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

Interpreting the 2H/1H ratios of short to long chain (C14-C30) n-alkanoic acids and n-alkanols is complicated by likely contributions from heterotrophs and/or vascular plants. These values generally did not correlate with lake water isotopes, nor did their fractionation factors correlate with total P. For most lipids there was no significant difference between sediment trap and surface sediment 2H/1H ratios. However, n-C14-n-C18 fatty acids were 2H-enriched in the surface sediments, most likely due to degradation in the water column. Our results indicate that interpretations of short-chain fatty acid 2H/1H ratios as a water isotope signal likely require supporting information about ecological conditions and community structure, but that paired H isotope measurements of phytoplankton-derived sterols and phytol may be developed as a proxy for phytoplankton growth.