EFFECTS OF A COAL-MINE EFFLUENT ON AQUATIC HYPHOMYCETES .1. FIELD-STUDY

1. The effect of a discharge from an abandoned coal mine on the struct ure and functioning of aquatic hyphomycete assemblages colonizing leaf material was investigated. The discharge resulted in elevated concent rations of iron, manganese, magnesium, calcium and nickel in the recei ving water. 2. The rate of processing of both alder and sycamore leave s was reduced downstream of the discharge. Measurements of oxygen upta ke by microbes associated with leaf material indicated a lower activit y at this station. This reduction in activity was particularly marked for the fungal assemblages associated with leaf material. 3. Scanning electron micrographs of leaf surfaces indicated that hyphal cover was also reduced on downstream-incubated leaf material. The observed reduc tion in fungal activity and hyphal cover below the mine discharge may have resulted from a change in species-specific fungal biomass and/or a change in the number of fungal species present. 4. Surveys indicated that the structure of the fungal assemblage was different below the d ischarge, with fewer species being recorded. 5. Results from this stud y therefore suggest that the reduction in leaf decomposition observed downstream of the mine discharge was due to a reduction in fungal acti vity associated with a change in species composition.