Dilution of 210Pb by organic sedimentation in lakes of different trophic states, and application to studies of sediment‐water interactions1

Abstract

Lake sediments reflect conditions in the water column and can be used for rapid, integrative measurements of limnological variables. Examination of 210Pb‐dated cores from 12 Florida lakes of widely differing trophic state (expressed as Carlson’s trophic state index: TSI) shows that net accumulation rate of organic matter is related to primary productivity in the water column. In 26 other lakes the activity of unsupported 210Pb g−1 organic matter in surficial sediments is inversely related to trophic state and, therefore, to organic accumulation rate. From this observation we develop a new method that uses fallout 210Pb as a dilution tracer to calculate net sedimentary accumulation rates of any material in surface mud. We demonstrate strong relationships between net loss rates of biologically important materials (C, N, P, and pigments) and their respective water concentrations (expressed as TSI). Multiple regression models incorporating net sediment accumulation rates of all four variables explain up to 70% of the lake‐to‐lake variation of TSI. The 210Pb‐dilution method has applications for studies of material cycling, paleolimnology, and sediment accumulation processes.