The contribution of rice agriculture to methylmercury in surface waters: A review of data from the Sacramento Valley, California

Journal of Environmental Quality
By: , and 

Links

Abstract

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.

Study Area

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title The contribution of rice agriculture to methylmercury in surface waters: A review of data from the Sacramento Valley, California
Series title Journal of Environmental Quality
DOI 10.2134/jeq2016.07.0262
Volume 46
Issue 1
Year Published 2017
Language English
Publisher American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.
Contributing office(s) National Research Program - Western Branch, California Water Science Center
Description 9 p.
First page 133
Last page 142
Country United States
State California
Other Geospatial Sacramento Valley