Concentrations of NHx, NO3
-, free amino acids, total and organic nitrogen, and inorganic
anions were determined for 78 rain events between September 1, 2002 and August 31, 2003, on
the campus of the University of North Carolina at Wilmington in southeastern North Carolina.
The majority of N in Wilmington rain (78%) is inorganic, occurring as NO3
- and NHx in
approximately equal proportions. Free amino acids make up a small portion of ON (11%).
Correlation analysis and back trajectory analysis indicate that regional sources, rather than local
emissions, determine the concentrations of inorganic N in UNCW rainwater and particle dry
deposition. NO3
- concentration in rainwater at UNCW has decreased from 1990 to the present
while wet deposition increased due to increased rainfall and possibly increased emissions from
growing population and expanding industry in North Carolina.
Wet and dry deposition of NHx are respectively 53% and 26% higher than a decade ago
reflecting an increase in regional and possibly local emissions. Similar temporal patterns in are
seen at UNCW and the NADP monitored sites with the greatest increase in Clinton, NC, where
NHx concentrations and depositions have increased 58% and 107% respectively. Concentrations
of H+ and major N analytes, with the exception of ON, vary significantly as a function of air
mass origin with major increases in analytes correlating with locations of known anthropogenic
sources. Seasonal and diurnal influences have a significant impact on the concentrations of H+
and N analytes in UNCW rainwater with significant concentration maximums in the spring and
significantly lower concentrations from 6:00AM to 10:00PM.
Direct atmospheric deposition is not a major source of bioavailable nitrogen to the Cape Fear
River Estuary. The average total daily NHx and NO3
- dry depositions were small in comparison
to their total amounts in the CFRE. Wet depositions of NHx reached 20% for a single event with an average per event deposition equivalent to 1.3% of NHx in the CFRE. Dry deposition
accounts for 17% of inorganic N deposition to the CFRE; though it is possibly underestimated in
this study
