Environmental Engineering Reference
In-Depth Information
5.1 Seasonal Variation in Sunlight and UV Radiation
on Photosynthesis
Solar radiation is the key driving force for the occurrence of photosynthesis in nat-
ural waters (Sinha et al.
2001
; Rastogi et al.
2010
; Jiang and Qiu
2011
; Sobek et
al.
2007
). Exposure of photosynthetic organisms to strong light (or UV light) can
significantly inhibit the PSII activity, with resulting photoinhibition of or photo-
damage to PS II (Aro et al.
1993
; Melis
1999
; Andersson and Aro
2001
; Han et
al.
2001
; Nishiyama et al.
2001
,
2008
; Adir et al.
2003
). Photoinhibition of photo-
synthesis is a process by which excessive irradiance, absorbed by the leaves, can
inactivate or impair the chlorophyll-containing reaction centers of chloroplasts,
thus inhibiting photosynthesis (Bertamini et al.
2006
). Because of the differ-
ences among the organisms, the effects of light can be classified into two sections
(aquatic microorganisms and higher plants) for their better understanding.
Effects of Sunlight on Aquatic Microorganisms
Cyanobacteria or phytoplankton cells can utilize photosynthetically active radia-
tion (PAR, 400-700 nm) to drive photosynthesis within the euphotic zone (see
also global warming chapter
“
Impacts of Global Warming on Biogeochemical
Cycles in Natural Waters
”) (Smith and Baker
1979
; Abboudi et al.
2008
; Li et
al.
2011
). Solar UV-A radiation (315-400 nm) acts as an additional source of
energy for photosynthesis to enhance the CO
2
fixation in tropical marine phyto-
plankton (Li et al.
2011
; Gao et al.
2007
,
2007
). However, UV-A does not bring
any enhancement to carbon fixation in pelagic water (Li et al.
2011
). The cells
of aquatic microorganisms can be exposed to ultraviolet radiation (UVR, 280-
400 nm), which can penetrate up to 60 m into the pelagic water column (Smith
and Baker
1979
). Furthermore, depletion of the stratospheric ozone layer can
cause additional penetration of UV radiation in the Arctic and Antarctic regions.
Such a phenomenon has detrimental effects on the processes involved in primary
production (see also chapter
“
Impacts of Global Warming on Biogeochemical
Cycles in Natural Waters
”
) (Huisman et al.
2006
; Häder et al.
2007
; Zhang et al.
2007
). Solar UV-B (280-315 nm), and partly UV-A (315-400 nm) can reduce
growth and photosynthetic rates, increase permeability of cell membranes, damage
proteins or DNA molecules, pigments, and even lead to cell death (see also chap-
(Jiang and Qiu
2011
; Wängberg et al.
2006
; Behrenfeld et al.
1993
; Sass et al.
1997
; Campbell et al.
1998
; Rajagopal et al.
2000
; Helbling et al.
2001
; He and
Häder
2002
; Buma et al.
2003
; Sobrino et al.
2004
; Litchman and Neale
2005
; Wu
et al.
2005
; Bouchard et al.
2006
; Agusti and Llabrés
2007
; Rath and Adhikary
2007
; Gao et al.
2008
; Pattanaik et al.
2008
; Jiang and Qiu
2005
).
It has been shown that, ranging from coastal (case 1) to pelagic (case 2) surface
seawaters, UV-B can cause similar inhibition whilst the inhibition of photosynthesis
by UV-A (315-400 nm) increases when passing from coastal to offshore waters (Li
et al.
2011
). UV-B inhibits photosynthesis up to 27 % and UV-A up to 29 %. It has
