Turning Tides, Turning Seasons part 2: Winter

This piece is the second installment of a year-long project that will detail the seasonal changes that occur in and around Lake Champlain. Throughout the 4 piece series, Turning Tides, Turning Seasons will not only examine the “how” and “why” behind these natural changes, but also ask an urgent question: “how are Lake Champlain’s yearly cycles impacted by our rapidly changing climate and landscape?”

For millennia, the freezing of Lake Champlain was a phenological certainty that created the basis for winter recreational activity and cultural practices within the basin. Throughout New York and Vermont, people engaged in ice fishing and ice harvesting, and even used the frozen lake as a public thoroughfare, up until the 20th century. However, the mid-1900s marked a period of transition. During this time, Lake Champlain began to show delayed freeze-up dates, and in certain years, it didn’t freeze over at all. Currently, Lake Champlain freezes roughly once every five years, and projections show that this may dwindle to a single freeze-over per decade by 2050. As warmer, more unpredictable winters become the new norm, Vermont locals have already begun to adapt. However, the transition for those who live under the ice may be less forgiving.

Decreased ice changes the “reverse stratification” event that occurs on large lakes during winter. During cold months, ice floats on top of the lake’s surface while covering warmer water below. Reduced or non-existent ice-cover reverses the positive effects of winter stratification by increasing evaporation, lake temperature, and sun exposure. Since ice is highly reflective, it plays an important role in refracting sunlight during the winter. Across major water bodies, a general decrease in ice-cover has the potential to increase global temperatures through more heat absorption from open water. At the same time, decreased ice cover and increased rain events can directly affect Lake Champlain’s natural cycling and habitat suitability for various species' ecological timing.

For creatures who inhabit the surrounding area, the changing season quietly rearranges the world they depend on, affecting everything from the timing of spring emergence to the stability of winter shelter. In the depths of Lake Champlain, leopard frogs hibernate at the bottom of the lake floor, relying on dissolved oxygen to survive the winter. Meanwhile, in shallow waters, female trout lay hundreds of eggs that incubate in the rocky substrate until the springtime. Like most creatures who inhabit Lake Champlain, these two species are cold blooded, which means that their internal body temperature is regulated by the surrounding environment. In this way, warmer winters may result in altered animal activity and hibernation events. Additionally, more winter rain events have the potential to scour streambeds, killing eggs, larvae, and adult fish. This might be especially problematic for burbot, one of the few predatory fish that are active during winter, as they move into rivers to spawn.

Warmer winters also affect nutrient dynamics. Historically, ice and snow acted as a natural barrier, keeping phosphorus, chloride, and other materials locked in place for months at a time. Now, increased winter snowmelt, rain, and “rain-on-snow” events make the surrounding environment porous, allowing excess nutrients to leech into Lake Champlain. Preliminary data from a study supported by the Lake Champlain Basin Program indicate that 15-55% of the annual phosphorus loads into Lake Champlain occur during the winter, a higher percentage than previous models projected. The mobilization of phosphorus during the winter will likely continue to intensify algal blooms during warmer months.

Chloride, another mobilized nutrient, is also deposited into Lake Champlain in high quantities during winter. The heavy application of road salt (which is composed of ~60% Chloride) to roads, driveways, and sidewalks reaches Lake Champlain through direct runoff or by seeping into groundwater. Chloride is toxic to aquatic biota, and has been known to decrease the biodiversity of fish and plant communities. Amphibians in the Champlain Basin are particularly vulnerable, as they absorb pollutants through their skin, leading to dehydration and impaired water balance. For wood frogs, data shows that exposure to road salt can even skew their male-to-female ratio, which could threaten long-term reproductive success. Also of concern is zooplankton reproduction, as they require freshwater to successfully hatch their eggs.

Increased salinity in freshwater ecosystems can also affect mixing events, since saltwater is denser than fresh water. If a significant concentration of salt enters a freshwater system, a dense, salty layer will form at the bottom of the lake floor. Immune to the pressures of seasonal stratification, this layer will remain a permanent deoxygenated (and thus uninhabitable) fixture in Lake Champlain. Since 1990, chloride in Lake Champlain has steadily risen to 15 mg/L. Though this is below the 230 mg/L toxicity threshold, chloride continues to accumulate year to year. According to Missouri's department of natural resources, “one teaspoon of salt permanently pollutes five gallons of freshwater.”

These shifts reverberate far beyond aquatic life and are beginning to influence the broader ecological community and the people who share the basin. Winter is starting to function less as a dormant season and more as a period of quiet environmental transformation. That reality shows just how tightly Lake Champlain’s health is linked to human decisions. Yet it also signals a place where collective choices matter. Small adjustments like substituting sand or alternative de-icers when conditions allow, and calibrating spreading equipment to avoid over-application of salt, can reduce environmental stress on wintering lakes. These shifts, multiplied across states, will prove that the future of Lake Champlain’s health is not just shaped by the climate, but by the stewards who care for it.