Wednesday, May 28, 2008 - 2:45 PM
446

Reaeration coefficients in a small lentic ecosystem using the propane injection method

Hwa-Seong Jin, Department of Biology, University of Louisville, 139 Life Sciences, Louisville, KY 40292, James B. Ramsey, Department of Biological Sciences, University of Alabama, Box 870206, Tuscaloosa, AL 35487, and David S. White, Murray State University, Hancock Biological Station, 561 Emma Dr, Murray, KY 42071.

In lentic ecosystems, reaeration coefficients have been estimated with indirect methods using diel DO profile (nighttime regression) or wind speed, while direct measurements using tracer gas evasion have been rarely conducted.  We used the propane injection method to directly measure the reaeration coefficient in a small (0.46 ha) beaver impoundment in conjunction with DO profiles.  We injected 99% propane for 1.5-2 hrs by towing propane gas diffusers slowly around the pond behind a canoe and then allowed 24 hrs for even distribution of the tracer gas. Daily water samples for tracer gas were taken at 5 locations with 60 ml plastic syringes and transferred immediately into 10 ml gas-tight glass syringes.  Propane was analyzed using Shimadzu GC 14 with a Flame Ionization Detector.  Measureable amounts of propane were present for 5-6 days following the injection.  This direct propane method resulted daily k values ranging from 0.64 to 0.89 (r2 = 0.99) in the pond, which were much lower than k estimated using the nighttime regression (≈5.85 d-1).  We concluded that community metabolism estimates in some types of lentic ecosystems may often be overestimated when k is estimated using the nighttime regression method alone.


Web Page: pond, reaeration coefficient, metabolism

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