Effects of antimicrobial-fungicide mixtures on leaf litter processing and growth of the amphipod Hyalella azteca

Leaf litter processing is important for ecosystem functioning (e.g., river continuum theory).  Rates of conversion of coarse particulate organic matter (CPOM) to fine particulate organic matter (FPOM) can affect energy flow and the C cycle. This processing is strongly tied to microbial and fungal communities. Certain contaminants (antimicrobials and fungicides) can affect these microbes and fungi in systems that receive WWTP effluents and urban runoff.  Mixtures of these compounds are likely in urban environments. The combination of antibiotics and fungicides may expand the overall spectrum of activity (i.e., the breadth of toxicity to microorganisms) and result in impacts that surpass a threshold maintained by functional redundancy. In this study we examined how mixtures of fungicides and antimicrobials affect leaf litter processing in the stream detritivore Hyalella azteca. A leaf shredder bioassay was used to assess the individual and mixture effects of antimicrobials and fungicides. Hyalella azteca were allowed to choose conditioned leaf disks that were exposed to each treatment and leaf processing was assessed.  Measured responses included loss of leaf ash-free dry mass, H. azteca mass and total body length, and growth indices. Results will be discussed. It is possibly the these results will suggest that complex mixtures involving common constituents in both WWTP effluent and urban runoff should be considered for understanding risk to aquatic invertebrates. Ultimately, effects on decomposition processes from these mixtures may have the potential to influence energy and nutrient flows through aquatic ecosystems and affect multiple tropic levels.