The Carbon Stock and Sequestration Rate in Tidal Flats From Coastal China

Abstract

Tidal flats form around the estuarine and coastal zone by continuous terrigenous sediment transport and deposition processes. Now a large body of published carbon research work frame within the vegetated area (mangrove forests, sea grass bed, and salt marshes). Nonvegetated tidal flats, which are characterized by predominantly silts and clays sediment, were generally impressed with low carbon stock due to their meager primary productivity. However, these regions may be a potentially important carbon sink, given their high burial rate, expanding areal coverage, and detrial organic carbon derived from watershed and adjacent vegetated area. Low carbon densities (<0.01 g cm −3) were found in Chinese tidal flat sediments by the study, but the carbon sequestration rates ranged from 35 to 361 g C m −2 yr −1 , which were comparable to rates of worldwide vegetated coastal areas. The high rates can be ascribed to rapid sedimentation rates (1-2 cm yr −1) during the past several decades. The highest areal carbon stocks were located at tidal flat sites proximal to mangrove forests. The majority of carbon stocks (100 cm) was found in the unvegetated tidal flats instead of in the vegetated tidal flats. The former occupied 87% of the entire tidal area, 6.7 times larger than the latter. Tidal flats in coastal China store 78.07 Tg C (100 cm), accounting for nearly 80% of the C deposited in entire coastal tidal area. The future carbon sequestration rates of Chinese tidal flats are facing uncertainties under the pressures of reduced fluvial sediment loads from major rivers.

Rapid carbon accumulation at a saltmarsh restored by managed realignment exceeded carbon emitted in direct site construction

“…Lower values of either one of these limits carbon accumulation. For example, In natural saltmarshes in China, carbon accumulation rates are low (0.35–3.61 tC ha -1 yr -1 ) despite accretion of 20 mm yr -1 because of low sediment carbon densities (< 0.01 t m -3 ) [ 67 ]. This variability in carbon accumulation rates between sites highlights the need for further work to support large-scale assessments of the carbon accumulation potential of saltmarsh restoration.…”

Source Identification and Estimation of Organic Carbon in the Intertidal Wetlands of the Eastern Coast of China

“…Among these, JL, ZJ, YL, and DZ were mangrove wetlands. The constant initial concentration (CIC) model and 137 Cs were adopted to calculate the sedimentation rates (cm yr −1 ) of the core sediments at the 12 sites, ranging from 0.84 to 2.82 cm yr −1 (Chen et al., 2020).…”

Tidal Flats as a Significant Carbon Reservoir in Global Coastal Ecosystems

“…Daily net primary productivity on tidal flats is only 10 to 20% of that of vegetated coastal wetlands (Lin et al, 2020). However, tidal flats also have high C sequestration capacity similar to that of vegetated coastal ecosystems, especially in estuaries where the hydrodynamic environment promotes C burial and riverine sediment supply provides large quantities of organic matter (Choi and Wang, 2004;Roberts et al, 2015;Chen et al, 2020).…”

“…As tidal flats occur across wide latitudinal ranges, including locations where vegetated wetlands are absent, making sediment C a significant component of the coastal C pool. For example, as the most widely distributed coastal ecosystems in China, tidal flats store nearly 78 Tg C within the sediments, which is about four times higher than that of mangroves and salt marshes in the country (Chen et al, 2020). Nevertheless, global data on C sequestration in tidal flats are scarce compared to those on vegetated coastal wetlands (Phang et al, 2015;Lin et al, 2020).…”