PARENT SESSION
Oral Session # 2: Paleoecology.
Presiding: B Lynch
Monday, August 4. 8:00 AM to 11:30 AM, SITCC Meeting Room 101.

Climatic control of UV radiation impacts on lakes.

Leavitt, Peter^*,1, Cumming, Brian², Smol, John², Reasoner, Mel³, Pienitz, Reinhard ⁴, Hodgson, Dominic⁵, ¹ University of Regina, Regina, SK, Canada² Queen's University, Kingston, ON, Canada³ Mountain Research Initiative Coordination Office, Bern, n/a, Switzerland⁴ Universite Laval, Quebec, QC, Canada⁵ British Antarctic Survey, Cambridge, n/a, UK

ABSTRACT- UV radiation (UVR) damages most biota, yet little evidence exists for its long-term impacts on natural ecosystems. Here, we used paleoecological techniques at three low elevation lakes to show that ecosystem production was depressed 10-fold by UVR during the first millennium of lake existence. Likewise, analysis of a lake near treeline showed that algal production declined 10- to 25-fold both early in the lake history and during the last ca. 4000 years when inputs of UVR-absorbing dissolved organic matter (DOM) declined despite constant nutrient levels since ca. 10,000 ¹⁴C yr BP. This rapid (-1.25%/yr) sustained (>600 years) suppression of ecosystem production arose from directional climatic change that reduced DOM inputs and occurred despite initial reservoirs of photoprotective DOM that were typical of most boreal lakes. Hence, we conclude that many lakes may be vulnerable to order-of-magnitude declines in production arising from future climate-DOM-UVR interactions.

Key words: UN radiation, lake evolution, climate, DOC