![[logo] US EPA](https://webarchive.library.unt.edu/eot2008/20081108091708im_/http://www.epa.gov/epafiles/images/logo_epaseal.gif){kind=logo}
HPLC and Stable Isotopic Measurements of Nitrogen Uptake by Phytoplankton
EPA Grant Number: U916135Title: HPLC and Stable Isotopic Measurements of Nitrogen Uptake by Phytoplankton
Investigators: York, Joanna K.
Institution: Boston University
EPA Project Officer: Cobbs, Gladys M.
Project Period: January 1, 2003 through January 1, 2006
Project Amount: $86,572
RFA: STAR Graduate Fellowships (2003)
Research Category: Academic Fellowships , Aquatic Ecosystems , Fellowship - Aquatic Ecology and Ecosystems
Description:
Objective:The objectives of this research project are to: (1) refine our knowledge about forms and sources of nitrogen (N) assimilated by phytoplankton; (2) use isotopic signatures to define sources, losses, and transformations of nitrate (NO3) and ammonium (NH4) available to phytoplankton; and (3) provide new data on the fate of N as it travels through estuaries.
Approach:This work will be conducted in the Waquoit Bay,
MA estuarine system, whose subestuaries have watersheds that vary in their
degree of development,
from Childs River's urbanized watershed to Sage Lot Pond's, which
is primarily forested. These differences in land use result in differences
in total N load to the estuary, differences in the relative amounts of NO3
and NH4 present in the estuarine water, and differences in the isotopic signatures
of NO3 and NH4. Waquoit Bay can be considered as a regional experimental layout
that will allow me to assess the relative importance of NO3 and NH4 in sites
where their relative ratio varies more than an order of magnitude. I will apply
newly developed techniques that combine stable isotopic and high performance
liquid chromatography approaches to address the issue of preferential uptake
of N forms by phytoplankton in the field. Previous work on this subject was
based on experiments with laboratory cultures; I will use natural phytoplankton
assemblages. To determine whether estuarine phytoplankton use NH4 or NO3, I
will compare isotopic signatures (
15N) of phytoplankton with 15N of NH4 and
NO3. The 15N of NH4 and NO3 will vary down estuary, affected not only by uptake
by phytoplankton, but also by mixing at tidal sites, denitrification, regeneration,
and other biogeochemical processes. Because of this mix of influences, I will
assess the uptake by phytoplankton within the context of denitrification and
regeneration, the major processes contributing to the change in isotopic signature.
To determine the importance of regenerated NH4, I will collect and incubate
sediment cores. Denitrification will be assessed by the relative fractionation
to heavier signatures in samples collected along a salinity gradient in all
sampling locations.
fellowship, high performance liquid chromatography, HPLC, phytoplankton, denitrification, nitrogen, N, total nitrogen load, nitrate, ammonium, regeneration, Waquoit Bay, MA, sediments, sediment cores, watershed, subestuaries, estuaries, land use, estuarine water
,
Ecosystem Protection/Environmental Exposure & Risk, Scientific Discipline, RFA, ECOSYSTEMS, Aquatic Ecosystems & Estuarine Research, Aquatic Ecosystem, Environmental Chemistry, Aquatic Ecosystems, Ecology and Ecosystems, phytoplankton, nitrogen uptake, ammonium, nitrate concentrations, stable isotopic measurement, estuaries
Relevant Websites:
2004 STAR Graduate Fellowship Conference Poster (PDF, 1p., 2.84MB, about PDF)