BENTHOS AND MACROINVERTEBRATE DRIFT IN 6 STREAMS DIFFERING IN ALKALINITY

The productive capacity of aquatic systems often is equated with the ' chemical richness' of the water. A primary objective of the present st udy was to relate macroinvertebrate benthos and drift to a streams' pr oductive capacity as indicated by absolute levels of alkalinity. We te sted this relationship in six 2nd-3rd order tributaries of the Salmon River, Idaho that ranged in alkalinity from 50 to 360 mg 1(-1). Benthi c density and biomass, drift biomass, and benthic organic matter incre ased with increasing levels of alkalinity, although not all relationsh ips were significant. The proportion of drift biomass to benthic bioma ss was similar among study streams suggesting that drift was primarily passive during the study period. The data suggest that spatial variat ions in landscape-scale geology may indirectly affect spatial patterns of macroinvertebrate benthic and drift standing crops among streams w ithin a single river basin by mediating lotic chemical richness as fou nd among tributaries of the Salmon River basin.