title: Tracing the influence of sewage nitrogen in a coastal ecosystem using stable nitrogen isotopes.
abstract: This paper reviews the use of stable nitrogen isotopes (delta15N) to delineate the influence of sewage nitrogen (N) in coastal ecosystems, drawing extensively on the case of Himmerfjärden, a Baltic Sea bay that receives 15N-enriched tertiary treated sewage that is discharged mainly as dissolved inorganic N (DIN). Gradients of delta15N in macroalgae (Fucus vesiculosus) and surface sediments traced sewage-derived N to 24 km from the outfall but elevated delta15N values (> 7 per thousand) indicated that the sewage influence was most pronounced within 10 km. Comparison of macroalgal delta15N values before and after enhanced tertiary treatment showed a decrease in the spatial impact of sewage N from about 24 km to 12 km from the outfall and a decrease to more marine delta15N values in more recent growth tissues. Sedimentary delta15N records showed that sewage has had a dominant influence on organic matter production in the bay with dramatic increases in sedimentary delta15N during the years of maximum sewage N loads. In cases where sewage N introduces a distinct isotopic signature into a system and where it has had a dominant influence on organic matter production, delta15N values in biota and sediments can be used to trace the spatial and temporal influence of sewage N in aquatic ecosystems.
authors.affiliation: Department of Marine Science, University of Otago, Dunedin, New Zealand. candida.savage@stonebow.otago.ac.nz
authors.forename: Candida
authors.initials: C
authors.lastname: Savage
mesh_terms: D017753:Ecosystem; D004784:Environmental Monitoring / Q000379:methods*; D056890:Eukaryota / Q000737:chemistry; D019015:Geologic Sediments / Q000737:chemistry; D009584:Nitrogen / Q000032:analysis*; D009587:Nitrogen Isotopes; D009659:North Sea; D012722:Sewage / Q000737:chemistry*; D013548:Sweden; D014873:Water Pollutants / Q000032:analysis*
chemical_list: D009587:Nitrogen Isotopes; D012722:Sewage; D014873:Water Pollutants; D009584:Nitrogen