The atmospheric concentration of CO2 is expected to at least double in the next 100 years and may influence carbon cycling in terrestrial and aquatic ecosystems. Elevated CO2 levels alter the foliar chemistry of terrestrial plant species, and these changes in leaf chemistry are conserved when they form detritus. Detritus enters streams as leaf litter and forms the carbon base of the stream ecosystem. Much detritus is processed by omnivorous crayfish, and the detritus is thus converted to more usuable forms for the rest of the biological community. This dissertation will elucidate whether changes in the carbon cycle of stream ecosystems could occur via the behavior of omnivorous crayfish and their interaction with leaf litter. First, crayfish were presented with detritus that was produced at ambient versus elevated CO2 levels in a Y-maze to determine whether 1) they could discriminate between the two types of detritus and 2) whether they showed a preference. Crayfish did discriminate between the two types of detritus and preferred the detritus from the ambient treatment. In the next experiment, crayfish were raised for 10 months on fish, detritus produced at ambient CO2, or detritus produced at elevated CO2. Crayfish in the elevated treatment had a lower ralative growth rate, molt frequency, and %body tissue of lipid or protein. Crayfish from the growth experiment were then tested for preference to detritus produced at ambient or elevated CO2 to determine if previous experience would affect detritus foraging decisions. Crayfish raised in either detritus growth condition preferred ambient CO2 detritus, indicating that chemical quality of leaf litter is more important than past experience. Lastly, crayfish orientation to another food source (fish) in the presence of dissolved organic matter (DOM) from each type of detritus was tested. Orientation efficiency was affected by elevated CO2 DOM, but only when present at a high concentration, evidenced by increased turning and heading angles to the source and decreased heading angles upstream. These studies indicate a potential alteration of omnivorous crayfish behavior toward detritus in an elevated CO2 future. This alteration of behavior has implication not only for community dynamcis, but for carbon cycling in stream ecosystems.