Abstract:
Pesticides applied into agricultural lands can contaminate waterways and affect the different
levels of the aquatic food web and key ecosystem processes underlying the provision of
ecosystem services from streams. Chlorothalonil is a commonly used fungicide, in agricultural
areas in Sri Lanka, but its effect on non-targets such as in-stream ecological processes is less
explored. The objectives of the present study were to assess the effects of Chlorothalonil on leaf
litter decomposition rate and freshwater plankton communities. The effect of fungicide
Chlorothalonil on Ficus racemosa and Panicum maximum litter breakdown rate and plankton
community composition were assessed in indoor microcosm systems with treatment tanks of
Chlorothalonil concentrations: 0.01, 0.025, 0.1, 0.25, 1 mg/L and in control tanks with
freshwater for 40 days. The leaf breakdown rates in treatment and control tanks for both leaf
types were compared using ANCOVA with time as covariate and plankton counts were compared
using one-way ANOVA. The results of the study indicated a significant reduction (p<0.05) of
litter breakdown rate in terms of % dry weight reduction, % organic matter reduction and %
nutrient content reduction in treatment tanks with Chlorothalonil in comparison to control
tanks in Ficus leaves. Moreover, a significant difference was observed only in the % dry weight
reduction and no significant difference was observed in % organic matter reduction and %
nutrient content reduction in Panicum leaves. The study further revealed that these alterations
were further modulated by leaf litter quality and inhibition of microbial colonisations on leaves.
Further, a significant reduction (p<0.05) of plankton counts was also observed in Chlorothalonil
treated tanks in comparison to control tanks after 20 days. The findings of the study suggests
that the fungicide Chlorothalonil can have multiple impacts on non-target organisms of litter
decomposing organisms and plankton communities and thus affecting the ecosystem processes
of aquatic systems.