BENTHIC MACROINVERTEBRATE ASSEMBLAGES IN NORTH SWEDISH STREAMS - ENVIRONMENTAL RELATIONSHIPS

An analysis of the relationships between lotic macroinvertebrates and environmental variables was carried out on material from 60 riffle sites in streams in northern Sweden. The approach involved the use of TWINSPAN classification and canonical correspondence analysis on presence/absence data from two seasons (spring and autumn). Variables most strongly associated with distribution patterns of assemblages were drainage area, elevation, water quality in terms of alkalinity, colour and phosphate, and the presence of macrophytes. The significance of affinities of different species to these variables are discussed. The eight clusters resulting from the TWINSPAN analysis could biologically be interpreted as classes of taxa related to stream size, chemical conditions and algae. A multiple regression analysis for predicting species richness using three independent variables, viz. drainage area, amount or organic matter, and discharge was constructed. The results of the study could be used as a starling point for further work on the community organization of benthic stream assemblages.