The effects of fungicide chlorothalonil on leaf litter breakdown rate in tropical streams: a microcosm study

Streams draining through agricultural catchments are subjected to multiple stressors including pollution with nutrients and pesticides. Pesticides, in interaction with other agricultural stressors, can impact microbial diversity and key ecosystem processes underlying the delivery of ecosystem services from streams. The understanding of how such stressors interact to alter ecosystem structure and function and how responses of biota reflect their longer-term disturbance history remains limited. Effects of the fungicide chlorothalonil on litter breakdown rates of riparian tree leaves of Ficus racemosa and sedge Panicum maximum were assessed in 40-day indoor microcosm systems. Litter breakdown rates were analysed in microcosms treated with chlorothalonil concentrations of 0.01, 0.025, 0.10, 0.25 and 1.0 mg/L and in control tanks without pesticides using the ANCOVA test. The results of the study indicated a significant reduction ( P < 0.05) of litter breakdown rate in chlorothalonil-treated tanks compared to the control tanks in terms of reduction percentage of dry weight and organic matter, microbial community sporulation and nutrient content. These alterations were modulated by the litter quality and microbial colonisations on leaf materials. Findings of the study emphasise the importance of considering indirect effects of pesticides on ecological processes. Stressing the need for deeper insight into how multiple stressors can affect the functioning of aquatic ecosystems and associated services.