Environmental Engineering Reference
In-Depth Information
This mechanism may help in the understanding of the production of autoch-
thonous DOM, particularly carbohydrate compounds, during the summer season
in natural waters. The new reaction mechanim for photosynthesis (Eq.
4.2
) has
been discussed in details in photosynthesis chapter (see chapter
“
Photosynthesis in
5.5 Photoinduced Formation of Nitrogenous Compounds
+
Nitrogenous photoproducts include the ammonium (NH
4
) and nitrate/nitrite
−
−
(NO
3
) that are released by photoinduced degradation of humic substances
and degradation of dissolved organic nitrogen (DON) in waters (Table
3
) (Mostofa
et al.
2011
; Li et al.
2008
; Bushaw et al.
1996
; Mack and Bolton
1999
; Carlsson
et al.
1993
; Stedmon et al.
2007
). Ammonium is produced by transformation of
aquatic dissolved organic matter in waters, and the production rates are 40-370 nM
for 895-3840
μ
M C of DOC and 20-86
μ
M of dissolved organic nitrogen (Bushaw
et al.
1996
). DON concentrations are 7-26
μ
M in Lake Hongfeng and 14-47
μ
M
in Lake Baihua (Li et al.
2008
), approximately 8.35
μ
M in the epilimnion of Lake
Biwa (Kim et al.
2006
), and approximately 10
μ
M in coastal waters (Bronk
2002
).
The high concentrations of NO
2
/NO
2
−
+
in Lakes Hongfeng and Baihua dur-
ing the summer stratification period suggest the regeneration of inorganic nitrogen
(NO
2
and NH
4
−
+
) in lakes (Li et al.
2008
). Photoinduced respiration or assimila-
tion of lake algae under natural sunlight can release NH
4
and NH
4
+
in waters, suggesting that
+
autochthonous organic matter is a major source of NH
4
in natural waters Mostofa
K et al. (unpublished). DOM in coastal waters derives from terrestrial humic sub-
stances (Carlsson et al.
1993
). This leads to an increase of the nitrogen availabil-
ity, which subsequently stimulates the rates of primary and secondary production.
The uptake of inorganic nitrogen by bacteria during a phytoplankton bloom can
be observed, particularly in lake or coastal waters where the inputs of terrestrial
humic substances are much higher (Kirchman et al.
1991
; Amon and Benner
1994
).
Photolytically produced ammonium can be assimilated by bacterial populations,
which can lead to an increase in the production of autotrophic and heterotrophic
biomass in planktonic environments. Photo release of inorganic nitrogen from
DOM is an important source of nitrogen availability in several aquatic ecosystems,
such as nitrogen-limited and high-latitude environments, and coastal waters where
high primary and secondary production are usually occurring.
5.6 Photoinduced Formation of Phosphate
Photoinduced degradation of DOM can lead to the release of phosphate (PO
4
3
−
) in
natural surface waters (Table
3
) (Reche et al.
1999
; Mostofa et al.
2011
; Zhang et
al.
2004
; Fang
2004
; Chen et al.
2001
; Karl and Tien
1997
; Suzumura and Ingall
