Soil Science of Temperate and Boreal Ecosystems, Büsgen-Institute, University of Göttingen, Büsgenweg 2, 37077 Göttingen, Germany.
Rapid Commun Mass Spectrom. 2011 Jul 30;25(14):1993-2006. doi: 10.1002/rcm.5066.
Aquifers within agricultural catchments are characterised by high spatial heterogeneity of their denitrification potential. Therefore, simple but sophisticated methods for measuring denitrification rates within the groundwater are crucial for predicting and managing N-fluxes within these anthropogenic ecosystems. Here, a newly developed automated online (15)N-tracer system is presented for measuring (N(2)+N(2)O) production due to denitrification in aquifer samples. The system consists of a self-developed sampler which automatically supplies sample aliquots to a membrane-inlet mass spectrometer. The developed system has been evaluated by a (15)N-nitrate tracer incubation experiment using samples (sulphidic and non-sulphidic) from the aquifer of the Fuhrberger Feld in northern Germany. It is shown that the membrane-inlet mass spectrometry (MIMS) system successfully enabled nearly unattended measurement of (N(2)+N(2)O) production within a range of 10 to 3300 µg N L(-1) over 7 days of incubation. The automated online approach provided results in good agreement with simultaneous measurements obtained with the well-established offline approach using isotope ratio mass spectrometry (IRMS). In addition, three different (15)N-aided mathematical approaches have been evaluated for their suitability to analyse the MIMS raw data under the given experimental conditions. Two approaches, which rely on the measurement of (28)N(2), (29)N(2) and (30)N(2), exhibit the best reliability in the case of a clear (15) N enrichment of evolved denitrification gases. The third approach, which uses only the ratio of (29)N(2)/(28)N(2), overestimates the concentration of labelled denitrification products under these conditions. By contrast, at low (15)N enrichments and low fractions of denitrified gas, the latter approach is on a par with the other two approaches. Finally, it can be concluded that the newly developed system represents a comprehensive and simply applicable tool for the determination of denitrification in aquifers.
农业流域含水层的硝酸盐还原潜力具有高度的空间异质性。因此，对于预测和管理这些人为生态系统中的氮通量，简单而复杂的地下水硝酸盐还原速率测量方法至关重要。这里提出了一种新开发的自动在线（15）N 示踪系统，用于测量含水层样品中由于反硝化作用而产生的（N2+N2O）。该系统由一个自开发的取样器组成，该取样器自动将样品等分试样供给膜进质谱仪。使用来自德国北部 Fuhrberger Feld 含水层的硫化和非硫化样品，通过（15）N 硝酸盐示踪剂孵育实验对开发的系统进行了评估。结果表明，在 7 天的孵育过程中，膜进质谱仪（MIMS）系统成功地实现了 10 至 3300 µg N L(-1) 范围内的（N2+N2O）产生的几乎无人值守测量。自动在线方法提供的结果与使用同位素比质谱（IRMS）的成熟离线方法同时获得的结果非常吻合。此外，评估了三种不同的（15）N 辅助数学方法，以评估它们在给定实验条件下分析 MIMS 原始数据的适用性。在反硝化气体中（15）N 明显富集的情况下，两种方法（一种依赖于（28）N2、（29）N2 和（30）N2 的测量，另一种依赖于（29）N2/（28）N2 比的测量）具有最佳的可靠性。在这些条件下，第三种方法仅使用（29）N2/（28）N2 比，会高估标记的反硝化产物的浓度。相比之下，在（15）N 富集度低和反硝化气体比例低的情况下，后一种方法与前两种方法相当。最后，可以得出结论，新开发的系统代表了一种用于确定含水层反硝化作用的全面而简单适用的工具。
