The Effects of Thermal Stratification on the Distribution of Benthic Protozoa in Esthwaite Water

Abstract

120 species of Protozoa, mainly Ciliata, were recorded from bottom samples taken over a three year period from the eutrophic Esthwaite Water in the English Lake District. Three major ecological groups were distinguished; those which are scattered in small numbers throughout conditions of high oxygenation and little putrefaction, those which are concentrated in regions of low oxygenation and much putrefaction, and those which are present in anoxic conditions. This last group includes many "sapropelic" forms; these appear to be facultative anaerobes, appearing occasionally in oxygenated conditions, but reaching their maximum numbers in the hypolimnion as the oxygen in this zone becomes progressively depleted. The development of associations of iron organisms at the boundary between oxidised and reduced conditions is described.