Effects of the Fungicide Tebuconazole on Leaf Litter Decomposition in Agricultural Streams: A Microcosm Study

Abstract

Fungicides have the potential to deleteriously affect the non-targeted aquatic microbial communities, macroinvertebrates communities and key ecosystem processes such as litter decomposition, nutrient recycling. Tebuconazole (TBZ) is a commonly used fungicide in agricultural areas in Sri Lanka. Although a few research looked at how other fungicides affected decomposer communities and aquatic ecosystem processes including leaf litter decomposition, there were no studies on Tebuconazole’s effects on stream ecosystems. The present study aimed at investigating the effects of TBZ on Terminalia arjuna decomposition in tropical streams. A 40-day indoor microcosm study was conducted to evaluate the leaf litter breakdown rate of Terminalia arjuna subjected to TBZ concentrations of 0.1mg/L, 1mg/L and control tanks with dechlorinated water. The leaf Decomposition Rates (DR) were analysed using the %Dry weight reduction (%DWR) and %organic matter reduction (%OMR) using ANCOVA keeping time as a covariate in microcosms. Dunnett’s post hoc test was used to determine the significant differences among treated and control channels. The results indicated that there was a lower decay coefficient (k) for TBZ treated leaf packs in comparison to control leaf packs (k control: -0.0104±0.0005> k 0.1mg/L: -0.0093±0.0007> k 1mg/L: -0.0087±0.0002), suggesting a delay in DR when exposed to TBZ contamination. There was a significant reduction of % dry weight in control tanks in comparison to treatment tanks (p<0.05) while no significant difference (p>0.05) of %OMR among the leaf packs in treated and control tanks. The finding of the study suggests that the fungicide TBZ can harm the non-target aquatic fungi which are not resistant to TBZ contamination thus affecting the leaf litter decomposition process. A high concentration of TBZ exposure suppresses the leaf litter decomposition process.