Chromophoric dissolved organic matter in coastal rainwater

UNCW Author/Contributor (non-UNCW co-authors, if there are any, appear on document)

Seth Neil Reid (Creator)

Institution

The University of North Carolina Wilmington (UNCW )

Web Site: http://library.uncw.edu/

Abstract: The quantity of chromophoric dissolved organic matter (CDOM) was measured in 125 rain events in Wilmington, NC between February 21, 2002 and August 11, 2003. All rain events had measurable CDOM, although there was much variability between events. The amount of fluorescent CDOM was affected by season and storm origin. There was significantly more fluorescent CDOM in winter and continental rain, relative to summer and coastal events. Diurnal variations were also seen where the amount of fluorescent CDOM decreased gradually from the morning through the afternoon and evening hours. In addition to measuring the quantity, the photolabilty of rainwater CDOM was also studied and compared to the photodegradation of CDOM in natural waters. There was significant photodegradation of CDOM in all events studied after 12hour exposure to simulated sunlight. Approximately half the fluorescence was lost upon irradiation of rainwater CDOM, which was similar to the amount of fluorescence loss of the Cape Fear River (CFR) CDOM. Maximum loss of CDOM absorbance in rainwater was in the UV-A region, while maximum loss shifted to the lower end of the UV-B region for the CFR. Monochromatic and filtered sunlight experiments demonstrated that the degree of photobleaching of rainwater CDOM was directly related to the amount of UV-A and UV-B irradiation present. The structural characteristics of the rainwater CDOM were also examined. The carbon to nitrogen ratio of extracted rainwater CDOM was 24, which is approximately half the CFR CDOM C/N ratio. The C/N ratio increased in rainwater while it decreased in CFR after irradiation, suggesting different mechanisms of photodegradation. The extracted fluorescent CDOM was also examined via 1H NMR. The fluorescent CDOM had primarily aliphatic character, while the CFR CDOM had relatively more aromatic character. Upon photolysis, rain CDOM lost primarily aliphatic moieties. In summary, rainwater contains significant amounts of photodegradable chromophoric dissolved organic matter. This has important ramifications with respect to the wavelength dependent spectral attenuation of solar radiation in atmospheric waters.

Chromophoric dissolved organic matter in coastal rainwater
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Created on 1/1/2009
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Additional Information

Publication

Thesis

A Thesis Submitted to the University of North Carolina at Wilmington in Partial Fulfillment Of the Requirements for the Degree of Master of Science

Language: English

Date: 2009

Keywords

Rain and rainfall--Environmental aspects--North Carolina--Wilmington, Water quality--Effect of minerals on--North Carolina--Wilmington, Fluorescence spectroscopy, Rain-water (Water-supply)--Testing--North Carolina--Wilmington

Subjects

Rain-water (Water-supply) -- Testing -- North Carolina -- Wilmington

Rain and rainfall -- Environmental aspects -- North Carolina -- Wilmington

Water quality -- Effect of minerals on -- North Carolina -- Wilmington

Fluorescence spectroscopy

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