River continuum relationships in an 8th-order river reach: Analyses of polar ordination,functional groups,and organic matter parameters

Data on macroinvertebrate functional groups and benthic and suspended organic matter were examined using polar ordination techniques to test for distribution patterns in relation to stream size along an extended section of the Salmon River, Idaho (U.S.A.). Responses over a 200-km 8th-order section were studied in autumn 1978 and the succeeding summer. Overall trends and those of individual parameters comprising the three categories studied were used to examine aspects of the River Continuum Concept of Vannoteet al. (1980). Community composition of functional groups changed in an orderly fashion as a function of stream size (measured as link magnitude) along the 8th-order section in autumn but not in summer.Likewise, the composition of transported and combined (benthic plus transported) organic matter was a statistically significant function of stream size in autumn but not in summer. Only selected, individual functional groups and organic matter parameters demonstrated significant river continuum patterns; again, these were more prevalent in autumn than in summer. We conclude that continuum relationships within a segment of a given order are discerned better through analysis of compositional trends based on polar ordination than a focus on individual parameters.