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.

Whole-system metabolism in small lake ecosystems: Challenging continuous free-water oxygen methods with mechanistic models.

Van de Bogert, Matthew^*,1, Cole, Jonathan¹, Pace, Michael¹, Hodgson, James², ¹ Institute of Ecosystem Studies, Millbrook, NY² St. Norbert College, DePere, WI

ABSTRACT- With the advent of reliable, continuous, free-water measurements of dissolved oxygen, researchers can directly measure net ecosystem production which is the difference between gross primary production (total photosynthesis; GPP) and ecosystem respiration (R). Since R can be estimated from dissolved oxygen and gas exchange at night, these continuous oxygen records can be used to estimate both GPP and R at relatively short time scales (minutes). Physiologically based models provide independent estimates of GPP from photosynthetic parameters (P_bmax, alpha), phytoplankton and/or periphyton biomass, and photosynthetically-available radiation. How well do physiologically-based models perform in reproducing continuous measurements of dissolved oxygen in the mixed-layers of small lakes? We generated physiologically-based models for 4 lake basins for which we had continuous oxygen data from sondes which recorded every 5 minutes for about 100 d during the ice-free season. The lake basins differed in DOC and food-web structure and one of the basins (Peter L. in 2002) was also eutrophied by daily additions of N and P. The lake basins also received daily additions of inorganic ¹³C which allowed us to further constrain carbon cycling parameters. Measured values of GPP varied from 31 to 104 mmol C m^-2 d^-1 among the basins and R from 32 to 79 mmol C m^-2 d^-1. GPP/R ratios were less than 1 in all but the fertilized lake and NEP ranged from -8 to +24 mmol C m^-2 d^-1. Physiological models using only pelagic compartments failed to reproduce the diel pattern and magnitudes in measured dissolved oxygen. The addition of benthic GPP and R significantly improved the fit. Inferred values of benthic GPP and R were large enough to affect the spatial patterns and magnitude in dissolved oxygen. The diel amplitude in oxygen increases dramatically from offshore to onshore, consistent with the models.

Key words: whole-lake metabolism, benthic-pelagic links, aquatic ecosystems, oxygen