Long-chain diols (LCDs) are lipids commonly found in freshwater environments. They are produced in lake waters and in low water-flow regions of rivers but their sources and the controls on their abundance are poorly constrained. To be able to use LCD as environmental proxy (e.g. for reconstructing lake temperature and as a freshwater indicator in marine systems) we need to understand the sources of these LCDs and the processes controlling their abundance and distribution. Therefore, we performed a seasonal study of suspended particulate matter in Lake Geneva, a temperate lake at the border of France and Switzerland in 2017–2018. LCDs were most abundant in lake surface water from late spring to early autumn, coinciding with the thermal stratification of the water column. Their distribution varied throughout the year, which points towards multiple producers. Incubation of lake water with ¹³C-labelled bicarbonate only showed uptake of inorganic carbon in LCDs during their peak seasonal abundance. An 18S rRNA gene amplicon analysis revealed that eustigmatophytes, known producers of LCDs, are present in Lake Geneva and show the same seasonal trend in abundance as the LCDs, indicating that these algae are likely the most important producers of LCDs in this lake. In combination with previous studies our results suggest that LCDs show potential to trace changes in lake water-column stratification, and validate the use of the C₃₂ 1,15-diol as a proxy for freshwater input from rivers and lakes in marine sediments.

长链二醇（LCD）是在淡水环境中常见的脂质。它们是在湖泊水域和河流水流量低的地区生产的，但其来源和丰度控制受到严格的限制。为了能够将LCD用作环境代理（例如，用于重建湖泊温度和用作海洋系统中的淡水指示器），我们需要了解这些LCD的来源以及控制其丰度和分布的过程。因此，我们对日内瓦湖（2017-2018年位于法国和瑞士交界的温带湖泊）的悬浮颗粒物进行了季节性研究。从春季末到初秋，LCD在湖面水中含量最高，这与水柱的热分层相吻合。他们的分布全年变化，指向多个生产者。与湖水孵化¹³ C标记的碳酸氢盐仅在LCD的峰值季节丰度期间显示出对无机碳的吸收。18S rRNA基因扩增子分析显示，已知的LCD的生产者洋桔梗存在于日内瓦湖中，并且与LCD相比显示出相同的季节性变化趋势，这表明这些藻类可能是该湖中LCD的最重要的生产者。与先前的研究相结合，我们的结果表明LCD可以显示出湖泊水柱分层变化的潜力，并验证了使用C ₃₂ 1,15-二醇作为从海洋沉积物中河流和湖泊输入的淡水的替代物的潜力。