Mercury cycling in agricultural and managed wetlands of California, USA: Seasonal influences of vegetation on mercury methylation, storage, and transport

Plants are a dominant biologic and physical component of many wetland capable of influencing the internal pools and fluxes of methylmercury (MeHg). To investigate their role with respect to the latter, we examined the changing seasonal roles of vegetation biomass and Hg, C and N composition from May...

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Bibliographic Details
Published in:The Science of the total environment 2014-06, Vol.484, p.308-318
Main Authors: Windham-Myers, Lisamarie, Marvin-DiPasquale, Mark, Kakouros, Evangelos, Agee, Jennifer L., Kieu, Le H., Stricker, Craig A., Fleck, Jacob A., Ackerman, Josh T.
Format: Article
Language:English
Subjects:
Agriculture
Bioaccumulation
Biomass
California
Environmental Monitoring
Litter
Mercury - analysis
Methylation
Methylmercury
Methylmercury Compounds - analysis
Rice
Root
Seasons
Water Pollutants, Chemical - analysis
Wetlands
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Summary:Plants are a dominant biologic and physical component of many wetland capable of influencing the internal pools and fluxes of methylmercury (MeHg). To investigate their role with respect to the latter, we examined the changing seasonal roles of vegetation biomass and Hg, C and N composition from May 2007–February 2008 in 3 types of agricultural wetlands (domesticated or white rice, wild rice, and fallow fields), and in adjacent managed natural wetlands dominated by cattail and bulrush (tule). We also determined the impact of vegetation on seasonal microbial Hg methylation rates, and Hg and MeHg export via seasonal storage in vegetation, and biotic consumption of rice seed. Despite a compressed growing season of ~3months, annual net primary productivity (NPP) was greatest in white rice fields and carbon more labile (leaf median C:N ratio=27). Decay of senescent litter (residue) was correlated with microbial MeHg production in winter among all wetlands. As agricultural biomass accumulated from July to August, THg concentrations declined in leaves but MeHg concentrations remained consistent, such that MeHg pools generally increased with growth. Vegetation provided a small, temporary, but significant storage term for MeHg in agricultural fields when compared with hydrologic export. White rice and wild rice seeds reached mean MeHg concentrations of 4.1 and 6.2ng gdw−1, respectively. In white rice and wild rice fields, seed MeHg concentrations were correlated with root MeHg concentrations (r=0.90, p
ISSN:0048-9697
1879-1026
DOI:10.1016/j.scitotenv.2013.05.027