Environmental Engineering Reference
In-Depth Information
the vertical stratification in large parts of lakes and oceans. An increase in pho-
toinduced and microbial degradation rates of OM (DOM and POM) by global
warming may affect water transparency and generation of photo- and microbial
products (H
2
O
2
, CO
2
, DIC, and so on), may modify seasonal patterns in chloro-
phyll or primary production, contents of nutrients (NO
2
, and PO
4
3
−
),
carbon cycling, pH values, microbial food web stimulation that varies seasonally
on a variety of time scales, and the depth of the mixing layer (see also chap-
Cycles in Natural Waters
”) (Mostofa et al.
2009
; Baulch et al.
2005
; Morris and
Hargreaves
1997
; Cooke et al.
2006
; Huisman et al.
2006
; Malkin et al.
2008
;
Davis et al.
2009
; Castle and Rodgers
2009
; Mostofa and Sakugawa
2009
;
Keeling et al.
2010
; Zepp et al.
2011
; Granéli et al.
1998
). Two phenomena can
result from this. First, in water with high contents of OM, photoinduced and
microbial processes that correspond to high photosynthesis may be prolonged,
thereby causing the prolongation of the primary productivity (Malkin et al.
2008
). This may eventually result into toxic or harmful algal bloom in natural
waters. Second, low photosynthesis could take place in waters with low contents
of OM, causing low production of photo- and microbial products. This can sub-
sequently reduce the vertical mixing and suppress the upward flux of nutrients,
leading to a decrease in primary production in oceans (Huisman et al.
2006
).
An increase in water temperature by global warming can also decrease the
concentration of dissolved oxygen (O
2
) in natural waters (Keeling et al.
2010
;
Epstein et al.
1993
; Garcia et al.
1998
; Sarmiento et al.
1998
; Plattner et al.
2001
;
Bopp et al.
2002
; Keeling and Garcia
2002
; Matear and Hirst
2003
). This could
enhance the growth of cyanobacteria and other algae (Epstein et al.
1993
) and/
or decrease the growth of other organisms (Keeling et al.
2010
). The decrease
of dissolved O
2
in the upper surface layer would occur because of decreased O
2
solubility in warmer water and due to photoinduced generation of superoxide radi-
mechanism) by the effect of global warming. An increase in O
2
can enhance the
production of H
2
O
2
(Moffett and Zafiriou
1990
) and different algae can show una-
like responses to O
2
concentration (Pope
1975
). This may for instance be linked
to eutrophication from excess algal growth. The most prominent symptoms of
eutrophication are oxygen depletion in bottom waters and harmful algal blooms
(Richardson and Jorgensen
1996
).
The decrease of dissolved O
2
in deeper waters would be caused by the
decrease in vertical mixing of the water column due to the longer stratification
period as a consequence of global warming. This effect can reduce the primary
production as well as to survival of organisms in deeper water layers, particularly
in lakes and oceans. Earlier studies did not provide any clear mechanisms about
the decrease of dissolved O
2
, which includes changes in ocean circulation rates
(Bindoff and McDougall
2000
; Shaffer et al.
2000
; Emerson et al.
2001
; Keller
−
−
, NO
3
