Seasonal and Spatial Variation in Algal Bloom Frequencies in Lake Okeechobee, Florida, U.S.A.

ABSTRACT

This study quantified the seasonal and spatial distribution of algal blooms (defined as chlorophyll a >40 μg L⁻¹) in Lake Okeechobee, based on 13 years of data collected from eight pelagic monitoring stations by the South Florida Water Management District Relationships between bloom frequencies and limnological parameters, including nutrient (nitrogen and phosphorus) loading rates, in-lake nutrient concentrations, Secchi transparencies, lake stage, and wind velocities, were investigated by rank correlation analyses. Blooms were found to vary both seasonally and spatially; they were most frequent during late spring and autumn, and they generally occurred in the northern and western regions of the pelagic zone. Blooms were least frequent in a central pelagic region where resuspension of soft mud sediments by wind produces frequent light limitation. Lake-wide bloom frequencies were uncorrelated with external loads of phosphorus and nitrogen, but were positively correlated with water temperatures (r = 0.19, p = 0.009) and Secchi transparencies (r = 0.22, p = 0.003). Blooms were negatively correlated with both wind velocity (r = −0.45, p = 0.05) and total phosphorus (r = −0.30, p < 0.001). The latter reflects a wind-driven resuspension of phosphorus-containing sediment particles, which produces low light availability and a subsequent decoupling of total phosphorus and algal blooms in this shallow lake ecosystem.

Key Words:

• algal blooms
• shallow lakes
• subtropical limnology
• Lake Okeechobee