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Stable isotopes trace estuarine transformations of carbon and nitrogen from primary-and secondary-treated paper and pulp mill effluent

Citation

Oakes, JM and Eyre, BD and Ross, DJ and Turner, SD, Stable isotopes trace estuarine transformations of carbon and nitrogen from primary-and secondary-treated paper and pulp mill effluent, Environmental Science and Technology , 44, (19) pp. 7411-7417. ISSN 0013-936X (2010) [Refereed Article]


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Copyright © 2010 American Chemical Society

DOI: doi:10.1021/es101789v

Abstract

Paper and pulp mills (PPM) are major sources of nutrients and organic matter (OM) to estuaries and may impact the receiving environment (1). Nutrients discharged to estuaries can stimulate algal production (2), and enhanced inputs of OM from PPM effluent or algal production can alter energy flows and deplete water column oxygen concentrations (3). The composition of PPM effluent depends not only on the fiber source and pulping method but also on the treatment processes employed. Studies assessing impacts of primarytreated effluent (PE) discharge mainly consider the effects of residual fiber and OM that demand oxygen (4). A primary objective of secondary treatment ofPPMeffluent is to reduce the load of oxygen-demanding OM. During secondary treatment, microbes remove organic carbon, producing dissolved inorganic carbon (DIC) that can be released as CO2 gas. Because of the relatively low nitrogen (N) content of effluent, nutrients are added to ‘feed’ the microbes (5). Secondary-treated effluent (SE) typically contains more labile OM (microbes) than PE (fiber) and can have a higher inorganic nutrient content. This may shift a system toward autotrophy by enhancing algal production. Conversely, respiration of the labile OM produced as well as microbes from SE can increase heterotrophy and offset reductions in OM loading and oxygen demand gained through secondary treatment. Although PPM can contribute significant carbon (C) and N to aquatic systems, this can be difficult to detect using traditional methods due to dilution (6), transformation, and inputs from other sources. Particularly in estuaries, spatial variation in physical and chemical characteristics can complicate detection of PPM inputs. Stable isotope analysis can be useful for tracing anthropogenic inputs in aquatic systems, provided that inputs have a distinct isotope signature. To our knowledge, only four studies, all in freshwater, have used stable isotopes to trace PPM material (6-9). These studies traced PPM material into suspended sediment and biota and determined the extent of PPM influence and/or exposure of biota to effluent. However, they provided no information on the transformation processes that affect PPM-derived material and did not compare the effects of PE and SE, despite the potential for treatment processes to affect the quality and quantity ofCand N. There have been no attempts to use stable isotopes to trace distribution and transformations of PPM material within an estuary. Deviations of isotope ratios and/or concentrations from conservative mixing models can provide insight into sources and transformations of material in estuaries. Based onknown isotope ratios or concentrations of a compound in marine and freshwater, conservative mixing models use salinity (a measure of physical mixing) to calculate the expected isotope ratio or concentration of the compound at a given point in an estuary. Deviations from this model are due to nonphysical processes (uptake, transformation, or production). Conservative mixing models have been applied toCstable isotope ratios (δ13C) of dissolved organic carbon (DOC-δ13C) and dissolved inorganic carbon (DIC-δ13C) to assess OM sources along estuaries (e.g. refs 10 and 11). This can be a powerful method, particularly in combination with other techniques, but there have been few measurements of DOC- δ13C or DIC-δ13C due to tedious analytical processes and/or difficultieswith analysis (11, 12). Where anthropogenic inputs have distinct δ13C values, DOC-δ13C and DIC-δ13C could provide insight into their transport and processing. However, no studies to our knowledge have used DOC-δ13C and DIC- δ13C to trace anthropogenic inputs. The combined approach of conservative mixing models and stable isotope analysis of C and N pools, including DOC and DIC, has potential to improve understanding of the distribution, tra

Item Details

Item Type:Refereed Article
Research Division:Environmental Sciences
Research Group:Ecological Applications
Research Field:Ecosystem Function
Objective Division:Environment
Objective Group:Ecosystem Assessment and Management
Objective Field:Ecosystem Assessment and Management of Coastal and Estuarine Environments
Author:Ross, DJ (Dr Jeff Ross)
ID Code:66855
Year Published:2010
Web of Science® Times Cited:25
Deposited By:TAFI - Marine Research Laboratory
Deposited On:2011-02-15
Last Modified:2011-04-08
Downloads:0

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