Potential Hg methylation and MeHg demethylation rates related to the nutrient status of different boreal wetlands

• Published in: Biogeochemistry 2012-04, Vol.108 (1-3), p.335-350
• Main Authors: Tjerngren, I, Karlsson, T, Björn, E, Skyllberg, U
• Format: Article
• Language: English
• Subjects: Alnus; Animal and plant ecology; Animal, plant and microbial ecology; Biogeochemistry; Biogeosciences; biological activity in soil; Biological and medical sciences; Bogs; carbon nitrogen ratio; Demethylation; Earth and Environmental Science; Earth Sciences; Earth, ocean, space; Ecosystems; Environmental Chemistry; Environmental Sciences related to Agriculture and Land-use; Exact sciences and technology; Fens; Forest soils; forests; Fundamental and applied biological sciences. Psychology; Geochemistry; iron; landscapes; Life Sciences; Mercury; Methylation; Methylmercury; methylmercury compounds; Miljö- och naturvårdsvetenskap; molybdates; Nutrient status; Nutrients; Sediments; Soil and rock geochemistry; soil microorganisms; Soil nutrients; soil pH; Soil samples; Soil water; Soils; Streams; Sulfate reduction; sulfate-reducing bacteria; Sulfates; Sulfur; Surficial geology; swamps; Synecology; Terrestrial ecosystems; Wetland soils; Wetlands
• ISSN: 0168-2563; 1573-515X; 1573-515X
• DOI: 10.1007/s10533-011-9603-1

Despite methylmercury (MeHg) production in boreal wetlands being a research focus for decades, little is known about factors in control of methylation and demethylation rates and the effect of wetland type. This is the first study reporting potential Hg methylation (k m ) and MeHg demethylation rate constants (k d ) in boreal wetland soils. Seven wetlands situated in northern and southern Sweden were characterized by climatic parameters, nutrient status (e.g. type of vegetation, pH, C/N ratio, specific UV-absorption), iron and sulfur biogeochemistry. Based on nutrient status, the wetlands were divided into three groups; (I) three northern, nutrient poor fens, (II) a nutrient gradient ranging from an ombrotrophic bog to a fen with intermediate nutrient status, and (III) southern, more nutrient rich sites including two mesotrophic wetlands and one alder (Alnus) forest swamp. The k m /k d ratio in general followed %MeHg in soil and both measures were highest at the fen site with intermediate nutrient status. Northern nutrient poor fens and the ombrotrophic bog showed intermediate values of %MeHg and k m /k d . The two mesotrophic wetlands showed the lowest %MeHg and k m /k d , whereas the alder swamp had high k m and k d , resulting in an intermediate k m /k d and %MeHg. Molybdate addition experiments suggest that net MeHg production was mainly caused by the activity of sulfate reducing bacteria. A comparison with other studies, show that k m and %MeHg in boreal freshwater wetlands in general are higher than in other environments. Our results support previous suggestions that the highest MeHg net production in boreal landscapes is to be found in fens with an intermediate nutrient status.