Environmental Engineering Reference
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inhibited by toxic compounds (Kaneko et al. 2004 ; Auclair et al. 1985 ; Steinberg
and Muenster 1985 ; Francko 1986 ; Jones et al. 1988 ). Humic substances can eas-
ily undergo photoinduced decomposition into several photoproducts such as CO 2 ,
H 2 O 2 , DIC, LMW DOM, and so on. These compounds are directly and indirectly
linked with photosynthesis and can stimulate primary production.
Primary producers or phytoplankton (or Chl a ) depend on the total nitrogen
(TN) as they can uptake both inorganic and organic N forms such as urea, NH 4
+
,
and NO 3
(McCarthy et al. 2007 , 2009 ; Walsh and Dugdale 1971 ; Kappers 1980 ;
Syrett 1981 ; Dugdale et al. 1990 ; Probyn 1992 ; Blomqvist et al. 1994 ; Berg et
al. 2003 ; Giani et al. 2005 ; Rolland et al. 2005 ; Heil et al. 2007 ). No evidence
has been found for a control of Chl a by TN in lake and marine environments
(Guildford and Hecky 2000 ). However, TN (mostly NO 3
+
) can limit
primary production in most cases where nutrients are limiting (Huszar et al. 2006 ;
Sarnelle et al. 1998 ; Barica et al. 1980 ; Smith 1982 ; Elser et al. 1990 ; Aldridge
et al. 1995 ; Levine et al. 1997 ; Philips et al. 1997 ; Lewis 1996 , 2002 ).
The nutrients-ratio theory predicts that cyanobacteria will dominate in lakes with
low TN:TP ratios, due to their superior ability to compete for dissolved N and, in
some cases, to fix atmospheric N (Smith 1983 ). Recent studies show that primary
production or cyanobacteria do not follow this predicted theory in a variety of waters,
with either high or low TN:TP ratio (Nõges et al. 2008 ; McCarthy et al. 2009 ; Xie
et al. 2003 ; Smith et al. 1995 ; Smith 1983 ; Smith and Bennett 1999 ; Downing et
al. 2001 ). The TN:TP ratio theory can not consistently predict cyanobacterial
dominance in a variey of waters. Indeed, recent studies show that nutrients such as
PO 4 3 and NO 3
and NH 4
are significantly produced from either POM (e.g. phytoplankton)
or allochthonous and autochthonous DOM (see chapters Dissolved Organic Matter
in Natural Waters , Photoinduced and Microbial Degradation of Dissolved Organic
Matter in Natural Waters Impacts of Global Warming on Biogeochemical Cycles
in Natural Waters ). Correspondingly, waters with extreme eutrification are com-
posed of excess PO 4 3 that does not follow this theory at all. This can be justified
by the observation that primary production is probably not limited by nutrient avail-
ability, because of the high nutrient loadings in natural water (McCarthy et al. 2007 ,
2009 ; Heath 1992 ). Primary productivity within a plume appears to rely upon recy-
cled nutrients, with organic fractions representing the majority of the nutrient pool
(Davies 2004 ). Furthermore, remineralized nutrients from the declining chlorophyll
bloom in surface waters are taken up by heterotrophic bacteria in the water-column
and by benthic microalgae in sediments (Darrow et al. 2003 ). Variations in DOM and
POM contents can greatly modify the contents of nutrients, and additional factors
would be involved into the variations of primary production.
Based on these studies, photosynthesis dependence on nutrients is quite com-
plex in natural waters. First, photosynthesis does not depend on nutrients in waters
with high contents of DOM and POM, particularly in lakes, estuarine and coastal
waters. High content of DOM and POM can often supply the nutrients (NO 3
and
PO 4 3 ) under both photoinduced and microbial assimilation or degradation, thus
the nutrients in excess have no effects on primary production. Second, photosyn-
thesis may depend on nutrients in waters with low contents of DOM and POM.
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