Aquifer heat storage: sulphate reduction with acetate at increased temperatures

Aquifer thermal energy storage in urban and industrial areas can lead to an increase in subsurface temperature to 70 °C and more. Besides its impacts on mineral and sorption equilibria and chemical reaction kinetics in an aquifer, temperature sensitively influences microbial activity and thus redox processes, such as sulphate reduction. Microorganism species can only operate within limited temperature ranges and their adaptability to temperature is a crucial point for the assessment of the environmental consequences of subsurface heat storage. Column experiments with aquifer sediment and tap water at 10, 25, 40, and 70 °C showed that under the constant addition of acetate sulphate reduction could be initiated after 26–63 pore volumes exchanged at all temperatures. Fastest initiation of sulphate reduction with the highest reduction rates was found at 40 °C. Maximum rate constants during experimental run-time were 0.56 h^?1 at 40 °C and 0.33, 0.36, and 0.25 h^?1 at 10 and, 25, and 70 °C, respectively. Hence, microbial activity was enhanced by a temperature increase to 40 °C but was significantly lowered at 70 °C. At 25 °C methane was found in solution, indicating the presence of fermenting organisms; at 10, 40, and 70 °C no methane production was observed. It could be shown that redox processes in an aquifer generally can adapt to temperatures significantly higher than in situ temperature and that the efficiency of the reduction process can be enhanced by temperature increase to a certain limit. Enhancement of sulphate reduction in an aquifer due to temperature increase could also allow enhanced degradation of organic ground water contaminants such as BTEX, where sulphate is an important electron acceptor.     

Effects of thermal energy storage on shallow aerobic aquifer systems: temporary increase in abundance and activity of sulfate-reducing and sulfur-oxidizing bacteria

Aquifer thermal energy storage may result in increases in the groundwater temperature up to 70 °C and more. This may lead to geochemical and microbiological alterations in the aquifer. To study the temperature effects on the indigenous microbial community composition, sediment column experiments at four different temperatures were carried out and the effluents were characterized geochemically and microbiologically. After an equilibrium phase at groundwater temperature of 10 °C for 136 days, one column was kept at 10 °C as a reference and the others were heated to 25, 40 and 70 °C. Genetic fingerprinting and quantitative PCR revealed a change in the bacterial community composition and abundance due to the temperature increase. While at 25 °C only slight changes in geochemical composition and gene copy numbers for bacteria were observed, increasing concentrations of total organic carbon in the 40 °C column were followed by a strong increase in bacterial abundance. Thermophilic bacteria became dominant at 70 °C. Temporary sulfate reduction took place at 40 and 70 °C and this correlated with an increased abundance of sulfate-reducing bacteria (SRB). Furthermore, a coexistence of SRB and sulfur-oxidizing bacteria (SOB) at all temperatures indicated an interaction of these physiological groups in the sediments. The results show that increased temperatures led to significant shifts in the microbial community composition due to the altered availability of electron donors and acceptors. The interplay of SRB and SOB in sedimentary biofilms facilitated closed sulfur cycling and diminished harmful sulfur species.     

A stratigraphic and geophysical approach to studying the deep-circulating groundwater and thermal springs, and their recharge areas, in Cimini Mountains–Viterbo area, central Italy

The stratigraphic and structural setting of the Cimini Mountains and Viterbo area of Italy has been reconstructed. The architecture of the tectonic edifice, below the Pleistocene Cimino and Vicano volcanic districts cover, is characterized by the Mesozoic–Cenozoic Tuscan Nappe and the similar Umbria-Marche Succession; both are capped by the overthrusted Ligurian Late Cretaceous–Eocene Tolfa Flysch. A shallow unconfined volcanic aquifer is separated, by a thick aquiclude, from the deep confined carbonate aquifer consisting of the Tuscan Nappe and the Umbria-Marche Succession. The volcanic aquifer hosts cold waters, whilst the carbonate aquifer hosts hot sulphate–alkaline earth waters that emerge in the thermal area of Viterbo with a temperature of 30–60°C. The recharge area of cold waters is located in the Cimini Mountains. Thermal waters of the Viterbo hot springs are derived from a circuit of waters that emerge along the River Nera near Narni (about 34 km ENE of Viterbo), with a high salinity, a temperature of 16–18°C, a sulphate–alkaline earth composition, and a discharge of 13 m³/sec, whose recharge area is located in the central pre-Apennines reliefs.     

Mineralisation of amethyst-bearing geodes in Ametista do Sul (Brazil) from low-temperature sedimentary brines: evidence from monophase liquid inclusions and stable isotopes

Fluid inclusion studies in combination with hydrogen, oxygen and sulphur isotope data provide novel insights into the genesis of giant amethyst-bearing geodes in Early Cretaceous Paraná continental flood basalts at Amestita do Sul, Brazil. Monophase liquid inclusions in colourless quartz, amethyst, calcite, barite and gypsum were analysed by microthermometry after stimulating bubble nucleation using single femtosecond laser pulses. The salinity of the fluid inclusions was determined from ice-melting temperatures and a combination of prograde and retrograde homogenisation temperatures via the density maximum of the aqueous solutions. Four mineralisation stages are distinguished. In stage I, celadonite, chalcedony and pyrite formed under reducing conditions in a thermally stable environment. Low δ³⁴S_V-CDT values of pyrite (?25 to ?32?‰) suggest biogenic sulphate reduction by organotrophic bacteria. During the subsequent stages II (amethyst, goethite and anhydrite), III (early subhedral calcite) and IV (barite, late subhedral calcite and gypsum), the oxidation state of the fluid changed towards more oxidising conditions and microbial sulphate reduction ceased. Three distinct modes of fluid salinities around 5.3, 3.4 and 0.3 wt% NaCl-equivalent characterise the mineralisation stages II, III and IV, respectively. The salinity of the stage I fluid is unknown due to lack of fluid inclusions. Variation in homogenisation temperatures and in δ¹⁸O values of amethyst show evidence of repeated pulses of ascending hydrothermal fluids of up to 80–90 °C infiltrating a basaltic host rock of less than 45 °C. Colourless quartz and amethyst formed at temperatures between 40 and 80 °C, while the different calcite generations and late gypsum precipitated at temperatures below 45 °C. Calculated oxygen isotope composition of the amethyst-precipitating fluid in combination with δD values of amethyst-hosted fluid inclusions (?59 to ?51?‰) show a significant ¹⁸O-shift from the meteoric water line. This ¹⁸O-shift, high salinities of the fluid inclusions with chloride-sulphate composition, and high δ³⁴S values of anhydrite and barite (7.5 to 9.9?‰) suggest that sedimentary brines from deeper parts of the Guaraní aquifer system must have been responsible for the amethyst mineralisation.     

Surface characterization of maize-straw-derived biochars and their sorption performance for MTBE and benzene

Biochars generated at various temperatures might show significant differences in sorption for organic contaminants. In this study, a series of biochars, generated from pyrolyzing maize straws at different temperatures, were systematically characterized. The characterization results showed that with increasing pyrolysis temperature, the surface areas, micropore areas and aromaticity of biochars were enhanced. Batch experiments were conducted to study methyl tert-butyl ether (MTBE) and benzene sorption to biochars. The results indicated that the sorption capacity of benzene to biochars was higher than that of MTBE. The higher pyrolyzed temperature of biochars resulted in a stronger sorption affinity for target compounds, and the dominant sorption mechanisms varied for biochars pyrolyzed at different temperatures. The sorption to biochars pyrolyzed at 700 and 800 °C performed a high adsorption capacity, which indicated that they might be a promising sorbent to remove MTBE and benzene from water. Biochar pyrolyzed at 400 °C showed transitional sorption mechanisms from partition to adsorption for MTBE and benzene. Pore-filling was a possible sorption mechanism to biochars pyrolyzed at high temperature.     

Shallow groundwater temperature in the Turin area (NW Italy): vertical distribution and anthropogenic effects

This study investigated the thermal regime of shallow groundwater in the Turin area (NW Italy), where the large energy demand has motivated a new interest for renewable sources, such as the use of ground-source heat pumps for domestic heating and cooling. The vertical variability of the groundwater temperature between the ground surface and 10–20 m was detected: deeper temperatures were higher than shallow temperatures in spring, while a decrease with depth occurred in autumn. These variations are connected with the heating and cooling cycles of the ground surface due to the seasonal temperature oscillation. Variations below the seasonal oscillation are likely to be connected with the presence of advective heat transport due to the groundwater flow, according to the hydraulic features of a shallow aquifer. Temperature values mostly ranged between 12 and 14 °C in rural areas, while the values were between 14 and 16 °C below the Turin city. This groundwater warming is attributed to a widespread urban heat island phenomenon linked to warmer land surface temperatures in Turin city. Sparse warm outliers are connected with point heat sources and site-specific conditions of land and subsurface use, which may cause the aquifer temperature to rise. A relatively stable temperature below the seasonal fluctuation zone combined with high productivity and legislated limits for deeper groundwater use represent favourable conditions for a large-scale diffusion of groundwater heat pumps within the shallow aquifer. Moreover, this heat surplus should be regarded as a resource for future geothermal installations.     

Effect of the addition of granitic powder to an acidic soil from Galicia (NW Spain) in comparison with lime

The impact of diffuse pollution, agricultural land use and climate change on the long-term response of subsurface–surface water quality is not well understood, but is a prerequisite for evaluation of water management options. The goal of this study is to model geochemical evolution of water chemistry from the infiltration through soil into the unsaturated zone, transport through bedrocks and granular aquifers to a river in order to identify zones of steep concentration gradients and high dynamics under transient flow conditions. A numerical model was constructed comprising a 2-D 1,500 m × 150 m vertical cross-section of typical sedimentary rock formations, a glacio-fluvial quaternary gravel aquifer in the valley and soil layers. The model coupled saturated/un-saturated flow and reactive transport under steady state and transient conditions. Geochemical interactions, include intra-aqueous kinetic reactions of oxygen with dissolved organic matter, as well as kinetics of carbonate dissolution/precipitation. This model section was chosen to provide insight in to the principal processes and time scales affecting water chemistry along different flow paths. The numerical simulator MIN3P was used, a finite volume program for variably saturated subsurface flow and multi-component reactive transport. The results show that subsurface water residence times range from approximately 2 to 2,000 years. Different zones are to be expected with respect to the development of mineral equilibria; namely, purely atmospherically influenced, as well as open and closed system carbonate dissolution. Short-term responses to daily averaged changes in precipitation, however, are only visible to some extent in the shallower and near-river parts of flow system and solute loads. This can most likely be explained by directional changes in flow paths, indicating that equilibrium geochemical condition predominate at the hillslope scale, i.e. water quality depends on transport pathways rather than on kinetic effects. The extent of reducing conditions is controlled by the presence of organic-rich layers (i.e. peat deposits), the dissolution kinetics of aquifer organic matter and the subsequent mixing with oxygenated water by hydrodynamic dispersion.     

Experimental and numerical simulation study of the mineral sequestration mechanism of the Shiqianfeng saline aquifers in the Ordos Basin,Northwest China

This study focused on typical injection layers of deep saline aquifers in the Shiqianfeng Formation used in the Carbon Capture and Sequestration Demonstration Projects in the Ordos Basin, Northwest China. The study employed experiments and numerical simulations to investigate the mechanism of CO₂ mineral sequestration in these deep saline aquifers. The experimental results showed that the dissolved minerals are plagioclase, hematite, illite–smectite mixed layer clay and illite, whereas the precipitated minerals are quartz (at 55, and 70 °C) and kaolinite (at 70 °C). There are rare carbonate mineral precipitations at the experimental time scale, while the precipitation of quartz as a product of the dissolution of silicate minerals and some intermediate minerals rich in K and Mg that transform to clay minerals, reveals the possibility of carbonate precipitation at the longer time scale. These results are consistent with some results previously reported in the literature. We calibrated the kinetic parameters of mineral dissolution and precipitation by these experimental results and then simulated the CO₂ mineral sequestration under deep saline aquifer conditions. The simulation results showed that the dissolved minerals are albite, anorthite and minor hematite, whereas the precipitated minerals are calcite, kaolinite and smectite at 55 and 70 °C. The geochemical reaction of illite is more complex. At 55 °C, illite is dissolved at the relatively lag time and transformed to dawsonite; at 70 °C, illite is precipitated in the early reaction period and then transformed to kaolinite. Based on this research, sequestrated CO₂ minerals, which are mainly related to the temperature of deep saline aquifers in Shiqianfeng Fm., are calcite and dawsonite at lower temperature, and calcite at higher temperature. The simulation results also establish that calcite could precipitate over a time scale of thousands of years, and the higher the temperature the sooner such a process would occur due to increased reaction rates. These characteristics are conducive, not only to the earlier occurrence of mineral sequestration, but also increase the sequestration capacity of the same mineral components. For a sequestration period of 10,000 years, we determined that the mineral sequestration capacity is 0.786 kg/m³ at 55 °C, and 2.180 kg/m³ at 70 °C. Furthermore, the occurrence of mineral sequestration indirectly increases the solubility of CO₂ in the early reaction period, but this decreases with the increase in temperature.     

Numerical investigation on the implications of spring temperature and discharge rate with respect to the geothermal background in a fault zone

Geothermal springs are some of the most obvious indicators of the existence of high-temperature geothermal resources in the subsurface. However, geothermal springs can also occur in areas of low average subsurface temperatures, which makes it difficult to assess exploitable zones. To address this problem, this study quantitatively analyzes the conditions associated with the formation of geothermal springs in fault zones, and numerically investigates the implications that outflow temperature and discharge rate from geothermal springs have on the geothermal background in the subsurface. It is concluded that the temperature of geothermal springs in fault zones is mainly controlled by the recharge rate from the country rock and the hydraulic conductivity in the fault damage zone. Importantly, the topography of the fault trace on the land surface plays an important role in determining the thermal temperature. In fault zones with a permeability higher than 1 mD and a lateral recharge rate from the country rock higher than 1 m³/day, convection plays a dominant role in the heat transport rather than thermal conduction. The geothermal springs do not necessarily occur in the place having an abnormal geothermal background (with the temperature at certain depth exceeding the temperature inferred by the global average continental geothermal gradient of 30 °C/km). Assuming a constant temperature (90 °C here, to represent a normal geothermal background in the subsurface at a depth of 3,000 m), the conditions required for the occurrence of geothermal springs were quantitatively determined.     

The seabed characteristics of the bottom floor of Damietta Branch,Egypt, using acoustic signals

The study area lies between 31.32°N, 31.70°E and 31.41°N, 31.78°E along Damietta branch, Nile River. It is about 24-km long. Acoustic classification (Quester Tangent Corporation—QTC) is used as a powerful tool to study seabed characteristics which is confirmed by the sediment analyses. Sediment characteristics of the study are presented by three acoustic classes: sand, mud and organic matter intercalated by clay. The depth varies from about ?12 m at Faraskour Bridge (southern part of the study area) to about ?2.5 m at Faraskour Dam (northern part of the study area). The average current velocity is detected as 4 cm/s and it has a very low effect on the transport of both sediment and waste debris. The sediment in the northern part characterized by organic matter reaches about 70 cm thickness under and around fish cages. This huge amount of organic matter deposit leads to the reduction of the dissolved oxygen and increase pH values. This study shows that the water quality in the northern part of the study area is at risk (drinking water for Damietta city) due to the presence of the huge amount of waste debris intercalated by organic matter. The rises of temperature in summer enhance oxygen consumption and the decomposition of the organic matter. This is rapidly increasing the growth of bacteria and phytoplankton, causing turbidity and algal blooms. Those affect the water quality and raise the water toxicity (drinking water).     

Spatial and Temporal Variability of Benthic Respiration in a Scottish Sea Loch Impacted by Fish Farming: A Combination of In Situ Techniques

The effects of fish farm activities on sediment biogeochemistry were investigated in Loch Creran (Western Scotland) from March to October 2006. Sediment oxygen uptake rates (SOU) were estimated along an organic matter gradient generated from an Atlantic salmon farm using a combination of in situ techniques: microelectrodes, planar optode and benthic chamber incubations. Sulphide (H₂S) and pH distributions in sediment porewater were also measured using in situ microelectrodes, and dissolved inorganic carbon (DIC) fluxes were measured in situ using benthic chambers. Relationships between benthic fluxes, vertical distribution of oxidants and reduced compounds in the sediment were examined as well as bacterial abundance and biomass. Seasonal variations in SOU were relatively low and mainly driven by seasonal temperature variations. The effect of the fish farm on sediment oxygen uptake rate was clearly identified by higher total and diffusive oxygen uptake rates (TOU and DOU, respectively) on impacted stations (TOU: 70 ± 25 mmol O₂ m^?2 day^?1; DOU: 70 ± 32 mmol O₂ m^?2 day^?1 recalculated at the summer temperature), compared with the reference station (TOU: 28.3 ± 5.5 mmol O₂ m^?2 day^?1; DOU: 21.5 ± 4.5 mmol O₂ m^?2 day^?1). At the impacted stations, planar optode images displayed high centimetre scale heterogeneity in oxygen distribution underlining the control of oxygen dynamics by small-scale processes. The organic carbon enrichment led to enhanced sulphate reduction as demonstrated by large vertical H₂S concentration gradients in the porewater (from 0 to 1,000 μM in the top 3 cm) at the most impacted site. The impact on ecosystem functions such as bioirrigation was evidenced by a decreasing TOU/DOU ratio, from 1.7 in the non-impacted sediments to 1 in the impacted zone. This trend was related to a shift in the macrofaunal assemblage and an increase in sediment bacterial population. The turnover time of the organic load of the sediment was estimated to be over 6 years.     

Characterization of the subsurface urban heat island and its sources in the Milan city area,Italy

Urban areas are major contributors to the alteration of the local atmospheric and groundwater environment. The impact of such changes on the groundwater thermal regime is documented worldwide by elevated groundwater temperature in city centers with respect to the surrounding rural areas. This study investigates the subsurface urban heat island (SUHI) in the aquifers beneath the Milan city area in northern Italy, and assesses the natural and anthropogenic controls on groundwater temperatures within the urban area by analyzing groundwater head and temperature records acquired in the 2016–2020 period. This analysis demonstrates the occurrence of a SUHI with up to 3 °C intensity and reveals a correlation between the density of building/subsurface infrastructures and the mean annual groundwater temperature. Vertical heat fluxes to the aquifer are strongly related to the depth of the groundwater and the density of surface structures and infrastructures. The heat accumulation in the subsurface is reflected by a constant groundwater warming trend between +0.1 and?+?0.4 °C/year that leads to a gain of 25 MJ/m² of thermal energy per year in the shallow aquifer inside the SUHI area. Future monitoring of groundwater temperatures, combined with numerical modeling of coupled groundwater flow and heat transport, will be essential to reveal what this trend is controlled by and to make predictions on the lateral and vertical extent of the groundwater SUHI in the study area.

     

Rapid and Intense Phosphate Desorption Kinetics When Saltwater Intrudes into Carbonate Rock

It is important to understand how phosphate sorption dynamics of coastal carbonate aquifers are affected by seawater intrusion, because many coastal aquifers are composed of carbonate rocks and subject to an increase in saltwater intrusion during relative sea-level rise. Twelve carbonate rock and unconsolidated sediment specimens were acquired from a test corehole spanning the full thickness of the Biscayne aquifer in southeastern Florida. All 12 samples exhibit low phosphorus content but variable contents of iron. Column leaching experiments were conducted with two carbonate aquifer samples, alternating between freshwater and saltwater flow. With the first influx of saltwater, phosphate concentration in leachate increased rapidly from a freshwater value of approximately 0.2 μM to peaks of between 0.8 and 1.6 μM. The phosphate concentration began to diminish as saltwater continued to flow, but sustained desorption continued for over 2 h. Overall, seawater drove sorption behavior much more than chemical composition for the aquifer rocks and sediment from the seven rock samples for which we did isotherm sorption experiments. Our results indicate that an immediate and intense pulse of phosphate desorption from carbonate rock and sediment with low phosphorus content occurs in response to an influx of seawater and that the duration of desorption will vary by layer within a single aquifer.     

Local climate change induced by groundwater overexploitation in a high Andean arid watershed,Laguna Lagunillas basin,northern Chile

The Laguna Lagunillas basin in the arid Andes of northern Chile exhibits a shallow aquifer and is exposed to extreme air temperature variations from 20 to ?25 °C. Between 1991 and 2012, groundwater levels in the Pampa Lagunillas aquifer fell from near-surface to ~15 m below ground level (bgl) due to severe overexploitation. In the same period, local mean monthly minimum temperatures started a declining trend, dropping by 3–8 °C relative to a nearby reference station. Meanwhile, mean monthly maximum summer temperatures shifted abruptly upwards by 2.7 °C on average in around 1996. The observed air temperature downturns and upturns are in accordance with detected anomalies in land-surface temperature imagery. Two major factors may be causing the local climate change. One is related to a water-table decline below the evaporative energy potential extinction depth of ~2 m bgl, which causes an up-heating of the bare soil surface and, in turn, influences the lower atmosphere. At the same time, the removal of near-surface groundwater reduces the thermal conductivity of the upper sedimentary layer, which consequently diminishes the heat exchange between the aquifer (constant heat source of ~10 °C) and the lower atmosphere during nights, leading to a severe dropping of minimum air temperatures. The observed critical water-level drawdown was 2–3 m bgl. Future and existing water-production projects in arid high Andean basins with shallow groundwater should avoid a decline of near-surface groundwater below 2 m bgl and take groundwater-climate interactions into account when identifying and monitoring potential environmental impacts.     

Sorption of Cd<Superscript>2+</Superscript> ions onto zeolite synthesized from perlite waste

In this work, the studies on the formation of zeolites from expanded perlite waste and their use in the sorption process of Cd²⁺ ions will be reported. Such approach is innovative and has not been investigated elsewhere. The results of the synthesis of zeolites from aluminosilicate waste using hydrothermal method were presented. By-product from the process production of expanded perlite was used as the starting material. Theoretical and practical aspects of Cd²⁺ ions sorption process onto material synthesized in selected conditions (a material with good sorption capacity can be obtained by 24 h reaction of 1 g of perlite waste in 10 mL of 4.0 M NaOH solution with at 70 °C) will be presented. The atomic absorption spectroscopy has been used as the main method, from which the effective cation exchange capacity as well as the proportion of ion exchange to chemisorption in the sorption process have been determined. Structural analyses of the sample before and after sorption process have been also carried out by the mid-infrared spectra measurement, especially pseudolattice range of the spectra was analyzed in detail in which changes caused by ion exchange of non-tetrahedral ions have been observed.     

Hydraulic response of a tidally forced coastal aquifer, Pontal do Paraná, Brazil

The unconfined aquifer supported by the extensive Holocene coastal plain of southern Brazil is found dissected at several places by tidally forced streams. One such unit of coastal plain, falling within the watershed limits of Perequê Stream in Paraná state, was analyzed using MODFLOW to assess the surface and subsurface water components under different stress conditions. The steady-state simulation suggests that ~23,000 m³/day of water forms the total budget of the designated aquifer zone and this zone discharges ~16,000 m³/day across the interface between the freshwater aquifer zone and the sea as direct submarine discharge. The maximum evaporation loss was assumed to be 2,700 m³/day. Any change in effective aquifer storage was insignificant, as there is no large-scale exploitation of local groundwater reserves. A calibration exercise, based on field measurements lasting 1 year, supports validity of the model considered. Simulations representing two different transient conditions point to the dynamic hydraulic response exhibited by the aquifer. A schematic map, showing directions and velocity of subsurface flows, and a three-dimensional model of the groundwater reserve helped to visualize the hydrogeologic changes and to formulate management plans.     

Improvement of anaerobic biodegradability of organic fraction of municipal solid waste by mechanical and thermochemical pretreatments

The effect of particle size of the organic fraction of municipal solid waste on methane potentiel was investigated and tested at different substrate-to-inoculum ratios (0.1, 0.5 and 1.0). The highest methane yield was obtained with particle size fraction > 3 mm at S/I of 0.1. Thermo-alkali and thermo-acid methods were also tested as pretreatment to increase the organic matter solubilization and subsequently methane production. The results indicated that maximum variation (63.6%) of soluble chemical oxygen demand was obtained by thermo-acid method. Optimum conditions of thermo-alkali pretreatment were pH 10, time reaction of 30 min and temperature of 105 °C. Soluble chemical oxygen demand and reducing sugar variations reached, respectively, 40 and 69% under these conditions. The methane yield of untreated and thermochemical pretreated OFMSW was determined in batch condition. The highest methane yield (260.9 L/kg VS) was obtained with thermo-alkali pretreatment, which was 21% higher than that of raw substrate. This study may pave a new way for industrial application of dealing with the organic fraction of municipal solid waste.     

Identifying vulnerable areas of aquifer under future climate change (case study: Hamadan aquifer,West Iran)

Groundwater is the main source of water in arid and semi-arid regions, so it is very important to recognize vulnerable parts of aquifer under future climate change conditions. In this research, 16 climate models were evaluated based on weighting approach. HADCM3 and CGCM2.3.2a models were selected for temperature and precipitation prediction, respectively. LARS-WG was used for downscaling AOGCMs outputs. Results show that temperature increase by 1.4 °C and precipitation changes between +10 and ?6 % under B1 and A2 emission scenario, respectively. Runoff volumes will decrease by ?39 % under A2 emission scenario whereas runoff volume will increase by +12 % under B1 emission scenario. Simulation of groundwater head variation by MODFLOW software indicates higher groundwater depletion rate under A2 scenario compared to B1 scenario. Groundwater model outputs indicate that the most vulnerable part of the aquifer is located in the southwest region. Large number of extraction wells and low aquifer transmissivity are the reasons for high vulnerability of the region.     

Hydrogeological and mixing process of waters in deep aquifers in arid regions: south east Tunisia

This study addresses the hydrogeochemistry of thermal and cold waters from south east Tunisia. Temperature intervals are 38.5–68 °C and 22–27.8 °C for thermal water and cold water, respectively. Three distinct hydrogeological systems supply water either for irrigation or for drinking; they are: (1) the Continental Intercalaire geothermal aquifer (CI), (2) the Turonian aquifer and (3) the Senonian aquifer. A synthetic study including hydrochemical, hydrogeological and geothermal approaches have been applied in order to evaluate the inter-aquifers water transfer in south east of Tunisia. By using silica geothermometers and saturation indices for different solid phases, estimated thermal reservoir temperature varies between 52 and 87 °C and between 75 and 110 °C, respectively. Based on chemical and thermal data, mixing, which occurs between the ascending deep geothermal water and shallow cold water, is about 57 % cold water.     

The influence of environmental conditions on weathering of porous rocks by gypsum: a non-destructive study using acoustic emissions

Gypsum is one of the most universally distributed salts in weathered materials but little is known about the influence of environmental conditions on the damage generated by gypsum in stones. To quantify the damage induced by gypsum crystallization acoustic emission techniques are employed to record the elastic energy released during salt crystallization cycles in a limestone. Different environmental conditions have been established during the cooling and drying periods in traditional salt crystallization cycles. During drying two different temperatures (50 and 25 °C) and relative humidity (low, 25 % at 50 °C and 65 % at 25 °C, and high, 99 %) have been applied. The acoustic emission signals are filtered by a frequency analysis in order to eliminate signals corresponding to external noise or artifacts. Our experimental results show that acoustic emission activity is higher under high relative humidity conditions than under low relative humidity conditions, and also higher when drying at 50 °C than at room temperature. Microscopic observations on the weathered samples indicated that under high relative humidity conditions and at room temperature, gypsum crystallizes not on the sample surface, like in the other samples, but deeper in the inner part of the sample, in good agreement with previously published data. We show that using acoustic emissions as usually done in rock mechanics is also very useful in the study of stone decay and weathering processes in the laboratory.