Last weekend, after giving a talk on the dynamics of snow and the animals that depend on it to survive cold winters at the Appalachian Mountain Club's Pinkham Notch Visitor Center, I stopped to admire the river flowing along Route 16.

This is the Ellis River, a tributary of the Saco River that originates at the height of land in Pinkham Notch, fed by snow from Tuckerman's Ravine. There is a trail across the road from the Visitor Center which cuts across two beaver ponds up there. One pond drains into the Ellis River, and the other drains into the Peabody River, which will eventually make its way into the Androscoggin. If you are ever up there, I highly recommend walking across the road and out to the beaver ponds. How often does one have the opportunity to stand at the headwaters, the origin points, of two separate river systems?

Animal adaptations were on my mind. I had ended my talk with a discussion of what we currently understand about how the rapidly changing winter weather in New England will affect wildlife during this extremely challenging season. Most of the species I covered rely on a deep, stable snowpack, which they could use for insulation. Too much warmth and rain in winter reduces the ability of the snowpack to insulate. I realized I hadn't even considered how a changing climate would affect aquatic life. How much do the residents of these upland streams rely upon snow or ice in the winter?

In a relatively recent review ("The Ecology of River Ice" by Thellman et al, JGR Biogeosciences, August 2021), the authors note that much of what we currently know of the dynamics of ice and river ecology comes from studies of fish in lakes and large rivers. They also noted more work needs to be done on smaller streams, particularly during winter months. So, there isn't going to be an easy answer to the question: How will the warming of New England affect life in these streams? What we do know certainly enhanced my appreciation of the life of animals in these streams, from tiny macroinvertebrates like the ubiquitous black fly larvae to small fish (young brook trout, for example).

Ice can be beneficial (e.g. insulating) and disruptive (e.g. limiting space or increasing current). Most of us know that aquatic organisms rely on ice floating instead of sinking to maintain open, livable, water at the bottom of large lakes and rivers. This dynamic gets more complicated in rivers, which can be shallow, have faster currents, and can sometimes freeze solid, depending upon the size of the river.

According to Thellman, "...fish tend to choose winter habitats to minimize energy expenditure and avoid adverse conditions such as ice jams, high flows, and low oxygen." Ice in a river can limit safe areas, refugia, for fish and other critters by simply limiting available space as well as causing an increase in current where flowing water is concentrated by ice. Ice (particularly when snow-covered) can also block incoming light, negatively affecting photosynthetic organisms and visual predators. On the other hand, ice insulates aquatic organisms from extreme weather events and can even act as a substrate for aquatic life to attach to or harbor beneath. To make things even more complicated, many of these effects vary according to river size and location.

Thellman notes that in small rivers especially, "ice jams reduce flow and form pools that can provide temporary habitat for organisms... However, under disrupting conditions (ice formation, freeze-thaw cycles, and breakup), ice and snow can scour or rearrange habitats, impede light, and alter riverine flow paths. The duration that ice-covered rivers spend in either stabilizing conditions or disrupting conditions varies by river size, orientation, and will likely change as winter temperatures continue to rise and winter whiplash events become more frequent."

The Ellis River had a beautiful thick layer of snow and ice. I left Pinkham Notch early to avoid the predicted rain and warming temperatures. This has happened a couple of times already this year, freezing cold and snow followed by unseasonable warmth and rain. This is what "winter whiplash" refers to - relatively rapid shifts between very different weather conditions. While research is ongoing into just how these destabilizing forces will affect our local rivers and streams, they certainly are not the best of conditions for those of us who love long, uninterrupted winters.

Susan Pike, a researcher and an environmental sciences and biology teacher at Dover High School, welcomes your ideas for future column topics. Send your photos and observations to [email protected]. Read more of her Nature News columns online at Seacoastonline.com and pikes-hikes.com, and follow her on Instagram @pikeshikes.