Recovery of aquatic insect-mediated methylmercury flux from ponds following drying disturbance

Small ponds exist across a permanence gradient and pond permanence is hypothesized to be a primary determinant of insect community structure and insect-mediated methylmercury (MeHg) flux from ponds to the surrounding terrestrial landscape. Here we present the first experiment examining the recovery of insect-mediated MeHg flux following a drying disturbance that converted permanent ponds with insectivorous fish to semi-permanent ponds without fish. We used floating emergence traps to collect emergent insects for 10 weeks in the spring and summer from five ponds with fish (permanent) and five ponds that were drained to remove fish, dried and refilled with water (semi-permanent). During the 73 day period after semi-permanent ponds were refilled, total MeHg flux from semi-permanent ponds was not significantly different than total MeHg flux from permanent ponds, indicating that insect-mediated MeHg flux had rapidly recovered in semi-permanent ponds following the drying disturbance. Methylmercury fluxes from dragonflies (Odonata: Anisoptera) and phantom midges (Diptera: Chaoboridae) were significantly greater from newly refilled semi-permanent ponds than permanent ponds but the MeHg fluxes from other eight emergent insect taxa did not differ between treatments. The present study demonstrates the impact of drying disturbance and the effect of community structure on the cross-system transport of contaminants from aquatic to terrestrial ecosystems. This article is protected by copyright. All rights reserved