Beetle-Infested Trees Are Causing Water Levels To Rise, And Its Quality To Worsen
Each year conservationists see blankets of green pine trees turn red or gray due to infestations from pesky little bugs known as bark beetles. Already, mountain landscapes across the Western United States have been significantly altered by these bugs, which got their name from their ability to thrive and breed in the trees' inner bark.
Among the different species of beetle, some, like the mountain pine beetle, attack and kill live trees. These beetles have caused an incredible amount of damage to pine trees, which are important for both commercial and aesthetic purposes. It is estimated that in Colorado alone, the beetles have destroyed more than 3.4 million acres of pine trees. Considering that trees are an important part of the water cycle, scientists have wondered how the beetles have impacted the water in areas with widespread infestation. They found that both the flow of streams and the water quality have been affected.
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"The unprecedented tree deaths caused by these beetles provided a new approach to estimating the interaction of trees with the water cycle in mountain headwaters like those of the Colorado and Platte Rivers," said hydrologist Reed Maxwell, of the Colorado School of Mines, in a press release.
During their study the researchers found that green trees use shallow groundwater in late summer for transpiration - when water is absorbed through the roots from the soil. But no transpiration occurs in red and gray phase, beetle-infested trees. The unabsorbed water, then, ends up as local groundwater, and flows to nearby streams, increasing water levels.
A higher flow of groundwater and water availability may seem positive but the total effect of large-scale tree death and increased water flow "has to be evaluated for how much of an increase, when does such an increase occur, and what's the water quality of the resulting flow?" said Tom Torgersen, the National Science Foundation's directorate for geosciences, in the release.
The researchers found that late-summer groundwater flows from affected watersheds were about 30 percent higher in beetle infested areas, when compared to watersheds with less severe beetle attacks. This proved to the researchers that a deficit in transpiration from beetle infestations could account for more groundwater in streams. They discovered this after looking at "fingerprints" of different water sources - essentially the water's chemical makeup, which told them where the water came from.
The researchers also assessed how the quality of water changes when millions of trees die. Their findings support earlier evidence that found a spike in carcinogenic disinfection byproducts during the late summer in local water treatment plants.
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