Environmental Engineering Reference
In-Depth Information
3.1.6 Total Content of Chlorophyll
a
Chloropigments (chlorophyll
a
and carotenoids) could be important determinants of
UV attenuation in natural waters (Zhang et al.
2009
; Dupouy et al.
2010
; Williamson
et al.
1996
; Belzile et al.
2002
; Kratzer et al.
2008
; Devlin et al.
2009
; Lund-Hansen
2004
; Morel and Bélanger
2006
; Smith et al.
1999
; Stambler
2005
; Baker and Smith
1982
; Gallegos and Bergstrom
2005
). Chlorophyll
a
(Chl
a
) or phytoplankton bio-
mass shows an absorption maximum around 440 nm (Fig.
4
a, c, d) (Zhang et al.
2009
; Bowers et al.
2000
). Phytoplankton absorption is maximal when Chl
a
and
phaeophytin-
a
are detected at the highest levels (Fig.
4
a, c, d) (Zhang et al.
2009
).
Extraordinary spring blooms of the dinoflagellate
Prorocentrum
minimum
can pro-
duce very high concentrations of chlorophyll, which increase for instance light atten-
uation in the upper Chesapeake Bay (Gallegos and Bergstrom
2005
). Chlorophyll
a
specific absorption coefficients for both UV and PAR domains are representative of
the dominant picophytoplankton in the Red Sea (Stambler
2005
).
The study showed a deep chlorophyll maximum at about 50-60 m, with
~1
×
10
8
cells L
−
1
dominated by high concentrations of
Prochlorococcus
(~75 %), whereas in the Gulf of Eilat (Aqaba) ~4
×
10
7
cells L
−
1
have been
reported. Eukaryotic algae (~20 %), cyanobacteria (
Synechococcus
) (~50 %)
and
Prochlorococcus
(~25 %), are distributed throughout the water column in
the Red Sea (Stambler
2005
). Microbial degradation of phytoplankton or chlo-
rophyll a are responsible for the decrease in Chl
a
or phytoplankton absorption
in waters (Zhang et al.
2009
). The share of light attenuation by phytoplankton
is on average 32 % and reaches up to 74 % at high Chl
a
concentrations in
estuarine-coastal waters (Lund-Hansen
2004
). Phytoplankton absorption is the
dominant optical component of light absorption (60-85 %) in spring along the
Patagonia shelf-break front (Ferreira et al.
2009
). Therefore the CDOM absorp-
tion is significantly dependent on the contents of phytoplankton or total con-
tents of Chl
a
in natural waters.
3.1.7 Water
Light absorption by natural waters depends on the water quality (clear or tur-
bid, presence of particulate matter, and CDOM content) (Kirk
1984
; Hayakawa
and Sugiyama
2008
; Gregg and Casey
2009
; Fournier
2007
; Belzile et al.
2002
;
Pérez et al.
2010
; Morris
2009
; Lund-Hansen
2004
; Effler et al.
2010
). Recent
studies show that water even in its purest form exhibits a complex absorption
spectrum and a significant amount of scattering caused by refractive index fluc-
tuations (Fournier
2007
). The optical properties of natural waters are typically
function of the underwater irradiance and of either the vertical attenuation coef-
ficient for downward irradiance (
K
d
) or the irradiance reflectance. It is
R
=
E
u
/
E
d
,
where
E
u
and
E
d
are the upward and downward irradiance at a given depth (Kirk
1984
). These optical properties significantly depend on the nature of the light field
