“Winter events tend to carry a little bit more pollution than the same size event in the growing season,” says Carol Adair, an environmental scientist at the University of Vermont and one of the study’s authors, to KCUR’s Eva Tesfaye. They looked at flooding in the Mississippi River Basin in 2019 and found that winter rain-on-snow events sent huge amounts of sediment and nutrients into the Gulf of Mexico-much more pollution than a similar amount of rain in the warmer months would have caused. To reach this conclusion, the team zeroed in on so-called “rain-on-snow” events, or instances where rain falls on top of snow that’s already on the ground and causes it to melt. When it rains during the winter, the falling water can melt snow that's on the ground and lead to runoff. “The assumption that discharge and nutrient transport remains low during the winter months no longer holds,” the researchers write in the paper.
With climate change increasing winter temperatures, nutrient pollution during the winter has gone from “rare or nonexistent” to “far worse” than during other seasons, according to a statement. But now, they’re beginning to understand its effects during other times of the year. Scientists have long been aware of nutrient pollution during the warmer growing seasons.
Then, the ice thaws in the spring, when plants can help soak up the nutrients and prevent them from running off into nearby waterways.īut as human-caused climate change warms the Earth, winter rains could release this nutrient pollution at a time when dormant plants can't absorb it, leading it to flow into streams, lakes and rivers, according to a new paper published in the journal Environmental Research Letters last week. This process, which researchers say could play out in more than 40 states, has the potential to cause big problems, including algae blooms and fish die-offs. In much of the United States, frigid temperatures and a blanket of snow lock the pollution in place, where it can’t do much environmental harm. Typically, leftover agricultural chemicals from manure and fertilizer freeze during the winter.
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