On groundwater flow and shallow geothermal potential: A surrogate model for regional scale analyses.

Many cities worldwide lay upon alluvial aquifers which have a great potential for low temperature geothermal installations thanks to the thermal diffusive properties of saturated porous media and the constant temperature of the subsurface. In addition, aquifers with fast moving groundwater have a higher potential due to the additional energy replenishment by advection, which is often underestimated. This work aims at bridging the gap between quantitative hydro-thermal numerical analysis and regional scale assessment developing a process-based surrogate model for the estimation of the thermal exchange (geothermal) potential of ground source heat pumps (GSHP) considering groundwater advection. The proposed method is based on a synthetic 3D FEM model reproducing the infinite line source configuration and introducing groundwater advection. Conductive/advective g-functions were derived from the numerically simulated space-time thermal perturbation for a comprehensive set of hydrogeological regimes, and a surrogate model was developed by a machine learning (ML) regression of the thermal response of the system. This solution, beyond the run time of the numerical study and the ML training phase, is very fast, applicable at any scale and scalable to any desired depth. The trained model can be used to predict the geothermal potential of GSHP for almost all sedimentary basins around the world upon the availability of the required input data (aquifer thickness and saturation, aquifer porosity and groundwater flow velocity). In this study, large scale geothermal potential maps were generated from input layers implemented in a GIS, for a demonstrative area in northern Italy showing highly variable groundwater flow (Darcy velocity from 10-3 to 10+3 m/y). A promising increase (up to +250 %) in the thermal exchange potential of GSHP due to the contribution of advection was highlighted discussing the benefits of groundwater flow and the amount of usable potential with implications on shallow geothermal energy management and development.

The subsurface urban heat island in Milan (Italy) - A modeling approach covering present and future thermal effects on groundwater regimes.

Knowledge on the intensity and extension of current subsurface urban heat islands (SUHI) is not only based on the availability of spatiotemporal high-resolution and long-term groundwater monitoring data but also in-depth investigations on the role of single natural and anthropogenic factors. A holistic city-scale 3D FEM model is presented to introduce possible thermal management applications in the Milan metropolitan area such as: (1) understanding the hydro-thermal regime of the urban aquifer disentangling the thermal contribution of natural and anthropogenic heat sources, (2) quantifying the geothermal potential and (3) investigating the effects of urbanization and climate change scenarios. Focusing on the most relevant heat sources (boundaries) and transport mechanisms (parameters), this work deals with (I) the reconstruction of large-scale aquifer heterogeneities to consider the advective dominated heat transport, (II) the accurate definition of the upper thermal boundary by a coupled analytical solution and (III) the integration of natural and human-related fluid/heat sources as transient boundary conditions. The model was calibrated against 15 groundwater head and temperature time series and validated in space and time by temperature profiles at 40 additional observation wells. Thus, a fluid and heat budget analysis revealed the most relevant natural and anthropogenic sources at the city-scale. The heat flow from buildings, surface infrastructures and tunnels contribute to 85% of the net annual heat accumulation in the subsurface which totals to 1.4 PJ/y. The results of the simulations were used to evaluate the geothermal potential of the shallow aquifer and to localize promising and critical areas that should be further investigated for an effective thermal management. Finally, it was demonstrated that possible future climate change and city expansion scenarios could lead to the highest thermal energy increment in the subsurface compared to shallow geothermics development which, for this reason, should be highly supported.

Hydro-stratigraphic datasets for the reconstruction of a large scale 3D FEM numerical model in the Milan metropolitan area (northern Italy).

One of the objectives of groundwater numerical modeling is to accurately reproduce the flow velocity field and the flow and transport pathways. In this article the hydro-stratigraphic dataset, used in the co-submitted article "Modeling the interference of underground structures with groundwater flow and remedial solutions in Milan" (De Caro et al., 2020) [1], is presented. The work aims to reconstruct the spatial variability of the hydraulic parameters in the shallow aquifers of the Milan City area (northern Italy) and to integrate them in a groundwater flow 3D finite element method (FEM) numerical model. This objective is achieved by converting qualitative borehole logs stratigraphic information into hydrogeological parameters (e.g. hydraulic conductivity and porosity) and by interpolating these parameters over the finite element mesh nodes by means of 3D kriging techniques. The modeling domain and the mesh nodes, the boundary surfaces between the aquifers as well as some of the piezometric data used to calibrate the model are presented to make the numerical experiment reproducible.

In vitro conservation and cryopreservation of ornamental plants.

Today, the conservation of ornamental germplasm can take advantage of innovative techniques which allow preservation in vitro (slow growth storage) or in liquid nitrogen (cryopreservation) of plant material. Slow growth storage refers to the techniques enabling the in vitro conservation of shoot cultures in aseptic conditions by reducing markedly the frequency of periodic subculturing, without affecting the viability and regrowth of shoot cultures. Cryopreservation refers to the storage of explants from tissue culture at ultra-low temperature (-196 degrees C). At such temperature, all the biological reactions within the cells are hampered, hence the technique makes available the storage of plant material for theoretically unlimited periods of time. An exhaustive review of papers dealing with the slow growth storage and the cryopreservation of ornamental species is reported here. Step-by-step protocols for the slow growth storage of rose germplasm, the production of synthetic seeds for the in vitro conservation of ornamentals, and the cryopreservation of Chrysanthemum morifolium are included.