Dynamics of phyto- and bacterioplankton in a high Arctic lake on Franz Joseph Land archipelago

Pelagic food web processes with focus on phyto- and bacterioplankton dynamics were followed in a high Arctic lake on Ziegler Island, Franz Joseph Land archipelago, during July and August 1996. The oligotrophic, permanently ice-covered lake is characterized by a rather short pelagic food web with rotifers representing the highest trophic level. Phytoplankton biomass and net primary production averaging 1.8 œg chl a l-1 and 22 œg C l-1 d-1, respectively, decreased during the investigation period. Photosynthetic extracellular release (Per) corrected for bacterial uptake was high and contributed between 31% (July) and 96% (August) of total primary production. The abundance of bacteria (9.3 to 17.3 × 105 ml-1) and flagellates (7.8 to 17.3 × 102 ml-1) varied within a narrow range. Bacterioplankton production ranging from 1.2 to 3.9 œg C l-1 d-1 and bacterial growth rates (0.1 to 0.3 d-1) increased with increasing % Per, indicating that algal exudates are the major carbon source for bacterioplankton. Bacterial carbon demand (assuming a 50% growth efficiency) amounted to 19% of gross pelagic primary production (Ppart + Per) and 31% of Per during the investigation period. Evidence was found that bacterioplankton metabolism responds quickly to slight increases in temperature (1.2 to 2.0°C) with increased growth. Overall, production rates of phyto- and bacterioplankton in this high Arctic lake are similar to other Arctic lakes studied thus far, and the food web structure is even simpler than in most lakes at similar latitudes.