Monday, January 30, 2012

Insights about Minnesota lakes: implications about Third Sister Lake

Hopefully, no one is naive to the fact that this winter's temperatures have been far above the long-term average. In fact, although we reached a low of 10F (well below the mean temperature for the night of Jan 29/Jan 30), the trend for most the entire previous week was that of above-average daytime and nighttime temperatures (and 20 of the previous 30 days in January have been above average, too, and today through February 4 is supposed to be not only above average - which is a daytime high temp of 28F - but above freezing, too).

This has meant many things for the forest, but it has meant a very critical thing for Third Sister Lake: the ice cover this year remains un-set: a small open pool remains toward the center of the lake, filling in only when temperatures stay below freezing, but opening again once the snows melt (and the rain falls). It is with this reality in mind that I was interested to read this story from Greg Laden's Blog titled, "Global Warming is Ruining Minnesota Winter".

In the post, Greg points out a few things about Minnesotan lakes that appear to generally hold true for Third Sister Lake as well:
Since the water is cold at the time of freezing, there is more oxygen in some of the lakes than there might otherwise be. Since some of the lake surface is covered with ice but not a thick layer of snow, sunlight gets into the lakes during the winter promoting photosynthesis in the algae living beneath the ice, which enhances oxygen supply. The occasional break-through of ice during the winter, if there is a warm up and sufficient wind, adds additional oxygen.

Meanwhile, if the ice gets thick fast and stays thick, fishermen and women can ice fish early, often, and well into the season. Many Minnesota lakes sport regular fish contests and festival's during the winter that depend on this thick ice.
Third Sister Lake has seen similar trends over the past couple of years, being able to literally support some illegal ice-fishing on the lake. Last year's ice sheet was quite thick and stayed set up well into March (and the ice didn't go away until April). However, there was also a lot of snow; the 8th most snow recorded in Ann Arbor. In some Minnesotan lakes, high levels of snow actually led to fish die-offs:
In recent years, there have been some changes owing to global warming. In a warmer world, there will be some years (but certainly not all) where Minnesota experiences much more snow than it used to. This happened last year. Some lakes had so much snow on them last year that the algal activity was stifled and there was less oxygen in the water, and so those lakes experienced large die-offs of fish. Die-offs happen every year in some lakes, but it seems that the extra snow may have caused more fish to die than usual.
Luckily for the bass and bluegill, this didn't happen in Third Sister Lake, despite the additional snow in the region (although a die-off of Gizzard Shad did occur elsewhere in Southeast Michigan). This could have been due to the existence of groundwater seeps into Third Sister Lake, but this is merely conjecture on my part.

While we cannot definitively say that the 2010-2011 winter's snowfall was caused by global warming, scientists do recognize that, under conditions of global warming, greater amounts of snowfall is expected in regions where snowfall is possible, such as the upper Midwest. (For an explanation as to why, check out this article from Feb 2010.)
In warmer years, such as we are experiencing this winter (and in many previous winters) the lack of thick ice has caused numerous accidents and even fatalities as Minnesotans wandering around on insufficiently frozen lakes, falling in now and then. This, to me, is the ultimate form of Global Warming Denialism. One ignores through ignorance, or willful ignorance, the obvious change in our climate and as a result dies. The number of people falling through ice and drowning in Minnesota seems to be on the rise (though even with increased numbers, the quantities are small enough that a statistical test may be impossible). An excellent indicator of the increased dangers of ice with global warming can be found in what is happening with fishing contests. Contests on lakes in the central part of the state have been repeatedly canceled, and in the case of the Big Lake contests, permanently abandoned as an activity after being canceled several years in a row. In other words, global warming has caused Big Lake to no longer reliably freeze. It's simply a new reality. 
Third Sister Lake has not - yet - set up. There remains a small hole toward the center of the lake, which opens up when the weather climbs above freezing and especially when there is rainfall. It could cause problems not only for the illegal ice-fishers, but also for the ecology classes that come out in February.

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