### Relationships between composition and size distribution of invertebrates colonizing navigation buoys and physico-chemical parameters of the St. Lawrence River, Montreal (Quebec).

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 Title: Relationships between composition and size distribution of invertebrates colonizing navigation buoys and physico-chemical parameters of the St. Lawrence River, Montreal (Quebec). Authors: Mercier, Vincent. Date: 1998 Abstract: Water, algae and invertebrates colonizing navigational buoys at 18 sites in the Montreal area of the St. Lawrence River were sampled during the spring, summer and fall of 1995 to assess which measures of invertebrate assemblages (density, biomass, size distribution, and taxonomic composition) best respond to wastewater discharge and to compare invertebrate responses among sampling dates. Increases of up to five orders of magnitude in fecal coliforms, 2-fold increases in TP and PO$\sb4,$ 20-fold increases in NH$\sb4$ concentration and 2-3-fold decreases in water clarity (Secchi depth, suspended matter) were found downstream of point sources of urban wastewater discharge. Despite these physico-chemical changes, invertebrate assemblages were only weakly related to wastewater exposure, since DFA on composition and size distribution only correctly classified 44-61% of sites into groups based on fecal coliform concentration for all four sampling dates. Fecal coliforms were best predicted by Chironomidae, other Diptera and Nematoda density in the fall (mult. reg. adj.r$\sp2$ = 0.69, p $$0.001), density of invertebrates in the size class 4-8 \mug in the fall (adj.r\sp2 = 0.65, p$$ 0.001), and total invertebrate density (adj.r$\sp2$ = 0.75, p = 0.002) in the spring. Periphyton biomass, suspended matter concentration and current velocity were the main environmental correlates of invertebrate composition and size distribution patterns in the fall. In the second chapter, spatio-temporal patterns of buoy invertebrate and algal size distributions were investigated, in relation to trophic gradients in the river. The size distributions were not significantly related to physico-chemical parameters of the river, although variability in the data may have been too high to detect trophic effects. Size spectra on buoys, despite the fact that protozoans were not accounted for, had striking similarities with other complete size distributions (containing algae, protozoans and invertebrates) from stream, lake and marine littoral zones. (Abstract shortened by UMI.) URL: http://hdl.handle.net/10393/4203http://dx.doi.org/10.20381/ruor-10146 Collection Thèses, 1910 - 2010 // Theses, 1910 - 2010