Analisi diacronica, pedogeochimica ed etnopedologica per lo studio dell’evoluzione storico-territoriale e delle condizioni attuali dei suoli e del paesaggio. La fascia costiera dell’Ambito di Paesaggio “Golfo di Oristano”(Sardegna centro-occidentale)

This research aims to show a possible integrated approach to the study of the coastal zone of the Gulf of Oristano, characterized by a complex and delicate environmental system and a production context historically significant in terms of agriculture. The purpose is to propose a tool for knowledge of the area through the analysis of the existing relationship between: - the landscape and its transformations, mostly related to the use and land cover; - the soil, which is one of the fundamental components of the landscape; - local knowledge expressed with toponyms (place names), which are often originated by the characteristics of the landscape to which they relate and contribute to the formation of the social representation of a territory. The starting point of the study has been the consciousness that in the last century the study area has undergone an intense transformation. A careful analysis of the evolutionary processes of land use and landscape has been performed, based on comparison of historical and geographical information of maps and orthophotos available for the study area, in order to understand the historical matrix of the landscape and recognize the stays and the changes imposed on the territory as a result of the man-environment interaction. Specifically, the study area has undergone a deep reconfiguration mainly due to the activities of land reclamation and to important changes towards the artificial land use of previously agricultural or natural/semi-natural areas. The soil consumption has been defined, as well as on a quantitative basis, also on the basis of the quality of the soils affected by the process of consumption. Soils mostly consumed in the period considered (1954-2008) belong to the intermediate classes of land capability. Bearing in mind that the soil functions can be defined in terms of chemical, physical and biological properties and related processes, the present study (carried out in collaboration with national and foreign research institutions) has determined in first analysis the parameters that give a general idea of the specific environmental system under study (physico-chemical analysis) and then has proceed with more specific surveys (biochemical analysis and analysis on PTEs - Potentially Toxic Elements), in order to perform a screening of the “state of health” and define the quality of soil in relation to different uses. The physico-chemical and pedo-geochemical survey has allowed to determine the quality level of the investigated soils and to differentiate the anthropic or geogenic/pedogenic origin of potential contaminants (Pb, Zn, Cd, Cu, Ni and As). It has been found that in the investigated area there is a form of punctual contamination quite limited and certainly not widespread. The data processing has showed that, with the exception of areas in which the contamination is clearly anthropic (River Sitzerri valley) or where the contamination is supposed (areas locally contaminated by Cu), the main factors that control the distribution and the concentration of PTEs in the study area are related to natural geological and pedological conditions. The evaluation of the effects of land use on soil quality has been based on the determination of biochemical parameters used as indicators of soil quality in response to land use representative of the study area (agricultural fields, Mediterranean scrub, garrigue, eucalyptus plantations, stands of pine, uncultivated). The biochemical analysis have examined the determination of enzymatic activities related to four soil enzymes (dehydrogenase, indicative of overall metabolic activities of microorganisms in soil and beta-glucosidase, phosphatase and protease, hydrolytic enzymes connected to the carbon, nitrogen and phosphorus cycle) and the determination of glomalin (glycoprotein produced by arbuscular mycorrhizal fungi). It has been found that the variations in the measured enzymtic activities and glomalin are related to the diversity of land uses. These parameters indeed increase mainly as a function of the input of organic matter and of the availability of substrates, and decrease in function of anthropic interference, showing always medium-low values in soils under stands of pine and agricultural fields, while high values are always related to the Mediterranean scrub and the eucalyptus plantations. Moreover in the research, in the light of the fact that the landscape (of which the soil is an integral part) can be considered as a mirror of all the local knowledge and perceptions of the lived space, it has been investigated through an ethno-pedologic integrated approach on the meaning and distribution of toponyms, with particular reference to those related to the soil resources (pedonyms) of the 14 municipalities bordering the coastal zone of the Gulf of Oristano. This approach has helped to identify the correspondence between local knowledge (deduced from the meaning of toponyms) and the scientific one (analytical parameters and information related to soil classification). The most important result of the research provides statistical evidence of the fact that the inhabitants of the study area, although not possessing the appropriate scientific expertise (at least in the past), have tried over time to distinguish the various types of soil and give them a name according to the characteristics of the soil especially related to fertility, the knowledge of which allowed to make the best use of the soils for agricultural purposes.