Paleoecological Investigations of Recent Lake Acidification in Northern Florida

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acidic deposition, diatoms, Florida, hydrology, paleoecology, sediment chemistry

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Thirty-two northern Florida lakes were analyzed to construct a transfer function relating surface sediment diatom assemblages to lakewater pH (R2=0.89, s.e.=0.34). A paleoecological analysis of sediment cores from six of these lakes indicated that two have become more acidic in the last 50 years. The diatom inferred (DI) pH of L. Barco has declined between 0.56-0.82 in the 1900's and DI ANC (acid neutralizing capacity) by 28-46 μeq l-1. The DI pH of nearby L. Suggs has declined 0.91 pH units and its DI ANC by 19 μeq l-1. The timing of the inferred acidification is synchronous with known increases in emissions of sulfates and nitrates that are associated with acidic precipitation. Also, the increasing accumulation of substances related to emissions from the burning of fossil fuels (e.g., Pb, PAH) co-occurs with the lowering of DI pH in the sedimentary record. However, other processes may have accounted for or contributed to recent lake acidification. For instance, the drawdown of local water tables by human consumption may decrease the inseepage of ANC to seepage lakes. Such an effect would be synchronous with increasing depositions of sulfate. There is also clear evidence that Florida lakes are naturally acidic. Thus, paleoecological results indicate acidic deposition to be at certain contributor, but not necessarily the sole cause, of the recent further acidification of some naturally acidic Florida lakes. © 1990 Kluwer Academic Publishers.

Citation / Publisher Attribution

Journal of Paleolimnology, v. 4, issue 2, p. 103-137