Carl Saunders (EcoLogical)
Nick Bouwes (EcoLogical)
Carol Volk (South Fork Research)
Estimates of GPP can describe the productive potential of watersheds, which is an extremely important component of fish habitat.
ISEMP conducted a study to evaluate the feasibility of collecting information on Dissolved Oxygen (DO) to estimate gross primary production (GPP) and stream respiration at CHaMP sites. DO is a by-product of photosynthesis from primary producers (e.g. algae) during the daytime, while at night time all organisms are respiring and consuming oxygen. Therefore, differences between DO during different times of day can be used to estimate GPP. Data loggers were used to collect DO measurements at 24 CHaMP sites. CHaMP data (temperature, solar input, and conductivity, which is related nutrient availability) were then used to create a predictive model of GPP. Additionally, network scale information was used to estimate GPP across the stream network. We were able to predict GPP using data collected at the CHaMP sites (r2=0.53) and from globally available GIS data (r2=0.43) (Saunders et al. submitted). Also, GPP was highly correlated with both fish density in the fall and summer, as well as the estimated amount of consumption (Pval) to grow to the observed size during the season. Finally, the GPP network model was able to describe juvenile steelhead densities from snorkel counts at 200 reaches throughout the Middle Fork John Day. Further validation of the GPP model across a greater range of conductivities is necessary for more robust estimates. Also, because terrestrial invertebrates entrained in the drift are a large part of fish diets, a model approximating terrestrial inputs requires further development to fully describe food availability for salmonids.
GPP estimates utilize conductivity, solar inputs, and stream temperature. Stream temperature varies by year, and gross primary production estimates are generated for respective years.
Findings and Uses
Estimates of GPP can describe the productive potential of watersheds, which is an extremely important component of fish habitat. This context is useful for managers to better understand and identify potential production limitations for salmon and steelhead.