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Paper No. 8
Presentation Time: 10:15 AM


WOLFE, Georgia L.1, MILLER, Todd R.2 and MCMAHON, Katherine D.1, (1)Environmental Engineering, University of Wisconsin - Madison, 5525 Microbial Sciences Building, 1550 Linden Drive, Madison, WI 53706, (2)Bacteriology, University of Wisconsin - Madison, 5525 Microbial Sciences Building, 1550 Linden Drive, Madison, WI 53706,

One of the predicted consequences of recent climate change is an increase in frequency and severity of harmful cyanobacterial blooms. Unfortunately, there are very few multi-year records of cyanobacterial abundances with which to test this prediction. Aquatic sediments can preserve algal DNA for thousands of years (Coolen et al. 2006), potentially allowing observation of changes in cyanobacteria blooms over longer time periods. To date, no studies have used sediment DNA to examine the effect of recently warming climate on cyanobacterial abundance.

Lake Wingra is a small eutrophic urban lake in Wisconsin, with a record of limnological observations dating back to the 1800s. The trophic status of the lake has not changed in at least the past 80 years (Baumann et al. 1974), making it an ideal system in which to study effects of climate change on human-impacted environments. DNA was extracted from 18 sections, each representing 3 years' worth of accumulation, of a single sediment core from the deepest part of Lake Wingra. Quantitative PCR targeting the cyanobacterial 16S small subunit ribosomal gene was used to estimate average cyanobacterial abundance from 1954 to the present.

Cyanobacterial abundance remained remarkably constant from 1954 to 1990 at approximately 5x105 16S gene copies per wet gram of sediment. During the 1990s average abundance increased to 2x106, and in the 2000s increased again to 9x106 copies/gram. This does not appear to be an artifact of DNA degradation as gene copy number actually increased with depth in the top 6 cm. Increases in cyanobacterial abundance coincided with regional increases in average annual precipitation and temperature over the past two decades. This is the first study to demonstrate that molecular DNA methods may be used to investigate historical responses of cyanobacteria to changing climate patterns.

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