Abstract:
The goal of this thesis is to investigate three different areas relating to the
characterization of dissolved organic matter (DOM): further determination of the
chemical compounds present in high molecular weight DOM (HMWDOM), the cycling
of individual compounds within the HMWDOM pool, and the biological controls on
DOM release.
The first section of this thesis provided additional molecular level characterization
of HMWDOM. While some individual components have been identified, the total yield
of compounds isolated is much smaller than the amount expected by spectroscopic
analysis by nuclear magnetic resonance (NMR) spectroscopy. Since the majority of the
as yet unidentified carbon was inferred to be carbohydrate, periodate over-oxidation was
used to analyze this fraction. Analysis of both surface and deep water HMWDOM
samples indicated that the majority of the carbon present was periodate over-oxidizable,
including 70% of the aliphatic NMR signal. Comparison of the periodate demand for
HMWDOM versus that for linear glucopolysaccharide standards indicated that
HMWDOM had a greater degree of branching. Based on the changes in the 'H NMR
spectra during the reaction, it was concluded that 6-deoxysugars were the primary
compounds in the unidentified fraction of HMWDOM.
Compound specific radiocarbon analysis can provide information about the
cycling and relative ages for individual HMWDOM components. In the second section
of this thesis, a new method was presented for the purification of individual underivatized
amino acids hydrolyzed from HMWDOM. This new separation protocol utilized various
chromatographic techniques, including cation exchange chromatography and high-pressure
liquid chromatography (HPLC) using C18 and strong cation exchange (SCX)
columns. Six amino acids were isolated from a HMWDOM sample with sufficient purity
and quantity for radiocarbon analysis. These amino acids had a range of Δ14C values,
from 121% to 454%.
The final section investigates biological controls on the dissolved organic nitrogen
(DON) pool. Total hydrolyzable amino acids (THAA), and nucleic acids were measured
for four incubations: a control incubation, a grazer added incubation, a zero virus
incubation, and a 10 times virus incubation. Comparison to the control showed THAA
and nucleic acid release were influenced by viruses but not grazers.
