An environmental problem hidden in plain sight? Small human-made ponds, emergent insects, and mercury contamination of biota in the Great Plains.

Mercury (Hg) contamination of small human-made ponds and surrounding terrestrial communities may be 1 of the largest unstudied Hg-pollution problems in the United States. Humans have built millions of small ponds in the Great Plains of the United States, and these ponds have become contaminated with atmospherically deposited mercury. In aquatic ecosystems, less toxic forms of Hg deposited from the atmosphere are converted to highly toxic methylmercury (MeHg). Methylmercury is incorporated into the aquatic food web and then can be transferred to terrestrial food webs via emergent aquatic insects. The authors present a conceptual model that describes the movement of MeHg produced in aquatic ecosystems to terrestrial consumers via insects emerging from small human-made ponds. The authors hypothesize that pond permanence and the level of Hg contamination of the food web control this emergent insect-mediated flux of MeHg. The highest insect-mediated flux of MeHg is predicted to be from fishless semipermanent ponds with food webs that are highly contaminated with MeHg. Further development and testing of the conceptual model presented in the present column, particularly in the context of a changing climate, will require research at the regional, watershed, and pond scales.