Factors controlling phytoplankton populations in maritime Antarctic lakes.

Abstract

The 17 lakes on Signy Island, S Orkney Islands, provide examples of most lake types found in the maritime Antarctic. There are considerable differences in nutrient and phytoplankton concentrations, linked to the level of natural enrichment (by birds and seals) occurring on the catchment areas. The interdependence of nutrient loadings, nutrient concentrations and standing crop of phytoplankton produced is a consistent feature of phytoplankton ecology. Under winter snow and ice cover, photosynthesis was undetectable, and phytoplankton populations decreased. Inorganic nutrient regeneration occurred in both oligotrophic and mesotrophic lakes but was much more extensive in the latter. Algae responded rapidly to increased light levels in spring and a shade-adapted population developed. In the oligotrophic lake, phosphate rapidly became limiting, whereas the winter accumulation permitted a dense population to develop in the mesotrophic lake despite low irradiance. Turbulent mixing under ice facilitated growth in the latter. Major losses to the outflow and grazers as well as the onset of nutrient limitation terminated this spring bloom. During summer, the oligotrophic lake remained phosphate limited, while the high P load from the animal-enriched catchment resulted in N-limitation in the mesotrophic lake. Relatively high production rates were maintained and may have been supported by rapid internal nutrient recycling.-from Author