Hypersaline endorheic aquatic systems (H-SEAS) are lakes/shallow playas in arid and semiarid regions that undergo extreme oscillations in salinity and severe drought episodes. Although their geochemical uniqueness and microbiome have been deeply studied, very little is known about the availability and quality of dissolved organic matter (DOM) in the water column.. A H-SEAS from the Monegros Desert (Zaragoza, NE Spain) was studied during a hydrological wetting-drying-rewetting cycle. DOM analysis included: (i) a dissolved organic carbon (DOC) mass balance; (ii) spectroscopy (absorbance and fluorescence) and (iii) a molecular characterization with Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). The studied system stored a large amount of DOC and under the highest salinity conditions, salt-saturated waters (i.e., brines with salinity > 30%) accumulated a disproportionate quantity of DOC, indicating a significant in-situ net DOM production. Simultaneously, during the hydrological transition from wet to dry, the DOM pool showed strong alterations of it molecular composition. Spectroscopic methods indicated that aromatic and degraded DOM was rapidly replaced by fresher, relatively small, microbial-derived moieties with a large C/N ratio. FT-ICR-MS highlighted the accumulation of small, saturated and oxidized molecules (molecular O/C > 0.5), with a remarkable increase in the relative contribution of highly oxygenated (molecular O/C>0.9) compounds and a decrease of aliphatic and carboxyl-rich alicyclic moleculesThese results indicated that H-SEAS are extremely active in accumulating and processing DOM, with the notable release of organic solutes probably originated from decaying microplankton under large osmotic stress at extremely high salinities.

高盐内流水系统 (H-SEAS) 是干旱和半干旱地区的湖泊/浅滩，在盐度和严重干旱事件中经历极端振荡。尽管对它们的地球化学独特性和微生物组进行了深入研究，但对水体中溶解有机物 (DOM) 的可用性和质量知之甚少。水文润湿-干燥-再润湿循环。DOM 分析包括： (i) 溶解有机碳 (DOC) 质量平衡；(ii) 光谱学（吸光度和荧光）和 (iii) 傅里叶变换离子回旋共振质谱 (FT-ICR-MS) 的分子表征。所研究的系统储存了大量的 DOC，并且在最高盐度条件下，盐饱和水（即原位净 DOM 生产。同时，在从湿到干的水文转变过程中，DOM 池显示出其分子组成的强烈变化。光谱方法表明，芳香和降解的 DOM 迅速被更新鲜、相对较小、具有大 C/N 比的微生物衍生部分所取代。FT-ICR-MS 突出了小分子、饱和分子和氧化分子（分子 O/C > 0.5）的积累，高氧化（分子 O/C>0.9）化合物的相对贡献显着增加，脂肪族和富含羧基的脂环分子这些结果表明，H-SEAS在积累和处理DOM方面非常活跃，有机溶质的显着释放可能源于在极高盐度的大渗透胁迫下腐烂的微浮游生物。