Environmental Engineering Reference
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(Draper and Crosby 1981 ; Zepp et al. 1992 ; Wang et al. 2001 ; White et al. 2003 ;
Nakatani et al. 2007 ; Vione et al. 2006 , 2009a , b ).
3.6 Occurence of H 2 O 2 and its Effect on Photosynthesis
In support of the involvement of H 2 O 2 in the photosynthetic reaction, several
H 2 O 2 -related phenomena have been observed in natural waters, which can be clas-
sified as follows (Mostofa et al. 2009 ). First, the correlation between carbon pro-
duction and photolytically formed H 2 O 2 concentration, suggesting a link between
hydrogen peroxide and organic matter photosynthesis in lake water (Anesio et al.
2005 ). Second, Chl a production in the epilimnetic layer (5-10 m) is typically
observed to increase with a decrease in total CO 2 contents (Talling 2006 ), sug-
gesting that photosynthesis is highest at the epilimnetic layer (5-10 m) than in
the uppermost epilimnion (0-1 m). Correspondingly, the O 2 and Chl a contents
reach a minimum when the water temperature become highest during the summer
stratification period (Talling 2006 ), suggesting that photoinduced degradation or
assimilation of Chl a may be responsible for the decrease in Chl a at the upper-
most layer. Here O 2 may be involved in the production of free radicals (H 2 O 2 or
HO
) that could inhibit photosynthesis (Mostofa and Sakugawa 2009 ; Moffett and
Zafiriou 1990 ). This result is similar to earlier studies where photosynthesis was
observed to be less effective in the uppermost layer (1 m) compared to the subse-
quent epilimnion (3 m) (Nozaki et al. 2002 ). A ratio of variable to maximal fluo-
rescence (Fv/Fm) of phytoplankton productivity showed a decrease as irradiance
increased during the morning and an increase as irradiance declined in the after-
noon. These results may be associated with both photoprotective strategies in the
antennae of PSII and photo damage of PSII reaction centers (Zhang et al. 2008 ).
Conversely, H 2 O 2 usually increases gradually starting in the morning, reaches a
maximum at noon and then gradually decreases in the afternoon (Mostofa and
Sakugawa 2009 ). It is therefore suggested that high production of H 2 O 2 and sub-
sequent photoinduced generation of HO
at noon is susceptible to damage the PSII
reaction centers.
Third, H 2 O 2 may be concentrated by particulate organic matter or small fungi
through rapid transpiration (Komissarov 1994 , 1995 , 2003 ). This hypothesis
can be supported by observation of relatively low production of H 2 O 2 in unfil-
tered samples compared to filtered ones during irradiation (Moffett and Zafiriou
1990 ; Cooper et al. 1988 ; Petasne and Zika 1997 ). An increase in the growth rate
of plants and mycelial fungi is detected when the H 2 O 2 concentration increases
up to an optimum level, from 1 nM to 10 M, and the growth rate decreases when
H 2 O 2 approaches 1 mM (Komissarov 2003 ; Ivanova et al. 2005 ). High levels of
H 2 O 2 may photolytically produce HO
, a strong oxidizing agent, that may cause
ecophysiological disorders in plants, decrease the CO 2 assimilation rate and
affect stomatal conductance, fluorescence and needle life span (Kume et al. 2000 ;
Kobayashi et al. 2002 ). In natural waters, HO
that is produced photolytically from
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