Download Obtaining a temporal record of heavy metal pollution from reservoirs

Obtaining a temporal record of heavy metal pollution from reservoirs in the
southern Pennines, UK.
LAURA SHOTBOLT
Telford Institute of Environmental Systems, Division of Geography, University of
Salford, Greater Manchester M5 4WT, UK.
SIMON M. HUTCHINSON
Telford Institute of Environmental Systems, Division of Environmental Resources,
University of Salford, Greater Manchester M6 6PU, UK.
ANDREW D. THOMAS
Telford Institute of Environmental Systems, Division of Geography, University of
Salford, Greater Manchester M5 4WT, UK.
ANDREW J. DOUGILL
School of the Environment, University of Leeds, Leeds LS2 9JT, UK
Abstract. The southern Pennine uplands, UK, are surrounded by urban industrial
areas and have been subject to a long history of industrially derived atmospheric
pollution. The potential for the sedimentary record of reservoirs in this area to
provide a temporal record of heavy metal inputs is assessed. Central cores from five
reservoirs demonstrate markedly similar magnetic susceptibility (lf) profiles both
within and between reservoirs, and therefore undisturbed sediment chronology in
these cores. Heavy metal profiles of sediment cores appear largely unaffected by
post-depositional metal mobilization with the exception of Fe and Mn. Reservoir
sediments are, concluded to provide a temporal record of heavy metal inputs and a
valuable resource for studying the history of atmospheric pollution in this area.
1
Introduction and aims
The southern Pennine uplands, north-central England, are surrounded by the urbanindustrial areas of Manchester, Leeds, Bradford, Stoke and Sheffield (Fig. 1). Northcentral England is considered the ‘cradle’ of the industrial revolution, and these
uplands have been subjected to atmospheric pollution from surrounding cities since
the eighteenth century. The high density of reservoirs in these uplands make it an
important water supply area for the surrounding population. Both contemporary
deposition, and the past accumulation of pollutants (in particular heavy metals) in
potentially erodible soils and in reservoir sediments is of concern.
No long-term record of heavy metal deposition is available in this region;
however, the use of lake sediments as an historical record of atmospheric pollution is
a well established technique.
Temporal records of atmospherically derived
particulates including trace metals, spherical carbonaceous particles (SCP), magnetic
minerals, and polycyclic aromatic hydrocarbons (PAH), have been documented in
lake sediment cores across the world (e.g. Rippey, 1990; Hermanson, 1993; Flower et
al., 1997).
While there are no lakes in the study area, the application of techniques used
in lake sediment analysis to reservoir sediments may provide an alternative historical
record. In the UK, reservoir sediments are rarely used as a temporal record: water
level drawdown can result in the erosion of marginal sediments, and their redeposition
in central areas, disturbing sediment chronology (Anderson et al., 1988). Exceptions
include work on heavy metal contamination in reservoirs in the English Midlands (eg.
Foster et al., 1991; Charlesworth and Foster, 1999) and a preliminary assessment of
the potential of southern Pennine reservoirs for reconstructing water quality and
pollution histories (Anderson et al., 1988). Anderson et al. conclude that, while it
2
will be difficult to find sites with undisturbed sediment in the southern Pennines, it
should be possible to obtain a temporal record of pollution from reservoir sediments.
To reconstruct a record of heavy metal deposition onto this area from the
reservoir sedimentary record it is necessary to ascertain the following: A, the
sediment profile has not been physically disturbed; B, there has been no modification
of the heavy metal profile by metal solubilisation and mobilization; and, C, the record
of atmospheric deposition has not been distorted by a variable input of sediment and
associated metals from the drainage basin (either from the weathering and erosion of
bedrock, or from metals previously deposited onto the drainage basin).
As part of a wider project investigating the history of heavy metal deposition
onto the southern Pennines, this study addresses criteria A and B.
It aims to
demonstrate that, where undisturbed and unmodified, sediment profiles can represent
a record of the net input of metals into the reservoir over its lifespan. This record of
inputs can then be used (where variable drainage basin inputs are considered) to
reconstruct a history of heavy metal deposition.
Site selection and core collection
Of the 192 reservoirs in the southern Pennines (Fig 1), only a few will be suitable for
reconstructing pollution histories (Anderson et al., 1988). A selection procedure
(Table 1) was designed to eliminate reservoirs where disturbance to the sediment is
likely (Shotbolt et al., in press), leaving those with the highest probability of an
undisturbed and retrievable sediment. Agden, Broomhead, Howden, Langsett and
Midhope reservoirs were initially selected for analysis (Fig. 1). Table 2 summarizes
the characteristics of these reservoirs and their drainage basins.
Between eight and ten 1 m sediment cores were collected from each reservoir
with a Mackereth mini-corer (Mackereth, 1969). Cores were taken from central,
3
intermediate and marginal zones. A depth sensor was used to ensure core sites
avoided former river channels.
Determination of sediment stratigraphy.
To determine whether sediment profiles have been disturbed (criteria A) volume
magnetic susceptibility () was logged at 2 cm intervals down the cores using a
Bartington MS2C loop sensor.
Magnetic susceptibility (is a measure of the
‘magnetisability’ of a material (Dearing, 1999). The magnetism is derived
predominantly from primary and secondary minerals eroded from the catchment, and
magnetic minerals deposited from the atmosphere, the majority of which are the
product of industrial processes and vehicular emissions (Thompson and Oldfield,
1986). The magnetic profile of an undisturbed sediment core will therefore reflect
changes in the amount and type of magnetic inputs through time. Many studies have
shown susceptibility profiles of central cores have a distinct ‘signature’ that is
repeated across this zone (eg. Thompson et al., 1975) suggesting either sediment has
remained undisturbed throughout this deep zone, or any disturbance has affected the
whole area. This can then be used to identify any anomalous or disturbed cores
(Thompson and Oldfield, 1986) and to identify cores suitable for further analysis. Fig
2 shows cores from Howden reservoir. Central cores are broadly similar and cores 3
and 4 from the deepest zone are almost identical. In contrast, frequently reworked
marginal cores show no such consistency.
As cores from the deepest zone of each reservoir were found to be most
replicable, three cores were selected from central areas of each reservoir for further
analysis. These cores were extruded, divided into 1 cm sections and dried at 40ºC.
Water content and bulk density were determined and used to identify the original soil
4
surface where this was retained. Organic matter content was determined, as loss-onignition, after heating to 500°C for eight hours (Rowell, 1994).
Sections were
homogenised and packed into 10 ml pots for single sample mass specific
susceptibility measurement. A Bartington MS2B single sample dual frequency sensor
was used to measure low (lf) and high frequency (hf) susceptibility. Frequency
dependent susceptibility (fd%) was calculated from this (Dearing, 1999).
The
measurement of susceptibility on a dry mass basis allows a more accurate and detailed
analysis of the susceptibility profile.
Frequency dependent susceptibility detects
ultrafine (<0.03 m) superparamagnetic minerals produced largely by biochemical
processes in soil (Dearing, 1999). All samples were measured from one core and
alternate samples from the other two selected.
Table 3 summarizes the main
characteristics of sediment cores from all reservoirs.
Fig. 3 showslf profiles of key cores from all reservoirs. The main features
are a peak between 10 and 15 cm from the surface and a general similarity between
the profiles. This similarity, both within, and between reservoirs, strongly suggests
sediments have not been significantly disturbed. The exception to this is Howden
reservoir, which has a zone of lower susceptibility at a depth of 15 to 28 cm. This
zone was also evident in deepwater cores collected in a previous study, where
137
Cs
dating located the whole zone between 1954 and 1963 (Hutchinson, 1995). This low
susceptibility zone is thought to be the result of the inwash of material removed from
exposed marginal sediments and drainage basin soils by a severe storm following a
protracted and exceptionally low drawdown in 1959 (Shotbolt et al. in press).
Reservoir and meteorological records show neither drawdown, nor the subsequent
storm event were as extreme in the other reservoirs, explaining the absence of any
corresponding inwash of low susceptibility material.
It appears that only a
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combination of extreme drawdown and heavy rainfall will disturb sediment in the
deepest zone of these reservoirs.
The similarity between susceptibility profiles also implies the same origin of
magnetic inputs.
Susceptibility will be predominantly derived from atmospheric
particulate deposition in this area: previous work has shown magnetically
impoverished Millstone Grit bedrock inputs to dilute lf concentrations in the
sediment (Hutchinson, 1995).
Radiometric dating is in progress. However, an approximate time scale
assuming a constant rate of sedimentation, and using cumulative dry bulk density to
remove effects of consolidation (Robbins, 1978), is used to date subsurface peaks to
between 1969 and 1981 (Fig 4). While constant rates of sedimentation are unlikely,
this approximate dating method is useful, demonstrating peaks are synchronous with
peaks of atmospheric pollutants found in studies across the UK. For example, Rose et
al. (1995) dated subsurface SCP peaks from 19 lakes from the UK and Ireland to
between 1969 and 1982.
The general similarity between susceptibility profiles both within and between
reservoirs shows, therefore, that neither variable drainage basin inputs, nor sediment
disturbance obscure overall deposition trends.
The sedimentary record of these
reservoirs appears no less valuable than that of natural lakes.
Furthermore, the
relatively rapid sedimentation (Table 3) means higher resolution data, and the original
soil surface/sediment interface provides a readily obtainable date for the base of the
core.
Heavy metal analysis of reservoir profiles.
6
Heavy metal analysis was carried out on the three selected cores from each reservoir
using a modified aqua-regia method by Jones and Laslett (1994). Figure 4 shows
metal concentration in cores from Agden and Howden Reservoirs.
Table 3
summarizes the range and mean metal concentrations in all sediment cores. In all
reservoirs concentrations of Zn > Pb > Cr > Cu = Ni. Analytical accuracy was
assessed by including two blanks, two duplicates and a certified reference sample in
each batch of thirty samples (Table 4).
Mn profiles show very high concentrations at the sediment surface. This
corresponds closely to water content profiles (Fig 4) and demonstrates solubilisation
and mobilization of Mn through the reduction of Mn oxides and hydroxides in
anaerobic sediment (Song & Muller, 1999). Fe profiles also show an increase in the
upper 5 cm of both cores largely attributable to redox induced mobilization. Mn and
Fe profiles will not therefore represent a temporal record of inputs of these metals to
the reservoir. However, there is no evidence of mobilization of any other metals:
peaks in Cu and Zn can be attributed to short term cycling of metals between the
surface sediments and the water column and are unlikely to affect the long term metal
record (Morfett et al., 1988). On the basis of analysis so far, heavy metal profiles,
with the exception of Mn and Fe do appear to represent a temporal record of inputs of
those metals thus satisfying criteria B.
To conclude, sediments from the deepest part of these reservoirs are physically
undisturbed and heavy metal profiles appear largely unaffected by remobilization
processes. Sediment profiles therefore represent a record of the net input of metals
into the reservoir. Future work aims to evaluate the importance of variable inputs of
metal contaminated sediment from the drainage basin, and natural baseline metal
levels, allowing interpretation of metal profiles as a record of atmospheric deposition
onto this area.
7
Acknowledgements The authors thank Beth Lethers, Tim Carr, Polly Hardy and
Tony Meachen for assistance with sample collection, and Gustav Dobrzynski for
cartography. Studies were undertaken in association with a research grant provided
by the Manchester Geographical Society.
References
Anderson, N.J., Patrick, S.T., Appleby, P.G., Oldfield, F., Rippey, B., Richardson, N.,
Darley, J. & Battarbee, R.W. (1988) An assessment of the use of reservoir sediments
in the southern Pennines for reconstructing the history and effects of atmospheric
pollution. Working Papers no.30, Palaeoecology Research Unit, Dept. Geography,
University College London.
Charlesworth, S.M. & Foster, I.D.L. (1999): Sediment budgets and metal fluxes in
two contrasting urban lake catchments in Coventry, UK. Applied Geography. 19, 199210.
Dearing. J.A. (1999) Environmental Magnetic Susceptibility: Using the Bartlington
MS2 System. Users Handbook. Second Edition.
Flower, R.J., Politov, S.V., Rippey, B., Rose, N.L., Appleby, P.G., & Stevenson, A.C.
(1997) Sedimentary records of the extent and impact of atmospheric contamination
from a remote Siberian highland lake. The Holocene. 7, 161-173.
Foster, I.D.L., Charlesworth, S. M. & Keen, D. H. (1991) A comparative study of
heavy metal contamination and pollution in four reservoirs in the English Midlands.
Hydrobiologia. 214, 155-162.
Hermanson, M.H. (1993) Historical accumulation of atmospherically derived
pollutant trace metals in the Arctic as measured in dated sediment cores. Wat. Sci.
Tech. 28, 33-41.
8
Hutchinson, S.M. (1995) Use of magnetic and radiometric measurements to
investigate erosion and sedimentation in a British upland catchment. Earth Surf.
Processes and Landforms. 20, 293-332.
Jones, B.R. & Laslett, R.E. (1994) Method for analysis of trace metals in marine and
other samples. MAFF.
Mackereth, F.J.H. (1969) A short core sampler for sub-aqueous deposits. Limnol.
Oceanogr. 14, 145-151.
Morfett, K., Davison,W. & Hamilton-Taylor, J. (1988) Trace metal dynamics in a
seasonally anoxic lake. Envir. Geol. Wat. Sci. 11, 107-114.
Rippey, B. (1990) Sediment chemistry and atmospheric contamination. Phil. Trans. R.
Soc. Lond. B 327, 311-317.
Rose, N.L., Harlock, S., Appleby, P.G. & Battarbee, R.W. (1995) Dating of recent
sediments in the United Kingdom and Ireland using spheroidal carbonaceous particle
(SCP) concentration profiles. The Holocene. 5, 328-335.
Robbins, J.A. (1978) Geochemical and geophysical applications of radioactive lead.
In: The biogeochemistry of lead in the environment. (ed. By J. O. Nriagu) Elsevier,
Amsterdam. 285-408.
Rowell, D.L. (1994) Soil science: methods and applications. Longman Scientific &
Technical, Harlow.
Shotbolt, L., Thomas, A.D., Dougill, A.J. & Hutchinson, S.M. Reconstructing the
history of heavy metal pollution in the southern Pennines from the sedimentary record
of reservoirs: methods and preliminary results. The North West Geographer (in press)
Song, Y. & Muller, G. (1999) Sediment-water interactions in anoxic freshwater
sediments: Mobility of heavy metal and nutrients. Springer–Verlag, Berlin.
Thompson, R. & Oldfield, F. (1986) Environmental Magnetism. Allen & Unwin:
London.
9
Thompson, R., Battarbee, R.W., O’Sullivan, P.E. & Oldfield, F. (1975) Magnetic
susceptibility of lake sediments. Limnology and Oceanography. 20, 687-698.
TABLES
Table 1. Selection criteria for elimination of unsuitable sites for sediment collection
Potential problems
Eliminated if…..
variable inputs from reservoir upstream
lifespan of reservoir
rapid sedimentation
not headwater reservoir
built after 1930
has >20% capacity loss
silted up with peat
no catchment
dredged
scour valves tested
drained
drawn down past max. normal extraction limit
residuum lodge
bywash
conduits
quarries in catchment
dam breached
no information is available
low sedimentation
mechanical sediment removal
reworking of sediment
catchment controls
No. eliminated No. remaining
192
73
119
6
113
3
110
4
106
9
97
2
95
9
86
8
78
15
63
21
42
8
34
7
27
3
24
2
22
9
13
Using data fromYorkshire Water plc, Western House, Bradford, BD6 2LZ; Severn Trent Water Ltd, Avon House, Coventry, CV3 6PR; British
Waterways, Pennine and Potteries Waterways Division, Church Lane, Marple, SK6 3BN; North West Water, Lingley Mere, Warrington, WA5 3LP.
Table 2. Reservoir and drainage basin characteristics of study sites.
Reservoir
Agden
Construction
Capacity
Max.
date
(Ml)
depth area
1869
2859
Surface
Drainage
Bedrock
(m)
(ha)
basin
Aarea (km2)
27.4
25
11.0
Vegetation
Sediment
infill (% of Σ
capacity)
Millstone forest plantation/
Grit
pasture/moorland
Broomhead
1929
5191
27.7
50
20.5
""
""
Howden
1912
8990
34.6
63
35.5
""
forest plantation/
1.2
5.2
no data
moorland
Langsett
1905
6400
29.0
51
23.0
""
""
14.3
Midhope
1904
1859
27.1
21
4.0
""
""
1.0
Using data from Yorkshire Water plc, Western House, Bradford, BD6 2LZ; Severn Trent Water Ltd, Avon House, Coventry, CV3 6PR; British
Waterways, Pennine and Potteries Waterways Division, Church Lane, Marple, SK6 3BN; North West Water, Lingley Mere, Warrington, WA5 3LP.
Table 3. Physical and chemical characteristics of sediment cores.
Agden
Broomhead
Howden
Langsett
Midhope
range
mean
range
mean
range
mean
range
mean
range
mean
Water depth (m)
21-25
23
12-24
22
26-31
29
18-26
22
12-16
15
Sediment depth (cm)
Sedimentation rate (cm yr-1)
33-42
37
25-28
26
37-50
45
28-46
37
37-39
38
0.26-0.33
0.28
0.36-0.41
0.38
0.43-0.58
0.52
0.30-0.49
0.40
0.39-0.41
0.40
LOI (%)
Bulk density (g cm-1)
10.0-36.2
23.1
16.4-28.8
19.5
10.0-30.1 24.0-6.0 15.9-28.7
19.3
10.1-23.2
12.4
0.03-0.85
0.43
0.15-0.78
0.50
0.06-0.68
0.43
0.16-0.62
0.44
0.11-0.63
0.41
lf (10-8 m3 kg-1)
fd %
14.3-113.5
54.7
7.1-77.9
35.5
10.3-45.6
24.1
7.3-59.6
32.0
15.2-71.6
48.3
0.0-4.5
2.1
0.0-4.0
2.1
0.0-3.9
1.7
0.0-4.8
1.8
0.4-5.8
3.5
Cr (g g-1)
49-85
70
54-87
73
46-90
64
57-87
76
51-90
75
Cu (g g-1)
27-191
53
35-52
39
29-232
41
31-48
39
25-49
40
Fe (mg g-1)
28-99
44
23-49
33
26-61
32
25-65
35
31-98
50
Mn (g g-1)
142-1868
170
121-230
146
122-1329
206
138-244
158
106-1123
170
35
Ni (g g-1)
35-58
48
33-59
42
35-51
43
42-76
56
18-43
Pb (g g-1)
54-248
177
115-213
168
77-179
119
71-133
98
62-131
92
Zn (g g-1)
145-336
241
178-525
230
142-344
168
91-359
141
106-203
137
10
Table 4
FIGURE CAPTIONS
Figure 1. The southern Pennines and location of reservoirs.
Figure 2. Volume susceptibility () profiles of cores from Howden Reservoir.
Figure 3. Mass specific susceptibility (lf) profiles from southern Pennine reservoirs.
Figure 4. Heavy metal, loss-on-ignition, and organic matter profiles from Agden and
Howden Reservoirs.
11

0
200

0

200 0

200 0
200 0


200 0
200

0

200 0

200 0

200 0
200
depth (cm)
0
20
40
60
80
Core 2
Core 1
100
Core 3
Core 4
Core 5
Core 6
Core 7
central cores
Agden
Core 8
Core 9
Core 10
marginal cores
Broomhead
Howden
Langsett
Midhope
lf (10 m kg )
-8
0
25
50
3
-1
75
100
0
25
50
75
0
25
50
0
25
50
75
0
0
0
0
0
0
10
10
10
10
10
1976
20
20
1973
1977
20
20
50
75
1981
20
1969
1929
30
25
30
30
30
40
40
40
30
1869
1904
40
40
1905
1912
0
10
20
fd (%)
0
10
lf
depth (cm)
0
50
f
g g-1
g g-1
0
100
0
0
500
0
10
g g-1
mg g-1
200
400
0
50
100
0
0
0
0
0
0
10
10
10
10
10
20
20
20
20
20
30
30
30
30
30
40
40
40
40
40
1000
2000
original soil surface
Cr
50
Zn
Ni
50
Pb
Cu
50
g g-1
0
50
0
50
50
0
100
250
0
500
250
mg g-1
0
500
50
100
0
0
0
0
0
10
10
10
10
10
20
20
20
20
20
30
30
30
30
30
40
Cr
50
Zn
40
50
Howden Reservoir
Pb
LOI
40
50
1000
50
0
50
LOI (%)
2000
Mn
40
water
Fe
Cu
Ni
20
g g-1
0
40
10
water content (g g-1)
LOI (%)
g g-1
Mn
water
Fe
0
g g-1
100
LOI
50
Agden Reservoir
depth (cm)
0
original soil surface
g g-1
250
10
50
100
0
10
20
water content (g g-1)
12
13
14