Aeration of Stockade Lake, South Dakota

Intermittent aeration of Stockade Lake (2,470 acre feet) during the summers of 1967 and 1968 temporarily altered the thermal profile and phytoplankton density. Continual aeration for 48 hours in the deepest portion of this eutrophic lake produced epilmnetic cooling, hypolimnetic warming and apparent reduction of algal populations at three sampling stations in various parts of the lake. Dye, released at the aeration site, was found at all depths throughout the lake after 461/2 hours aeration. Air bubbles, rising from diffuser blocks near the lake bottom, carried cold, hypolimnetic water to the surface at a rate of 4.7 million gallons per hour. A dye-movement study indicated that most of the uplifted water moved a short distance from the aeration area in a radial-horizontal direction, sank to approximately the 15-foot depth and traveled at this depth throughout the lake as eddies dispersed water upwards and downwards. The eddies apparently increased with aeration time. A homothermous condition was not achieved and dissolved oxygen concentrations in the hypolimnion were not raised sufficiently to increase the volume of fish habitat. The effects of aeration described in this paper show that individual lake characteristics and weather may determine the extent of limnological changes