Effect
of
sediment
resuspension
on
underwater
light
field
in
shallow
lakes
in
the
middle
and
lower
reaches
of
the
Yangtze
River
:
A
case
study
in
Longgan
Lake
and
Taihu
Lake
Made
by
Katherine
Bukina
Krasnoyarsk,
2011
INTRODUCTION
1
Effect
of sediment
resuspension
on underwater light field in shallow lakes
Shallow
lakes
are
easily
affected
by
wind
-
induced
sediment
resuspension
.
Sediment
resuspension
plays
an
important
role
in
controlling
structures
and
functions
of
shallow
lake
ecosystems,
and
its
ecological
significance
is
shown
in
two
aspects
:
Wind
-
induced sediment
resuspension
often increases the concentrations of
suspended matter and hence promotes
light attenuation.
The release of nutrients from sediment
and resuscitation of phytoplankton could
increase concentrations of nutrients in
water bodies, promote the growth of
algae and increase primary productivity.
INTRODUCTION
2
Effect
of sediment
resuspension
on underwater light field in shallow lakes
Blom
et al. found that total suspended particulate matter contributed to light
attenuation by 40% annually in open, wind
-
exposed, shallow lakes with
silty
sediment, but by 80% during storm events.
Van
Duin
et al. simulated the relationships between underwater light field and
sedimentation,
resuspension
, water quality, autotrophic growth. Sediment
resuspension
could cause the increase in the concentration of suspended matter
and the decrease in
euphotic
depth, thus primary productivity was inhibited,
especially in winter with weak light intensity. This is an antagonistic process.
The study on the development of antagonism is the core to reveal the effects of
resuspension
on ecosystems and environments further.
INTRODUCTION
3
Effect
of sediment
resuspension
on underwater light field in shallow lakes
In
the
past
20
years,
the
heightening
human
activities
have
caused
serious
lake
water
pollution
in
the
middle
and
lower
reaches
of
the
Yangtze
River
.
Lake
ecosystems
have
been
altering
significantly
.
The
serious
situations
of
eutrophication
and
algal
blooming
in
lakes
have
directly
endangered
the
sustainable
development
of
local
social
economy
.
Not
only
the
study
of
the
internal
source
of
nutrients
from
lakes
should
be
taken
into
account
but
also
controlling
the
external
source
which
enters
lakes
in
order
to
control
eutrophication
of
shallow
lakes
.
One
of
the
effective
approaches
to
control
the
internal
source
of
nutrients
from
lakes
is
the
restoration
of
macrophytes
in
order
to
limit
sediment
resuspension
and
nutrients
release
.
INTRODUCTION
4
Effect
of sediment
resuspension
on underwater light field in shallow lakes
The
macrophytes
can
compete
with
algae
for
nutrients
and
light,
moreover
the
allelopathy
of
submerged
plants
could
be
used
to
inhibit
algal
growth
.
In
these
shallow
eutrophic
lakes
with
high
concentrations
of
suspended
matter,
phytoplankton
and
dissolved
matter,
the
lake
water
transparency
is
very
low
with
a
rather
poor
light
field
.
Therefore,
the
effective
restoration
of
macrophytes
first
requires
a
study
on
the
optical
properties
of
lake
waters,
especially
the
change
of
the
underwater
light
field
resulting
from
sediment
resuspension
,
to
explore
the
dominant
factors
which
affect
light
attenuation,
and
finally
to
take
some
measures
to
improve
underwater
light
condition
.
INTRODUCTION
5
Effect
of sediment
resuspension
on underwater light field in shallow lakes
algal
-
dominated lakes
(
Taihu
Lake )
algal
-
macrophyte
transition lakes
macrophyte
-
dominated lakes
(
Longgan
Lake)
Yang
et
al
.
found
that
algal
-
dominated
and
macrophyte
-
dominated
lakes
possessed
an
evident
difference
in
optical
properties
of
lake
waters
and
underwater
light
fields
.
Longgan
Lake
and
Taihu
Lake
are
selected
to
study
the
effects
of
sediment
resuspension
resulting
from
wind
waves
processes
on
optical
properties
of
water
bodies
to
determine
the
quantitative
relationship
between
sediment
resuspension
and
euphotic
depth
under
different
wind
waves
in
the
middle
and
lower
reaches
of
the
Yangtze
River
.
Three types of shallow lakes could
be divided in the middle and lower
reaches of the Yangtze River:
6
Effect
of sediment
resuspension
on underwater light field in shallow lakes
Fig. 1. Location of sampling sites (MB:
Meiliang
Bay; ST: Station near TLLER; LL:
Longgan
Lake).
Underwater
spectroradiometer
,
wave
meters,
3
D
ultrasound
current
meters
and
automatic
wind
vane
and
anemometer
were
set
up
to
conduct
a
continuous
measurement
under
different
wind
wave
conditions
at
the
center
in
the
Meiliang
Bay,
Taihu
Lake
during
12
-
ㄷ
䩵ly,
㈰〳
慮d
慴
瑨e
eastern
p慲a
楮
L潮ggan
L慫e
du物湧
㈷
-
㌱
䩵汹,
㈰〳
⡆楧
.
1
)
.
䱡Le
water
摥灴h
w慳
2
.
6
m
a湤
瑨t
se摩d敮t
摥灴h
w慳
0
.
8
m
慴
䵂
.
Water
depth
was
3
.
4
m,
sediment
depth
was
1
.
8
m,
and
there
was
no
macrophyte
during
the
measurement
period
at
LL
.
MATERIALS
AND
METHODS
Sampling time and location
MATERIALS
AND
METHODS
Underwater irradiance and transparency
measurements
7
Effect
of sediment
resuspension
on underwater light field in shallow lakes
Secchi
disk pattern
Downward
photosynthetically
active
irradiance
(PAR,
400
-
㜰7
湭n
慴
瑨t
wat敲
surface
and
at
different
depths
(
0
.
2
,
0
.
5
,
1
.
0
,
1
.
5
and
2
.
0
m)
was
measured
using
LI
-
192
SA
underwater
cosine
corrected
sensor
connected
to
Li
-
1400
datalogger
.
Downward
spectra
of
the
PAR
radiation
at
different
depths
were
measured
with
a
scanning
spectroradiometer
(
Macam
SR
9910
,
Livingston,
UK)
.
Secchi
disc
transparency
was
measured
with
a
30
cm
diameter
black
and
white
quadrant
disc
.
The
Secchi
disk,
created
in
1865
by
Pietro
Angelo
Secchi
SJ,
is
a
circular
disk
used
to
measure
water
transparency
.
The
disc
is
mounted
on
a
pole
or
line,
and
lowered
slowly
down
in
the
water
.
The
depth
at
which
the
pattern
on
the
disk
is
no
longer
visible
is
taken
as
a
measure
of
the
transparency
of
the
water
.
Black and white
quadrant
Secchi
disc
MATERIALS
AND
METHODS
Other
measurements
8
Effect
of sediment
resuspension
on underwater light field in shallow lakes
1.
Total absorption coefficient:
a(
λ)=
a
p
(
λ)+
a
CDOM
(
λ)+
a
w
(
λ)
2.
Average wind velocity in half an hour:
less than 4 m∙s
−1
are defined as small wind waves
between 4 and 6 m∙s
−1
defined as middle wind waves
more than 6 m∙s
−1
defined as large wind waves
3.
Diffuse attenuation coefficients for downward spectral irradiance and PAR :
4.
The
euphotic
zone in the water bodies is defined as the upper layer of water
irradiated with sufficient daylight to make photosynthesis possible. Its lower
boundary is often roughly defined. Therefore,
euphotic
depth:
Z
eu
(PAR) = 4.605/K
d
(PAR)
Results
In
Longgan
Lake
9
Effect
of sediment
resuspension
on underwater light field in shallow lakes
Fig. 2. Spectral and PAR diffuse attenuation coefficients under different wind wave conditions at LL.
The
spectral
diffuse
attenuation
coefficients
and
PAR
diffuse
attenuation
coefficients
within
400
-
㜰7
湭
were
楮
瑨t
r慮ge
潦
0
.
㤸
-
2
.
㤷
m
−
1
and
1
.
74
m
−
1
,
respectively
under
a
small
wind
wave
condition
on
July
30
.
On
July
27
,
the
values
in
-
creased
up
to
1
.
34
-
3
.
㤵
m
−
1
and
2
.
02
m
−
1
under
a
middle
wind
wave
condition,
respectively
.
And
on
July
28
,
they
were
up
to
1
.
82
-
5
.
㐰
m
−
1
and
2
.
45
m
−
1
under
a
large
wind
wave
condition
.
PAR
euphotic
depth
under
3
different
wind
wave
conditions
were
2
.
65
m,
2
.
28
m
and
1
.
88
m
.
The
PAR
diffuse
attenuation
coefficients
increased
by
16
%
and
29
%
,
with
a
decrease
of
14
%
and
29
%
for
PAR
euphotic
depth
.
Results
In
Meiliang
Bay of
Taihu
Lake
10
Effect
of sediment
resuspension
on underwater light field in shallow lakes
According
to
the
35
times
of
measurement
of
underwater
PAR,
PAR
attenuation
coefficient
had
an
average
value
of
3
.
63
±
0
.
47
m
-
1
,
and
corresponding
euphotic
depth
had
an
average
value
of
1
.
29
±
0
.
18
m
.
The PAR diffuse
attenuation coefficients
Date
Time
2.63 m
−1
July 13
9:00
3.72 m
−1
July 15
17:00
4.37 m
−1
July 16
17:00
PAR diffuse
attenuation
coefficient was
increased by 66%,
with a decrease of
40% of
euphotic
depth.
Results
In littoral zone near TLLER
11
Effect
of sediment
resuspension
on underwater light field in shallow lakes
Fig. 3. The correlation between PAR diffuse attenuation coefficient and transparency, mean wind velocity within half an hour
at
ST.
PAR
diffuse
attenuation
coefficient
increased
by
28
.
6
%
from
middle
to
large
wind
wave
conditions
during
the
measurement
period
.
The PAR attenuation
coefficients
Conditions
6.74
±
0.35 m
−1
large wind waves
5.24
±
0.50 m
−1
middle wind waves
Discussion
12
Effect
of sediment
resuspension
on underwater light field in shallow lakes
Underwater
light
field
is
very
important
to
the
growths
of
phytoplankton
and
macrophyte
.
Essentially
all
the
light
attenuation
in
water
is
attributed
to
four
components
of
aquatic
ecosystem
:
the water itself
dissolved matter
particulate matter including non
-
algal
phytoplankton
Dissolved
matter
mainly
absorbs
light,
whereas
non
-
algal
particulate
matter
and
phytoplankton
not
only
absorbs
light
but
also
scatters
it
.
Phytoplankton
and
submerged
macrophyte
not
only
compete
with
each
other
but
also
compete
with
other
light
attenuation
components
for
light
energy
.
In
oceans,
deep
lakes
and
eutrophic
shallow
lakes
without
wind
-
induced
resuspension
,
the
largest
contribution
to
light
attenuation
often
originated
from
phytoplankton
.
In
the
shallow
lakes
easily
disturbed
by
wind
waves,
sediment
resuspension
driven
by
wind
waves
played
a
very
important
role
in
controlling
the
concentrations
of
suspended
matter
and
light
attenuation
.
Discussion
13
Effect
of sediment
resuspension
on underwater light field in shallow lakes
All
PAR
euphotic
depths
measured
at
MB
and
ST
were
less
than
1
.
5
m,
so
the
average
thickness
of
the
photosynthetic
zone
was
less
than
1
.
5
m,
which
meant
that
primary
productivity
of
phytoplankton
was
mainly
produced
in
the
surface
1
.
5
m
water
layer
.
At
the
depth
of
more
than
1
.
5
m,
phytoplankton
and
macrophyte
could
not
grow
well
lacking
enough
sunlight
for
photosynthesis
.
Compared
with
MB,
euphotic
depth
in
LL
was
much
higher
.
So,
the
low
euphotic
depth
might
be
one
of
most
important
factors
to
restrict
the
growth
of
submerged
macrophyte
.
The
change
of
suspended
matter
concentrations
causing
by
wind
wave
disturbance
was
the
primary
factor
leading
to
underwater
light
attenuation
in
the
shallow
lakes,
the
maximum
was
generally
in
the
range
of
blue
light
around
400
nm,
reflecting
the
optical
properties
of
shallow
inland
lakes
.
Discussion
14
Effect
of sediment
resuspension
on underwater light field in shallow lakes
These
results
show
that
wind
waves
affected
the
underwater
light
fields
in
shallow
lakes
by
increasing
the
concentrations
of
non
-
algal
particulate
to
enhance
light
attenuation
.
Fig
.
5
.
Relative
contributions
of
the
absorption
coefficients
of
pure
water
(
a
w
),
CDOM
(
a
CDOM
),
non
-
algal
particulate
matter
(a
d
)
and
phytoplankton
(
a
ph
)
under
middle
(a)
and
large
(b)
wind
wave
condition
.
Discussion
15
Effect
of sediment
resuspension
on underwater light field in shallow lakes
Sediment
resuspension
occurs
in
lakes
when
the
shearing
stress
produced
by
wind
waves
and
lake
currents
is
more
than
its
critical
shearing
stress
.
Factors
affecting
sediment
resuspension
include
:
water depth
components of sediments
macrophyte
wind velocity
wind fetch length
the set of the wind
They would affect the distribution of
underwater light fields indirectly.
Lake
PAR
attenuation
coefficient
Water depth
LL
2.45
m
-
1
3.4 m
MB
4.37 m
-
1
2.6 m
ST
6.74 m
-
1
1.8 m
The
deeper
the
water
is,
the
weaker
the
buoyancy
acts
on
bed
sediment,
and
the
less
on
the
suspended
sedimentsunder
the
same
wind
wave
condition
.
Discussion
16
Effect
of sediment
resuspension
on underwater light field in shallow lakes
Sediment
resuspension
resulting
from
wind
wave
disturbance
makes
the
thickness
of
photosynthetic
zone
decease
greatly
in
shallow
lakes
in
the
middle
and
lower
reaches
of
the
Yangtze
River
.
The regression analysis showed that optical
parameters, such as PAR
attenua
-
tion
coefficient,
euphotic
depth, transparency
were all significantly correlated with the
concentrations of suspended matter, wind
velocity and wave height. The absorption
coefficients of CDOM at ST changed slightly,
whereas the absorption coefficients of
phytoplankton to some extent decreased but
the absorption of non
-
algal particulates
resulting from sediment
resuspension
increased significantly.
Lake
PAR
euphotic
depth
LL
0.40 m
MB
0.19 m
ST
0.20
m
Therefore,
when
wind
velocity
is
increased,
the
shearing
stress
is
enhanced
on
lakebed
by
enhancing
waves
leading
to
sediment
resuspension
,
and
then
increasing
light
attenuation
through
increasing
inorganic
particulates
in
water
bodies
.
A time to ask something
17
Effect
of sediment
resuspension
on underwater light field in shallow lakes
Questions?
Adieu
18
Effect
of sediment
resuspension
on underwater light field in shallow lakes
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