Digital Theses Archive


Tesi etd-04212023-012945

Type of thesis
Scientific disciplinary sector
Istituto di Scienze della Vita - PHD IN AGROBIOSCIENZE
Relatore Dott. ROSSETTO, RUDY
  • Artificial Recharge of Aquifers
  • hydrochemistry
  • hydrogeochemistry
  • hydrogeology
  • Infiltration Basin
  • Managed Aquifer Recharge
  • Water Harvesting
Exam session start date
Groundwater is a widely used resource at global scale for drinking, irrigation, and industrial uses. Moreover, it largely sustains aquatic ecosystems. Notwithstanding anthropic uses, climate change is going to have large impacts on this resource. <br>The research presented in this study deals with the impacts of climate change on the groundwater resource and on investigations of processes occurring in aquifers during Managed Aquifer Recharge operations in order to design smarter operations methods. Main objectives are: 1) understand the presence, the temporal and spatial distribution of the hydrodynamics and hydrogeochemical changes and processes occurring during the development of droughts in aquifers; 2) evaluate a temperature-based methodology to determine the area of direct impact of the operations of infiltration basins tracing the extension of the recharged bulb; 3) assess the presence, the temporal and spatial distribution of the hydrodynamics and hydrogeochemical changes and processes induced in an aquifer as a short-term response to Managed Aquifer Recharge operations, via intensive sampling campaigns. The research activities were run at the LIFE REWAT Suvereto infiltration basin by main of three main large experiments.<br>While several studies dealt with the impact of climate change on groundwater levels, little is still known on the processes occurring at hydrochemical level and their relations with hydrodynamics. My results suggest that droughts induce hydrogeochemical changes into aquifers, impacting the quantitative and qualitative availability of groundwater. The drought propagates from meteorological conditions (i.e., intensity, and frequency of precipitations) to surface water bodies (e.g., rivers, lakes, basins, etc.) and finally to aquifers and groundwater. The quantitative availability of groundwater decreases during droughts, being affected by the reduction of the recharge sources. These recharge sources would decrease until eventually ceasing. <br>The chemical quality of groundwater also decreases during droughts, potentially affecting its suitability for agriculture or drinking purposes. My work effectively observed the progressive degradation of the groundwater chemical quality during the development of a drought period. As the groundwater level drops, the groundwater flow slows down, allowing a longer contact time between the water and the aquifer matrix. This increase of the groundwater residence time enables slower reactions to occur, consenting further concatenated chemical reactions to also take place. A larger dissolution of minerals is thus facilitated, increasing the concentration of several elements. The elements absorbed onto the surfaces of these minerals are also released and dissolved in groundwater.<br>Managed Aquifer Recharge (MAR) schemes may constitute effective and robust solutions to water scarcity and could serve as a prevention measure and a buffer to droughts periods. For smooth operations of such schemes, devising new techniques in order to detect the evolution of the recharge plume is of great interest. In my study, the development of the recharged plume can be traced by temperature data, especially when the temperature difference between the source water and the groundwater are noteworthy. The area of direct impact of the MAR operations can be delimited by the extension of the plume using it to improve the management and monitoring of the MAR scheme, providing cost-effective observations.<br>Likewise, few information is available on the chemical changes occurring in an aquifer during recharge. My study investigated the changes occurring in an aquifer under MAR operations in oxic conditions. MAR operations induced hydrogeochemical changes into the aquifer, impacting the quantitative and qualitative availability of groundwater even in the short-term. MAR affects the groundwater natural flow by introducing a new vertical component into the system, forcing the recharged water to mix with the native groundwater. The chemical quality of the groundwater improved during MAR in our study site. While there have been observed increasing concentration and mobilisation of harmful trace elements in other MAR schemes around the world, this does not seem to be the case. Contrarily, the majority of the trace elements present a decreasing trend in our study. Our results suggest that a combination of dilution from the source water, and absorption onto newly precipitated minerals, resulting from oxidative processes, attenuates these contaminants. The results also suggest that an eventual remobilisation of the contaminants could take place if reducing conditions are present. Thus, the periodical monitoring of the source water for the absence of reducing agents such as Dissolved Organic Carbon (DOC), and sulphides, may be necessary. Further analysis, such as batch experiments using the soil, source water, and native groundwater, are needed to verify the mobilisation conditions of the contaminants. Likewise, reactive transport modelling could elucidate and quantify the weight of the identified processes.<br>As groundwater quality and concentrations of chemicals may change also in short time, both during drought periods and during MAR operations, thorough characterisation of the chemical status of groundwater bodies deemed for human uses and irrigation should be performed, considering varying hydrological conditions. <br>Finally, becoming groundwater a prominent freshwater resource worldwide in the context of climate change, actively managing groundwater quality and availability, even in the context of drought, is of utmost importance for securing drinking water and agricultural crop production, besides maintaining the quality of ecosystems, and finally for defining the rates for sustainable groundwater abstraction.<br>