The southernmost part of the Venice Lagoon catchment was progressively reclaimed from marshland starting from the end of the 19th century and finishing in the late 1930s (Figure 1). As a major result, the area was turned into a fertile farmland. At present, the area is kept dry by a distributed drainage system that collects the water from a capillary network of ditches, and pumps it into the lagoon or the sea. By its very origin, this area lies below sea level and progressively sinks mainly because of bio-oxidation of the histosols (soils with high organic content) that represent a large fraction of the outcropping soil in the area. The biooxidation process occurs in close connection with the agricultural practices and is currently responsible for a subsidence rate of between 1.5 and 2 cm/yr. The Venice Organic Soil Subsidence (VOSS)project was undertaken with the objective of understanding the process of land settlement in this area, quantifying past and present subsidence rates, and advancing possible remedial measures that would not penalize the current agricultural activities of the area. The study,conducted in close collaboration with the local Land Reclamation Authority (Consorzio di Bonifica) and the farmland owners, is focused on a hydrologically controlled catchment, the Zennare Basin (Venice, Italy). Land subsidence in peaty areas is a major consequence of the oxidation of the soil organic fraction in the upper aerated zone [Stephens et al., 1984; Deverel and Rojstaczer, 1996]. The release of carbon dioxide into the atmosphere causes a soil mass loss which manifests itself as land subsidence. The organic soil derives from the accumulation and decomposition of reeds (Phragmite Australis) grown in the ancient marshy area of the lagoon surroundings. Seasonal ploughing contributes to the exposure of new organic material to the atmosphere, which promotes new subsidence. The bio-oxidation reaction is controlled primarily by temperature and the presence of oxygen, with its rate increasing at low soil water content and high ambient temperature. Since moisture content is sensitive to the amount of precipitation, dry and hot seasons are most favorable for the occurrence of the reaction. By distinction, in winter soil oxidation slows down almost to zero. In light of the above, it is expected that anthropogenic land subsidence in the future might increase should the extreme climate events (i.e., hotter and dryer seasons) become more frequent, as the most recent meteorological records seem to indicate.
Peatland Oxidation Enhances Subsidence in the Venice Watershed
Rizzetto F;Tosi L
2005
Abstract
The southernmost part of the Venice Lagoon catchment was progressively reclaimed from marshland starting from the end of the 19th century and finishing in the late 1930s (Figure 1). As a major result, the area was turned into a fertile farmland. At present, the area is kept dry by a distributed drainage system that collects the water from a capillary network of ditches, and pumps it into the lagoon or the sea. By its very origin, this area lies below sea level and progressively sinks mainly because of bio-oxidation of the histosols (soils with high organic content) that represent a large fraction of the outcropping soil in the area. The biooxidation process occurs in close connection with the agricultural practices and is currently responsible for a subsidence rate of between 1.5 and 2 cm/yr. The Venice Organic Soil Subsidence (VOSS)project was undertaken with the objective of understanding the process of land settlement in this area, quantifying past and present subsidence rates, and advancing possible remedial measures that would not penalize the current agricultural activities of the area. The study,conducted in close collaboration with the local Land Reclamation Authority (Consorzio di Bonifica) and the farmland owners, is focused on a hydrologically controlled catchment, the Zennare Basin (Venice, Italy). Land subsidence in peaty areas is a major consequence of the oxidation of the soil organic fraction in the upper aerated zone [Stephens et al., 1984; Deverel and Rojstaczer, 1996]. The release of carbon dioxide into the atmosphere causes a soil mass loss which manifests itself as land subsidence. The organic soil derives from the accumulation and decomposition of reeds (Phragmite Australis) grown in the ancient marshy area of the lagoon surroundings. Seasonal ploughing contributes to the exposure of new organic material to the atmosphere, which promotes new subsidence. The bio-oxidation reaction is controlled primarily by temperature and the presence of oxygen, with its rate increasing at low soil water content and high ambient temperature. Since moisture content is sensitive to the amount of precipitation, dry and hot seasons are most favorable for the occurrence of the reaction. By distinction, in winter soil oxidation slows down almost to zero. In light of the above, it is expected that anthropogenic land subsidence in the future might increase should the extreme climate events (i.e., hotter and dryer seasons) become more frequent, as the most recent meteorological records seem to indicate.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
