Design and testing of two ice-preserving winter lake aeration systems

As part of an effort to achieve ice-preserving lake aeration for winterkill prevention, two non-mixing lake aeration systems were designed and field tested. Each creates a fish refuge by oxygenating a layer of the lake while preserving water temperature stratification and ice cover such that no open water is generated. Both systems withdraw near-anoxic water from one part of a lake and discharge the water after on-shore aeration to another part of the lake. Both employ cascade aerators having design discharge and dissolved oxygen input rates of roughly 60 l/s and 40 kg/day, respectively. Aerated water is discharged near mid-depth with minimal disturbance of the ambient water through specially designed manifold/diffusers. The diffuser in one case is linear and 15 m long while the other is axisymmetric and 2 m in diameter. The manifold/diffuser designs were developed by extensive laboratory experimentation followed by prototype manufacture and field testing. The aerators are currently in use in Minnesota lakes.