Aquatic and Terrestrial Plant Contributions to Sedimentary Plant Waxes in a Modern Arctic Lake Setting

Sedimentary plant wax delta H-2 values are common proxies for hydrology, a poorly constrained variable in the Arctic. However, it can be difficult to distinguish plant waxes derived from aquatic versus terrestrial plants, causing uncertainty in climate interpretations. We test the hypothesis that Arctic lake sediment mid- and long-chain plant waxes derive from aquatic and terrestrial plants, respectively. We compare n-alkanoic acid and n-alkane chain-length distributions and n-alkanoic acid delta H-2 and delta C-13 values of the 29 most abundant modern plant taxa to those for soils, water filtrates, and lake sediments in the Qaupat Lake (QPT) catchment, Nunavut, Canada. Chain length distributions are variable among terrestrial plants, but similar and dominated by mid-chain waxes among submerged/floating aquatic plants. Sedimentary wax distributions are similar to those in submerged/floating aquatic plants and to Salix spp., which are among the most abundant terrestrial plants in the QPT catchment. Mid-chain n-alkanoic acid delta H-2 values are similar in sediments and submerged/floating aquatic plants, but 50 parts per thousand lower than Salix spp. In contrast, sedimentary long-chain n-alkanoic acid delta H-2 values fall between those for submerged/floating aquatic plants and Salix spp. We therefore infer that mid-chain waxes in QPT are primarily from aquatic plants, whereas long-chain waxes are from a mix of terrestrial and aquatic plants. In Arctic lakes like QPT, terrestrial wax transport via leaf litter and surface flow is limited by low-lying topography and sparse vegetation. If these lakes also have abundant aquatic plants growing near the sediment-water interface, the aquatic plants can contribute large portions of sedimentary waxes.