J. M. Thompson R. E. Stauffer 1978 <p>Ninety-seven hot-spring and geyser samples (field acidified to pH&lt;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&nbsp;concentrations ranged from below detection limit (~1-73 micrograms per liter). Twenty-five springs had PO₄-P&nbsp;concentrations exceeding 6.8 <span>&mu;</span>g/L; seven spring samples exceeded 20 &mu;g/L. Elevated PO₄-P&nbsp;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 (&gt;400 milligrams per liter) hydrothermal waters from Upper and Norris Geyser Basins had PO₄-P&nbsp;concentrations below 2 &mu;g/L and represent the low end of the range of PO₄-P&nbsp;contents in natural waters.</p> application/pdf en U.S. Geological Survey Phosphorus in hydrothermal waters of Yellowstone National Park, Wyoming article