The concentration of dissolved oxygen in aquatic systems helps to regulate biodiversity^1,2, nutrient biogeochemistry³, greenhouse gas emissions⁴, and the quality of drinking water⁵. The long-term declines in dissolved oxygen concentrations in coastal and ocean waters have been linked to climate warming and human activity^6,7, but little is known about the changes in dissolved oxygen concentrations in lakes. Although the solubility of dissolved oxygen decreases with increasing water temperatures, long-term lake trajectories are difficult to predict. Oxygen losses in warming lakes may be amplified by enhanced decomposition and stronger thermal stratification^8,9 or oxygen may increase as a result of enhanced primary production¹⁰. Here we analyse a combined total of 45,148 dissolved oxygen and temperature profiles and calculate trends for 393 temperate lakes that span 1941 to 2017. We find that a decline in dissolved oxygen is widespread in surface and deep-water habitats. The decline in surface waters is primarily associated with reduced solubility under warmer water temperatures, although dissolved oxygen in surface waters increased in a subset of highly productive warming lakes, probably owing to increasing production of phytoplankton. By contrast, the decline in deep waters is associated with stronger thermal stratification and loss of water clarity, but not with changes in gas solubility. Our results suggest that climate change and declining water clarity have altered the physical and chemical environment of lakes. Declines in dissolved oxygen in freshwater are 2.75 to 9.3 times greater than observed in the world’s oceans^6,7 and could threaten essential lake ecosystem services^2,3,5,11.

水生系统中溶解氧的浓度有助于调节生物多样性^1,2、营养生物地球化学³、温室气体排放⁴和饮用水质量⁵。沿海和海水中溶解氧浓度的长期下降与气候变暖和人类活动有关^6,7，但对湖泊中溶解氧浓度的变化知之甚少。虽然溶解氧的溶解度随着水温的升高而降低，但长期的湖泊轨迹很难预测。变暖的湖泊中的氧气损失可能会因分解增强和热分层增强而加剧^8,9或者由于初级生产的增加，氧气可能会增加¹⁰. 在这里，我们分析了总共 45,148 个溶解氧和温度分布，并计算了 393 个温带湖泊从 1941 年到 2017 年的趋势。我们发现溶解氧的下降在地表和深水栖息地普遍存在。地表水的减少主要与较高水温下溶解度降低有关，尽管在高产的变暖湖泊的一个子集中，地表水中的溶解氧增加，这可能是由于浮游植物产量的增加。相比之下，深水的下降与更强的热分层和水透明度的丧失有关，但与气体溶解度的变化无关。我们的研究结果表明，气候变化和水清澈度下降已经改变了湖泊的物理和化学环境。淡水中溶解氧的下降幅度为 2。^6,7并可能威胁到基本的湖泊生态系统服务^2,3,5,11。