Wetland MeHg

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 types 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 (1) to characterize links between MeHg production and wetland type and (2) to provide management strategies that will aid in achieving TMDL MeHg reduction goals.

Bachand & Associates’ role was to quantify the surface water hydrology and estimate constituent loads.  Bachand & Associates (1) recommended an approach to measure flow across the different types of wetlands, (2) instrumented and maintained pressure transducers to estimate flow over weirs, (3) worked closely with USGS to manually measure flow across the system, and (4) analyzed the resulting water flow and water quality data. 

Publications and Final Reports