Sometimes they are called amateur observers or citizen scientists or sometimes naturalists. These are people who make observations of the relationships between organisms and their environments, as well as how those relationships change over time. The late John Popa, my brother-in-law, was one of these people. He had an intense curiosity about many things including the natural world. John was always watching for turtle nests and counting the days until the hatch, watching the eagles eat bait on the ice, impatiently watching for blueberry season to begin so he could make pies and many other things that kept his busy mind satisfied.
One thing that John has left us with is his record of the ice cover history on South Lake Leelanau spanning over 40 years. Starting in 1982 he began recording when the south basin of South Lake Leelanau froze over across the entire lake and when the lake opened in the spring. The south basin is the deepest part of the South Lake Leelanau and is located off Lakeview Road.
His short commentary on each season included notes like “Drove on the ice in January!!!!!”
I am glad to say that his little brother and my husband, Thad, will take over as South Lake Leelanau’s amateur observer of ice cover.
Dr. Steve Hamilton provides a scientific perspective below on the ice cover data that John recorded:
Lakes in northern Michigan, including the Great Lakes, normally freeze over for several months each year. This seasonal ice cover is very important for our lakes. Ice cover affects the lake water balance (evaporation ceases once ice forms), and ice protects shallow sediments and shorelines from erosion during winter storms. The timing of spring mixing and warming is determined by thawing of ice cover. Ice on shallow lakes can lead to winterkill of fishes due to depletion of dissolved oxygen.
Strong ice cover permits activities like ice fishing and ice boating. Weak ice, on the other hand, can present a hazard to people who venture out on it.
The duration of ice cover on many large lakes in temperate latitudes has been on the decline in recent decades, and this is widely attributed to climate change. The Great Lakes—including Grand Traverse Bay—and Gull Lake in southwest Michigan are examples. But every lake is different because freezing and thawing depend on a variety of factors in addition to air temperature, including water depth, exposure to wind, and water temperature at the start of winter. Year-to-year variability is commonly high, so many years of observations are needed to identify trends.
As was the case throughout the Great Lakes region, Lake Leelanau had a very short period of ice cover last winter—just 29 days. Fortunately, we can put last winter’s ice cover into perspective because the late John Popa maintained a long-term record of ice cover on South Lake Leelanau since 1981. A chart of those observations appears below.
Last winter had the shortest ice duration in the record. Unlike the aforementioned lakes, however, there is no statistically significant trend in duration over the record, nor is there a trend in the dates of freezing or thawing (based on a 95% probability). A longer record may have revealed trends, although much of the global warming we have experienced has occurred since 1980. Why Lake Leelanau would not show the trend of declining ice cover duration seen so often elsewhere is a mystery.
The long-term average duration of ice cover is 101 days, and the shortest duration before last year was 44 days in 2006.
With the passing of the torch to Thad, data will continue to be collected. Time will tell if a trend emerges with more data.
Main photo credit: Rob Mackenzie