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The Cosumnes River watershed has seasonal, non-point source hotspots for total mercury and methylmercury production, which discharge to the Sacramento-San Joaquin River Delta in north-central California. To reduce mercury loads to the Delta, researchers created open-water deep cells at the downstream end of wetlands.
Additionally, hydrology was manipulated so that there was a constant flow-through of water, while control wetlands utilized the standard, “fill-and-maintain” approach. Deep cells in seasonal wetlands were effective in lowering methlymercury exports under flow-through hydrology; however, fill-and-maintain hydrology had lower exports overall because of a single major drainage event. Researchers concluded that reductions in methlymercury concentrations in surface water and fish may require higher flow rates to achieve regulatory goals, which may not be feasible for these managed wetlands. Future studies that focus on limiting methylmercury export could consider combining deep cells with the fill-and-maintain or fill-and-trickle hydrologic management approach.
Marvin-DiPasquale, M., Windham-Myers, L., Fleck, J.A., Ackerman, J.T., Eagles-Smith, C., and McQuillen, H., 2018, Mercury on a landscape scale—Balancing regional export with wildlife health: U.S. Geological Survey Open File Report 2018–1092, 93 p., https://doi.org/10.3133/ofr20181092.