similar in physical and chemical parameters which directly affect metabolism. Preweighed leaves were placed in all four lakes for 8 wk; half of the leaves were confined in mesh bags to exclude shredders, while the others were not confined. Decay rates of confined leaves were not different among lakes, yet were lower than non-confined leaves in the alkaline lakes, suggesting shredders were important vectors of leaf decay in the alkaline lakes, but not in the acid lakes. Shredders comprised 65.9% of all invertebrates in Douglas Lake (pH = 8.0) and decreased in abundance (to 1.1%) with decreasing pH. Crustaceans and molluscs were few or absent in the acid lakes probably because of low pH and Ca +2 levels. Although microbial biomass on leaves appeared to be highest in acid lakes, estimates of microbial activity were significantly lower in the acid lakes, suggesting microbial metabolic inhibition at low pH.