Environmental Engineering Reference
In-Depth Information
a
maxima in the upper epilimnion (0-8 m). Such an effect has been observed in
the lakes Hongfeng, Baihua and Kinneret, and is quite different from Lake Biwa
(0-20 m) and Lake Baikal where DOM contents are relatively low (see also chap-
Degradation in Nature
”) (Fu et al.
2010
; Mostofa KMG et al., unpublished data;
Hayakawa
2004
; Yacobi
2006
). Waters with high contents of DOM and POM are
responsible for the occurrence of toxic algal blooms through high photosynthesis.
The latter would be linked to elevated amounts of photo- and microbial products,
provided that algal growth is limited by nutrient availability and not by light, and
would also be affected by global warming (see later).
The second issue is the dependence of photosynthesis on allochthonous DOM.
It has been shown that photosynthetic primary production is significantly depend-
ent on allochthonous humic substances (fulvic and humic acids) in natural waters.
It has been observed an increase of bacterial biomass with high humic contents
(Jones
1992
; Tranvik
1988
;
1989
; Hessen
1985
; Tranvik and Höfle
1987
). Typhoon-
enhanced terrestrial discharges can elevate Chl
a
concentrations by four times and
shift phytoplankton composition (spectral class-based), from an initial dominance of
diatoms and green microalgae to the dominance of blue green microalgae (cyano-
bacteria are increased by more than 200 %) and cryptophytes (Blanco et al.
2008
).
This enhancement is likely caused either by favorable nutrient availability (Blanco
et al.
2008
) or by high input of allochthonous DOM including humic substances.
A higher ratio of bacterial production to primary production has been observed in a
humic lake compared with a clear-water lake, suggesting that the bacterioplankton of
the humic lake utilized allochthonous substrates in addition to substrates originating
from autochthonous primary production (Tranvik
1989
). Moreover, a isolated (ca.
Pseudomonas sp.
) bacterial cell does not utilize fulvic acid, but in the presence of
added lactate fulvic acid is partially degraded and causes an increase in the cell yield
because of co-metabolism (Stabel et al.
1979
; Wright
1988
; de Haan
1974
). Bacteria
(ca.
Arthrobacter
sp.) can utilize fulvic acid, but this is only partially degraded and
produces a small cell yield compared to e.g. benzoate. However, in media containing
benzoate and fulvic acid, bacteria have higher growth rate and cell yield compared to
media with only benzoate or fulvic acid (de Haan
1977
). The fluctuations in the con-
tent of fulvic acids and the amount of benzoate-oxidizing bacteria suggest that the
priming effect might be more important than co-metabolism during the decomposi-
tion of fulvic acids in lake water (de Haan
1977
). The mechanism behind this phe-
nomenon is, presumably, the acceleration of the photoinduced degradation of fulvic
acid in the presence of benzoate. It may cause enhanced production of biologically
labile substrates that subsequently increase bacterial production. Benzoate (C
6
H
5
-
COONa) may photolytically release electrons (e
aq
−
) in aqueous solutions of fulvic
acid (Fujiwara et al.
1993
; Zepp et al.
1987
; Assel et al.
1998
; Richard and Canonica
2005
), an effect that might lead to the production of hydrogen peroxide in natural
waters (Mostofa and Sakugawa
2009
; Fujiwara et al.
1993
).
The generation of hydrogen peroxide (H
2
O
2
) upon irradiation of ultra-filtered
river DOM is substantially increased, from 15 to 368 nM h
−
1
, with increasing salin-
ity at circumneutral pH values (Osburn et al.
2009
). Production of HO
•
from H
2
O
2
