(AMBI), to identify spatial and temporal impact gradients on benthic

ICES CM 2003/Session J-01
THE USE OF A BIOTIC INDEX (AMBI), TO IDENTIFY SPATIAL
AND TEMPORAL IMPACT GRADIENTS ON BENTHIC
COMMUNITIES IN AN ESTUARINE AREA
Iñigo Muxika, Á. Borja and J. Franco
AZTI Foundation
Department of Oceanography and Marine Environment
Herrera Kaia, Portualdea, z/g
20110 – Pasaia (Spain)
Tel: +34-943-004800; fax: +34-943-004801
e-mail: [email protected]
Abstract
Recently, several classification tools for the establishment of the quality of the marine
environment have been developed in Europe. Benthic macroinvertebrates are the most
traditionally used biological indicators of marine ecosystem health. AZTI has developed a
tool (AMBI: www.azti.es), which provides assistance in determining the impacts and quality
status within soft-bottom marine benthic communities; it is presently being used broadly
along European coasts. In this communication, this tool is applied to the determination of
spatial (at 8 sampling stations) and temporal (an 8 year data series) gradients within an
estuarine system, together with its adjacent coastal area. This analysis was undertaken in
order to determine both the impacts and improvement of the system quality. This tool has
demonstrated its usefulness in detecting punctual impacts, being less influenced by the
natural variability of the ecosystem.
Keywords: biotic coefficient, impact evaluation, soft-bottom benthos, spatial gradient,
temporal gradient
Introduction
Recently, several classification tools for the establishment of the quality of the marine
environment have been developed in Europe, based upon different biotic compartments, as
outlined below:
Phytoplankton
✓ IFREMER is developing a tool, based on phytoplankton in France.
Angiosperms and rocky shore communities:
✓ Swedish Classification Tool for Angiosperms and Rocky Shore Communities,
developed bay the Swedish Environmental Protection Agency (2000).
✓ Ecological Evaluation Index: developed in Greece by Orfanidis et al. (2001),
based upon seaweed and seagrasses.
Soft-bottom macrozoobenthos
✓ Norvegian Classification Tool: developed by Molvaer et al. (1997), integrating
chemical elements and benthic invertebrates.
✓ AMBI: developed by Borja et al. (2000), for use in European estuarine and
coastal environments.
✓ Bentix: designed by Simboura and Zenetos (2002), for use in Mediterranean
environments.
Fish
✓ Biological Health Index (BHI): developed in South Africa by Cooper et al.
(1994), it is currently being tested in the UK.
✓ Estuarine Fish Index (EFI): consists of seven metrics related to different
functional aspects of the estuarine fish assemblages in order to integrate the
quality of the ecosystem. It has been applied in the Scheldt estuary (Goethals et
al., 2002; Adriaenssens et al., 2002a; Adriaenssens et al., 2002b).
The AMBI (AZTI’s Marine Biotic Index) was developed to determine the impacts and
the quality status in soft-bottom marine benthic communities. Subsequently, it has been
applied under different impact sources, demonstrating its usefulness in detecting specific
localized impacts as well as “diffuse pollution” (Borja et al., 2003a). Nowadays, it is being
used broadly along European coasts. The principal advantage of this tool is that it is less
influenced by cyclical natural variability of the ecosystem, that by changes in impact sources.
The aim of this communication is to apply AMBI to an estuarine system (Plentzia,
Spain; Figure 1) and its adjacent coastal area, to determine the spatial gradient induced by the
pollution sources: (a) riverine imputs; (b) an aquaculture enterprise; (c) several outfalls,
discharging into the estuary until 1998; (d) and a submarine outfall (see Figure 2) in the zone
(Borja et al., 2003b). Likewise, the temporal evolution in the quality status, due to the
changes in those pollution sources.
Tallinn
Plentzia
Figure 1: Location of Plentzia (Spain) and Tallinn (Estonia).
Material and Methods
Station 1 was sampled from 1996 to 2002, Station 2 was sampled from 1995 to 2002
and three stations (3, 4 and 6) were sampled from 1997 to 2002, to establish the temporal
evolution. Station 1 is littoral; the other four are estuarine stations (Figure 2). Each of the
stations was sampled once a year, in autumn/winter.
11
2
1
10
9
8
Plentzia
d
2
c
3
4
7
5
6
b
a
Figure 2: Location of the sampling stations (1 to 11). The stations sampled from
1995 to 2002 are shown in red; the stations sampled from 1997 to 2002 are
shown in black. All the stations have been used to establish the spatial
gradient. The main pollution sources (a to d) are shown by arrows (for
explanation, see text).
Eleven locations were sampled in autumn/winter 2002/2003, to establish the spatial
gradient: Station 1 is in the littoral zone; Stations 2, 3, 4, 5, 6 and 7 are estuarine; and
Stations 8, 9, 10 and 11 are located inside Plentzia harbour (Figure 2).
For the calculation and interpretation of AMBI, see Borja et al. (2000, 2003a). The
representation of the values, in the various plots, was made by means of Surfer 8.
The load pollution index (LPI) was calculated on the basis of data abstracted from
Borja et al. (2003b) and Franco et al. (2002), following the methodology proposed by
Tomlinson et al. (1980). Heavy metals used to calculate LPI were: As, Cd, Cr, Cu, Fe, Hg,
Mn, Ni, Pb and Zn. Background levels were those proposed by Borja et al. (1997).
Results
Determination of temporal gradients
The temporal evolution for each of the stations is shown in Figure 3.
Station 1
Station 2
STATION 1
STATION 2
e
d
c
6
5
4
3
b
a
2
1
0
1996
1997
1998
1999
2000
2001
7
Biotic Coefficient
Biotic Coefficient
7
e
d
c
6
5
4
3
b
a
2
1
0
2002
1995 1996 1997 1998 1999 2000 2001 2002
Sampling Year
Sampling Year
Station 3
Station 4
STATION 3
STATION 4
7
e
d
c
6
5
4
3
Biotic Coefficient
Biotic Coefficient
7
b
a
2
1
0
1997
1998
1999
2000
2001
e
d
c
6
5
4
3
b
a
2
1
0
2002
1997
1998
1999
Sampling Year
2000
2001
2002
Sampling Year
Station 6
STATION 5
Biotic Coefficient
7
e
d
c
6
5
4
3
b
2
1
a
0
1997
1998
1999
2000
2001
2002
Sampling Year
Figure 3: Temporal evolution of AMBI (the Biotic Coefficient) for each station,
with the standard error shown as vertical error bars: a = unpolluted; b =
slightly polluted; c = meanly polluted; d = heavily polluted; e = extremely
polluted (Borja et al., 2000).
Station 1 was slightly polluted in 1997, 1999, 2000 and 2002, and unpolluted in 1996
and 1998; nevertheless, it was with very similar values and restricted standard errors.
Station 2 improved from 1995, when it was meanly polluted, to 1998 (slightly polluted
over the three years). In 1999, this location was classified as heavily polluted; however, it
improved to unpolluted in 2000. Subsequently, the AMBI has varied, but the station has been
classified as slightly polluted in 2001, as well as in 2002.
Station 3 has been classified as slightly polluted on all of the sampling occasions,
except in 2000 and 2001, when it was meanly polluted. However, the derived AMBI values
have been very similar throughout the time series.
Station 4 was classified as slightly polluted, from 1997 to 1999. Subsequently, it
worsened and has been classified as meanly polluted in 2000 and 2002. In 2001, it improved
a little and was classified again as slightly polluted, but the AMBI value was still higher than
in the first three years of the time series.
Station 6 varied less throughout the time series; it has been classified throughout as
meanly polluted.
Determination of the spatial gradient
The spatial gradient for each of the stations is shown in Figures 4 and 5.
Figure 4: Spatial gradient of the AMBI values, in 2002. Note: for locations of the
sampling stations, see Figure 2.
The sampling stations can be divided into 3 groups, in terms of their classification.
1. Stations located adjacent to the mouth of an estuary (Stations 1 and 2): slightly
polluted, with AMBI values ofaround 1.5.
2. “Estuarine” stations (3, 4, 5, 6 and 7): slightly polluted, but with AMBI values
of around 3.0, except for Station 4 which is meanly polluted but with a high
standard error (1.333).
3. Stations located in the harbour (8, 9, 10 and 11): meanly (the station located at
the mouth of the harbour) or heavily polluted.
7
e
d
Biotic Coefficient
6
5
c
4
3
b
2
1
a
0
1
2
3
4
5
6
7
8
9
10
11
Station
Figure 5: Spatial gradient of the AMBI values (Biotic Coefficient) in 2002. a =
unpolluted; b = slightly polluted; c = meanly polluted; d = heavily polluted;
e = extremely polluted.
Discussion
Temporal evolution
There are no important pollution sources within the estuary (Borja et al., 2003b). The
most important pollutants are transported by the river, from metallurgical and chemical
industries: the main source of organic matter are farms. Hence, it is not a particularly stressed
estuary. There are some sewerage works present and two water-treatment plants have been
constructed in 1998. However, there is no particular trend within the series. This particular
pattern could be explained in terms of the fact that the original situation was not particularly
bad, in terms of pollutant levels: almost all of the stations were only slightly polluted. There
is also a small outfall located near Station 1 (see Figure 2), but it does not seem to affect very
much to the benthic community. The most important changes in the AMBI can be explained
in terms of inputs under specific conditions, or through accidental waste disposal, through
outfalls that are not used normally, but are used in specific situations (as floods).
Spatial gradient
The spatial gradient is as expected. The inner stations are more stressed, in response to
changes in salinity pollutant inputs carried by the river. All of the stations in the estuary are
classified as slightly polluted, except Station 4 which is meanly polluted (situated near the
outfall of an aquaculture enterprise, see Figure 2). However, the outer stations (1 and 2) are
located adjacent to the no pollution limit (AMBI = 1.2); likewise, the inner stations (3, 5, 6
and 7) are located nearer to the mean pollution limit (AMBI = 3.3).
Inside the harbour, all of the stations are heavily polluted due to the restricted exchange
of waters. This restriction implies: (i) slow water renewal; (ii) important pollutant retention;
and (iii) increased levels of organic matter. The spatial gradient can be explained in terms of
water renewal: (i) Station 8, in the mouth, is meanly polluted and the standard error is large
(0.661), indicating a changing environment as the water enters and leaves, with the tidal
movement carrying sediments; (ii) Station 9, the inner location, which presents less water
renewal, (as such, it could be expected to be the most stressed station); (iii) Station 10,
similar to the previous station, but the AMBI value is lower, as this station is nearer to the
mouth of the harbour; (iv) Station 11 is very near to the mouth, presenting a lower value of
AMBI and a higher standard error (0.386), indicating a changing environment (but not as
important as at Station 8).
General Discussion
The contamination classification obtained using AMBI is listed in Table 3, with the
classification obtained using the LPI (Borja et al. 2003b). The classification obtained by both
methods appears consistent: the results are the same or very similar, except for Station 1 in
2001, Station 2 in 1995 and 1999, Station 4 in 2002, Stations 9 and 10 in 2002. These
inconsistencies may be related to the greater or less bioavailability of metals, within the
sediments.
Table 3: AMBI classification, LPI classification and classification by toxicity
criteria, for each station during each of the years. Key: UP=unpolluted;
SP=slightly polluted; MP=meanly polluted; HP=heavily polluted.
1995
1996
1997
1998
1999
2000
2001
2002
AMBI LPI AMBI LPI AMBI LPI AMBI LPI AMBI LPI AMBI LPI AMBI LPI AMBI LPI
St. 1
UP SP SP SP UP SP SP SP SP SP UP MP SP SP
St. 2
MP UP SP UP SP SP SP UP HP UP UP
SP SP SP SP
St. 3
SP SP SP SP SP SP MP SP MP SP SP SP
St. 4
SP SP SP SP SP SP MP SP SP MP MP UP
St. 5
SP SP
St. 6
MP SP MP SP MP SP MP SP MP SP SP UP
St. 7
SP SP
St. 8
MP
St. 9
HP SP
St. 10
HP SP
St. 11
HP
Conclusions
a. AMBI permits the visualisation of spatial gradients, as well as temporal gradients. The
results are consistent with those expected; They do not show any change, when there
are no changes in the pollution sources.
b. Nonetheless, the AMBI changes very rapidly when a new pollution source is introduced.
However, when an input disappears, the AMBI shows a slow recovery; this reflects the
slow recovery of the benthic community.
c. AMBI is very easily understandable and a program is freely available in www.azti.es,
which it can be calculated.
Acknowledgements
The study of the Plentzia estuary was supported by different contracts undertaken
between the Departmento de Ordenación del Territorio, Vivienda y Medio Ambiente of the
Basque Government and AZTI and between the Consorcio de Aguas Bilbao-Bizkaia and
AZTI. The study of Plentzia harbour was supported by a contract between Dirección de
Puertos of the Basque Government. One of the authors, I. Muxika was supported by a grant
from the Technological Centres Foundation of the Basque Country. We wish to thank also
Professor Michael Collins (School of Ocean and Earth Science, University of Southampton,
UK) for kindly advising us on some details of this paper.
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