Spheroidal Carbonaceous Particles in Reservoir Sediments

trextemperMécanique

22 févr. 2014 (il y a 3 années et 8 mois)

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Faculty of Science

Charles University, Prague









Spheroidal Carbonaceous Particles

in Reservoir Sediments



Extended abstract of PhD thesis





Jasna Vukić









Prague, 2004






Introduction


Spheroidal carbonaceous particles (SCPs) are derived f
rom fossil
-
fuel combustion and are
solely of anthropogenic origin (Rose, 1996). Since they are composed mostly of elemental
carbon they are well preserved in lake sediments and are therefore excellent markers of
industrial pollution. As a result, they have

been used in palaeolimnological studies concerned
with reconstructing the history of atmospherically deposited pollutants (Renberg & Wik,
1984; Rose et al., 1995, 1998) or human impact on a lake (Renberg et al., 1993; Bindler et al.,
2002).

Due to their
characteristic morphology, SCPs are easy to distinguish from other
carbonaceous particles, such as those produced by wood or grass burning (Griffin &
Goldberg, 1981). Rose et al. (1999) described SCPs in lake sediments as having diameters
usually between 2
-
20 µm, and up to 50 µm at sites close to the source of the emission.
However, Fott et al. (1998) found that diameters of largest particles reached almost 200 µm at
certain sites in the Czech Republic.

The onset of the SCP record in sediments occurs in la
yers dating from the early stages
of industrialisation at which time there was a rapid expansion of fossil
-
fuel combustion
(Griffin & Goldberg, 1979, 1981; Rose et al., 1995). Where the record of industrialisation is
well known, some of the main features o
f the SCP record (the onset, the rapid increase, the
peak in concentrations and subsequent decline) have been used for sediment dating (Renberg
& Wik, 1985; Marchetto & Lami, 1994; Rose et al., 1995; Korhola & Blom, 1996) and
recently also for peat dating
(Chambers et al., 1999; Barber et al., 2000; Yang et al., 2001a,
2001b). SCPs in surficial lake sediments have been used for monitoring contemporary
atmospheric deposition over a region (e.g., Wik
& Renberg, 1991;
Rose & Juggins, 1994;
Solovieva et al., 20
02).

Fossil
-
fuel burning gives rise also to emissions of SO
2

and NO
x
, gases which are the
main

cause of anthropogenic acidification, as well as to emissions of heavy metals and
polycyclic aromatic hydrocarbons (PAHs). Since SCPs are chemically inert, their

records can
potentially act as a surrogate for records of other pollutants originating from fossil
-
fuel
burning, which do not leave permanent records (Wik & Natkanski, 1990; Wik & Renberg,
1991).





In most studies on SCP palaeolimnological records, SCPs ha
ve been studied in lake
sediments. In countries such as the Czech Republic where there are few natural lakes,
reservoir sediments are the main potential alternative for studying records of
atmospherically deposited pollutants. In many ways, however, reserv
oirs are more
complicated systems than natural lakes (Kalff, 2002) and sedimentation processes in
various reservoirs within one region are not uniform (Fott et al., 1998). With the aim
to
check whether reservoir sediments provide a reliable alternative to
lake sediments for
studies of SCP records
, I have studied the spatial and temporal distribution of SCPs in
sediments of Dr
ásov R
eservoir situated near
the town P
říbram

in the central Czech
Republic.



SCPs deposit both to lakes and their catchments. Considerable input of SCPs from the
catchment to a reservoir may lead to an incorrect interpretation of the SCP sediment
record. With the purpose
to evaluate to what ex
tent the SCP sediment record in Drásov
Reservoir is influenced by the SCP indirect input from the reservoir catchment
, I have
studied inputs and sinks of SCPs in Dr
ásov Reservoir.



Although SCP concentrations in sediments and SCP accumulation rates in sedi
ments are
widely used for determination pollution exposure of regions, these alone cannot tell
anything about the scale of exposed regions, as sites can be affected by emissions from a
local source.
SCP size distribution in sediments could be a useful tool
, which could give
more information on the vicinity of the source and on the character of the SCP transport
.
In order
to test this hypothesis

I have studied size

distribution of SCPs in sediments of
Dr
ásov R
eservoir and six other sites in the Czech Republi
c (Fl
áje and Přísečnice
reservoirs in the Krušné Mountains, Bedřichov and Souš reservoirs in the Jizerské
Mountains, Černé
Lake in the
Šumava Mountains
, and a small experimental concrete pool
in the centre of Prague, CU pool).

The sites for this work were chose
n on the basis of a previous study (Fott et
al., 1998),
which shoved that they had highest SCP concentrations in surface sediments within 32
localities studied in the Czech Republic. Drásov Reservoir had the overall highest SCP
concentrations in surface se
diments and SCPs with greatest diameters.





Main results and conclusions


1.
I have studied SCP records in five sediment cores collected from different depths and along
two transects in Drásov Reservoir.

2. The results suggested that wind
-

and inlet
-
indu
ced currents had an important influence on
both SCP and sediment distribution in the reservoir, and that the distribution of SCPs on the
reservoir bottom was different to that of sediments
(Figure 1)
.

Figure 1.

SCP inventories and lengths of five cores tak
en along two transects (longitudinal transect A
-
D
-
E and transverse transect A
-
B
-
C) from Dr
ásov
Reservoir
. Cores A
-
C were taken in down
-
wind side
of the reservoir near the dam. Core E was influenced by allochthonous material from the input stream.


3. Sedim
ents in down
-
wind area of the reservoir provided good evidence of the history of
solid emissions. Although most reliable SCP record was contained in a deep
-
water core
(A)
,
the records in shallower
-
water cores from the down
-
wind side of the reservoir (cores

B and C)
were also good (Figure 2). SCP accumulation rates in sediment correlated well with solid
emissions from a local source located 3

km away from the reservoir (Spearman R

=

0.87,
p

=

0.001). Records of emissions from individual combustion sources go

back to 1982. A
good representation of the history of the solid emissions by the pre
-
1982 SCP sediment record
was confirmed by a good correlation between the SCP accumulation rate in sediment core A
A
7 m
sediment core length, cm
0
4
8
12
16
20
SCP inventory, SCP x 10
8
m
-2
0
2
4
6
8
sediment
SCP inventory
B
4.5 m
C
2.5 m
D
4.5 m
E
2.5 m

from Dr
ásov Reservoir

and tariffs for exceeding the soli
d emission limit paid by the same
combustion source in the period 1968 to 1982 (Spearman R

=

0.83, p

<

0.001).

Figure 2.

Spheroidal carbonaceous particle profiles for cores A

E from Drásov Reservoir and solid
emissions from the local source.
Cores A
-
C wer
e taken in down
-
wind side of the reservoir near the
dam. Core D was taken in the middle of the reservoir, while core E approximately 160

m from the
inflow.







4. I have studied inputs and sinks of SCPs in Drásov Reservoir during a year period
(1998/99).

I have examined the atmospheric deposition of SCPs, their input into the reservoir
by the tributary, the SCP concentration in the reservoir water, removal of SCPs from the
reservoir water by the take
-
off by the water treatment plant and by the outflow, an
d the SCP
deposition to sediment traps. Additionally, I analysed the SCP storage in two soil cores from
the reservoir catchment.

1999
1997
1994
1991
1986
1980
1974
1966
1959
emissions, 10
2
t y
-1
SCP x 10
3
g
-1
SCP x 10
3
g
-1
SCP x 10
3
g
-1
SCP x 10
3
g
-1
core A, 7 m
SCP x 10
3
g
-1
0
10
20
30
sediment depth, cm
0
4
8
12
16
emissions
SCPs
core E, 2.5 m
0
5
10
0
4
8
12
16
core B, 4.5 m
0
10
20
30
0
2
4
6
8
10
12
14
core C, 2.5 m
0
10
20
30
0
2
4
6
8
core D, 4.5 m
0
5
10
sediment depth, cm
0
2
4
6
8
1999
1997
1994
1991
1986
1980
1974
1966
1959
core D, 4.5 m

5. The predominant input of SCPs into the reservoir was by the direct atmospheric deposition
(92.4

%), see Figure 3. The SCP i
nput from the catchment by the tributary was negligible
(7.6

%). Moreover, most of SCPs brought by the tributary into the reservoir were carried in
during the two periods with exceptionally high tributary discharge, when the tributary eroded
soil. The pred
ominant SCP sink from the reservoir water was by the sedimentation. Only 4

%
of the total SCP input was removed from the reservoir by the take
-
off by the water treatment
plant and by the outflow over the spillway. A similar pattern of SCP input to a lake c
an be
expected in lowland temperate sites, which are not exposed to soil erosion. The contribution
of the tributary to the SCP input to the lake will depend on the extent to which it erodes soil
and to its area relative to the lake area.

Figure 3.

Total nu
mber of SCPs in the water of D
rásov

Reservoir, cumulative input of SCPs to the
reservoir from the atmosphere and by the tributary, and cumulative SCP removal by take
-
off by the
water treatment plant during the period May
1998 to May 1999
.


6. The results s
uggested that in shallow water bodies with changing water level, SCP
concentration in water and SCP deposition to sediments is strongly influenced by changes of
the lake volume
(i.e., lake depth and area)
and
internal movement processes within the lake.

7
. The results from the sediment traps gave evidence of SCP resuspension and focusing, and
supported the results from sediment core analysis, that SCPs had greater spatial variability
than sediments.

27.5.-24.6.
24.6.-22.7.
22.7.-19.8.
19.8.-16.9.
16.9.-14.10.
14.10.-10.11.
10.11.-9.12.
9.12.-6.1.
6.1.-3.2.
3.2.-3.3.
3.3.-31.3.
31.3.-28.4.
28.4.-26.5.
no. SCP, SCP x 10
8
cumulative SCP input by tributary, SCP x 10
8

cumulative SCP atmosph. input, SCP x 10
9

cumulative SCP take-off, SCP x 10
8
0
5
10
15
20
25
30
no. SCPs in reservoir water
atmospheric input
input by tributary
sink by take-off

8. Although forests enhance SCP deposition from the atmo
sphere to the catchment, these are
not transported to the reservoir, as they remain in catchment soils. Catchment soils are a
major store of SCPs deposited to the catchment.







9. I have examined SCP size distribution in surface sediments of seven sites

in the Czech
Republic. Additionally, I have studied the temporal distribution of SCP sizes in a full
sediment core from Drásov Reservoir.

10. The SCP size distribution revealed that two sites (Drásov Reservoir and CU pool) were
influenced by local emissi
ons, whereas SCPs at other studied sites were transported regionally
(Figure 4). The presence of SCPs with diameters over 100


m in sediments indicates a local
source of SCPs, which does not have efficient particle retention equipment. The source is not
mo
re than a few kilometres away from the site where so large SCPs occur.


Figure 4.

SCP size distribution in surface sediments of seven sites in the Czech Republic. CU pool is
a
small
concrete pool in Prague. Fl
áje and Přísečnice reservoirs are situated in t
he Krušné Mountains,
Bedřichov and Souš reservoirs in the Jizerské Mountains, while Drásov
Resrvoir near the town
P
říbram in the central Czech Republic. Černé
Lake is in the
Šumava Mountains.

Fláje
N=252
<10
10-20
20-40
40-80
80-160
>160
no. SCP, %
0
10
20
30
40
50
Bedøichov
N=423
<10
10-20
20-40
40-80
80-160
>160
0
10
20
30
40
50
Drásov
N=306
<10
10-20
20-40
40-80
80-160
>160
0
10
20
30
40
50
CU pool
N=417
<10
10-20
20-40
40-80
80-160
>160
0
10
20
30
40
50
Souš
N=217
<10
10-20
20-40
40-80
80-160
>160
0
10
20
30
40
50
Pøíseènice
N=107
<10
10-20
20-40
40-80
80-160
>160
0
10
20
30
40
50
SCP diameters,

m
<10
10-20
20-40
40-80
80-160
>160
0
10
20
30
40
50
no. SCP, %
no. SCP, %
SCP diameters,

m
SCP diameters,

m
Èerné
N=257

11. A significant change occurred in the size distribution of S
CPs within the vertical profile of
sediment core (F) from
Drásov
Resrvoir (Figure 5). This c
hange corresponded to a change in
combustion policy by the predominant source of SCPs in the reservoir. Such a change in SCP
size distribution within a sediment cor
e can precisely indicate the age of the sediment layer in
which it occurs if the source is known and the history of combustion is recorded.


Figure 5.

Vertical profiles of several size categories of SCP diameters in sediment core F from Drásov
Reservoir.


12. The presence of large SCPs (with diameters over 40


m) in sediments from all sites
revealed that particle retention equipment of combustion sources in the Czech Republic was
in an unsatisfactory condition in the early 1990s.






sediment core depth, cm
SCP, %
0
10
20
30
40
50
60
70
0
2
4
6
8
10
< 10

m
10-20

m
20-100

m
>100

m

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