Multivariate analysis of the water quality of a set of Quebec lakes: finding watershed explicative factors of the acidification process

Abstract

In this study, a new methodological approach is proposed to analyze the spatial variability of the water quality of a set of lakes. The Quebec region under study is located in the southeast part of the Canadian Shield between the Ottawa River and the Saguenay River. The proposed methodology is based on the combined use of correspondence analysis and hierarchical classification analysis. These methods provided the analyst with a geometric representation of the spatial variation of the physicochemical parameters of the water quality (pH, alkalinity, calcium + magnesium, sulfate) recognized as indicators of the acidification of aquatic ecosystems. Afterwards by imposing a contiguity constraint in hierarchical classification, the analysis led to the delimitation of five geographical regions that are similar with respect to the four variables related to the acidification process. Then the relations between the water quality variables and some biophysical variables are examined. The multiple correspondence analysis made it easier to identify the biophysical variables of the watershed that are explicative of the water quality variables. Amongst these explicative variables examined, we have identified that the sulfate concentration in the precipitation, the annual precipitation, the altitude of lakes, and the type of vegetation and geology are more or less explicative for the alkalinity, the pH, the Ca + Mg, and the sulfate. The results can be used to build a regression model for the prediction of some physicochemical variables from the knowledge of certain key variables describing the biophysical characteristics of the watersheds. Key words: spatial variability, multivariate analysis, acidification, water quality, explicative factors, lakes, Quebec.