Environmental Engineering Reference
In-Depth Information
Fig. 3
Relationship between
absorption coefficients
examined at 320 and 480 nm
and molecular weight
fractionations of extracted
humic acid (HA) and fulvic
acid (FA) in sediment
samples collected from Tokyo
Bay using Amicon Diaflo
Ultrafilters. Figure produced
from
Data source
Hayase and
Tsubota (
1985
)
25
A
FA-320 nm
A
FA-480 nm
A
HA -320 nm
A
HA-480 nm
20
15
10
5
0
<10kDa
10-50 kDa
50-100 kDa 00-300 kDa
300 kDa
Molecular weight fractionations of HA and FA
may have a large influence on the absorption of UV light through the water col-
umn (Vernet and Whitehead
1996
; Kahru and Mitchell
1998
; Whitehead and
Vernet
2000
; Vernet et al.
1989
). The MAAs are frequently identified in a wide
phyletic assortment of marine organisms and can provide partial photoprotec-
tion from UV radiation (Karentz et al.
1991
; Bandaranayake
1998
; Jeffrey et al.
1999
). It is reported that
Lingulodinium polyedrum
(formerly known as
Gonyaulax
polyedra
(Dodge
1989
)) produces seven types of MAAs with absorption maxima
ranging between 310 and 364 nm (Vernet and Whitehead
1996
). It is shown that
radiation absorption by dissolved MAAs, assessed from the measured MAAs con-
centrations, significantly correlates with DOM UV absorption (
r
2
=
0.77) and
accounts for up to 10 % of the total DOM absorption at 330 nm (Whitehead and
Vernet
2000
). The chlorophyll-specific absorption coefficient for phytoplankton
is high during the summer season and low during the spring bloom season. This
might be the consequence of the occurrence of large diatoms during the spring
bloom, while small phytoplankton dominates during the summer period (Sasaki
et al.
2005
). In addition, the autochthonous CDOM originated from algal or phy-
toplankton biomass shows strong absorption at 250-700 nm (Zhang et al.
2009
;
Jennings and Steinberg
1994
; Rochelle-Newall and Fisher
2002
; Wada et al.
2007
;
Helms et al.
2008
; Hulatt et al.
2009
). A study of Bay waters has shown that the
relative contribution of CDOM absorption to the total absorption coefficient is
>50 % (Sasaki et al.
2005
).
Particulate material (phytoplankton or algae and detritus) have absorption
spectra in the UV and visible region with several shoulders (Fig.
4
a) (Zhang et
al.
2009
; Odriozola et al.
2007
; Smith et al.
2004
; Vantrepotte et al.
2007
).
Phytoplankton shows a strong absorption around 440 and a relatively weak
absorption around 680 nm in aqueous media (Fig.
4
a), (Zhang et al.
2009
). The
absorption coefficients of phytoplankton at 440 nm are significantly higher
(63-88 %) than those of detritus studied during dry and wet seasons in seawater
(Odriozola et al.
2007
).
Blue light attenuation in the water column is often dominated by CDOM rather
than by phytoplankton absorption. For instance, average CDOM absorption in
