Temporal and spatial environmental variability in the Upper Rhône River and its floodplain

Abstract

SUMMARY This paper develops a framework of spatial and temporal variability for a habitat typology of the Upper Rhône River (France) and its alluvial floodplain that is based on about 17 years of data collection and analysis. The aim was to provide a scale of spatial‐temporal variability for river habitat templet predictions on trends in species traits and species richness. In developing this framework, eight physical‐chemical variables were available and could be considered for twenty‐two habitat types: seventeen superficial (surface) and five interstitial (0.5 m below the substrate surface). These habitat types were selected in two areas (Jons and Brégnier‐Cordon) after geomorphological considerations and because of differences in their biological characteristics. The data sets used were processed by a ‘fuzzy coding’ method using, for each variable, the frequency distribution (by modalities = categories) of all measurements and monthly means over an annual scale. Two tables were produced; the first corresponded to an expression of the total variability, and the second represented an evaluation of the temporal variability. Each of these tables was analysed by correspondence analysis, which provided factorial scores that were used to calculate, by habitat type and by variable, a total variability and a temporal variability in terms of cumulated variability of factorial scores for the eight physical–chemical variables. The rationale in describing variability from these two tables is that total variability equals temporal variability plus spatial variability. The spatial variability was then determined by the difference between total and temporal variability. From this procedure, a positioning of the twenty‐two habitat types on the spatial and temporal variability axes was obtained. The estimate of spatial variability did not consider any error term that may have occurred in the above model; it was then tested by an independent assessment of the spatial variability using thirteen variables in nine major habitat types. A high correlation between the two ways of assessing spatial variability (r = 0.85, P < 0.004) underscored the reliability of the spatial variability that was calculated previously. The river habitat templet obtained for the Upper Rhône and its alluvial floodplain appears to be appropriate to test the predictions on patterns of species traits and species richness in the framework of spatial and temporal variability.