Libby Dam Hydro-electric Project Mitigation: Efforts for Downstream Ecosystem Restoration.
Construction of Libby Dam, a large hydropower and flood control dam occurred from 1966 to 1975 on the Kootenai River, near Libby, Montana in the Northwestern United States. Live reservoir storage is substantial, with water residence time of about 5 1/2 months (based on mean annual discharge of about...
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2009
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| Online Access: | http://www.osti.gov/servlets/purl/962146 https://www.osti.gov/biblio/962146 https://doi.org/10.2172/962146 |
| Summary: | Construction of Libby Dam, a large hydropower and flood control dam occurred from 1966 to 1975 on the Kootenai River, near Libby, Montana in the Northwestern United States. Live reservoir storage is substantial, with water residence time of about 5 1/2 months (based on mean annual discharge of about 440 m{sup 3}/s). Downstream river discharge and thermal regimes and the dependent habitat conditions have been significantly altered by dam construction and operation relative to pre-dam conditions. Highly valued Kootenai River fish populations, including white sturgeon Acipenser transmontanus, burbot Lota lota and bull trout Salvelinus confluentus and their supporting ecological conditions have been deteriorating during post-dam years. Measurements of the presence of very low (ultraoligotrophic) concentrations of dissolved phosphorus in the river downstream from Libby Dam were identified as a critical limitation on primary production and overall ecosystem health. A decision was made to initiate the largest experimental river fertilization project to date in the Kootenai River at the Montana-Idaho border. Pre-treatment aquatic biomonitoring began in 2001; post-treatment monitoring began in 2005. A solar-powered nutrient addition system was custom designed and built to dose small releases of dissolved nutrients at rates from 10 to 40 L/hour, depending on river discharge, which averaged several hundred m3/s. Closely monitored experimental additions of ammonium polyphosphate solution (10-34-0) into the river occurred during the summers of 2005 through 2008. Targets for mixed in-river P concentrations were 1.5 {micro}g/L in 2005, and 3 {micro}g/L in subsequent years. Primary productivity and algal accrual rates along with invertebrate and fish community metrics and conditions were consistently measured annually, before and after experimental fertilization. Initial results from the program are very encouraging, and are reported. |
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