Primary Productivity in a Large, Temperate Lake with River Interflow: Kootenay Lake, British Columbia

Phytoplankton productivity in a large, deep lake with river interflow was determined using an incubator method modified to include vertical distributions of chlorophyll and temperature together with continuous surface irradiance measurements. The annual average areal production, in 1977, was 170 g C∙m−2 with daily areal productions ranging from 100 to 2800 mg C∙m−2. Pmax for all samples correlated well with chlorophyll a (r = 0.79). No large horizontal trends in areal productivity or Pmax were found in the lake at any time of the year. However, pronounced differences with depth in the photosynthetic characteristics of populations within the euphotic zone were common during the stratified season. The two large inflowing rivers are thought to be important to the productivity of Kootenay Lake as they initiate the spring production peak and supply nutrients to the deeper phytoplankton populations during the summer and fall period.Key words: phytoplankton, productivity, incubator, riverine lake, vertical structure