Environmental Engineering Reference
In-Depth Information
(Rutledge et al.
2010
; O'Reilly et al.
2003
; Letelier et al.
2004
; Porcal et al.
2009
;
Morrison et al.
2002
; Ryther
1956
). Notes that the depth of the euphotic zone is
defined as the depth where the photon flux density equals 1 % of that measured at
the air-sea interface (Ryther
1956
). The temperature increase is a global effect, but
it is higher northern latitudes. Average Arctic temperatures have in fact increased
at almost twice the global average rate in the past 100 years (IPCC
2007a
).
Temperatures at the top of the permafrost layer have generally increased in the
Arctic by up to 3 °C since the 1980s (IPCC
2007a
). The global average surface air
temperature has increased by 0.74 °C over the past century and is projected to rise
by another 1.1 to 6.4 °C before 2100. The sea level could increase by 0.2 to 0.6 m
or more before 2100 (Hansen and Sato
2004
; IPCC
2007b
). The long-term obser-
vations in European seas show that the increase of the sea-surface temperature
rate is around 0.01 ºC yr
−
1
since the 1860s (Wiltshire and Manly
2004
; Vargas-
Yañez et al.
2005
; Mackensie and Schiedek
2007
). The combination of tempera-
ture increase and of the decrease in water flow allow the prediction of a 10-fold
increase, by the end of this century, of the number of days when the temperature
of the Fraser River exceeds 20 °C. Such a phenomenon may threaten the survival
of some specific fish and other aquatic microorganisms (Morrison et al.
2002
).
Global warming may expand the summer season and increase the water column
transparency as well as the water temperature, which might accelerate the photoin-
duced degradation of DOM through e.g. an enhanced production of HO
•
(Huisman
et al.
2006
; Zellner et al.
1990
; Malkin et al.
2008
). At the same time, there can be
an increase of UV radiation during ozone hole events (Huisman et al.
2006
; Kerr
and McElroy
1993
; Varotsos and Kondratiev
1995
; Qian et al.
2001
; Sarmiento
et al.
2004
; Schmittner
2005
). Previous studies show that the incident UV-B radia-
tion has increased at a rate of 10-20 % per decade at temperate latitudes (Kerr and
McElroy
1993
), and a total ozone reduction of 2.5 % per decade during summer
would cause a 5 % increase in the UV irradiance (Varotsos and Kondratiev
1995
).
Although the increase of the chlorine concentration in the stratosphere has
slowed down, reflecting the execution of the Montreal Protocol, the time required
for the recovery of the ozone layer is unconvincing and will rely on the impacts
of the climate change on the stratosphere (Weatherhead and Andersen
2006
). The
global warming phenomenon is expected to enhance the temperature in the tropo-
sphere, but at the same time there will be cooling effects in the stratosphere that
can enhance ozone depletion. An increase of UV-B radiation may greatly enhance
the production of HO
•
−
−
due to an increase in direct photolysis rates of NO
2
, NO
3
and Chromophoric Dissolved Organic Matter (CDOM), and also other redox reac-
tions may be enhanced, in particular in the Antarctic and Arctic regions (Qian
et al.
2001
; Randall and Harvey
2005
). The HO
•
formation from nitrate, nitrite and
CDOM significantly increases during ozone hole conditions (Qian et al.
2001
).
Two effects may derive from this scenario. First, ozone hole conditions may
enhance the photoinduced degradation of aquatic DOM, which can subsequently
release a large amount of CO
2
to atmosphere. Second, high production of HO
•
can
reduce the biological activity through oxidative damages to the living cells of biota
in the aquatic environments (Berlett and Stadtman
1997
; Paradies et al.
2000
;
