Iron and Sulfur Porewater and Surface Water Biogeochemical Interactions in Subtropical Peatlands. Issue 3 (24th June 2016)

• Record Type: Journal Article
• Authors: Julian, Paul; Wright, Alan L.; Osborne, Todd Z.
• Is Part Of: Soil Science Society of America Journal. Volume 80:Issue 3(2016)
• Page Start: 794
• Page End: 802
• Publication Date: 2016-06-24
• Subjects: Soils -- United States -- Periodicals; Soil science -- Periodicals; Periodicals; 631.4973
• DOI: 10.2136/sssaj2015.11.0418
• Languages: English
• ISSNs: 0361-5995

Abstract

Abstract : Core Ideas: Surface water sulfate has been implicated in influencing Hg cycling and methylation, this relationship is tenuous at best therefore other variables and biogeochemical cycles could be involved with Hg methylation dynamics. While thought of as a minor biogeochemical constituent, Fe is involved several biogeochemical interactions including the regulation of surface water sulfate concentrations by producing iron minerals. The results of this study suggest that dissolved organic C supply has the ability to regulate dissimilatory sulfate reduction, rather than sulfate supply within the Everglades marsh. Elevated sulfate (SO4 2− ) concentrations have been implicated in affecting Hg cycling and methylation within the Everglades, leading to environmental concerns regarding methyl‐Hg (MeHg) accumulation in wildlife. The interaction of S and Hg cycles is not fully understood in freshwater wetlands, and factors regulating these elemental cycles are warranted. Iron has been demonstrated to influence S cycling patterns, which in turn could influence Hg cycling. Therefore, this study explores Fe and S interactions across three distinct Everglades freshwater marshes in South Florida. Surface water SO4 2− was positively correlated with porewater sulfide (S 2− ) concentrations ( r = 0.57) due to reducing conditions favoring conversion of SO4 2− to S 2− . Dissolved Fe concentrations were lower in surface water than in porewater presumably due to geologic or biogeochemical reactions that precipitate Fe, essentially removing it from the water column. Both porewater S 2− and surface water SO4 2− were negatively related with Fe porewater concentrations ( r = −0.64 and r = −0.72, respectively). Sulfate reduction estimates were highly variable between sampling locations with high S 2− to SO4 2− ratios occurring at relatively low porewater Fe concentrations, while low S 2− to SO4 2− ratios occurred at high Fe concentrations. Porewater dissolved organic carbon (DOC) significantly influenced porewater S 2− concentrations ( R 2 = 0.55 and slope = 0.74), suggesting that organic substrate supply could in part be regulating SO4 2− reduction. Iron was a major control of SO4 2− reduction and S cycling and thus has the potential to indirectly affect Hg cycling by altering patterns of SO4 2− reduction and mitigating SO4 2− reduction‐induced Hg methylation.