Environmental Engineering Reference
In-Depth Information
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 concen-
tration (Heiskary and Markus
2003
; Miltner
2010
). Moreover, a 10 mg L
−
1
differ-
ence 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 impor-
tant 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 con-
sistent 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 expo-
sure to UV radiation can cause enhanced carotenoid production, which can subse-
quently increase Chl
a
-speciic 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 activ-
ity with highest Chl
a
contents. It is usually a region lacking a pronounced den-
sity 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 char-
acteristic 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
