HR: 15:30h
AN: NB24F-01    [Abstracts]
TI: A ¹⁵N Tracer Study of Nitrate Retention in a Third-Order Stream Flowing Through Different Land Use Conditions, Willamette Valley, Oregon
AU: * Sobota, D J
EM: sobotad@onid.orst.edu
AF: Department Fisheries and Wildlife, Oregon State University, 104 Nash Hall, Corvallis, OR 97331 United States
AU: Johnson, S L
EM: johnsons@fsl.orst.edu
AF: USDA Forest Service, Pacific NW Research Station, 3200 SW Jefferson Way, Corvallis, OR 97331 United States
AU: Ashkenas, L R
EM: linda.ashkenas@orst.edu
AF: Department Fisheries and Wildlife, Oregon State University, 104 Nash Hall, Corvallis, OR 97331 United States
AU: Gregory, S V
EM: stanley.gregory@orst.edu
AF: Department Fisheries and Wildlife, Oregon State University, 104 Nash Hall, Corvallis, OR 97331 United States
AU: Irvin, C
AF: Department Fisheries and Wildlife, Oregon State University, 104 Nash Hall, Corvallis, OR 97331 United States
AB: We conducted ¹⁵NO₃^- tracer studies in three reaches of Oak Creek, a third-order stream in the Willamette Valley, Oregon, in summer 2003 as part of the Lotic Intersite Nitrogen eXperiment II (LINX II). Nitrate-nitrogen uptake length was longest (960 m) in a forested reach (discharge = 7.5 L s^-1), and declined to 670 m in an agricultural reach (5.5 L s^-1) and 570 m in an urban reach (3.9 L s^-1), corresponding to differences in discharge among reaches. When uptake rates were corrected for stream velocity and depth, nitrate-nitrogen uptake velocity declined from the forest (0.22 mm min^-1) to the agricultural (0.19 mm min^-1) and urban (0.13 mm min^-1) reaches. Denitrification, determined through ¹⁵N₂ and ¹⁵N₂O gas production following tracer additions, was not detectable in the forest but accounted for 2 and 5% of nitrate-nitrogen uptake in agricultural and urban reaches, respectively. Other sinks for retained nitrate-nitrogen varied among the reaches. In the forest, allochthonous organic matter had the highest biomass-specific uptake. In the agricultural and urban reaches, autotrophic components played increasingly important roles in nitrate retention. Collectively, these results indicate significant shifts in retention pathways of nitrate-nitrogen in response to adjacent land use practices along this stream.
DE: 1806 Chemistry of fresh water
SC: North American Benthological Society [NB]
MN: 2005 Joint Assembly