Phosphorus in hydrothermal waters of Yellowstone National Park, Wyoming

Ninety-seven hot-spring and geyser samples (field acidified to pH<1.4 with HCl or HNO₃) from Yellowstone National Park, Wyo., were analyzed for PO₄-P using reduced molybdenum-blue and the selective arsenate reducing agent, metabisulfite-thiosulfate. The PO₄-P concentrations ranged from below detection limit (~1-73 micrograms per liter). Twenty-five springs had PO₄-P concentrations exceeding 6.8 μg/L; seven spring samples exceeded 20 μg/L. Elevated PO₄-P contents were invariably associated with mixed springs, as evidenced by diluted chloride concentrations and, commonly, subboiling temperatures, low pH's, and elevated calcium concentrations. Alkaline high-chloride (>400 milligrams per liter) hydrothermal waters from Upper and Norris Geyser Basins had PO₄-P concentrations below 2 μg/L and represent the low end of the range of PO₄-P contents in natural waters.