The impact of oil and oil-dispersant mixtures on fungi in freshwater ponds.

The impact of oil and oil-dispersant mixtures on the mycoflora of a freshwater ecosystem was assessed using man made ponds. Data indicated that the ponds were well stabilized before pond treatment. Sufficient Norman Wells crude oil to give 100 ppm was added to each treated pond. The dispersant, Corexit 9527, was initially one-fifth of the oil concentration in the oil-dispersant-treated ponds. After pond treatment, an immediate increase occurred in the number of geoaquatic fungi in the oil-treated pond whereas an increase, followed by a sharp decrease, which was in turn followed by a recovery occurred in the oil-dispersant-treated ponds. The fungal enhancement effects, which were slight, were largely short term in duration (7-83 days). No clear cut medium or long term geoaquatic fungal enhancement effects were observed. The pond treatments had no detectable effect on the vertical distribution of fungi in the ponds. No significant treatment effects were observed on the water mould levels in the treated ponds. No obvious treatment effect was observed on the percentage of viable fungi capable of growth on non-degraded or biodegraded oil as a sole carbon source. Fifteen of 39 selected pond water fungi were able to grow on non-degraded Norman Wells oil. Corexit 9527 incorporated into agar plates inhibited the radial growth of the oil utilizing fungal isolates; EC50 values were determined.