The outside air is crisping up, snow is starting to fall and the winter layers are coming out of storage. The larches are losing their needles, the last of the migrating birds are flying over and nature seems inclined for rest. Now, we look forward to the lakes freezing over so we can fully embrace the pleasures of winter!
Most lakes and ponds don’t completely freeze through top to bottom. The layer of ice and snow insulates the water below allowing for overwintering habitat for fish and aquatic organisms. Also, thanks to ice being less dense than water, ice floats at the surface of lakes. If that
wasn’t the case, there would be no habitat for underwater living organisms. While the freezing point for water is zero degrees celsius, the under-ice temperatures are usually below 4 degrees celsius. In summer, water is usually warmer at the surface and becomes cooler as depth increases. In winter, a reverse pattern forms where it is coolest and less dense at the surface and as you go deeper, it gets warmer and thus, more dense, sinking to the bottom. These seasonal elements are essential for sustaining aquatic life throughout the seasons.
How does everything and everyone prepare for the frozen months? Starting at the surface, most aquatic insects remain active under ice, in their larvae or nymph stage, feeding at the bottom in the sediment. Once the ice melts, insects such as stoneflies, dragonflies and mayflies emerge out of the water as adults. Other surface dwelling insects hibernate, finding shelter in grasses, leaves and under stones.
Now, how about that underwater jungle that grew into a vibrant green over summer? Aquatic plants die back over winter because the ice blocks plants from receiving enough sunlight to continue growing. However, like perennials, their root systems remain intact and store energy, ready to produce new growth in the spring. Without the plants photosynthesizing, oxygen supplies are low over winter. So what happens to the fish who depend on dissolved oxygen to survive?
Fish have developed adaptations to survive in cold, low-oxygen environments. Some fish move to areas with slightly higher oxygen levels, such as inlets, edges of lakes, or near the ice surface. However, just below the ice, the water is coldest, where fish risk hypothermia. To combat the cold environment fish conserve energy by entering a state of semi-dormancy where they slow their metabolism, limit movement, breathing rate and primary bodily functions. On the other hand, there are some fish like Trout, who thrive in cold waters, increasing their activity and breathing to stay warm and actively feed through the winter despite the scarce resources. These active fish often become an easy target for ice fishing!
This delicate balance between all these creatures and their environment showcases the interconnectedness and complexity of nature, highlighting the resilience of natural systems to persist in harsh conditions.
