Chemical Characterization of Dissolved Organic Carbon and Dissolved Organic
Nitrogen in the Florida Coastal Everglades: Preliminary Results.
R. Jaffé, N. Maie, and K. Parish
Florida International University, Miami, FL, USA.
M. Toshikatzu
AIST, Macromolecular Technology Research Center, Tsukuba, Japan.
H. Knicker
Technische Universität München, Dept. Soil Sciences, Freising, Germany.
V. Jones and G. Wolff
The University of Liverpool, Oceanography Labs., Liverpool, UK.
The Everglades Restoration Project involves redistribution of water within the
terrestrial ecosystem that will affect water entering the marine ecosystem. As a
result, flow into Florida Bay is expected to increase and there is concern that
increased nutrient loading will occur in the form of dissolved organic matter
(DOM). Characterization of DOM can therefore be a valuable tool for
understanding how changes in flow and thus DOM can affect ecosystem
processes.
This study focuses on the molecular characterization of DOM from Florida Bay,
and from Taylor Slough and the C-111 Basin in the northeast section of the Bay,
as this is the Bay’s main freshwater supply outside of rainfall. Detailed molecular
characterization of DOM at 6 representative sites collected during the wet season
(September 2002) will be presented. Results of several months of monitoring at
11 sites along two transects extending from the freshwater marshes of Taylor
Slough and the C-111 Canal Basin through the mangrove fringe into and
throughout Florida Bay will be presented as well.
In this study several approaches to chemical characterization were used to assess
the source, bioavailability, and fate of DOM. Analytical techniques used for the
characterization include pyrolysis-GC/MS, 13C and 15N NMR, gel electrophoresis,
and LC/MS. The various techniques provide unique, complementary, and
confirmatory information on the sources and fate of DOM. Representative
examples of 13C and 15N NMR spectra of typical freshwater Taylor Slough and
Florida Bay DOM samples are shown in Figure 1. The 13C NMR spectrum allows
observation of variations in relative intensities of different functional groups in
relation to different sources and/or biogeochemical transformations. 13C NMR
spectra show that DOM in Florida Bay contain very low abundance of aliphatic
and aromatic components but relatively high abundance of carbohydrates
compared to Taylor Slough. Characterization using 15N NMR spectroscopy
indicates mostly proteinaceous material in the DON pool. Pyrolysis-GC/MS
examines the fragmented chemical products of pyrolytic thermal degradation and
allows reconstruction of source materials. Characterization of intact proteins
through electrophoretic means was performed to gain insight into the role of
proteins in the DON cycle. For additional DON characterization, total protein
content is being determined by colorimetric methods on a monthly basis.
T aylor Slough
T aylor Slough
Florida Bay
Florida Bay
300
200
100
ppm
0
0
-100
-200
-300
-400
ppm
Fig. 1. Typical 13C NMR and 15N NMR spectra of HMWDOM (> 1 kDa)
collected from Taylor Slough and Florida Bay.
In addition to the chemical characterization effort, monthly monitoring of water
samples from the above-mentioned sites has been undertaken to assess seasonal
variability in the DOM composition. Water quality parameters such as total
nitrogen (TN), dissolved organic nitrogen (DON), dissolved organic matter
(DOM), and other basic water quality parameters are being monitored for this
purpose. Fluorescence measurements are also being recorded. In general,
spectroscopic methods provide an assessment of terrestrially vs. marine derived
DOM, an indication of organic carbon content, and estimate of the relative
abundances of protein-like materials relative to humic material.
Monthly water samples were also examined for amounts of humic vs. non-humic
substances. Non-humic substances are a class of compounds that include
carbohydrates, proteins, fatty acids, and other low-molecular-weight organic
substances. Humic substances form most of the organic matter of water and are
largely the result of microbial transformation of higher plant material. Humic
substances are dark-colored amorphous polymeric substances, whose
compositions vary with the source materials and the state of degradation. The
study of humic substances is warranted by their multiple chemical functions of
biological importance.
Carbohydrates are an important potential energy source in aquatic environments.
Information on carbohydrates can provide insight into the overall cycling of
organic carbon. Total carbohydrates are being determined on a monthly basis.
Further characterizations of carbohydrates in DOM have been performed to
determine percent composition of individual sugars, and to use these in the
assessment of DOM sources and transformations.
Finally, molecular weight distributions performed by gel filtration
chromatography suggest differences in the chemical characteristics of DOM
collected from Taylor Slough versus Florida Bay. Figure 2 is a typical elution
chromatogram of water samples from these two sites, showing a higher weight
distribution from Taylor Slough compared to Florida Bay.
Absorbance at 254 nm
(arbitrary unit)
25000
Fig. 2. Sample of elution curves
of DOM collected from Taylor
Slough and Florida Bay using a
gel filtration chromatography.
Taylor Slough
20000
15000
10000
Florida Bay
5000
0
10
20
30
40
Retention time (min.)
Overall, the molecular characteristics of DOM in the Florida Coastal Everglades
show clear differences between Everglades and Florida Bay samples. Optical and
chemical characteristics suggest that much of the DOM in Florida Bay is of
autochthonous origin.
Kathleen Parish, Florida International University, University Park, Miami, FL,
33199, Phone: 305-348-3118; Fax: 305-348-4096. kathleen.parish@fiu.edu,
Question 2