Selenium removal processes from Great Salt Lake, Utah: estimating sedimentation and verifying volatilization fluxes

Removal processes for selenium (Se) from the Great Salt Lake, Utah (GSL) are investigated by estimation of sedimentation flux from analysis of lake cores and direct measurement of volatilization flux for comparison to a predictive model. To estimate Se removal by sedimentation, lake sediment cores were used to delineate qualitative sedimentation regions, estimate mass accumulation rates (MAR), and determine sediment 210 226 7 137 Se concentrations. Quantifiable MAR results from analysis of Pb, Ra, Be, and Cs activity in 8 deep cores ranged from 0.010 to 0.049 g/cm2/yr. Contemporary sediment Se concentrations from the upper 2 cm of each deep core ranged from 0.79 to 3.12 |ig/g. A representative MAR and Se concentration was assigned based on deep cores located within each sedimentation region. Coupling these with region area, mean annual Se removal by sedimentation was estimated to be 520 Kg/yr within a range of uncertainty between 45 and 990 Kg/yr. Volatilized Se from the water surface was contained and concentrated using a floating emission isolation flux chamber (St. Croix Sensory, Inc.) and captured in a cryogenic finger trap. These samples were taken concurrently with volatile Se concentration, wind velocity, and surface water temperature for input into the Se flux predictive model. Direct flux measurements under controlled laboratory conditions in which Se concentration varied and was independently verified suggest that 10% of actual flux was captured by the direct measurement. After correction for background and 10% measurement inefficiency, measured fluxes approximated, but were generally higher than predicted fluxes. The specific cause of this discrepancy is unclear, but the correspondence is strong enough with the limited number of direct measurements that a correction of the predicted flux is not warranted. The results of these two investigations compared to estimated loadings of Se suggest that volatilization, not permanent sedimentation, is primary removal process for Se from the GSL.