HR: 0800h
AN: H41D-0327    [Abstracts]
TI: Managing Nutrients in two New England Estuaries: The Feasibility of Using Stable Isotopes to Monitor Nitrate Sources
AU: * Barnes, R T
EM: rebecca.barnes@yale.edu
AF: Yale School of Forestry and Environmental Studies, 210 Prospect Street, New Haven, CT 06511 United States
AU: Benoit, G
EM: gaboury.benoit@yale.edu
AF: Yale School of Forestry & Environmental Studies, 205 Prospect Street, New Haven, CT 06511 United States
AU: Anisfeld, S
EM: shimon.anisfeld@yale.edu
AF: Yale School of Forestry & Environmental Studies, 205 Prospect Street, New Haven, CT 06511 United States
AB: Nitrogen is the limiting nutrient in many estuaries, and the rising availability of nitrogen has led to increased eutrophication in many coastal ecosystems. In order to reduce nitrogen loading to coastal waters it is necessary to know the relative importance of the various sources, both point and non-point. Recent studies have shown that sources of nitrate, the most bioavailable form of nitrogen, can be differentiated based on their isotopic signature using a dual stable isotope approach (\delta$^{15}$N and \delta$^{18}$O). Currently, the range of isotopic values in the literature for nitrate sources (sewage, atmospheric deposition, microbial nitrification, fertilizer and animal waste) across various systems is too large to clearly differentiate between sources. In this study, I will use a stratified sampling plan to assess the feasibility of using this stable isotope approach to determine the relative importance of various nitrogen inputs in a limited geographic region. I will examine how these isotope signatures vary spatially across different watersheds and how much sampling (spatially and temporally) is needed to accurately assess the delivery of nitrogen to a given estuary. In particular, four estuarine catchments within two different New England estuaries will be sampled at three different scales. At the smallest scale, first and second order forested, agricultural, and urban catchments will be sampled to identify source signatures of these landscapes. Tributaries, mostly third order streams, will be sampled to gain additional information about the relationship between land cover and isotopic signatures. At the largest scale, longitudinal sampling will be done along the main stems to assess the relative contributions of different tributaries and to provide further information regarding nitrogen cycling within these systems. Various chemical indicators of nitrogen loading will also be measured to assess their use in conjunction with the stable isotopes. This suite of measurements will help determine the best strategy (in terms of both time and cost) for detecting watershed nitrogen loading to estuaries.
DE: 1803 Anthropogenic effects
DE: 1871 Surface water quality
DE: 1040 Isotopic composition/chemistry
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting