Annual Lateral Organic Carbon Exchange Between Salt Marsh and Adjacent Water: A Case Study of East Headland Marshes at the Yangtze Estuary

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.

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A new, mechanistic model for organic carbon fluxes in the ocean based on the quantitative association of POC with ballast minerals

Deep Sea Research Part II Topical Studies in Oceanography ◽

10.1016/s0967-0645(01)00101-1 ◽

2001 ◽

Vol 49 (1-3) ◽

pp. 219-236 ◽

Cited By ~ 624

Author(s):

Robert A. Armstrong ◽

Cindy Lee ◽

John I. Hedges ◽

Susumu Honjo ◽

Stuart G. Wakeham

Keyword(s):

Organic Carbon ◽

Mechanistic Model ◽

Carbon Fluxes ◽

Organic Carbon Fluxes

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The ballast effect of lithogenic matter and its influences on the carbon fluxes in the Indian Ocean

Biogeosciences ◽

10.5194/bg-16-485-2019 ◽

2019 ◽

Vol 16 (2) ◽

pp. 485-503 ◽

Cited By ~ 10

Author(s):

Tim Rixen ◽

Birgit Gaye ◽

Kay-Christian Emeis ◽

Venkitasubramani Ramaswamy

Keyword(s):

Indian Ocean ◽

Organic Carbon ◽

Spatial Variability ◽

Primary Production ◽

Carbon Flux ◽

Carbon Fluxes ◽

Matter Content ◽

Organic Carbon Flux ◽

The Indian Ocean ◽

Organic Carbon Fluxes

Abstract. Data obtained from long-term sediment trap experiments in the Indian Ocean in conjunction with satellite observations illustrate the influence of primary production and the ballast effect on organic carbon flux into the deep sea. They suggest that primary production is the main control on the spatial variability of organic carbon fluxes at most of our study sites in the Indian Ocean, except at sites influenced by river discharges. At these sites the spatial variability of organic carbon flux is influenced by lithogenic matter content. To quantify the impact of lithogenic matter on the organic carbon flux, the densities of the main ballast minerals, their flux rates and seawater properties were used to calculate sinking speeds of material intercepted by sediment traps. Sinking speeds in combination with satellite-derived export production rates allowed us to compute organic carbon fluxes. Flux calculations imply that lithogenic matter ballast increases organic carbon fluxes at all sampling sites in the Indian Ocean by enhancing sinking speeds and reducing the time of organic matter respiration in the water column. We calculated that lithogenic matter content in aggregates and pellets enhances organic carbon flux rates on average by 45 % and by up to 62 % at trap locations in the river-influenced regions of the Indian Ocean. Such a strong lithogenic matter ballast effect explains the fact that organic carbon fluxes are higher in the low-productive southern Java Sea compared to the high-productive western Arabian Sea. It also implies that land use changes and the associated enhanced transport of lithogenic matter from land into the ocean may significantly affect the CO2 uptake of the organic carbon pump in the receiving ocean areas.

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