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 2LoPb-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 *l"Pb g-l 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 *l"Pb 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.

Comment on “Dilution of 210Pb by organic sedimentation in lakes of different trophic states, and application to studies of sediment‐water interaction“ (Binford and Brenner)

“…We thank Benoit and Hemond (1988) for their comments on our paper (Binford and Brenner 1986). They criticize our assumptions and the literature citations supporting them, and question our interpretations and proposed applications of the results.…”

“…I also welcome short quotations, original thoughts in prose or verse, cartoons, and other lighter contributions to fill small patches of white space. Comment on "Dilution of 2 *OPb by organic sedimentation in lakes of different trophic states, and application to studies of sediment-water interaction" (Binford and Brenner) Binford and Brenner (1986) propose to evaluate two hypotheses: that organic matter accumulation in lake sediments is directly related to primary productivity, and that specific activity of 210Pb in surficial sediments is inversely related to sediment accumulation rate. The second hypothesis is based on the assumption that the *lOPb supply rate to lake sediments is constant so that ?lOPb concentration in surficial sediments is determined only by dilution by other sedimentary components.…”

Estimating modern carbon burial rates in lakes using a single sediment sample

“…We incorporate the earlier work of Binford and Brenner (1986), who formulated an approach to estimate the trophic state of a lake based similarly on the degree of 210 Pb dilution in the surface sediments. We demonstrate-by validation against conventional measures of whole-lake OC burial-the applicability of this method in a variety of lake types covering a large range of size and depth, and show how this approach furthers our understanding of the transport, focusing, and burial of OC and atmospheric 210 Pb.…”

Reply to comment by Benoit and Hemond

“…Oceanogr., 33(2), 1988, 304-310 0 1988, by the American Society of Limnology and Oceanography, Inc Reply to comment by Benoit and Hemond We thank Benoit and Hemond (1988) for their comments on our paper (Binford and Brenner 1986). They criticize our assumptions and the literature citations supporting them, and question our interpretations and proposed applications of the results.…”

“…In the study of Binford (in prep. ), which includes different Florida lakes from Binford and Brenner (1986), each region has a slightly different mean (0.3540.33, 0.40+0.20,0.48+0.11, and 0.55kO.32 pCi cm-2 yr-I).…”