Limnological characteristics of 25 lakes of the French Massif Central

Abstract

Concentrations of a wide range of chemical variables were determined in 206 water samples taken between May 1996 and May 1998 from a set of 25 natural lakes in the French Massif Central. From each lake 6 to 9 samples were collected. Mean and standard deviation of total alkalinity, conductivity, pH, concentrations in K⁺ , Mg²⁺ , Ca²⁺ , Na⁺ , Cl^-, SO² ₄ , total phosphorus, nitrate-nitrogen, dissolved silica, chlorophyll a, and water colour were calculated for each lake. These results are briefly compared with those obtained in an earlier study in which chemical analyses were carried out on a reduced set of lakes from the same region. In most lakes and for most elements, concentrations observed in the present study were similar to those observed previously. The seasonal variations of the elements which are most strongly influenced by biological processes were also investigated. Using hierarchical cluster analysis three main lake groups were distinguished : i) alkaline lakes, ii) deep lakes with lowalkalinity and iii) shallow lakes with low alkalinity. The major patterns of variation in the data set were also investigated using principal components analysis (PCA), which confirms that total alkalinity and maximum water depth are the main environmental gradients in this set of lakes. In conclusion, the potential of this data-set for building diatom-based transfer functions to reconstruct past limnological conditions is discussed.