Ammonium in thermal waters of Yellowstone National Park: Processes affecting speciation and isotope fractionation

Dissolved inorganic nitrogen, largely in reduced form ( NH 4 ( T ) ≈ NH 4 ( aq ) + + NH 3 ( aq ) o ), has been documented in thermal waters throughout Yellowstone National Park, with concentrations ranging from a few micromolar along the Firehole River to millimolar concentrations at Washburn Hot Springs. Indirect evidence from rock nitrogen analyses and previous work on organic compounds associated with Washburn Hot Springs and the Mirror Plateau indicate multiple sources for thermal water NH4(T), including Mesozoic marine sedimentary rocks, Eocene lacustrine deposits, and glacial deposits. A positive correlation between NH4(T) concentration and δ18O of thermal water indicates that boiling is an important mechanism for increasing [...]