9629268 Wallace Stream Ecosystem Response to Decoupling Terrestrial-Aquatic Linkages This project involves wood removal and continued leaf exclusion from a headwater stream. During the last 3 years, leaf exclusion from a 180 meter reach of stream has resulted in decreased animal production, shifts to alternative foods, increased relative importance of algae, increased export of small organic and inorganic particles, less within stream dissolved organic carbon (DOC) generation, and longer nutrient uptake lengths compared to a stream with normal inputs of leaves. Some results were unexpected, such as greater microbial activity on inorganic substrates and wood and no decrease in either organic matter quality or nutrient export. Microbial biofilms, growing on the surfaces of wood and inorganic substrates, and increased algal growth are now important nutrient sinks in the leaf exclusion stream. Wood remains a conspicuous and prevalent form of terrestrially derived organic matter. This project will continue leaf exclusion and remove small (year 1) and large wood (year 3) to reduce: a) metabolically active microbial biofilms on wood, b) physical stability of the stream, c) particle and nutrient retention, and d) a large but refractory (wood) terrestrial input. The two stage manipulation allows the investigators to distinguish the food resource role and structural role of wood in streams. This long-term, ecosystem-level manipulation on this detritus-based food web will improve general understanding of the role of important terrestrial linkages to the structure and function of stream ecosystems.
