2015 Student Writing Contest: WINNER
Michelle Lavery, E-mail: lavery.j.m@gmail.com
For many hydrologic regimes of the world, streams and rivers are ice covered for the majority of the year, yet minimal research is conducted during this period compared with the more “researcher-friendly” open-water water period. Without a doubt, scientific progress is hampered by the logistical difficulties and high cost associated with conducting “winter” research. (Prowse, 2001 [part II])
It seems as though every winter ecology paper contains some variant of this sentiment—we know that winter is important, but we’re not crazy enough to study it. As researchers, we’ve built sampling regimes that ignore an entire season because winter is considered harsh and unforgiving. It’s cold, sharp, and sometimes deadly to us, and so we operate under the assumption that the same goes for the creatures we study.
Alas, it is not so. There’s a lot going on under the snow, and even more going on under the ice. For example, Atlantic Salmon Salmo salar eggs incubate in the gravel under river ice in Eastern Canada for six frigid, snowy months at water temperatures barely above freezing. They emerge from the gravel during the spring melt period, when ice jams bulldoze forests and water levels climb meters in minutes. These tiny fish are at the mercy of a dynamic and unpredictable season, yet we barely know anything about it.
As a pampered girl from “tropical” Toronto, I never imagined myself riding a snowmobile and hacking through river ice in the middle of the woods. However, through a serendipitous connection, I recently found myself doing both—while pursuing a master’s degree supervised by Richard Cunjak at the Canadian Rivers Institute.
In Eastern Canada’s Miramichi River system, salmon eggs incubate in the gravel riverbed from late October to early May, during which time they experience highly variable winter conditions. In November, air temperatures can drop dramatically overnight (usually to about -20°C or -4°F), causing water to reach its freezing point quickly and inconsistently. As water crystallizes, it can stick to itself and the river substrate, forming anchor ice—a squishy carpet of ice crystals on the riverbed. If this ice forms on top of salmon nests (or “redds”), it can block water flow through the gravel and alter the temperature and dissolved oxygen levels surrounding the developing eggs.
Once full ice cover forms and surface runoff is locked up in the snowpack, long-residence groundwater may be the major contributor to river discharge. “Long-residence” groundwater refers to water that has spent a considerable amount of time in an aquifer deep underground. Consequently, it is often warmer than the surface water in the winter, and can have significantly lower dissolved oxygen concentrations (since it has not been recently aerated). As this groundwater seeps through the river substrate, the conditions in salmon redds can change dramatically. Depending on the size of the seep, eggs may develop faster due to warmer water temperatures and require more oxygen to sustain this accelerated rate of development. However, the oxygen-poor groundwater is usually unable to meet their biological demands. Without enough oxygen, these eggs may die or experience “sub-lethal” effects—onsequences that may impact their survival later in life as free-swimming fish. These may include stunted growth or developmental deformities that may impair gas exchange, swimming ability, neurological function, etc.
During the spring melt period, silt and clay can be eroded into rivers by the surface runoff water. Depending on the grain size, these sediments may clog the egg membrane and prevent diffusion of oxygen to the embryo, effectively suffocating the fish. Furthermore, as ice breaks up and moves out of rivers, scour along the riverbed may significantly disturb the gravel and damage the embryos underneath.
It is hard to believe, after considering all of the variation inherent in winter and its potential effects on one life stage of one species in one type of habitat, that winter goes largely unnoticed in the scientific literature. It is, certainly, a challenging season to research. I’ve had my fair share of winter mishaps, including digging a snowmobile out of a slush puddle for three hours, miscalculating ice thickness (not ideal!), hypothermic near-misses, and tethering myself to a tree during the spring melt. However, if we can get past our numb fingers and dripping noses, there’s a whole season waiting to be studied. One could argue that winter research is the last true frontier of freshwater ecology—there are so many unknowns to explore, and so many questions left unanswered. It might not be a “researcher-friendly” season, but it’s definitely exciting! Plus, who doesn’t love a good mid-river snowball fight?
REFERENCE
Prowse, T. D. 2001. River-ice ecology. 2: Biological aspects. Journal of Cold Regions Engineering 15:17-33.
RELATED MATERIALS
Cunjak, R. A., T. D. Prowse, and D. L. Parrish. 1998. Atlantic Salmon Salmo salar in winter: “the season of parr discontent”? Canadian Journal of Fisheries and Aquatic Sciences 55(1):161-180.
Flanagan, J. J. 2003. The impacts of fine sediments and variable flow regime on the habitat and survival of Atlantic Salmon Salmo salar eggs. Master’s thesis: University of New Brunswick, Fredericton.
Greig, S. M., D. A. Sear, and P. A. Carling. 2005. The impact of fine sediment accumulation on the survival of incubating salmon
progeny: Implications for sediment management. Science of the Total Environment 344(1-3):241-258.
Kane, T. R. 1988. Relationship of temperature and time of initial feeding of Atlantic Salmon. Progressive Fish-Culturist 50:93-97.
Louhi, P., M. Ovaska, A. Maki-Petays, J. Erkinaro, T. Muotka, and J. Rosenfeld. 2011. Does fine sediment constrain salmonid alevin development and survival? Canadian Journal of Fisheries and Aquatic Sciences 68(10):1819-1826.
Malcolm, I. A., S. M. Greig, A. F. Youngson, and C. Soulsby. 2008. Hyporheic influences on salmon embryo survival and performance. Pages 1-24 in D. A. Sear and P. DeVries, editors. Salmonid spawning habitat in rivers: physical controls, biological responses, and approaches to remediation. American Fisheries Society, Symposium 65, Bethesda, Maryland.
Malcolm, I. A., C. Soulsby, A. F. Youngson, D. M. Hannah, I. S. McLaren, and A. Thorne. 2004. Hydrological influences on hyporheic water quality: implications for salmon egg survival. Hydrological Processes 18(9):1543-1560.
Malcolm, I. A., C. Soulsby, A. F. Youngson, and D. M. Hannah. 2005. Catchment-scale controls on groundwater-surface water interactions in the hyporheic zone: implications for salmon embryo survival. River Research and Applications 21(9):977-989.
Malcolm, I. A., C. Soulsby, A. F. Youngson, and D. Tetzlaff. 2008b. Fine scale variability of hyporheic hydrochemistry in salmon spawning gravels with contrasting groundwater-surface water interactions. Hydrogeology Journal 17(1):161-174.
Malcolm, I. A., A. F. Youngson, and C. Soulsby. 2003. Survival of salmonid eggs in a degraded gravel-bed stream: effects of groundwater-surface water interactions. River Research and Applications 19(4):303-316.
Prowse, T. D. 2001. River-ice ecology. 1: hydrologic, geomorphic, and water-quality aspects. Journal of Cold Regions Engineering 15:1-16.
Soulsby, C., A. F. Youngson, H. J. Moir, and I. A. Malcolm. 2001. Fine ediment influence on salmonid spawning habitat in a lowland agricultural stream: a preliminary assessment. Science of the Total Environment 265(1-3):295-307.
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