Resolving Community Metabolism of Eelgrass (Zostera marina) Meadows by Benthic Chambers and Eddy Covariance in Dynamic Coastal Environments

Seagrasses grow in shallow settings where hydrodynamics and light are important drivers of benthic O₂ dynamics. To understand in situ patterns of O₂ production and consumption we measured eelgrass (Zostera marina) metabolism in the Baltic Sea (SW Finland) using two state-of-the-art methods: flume-like chamber incubations and aquatic eddy covariance. Benthic O₂ fluxes resolved by the two methods agreed well during quiescent weather conditions (±10% of each other), with a distinct diel pattern and an average daily net ecosystem metabolism (NEM) of ~20 mmol O₂ m^-2 d^-1. However, wind-induced resuspension stimulated the eddy O₂ uptake 5-fold, while chamber fluxes remained relatively unaffected. Over the 10 day-long study period, the NEM resolved by the chamber and eddy were 0.4 and -192 mmol O₂ m^-2 d^-1 respectively, underpinning the importance of capturing the effect of dynamic conditions, such as resuspension, to resolve the natural variability in benthic O₂ fluxes. Based on the local meteorological conditions, similar resuspension periods were estimated to occur on average every 9 days during summer at our study site, thus emphasizing the need of long-term, non-invasive measurements to accurately assess benthic O₂ exchange rates and the potential role of seagrass meadows for carbon sequestration.