Phytoplankton in Lake Tahoe: Deep‐living Populations1

Most of the phytoplankton biomass in Lake Tahoe is located below the euphotic zone. Algae from deep water (100–400 m) appear healthy and fix CO2 at significant rates when exposed to near‐surface illumination. The relationship between the distributions of phytoplankton standing crop and production is best explained by passive sinking of cells out of the euphotic zone and accumulation in deep waters. This recruitment of deep phytoplankton from surface waters may be an important feature of deep oligotrophic lakes, limiting primary production and nutrient regeneration in the euphotic zone.