Dr. Danny Ionescu (Leibniz-Institute for Freshwater Ecology and Inland Fisheries, Berlin)
Abstract:
The Dead Sea is a terminal, desert, hypersaline lake located on the borders of Jordan, the Palestinian Authority and Israel. The lake was stratified till 1979 when due to increased evaporation and reduced freshwater input the salinity in the upper layer was enough to overturn the lake. Despite concentrations of over 35 % total dissolved salts, it is not the high salinity that makes the lake’s water toxic to life but rather the high concentration of divalent cations as Mg2+ and Ca2+. In my talk I will present and discuss a series of findings we made in the lake during our research in the past 10 years. First, we identified numerous underwater freshwater springs, originating from the nearby Judea mountain aquifers. These springs emerge on the sediment of the Dead Sea at depths of up to ca. 40 m either as dispersed seepage or by forming underwater sinkholes. The freshwater input results in active and dense phototrophic and chemotrophic microbial biofilms. Here, aside of oxygenic photosynthesis we could identify sulfide oxidation, sulfate reduction and ammonia oxidation, as well as suggest who are the responsible microorganisms. Second, we examined the composition of dissolved organic matter in the Dead Sea waters along a vertical and horizontal transect and discovered surprising heterogeneity in concentration and composition. Fingerprinting analysis was further conducted on dissolved organic mater from the underwater springs and water from the feeding aquifers, which alongside 14C dating suggests the organic matter in the Dead Sea is a long-term accumulation of recalcitrant organic matter.
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