Reclamation-induced tidal restriction increases dissolved carbon and greenhouse gases diffusive fluxes in salt marsh...

Intertidal creeks play an important role in transporting nutrients between coastal ecosystems and ocean. Reclamation is a predominant anthropogenic disturbance in coastal regions; however, the influence of reclamation on carbon and nitrogen species and greenhouse gas (GHG) fluxes in creek remains unclear. In a subtropical salt marsh of eastern China, the seasonal patterns of dissolved carbon (DOC, DIC, CO₂, and CH₄) and inorganic nitrogen (NH₄⁺-N, NO₂^--N, and NO₃^--N and N₂O) species, and the diffusive fluxes of CO₂, CH₄, and N₂O, were compared between the natural tidal creeks and the reclaimed creeks. Due to notably changed hydrological and biological conditions in the reclaimed creeks, concentrations of all dissolved carbon species, NH₄⁺-N and NO₂^--N increased significantly by 60.2-288.2%, while NO₃^--N and N₂O decreased slightly, compared to the natural tidal creeks. DIC and NO₃^--N were the primary components of the total dissolved carbon and inorganic nitrogen in both creek types; however, their proportions decreased as a result of elevated DOC, CO₂, CH₄, NH₄⁺-N, and NO₂^--N following reclamation. Significantly higher global warming potential (0.58 ± 0.15 g CO₂-eq m^-2 d^-1) was found in the reclaimed creeks, making them hotspot of greenhouse effects, compared to the natural tidal creeks. Our results indicated that changes in flow velocity, salinity, Chlorophyll a, and pH were the main factors controlling the dissolved carbon and nitrogen and consequent GHG emissions, due to reclamation. This study is helpful in understanding of carbon and nitrogen sink-source shifts resulting from land use changes in coastal wetlands.