Environmental Engineering Reference
In-Depth Information
also been shown that the daily integrated inhibition by UV-A can reach 4.3 % and
13.2 %, whilst that by UV-B can reach 16.5 % and 13.5 % in coastal and offshore
waters, respectively (Li et al.
2011
). Additionally, exclusion of UV radiation can
increase photosynthesis by 10-65 % in algae from the Mediterranean, 17-46 % in
intertidal algae from southern Chile, and 15-20 % in algae (
Laminaria Saccharina
)
from the North Sea (Hanelt et al.
1997
; Jiménez et al.
1998
; Gómez et al.
2004
).
UV-stimulated inorganic carbon acquisition is often observed in phytoplank-
ton species (Beardall et al.
2009
; Wu and Gao
2009
). Phytoplankton cells grown
in nutrient replete conditions are more resistant to solar UV radiation, and also
their contents of UV-absorbing compounds increases (Marcoval et al.
2008
).
Microplankton (>20 m) are more plentiful in coastal waters, while picoplankton
(<2 m) are more abundant in open oceans (Marañón et al.
2001
; Ho et al.
2008
).
In terms of their responses to UV, large cells are capable of synthesizing and accu-
mulating UV-absorbing compounds that play a protective role against UV. These
screening compounds are not found in picoplankton cells (Raven
1991
; Garcia-
Pichel
1994
) that, therefore, would be more sensitive to solar UV. This issue is
partially offset by a much faster repair process of damaged DNA (Helbling et
al.
2001
; Callieri et al.
2001
). Because taxonomic composition, accumulation of
UV-absorbing compounds and nutrient availability are typically different, physio-
logical responses of phytoplankton assemblages to solar UV can differ geographi-
cally from coastal to pelagic waters (Li et al.
2011
).
Cyanobacteria are important and ubiquitous prokaryotes that populate terres-
trial and aquatic habitats, and they are important contributors to global photosyn-
thetic biomass production (Whitton and Potts
2000
). Enhanced UV-B radiation can
affect cyanobacterial growth, photosynthetic efficiency, pigments, morphology, as
well as cell size and shape. Anyway, different responses are observed in different
species exposed to different UV doses (Wu et al.
2005
; Rath and Adhikary
2007
;
Pattanaik et al.
2008
; Jiang and Qiu
2005
; Harrison and Smith
2009
). It has also
been shown that exposure to UV radiation can reduce the activity of alkaline phos-
phatase, a common extracellular enzyme, by up to 57 %. Interestingly, it is more
often decreased under ultraviolet A than ultraviolet B exposure (Tang et al.
2005
).
As already mentioned, algal nutritional status can influence the UV radiation sen-
sitivity but, on the other hand, UV radiation can inhibit uptake and assimilation of
inorganic nutrients (Harrison and Smith
2009
). This is likely caused by the rapid
UV radiation-induced changes of nitrate into HO
•
•
−
and
NO
2
/NO
2
, which may
−
reduce the availability of NO
3
for primary production (see chapter
“
Photoinduced
It is estimated that, depending on location, ambient UV radiation can reduce
carbon fixation rates up to 65 % in surface waters of the Antarctic region, down
to undetectable levels at 36 m (Boucher and Prezelin
1996
). On average, up to
42 % of primary production inhibition in the water column is carried out by
UV radiation on a daily basis outside the ozone hole (Wängberg et al.
2006
;
Harrison and Smith
2009
; Helbling et al.
1992
; Smith et al.
1992
; Holm-Hansen
et al.
1993
; Bertoni et al.
2011
). In contrast, during a ozone hole depletion event,
the inhibition is increased to ~50 %. This can be supported by the experimental
