Environmental and climatic factors affecting winter hypoxia in a freshwater lake: evidence for a hypoxia refuge and for
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PRIMARY RESEARCH PAPER
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
. Kyle A. Cutting . Matthew E. Jaeger
Received: 26 March 2020 / Revised: 7 July 2020 / Accepted: 10 August 2020 Ó The Author(s) 2020
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 B 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.
Handling editor: Pauliina Louhi
Keywords
M. N. Davis T. E. McMahon Fish and Wildlife Ecology and Management Program, Ecology Department, Montana State University, Post Office Box 173460, Bozeman, MT 59717, USA
Introduction
Present Address: M. N. Davis (&) American Rivers, 2150 Allston Way, Suite 320, Berkeley, CA 94704, USA e-mail: [email protected] K. A. Cutting U.S. Fish and Wildlife Service, Red Rock Lakes National Wildlife Refuge, 27650B South Valley Road, Lima, MT 59739, USA M. E. Jaeger Montana Department of Fish, Wildlife and Parks, 730 North Montana Road, Dillon, MT 59725, USA
Winter Hypoxia Grayling
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
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Hydrobiologia
algae and submerged vegetation (Welch & Kalff, 1974; Malm et al., 1998; Terzhevik et al., 2009). If ice cover persists for a sufficient duration, the consumption of oxygen by microbial decomposition of dead and decaying organic matter and by absorption from bottom
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