Environmental Engineering Reference
In-Depth Information
Evans et al.
2005
,
2006
; Roulet and Moore
2006
; de Wit et al.
2007
; Monteith
et al.
2007
; Dorodnikov et al.
2011
). The decomposition of soil OM by microbial
biomass is significantly increased under elevated atmospheric CO
2
(Dorodnikov
et al.
2011
; Heath et al.
2005
; Lagomarsino et al.
2009
; Blagodatskaya et al.
2010
,
2011
). High turnover rates of soil OM are apparently driven by the increasing
activity of soil microorganisms under elevated CO
2
conditions (Blagodatskaya
et al.
2010
,
2011
; Dorodnikov et al.
2009
). It is also shown that the increas-
ing activity of soil microorganisms under elevated CO
2
could accelerate the
decomposition of older and fresh plant residues (Dorodnikov et al.
2009
,
2011
;
Blagodatskaya et al.
2010
; Marhan et al.
2010
). In addition, the labile organic car-
bon released by roots stimulates microbial activity, leading to enhanced degrada-
tion of soil OM. This process is known as the 'priming mechanism' (Kuzyakov
2002
). Elevated CO
2
can enhance soil organic matter mineralization by 83-218 %
in a simulated wetland (Wolf et al.
2007
). Therefore, elevated atmospheric CO
2
concentrations could enhance both primary production and soil respiration, induc-
ing increased export of DOC to nearby natural waters (Porcal et al.
2009
).
4.5 Changes in the Primary Production and Disorders
in Chlorophyll
a
Maxima
Global warming may affect the seasonal patterns of primary production, the chlo-
rophyll concentrations in the surface chlorophyll
a
maxima (SCM) and in the deep
chlorophyll
a
maxima (DCM) in natural waters (Letelier et al.
2004
; Huisman
et al.
2006
; Mostofa et al.
2009b
; Baulch et al.
2005
; Castle and Rodgers
2009
;
Davis et al.
2009
; Hobson and McQuoid
2001
). It is estimated that, depending on
location, ambient UV radiation can reduce carbon fixation rates up to 65 % in sur-
face waters of the Antarctic region, down to undetectable levels at 36 m (Boucher
and Prézelin
1996
). A reduction of stratospheric O
3
concentrations by 50 % would
further inhibit the near-surface primary production by 8 % and the integrated
primary production by 5 % (Boucher and Prézelin
1996
). This effect causes the
occurrence of subsurface maxima of primary production in the presence of UVR
(Boucher and Prézelin
1996
). About 67 % of the variability of the observed pri-
mary production indicates that estuarine production is mainly controlled by light
availability and temperature. In contrast, high nutrient concentrations do not stim-
ulate primary production (Yoshiyama and Sharp
2006
).
Global warming will increase the stability of the vertical stratification in large parts
of the lakes and oceans, reducing vertical mixing and suppressing the upward flux of
nutrients. The effect would be a decrease in primary production (O'Reilly et al.
2003
;
Huisman et al.
2006
). Reduced vertical mixing can generate oscillations and chaos in
phytoplankton biomass and species composition of DCM, which is generated by the
difference in timescale between the sinking flux of phytoplankton and the upward flux
of nutrients (Huisman et al.
2006
; Barbiero and Tuchman
2004
). The increased sta-
bility of the water column due to global warming can thus destabilize phytoplankton
