Protozoan communities and contamination of several fluvial systems

Abstract

Eleven stations in six rivers in the Comunidad Autonoma de Madrid (Spain) were studied during February 1993 to describe the protozoan communities and analyze the presence of lead and cadmium. The most polluted areas were Fuente del Fresno (Jarama River), where the levels of dissolved heavy metals were 10 μg/L of cadmium and 1 140 μg/L of lead acid, Torrej6n de Ardoz (Henares River) where there was 15 μg cadmium and 1 140 μg/L of lead. These two areas showed the greatest amount of industrial effluents, and the protozoan response expressed itself by the presence of resistant species such Euglena gracilis; density and biomass were not affected, although there were changes in the trophic structure, with a predominance of bacterivore and nonselective protozoans. The effects of the heavy metals were masked by the organic pollution. In the stations in well‐oxygenated waters, there was a predominance of photoautotrophs and diatoms. In all zones a significant correlation between the density of bacteria and protozoans was observed. The trophic structure of the protozoan communities in the different water courses was influenced by the amount of food available and by organic pollution.