A Study of Ciliate Protozoa from a Small Polluted Stream in East-Central Illinois

The role of species of ciliate Protozoa in trickling filterwaste treatment processes awaits redefinition. Using the smallfresh-water Salt Fork stream for our study, a stream which receivesall of the discharge from the Champaign-Urbana Waste TreatmentPlant in east-central Illinois, analyses of samples of carefullyidentified ciliates taken from selected sites over a three-yearperiod yielded some interesting results. Four specific situationswere noted: (1) free-swimming microphagous forms feeding selectivelyon primarily attached bacteria, and, in turn, being fed on bycarnivorous ciliates; (2) sessile ciliates (peritrichs) feedingon non-attached bacterial species, but with high selectivity;(3) free-swimming carnivorous gymnostomes feeding on the sessileperitrichs but, again in turn, serving as prey themselves tostalked suctorian species attached to the peduncles of the peritrichs;(4) attached peritrichs and suctorians both serving as foodfor several groups of small invertebrates frequenting the stream.With respect to numbers and diversity of ciliates found, some155 different species, belonging to 93 genera, were identified(including several to be described elsewhere as new species)in the stream and/or the trickling filter settling basin. Thehighest populations and greatest diversity were found at sitesclosest to the waste water influx; such protozoan populationsmight thus be considered as a form of tertiary treatment inthe drainage basin.