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OKIsItJustMe

(19,933 posts)
Wed Jun 22, 2016, 05:09 PM Jun 2016

Neutralizing acidic forest soils boosts tree growth, causes spike in nitrogen export

http://www.caryinstitute.org/newsroom/neutralizing-acidic-forest-soils-boosts-tree-growth-causes-spike-nitrogen-export
[font face=Serif][font size=5]Neutralizing acidic forest soils boosts tree growth, causes spike in nitrogen export[/font]

Monday, June 20, 2016

[font size=4]Unexpected results took a decade to emerge, shed new light on watershed dynamics[/font]

[font size=3]A legacy of acid rain has acidified forest soils throughout the northeastern US, lowering the growth rate of trees. In an attempt to mitigate this trend, in 1999 scientists added calcium to an experimental forest in New Hampshire. Tree growth recovered, but a decade later there was a major increase in the nitrogen content of stream water draining the site. So reports a new paper in the Proceedings of the National Academy of Sciences by a team of scientists from the Cary Institute of Ecosystem Studies, Duke University, and Syracuse University.

Gene Likens, President Emeritus of the Cary Institute and co-author on the paper, participated in the calcium addition in 1999. It took place at Hubbard Brook Experimental Forest, a 7,800-acre living laboratory in New Hampshire’s White Mountains. Calcium concentrations in forest soils at the site had been depleted due to prolonged exposure to acid rain. The goal of the large-scale experiment was to test if restoring calcium to these soils would result in improved forest growth.

Likens and colleagues added 2,600 pounds of Wollastonite pellets, a calcium silicate source, to a 30-acre forested watershed. And they waited. The soil pH and acid-neutralizing capacity of soils and stream water increased significantly, and forest growth rebounded. Sugar maples, a dominant canopy species with a high calcium requirement, began to recover.

“For nearly ten years, it looked like our predictions were correct,” Likens explains. “The calcium was largely retained and the forest was growing. Then, in 2010, we noticed streams draining the treated site had elevated nitrogen levels. By 2013, yearly inorganic nitrogen losses were thirty times what we expected, an increase we had only seen after forest clear-cutting experiments.”

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