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

Abstract

There is increasing urgency to implement climate change mitigation strategies that enhance greenhouse gas removal from the atmosphere and reduce carbon dioxide (CO2) emissions. Recently, coastal “blue carbon” habitats⁠—mangroves, salt marshes, and seagrass meadows—have received attention for their ability to capture CO2 and store organic carbon (OC), primarily in their sediments. Across habitat types and regions, however, information about the sequestration rates and sources of carbon to local sediments remains sparse. Here we compiled recently obtained estimates of sediment OC stocks and sequestration rates from 139 cores collected from temperate seagrass (Zostera marina) meadows in Alaska, British Columbia, Washington, and Oregon. Across all cores sediment OC content averaged 0.75%. Organic carbon stocks in the top 25 cm and 1 m of the sediment averaged 1,846 and 7,168 g OC m−2, respectively. Carbon sequestration rates ranged from 4.6 to 93.0 g OC m−2 yr−1 and averaged 24.8 g OC m−2 yr−1. Isotopic data from this region suggest that OC in the sediments is largely from noneelgrass sources. In general, these values are comparable to those from other temperate Z. marina meadows, but significantly lower than previously reported values for seagrasses globally. These results further highlight the need for local and species‐level quantification of blue carbon parameters. While temperate eelgrass meadows may not sequester and store as much carbon as seagrass meadows elsewhere, climate policy incentives should still be implemented to protect existing sediment carbon stocks and the other critical ecosystem services associated with eelgrass habitats.

The influence of hydrodynamic exposure on carbon storage and nutrient retention in eelgrass (Zostera marina L.) meadows on the Swedish Skagerrak coast

“…Sediment characteristics are considered the most important factors for carbon storage in Z. marina meadows, whereas seagrass structural complexity and biomass properties, such as canopy height and plant dry weight, have been found to be of minor relevance 14,15,25,31,45 . This also explains why seagrass biomass has a relatively low contribution to the sedimentary organic carbon pool in Z. marina meadows 15,46 and highlights the importance of hydrodynamic exposure and transport of allochthonous organic matter for the carbon sink function in these environments. In fact, seagrass structural complexity influences the hydrodynamic forces by reducing water velocity within the meadow 20 , while at the same time exposure to hydrodynamic forces can influence the meadow properties 27 and morphology of the seagrass plants 28,47 .…”

Global Trends in Air‐Water CO2 Exchange Over Seagrass Meadows Revealed by Atmospheric Eddy Covariance

“…These average CO 2 evasion/invasion rates are plotted (Figure 4) alongside organic carbon burial rates (CBR) taken from a global literature review (Samper‐Villarreal et al., 2018 [A], Prentice et al., 2020 [B], Duarte et al., 2005 [C], Kennedy et al., 2010 [D], and Sanders et al., 2019 [E]). Converted into the same unit as FCO 2 , these literature CBRs ranged from −0.025 to −0.23 µmol C m −2 s −1 , for a global average of −0.126 ± 0.082 µmol C m −2 s −1 .…”

“…The coastal ocean plays a disproportionately large role in global and regional carbon (C) cycles (Fennel et al., 2019; Friedlingstein et al., 2019; Laruelle et al., 2018). In particular, seagrass‐inhabited regions receive large quantities of terrestrial and marine organic carbon, much of which is sequestered in sediments and stabilized by extensive root mats (Prentice et al., 2020; Röhr et al., 2018). Carbon fixed locally by seagrasses and their epiphytes is also buried here, constituting a net removal of C from the atmosphere (Duarte et al., 2005; Kennedy et al., 2010).…”

Can the Non-native Salt Marsh Halophyte Spartina alterniflora Threaten Native Seagrass (Zostera japonica) Habitats? A Case Study in the Yellow River Delta, China

“…Significant quantities of carbon can be sequestered by, stored in, and released from seagrass meadows ( Prentice et al, 2020 ). Salinas et al (2020) reported that the loss of seagrass due to human and natural disturbances may have caused the release of 11–21 Tg CO 2 –eq in Australia since the 1950s.…”