Fingerprinting Blue Carbon: Rationale and Tools to Determine the Source of Organic Carbon in Marine Depositional Environments

Abstract

Blue carbon is the organic carbon in oceanic and coastal ecosystems that is captured on centennial to millennial timescales. Maintaining and increasing blue carbon is an integral component of strategies to mitigate global warming. Marine vegetated ecosystems (especially seagrass meadows, mangrove forests, and tidal marshes) are blue carbon hotspots and their degradation and loss worldwide have reduced organic carbon stocks and increased CO 2 emissions. Carbon markets, and conservation and restoration schemes aimed at enhancing blue carbon sequestration and avoiding greenhouse gas emissions, will be aided by knowing the provenance and fate of blue carbon. We review and critique current methods and the potential of nascent methods to track the provenance and fate of organic carbon, including: bulk isotopes, compound-specific isotopes, biomarkers, molecular properties, and environmental DNA (eDNA). We find that most studies to date have used bulk isotopes to determine provenance, but this approach often cannot distinguish the contribution of different primary producers to organic carbon in depositional marine environments. Based on our assessment, we recommend application of multiple complementary methods. In particular, the use of carbon and nitrogen isotopes of lipids along with eDNA have a great potential to identify the source and quantify the contribution of different primary producers to sedimentary organic carbon in marine ecosystems. Despite the promising potential of these new techniques, further research is needed to validate them. This critical overview can inform future research to help underpin methodologies for the implementation of blue carbon focused climate change mitigation schemes.

A Synthesis of Blue Carbon Stocks, Sources, and Accumulation Rates in Eelgrass (Zostera marina) Meadows in the Northeast Pacific

“…Future work should continue to obtain finer resolution data on the sources of carbon to coastal sediments. For example, using environmental DNA has recently been suggested as having promising potential to precisely identify the sources and contributions of different primary producers to sediment carbon in coastal ecosystems (Geraldi et al, ; Reef et al, ).…”

Environmental DNA identifies marine macrophyte contributions to Blue Carbon sediments

“…Identification of these sources and estimation of their contribution is relevant for blue carbon assessments, and to target which habitats to be conserved. Nevertheless, identification of degraded marine macrophytes within the sediment is one of the main challenges in the study of blue carbon (Geraldi et al 2019). Traditional methods such as stable isotopes (δ 13 C and δ 15 N) are used to differentiate among terrestrial and marine organic matter in the sediment carbon pool; moreover, this method is useful to trace vegetated organic matter throughout the food web, as the isotopic signature of primary producers is preserved (Kennedy et al 2010; Geraldi et al 2019).…”

A muddy time capsule: using sediment environmental DNA for the long-term monitoring of coastal vegetated ecosystems

“…Such information can be applied to determining sources of organic carbon in coastal plant environments as in Reef et al (2017). Extrapolating these data to long-term trends will provide insight into which vegetation communities were responsible for the historic sequestration of stored organic carbon in coastal sediments (Geraldi et al 2019), which can then inform the way these environments are managed. The species-specific genetic data uncovered with this approach can also be applied to population-level variability within species because there is a higher likelihood of detecting within-species variability because multiple genes are targeted.…”