Oxygen measurements in the burrows of freshwater insects

1. Thin-tipped micro-electrodes were used to measure oxygen concentrations in the burrows of two common aquatic insects, the mayfly Hexagenia limbata and the alderfly Sialis velata. Both species maintain their surroundings ox ygenated by drawing water from above the sediment surface into their tubes. 2. The temporal pattern of oxygen in the burrows differed between the speci es. The constant high oxygen concentration ( > 75% of air saturation) measu red in the tubes of the mayfly suggest that this animal pumps water almost continuously, which is consistent with its high oxygen requirements. In con trast, oxygen concentration in burrows of the alderfly fluctuated widely ov er time, suggesting that this animal irrigates only irregularly, probably b ecause it can tolerate short periods of low oxygen concentration in its bur row. 3. The interval between pumping episodes by the alderfly decreased with inc reasing temperature, a result of increased oxygen consumption by the animal and by sediment at high temperature. 4. Based on the tube dimensions, oxygen penetration depth and animal densit y in lakes, we estimate that Hexagenia could create an oxic micro-environme nt equivalent to 3-35% of the volume of the surface oxidized sediment layer created by molecular diffusion. The mosaic of oxic micro-environments crea ted by the burrowing and irrigation of freshwater animals could influence c hemical and biological processes in sediments, the fluxes of materials betw een the sediment and the overlying water column, and the exposure of benthi c animals to sedimentary contaminants.