Environmental Engineering Reference
In-Depth Information
(a)
2.5 m
10 m
20 m
40 m
70 m
15
12
9
6
3
0
(b)
140
130
120
110
100
90
80
70
1999
2000
2001
Sampling (month)
Fig. 3
Vertical changes in the chlorophyll
a
(
a
) and dissolved organic carbon (DOC) concen-
trations (
b
) in monthly collected samples from Lake Biwa and
Error bars
indicate the standard
deviation
Data source
Mostofa et al. (
2005
), Mostofa KMG et al. (unpublished data)
to conditions in lakes. An upper-surface mixed layer commonly occurs in lakes
and oceans, due to mechanical perturbation of surface waters (e.g. by wind, waves
and storms) (Deuser
1987
; Venrick
1993
; Law et al.
2003
; Moum et al.
1989
;
Brainerd and Gregg
1995
). It is characterized by strong turbulent mixing, up to a
depth of approximately 30-200 m or more. Note that few studies have reported the
occurrence of DCM (or subsurface Chl a maximum) at a depth of 5-25 m or more
(Table
1
) (Parab et al.
2006
; Sawatzky et al.
2006
; Xiu et al.
2009
; Hamilton et al.
2010
; Fee
1976
; Sommaruga and Augustin
2006
). Considering the surface mixing
zone of the water column, it might be supposed to have a similar meaning as the
surface Chl
a
maximum (SCM). A high content of Chl
a
at a depth of 5-15 m may
be due to the occurrence of strong photoinduced degradation of Chl
a
in the upper
surface layer, e.g. at 0-4 m depth. Note that subsurface Chl
a
maxima have been
considered as DCM in several earlier studies, while in this chapter a similar mean-
ing (SCM) is adopted for the subsurface Chl
a
maximum (at e.g. 5-15 m depth)
and for the surface Chl
a
maximum (0-30 m depth). SCM should thus be well
differentiated from DCM to avoid any confusion. Such a rationalization could be
useful to avoid confusion between SCM and DCM in future studies.
