April 2005

The DNR communications team works with agency experts to develop the weekly questions and provide the answers. This feature addresses current DNR issues, interesting topics, or the most frequently asked questions from around Minnesota.






How important is the spring run-off to Minnesota's ground water supply?

Snowmelt and rainfall during the spring months are the sources of major replenishment for the entire hydrologic system in Minnesota, including ground water. While a great deal of the spring run-off melts into lakes and rivers, some of it infiltrates the soil into two principal zones: saturated and unsaturated. The saturated zone is where aquifers are found. Water stored as ground water flows into rivers and lakes through springs and seeps, helping to maintain their levels. Most of the summer precipitation is taken up by growing vegetation or is evaporated. Ground water pumped from aquifers supplies 75 percent of Minnesota's drinking water and nearly 90 percent of the water used for agricultural irrigation.

Sarah Tufford, Ground Water & Climatology Section Administrator


National Volunteer Week is April 17-23. The Minnesota Department of Natural Resources (DNR) has a lot of volunteer opportunities for the public. How much of an impact do volunteers have on DNR activities and our natural resources?

More than 33,000 volunteers assist the DNR annually with a variety of natural resource projects. Last year, these volunteers donated approximately 455,000 hours. This would be the equivalent of hiring an additional 218 full-time staff to clean rivers, conduct wildlife surveys, teach firearms safety, plant trees, restore stream habitat, enter data and serve as campground hosts. As a result, the time and effort spent by those volunteers to help manage and preserve Minnesota's natural resources had a value of about $7.8 million. To learn more, check out Volunteering Opportunities on the web or by calling DNR Volunteer Programs at 651- 259-5249 or toll free 1-888-MINNDNR (646-6367). Opportunities change on a seasonal basis.

Renee Vail, DNR Volunteer Program Director


It's not uncommon for lakeshore property owners to return to their cabins in the spring to find damage to their shoreline, docks and boat lifts bent, retaining walls and sometimes to the cabins themselves. What causes this?

This type of property damage is caused by "ice heaving" or "ice jacking." As ice freezes and thaws, cracks form because of the different contraction rates at the top and bottom of the ice sheet. This is especially true in years when there's a lack of insulating snow cover, which means our current conditions this year may result in a lot of property damage around the state. When the water rises in the cracks and freezes, the ice sheet expands slightly. Rising air temperatures warms the ice, which causes the additional expansion to exert a tremendous thrust against the shore. This powerful natural force forms a feature along the shoreline known as an ice ridge. These ridges can sometimes reach as high as five feet or more. Additional warming and cooling of an ice sheet can cause additional pushing action that possess enough power to nudge bridge masonry piers out of plumb and push houses off their foundations.

Glen Yakel, DNR Division of Waters hydrographics supervisor


The spring thaw means the sap from maple tress begins to flow. Making maple syrup is a popular springtime activity in Minnesota. How is sap converted to the syrup used on our pancakes and French toast?

Maple sap contains all the sugar and flavor of maple syrup, diluted by a large amount of water. To turn sap into syrup, the sap must be boiled to remove the excess water. The amount of boiling needed depends on the sugar content of the sap. For example, sugar maple sap containing at least 2 ½ percent sugar will require 35 gallons of sap in order to yield one gallon of pure maple syrup. Cooking usually takes hours or even days, depending on how much sap you have to boil, and it is usually done outside under a roof or tarp. If you boil that much water inside a house, be prepared to redecorate, because the humidity that's generated will cause all your wallpaper to come unglued. One way to determine when it's time to stop boiling is to monitor boiling temperature with a candy thermometer - 219 degrees means you've made pure maple syrup.

Dave Crawford, Wildlife River State Park Naturalist


DNR Question of the Week Archive