Vegetated coastal ecosystems cover only 0.2% of the ocean, yet they are disproportionally important in sequestering organic carbon relative to other ecosystems and may account for as much as 50% of all the carbon buried in marine sediments Although less abundant than saltmarshes or mangrove ecosystems, seagrass meadows represent important sites of organic carbon accumulation that may account for as much as 15% of that buried carbon.
This research will develop a predictive understanding of the fundamental relationships between seagrass density, species-specific structure/function and sediment geochemistry that will provide a greater mechanistic understanding of the role of seagrasses in the global carbon cycle and ultimately lead to pathways for up-scaling these numbers to global estimates with greater reliability.
This work will develop a quantitative understanding of key factors that control carbon cycling in seagrass meadows, increasing our ability to quantify their potential as Blue Carbon sinks. The study will utilize cutting-edge methods for evaluating oxygen and carbon exchange (Eulerian and eddy covariance techniques) combined with biomass, sedimentary, and water column measurements to develop and test numerical models that can be scaled up to quantify the dynamics of carbon cycling and sequestration in seagrass meadows. This comparative analysis across latitudinal and geochemical gradients will address the relative contributions of different species and geochemical processes to better constrain the role of seagrass carbon sequestration to global biogeochemical cycles.
Specifically, the research will quantify:
(i) the relationship between C stocks and standing biomass for different species with different life histories and structural complexity,
(ii) the influence of above- and below-ground metabolism on carbon exchange, and
iii) the influence of sediment type (siliciclastic vs. carbonate) on Blue Carbon storage.
Seagrass biomass, growth rates, carbon content and isotope composition (above- and below-ground), organic carbon deposition and export will be measured. Sedimentation rates and isotopic composition of PIC, POC, and iron sulfide precipitates, as well as porewater concentrations of dissolved sulfide, CO2, alkalinity and salinity will be determined in order to develop a bio-optical-geochemical model that will predict the impact of seagrass metabolism on sediment geochemical processes that control carbon cycling in shallow waters. Model predictions will be validated against direct measurements of DIC and O2 exchange in seagrass meadows, enabling us to scale-up the density-dependent processes to predict the impacts of seagrass distribution and density on carbon cycling and sequestration across the submarine landscape.