Extreme rates and diel variability of planktonic respiration in a shallow sub-arctic lake

Abstract

Planktonic community respiration (CR) is a major component of aquatic biogeochemical cycling and food web energetics. Accurate, direct characterizations of short-term patterns and drivers of plankton CR are needed to understand aquatic biogeochemical processes and food web functioning. Recent work indicates CR may be commonly underestimated, and may undergo considerable diel changes that are missed using standard methodological approaches. To explore these possibilities, we applied an immediate, in situ, dark incubation approach at ~ 3 h intervals over 2.5 diel cycles in a shallow, productive, sub-arctic lake in interior Alaska, USA. Rates of CR varied 17-fold, strongly coupled to diel oscillations in water temperature. A weak inverse relationship to ~ 3 mg L−1 diel changes in dissolved organic carbon concentrations suggests CR partially modulated the standing stock of organic matter over short timescales. Average rates of CR were ~ 6 to 100-fold greater than published, conventional CR measurements, but comparable to existing free-water estimates of ecosystem respiration for nearby Alaskan lakes. Overall, this study places new weight on the importance of CR in whole-ecosystem biogeochemical transformations by supporting recent suggestions that planktonic CR may be commonly underestimated.