Nutrient Limitation in Two Arctic Lakes, Alaska

Abstract

Batch-culture algal bioassays of Selenastrum capricornutum were used to predict the limiting nutrient in two small arctic–tundra lakes in 1979. In 1980 bioassays were performed again, and fertilizer was added to the lakes to test the predictions made from the 1979 bioassay results. In 1980, after the addition of phosphorus fertilizer, phytoplankton standing crop increased ~10-fold. After the addition of nitrogen fertilizer, another 10-fold increase in phytoplankton growth was measured. Concurrently, maximum daytime dissolved oxygen increased from 100 to 150% saturation, and pH increased from 7.0 to about 9.2. Further additions of fertilizer in late August and early September 1980 caused no significant increase in primary production. If the nitrogen content of the lake water is increased but that of phosphorus is not, no increase in algal growth occurs. Growth increases with phosphorus additions, but the magnitude of this increase is determined by the available nitrogen. When additional nitrogen is supplied to the system, further increases in algal growth occur. When nitrogen and phosphorus are supplied in excess, physical factors such as light or temperature become limiting in the lakes.