Vertical Diffusivity in the Stratified Layers of the Mixolimnion of Green Lake, Jamesville, NY

The distribution of the turbulent component of vertical diffusivity for heat (Khz′), and the relative contributions of vertical mixing and solar radiation to heating, in the stratified layers of the mixolimnion of bio-genitally meromictic Green Lake, Jamesville, NY, were evaluated for a six month period of 1978. Field measurements included temperature and PAR (photo-synthetically active radiation) extinction profiles, collected biweekly on 13 occasions, and continuously monitored incident PAR. Khz′ varied temporally and vertically. The values were particularly low in the metalimnion, where the major mechanism of vertical heat transfer was absorption of solar radiation coupled with molecular diffusivity. Most of the heating in the hypolimnion was accomplished through turbulent processes. The vertical distribution of Khz′ was well described by Khz′ = b(N2)m, where b and m are ecosystem specific constants, and N is the Brunt-Vaisala frequency, supporting a previous theoretical prediction and the results of a similar field investigation. The specific distribution in Green Lake (m = −0.60) indicates the turbulence is largely generated by local small scale processes.