Original paper

Distribution of heterotrophic nano- and microflagellates in sediments of two small mesotrophic lakes

Auer, Brigitte; Kiertucki, Edyta; Arndt, Hartmut

Abstract

The taxonomic composition, abundance and biomass of heterotrophic flagellates (HF) in the sediment of Lake Fühlinger See, a complex of gravel pit lakes, were studied at three sampling periods along a transect from littoral to profundal. One lake treated with hypolimnetic aeration was compared with an untreated lake. Abundances of heterotrophic flagellates ranged from 150 to 6370 ind./cm3 and were significantly higher in the upper zone of the lake (0-4 m depth) than in the lower zone (7-14m). Only minor variations were observed between the sampling dates in winter, spring and summer regarding both total abundance and structure of the benthic community. Bodonids and euglenids formed the major part of HF in numbers and biomass. Other groups such as chrysomonads, thaumatomastigids and other representatives of Protista incertae sedis were of minor importance. Diplomonads including anaerobic species were mainly observed in the profundal. Among the abiotic parameters, we assume oxygen concentration as the driving factor in determining the total flagellate abundances, but strong interactions between other sediment parameters inhibit a clear analysis of single effects. In a short-term experiment with artificial aeration of profundal sediments, the flagellate densities strongly increased for 15 days subsequent to growing bacteria numbers, but returned to the initial values after three weeks.

Keywords

heterotrophic flagellatessedimentstaxonomic compositionwater depth