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Methylmercury Dynamics in Upper Sacramento Valley Rice Fields with Low Background Soil Mercury Levels
Author(s) -
Tanner K. Christy,
WindhamMyers Lisamarie,
MarvinDiPasquale Mark,
Fleck Jacob A.,
Tate Kenneth W.,
Linquist Bruce A.
Publication year - 2018
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq2017.10.0390
Subject(s) - methylmercury , mercury (programming language) , soil water , growing season , paddy field , irrigation , drainage , oryza sativa , surface water , environmental science , chemistry , water quality , agronomy , environmental chemistry , hydrology (agriculture) , bioaccumulation , environmental engineering , ecology , soil science , biology , geology , biochemistry , geotechnical engineering , computer science , gene , programming language
Few studies have considered how methylmercury (MeHg, a toxic form of Hg produced in anaerobic soils) production in rice ( Oryza sativa L.) fields can affect water quality, and little is known about MeHg dynamics in rice fields. Surface water MeHg and total Hg (THg) imports, exports, and storage were studied in two commercial rice fields in the Sacramento Valley, California, where soil THg was low (25 and 57 ng g −1 ). The median concentration of MeHg in drainage water exiting the fields was 0.17 ng g −1 (range: <0.007–2.1 ng g −1 ). Compared with irrigation water, drainage water had similar MeHg concentrations, and lower THg concentrations during the growing season. Significantly elevated drainage water MeHg and THg concentrations were observed in the fallow season compared with the growing season. An analysis of surface water loads indicates that fields were net importers of both MeHg (76–110 ng m −2 ) and THg (1947–7224 ng m −2 ) during the growing season, and net exporters of MeHg (35–200 ng m −2 ) and THg (248–6496 ng m −2 ) during the fallow season. At harvest, 190 to 700 ng MeHg m −2 and 1400 to 1700 ng THg m −2 were removed from fields in rice grain. Rice straw, which contained 120 to 180 ng MeHg m −2 and 7000–10,500 ng m −2 THg was incorporated into the soil. These results indicate that efforts to reduce MeHg and THg exports in rice drainage water should focus on the fallow season. Substantial amounts of MeHg and THg were stored in plants, and these pools should be considered in future studies. Core Ideas MeHg dynamics were studied in two rice fields with soil THg near background levels. Surface water MeHg and THg imports and exports and soil and plant storage were quantified. Net surface water MeHg and THg import occurred in the growing season. Net surface water MeHg and THg export occurred in the fallow season. Annual MeHg and THg pools in straw and grain were similar to surface water loads.