Direct and Indirect Effects of Resource Manipulation on Structure and Function of a Longitudinally-linked Ecosystem

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This study will test the concepts that community structure and ecosystem processes in streams are strongly influenced by the resource base and assess the strengths of upstream-downstream linkages in streams. The investigators will do this by examining the effects of excluding allochthonous leaf litter for three years from a headwater stream draining a forested watershed at Coweeta Hydrological Laboratory, North Carolina. This manipulation will allow them to examine changes in organic matter standing crop, food quality, and benthic community structure in response to the decrease in resources and accompanying changes in ecosystem processes such as organic matter transport and nutrient dynamics. It will also allow them to assess the relative importance of external and "new" (e.g. from annual litterfall) vs. internal and "old" (e.g. from leaching of stored organic matter) sources of nutrients and dissolved organic carbon (DOC). The investigators have seven years of pretreatment data for both the manipulated and reference streams for many of the parameters proposed to be measured in this study and propose an additional pretreatment year for other parameters. This study assesses two important linkages proposed for stream ecosystems: 1) major aquatic- terrestrial linkages (litter inputs) will be severely curtailed, and 2) the upstream-downstream linkage in a stream segment (recovery zone) immediately below the manipulated catchment will be assessed with respect to benthic invertebrates, particulate and dissolved organic matter transport.