Environmental Engineering Reference
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X CO 2 ( H 2 O) + Y H 2 O 2 ( H 2 O) + H υ → C X ( H 2 O ) Y + O 2 + E (±)
(3.3)
(3.4)
2H 2 O 2 + H υ → 2H 2 O + O 2
where C x (H 2 O) y represents a generic carbohydrate (Eq. 3.3 ). According to this
hypothesis, H 2 O 2 acts together with carbon dioxide (CO 2 ) to form carbohydrates
and oxygen (Eq. 3.3 ). The formation of oxygen occurs via H 2 O 2 disproportiona-
tion (Eq. 3.4 ) that is a common conversion reaction of H 2 O 2 in water ecosystems
and the atmosphere (see the photosynthesis chapter for detailed description for
these reactions) (Liang et al. 2006 ; Buick 2008 ). In Eq. ( 3.3 ), E ( ± ) is the energy
produced during photosynthesis.
Currently, model results imply that the progressive release of DON in
the ocean's upper layer during summer increases the primary production by
30-300 %. This will in turn enhance the DOC production mostly from phyto-
plankton exudation in the upper layer and the solubilization of POM deeper in
the water column (Druon et al. 2010 ). Experimental studies observe that both the
quantity and the spectral quality of DOM produced by bacteria can be influenced
by the presence of photoproducts in aqueous media (Ortega-Retuerta et al. 2009 ).
Photosynthetically produced POM (algae or phytoplankton) and their photo- and
microbial respirations are significantly influenced by several key factors, such as
chemical nature and contents of DOM (Jones 1992 ; Hessen 1985 ; Tranvik and
Hafle 1987 ; Tranvik 1989 ); high precipitation (Freeman et al. 2001a ; Tranvik and
Jasson 2002 ; Hejzlar et al. 2003 ; Zhang et al. 2010 ); land use changes that cause
high transport of DOC from catchments to adjacent surface waters (Worrall et al.
2004a ; Raymond and Oh 2007 ); nitrogen deposition (Pregitzer et al. 2004 ; Findlay
2005 ); sulfate (SO 4 2 ) deposition (Zhang et al. 2010 ; Evans et al. 2006 ; Monteith
et al. 2007 ); droughts and alteration of hydrologic pathways (Hongve et al. 2004 ;
Worrall and Burt 2008 ); changes in total solar UV radiation or an increase in tem-
perature due to global warming (Freeman et al. 2001a ; Zhang et al. 2010 ; Sinha
et al. 2001 ; Sobek et al. 2007 ; Rastogi et al. 2010 ).
Finally, H 2 O 2 can react with CO 2 under abiotic conditions to produce vari-
ous organic substances (CH 2 O, HCOOH, CH 3 OH, CH 4 , C 6 H 12 O 6 ; Eqs. 3.5 - 3.9 ,
respectively) in aqueous solution (Lobanov et al. 2004 ). The reactions between
H 2 O 2 and CO 2 as well as their thermodynamic parameters such as enthalphy
changes ( Δ H 0 ) and the Gibbs free energy changes ( Δ G 0 ) are as follows (Lobanov
et al. 2004 ):
H 2 O 2 + CO 2 CH 2 O + 3 / 2O 2
(3.5)
H 0 = 465kJ , G 0 = 402kJ
H 2 O 2 + CO 2 HCOOH + O 2
(3.6)
H 0 = 172kJ , G 0 = 166kJ
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