Water hits and sticks: findings challenge a century of assumptions about soil hydrology

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Source: ScienceDaily

Researchers have discovered that some of the most fundamental assumptions about how water moves through soil in a seasonally dry climate such as the Pacific Northwest are incorrect -- and that a century of research based on those assumptions will have to be reconsidered.

A new study by scientists from Oregon State University and the Environmental Protection Agency showed -- much to the surprise of the researchers -- that soil clings tenaciously to the first precipitation after a dry summer, and holds it so tightly that it almost never mixes with other water.

The finding is so significant, researchers said, that they aren't even sure yet what it may mean. But it could affect our understanding of how pollutants move through soils, how nutrients get transported from soils to streams, how streams function and even how vegetation might respond to climate change.

The research was just published online in Nature Geoscience, a professional journal.

'Water in mountains such as the Cascade Range of Oregon and Washington basically exists in two separate worlds,' said Jeff McDonnell, an OSU distinguished professor and holder of the Richardson Chair in Watershed Science in the OSU College of Forestry. 'We used to believe that when new precipitation entered the soil, it mixed well with other water and eventually moved to streams. We just found out that isn't true.'

'This could have enormous implications for our understanding of watershed function,' he said. 'It challenges about 100 years of conventional thinking.'

What actually happens, the study showed, is that the small pores around plant roots fill with water that gets held there until it's eventually used up in plant transpiration back to the atmosphere.

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