Effects of Bubble Plumes on Lake Dynamics, Near-Bottom Turbulence, and Transfer of Dissolved Oxygen at the Sediment-Water Interface
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AbstractWe quantify the lake dynamics, nearbottom turbulence, flux of dissolved oxygen (DO) across the sedimentwater interface (SWI) and their interactions during oxygenation in two lakes. Field observations show that the lake dynamics were modified by the bubble plumes, showing enhanced mixing in the nearfield of the plumes. The interaction of the bubbleinduced flow with the internal density structure resulted in downwelling of warm water into the hypolimnion in the farfield of the plumes. Within the bottom boundary layer (BBL), both lakes show weak oscillating flows primarily induced by seiching. The vertical profile of mean velocity within 0.4m above the bed follows a logarithmic scaling. One lake shows a larger drag coefficient than those in stationary BBLs, where the classic lawofthewall is valid. The injection of oxygen elevated the water column DO and hence, altered the DO flux across the SWI. The gas transfer velocity is driven by turbulence and is correlated with the bottom shear velocity. The thickness of the diffusive boundary layer was found to be consistent with the Batchelor length scale. The dynamics of the surface renewal time follow a lognormal distribution, and the turbulent integral time scale is comparable to the surface renewal time. The analyses suggest that the effect of bubble plumes on the BBL turbulence is limited and that the canonical scales of turbulence emerge for the timeaverage statistics, validating the turbulence scaling of gas transfer velocity in lowenergy lakes.
