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Marine Pollution Bulletin xxx (2008) xxx–xxx
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Distribution and ecological relevance of fine sediments
in organic-enriched lagoons: The case study of the Cabras
lagoon (Sardinia, Italy)
P. Magni a,b,*, G. De Falco a,b, S. Como b, D. Casu c, A. Floris d,
A.N. Petrov e, A. Castelli f, A. Perilli a,b
a
CNR-IAMC, National Research Council – Institute for Coastal Marine Environment Località Sa Mardini, Torregrande, 09072 Oristano, Italy
b
International Marine Centre, Località Sa Mardini, Torregrande, 09072 Oristano, Italy
c
Dip. di Botanica ed Ecologia vegetale, Università di Sassari, 07100 Sassari, Italy
d
Dip. di Zoologia e Genetica evoluzionistica, Università di Sassari, 07100 Sassari, Italy
e
Institute of Biology of the Southern Seas NASU, 99011 Sevastopol, Ukraine
f
Dip. di Biologia, Università di Pisa, 56126 Pisa, Italy
Abstract
In organic-enriched sedimentary systems, like many Mediterranean coastal lagoons, a detailed analysis of sediment grain size composition and partitioning within the muds is crucial to investigate sedimentological trends related to both hydrodynamic energy and
basin morphology. In these systems, sediment dynamics are particularly important because the partitioning and transport of fine sediments can strongly influence the redistribution and accumulation of large amounts of organic matter, and consequently the distribution
of benthic assemblages and the trophic status and functioning of a lagoon. Nevertheless, studies on benthic–sediment relationships have
been based mainly on a rather coarse analysis of sediment grain size features. In muddy systems, however, this approach may impede a
proper evaluation of the relationships and effects of the distribution of fine sediment and organic matter on the biotic benthic components. Here we show that the distribution of sedimentary organic matter (OM) and total organic carbon (TOC) in the Cabras lagoon
(Sardinia, Italy) can be explained (i.e., predicted) as a function of a nonlinear increase in the amount of the cohesive fraction of sediments
(68 lm grain size particles) and that this fraction strongly influences the structure, composition and distribution of macrobenthic assemblages. Even in such a homogeneously muddy system, characterized by ‘‘naturally” occurring impoverished communities, impaired benthic assemblages were found at 68 lm, OM, TOC contents of about 77%, 11% and 3.5%, respectively. A review of studies conducted in
Mediterranean coastal lagoons highlighted a lack of direct integrated analysis of sediment features and the biotic components. We suggest that, especially in organic-enriched coastal lagoons, monitoring programs should primarily investigate and consider the cohesive
fraction of sediments in order to allow a better assessment of benthic–sediment relationships and ecological quality of the system.
Ó 2007 Elsevier Ltd. All rights reserved.
Keywords: Fine sediments; Mud; Organic matter (OM); Macrofauna; Ecological quality; Coastal lagoons
1. Introduction
*
Corresponding author. Address: CNR-IAMC, National Research
Council – Institute for Coastal Marine Environment Località Sa Mardini,
Torregrande, 09072 Oristano, Italy. Tel.: +39 0783 22027; fax: +39 0783
E-mail address: [email protected] (P. Magni).
Transitional waters such as estuaries and coastal
lagoons are classified by the European Water Framework
Directive (WFD; 2000/60/EC) as one of the five categories
of ‘‘surface water”, which also include coastal waters, rivers, lakes, and artificial and heavily modified bodies of
water. Due to their partly saline character ‘‘substantially
0025-326X/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.marpolbul.2007.12.004
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influenced by freshwater flows” and their usually high sediment-surface-area to water-volume ratio, transitional
waters can be considered a very sensitive aquatic system
where benthic components and processes play an important regulatory function for the whole ecosystem (Viaroli
et al., 2004). Accordingly, there has been a major development of biotic benthic indices in Europe in recent years,
with special attention paid to the use of macroinvertebrate
communities, in assessing the ecological quality status of
coastal and estuarine waters (Borja et al., 2000; Simboura
and Zenetos, 2002; Rosenberg et al., 2004; Dauvin and
Ruellet, 2007; Muxika et al., 2007), as well as coastal
lagoons (Reizopoulou et al., 1996; Fano et al., 2003; Basset
et al., 2004; Ponti and Abbiati, 2004; Reizopoulou and Nicolaidou, 2007; Mistri and Marchini, in press). Comparisons
of different biotic indices and assessments of their applicability in different geographical areas of the world are now
also on the rise (Dı́az et al., 2004; Arvanitidis et al., 2005;
Magni et al., 2005a; Quintino et al., 2006; Fleischer et al.,
2007; Pranovi et al., 2007; Zettler et al., 2007; Blanchet
et al., in press; Borja et al., in press). In contrast, the physical and chemical characteristics of sediments appear to be
less explored and more controversial in terms both of their
integration in the biological elements and their relevance in
assessments of environmental quality (Crane, 2003; Borja
et al., 2004; Borja and Heinrich, 2005; Marı́n-Guirao
et al., 2005). This is particularly true in non-tidal (sensu
McLusky and Elliott, 2007) transitional systems, such as
Mediterranean coastal lagoons. Here, only recently quality/vulnerability biogeochemical tools and integrated measurements of status variables and system metabolism are
being proposed (Viaroli and Christian, 2003; Viaroli
et al., 2004; Giordani et al., in press).
It is a classical, general assumption that sedimentary
organic matter (OM) influences the composition and distribution of macrobenthos (Rhoads, 1974; Pearson and
Rosenberg, 1978; Gray, 1979). It is also well known that
the level of OM is related to the grain size composition of
sediments. In particular, a higher content of OM tends to
occur at an increasing mud (clay) content due to a greater
surface area and higher number of complexing sites of the
sediments (Buchanan and Longbottom, 1970; Mayer,
1994a,b; Tyson, 1995). A high mud content together with
excessive OM may then result in a lower permeation of
oxygen, an increased microbial oxygen uptake/demand
and a subsequent buildup of toxic byproducts (e.g.,
ammonia, dissolved sulphide) (Florek and Rowe, 1983;
Santschi et al., 1990; Fenchel et al., 1998). This can lead
to impoverished benthic communities, dominated by few
resistant r-selected opportunistic species (Dı́az and Rosenberg, 1995; Como et al., 2007). Notwithstanding combined and confounding effects of other major
environmental factors such as bathymetry and salinity
(e.g., Jones et al., 1986; Schlacher and Wooldridge,
1996; Teske and Wooldridge, 2003), clear patterns of
macrobenthos change have been demonstrated for some
time along marked gradients of mud and/or organic mat-
ter enrichment (e.g., Ishikawa, 1989; Quintino and Rodrigues, 1989). In fact, it appears that works on benthos–
sediment relationships in marine and estuarine waters
have been mainly based on a rather coarse analysis of
sediment grain size features, e.g., on the sand vs. mud
fractions, generally restricted to the few uppermost integrated centimeters (e.g., see Table 1 in Snelgrove and Butman, 1994). Several benthic studies on animal–sediment
associations have also been conducted in lagoon systems.
Especially in muddy systems, however, like many of the
coastal lagoons in the Mediterranean Sea, this approach
may be of little use. In contrast, a detailed analysis of sediment grain size composition within the muds may reveal
sedimentological trends related to both hydrodynamic
energy and lagoon morphology which are not detectable
otherwise (De Falco et al., 2004). In these often eutrophic
and organic-enriched systems, such analysis is important
also because the partitioning and transport of fine sediment particles may strongly influence the redistribution
and accumulation of large amounts of organic matter,
and consequently the distribution of macrozoobenthos
and the overall trophic status and functioning of a
lagoon. However, there is a lack of studies linking the distribution and dynamics of fine sediments to the distribution of benthic macroinvertebrate communities in
coastal lagoons.
In the present study, we aimed at assessing the relationships between the distribution of fine sediments, the levels
of organic matter in the sediments and the structure and
composition of macrobenthic assemblages in a Mediterranean lagoon system, as well as evaluating the overall ecological relevance of such relationships. For these
purposes, we used the Cabras lagoon (Sardinia, Italy) as
a case study, where we had previously conducted extended
surveys on both sediment characteristics (De Falco et al.,
2004) and macrozoobenthic assemblages (Magni et al.,
2004b, 2005b). For the present study, we made a detailed
analysis of sediment particle distribution within the muds,
with specific analytical size intervals of 0.5 lm, and focused
on the 68 lm grain size fraction of sediments (hereafter
‘‘fine sediments”). This was based on the fact that the
8 lm boundary is known to separate non-cohesive from
cohesive sediments (McCave et al., 1995) and because this
fraction was found to be most correlated with the total
organic carbon (TOC) content of sediments in the Cabras
lagoon (De Falco et al., 2004). As for the macrozoobenthos, the biomass of individual taxa as well as species’ richness and diversity, not used in our previous study (Magni
et al., 2004b), were analyzed together with the total abundances. A review of studies reporting OM and/or TOC
content of sediments, as well as grain size and biological
benthic features, in Mediterranean coastal lagoons was
also made. This was to provide a general assessment of
benthic–sediment studies and monitoring schemes in these
systems on a regional scale, as well as an operational
framework for both lagoon ecology and management
issues.
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2. Materials and methods
2.1. Study area
The Cabras lagoon is a shallow transitional system
located in the Gulf of Oristano, on the west coast of the
island of Sardinia (Italy), western Mediterranean Sea
(Fig. 1). With an area of about 22 km2, it is the largest
lagoon in Sardinia and one of the major brackish systems
of the western Mediterranean Sea. The drainage system
of the Cabras lagoon has a total extension of 432 km2
(Casula et al., 1999) and is characterized by two main tributaries called ‘‘Riu Mare Foghe” and ‘‘Riu Tanui”, located
in the northern and southern sectors of the lagoon, respectively. The ‘‘Riu Tanui” subtends a watershed which is
much smaller than the ‘‘Riu Mare Foghe”, but its contribution to the loading formation is very important because of
the presence of intensive agricultural activities in this area.
In addition, the ‘‘Riu Tanui” has been subjected to the disposal of untreated urban waste waters which were discharged into the Cabras lagoon till the year 2000.
Nutrient loading from the drainage basin has been calculated at 16 tons of total phosphorous and 240 tons of total
3
nitrogen per year (Casula et al., 1999). Despite the current
trend in increasing salinity caused by a progressive reduction of freshwater input and an increasing demand for
water for land use (e.g., agriculture), salinity may drop to
<10 psu following rainfall, while it rises to >30 psu during
dry periods (Magni et al., 2005b).
In the southern sector of the lagoon, the water exchange
between the lagoon and the adjacent Gulf of Oristano has
been severely affected by a channel constructed in the late
1970s, closed by a dam which raises the high-tide water
level (Fig. 1). Connection to the adjacent coastal sea of
the Gulf of Oristano is through narrow, convoluted creeks
which flow into the main channel (Como et al., 2007).
Additional man-made barriers were built in this area in
the late 1990s for capturing fish. The Cabras lagoon is thus
characterized by limited water exchange with the adjacent
gulf (tidal amplitude <25 cm). In contrast, tide- and
wind-induced currents seem to be effective in circulating
the internal water mass enough to influence the resuspension and distribution of fine sediment particles within the
basin (De Falco et al., 2004).
The Cabras lagoon historically has a high economic
rating due to fishery activities (e.g., Liza ramado, Mugil
Lagoon
inlet
Sampling
stations
39°59'N
Mare e Foghe
River
Down-core
samples
C2
C1
C4
C3
C7
C6
C5
C10
C9
C8
C14
C13
C12
C11
C18
C17
C16
C15
C24
C23
C22
C28
C27
Cabras
Lagoon
0
0
2 km
-5 m
-10 m
1km
western
Mediterranean
-20 m -10 m -10 m
C29
-5 m
ITALY
Gulf of
Oristano
Cabras
Lagoon
C21
C20
C19
C26
C25
C31
C30
Dam
Cabras
Tanui
River
Creeks
39°55'N
Gulf of Oristano
(western Mediterranean)
008°32'E
-10 m
Channel
-5 m
Sardinia
Lagoon
mouth
008°27'E
Fig. 1. Study area and location of sampling stations in the Cabras lagoon (Sardinia, western Mediterranean sea). indicates the nine stations where grain
size composition and organic matter (OM) content were determined in the 0–24 cm sediment horizon. The W-shaped dam in the southern sector of the
lagoon which limits the lagoon-gulf water exchange though the channel, and the two main tributaries ‘‘Riu Mare e Foghe” and ‘‘Riu Tanui” (northern and
southern sectors, respectively) are also indicated.
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cephalus, Anguilla anguilla) which involve about 250 fishermen, with a yearly fish catch up to about 850 tons
(400 kg ha1 year1), as in 1998 (Murenu et al., 2004).
However, especially during the warm season, there is a tendency for hypoxic and anoxic conditions to occur in nearbottom waters. This may lead to dystrophic events such as
the severe one which occurred in June 1999, causing a
major loss of the biological resources of the lagoon and a
drastic reduction of total catches in the subsequent years,
falling below 80 tons in 2002 (Murenu et al., 2004). In
2006, the total fish catch was reported to be still as low
as 120 tons. The major causes of these events are thought
to be eutrophication and excessive organic enrichment of
sediments, which cause the enhancement of sulphate reduction rates during the warm season and the subsequent
release of toxic dissolved sulphide from the sediment pore
water into the water column (Magni et al., 2005b, in press).
2.2. Field surveys and laboratory analysis
Four sampling campaigns were conducted between the
end of April and the beginning of May 2001. Thirty-one
sampling stations spaced 750 m one another were selected
on a regular grid covering the whole lagoon (Fig. 1). Previous published work (De Falco et al., 2004) reported the
analysis of sediment grain size composition, and organic
matter (OM) and total organic carbon (TOC) contents of
surface sediments (0–2 cm). For this work, we analyzed
the sediment vertical profiles from cores collected at nine
stations on the grid (see Fig. 1) using a manual corer
(40 cm long, 5.5 cm £). Sediment samples were sliced at
2 cm intervals (4 cm in the last layer) down to the 24 cm
layer. Sub-samples from each layer were analyzed for grain
size composition and OM content (see De Falco et al., 2004
for the description of the analytical procedure). At each of
the 31 stations (except Stns. 15 and 19), duplicate samples
were collected for macrozoobenthos using a 216 cm2
Ekman-Birge grab. In the laboratory, the macrozoobenthos were sorted, identified to the species level, when possible, counted under a stereo-microscope and preserved in
75% ethanol. Following a description of the spatial distribution of the abundances of the most dominant taxa
(Magni et al., 2004b), the wet weight (WW) biomass of
each taxa was obtained for this work after excess fluid
was carefully blotted off.
2.3. Data analysis
2.3.1. Sediment vertical profiles
The variability of sediment grain size and OM in the vertical profile (0–24 cm sediment horizon) of the nine sediment cores was evaluated using the Hierarchical Cluster
Analysis. Individual layers (n = 99) were used as the sample data. The entire grain size spectrum, expressed at one
phi intervals, and the OM contents were used as data input,
after the ranking of data value. The significance of the differences among groups of samples identified by the cluster
analysis was then tested by Discriminant Analysis. Grain
size (one phi interval) and OM data were used as data input
after ranking. Discriminant Analysis allowed us to investigate the significance of group separation, the weight of the
variables which provide the clustering, and the closeness of
the single cases (samples) to the centroids of the groups, in
order to individuate the outliers.
2.3.2. Relationships between sediment variables
The relationship between fine sediments (i.e., 68 lm
grain size particles) and OM was evaluated by means of
a nonlinear least-squares regression model (Bates and
Watts, 1988), using the nine sediment cores samples as
the input data (n = 99). The function was of the form:
y ¼ a ebe
cx
;
where y is the fine sediments (%), x is the OM (%), and a, b,
and c are the parameters of the equation, where a is the
‘plateau’ value (% fine sediments), b is the ln(a/i), and i is
the y value for x = 0, and c is the constant of the model.
According to this function, OM increases nonlinearly with
the increase of fine sediments up to a certain ‘plateau’ value, beyond which the OM increase is independent from
the percentage of fine sediments. The estimate of the a, b,
and c parameters is the result of the best fitting between observed data and the predicting function by minimizing the
square root of the sum of the square errors between observed and predicted values. A Non-Linear-Estimation
based on the Quasi–Newton algorithm for nonlinear optimization was used.
2.3.3. Macrozoobenthos and relationships with sediment
variables
Differences in macrozoobenthic assemblages were analyzed using a non-metric multidimensional-scaling
(nmMDS) ordination model based on the Bray-Curtis dissimilarity matrix (Clarke and Warwick, 2001) calculated on
the mean values among replicates within each station. A
one-way ANOSIM randomization/permutation test was
used to check for the significance of differences among
groups of stations identified by the nmMDS ordination
model (Clarke and Warwick, 2001). Taxa which contributed the most to these differences were identified by the
similarity percentages procedure SIMPER (Clarke and
Warwick, 2001). Correlation coefficients (R) were calculated in order to evaluate the relationships between sediment variables (i.e., 68 lm grain size particles, OM and
TOC) and the macrozoobenthos. The total number of species (S) and individuals (N, ind. 216 cm2), the total biomass (gWW 216 cm2), the Shannon–Weaver diversity (H0 ,
calculated with natural logarithm) index, and the abundances of taxa identified by SIMPER were used as the biological variables.
The graphical representation of the spatial distribution
of sediment variables and the total abundance and biomass
of macrozoobenthos was performed using the Surfer 7.0Ò
software. Smooth-line kriging was used as the gridding
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method, where the x and y data columns are the latitude
and the longitude of the sampling stations, respectively,
and the z data column is the selected variable. All statistical
analyses were done using the Statistica program of the
StatSoft Inc. (release 6.1) and the PRIMER v5.2 package
(Clarke and Warwick, 2001).
3. Results
3.1. Sediment vertical profiles
Fig. 2 shows the vertical profiles of fine sediments and
OM in the 0–24 cm depth horizon at nine stations randomly
chosen in the Cabras lagoon. At most stations, both variables showed a sharp increase in the uppermost layers. From
the whole set of data, irrespective of individual stations and
different layers, two major groups of samples were identified
by cluster analysis (plots not shown) as being characterized
by fine sediment contents of 74.3% ± 6.3 and 54.7% ± 14.3,
and OM contents of 9.3% ± 1.9 and 6.6% ± 1.6, respectively. By applying the Discriminant Analysis, the two
groups of samples (clusters 1 and 2) were found to be signif-
Sediment depth (cm)
Sediment depth (cm)
Sediment depth (cm)
icantly different from each other (93% allocation success,
d2 = 0.73, P = 0.0001). This allowed us to distinguish finer
organic-enriched samples from coarser less organicenriched samples consistently across different core levels,
as graphically represented in Fig. 3. Based on this analysis,
the thickness of the fine-grained, organic-enriched layer
was found to increase from north to south, most noticeably
at Stns. C22, C26 and C31. In contrast, near-shore stations
had fewer (Stn. C1) or no (Stn. C30) samples belonging to
the organic-enriched group.
3.2. Relationships between sediment variables
OM and TOC contents in the Cabras lagoon showed a
highly significant (P < 0.001) linear relationship, accounting TOC for 30% of OM (Fig. 4a). In contrast, the bestfit relationship between fine sediments and OM was
described by a nonlinear least-squares regression model
(Fig. 4b, see Section 2). According to this model, OM
increases progressively as fine sediments increase in the
range of about 3–7% and much faster in the range of about
8–12%. At 82% of fine sediment content, OM increase
≤8 µm (%)
≤8 µm (%)
30
60
90
0
50
0
75
≤8 µm (%)
100
50
0
5
5
5
10
10
10
15
15
15
20
25
≤8 µm
OM
C1
5
50
10
OM (%)
15
≤8 µm (%)
75
100
0
20
25
5
50
0
10
OM (%)
15
≤8 µm (%)
75
100
25
5
5
10
10
15
15
15
0
20
C18
5
50
10
OM (%)
15
≤8 µm (%)
75
100
25
0
5
0
10
OM (%)
15
≤8 µm (%)
30
60
25
5
5
10
10
15
15
15
20
C28
5
10
OM (%)
15
25
15
≤8 µm (%)
75
100
4
OM (%)
10
OM (%)
15
≤8 µm (%)
75
100
20
C30
0
C26
5
50
0
5
25
10
OM (%)
20
C22
10
20
100
C12
5
50
0
5
25
75
20
C6
10
20
5
8
25
C31
5
10
15
OM (%)
Fig. 2. Vertical profiles of fine sediments (i.e., 68 lm grain size particles) and organic matter (OM) at the nine stations (circled in Fig. 1) randomly chosen
in the Cabras lagoon. Note the different scales at some stations. Fine sediments (i.e., 68 lm grain size fraction): all stations 50–100% range, except Stns. C1
(30–90%) and C30 (0–60%); OM: all stations 5–15% range, except Stn. C30 (0–8%).
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a
5
y = 0.30x
R 2 = 0.75 (n=62)
TOC (%)
4
3
2
1
0
0
3
6
9
12
15
9
12
15
OM (%)
b
100
-3.2e
80
≤8 µm (%)
-0.36x
y = 82.1e
R 2 = 0.67 (n=99)
60
40
20
0
0
3
6
OM (%)
Fig. 4. (a and b) Relationships between (a) organic matter (OM) and total
organic carbon (TOC), and (b) OM and fine sediments (i.e., 68 lm grain
size particles). In (a), the grey circles refer to the surface sediment (0–2 cm)
samples (n = 31, see Fig. 7b and c); the black circles refer to the vertical
profiles of Stns. C1, C12, and C26 (OM: Fig. 2; TOC: De Falco et al.
(2004)). The linear regression line includes all samples (n = 62). In (b), the
best-fit nonlinear least-squares regression equation is represented (n = 99,
see Fig. 2).
Fig. 3. Graphical representation of individual-layer samples in nine core
sections (x-axis indicates the sediment depth in cm) belonging to either
Cluster 1 or Cluster 2 (see below legend) characterized by significantly
marked differences in fine sediment (i.e., 68 lm grain size particles) and
OM contents (tested by the Discriminant Analysis, see Section 2). Legend:
j Black samples: Cluster 1 (fine sediments [68 lm grain size particles]:
74.3% ± 6.3; OM: 9.3% ± 1.9). h White samples: Cluster 2 (fine sediments
[68 lm grain size particles]: 54.7% ± 14.3; OM: 6.6% ± 1.6).
reaches a plateau, indicating that any further increase is
independent of fine sediment content (Fig. 4b).
3.3. Macrozoobenthos and relationships with sediment
variables
As detailed in Magni et al. (2004b), macrozoobenthic
assemblages were mainly represented by polychaetes
(79.5%), oligochaetes (9.9%), crustaceans (5.7%) and bivalves (3.2%). Among the most dominant taxa, the serpulid
Ficopomatus enigmaticus and the spionid Polydora ciliata
accounted for 40.9% and 30.1% of the total abundance,
respectively. Polychaetes also dominated in biomass
(88.8%), with a major contribution of Neanthes succinea
(62.2%) and F. enigmaticus (21.3%). At individual stations,
the total abundance and biomass varied from 13.5 to
1552.5 ind. 216 cm2, and from 0.05 to 9.35 gWW
216 cm2, respectively.
Multivariate analysis revealed major differences in the
structure and species composition of macrozoobenthic
assemblages among three groups of stations (Fig. 5 and
Table 1). As indicated by the nmMDS ordination model
(Fig. 5), one group (hereafter ‘‘Central”) included stations
located in the relatively deeper, central sector of the lagoon
(mean water depth 1.9 m). The other two groups included
shallower stations (mean water depth 1.6 m) which were
named ‘‘Shore” and ‘‘Reef-shore” based on the exclusive
presence of F. enigmaticus in the latter group. The ANOSIM test confirmed the differences among these three
groups of stations (ANOSIM test, global R: 0.673,
P < 0.001). As indicated by the pairwise test, the highest
R values were found when comparing the Central with
Shore and Reef-shore stations (Table 1). Four taxa were
mainly responsible for the differences among the three
groups of stations (SIMPER, cut-off 60%; Table 2). F. enigmaticus was present exclusively in the Reef-shore stations.
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23
16 17
24
27
22
26 13
11 12
28
6
5
4
9
21
7
14
25
29
8
2
30
3
31
10
20
18
1
Fig. 5. Non-metric multidimensional-scaling (nmMDS) ordination model.
Stress = 0.15. Symbols: black circles [Central], grey triangles [Shore], white
squares [Reef-shore]. Stations number (see Fig. 1) is indicated.
Table 1
Results of pairwise test from one-way ANOSIM for differences among
groups of stations (Central, Shore, Reef-shore)
Also, at the Reef-shore stations the abundances of N. succinea and the oligochaetes Tubificidae were higher than
at the Central and Shore stations. In contrast, P. ciliata
was most abundant in the Central stations (Table 2).
A graphical representation of the distribution of macrozoobenthos clearly showed a marked spatial trend, with several central stations being the most impoverished both in
terms of total abundances and total biomass (Figs. 6a and
b). In contrast, the spatial distribution of fine sediments,
OM and TOC in the surface sediments showed an opposite
trend with values increasing from the near-shore to the central stations (Figs. 7a–c, respectively). Consistently, we
found several significant (P < 0.05) correlations between
macrozoobenthos and the sediment variables, all of them
negative (Table 3). Most noticeably, the fine sediments correlated negatively with most biotic univariate measures,
including S, N, and the total biomass, as well as the abundances of F. enigmaticus, Tubificidae and N. succinea.
Among the dominant taxa, N. succinea correlated negatively
with all three sediment variables considered in this study. In
contrast, P. ciliata did not show any significant correlation.
Group
R
P (%)
Possible
permutations
Actual
permutations
4. Discussion
Central vs. Shore
Central vs. Reef-shore
Shore vs. Reef-shore
0.782
0.688
0.383
0.1
0.1
1.3
38,760
817,190
5005
999
999
999
4.1. Fine sediment distribution and organic matter
enrichment
Table 2
Differences (< and >) in average abundance of taxa which contribute to
dissimilarity (cut-off 60%) between groups of stations (Central, Shore,
Reef-shore) identified by SIMPER
Ficopomatus enigmaticus
Tubificidae
Neanthes succinea
Polydora ciliata
Central
Shore
0
13.93
5.43
116.29
0
5.5
30.83
7.17
>
<
>
Reef-shore
<
<
<
<
373.89
65.56
34.67
89.11
7
Despite the fact that the relationship between sediment
grain size and organic matter is well known (e.g., Mayer,
1994b; Tyson, 1995), an evaluation of the distribution of
organic matter in relation to the sediment dynamics in
coastal lagoons has received less attention. Such an analysis is particularly important because the partitioning and
transport of fine sediments may strongly influence the
redistribution and accumulation of large amounts of sedimentary organic matter which often characterize these systems. In our companion paper (De Falco et al., 2004), we
Fig. 6. (a and b) Spatial distribution of (a) the total abundance (ind. 216 cm2) and (b) total biomass (gWW 216 cm2) of the macrozoobenthos.
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Fig. 7. (a, b, and c) Spatial distribution of (a) fine sediments (i.e., 68 lm grain size particles), (b) organic matter (OM), and (c) total organic carbon (TOC)
in surface sediments (0–2 cm) in the Cabras lagoon.
Table 3
Correlation coefficient R between sediment variables (fine sediments
[68 lm grain size], organic matter [OM] and total organic carbon [TOC])
and the total number of species [S] and individuals [N], total biomass,
Shannon–Weaver diversity [H0 ] index, and the most dominant taxa
identified by SIMPER (ns non-significant, *P < 0.05, **P < 0.01)
68 lm
*
OM
TOC
S
N
Biomass
H0
0.38
0.47*
0.50**
ns
ns
ns
ns
ns
0.43*
ns
ns
ns
Abundances
Ficopomatus enigmaticus
Tubificidae
Neanthes succinea
Polydora ciliata
0.41*
0.49**
0.44*
ns
ns
ns
0.38*
ns
ns
ns
0.39*
ns
Note: all significant correlations are negative.
showed that the surface sediments of the Cabras lagoon are
quite homogeneously muddy and that the spatial variability of TOC can be explained in terms of grain size fractionation within the muds. In particular, the 68 lm grain size
particles of sediments are found to be most strongly correlated with TOC, while the 8–64 lm fractions do not show
clear trends. The fractionation of muddy sediments has
been attributed to the resuspension of sediment in highenergy areas, resulting in a transport of fine sediments
and organic matter to the relatively deeper, low-energy sectors of the lagoon (De Falco et al., 2004). The primary
sources of organic matter in the sediments of the Cabras
lagoon can be related to both a high primary production
in the water column, with up to about 40 lg l1 of chlorophyll a measured in winter (Magni et al., unpublished), and
to an external input from the two main tributaries. As for
the latter input, the ‘‘Riu Mare Foghe” and the ‘‘Riu
Tanui”, in the northern and southern sectors of the lagoon,
respectively (Fig. 1), subtend watersheds with intensive
diary and agricultural activities, respectively. In addition,
the southern sector of the lagoon was subjected to the loading of high amounts of untreated urban waste waters discharged into the lagoon through the ‘‘Riu Tanui” until
2000. This helps explain a major accumulation of
organic-enriched fine sediments in several southern stations
of the lagoon (e.g., Stns. C22, C26, C31), as revealed by the
analysis of down-core profiles (Figs. 2 and 3). The findings
of this study also support our earlier hypothesis that the
construction of an artificial channel and a dam at the
lagoon’s inlet at the end of the 1970s has reduced the internal hydrodynamic energy of the lagoon (De Falco et al.,
2004). This may have favoured the trapping, deposition
and accumulation of organic C-bounding fine sediment
particles inside the lagoon over the past few decades.
In the present study, we also show that the distribution
of organic matter (OM) can be explained (i.e., predicted) as
a function of a nonlinear increase in the amount of fine sediments (i.e., 68 lm grain size particles). According to this
relationship (Fig. 4b), the OM content of sediments shows
two different trends. In its lower range (about 3–7%), OM
increases progressively as fine sediment increases, while in
the upper range of about 8–12% (or about 2.4–3.6% of
TOC) OM increases at a much faster rate than the relative
increase of fine sediments. Such a rapid increase is then followed by a plateau, indicating that at values of above 80%
of fine sediments, OM starts varying independently from
grain size, thus having a less predictable behaviour. The
above two OM ranges (3–7% and 8–12% OM) roughly correspond to the two groups of samples identified by Discriminant Analysis (Fig. 3), i.e., coarser less organicenriched samples (mean values: 54.7% 68 lm, 6.6% OM)
and finer organic-enriched samples (mean values: 74.3%
68 lm, 9.3% OM), respectively (Fig. 3). The latter samples
were mostly found in the upper layers of the sediment cores
suggesting that they can be used as a proxy for evaluating
the amount of organic matter accumulated in the sediments
over the last few decades. The relationship between OM
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and grain size thus clearly demonstrates the importance of
quantifying the amount of fine sediments present in each
lagoon system in order to evaluate the extent of organic
matter enrichment. In fact, the term ‘‘organic enrichment”
cannot be given an absolute value because it depends on
the system considered. This study provides one such an
example by defining threshold values and ranges of fine
sediments within the muds. This knowledge is also important because, in anthropogenic-polluted lagoons, the presence of high amounts of organic-C bounding fine
sediments can lead to the mobilization and transport of
contaminants (e.g., heavy metals), with a potential
enhancement of the toxic effects to biota.
4.2. Benthic–sediment relationships
This study provides novel insights on benthic–sediment
relationships using the Cabras lagoon, an enclosed, muddy
coastal lagoon of the Mediterranean Sea, as a case study.
In fact, while large variations in grain size composition
and/or organic matter content of sediments may evidence
clear patterns in the distribution of the benthos (e.g., Snelgrove and Butman, 1994), the muddy sediments often
found in Mediterranean coastal lagoons render such investigations more difficult. In addition, it is well known that
the lagoon systems are increasingly affected by excessive
inputs of nutrients and organic matter. This is often a
direct consequence of human activities (e.g., sewage discharge, fish farming) or an indirect consequence (e.g.,
eutrophication) of the same. These factors, as well as the
large environmental variability typical of these systems,
determine a selection of species and communities which
are able to cope with disturbed conditions and to recolonize relatively quickly (Magni et al., in press). Here, we
could assess the benthic–sediment relationships upon a
detailed analysis of grain size fractionation within the muds
(specific analytical size intervals of 0.5 lm), with a special
focus on the cohesive fraction of sediments (i.e., 68 grain
size particles). The most impaired benthic assemblages, in
terms of lowest species’ diversity and biomass, were found
in the central-southern sector of the lagoon. In particular,
one single species in the Central group stations, the spionid
P. ciliata, dominated numerically without showing any
negative correlation with fine sediments, OM or TOC
(Table 3). This is consistent with the fact that spionids
are very opportunistic and show high resilience after disturbances. In fact, larval and post-larval stages of Polydora
spp. are reported to colonize patches of sediment all year
round (Hansen, 1999). Furthermore, spionids are also
known to switch their feeding mode from filter feeding to
deposit feeding depending on the environmental conditions
such as hydrodynamics (Kihslinger and Woodin, 2000).
Consistently, the Central group stations were characterized
by the highest mean contents of fine sediments, OM and
TOC in the surface layer, i.e., 77.5% ± 1.6, 11.3% ± 0.3,
and 3.5% ± 0.1, respectively. In these organic-enriched sectors of the lagoon, the periodic occurrence of severe envi-
9
ronmental conditions (e.g., extreme hypoxia or anoxia)
and/or the development of toxic compounds (e.g., dissolved sulphide) strongly contribute to a major impoverishment of benthic assemblages (Magni et al., 2005b). The
TOC values found in the Central group stations support
the results of Hyland et al. (2005) who have shown a major
shift in the benthic data obtained from seven coastal
regions of the world and have highlighted the high risks
of reduced species richness at TOC values >3.5%. It is
our hope that synoptic data on the structure of benthic
communities and TOC content of sediments from different
lagoons will be merged and analyzed in order to further test
such relationships as a general screening-level indicator for
evaluating the likelihood of reduced sediment quality and
associated bioeffects in coastal lagoons (Magni et al.,
2005a).
Multivariate analysis of macrozoobenthos also revealed
that, in contrast, the serpulid F. enigmaticus was exclusive
to the Reef-shore group. We have previously shown that F.
enigmaticus, in association with the amphipod Corophium
sextonae, correlates positively with the sediment sorting
(r); an index of sediment selection due to hydrodynamic
energy (Magni et al., 2004b). This is consistent with the
inference that F. enigmaticus may take advantage of resuspended food particles along the shores with its filter-feeding
activity. In the Reef-shore stations, all dominant taxa,
including Tubificidae, N. succinea and P. ciliata, as well as
the highest number of species, abundances and biomass were
found. These results are consistent with the facilitative role
played by serpulid reefs. F. enigmaticus is an invasive cosmopolitan species which is highly tolerant of environmental
stress and anthropogenic disturbance (Bianchi and Morri,
2001). Extremely common in sheltered bays, coastal lagoons
and harbors, serpulid reefs can strongly modify the hydrological and sedimentary features of a basin by completely
refilling shallow areas (Schwindt and Iribarne, 2000; Bianchi
and Morri, 2001). At the same time, serpulid reefs create secondary hard bottoms (Bianchi and Morri, 2001). They
increase the habitat structures and provide refuge from predators for many, thus favouring the recruitment and the
coexistence of different animals (Bianchi and Morri, 1996;
Schwindt and Iribarne, 2000). Overall, stations along the
shores were characterized by lower contents of fine sediments, OM and TOC than the Central group stations. Here,
more oxygenated waters may help to explain the relatively
richer associations in spite of the opportunistic characteristics of the dominant taxa found in the Cabras lagoon,
including tubificids, nereids and spionids.
The relationship of the macrozoobenthos with fine sediments and OM was largely supported by the sediment
analysis of vertical profiles (i.e., 0–24 cm depth horizon).
In particular, several stations characterized by a thick layer
of fine-grained organic-enriched sediments, such as Stns.
C22, C26, and C28 (Fig. 3), had impoverished macrozoobenthos belonging to the Central stations (Fig. 5). In contrast, stations characterized by a vertical profile with
coarser, less organic-enriched sediments, such as Stns. C1
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and C31, had relatively richer macrozoobenthic assemblages belonging to the Reef-shore stations. The analyses
of sediment horizons also highlighted an increase of the
thickness of the fine-grained organic-enriched layer from
the north to the central-south area of the lagoon, the latter
considered to be critical in terms of development of dystrophic events. In a subsequent temporal study, we have
shown a marked impoverishment of the benthic communities in the southern sector of the lagoon at the end of summer (Magni et al., 2005b). This was thought to be the result
of severe hypoxic conditions and an increase in acid-volatile sulphide concentrations of sediments caused by excessive amounts of sedimentary organic matter. The results
of the present study clearly indicate the importance of
not restricting the analysis of sediment grain size features
and composition to a single uppermost layer. In fact, we
showed that a detailed analysis of the sectioned sediment
horizons was instrumental in assessing the extent (i.e.,
thickness) of the organic-enriched layer of sediments in different sectors of the lagoon (see also Magni et al., in press).
This allowed for a better evaluation of the ecological quality of the lagoon and the identification of areas characterized by impoverished assemblages which could be more
subject than others to the risks of developing dystrophic
crisis (Magni et al., 2005b, in press).
4.3. Implications for monitoring and ecological quality
assessment of coastal lagoons
A significant challenge in studying shallow transitional
waters such as estuaries and coastal lagoons is that they
are under the influence of multiple factors and have a great
internal patchiness and heterogeneity, which can often bias
the application of the most common indicators and indices
of environmental quality and health status. In these systems, water-quality criteria that are suited for deep lakes
and marine ecosystems cannot be used due to the shallow
depth, the pelagic components being quantitatively less
important than the benthic subsystem. Overall, in coastal
lagoons, the sediment-surface-area to water-volume ratio
is of paramount importance in determining levels of ecosystem metabolism throughout benthic communities.
There is therefore a need for a common, integrated set of
indicators and monitoring approaches for use in shallow
transitional waters that takes the unique properties of these
systems into account. Yet, because of the complexity of
most stressor–response relationships in nature, it is usually
impractical if not impossible to completely characterize all
contributing variables (Fisher et al., 2001). Under these circumstances, one should identify a set of basic benthic/sedimentary variables indicative of operative ecosystem
properties and functions, which could then be used for classification and quality-assessment purposes (Viaroli et al.,
2004; Hyland et al., 2005; Magni et al., 2005a).
This work aims at providing a scientific assessment of
benthic studies carried out on a regional scale in Mediterranean coastal lagoons in order to evaluate some general
features of these systems and the monitoring approaches
adopted. Coastal lagoons are often described as organicenriched sedimentary systems. However, this information
is mostly found in individual studies, while a quantitative
comparison of organic matter content of sediments in different lagoons at the regional (Mediterranean) level is lacking. Within this context, Table 4 provides an overview of
OM and TOC content of sediments reported for several
coastal lagoons in the Mediterranean Sea, as well as the
methodology used to determine them. The OM and TOC
contents indicate that these systems have generally much
higher values than those found in coastal marine and
estuarine systems (e.g., Tyson, 1995) when we exclude sites
impacted by aquaculture activities (e.g., Cancemi et al.,
2003) or accumulations of seagrass leaf litter (e.g., Como
et al., 2007). Table 4 also demonstrates the wide use of loss
of weight on ignition method (LOI) for OM determination.
Yet, it should be noted that there is a large variability
among studies in the analytical conditions used, such as
the temperature and the time of ignition, as well as in the
sediment layer considered, in most cases as being restricted
to one single uppermost layer. The Cabras lagoon was one
of the very few lagoons where both OM and TOC contents
were determined and the sediment horizon sectioned and
analyzed in detail, with values of both surface and several
deeper layers (Fig. 2) in the upper ranges of the studies considered. Whereas the determination of OM by LOI is a
more direct and less expensive procedure, it is a semi-quantitative method. A parallel analysis of organic matter using
a CHN analyzer is strongly suggested, at least on a subset
of samples, in order to obtain a more accurate measure of
the total organic carbon content of sediments (Leong and
Tanner, 1999). The determination of OM by LOI could
then be reasonably employed on a larger group of samples,
e.g., for routine/monitoring surveys, applying site-specific
OM vs. TOC conversion factors. In fact, we suggest that,
due to the large variability in the pool of sedimentary
organic matter in the lagoon systems (e.g., Pusceddu
et al., 1999; Frangipane, 2005), such relationships should
be tested and applied in each individual lagoon. On a
related note, we must caution that methodological differences in the determination of OM among the various studies (Table 4) may render a comparison difficult between
different lagoons and/or studies if no proper standardization is made.
The analysis of case studies reported in Table 4 also
highlights that sediment grain size is often not considered
at all (about half of cases), with only 9 out of 40 studies
reporting combined analysis of grain size, organic matter
(either as OM or TOC) and benthic communities. Furthermore, among these cases, grain size data are mostly
reported to describe the general characteristics of sediments
of the investigated environment without any statistical correlation with the chemical and biological variables. Confounding terms are even used sometimes to describe
sediment classes (e.g., the use of the term ‘silt’ is sometimes
referred to the <63 lm grain size intervals). This review
Please cite this article in press as: Magni, P. et al., Distribution and ecological relevance of fine sediments ..., Mar. Pollut. Bull. (2008),
doi:10.1016/j.marpolbul.2007.12.004
Lagoon
Subbasin
Sediment
layer (cm)
OM (%)a
TOC (%)e
Grain size
Benthos
Authors
De Falco and
Guerzoni (1995)
Mesnage and Picot
(1995)
Bartoli et al. (1996)
Mean and/or
range(s) (±SD)
LOI temperature/
time
Mean and/or
range (±SD)
Variable used
Method
350 °C/18 h
Nd
Sand–Mud
Sieve + Laser
Nd
Nd
0.67-4.84
Sand–Silt–Clay
Laser
Nd
550 °C/‘‘Until
constant weight”
500 °C/6 h
Nd
Nd
Nd
Nd
Nd
Sand–Silt
Sieve
Nd
450 °C/24 h
Nd
Nd
Nd
Nd
Nd
2.4 ± 1.6 (0.1–6.3)
Sand–Silt–Clay
Na
Nd
SWE
0–5
NWE
0–5
2.0 ± 1.2–
10.0 ± 3.0
Nd
3. Prévost (France)
NWE
0–10
10.1 ± 1.4
4. Thau (France)
NWE
0–5
5. Sacca di Goro (Italy)
ADR
0–2
6. Nador (Morocco)
ALB
‘‘Surface”
1.3 ± 0.2–
5.0 ± 2.5
5.3 ± 1.0–
13.7 ± 1.9
Nd
7. Méjean-Pérols (France)
8. Venice, Palude della Rosa
(Italy)
9. Stagnone Marsala (Italy)
NWE
ADR
0–5
0–5
Nd
6.8–12.8
Nd
550 °C/Na
5.1 (2.6–7.1)
Nd
Sand–Silt–Clay
Nd
Laser
Nd
Nd
Macrobenthos
TYR
0–1
10.4–17.2b
450 °C/2 h
1.37–2.37f
Nd
Nd
Nd
10.
11.
12.
13.
TYR
ADR
TYR
SWE
0–2
0–2
0–1
0–5
Nd
550 °C/3 h
450 °C/4 h
600 °C/Na
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Macrobenthos
Ndi
14. Sacca di Goro (Italy)
ADR
0–10
450 °C/4 h
Nd
Sand–Silt–Clay
Sieve + Pipette
Macrobenthos
15. Bardawil (Egypt)
SLE
0–2
Nd
11.4 ± 3.5
4–16h
9.4 ± 8.7 (0.6–
23.6)
12.0 ± 0.1–
16.4 ± 0.1
Nd
De Casabianca et al.
(1997)
Giordani et al.
(1997)
El-Alami et al.
(1998)
Gomez et al. (1998)
Tagliapietra et al.
(1998)
Pusceddu et al.
(1999)
Added (2001)
Azzoni et al. (2001)
Lardicci et al. (2001)
Draredja and Beldi
(2001)
Mistri et al. (2001)
Nd
Sand–Silt–Clay
Sieve + Pipette
Nd
Taher (2001)
16. Fattibello and Spavola
(Italy)
17. Lesina (Italy)
18. Valli di Comacchio (Italy)
19. Berre (France)
ADR
0–2
Nd
Nd
Sand–Mud
Frascari et al. (2002)
Nd
7–20h
Nd
Nd
500 °C/Na
Nd
Meiobenthos
Macrobenthos
Macrobenthos
20. Cabras (Sardinia, Italy)
SWE
0–1
0–0.5
‘‘Sed–water
interface”
0–2
Sieve-X-ray
Sedigraph
Sieve
Nd
Laser
Nd
ADR
ADR
NWE
1.2 ± 0.45 (0.87–
2.4)
2.34 ± 1.16–
2.85 ± 1.04
0.4–1.7f
Nd
2.30–2.93
500 °C/3 h
21. Monolimni (Greece)
22. Cabras (Sardinia, Italy)
23. Stagnone Marsala (Italy)
AEG
SWE
TYR
0–10
0–2
0–10
Na
Nd
450 °C/4 h
24. Tsopeli, Tsoukalio, Rodia
and Logarou (Greece)
ION
0–2
10.5 ± 2.4 (3.5–
14.3)
0.15–2.2
Nd
0.6 ± 0.1–
15.6 ± 1.3
Nd
Gambi et al. (2003)
Munari et al. (2003)
Rosenberg et al.
(2003)
De Falco et al.
(2004)
Kevrekidis (2004)
Magni et al. (2004b)
Mirto et al. (2004)
25. Papas (Greece)
ION
0–2
Nd
Nd
26. Molino (Italy)
ADR
0–3
7.8–13.4
Na
Ghar El Melh (Tunisia)
Valle Smarlacca (Italy)
Orbetello (Italy)
Mellah (Algeria)
Nd
3.28 ± 0.72 (0.96–
4.29)
Nd
Nd
0.2 ± 0.1–
2.1 ± 0.6f
2.82 ± 1.55–
3.11 ± 0.96 (1.1–
5.3)
4.61 ± 0.17 (2.95.6)
Nd
Sand–Mud
Nd
Sand–Mud
All grain size spectra
(one phi interval)
Median
Statistical moments
Nd
Sieve + Laser
Ndj
Sieve + Pipette
Sieve + Laser
Nd
Macrobenthos
Macrobenthos
Meiobenthos
Sand–Silt–Clay
Sieve + Pipette
Macrobenthos
Sand–Silt–Clay
Sieve + Pipette
Macrobenthos
Nd
Nd
Reizopoulou and
Nicolaidou (2004)
Reizopoulou and
Nicolaidou (2004)
Macrobenthos Sorokin et al. (2004)
(continued on next page)
ARTICLE IN PRESS
1. S’Ena Arrubia (Sardinia,
Italy)
2. Thau (France)
P. Magni et al. / Marine Pollution Bulletin xxx (2008) xxx–xxx
11
Please cite this article in press as: Magni, P. et al., Distribution and ecological relevance of fine sediments ..., Mar. Pollut. Bull. (2008),
doi:10.1016/j.marpolbul.2007.12.004
Table 4
Comparison of organic matter (OM) and total organic carbon (TOC) content of sediments in Mediterranean coastal lagoons
12
Lagoon
Subbasin
Sediment
layer (cm)
27. Lesina (Italy)
ADR
28. Venice (Italy)
OM (%)a
TOC (%)e
Grain size
Authors
Sieve
Meiobenthos
Sieve + Pipette
Ndk
Fabbrocini et al.
(2005)
Frangipane (2005)
Nd
Macrobenthos
Magni et al. (2005b)
Nd
Nd
Macrobenthos
Median
Sieve + Pipette
Macrobenthos
Sand–
Mud
Nd
Sieve
Nd
Marı́n-Guirao et al.
(2005)
Mogias and
Kevrekidis (2005)
Sfriso et al. (2005)
Nd
Nd
Nd
Sieve-X-ray
Sedigraph
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Sand–
Silt–Clay
Nd
Nd
Macrobenthos
Nd
450 °C/2 h
Nd
Nd
Nd
Nd
1.9–16.7
500 °C/3 h
0.48–4.25
Nd
Nd
Macrobenthos
8.1 ± 2.2 (2.6–12.9)
500 °C/3 h
3.28 ± 0.72 (0.96–
4.29)g
68 lm
Sieve + Laser
Macrobenthos
LOI
temperature/
time
Mean and/or
range (±SD)
Variable
used
Method
0–5
9.8 ± 1.7–17.3 ± 1.3
550 °C/3 h
Nd
ADR
0–5
0.3–22.3
350 °Cc/16 h
0.21–15.0
29. Cabras (Sardinia, Italy)
SWE
0–2
500 °C/3 h
Nd
30. Mar Menor (Spain)
SWE
0–5
14.5 ± 3.1 (8.6–
22.2)
2.2 ± 0.1–8.2 ± 0.3
Sand–
Mud
Sand–
Silt–Clay
Nd
450 °C/6 h
31. Laki (Greece)
AEG
0–10
0.31–2.15
Na
0.90 ± 0.02–
1.60 ± 0.24
Nd
32. Venice, central basin (Italy)
ADR
0–5
Nd
Nd
0.3–2h
33. Bizerte (Tunisia)
TYR
‘‘Top”
Nd
Nd
0.23–1.91
34. Marsala (Italy)
35. Tsopeli, Tsoukalio, Rodia and
Logarou (Greece)
36. Valle Smarlacca (Italy)
37. Lesina (Italy)
TYR
ION
0–1
‘‘Surface”
0.8–5.2d
Nd
450 °C/4 h
Nd
Nd
2.92–6.55
ADR
ADR
Na
0–5
550 °C/8 h
450 °C/2 h
38. Sacca di Goro (Italy)
ADR
0–5
3.5–17.7
12.9 ± 1.5–
22.8 ± 1.6b
1.8 ± 1.0–14.5 ± 0.6
39. Santa Giusta (Sardinia, Italy)
SWE
0–20l
40. Cabras (Sardinia, Italy)
SWE
0–24l
Trabelsi and Driss
(2005)
Culotta et al. (2006)
Karageorgis (2007)
Ponti et al. (2007)
Giordani et al. (in
press)
Giordani et al. (in
press)
Magni et al. (in
press)
This study
Details on sediment grain size and benthic invertebrate assemblages are also given when available (SD: standard deviation; Nd: not determined; Na: not available). Lagoons were classified according to
the ten marine sub-basins in which the whole Mediterranean basin is usually divided (UNEP/FAO/WHO/IAEA (1990)). ADR, Adriatic Sea; AEG, Aegean Sea; ALB, Alboran Sea; ION, Ionian Sea;
NWE, Northwestern Mediterranean Sea; SLE, South-Levantine Sea; SWE, Southwestern Mediterranean Sea; TYR, Tyrrhenian Sea (not present: Central Sea and North Levantine Sea sub-basins).
Studies are listed by the year of publication and, within one year, by alphabetical order of Authors.
a
Organic matter (OM) determined by loss of weight on ignition (LOI), except: Sorokin et al., 2004 (wet chromic oxidation, assuming 40% of TOC in OM); Kevrekidis, 2004; and Mogias and
Kevrekidis, 2005 (oxidation by H2O2).
b
OM bulk in the highest range mainly associated with angiosperms.
c
OM determined by fractionation at various temperatures (i.e., 250 °C, 350 °C, 450 °C, and 550 °C).
d
OM determined after elimination of carbonates.
e
Total organic carbon (TOC) determined by CHN elemental analyzer, except: Mesnage and Picot, 1995 (reported as a pers. comm. by Gadel); El-Alami et al., 1998; Pusceddu et al., 1999; Gambi
et al., 2003; Mirto et al., 2004 (colorimetric method); Added, 2001 (chemical oxidation); Reizopoulou and Nicolaidou, 2004 (Tsopeli, Tsoukalio, Rodia and Lagarou lagoons: titration); Trabelsi and
Driss, 2005 (titration). In Sfriso et al. (2005), TOC calculated as the difference between total carbon and inorganic carbon (determined by CHN elemental analyzer).
f
Biopolymeric carbon (sum of carbohydrate, protein and lipid C-equivalents).
g
Based on De Falco et al. (2004).
h
Values estimated from figure.
i
Macrobenthos investigated by: Draredja (2005).
j
Macrobenthos investigated by: Magni et al. (2004b).
k
Macrobenthos investigated by: Pessa (2005).
l
Sectioned cores at 2 cm intervals.
ARTICLE IN PRESS
Benthos
Mean and/or
range(s) (±SD)
P. Magni et al. / Marine Pollution Bulletin xxx (2008) xxx–xxx
Please cite this article in press as: Magni, P. et al., Distribution and ecological relevance of fine sediments ..., Mar. Pollut. Bull. (2008),
doi:10.1016/j.marpolbul.2007.12.004
Table 4 (continued)
ARTICLE IN PRESS
P. Magni et al. / Marine Pollution Bulletin xxx (2008) xxx–xxx
highlights that (bio)geochemical approaches often do not
consider benthic-community features, while biologicallyoriented approaches lack an evaluation of the (bio)geochemical properties of a specific lagoon system.
A final consideration can be made of the geographical
distribution of the studies analyzed here. The Adriatic
sub-basin was the most studied area (ADR, 14 out of 40
studies) followed by the southwestern sub-basin (SWE,
eight out of 40 studies), whereas significant data gaps
existed in the south and southeastern basin. In addition,
most studies (87.5%) were conducted in fewer European
countries (Italy, France, Greece, and Spain). This calls
for increased cooperation and coordination among scientists and institutions in the whole Mediterranean basin
towards a better understanding of the lagoon and of
coastal marine and estuarine systems at the regional (basin)
level (Magni, 2003; Magni et al., 2004a).
Overall, it appears that much still remains to be done
with regard to the monitoring of Mediterranean coastal
lagoons and the integration of the results from different disciplines, such as analysis of sediment grain size and compositional trends in relation to the distribution and
composition of the biotic components. We have provided
here a framework for evaluating the importance of investigating the distribution and dynamics of fine sediments in
relation to both organic enrichment and benthic macroinvertebrate communities. We suggest that monitoring programs, especially in organic-enriched lagoons, should
consider the sediment fraction most tightly correlated with
organic matter (often being the overlooked cohesive fraction of sediments) to be integrated in direct correlation
analysis with other major abiotic (e.g., TOC) and biotic
(e.g., benthic assemblages) variables in order allow a better
assessment of benthic–sediment relationships and the ecological quality of the system.
Acknowledgements
This paper was elaborated as part of the SIGLA project
(Sistema per il Monitoraggio e la Gestione di Lagune ed
Ambiente) funded by the Italian Ministry for Scientific Research. We gratefully acknowledge an anonymous reviewer
for providing insightful comments on the manuscript. It is
contribution number MPS-08001 of the EU Network of
Excellence MarBEF.
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