Environmental Engineering Reference
In-Depth Information
and Fisher
2002a
; Hiriart-Baer and Smiith
2005
). This process can give a signifi-
cant contribution to autochthonous DOM in natural waters. Second, solar radiation
causes changes in the molecular structure of DOM and decomposes its functional
groups. This effect can be detected chemically as mineralization of DOC, by
approximately 0-54 % during irradiation times ranging from hours to months.
It can also be detected optically as alteration of either chromophoric dissolved
organic matter (CDOM) or fluorescent dissolved organic matter (FDOM) (see
Photoinduced degradation can also reduce the mean molecular size of the high
molecular weight DOM (Lovley and Chapelle
1995
; Lovley et al.
1996
; Yoshioka et
al.
2007
; Amador et al.
1989
), which subsequently produces low molecular weight
(LMW) intermediates (Lovley et al.
1996
; Wetzel et al.
1995
; Amon and Benner
1994
; Dahlén et al.
1996
). This process ultimately ends up in mineralization with
formation of e.g. COS, CO, CO
2
, DIC, ammonium and gaseous hydrocarbons
(Miller and Zepp
1995
; Miller
1998
; Johannessen and Miller
2001
; Ma and Green
2004
; Xie et al.
2004
; Johannessen et al.
2007
; Gennings et al.
2001
; Clark et al.
2004
). Photoinduced degradation generally occurs in the mixing zone and decreases
with an increase in water depth (Bertilsson and Tranvik
2000
; Ma and Green
2004
;
Vähätalo et al.
2000
; Mostofa et al.
2005a
; Granéli et al.
1996
). The photoreactivity
of fluorescent DOM is greatly decreased when passing from freshwater to marine
waters, but deep waters in lakes or marine environments are often more sensitive
to photoinduced degradation processes than surface waters (Mostofa et al.
2011
).
Similar effects have been observed as far as photomineralization is concerned
(Vione et al.
2009
). Photoinduced degradation is significantly affected by several
key factors, such as solar radiation, water temperature, effects of total dissolved
Fe and photo-Fenton reaction, occurrence and quantity of NO
2
−
−
ions,
molecular nature of DOM, water pH and alkalinity, dissolved oxygen (O
2
), water
depth, physical mixing in the surface mixing zone, increased UV-radiation during
ozone hole events, global warming, and salinity (see chapter
“
Photoinduced and
and NO
3
6.6 Photosynthesis in Natural Waters
Autochthonous production of DOM in natural waters is mostly accompanied by
photosynthesis (Takahashi et al.
1995
; Hamanaka et al.
2002
; Marañòn et al.
2004
).
Photosynthetically produced POM (mostly algae or phytoplankton) and the related
release of new DOM are significantly influenced by several key factors, such as
high precipitation (Freeman et al.
2001a
; Tranvik and Jasson
2002
; Hejzlar et al.
2003
; Zhang et al.
2010
), 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
), and changes in total solar UV radiation or an increase in temperature due to
