Mercury, methylmercury, and related geochemical data from incubations of materials flocculated in mesocosms within the Cache Creek Settling Basin, California

The U.S Geological Survey (USGS) is assessing the potential for in-situ addition of metal-based coagulants to enhance mercury (Hg) capture in the Cache Creek Settling Basin (CCSB), a wetland-like environment designed to trap mercury-contaminated sediments from upstream historical mining activities in the Cache Creek watershed. Laboratory and field tests by the USGS show that three tested coagulants enhanced removal of total mercury and methylmercury (MeHg). The three coagulants tested included ChitoVan, an organic/shell-based coagulant, Ferralyte, a ferric-sulfate-based coagulant, and Ultrion, a polyaluminum chloride coagulant. However, there is some concern that sorption of mercury by these coagulants may promote mercury methylation upon soil rewetting in the basin. To test the hypothesis that coagulate coagulant addition to CCSB soils enhances the potential for rewetted soils to produce and release MeHg, we performed two sets of microcosm incubations. We performed a set of batch incubation experiments in which soils from a previous USGS field experiment in CCSB were rewetted and mercury in water and on soil were tracked for 16 days, along with several key water and soil quality parameters. Microcosm incubations consisted of 50 g of soil and 200 milliliters (ml) of Cache Creek water. Treatments included ChitoVan, Ferralyte, and Ultrion and a non-amended control soil, each from three field sites (A, B and C). A second “stress test” experiment was performed in which organic matter, a key stimulator of Hg methylation in aquatic systems, in the form of spirulina powder (SP), was added to treatment soils from site C. Data reported here are compiled into various tables - soil characterization measurements; water and sediment data from incubation experiments; replicate and blank data from the incubation experiments; full fluorescence spectra in vectorized format; full absorbance spectra; analytical quality assurance data for mercury analyses; and a general summary of quality assurance data for incubation.