MIXING AND THE DYNAMICS OF THE DEEP CHLOROPHYLL MAXIMUM IN LAKE TAHOE

Chlorophyll-temperature profiles were measured across Lake Tahoe about every 10 days from April-July 1980. Analysis of the 123 profiles and associated phytoplankton productivity and nutrient data identified 3 important processes in the formation and dynamics of the deep chlorophyll maximum (DCM): turbulent diffusion, nutrient supply rate and light availability. Seasonal variation in these 3 processes resulted in 3 regimes: a diffusion-dominated regime with a weak DCM, a variable-mixing regime with a pronounced, nutrient supply-dominated DCM and a stable regime with a deep, moderate light availability-dominated DCM. The transition between the 1st 2 regimes occurred in about 10 days, the transition between the last 2 more gradually over .apprx. 3 wk. The degree of spatial variability of the DCM was highest in the 2nd regime and lowest in the 3rd. The DCM in Lake Tahoe is constant in neither time nor space.