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Evaluating nitrate uptake in a Rocky Mountain stream using labelled 15 N and ambient nitrate chemistry
Author(s) -
Hubbard K. A.,
Lautz L. K.,
Mitchell M. J.,
Mayer B.,
Hotchkiss E. R.
Publication year - 2010
Publication title -
hydrological processes
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.222
H-Index - 161
eISSN - 1099-1085
pISSN - 0885-6087
DOI - 10.1002/hyp.7764
Subject(s) - nitrate , hyporheic zone , chemistry , environmental chemistry , denitrification , tracer , nitrogen , hydrology (agriculture) , environmental science , surface water , geology , environmental engineering , physics , geotechnical engineering , organic chemistry , nuclear physics
Background aqueous chemistry and 15 N nitrate tracer injection methods were used to calculate in‐stream nitrate uptake metrics at Red Canyon Creek, a third‐order stream in the Rocky Mountains in the state of Wyoming, United States. ‘Net’ nitrate uptake lengths, which reflect both nitrate uptake and regeneration, and ‘gross’ nitrate uptake lengths, which exclude re‐mineralization, were quantified separately from background nitrate chemistry and 15 N labelling tracer data, respectively. Gross nitrate uptake lengths, from tracer injections of 15 N labelled nitrate, ranged from 502 to 3140 m. Net nitrate uptake lengths, from background nitrate chemistry downstream of a point source, ranged from 1170 to 4330 m. Diurnal changes in uptake lengths suggest the importance of nitrate utilization by autotrophs in the stream and benthic zone. The differences between net and gross nitrate uptake lengths along lower reaches of Red Canyon Creek allowed us to estimate the nitrate regeneration rate, which was 0·056–0·080 µmol m −2 s −1 during the day and 0·0062–0·0083 µmol m −2 s −1 at night. Spatial patterns of streambed pore water chemistry indicate those areas of the hyporheic zone where denitrification was likely occurring. Permanent log dams generated stronger redox gradients in the hyporheic zone than areas with transient beaver dams. By combining isotopically labelled nitrate additions, estimates of uptake from background aqueous nitrate chemistry and characterization of redox conditions in the hyporheic zone, we were able to determine the nitrate regeneration rate and the redox processes responsible for nitrogen cycling in the hyporheic zone. Copyright © 2010 John Wiley & Sons, Ltd.