Researchers Discover Hidden “Rock Moisture” Layer

Reader Contribution by University Of Texas At Austin
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Recently, researchers have discovered a layer of rock that is able to hold significant amounts of water that may serve as a vital reservoir for trees in times of drought.

The study, published in the journal PNAS on February 26, looked at the water stored inside of a layer of weathered bedrock that is commonly found under soils in mountainous regions and environments. This layer is a transitional layer between the common soil level and groundwater level. It is often overlooked when it comes to studying hydrological processes, but recently researchers have been taking a closer look at this layer.

“There are significant hydrologic dynamics in weathered bedrock environments, but they are not traditionally investigated because they are hard to access,” said lead author Daniella Rempe, an assistant professor in the Department of Geological Sciences at the UT Austin Jackson School of Geosciences.

The research team behind this study has found that the amount of water hidden in this bedrock layer has the ability to sustain trees through droughts, even after the surface soils have become dry. At a field site, the team found that up to 27 percent of rainwater can be stored in this rock layer, as “rock moisture”. This newly found rock layer has helped explain how trees and other plants in times of serve droughts are able to survive.

“How trees can survive extended periods of severe drought has been a mystery,” said Richard Yuretich, director of the National Science Foundation’s Critical Zone Observatories program, which funded the research. “This study has revealed a significant reservoir of trapped water that has gone unnoticed in the past. Research of this kind can help greatly in managing natural resources during times of environmental stress.”

In order to research the extent of this “rock moisture” layer, the team studied nine wells drilled into weather bedrock over the course of 3 years, using a neutron probe, a tool that measures the amount of water in the area by detecting hydrogen. They found that the layer had built up 4 to 21 inches of rock moisture, and the maximum moisture held in the rock layer stayed the same no matter how heavily or little it rained that year. This means that the rock moisture will build to the same level each year, ensuring that there is enough rainwater stored to prepare trees for times of drought.

This research could also be valuable for future climate studies; the rock moisture could potentially travel back into the atmosphere via evaporation from tree leaves, which would have a broad impact on the weather and climate or the region. Incorporating this newfound rock moisture into climate studies could answer some questions about climate sciences.

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