title: Discharge Driven Nitrogen Dynamics in a Mesoscale River Basin As Constrained by Stable Isotope Patterns.
abstract: Nitrate loads and corresponding dual-isotope signatures were used to evaluate large scale N dynamics and trends in a river catchment with a strong anthropogenic gradient (forest conservation areas in mountain regions, and intensive agriculturally used lowlands). The Bode River catchment with an area of 3200 km(2) in the Harz Mountains and central German lowlands was investigated by a two years monitoring program including 133 water sampling points each representing a subcatchment. Based on discharge data either observed or simulated by the mesoscale hydrological model (mHM) a load based interpretation of hydrochemical and isotope data was conducted. Nitrate isotopic signatures in the entire catchment are influenced by (I) the contribution of different nitrogen sources, (II) by variable environmental conditions during the formation of nitrate, and (III) by a minor impact of denitrification. For major tributaries, a relationship between discharge and nitrate isotopic signatures is observed. This may in part be due to the fact, that during periods of higher hydrologic activity a higher wash out of isotopically lighter nitrate formed by bacterial nitrification processes of reduced or organic soil nitrogen occurs. Beyond that, in-stream denitrification seems to be more intense during periods of low flow.
authors.affiliation: Helmholtz Center for Environmental Research UFZ - Department Catchment Hydrology - Stable Isotope Group, Theodor-Lieser-Straße 4, D-06120 Halle (Saale), Germany.
authors.forename: Christin
authors.initials: C
authors.lastname: Mueller
authors.affiliation: Helmholtz Center for Environmental Research UFZ - Department Computational Hydrosystems - Permoserstraße 15, 04318 Leipzig, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Zink
authors.affiliation: Helmholtz Center for Environmental Research UFZ - Department Computational Hydrosystems - Permoserstraße 15, 04318 Leipzig, Germany.
authors.forename: Luis
authors.initials: L
authors.lastname: Samaniego
authors.affiliation: Helmholtz Center for Environmental Research UFZ - Department Catchment Hydrology - Stable Isotope Group, Theodor-Lieser-Straße 4, D-06120 Halle (Saale), Germany.
authors.forename: Ronald
authors.initials: R
authors.lastname: Krieg
authors.affiliation: Helmholtz Center for Environmental Research UFZ - Department Catchment Hydrology - Stable Isotope Group, Theodor-Lieser-Straße 4, D-06120 Halle (Saale), Germany.
authors.forename: Ralf
authors.initials: R
authors.lastname: Merz
authors.affiliation: Helmholtz Center for Environmental Research UFZ - Department Aquatic Ecosystem Analysis - Brückstraße 3a, 39114 Magdeburg, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Rode
authors.affiliation: Helmholtz Center for Environmental Research UFZ - Department Catchment Hydrology - Stable Isotope Group, Theodor-Lieser-Straße 4, D-06120 Halle (Saale), Germany.
authors.forename: Kay
authors.initials: K
authors.lastname: Knöller
mesh_terms: D004784:Environmental Monitoring; D007554:Isotopes; D009566:Nitrates; D009584:Nitrogen; D045483:Rivers; D014874:Water Pollutants, Chemical
chemical_list: D007554:Isotopes; D009566:Nitrates; D014874:Water Pollutants, Chemical; D009584:Nitrogen