Measuring nitrification in sediments – comparison of two techniques and three¹⁵NO measurement methods

Abstract

Nitrification is a crucial process in sediment nitrogen cycling. We compared two (15)N tracer-based nitrification measurement techniques (isotope pairing technique (IPT) combined with (15)N nitrate pool dilution and (15)N ammonium oxidation) and three different (15)N analyses from bottom water nitrate (ammonia diffusion, denitrifier and SPINMAS) in a sediment mesocosm. The (15)N 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 (15)N ammonium oxidation technique. The (15)N ammonium oxidation technique, however, is not applicable for sediments that have high ammonium content. If nitrate concentration and the amount of (15)N label in the sample are low, the (15)N nitrate analysis should be done with the denitrifier method. In higher (15)N concentrations, the less sensitive SPINMAS method can also be applied. The ammonia diffusion method is not suitable for bottom water (15)N nitrate analyses.

Measuring 15N Abundance and Concentration of Aqueous Nitrate, Nitrite, and Ammonium by Membrane Inlet Quadrupole Mass Spectrometry

“…This corresponds to results of a comparison study where the SPIN–MAS method was compared with the diffusion method and the denitrifier method for 15 N analyses in nitrate from bottom water of a sediment mesocosm experiment. It was found that for 15 N-enriched samples the SPIN–MAS and denitrifier method gave similar results but that the diffusion method was not suitable for bottom water 15 N nitrate analysis probably due to cross-contamination . This backs up our finding that the SPIN–MIMS method, relying on the same chemical reactions as the SPIN–MAS method, is precise enough to analyze samples from enrichment studies even at low enrichment levels, and measurements are much faster and more convenient than all off-line methods.…”

The Response of Estuarine Ammonia-Oxidizing Communities to Constant and Fluctuating Salinity Regimes

“…The analyses were determined using the denitrifier method (Sigman et al, 2001) at Appalachian Lab, University of Maryland. Potential nitrification rates were calculated based on the [ 15 N] fractional change (R 15 14 N) after 2 h of incubation, and the [NO 3 − ] and [NO 2 − ] existent at the same period, using the equation described by Jantti et al (2012).…”

Application of the isotope pairing technique in sediments: Use, challenges, and new directions

“…In many benthic environments, particularly those with low bottom water NO 3 − , denitrification rates have been shown to be coupled to nitrification, which in turn is controlled by oxygen availability and transport limitation in the sediment due to the varying thickness of the oxic zone (Jensen et al ; Gihring et al ; Marchant et al ). Direct methods for the determination of nitrification rates are compromised by the fact that 15 NH 4 + additions increase the NH 4 + pool at low pore‐water NH 4 + concentrations several‐fold, thereby artificially enhancing rates of NH 4 + ‐limited nitrification (Jäntti et al ). Alternatively, isotope dilution approaches with added 15 NO 2 − have been used to quantify nitrification rates (e.g., Jäntti et al ; Marchant et al ).…”

“…Direct methods for the determination of nitrification rates are compromised by the fact that 15 NH 4 + additions increase the NH 4 + pool at low pore‐water NH 4 + concentrations several‐fold, thereby artificially enhancing rates of NH 4 + ‐limited nitrification (Jäntti et al ). Alternatively, isotope dilution approaches with added 15 NO 2 − have been used to quantify nitrification rates (e.g., Jäntti et al ; Marchant et al ). Other ways of applying the IPT have also been implemented (e.g., see Steingruber et al ), such as stand‐alone slurries or bag incubations (e.g., Engström et al ; Brandsma et al ) which provide potential rates of NO 3 − ‐reducing processes but cannot be reliably used to reflect in situ rates.…”

“…The determination of DNRA through experimental 15 NO 3 − addition has been carried out for many years (Koike and Hattori ; Sørensen ; Jørgensen ; Binnerup et al ). However, the implications for the co‐occurrence of denitrification and anammox with DNRA have only been discussed (Hietanen ; Jäntti et al ) and measured (Dong et al ; Trimmer and Nicholls ; De Brabandere et al ; Song et al ; Bonaglia et al ; Salk et al ) more recently. In the case of all three processes co‐occurring, the application of the IPT becomes further complicated, with movement of 15 N from the NO 3 − to NH 4 + pools through DNRA leading to additional 30 N 2 production from anammox (Fig.…”