342
A. Sfriso and A. Marcomini
(accounting for nearly 300000 inhabitants) enter the lagoon. In addition,
treated industrial waste waters are discharged from the chemical and steel
plants of the Marghera industrial district (equivalent to 40000 inhabitants).
Eutrophicating substances (phosphorus and nitrogen compounds) as
well as organic pollutants such as PCBs, DDTs or PAHs, together with
heavy metals (Hg, Fe, Mn, Zn, Ni, Cd, Cu, Pb, Cr) accumulated in the
surface sediments, mainly in the central basin, which receives both industrial and municipal effluents (Marco mini et al. 1986; Pavoni et al.
1986; Orio and Donazzolo 1987).
The spread of chemical pollution in the central lagoon was significantly influenced by the changes of tidal movements as a result of dredging
two important canals (Vittorio Emanuele 1919-1930; MalamoccoMarghera 1961-1969; both about 100m wide and 13-20m depth). These
canals were intended to improve the waterway access to the industrial
district of Porto Marghera from the Lido and Malamocco inlets. Strong
tidal flows were conveyed toward the industrial district, whereas natural
channels ("ghebbi") and wide lagoon areas precluded from tidal water
renewal, progressively silted up.
From the literature of the last 30 years (Giordani Soika and £erin
1970, 1974 a,b; Zucchetta 1983; Battaglia et al. 1983; Ministry of Public
Works etal. 1985; ENEA 1988, 1990; Consorzio Venezia Nuova 1989), it
is apparent that many efforts have been made to reduce the input of
eutrophic substances into the lagoon. In particular, two large treatment
plants have been built, one in Fusina to process mainly industrial effluents, and one in Campalto mainly for urban sewage treatment.
The main effect of these interventions was a notable reduction in
water ammonium concentration which decreased in the area near the
Porto Marghera industrial district (Ministry of Public Works et al. 1985;
ENEA 1988, 1990) by two orders of magnitude (from 10002500 J..lmoldm- I in 1962-1964 to 5-50 J..lmoldm- I in 1985-1990). Unfortunately, changes were not observed for the nitrogen oxidized species
(nitrate + nitrate, NO x ) which were recorded at concentrations of
50-70 J..lmoldm -I (Ministry of Public Works et al. 1985). The contribution from agricultural drainage is thought to be the main reason for the
constant input of NO x ' Similarly, only minor variations of orthophosphate concentrations were observed from the 1970s on (Consorzio
Venezia Nuova 1989), in spite of both the sewage treatment plants which
came into operation and the progressive reduction in detergent
phosphorus (initially by 8%, then 5% from 1984, 2.5% from 1986, 1%
from 1988 and not at all from 1990). The surface sediment concentrations of phosphorus and nitrogen increased by up to 30 and 2.4 times
respectively, compared with the levels recorded in the 1960s.
A. Sfriso and A. Marcomini
(accounting for nearly 300000 inhabitants) enter the lagoon. In addition,
treated industrial waste waters are discharged from the chemical and steel
plants of the Marghera industrial district (equivalent to 40000 inhabitants).
Eutrophicating substances (phosphorus and nitrogen compounds) as
well as organic pollutants such as PCBs, DDTs or PAHs, together with
heavy metals (Hg, Fe, Mn, Zn, Ni, Cd, Cu, Pb, Cr) accumulated in the
surface sediments, mainly in the central basin, which receives both industrial and municipal effluents (Marco mini et al. 1986; Pavoni et al.
1986; Orio and Donazzolo 1987).
The spread of chemical pollution in the central lagoon was significantly influenced by the changes of tidal movements as a result of dredging
two important canals (Vittorio Emanuele 1919-1930; MalamoccoMarghera 1961-1969; both about 100m wide and 13-20m depth). These
canals were intended to improve the waterway access to the industrial
district of Porto Marghera from the Lido and Malamocco inlets. Strong
tidal flows were conveyed toward the industrial district, whereas natural
channels ("ghebbi") and wide lagoon areas precluded from tidal water
renewal, progressively silted up.
From the literature of the last 30 years (Giordani Soika and £erin
1970, 1974 a,b; Zucchetta 1983; Battaglia et al. 1983; Ministry of Public
Works etal. 1985; ENEA 1988, 1990; Consorzio Venezia Nuova 1989), it
is apparent that many efforts have been made to reduce the input of
eutrophic substances into the lagoon. In particular, two large treatment
plants have been built, one in Fusina to process mainly industrial effluents, and one in Campalto mainly for urban sewage treatment.
The main effect of these interventions was a notable reduction in
water ammonium concentration which decreased in the area near the
Porto Marghera industrial district (Ministry of Public Works et al. 1985;
ENEA 1988, 1990) by two orders of magnitude (from 10002500 J..lmoldm- I in 1962-1964 to 5-50 J..lmoldm- I in 1985-1990). Unfortunately, changes were not observed for the nitrogen oxidized species
(nitrate + nitrate, NO x ) which were recorded at concentrations of
50-70 J..lmoldm -I (Ministry of Public Works et al. 1985). The contribution from agricultural drainage is thought to be the main reason for the
constant input of NO x ' Similarly, only minor variations of orthophosphate concentrations were observed from the 1970s on (Consorzio
Venezia Nuova 1989), in spite of both the sewage treatment plants which
came into operation and the progressive reduction in detergent
phosphorus (initially by 8%, then 5% from 1984, 2.5% from 1986, 1%
from 1988 and not at all from 1990). The surface sediment concentrations of phosphorus and nitrogen increased by up to 30 and 2.4 times
respectively, compared with the levels recorded in the 1960s.