Controls on Sediment Accretion and Blue Carbon Burial in Tidal Saline Wetlands: Insights From the Oregon Coast, USA

Abstract

Oregon estuaries provide important opportunities to assess controls on tidal saline wetland carbon burial and sediment accretion as both rates of relative sea level rise (RSLR; −1.4 ± 0.9 to 2.8 ± 0.8 mm yr−1) and fluvial suspended sediment load relative to estuary area (0.23 to 17 × 103 t km−2 yr−1) vary along the coast. We hypothesized that vertical accretion, measured using excess 210Pb in least‐disturbed wetlands within seven Oregon estuaries, would vary with either RSLR or sediment load relative to estuary area, and carbon burial would correlate strongly to sediment accretion. Mean rates of high marsh accretion (0.8 ± 0.2 to 4.1 ± 0.2 mm yr−1) indicate that Oregon tidal wetlands have mainly kept pace with twentieth‐century RSLR with the exception that the accretionary balance in the central coast is negative, suggesting drowning. Experiencing the fastest rates of RSLR, central‐coast estuaries may foreshadow the fates of other Oregon estuaries under future accelerated sea level rise. Comparison of mass accumulation rates with sediment loads, however, indicates low trapping efficiency and therefore no fluvial sediment limitation. Thus, nonlinear feedback between RSLR and sediment accretion may enhance wetland resistance to drowning. Among wetlands keeping pace with or exceeding RSLR, sediment accretion displays no significant relationship with elevation but rather appears controlled by both the rate of RSLR and relative sediment load, highlighting the importance of incorporating both factors into future studies of tidal saline wetlands. Carbon burial rates, controlled by sediment accretion, will likely increase with future accelerated sea level rise.

Microbial Community Characteristics Largely Unaffected by X-Ray Computed Tomography of Sediment Cores

“…OM in the Southern cores was higher: approximately 17, 5, and 31% for above, within, and below the tsunami deposit, respectively. Our DBD and OM trends followed an inverse relationship, consistent with previously collected data from the same sites ( Peck et al, 2020 ).…”

“…To examine the effect of X-ray CT scanning on microbial communities in sediments, duplicate 1.5 m-long, 10 cm-diameter geological cores were collected on July 5, 2018 from two areas in the Netarts Bay high marsh on the Oregon coast (45.373778, −123.96489 and 45.372197, −123.964223, with elevations 2.772 m and 2.765 m, respectively, Supplementary Figure S1 ) as previously described ( Peck et al, 2020 ). Air and sediment temperatures were not measured at the time of sampling; however, Netarts Bay water temperatures have been reported to range between 10 and 13°C in July ( Barton et al, 2012 ).…”

“…The Northern site is more proximal to the estuarine waterline ( Supplementary Figure S1 ), therefore allowing greater tidal influence and resulting in increased water and nutrient fluxes. The dominant vegetation types in both coring areas at the time of collection were Deschampsia cespitosa (tufted hairgrass) and Juncus balticus (Baltic rush; Peck et al, 2020 ). These locations, defined as tidal saline high marsh/scrub-shrub wetlands, were chosen because Peck et al described easily accessible short cores with variable OM content.…”

Tidal marsh restoration enhances sediment accretion and carbon accumulation in the Stillaguamish River estuary, Washington

“…For example, carbon density at six Snohomish tidal marsh sites ranged from 0.018 g C cm -3 to 0.032 g C cm -3 , whereas Stillaguamish marsh carbon density ranged from 0.012 g C cm -3 to 0.026 g C cm -3 . Oregon tidal marsh carbon density is higher than both these Washington estuaries, with an Oregon mean of 0.034 g C cm -3 [25] compared to this study's natural marsh mean of 0.20 g C cm -3 . Although these two neighboring estuaries are only separated by approximately 20 miles, the most likely explanation for the difference in sediment characteristics is their differing hydrodynamics.…”

Comment on bg-2021-27

“…habitats for their ability to store disproportionally high levels of organic carbon (OC) in their sediments relative to other habitat types (McLeod et al, 2011). This can be attributed largely to the tendency for these habitats to exhibit high sediment accretion rates and low decomposition rates, driven by their exposure to permanent or regular inundation (Peck et al, 2020;. This value has led to increasing interest in blue carbon habitats, given their conservation can prevent significant emissions of carbon (Lovelock et al, 2017;Pendleton et al, 2012) and their restoration can lead to increased drawdown of atmospheric CO2 (Freedman et al, 2009;Greiner et al, 2013).…”