Low dissolved oxygen, or hypoxia, is a common phenomenon in ice-covered lakes in winter. We measured dissolved oxygen (DO) before, during, and after ice-over to characterize the timing, severity, and spatial variability of winter hypoxia in Upper Red Rock Lake, Montana, home to one of the last remaining lacustrine populations of endemic Montana Arctic Grayling (Thymallus arcticus). Unlike most previous investigations of winterkill-prone lakes, we observed considerable horizontal spatial variability in DO, a non-linear winter oxygen depletion rate, and lake-wide re-oxygenation 2–4 weeks prior to spring ice loss. Parts of the upper 1 m of the lake and near stream mouths remained well-oxygenated even during late winter. DO levels were strongly associated with maximum daily air temperature. Our analysis of a 28-year weather record revealed large interannual variability in risk of winter hypoxia, with a slight declining trend in winter severity (number of days with maximum air temperatures ≤ 0°C) in Upper Red Rock Lake. The approach we used in our study provides a useful framework for quantifying and mapping the seasonal dynamics of the extent and severity of winter hypoxia, and for identifying critical winter habitats.

中文翻译：

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影响淡水湖冬季缺氧的环境和气候因素：缺氧避难所和春季冰层流失前再充氧的证据

低溶解氧或缺氧是冬季冰雪覆盖的湖泊的普遍现象。我们在冰盖之前、期间和之后测量了溶解氧 (DO)，以描述蒙大拿州上红岩湖冬季缺氧的时间、严重程度和空间变异性，该湖是蒙大拿州北极地区最后剩余的湖泊种群之一格雷林（Thymallus arcticus）。与之前对易发生冬季死亡的湖泊进行的大多数调查不同，我们观察到 DO 的相当大的水平空间变异、非线性冬季氧气消耗率以及春季冰损失前 2-4 周的湖泊范围内的再充氧。即使在冬末，湖上 1 m 的部分和靠近溪流口的部分仍保持良好的含氧量。溶解氧水平与最高日气温密切相关。我们对 28 年天气记录的分析显示，冬季缺氧风险存在较大的年际变化，冬季严重程度（最高气温≤ 0°C 的天数）略有下降趋势。我们在研究中使用的方法为量化和绘制冬季缺氧程度和严重程度的季节性动态以及确定关键的冬季栖息地提供了一个有用的框架。