Seasonality of Odonate-Mediated Methylmercury Flux
Methylmercury (MeHg) is an aquatic contaminant that can be transferred to terrestrial predators by emergent aquatic insects such as odonates (damselflies and dragonflies). We observed the effects of season on odonate-mediated MeHg flux (calculated as emergent odonate biomass × MeHg concentration) in 20 experimental ponds and the potential risk to nestling Red-winged Blackbirds (Agelaius phoeniceus) posed by consuming MeHg-contaminated odonates. Emergent odonates were collected weekly from ponds using emergence platforms from February to October 2017. The MeHg flux from damselflies, aeshnid dragonflies, and libellulid dragonflies began in March and peaked in May, June, and July, respectively, and then declined throughout the rest of the summer. Nesting of Red-winged Blackbirds overlapped with peak odonate emergence and odonate-mediated MeHg flux, suggesting that MeHg-contaminated odonates may pose a health risk to nestling Red-winged Blackbirds.