[SIO GP Seminars] [SIO Students]Final Reminder: Tracing Anthropogenic Sources of N in Rain Using Isotopes

[Cassandra Gaston]

 Please join us Today for the Earth Section seminar.
 Hubbs Hall 4500

 Carol Kendall, USGS
 "Tracing Anthropogenic Sources of N in Rain Using Isotopes"


 3:15, refreshments at 3:00


 Abstract:
 Global emissions of NOx have increased dramatically during the past
150 years. Contemporary global inputs of NOx are dominated by fossil
fuel combustion from both power plants
 and vehicles, and far exceed natural NOx sources such as lightning,
biogenic soil processes, and wildfires. Atmospheric nitrogen
deposition can alter the structure and function of terrestrial
ecosystems because nitrogen is often a primary limiting nutrient on
overall productivity. These alterations can drive losses of
biodiversity, as species adapted to high-N conditions (e.g., invasive
annual grasses) out-compete species adapted to more pristine
conditions. For example, high levels of NOx deposition near major
highways in northern CA have been linked to the decline of the
endangered checkerspot butterfly.  However, quantifying NOx
contributions from different sources to any given location -- and
distinguishing this nitrate from natural, agricultural, and sewage
sources of nitrate -- remains a difficult challenge, despite the need
for this information to develop sound regulatory and mitigation
strategies.

 As part of a national-scale investigation of the usefulness of
nitrate isotopes as tracers of NOx sources to terrestrial and coastal
ecosystems, we have analyzed the d15N and d18O of nitrate in
composited bimonthly wet precipitation samples from ~150 National
Atmospheric Deposition Program (NADP) sites, using archived samples
from 2000.  Nitrate samples from a subset of NADP sites in the NE have
also been analyzed for D17O.  These data show that spatial and
temporal variations in 15N are strongly correlated with NOx emissions
from power plant sources, and hence that 15N can be a strong
complement to existing tools for assessing relationships between NO3-
deposition and regional emission inventories, and for evaluating
progress towards NOx reduction goals required by recent EPA
regulations. This talk will present an overview of the problem and
show examples of how isotopes can help determine the relative
contributions of nitrate derived from natural sources, vehicle
exhaust, and power plant emissions to airsheds, watersheds, and
groundwater."


 Cheers,

Cassie

-- 
Cassandra Gaston
PhD Student
Scripps Institution of Oceanography
Prather Lab
858-822-5745
http://atofms.ucsd.edu