Source and fate of inorganic solutes in the Gibbon River, Yellowstone National Park, Wyoming, USA. II. Trace element chemistry

The Gibbon River in Yellowstone National Park receives inflows from several geothermal areas, and consequently the concentrations of many trace elements are elevated compared to rivers in non-geothermal watersheds. Water samples and discharge measurements were obtained from the Gibbon River and its major tributaries near Norris Geyser Basin under the low-flow conditions of September 2006 allowing for the identification of solute sources and their downstream fate. Norris Geyser Basin, and in particular Tantalus Creek, is the largest source of many trace elements (Al, As, B, Ba, Br, Cs, Hg, Li, Sb, Tl, W, and REEs) to the Gibbon River. The Chocolate Pots area is a major source of Fe and Mn, and the lower Gibbon River near Terrace Spring is the major source of Be and Mo. Some of the elevated trace elements are aquatic health concerns (As, Sb, and Hg) and knowing their fate is important. Most solutes in the Gibbon River, including As and Sb, behave conservatively or are minimally attenuated over 29 km of fluvial transport. Some small attenuation of Al, Fe, Hg, and REEs occurs but primarily there is a transformation from the dissolved state to suspended particles, with most of these elements still being transported to the Madison River. Dissolved Hg and REEs loads decrease where the particulate Fe increases, suggesting sorption onto suspended particulate material. Attenuation from the water column is substantial for Mn, with little formation of Mn as suspended particulates.