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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 (<1%), DOC fluxes were more important for PHY (41%) than ASB (12%). Faster downward transport and loss suggest that tauna prefer PHY, due to its lability and/or toxins associated with ASB; this may account for different carbon pathways. Secondary-treated PPM effluent has lower oxygen demand than primary-treated effluent, but ASB accumulation may contribute to sediment anoxia, and respiration of ASB and PHY-derived DOC may make the water column more heterotrophic. This highlights the need to optimize secondary-treatment processes to control the quality and quantity of organic carbon associated with PPM effluent. [ABSTRACT FROM AUTHOR]

To determine the role of sediment denitrification in removing inputs of primary- (PE) and secondary-treated effluent (SE) from a pulp and paper mill (PPM), organic matter (OM) associated with PE (residual wood fiber) and SE (activated sludge biomass and phytoplankton) was added to estuarine intertidal sediments and denitrificatian rates were measured over 27 days. Labile sludge biomass and phytoplankton initially stimulated denitrification, including for pre-existing sediment N. After 2.5 d, however, denitrification was suppressed apparendy due to microbial competition for N to process the refractory (high C:N) material remaining. Wood fiber suppressed denitrification throughout the experiment due to competition for N to process the refractory OM. Ultimate long-term denitrification suppression by phytoplankton is offset by initial enhanced denitrification rates. Although nutrient release during degradation of sludge biomass and wood fiber may stimulate phytoplankton production, N equivalent to 127% of the expected daily phytoplankton load was denitrified within 24 h, allowing for permanent removal of PPM-derived N. Compared to primary treatment, secondary treatment of PPM effluent has greater potential for N removal. [ABSTRACT FROM AUTHOR]

Stable isotope analysis of a novel combination of carbon and nitrogen pools traced inputs and processing of primary- treated (PE) and secondary-treated effluent (SE) from a paper and pulp mill (PPM) in a temperate Australian estuary. Distinct carbon stable isotope ratios of dissolved organic carbon (DOC) near the PPM outfall indicated large PE and reduced SE inputs of DOC. DOC was remineralized to dissolved inorganic carbon regardless of season, but rates were lower in winter. PE discharge in winter elevated DOC concentrations along much of the estuary. Distinct stable isotope ratios confirmed particulate organic matter (POM) input from PE and SE to the water column and into the sediment This was relatively localized, indicating rapid POM settlement regardless of season SE discharge increased nutrient inputs and enhanced algal productivity, particularly in summer when chlorophyll-a concentrations were elevated throughout the estuary. SE discharge reduced pCO2 from levels associated with PE discharge. However, the estuary remained heterotrophic as subsequent respiration or decomposition of algal material offset reductions in PPM organic matter input. The influence of the PPM was apparent throughout the estuary, demonstrating the ability of anthropogenic inputs, and changes to these, to affect ecosystem functioning. [ABSTRACT FROM AUTHOR]

To determine the benthic transformation pathways and fate of carbon associated with secondary-treated pulp and paper mill (PPM) effluent, (13)C-labeled activated sludge biomass (ASB) and phytoplankton (PHY) were added, separately, to estuarine intertidal sediments. Over 28 days, (13)C 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 (13)C loss from PHY and ASB plots via DIC (58% and 56%, respectively) and CO2(g) fluxes (<1%), DOC fluxes were more important for PHY (41%) than ASB (12%). Faster downward transport and loss suggest that fauna prefer PHY, due to its lability and/or toxins associated with ASB; this may account for different carbon pathways. Secondary-treated PPM effluent has lower oxygen demand than primary-treated effluent, but ASB accumulation may contribute to sediment anoxia, and respiration of ASB and PHY-derived DOC may make the water column more heterotrophic. This highlights the need to optimize secondary-treatment processes to control the quality and quantity of organic carbon associated with PPM effluent.