Biogeochemical transformations in wetlands impact water quality, nutrient transport across landscapes, and greenhouse gas exchanges with the atmosphere. This study examined anaerobic microbial respiration and methanogenesis in surficial sediments of six wetlands lying on glacial terrain in southwest Michigan, USA. Three of the wetlands were mainly groundwater-fed and three were mainly precipitation-fed. Ambient rates of denitrification, sulfate reduction, iron reduction, methanogenesis, and acetate turnover were measured at each wetland. Ambient denitrification rates were not detectable in any wetland, but denitrifying enzyme activity, measured in two wetlands, indicated that the potential to remove nitrate was higher in a groundwater-fed wetland. Iron reduction was measurable mainly in precipitation-fed wetlands while sulfate reduction was only measurable in the groundwater-fed wetlands. Methanogenesis was measurable in all wetlands, with no differences between wetlands with contrasting water sources, indicating that methanogenesis is important regardless of water source. Acetate turnover rates, which reflect total anaerobic respiration and methanogenesis, were higher in the groundwater-fed wetlands and proportional to the sum of the individual carbon mineralization rates across all wetlands. Even though there was substantial variation in the process rates among these wetlands, the general patterns indicate that water source influences the biogeochemical function of wetlands.