Changes in concentration of aquatic hyphomycete spores in Lees Creek, ACT, Australia

Aquatic hyphomycetes in Lees Creek were sampled by membrane filtration: (i) every fourth hour over 12 h at one site; (ii) at six sites along the stream, the first five sites being situated within the same native riparian vegetation while the last site was located after the stream had passed through several kilometres of exotic riparian vegetation; (iii) immediately before and after a debris dam. Spore numbers increased as the day progressed, with afternoon collections being significantly higher than morning collections. Total spore numbers increased significantly at successive sites but decreased when the stream flowed through exotic riparian vegetation. A constant supply of substrata as the stream flows through the native vegetation probably enables spores to be added to the stream faster than they are lost, while the downstream exotic vegetation fails to supply sufficient substrata and losses of spores exceed spore input. No significant differences occurred between the total number of spores collected either side of the debris dam, although there were changes in the relative abundance of some species, indicating a differential removal and addition of spores as the stream passed the dam.