Dissolved oxygen (DO) concentration is a fundamental metric to describe climate-related alterations in deep lakes. Increasing water temperatures enhance thermal stratification, leading in temperate basins to a growing isolation of deep waters. This leads to the depletion of hypolimnetic DO, which adds up to limited nutrient circulation and restricted replenishment of the trophogenic layers. With vanishing convective mixing, it is commonly believed that the only source of hypolimnetic DO replenishment will be represented by deep intrusions of cold oxygenated waters from the tributaries. In this study, we first analyse the 1993–2020 long-term observed trends of DO concentrations in the subalpine deep oligomictic Lake Maggiore (Italy/Switzerland). Then, through an algorithm calculating daily intrusion depths and mass discharges of DO for the major tributaries, we show that deep insertions are suppressed for increasing winter water temperatures and residual thermal stratification. Turbulent entrainment is proved fundamental for DO replenishment, leading to mass discharges of DO released into the deep hypolimnion up to more than two orders of magnitude larger than the original ones from the tributaries. Last, we discuss the results of simulations made through a one-dimensional coupled ecological–hydrodynamic model about the possible effects of a full turnover on DO concentrations in the deep hypolimnion. Two cases are displayed, with the turnover taking place either now or with an anoxic hypolimnion deriving from decades of isolation due to severe climate warming. Through this study, climate warming is shown to be a fundamental driver of DO in Lake Maggiore, its depletion harming both water quality and the ecosystem.

溶解氧 (DO) 浓度是描述深湖气候相关变化的基本指标。水温升高会增强热分层，导致温带盆地的深水越来越孤立。这会导致低浓度溶解氧的消耗，从而导致营养循环受限和营养层的补充受限。随着对流混合的消失，人们普遍认为，低浓度 DO 补充的唯一来源将是来自支流的冷含氧水的深层侵入。在这项研究中，我们首先分析了 1993-2020 年长期观察到的亚高山深低聚马焦雷湖（意大利/瑞士）中 DO 浓度的趋势。然后，通过计算主要支流 DO 的每日侵入深度和质量排放的算法，我们表明，由于冬季水温升高和残余热分层，深层插入受到抑制。湍流夹带被证明是 DO 补充的基础，导致释放到深水层的 DO 的大量排放比支流的原始排放量大两个数量级以上。最后，我们讨论了通过一维耦合生态-水动力模型进行的模拟结果，该模型涉及完全周转对深潜层中溶解氧浓度的可能影响。展示了两个案例，要么是现在发生了更替，要么是由于严重的气候变暖而导致数十年的隔离导致缺氧低潮。通过这项研究，