Relationships of Annual Chlorophyll a Means, Maxima, and Algal Bloom Frequencies in a Shallow Eutrophic Lake (Lake Okeechobee, Florida, USA)

ABSTRACT

Fifteen years of historical data from Lake Okeechobee, Florida, were used to quantify relationships between annual mean and extreme values of algal biomass, measured as chlorophyll a Yearly chlorophyll a maxima and algal bloom frequencies (the percent of samples during a year containing >40 μg L⁻¹ chlorophyll a) increased approximately 2-fold for each unit increase in the annual chlorophyll a mean, although there was some variation in these relationships among different regions of the lake. Threshold chlorophyll a concentrations (15–21 μg L⁻¹) were also identified, below which bloom frequencies were reduced to near zero. Results indicate that if nutrient diversion strategies are successful in reducing annual mean chlorophyll a concentrations in Lake Okeechobee, even more pronounced reductions in algal blooms will occur. Reductions of lake-wide chlorophyll a means to early 1980s levels might nearly eliminate algal blooms as defined here.

Key Words:

• chlorophyll a
• algal blooms
• Lake Okeechobee
• subtropical lakes