HR: 1330h
AN: NB33F-03    [Abstracts]
TI: Investigation of Hyporheic Nitrate Retention Using ¹⁵NO₃^- Additions: Preliminary Results from Mack Creek, Oregon
AU: * Haggerty, R
EM: haggertr@geo.oregonstate.edu
AF: Oregon State University, Dept. of Geosciences, 104 Wilkinson Hall, Corvallis, OR 97331 United States
AU: LaNier, J
EM: lanierj@geo.oregonstate.edu
AF: Oregon State University, Dept. of Geosciences, 104 Wilkinson Hall, Corvallis, OR 97331 United States
AU: Crenshaw, C L
EM: chelsea1@unm.edu
AF: University of New Mexico, Dept. of Biology, Albuquerque, NM 87131 United States
AU: Wondzell, S M
EM: swondzel@fs.fed.us
AF: U.S. Forest Service, Pacific Northwest Research Station, 3625 93rd SW, Olympia, WA 98512 United States
AU: Baker, M A
EM: mbaker@biology.usu.edu
AF: Utah State University, Dept. of Biology, Logan, UT 84322 United States
AU: Gooseff, M N
EM: mgooseff@mines.edu
AF: Colorado School of Mines, Dept. of Geology and Geologic Engineering, 1516 Illinois Street, Golden, CO 80401 United States
AB: We have initiated an investigation to understand the factors controlling nitrate (NO₃^-) retention and denitrification in hyporheic zones of small streams and to quantify the fraction of nitrate retention in these streams due to hyporheic exchange. We are testing three hypotheses: (1) hyporheic denitrification in headwater, forested streams will be low because of substrate and rate limitations, yet biotic assimilation will be high, relative to agricultural and urban streams, because of inorganic N-limitation; (2) hyporheic denitrification will be greatest in mid-network locations where surrounding land use is predominantly agricultural, however, total loss of NO₃^- will be transport-limited and biotic assimilation will be reduced because nitrogen is less limiting; and (3) potential rate of denitrification in the hyporheic zone will be high in the urban stream reaches, but total nitrate retention in the hyporheic zone will be low because both denitrification and biotic assimilation will be severely transport-limited. We will present preliminary data from the LINX II ¹⁵NO₃^- injection in an old-growth reach of 3rd-order Mack Creek, Oregon, where we installed a network of 17 hyporheic wells. Prior to and following the LINX II injection of ¹⁵NO₃^-, the wells were sampled for ¹⁴N- and ¹⁵N-species including ¹⁵N₂ and ¹⁵N₂O. Additionally, in-well salt tracer tests were conducted, and a preliminary groundwater flow model of the site has been developed.
DE: 0400 Biogeosciences
DE: 1829 Groundwater hydrology
DE: 1832 Groundwater transport
DE: 4845 Nutrients and nutrient cycling
DE: 4870 Stable isotopes
SC: North American Benthological Society [NB]
MN: 2005 Joint Assembly