Net production and net heterotrophy in Lake Apopka : a comment on SCHELSKE et al. (2003). Commentary and Authors' reply

We found the conclusion of SCHELSKE et al. (2003, Arch. Hydrobiol. 157:145-172) that Lake Apopka was not net heterotrophic was incorrect when annual rates of production and respiration for the entire lake ecosystem are taken into consideration. A new carbon budget for the water and sediments showed for the period of study the sum of the annual sources of organic carbon including primary production and inflows (765 g C m -2 yr -1 ) was less than the sum of the annual losses including respiration in the water and sediments and outflows (2497 g C m -2 yr -1 ). Diel oxygen curves demonstrated that it is possible to have oxygen supersaturation at the surface near midday and still have net heterotrophy over 24-h.