Soto, D. Universidad Austral de Chile, Facultad de Pesquerías y Oceanografía, dsoto@uach.cl
Fee, E. University of Calgary, efee@telusplanet.net

 
THE ROLE OF LIGHT-NUTRIENT LIMITATION IN SOUTHERN CHILEAN TEMPERATE LAKES: ARE FOOD WEBS THAT RELEVANT HERE??
 
Lakes in southern Chile are monomictic, very deep, and quite oligotrophic (low Chl a concentration and plankton biomass, and high water transparency. Most of the lakes have epilimnia deeper than 20 m in summer, and those with lowest Chl a, have epilimnia deeper than 40 m. Six years of data from four of the largest and deepest lakes show very low dissolved N/P ratios. Experimental manipulations in limnocorrals in two oligotrophic lakes usually indicated co-limitation by N and P; but often there was no indication of nutrient limitation (particulate C:N:P ratios were often near the Redfield ratio). These lakes are thus more similar to marine pelagic ecosystems with regard to nutrient limitation. A striking result of two limnocorral experiments was that phytoplankton biomass and Chl a increased in the control bags (with respect to the lakes). This result, in conjunction with data on the daily mean irradiance in the water column (calculated from surface irradiance, mixing depth, and transparency data), lead us to hypothesize that light is an important factor limiting phytoplankton productivity in these lakes. That is, phytoplankton can not fully utilize the available nutrients because of low light levels. In such scenario, foodweb structure and grazers role (mostly calanoids) on nutrient availability may be less relevant on a large scale perhaps as in marine pelagic ecosystems.
 
Day: Wednesday, Feb. 3
Time: 02:30 - 02:45pm
Location: Sweeney Center
 
Code: SS49WE0230S