December 11, 2010
Iron Legacy Leaves Soil High In Manganese
Iron furnaces that once dotted central Pennsylvania may have left a legacy of manganese enriched soils, according to Penn State geoscientists. This manganese can be toxic to trees, especially sugar maples, and other vegetation.
The research, which quantified the amounts of manganese in soil core samples, was part of work done at the Shale Hills Critical Zone Observatory funded by the National Science Foundation.
"Our group's focus was to study the soil chemistry," said Elizabeth M. Herndon, graduate student in geosciences. "We saw excess manganese in the soil and decided that we needed to quantify the manganese and determine where it came from."
Typically, manganese in soils comes from the disintegration of the bedrock as soil forms. Bedrock in this area is shale and the average amount of manganese in the shale is about 800 parts per million. However, the researchers found 14,000 parts per million of manganese in some of the soil samples. This is more than 17 times as much manganese as in the bedrock.
The researchers sampled 21 sites along a ridge at Shale Hills. They took core samples from the surface down to bedrock. At 20 of the sites they found elevated manganese. The core samples, which are about 12 inches long, encompass about 7,000 years of soil formation.
"We needed to quantify how much extra manganese there actually was in the samples," said Herndon. "While soil formation puts manganese into the soil, chemical weathering and physical erosion remove manganese from the soil, so we used a mass balance model to account for these inputs and outputs."
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