Mercury cycling in agricultural and managed wetlands, Yolo Bypass, California: Spatial and seasonal variations in water quality

The seasonal and spatial variability of water quality, including mercury species, was evaluated in agricultural and managed, non-agricultural wetlands in the Yolo Bypass Wildlife Area, an area managed for multiple beneficial uses including bird habitat and rice farming. The study was conducted durin...

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Bibliographic Details
Published in:The Science of the total environment 2014-06, Vol.484, p.276-287
Main Authors: Alpers, Charles N., Fleck, Jacob A., Marvin-DiPasquale, Mark, Stricker, Craig A., Stephenson, Mark, Taylor, Howard E.
Format: Article
Language:English
Subjects:
Agriculture
California
Environmental Monitoring
Iron-reduction
Manganese
Mercury - analysis
Methylmercury
Rice agriculture
Sulfate-reduction
Water Pollutants, Chemical - analysis
Wetlands
Wild rice
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Summary:The seasonal and spatial variability of water quality, including mercury species, was evaluated in agricultural and managed, non-agricultural wetlands in the Yolo Bypass Wildlife Area, an area managed for multiple beneficial uses including bird habitat and rice farming. The study was conducted during an 11-month period (June 2007 to April 2008) that included a summer growing season and flooded conditions during winter. Methylmercury (MeHg) concentrations in surface water varied over a wide range (0.1 to 37ngL−1 unfiltered; 0.04 to 7.3ngL−1 filtered). Maximum MeHg values are among the highest ever recorded in wetlands. Highest MeHg concentrations in unfiltered surface water were observed in drainage from wild rice fields during harvest (September 2007), and in white rice fields with decomposing rice straw during regional flooding (February 2008). The ratio of MeHg to total mercury (MeHg/THg) increased about 20-fold in both unfiltered and filtered water during the growing season (June to August 2007) in the white and wild rice fields, and about 5-fold in fallow fields (July to August 2007), while there was little to no change in MeHg/THg in the permanent wetland. Sulfate-bearing fertilizer had no effect on Hg(II) methylation, as sulfate-reducing bacteria were not sulfate-limited in these agricultural wetlands. Concentrations of MeHg in filtered and unfiltered water correlated with filtered Fe, filtered Mn, DOC, and two indicators of sulfate reduction: the SO42−/Cl− ratio, and δ34S in aqueous sulfate. These relationships suggest that microbial reduction of SO42−, Fe(III), and possibly Mn(IV) may contribute to net Hg(II)-methylation in this setting. •Surface water Hg chemistry was studied in agricultural and non-agricultural wetlands.•MeHg concentrations were highest during wild-rice harvest and winter flooding.•MeHg concentrations correlated with Mn, Fe, DOC, and δ34S of dissolved sulfate.•Sulfate-bearing fertilizer amendments had no effect on Hg(II)-methylation.
ISSN:0048-9697
1879-1026
DOI:10.1016/j.scitotenv.2013.10.096