Soil Contamination And Land Subsidence Raise
Concern In The Venice Watershed, Italy
Author(s)
L. Carbognin, G. Gambolati, M. Putti, F. Rizzetto, P. Teatini
& L. Tosi
Abstract
The southern catchment of the Venice watershed is threatened by shallow aquifer
salinization and anthropogenic land subsidence due primarily to the microbial
oxidation of organic soils that outcrop in the coastal farmland reclaimed from the
Adriatic Sea over the last century. Recent hydrogeological and geophysical
surveys provide documentary evidence that saltwater intrusion may extend
inshore up to 20 km away from the Adriatic coastline with the contaminant
plume from near ground surface down to 100 m depth in some areas. The actual
salt distribution is the outcome of a number of factors, including the ground
elevation markedly below the mean sea level (down to -4 m locally), the
seawater encroachment along the final 10-15 km of the regional watercourses
(Brenta, Bacchiglione, Adige, Gorzone), and the drainage practices implemented
in the reclaimed area. The fresh-salt water interface is generally between 2 and
30 m deep and exhibits a pronounced seasonal variation. At the same time an
ongoing settlement due to peat oxidation promoted by farming activities is
observed in most of the area south of the Venice Lagoon that was reclaimed
from 1892 to 1967 and is rich in organic matter. Overall land subsidence over the
last 70 years ranges between 1.5-2 m and is still in progress at a rate of
1.5-2 cm/y. As a major result a large fraction of the reclaimed land lies below the
mean sea level with an increasing exposure to flooding during severe winter
storms and saltwater intrusion from the Adriatic Sea, the nearby Venice Lagoon,
and the river beds that locally lie above the surrounding ground surface. To
mitigate both hazards the implementation of a drainage strategy of the reclaimed
area intended to maintain the water table as high as possible would be required.
This could decelerate the peat oxidation (hence the related land subsidence) and
oppose the inland subsurface salt convection and dispersion. Moreover the
design of mobile gates at a few river mouths (e.g. the Brenta river) could create
an effective barrier against the seawater migration upstream the watercourses in
the hottest and driest summers.
Keywords: saltwater intrusion, land subsidence, peat oxidation, soil salinization.
Keywords
saltwater intrusion, land subsidence, peat oxidation, soil salinization.
Related Book
Other papers in this volume
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