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The effects of hydrologic fluctuation and sulfate regeneration on mercury cycling in an experimental peatland
Author(s) -
Coleman Wasik J. K.,
Engstrom D. R.,
Mitchell C. P. J.,
Swain E. B.,
Monson B. A.,
Balogh S. J.,
Jeremiason J. D.,
Branfireun B. A.,
Kolka R. K.,
Almendinger J. E.
Publication year - 2015
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
eISSN - 2169-8961
pISSN - 2169-8953
DOI - 10.1002/2015jg002993
Subject(s) - peat , sulfate , environmental chemistry , methylmercury , deposition (geology) , chemistry , dissolved organic carbon , cycling , environmental science , mercury (programming language) , hydrology (agriculture) , ecology , geology , sediment , bioaccumulation , history , paleontology , archaeology , geotechnical engineering , organic chemistry , computer science , biology , programming language
Abstract A series of severe droughts during the course of a long‐term, atmospheric sulfate‐deposition experiment in a boreal peatland in northern Minnesota created a unique opportunity to study how methylmercury (MeHg) production responds to drying and rewetting events in peatlands under variable levels of sulfate loading. Peat oxidation during extended dry periods mobilized sulfate, MeHg, and total mercury (Hg T ) to peatland pore waters during rewetting events. Pore water sulfate concentrations were inversely related to antecedent moisture conditions and proportional to past and current levels of atmospheric sulfate deposition. Severe drying events caused oxidative release of MeHg to pore waters and resulted in increased net MeHg production likely because available sulfate stimulated the activity of sulfate‐reducing bacteria, an important group of Hg‐methylating bacteria in peatlands. Rewetting events led to increased MeHg concentrations across the peatland, but concentrations were highest in peat receiving elevated atmospheric sulfate deposition. Dissolved Hg T concentrations also increased in peatland pore waters following drought but were not affected by sulfate loading and did not appear to be directly controlled by dissolved organic carbon mobilization to peatland pore waters. Peatlands are often considered to be sinks for sulfate and Hg T in the landscape and sources of MeHg. Hydrologic fluctuations not only serve to release previously sequestered sulfate and Hg T from peatlands but may also increase the strength of peatlands as sources of MeHg to downstream aquatic systems, particularly in regions that have experienced elevated levels of atmospheric sulfate deposition.