The eutrophication of Cayuga Lake: a historical analysis of the phytoplankton's response to phosphate detergents

SUMMARY. Phytoplankton surveys of Cayuga Lake over the past 60 years indicate that summer algal crops have doubled and spring algal crops have increased 20-fold. The pattern of algal seasonal succession has changed from a summer maximum comprised of a mixture of diatoms, greens and blue-greens to a spring maximum comprised of diatoms followed by diminished summer levels with dominance by greens and blue-greens. Summer algal standing crop and the shift to a spring pulse are shown to be related phenomena resulting from the pattern of phosphorus loading to the lake. The combination of data on algal biomass, chlorophyll and Secchi disc transparency serve to describe the long-term trend in the lake's trophic state and demonstrate a large increase in algal standing crop in the period roughly coincidental with the advent of phosphorus-based detergents. The increase in algal standing crop from pre-1940 levels to present levels closely corresponds with that predicted by the Oglesby—Schaffner regression model from the increase in phosphorus loading due to phosphorus-based detergents.