Relationships Between Concentrations of Sedimentary Variables and Trophic State in Florida Lakes

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Abstract
Midlake sediment samples from 97 Florida lakes were analyzed for organic matter (LOI 550 °C), carbonate (LOI 550–990 °C), total C, N, and P, and pigment (SCDU665) content. We used simple correlation and multiple regression to examine relationships between concentrations of selected sediment constituents, or their ratios, and trophic state (Carlson's TSI) of the overlying waters. Simple concentrations of sediment variables are poor predictors of TSI. The best simple correlation relates N per gram of organic matter to TSI–Chl a but explains only 27% of the variance in trophic state. The best multiple regression model incorporates five independent sediment variables and accounts for 43% of the variance in TSI–Chl a. Reasons for the poor relationships include (1) interlake variation in the dilution of organic matter and pigments by allochthonous inorganics, (2) variation among lakes in the diagenesis of surface sediments, (3) differential contributions of insoluble, large particulate, inorganic P, and (4) failure of open-water TSI measures to account for contributions to sediments from littoral and allochthonous sources.