GRAZING AND THE DISTRIBUTION OF SEDIMENT PARTICLE SIZES IN ARTIFICIALSTREAM SYSTEMS

Recent research has shown that grazing by the algivorous minnows of th e genus Campostoma can have a significant effect on both structural an d functional parameters in stream ecosystems, influencing algal height and type, primary productivity, carbon dynamics, bacterial biomass an d the size fractionation of benthic organic matter. This study was und ertaken to evaluate the effect of minnow grazing on benthic particulat e organic matter (BPOM) under the controlled conditions available in e xperimental streams. For this study, four grazed and four ungrazed art ificial streams were sampled for BPOM on two dates. The samples were p artitioned into large, medium, fine and ultrafine fractions via wet fi ltration. Fish grazed systems had significantly larger percentages of the fine fraction and significantly smaller percentages of the ultrafi ne fraction. The ability of grazers to alter particle size distributio n is important to overall stream organic matter dynamics because recen t studies have shown the importance of particle size in determining ba cterial numbers and activity, which in turn influence fundamental stre am process like respiration and organic carbon dynamics.