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Comunicações Geológicas (2014) 101, Especial I, 1225-1229
IX CNG/2º CoGePLiP, Porto 2014
ISSN: 0873-948X; e-ISSN: 1647-581X
Multidisciplinary characterization of sediments from two
Portuguese river beaches for forensic application
Caracterização multidisciplinar de sedimentos de duas praias
fluviais do norte de Portugal para aplicação forense
Á. Carvalho1*, L. Dawson2, H. Ribeiro1, R. Mayes2, A. Guedes1,3, I. Abreu1,4,
F. Noronha1,3
Resumo
Abstract
© 2014 LNEG – Laboratório Nacional de Geologia e Energia IP
Abstract: Soil analysis is one of the most ancient applications of
Earth sciences to forensic case work. The inorganic and organic
features of soils, partially independent from each other, should be
taken into account when soil analysis is performed in order to
achieve improved resolution of comparison. In our study, seventyseven samples were collected during one year from two river
beaches located at the southern bank of the Douro river estuary in
Portugal to perform beach sediments characterization and
discrimination. Pollen, space plant wax-marker (n-alkane and
alcohols) and particle size distribution analyses were performed.
The results showed that the combination of these techniques
allowed the discrimination between two river beaches,
geographically close, and also in both beaches it was possible to
discriminate samples in relation to their distance from the river.
Seasonal effects were not relevant as a discriminant factor.
Keywords: River beach, Beach sediments, Pollen, Plant waxmarkers, Particle size distribution.
Resumo: A análise de solos é uma das mais antigas aplicações das
ciências da Terra a casos forenses. As características inorgânicas e
orgânicas dos solos, parcialmente independentes, devem ser tidas
em consideração aquando da realização de análise de solos a fim de
alcançar uma melhor resolução na comparação. No presente estudo,
com o objetivo de efetuar uma caracterização e discriminação de
sedimentos de praia, setenta e sete amostras foram colhidas durante
um ano em duas praias fluviais situadas na margem sul do estuário
do rio Douro. Foram realizadas análises polínicas, de
biomarcadores (n-alcanos e álcoois) e de distribuição
granulométrica. Os resultados mostraram que a combinação destas
técnicas permitem discriminar as duas praias fluviais,
geograficamente próximas, bem como as amostras em relação à sua
distância ao rio. Os efeitos sazonais não revelaram ser um
importante fator de discriminação.
Palavras-chave: Praia fluvial, Sedimentos de praia, Pólen,
Biomarcadores, Distribuição granulométrica.
1
Centro de Geologia da Universidade do Porto (CGUP), Portugal, Rua do
Campo Alegre 687, 4169-007 Porto.
Environmental and Biochemical Sciences and Ecological Group, James
Hutton Institute, Scotland, AB15 8QH.
3
Departamento de Geociências, Ambiente e Ordenamento do Território da
Faculdade de Ciências da Universidade do Porto, Portugal, Rua do Campo
Alegre 687, 4169-007 Porto.
4
Departamento de Biologia da Faculdade de Ciências da Universidade do
Porto, Portugal, Rua do Campo Alegre s/n, 4169-007 Porto.
* Corresponding author / Autor correspondente: [email protected]
2
1. Introduction
Soil can be analysed and used in legal matters helping in
the resolution of issues related with criminal,
environmental, humanitarian, military and engineering
forensic investigations (Ruffell & Dawson, 2009; Pringle
et al., 2012). Soil can hold a diversity of inorganic and
organic compounds, providing a fingerprint as a result of
its complex mix (types and proportion of materials),
originated from both natural and anthropogenic sources
(Dawson & Hillier, 2010). Its characterization normally
implies the identification of its components and
comparison of samples to establish their similarity, and
assessing whether it is possible to exclude samples from a
similar provenance (Morgan & Bull, 2007; Dawson &
Hillier, 2010).
As the soil comprises a large variety of components,
there are several analyses that can be performed, providing
different types of information in order to use soil in a
forensic investigation (Morgan & Bull, 2007; Dawson &
Hillier, 2010). The major mineralogical differences of soil
tend to vary at a regional scale, while the organic
component of soil which is associated with plants, animals
and microorganisms normally vary over more local scales
and time frames (Mayes et al., 2009; Dawson & Hillier,
2010). Several authors showed the usefulness of
performing a combination of different but complementary
methods of analysis that are not dependent upon each other
for their end result (Bull et al., 2008; Dawson & Hillier,
2010). To assess the usefulness of combined results of
pollen, plant wax markers and particle size distribution
analysed in beach sediments, seventy-seven samples were
collected in different seasons over a period of one year, in
two river beaches located at the southern bank of the
Douro river estuary in the North of Portugal.
2. Materials and methods
2.1. Sample collection and handling
The two river beaches selected were Areínho Oliveira do
Douro and Areínho Avintes in Vila Nova de Gaia.
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Samples were collected in all seasons of the year along
transects perpendicular to the river side and spaced 15 m
in both beaches. The same sampling procedure was used
on each date. In the Areínho Oliveira do Douro beach
samples were collected from eight locations and in the
Areínho Avintes beach from five locations. A more
detailed description of the method of sample collection
and handling can be found in Carvalho et al. (2013a).
2.2. Pollen analysis
Ten grams of material from each beach sediment sample
was submitted to a series of sequential chemical procedures
to remove mineral material and extraneous organic matter.
To remove the adhering fine organic material and the pollen
cytoplasm, samples were submitted to acetolysis.
Subsequently, pollen residue was mounted onto microscope
slides in glycerol jelly and the pollen types were identified
and quantified. A more detailed description of this method
can be found in Carvalho et al. (2013a).
2.3. Plant wax-marker analysis
Extraction of n-alkanes and alcohols was carried out on 0.5
g or 1 g aliquots of dried milled sieved (< 2 mm) bulk
samples using a protocol originally developed by Dove &
Mayes (2006) subsequently modified for sediment analysis.
The concentrations of internal standards were reduced; the
solvents were redistilled prior to use and glass silica-gel
fractionation columns were used. The alcohol fraction was
purified using a Urea adduction method. The n-alkanes and
alcohols were identified and quantified by reference to
standard mixtures.
A more detailed description of this method can be found
in Carvalho et al. (2013a).
2.4. Particle size distribution
After the removal of leaves, twigs and other discrete organic
items, the bulk samples were weighed prior to dry sieving.
The sieving was carried out using a column of ten sieves,
resulting in eleven size fractions for each sample: > 32 mm;
32-16 mm; 16-8 mm; 8-4 mm; 4-2 mm; 2-1 mm; 1-0.5 mm;
0.5-0.25 mm; 0.25-0.125 mm; 0.125-0.063 mm and < 0.063
mm. Each individual size fraction was weighed after
sieving. The data were analysed statistically using Microsoft
Office Excel 2007 and GRADISTAT software (Blott & Pye,
2001).
2.5. Statistical analysis
A hierarchical cluster analysis was performed in order to
ascertain if it was possible to obtain discrimination: i)
between composite season samples from both beaches
and ii) between composite samples along a profile of
each beach in each season, using the techniques that were
applied. The cluster analysis was performed on
standardized values in order to reduce effects of scale,
and the number of clusters was determined using: i) the
squared Euclidean distance as a distance measure and ii)
the Ward´s method as a linking method.
All the statistical analysis were performed using the
software SPSS (21.0).
3. Results and discussion
3.1. Pollen analysis
In the Areínho Oliveira do Douro beach seventy different
pollen types were identified. Pollen from trees was
dominant followed by pollen from herbs, grasses and shrubs
(Fig. 1a). In the Areínho Avintes beach sixty pollen types
were identified being the pollen from grasses dominant,
followed by pollen from herbs, trees and shrubs (Fig. 1b).
Spores had lower representativeness in both river beaches
(Fig. 1a, b) and they appeared mainly in the autumn
probably related with the fern species identified. Also,
similar pollen types were observed along the sampling
profile in each beach but the relative abundance of the
pollen was different, with some pollen types predominantly
found near the river and other ones furthermost from the
river. Horrocks et al. (1998) concluded that if soil samples
are localized in different areas even having similar
vegetation, they could have significantly different pollen
assemblages. Our study in sediment samples showed that
the pollen assemblages observed in both beaches differed in
their pollen relative abundance (Fig. 1a, b).
3.2. Plant wax-marker analysis
In both river beaches, the n-alkane and alcohol data showed
that their concentration increased moving landward (Fig.
1c, d, e, f). The Areínho Oliveira do Douro beach presented
a higher concentration of n-alkanes and alcohols than the
Areínho Avintes beach. Also, in the Areínho Oliveira do
Douro beach a higher concentration and a wider range of nalkanes was observed at the distance of 30 m from the river
which can be associated with the limit between the high
tide level and the starting growth of the overlying
vegetation. At this location a larger diversity of pollen was
found. This situation was not so apparent in Areínho
Avintes.
Plant wax markers together with pollen profile analysis
in soils were used by Dawson et al. (2004) to characterize
soil organic matter. Patterns and concentrations of nalkanes in the soil organic matter reflected globally the
signatures specific to the overlying vegetation. The
comparison between the n-alkane analytical results with the
ones obtained through pollen analyses revealed that these
two different sources of information were in agreement.
Carvalho et al. (2013a) obtained similar concordance
between pollen, n-alkane and alcohol indicators.
3.3. Particle size distribution
The Areínho Oliveira do Douro beach presented a relatively
homogeneous particle size distribution while the Areínho
Avintes beach revealed sediments more heterogeneous,
particularly in samples taken from different locations along
the Areínho Avintes sampling profile (Table 1). As had
already been observed in Carvalho et al. (2013b), as the
transect moved landward the samples showed an increase of
finer sediments.
Characterization of river beaches for forensic application
3.4. Statistical analysis
Analysing each technique individually it was not possible,
using cluster analysis, to obtain a clear discrimination
between samples from the two river beaches. However,
when all the techniques were combined, discrimination
was achieved by cluster analysis (Fig. 2a).
Combining the three techniques described in this study,
it was also possible to obtain, by cluster analysis, a good
discrimination between samples along the sampling
profiles from the two river beaches. In the Areínho
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Oliveira do Douro beach the sampling profiled was
discriminated into four groups: samples nearest the river (0
and 15 m), samples from the middle of the profile (45, 60,
75 and 90 m) and the sample location at 30 and at 105 m
separately (Fig. 2b). In the Areínho Avintes beach the
sampling profile was discriminated into three groups:
samples nearest the river (0 and 15 m), samples from the
middle of the profile (30 and 45 m) and sample furthest
from the river (60 m) (Fig. 2c). These clusters are probably
related with the influence of the river and the development
of plant species in the sands.
Fig. 1. Annual percentage of the pollen (a, b) and annual patterns of n-alkane signatures (c, d) and alcohol signatures (e, f) along the sampling profile and
profile averages (PA) of the Areínho Oliveira do Douro and Areínho Avintes river beaches (bars represent standard deviation; Areínho Oliveira do Douro,
n = 8; Areínho Avintes, n = 5).
Fig. 1. Percentagem anual de pólen (a, b) e padrões anuais de assinaturas de n-alcanos (c, d) e assinaturas de álcoois (e, f) ao longo do perfil de
amostragem e médias de perfil (PA) das praias fluviais do Areínho de Oliveira do Douro e do Areínho de Avintes (barras representam o desvio padrão;
Areínho de Oliveira do Douro, n = 8; Areínho de Avintes, n = 5).
Fig. 2. Dendogram of cluster analysis performed using average values from composite season samples (a) and composite profile samples (b, c), obtained
by the combination of all the results from the different analyses in the Areínho Oliveira do Douro (OD) and in the Areínho Avintes (Av) river beaches in
the North of Portugal (Sp = spring; Su = summer; A= autumn; W = winter; m = meters, distance from the river; 1–0 m, 2–15 m; 3–30 m; 4–45 m; 5–60 m;
6–75 m; 7–90 m; 8–105 m).
Fig. 2. Dendogramas de análise de grupos ou clusters realizado usando os valores médios a partir de amostras sazonais compósitas (a) e amostras
compósitas de perfis (b, c), obtidos pela combinação de todos os resultados das diferentes análises nas praias fluviais do Areínho de Oliveira do Douro
(OD ) e no Areínho de Avintes (Av) no Norte de Portugal (Sp = primavera; Su = verão; A = outono; W = inverno; m = metros, distância do rio; 1-0 m, 215 m; 3-30 m; 4-45 m; 5-60 m; 6-75 m; 7-90 m; 8-105 m).
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Á. Carvalho et al. / Comunicações Geológicas (2014) 101, Especial I, 1225-1229
Table 1. Descriptive analysis (after Folk & Ward, 1957) of the annual data related to the particle size distribution of the samples collected along the
sampling profiles in the Areínho Oliveira do Douro and in the Areínho Avintes river beaches.
Tabela 1. Análise descritiva (adaptada de Folk & Ward, 1957) dos dados anuais relacionados com a distribuição do tamanho das partículas das amostras
colhidas ao longo dos perfis de amostragem nas praias fluviais do Areínho de Oliveira do Douro e do Areínho de Avintes.
4. Conclusions
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Acknowledgements
Áurea Carvalho thanks the Fundação da Ciência e
Tecnologia (QREN-POPH-Type 4.1 Advanced Training,
subsidized by the European Social Fund and national funds
MCTES) for funding her PhD (SFRH/BD/61460/2009).
Helena
Ribeiro
benefits
from
a
scholarship
(SFRH/BDP/43604/2008) financed by QREN-POPH and
FCT. This work was supported by FEDER funds through
the Operational Program Competitiveness Factors –
COMPETE and National Funds through FCT –
Foundation for Science and Technology in the project
PEst-OE/CTE/UI0039/2011-UI 39.
The authors would like to thank Jasmine Ross for her
technical assistance and to the James Hutton Institute for
hosting the plant wax-marker laboratory analyses.
Characterization of river beaches for forensic application
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