Effects of Bubble Plumes on Lake Dynamics, Near-Bottom Turbulence, and Transfer of Dissolved Oxygen at the Sediment-Water Interface

We quantify the lake dynamics, near-bottom turbulence, flux of dissolved oxygen (DO) across the sediment-water 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 near-field of the plumes. The interaction of the bubble-induced flow with the internal density structure resulted in downwelling of warm water into the hypolimnion in the far-field 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 0.4 m above the bed follows a logarithmic scaling. One lake shows a larger drag coefficient than those in stationary BBLs, where the classic law-of-the-wall 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 log-normal 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 time-average statistics, validating the turbulence scaling of gas transfer velocity in low-energy lakes.

Automated summary

We quantified lake dynamics, near-bottom turbulence, dissolved oxygen (DO) flux across the sediment-water interface (SWI), and their interactions during oxygenation in two lakes. Field observations revealed that lake dynamics were modified by bubble plumes, leading to enhanced mixing in the near-field. The interaction of bubble-induced flow with the internal density structure resulted in the downwelling of warm water into the hypolimnion in the far-field. Weak oscillating flows within the bottom boundary layer (BBL), primarily induced by seiching, were observed in both lakes. The injection of oxygen elevated water column DO and altered DO flux across the SWI. Gas transfer velocity was driven by turbulence and correlated with the bottom shear velocity. The diffusive boundary layer thickness was found to be consistent with the Batchelor length scale. Bubble plumes had limited effects on BBL turbulence, and canonical scales of turbulence emerged for time-average statistics, validating the turbulence scaling of gas transfer velocity in low-energy lakes.