- We used an in situ steady state ¹⁵N-labeled nitrate (¹⁵NO₃⁻) and acetate (AcO⁻)
well-to-wells injection experiment to determine how the availability of labile dissolved
organic carbon (DOC) as AcO⁻ influences microbial denitrification in the hyporheic zone
of an upland (third-order) agricultural stream. The experimental wells receiving
conservative (Cl⁻ and Br) and reactive (¹⁵NO₃⁻) solute tracers had hyporheic median
residence times of 7.0 to 13.1 h, nominal flowpath lengths of 0.7 to 3.7 m, and hypoxic
conditions (<1.5 mg O₂ L⁻¹). All receiving wells demonstrated ¹⁵N₂ production during
ambient conditions, indicating that the hyporheic zone was an environment with active
denitrification. The subsequent addition of AcO⁻ stimulated more denitrification as
evidenced by significant δ¹⁵N₂ increases by factors of 2.7 to 26.1 in receiving wells and
significant decreases of NO₃⁻ and DO in the two wells most hydrologically connected to the
injection. The rate of nitrate removal in the hyporheic zone increased from 218 kg ha⁻¹ yr⁻¹
to 521 kg ha⁻¹ yr⁻¹ under elevated AcO⁻ conditions. In all receiving wells, increases
of bromide and ¹⁵N₂ occurred without concurrent increases in AcO⁻, indicating that
100% of AcO⁻ was retained or lost in the hyporheic zone. These results support the
hypothesis that denitrification in anaerobic portions of the hyporheic zone is limited by
labile DOC supply.
- Zarnetske, J. P., R. Haggerty, S. M. Wondzell, and M. A. Baker (2011), Labile dissolved organic carbon supply limits hyporheic denitrification, Journal of Geophysical Research, 116, G04036, doi:10.1029/2011JG001730.
|Funding Statement (additional comments about funding)
- Support for this project was primarily provided by a NSF Ecosystem Informatics IGERT fellowship (grant DGE-0333257) to J.P.Z.; research grants from the OSU Institute for Waterand Watersheds and a North American Benthological Society Endowment Fund to J.P.Z.; and NSF grants EAR-0409534 and EAR-0409591 to R.H.,S.M.W., and M.A.B. Additional support was provided by the Hollis M. Dole Environmental Geology Fund at OSU.
- This is the publisher’s final pdf.
- Journal of Geophysical Research
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- Vol. 116 no. G04036