Limnetica 31

The waters of the reservoirs Paso Bonito, Avilés, Abreus and El Salto, located at south-center of Cuba, are used in agriculture, fishing, industries and human consumption. The aim of this research was to identify the physicochemical characteristics of the water of these reservoirs and the influential processes. Application of Gibbs and Piper diagrams to the major ions of the water, measured during the period 1986-2005, identified weathering as the natural process with greater influence on chemical composition of the water. The concentrations of major ions were only significantly different between periods (dry and wet) in Abreus reservoir, in relationship to its position within basin. Significant similarities according to ANOVA were frequent between Abreus and El Salto, where the alkalinity was also higher by silicates weathering in correspondence with its geology. The influence of anthropogenic activities on water quality was revealed by mean of Cl⁻ : Na⁺ + K⁺, Ca²⁺ + Mg²⁺ : Na⁺ + K⁺ ratios and trophic state index determined by measurements of transparency, nutrients and chlorophyll a. Eutrophy was predominant in reservoirs, where the basins are more antropized. The application of a graphical method revealed that values of Chlorophyll a were the cause of turbidity of water in Aviles, Abreus and El Salto and that nitrogen was the limiting nutrient for phytoplankton growth.