SS3.21 Deconstructing Rivers: The Ecological, Geomorphic, and Social Consequences of Dam Removal
Date: Thursday, June 13, 2002
Time: 11:45:00 AM
Location: Colwood
 
StanleyEH, University of Wisconsin, Madison, USA, ehstanley@facstaff.wisc.edu
Doyle, M, W, Purdue University, West Lafayette, USA, mdoyle@purdue.edu
 
CHANGES IN PHOSPHORUS RETENTION AND STORAGE FOLLOWING REMOVAL OF A LOW-HEAD DAM IN SOUTHERN WISCONSIN
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We examined phosphorus concentrations above and below a reservoir in Koshkonong Creek, Wisconsin before and after dam removal. The creek has high suspended sediment (0.02- 0.20 g/L) and nutrient (NO3- N >3.0 mg/L, SRP >0.10 mg/L) concentrations. Particulate P (PP) and soluble reactive P (SRP) concentrations entering and exiting the millpond were monitored before, during, and over the year following dam removal, and volume and P content of reservoir sediments were estimated before and after the breach. Prior to dam removal, SRP and PP entering the impoundment were significantly greater than concentrations immediately below the dam. After removal, the study reach continued to act as an SRP sink, but became a PP source. The magnitude of PP loss was substantially greater than SRP retention, so there was an average increase in P concentration of 0.1 mg/L below the reservoir. Sediment P content averaged 1400 mg/kg, and removal resulted in an estimated loss of >22,000 kg P from the reservoir. Thus, the shift from sink to source after removal was driven by loss of nutrient-rich sediments from the former reservoir.