Centimeter-scale patterns in dissolved oxygen and nitrification rates in aprairie stream

Dissolved oxygen (O-2) was measured with microelectrodes in shallow subsurf ace microsites in a prairie stream and related to rates of nitrification de termined in the laboratory using the nitrapyrin method. Substrata sampled i ncluded diatom mats, leaves and wood (coarse benthic organic matter, CBOM), filamentous green algae, bryophytes, and fine benthic organic matter (FBOM ). Significant differences in O-2 concentrations were found among the subst rata, with anoxic zones occurring primarily in FBOM from deep pool sediment s and CBOM from litter accumulations. Filamentous green algae and bryophyte s had average O-2 concentrations near saturation and intermediate rates of nitrification. Diatom mats had the highest concentrations Of O-2 (up to sev eral times saturation) and the highest rates of nitrification. In the summe r, O-2 concentrations were above saturation in epilithon and filamentous gr een algal mats. Nitrification rates were highest in epilithon and filamento us green algae samples taken in the spring and autumn. A significant positi ve relationship between nitrification rates and O-2 concentration was obser ved in all seasons except summer. These data suggest that O-2 concentration could control nitrification in prairie streams.