The flux and optical properties of dissolved carbon in the tidal marshes surrounding the Yangtze Estuary.

Abstract:

The lateral outwelling of dissolved carbon, including dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC), from tidal marsh is essential to the ‘blue carbon’. In the present study, the flux of DIC and DOC, and the optical properties of DOM were evaluated in Xisha tidal freshwater marsh (XS) and Jiuduansha saltmarsh (JDS) creek mouths located in the Yangtze Estuary, China. The discrete samples were collected every hour during a full tidal cycle of 24h using a Teledyne ISCO-7300 automatic water sampler. The in-situ FDOM sensor (EXO2, YSI) and a self-made equilibrium chamber were developed to collected long-term high-frequency data of FDOM and pCO₂, respectively. For the DOM properties, five fluorescent components were resolved from excitation emission matrix (EEM) combined with parallel factor analysis (PARAFAC) as 2 terrestrial humic acid components (C1 from wetland and C3 from estuary), 2 autochthonous protein-like components (C4 from wetland and C5 from estuary), and 1 artifact of the fluorometer (C2). The principal component analysis (PCA) further highlighted the different effects of seasonal variation (PC1) and wetland terrestrial signatures (PC2) on the DOM composition. The in-situ FDOM sensor was first applied in the highly turbid tidal creek in the Yangtze Estuary to evaluate the lateral DOC flux of the tidal marsh, and the in-situ data was corrected to eliminate the temperature and turbidity interference. The membrane pump was connected to a self-made shower head equilibrium chamber, and the sample was pumped from the tidal creek continuously through a stainless steel filtration equipment to remove the majority of microorganism. The CO₂ of the chamber head space was detected by a gas analyzer (LGR), while the pCO₂ and DIC concentration were calculated from the inorganic carbonate equilibrium equation. The dissolved carbon flux was combined the calculated long-term high-frequency DOC and DIC concentration with water flux detected simultaneously. Results from this work will provide a better understanding of dissolved carbon flux and DOM biogeochemistry in wetland during the different time scale, and specify the lateral carbon flux interactions between the wetland and estuary.