Aquatic insect emergence at a landscape scale: an example from the Icelandic “midge lake”

Aquatic insects are capable of transferring large amounts of aquatically-derived biomass and nutrients to terrestrial ecosystems. One outstanding example of this phenomenon is Lake Mývatn (Icelandic “midge lake”) in Northeast Iceland, known for over 1000 years for its massive midge (Chironomidae) swarms. Billions of midges emerge annually, forming mating columns over the lakeshore, with many eventually dying there. Since 2008 we have been describing patterns of midge flux from the lake to the surrounding land. We have measured midge emergence from the lake and midge density at various distances from the lake margin. Using these data we have determined the scale and spatial distribution of the transfer. In the first two years total midge emergence from Lake Mývatn averaged over 100 metric tons annually, depositing in excess of 30 kg ha-1 yr-1 of midges within the first 50 meters of lakeshore, equal to over 3 kg ha-1 yr-1 N. Our data demonstrate the importance of aquatic insect movement to land, while also highlighting lakes as significant sources of aquatic insects in addition to rivers and streams. The flux of midges into the terrestrial ecosystem has profound consequences for terrestrial plant and arthropod assemblages; nearly matching background rates of atmospheric N deposition and providing prey and carcasses to predatory arthropods and detritivores respectively.