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

Geochimica et Cosmochimica Acta
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Abstract

Dissolved inorganic nitrogen, largely in reduced form (NH4(T)≈NH4(aq)++NH3(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 concentrations of NH4(T) and other solutes in some areas. The isotopic composition of dissolved NH4(T) is highly variable (δ15N = −6‰ to +30‰) and is positively correlated with pH values. In comparison to likely δ15N values of nitrogen source materials (+1‰ to +7‰), high δ15N values in hot springs with pH >5 are attributed to isotope fractionation associated with NH3(aq)o loss by volatilization. NH4(T) in springs with low pH typically is relatively unfractionated, except for some acid springs with negative δ15N values that are attributed to NH3(g)o condensation. NH4(T) concentration and isotopic variations were evident spatially (between springs) and temporally (in individual springs). These variations are likely to be reflected in biomass and sediments associated with the hot springs and outflows. Elevated NH4(T) concentrations can persist for 10s to 1000s of meters in surface waters draining hot spring areas before being completely assimilated or oxidized.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Ammonium in thermal waters of Yellowstone National Park: processes affecting speciation and isotope fractionation
Series title Geochimica et Cosmochimica Acta
DOI 10.1016/j.gca.2011.05.036
Volume 75
Issue 16
Year Published 2011
Language English
Publisher Elsevier
Contributing office(s) Crustal Geophysics and Geochemistry Science Center
Description 26 p.
Larger Work Type Article
Larger Work Subtype Journal Article
Larger Work Title Geochimica et Cosmochimica Acta
First page 4611
Last page 4636
Country United States
Other Geospatial Yellowstone National Park