SS3.10 Ecological Implications of Terrestrial Inputs into Lakes and Ponds
Date: Tuesday, June 11, 2002
Time: 12:00:00 PM
Location: Esquimalt
 
McKnightDM, University of Colorado, Boulder, USA, mcknight@snobear.colorado.edu
Brown, A, , University of Colorado, Boulder, USA, brown@polar.org
Chin, Y, , Ohio State University, Coumbus, USA, chin@ohio_stae.edu
 
The Influence of Mixotroph Growth on DOM Chemistry in Pony Lake, a Eutrophic Coastal Pond in Antarctica
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We studied DOM changes in a eutrophic antarctic pond. Over a three-week period, Chlamydomonas intermedia was replaced as the dominant algal species by Cryptomonas sp., which can exhibit mixotrophic growth. During this period, DOC concentrations decreased from 92 mgC/L to 32 mgC/L. We hypothesized that changes in the chemical characteristics of DOM would reflect differences in DOM bioavailability to bacteria and cryptophytes. The DOM distribution between three size fractions did not change between the two blooms. However, the N-content of fulvic acid fractions decreased twofold and d15N values became heavier, suggesting either N-loss through photolysis or preferential uptake of N-rich molecules. The 13C-NMR spectra for all fractions showed a decrease in the amide carbons peak and there were no changes in the main carbon moieties. Based on reported rates of DOM uptake by bacteria and cryptophytes, mixotrophic uptake of DOM may have been more important in causing the abrupt DOM decrease. In the context of the turnover of DOM through the microbial loop, differential bioavailability of DOM substrates may be less important for mixotrophic algae than for heterotrophic bacteria.