The roles of vegetation, tide and sediment in the variability of carbon in the salt marsh dominated tidal creeks

Combined effects of vegetation, tide and sediment on the carbon dynamics in the intertidal creek-marsh systems remain unclear. We investigated the variability of dissolved organic (DOC) and inorganic carbon (DIC), and particulate organic (POC) and inorganic carbon (PIC) in the tidal creeks within the Poaceae and Cyperaceae communities on flood-ebb cycle in a salt marsh of eastern China. In the Poaceae creek with high plant biomass and soil carbon stock, the DOC concentrations were higher by on average 1.00–1.48 times than that in the Cyperaceae creek across all seasons and spring and neap tide stages, while the difference of DIC was not notable. The POC and PIC concentrations were lower in the Poaceae creek compared to the Cyperaceae creek. Spring tides increased the carbon concentrations (except for PIC) in both creeks by on average 7–40%, relative to neap tides. Seasonal variations of sedimentary rate within the communities probably result in the discrepancy of particulate carbon loading between the creeks. The Poaceae creek functioned as a source of DOC and DIC throughout a year but as a sink of POC and PIC in summer and autumn, while it turned to a weak source of PIC in winter and spring. The Cyperaceae creek exhibited as a source of all carbon components throughout a year. We suggest that vegetation type (with soil carbon stocks), tidal regimes and sedimentary dynamics would synergistically determine the fate of carbon in the creeks. Our results are helpful in reliable estimates of carbon transport between the coastal marsh and the adjacent ocean.