Geoscience Reference
In-Depth Information
A: Conductivity = 8.50mS cm
-1
B: Conductivity = 11.50mS cm
-1
600
600
1.2
3
550
550
1
2.5
500
500
0.8
2
450
C
450
C
0.6
1.5
A
A
Int
Int
400
400
M
M
0.4
1
N
N
350
350
0.2
0.5
T
T
B
B
300
0
300
0
250
300
350
400
450
250
300
350
400
450
Excitation wavelength (nm)
Excitation wavelength (nm)
C: Conductivity = 15.10mS cm
-1
D: Conductivity = 19.75mS cm
-1
600
600
550
550
4
8
500
500
3
6
450
C
450
C
A
A
2
4
Int
Int
400
M
400
M
N
N
1
2
350
350
T
T
B
B
300
300
0
0
250
300
350
400
450
250
300
350
400
450
Excitation wavelength (nm)
Excitation wavelength (nm)
Figure 7.5. The change in EEM fluorescence of Alkaline Lake CDOM (North Dakota).
(A)
June
2001.
(B)
May 2004.
(C)
August 2004.
(D)
August 2005. The lake water conductivity is indicated for
each measurement and the boxes and letter codes describe peak regions as for
Figure 7.2
. A decided
enhancement of the Int peak intermediate between the microbial M peak region and the terrestrial C
peak region is apparent.
saline lakes (Arts et al.,
2000
; Anderson and Stedmon,
2007
; Mariot et al.,
2007
; Ortega-
Retuerta et al.,
2007
). Although evapoconcentration appears to be a forcing factor on DOM
fluorescence as salts, and hence ionic strength, increase along with organic matter, Osburn
et al. (
2011
) also suggested that microbial processing of DOM in saline lakes exerts an
influence on fluorescence properties in these ecosystems, rather than a strict concentration
of allochthonous fluorescent DOM.
A saline lake (Lake Alkali) in North Dakota, USA, sampled during summer in 2001,
2004, and 2005 showed marked changes to EEM fluorescence of DOM as conductivity
increased in the lake, from 8.50 mS cm
-1
to 19.75 mS cm
-1
(
Figure 7.5
; Osburn et al.,
2011
). Note that the intensity of fluorescence in these EEMs increases, which suggests that
photodegradation was not a strong forcing factor on this DOM. Although seasonal inputs