715
Chlorophylls and their Degradation in Nature
Sect. 5.5, chapter “Photosynthesis in Nature: A New Look”). It has recently been
shown that dissolved O 2 is significantly related to benthic or sestonic Chl concentration (Heiskary and Markus 2003; Miltner 2010). Moreover, a 10 mg L −1 difference between daytime and nighttime dissolved O 2 concentrations was observed at
an enriched site, where benthic Chl a levels exceeded 500 mg m −2 (Sabater et al.
2000). Variation in dissolved O 2 concentration forced by algal respiration is an important link between increasing nutrients and decreasing biological quality, as shown in a
study of medium to large rivers (Heiskary and Markus 2003). These findings are consistent with the hypothesis that photoinduced formation of H 2 O 2 from dissolved O 2
may be involved in SCM formation or primary production. Correspondingly, when
cyanobacterial blooms are accumulated as scums in surface waters, prolonged exposure to UV radiation can cause enhanced carotenoid production, which can subsequently increase Chl a-specific photosynthetic production of O 2 (Jeffrey et al. 1997).
3.2 Deep Chl a Maximum
The Deep Chl a maximum (DCM) is a well-known phenomenon occurring in the
presence of maximal Chl a contents in the deeper layer of the euphotic zone of the
water column (Table 1) (Fennel and Boss 2003; Letelier et al. 2004; Huisman et al.
2006; Steele and Yentsch 1960; Anderson 1969; Klausmeier and Litchman 2001;
Hodges and Rudnick 2004; Beckmann and Hense 2007; Hense and Beckmann
2008; Ryabov et al. 2010; Pérez et al. 2007; Gomes et al. 2000; Camacho 2006;
Sawatzky et al. 2006; Fee 1976; Kiefer et al. 1972; Cullen 1982; Moll and
Stoermer 1982; Abbott et al. 1984; Pick et al. 1984; Steinhart et al. 1994; Varela
et al. 1994; Budy et al. 1995; Ediger and Yilmaz 1996; Gross et al. 1997; Goericke
and Welschmeyer 1998; Marañón et al. 2000; Wurtsbaugh et al. 2001; Cuny et al.
2002; Pérez et al. 2002; Tittel et al. 2003; Barbiero and Tuchman 2004; Chapin
et al. 2004; Holm-Hansen and Hewes 2004; Park et al. 2004; Ghai et al. 2010;
Johnson et al. 2010; Harrison and Smith 2011; Mellard et al. 2011). According to
these studies, DCM can be defined as a zone of maximum photosynthetic activity with highest Chl a contents. It is usually a region lacking a pronounced density gradient, generally occurring in or below the thermocline (the metalimnion).
It is a stable and common feature occurring in the presence of sufficient light and
nutrients under low temperature and low turbulence, and it is a remarkable characteristic of clear water with low nutrients in the deep layer, particularly in lakes
and oceans. The DCM is a stable feature in tropical waters whilst it is a seasonal
phenomenon in the Mediterranean and other temperate waters, following seasonal
changes in incident light intensity and nutrient conditions (Letelier et al. 2004;
Huisman et al. 2006; Ghai et al. 2010). The DCM is found to vary from 20 to
350 m in lakes and from 30 to 139 m in oceans (Table 1).
DCM is entirely different in Lake Superior and Lake Michigan. It is observed
in the upper hypolimnion at a depth of 23–35 m in Lake Superior, whilst its depth
in Lake Michigan changes seasonally. Depth varies from 15 to 30 m during early
thermal stratification primarily in June, to 25–50 m by mid-stratification in July,
Chlorophylls and their Degradation in Nature
Sect. 5.5, chapter “Photosynthesis in Nature: A New Look”). It has recently been
shown that dissolved O 2 is significantly related to benthic or sestonic Chl concentration (Heiskary and Markus 2003; Miltner 2010). Moreover, a 10 mg L −1 difference between daytime and nighttime dissolved O 2 concentrations was observed at
an enriched site, where benthic Chl a levels exceeded 500 mg m −2 (Sabater et al.
2000). Variation in dissolved O 2 concentration forced by algal respiration is an important link between increasing nutrients and decreasing biological quality, as shown in a
study of medium to large rivers (Heiskary and Markus 2003). These findings are consistent with the hypothesis that photoinduced formation of H 2 O 2 from dissolved O 2
may be involved in SCM formation or primary production. Correspondingly, when
cyanobacterial blooms are accumulated as scums in surface waters, prolonged exposure to UV radiation can cause enhanced carotenoid production, which can subsequently increase Chl a-specific photosynthetic production of O 2 (Jeffrey et al. 1997).
3.2 Deep Chl a Maximum
The Deep Chl a maximum (DCM) is a well-known phenomenon occurring in the
presence of maximal Chl a contents in the deeper layer of the euphotic zone of the
water column (Table 1) (Fennel and Boss 2003; Letelier et al. 2004; Huisman et al.
2006; Steele and Yentsch 1960; Anderson 1969; Klausmeier and Litchman 2001;
Hodges and Rudnick 2004; Beckmann and Hense 2007; Hense and Beckmann
2008; Ryabov et al. 2010; Pérez et al. 2007; Gomes et al. 2000; Camacho 2006;
Sawatzky et al. 2006; Fee 1976; Kiefer et al. 1972; Cullen 1982; Moll and
Stoermer 1982; Abbott et al. 1984; Pick et al. 1984; Steinhart et al. 1994; Varela
et al. 1994; Budy et al. 1995; Ediger and Yilmaz 1996; Gross et al. 1997; Goericke
and Welschmeyer 1998; Marañón et al. 2000; Wurtsbaugh et al. 2001; Cuny et al.
2002; Pérez et al. 2002; Tittel et al. 2003; Barbiero and Tuchman 2004; Chapin
et al. 2004; Holm-Hansen and Hewes 2004; Park et al. 2004; Ghai et al. 2010;
Johnson et al. 2010; Harrison and Smith 2011; Mellard et al. 2011). According to
these studies, DCM can be defined as a zone of maximum photosynthetic activity with highest Chl a contents. It is usually a region lacking a pronounced density gradient, generally occurring in or below the thermocline (the metalimnion).
It is a stable and common feature occurring in the presence of sufficient light and
nutrients under low temperature and low turbulence, and it is a remarkable characteristic of clear water with low nutrients in the deep layer, particularly in lakes
and oceans. The DCM is a stable feature in tropical waters whilst it is a seasonal
phenomenon in the Mediterranean and other temperate waters, following seasonal
changes in incident light intensity and nutrient conditions (Letelier et al. 2004;
Huisman et al. 2006; Ghai et al. 2010). The DCM is found to vary from 20 to
350 m in lakes and from 30 to 139 m in oceans (Table 1).
DCM is entirely different in Lake Superior and Lake Michigan. It is observed
in the upper hypolimnion at a depth of 23–35 m in Lake Superior, whilst its depth
in Lake Michigan changes seasonally. Depth varies from 15 to 30 m during early
thermal stratification primarily in June, to 25–50 m by mid-stratification in July,