An evaluation of techniques for measuring periphyton metabolism in chambers

Experiments were performed to compare C-14 uptake, dissolved O-2 and CO2 change, and microelectrode techniques for measuring benthic primary productivity and community metabolism at a site on the South Saskatchewan River, Saskatchewan. The highest estimates of primary productivity were obtained with O-2 microelectrodes (two to four times higher than simultaneous estimates from bulk-water dissolved O-2 measurements), presumably because measurements are biased toward active communities under optimal conditions for photosynthesis. In daytime experiments lasting similar to 1.3 and 2.4 h, estimates from C-14 uptake were higher than those measured simultaneously from dissolved O-2 and CO2 change, suggesting that C-14 uptake measured gross primary production (GPP) in these short-term incubations. Differences in experimental water velocity ranging from 0.2 to >6.5 cm . s(-1) had less of an effect than chlorophyll a concentration on metabolic rates in diel experiments with rocks taken from a site where velocities were from 5.6 to 7.8 cm . S-1. There was a potential for phosphorus and possibly NH4 limitation of metabolic activity during long-term incubations. Results highlight areas in which further research is needed when using chambers to determine periphyton metabolism.