128
P. Rossini et at
Atmospheric versus Riverine Fluxes
In order to evaluate the role of atmospheric
deposition to aquatic surfaces, we calculated the
supply rates of metals to the lagoon of Venice
(surface area = 546 km 2 ) and to the northern
Adriatic Sea (Tables 3 and 4), and compared
them with riverine loads. For Venice we examined data for several river tributaries of the
lagoon (Silone) Dese. Osellino, Naviglio, Brenta.
Loca, Taglio Novissimo,Montalbano and Trezze), .
and for the north Adriatic sea comparisons were
made with the Po. As Table 3 shows, compared
with riverine inputs of respectively 0.42, 4.0 and
5.5 tonnes year-I, at Venice one-third of Cd (0.12
tonnes year I ), nearly half of Ni (1.9 tonnes
yearI) and an almost equal amount of Cu (6.2
tonnes year l ) is atmospherically derived, whereas the deposition flux of Pb is estimated to be
11.5 tonnes year-I, i.e. 60% higher than the riverine input of 7 tonnes year-l. For comparison with
the Po, the atmospheric deposition was obtained
by averaging data recorded in 1995-96 at the
Cesenatico, AGIP and Venice stations. The deposition area of 25000 km 2 was chosen for budget
purposes within the PRISMA project (a research
Table 3. Supply rates of metals to the lagoon of Venice
(tonnes year-I). Atmospheric annual deposition obtained by
averaging three years of data recorded in 1993-97. Deposition
area = 546 km 2
Cd
Cu
Ni
Pb
Rivers .. b
0.42
5.5
4.0
7.0
Atmosphere'
0.12
6.2
1.9
11.5
Atmlrivers
0.3
1.1
0.5
1.6
• Arcan et al. (1985)
b Bernardi et al. (1986)
C Atmospheric annual deposition obtained by averaglng three years of
data recorded in 1993-97. Deposition area = 546 km a
Table 4. Supply rates of metals to the northern Adriatic
(tonnes year l )
Rivers poa
Atmosphere b
AtmlPo
Cd
7
5
0.7
a Camusso et aL (1993)
Cu
281
201
0.7
Ni
514
63
0.1
Pb
151
300
2.0
b Atmospheric deposition is obtained by averaging data recorded in
1995-96 at Cesenatico, AGIP and Venice. Deposition area =25000 km 2
programme on the Adriatic Sea from the Italian
government). In this area the total amount of
water load was estimated to be 20x10 9 m 3 ·year-1,
equivalent to 40% of the mean annual discharge
of the Po River (Tartari et al. 1997). As Table 4
shows, compared with riverine inputs of respectively 7. 281 and 514 tonnes year I , in the northern Adriatic an almost equal amount of Cd (5
tonnes yearI) and Cu (20l tonnes year-I) and
nearly 1/10 of Ni (63 tonnes year I ) is atmospherically derived, whereas the deposition flux of
Pb (300 tonnes year-I) is twofold higher than
riverine input (151 tonnes year I ).
The extrapolation of these deposition data to
calculate the atmospheric flux of metals must be
considered with care. The high spatial and temporal variability of atmospheric transport and
deposition, coupled with the short duration of
oceanographic research cruises, made it difficult
to obtain good estimates of atmospheric deposition to those areas of the open sea devoid of
islands at which continuous sampling can be
undertaken. Encouragingly, however, recent
results from ship-board collections of aerosol
metals over the North Sea, where a steep spatial
gradient in aerosol concentration is found, are
comparable with samples collected at the coast
(Guerzoni et al. 1999). This finding suggests that
atmospheric fluxes estimated from coastal sites
may be extrapolated to adjacent marine areas.
Thus, even though it would be important to have
more sampling stations, the data derived from
our study can usefully increase knowledge of
eolian deposition in the North Adriatic.
Conclusions
1. Bulk samplers may be useful to assess the
importance of atmospheric loads at sea in
sites where sampling is difficult to manage.
2. Total daily fluxes of metals were very variable
at all stations; the highest fluxes were
observed at urban sites, and the lowest at sea.
3. Atmospheric loads of Cd and Pb were comparable with estimates made by other
Authors in different Mediterranean coastal
sites.
4. The atmospheric deposition observed at
Venice was 2- to 7-fold higher than that of
Cesenatico for Ni, Cu, and Pb, and comparable for Cd.
5. The magnitude of atmospheric input indi-
P. Rossini et at
Atmospheric versus Riverine Fluxes
In order to evaluate the role of atmospheric
deposition to aquatic surfaces, we calculated the
supply rates of metals to the lagoon of Venice
(surface area = 546 km 2 ) and to the northern
Adriatic Sea (Tables 3 and 4), and compared
them with riverine loads. For Venice we examined data for several river tributaries of the
lagoon (Silone) Dese. Osellino, Naviglio, Brenta.
Loca, Taglio Novissimo,Montalbano and Trezze), .
and for the north Adriatic sea comparisons were
made with the Po. As Table 3 shows, compared
with riverine inputs of respectively 0.42, 4.0 and
5.5 tonnes year-I, at Venice one-third of Cd (0.12
tonnes year I ), nearly half of Ni (1.9 tonnes
yearI) and an almost equal amount of Cu (6.2
tonnes year l ) is atmospherically derived, whereas the deposition flux of Pb is estimated to be
11.5 tonnes year-I, i.e. 60% higher than the riverine input of 7 tonnes year-l. For comparison with
the Po, the atmospheric deposition was obtained
by averaging data recorded in 1995-96 at the
Cesenatico, AGIP and Venice stations. The deposition area of 25000 km 2 was chosen for budget
purposes within the PRISMA project (a research
Table 3. Supply rates of metals to the lagoon of Venice
(tonnes year-I). Atmospheric annual deposition obtained by
averaging three years of data recorded in 1993-97. Deposition
area = 546 km 2
Cd
Cu
Ni
Pb
Rivers .. b
0.42
5.5
4.0
7.0
Atmosphere'
0.12
6.2
1.9
11.5
Atmlrivers
0.3
1.1
0.5
1.6
• Arcan et al. (1985)
b Bernardi et al. (1986)
C Atmospheric annual deposition obtained by averaglng three years of
data recorded in 1993-97. Deposition area = 546 km a
Table 4. Supply rates of metals to the northern Adriatic
(tonnes year l )
Rivers poa
Atmosphere b
AtmlPo
Cd
7
5
0.7
a Camusso et aL (1993)
Cu
281
201
0.7
Ni
514
63
0.1
Pb
151
300
2.0
b Atmospheric deposition is obtained by averaging data recorded in
1995-96 at Cesenatico, AGIP and Venice. Deposition area =25000 km 2
programme on the Adriatic Sea from the Italian
government). In this area the total amount of
water load was estimated to be 20x10 9 m 3 ·year-1,
equivalent to 40% of the mean annual discharge
of the Po River (Tartari et al. 1997). As Table 4
shows, compared with riverine inputs of respectively 7. 281 and 514 tonnes year I , in the northern Adriatic an almost equal amount of Cd (5
tonnes yearI) and Cu (20l tonnes year-I) and
nearly 1/10 of Ni (63 tonnes year I ) is atmospherically derived, whereas the deposition flux of
Pb (300 tonnes year-I) is twofold higher than
riverine input (151 tonnes year I ).
The extrapolation of these deposition data to
calculate the atmospheric flux of metals must be
considered with care. The high spatial and temporal variability of atmospheric transport and
deposition, coupled with the short duration of
oceanographic research cruises, made it difficult
to obtain good estimates of atmospheric deposition to those areas of the open sea devoid of
islands at which continuous sampling can be
undertaken. Encouragingly, however, recent
results from ship-board collections of aerosol
metals over the North Sea, where a steep spatial
gradient in aerosol concentration is found, are
comparable with samples collected at the coast
(Guerzoni et al. 1999). This finding suggests that
atmospheric fluxes estimated from coastal sites
may be extrapolated to adjacent marine areas.
Thus, even though it would be important to have
more sampling stations, the data derived from
our study can usefully increase knowledge of
eolian deposition in the North Adriatic.
Conclusions
1. Bulk samplers may be useful to assess the
importance of atmospheric loads at sea in
sites where sampling is difficult to manage.
2. Total daily fluxes of metals were very variable
at all stations; the highest fluxes were
observed at urban sites, and the lowest at sea.
3. Atmospheric loads of Cd and Pb were comparable with estimates made by other
Authors in different Mediterranean coastal
sites.
4. The atmospheric deposition observed at
Venice was 2- to 7-fold higher than that of
Cesenatico for Ni, Cu, and Pb, and comparable for Cd.
5. The magnitude of atmospheric input indi-