Environmental Engineering Reference
In-Depth Information
direct excitation of the primary donor by 1-5 ps (Prokhorenko and Holzwarth
2000
; Tang et al.
1990
; Germano M et al.
1995
; Groot et al.
1997
; Konermann
et al.
1997
; Greenfield et al.
1999
), or be slowed down by energy transfer to the
primary donor in tens or hundreds of picoseconds (Groot et al.
1997
; Greenfield
et al.
1999
). However, calculations based on structural information, from both the
crystallographic structure and a model, predict subpicosecond excitation energy
equilibration among the six central cofactors (Durrant et al.
1995
; Renger and
Marcus
2002
; Zouni et al.
2001
; Kamiya and Shen
2003
; Svensson et al.
1996
;
Leegwater et al.
1997
). Electron transfer thus occurs from other Chls, and the
slower components observed in the tens of picoseconds timescale at low tempera-
tures are due to secondary electron transfer (Prokhorenko and Holzwarth
2000
). A
model study has shown that the ~67 % variability of observed primary production
indicates that estuarine production is mainly controlled by light availability and
temperature (Yoshiyama and Sharp
2006
). Bacterial abundance (12
×
10
6
mL
−
1
)
and production (1.7 g C L
−
1
h
−
1
) depend on temperature. During late spring and
summer, at constantly higher temperatures, bacterial production can correlate posi-
tively with readily utilisable substrates and humic compounds (Freese et al.
2007
).
High surface temperatures and heavy precipitation in late spring and summer can
give rise to a highly-stratified water column that can stimulate a series of phytoplankton
blooms. During winter in Tokyo bay, a weakly-stratified and deeply-mixed water col-
umn can lead to a rapid decline in phytoplankton biomass under light-limited growth
conditions (Bouman et al.
2010
). The effect of high WT can be a decrease in PSII effi-
ciency, which can ultimately cause cell stress (Lesser and Gorbunov
2001
).
At highly elevated WT, several effects on phytoplankton can take place such as
disorganization of thylakoid membranes, disrupted electron flow to the dark reac-
tions of photosystem II, elevated concentrations of damaging oxygen and hydroxyl
radicals, and the loss of the D1 repair protein (Goulet et al.
2005
). The mecha-
nism behind the changes in photosynthetic efficiency caused by WT, driven by
natural solar intensity, mostly follows a similar mechanism as sunlight effects (see
the earlier section). However, WT can cause photosynthetic efficiency to be either
enhanced or decreased, an issue that involves three facts: First, at low WT (lower
than 12 °C, including chilling stress that generally refers to nonfreezing tempera-
tures at 0-12 °C) the key reactants such as CO
2
, H
2
O
2
and DIC (generated both
photolytically and microbially from DOM and POM) are quite low at low sun-
shine in natural surface waters. Low availability of these reactants can decrease the
photosynthetic efficiency of aquatic microorganisms in natural waters.
Second, at moderate WT (approximately 12-25 °C) and with an increase in
WT, the key reactants are significantly increased, usually also because of enhanced
sunlight intensity. This effect may greatly enhance photosynthesis at optimum WT
and, as a consequence, primary production in waters. It has been shown that the
Chl
a
concentrations at the epilimnion are well correlated with WT in lakes, but
those correlations are not observed in the deeper layers (Fu et al.
2010
; Mostofa
KMG et al., unpublished data). This suggests that an optimum water temperature,
driven by solar intensity, may play a significant role in the origin of Chl
a
or in
enhancing phytoplankton biomass in natural waters.
