Water Resources Research Act Program

Details for Project ID 2015CA338B

Quantifying methylmercury loads from California rice fields

Institute: California
Year Established: 2015 Start Date: 2015-03-01 End Date: 2017-02-28
Total Federal Funds: $13,580 Total Non-Federal Funds: $3,531

Principal Investigators: Bruce Linquist

Project Summary: Methylmercury (MeHg) is found in anoxic environments and can be toxic to wildlife at low levels. Recent studies from the Yolo Bypass in the Sacramento-San Joaquin Delta suggest that rice systems may be a significant source of MeHg to the Delta. Rice acreage in the Delta is limited and not representative of the Sacramento Valley where most rice production occurs. The California Rice Research Board (CCRB) initiated a project to investigate the MeHg contribution of rice systems to surface waters. This study evaluated historical MeHg data along the Sacramento River to determine if agricultural drain waters increase river MeHg levels. While useful, it was apparent from this study, due to insufficient flow data to calculate loads (especially during the winter), that field studies were necessary. The objectives of this study are to (1) quantify MeHg loads from rice fields and (2) determine at what time of year loads are greatest. This work was initiated in 2014 with funding from the CCRB. A rice field was set up with instrumentation to budgets for a full year and water samples taken regularly for analysis of Hg and MeHg in filtered and unfiltered samples in order to understand the mechanisms of Hg transport. Another year of study on a different rice field is necessary in order to more broadly extrapolate results. This research will provide critical data on the types of loads we may expect from rice fields, when MeHg loads may be of concern, and provide some indication of the mechanisms.