Hydrogen isotope biogeochemistry of plant waxes in paired lake catchments

Abstract

Studies of plants in modern catchment systems can serve to improve the level of understanding of sedimentary plant wax hydrogen isotope (δ2H) data by directly investigating the link between local climate conditions, plant source water, leaf water, and plant lipids for individual plant species. Here we present such an application to compare two lake catchments with different basin morphologies in Estonia. We sampled leaf and xylem water, as well as leaf waxes from the seven common plant species in each catchment, and soil water. We then measured the δ2H values of all waters, and of n-alkanes (δ2Hn–alk) from the plant waxes, as well as surface lake sediments. We applied a Péclet modified Craig-Gordon leaf water model using local precipitation isotope and climate data to characterize the δ2H values of the biosynthetic source water pool throughout the entire growth season. The data and model results provide a detailed view of how the input hydro-climatic signals from the precipitation δ2H values were modified by environmental and plant physiological conditions and ultimately by the biosynthetic isotope fractionation associated with n–alkane production by each plant species. We report both average apparent (εapp = –92 ± 21 ‰) and biosynthetic (εbio = –132 ± 19 ‰) hydrogen isotope fractionation factors of all species from the studied catchments. This information serves as a foundation for sedimentary organic geochemistry and paleoclimate studies, which allows for more direct and quantitative links to be made between sedimentary plant wax δ2H values and the climate signal contained in plant source water.