PARENT SESSION
Oral Session # 51: Limnology II: Plankton; Carbon.
Presiding: K Forshay
Wednesday, August 6. 1:30 PM to 5:00 PM, SITCC Meeting Room 101.

Carbon sources for invertebrate predators in a whole-lake experiment.

Fankhauser, Crystal^*,1, Bade, Darren¹, Carpenter, Stephen¹, ¹ University of Wisconsin-Madison, Madison, Wisconsin, USA

ABSTRACT- Chaoborus, the phantom midge, is an important invertebrate predator in many lake ecosystems. The carbon in Chaoborus could be derived from endogenous (autochthonous) primary production of the lake itself, or from exogenous (terrestrial) sources. Using results from a whole-lake addition of inorganic ¹³C, we estimated ecosystem level inflows and outflows of carbon to Chaoborus spp. Using a simple dynamic model fitted to the data, we estimated the proportion of Chaoborus carbon that derives from primary production within the lake. Chaoborus ¹³C signature changed from -36 to -11 per mil following the isotope addition. Carbon inputs to Chaoborus were estimated at 20 mmol C m^-2 d^-1. Although this is less than half of the mean gross primary production during the experiment (49 mmol C m^-2 d^-1), using our model, we found that 20 to 50% of Chaoborus carbon originated from outside the lake (exogenous sources). This represents a significant terrestrial subsidy to this pelagic invertebrate predator and to the secondary production of this lake ecosystem.

Key words: carbon, Chaoborus, stable isotopes