Temporal trends of trophic state variables in a shallow hypereutrophic subtropical lake, Lake Griffi n, Florida, USA

Changes in the concentrations of selected trophic state parameters in Lake Griffi n were examined over a 22-year period. Parameters included chlorophyll-a, total nitrogen and total phosphorus. Additional information was obtained for phytoplankton composition and nutrient limitation status of phytoplankton growth over a shorter period of time, from 2000 to 2002. The central goal of the study was to examine whether the efforts to manage water quality and habitat in the system by management agencies over the study period yielded observable changes in these trophic state parameters and the relationships between them. The results of the study show a downward trend in phosphorus concentrations over the study period. Variability in meteorological conditions had an apparent effect on short-term responses of trophic state parameters. The results also point toward a role for nitrogen availability in phytoplankton dynamics, and a stronger relationship between total phosphorus concentrations and chlorophyll-a toward the latter part of the sampling period, suggesting an increasing potential for phosphorus limitation.