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Experimental removal of wetland emergent vegetation leads to decreased methylmercury production in surface sediment

Journal of Geophysical Research G: Biogeosciences

By:
, , , , , , , and
DOI: 10.1029/2008JG000815

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Abstract

We performed plant removal (devegetation) experiments across a suite of ecologically diverse wetland settings (tidal salt marshes, river floodplain, rotational rice fields, and freshwater wetlands with permanent or seasonal flooding) to determine the extent to which the presence (or absence) of actively growing plants influences the activity of the Hg(II)-methylating microbial community and the availability of Hg(II) to those microbes. Vegetated control plots were paired with neighboring devegetated plots in which photosynthetic input was terminated 4-8 months prior to measurements, through clipping aboveground biomass, severing belowground connections, and shading the sediment surface to prevent regrowth. Across all wetlands, devegetation decreased the activity of the Hg(II)-methylating microbial community (kmeth) by 38%, calculated MeHg production potential (MP) rates by 36%, and pore water acetate concentration by 78%. Decreases in MP were associated with decreases in microbial sulfate reduction in salt marsh settings. In freshwater agricultural wetlands, decreases in MP were related to indices of microbial iron reduction. Sediment MeHg concentrations were also significantly lower in devegetated than in vegetated plots in most wetland settings studied. Devegetation effects were correlated with live root density (percent volume) and were most profound in vegetated sites with higher initial pore water acetate concentrations. Densely rooted wetlands had the highest rates of microbial Hg(II)-methylation activity but often the lowest concentrations of bioavailable reactive Hg(II). We conclude that the exudation of labile organic carbon (e.g., acetate) by plants leads to enhanced microbial sulfate and iron reduction activity in the rhizosphere, which results in high rates of microbial Hg(II)-methyation and high MeHg concentrations in wetland sediment.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Experimental removal of wetland emergent vegetation leads to decreased methylmercury production in surface sediment
Series title:
Journal of Geophysical Research G: Biogeosciences
DOI:
10.1029/2008JG000815
Volume
114
Issue:
G2
Year Published:
2009
Language:
English
Publisher:
American Geophysical Union
Contributing office(s):
National Research Program - Western Branch
Description:
14 p.
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Journal of Geophysical Research G: Biogeosciences
Number of Pages:
14