Natural variability of carbon dioxide and net epilimnetic production in the surface waters of boreal lakes of different sizes

The variability of surface water carbon dioxide concentration, or partial p ressure (pCO(2)) was studied in 11 lakes of greatly varying size (2.4 ha up to 8 million ha) in Northwest Ontario, Canada. Six of these lakes were cho sen to be as similar as possible in all respects except surface area (the N orthwest Ontario Lake Size Series [NOLSS], which range from 88 to 35,000 ha ). Spatial and temporal variability of pCO(2) within a single lake was no g reater in the larger lakes than in the smaller lakes. Interannual variabili ty was significant and synchronous, which indicates that weather patterns w ere important and affected the different lakes within the region in a simil ar manner. However, annual pCO(2) averages were not related to annual diffe rences in planktonic photosynthetic activity, measured by (CO2)-C-14 fixati on. In the six NOLSS lakes, there was not a significant relationship of ave rage pCO(2) with lake size. For all 11 lakes, however, there was a signific ant negative correlation of pCO(2) with lake size, which was likely due to several characteristics of the very small and very large lakes that covarie d with size. The larger lakes were deeper and had longer water residence ti mes and lower DOC, which suggests lower CO2 production from allochthonous o rganic carbon inputs. Also, the ratio of epilimnetic sediment area/epilimne tic volume (A(e)V(e)) was smaller in the larger lakes, which likely resulte d in lower rates of recycling of fixed carbon to CO2 during summer stratifi cation.