Stream metabolism is an important ecosystem function, representing the relative photosynthesis and respiration in a stream. Land use is an important driver of metabolism because, among other things, it can drive nutrient inputs. Different lands use types (e.g. urban, manure applied row-cropping, or concentrated animal feeding operations or CAFOs) are associated with different absolute nutrient loading and different relative nutrient loading (i.e. nitrogren:phosphorus). We predicted that relative nutrient loading from different land use types will be correlated with metabolic rates because nitrogen concentration is positively correlated with metabolism, but phosphorus concentration is not. We estimated stream metabolism in one urban-, one row-crop- and one CAFO- influenced stream near Scottsbluff, NE by using continuous oxygen measurements and the program Stream Metabolizer.
Nutrient concentrations in the mainstem North Platte River were on average 52 µg/L SRP and 2 mg/L NO3-. An important part of the agricultural land use in the Scottsbluff, NE area is a canal system that affects stream flows throughout the summer. We found that this was an important component of metabolic dynamics because of how discharge interacted with channel morphology (in some cases velocity was more affected and in others depth was more affected). Additional preliminary results suggest elevated metabolic rates in the urban-, row-crop- and CAFO- adjacent stream relative to published values in less anthropogenically modified streams. However, some of these effects were offset by elevated flows when the canal system was used for irrigation during later summer.