Environmental Engineering Reference
In-Depth Information
stimulate bacterioplankton production when the in situ temperatures are low, i.e.,
in the hypolimnion in summer and in the mixed water column in autumn (Vrede
2005
). At low temperatures, both the temperature increase and the addition of P
(in the hypolimnion in summer) or C (in autumn) had strong effects on bacterio-
plankton production (Vrede
2005
). The interaction between P and temperature is
only significant in the epilimnion in summer. At the same time, temperature alone
had no effect whilst P alone had a strong effect on bacterioplankton production
(Vrede
2005
). It is hypothesized that high temperature can accelerate the pho-
toinduced and microbial release of nutrients, labile organic substrates and other
products (e.g. H
2
O
2
, CO
2
and DIC) from algae, phytoplankton or DOM. Such pro-
cesses take place in both the epilimnion and the hypolimnion and are susceptible
to enhance the bacterioplankton production in natural waters.
4.4 Changes in Photosynthetic Processes in Natural Waters
Phytoplankton cells within the euphotic zone utilize photosynthetically active
radiation (PAR, 400-700 nm) to drive photosynthesis; at the same time, they are
exposed to UV radiation (UVR, 280-400 nm) that can penetrate up to 60 m into
the pelagic water column (Smith and Baker
1979
). Short-term UV-B exposure
can severely inhibit the photosynthetic capability, which can be restored quickly
after transfer to low PAR conditions (Jiang and Qiu
2011
). Solar UV-A radiation
can act as an additional source of energy for the photosynthesis carried out by
coastal marine phytoplankton assemblages in tropical areas (Li et al.
2011
; Gao
et al.
2007a
,
b
), although a similar effect is not observed in pelagic water (Li et al.
2011
). Global warming can significantly affect aquatic photosynthesis in different
ways, by altering physical and chemical environmental conditions. First, warming
of the upper ocean leads to stratification and to shoaling of the upper mixing layer.
Phytoplankton cells in the upper mixing layer will be exposed to higher levels of
solar UV radiation due to reduced mixing rate and depth. In this context, global
warming and ozone depletion can act together to influence the primary producers.
On the other hand, where higher contents of chemical constituents result in DOM-
rich waters, ocean warming may stimulate photosynthesis by increasing the avail-
ability of limiting nutrients. The ongoing ocean acidification following enhanced
dissolution of CO
2
may also interact with ocean warming and affect the primary
production.
The photoinduced degradation of DOM and OM can produce H
2
O
2
, CO
2
and
DIC (Molot et al.
2005
; Johannessen et al.
2007
; Mostofa and Sakugawa
2009
;
Mostofa et al.
2009b
; Xie et al.
2004
; Clark et al.
2004
; Miller and Zepp
1995
;
Dillon and Molot
1997
; Gennings et al.
2001
; Johannessen and Miller
2001
;
Ma and Green
2004
). Similarly, microbial degradation of DOM and OM yields
for instance H
2
O
2
, CO
2
, DIC, PO
4
3
−
, NH
4
+
and CH
4
(Mostofa and Sakugawa
2009
; Ma and Green
2004
; Fu et al.
2010
; Palenik and Morel
1988
; Lovley et
al.
1996
; Zhang et al.
2004
,
2009
; Kim et al.
2006
; Li et al.
2008
). The CO
2
