Ecological Factors Controlling Insect-Mediated Methyl Mercury Flux from Aquatic to Terrestrial Ecosystems: Lessons Learned from Mesocosm and Pond Experiments

Abstract

The diets of terrestrial consumers can be subsidized by emerging adult aquatic insects that transport energy and nutrients from aquatic to terrestrial ecosystems. However, these cross-ecosystem subsidies can have a “dark side” because emerging aquatic insects also transport bioaccumulative contaminants such as methyl mercury (MeHg) to terrestrial ecosystems (i.e., insect-mediated MeHg flux). Although ecological factors (such as aquatic community structure) are known to influence aquatic insect emergence and the cross-ecosystem transport of energy and nutrients, less is known about the ecological factors that regulate insect-mediated MeHg flux. This chapter provides an overview of our mesocosm and pond experiments that investigated how ecological factors affect the transport of MeHg out of aquatic ecosystems by emerging insects. The factors we investigated were (1) fish predation and community structure, (2) nutrient levels and trophic state, (3) drying disturbance and pond permanence, and (4) seasonality of insect emergence. Based on the results of our experiments, we hypothesize that the potential for insect-mediated MeHg flux increases with MeHg contamination of the ecosystem but that the realized insect-mediated MeHg flux is determined by ecological factors that regulate production of adult aquatic insects and composition of aquatic insect communities. © Springer Nature Switzerland AG 2020.