ScienceDaily (Oct. 9, 2007) — Elevated levels of carbon dioxide (CO₂) in the Earth's atmosphere could seriously impact air, weather and vegetation. Now a scientist with the Agricultural Research Service (ARS) is taking a closer look at what could happen underground.

If atmospheric CO₂ levels double within this century, as many climate models predict, some areas could experience large increases in the rate of groundwater recharge, the process by which water filters through the soil and enters aquifers. That's the conclusion of a recent study conducted by ARS scientist Tim Green, a hydrologist in the agency's Agricultural Systems Research Unit at Fort Collins, Colo.

Green worked with Australia's Commonwealth Scientific and Industrial Research Organisation (CSIRO) to investigate how climate change impacts groundwater and the vadose zone, the region between soil surface and water table.

The rate at which water filters through the vadose zone is controlled by interactions between soil, water and plant systems. Green and his colleagues found that this rate was increased by the changes in precipitation and temperature that elevated CO₂ levels are expected to bring about.

The scientists developed a method for simulating the effects of elevated CO₂ levels on plants, groundwater and the vadose zone. Then they applied it to two locations in Australia—one subtropical, one Mediterranean—where eucalyptus, pine and native perennial Australian grasses grow. They found that the Mediterranean location responded more to temperature changes, whereas the subtropical climate was more influenced by the frequency and volume of precipitation.

In both locations, changes caused to soil, precipitation and plant transpiration by simulated climates with twice the existing CO₂ led to significant changes to the rate of groundwater recharge. Water recharged from 34 percent slower to 119 percent faster in the Mediterranean climate, and from 74 to 500 percent faster for the subtropical climate.

While the opportunity for decreased recharge rates exists, the general trend is towards increase. Future research will investigate whether those changes would benefit or harm those ecosystems.

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Adapted from materials provided by US Department of Agriculture.

ARS scientists Mike Murphy (left) and Rob Erskine measure soil moisture in an Oklahoma pasture. Some of that moisture will drain through the soil beneath the root zone to recharge groundwater reserves. Hydrologist Tim Green’s simulation studies in Australia show that climate change impacts this process. (Credit: Tim Green)

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