Abstract
Blue carbon (C) ecosystems (mangroves, salt marshes, and seagrass beds) sequester high amounts of C, which can be respired back into the atmosphere, buried for long periods, or exported to adjacent ecosystems by tides. The lateral exchange of C between a salt marsh and adjacent water is a key factor that determines whether a salt marsh is a C source (i.e., outwelling) or sink in an estuary. We measured salinity, particulate organic carbon (POC), and dissolved organic carbon (DOC) seasonally over eight tidal cycles in a tidal creek at the Chongming Dongtan wetland from July 2017 to April 2018 to determine whether the marsh was a source or sink for estuarine C. POC and DOC fluxes were significantly correlated in the four seasons driven by water fluxes, but the concentration of DOC and POC were positively correlated only in autumn and winter. DOC and POC concentrations were the highest in autumn (3.54 mg/L and 4.19 mg/L, respectively) and the lowest in winter and spring (1.87 mg/L and 1.51 mg/L, respectively). The tidal creek system in different seasons showed organic carbon (OC) export, and the organic carbon fluxes during tidal cycles ranged from –12.65 to 4.04 g C/m2. The intensity showed significant seasonal differences, with the highest in summer, the second in autumn, and the lowest in spring. In different seasons, organic carbon fluxes during spring tides were significantly higher than that during neap tides. Due to the tidal asymmetry of the Yangtze River estuary and the relatively young stage, the salt marshes in the study area acted as a strong lateral carbon source.
Highlights
Coastal salt marshes have a powerful carbon sink function, which is an important way to reduce atmospheric carbon dioxide (CO2) and mitigate global climate change, due to the influence of tides (Bonan, 2008)
We investigated seasonal dissolved organic carbon (DOC) and particulate organic carbon (POC) concentrations and fluxes in a tidal creek at the Chongming Dongtan salt marsh
Organic Carbon Concentrations As the world’s third largest river estuary, the Yangtze Estuary receives high amounts of carbon, nitrogen, phosphorus and other elements transported by the strong runoff
Summary
Coastal salt marshes have a powerful carbon sink function, which is an important way to reduce atmospheric carbon dioxide (CO2) and mitigate global climate change, due to the influence of tides (Bonan, 2008). Wang et al (2021a) estimated that the global carbon sequestration rate of salt marsh wetlands and mangroves was about 53.65 Tg C/yr. The carbon sequestration rate per unit area was 15 times that of terrestrial ecosystems, and about 50 times that of marine ecosystems (Wang et al, 2021b). This value is only the carbon burial rate in the vertical direction, but a large amount of carbon is exported to the ocean through the exchange process of tidal action, which is rarely reported due to methodological constraints
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