La caractérisation d'herbiers aquatiques du lac des Deux-Montagnes (Québec) à partir de paramètres physiques de l'eau

Abstract

Forty-four sites of aquatic plant communities of lac des Deux-Montagnes were studied during the summer of 1981 for floristic composition and six physical parameters (depth, pH, amount of phosphate, conductivity, alkalinity, and amount of dissolved oxygen). In a first step, the percent cover of every species in each community served to calculate the similarity between the 44 sites. The data were then analysed by principal coordinate analysis and hierarchic agglomeration cluster analysis. The study of the ordination and the dendrogram revealed 12 principal groups. Subsequently, a discriminant analysis, based upon six physical parameters, identified the parameters which most contribute to discrimination between the groups. Those parameters are pH, depth, alkalinity, and amount of dissolved oxygen. The classification resulting from the discriminant analysis agrees in a proportion of 72.97% with the original classification based on the floristic composition. A contingency table has been analysed to establish the role of each individual parameter on every one of the groups. Finally, the causality of this discrimination is discussed in relation to fine partitioning of shallow waters in the littoral zone.