SELENIUM SPECIATION AND MOBILIZATION IN A CONTROLLED WETLAND SYSTEM: PARIETTE WETLANDS, UT

Pariette Wetlands is a 9000 acre Bureau of Land Management controlled wetland system composed of 20 ponds located at the confluence of Pariette Draw and the Green River. Since its construction in 1975 Pariette Wetlands has been home to a rich and diverse wetland ecosystem located in the arid Uintah Basin of Northeastern Utah. With headwaters in the heavily irrigated Pleasant Valley, Pariette Wetlands has been reported to be an area of high selenium concentrations in both its water and sediments. While selenium is known to be an important nutrient to sustain life, it is toxic at high concentration for many aquatic organisms in their developmental stages. In order to determine the relationship between the Se concentrations in the water and sediments, water and sediments were sampled throughout the reach of Pariette Draw. To establish Pariette Draw’s contribution of Se to the Green river, water and sediments were also sampled from the Green River up and downstream of its confluence with Pariette Draw. Along with the water samples in situ pH, ORP, temp., Sp. Cond., and DO were monitored with a Hach Hydrolab®. An observed trend of increased pH from upstream, 8.4, to downstream, 9.2 and the relative stability of ORP, 343-490 mV with a mean on 438 mV, suggest that the Pariette Wetlands are a pH controlled system. An exception to the increasing trend was found in two midstream locations where the channel runs directly over the bedrock composed of a green siltstone. This suggests rock/sediment water interactions play a key role in the system. The DO trend mirrored that of the pH but showed no deviation at the midstream locations implying that the DO is not controlled by the rock/sediment water interactions. Water samples are being analyzed for total anions and cations via IC and ICPMS and other major and minor constituents along with total Se and Se speciation by HPLC-ICPMS. Sediments are being analyzed for total Se by ICPMS along with a sequential extraction procedure to locate the labile fractions of mostly inorganic bound Se. In addition to quartz, feldspars, carbonates, and muscovite other major minerals are being identified by petrographic examination and used in conjunction with in situ water parameters and water constituents to develop an understanding of the rock/sediment water interactions and their effect on Se mobilization.