Xenopoulos, M. A. Department of Biological Sciences, University of Alberta, firstname.lastname@example.org
Schindler, D. A. Department of Biological Sciences, University of Alberta,
IMPORTANCE OF NEAR-SURFACE THERMOCLINES IN COMBINATION WITH UV RADIATION IN BOREAL LAKES
Shallow near-surface thermoclines form under hot and windless conditions and can retain the plankton under photoinhibitory irradiances, including UV radiation, for prolonged periods of time. We investigated the frequency of occurrence of near-surface thermoclines in a large number of lakes (40) varying several orders of magnitude in surface area and transparency. Archived temperature data from the Experimental Lakes Area (ELA) and Northwest Ontario Lake Size Series (NOLSS; Ontario, Canada) were used to detect size-related differences. The incidence of transient thermoclines decreases with increasing lake size from 75% of all summer days in small ELA lakes (4 ha) to 25% in one of the larger NOLSS lakes (706 ha). Four ELA lakes were selected to investigate phytoplankton production on calm days with high incident UV. Preliminary results indicate a reduction of 10-50% in near-surface primary production in periods of very low mixing and high UV.
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