Changes In Groundwater Temperature Research Articles

Deciphering the mechanism of groundwater temperature changes associated with longwall mining in a coalfield, China, using the extreme gradient boosting method

Deciphering the mechanism of groundwater temperature changes associated with longwall mining in a coalfield, China, using the extreme gradient boosting method

Some like it hot: Thermal preference of the groundwater amphipod Niphargus longicaudatus (Costa, 1851) and climate change implications

Groundwater is a crucial resource for humans and the environment, but its global human demand currently exceeds available volumes by 3.5 times. Climate change is expected to exacerbate this situation by increasing the frequency of droughts along with human impacts on groundwater ecosystems. Despite prior research on the quantitative effects of climate change on groundwater, the direct impacts on groundwater biodiversity, especially obligate groundwater species, remain largely unexplored. Therefore, investigating the potential impacts of climate change, including groundwater temperature changes, is crucial for the survival of obligate groundwater species. This study aimed to determine the thermal niche breadth of the crustacean amphipod species Niphargus longicaudatus by using the chronic method. We found that N. longicaudatus has a wide thermal niche with a natural performance range of 7–9 °C, which corresponds to the thermal regime this species experiences within its distribution range in Italy. The observed range of preferred temperature (PT) was different from the mean annual temperature of the sites from which the species has been collected, challenging the idea that groundwater species are only adapted to narrow temperature ranges. Considering the significant threats of climate change to groundwater ecosystems, these findings provide crucial information for the conservation of obligate groundwater species, suggesting that some of them may be more resilient to temperature changes than previously thought. Understanding the fundamental thermal niche of these species can inform conservation efforts and management strategies to protect groundwater ecosystems and their communities.

Diurnal Variations in Vegetation Activity affecting Shallow Groundwater Flow identified by Microthermal Measurements

Observations of summer microthermal temperature variations suggest, next to hydrological factors, a significant influence of plant activity on groundwater flow in fractured claystone materials. Variations in groundwater microtemperature were compared to variations in meteorological parameters and electrical potential of plants. With an increase in surface temperature, relative air humidity decreases and an increase in tree electrical potential, measured as the difference between the northern and the southern stem exposure (N–S), can be observed. This increase in electrical potential is concomitant with a change in groundwater temperature of approximately 2 mK. This relationship does not always occur. At high temperatures (+30°C) the decrease amounts to just 1 mK. This fact is related to the change in transpiration of plants, decreased or even suspended at high surface temperatures. A frequency analysis of all data showed a daily frequency of high magnitude in all parameters. Possibly changes in the macro weather situation events were observed in the results of atmospheric pressure, southern electric potential and groundwater temperature. The lag time between changes in electric potential and subsurface microtemperature changes amounts to 17 hours, possibly a result of the electrical potential difference between the northern and the southern exposure of the stem (N–S), and 5 hours, the result of the change in electrical potential difference between the southern and the northern stem exposure side (S–N). A comparison between potential changes and the computed change in gravity resulting from earth tidal effects showed that the correlation between the subsurface temperature variation with up to 2 mK and the change in surface temperature variation does not match directly. Other study shows that the impact of earth tides on subsurface microtemperature variation amounts to ca. 1mK. The effect of groundwater abstraction by mature vegetation is determined at the same range. Atmospheric tides can be correlated with the changes in north and south electric potentials.

Groundwater level and temperature changes following the great Tangshan earthquake of 1976 near the epicenter

Several meters of rise in groundwater level with significant changes in groundwater temperature were observed near the epicenter of the 1976 Tangshan earthquake—an intraplate earthquake with a magnitude of M S=7.8 that occurred in northern China. The origin of the groundwater level rise, however, remains a mystery. Studying the groundwater level rise can provide insight into the faulting process and has implications for water resources. In this study, we analyze the indications of the groundwater temperature data on the characteristics of the rising groundwater. The results show that the upward flow was maintained for approximately 5 days, and the depth of the rising groundwater was about 1–2 km. We then examine the groundwater level and temperature data with several reported models in order to explain the cause of the groundwater level rise. The results indicate that the groundwater level rise is attributable to the earthquake-induced enhancement of vertical hydraulic connection between the shallow and deep aquifers, leading to the upwelling of deep fluids that causes the groundwater levels to rise.

ღრმად განლაგებული სითხის გეოთერმული პირობები კოლხეთის არტეზიულ აუზში: წყლის ქიმიური შედგენილობა და გეოთერმომეტრია

Among the most important issues to be characterized is the temperature of the aquifer in any geothermal system. Fluids located deep within a hydrothermal system provide heat, and they control thermal groundwater temperature changes in aquifers. Geothermometers based on water chemistry have been used to estimate groundwater temperatures in various complexes. However, the average temperature measured by hydrochemical geothermometers is often variable, and it is difficult to assign a corresponding average geothermal fluid temperature because temperature and pressure change as the geothermal fluid moves upward. Different geothermometers cover different temperature ranges. Some hydrochemical geothermometers are suitable for high temperature geothermal systems, while others are suitable for medium and low temperature. Based on these geothermometers, it is difficult to assign a temperature that is close to the actual temperature of the geothermal system, because the influence of atmospheric precipitation, which causes a decrease in the concentration of chemical components and dilution due to mixing with shallow groundwater.

Modeling Semiarid River–Aquifer Systems with Bayesian Networks and Artificial Neural Networks

In semiarid areas, precipitations usually appear in the form of big and brief floods, which affect the aquifer through water infiltration, causing groundwater temperature changes. These changes may have an impact on the physical, chemical and biological processes of the aquifer and, thus, modeling the groundwater temperature variations associated with stormy precipitation episodes is essential, especially since this kind of precipitation is becoming increasingly frequent in semiarid regions. In this paper, we compare the predictive performance of two popular tools in statistics and machine learning, namely Bayesian networks (BNs) and artificial neural networks (ANNs), in modeling groundwater temperature variation associated with precipitation events. More specifically, we trained a total of 2145 ANNs with different node configurations, from one to five layers. On the other hand, we trained three different BNs using different structure learning algorithms. We conclude that, while both tools are equivalent in terms of accuracy for predicting groundwater temperature drops, the computational cost associated with the estimation of Bayesian networks is significantly lower, and the resulting BN models are more versatile and allow a more detailed analysis.

Climate change effects on groundwater recharge and temperatures in Swiss alluvial aquifers

Climate change will have both quantitative and qualitative effects on groundwater resources. These impacts differ for aquifers in solid and unconsolidated rock, in urban or rural locations, and in the principal processes of groundwater recharge.Having knowledge about the intrinsic key parameters (aquifer geometries, storage properties, groundwater renewal rates, residence times, etc.), the principal groundwater recharge processes, and the temperature imprinting makes it possible to compare and forecast the sensitivity of individual aquifers to climate change.The sensitivity of future groundwater temperature development for selected climate projections was qualitatively investigated for representative Swiss unconsolidated rock groundwater resources in the Central Plateau as well as the Jura and Alpine region.For non-urban and rural areas, climate change is expected to have a strong overall impact on groundwater temperatures. In urban areas, however, direct anthropogenic influences are likely to dominate. Increased thermal subsurface use and waste heat from underground structures, as well as adaptation strategies to mitigate global warming, increase groundwater temperatures. Likewise, measurements for the city of Basel show that groundwater temperatures increased by an average of 3.0 ± 0.7 °C in the period from 1993 to 2016, and that they can exceed 18 °C, especially in densely urbanized areas. Similarly, regarding shallow aquifers with low groundwater saturated zone thicknesses, such as in Davos (Canton Grisons), groundwater temperatures will strongly be influenced by changes in groundwater recharge regimes. In contrast, groundwater temperature changes within deep aquifers with large groundwater saturated zone thicknesses, such as in Biel/Bienne (Canton Bern), or in some cases in aquifers with large distances from the land surface to the groundwater table and extended unsaturated zones, such as in Winterthur (Canton Zurich), are strongly attenuated and can only be expected over long time periods.In the context of the presented research we hypothesized that quantitative groundwater recharge and the associated temperature imprinting of aquifers is primarily determined by infiltrating surface waters (i.e. “river-fed aquifers”). We show that seasonal shifts in groundwater recharge processes could be an important factor affecting future groundwater temperatures. Moreover, the interaction with surface waters and increased groundwater recharge during high runoff periods are likely to strongly influence groundwater temperatures. Accordingly, for the “business as usual” climate change scenario and for the end of the century, a shift in precipitation and river flood events from summer to winter months could be accompanied by an increase in groundwater recharge in comparatively cool seasons, which would be accompanied by a tendency to “cool down” groundwater resources.

Application of 222Rn and microbial diversity to characterize groundwater/surface-water interactions in a riverside area (South Korea)

The interactions between groundwater and surface water under a river island in South Korea were investigated. Sampling was focused on the western part of the island, where a groundwater heat pump system with groundwater monitoring wells has been installed. A riverside area was selected for the system because a high specific capacity was expected. However, surface-water intrusion remains a major concern, as the efficiency of the system can be impaired by groundwater temperature changes following surface-water infiltration. A combination of radon (222Rn) concentrations and microbial diversity was analyzed, along with hydraulic data. A process for estimating residence time based on 222Rn data and flow direction was developed to identify relationships with microbial diversity. The spatial distribution of 222Rn concentration was affected by fluctuations of river water levels caused by surrounding dam discharge and seasonal effects. Groundwater flowmeter data supported observations on these distributions. The estimated residence times indicated that river-water infiltration into the study site affected the groundwater flow direction. The microbial diversity, based on cluster analyses after pyrosequencing, showed significant variation with river flow direction and rainfall events, which was in accordance with the 222Rn tracer results. The combination of frequent 222Rn concentration measurements with microbial data allows better characterization of the dynamic interactions between groundwater and surface water.

Radon concentration in groundwater sources of the Baikal region (East Siberia, Russia)

In this study, we conduct a systematic study of groundwater radioactivity in the territories around Lake Baikal in Siberia, including Pribaikalie and Transbaikalia. The database includes more than 200 measurements of 222Rn from monitored water sources in the study region. We classify the groundwater sources in the Baikal region into seven groups (I–VII) that differ in radon concentration in space and time. The spatial distribution of water sources belonging to certain groups depend on geochemical and structural factors. In Transbaikalia, intrusive rocks with elevated contents of uranium are abundant. In Pribaikalie, many water sources are classified into Groups I and II (Q < 100 Bq/L). Group I includes groundwater with background concentrations, and Group II includes groundwater with anomalous concentrations of radon. Water sources belonging to elevated radon concentration Groups III to VI are considered as anomalies. Faulting is one of the main causes of radon anomalies as groundwater in the fault zones is enriched with 222Rn due to the increased permeability of rocks and rock crushing resulting from displacements of the fault walls.Monitoring of water sources in Pribaikalie shows that 222Rn concentrations vary also in time mainly within the range of values corresponding to a particular group. The oscillatory pattern of the temporal variations is clearly revealed by radon measurements conducted every two weeks and depends mainly on meteorological factors. Seasonal variations in air temperature and atmospheric pressure lead to changes in groundwater temperature, dilution of groundwater due to precipitation, freezing the top layer of soil, and other phenomena. As a result, the concentration regularly increases in winter and decreases in summer. In this study, seismic activity has not been revealed as significant factor of impact on the concentration of radon in groundwater, since strong earthquakes did not occur during the monitoring period.

Temperature-driven groundwater convection in cold climates

The aim was to study density-driven groundwater flow and analyse groundwater mixing because of seasonal changes in groundwater temperature. Here, density-driven convection in groundwater was studied by numerical simulations in a subarctic climate, i.e. where the water temperature was <4 °C. The effects of soil permeability and groundwater temperature (i.e. viscosity and density) were determined. The influence of impermeable obstacles in otherwise homogeneous ground was also studied. An initial disturbance in the form of a horizontal groundwater flow was necessary to start the convection. Transient solutions describe the development of convective cells in the groundwater and it took 22 days before fully developed convection patterns were formed. The thermal convection reached a maximum depth of 1.0 m in soil of low permeability (2.71 · 10−9 m2). At groundwater temperature close to its density maximum (4 °C), the physical size (in m) of the convection cells was reduced. Small stones or frost lenses in the ground slightly affect the convective flow, while larger obstacles change the size and shape of the convection cells. Performed simulations show that “seasonal groundwater turnover” occurs. This knowledge may be useful in the prevention of nutrient leakage to underlying groundwater from soils, especially in agricultural areas where no natural vertical groundwater flow is evident. An application in northern Sweden is discussed.

Shallow groundwater thermal sensitivity to climate change and land cover disturbances: derivation of analytical expressions and implications for stream temperature modeling

Abstract. Climate change is expected to increase stream temperatures and the projected warming may alter the spatial extent of habitat for cold-water fish and other aquatic taxa. Recent studies have proposed that stream thermal sensitivities, derived from short-term air temperature variations, can be employed to infer future stream warming due to long-term climate change. However, this approach does not consider the potential for streambed heat fluxes to increase due to gradual warming of the shallow subsurface. The temperature of shallow groundwater is particularly important for the thermal regimes of groundwater-dominated streams and rivers. Also, recent studies have investigated how land surface perturbations, such as wildfires or timber harvesting, can influence stream temperatures by changing stream surface heat fluxes, but these studies have typically not considered how these surface disturbances can also alter shallow groundwater temperatures and streambed heat fluxes. In this study, several analytical solutions to the one-dimensional unsteady advection–diffusion equation for subsurface heat transport are employed to estimate the timing and magnitude of groundwater temperature changes due to seasonal and long-term variability in land surface temperatures. Groundwater thermal sensitivity formulae are proposed that accommodate different surface warming scenarios. The thermal sensitivity formulae suggest that shallow groundwater will warm in response to climate change and other surface perturbations, but the timing and magnitude of the subsurface warming depends on the rate of surface warming, subsurface thermal properties, bulk aquifer depth, and groundwater velocity. The results also emphasize the difference between the thermal sensitivity of shallow groundwater to short-term (e.g., seasonal) and long-term (e.g., multi-decadal) land surface-temperature variability, and thus demonstrate the limitations of using short-term air and water temperature records to project future stream warming. Suggestions are provided for implementing these formulae in stream temperature models to accommodate groundwater warming.

Temperature Fluctuations in a Landfill in Response to Periodic Changes in Surface and Tide-Driven Groundwater Temperatures

In Australia, the concentration of population along the coastal regions has resulted in the construction of landfills near the coastal regions. The wastes buried in these unlined landfills are therefore exposed to tidal influence, often resulting in the dispersion of organic and inorganic pollutants to the surrounding environment. In a project cosponsored by the Rockhampton Regional Council, a number of processes at a landfill site situated in the flood plains of the Fitzroy River are being investigated. The processes include those in terms of multiphase flow consisting of gas (methane), solute (measured as salts, via EC and pH) and water in a porous media. In this paper we analyse temperature changes in groundwater and porous media of the landfill which is subject to periodic surface and tide-driven temperatures. The heat equation is solved, subject to two periodic boundary conditions (BC): the top BC is a periodic surface temperature due to the change in air temperature, and bottom BC is a periodic function to account for the changes in groundwater temperature induced by tides. The methods can be used to locate key parameters and variables of concern in the porous media, and to forecast their variability with time, using publicly available air temperature and tide data.

Basin‐scale transport of heat and fluid induced by earthquakes

Large earthquakes are known to cause widespread changes in groundwater flow, yet their relation to subsurface transport is unknown. Here we report systematic changes in groundwater temperature after the 1999 Mw7.6 Chi‐Chi earthquake in central Taiwan, documented by a dense network of monitoring wells over a large (17,000 km2) alluvial fan near the epicenter. Analysis of the data reveals a hitherto unknown system of earthquake‐triggered basin‐wide groundwater flow, which scavenges geothermal heat from depths, changing groundwater temperature across the basin. The newly identified earthquake‐triggered groundwater flow may have significant implications on postseismic groundwater supply and quality, contaminant transport, underground repository safety, and hydrocarbon production.

Potential surface temperature and shallow groundwater temperature response to climate change: an example from a small forested catchment in east-central New Brunswick (Canada)

Abstract. Global climate models project significant changes to air temperature and precipitation regimes in many regions of the Northern Hemisphere. These meteorological changes will have associated impacts to surface and shallow subsurface thermal regimes, which are of interest to practitioners and researchers in many disciplines of the natural sciences. For example, groundwater temperature is critical for providing and sustaining suitable thermal habitat for cold-water salmonids. To investigate the surface and subsurface thermal effects of atmospheric climate change, seven downscaled climate scenarios (2046–2065) for a small forested catchment in New Brunswick, Canada were employed to drive the surface energy and moisture flux model, ForHyM2. Results from these seven simulations indicate that climate change-induced increases in air temperature and changes in snow cover could increase summer surface temperatures (range −0.30 to +3.49 °C, mean +1.49 °C), but decrease winter surface temperatures (range −1.12 to +0.08 °C, mean −0.53 °C) compared to the reference period simulation. Thus, changes to the timing and duration of snow cover will likely decouple changes in mean annual air temperature (mean +2.11 °C) and mean annual ground surface temperature (mean +1.06 °C). Projected surface temperature data were then used to drive an empirical surface to groundwater temperature transfer function developed from measured surface and groundwater temperature. Results from the empirical transfer function suggest that changes in groundwater temperature will exhibit seasonality at shallow depths (1.5 m), but be seasonally constant and approximately equivalent to the change in the mean annual surface temperature at deeper depths (8.75 m). The simulated increases in future groundwater temperature suggest that the thermal sensitivity of baseflow-dominated streams to decadal climate change may be greater than previous studies have indicated.

Evaluating the effect of temperature induced water viscosity and density fluctuations on virus and DOC removal during river bank filtration - a scenario analysis

Riverbank fi ltration is considered an effi cient method for removing contaminants from infi ltrated surface water in the subsurface. Despite indications that changing water temperatures affect the biochemical and biological mediated removal processes of contaminants, the impact of temperature induced fl uid viscosity and density effects on contaminant removal during riverbank fi ltration is not well understood. This paper investigates the viscosity and density effects associated with seasonal changes in groundwater temperature on virus and dissolved organic carbon (DOC) removal during riverbank fi ltration. Hypothetical aquifer and fl ood wave scenarios were assumed. Data on groundwater temperature were taken from an Austrian fi eld site of the River Danube recorded during 2010/2011. Based on removal rates taken from previously published fi eld experiments, virus and DOC transport was simulated for highly permeable gravel, fi ne gravel and fi ne sandy gravel material. Our simulations indicate that for DOC and a wide range of virus types the viscosity and density effects induced by water temperature changes can counteract with temperature dependent decay and inactivation rates. For particular situations, however, such as for receding fl oods during colder periods, our simulations indicate that fl uid viscosity and density effects can result in a net de- crease in the virus removal effi ciency during colder periods. Persistent types of viruses (e.g. polio 1 or HAV ) can be reduced less effectively and may travel by up to 25 % faster during warmer than during colder periods. Our simula- tions indicate that viscosity and density effects induced by temperature changes should be considered for studying and simulating virus or DOC removal and transport during riverbank fi ltration. The effects may be important spe- cifi cally at fi eld sites with a high river-aquifer exchange and large variations in groundwater temperature.

Groundwater responses to the 2011 Tohoku Earthquake on Jeju Island, Korea

AbstractGroundwater responses at 15 monitoring wells on Jeju Island were observed in relation to the magnitude 9.0 Tohoku Earthquake off the Pacific coast of Honshu, Japan, on 11 March 2011, at 14:46:23 h local time (05:46:24 h UTC time). In coastal areas, the groundwater level responses to the earthquake were oscillatory at 12 wells, and the range of the maximum groundwater level changes was 3–192.4 cm. The response durations were approximately 1–62 min. The relationship between the maximum groundwater level changes and the response durations displayed a high correlation coefficient (r = 0.81). Groundwater temperature changes were also observed at 7 of 12 wells 3–10 min after the seismic wave arrived, and the range was from 0.01 °C to 1.20 °C. In mid‐elevation areas, the groundwater level changes appeared in three different forms: oscillatory, spiky and persistent. The groundwater temperature changes were also observed at two wells. One indicated decreasing and recovering temperatures, and the other exhibited rising and persistent temperatures. The primary temperature changes occurred 5–6 min after the earthquake and 2–3 min after the seismic wave arrived. In addition, the electrical conductivities at the depth of the transition zone were monitored, and the responses to the earthquake appeared at all three wells. Although the electrical conductivity and temperature changes were not well understood, groundwater inflow and mixing were likely caused by the earthquake, and the responses were various and site specific. The responses to the earthquake were closely related to the hydrogeological characteristics at each monitoring well, and a more detailed hydrogeological characterization is needed to understand the mechanisms related to earthquakes in general. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Transient change in groundwater temperature after earthquakes

Research Article| February 01, 2012 Transient change in groundwater temperature after earthquakes Chi-yuen Wang; Chi-yuen Wang 1Earth & Planetary Science, University of California, Berkeley, California 94720, USA Search for other works by this author on: GSW Google Scholar Michael Manga; Michael Manga 1Earth & Planetary Science, University of California, Berkeley, California 94720, USA Search for other works by this author on: GSW Google Scholar Chung-Ho Wang; Chung-Ho Wang 2Institute of Earth Sciences, Academia Sinica, Nankang, Taipei 11529, Taiwan Search for other works by this author on: GSW Google Scholar Chieh-Hung Chen Chieh-Hung Chen 2Institute of Earth Sciences, Academia Sinica, Nankang, Taipei 11529, Taiwan Search for other works by this author on: GSW Google Scholar Author and Article Information Chi-yuen Wang 1Earth & Planetary Science, University of California, Berkeley, California 94720, USA Michael Manga 1Earth & Planetary Science, University of California, Berkeley, California 94720, USA Chung-Ho Wang 2Institute of Earth Sciences, Academia Sinica, Nankang, Taipei 11529, Taiwan Chieh-Hung Chen 2Institute of Earth Sciences, Academia Sinica, Nankang, Taipei 11529, Taiwan Publisher: Geological Society of America Received: 20 Jun 2011 Revision Received: 25 Aug 2011 Accepted: 12 Sep 2011 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2012 Geological Society of America Geology (2012) 40 (2): 119–122. https://doi.org/10.1130/G32565.1 Article history Received: 20 Jun 2011 Revision Received: 25 Aug 2011 Accepted: 12 Sep 2011 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Chi-yuen Wang, Michael Manga, Chung-Ho Wang, Chieh-Hung Chen; Transient change in groundwater temperature after earthquakes. Geology 2012;; 40 (2): 119–122. doi: https://doi.org/10.1130/G32565.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Postseismic decrease in groundwater temperature was documented on the upper rim of a large alluvial fan near the epicenter of the 1999 Mw 7.5 Chi-Chi earthquake (Taiwan). We use a model of coupled heat transport and groundwater flow, constrained by documented water-level changes, to interpret this change. We show that groundwater temperature is sensitive to earthquake-induced flow and the observed temperature decrease may be explained by increased groundwater discharge due to earthquake-enhanced vertical permeability. The result implies that heat flow near active mountain fronts may be lowered by recurrent earthquakes. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

온도, 유동특성 및 지화학분석 자료를 이용한 지표수-지하수 연계특성 평가

We examined the interactions between surface and groundwater through (1) flowmeter logging, (2) measurements of seasonal and vertical changes in temperature within a well, and (3) geochemical analyses of water samples from nine groundwater-monitoring wells. At two wells adjacent to a stream, subsurface water was found to flow from the stream to a surrounding alluvial fan, and the seasonal change in groundwater temperature is similar to those of surface water and air. Geochemical analyses at two wells indicated hydro-geochemical features affected by streamwater inflow, showing seasonal variations. Accordingly, these two wells are located in an area with active interaction between surface water and groundwater. The Thermochron I-button used in the present study is useful for this type of study of groundwater?surface water interaction because of its low cost and small size.

Seasonal groundwater turnover

Seasonal air temperature variations and corresponding changes in groundwater temperature cause convective movements in groundwater similar to the seasonal turnover in lakes. Numerical simulations were performed to investigate the natural conditions for thermally driven groundwater convection to take place. Thermally driven convection could be triggered by a horizontal groundwater flow. Convection then starts at a considerably lower Rayleigh number (Ra) than the general critical Rayleigh number (Rac) assuming that 10°C groundwater is cooled to 4°C, i.e. heated from below convection in porous media. This study supports the hypothesis that seasonal temperature variations, under certain conditions, initiate and drive thermal convection.

Influence of climatic changes on freshwater travertine deposition: A new hypothesis

Observations made in different parts of the world on freshwater travertine deposits show that in most cases their formation started during the Early Holocene and generally came to an end, or underwent a strong decline, in the Post-Atlantic. A similar trend seems to have also characterised the previous warm stages (Interglacials and Interstadials) of the Quaternary. A satisfactory explanation of this decline is not yet available even though different hypotheses have been proposed by several authors: some of them point out the influence of climatic changes, while others invoke the effects of human impact.However, no specific reference has been made to a possible role of groundwater temperature changes, notwithstanding their well-known influence on the calcium carbonate dissolution equilibrium. In particular, differences between lower temperature of ground waters (influenced by deep penetration into the limestone bedrock of Late Pleistocene surface temperatures) and the higher external temperature at the spring may have played an important role. The infiltrating waters, enriched in CO2 by percolating through the newly formed soils, acquired higher CaCO3 dissolution capacity because of underground temperatures being colder by several °C. The higher temperatures at the emergence, in conjunction with algal-bacterial activity, may have caused loss of CO2 and travertine deposition. This process may have continued for a long time because of the low thermal capacity of the limestone bedrock, where ground water circulated through fissures and channels within large volumes of dry rock, and the progressive increase of atmospheric temperature during Lower-Middle Holocene.