University of Minnesota
University of Minnesota

Unthawing the Truth about the River in Winter

This year we can thank the Arctic winds for really showing us what winter means. On the surface we bundle up, the heating bills skyrocket and the river, that many of us pass everyday freezes. But what really happens to the river in winter?

On February 11th as part of River Life’s Water Walk series, we gathered at the University’s Campus Club with a view of the Mississippi to meet with hydrologist, Barbara Heitkamp from the St. Anthony Falls Laboratory to discuss the implications weather has on rivers. When thinking about rivers in winter, Barbara and the rest of the St. Anthony Falls team consider three primary elements: Hydrology, water quality impacts, and ecosystems, each of which contributes to the overall health of the river and its communities.

The hydrology of the river differs seasonally in terms of discharge, temperature, surface water, and groundwater. Throughout summer and fall groundwater sustains the base of the river, but in the winter all of the precipitation comes down as snow, gathering as a mass of water on top of the landscape waiting to melt. Therefore the river does not have a lot of stream energy so water tends to be the clearest in the winter. As snow starts to melt the river gets enough energy to erode sediments.

Erosion is only one component of water quality. These cold months for the river could be the calm before the storm if water quality practices are not in place. In Minnesota we use a lot of road salt (aka sodium chloride), which can taint our rivers directly, but can also seep through our groundwater and lakes, spiking chloride levels. In fact the Minnesota Pollution Control Agency and DNR listed 11 streams that are tributaries to the Mississippi as impaired for chloride. High chloride levels can inhibit plant growth, disrupt ecosystems, and affect the salinity of fresh water lakes leaving future ecological implications.

Throughout our discussion Barbara referred to rivers as “the life bloods of communities and ecosystems”, acknowledging that the hydrology, water quality, and seasonality of the river impacts both aquatic and terrestrial ecosystems. With an ice-covered river it’s easy to wonder what happens down there, but Barbara reassured us that life just slows down. Plants can still photosynthesize and fish and fresh water mussels will try to find sections of the channel with low currents to conserve energy. However, life for terrestrial beings tends to thrive as the river gets ice shelves, which increases area to hunt and forage. We may hibernate into the great indoors, but life on the river still goes on through these Arctic temperatures.

After demystifying the frozen Mississippi from a much warmer location it became clear that even in the winter the river is part of our complex system of life here in Minnesota. To further explore our river system join us at next month’s Water Walk…in hopefully more pleasant weather!

View the full Water Walk here.


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