Lake-size dependency of wind shear and convection as controls on gas exchange

High-frequency physical observations from 40 temperate lakes were used to examine the relative contributions of wind shear (u(*)) and convection (w(*)) to turbulence in the surface mixed layer. Seasonal patterns of u(*) and w(*) were dissimilar; u(*) was often highest in the spring, while w(*) increased throughout the summer to a maximum in early fall. Convection was a larger mixed-layer turbulence source than wind shear (u(*)/w(*) < 0.75) for 18 of the 40 lakes, including all 11 lakes < 10 ha. As a consequence, the relative contribution of convection to the gas transfer velocity (k, estimated by the surface renewal model) was greater for small lakes. The average k was 0.54 m day(-1) for lakes < 10 ha. Because u(*) and w(*) differ in temporal pattern and magnitude across lakes, both convection and wind shear should be considered in future formulations of lake-air gas exchange, especially for small lakes. Citation: Read, J. S., et al. (2012), Lake-size dependency of wind shear and convection as controls on gas exchange, Geophys. Res. Lett., 39, L09405, doi:10.1029/2012GL051886.