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

Michael N Davis,Thomas E Mcmahon,Matthew E Jaeger,Kyle A Cutting

doi:10.1007/s10750-020-04382-z

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.

Highlights

Low dissolved oxygen (DO), or hypoxia, is a common and widespread phenomenon in ice-covered lakes in winter (Greenbank, 1945; Agbeti & Smol, 1995; Hasler et al, 2009)
Our study focused on Upper Red Rock Lake, Montana, a shallow, eutrophic, high-elevation lake with high potential for development of hypoxia during winter ice cover (Gangloff, 1996)
The extent of ice cover was uniform across the lake except around intermittent, small openings (\ 100 m2) at the mouth of Elk Springs, Red Rock, Shambow, and Grayling creeks

Summary

Introduction

Low dissolved oxygen (DO), or hypoxia, is a common and widespread phenomenon in ice-covered lakes in winter (Greenbank, 1945; Agbeti & Smol, 1995; Hasler et al, 2009). The onset of ice cover begins a period of physical separation of water and the atmosphere, which slows or halts processes that replenish DO. Ice and snow cover prevents oxygenation of lake water by diffusion and aeration, slows convective mixing, and reduces the amount of light available for photosynthetic production of oxygen by algae and submerged vegetation (Welch & Kalff, 1974; Malm et al, 1998; Terzhevik et al, 2009). Photosynthesis and DO production may continue to occur if light can still penetrate ice and snow cover. The winter oxygen-limiting period ends with the breakup of lake ice in spring (Barica & Mathias, 1979)

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