Diatom-inferred dissolved organic carbon reconstructions provide assessments of past UV-B penetration in Canadian Shield lakes

Paleolimnological approaches have provided strong inference models for lake -water acidity and metal concentrations in Sudbury-area lakes, but calibrat ion data have not yet been explored for inferring lake-water dissolved orga nic carbon (DOC). A review of available limnological data provided DOC valu es for 80 of our 105 calibration lakes, allowing us to examine the relative importance of DOC in determining the distribution of diatom assemblages in Canadian Shield lakes, such as those in the Sudbury region. Canonical corr espondence analysis (CCA) indicated that lake-water DOC explained a signifi cant proportion of variation in the diatom data. Our weighted-averaging DOC model showed a strong relationship (r(2) = 0.63) between measured and infe rred DOC. Using this model, we reconstructed historical DOC concentrations in three Sudbury-area lakes, and then estimated temporal changes in UV-B pe netration. These reconstructions showed that lake water DOC concentrations and underwater UV-B penetration have changed markedly in two of the three l akes modeled. The close correspondence between inferred and measured DOC fo r the 1980s in all three lakes provides further evidence that we have accur ately inferred DOC concentrations. Quantitative DOC reconstructions in Sudb ury-area lakes offer an excellent technique for assessing past changes in D OC concentrations and UV-B penetration in Canadian Shield lakes.