Correcting for Biogenic Gas Matrix Effects on Laser‐Based Pore Water‐Vapor Stable Isotope Measurements

Abstract

However, only air‐inflated samples could be reliably corrected using instrument‐specific sensitivity factors that were empirically determined by interpretation of periodically repeated isotope measurements. Corrected water isotope data were confirmed by similarity with local precipitation and suction cup isotope data. Residual uncertainties were well below the natural variations of soil water isotope values and independent of storage time, thus allowing for consistently reliable interpretations of soil water isotope profiles. We conclude that, especially for pore water sampling that requires small sample volumes and/or long storage times, metalized sample bags should be used to prevent evaporation notwithstanding the enhanced buildup of biogenic gases. Further, if gas matrix effects cannot be excluded, air inflation is preferred over pure N2, as only in that case can reliable postcorrections be performed by using internal data only.