Project no. GOCE-CT-2003-505540
Project acronym: Euro-limpacs
Project full name: Integrated Project to evaluate the Impacts of Global Change on European
Freshwater Ecosystems
Instrument type:
Integrated Project
Priority name:
Sustainable Development
D239: Inferring environmental change in a riparian wetland using a
palaeoecological approach: potential and problems.
Due date of deliverable: 31 January 2009
Actual submission date: 31 January 2009
Start date of project: 1 February 2004
Duration: 5 years
Project coordinator name: Simon Patrick
Project coordinator organisation name: University College London (UCL)
Revision: Final Report
Project co-funded by the European Commission within the Sixth Framework Programme
(2002-2006)
PU
PP
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Dissemination Level
Public
Restricted to other programme participants (including the Commission Services)
Restricted to a group specified by the consortium (including the Commission Services)
Confidential, only for members of the consortium (including the Commission Services)
Contributing Authors
Dr Helen Bennion, Environmental Change Research Centre, Department of Geography, University
College London, UK. (UCL)
Dr Liselotte Johansson, National Environmental Research Institute, Department of Freshwater
Ecology, Denmark (NERI).
Dr Jonathan Homes, Environmental Change Research Centre, Department of Geography,
University College London, UK. (UCL).
Dr Neil Rose, Environmental Change Research Centre, Department of Geography, University
College London, UK (UCL).
Dr Simon Turner, Environmental Change Research Centre, Department of Geography, University
College London, UK (UCL).
Dr Handong Yang, Environmental Change Research Centre, Department of Geography, University
College London, UK (UCL).
2
Introduction
A palaeoecological study of a single wetland site, Boxford Water Meadows in England, was
conducted to explore the potential of sediment records from wetlands for assessing long-term,
nutrient-climate change interactions. The methods for using lake sediment cores to assess
changes in lake level associated with climate (e.g. Fritz et al. 1999) and changes in trophic status
associated with nutrient inputs (e.g. Hall and Smol 1999) are well established. However, the
potential for employing sediment cores from wetlands to assess these environmental impacts has
until now not been explored. Wetland sediments are likely to be more disturbed than deep lake
sediments and, therefore, this task aimed to evaluate whether they are suitable for
palaeoecological investigations of this kind. This paper highlights the potential and problems of
inferring environmental change in a riparian wetland using a palaeoecological approach.
Study site description
Boxford Water Meadows (UK grid reference SU 428719) is a Site of Special Scientific Interest
(SSSI) covering an area of approximately 14 hectares (Figures 1 & 2). The site comprises a series
of flood pastures and disused water meadows along the River Lambourn. The site overlies
alluvium and the soils consist of calcareous alluvial gleys. Traditionally the water meadows would
have been managed as pasture for cattle or horses with controlled flooding along specially
constructed carrier streams providing a supply of warm water in spring to encourage early growth
of the sward. The meadows have not been grazed, with the exception of the southern-most field,
for around 40 years and the vegetation types reflect both this and the gradient in soil moisture. The
plant communities grade from Carex acutiformis swamp-fen to Cynosurus cristatus-Caltha palustris
flood-pasture and water-meadow vegetation southwards across the site.
Methods
Core collection and lithostratigraphy
A total of eight cores were taken along a south to north transect on the west side of the river on
27th April 2005 using a gouge coring device (Figure 3). Core site 8 at the northern-most end of the
transect (grid reference SU 42880, 72213) was selected as the site for further study owing to it’s
location on the site of an old river channel, the depth of sediment accumulation and the interesting
stratigraphic changes observed. Hence, two overlapping drives with a standard Russian corer were
taken and the core was coded BOXF1. Drive 1 covered the section from the sediment surface to a
depth of 50 cm and drive 2 covered the section 40-90 cm (Figure 4). The core was extruded into
plastic holders, wrapped in cling-film and transported to the laboratory for analysis.
In the laboratory, drive 1 of core BOXF1 was subsampled at 0.5 cm contiguous intervals from 0-50
cm and drive 2 was subsampled at 1 cm contiguous intervals from 50-90 cm. The main
characteristics of the sediment and any stratigraphic changes were noted. The percentage dry
weight (DW %) which gives a measure of the water content of the sediment, and percentage loss
on ignition (LOI 550) which gives a measure of the organic matter content were determined for all
subsamples, and carbonate content was determined for the section 40-90 cm only. All analyses
followed standard techniques (Dean 1974).
Chronology
An approximate chronology for the core was established using spheroidal carbonaceous particles
(SCPs) (Rose 1994). In addition, sediment samples from BOXF1 were analysed for 210Pb, 226Ra,
137
Cs and 241Am by direct gamma assay in the Bloomsbury Environment Institute at University
College London (Appleby et al. 1986) in an attempt to provide a further independent chronology for
the core.
3
Biological analyses
A total of 23 sub-samples were prepared and analysed for diatoms using standard methods
(Battarbee et al. 2001). At least 300 valves were counted in each sample except where
preservation was exceptionally poor and in some cases only ~100-200 valves could be found on
the whole slide. Principal floras used in identification were Krammer and Lange-Bertalot (19861991). The diatom data were expressed as percentage relative abundance. A diatom-total
phosphorus (TP) transfer function was applied to the diatom data following taxonomic
harmonisation between the training set and the fossil data. Reconstructions of diatom-inferred TP
(DI-TP) were produced using a Northwest European training set of 152 relatively small, shallow
lakes (< 10 m maximum depth) with a median value for the dataset of 104 µg TP l-1 and a root
mean squared error of prediction (RMSEP) of 0.21 log10 µg TP l-1 for the weighted averaging partial
least squares component 2 (WA-PLS2) model (Bennion et al. 1996).
Ten sub-samples at 10 cm intervals throughout the core were prepared and analysed for
cladocera. The samples (approximately 1 g wet weight) were boiled in 30 ml 10% KOH for ~20 min
and subsequently kept cold for no longer than two weeks before counting.
After manual filtering, fragments larger than 80 µm were counted and identified using a
stereomicroscope and an inverted light microscope. For the identification, keys of Frey (1959),
Margaritora (1985), Hann (1990), Røen (1995) and Flössner (2000) were used. The cladocera data
were expressed as numbers per gram dry weight and were subsequently converted into relative
percentage abundance values.
The resulting diatom and Cladocera profiles were zoned based on cluster analysis to facilitate
description and allow comparison of the two datasets. Cluster analysis was performed using
CONISS (Grimm 1987), implemented by TILIA and TILIAGRAPH (Grimm 1991). CONISS is a
program for stratigraphically constrained cluster analysis by the method of incremental sum of
squares.
It was anticipated at the outset of the project that ostracods may be particularly useful for
identifying periods of wetting and drying of the wetland versus permanently wet episodes.
Therefore, wet sub-samples from BOXF1 were sieved at 125 µm by UCL to assess the amount of
ostracod and mollusc remains. Unfortunately, only a few shells and fragments were found and
ostracods were generally rare and poorly preserved. Calcareous remains were absent from the
upper peat section, most likely as a result of post depositional dissolution. However, in the chalky,
limnic sediments from 76 cm to the base ostracod and mollusc remains were found although
preservation was poor. Even the smaller mesh size of 80 µm, employed during the cladoceran
analysis, failed to find more than a few fragments of ostracods in the 40-90 cm section and they
were absent in the upper 40 cm. The lack of such remains throughout the core sequence made it
impossible to pursue carbonate isotope analysis. Likewise, it was originally hoped that plant
macrofossils could be analysed to assess shifts in vegetation but unfortunately insufficient remains
were present in the core to pursue this method.
Results and discussion
Stratigraphy
The upper 25 cm of drive 1 was a dark brown, sedge peat with abundant root linings (Figure 5).
The uppermost 16 cm had a very high organic content of ~80%, gradually decreasing to ~30%
over the section 16-25 cm. The colour grades from dark brown to a lighter brown at ~25-30 cm and
the light brown sedge peat then continues for a large section of the core sequence from ~25-70
cm. Organic matter content remained at ~30% from 25-57 cm but then declined to ~10-15%
coincident with the presence of mineral fragments and chalk particles in the section 58-70 cm.
From 70-80 cm, the sediment becomes lighter in colour and is comprised of a chalky mud matrix.
The carbonate content fluctuates between ~10-20% over the section 40-80 cm. At 80 cm there
was a marked change to a coarse chalk aggregate which was white in colour and consequently
carbonate content rises to ~30-35%. The lowermost 10 cm were comprised of a fine grained
calcareous mud with chalk clasts.
4
Chronology
Owing to very low concentrations, 210Pb dating of the BOXF1 core was not possible. However, a 137
Cs peak was identified at 5.5-6 cm and, whilst this should be interpreted with caution, it is likely to
represent 1963, the year of peak fallout from the atmospheric testing of nuclear weapons.
The core BOXF1 contains the full SCP record indicating that it covers the last ~150 years (Figure
6). In spite of being taken from a riparian wetland rather than from a lake basin, the SCP record
exhibits features that are recognisable in many lake sediment cores across the UK and Europe
(Rose et al. 1995). However, a large peak occurred at 14 – 14.5 cm and it is unclear whether this is
a real peak or an analytical artefact owing to relatively low sample resolution. Nevertheless, three
dates representing the start of the SCP record, the start of the rapid increase in concentration and
the SCP concentration peak could be ascribed to this profile (Figure 7). These data suggest a
reasonably linear accumulation over the last 150 years and show agreement with the limited
radiometric data (137Cs peak) and, when extrapolated, the date of coring. This being the case, a
mean sedimentation for BOXF1 over the last 150 years is ~ 0.148 cm yr-1.
Biological analyses
Diatoms were present in all of the samples although at varying degrees of preservation. A total of
88 diatom taxa were observed in the core although individual samples were not particularly diverse
containing between 20 and 38 taxa. The cluster analysis identified six zones (Figure 8).
In Zone 1 (below 62 cm), the frustules in the lowermost sample (88-90 cm) which represents the
most calcareous section of the core, were very well preserved. In contrast, the other samples in
this zone contained high amounts of mineral matter and relatively few complete frustules. This
zone was dominated by benthic Fragilaria spp, namely Fragilaria pinnata, Fragilaria brevistriata
and Fragilaria construens var venter, which are cosmopolitan taxa commonly observed in relatively
productive, alkaline shallow waters (Bennion et al. 2001). The other taxa present were all nonplanktonic forms commonly found attached to plant, stone or mud surfaces, including Cocconeis
(disculus and pseudothumensis), Amphora pediculus, a number of small Navicula species
(subatomoides, menisculus and subrotundata), Gyrosigma attenuatum and Achnanthes clevei.
The DI-TP values were high, fluctuating between ~150-190 µg l-1.
In Zones 2 and 3 (62-15 cm) which represent the period prior to ~1900 AD, diatom preservation
was highly variable. As in Zone 1, the assemblages were dominated by Fragilaria taxa. However a
number of taxa that had been relatively abundant in Zone1 decreased, particularly Cocconeis
disculus, Cocconeis pseudothumensis, Amphora pediculus, Navicula menisculus, Navicula
subrotundata, Gyrosigma attenuatum and Achnanthes clevei. Conversely, Synedra ulna, Cyclotella
radiosa and Meridion circulare increased. Cyclotella radiosa is a planktonic species whilst Synedra
ulna and Meridion circulare are common river diatoms and, therefore, the expansion of these taxa
could signify an increase in water level from inputs of river water to the wetland. The DI-TP values
were similar to those in Zone 1, ranging from ~160-200 µg l-1 in Zone 2 and ~150-160 µg l-1 in Zone
3.
Zones 4 to 6 (15-0 cm) represent the period from ~1900 AD to present which coincides with the
dark brown sedge-peat, and here the diatoms were poorly preserved. The benthic Fragilaria taxa
remained dominant in all except the surface sample. The most notable change in these upper
zones was the marked increase in Achnanthes lanceolata and Fragilaria nitzschioides and, to a
lesser extent, Fragilaria capucina which, based on the ecology of these taxa, would indicate an
increase in nutrient levels. This is reflected in the DI-TP values which increase towards the top of
the core to values of ~190 µg l-1. Conversely the relative abundances of Synedra ulna and
Cyclotella radiosa declined which may reflect lower water levels than in Zones 2 and 3.
The Cladocera analyses identified a total of 19 different types of remain distributed among 12 taxa.
The whole core was dominated by macrophyte associated and benthic chydorids and no true
pelagic taxa were present indicating low water level throughout the period represented by the
sediment record. Cluster analysis identified three major zones (Figure 9).
5
Zone 1 (90-75 cm) contained very few Cladocera fragments. The basal sample, the most
calcareous section of the core, was comprised of Pleuroxus spp and Chydoridae spp. In Zone 2
(75-15 cm), Chydoridae spp. continued to be abundant but there were higher abundances of Alona
affinis and Acroperus spp. relative to Zone 1 which could indicate an increase in the water level as
these species are typically associated with macrophytes or with the sediment around macrophytes,
and aquatic plants would need sufficient water depth to survive. The samples in Zone 3 (15-0 cm)
were coincident with the dark brown sedge-peat and saw the disappearance of Alona affinis and
expansion of Alona quarangularis. Whilst Cladocera remains have not previously been analysed in
wetland complexes such as Boxford, in lakes this shift would indicate a reduction in plant cover
typically associated with an increase in nutrient concentrations. Therefore, in recent times the
wetland may have received water with higher nutrient concentrations than in the past.
Comparison of diatom and cladocera results
There is reasonable agreement between the timing and nature of the main shifts in the diatom and
Cladocera assemblages although both sets of data are difficult to interpret in the context of
hydrological fluctuations or productivity changes. The assemblages of both biological groups are
dominated by non-planktonic taxa throughout the record indicating that water levels have not
altered dramatically during the period represented by the core. However there is a slight increase
in planktonic diatom forms in the middle of the sequence (55-25 cm), namely Cyclotella radiosa
and Synedra ulna, and this overlaps with the increased amounts of Alona affinis and Chydorus
spp., which could suggest that water levels were higher at this time. Both the diatom and the
Cladocera assemblages change in the upper 15 cm (post-1900) which appears to signify nutrient
enrichment.
Conclusions
The shifts in the diatom and Cladocera assemblages were difficult to interpret in the context of
hydrological fluctuations or productivity changes. Nevertheless, the coherence in the biological
records and the success in dating the core using the SCP method suggest that sediment cores
from riparian wetlands can potentially be used for palaeoenvironmental reconstruction. However,
the study highlights the need for very careful site selection and screening of material to ensure that
sufficient remains of the proxies of interest are preserved. Further ecological studies of the key
diatom and Cladocera taxa are required to interpret the findings more fully.
6
References
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Pb dating by low background gamma counting. Hydrobiologia 141: 21-27
Battarbee RW, Jones VJ, Flower RJ, Cameron NG, Bennion H, Carvalho L, Juggins S. (2001)
Diatoms. In: Smol JP, Birks HJB, Last WM (eds) Tracking Environmental Change Using Lake
Sediments. Volume 3: Terrestrial, Algal, and Siliceous Indicators. Kluwer Academic Publishers,
Dordrecht, The Netherlands, pp. 155-202
Bennion H, Juggins S, Anderson NJ (1996) Predicting epilimnetic phosphorus concentrations using
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UK: implications for the role of diatom-total phosphorus transfer functions in shallow lake
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Dean WE Jr (1974) Determination of carbonate and organic matter in calcareous sediments and
sedimentary rocks by loss on ignition: Comparison with other methods. J Sed Petrol 44,: 242–248
Flössner D (2000) Die Haplopoda und Cladocera (ohne Bosminidae) Mitteleuropas. Backhuys
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Frey DG (1959) The taxonomic and phylogenetic significance of the head pores of the Chydoridae
Cladocera. Int Rev Gesamt Hydrobiol 44: 27–50
Fritz SC, Cumming BF, Gasse F and Laird KR (1999) Diatoms as indicators of hydrologic change
and climate change in saline lakes. In: Stoermer EF, Smol JP (eds) The Diatoms: Applications for
the Environmental and Earth Sciences. Cambridge University Press, Cambridge, pp 41-72.
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the method of incremental sum of squares. Comput Geosci 13: 13-35
Grimm EC (1991) TILIA version 1.11. TILIAGRAPH version 1.18. In: Gear A (ed) A Users Notebook.
Illinois State Museum, Springfield, USA.
Hall RI and Smol JP (1999) Diatoms as indicators of lake eutrophication. In: Stoermer EF, Smol JP
(eds) The Diatoms: Applications for the Environmental and Earth Sciences. Cambridge University
Press, Cambridge, pp 128-168
Hann BJ (1990) Cladocera. In: Warner BG (ed) Methods in Quaternary Ecology. Geoscience
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Mollenhauer M (eds) Süsswasserflora von Mitteleuropa. Gustav Fischer Verlag, Stuttgart.
Margaritora FG (1985) Cladocera. Fauna D´Italia Vol. XXIII, Edizioni Calderini Bologna.
Røen UI (1995) Danmarks Fauna Bd. 85, Krebsdyr V, Gællefødder Branchiopoda og Karpelus
Branchiura. Dansk Naturhistorisk Forening, Viderup Bogtrykkeri A/S. (In Danish).
Rose NL (1994) A note on further refinements to a procedure for the extraction of carbonaceous flyash particles from sediments. J Paleolimnol 11: 201-204
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Holocene 5: 328-335
7
Figure 1 Aerial photograph of Boxford Water Meadows, Berkshire
a)
b)
Figure 2 Photograph of a) coring site at Boxford Water Meadows, and b) River Lambourn
adjacent to coring site
8
Figure 3 Map showing the location of the coring transect and site of the Russian core
BOXF1. The GPS coordinates of core BOXF1 and the core transect are overlaid on an Ordnance Survey
map from 1882. Channels within the water meadows on the west side of the river are clearly visible.
a)
b)
Figure 4 Photographs of Boxford Water Meadows core BOXF1, a) drive 1 (0-50 cm)
and b) drive 2 (40-90 cm)
9
Carbonate content analysis carried out on the 40-90 cm section only; no carbonate data for 0-40 cm section
DW, LOI 550 and carbonate content data are all expressed as percentages.
Figure 5 Summary stratigraphic diagram of Boxford Water Meadows core BOXF1
10
-1
g DM
0
2000
4000
6000
8000
0
2
4
6
8
10
Depth cm
12
14
16
18
20
22
24
26
28
Boxford (BOXF1) SCP Profile
30
Figure 6 Spheroidal carbonaceous particle concentration results for BOXF1
2010
1990
1970
1950
1930
1910
1890
1870
1850
1830
1810
0
2
4
6
8
10
SCP dates
12
137Cs
14
16
18
20
22
24
coring date
Figure 7 Depth-age profile for BOXF1 showing SCP data, the best available date from the
137
Cs data, and the coring date
11
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13
Note that taxa are represented by head capsules in all samples except for Chydorus spp. (0-70 cm), Alonella nana (70 cm), Graptoleberis testudinaria (30 cm),
Pleuroxus trigonellus (10 cm), Pleuroxus uncinatus (50 cm), Pleuroxus spp. (10-20 cm) which are represented by carapaces, and Simocephalus sp. (1 cm) which is
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90
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14