DIEL VARIATIONS IN PARTICULATE HG AND OTHER TRACE ELEMENTS IN A TEMPERATE WETLAND ADJACENT TO FARMINGTON BAY, GREAT SALT LAKE, UTAH

Total Hg, methyl Hg, trace elements and field parameters were monitored over a 24 hr period at the inlet and outlet of a pond located in a wetland complex adjacent to the Great Salt Lake, Utah, during August 20-21, 2008. Unfiltered and filtered (0.45 micron) samples were collected hourly for all trace elements. Preliminary results indicate significant diel variations in the unfiltered Hg samples from both sampling sites but no diel variation in the filtered Hg samples, suggesting that the diel variation is driven by the particulate-bound phase of Hg. Methyl Hg values were low (~0.02 ng/L) at both sites for the diurnal period, indicating little methylation potential at this pond. The pond inlet shows afternoon/evening particulate Hg maxima (4 ng/L) are a factor of 2 times higher than the morning minima (2 ng/L). Somewhat higher (factor of 4) diel variations were observed in pond outlet. Other trace metals (Al, Be, Cd, Co, Cr, Cu, Fe, Ni, and Pb) also showed particulate-based diel variations in phase with total Hg but of differing magnitude. Two groupings of trace elements were found: those that correspond to particulate variations and those that respond to redox conditions (dissolved oxygen, pH, nitrate/nitrite, temperature). The oxyanions (Se, V, and Sb) were high in daylight hours corresponding to oxic conditions and low in dark hours corresponding to suboxic conditions. Temporal associations of particulate based metals and the redox sensitive oxyanions were confirmed mathematically via a principle component analysis. While the temporal variations in the redox sensitive oxyanions are understood, further work will examine the mechanisms behind the particulate distributions over the diurnal cycle and to understand the size of the particles with which various trace metals are associated.