Environmental Engineering Reference
In-Depth Information
than the mean atmospheric one in the Arctic in summertime, suggesting that
CO
2
might derive from high rates of bacterial respiration (Semiletov et al.
2007
).
Ambient partial pressure values of CO
2
(
p
CO
2
=
21-73.5 Pa) are produced dur-
ing the coral reef metabolism in Eastern Pacific reef sites. Such values are highly
variable depending on depth, time, space and upwelling-nonupwelling period
(Manzello
2010
).
Photoinduced and microbial degradation of DOM and OM is a source of
atmospheric greenhouse gases such as CO
2
and CH
4
, thereby contributing to
global carbon cycle and further global warming (Porcal et al.
2009
; Knorr et al.
2005
; Davidson and Janssens
2006
). Elevated CO
2
enhances DOC supply in peat
soils, an effect that is attributed to elevated net primary productivity and increased
root exudation of DOC. Enhanced DOC in soil will ultimately leach into aquatic
ecosystems (Freeman et al.
2004
; Barbiero and Tuchman
2004
; Kang et al.
2001
;
Pastor et al.
2003
; Lavoie et al.
2005
; Fenner et al.
2007a
,
b
). Global warm-
ing could also increase soil respiration (Freeman et al.
2001
,
2004
; Tranvik and
Jasson
2002
; Evans et al.
2005
,
2006
; Roulet and Moore
2006
; de Wit et al.
2007
;
Monteith et al.
2007
; Dorodnikov et al.
2011
).
Freshwater ecosystems that are presently located across vegetation gradients
will experience significant shifts in underwater spectral irradiance. The main rea-
sons are the effects of climate change on catchment vegetation and the export of
colored DOM (Pienitz and Vincent
2000
). Overall, elevated atmospheric CO
2
concentrations would increase primary production, with a consequent increase of
the decomposition of soil OM and an increased export of DOC to nearby natu-
ral waters (Porcal et al.
2009
). These processes can also contribute to enhance the
DOM contents in natural waters.
4.7 Changes in Nutrients Cycle
−
−
+
The mass balance of nutrients (NO
2
and total P) is linked
with the major external inputs (terrestrial and atmospheric deposition),
internal sources and transformations (primary and bacterial production,
secondary production, photo- and/or microbial-assimilation of algae or phy-
toplankton and plant debris), photoinduced transformation of both exter-
nal and internal sources of nutrients, nitrification, sedimentation and outputs
in natural waters (Mostofa et al.
2009b
; Fu et al.
2005
; Minero et al.
2007
;
Stedmon et al.
2007a
,
b
; Sterner et al.
2008
; Ma and Green
2004
; Zhang
et al.
2004
; Kim et al.
2006
; Li et al.
2008
; Carrillo et al.
2002
; Mallet et al.
1998
; Kopácˇ ek et al.
1995
,
2000
,
2004
; Lehmann and Bernasconi
2004
;
Schindler
1988
,
1994
; Carlsson et al.
1993
; Urabe
1993
; Bushaw et al.
1996
; Goldman et al.
1996
; Ramm and Scheps
1997
; Mack and Bolton
1999
;
Sterner and Elser
2002
; Demott
2003
; Xie et al.
2003
; Kopácˇ ek et al.
2003
;
Ahlgren et al.
2005
). Coastal waters are generally nutrient-rich whereas open
oceans are often oligotrophic, thus they are usually less productive due to
, NO
3
, NH
4
