Methyl mercury (MeHg) cycling and export from agricultural and natural wetlands in the Yolo Bypass.  2007 - 2010

Collaborating Organizations:

California Department of Fish and Game (CDFG); US Geological Survey (USGS)  CA Water Science Center; USGS Biological Resource Division; USGS National Research Program; Moss Landing Marine Labs (MLML); Yolo Basin Foundation; Battelle Marine Sciences Laboratories (MSL); San Jose State and Bachand & Associates

Funding Organization:

State Water Resources Control Board

Project Description:

MeHg is a critical water quality pollutant affecting commercial and recreational fishing within the  San Francisco Bay-Delta (SFB-D) . Wetlands are significant MeHg production sites in the San Francisco Bay Delta and elsewhere; delta wetlands are estimated to produce approximately 40% of the aqueous MeHg present in the San Francisco estuary.  Of the 8 sub-watersheds in the Delta, the wetland-dominated Yolo Bypass (YB) has the highest average annual surface water MeHg concentration, requiring a 70% reduction to meet total maximum daily load (TMDL) goals. 

The primary wetland typs in the YB include rice and wild rice fields farmed annually, fields that undergo crop rotation management, and non-farmed seasonal and permanently flooded wetlands. The purpose of the project was to characterize links between MeHg production and wetland type and management so that TMDL MeHg reduction goals can someday be met.

 Bachand & Associates’ role was to quantify the surface water hydrology and to estimate constituent loads.  Bachand & Associates recommended an approach to measure flow across the different types of wetlands, instrumented and maintained pressure transducers to estimate flow over weirs, worked closely with the USGS to manually measure flow across the system, and analyzed the resulting data together with water quality data.

Publications and Final Reports

Bachand, P.A.M., S. Bachand, J. Fleck, F. Anderson, C. Alpers.  2011.  Utilizing Reactor Models to Estimate Transpiration in Aquatic Crops and More Accurately Quantify Constituent Transport and Field Hydrology Utilizing Reactor Models to Estimate Transpiration in Aquatic Crops and More Accurately Quantify Constituent Transport and Field Hydrology.  Under preparation for submittal to Science of the Total Environment for special issue on mercury.

Bachand, P.A.M., S. Bachand, F. Anderson, J. Fleck. 2011.  Transpiration Driven Diel and Seasonal Hydrologic Transport Patterns in the Root Zone of Aquatic Crops and Implications on Soil Biogeochemical Processes and System Management. Under preparation for submittal to Science of the Total Environment for special issue on mercury.

Windham-Myers, L., M. Marvin-DiPasquale, J. Fleck, C.N. Alpers, J. Ackerman, C. Eagles-Smith, C. Stricker, M. Stephenson, D. Feliz, G. Gill, P. Bachand, A. Brice, and R. Kulakow. 2010. Methylmercury cycling, bioaccumulation, and export from agricultural and non-agricultural wetlands in the Yolo Bypass. Final Report to the Central Valley Regional Water Quality Control Board. September 2010. 266 p.   (Available from CA. State Water Resources Control Board).