Document: MAR-3-70-2

The influence of ultraviolet radiation on phytoplankton growth rates and elemental composition.

XENOPOULOS, M.A.* ¹, P.C.FROST ², D.W.SCHINDLER ¹ and J.J.ELSER ²

University of Alberta, Edmonton, Alberta, T6G 2E9 ¹
Arizona State University, Tempe, Arizona, 85287-1501 ²

Abstract:
Solar radiation is a fundamental ecological factor that simultaneously affects physical, chemical, and biological processes in lake ecosystems. We examined the influence of solar radiation, including UV-A and UV-B on phytoplankton in situ growth rates and elemental composition in two boreal lakes at the Experimental Lakes Area (Ontario, Canada) with the use of dilution bioassays. Phytoplankton maximum growth rates and elemental composition were strongly influenced by UV-A and UV-B but the magnitude of change depended strongly on the time the experiment was done (spring versus summer). In general, the sensitivity to UV-A and UV-B decreased from spring to summer. Maximum growth rates were reduced by 23- 87% in treatments that included both UV-A and UV-B compared to PAR only treatments. Excluding UV-B increased maximum growth by 8-50% compared to treatments which didn't filter any sunlight out. The carbon:phosphorus ratio (C:P) increased in the UV-B exposed spring community and decreased in the UV-B exposed summer community. C:P ratios were not changed by UV-A or UV-B in late summer. So far, factors such as temperature, PAR, and nutrients have been considered to be the primary ecological factors that control algal growth rates and elemental composition in lakes but we demonstrate here that UV-A and UV-B also play an important role in controlling these processes.

Keywords: Ultraviolet, phytoplankton growth, elemental composition

This abstract is being presented at: 9:45 AM in session:
Oral Session #37: Phytoplankton.