Abstract 98-06466 Findlay Hyporheic microbial response to variations in supply of dissolved organic carbon Microbes are responsible for many important transformations of organic materials in aquatic ecosystems and their activity varies dramatically among ecosystems and among habitats within ecosystems. This project will examine whether differences in bacterial consumption of dissolved organic carbon (DOC) in stream sediments are accompanied by shifts in the relative abundance of bacterial species. In some streams there are large declines in DOC as water moves along subsurface flowpaths and these declines are accompanied by significant drops in bacterial abundance, growth and shifts in allocation among carbon-acquiring extracellular enzymes. We will use DNA-DNA hybridization to reveal the degree of similarity among streams and along flowpaths. Our experiments will use water from streams known to vary in subsurface DOC patterns. This range in variability will be augmented with additions of specific classes of compounds (e.g. humic acids) expected to result in large differences in microbial activity. Our access to well-defined gradients in microbial function permits a powerful test of the potential link between function and structure in microbial communities.
