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Enviroscan Ukrainian Institute of Speleology and Karstology


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Community news

Speleology in Kazakhstan

Shakalov on 04 Jul, 2018
Hello everyone!   I pleased to invite you to the official site of Central Asian Karstic-Speleological commission ("Kaspeko")   There, we regularly publish reports about our expeditions, articles and reports on speleotopics, lecture course for instructors, photos etc. ...

New publications on hypogene speleogenesis

Klimchouk on 26 Mar, 2012
Dear Colleagues, This is to draw your attention to several recent publications added to KarstBase, relevant to hypogenic karst/speleogenesis: Corrosion of limestone tablets in sulfidic ground-water: measurements and speleogenetic implications Galdenzi,

The deepest terrestrial animal

Klimchouk on 23 Feb, 2012
A recent publication of Spanish researchers describes the biology of Krubera Cave, including the deepest terrestrial animal ever found: Jordana, Rafael; Baquero, Enrique; Reboleira, Sofía and Sendra, Alberto. ...

Caves - landscapes without light

akop on 05 Feb, 2012
Exhibition dedicated to caves is taking place in the Vienna Natural History Museum   The exhibition at the Natural History Museum presents the surprising variety of caves and cave formations such as stalactites and various crystals. ...

Did you know?

That mechanical dispersion is the process whereby solutes are mechanically mixed during advective transport caused by the velocity variations at the microscopic level. synonymous with hydraulic dispersion [22].?

Checkout all 2699 terms in the KarstBase Glossary of Karst and Cave Terms


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Featured articles from Cave & Karst Science Journals
Chemistry and Karst, White, William B.
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Featured articles from other Geoscience Journals
Karst environment, Culver D.C.
Mushroom Speleothems: Stromatolites That Formed in the Absence of Phototrophs, Bontognali, Tomaso R.R.; D’Angeli Ilenia M.; Tisato, Nicola; Vasconcelos, Crisogono; Bernasconi, Stefano M.; Gonzales, Esteban R. G.; De Waele, Jo
Calculating flux to predict future cave radon concentrations, Rowberry, Matt; Marti, Xavi; Frontera, Carlos; Van De Wiel, Marco; Briestensky, Milos
Microbial mediation of complex subterranean mineral structures, Tirato, Nicola; Torriano, Stefano F.F;, Monteux, Sylvain; Sauro, Francesco; De Waele, Jo; Lavagna, Maria Luisa; D’Angeli, Ilenia Maria; Chailloux, Daniel; Renda, Michel; Eglinton, Timothy I.; Bontognali, Tomaso Renzo Rezio
Evidence of a plate-wide tectonic pressure pulse provided by extensometric monitoring in the Balkan Mountains (Bulgaria), Briestensky, Milos; Rowberry, Matt; Stemberk, Josef; Stefanov, Petar; Vozar, Jozef; Sebela, Stanka; Petro, Lubomir; Bella, Pavel; Gaal, Ludovit; Ormukov, Cholponbek;
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Your search for sensitivity (Keyword) returned 71 results for the whole karstbase:
Showing 31 to 45 of 71
Comparison of immunofluorescence assay and immunomagnetic electrochemiluminescence in detection of Cryptosporidium parvum oocysts in karst water samples, 2003,
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Kuczynska E. , Boyer D. G. , Shelton D. R. ,
Immunofluorescence assay (IFA) and immunomagneticelectrochemiluminescence (IM-ECL) were used for comparison of the percent recovery of Cryptosporidium parvum in environmental water samples obtained from a spring draining a karst basin. The monoclonal antibodies to C. parvum, isotype IgG3 were used for optimization of the IM-ECL protocol. The combination of biotinylated and TAG-labeled anti-C. parvum antibodies with the streptavidin beads gave a linear regression slope for log ECL vs. log fresh oocysts of 0.79 (from 5 to 5000 oocysts), which indicates a constant ECL signal per oocyst. Standard curves gave a dynamic range of 5 to 5000 oocysts/ml (fresh) and 10 to 100,000 cells/ml (4-month-old oocysts) with the maximum limit of linear detection higher than 100,000. The linear slope of 4-month-old oocysts decreased to 0.62, which indicates that ECL signal is a function of oocyst age. The experiment associated with bead storage time shows that even after 4 months of storage of the biotinylated antibodies, the complex retains the ability for binding the oocysts and generating the ECL signal. Based on the IFA results in the experiment evaluating different protocols for oocysts recovery from karst water samples, the most efficient protocol involved dispersion, followed by flotation and immunomagnetic separation (IMS) (24% recovery). The ECL results obtained in that experiment were very similar to the results obtained in the IFA method, which indicates that the IM-ECL method is accurate. Results of the IFA in the study of the prevalence of C. parvum in the groundwater showed that oocysts were present in 78% of 1 L water samples with average number of oocysts of 6.4 5.5 and ranged from 0 (13 samples) to 23.3 (2 samples). The ECL signal generated from these water samples ranged from 3771 to 622 (average 1620 465). However, the background value estimated in groundwater samples with low number of oocysts detected by IFA was highly variable and elevated (from 3702 to 272, average 1503 475). The background value as a result of nonspecific binding to beads by unidentified organic components in the water can inhibit or even completely mask the signal generated by oocysts. Our investigations showed that the IM-ECL method appears to be promising for the qualitative and quantitative detection of C parvum from the environmental water; however, the method requires further development to improve sensitivity and account for background signals. Published by Elsevier Science B.V

Sequence Stratigraphy and Carbonate-Siliciclastic Mixing in a Terminal Proterozoic Foreland Basin, Urusis Formation, Nama Group, Namibia, 2003,
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Saylor Beverly Z. ,
Superb three-dimensional exposures of mixed carbonate and siliciclastic strata of the terminal Proterozoic Urusis Formation in Namibia make it possible to reconstruct cross-basin facies relations and high-resolution sequence stratigraphic architecture in a tectonically active foreland basin. Six siliciclastic facies associations are represented: coastal plain; upper shoreface; middle shoreface; lower shoreface; storm-influenced shelf; and pebble conglomerate. Siliciclastic shoreface facies pass seaward into and interfinger with facies of an open carbonate shelf. Four carbonate facies associations are present: mid-shelf; shelf crest; outer shelf; and slope. Facies are arranged hierarchically into three scales of unconformity-bounded sequences. Small-scale sequences are one to tens of meters thick and span a few thousand years. They consist of shelf carbonate with or without shoreface siliciclastic facies near the bottom. Medium-scale sequences are tens of meters thick and span a few hundred thousand years. They consist of shoreface siliciclastic facies in their lower parts, which grade upward and pass seaward into shelf carbonate. Large-scale sequences are tens to hundreds of meters thick and span 1 to 2 million years. They are identified by widespread surfaces of exposure, abrupt seaward shifts in shoreface sandstone, patterns of facies progradation and retrogradation, and shoreline onlap by medium-scale sequences. Patterns of carbonate-siliciclastic mixing distinguish tectonic from eustatic controls on the evolution of large-scale sequences. Characteristics of eustatically controlled large-scale sequences include: (1) basal unconformities and shoreface sandstone that extend across the shelf to the seaward margin; (2) retrograde carbonate and siliciclastic facies belts that onlap the shoreline together, symmetrically, during transgression; and (3) upper shoreface sandstone that progrades seaward during highstand. In contrast, tectonically controlled sequences feature: (1) basal erosion surfaces and upper shoreface sandstone that are restricted to near the landward margin and pass seaward into zones of maximum flooding; and (2) asymmetric stratigraphic development characterized by landward progradation of carbonate from the seaward margin coincident with backstepping and onlap of the shoreline by siliciclastic facies. A two-phase tectonic model is proposed to account for the stratigraphic asymmetry of tectonically controlled sequences. Increased flexural bending during periods of active thrust loading caused submergence of the seaward margin and uplift of the landward margin. Rebound between thrusting episodes flattened the basin gradient and submerged the landward margin, causing expansion of carbonate facies from the seaward margin and simultaneous transgression of the landward margin. Although the two-phase model should apply to single-lithology successions deposited in active foreland basins, the mixing of carbonate and siliciclastic facies provides a particularly sensitive record of tectonic forcing. The sensitivity may be sufficient for medium- and small-scale sequences to record higher-frequency variations in flexural warping

Hydraulic calculations of postglacial connections between the Mediterranean and the Black Sea, 2003,
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Myers Paul G. , Wielki Chris, Goldstein Shoshana B. , Rohling Eelco J. ,
A series of simple hydraulic calculations has been performed to examine some of the questions associated with the reconnection of the Black Sea to the Mediterranean through the Turkish Strait System during the Holocene. Ryan et al.'s catastrophic flood scenario, whereby the erosive power of the marine in-fluxes, initiated after eustatic sea level reached the sill depth, opened up the Bosphorus, allowing saline water to pour into the Black Sea and filling it on a short time scale, is examined. The calculations show that although it might be possible to fill the palaeo-Black Sea within the order of a decade, a 1-2 year filling time scale is not physically possible. A hydraulic model is also used to examine the more traditional connection hypothesis of (near-)continuous freshwater outflow from the Black Sea, with a slowly increasing saline inflow from the Mediterranean beginning around 8-9 kyr BP. The model considers two forms for the structure of the Bosphorus: a shallow sill as seen today and a deep sill associated with no sediments filling the 100 m gorge above the bedrock in the strait. Sensitivity experiments with the hydraulic model show what possible strait geometric configurations may lead to the Black Sea reaching its present-day salinity of 18 psu. Salinity transients within the Black Sea are shown as a function of time, providing for values that can be validated against estimates from cores. To consider a deep, non-sediment-filled Bosphorus (100 m deep), the entry of Mediterranean water into the Sea of Marmara after 12.0 kyr BP is examined. A rapid entry of marine water into the Sea of Marmara is only consistent with small freshwater fluxes flowing through the Turkish Strait System, smaller than those of the present day by a factor of at least 4. Such a small freshwater flux would lead to the salinification of the Black Sea being complete by an early date of 10.2-9.6 kyr BP. Thus the possibility of a deep Bosphorus sill should be discounted

Karst aquifers vulnerability or sensitivity?, 2003,
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Kovač, Ič, Gregor, Ravbar Nataš, A

The concept of karst aquifer vulnerability mapping is commonly used for the determination of water protection zones and planning of land use in the background of the captured karst sources and wells. Several different methodologies for karst aquifer vulnerability mapping exist and the examination of scientific literature shows considerable variations in the definition of the term vulnerability. The authors suggest the distinction between the terms vulnerability and sensitivity of karst aquifers, since the former includes more information, which are required for efficient protection. The interpretation of the applied terms is founded on the conceptual background of the environmental vulnerability studies, which are declared with the Slovene 1993 Environmental Protection Act.


The case study on soil fauna diversity in different ecological system in Shilin national park, Yunnan, China, 2003,
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Xiang C. , Song L. , Zhang P. , Pan G.

A preliminary study of the distribution and diversity of soil fauna in a sequence of ecosystem degradation in the Shilin National Park, Yunnan, China has been made. The degraded ecologic system includes 5 types of vegetation cover: (1) natural bush; (2) human planted cypress forest; (3)natural grass; (4)secondary grass and (5) bared red earth. A quadrate of 1m_1m in each eco-tessera was sampled for soil fauna collection. The animals were obtained either by picking up or by heat-removing. The soil fauna were dominated by Acarina, Collembola, Nematode, Coleoptera,and Opistopora in these soils. However, Erchytraeidae, Araneida, Lepidoptera and Diptera were also common groups. The diversity index H turned to be less than 1.5, drastically decreasing with the vegetation degradation trend. In the karst soils, Parholaspidae was one of the most populous among the mites. The biomass of Trhypochthoniidae and Ologamasidae was very concentrated in the natural bush ecosystem, showing high sensitivity of mites to vegetation degradation. The biomass ratio of Acarina to Collembola in the studied soils ranged from 0.70 to 1.50, which was in great discrepancy to the results reported of the natural soils at similar latitude. The small soil fauna biomass and less diversity indicated that the studied soil was in a state of deterioration of soil fauna habitats and, in turn, the soil ecosystem health. The results also evidenced that the soil fauna in the karst soil was definitely vulnerable as regarded to the sustainable development of the Shilin Park.


Surface cover infiltration index: a suggested method to assess infiltration capacity for intrinsic vulnerability in karstic areas in absence of quantitative data, 2004,
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Ekmekci Mehmet, Tezcan Levent
Karst is a hydrogeological environment of importance not only for its water resources potential but also for its scenic and economic potential, thereby increasing the intensity of human impact. The uniqueness of karst in this regard stems from its high sensitivity and vulnerability to imposed pressures and its distinctive response to these pressures. Therefore, a clear definition and formulation of the concept of intrinsic vulnerability is essential for the design of vulnerability and/or management criteria of the karstic system as a resource. In this regard, the recharge rate, the amount of water passing through the unsaturated zone into the aquifer, is among the principal attributes of the intrinsic vulnerability. Where data and measurements are available for even large areas, recharge can be evaluated quantitatively on the basis of field measurements and the water balance equation. However, particularly for countries suffering from lack of essential data for a quantitative evaluation of the net recharge rate, the recharge can be estimated using some derived parameters such as the so called Surface Cover Infiltration Index proposed in this paper. The DRASTIC method which is modified by using SCI, soil thickness and precipitation, allows the unique hydrological behavior of karst to be considered by redistributing of the intrinsic vulnerability values on the basis of hydrologic connections between neighboring cells. Following a detailed description of the SCI index and the modification of DRASTIC method for karst aquifers, a case study carried out to demonstrate this method is presented in this paper whose objective is to discuss and thus elaborate the suggested methodology. The Olimpos National Park area was selected because the great variation in lithology, landuse and topography. It was found that the relative vulnerability may vary particularly in the neighborhood of the highly vulnerable cells covered by carbonate rocks. The methodology was applied using ARC-GIS software. All spatial features used in computations were classified by the appropriate functions built into the software.

Speleothem rupture in karst: tectonic or climatic origin? U-Th dating of rupture events in Salamandre Cave (Gard, southeastern France), 2004,
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Ponsbranch, Hamelin B. , Brulhet J. , Bruxelles L. ,
Caves are relatively protected from the main external erosional factors. Therefore, they constitute potentially reliable places for long-term conservation of continental history. Moreover their secondary carbonated deposits, the speleothems, can be dated precisely on the 0-500 ka time-scale using U-series isotopes measured by thermo-ionisation mass spectrometry (TIMS). Tectonic events (tectonic displacements and earthquakes) may change cave morphology and induce speleothem breaking or displacement as has been shown by previous studies performed mainly in Italy [Forti et Postpischl, 1984; Postpischl et al., 1991 for example]. Nevertheless, collapses of speleothems observed today in caves are difficult to interpret as their origin may be linked to several other natural processes. We studied the Aven de la Salamandre cave located in southeastern France (Gard), an area between the Cevennes fault and the Nimes fault, where evidence of Quaternary vertical movements was previously described. However, this region is not considered to be a seismic active zone. The Aven de la Salamandre cave is characterized by numerous broken speleothems. Some of them are very large and a lot of them are covered by growth of new calcite or new speleothem generation. We report here 13 TIMS U/Th analysis performed on two broken speleothems recovered by second generation calcite growth. Dating results are discussed through time corrections due to detrital content of calcite. In the first sequence, a 7 0.35 ka fracture event is identified. In the second sequence, the age of the breakdown is between 1.1 0.1 and 6.3 2 ka. These events could thus be contemporary. Hypotheses for the origin of this fracture event are presented and discussed: (i) karstic catastrophic event due to intense climatic changes or to cavity collapse (break down of hanging wall, gravity, landslide...); (ii) co-seismic ruptures. The first conclusion of this study is that these collapse episodes in the Aven de la Salamandre cave cannot be due to the direct effect of an earthquake or climatic event. Only indirect effects of flooding (by mobilization of the argillaceous components of the floor and consecutive destabilization of the speleothems growing upon it) or earthquake effects (more likely by local effects than by wave front passage) are privileged. By comparing our dating with regional destructive known events (in other karsts, in cliffs and scarps), dated by relative chronology, we are lead to propose a regional generalized event precisely dated here at 7 ka. This second conclusion doesn't contradict the presence of unbroken speleothems older than 100 ka found in other caves in the neighborhood as local effects is one of the predominant factors relative to speleothem stability. As a final conclusion, this paper promotes the use of speleothems as reliable datable tools for assessing regional stability problems (sensitivity to seismic hazards, to destructive intense climatic events...) as is done for paleoclimatic reconstruction

How types of carbonate rock assemblages constrain the distribution of karst rocky desertified land in Guizhou Province, PR China: Phenomena and mechanisms, 2004,
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Wang S. J. , Li R. L. , Sun C. X. , Zhang D. F. , Li F. Q. , Zhou D. Q. , Xiong K. N. , Zhou Z. F. ,
In Southwestern China karst rocky desertification (a process of land degradation involving serious soil erosion, extensive exposure of basement rocks, drastic decrease of soil productivity and the appearance of a desert-like landscape) results from irrational land use on the fragile, thin karst soil. Soil particles in the Guizhou karst plateau were accumulated predominantly from residues left behind after the dissolution of carbonate rocks, and the thickness of the soil layer is related to the amount of argillaceous substances in the lost carbonate rock. This paper examines the spatial distribution of karst rocky desertified (KRD) land in Guizhou Province, and relates it to the different assemblages of basement carbonate rocks. Types of carbonate rock assemblages are discussed using a 1 : 500000 scale digital-distribution map. Their distribution and sensitivity to erosion are analysed, demonstrating that the occurrence of KRD land is positively correlated to homogeneous carbonate rocks. Differences in physical and chemical properties of limestone and dolomite rocks lead to differences in dissolution, accumulation rate of soil particles and relief on the surface, and these factors influence land-use potential.

Characterizing a coastal karst aquifer using an inverse modeling approach: The saline springs of Thau, southern France, 2004,
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Pinault J. L. , Doerfliger N. , Ladouche B. , Bakalowicz M. ,
[1] A methodological approach using inverse modeling was used to characterize the functioning of the deep and shallow reservoirs of the Thau karst aquifer system. Three springs were monitored at the convergence of rising saline water diluted with shallow groundwater in karst conduits and unmixed shallow groundwater that behaves as confined groundwater. In such a method, impulse responses of flow and fluxes are combined in order to separate hydrographs. The model explains the salinity and hydraulic head variations of the submarine and inland springs. It confirms and improves the conceptual model of this groundwater system in which mixing of saline and subsurface waters occurs. The different forces driving the upward flowing mixed water into the drainage axis and faults were studied in order to elucidate the springs' functioning. A comparative study of spring functioning is proposed, which clearly shows the very high sensitivity of the groundwater system to changes in recharge and discharge conditions

New risk-consequence rockfall hazard rating system for Missouri highways using digital image analysis, 2005,
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Maerz N. H. , Youssef A. , Fennessey T. W. ,
The Missouri Rockfall Hazard Rating System (MORFH RS) is a new scheme for rating rockfall hazards along the roads of the Missouri State highway system. Existing rating systems used in other jurisdictions focus on the risk of failure and ignore the consequence of failure, or they lump the ratings for risk and consequence together. Missouri highway rock cuts tend to have low heights but are typically highly weathered, with special problems from karst and paleokarst. In MORFH RS, risk and consequence factors are given equal weight but isolated from each other. MORFH RS utilizes two phases: 1) identification of the most potentially problematic rock cuts using mobile digital video logging; 2) characterization and prioritization of remediation for the potentially problematic rock cuts identified in phase 1, using MORFH RS. In phase 2 four types of parameters are evaluated: 1) parameters that can be measured on computer scaled video images; 2) parameters which are descriptive, and need field evaluation; 3) parameters which are obtained from MODOT records; 4) conditional parameters which are evaluated under specific conditions. Only those parameters were selected that were deemed meaningful and/or relatively easy to measure or estimate. Parameters were assigned to either a risk or consequence category or both. MORFH RS has been tested on sections of Missouri highways. About 300 rock cuts were evaluated and used to prepare, modify, test, and verify the system. Sensitivity analysis of the system was done by quantifying potential errors in the video measurements and by a rating comparison of 12 MODOT and University of Missouri-Rolla (UMR) personnel on 10 rock cuts along Highway 63

Analysis of the environmental sensitivities of a typical dynamic epikarst system at the Nongla monitoring site, Guangxi, China, 2005,
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Cheng Z, Daoxian Y, Jianhua C,

Temperature as a marker for karstic waters hydrodynamics. Inferences from 1 year recording at La Peyrére cave (Ariège, France), 2005,
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Genthon P, Bataille A, Fromant A, D'hulst D, Bourges F,
We present temperature measurements recorded at a 15 min time step between October 2002 and April 2003 inside the La Peyrére cave (Baget karstic system, Central Pyrenees) on six 0.01 °C sensitivity sensors distributed on the whole recognized cave, down to a depth of 57 m. Rainy events are associated to a steep signal of a few hundredth to a few tenth of degrees in amplitude starting 1 h to one day after rain, and with a sign depending mostly of the outside temperature. The temperature signal does not correlate well with the rainfall, while the water level does with a maximum water rising rate 2.5 h after rain. The spectral density of the temperature signal displays one peak at a period of 3 days, which is also present in the rain signal and which is likely to be related to climatic parameters, and a broad smooth zone of spectral energy close to a 1 day period.By comparing a 'superficial' and a 'deepest' group of sensors, we note that the flood signal is more pronounced on the deepest sensor group whatever the outside temperature, and that the annual temperature variation is also larger on this sensor group. This could indicate that rain water flows in the cave through its base and explain the development in depth of the cave. Due to the arrival of water with different temperatures and mineralizations at different levels, double diffusive convection is likely to be triggered in the cave. We suggest that the onset of convection could be associated to the oscillations observed on the temperature signal at the onset of the flood

Temperature as a marker for karstic waters hydrodynamics. Inferences from 1 year recording at La Peyrere cave (Ariege, France), 2005,
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Genthon P, Bataille A, Fromant A, D'hulst D, Bourges F,
We present temperature measurements recorded at a 15 min time step between October 2002 and April 2003 inside the La Peyrere cave (Baget karstic system, Central Pyrenees) on six 0.01 degrees C sensitivity sensors distributed on the whole recognized cave, down to a depth of 57 m. Rainy events are associated to a steep signal of a few hundredth to a few tenth of degrees in amplitude starting 1 h to one day after rain, and with a sign depending mostly of the outside temperature. The temperature signal does not correlate well with the rainfall, while the water level does with a maximum water rising rate 2.5 h after rain. The spectral density of the temperature signal displays one peak at a period of 3 days, which is also present in the rain signal and which is likely to be related to climatic parameters, and a broad smooth zone of spectral energy close to a I day period. By comparing a 'superficial' and a 'deepest' group of sensors, we note that the flood signal is more pronounced on the deepest sensor group whatever the outside temperature, and that the annual temperature variation is also larger on this sensor group. This could indicate that rain water flows in the cave through its base and explain the development in depth of the cave. Due to the arrival of water with different temperatures and mineralizations at different levels, double diffusive convection is likely to be triggered in the cave. We suggest that the onset of convection could be associated to the oscillations observed on the temperature signal at the onset of the flood. (c) 2005 Elsevier B.V. All rights reserved

A quantitative method for the characterisation of karst aquifers based on spring hydrograph analysis, 2005,
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Kovacs A. , Perrochet P. , Kiraly L. , Jeannin P. Y. ,
This paper presents a method for characterizing flow systems in karst aquifers by acquiring quantitative information about the geometric and hydraulic aquifer parameters from spring hydrograph analysis. Numerical sensitivity analyses identified two fundamentally different flow domains, depending on the overall configuration of aquifer parameters. These two domains have been quantitatively characterized by deducing analytical solutions for the global hydraulic response of simple two-dimensional model geometries. During the baseflow recession of mature karst systems, the hydraulic parameters of karst conduits do not influence the drainage of the low-permeability matrix. In this case the drainage process is influenced by the size and hydraulic parameters of the low-permeability blocks alone. This flow condition has been defined as matrix-restrained flow regime (MRFR). During the baseflow recession of early karst systems and fissured systems, as well as the flood recession of mature systems, the recession process depends on the hydraulic parameters and the size of the low-permeability blocks, conduit conductivity and the total extent of the aquifer. This flow condition has been defined as conduit-influenced flow regime (CIFR). Analytical formulae demonstrated the limitations of equivalent models. While equivalent discrete-continuum models of early karst systems may reflect their real hydraulic response, there is only one adequate parameter configuration for mature systems that yields appropriate recession coefficient. Consequently, equivalent discrete-continuum models are inadequate for simulating global response of mature karst systems. The recession coefficient of equivalent porous medium models corresponds to the transition between matrix-restrained and conduit-influenced flow. Consequently, equivalent porous medium models yield corrupted hydrographs both in mature and early systems, and this approach is basically inadequate for modelling global response of karst aquifers. (c) 2004 Elsevier B.V. All rights reserved

Calcite dissolution kinetics and solubility in Na-Ca-Mg-Cl brines of geologically relevant composition at 0.1 to 1 bar pCO2 and 25 to 80°C. Doctoral dissertation, Texas A&M University. , 2005,
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Gledhill, Dwight Kuehl

Sedimentary basins can contain close to 20% by volume pore fluids that are commonly classified as brines. These fluids can become undersaturated with respect to calcite as a result of processes such as migration, dispersive mixing, or anthropogenic injection of CO2. This study measured calcite solubility and dissolution rates in geologically relevant Na-Ca-Mg-Cl synthetic brines (35 to 200 g L-1 TDS). In brines < 50 g L-1 TDS, the EQPITZER calculated calcium carbonate ion activity product (IAP) at steady-state was in reasonable agreement (±10%) with the thermodynamic solubility constant for calcite (Kc). However, the IAP systematically exceeded Kc in more concentrated brines. The deviation was strongly correlated with calcium concentration and also was observed in magnesium-free solutions. This is interpreted as an uncertainty in the carbonate ion activity coefficient, and minor adjustment in stoichiometric association constants (K*M2+CO30) for the CaCO30 or MgCo30 ion pairs would correct for the error. The dissolution rate dependency on brine composition, pCO2 (0.1 to 1 bar), and temperature (25.0 to 82.5 °C) was modeled using the empirical rate equation ()nkRΩ−=1 where R is the rate, k and n are empirical fitting terms, and Ω the degree of disequilibrium with respect to calcite. When Ω was defined relative to an apparent kinetic solubility, n could be assumed first-order over the range of Ω investigated (Ω = 0.2 to 1.0). Rates increased with increasing pCO2 as did the sensitivity to brine concentration. At 0.1 bar, rates were nearly independent of concentration (k = 13.0 ±2.0 x 10-3 moles m-1 hr-1). However, at higher CO2 partial pressures rates became composition dependent and the rate constant, k, was shown to be a function of temperature, pCO2, ionic strength, and calcium and magnesium activity. The rate constant (k) can be estimated from a multiple regression (MR) model of the form k = B0 + B1(T) + B2(pCo2) + B4(aCa2+) + B5(aMg2+). A relatively high activation energy (Ea = 20 kJ mol-1) was measured, along with a stirring rate independence suggesting the dissolution is dominated by surface controlled processes at saturation states Ω > 0.2 in these calcium-rich brines. These findings offer important implications to reaction-transport models in carbonate-bearing saline reservoirs.


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