Yaoundé, Cameroon
Yaoundé, Cameroon

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Schwab V.F.,Max Planck Institute For Biogeochemie | Garcin Y.,University of Potsdam | Sachse D.,University of Potsdam | Sachse D.,Helmholtz Center Potsdam | And 5 more authors.
Organic Geochemistry | Year: 2015

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, mixotrophs and 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 dinosterol in 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 dinosterol correlated with lake water δD values, confirming a first order influence of source water δD values. However, we observed that sedimentary dinosterol was 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 (Eh OAI). The observations suggest that paleohydrologic reconstruction from δD values of dinosterol in the sediments of stratified tropical lakes ought to be sensitive to the depositional environment, in addition to lake water δD values, with more positive dinosterol δD values potentially reflecting increasing lake eutrophication. Furthermore, in lake sediments, the concentration of partially reduced vs. non-reduced C34 botryococcenes, stanols vs. stenols, and bacterial (diploptene, diplopterol and ββ-bishomohopanol) vs. planktonic/terrestrial lipids (cholesterol, campesterol and dinosterol) correlated with Eh OAI. We suggest using such molecular proxies for lake redox conditions in combination with dinosterol δD values to evaluate the effect of lake trophic status on sedimentary dinosterol δD values, as a basis for accurately reconstructing tropical lake water δD values. © 2015 Elsevier Ltd.

Desjardins T.,French National Institute for Agricultural Research | Turcq B.,French National Center for Scientific Research | Nguetnkam J.-P.,University of Ngaoundéré | Achoundong G.,Herbier National du Cameroun | And 3 more authors.
Comptes Rendus - Geoscience | Year: 2013

In order to better understand the dynamics of the forest-savanna mosaic from central Cameroon, we analyzed 13C and 14C profiles of six oxisols: two under forests and four under savannas. The δ13C soil profiles collected in the forests indicate that these environments are stable at least since the mid-Holocene, whereas the areas currently covered by savannas were formerly occupied by more forested vegetations. The 14C dating of organic matter indicate that the late extension of the savannas in central Cameroon date from the Late Holocene, starting from 4000-3500 14C yr BP. © 2013 .

Ghogue J.-P.,Herbier National du Cameroun | Huber K.A.,University of Zürich | Rutishauser R.,University of Zürich
Nordic Journal of Botany | Year: 2013

A new species is added to the monotypic African genus Djinga. Djinga cheekii Ghogue, Huber & Rutish. (Podostemaceae) is described as a new species from Cameroon (Littoral Province) and its morphological affinities and conservation status are assessed. The main distinguishing characters are: stamens 2 (not 1 as in D. felicis), flower buds inside spathella strongly inclined (not only slightly inclined as in D. felicis), and stems lacking or only up to 6 mm long (not up to > 6 cm as in D. felicis). A molecular analysis revealed that D. cheekii is sister to D. felicis, and both together are sister to Ledermanniella linearifolia and L. pusilla which show completely inverted flower buds inside the spathella, as typical for the large and still artificial genus Ledermanniella. © 2013 The Authors.

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