@article{SchwabGarcinSachseetal.2015,
  author    = {Schwab, Valerie F. and Garcin, Yannick and Sachse, Dirk and Todou, Gilbert and Sene, Olivier and Onana, Jean-Michel and Achoundong, Gaston and Gleixner, Gerd},
  title     = {Dinosterol delta D values in stratified tropical lakes (Cameroon) are affected by eutrophication},
  series = {Organic geochemistry : the international journal for rapid publication of current research in organic geochemistry and biochemistry},
  volume    = {88},
  journal   = {Organic geochemistry : the international journal for rapid publication of current research in organic geochemistry and biochemistry},
  publisher = {Elsevier},
  address   = {Oxford},
  issn      = {0146-6380},
  doi       = {10.1016/j.orggeochem.2015.08.003},
  pages     = {35 -- 49},
  year      = {2015},
  abstract  = {In freshwater settings, dinosterol (4 alpha,23,24-trimethyl-5 alpha-cholest-22E-en-3 beta-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 (delta D) 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 delta D 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 delta D values of dinosterol correlated with lake water delta D values, confirming a first order influence of source water delta D 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 (E-h OAI). The observations suggest that paleohydrologic reconstruction from delta D values of dinosterol in the sediments of stratified tropical lakes ought to be sensitive to the depositional environment, in addition to lake water delta D values, with more positive dinosterol delta 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 beta beta-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 delta D values to evaluate the effect of lake trophic status on sedimentary dinosterol delta D values, as a basis for accurately reconstructing tropical lake water delta D values. (C) 2015 Elsevier Ltd. All rights reserved.},
  language  = {en}
}
@article{BoettcherMerzLischeidetal.2014,
  author    = {B{\"o}ttcher, Steven and Merz, Christoph and Lischeid, Gunnar and Dannowski, Ralf},
  title     = {Using Isomap to differentiate between anthropogenic and natural effects on groundwater dynamics in a complex geological setting},
  series = {Journal of hydrology},
  volume    = {519},
  journal   = {Journal of hydrology},
  publisher = {Elsevier},
  address   = {Amsterdam},
  issn      = {0022-1694},
  doi       = {10.1016/j.jhydrol.2014.09.048},
  pages     = {1634 -- 1641},
  year      = {2014},
  abstract  = {Due to increasing demands and competition for high quality groundwater resources in many parts of the world, there is an urgent need for efficient methods that shed light on the interplay between complex natural settings and anthropogenic impacts. Thus a new approach is introduced, that aims to identify and quantify the predominant processes or factors of influence that drive groundwater and lake water dynamics on a catchment scale. The approach involves a non-linear dimension reduction method called Isometric feature mapping (Isomap). This method is applied to time series of groundwater head and lake water level data from a complex geological setting in Northeastern Germany. Two factors explaining more than 95\% of the observed spatial variations are identified: (1) the anthropogenic impact of a waterworks in the study area and (2) natural groundwater recharge with different degrees of dampening at the respective sites of observation. The approach enables a presumption-free assessment to be made of the existing geological conception in the catchment, leading to an extension of the conception. Previously unknown hydraulic connections between two aquifers are identified, and connections revealed between surface water bodies and groundwater. (C) 2014 Elsevier B.V. All rights reserved.},
  language  = {en}
}