Lake to land subsidies: experimentally simulating aquatic insect deposition

Aquatic insects are an important subsidy to terrestrial systems yet little is known about how these inputs affect terrestrial food webs. In 2008, approximately 1 trillion midges emerged from Lake Mývatn, a shallow eutrophic lake in northern Iceland. We simulated the Mývatn lake-to-land subsidy by collecting midges from Mývatn and spreading their dried carcasses on 1-m2 plots at a nearby site that does not receive midge deposition. By manipulating the nutrient pulse delivered by midges we were able to elucidate ecosystem and food web consequences of midge deposition that are difficult to determine based on comparative approaches. Midge addition resulted in significantly increased densities of arthropods in comparison to control plots. Plant-available nitrogen was also higher in midge-addition plots. Arthropod responses were taxon-specific and Diptera, Hymenoptera and Collembola responded especially strongly.