Saline-alkaline lakes of the East African Rift are known to have an extremely high primary production supporting a potent carbon cycle. To date, a full description of carbon pools in these lakes is still missing. More specifically, there is not detailed information on the quality of dissolved organic matter (DOM), the main carbon energy source for heterotrophs prokaryotes. We report the first exhaustive description of DOM molecular properties in the water column of a meromictic saline-alkaline lake of the East African Rift. DOM availability, fate and origin were studied either quantitatively, in terms of dissolved organic carbon (DOC) and nitrogen (DON) or qualitatively, in terms of optical properties (absorbance) and molecular characterization of solid-phase extracted DOM (SPE-DOM) through negative electrospray ionization Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). DOM availability was high (DOC ∼ 8.1 mM in surface waters) and meromixis imprinted a severe quantitative and qualitative change on DOM pool. At the surface, DOM was rich in aliphatic and moderately in aromatic molecules and thus mirroring autochthonous microbial production together with photodegradation. At the bottom changes were extreme: DOC increased up to 5 times (up to 50 mM) and, molecular signature drifted to saturated, reduced and non-aromatic DOM suggesting intense microbial activity within organic sediments. At the chemocline, DOC was retained indicating that this interface is a highly reactive layer in terms of DOM processing. These findings underline that saline-alkaline lakes of the East African Rift are carbon processing hot spots and their investigation may broaden our understanding of carbon cycling in inland waters at large.

中文翻译：

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在东非大裂谷的热带盐碱湖中溶解的有机物。

众所周知，东非大裂谷的盐碱湖泊的初级生产力非常高，可支持有效的碳循环。迄今为止，仍缺少对这些湖泊中碳池的完整描述。更具体地说，没有关于异养原核生物主要碳能源的溶解有机物（DOM）质量的详细信息。我们报道了东非大裂谷的一个盐溶盐碱湖的水柱中的DOM分子特性的第一个详尽的描述。从溶解性有机碳（DOC）和氮（DON）的角度定量地研究了DOM的可用性，命运和起源。负电喷雾电离傅立叶变换离子回旋共振质谱（FT-ICR-MS）的固相萃取DOM（SPE-DOM）的光学性质（吸光度）和分子表征方面的研究。DOM的利用率很高（地表水中的DOC约为8.1 mM），混合菌在DOM池中留下了严重的数量和质量变化。在表面上，DOM富含脂肪族分子和中等程度的芳香族分子，因此反映了土生微生物的产生以及光降解作用。最底部的变化是极端的：DOC增加了5倍（高达50 mM），并且分子标记漂移到饱和的，还原的和非芳香的DOM，表明有机沉积物中微生物的活性很高。在chemocline，保留了DOC，表示就DOM处理而言，此接口是高度反应性的层。这些发现表明，东非大裂谷的盐碱湖是碳加工的热点，它们的研究可能会拓宽我们对内陆水域碳循环的认识。