title: Opening Opportunities for High-Resolution Isotope Analysis - Quantification of δ15NNO3and δ18ONO3in Diffusive Equilibrium in Thin-Film Passive Samplers.
abstract: The fate of nitrate transported across groundwater-surface water interfaces has been intensively studied in recent decades. The interfaces between aquifers and rivers or lakes have been identified as biogeochemical hotspots with steep redox gradients. However, a detailed understanding of the spatial heterogeneity and potential temporal variability of these hotspots, and the consequences for nitrogen processing, is still hindered by a paucity of adequate measurement techniques. A novel methodology is presented here, using Diffusive Equilibrium in Thin-film (DET) gels as high-spatial-resolution passive-samplers of δ15NNO3and δ18ONO3to investigate nitrogen cycling. Fractionation of δ15NNO3and δ18ONO3during diffusion of nitrate through the DET gel was determined using varying equilibrium times and nitrate concentrations. This demonstrated that nitrate isotopes of δ15NNO3and δ18ONO3do not fractionate when sampled with a DET gel. δ15NNO3values from the DET gels ranged between 2.3 ± 0.2 and 2.7 ± 0.3‰ for a NO3-stock solution value of 2.7 ± 0.4‰, and δ18ONO3values ranged between 18.3 ± 1.0 and 21.5 ± 0.8‰ for a NO3-stock solution of 19.7 ± 0.9‰. Nitrate recovery and isotope values were independent of equilibrium time and nitrate concentration. Additionally, an in situ study showed that nitrate concentration and isotopes provide unique, high-resolution data that enable improved understanding of nitrogen cycling in freshwater sediments.
authors.affiliation: School of Geography, Earth and Environmental Sciences, University of Birmingham , Edgbaston, Birmingham B15 2TT, U.K.
authors.forename: Sophie A
authors.identifier: 0000-0003-1260-3151
authors.initials: SA
authors.lastname: Comer-Warner
authors.affiliation: School of Geography, Earth and Environmental Sciences, University of Birmingham , Edgbaston, Birmingham B15 2TT, U.K.
authors.forename: Stefan
authors.initials: S
authors.lastname: Krause
authors.affiliation: British Geological Survey, Maclean Building, Wallingford, Oxfordshire OX10 8BB, U.K.
authors.forename: Daren C
authors.initials: DC
authors.lastname: Gooddy
authors.affiliation: NERC Isotope Geoscience Laboratory, British Geological Survey , Keyworth, Nottingham NG12 5GG, U.K.
authors.forename: Sarah A
authors.initials: SA
authors.lastname: Bennett
authors.affiliation: Centre for Ocean and Atmospheric Sciences, School of Environmental Sciences, University of East Anglia , Norwich Research Park, Norwich NR4 7TJ, U.K.
authors.forename: Sarah K
authors.initials: SK
authors.lastname: Wexler
authors.affiliation: Centre for Ocean and Atmospheric Sciences, School of Environmental Sciences, University of East Anglia , Norwich Research Park, Norwich NR4 7TJ, U.K.
authors.forename: Jan
authors.identifier: 0000-0002-1553-4043
authors.initials: J
authors.lastname: Kaiser