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The contribution of rice agriculture to methylmercury in surface waters; a review of data from the Sacramento Valley, California
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|Authors:||Tanner, K. Christy; Windham-Myers, Lisamarie; Fleck, Jacob A.; Tate, Kenneth W.; McCord, Stephen A.; Linquist, Bruce A.|
|Author Affiliations:||Primary: |
University of California, Davis, Department of Plant Sciences, Davis, CA, United States
U. S. Geological Survey, United States
McCord Environmental, United States
|Volume Title:||Journal of Environmental Quality|
|Source:||and [Journal of Environmental Quality, 46(1), p.133-142. Publisher: American Society of Agronomy,] Crop Science Society of America, Soil Science Society of America, Madison, WI, United States. ISSN: 0047-2425|
|Note:||In English. 80 refs.; illus., incl. 1 table, sketch map|
|Summary:||Methylmercury (MeHg) is a bioaccumulative pollutant produced in and exported from flooded soils, including those used for rice (Oriza sativa L.) production. Using unfiltered aqueous MeHg data from MeHg monitoring programs in the Sacramento River watershed from 1996 to 2007, we assessed the MeHg contribution from rice systems to the Sacramento River. Using a mixed-effects regression analysis, we compared MeHg concentrations in agricultural drainage water from rice-dominated regions (AgDrain) to MeHg concentrations in the Sacramento and Feather Rivers, both upstream and downstream of AgDrain inputs. We also calculated MeHg loads from AgDrains and the Sacramento and Feather Rivers. Seasonally, MeHg concentrations were higher during November through May than during June through October, but the differences varied by location. Relative to upstream, November through May AgDrain least-squares mean MeHg concentration (0.18 ng L-1, range 0.15-0.23 ng L-1) was 2.3-fold higher, while June through October AgDrain mean concentration (0.097 ng L-1, range 0.6-1.6 ng L-1) was not significantly different from upstream. June through October AgDrain MeHg loads contributed 10.7 to 14.8% of the total Sacramento River MeHg load. Missing flow data prevented calculation of the percent contribution of AgDrains in November through May. At sites where calculation was possible, November through May loads made up 70 to 90% of the total annual load. Elevated flow and MeHg concentration in November through May both contribute to the majority of the AgDrain MeHg load occurring during this period. Methylmercury reduction efforts should target elevated November through May MeHg concentrations in AgDrains. However, our findings suggest that the contribution and environmental impact of rice is an order of magnitude lower than previous studies in the California Yolo Bypass.|
|Subjects:||Agricultural waste; Agriculture; Bioaccumulation; Biota; Concentration; Critical load; Evapotranspiration; Floods; Geologic hazards; Hydrology; Irrigation; Land use; Mercury; Metals; Methylmercury; Natural hazards; Organo-metallics; Paddy soils; Pollutants; Pollution; Soils; Sulfate ion; Surface water; Toxic materials; Waste disposal; Water pollution; Wetlands; Yields; California; Sacramento Basin; Sacramento California; Sacramento County California; Sacramento Valley; United States|
|Coordinates:||N383000 N391500 W1212500 W1223000|
|Copyright Information:||GeoRef, Copyright 2021 American Geosciences Institute.|
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