Diatoms epiphytic on Cladophora were examined from 36 sites in the Saint Lawrence River between Salaberry-de-Valleyfield and Ile d’Orleans (Quábec, Canada). A total of 129 diatom taxa were identified from Cladophora in June 1995, and of these, 34 species were present at a relative abundance ≥ 1% at three or more sites. The four most abundant taxa were Cocconeis pediculus, Achnanthes minutissima, Rhoicosphenia abbreviata and Gomphonema minutum. Canonical correspondence analysis (CCA) was used to explore the relationship between diatom assemblages on Cladophora and measured environmental variables. Conductivity, turbidity, temperature, distance downstream from Cornwall (Ontario), and fecal coliform concentrations were significantly (p>0.05) related to the distribution of the diatoms; the primary response was to conductivity. Although this relationship was not strong (λ1=0.13 and λ2=0.08), the calibration set model generated to infer conductivity had moderate predictive ability (r2jack=0.24 and RMSEjack=51.7). Based on modelling statistics and general observations, epiphytic diatoms on Cladophora may prove to be a useful biomonitor of water quality in the river.
Bibliographical noteFunding Information:
This project was partially supported by a Tri-Council grant to J.P. Smol, as well as a research
grant from the Natural Sciences and Engineering Research Council of Canada. We thank Brian F. Cumming for critical reviews of earlier drafts of this manuscript, as well as M. Sullivan and two anonymous reviewers. Chantal Vis at the University of Montreal and the Government of Quebec Ministry of Environment provided some of the environmental data. John R. Clew provided the map of sample locations.
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