HR: 15:30h
AN: H44A-01    [Abstracts]
TI: Environmental Factors That Control the Expression of Stable Isotope Fractionation During Nitrate Utilization by Phytoplankton
AU: * Needoba, J
EM: needoba@mbari.org
AF: Monterey Bay Aquarium Research Institute, 7700 Sandholdt Road, Moss Landing, CA 95039 United States
AB: Kinetic isotope fractionation of the stable isotopes ¹⁵N and ¹⁴N during nitrate utilization by phytoplankton is a central process in determining the stable nitrogen isotope composition of organic matter within aquatic ecosystems. Many important applications of stable isotope research rely on knowledge of this fractionation factor in order to correctly interpret ¹⁵N/¹⁴N measurements, such as determination of trophic level within food webs, detection of the source of nitrogen to an ecosystem, and estimates of the extent of nitrate utilization in an environment. Variations in the isotope fractionation factor can alter both the organic and inorganic components of the nitrogen cycle and serve to complicate the interpretation of stable isotope measurements. I will summarize recent findings that resolve the mechanism for nitrate isotope fractionation by phytoplankton and illustrate how environmental parameters that affect growth rates can cause a reduction in the expression of the intrinsic fractionation factor. I will also show evidence that combining knowledge of these parameters with an understanding of the physical supply of nitrate to an ecosystem allows for the fractionation factor to be accurately incorporated into interpretations of ¹⁵N/¹⁴N within aquatic environments.
DE: 4845 Nutrients and nutrient cycling
DE: 4870 Stable isotopes
SC: Hydrology [H]
MN: 2005 Joint Assembly