Warner Corner - December 2008
Did You Catch the Change?
Ron Lawrenz, Director
It was late November and as I made my morning commute to the Warner Nature Center it became evident that today, despite what the calendar and others might say, would be my personal choice for the start of winter. It was the first morning of the season to bring calm winds and single digit temperatures to the region, and my focus was riveted on a singular overnight change in the landscape. As the low, post-dawn sunlight raked across the surface of lakes and ponds it revealed a hard stillness where there had been ripples and motion just yesterday. The reflection of last night's sunset was now replaced with the cold, steely look of bare ice. It was "ice up".
It should be no surprise; after all, it is that time of year and the signs had been appearing for a few weeks now. The smaller, shallower wetlands were progressively icing over and even the deeper lakes were encircled in a rim of ice as the air and water temperatures inexorably trended downward. I am a water geek, having lived on, played in, and studied water, and the things that live in it, for most of my life. I knew that this change was inevitable, that it had to come. Yet every year, like someone who has lost track of the time, I seem to get caught off guard when it finally happens.
I must also confess to being a seasonal clock-watcher of sorts, and I know that I'm not alone. Many dedicated observers faithfully record both ice up and ice out on their favorite lakes. Perhaps they use it like I do, as a milepost for the progression of seasons and life. However, the reason isn't as important as the fact that they are searching for answers, and inquiry needs no other reason than curiosity.
Ice up has held my interest all these years because I am aware of the serious and irreversible processes that it sets in motion. Like a lid on a canning jar, last nights ice has separated and sealed the lakes and ponds from a lifeline connection to air and light, and thus life-giving dissolved oxygen. Without adequate oxygen dissolved in the water many aquatic organisms, but most notably fish, would die before spring.
We euphemistically refer to this dissolved oxygen depletion and fish kill as a "freeze out". In reality, it has much more to do with life than death, for it is also a wonderful story of natural selection and adaptation. Have you ever wondered why shallow lakes tend to be dominated by Black Bullheads and not Walleyes? The simple answer is that, unlike Walleyes, the Black Bullhead has evolved to withstand very low oxygen levels and thrives in the absence of competition from less tolerant species.
Many factors can play a role in freeze out, and it's dangerous to generalize, but the most straightforward, and probably most important, reason is water depth and volume. First, it is important to know that, even in the best of conditions, water can only hold very limited quantities of dissolved oxygen. A deep lake holds a larger volume of water than a shallow lake with similar surface area. That means that deep lakes hold or "store" more total dissolved oxygen from the get go. The reverse is true for shallow lakes. Deeper lakes also tend to only have plants growing near the shore while shallow lakes typically have aquatic plants growing over most of the lake bottom. This becomes important in winter when the plants die back and decompose, consuming oxygen in the process. Thick snow cover is another important factor because it reduces light levels below the ice, stopping oxygen producing photosynthesis and killing the plants, which then, ironically, end up consuming oxygen.
As I near the entrance to the nature center and look out across East and West Boot Lakes I am pleased to have once again been witness to this overnight change. Until spring removes the cover of ice, I will continue to wonder what winter has wrought for those sealed below. It's not a deathwatch because I know that some life will emerge because life is tenacious, always adapting to survive on the edge of what is possible. That is the hope life brings and a reason to celebrate change this day, this season.
