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 structure and functioning of aquatic hyphomycete assemblages colonizing leaf material was investigated. The discharge resulted in elevated concentrations of iron, manganese, magnesium, calcium and nickel in the receiving water. 2. The rate of processing of both alder and sycamore leaves was reduced downstream of the discharge. Measurements of oxygen uptake by microbes associated with leaf material indicated a lower activity 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 reduction 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 discharge, with fewer species being recorded. 5. Results from this study therefore suggest that the reduction in leaf decomposition observed downstream of the mine discharge was due to a reduction in fungal activity associated with a change in species composition.