Gas exchange, carbon flows, and ecosystem metabolism over a temperate seagrass meadow

Blue carbon ecosystems such as seagrass meadows are widely regarded as carbon sinks that can partially mitigate the effects of anthropogenic climate change. However, the carbon sequestration potential of seagrass meadows is poorly constrained on local and regional scales due to methodological uncertainties and variability in biogeochemical processes such as air-water greenhouse gas exchange of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). In this dissertation, I describe several projects that evaluate biogeochemical processes in a seagrass meadow in South Bay, a shallow coastal lagoon in the Virginia Coast Reserve (VCR), and educate the community about blue carbon ecosystems. 1) A new oxygen optode system for aquatic eddy covariance was rigorously evaluated over the full range of oxygen saturation states in the lab and in the field. The system was well-suited for aquatic eddy covariance and the protocols developed established a new standard for future systems. This work is increasingly relevant as aquatic eddy covariance can be used to derive seagrass metabolism estimates and estimates of air-water gas exchange. 2) The diurnal variability in the gas transfer velocity and CO2 flux was evaluated using high-frequency data during peak seagrass density. South Bay was primarily a CO2 sink during the day and a source overnight, following the diurnal pattern of seagrass photosynthesis and respiration. The gas transfer velocity was best predicted with empirical parameterizations based on wind speed. 3) Air-water CO2 and CH4 fluxes were derived throughout the seagrass growing season. South Bay was a moderate CO2 sink and was a consistent source of CH4 that increased throughout the growing season. CH4 flux pathways were also assessed. Dissolved and ebullitive CH4 fluxes were quantified, and CH4 flux from plant-mediated transport was also identified. Finally, our knowledge of coastal processes in the VCR is leveraged to 4) develop a series of best practices for scientists co-developing authentic science learning experiences with teachers using evidence-based practices.