Dinosterol δD values in stratified tropical lakes (Cameroon) are affected by eutrophication
2015
Abstract In freshwater settings,
dinosterol(4α,23,24-trimethyl-5α-cholest-22E-en-3β-ol) is produced primarily by dinoflagellates, which encompass various species including autotrophs,
mixotrophsand heterotrophs. Due to its source specificity and occurrence in lake and marine sediments, its presence and hydrogen isotopic composition (δD) should be valuable proxies for paleohydrological reconstruction. However, because the purity required for hydrogen isotope measurements is difficult to achieve using standard wet chemical purification methods, their potential as a paleohydrological proxy is rarely exploited. In this study, we tested δD values of
dinosterolin both
particulate organic matter(POM) and sediments of stratified tropical freshwater lakes (from Cameroon) as a paleohydrological proxy, the lakes being characterized by variable degrees of eutrophication. In POM and sediment samples, the δD values of
dinosterolcorrelated with lake water δD values, confirming a first order influence of source water δD values. However, we observed that sedimentary
dinosterolwas D enriched from ca. 19 to 54‰ compared with POM
dinosterol. The enrichment correlated with lake water column conditions, mainly the redox potential at the oxic–anoxic interface ( E h OAI). The observations suggest that paleohydrologic reconstruction from δD values of
dinosterolin the sediments of stratified tropical lakes ought to be sensitive to the depositional environment, in addition to lake water δD values, with more positive
dinosterolδD values potentially reflecting increasing lake eutrophication. Furthermore, in lake sediments, the concentration of partially reduced vs. non-reduced C 34 botryococcenes, stanols vs. stenols, and bacterial (diploptene, diplopterol and ββ-bishomohopanol) vs. planktonic/terrestrial lipids (cholesterol,
campesteroland
dinosterol) correlated with E h OAI. We suggest using such molecular proxies for lake redox conditions in combination with
dinosterolδD values to evaluate the effect of lake trophic status on sedimentary
dinosterolδD values, as a basis for accurately reconstructing tropical lake water δD values.
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