Environmental Engineering Reference
In-Depth Information
Blokhina et al.
2003
). Ocean warming and acidification due to increased atmos-
pheric CO
2
concentration may exacerbate the detrimental effects of solar UV-B
radiation (Häder
2011
). Finally, exposure to solar UV radiation can reduce produc-
tivity, affect reproduction and development, and increase the mutation rate in phy-
toplankton, macroalgae, eggs, and larval stages of fish and other aquatic animals
(Häder et al.
2007
). Consequences of decreased productivity are a reduced sink
capacity for atmospheric carbon dioxide and negative effects on species diversity,
ecosystem stability, trophic interactions and ultimately global biogeochemical
cycles (Zepp et al.
2007
).
Since 1993 the thermal expansion of the oceans has contributed about 57 %
of the overall sea level rise, while decreases in glaciers and ice caps contributed
about 28 % and the remainder was accounted for by losses from the polar ice
sheets (IPCC
2007a
).
4.2 Increase of Photoinduced Activity in Natural Waters
Global warming causes an increase in water temperature that can accelerate the
photoinduced activity of DOM and of other chemical constituents in surface
waters. Photoinduced degradation of DOM and OM can produce a number of
photo-products including H
2
O
2
and DIC (dissolved CO
2
, H
2
CO
3
, HCO
3
−
, and
CO
3
2
−
) (Molot et al.
2005
; Johannessen et al.
2007
; Mostofa and Sakugawa
2009
;
Mostofa et al.
2009a
,
b
,
2011
; Xie et al.
2004
; Clark et al.
2004
; Miller and Zepp
1995
; Thomas and Lara
1995
; Dillon and Molot
1997
; Miller
1998
; Gennings
et al.
2001
; Johannessen and Miller
2001
; Rochelle-Newall and Fisher
2002
;
Ma and Green
2004
; Hiriart-Baer and Smith
2005
). Autochthonous DOM can
be released in natural waters by algae or phytoplankton upon photoinduced deg-
radation or photorespiration (Mostofa et al.
2009a
,
b
; Stedmon et al.
2007a
,
b
;
Thomas and Lara
1995
; Rochelle-Newall and Fisher
2002
; Fu et al.
2010
), and
it has recently been shown that the algal-derived CDOM is a more efficient pho-
toinduced substrate than terrigenous material (Johannessen et al.
2007
). In situ
incubation of natural phytoplankton assemblages in Antarctic waters indicates
that, under normal ozone conditions, UV-B radiation is responsible for a loss of
approximately 4.9 % of the primary production in the euphotic zone. UV radiation
with wavelengths between 320 and 360 nm causes a loss of approximately 6.2 %
(Holm-Hansen et al.
1993a
). Ambient levels of UV radiation (280-400 nm) are
observed to decrease substantially the rates of carbon fixation by phytoplankton
(Holm-Hansen et al.
1993a
; Karentz et al.
1991
; Cullen et al.
1992
; Helbling et al.
1992
; Smith et al.
1992
; Li et al.
2011
), and photoinduced release of DOM from
phytoplankton can also take place. UV-B radiation accelerates the decomposi-
tion of colored DOM entering the sea via terrestrial runoff, thus having important
effects on the oceanic carbon cycle (Zepp et al.
2003
).
The increase of water temperature significantly enhances the efficiency of the
Fenton and photo-Fenton reactions, as well as the photolysis of NO
2
−
−
, NO
3
and
