PARENT SESSION
Symposium #23: Dam removal as river restorations: Linking ecological, engineering, social, and legal perspectives.
Sponsored by ESA Aquatic Ecosystems Section
Organized by: D. D. Hart and N. L. Poff.
Friday, August 10, 2001. 8:00 AM to 12:00 PM. Madison Ballroom A
Ecosystem responses to removal of low-head dams from two Wisconsin Rivers.
Stanley, Emily1, Doyle, Martin2, 1 2
ABSTRACT- Removal of low-head dams produces conspicuous changes in physical attributes of riverine ecosystems. Coupled chemical and biological responses may be equally dramatic, but in the absence of detailed research, are less obvious. Many dams targeted for removal in Wisconsin are old (>100 years), and impoundments typically contain extensive sediment deposits. The fate of stored sediment represents a major research and management challenge in terms of upstream and downstream habitat alteration, as well as nutrient distribution and transformation. In this context, we have been investigating short-term changes in riverine nutrient and sediment transport following dam removal. Dam removal can shift impounded reaches from sediment and nutrient (N and P) sinks to sources. Changes in P retention are associated with mobilization and downstream transport of reservoir sediments, whereas N dynamics appear to be governed by loss of conditions suitable for denitrification. These findings raise several questions regarding nutrient transport in the context of dam removal, including: How long do formerly impounded reaches act as nutrient and sediment sources? How much of the nutrient pool stored in reservoir is mobilized to downstream reaches? What is the extent of downstream effects of sediment and nutrient inputs? How does the redistribution of sediment affect nutrient retention in downstream reaches? Given current concerns about riverine nutrient transport and retention, there is a critical need to address these questions, particularly in nutrient-enriched riverine systems.
KEY WORDS: dams, nitrogen, phosphorus, restoration