Environmental Engineering Reference
In-Depth Information
also been shown that UV-B influences the CO
2
-concentrating mechanism of
M.
aer-
uginosa
, and this cyanobacterium has many adaptive strategies to cope with prolonged
UV-B exposure (Jiang and Qiu
2005
; Song and Qiu
2007
). Enhanced solar UV-A
(315-400 nm) and/or UV-B radiation (280-315 nm) can reduce growth and photo-
synthetic rates, inhibit pigment production, increase permeability of cell membranes,
damage proteins or DNA molecules, and even lead to cell death (Jiang and Qiu
2005
,
2011
; Behrenfeld et al.
1993
; Sass et al.
1997
; Helbling et al.
2001
; Buma et al.
2003
;
Sobrino et al.
2004
; Litchman and Neale
2005
; Wu et al.
2005
; Agustí and Llabreés
2007
; Rath and Adhikary
2007
; Pattanaik et al.
2008
; Gao et al.
2008
). At normal
ozone concentrations (i.e. 344 Dobson Units), UV radiation can reduce primary pro-
ductivity in surface waters by as much as 50 % (Cullen et al.
1992
; Holm-Hansen et
al.
1993b
; Cullen and Neale
1994
). A normal level of UV radiation also reduces phy-
toplankton production by 57 % at a depth of 1 m, while such inhibition decreases to
<5 % at 30 m, at 50ºS in mid December (Arrigo
1994
). Such effects on aquatic organ-
isms might be caused directly by UV radiation and indirectly through high production
of HO
•
in epilimnetic (upper layer) waters. Both effects are able to alter the structural
configuration of organisms with release of many organic substances in epilimnetic
(surface layer) waters (Mostofa et al.
2009a
,
b
; Sinha et al.
2001
; Rastogi et al.
2010
;
Gauslaa and McEvoy
2005
; Lesser
2008
; Hylander et al.
2009
; Ingalls et al.
2010
).
To conclude, global warming may greatly impact primary production, species
composition, carbon export, and finally biological activities in the aquatic envi-
ronment (Huisman et al.
2006
; Häder
2011
; Häder et al.
2003
,
2007
; Sinha et al.
2001
; Rastogi et al.
2010
; Petchey et al.
1999
).
4.6 Changes in DOM Dynamics and the Global Carbon Cycle
The increase of DOC concentration in many catchments in Europe and North
America might be the concequence of a climate effect (Zepp et al.
2011
; Burns
et al.
2006
; Vuorenmaa et al.
2006
; Sobek et al.
2007
; Zhang et al.
2010
; Freeman
et al.
2001
,
2004
; Evans et al.
2005
; Skjelkvåle et al.
2001
; Löfgren et al.
2003
;
Hongve et al.
2004
; Worrall et al.
2005
; Larsen et al.
2011
). An increase of DOC
in natural waters because of global warming could be linked to the production
of autochthonous DOM by phytoplankton or algae under both photoinduced and
microbial-assimilation (Johannessen et al.
2007
; Mostofa et al.
2009a
,
b
; Fu et al.
2005
,
2010
; Stedmon et al.
2007a
; Zhang et al.
2009
; Biddanda and Benner
1997
;
Carrillo et al.
2002
; Mallet et al.
1998
; Lehmann and Bernasconi
2004
). Indeed,
increasing temperature can increase the release of organic substrates by phyto-
plankton (Morán et al.
2006
; Watanabe
1980
; Verity
1981
; Zlotnik and Dubinsky
1989
). Such phenomena can in turn enhance photosynthesis and primary produc-
tion, as already explained, particularly in DOM-rich waters.
On the other hand, global warming can affect waters with low contents of DOM
in the opposite direction, inhibiting the production of various compounds that ulti-
mately limit photosynthesis and primary production. This effect can proceed either
