THE INFLUENCE OF WATER CIRCULATION ON CHLOROPHYLL-TURBIDITY RELATIONSHIPS IN LAKE OKEECHOBEE AS DETERMINED BY REMOTE-SENSING

The spatial distribution of phytoplankton can be difficult to assess in shallow, productive aquatic systems due to frequent algal blooms, high turbidity and sediment-resuspension events. We conducted a study to assess the distribution of suspended particles in Lake Okeechobee, Florida, utilizing both Landsat (1974-75) or Advanced Very High Resolution Radiometer (AVHRR) (1987) satellite remote sensing. Surface water samples were collected by helicopter to determine in situ chlorophyll-a and turbidity levels at 20 stations on four dates in 1974-75 and six dates in 1987. Remotely sensed reflectance values agreed well with in situ particle densities at the 20 in-lake stations (average R(2): Landsat = 0.81, AVHRR = 0.53) and independent, synoptic boat mapping of algal blooms (r(2) = 0.79, P < 0.01). Basin-wide maps of chlorophyll and turbidity, as well as additional spatial sampling, both indicated that these parameters are not necessarily coupled in Lake Okeechobee. Our data concur with the hypothesis that the spatial distributions of chlorophyll and turbidity are shaped by different forces. The highest concentrations of chlorophyll occurred in the vicinity of tributary nutrient inputs at the lake's perimeter, while turbidity increased towards the center of the lake, reflecting predominant water circulation patterns.