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Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Paper number  701P0904,  . (doi: 10.13031/2013.17434)
Authors:   Matthew Nechvatal and Timothy Granata

Dams have historically been constructed as public works projects for water supply, hydropower, recreation, flood control, and transportation, however, dams disconnect the aquatic ecosystem, degrade water quality, and alter aquatic habitats. Dam removal has recently become a new restoration tool for restoring stream and river ecosystems. St. Johns Dam was a concrete lowhead dam constructed in the 1930s on the Sandusky River in north central Ohio. The dam was 2.2 m high, 4.6 m wide, and its reservoir served as a water supply for the city of Tiffin. The St. Johns Dam was removed on November 17, 2003. Studies are being performed to determine how dam removal is affecting water quality above and below the dam. As part of this work, a YSI water quality sonde was attached to a canoe to sample surface water quality longitudinally from upstream of the dam to the dam. These longitudinal transects show spatial variation in oxidation reduction potential, dissolved oxygen, temperature, specific conductivity, turbidity, and pH. Transects were performed before and after dam removal. Water samples were also taken at four sites below the dam and four sites above the dam to determine how nutrient concentrations (PO4 3-, NO3 -, NH4 +) change with removal. Results from preliminary studies showed increasing temperature and turbidity starting 17.4 km above the dam to just above the dam. After removal there was no increase in temperature or turbidity as you moved down the former impoundment. Prior to dam removal, nitrate levels increased toward the impoundment while after removal nitrate was less variable. Phosphate and ammonium levels were undetectable above and below the dam. Removal did not seem to affect the levels of nitrate below the dam. Time series data showed a significant increased (spike) in turbidity below the dam during removal, a decrease in ORP, and slow increase in temperature as the water was released downstream.

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