Seasonal Patterns of Chlorophyll, Nutrient Concentrations and Secchi Disk Transparency in Florida Lakes

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Abstract
Florida lakes as a group exhibited a distinct seasonal pattern in the concentration of algal chlorophylls. This conclusion was based on an analysis of data from the Florida LAKEWATCH 1994 database containing 416 lake-years of observations from 209 lakes. For oligotrophic, mesotrophic, and eutrophic lakes, monthly chlorophyll concentrations were typically lower than the annual mean chlorophyll concentration from December to May and were higher from August to October. Hypereutrophic lakes (annual mean chlorophyll > 40 μg·L−1) tend to have high fluctuating levels of algal chlorophyll for most of the year except for low levels in December, January, and February. Maximum chlorophyll concentrations tended to occur most frequently from August to October, however the maximum or minimum level in any given lake can occur at any time of the year. The variance (s2) in monthly chlorophyll concentrations over the course of a year increased with increasing annual mean chlorophyll for Florida lakes. There was also seasonal variation in the monthly values for total phosphorus, total nitrogen, and Secchi disk transparency though the magnitude of the fluctuations was about half that for chlorophyll. They also showed increasing variance with increasing lake means. The 95% confidence limits for estimates of annual mean chlorophyll concentrations in these lakes with 12 monthly samples was ±27% of the mean. Similar confidence limits for means of total phosphorus, total nitrogen, and Secchi disk transparency were 15%, 9%, and 10%, respectively.