Under Ice Water Movements Induced by Mechanical surface Aeration and Air Injection

ABSTRACT

We tested the hypothesis that successful lake aeration for winterkill prevention induces large-scale (whole-lake) convective flow rather than discrete aerated cells. Discrete circulating cells were not identified using mechanical surface aeration or air injection. Thermal destratification reached the most distant shorelines (up to 900 m). However, dissolved oxygen levels began to decline at about 600 m in lakes with surface aerators and at about 800 m with air injection. Vertical mixing was determined by the depth below the diffusers or surface aerators (as opposed to z_max). In addition, small depressions or distinct basins separated from the aerated basin by a shallow sill stratified and tended toward anoxia as winter progressed. Near-field velocity and dye measurements helped define zones of detrainment and entrainment near the aeration devices. These observations revealed a new conceptual model comprised of single detrainment and entrainment plumes separated by a sheer zone.

Key Words:

• winter lake aeration
• destratification
• mixed layer
• entrainment and detrainment plume