Environmental Engineering Reference
In-Depth Information
Changes of CDOM content in surface water modify the light distribution within
the water column and therefore potentially affect the entire ecosystem
4,47
. For example,
a two- to three-fold reduction of surface CDOM (Figure 5A) can increase the amount of
light penetrating down the water column by several order of magnitude depending on
the wavelength of observation and original level of CDOM (Figure 5B). Thus, small
changes of CDOM can dramatically increase the amount of radiation potentially
damaging living organisms.
12.0
10.0
1
8.0
6.0
2
3
4.0
2.0
A
0.0
10
14
10
13
10
12
10
11
10
10
10
9
10
8
10
7
10
6
10
5
10
4
3
1
2
10
3
10
2
B
10
1
10
0
300
350
400
450
500
550
600
Wavelength (nm)
Figure 5.
CDOM absorption spectra (A) and calculated downwelling irradiance at 10 m depth (B) in
the Delaware River (DR) at 39q41.33'N and 75q31.11'W. A: 1. DR (); 2. DR diluted two fold
(······); 3. DR diluted three fold (). B: Calculated downwelling irradiance on a logarithmic scale
in presence of CDOM 1-2-3.
Field and laboratory studies have also shown an increase in the CDOM spectral
slope (
S
) induced by light exposure
14,20,28,40,48-49
. Other studies, however, have shown the
opposite trend
41,50-51
; the reason for this discrepancy is still unknown, but it may be due
to the different protocols employed in calculating the
S
values.
An increase in
S
is also observed at higher salinity (~32 ppt)
20
, concomitant with
a blue-shift in the CDOM emission maximum
52-55
. The increase in
S
and the blue-shift
of the emission maximum are observed at high salinity values where presumably the
terrestrial CDOM is diluted enough to allow photobleaching to become evident.
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