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M. Ravaioli et al.
bottom sampies were taken using a box corer (23 cm wide, 42 cm long and 50 cm
high), which collects a maximum volume of 38.6 1 over a surface of about 0.1 m2.
In order to assess latéral variability of benthic populations, seven replicate cores
were collected in the area of sites B and C, whereas at site A only two core replicates were taken, due to logistic constraints. Biogeochemical déterminations
were carried out on one or two sampies per site.
Sédiment sampies were described and X-radiographed; then grain size composition was obtained using common methods involving the use of sieves and an
X-ray sedigraph. Biogenic silica concentrations were determined by the progressive dissolution method suggested by DeMaster [13,14]. We used NaOH 0.5 N as
extradant, in view of large quantities of biogenic silica in our sampies. The
extraction was carried out on 20 mg of sample at 85 °C, by taking 0.2-ml aliquots
for analysis every hour for 4 h. Organic carbon and nitrogen were determined by
a Carlo Erba 1108 CHN Elément Analyser. The carbonate fraction was eliminated by a preliminary treatment of the sample with 2 N HCl directly in a silver capsule. Alpha counting of 210Po was used for 210Pb déterminations, assuming secular equilibrium between the two isotopes. 210Po was extracted from sédiments
and plated on silver dises as in Frignani and Langone [ 15 ]. To calculate the excess
210Pb (210Pbex) we assumed that supported 210Pb activity in each core is constant.
The value was estimated from the total activity at the base of the profiles, where
2l0Pb and 226Ra were considered to be in radioactive equilibrium. Mass depths in
cores were calculated from sédiment porosity, assuming a particle density of 2.5
g cm'3. Inventories were obtained integrating the excess 210Pb activity-depth profiles vs. mass depth. Expected 210Pbex inventories were calculated from the integrated production in the water column by 226Ra decay (0.2 dpm T1; Ku and Li,
1976, cited in [4]).
The stratification of the macrobenthos was studied, subdividing the sédiment
box core into various levels. At site A a maximum of three levels was considered
(0-5; 5-10 and 10-20 cm). At site B five levels were sampled (0-5,5-10,10-15,15-20
and below 20 cm). Finally, at site C, due to the features of the sédiments (pebbles
and coarse biodetritic material), and to the very different quantity of material
sampled in each of the replicates, the sédiment sections varied from two to three:
the interface, generally from the surface to the First 2 to 6 cm depth, the deeper
layer, generally from 2 6 to 10 cm depth, and the level below 10 cm, this latter
obtained only for two of the replicates. The sédiment of each section was sieved
with a 0.5 mm mesh size screen. The collected benthic organisms were fixed in 4%
formaldéhyde. The benthic macrofauna was separated into the major taxonomie
groups; for each site, ali specimens belonging to the different groups were counted. At each station the dominance of the major taxa and the total mean number
of individuals (expressed as number of individuals per square meter) were calculated, as well as the mean abundance in each of the sédiment layers considered for
the investigated site. A First évaluation of the potential of bioturbation of the
fauna was performed on the basis of the eto-ecological literature on the main
taxa.
M. Ravaioli et al.
bottom sampies were taken using a box corer (23 cm wide, 42 cm long and 50 cm
high), which collects a maximum volume of 38.6 1 over a surface of about 0.1 m2.
In order to assess latéral variability of benthic populations, seven replicate cores
were collected in the area of sites B and C, whereas at site A only two core replicates were taken, due to logistic constraints. Biogeochemical déterminations
were carried out on one or two sampies per site.
Sédiment sampies were described and X-radiographed; then grain size composition was obtained using common methods involving the use of sieves and an
X-ray sedigraph. Biogenic silica concentrations were determined by the progressive dissolution method suggested by DeMaster [13,14]. We used NaOH 0.5 N as
extradant, in view of large quantities of biogenic silica in our sampies. The
extraction was carried out on 20 mg of sample at 85 °C, by taking 0.2-ml aliquots
for analysis every hour for 4 h. Organic carbon and nitrogen were determined by
a Carlo Erba 1108 CHN Elément Analyser. The carbonate fraction was eliminated by a preliminary treatment of the sample with 2 N HCl directly in a silver capsule. Alpha counting of 210Po was used for 210Pb déterminations, assuming secular equilibrium between the two isotopes. 210Po was extracted from sédiments
and plated on silver dises as in Frignani and Langone [ 15 ]. To calculate the excess
210Pb (210Pbex) we assumed that supported 210Pb activity in each core is constant.
The value was estimated from the total activity at the base of the profiles, where
2l0Pb and 226Ra were considered to be in radioactive equilibrium. Mass depths in
cores were calculated from sédiment porosity, assuming a particle density of 2.5
g cm'3. Inventories were obtained integrating the excess 210Pb activity-depth profiles vs. mass depth. Expected 210Pbex inventories were calculated from the integrated production in the water column by 226Ra decay (0.2 dpm T1; Ku and Li,
1976, cited in [4]).
The stratification of the macrobenthos was studied, subdividing the sédiment
box core into various levels. At site A a maximum of three levels was considered
(0-5; 5-10 and 10-20 cm). At site B five levels were sampled (0-5,5-10,10-15,15-20
and below 20 cm). Finally, at site C, due to the features of the sédiments (pebbles
and coarse biodetritic material), and to the very different quantity of material
sampled in each of the replicates, the sédiment sections varied from two to three:
the interface, generally from the surface to the First 2 to 6 cm depth, the deeper
layer, generally from 2 6 to 10 cm depth, and the level below 10 cm, this latter
obtained only for two of the replicates. The sédiment of each section was sieved
with a 0.5 mm mesh size screen. The collected benthic organisms were fixed in 4%
formaldéhyde. The benthic macrofauna was separated into the major taxonomie
groups; for each site, ali specimens belonging to the different groups were counted. At each station the dominance of the major taxa and the total mean number
of individuals (expressed as number of individuals per square meter) were calculated, as well as the mean abundance in each of the sédiment layers considered for
the investigated site. A First évaluation of the potential of bioturbation of the
fauna was performed on the basis of the eto-ecological literature on the main
taxa.