High rates of daytime respiration in three streams: Use of δ 18 O O2 and O 2 to model diel ecosystem metabolism

Photosynthesis and respiration determine the carbon and oxygen (O 2 ) balance of ecosystems. Current methods used to estimate ecosystem respiration (ER) do not include diel ER fluctuations, which limit testing predictions about short‐term drivers of ecosystem metabolism. Diel changes in δ 18 O O2 2 can be used to estimate diel ER due to discrimination against δ 18 O O2 2 during respiration. We monitored diel δ 18 O O2 2 , O 2 , light, and water temperature in three Wyoming streams and measured respiration fractionation ( α R ) against δ 18 O O2 2 in dark benthic flow chambers in two streams. The ranges of measured and literature α R values were used to estimate uncertainty in metabolism parameters associated with not measuring α R directly. Daytime ER was 54–340% higher than nighttime ER using δ 18 O O2 2 , but diel ER parameter estimates were highly uncertain relative to traditional estimates of ecosystem metabolism. Diel variations in water temperature only accounted for 4–55% of the range of diel ER calculated using diel δ 18 O O2 2 . Measured benthic flow chamber α R varied within the range of literature values: from 0.9755 to 0.9954. Metabolism parameter estimates were very sensitive to choice of α R within the measured and published range of values. The mean and uncertainty of diel ER estimates increased with decreasing α R , with daily ER more than ten times higher given an α R of 0.975 vs. 0.999. Diel changes in ER can be modeled using δ 18 O O2 2 and O 2 , but diel ER estimates depend on the choice of α R , suggesting the need to better understand how α R may vary within spatial and temporal scales appropriate for δ 18 O O2 2 metabolism models.