Environmental Engineering Reference
In-Depth Information
regardless of DOM source or the presence or absence of carbonate ions (Grebel
et al. 2009 ). In another study, a decrease in CDOM photobleaching at 280 nm
is detected when humic CDOM is added to an artificial salinity gradient used to
mimic coastal mixing (Minor et al. 2006 ). Dissolved lignin phenols are significantly
affected by salinity and at salinities >25 psu, photooxidation is a dominant factor
influencing lignin compositions and concentrations (Hernes and Benner 2003 ).
The mechanism behind the high photoinduced degradation of DOM with salinity
apparently involves two factors: first, irradiated CDOM can induce photoinduced pro-
duction of hydrogen peroxide (H 2 O 2 ) that is a HO source via photolysis or the Fenton
reaction, and the photoinduced generation of H 2 O 2 is enhanced by salin-
ity. Trace metal ions (M) in salinity or sea waters can complex with DOM
(M-DOM) forming a strong π-electron bonding system between metal ions
and the functional groups in DOM (see chapter Complexation of Dissolved
Organic Matter With Trace Metal Ions in Natural Waters ” for in details expla-
nation). This π-electron in M-DOM complex is rapidly excited photolyti-
cally, which is responsible for high production of aqueous electrons (e aq ) and
subsequently the high production of superoxide ion (O 2 ), H 2 O 2 and HO , respec-
tively. Indeed, photogeneration of H 2 O 2 from ultrafiltered river DOM is substan-
tially increased with salinity, from 15 to 368 nM h −1 at circumneutral pH (Osburn
et al. 2009 ). Salinity or NaCl salts can substantially increase the aqueous electrons
(e aq ) from DOM components photolytically in aqueous media (Assel et al. 1998 ;
Gopinathan et al. 1972 ). This effect subsequently can enhance the H 2 O 2 production
from DOM components in waters (Moore et al. 1993 ; Mostofa and Sakugawa 2009 ;
Richard et al. 2007 ; Fujiwara et al. 1993 ). Recent studies observe that the sea-salt par-
ticulate matter extracted from coastal seawaters show substantially high HO produc-
tion (rate: ~2778-27778 M s −1 ), approximately 3-4 orders of magnitude greater than
HO photoformation rates in surface seawater (Anastasio and Newberg 2007 ), which
may support the above phenomena.
Second, the reaction of HO with halide ions (X ) can form reactive halogen
radicals (BrX ) that can react with electron-rich functional groups within DOM
more selectively than HO (Goldstone et al. 2002 ; Grebel et al. 2009 ; Salinity can
significantly affect the CDOM or FDOM properties, which are responsible for their
high photoinduced behavior, which are discussed in detail in other chapters (see
chapters Colored and Chromophoric Dissolved Organic Matter in Natural Waters ,
Fluorescent Dissolved Organic Matter in Natural Waters ” and Complexation of
Dissolved Organic Matter With Trace Metal Ions in Natural Waters ”).
4 Factors Controlling the Microbial Degradation of DOM
in Waters
Microorganisms are generally responsible for catalyzing the oxidation of organic
matter and for inducing changes in the functional groups of DOM, either in deeper
waters or in soil and sediment pore waters (Mostofa et al. 2007 ; Moran et al.
Search WWH ::




Custom Search