The effect of fungicides on aquatic fungi and leaf decay

S. Herbert¹, J.L. Meyer¹, and K.L. Armbrust². ¹Institute of Ecology, University of Georgia, Athens, Georgia, USA 30602, ²Mississippi State Chemical Lab, Mississippi State University, MS State, MS 39762

Pesticides are frequently detected in suburban streams, where runoff from residential areas is piped directly to streams. Stream food webs could be altered by adverse effects of pesticides on non–target organisms such as aquatic fungi, which play a crucial role in the breakdown of leaves. In this study, we tested whether the concentrations of three fungicides typically found in suburban streams – flutolanil, chlorothalonil and its degradation product hydroxychlorothalonil – had an effect on biomass accumulation of aquatic fungi and decay rates of tulip-poplar leaves (Liriodendron tulipifera) in stream microcosms. Low fungicide concentrations were comparable to those measured in suburban streams, and high concentrations were comparable to those measured at a golf course tile drain. No effect of chlorothalonil or flutolanil on fungal biomass was observed; however, with increasing hydroxychlorothalonil concentrations, three measures of fungal growth decreased. Significant leaf decay occurred in the control flasks, and in one of the flutolanil treatments, but there was no leaf decay in any other treatment. These low, but environmentally realistic concentrations of fungicides inhibited leaf decay, and the degradation product of chlorothalonil, hydroxychlorothalonil, reduced fungal biomass. Frequent fungicide detection in streams requires further research on the adverse effects of these compounds on non–target organisms and ecological processes.