Nitrogen transformations in hot spring runoff, Yellowstone National Park, USA

摘要

Total nitrogen concentrations in hot springs at Yellowstone National Park vary widely in concentration, from < 0.3 μM to 42.7 mM as N, with ammonium often occurring as the dominant nitrogen species. Two chemically distinct hot springs in Yellowstone National Park, acidic Nymph Creek and circumneutral Washburn Inkpot were investigated to determine variations in nitrogen concentration and speciation in hot-spring runoff. Ammonium concentration decreased by 41 percent (92 to 54 μM N-NH_4~+) over 148 m along Nymph Creek. There was no readily discernable decrease in ammonium in the drainage from the Washburn Inkpot (15.8 mM N-NH_4~+) over approximately 5 minutes of travel time along the 26 m reach. Nitrite concentration increased downstream in Nymph Creek from < 0.2 to 1 μM N-NO_2~- and increased from 0.6 to 8.1 μM N-NO_2~- in the Washburn drainage. While there is some evidence from δ~(15)N-NH_4~+ measurements and denitrification assays for microbial nitrogen transformations in Nymph Creek and the Washburn drainage, nitrification of ammonium to nitrite and nitrate may be a rate-limiting step in nitrogen cycling for these hot spring drainages.