The composition of periphyton commun-ities was assessed over an extensive range of New Zealand river environments during late-summer low flows. The chemical, hydrological, and watershed characteristics of the sites were determined and broad associations developed between communities and several key variables. Eight communities were identified and 91 sites classified into groups according to the presence of the first seven of these communities. Most were dominated by filamentous periphyton taxa. A taxonomic-biomass classification was also developed by condensing the site groups into three, more general, classes based on their biomass. Sixty-eight percent of the sites were in the low-biomass class (i.e., < 20 g m~ 2 ash-free dry weight). Twenty-two environmental characteristics of the sites varied significantly across the periphyton groups indicating strong habitat associations by the periphyton. Conductivity of the water was the most important environmental variable. A discriminant model was tested for each classification using an independent dataset to determine whether the groups or classes could be predicted accurately from environmental factors. The models were moderately successful (50 and 57% correct predictions, respectively), but were only sensitive to major changes in values of individual environmental variables.
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