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2012 EPA Research Progress Report

Sediment Removal to Improve Water Quality

Legacy sediment layers visible in Big Spring Run steam bank. (Image courtesy of Dr. Dorothy Merritts.)

Excess sediments and nutrients, especially nitrogen and phosphorous, are a leading cause of water quality impairment in streams and wetlands throughout the nation, particularly in the mid-Atlantic region. Legacy sediments are the deposits of sediment and nutrients that built up as a result of historic mill dam construction. EPA scientists are researching the removal of legacy sediments as a cost-effective and sustainable means of reducing sediment and nutrient pollution in watersheds.

Historic damming of streams and rivers led to a huge backup of sediment and the destruction of natural water and soil systems. Most of the dams are now abandoned, but as the natural water systems return, they threaten to release massive amounts of sediment and nutrients to downstream waters. EPA, in collaboration with federal, state, and academic partners, focused research efforts on Big Spring Run (PDF) (3 pp, 212K), a rural stream in Lancaster County, Pennsylvania that is impacted by legacy sediments.

Beginning in 2009, legacy sediments were removed from Big Spring Run and buried wetlands were exposed and reconnected to the floodplain water system. Water quality and geologic assessments of the area showed that stream bank erosion was more extreme than expected and nutrient levels were high in ground and surface waters. Restoration is expected to greatly reduce sediment transport and nutrient contamination, especially because healthy wetlands will naturally filter and convert harmful excess nutrients out of the water system.

Restoration of Big Spring Run was completed in September 2012. Researchers found that since September, the plant community composition has changed significantly, showing signs of healthy wetlands. These early results point to a promising method for protecting downstream waters from further sediment and nutrient pollution by the removal of legacy sediments and the associated wetland restoration.

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