Seasonal changes in plankton and nutrient dynamics and carbon flow in the pelagic zone of a large, glacial lake: Effects of suspended solids and physical mixing

Abstract The abundance and distribution of phytoplankton and zooplankton were followed from January 1993 to March 1994 in Lake Coleridge, a deep oligotrophic alpine lake in the Canterbury high country of New Zealand. Our data suggest physical processes associated with deep mixing and inputs of suspended sediments combined to limit planktonic biomass, diversity, and determine vertical distribution. The lake was strongly stratified in summer with a surface mixed layer of 20 m gradually extending down to 100 m by May. Over 50 taxa of phytoplankton were recorded. Changes in vertical distribution of most planktonic groups coincided with changes in the depth of vertical mixing. Phytoplankton biomass increased through summer with a diatom‐dominated peak in autumn. Cell numbers however, peaked in spring and were dominated by small chlorophytes. Phytoplankton photosynthetic production was highest in autumn but specific growth rates were highest in summer as a result of greater light availability combined with warm...