A 10 year study at four sites of the middle course of the River Loire I - Patterns of change in hydrological, physical and chemical variables in relation to algal biomass

Abstract

The hydrobiological, physico-chemical characteristics and algal biomass were studied for ten years at the level of Dampierre-en-Burly, Saint-Laurent des Eaux and Chinon situated in the mean part of the River Loire from spring to Autumn. We proceeded to modelling data of 12 abiotic parameters and 1 biological parameter and then to graphical representation of Principal Component Analysis in order to determine the major characteristics of this part of the River. We examined the differences between the upstream and downstream sites and the average seasonal pattern of the River, and the between-months and between-years variability. The characteristics of the middle Loire are typical of an eutrophic river, nutrients were never depleted in these sites. Flow was the most influential factor on the changes in algal biomass. The inter-month analysis illustrated the displacements of the time course of the seasons from upstream to downstream. An increase of the algal biomass was observed from Dampierre-en-Burly to Saint-Laurent des Eaux in relation with the decrease in nutrients and silicate, while the algal biomass was globally lower at the downstream site of Chinon. The inter-month variability seemed to be higher than the inter-annual changes. These results will conduce to observe with more attention the seasonal succession of algae.