PARENT SESSION
Oral Session #65: Aquatic Ecology: Stream and Lake.
Presiding: C. Osenberg
Wednesday, August 7. 1:00 PM to 4:45 PM. Coconino Meeting Room, TCC.

How consistent are the reponses of lakes to fertilization?

Irvine, Robyn^*,1, ¹ University of Calgary, Calgary, Alberta, Canada

ABSTRACT- In any ecological study, we must decide how to incorporate and address variability. Ecosystem studies often measure average responses across space and time, implicity assuming that variation at these levels is "noise" that will not affect average responses. However, fixed differences in space and time can alter system dynamics, such that different processes operate at different sites and years. In this study, I analyze the relationship between productivity, light, and nutrients using six years of data (1980-1985) from 22 British Columbian (Canada) lakes that were part of a long-term lake enrichment program. Specifically, I fit light saturation curves to data from fertilized and unfertilized lakes, pooled at different levels of spatial and temporal resolution. Based on Akaike Information Criteria, I found that relationships between light and productivity differed among lakes, and among sampling stations within lakes, as well as with fertilization. If all the lakes were homogeneous in nature then the best model would be the unseparated one (all data pooled over space and time), but this is, in fact, the worst model of the sixteen models assessed. Surprisingly, for this system of lakes, annual variation did not significantly change the relationship between primary productivity and light. I explore the causes of spatial variation, and their consequences for predicting responses of lakes to enrichment.

KEY WORDS: variability, AIC, lake, fertilization