SPATIAL AND TEMPORAL VARIABILITY OF TROPHIC STATE PARAMETERS IN A SHALLOW SUBTROPICAL LAKE (LAKE OKEECHOBEE, FLORIDA, USA)

Spatial and temporal variations of chlorophyll-a, total phosphorus, total nitrogen, total suspended solids and light availability were examined for the limnetic environment of Lake Okeechobee. Results indicate that spatial and temporal heterogeneity for these trophic state parameters preclude a ''whole'' lake approach to modelling chlorophyll-a. Discriminant function, correlation, and stepwise regression analyses involving the five parameters reveal four distinct ecological zones. These results and related work point toward a number of hypotheses relating phytoplankton standing crops in these zones to different combinations of factors that affect light and nutrient limitation. In the center of the lake, frequent resuspension of muddy sediments creates a strong potential for light limitation of phytoplankton standing crop. Along the perimeter, shallow depth and extensive populations of benthic primary producers accentuate nutrient limitation of phytoplankton standing crop. Highest chlorophyll-a levels are found in the northern and western regions of the lake, which are closest to point sources of phosphorus-rich water inflow. In the latter two regions nitrogen availability appears to be the dominant factor in the control of phytoplankton standing crop.