Department de Biologia Evolutiva, Ecologia y Ciencies Ambientals, Universitat de Barcelona, Catalonia, Spain.
Department Lake Research, Helmholtz Centre for Environmental Research (UFZ), Magdeburg, Germany.
Water Res. 2020 Apr 15;173:115532. doi: 10.1016/j.watres.2020.115532. Epub 2020 Jan 28.
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.
东非大裂谷的咸水-碱性湖泊以极高的初级生产力支持强大的碳循环而闻名。迄今为止，这些湖泊中碳库的完整描述仍然缺失。更具体地说，对于溶解有机物质（DOM）的质量，即异养原核生物的主要碳能源，没有详细信息。我们报告了东非大裂谷一个分层咸水-碱性湖泊水柱中 DOM 分子特性的首次详尽描述。通过负电喷雾电离傅里叶变换离子回旋共振质谱（FT-ICR-MS），无论是从溶解有机碳（DOC）和氮（DON）的数量上，还是从吸收的光学特性和固相提取 DOM（SPE-DOM）的分子特征的质量上，都对 DOM 的可用性、命运和起源进行了研究。DOM 的可用性很高（表层水中的 DOC 约为 8.1 mM），分层混合对 DOM 库产生了严重的定量和定性变化。在表面，DOM 富含脂肪族和中等芳香族分子，因此反映了自生微生物的产生以及光降解。在底部，变化是极端的：DOC 增加了 5 倍（高达 50 mM），分子特征漂移到饱和、还原和非芳香 DOM，表明有机沉积物中存在强烈的微生物活动。在化变层，DOC 被保留下来，这表明该界面是一个在 DOM 处理方面具有高反应性的层。这些发现强调了东非大裂谷的咸水-碱性湖泊是碳处理热点，它们的研究可能会扩大我们对内陆水域碳循环的理解。
