Greg Carling

Abstract: Trace element particulate pulse and diel (24-hr) variations in a freshwater wetland adjacent to Great Salt Lake

Greg Carling, PhD Candidate, University of Utah

Avian wildlife exposure to trace elements such as mercury and selenium is a result of trace element loads and removal processes occurring in lakes and wetlands.  Trace element loads to Great Salt Lake are generally calculated using concentrations measured during daytime hours.  However, certain trace elements are known to vary on a diel (24-hr) cycle due to a variety of physical and chemical processes.  Loads are an important aspect of calculating numerical water quality standards.  Therefore, failing to account for nighttime trace element concentrations could potentially lead to miscalculated trace element loads and biased numerical standards.  In order to more fully understand diel cycling in freshwater wetlands which drain to Great Salt Lake, trace elements and water chemistry (dissolved oxygen, pH, water temperature, etc.) were monitored over a 24-hr period from the outlet of  two ponds located at the Ambassador Duck Club wetland complex during August 20-21, 2008 and September 14-15, 2009.  Unfiltered and filtered (0.45 micron) samples were collected hourly for all trace elements.  Al, Fe, Hg, and Pb were predominantly (>75% of mass) associated with the >0.45 micron, or particulate, fraction.  Cd, Cu, Cr, Mn, and Ti were also associated with the particulate fraction to a lesser extent (25-75% of mass).   As, Li, Mg, Mo, Sb, Se, Sr, U, and V were predominantly in the “dissolved” (<0.45 micron) form.  The particulate-associated elements showed large variations in concentration (up to a factor of 4), most likely due to settling and resuspension of particulate matter in the water column.  Certain “dissolved” trace elements (Sb, Se, Sr, U, and V) showed a diel variation in phase with dissolved oxygen, pH and water temperature: high in daylight hours corresponding to oxic conditions and low in nighttime hours corresponding to suboxic conditions.  Methyl mercury, which has been shown to vary on a diel cycle in other locations, was consistently low at both ponds, indicating little methylation potential in the Ambassador Duck Club ponds.