PARENT SESSION
Oral Session #27: Aquatic Ecology: Lake structure and function. Presiding: L.A. Hansson.
Tuesday, August 7, 2001. 8:00 AM to 11:30 AM. Hall of Ideas I.

Predicting the stable isotope signature of dissolved inorganic carbon in lakes.

Bade, Darren¹, Carpenter, Stephen¹, Cole, Jonathan², Pace, Michael², Hanson, Paul¹, ^{1 2}

ABSTRACT- Dissolved inorganic carbon (DIC) in lake water arises from four sources: atmospheric exchange, hydrologic inputs, organismal respiration, and carbonate dissolution. Each of these sources, in addition to other processes (e.g. photosynthesis), influences the carbon isotope signature of the DIC. We conducted a comparative study of nine lakes in Northern Wisconsin. The 13C–DIC in these lakes ranged from –28‰ to –5‰ spanning nearly the entire range of values previously reported in the literature. The isotope signature was highly correlated with pH (R² = 0.88). However, this relationship does not explain the importance of different sources of DIC or processes acting on the DIC. We constructed a mechanistic model to predict carbon isotope signatures of DIC in lakes and tested the model using data from the comparative study. In the model, total phosphorus and dissolved organic carbon are predictors of photosynthesis and respiration; lake area, mean depth and landscape position are predictors of atmospheric exchange and hydrologic regime. Respiration and photosynthesis exhibit a greater control on the carbon isotope signature of smaller lakes, while hydrology and atmospheric exchange are of greater importance for larger lakes. The ability to predict the isotope signature of DIC increases our understanding of carbon cycling in lakes and has important implications for aquatic food web studies that employ stable isotope techniques.

KEY WORDS: carbon, stable isotope, dissolved inorganic carbon, lake