Environmental Engineering Reference
In-Depth Information
are generally accounted for by various substances such as proteins, amino acids
and other organic components bound to PSI and PSII. These compounds are all
susceptible to undergo microbial decompositon (see chapters
“
Photoinduced and
Dissolved Organic Matter in Natural Waters
”
). On the other hand, Chls that absorb
radiation in the longer wavelength region are susceptible to undergo photochemical
decomposition (see chapters
“
Photoinduced and Microbial Degradation of Dissolved
Natural Waters
”
). Absorbance in the longer wavelength regions (>600 nm) is gener-
ally linked to the easiest way of electron release from the functional groups bound
to the parent molecule. Chl molecules are thus responsible for the absorption peaks
located at
λ
> 600 nm. Interestingly, longer wavelength absorption peaks (>600 nm)
are often observed for some functional groups that are present in terrestrial humic
Therefore, changes in functional groups or molecules bound to PSI and PSII, which
take place through either photoinduced or microbial processes, may affect the
absorption peaks. Note that peaks appearing in the green region (500-600 nm) are
small compared to those located in the blue (<500 nm) and red (>600 nm) regions
(Aguirre-Gomez et al.
2001
).
Considering the previously reported findings, the following suggestions can
be followed for Chl determination: First, measurement of Chl
a
should be con-
ducted only at a single wavelength, not at several ones. The most suitable is at
around 665-675 nm, and absence of light should be ensured during sample
processing and measuring. Second, Chl
b
should be measured only at around
643-650 nm. In earlier studies, the measurement of Chl
b
has been carried out
using its absorption peaks at 465-470 or 483, 585-595 and 643-650 nm, but only
the latter provides sufficiently accurate results (Satoh et al.
2001
; Aguirre-Gomez
et al.
2001
; Bidigare et al.
1989
; Millie et al.
1997
). Some differences in absorp-
tion wavelengths in Chl
b
can be caused by the occurrence of various forms of
this Chl, as mentioned before. The third issue is that Chl
c
should be detected at
630-639 nm, although earlier studies have adopted absorption peaks at 465-470,
589, and 630-639 nm (Bidigare et al.
1989
; Millie et al.
1995
,
1997
). The many
absorption peaks used in earlier studies, in particular at short wavelengths, should
not be adopted for the measurement of any Chl molecule. The reason is that
absorbance at shorter wavelengths has been observed for other pigments that could
interfere with Chl determination, such as hycoerythrin (detected at 543-550 and
566-568 nm) (Payri et al.
2001
; Smith and Alberte
1994
); phycoerythrocyanin
(~550 nm and ~575 nm) (Millie et al.
2002
); phycocyanin (625-630 nm) (Payri
et al.
2001
; Millie et al.
2002
); fucoxanthin (521-531 nm) (Bidigare et al.
1989
);
and different carotenoids (490-495 nm) (Millie et al.
1997
; Owens et al.
1987
).
Furthermore, CDOM absorbs radiation in lower wavelength regions (250-500 nm)
because of the functional groups present in allochthonous and autochthonous
