We examined how different landscape areas in a catchment containing a northern ombrotrophic peatland and upland mineral soils responded to dramatic decreases in atmospheric deposition of lead (Pb). Pb concentrations in the outflow stream from the peatland measured from 2009-2015 indicated continued mobilization and export of Pb derived from historic inputs to the bog. In contrast, Pb concentrations in surface peat and runoff from upland mineral soils have declined in response to reductions in atmospheric deposition. Relative to the early 1980s, Pb concentrations in the streamflow decreased only ∼50%, while Pb in surface peat and upland subsurface runoff decreased by more than 90%. Water level fluctuations in the slow-accumulating peat have allowed dissolved organic matter (DOM) to continue mobilizing Pb deposited in the peatland decades earlier. Strong correlations between dissolved organic carbon (DOC) and Pb concentrations in outflow from the peatland and in bog porewaters demonstrate Pb mobility related to DOM production. Peat stores of Pb in 2016 were less than or equal to those reported in the early 1980s despite the dry mass inventory increasing by 60-80%. Much of the loss in Pb stored in peat can be accounted for by stream runoff from the peatland.
Bibliographical noteFunding Information:
We acknowledge the external reviewers whose helpful comments improved the manuscript. We thank Rachel Lund, Jamison Utzig, Nick Alverson, Dan Marino, Michael Walker, and Nathan Olson for sampling assistance. Tina Dahlseid processed and assisted with analyzing samples. We thank Martin Tsui for sharing stream samples he collected. Various USDA Forest Service personnel or affiliates collected water samples, maintained long-term hydrological and meteorological monitoring, or analyzed basic water chemistry, including J Prososki, M. Wiley, M Olds, M. Mack, B. Munson, D. Kyllander, C Dorrance, J. Larson, and K. Oleheiser. Their contributions, with those of S. Sebestyen, and chemical analyses were funded by the Northern Research Station of USDA Forest Service. Additional funding was provided by the National Science Foundation (Research award number 0923430 to J. Jeremiason, IGERT funding to M. Funke and NSF-IOS 1257571 to J. Cotner) and Gustavus Adolphus College.
Their contributions, with those of S. Sebestyen, and chemical analyses were funded by the Northern Research Station of USDA Forest Service. Additional funding was provided by the National Science Foundation (Research award number 0923430 to J. Jeremiason IGERT funding to M. Funke and NSF-IOS 1257571 to J. Cotner) and Gustavus Adolphus College.
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