Environmental and climatic factors affecting winter hypoxia in a freshwater lake: evidence for a hypoxia refuge and for re-oxygenation prior to spring ice loss

Abstract

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.

Dissolved Oxygen in a Shallow Ice-Covered Lake in Winter: Effect of Changes in Light, Thermal and Ice Regimes

“…We assume that the most likely reason for this increase may be the release of oxygen as a result of photosynthesis of phytoplankton. Aquatic ecosystems can have high productivity in winter [21,30,59,60]; consequently, some increase in DO content due to photosynthesis of phytoplankton can be expected [11,12,14].…”

Near‐bed stratification controls bottom hypoxia in ice‐covered alpine lakes

“…Therefore, in many ice‐covered lakes, the near‐bottom oxygen concentration decreases for most of the wintertime, sometimes down to the point that bottom waters become hypoxic (Mathias and Barica 1980; Malm et al 1998; Stefanovic and Stefan 2002). The vertical extent of the hypoxic layer and duration of hypoxia determine the availability of oxic refuges for many organisms actively overwintering under the ice (Davis et al 2020) and, over the long‐term, shape biological communities according to their abilities and adaptations to low ambient DO conditions (Magnuson et al 1985). With oxygen depletion, microbial metabolism shifts to other electron‐acceptors, modifying the partitioning and concentrations of major elements (N, C, S, P, Fe) under the ice, with potentially far‐reaching consequences for the following open water season (Gammons et al 2014; Kincaid et al 2022).…”