THROUGH THE WOODS: Life under the ice

IT IS INTERESTING TO KNOW what happens to different life forms during winter and what happens to them in different environments, in particular bodies of water. In summer we spend time swimming, fishing and generally enjoying time around our lakes and ponds. These areas teem with life, with various plants, fish, amphibians, reptiles and insects. Once temperatures reach freezing, almost everything disappears from view except the warm-blooded animals like rabbits, deer, squirrels and, of course, the birds.

Interestingly, back in the Middle Ages people thought the birds disappeared into the mud for the winter. They did not understand that birds migrate. So where has everything gone and what is happening below the water’s surface? As temperatures decrease the surface of the water eventually reaches its maximum density at about 39 degrees F. This heavier water sinks down to the bottom and eventually the water temperature is nearly the same throughout, as the ice, which is less dense, covers the surface. Just below the ice is a thin layer of slightly warmer water that contains more oxygen.

At this stage, a lake is said to be stagnant. The cold water looks clear and transparent because algae and other small life forms have died off and gone to the bottom, and those few still remaining reproduce slowly because of the low temperature and lack of sunlight. Some things go into a sort of hibernation or inactivity until temperatures begin to rise in the spring.

Turtles burrow into the mud and slow their heart rates until their heartbeat is difficult to detect. Some may change the composition of their blood so it doesn’t freeze. The snapping turtle can take in oxygen from the water through the skin lining their throats. Amazingly, painted turtles have altered their metabolism and can survive up to three months without oxygen. Painted turtles may surface during warm periods in the winter but if they stay out as temperatures rapidly drop below freezing they may die.

Frogs are amphibians and need to take in oxygen through their skin. Aquatic frogs such as the leopard and American bullfrogs also go to the bottom of a body of water and lie on top of the mud so they can get more oxygen. They may also slowly swim about from time to time. Terrestrial frogs (such as wood frogs and spring peepers) and toads can form antifreeze in their bodies and may burrow deep into the soil, into crevices, or into the leaf litter. Wood frogs can freeze and then thaw out and come back to normal.

Salamanders such as the spotted salamander (about 7” long, usually black with yellow spots) will breed and lay their eggs in water but spend most of the warm weather in the woods. Tracking technology has improved and miniaturized so was used to show that they follow tunnels and burrows of animals such as shrews and chipmunks. They do not survive freezing conditions so find burrows that go deep underground for the winter. Another common salamander is the eastern newt which overwinters in ponds and remains active. A woman in Vermont noted an open area at the edge of a pond where several of these greenish-spotted newts were swimming around together while she was bundled up against the cold.

Our northern water snakes spend warm weather in or near water and spend their winters in underground dens in rock crevices with other snakes, have been found in wells, and often stay in beaver and muskrat lodges. Insects can stay in water during the winter in their nymph stage or as eggs and go to the next stage of their cycle in the spring.

Cattails and wild irises and other plants die back while their roots, corms and rhizomes rest in the mud until warmer water and sunlight coax them to grow new shoots in spring. Fish remain active in cool water. When it gets down to 39 degrees and lower they slow down and can die near the freezing point. Thick ice with snow cover reduces sunlight to the water and cuts off oxygen. If there is low oxygen and a lot of rotting vegetation fish kills may be large. Oxygenated, flowing water that enters a body of water can counteract this problem and fish may be drawn to this area. Shallow ponds may have the most problems and a bubbler may have to be added to keep part of the water surface open for the fish.

I love our ponds in summer, and in winter think of what life is lurking below the ice, and look forward to the promise of life returning in spring.

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