Environmental Engineering Reference
In-Depth Information
del Vecchio and Blough
2002
; Vähätalo et al.
2000
; Bertilsson and Tranvik
2000
;
Allard et al.
1994
; Amador et al.
1989
; Fujiwara et al.
1995
; Bertilsson and Allard
1996
; Granéli et al.
1996
; Granéli et al.
1998
; Miller and Moran
1997
; Clark et al.
2004
; Xie et al.
2004
; Johannessen et al.
2007
; Fichot and Miller
2010
). In surface
waters, the rate of photoinduced mineralization of CDOM (
pm
z
, mol C m
−
3
d
−
1
),
modified by Vähätalo et al. (
2000
) from Schwarzenbach et al. (
1993
) and Miller
(
1998
), can be expressed as follows (Eq.
4.1
):
λ
MAX
PM
Z
=
ϕ
λ
Q
S,Z,
λ
A
CDOM,
λ
D
λ
(4.1)
λ
MIN
where
ϕ
λ
is the spectrum of the apparent quantum yield for photoinduced min-
eralization (mol produced DIC/mol absorbed photons), Q
s,z,
λ
is the scalar photon
flux density spectrum at the depth
z
(also referred to as actinic flux, mol photons
m
−
2
d
−
1
), and
λ
a
CDOM,
λ
is the absorption spectrum of CDOM (m
−
1
). The param-
eters
λ
max
and
λ
min
are the minimum and maximum wavelengths contributing to
photoinduced mineralization.
In the whole water column the rate of photoinduced mineralization, modified by
Vähätalo et al. (
2000
) from Miller (
1998
), can be expressed as follows (Eq.
4.2
):
λ
MAX
PM
=
ϕ
λ
Q
A,
λ
(
A
CDOM,
λ
/
A
TOT,
λ
)
D
λ
(4.2)
λ
MIN
where
Q
a,
λ
represents the photons absorbed by the water column (mol photons
m
−
2
d
−
1
) and the
a
CDOM,
λ
/
a
tot,
λ
ratio expresses how much CDOM contributes
to the total absorption. In infinitely deep waters,
Q
a,
λ
roughly equals the down-
ward vector photon flux density just below the surface (
Q
d,v,0-
λ
) (Sikorski and Zika
1993
; Sikorski and Zika
1993
).
The quantum yields related to CDOM decrease exponentially with increasing
wavelength (Moran and Zepp
1997
; Vähätalo et al.
2000
; Sikorski and Zika
1993
;
Ratte et al.
1998
; Gao and Zepp
1998
. A generalized equation linking quantum
yield and wavelength (Vähätalo et al.
2000
) can be expressed as below (Eq.
4.3
):
ϕ
λ
=
c
×
10
−
d
λ
(4.3)
where
c
(dimensionless) and
d
(nm
−
1
) are positive constants and
λ
is wavelength
(nm). Different combinations of
c
and
d
can cover a wide range of exponential
relationships between quantum yield and wavelength.
4.3.2 CDOM Absorption Loss in Long- and Short-Wavelengths
Due to Photoinduced Degradation
Photoinduced degradation rapidly lowers the CDOM absorption coefficients
across the entire spectrum, both in natural waters and in standard organic sub-
stances (Fig.
1
) (Vodacek et al.
1997
; Zhang et al.
2009
; Shank et al.
2010
; Moran
et al.
2000
; Hernes and Benner
2003
; Winter et al.
2007
; del Vecchio and Blough