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Alum Treatment at Teedyuskung Lake a Success by Rebecca Buerkett, Project Scientist | |||||||||||||||||||||||||||||||||||||||||||||||||
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Teedyuskung Lake has been eutrophic for the past 17+ years, as evidenced by high nutrient concentrations, high chlorophyll a concentrations, high algal counts and densities, domination by bluegreen algae (cyanobacteria), hypolimnetic oxygen depletion, and decreased water transparency. Low dissolved oxygen conditions at the bottom of the lake were causing phosphorus to be released from the sediments, subsequently fueling algae growth. A batch alum treatment was performed on Teedyuskung Lake to seal the bottom, phosphorus-rich sediments and prevent phosphorus resuspension in the water column. F. X. Browne, Inc. performed an in-depth study of Teedyuskung Lake which included water sampling, alum and sodium aluminate jar tests, sediment testing for phosphorus content, a bathymetric survey of the lake, and calculations of the doses of alum and sodium aluminate required. The jar tests were performed to measure the dose required to treat the water column of the lake. Additional jar tests were performed to determine the combination of alum and sodium aluminate required to maintain a pH of 6 or greater. A dose of aluminum of 13 mg/l was added to the
80 acre lake by applying 33,000 gallons of alum and 16,000 gallons of
sodium aluminate to the lake. This dose was in the mid-range of alum doses
used on lakes throughout the country. |
Teedyuskung
Lake Alum Slideshow
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more presentations from Frank Browne. | ||||||||||||||||||||||||||||||||||||||||||||||||
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F. X. Browne, Inc. conducted pre- and post- alum
treatment water quality monitoring at Teedyuskung Lake in 2007 and 2008 in
order to document the success of the treatment. The monitoring results
showed a dramatic improvement in surface water quality after treatment in
2007 and continuing through the 2008 growing season, as shown in Table 1.
In particular, the total phosphorus and chlorophyll a
concentrations and Secchi disk readings improved from the eutrophic range
pre-treatment to the oligotrophic or borderline oligotrophic-mesotrophic
range post-treatment. The 2008 bottom water quality total phosphorus
average was much improved over the 2007 pre-treatment average hypolimnetic
total phosphorus average.
The phytoplankton (algae) populations dropped dramatically post-treatment. Additional monitoring during future field seasons will determine whether or not these water quality improvements will be long-lasting, but that is expected to be the case.
* Surface parameter only
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