Transport and Fate of Riverine Nitrogen: Understanding Hydrologic, Physiochemical, and Biological Interactions.

EPA Grant Number: F6E11040
Title: Transport and Fate of Riverine Nitrogen: Understanding Hydrologic, Physiochemical, and Biological Interactions.
Investigators: Helton, Ashley M
Institution: University of Georgia
EPA Project Officer: Lee, Sonja
Project Period: August 1, 2006 through August 1, 2009
Project Amount: $106,720
RFA: STAR Graduate Fellowships (2006) RFA Text |  Recipients Lists
Research Category: Academic Fellowships , Aquatic Ecosystems , Fellowship - Aquatic Systems Ecology


The purpose of this study is to examine how two major patterns of large-scale climate variability, the so-called Northern and Southern Annular Modes, are related to variations in atmospheric carbon dioxide concentrations. Both patterns exert substantial influence on surface climate in their respective hemispheres, and both patterns have exhibited trends over the past few decades. Nevertheless, it remains unknown to what extent the climate impacts of these patterns feedback onto the global carbon cycle. In addition to exploring the effects of the annular modes on the carbon cycle, I will also study how increasing human emissions of carbon dioxide and chlorofluorocarbons impact the atmospheric circulation.


Using atmospheric carbon dioxide measurements from the NOAA Global Monitoring Division, I will first look for statistical relationships between the times series of the annular modes and atmospheric carbon dioxide at various stations around the globe. I will also examine the mechanisms responsible for any observed relationships by investigating the links between the annular modes and atmospheric inversion model CO2 flux estimates, sea surface temperature fields and near-surface wind fields.

Expected Results:

Because the Northern Annular Mode effects high-latitude temperatures, it may impact the uptake of carbon dioxide from the terrestrial biosphere through changes in the length of the growing season. Due to lack of nearby land regions with significant vegetation in the Southern Hemisphere, the Southern Annular Mode is thought to impact atmospheric carbon dioxide via air-sea flux exchange. Based on preliminary results, I predict that the annular modes are indeed coupled to variations in atmospheric CO2 in a manner consistent with these theories.

Supplemental Keywords:

annular mode, carbon dioxide, global carbon cycle, climate variability, chlorofluorocarbons,, RFA, Scientific Discipline, Air, climate change, Air Pollution Effects, Environmental Monitoring, Atmosphere, anthropogenic stress, atmospheric carbon dioxide, climatic influence, green house gas concentrations, emissions impact, carbon dioxide, CO2 concentrations, greenhouse gases, global warming, aquatic ecology

Progress and Final Reports:

  • 2007
  • 2008
  • Final