Examining controls on ecosystem metabolism in urban streams

Stream ecosystem primary production, respiration and ecosystem metabolism are holistic measures of stream function that are sensitive to abiotic and biotic factors in the stream and watershed.  Since urbanization tends to increase nutrient loads and reduce canopy cover we initially expected that urban streams would have higher rates of GPP and be more autotrophic than their forested counterparts.  Yet initial studies of 12 streams in the NC piedmont failed to show significant differences in any metabolic measurement between urban and forested streams.  Previous results suggested that, in addition to reduced canopy cover and higher nutrient loads, these urban streams also had higher temperatures, more frequent disturbance, and more labile dissolved organic carbon. We decided to examine fine-scale temporal variation through continuous measurements of metabolism in 2 urban and 2 forested streams over an annual cycle to ask: Are maximum rates of primary production higher in urban streams?  Are rates of respiration in urban streams less seasonal than in forested streams and are they correlated with DOC loading?  Are there different correlates of GPP and R in urban and forested streams? Our preliminary results suggest that urban stressors are having strong but contrasting effects on stream metabolism.