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, to tal nitrogen, total suspended solids and light availability were exami ned for the limnetic environment of Lake Okeechobee. Results indicate that spatial and temporal heterogeneity for these trophic state parame ters preclude a ''whole'' lake approach to modelling chlorophyll-a. Di scriminant function, correlation, and stepwise regression analyses inv olving the five parameters reveal four distinct ecological zones. Thes e results and related work point toward a number of hypotheses relatin g phytoplankton standing crops in these zones to different combination s 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 prim ary producers accentuate nutrient limitation of phytoplankton standing crop. Highest chlorophyll-a levels are found in the northern and west ern regions of the lake, which are closest to point sources of phospho rus-rich water inflow. In the latter two regions nitrogen availability appears to be the dominant factor in the control of phytoplankton sta nding crop.