Sediment carbon and nutrient fluxes from cleared and intact temperate mangrove ecosystems and adjacent sandflats

The loss of mangrove ecosystems is associated with numerous impacts on coastal and estuarine function, including sediment carbon and nutrient cycling. In this study we compared in situ fluxes of carbon dioxide (CO₂) from the sediment to the atmosphere, and fluxes of dissolved inorganic nutrients and oxygen across the sediment-water interface, in intact and cleared mangrove and sandflat ecosystems in a temperate estuary. Measurements were made 20 and 25months after mangrove clearance, in summer and winter, respectively. Sediment CO₂ efflux was over two-fold higher from cleared than intact mangrove ecosystems at 20 and 25months after mangrove clearance. The higher CO₂ efflux from the cleared site was explained by an increase in respiration of dead root material along with sediment disturbance following mangrove clearance. In contrast, sediment CO₂ efflux from the sandflat site was negligible (≤9.13±1.18mmolm^-2d^-1), associated with lower sediment organic matter content. The fluxes of inorganic nutrients (NH₄⁺, NO_x and PO₄^3-) from intact and cleared mangrove sediments were low (≤20.37±18.66μmolm^-2h^-1). The highest NH₄⁺ fluxes were measured at the sandflat site (69.21±13.49μmolm^-2h^-1). Lower inorganic nutrient fluxes within the cleared and intact mangrove sites compared to the sandflat site were associated with lower abundance of larger burrowing macrofauna. Further, a higher fraction of organic matter, silt and clay content in mangrove sediments may have limited nutrient exchange.