title: Use of stable nitrogen isotope signatures of riparian macrophytes as an indicator of anthropogenic N inputs to river ecosystems.
abstract: Deterioration of aquatic ecosystems resulting from enhanced anthropogenic N loading has become an issue of increasing concern worldwide, and methods are needed to trace sources of N in rivers. Because nitrate from sewage is enriched in 15N relative to nitrate from natural soils, delta(15)N values of stream nitrate (delta(15)Nnitrate) should be an appropriate index of anthropogenic N loading to rivers, as should the delta(15)N values of riparian plants (delta(15)Nplant) because they are consumers of nitrate. We determined the delta(15)N values of stream nitrate and six species of riparian macrophytes in 31 rivers in the Lake Biwa Basin in Japan. We then tested the correlation between these values and various land-use parameters, including the percentage of land used for residential and agricultural purposes as well as for natural areas. These delta(15)N values were significantly positively correlated with land use (%) that had a high N load (i.e., residential or agricultural use) and significantly negatively correlated with forest (%). These findings indicate that delta(15)N values of stream nitrate and riparian plants might be good indicators of anthropogenic inputs of nitrogen.
authors.affiliation: Japan Science and Technology Agency, Saitama 332-0012, Japan. kohzu@nies.go.jp
authors.forename: Ayato
authors.initials: A
authors.lastname: Kohzu
authors.forename: Toshihiro
authors.initials: T
authors.lastname: Miyajima
authors.forename: Ichiro
authors.initials: I
authors.lastname: Tayasu
authors.forename: Chikage
authors.initials: C
authors.lastname: Yoshimizu
authors.forename: Fujio
authors.initials: F
authors.lastname: Hyodo
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Matsui
authors.forename: Takanori
authors.initials: T
authors.lastname: Nakano
authors.forename: Eitaro
authors.initials: E
authors.lastname: Wada
authors.forename: Noboru
authors.initials: N
authors.lastname: Fujita
authors.forename: Toshi
authors.initials: T
authors.lastname: Nagata
mesh_terms: D017753:Ecosystem; D006801:Humans; D007564:Japan; D009566:Nitrates / Q000032:analysis; D009584:Nitrogen / Q000032:analysis*; D009587:Nitrogen Isotopes; D010944:Plants / Q000737:chemistry*; D045483:Rivers / Q000737:chemistry*; D012621:Seasons; D014867:Water / Q000737:chemistry
chemical_list: D009566:Nitrates; D009587:Nitrogen Isotopes; D014867:Water; D009584:Nitrogen