Lake level and trophic state variables among a population of shallow Florida lakes and within individual lakes

Monthly total phosphorus, total nitrogen, and chlorophyll concentrations, Secchi depth, and lake water level data for 84 Florida lakes were used to examine relations between trophic state variables and water level fluctuation. Lake size averaged 566 ha (range 4.0 to 5609 ha), with the period of record for individual lakes averaging 57 months (range 7 to 175 months). Lake level fluctuation for individual lakes averaged 1.3 m (range 0.1 to 3.5 m). The lakes also ranged from oligotrophic to hypereutrophic, with average chlorophyll values for individual lakes ranging from 1 to 97 mu g center dot L-1. No overall relation between trophic state variables and lake level fluctuation could be found among the population of lakes. However, individual lakes showed direct, inverse, or no significant relations between lake trophic state variables and water level fluctuation, regardless of the magnitude of water level fluctuation. These data suggest that predicting how water level fluctuations will impact trophic state variables among a population of lakes will be difficult, if not impossible, and that any accurate predictions will have to be made after first examining several mechanisms within individual lake systems.