Production and Respiration in Lake Erie Plankton Communities

Planktonic community metabolism (photosynthesis and respiration) was assessed in the oligotrophic east basin of Lake Erie, from November 2001 to October 2002 using O2 and 14C methods. Areal gross production (AGP; mmol O2 m−2 d−1) exceeded areal respiration (AR; mmol O2 m−2 d−1) in the surface mixed layer for 69% of the observations during the study period. The median AGP:AR for the entire study period was 1.32. A significant positive relationship between AGP and AR existed, but AGP explained only 25% of the variation in AR. AGP:AR varied seasonally, being below 1.0 in the fall/winter of 2001 and in early spring 2002. High (>> 1.0) AGP:AR was observed in late spring (May) and AGP:AR remained > 1.0 for most of the summer stratified period (July–September). AGP:AR was > 1.0 in the fall of 2002, but the magnitude was less than observed during spring. The results supported traditional concepts of the seasonal production and consumption cycles in planktonic communities of large oligotrophic lakes. Parallel incubations of 14C uptake and gross O2 production determined with the light and dark bottle method revealed a mean experimental gross photosynthetic quotient (PQG) of 1.29 ± 0.48, indicating that the 14C method used here had a variable but, on average, close relationship to gross production as it is commonly measured.