Abstract
Results and Discussion
Results and Discussion
1.6
29
1.2
1
0.8
0.6
0.4
0.2
0
<10
10-100
>100
• As the SUVA254 values increase, so do the sizes of OM (Figure 2).
• The larger the size fraction, the larger the humic substances;
Weishaar et al (2003) showed a correlation between aromatic
carbon and aromaticity.
• The SUVA254 values from this study fall in the 6-12% aromatic
carbon range. These sites have very little vegetation. The sites
from the Weishaar et al. 2003 study that are in the same 6-12%
aromatic carbon range, and have similar SUVA254 values, are
also from lakes with very little organic material (Table 1).
• Sites with higher SUVA254 values in the Weishaar study have as
much as 35% aromaticity. These sites are from regions that are
more forested and therefore contain more organic material with a
higher aromaticity. The higher the SUVA254 value, the higher the
aromaticity, the more vegetation and the more autochthonous
they are. The SUVA254 value increases with increasing molecular
weight.
25
• Lakes SS1381 and SS1590 are in Kellyville, Greenland and are
further from the glacier. Their SUVA254 values are higher, possibly due
to the arctic tundra vegetation.
• Lakes SS901, SS903, SS904, and SS906 are closer to the glacier
and lighter because of the glacial flower which is powdered rock from
the expanding and contracting of that accumulates after the glacier
retreats and advances. The lakes become darker and larger over time
due to precipitation.
Figure 1. Sampling Sites consist of
various lakes in Kangerlussuaq,
Greenland (Source: Google Earth)
Study Sites
19
• As lakes mature, they have decided changes in organic matter quality
which is important for understanding lake ecosystems over time.
• An increase in absorbance, or concentration of aromatic rings, is
an indicator of an increase in humic substances. a254 is the
concentration of aromatic rings. If the number of aromatic rings
increases, that will increase the conjugation and therefore larger
molecules will generate absorbance at larger wavelengths.
• The older a lake is in its watershed, the longer time it has for soil
development and opportunity for organic matter to develop.
• The slope is how fast absorbance changes over a wavelength.
Findings
•
•
•
•
17
0
B
50
100
150
a₂₅₄ (m⁻¹)
200
250
29
10-100
>100
<10
27
25
Slope
Sample Sites
23
21
Size Fraction
Figure 2. Standard Deviation of SUVA254 Values by Size Fraction
SS1381
SS1590
SS2
SS8
SS85
SS901
SS903
SS904
SS906
27
Slope
1.4
SUVA254 (Lm⁻¹mgC⁻¹)
Dissolved organic matter (DOM) is an important property of lake ecosystems,
resulting from the decomposition of organic matter stored in soils and of plankton in
the water column. Colored dissolved organic matter (CDOM), the fraction that absorbs
ultraviolet (UV) and visible light, is the controlling factor for the optical properties of
many surface waters. Little is known about the mechanisms by which DOM and
CDOM evolve in lakes formed during glacial retreat. As part of a larger study of the
ecosystems in glacial lakes, the present project examined the quality of DOM and
CDOM in lakes in SW Greenland. Nine lakes in Kangerlussuaq, Greenland were
studied. The specific ultraviolet absorbance (SUVA) of a water sample at 254 nm
(SUVA254), computed by normalizing absorption (a254) to dissolved organic carbon
(DOC) concentration, is related to the aromatic carbon content of DOM. The ratio of
the slope of CDOM absorption at 275-295 nm to the slope of CDOM absorption at
350-400 nm (SR) is another method of characterizing the quality of OM. a254, SUVA254,
DOC, and SR values were studied to analyze DOM quality in these lakes. In addition,
DOM was fractionated into different sizes to examine trends in organic matter quality
in Greenland lakes. The aim of this project was to compare the aromatic content in
lakes (for which SUVA254 is an index) among the size fractions and between young
lakes near the glacial meltwater and “adolescent” lakes located approximately 38
kilometers away.
A
Findings
23
21
In each graph from Figure 3, there are three separate groupings,
each with a negative trend.
In the first group, lakes SS901, SS903, SS904, and SS906 are
closer to the glacier.
In the second group, lakes SS1381, SS1590, and SS2 are further
away from the glacier.
The third group is comprised of lakes SS8 and SS85. Further
research is needed to understand this separation, since the second
and third groups are essentially in the same area.
19
17
0
50
100
150
200
250
a₂₅₄ (m⁻¹)
C
Acknowledgements
Acknowledgements
Methods
•Water samples were collected from 9 sampling sites.
•Absorption was measured for each filtered sample on Varian Cary 300
spectrophotometer.
•Once absorption data was obtained, the samples were preserved with an 85%
solution of phosphoric acid (H3PO4).
•DOC was measured for each acidified sample using an Aurora 1030 TOC analyzer.
•Appropriate instrument corrections were applied where necessary
•SUVA254 values were obtained using the following equation:
Sample Site
SUVA254 (Lm⁻¹mgC⁻¹)
Source
SS903
SS906
SS1381
SS85
SS901
SS2
SS904
SS1590
SS8
Pony Lake FAa
0.5
0.7
0.7
0.9
0.9
0.9
1.1
1.2
1.6
1.7
This Study
This Study
This Study
This Study
This Study
This Study
This Study
This Study
This Study
Weishaar et al. 2003
Lake Fryxell HPOA
1.8
Weishaar et al. 2003
Upper Shingobee HPOA
2.9
Weishaar et al. 2003
Suwannee River FA
3.2
Weishaar et al. 2003
Ogeechee River FA
3.8
Weishaar et al. 2003
Ogeechee River HA
5.3
Weishaar et al. 2003
Table 1. SUVA254 values from this study and Weishaar et al. 2003, by sample
site.
NC DENR 319 NPS Program Grant #4443, Wake Technical Community
College MEAS Program, UNC-IMS MODMON Program
References
50.00
Weishaar, J. L., Aiken, G. R., Bergamaschi, B. A., Fram, M. S., Fujii, R.,
& Mopper, K. (2003). Evaluation of specific ultraviolet absorbance as an
indicator of the chemical composition and reactivity of dissolved organic
carbon. Environmental Science & Technology, 37(20), 4702-4708.
40.00
References
Anderson, N. J., and Stedmon, C. A. (2007) The effect of
evapoconcentration on dissolved organic carbon concentration and
quality in lakes of SW Greenland. Freshwater Biology 52.2 280-289.
Print.
Findlay, S. (2003) Aquatic ecosystems interactivity of dissolved organic
matter. Amsterdam: Academic Press. Print.
Williamson, C. E., Morris, D. P., Pace, M. L., and Olson, O. G. (1999)
"Dissolved organic carbon and nutrients as regulators of lake
ecosystems: Resurrection of a more integrated paradigm." Limnology
and Oceanography 44.3_part_2 795-803. Print.
SS1381
SS1590
SS2
SS8
SS85
SS901
SS903
SS904
SS906
60.00
DOC (mg/L)
Methods
70.00
30.00
20.00
10.00
0.00
0
50
100
150
a254 (m⁻¹)
200
Figure 3. a254 vs. (A) Slope by Lake, (B) Slope by Size fraction, and (C)
DOC.
250