Salish Sea Ecosystem Conference

Examining sources of sediment carbon stored in seagrass habitats across the Skagit Delta and Padilla Bay

The potential for seagrass (Zostera marina) habitats to store carbon is a topic of interest to resource managers and ecosystem scientists as they strive to develop and evaluate climate change mitigation strategies. I investigated the sources of carbon and nitrogen stored in Zostera marina habitats within the Salish Sea. I compared two sites, the Skagit River delta (delta) and Padilla Bay (embayment), in order to compare carbon storage and the sources of stored carbon between these two shoreline types. Within each site, I collected sediment cores in Z. marina meadows and on unvegetated mudflat. I measured changes in carbon density and isotopic signatures of carbon and nitrogen with depth. Isotopic signatures showed significant differences in carbon and nitrogen between the delta and embayment sites and also between Z. marina meadows and unvegetated mudflat. In the Skagit delta, cores taken from Z. marina habitat were depleted in ∂13C compared with cores taken from unvegetated habitat. Conversely, in the Padilla Bay embayment, cores taken from Z. marina habitat were enriched in ∂13C compared with cores taken from unvegetated habitat, suggesting that carbon and nitrogen sources varied between each site and within Z. marina habitats. In the next step of this research, a Bayesian mixing model will be used to estimate the contribution of likely carbon sources within the Skagit delta and Padilla Bay embayment. This analysis may clarify the differences between source(s) of carbon and nitrogen supplied to each site, and whether sources have changed over time. In addition, this model may uncover the different source(s) of carbon and nitrogen stored within Z. marina meadows and unvegetated mudflat. This research may help shed light on the carbon and nitrogen storage dynamics within these sites and the mechanisms that drive carbon storage within the Skagit Delta and Padilla Bay.