The sediments below and adjacent to the stream channel are collectively called the hyporheic zone (hypo - beneath and rheos - flow, therefore, below the flow). The microbial communities in these sediments rely on the supply of materials from surface water entering the hyporheic zone. This research project will examine how these microbes respond to variations in the supply of dissolved organic carbon entering this zone. The principal investigators will vary carbon supply in an experimental mesocosm facility to determine whether the bacteria in this zone simply change their growth rates or whether a new set of bacteria become predominant as the carbon supply changes. By extracting bacterial DNA from samples collected from different hyporheic sediments they will determine the similarity among hyporheic bacterial communities. The investigators will perfect techniques to extract DNA from hyporheic sediments and conduct DNA-DNA hybridization assays. Stream ecologists have recognized that the sediments beneath the visible stream channel are an important habitat for a wide range of aquatic organisms. Many of the chemical changes that occur in stream water can be attributed to the action of microbes inhabiting the subsurface sediments adjoining streams. Human activity tends to increase dissolved organic carbon in streams, and understanding the response of microbial communities to chemical changes in streams will enhance management of stream water quality and stream community function.
