339
Photoinduced and Microbial Degradation
This mechanism may help in the understanding of the production of autochthonous 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
Nature: A New Look”).
5.5 Photoinduced Formation of Nitrogenous Compounds
Nitrogenous photoproducts include the ammonium (NH 4
+ ) and nitrate/nitrite
(NO 3
− /NO 2
− ) 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 μM C of DOC and 20–86 μM of dissolved organic nitrogen (Bushaw
et al. 1996). DON concentrations are 7–26 μM in Lake Hongfeng and 14–47 μM
in Lake Baihua (Li et al. 2008), approximately 8.35 μM in the epilimnion of Lake
Biwa (Kim et al. 2006), and approximately 10 μM in coastal waters (Bronk 2002).
The high concentrations of NO 2
− and NH 4
+ in Lakes Hongfeng and Baihua during the summer stratification period suggest the regeneration of inorganic nitrogen
(NO 2
− and NH 4
+ ) in lakes (Li et al. 2008). Photoinduced respiration or assimilation of lake algae under natural sunlight can release 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 (unpublished).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 substances (Carlsson et al. 1993). This leads to an increase of the nitrogen availability, 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
Photoinduced and Microbial Degradation
This mechanism may help in the understanding of the production of autochthonous 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
Nature: A New Look”).
5.5 Photoinduced Formation of Nitrogenous Compounds
Nitrogenous photoproducts include the ammonium (NH 4
+ ) and nitrate/nitrite
(NO 3
− /NO 2
− ) 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 μM C of DOC and 20–86 μM of dissolved organic nitrogen (Bushaw
et al. 1996). DON concentrations are 7–26 μM in Lake Hongfeng and 14–47 μM
in Lake Baihua (Li et al. 2008), approximately 8.35 μM in the epilimnion of Lake
Biwa (Kim et al. 2006), and approximately 10 μM in coastal waters (Bronk 2002).
The high concentrations of NO 2
− and NH 4
+ in Lakes Hongfeng and Baihua during the summer stratification period suggest the regeneration of inorganic nitrogen
(NO 2
− and NH 4
+ ) in lakes (Li et al. 2008). Photoinduced respiration or assimilation of lake algae under natural sunlight can release 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 substances (Carlsson et al. 1993). This leads to an increase of the nitrogen availability, 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