HR: 13:30h
AN: NB13B-01    [Abstracts]
TI: Extrapolating Ambient Nutrient Uptake From Multiple Nutrient Amendments: A Method Evaluation
AU: * Earl, S R
EM: Earl.Stevan@epa.gov
AF: US EPA, Ecosystems Research Division 960 College Station Road, Athens, GA 30605 United States
AU: Payn, R A
EM: robpayn@cc.usu.edu
AF: Utah State University, College of Natural Resources, Logan, UT 84322-5210 United States
AU: Valett, H M
EM: mvalett@vt.edu
AF: Virginia Tech, Department of Biology, Blacksburg, VA 24061-0406 United States
AU: Webster, J R
EM: jwebster@vt.edu
AF: Virginia Tech, Department of Biology, Blacksburg, VA 24061-0406 United States
AB: Nutrient dynamics in streams are often quantified with short-term nutrient amendments that elevate stream water nutrient concentration. However, elevating nutrient concentration can alter nutrient uptake from ambient conditions. Previous studies have documented that the relationship between nutrient concentration and uptake follows Michaelis-Menten kinetics and that ambient uptake length can be estimated by extrapolation from a series of increasing nutrient amendments. We tested this approach in five streams spanning a gradient of nitrate concentration. We used an isotope tracer (¹⁵NO₃-N) to quantify the ambient uptake length (S_w). We compared S_w to the uptake length determined by a single nitrate amendment and to the uptake length extrapolated from a series of amendments in which nitrate concentration was incrementally elevated. Extrapolated ambient uptake length was a better predictor of S_w than single amendment-derived uptake length in three streams. Extrapolated ambient uptake length was negative in two streams with high background nitrate concentrations. Our data suggest that nitrogen limitation was weak in these two streams and that the relationship between nitrate concentration and uptake deviated from Michaelis-Menten kinetics. The extrapolation technique proved to be a useful method; however, this approach may be less effective in streams where the studied nutrient is not limited.
DE: 1806 Chemistry of fresh water
DE: 1871 Surface water quality
SC: North American Benthological Society [NB]
MN: 2005 Joint Assembly