Processing of Particulate Organic Carbon Associated with Secondary-Treated Pulp and Paper Mill Effluent in Intertidal Sediments: A 13C Pulse-chase Experiment

To determine the benthic transformation pathways and fate of carbon associated with secondary-treated pulp and paper mill (PPM) effluent, 13C-labeled activated sludge biomass (ASB) and phytoplankton (PHY) were added, separately, to estuarine intertidal sediments. Over 28 days, 13C was traced into sediment organic carbon, fauna, seagrass, bacteria, and microphytobenthos and into fluxes of dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC) from inundated sediments, and carbon dioxide (CO2(g)) from exposed sediments. There was greater removal of PHY carbon from sediments (∼85% over 28 days) compared to ASB (∼75%). Although there was similar 13C loss from PHY and ASB plots via DIC (58% and 56%, respectively) and CO2(g) fluxes (