Interplay of community dynamics, temperature, and productivity on the hydrogen isotope signatures of lipid biomarkers

Abstract

Abstract. The hydrogen isotopic composition (δ 2 H) of lipid biomarkers has diverse applications in the fields of paleoclimatology, biogeochemistry, and microbial community dynamics. Large changes in hydrogen isotope fractionation have been observed among microbes with differing core metabolisms, while environmental factors including temperature and nutrient availability can affect isotope fractionation by photoautotrophs. Much effort has gone into studying these effects under laboratory conditions with single species cultures. Moving beyond controlled environments and quantifying the natural extent of these changes in freshwater lacustrine settings and identifying their causes is essential for robust application of δ 2 H values of common short-chain fatty acids as a proxy of net community metabolism and of phytoplankton-specific biomarkers as a paleohydrologic proxy.This work targets the effect of community dynamics, temperature, and productivity on 2 H/ 1 H fractionation in lipid biomarkers through a comparative time series in two central Swiss lakes: eutrophic Lake Greifen and oligotrophic Lake Lucerne. Particulate organic matter was collected from surface waters at six time points throughout the spring and summer of 2015, and δ 2 H values of short-chain fatty acids, as well as chlorophyll-derived phytol and the diatom biomarker brassicasterol, were measured. We paired these measurements with in situ incubations conducted with NaH 13 CO 3 , which were used to calculate the production rates of individual lipids in lake surface water. As algal productivity in-

Lipid compound classes display diverging hydrogen isotope responses in lakes along a nutrient gradient

“…121! in central Switzerland were lower than those of brassicasterol in a nearby oligotrophic 122! lake (Ladd et al, 2017). There was, however, no significant difference in α Lipid-Water 123!…”

“…There was, however, no significant difference in α Lipid-Water 123! values for short-chain fatty acids and phytol between the two lakes (Ladd et al, 2017).…”

“…filter samples in suspended particles in the surface waters of Lakes Greifen and 709! Lucerne decrease from spring to summer by as much as 150‰ (Ladd et al, 2017). The 710!…”

“…From Lakes Greifen and Lucerne water samples were also collected at 188! four additional time points (Ladd et al, 2017).…”

The paleolimnologist's guide to compound-specific stable isotope analysis – An introduction to principles and applications of CSIA for Quaternary lake sediments

“…However, such interspecies differences appear to be averaged 411 out in the soil as n-alkanes from soil samples did show a good correlation between wax C28 n-fatty acid reported from the sedimentary record of an Alpine lake may be due to 414 local factors such as length of growing season, amount of snowfall or anthropogenic 415 modification of the local vegetation (Wirth and Sessions, 2016), factors that are not always 416 well constrained. Ladd et al (2017) investigated the influence of growth rate and temperature 417 on the δ 2 H value of algal lipids (fatty acids and brassicasterol) in an oligotrophic and a 418 eutrophic lake. Although the authors found significant variability in the δ 2 H values of fatty acids 419 throughout the growing season the average δ 2 H value of the C16 n-fatty acid matched the δ 2 H 420 value of the lake water and was also preserved in the surface sediment.…”