Littérature scientifique sur le sujet « Contenuto idrico del suolo »

L'impatto economico dei Cambiamenti Climatici sulla disponibilitŕ di acqua irrigua in un'area del Mediterraneo, di Gabriele Dono e Graziano Mazzapicchio Questo studio valuta alcuni effetti economici e produttivi del cambiamento climatico sull'agricoltura di un'area irrigua dell'Italia meridionale. Esso considera, in particolare, la variazione dovuta al cambiamento nel regime delle piogge sulla disponibilitŕ d'acqua per l'irrigazione in una diga. Stimato il rapporto tra precipitazioni e volumi d'acqua nella diga, si definiscono le distribuzioni dei vari stati d'invaso idrico nel passato, nel presente e in uno scenario futuro. Queste distribuzioni sono usate per rappresentare le attese degli agricoltori sulle condizioni di disponibilitŕ idrica che potrebbero affermarsi passando da una situazione di stabilitŕ a una di crescente variabilitŕ dei fenomeni piovosi. In particolare, tali distribuzioni sono inserite in un modello di Programmazione Stocastica Discreta che riproduce le scelte delle aziende agricole dell'area, dato il valore stocastico atteso per l'acqua d'irrigazione disponibile in diga. I risultati delle simulazioni ottenuti confrontando gli scenari del presente e del futuro con quello del passato, evidenziano un calo dei redditi e dell'occupazione soprattutto in alcune tipologie aziendali. Emergono anche modifiche nell'uso del suolo, con un calo nell'uso dei fattori produttivi e un aumento della quantitŕ di acqua estratta dai pozzi aziendali.

La salvaguardia della risorsa suolo, bene comune da preservare per le future generazioni, sollecita l’adozione di principi dell’agroecologia nella gestione dei vigneti. In questo contesto, il lavoro di Tesi condotto in un vigneto della cv Sangiovese (Castel Bolognese, RA) si è focalizzato sugli effetti delle strategie agroecologiche di gestione del suolo e, in particolare, sul fenomeno delle crepacciature attraverso lo sviluppo di un approccio metodologico basato sull’elaborazione ed analisi di immagini. Il suolo gestito attraverso l’utilizzo di un inerbimento “modulato a strisce”, caratterizzato dalla presenza di un miscuglio a base di leguminose autoriseminanti lungo il filare, ha migliorato lo stato idrico delle viti. La Tesi ha dimostrato che le strategie agronomiche implementate nel campo sperimentale, riducendo le lavorazioni meccaniche del suolo e limitandole alle sole operazioni di semina dei miscugli, possono contribuire significativamente alla conservazione della risorsa suolo. La metodologia per lo studio delle crepacciature, ideata e resa replicabile nel lavoro di Tesi, potrà essere adottata e sviluppata per confermare i benefici delle strategie agroecologiche.

Lo scopo del monitoraggio è quello di determinare la risposta idrologica del terreno alle precipitazioni. Tale risposta è importante per calcolare le variazioni di quota dovute al rigonfiamento o alla consolidazione del mezzo poroso. L'effettiva variazione della pressione efficace è infatti legata alle oscillazioni della tavola d'acqua e alla conseguente variazione della pressione dei pori nella zona vadosa.

Alle interazioni tra le diverse componenti del sistema suolo-pianta-atmosfera (SPA) è attribuito un ruolo critico nel ciclo idrologico e della biosfera terrestre. La comunità scientifica specializzata è sempre più consapevole della necessità di portare avanti studi a carattere interdisciplinare per la comprensione delle interazioni funzionali tra le risorse naturali ed i relativi problemi di sostenibilità del sistema SPA. All interno di tali studi interdisciplinari, l analisi delle interazioni suolo-radice risulta rilevante anche per la gestione ottimale dell'irrigazione, in particolare nelle zone caratterizzate da scarsa disponibilità idrica, come le aree mediterranee. A tal fine nasce l esigenza di valutare, ad alta risoluzione sia spaziale che temporale, le dinamiche idrologiche del sistema SPA, sino alla scala dell apparato radicale. Il contributo della tesi di dottorato consiste nell applicazione di tecniche di monitoraggio avanzate e minimamente invasive, per valutare gli scambi di massa ed energia all'interno del sistema SPA. L aspetto innovativo del lavoro di tesi consiste nell integrazione di tecniche geofisiche con misure micrometeorologiche e dati di traspirazione, al fine di interpretare alcuni dei principali processi di trasferimento di flussi nel sistema SPA (evapotraspirazione ed assorbimento radicale) in ambiente semi-arido. Tale approccio, è stato applicato a due Casi studio con l obiettivo di monitorare le complesse interazioni del sistema suolo-pianta, con particolare riferimento al processo di assorbimento radicale di alberi di agrume. Nel primo Caso studio, la tecnica della tomografia di resistività elettrica (ERT) tridimensionale è stata integrata con dati di traspirazione, misure micrometeorologiche e modellistica idrologica al fine di delineare la porzione di suolo non satura interessata dalle radici attive di un aranceto adulto. Nel secondo Caso studio, il monitoraggio ERT è stato integrato con misure di traspirazione al fine di delineare i pattern di RWU di alberi di arancio irrigati in regime di deficit. I risultati del lavoro di tesi dimostrano l abilità della tecnica di monitoraggio geofisico ERT nello spiegare le dinamiche idriche del suolo e la risposta fisiologica della pianta, in termini di attività delle radici nel processo di uptake, contribuendo, in tal senso, a migliorare la conoscenza dei processi di assorbimento radicale.

Despite significant efforts have been directed toward reducing waste generation and encouraging alternative waste management strategies, landfills still remain the main option for Municipal Solid Waste (MSW) disposal in many countries. Hence, landfills and related impacts on the surroundings are still current issues throughout the world. Actually, the major concerns are related to the potential emissions of leachate and landfill gas into the environment, that pose a threat to public health, surface and groundwater pollution, soil contamination and global warming effects. To ensure environmental protection and enhance landfill sustainability, modern sanitary landfills are equipped with several engineered systems with different functions. For instance, the installation of containment systems, such as bottom liner and multi-layers capping systems, is aimed at reducing leachate seepage and water infiltration into the landfill body as well as gas migration, while eventually mitigating methane emissions through the placement of active oxidation layers (biocovers). Leachate collection and removal systems are designed to minimize water head forming on the bottom section of the landfill and consequent seepages through the liner system. Finally, gas extraction and utilization systems, allow to recover energy from landfill gas while reducing explosion and fire risks associated with methane accumulation, even though much depends on gas collection efficiency achieved in the field (range: 60-90% Spokas et al., 2006; Huitric and Kong, 2006). Hence, impacts on the surrounding environment caused by the polluting substances released from the deposited waste through liquid and gas emissions can be potentially mitigated by a proper design of technical barriers and collection/extraction systems at the landfill site. Nevertheless, the long-term performance of containment systems to limit the landfill emissions is highly uncertain and is strongly dependent on site-specific conditions such as climate, vegetative covers, containment systems, leachate quality and applied stress. Furthermore, the design and operation of leachate collection and treatment systems, of landfill gas extraction and utilization projects, as well as the assessment of appropriate methane reduction strategies (biocovers), require reliable emission forecasts for the assessment of system feasibility and to ensure environmental compliance. To this end, landfill simulation models can represent an useful supporting tool for a better design of leachate/gas collection and treatment systems and can provide valuable information for the evaluation of best options for containment systems depending on their performances under the site-specific conditions. The capability in predicting future emissions levels at a landfill site can also be improved by combining simulation models with field observations at full-scale landfills and/or with experimental studies resembling landfill conditions. Indeed, this kind of data may allow to identify the main parameters and processes governing leachate and gas generation and can provide useful information for model refinement. In view of such need, the present research study was initially addressed to develop a new landfill screening model that, based on simplified mathematical and empirical equations, provides quantitative estimation of leachate and gas production over time, taking into account for site-specific conditions, waste properties and main landfill characteristics and processes. In order to evaluate the applicability of the developed model and the accuracy of emissions forecast, several simulations on four full-scale landfills, currently in operative management stage, were carried out. The results of these case studies showed a good correspondence of leachate estimations with monthly trend observed in the field and revealed that the reliability of model predictions is strongly influenced by the quality of input data. In particular, the initial waste moisture content and the waste compression index, which are usually data not available from a standard characterisation, were identified as the key unknown parameters affecting leachate production. Furthermore, the applicability of the model to closed landfills was evaluated by simulating different alternative capping systems and by comparing the results with those returned by the Hydrological Evaluation of Landfill Performance (HELP), which is the most worldwide used model for comparative analysis of composite liner systems. Despite the simplified approach of the developed model, simulated values of infiltration and leakage rates through the analysed cover systems were in line with those of HELP. However, it should be highlighted that the developed model provides an assessment of leachate and biogas production only from a quantitative point of view. The leachate and biogas composition was indeed not included in the forecast model, as strongly linked to the type of waste that makes the prediction in a screening phase poorly representative of what could be expected in the field. Hence, for a qualitative analysis of leachate and gas emissions over time, a laboratory methodology including different type of lab-scale tests was applied to a particular waste material. Specifically, the research was focused on mechanically biologically treated (MBT) wastes which, after the introduction of the European Landfill Directive 1999/31/EC (European Commission, 1999) that imposes member states to dispose of in landfills only wastes that have been preliminary subjected to treatment, are becoming the main flow waste landfilled in new Italian facilities. However, due to the relatively recent introduction of the MBT plants within the waste management system, very few data on leachate and gas emissions from MBT waste in landfills are available and, hence, the current knowledge mainly results from laboratory studies. Nevertheless, the assessment of the leaching characteristics of MBT materials and the evaluation of how the environmental conditions may affect the heavy metals mobility are still poorly investigated in literature. To gain deeper insight on the fundamental mechanisms governing the constituents release from MBT wastes, several leaching experiments were performed on MBT samples collected from an Italian MBT plant and the experimental results were modelled to obtain information on the long-term leachate emissions. Namely, a combination of experimental leaching tests were performed on fully-characterized MBT waste samples and the effect of different parameters, mainly pH and liquid to solid ratio (L/S,) on the compounds release was investigated by combining pH static-batch test, pH dependent tests and dynamic up-flow column percolation experiments. The obtained results showed that, even though MBT wastes were characterized by relatively high heavy metals content, only a limited amount was actually soluble and thus bioavailable. Furthermore, the information provided by the different tests highlighted the existence of a strong linear correlation between the release pattern of dissolved organic carbon (DOC) and several metals (Co, Cr, Cu, Ni, V, Zn), suggesting that complexation to DOC is the leaching controlling mechanism of these elements. Thus, combining the results of batch and up-flow column percolation tests, partition coefficients between DOC and metals concentration were derived. These data, coupled with a simplified screening model for DOC release, allowed to get a very good prediction of metal release during the experiments and may provide useful indications for the evaluation of long-term emissions from this type of waste in a landfill disposal scenario. In order to complete the study on the MBT waste environmental behaviour, gas emissions from MBT waste were examined by performing different anaerobic tests. The main purpose of this study was to evaluate the potential gas generation capacity of wastes and to assess possible implications on gas generation resulting from the different environmental conditions expected in the field. To this end, anaerobic batch tests were performed at a wide range of water contents (26-43 %w/w up to 75 %w/w on wet weight) and temperatures (from 20-25 °C up to 55 °C) in order to simulate different landfill management options (dry tomb or bioreactor landfills). In nearly all test conditions, a quite long lag-phase was observed (several months) due to the inhibition effects resulting from high concentrations of volatile fatty acids (VFAs) and ammonia that highlighted a poor stability degree of the analysed material. Furthermore, experimental results showed that the initial waste water content is the key factor limiting the anaerobic biological process. Indeed, when the waste moisture was lower than 32 %w/w the methanogenic microbial activity was completely inhibited. Overall, the obtained results indicated that the operative conditions drastically affect the gas generation from MBT waste, in terms of both gas yield and generation rate. This suggests that particular caution should be paid when using the results of lab-scale tests for the evaluation of long-term behaviour expected in the field, where the boundary conditions change continuously and vary significantly depending on the climate, the landfill operative management strategies in place (e.g. leachate recirculation, waste disposal methods), the hydraulic characteristics of buried waste, the presence and type of temporary and final cover systems.

The aim of this thesis is to develop indirect and non-invasive methodologies for the tree root distribution analysis, with a multidisciplinary approach. Slope stability study needs the quantification of the root distribution. Current techniques carries out direct measurements on the root system by digging, uprooting and other invasive, non-replicable and onerous techniques. The methodologies, applied in this study, come from geophysics (I) and biomechanics (II). With the first approach, the geoelectric method is applied, in order to quantify the soil resistivity, in relation to water content. By this methodology a electrical resistivity tomography of a soil profile is obtained, which has been elaborated to evaluate the variation of the resistivity in relation to the presence of plant roots. With the second approach, controlled pulling tests on trees of different sizes and different species are performed, in order to build a new mathematical model for assessing the safety factor of a plant, subject to an external force such as wind. Thanks to the model, it is possible to evaluate the root system effect, in terms of stabilizing moment, depending on the soil characteristics. The results obtained show that both methodologies are able to provide important information about the root distribution of plants. In addition, the techniques and models developed with this study can provide innovative tools in other areas of research, for example for assessing plant stability and developing innovative bioengineering works.