measurement methods![Sample our Physical Sciences journals, sign in here to start your FREE access for 14 days]({"type":"image" , "src" : "/sda/110819/TOC-Subject-Sample-2021-Physical-Sciences.jpg"})
Abstract
Nitrification is a crucial process in sediment nitrogen cycling. We compared two 15N tracer-based nitrification measurement techniques (isotope pairing technique (IPT) combined with 15N nitrate pool dilution and 15N ammonium oxidation) and three different 15N analyses from bottom water nitrate (ammonia diffusion, denitrifier and SPINMAS) in a sediment mesocosm. The 15N nitrate pool dilution technique combined with IPT can be used to quantify the in situ nitrification, but the minimum detection limit for the total nitrification is higher than that in the 15N ammonium oxidation technique. The 15N ammonium oxidation technique, however, is not applicable for sediments that have high ammonium content. If nitrate concentration and the amount of 15N label in the sample are low, the 15N nitrate analysis should be done with the denitrifier method. In higher 15N concentrations, the less sensitive SPINMAS method can also be applied. The ammonia diffusion method is not suitable for bottom water 15N nitrate analyses.
Acknowledgements
We thank Adrien Vetterli from the Department of Environmental Sciences, University of Helsinki, Finland, for help during the sample processing and Christo Buizert from Ice and Climate Centre, University of Copenhagen, Denmark, for helping with the gas analyses. We also thank Professor Daniel Sigman from Department of Geosciences, Princeton University, USA, for inviting Helena Jäntti to learn stable isotope techniques in his laboratory. We acknowledge financial help from the Onni Talas Foundation, Academy of Finland (116477), Maa-ja vesitekniikan tuki ry and EU-Bonus+ project Assessment and Modelling of Baltic Ecosystem Response (AMBER). We thank for the helpful comments provided by the anonymous reviewers.