PARENT SESSION
Oral Session # 39: Limnology I: Ecosystems, Eutrophication, and Restoration.
Presiding: KL Cottingham
Wednesday, August 6. 8:00 AM to 11:30 AM, SITCC Meeting Room 101.

Diel respiration measured using oxygen stable isotopes in fertilized, clear, and colored lakes.

Roberts, Brian^*,1, Cole, Jon², Pace, Michael², Bade, Darren³, Van de Bogert, Matthew², ¹ Cornell University, Ithaca, NY, USA² Institute of Ecosystem Studies, Millbrook, NY, USA³ University of Wisconsin-Madison, Madison, WI, USA

ABSTRACT- Diel patterns in respiration rates were examined in three lakes as part of a seasonal study on carbon cycling. Peter Lake received N and P fertilizations resulting in a net autotrophic state while net heterotrophy was maintained in Paul (clear) and Tuesday (colored) lakes. Continuous measurements of O₂ and CO₂ were made throughout the experiment. Daytime rates of respiration were quantified by making multiple daytime measurements (2-6 sampling times) of both ¹⁶O and ¹⁸O from each lake on five different dates. Respiration rates were greater during day than night throughout the experiment. Significant differences in day: night R ratios existed between lakes. The highest daytime respiration rates were in the fertilized lake (Peter) where day R was much greater than night R. The clear, unmanipulated lake (Paul) exhibited intermediate day: night ratios while the day: night R ratios in the colored lake (Tuesday) were consistently lowest. These results have implications for accurately estimating gross oxygen evolution and consumption rates in lakes.

Key words: gross primary production, carbon cycling, diel respiration, oxygen isotopes