The Gentle Winter of 2011-2012 and Minnesota's Water
By Cindy Hagley
Compared to Minnesota long-term averages, the winter of 2011-2012 was relatively snow-free. In a typical low-snow winter, Rich Axler, water resources scientist at the Natural Resources Research Institute at the University of Minnesota Duluth, said cold temperatures without the insulating effects of snow could1:
- Increase frost depths, resulting in damage to wastewater systems and water lines.
- Cause ice on lakes and streams to be thicker than normal. In small streams, shallow lakes, and wetlands, the extra ice can reduce liquid water volume, which can lead to low oxygen and reduced habitat for fish.
- Allow streams to freeze solid, resulting in winterkills of fish and other aquatic biota.
Not this year! This winter was not only low on snow, but temperatures were unusually warm, resulting in some broken records. For example, the Minnesota Climatology Working Group reported, "2012 will go down as one of the more memorable early ice out seasons in Minnesota history. Many lakes in the state set new ice out records, including lakes that have ice out data for 75 years or more."2
Here's what the experts tell us the unusual winter means for Minnesota's waters:
- Despite the lack of snow cover, frost did not penetrate deeply because of warm temperatures, resulting in less damage to water systems and an early start to the growing season.
- Thin ice and lack of snow allowed light to penetrate the water, resulting in increased photosynthesis by algae and some plants.
- Photosynthesizing plants release oxygen, helping to prevent winterkill in some shallow, productive lakes.
- Lake ice-out dates were three to four weeks earlier than historical averages,3 providing a head start on the growing season that could result in excessive algal and plant growth by mid-summer.
- The unusual conditions favor adaptable invasive aquatic plants such as curly-leaf pondweed or Eurasian watermilfoil.
Since the autumn of 2011 was the driest in Minnesota's modern climate record, many lakes and streams had low water levels going into winter. Lower than normal precipitation over the last eight months left the water levels of many Minnesota lakes low when compared with historical averages for this time of year. The U. S. Drought Monitor4 as of early April depicted nearly every Minnesota county as experiencing drought, from moderate throughout most of the state to severe in parts of the northeast and much of south.
Such drought decreases soil moisture and increases the risk of wildfires. Without adequate snowmelt, temporary wetlands (vernal pools) may not hold enough water for frog populations to breed and mature. In the northeast, the drought resulted in an extremely short period of snowmelt runoff, low peak flows, and low base flow in streams. This concerns fisheries biologists particularly along the North Shore of Lake Superior.5 MN DNR staff have had to truck trout around waterfalls because fish returning from Lake Superior are struggling to pass hurdles that are usually surmountable. Without much soil moisture to start with, the base flows of streams may remain low as the year progresses. Low flow can stress coldwater species like trout and the insects they eat since less water often leads to higher stream temperatures, and the combination of reduced flow and warmer temperatures can result in less oxygen.
Want to know more? Listen to an interview with researcher Sapna Sharma (Climate, Weather, and Breaking Ice) at www.seagrant.umn.edu/radio/sgf.