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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. ...

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. ...

Speleology in Kazakhstan

Shakalov on 11 Jul, 2012
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. ...

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Featured articles from Cave & Karst Science Journals
Chemistry and Karst, White, William B.
Engineering challenges in Karst, Stevanović, Zoran; Milanović, Petar
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Featured articles from other Geoscience Journals
Geochemical and mineralogical fingerprints to distinguish the exploited ferruginous mineralisations of Grotta della Monaca (Calabria, Italy), Dimuccio, L.A.; Rodrigues, N.; Larocca, F.; Pratas, J.; Amado, A.M.; Batista de Carvalho, L.A.
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
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Your search for geochemical model (Keyword) returned 21 results for the whole karstbase:
Showing 1 to 15 of 21
Geochemical models for the origin of macroscopic solution porosity in carbonate rocks, 1995, Palmer A. N.

Dedolomitization as a driving mechanism for karst generation in Permian Blaine formation, southwestern Oklahoma, USA, 1997, Raines M. A. , Dewers T. A. ,
Cyclic deposits of Permian shales, dolomites, and halite and gypsum-bearing strata in the Blaine Formation of Southwestern Oklahoma contain abundant karst features. The present study shows that an important mechanism of karst development in these sequences is dedolomitization, wherein gypsum and dolomite in close spatial proximity dissolve and supersaturate groundwaters with respect to calcite. The net loss of mass accompanying this process (dolomite and gypsum dissolution minus calcite precipitation) can be manifest in secondary porosity development while the coupled nature of this set of reactions results in the retention of undersaturated conditions of groundwater with respect to gypsum. The continued disequilibrium generates karst voids in gypsum-bearing aquifers, a mineral-water system that would otherwise rapidly equilibrate. Geochemical modeling (using the code PHRQPITZ, Plummer et al 1988) of groundwater chemical data from Southwestern Oklahoma from the 1950's up to the present suggests that dedolomitization has occurred throughout this time period in evaporite sequences in Southwestern Oklahoma. Reports from groundwater well logs in the region of vein calcite suggest secondary precipitation, an observation in accord with dedolomite formation In terms of the amounts of void space produced by dissolution, dedolomitization can dominate gypsum dissolution alone, especially in periods of quiescent aquifer recharge when gypsum-water systems would have otherwise equilibrated and karst development ceased. Mass balance modeling plus molar volume considerations show that for every cubic cm of original rock (dolomite plus gypsum), there is 0.54 cm(3) of calcite and 0.47 cm(3) of void space produced Only slightly more pore space results if the dedolomitization reaction proceeds by psuedomorphic replacement of dolomite by calcite than in a reaction mechanism based on conservation of bicarbonate

Changes in the isotopic and chemical composition of ground water resulting from a recharge pulse from a sinking stream, 1998, Katz B. G. , Catches J. S. , Bullen T. D. , Michel R. L. ,
The Little River, an ephemeral stream that drains a watershed of approximately ss km(2) in northern Florida, disappears into a series of sinkholes along the Cody Scarp and flows directly into the carbonate Upper Floridan aquifer, the source of water supply in northern Florida. The changes in the geochemistry of ground water caused by a major recharge pulse from the sinking stream were investigated using chemical and isotopic tracers and mass-balance modeling techniques, Nine monitoring wells were installed open to the uppermost part of the aquifer in areas near the sinks where numerous subterranean karst solution features were identified using ground penetrating radar. During high-flow conditions in the Little River, the chemistry of water in some of the monitoring wells changed, reflecting the mixing of river water with ground water. Rapid recharge of river water into some parts of the aquifer during high-flow conditions was indicated by enriched values of delta O-18 and delta deuterium (-1.67 to -3.17 per mil and -9.2 to -15.6 per mil, respectively), elevated concentrations of tannic acid, higher (more radiogenic) Sr-87/Sr-86 ratios, and lower concentrations of Rn-222, silica, and alkalinity compared to low-how conditions. The proportion of river water that mixed with ground water ranged from 0.10 to 0.67 based on binary mixing models using the tracers O-18, deuterium, tannic acid, silica, Rn-222, and Sr-87/Sr-86. On the basis of mass-balance modeling during steady-state how conditions, the dominant processes controlling carbon cycling in ground water are the dissolution of calcite and dolomite in aquifer material, and aerobic degradation of organic matter. (C) 1998 Elsevier Science B.V. All rights reserved

Processes controlling colloid composition in a fractured and karstic aquifer in eastern Tennessee, USA, 1998, Mccarthy J. F. , Shevenell L. ,
Groundwater was sampled from a number of wells along recharge pathways between fractured shale and karstic formations to evaluate the chemical and hydrologic mechanisms controlling the nature and abundance of groundwater colloids. The colloids recovered using low flow rate purging and sampling exhibited a composition and abundance consistent with lithology, flow paths, and effects of hydrology and aqueous chemistry on colloid mobilization and stability. In general, the larger-size colloids and Ca-containing colloids were more abundant in the karstic lithologies, while Na-containing colloids were more important in the shales. The composition of the colloids reflected recharge pathways from the fractured shale and dolomite formations on the ridges into the limestone in the valley floor. The Mg-colloids in the limestone reflect the possible contributions from the dolomite, while the Na, K, and Si reflect possible contributions from the shale, However, it was not possible to use the colloid composition as a signature to demonstrate colloid transport from one lithology to another. Mixing of recharge water from the shale with groundwater within the limestone formation and precipitation/dissolution reactions could account for the colloids present in the limestone without invoking transport of specific shale-derived colloids into the limestone formation. The abundance of colloids in groundwater appears to be controlled by both chemical factors affecting colloid stability, as well as physical factors related to hydrology (storm-driven recharge and water velocities). In general, colloids were more abundant in wells with low ionic strength, such as shallow wells in water table aquifers near sources of recharge at the top of the ridges, Increases in cation concentrations due to dissolution reactions along Bow paths were associated with decreases in colloid abundance. However, in spite of elevated ionic strength, colloid concentrations tended to be unexpectedly high in karstic wells that were completed in cavities or water-bearing fractures. The higher levels of colloids appear to be related to storm-driven changes in chemistry or flow rates that causes resuspension of colloids settled within cavities and fractures. Published by Elsevier Science B.V

Geochemical modeling of groundwater in karst area and its application at Pingdingshan coalfield, 1998, Wang G. C. , Tao S. , Shen Z. L. , Zhong Z. X. ,
Several approaches including hydrogeochemistry and isotope hydrogeology have been used to investigate the karst groundwater systems at Pingdingshan coalfield in recent years. The results of the modeling and evaluation of groundwater chemistry, as parts of recent research progress at the area, are presented. The characteristics of Cambrian karst groundwater flow was analyzed in terms of tritium distribution of groundwater based on the fact that the Guodishan fault, the largest one within the coalfield, is divided into permeable (southern and northern) and impermeable (middle) sections. The evolution of groundwater chemistry, the suitability of geothermometers and the feature of karst development were deduced and discussed using the speciation modeling and mass balance approach

Geostatistical and geochemical analysis of surface water leakage into groundwater on a regional scale: a case study in the Liulin karst system, northwestern China, 2001, Wang Y. , Ma T. , Luo Z. ,
The Liulin karst system is typical of hydrogeological systems in northern China, with a group of springs as the dominant way of regional groundwater discharge. Surface water leakage into groundwater has been observed in six sections of the rivers in the study area. To extract hydrogeological information from hydrochemical data, 29 water samples were collected from the system. On a trilinear diagram, most of the groundwater samples are clustered around the surface waters, indicating the effect of leakage on their chemistry. R-mode factor analysis was made on seven variables (Na, Ca, Mg, SO4, Cl, HCO3, and NO3) of the samples and three principal factors were obtained: the F-1 factor is composed of Ca, Mg and SO4, the F-2 of HCO3 and NO3, and the F-3 of Na and Cl. These factors are then used as regionalized variables in ordinary Kriging for unbiased estimates of the spatial variations of their scores. Considering regional hydrogeological conditions, the hydrogeological implications of the spatial distribution of the factor scores as related to the effects of the surface leakage are discussed. To evaluate the geochemical processes, the geochemical modeling code NETPATH was employed. The modeling results: show that mixing commonly occurs in the system and dolomite dissolution is more important than calcite dissolution. Dedolomitization (calcite precipitation and dolomite dissolution driven by anhydrite dissolution) is locally important, in the western flank of the system where the surface water leakage has the least effect.

Trace element (Th, U, Pb, REE) behaviour in a cryptokarstic halloysite and kaolinite deposit from Southern Belgium: importance of 'accessory' mineral formation for radioactive pollutant trapping, 2002, De Putter T, Andre L, Bernard A, Dupuis C, Jedwab J, Nicaise D, Perruchot A,
Hectometer wide cryptokarsts in Paleozoic limestone from Southern Belgium have been studied, to determine to what extent U, Th, Ph and rare earth elements (REE) have been mobilized in the karst sedimentary filling, during a Miocene weathering event. The weathering process resulted in the massive halloysite/kaolinite formation at the karst wall. As with most fossil systems, data on weathering fluid chemistry are lacking, hence it is difficult to quantify relevant parameters such as pH, Eh, and to address solution chemistry. However, on the basis of both field studies of more recent systems, and of geochemical modeling, it is proposed that moderately acid fluids percolated through a multi-layer sedimentary filling, in near-surface conditions and in a temperate/warm climate. Special attention is paid to the trace element immobilization/trapping processes, in newly crystallized REE phosphates, at the karst wall. Analytical methods used include major/trace element geochemistry (emission ICP, ICP-MS) and mineralogy (XRD, SEM, TEM, microprobe). The results suggest that both the sandy sediments that are in contact with the karst carbonate wall, and the carbonate wall itself acted as a kind of geochemical 'barrier'. Mineralization cells settled there, at the decimeter to meter scale. This results in sequential trace element (Pb, Th, REE, U) trapping, according to the affinity of these elements for the aqueous solution. At the end of the sequence, minute U-rich automorphic (Ce, Nd) monazite crystals (from 3 nm upwards) formed on kaolinite flakes. Though the analogy between the studied cryptokarst and planned surface-based repositories for low-level radioactive waste (LLW) in argillaceous context is far from complete, the results outlined here are relevant because they show that even in natural-i.e. intrinsically uncontrolled and unmonitored-systems, 'pollutant' radionuclide (U, Th, REE, Pb) migration paths are often limited in space. Various processes converge towards trapping of these elements, that are present in the radioactive waste. (C) 2002 Elsevier Science Ltd. All rights reserved

Formation of Willemite in Hydrothermal Environments, 2003, Brugger J, Mcphail Dc, Wallace M, Waters J,
Willemite (zinc silicate) is the main zinc mineral in some carbonate-hosted ore deposits (e.g., Franklin, New Jersey; Vazante, Brazil; Beltana, South Australia; Kabwe, Zambia). Recent interest in these unconventional zinc deposits has increased because of high zinc grades that exceed 40 wt percent, relatively low environmental impact of ore processing owing to the lack of acid-generating sulfides in the waste, and advances in ore processing technologies. In the past, most metallogenic studies proposed formation of willemite deposits by supergene or hypogene alteration of preexisting sulfide deposits. However, recent data on the Vazante, Beltana, and Kabwe deposits indicate willemite crystallization at temperatures in excess of 150{degrees}C, raising the possibility of primary precipitation from hydrothermal fluids. We use numerical geochemical modeling to examine the formation of willemite under hydrothermal conditions. Activity-activity diagrams reveal that, in the presence of dissolved sulfur and quartz, willemite instead of sphalerite will precipitate under oxidizing (e.g., hematite-stable, sulfate-predominant) and alkaline (pH higher than K feldspar-muscovite-quartz) conditions. Willemite also becomes more stable, relative to sphalerite, at high temperature, and willemite can coexist with magnetite at 300{degrees}C. The stabilities and solubilities of sphalerite, willemite, smithsonite, hydrozincite, and zincite were calculated for wide ranges of temperature (25{degrees}-300{degrees}C), chloride concentration, dissolved sulfur and carbon concentrations, pH, quartz saturation, and oxidation potential. Plots of the solubility of the different minerals as a function of two variables (e.g., temperature and redox state; pH and redox state) allow us to predict the effects of changing chemical conditions, which in turn permits an estimate of the efficiency of particular precipitation processes. Cooling is an effective process for precipitating sphalerite but not willemite, whereas pH increase (e.g., by acidic fluids reacting with carbonates) is effective for precipitating willemite but not sphalerite. Dynamic geochemical models that simulate physicochemical processes are used to understand the formation of the Beltana willemite deposit in the Adelaide geosyncline of South Australia. This small, high grade deposit (850,000 t at 36% Zn) is hosted in dolomite of the Cambrian Ajax Limestone, next to a tectonic contact with the diapiric, halite-bearing clastic sediments of the Callanna Group. The orebody is associated with hematite alteration and is characterized by the total absence of sulfides; willemite is the only zinc ore mineral, and the arsenate hedyphane (Ca2Pb3[AsO4]3Cl) is the main lead mineral. The model results show that willemite will precipitate in response to water-rock interaction and fluid mixing processes at temperatures above 120{degrees}C. The presence of arsenate in the hydrothermal fluid is likely to have been important at Beltana; in arsenate-absent models sulfate is reduced to sulfide by the precipitation of ferrous iron as hematite, resulting in the precipitation of sphalerite and galena. In contrast, in models including arsenate the reduction of sulfate to sulfide is inhibited and willemite is predicted to precipitate

Soil and karst aquifer hydrological controls on the geochemical evolution of speleothem-forming drip waters, Crag Cave, southwest Ireland, 2003, Tooth Anna F. , Fairchild Ian J. ,
In recent years there has been increased interest in cave speleothems as archives of palaeoclimate. Monitoring of rainfall and soil and karst water chemistries was performed at Crag Cave, Castleisland, Co. Kerry, southwest Ireland, in August 1997 and January 1998 in order to understand temporal and spatial variations in karst water hydrology and chemistry and their implications for interpreting the potential palaeohydrological signal preserved by speleothems at this site. Temporal variations in karst water drip rates and geochemistry allow drips to be classified by hydrological response to rainfall and the associated processes of dilution, piston flow, source change and prior calcite precipitation during aquifer throughflow. Evolution from soil matrix and preferential flow solutions has also been determined to exert an important control on karst water chemistries. As a result of these findings we present hydrogeochemical models and plumbing diagrams that delineate the controls on karst water evolution at a number of sampling locations within the cave at this site. We propose that a palaeohydrological signal may be recorded by Crag Cave speleothems that may be interpreted via the study of Mg/Ca ratios in speleothems linked to monitoring of modern drip water chemistry

Role of fluid mixing in deep dissolution of carbonates, 2003,

The presence of cavities filled with new minerals in carbonate rocks is a common feature in oil reservoirs and lead-zinc deposits. Since groundwater equilibrates rapidly with carbonates, the presence of dissolution cavities in deep carbonate host rocks is a paradox. Two alternative geochemical processes have been proposed to dissolve carbonates at depth: hydrogen sulfide oxidation to sulfuric acid, and metal sulfide precipitation. With the aid of geochemical modeling we show that mixing two warm solutions saturated with carbonate results in a new solution that dissolves limestone. Variations in the proportion of the end-member fluids can also form a supersaturated mixture and fill the cavity with a new generation of carbonate. Mixing is in general more effective in dissolving carbonates than the aforementioned processes. Moreover, mixing is consistent with the wide set of textures and mineral proportions observed in cavity infillings

Stable isotope (H-2, O-18 and Sr-87/Sr-86) and hydrochemistry monitoring for groundwater hydrodynamics analysis in a karst aquifer (Gran Sasso, Central Italy), 2005, Barbieri M, Boschetti T, Petitta M, Tallini M,
This paper deals with chemical and isotope analyses of 21 springs, which were monitored 3 times in the course of 2001; the monitoring program was focused on the groundwater of the Gran Sasso carbonate karst aquifer (Central Italy), typical of the mountainous Mediterranean area. Based on the hydrogeological setting of the study area, 6 groups of springs with different groundwater circulation patterns were distinguished. The hydrogeochemistry of their main components provided additional information about groundwater flowpaths, confirming the proposed classification. The spatial distribution of their ion concentrations validated the assumptions underlying the hydrogeological conceptual model, showing diverging groundwater flowpaths from the core to the boundaries of the aquifer. Geochemical modelling and saturation index computation elucidated water-carbonate rock interaction, contribution by alluvial aquifers at the karst aquifer boundaries, as well as impacts of human activities. The analysis of O-18/O-16 and H-2/H values and their spatial distribution in the aquifer substantiated the hydrogeology-based classification of 6 groups of springs, making it possible to trace back groundwater recharge areas based on mean isotope elevations; the latter were calculated by using two rain monitoring stations. Sr-87/Sr-86 analyses showed seasonal changes in many springs: in winter-spring, the changes are due to inflow of new recharge water, infiltrating into younger rocks and thus increasing (87)sr/Sr-86 values; in summer-autumn, when there is no recharge and spring discharge declines, changes are due to base flow groundwater circulating in more ancient rocks, with a subsequent drop in Sr-87/Sr-86 values. The results of this study stress the contribution that spatio-temporal isotope monitoring can give to the definition of groundwater flowpaths and hydrodynamics in fissured and karst aquifers, taking into account their hydrogeological and hydrogeochemical setting. (c) 2005 Elsevier Ltd. All rights reserved

The geochemistry of fluids from an active shallow submarine hydrothermal system: Milos island, Hellenic Volcanic Arc, 2005, Valsamijones E. , Baltatzis E. , Bailey E. H. , Boyce A. J. , Alexander J. L. , Magganas A. , Anderson L. , Waldron S. , Ragnarsdottir K. V. ,
Geothermal activity in the Aegean island of Milos (Greece), associated with island-arc volcanism, is abundant both on-and off-shore. Hydrothermal fluids venting from several sites, mainly shallow submarine (up to 10 m), but also just above seawater level in one locality, were sampled over four summer field seasons. Some of the discharging fluids are associated with the formation of hydrothermal edifices. Overall, the main characteristics of the hydrothermal fluids are low pH and variable chlorinity. The lowest recorded pH was 1.7, and chlorinity ranged from 0.1 to 2.5 times that of seawater. The highest fluid temperatures recorded on site were 115 degrees C. Two main types of fluids were identified: low-chlorinity fluids containing low concentrations of alkalis (potassium, lithium, sodium) and calcium, and high concentrations of silica and sulphate; and high-chlorinity fluids containing high concentrations of alkalis and calcium, and lower concentrations of silica and sulphate. The type locality of the high-chlorinity fluids is shallow submarine in Palaeochori, near the cast end of the south coast of the island, whereas the type locality of the low-chlorinity fluids is a cave to the west of Palaeochori. The two fluid types are therefore often referred to as 'submarine' and 'cave' fluids respectively. Both fluid types had low magnesium and high metal concentrations but were otherwise consistently different from each other. The low-chlorinity fluids had the highest cobalt, nickel, aluminium, iron and chromium (up to 1.6 mu M, 3.6 mu M, 1586 mu M, 936 mu M and 3.0 mu M, respectively) and the high-chlorinity fluids had the highest zinc, cadmium, manganese and lead (up to 4.1 mu M, 1.0 mu M, 230 mu M and 32 mu M, respectively). Geochemical modelling suggests that metals in the former are likely to have been transported as sulphate species or free ions and in the latter as chloride species or free ions. Isotopic values for both water types range between delta D -12 to 33 parts per thousand and delta(18)O 1.2 to 4.6 parts per thousand. The range of fluid compositions and isotopic contents indicates a complex history of evolution for the system. Both types of fluids appear to be derived from seawater and thus are likely to represent end members of a single fluid phase that underwent phase separation at depth. Crown Copyright (c) 2005 Published by Elsevier B.V. All rights reserved

Strontium isotope characterization and major ion geochemistry of karst water flow, Shentou, northern China, 2006, Wang Yanxin, Guo Qinghai, Su Chunli, Ma Teng,
SummaryKarst water is the most important source of water supply for Shanxi province, northern China. The Shentou springs are representative of the 19 major karst springs at Shanxi. The total area of the Shentou karst water system is 5316 km2, the Middle Ordovician limestone being its major karst aquifer. In this study, data about the strontium isotope geochemistry and major ion hydrochemistry were analyzed to understand the flow patterns and hydrogeochemical processes of karst water at Shentou. The contour map of TDS value of karst water and that of Sr concentration are similar, showing the general tendency of increase from the northern, western and southern boundary to the discharge area. The average values of 87Sr/86Sr ratios of karst water decrease from recharge (0.7107) to discharge area (0.7102), evolving towards those of limestone hostrocks. Comparison of 87Sr/86Sr ratios with Sr content suggests that isotopic compositions of some karst water samples from the recharge and flow through area should be the result of interaction between aquifer limestone matrix and strontium-poor recharge waters of meteoric origin. However, for samples from the discharge area that are plotted above the mixing line, mixing with groundwater in the Quaternary aquifers with high 87Sr/86Sr ratios may be another factor controlling Sr isotope chemistry. Two major groundwater flow paths were discerned from hydrogeological and geochemical data. Along both flow paths, the 87Sr/86Sr ratios of karst water show a general tendency of decrease. Geochemical modeling of the major ion geochemistry of karst water using PHREEQC also indicates that the chemistry of springs should be affected by the incorporation of groundwater in Quaternary aquifer. The effect of the mixing action on the spring hydrochemistry in flow path 1 is more remarkable than that in flow path 2, according to different mixing ratios in both paths (30% in flow path 1 and 5% in flow path 2)

Unusual Phosphate Concretions Related to Groundwater Flow in a Continental Environment, 2006, Thiry Medard, Galbois Jean, Schmitt Jean Michel,
Occurrence of phosphate cemented-sandstone concretions in alluvial sand containing archaeological layers implies that they have formed during the last 2000 years. Morphology and petrography of the concretions indicates a relationship with groundwater cementation. The phosphate cement of the concretions consists of concentric isopachous aureoles, about 10 {micro}m thick, that wrap the detrital grains. Aureoles are formed of collophane, the cryptocrystalline or amorphous variety of hydroxyapatite. Geochemical modeling indicates that the apatite cement likely results from the leaching of a preexisting phosphate deposit (bones?) in an acidic soil environment and the precipitation of dissolved phosphate under pH control at the mixing zone of down-moving soil-water with the calcite-saturated groundwater

Mixing of shallow and deep groundwater as indicated by the chemistry and age of karstic springs, 2006, Toth D. J. , Katz B. G.

Large karstic springs in east-central Florida, USA were studied using multi-tracer and geochemical modeling techniques to better understand groundwater flow paths and mixing of shallow and deep groundwater. Spring water types included Ca–HCO3 (six), Na–Cl (four), and mixed (one). The evolution of water chemistry for Ca– HCO3 spring waters was modeled by reactions of rainwater with soil organic matter, calcite, and dolomite under oxic conditions. The Na–Cl and mixed-type springs were modeled by reactions of either rainwater or Upper Floridan aquiferwater with soil organic matter, calcite, and dolomite under oxic conditions and mixed with varying proportions of saline Lower Floridan aquifer water, which represented 4–53% of the total spring discharge. Multiple-tracer data—chlorofluorocarbon CFC-113, tritium (3H), helium- 3 (3Hetrit), sulfur hexafluoride (SF6)—for four Ca–HCO3 spring waters were consistent with binary mixing curves representing water recharged during 1980 or 1990 mixing with an older (recharged before 1940) tracer-free component. Young-water mixing fractions ranged from 0.3 to 0.7. Tracer concentration data for two Na–Cl spring waters appear to be consistent with binary mixtures of 1990 water with older water recharged in 1965 or 1975. Nitrate-N concentrations are inversely related to apparent ages of spring waters, which indicated that elevated nitrate-N concentrations were likely contributed from recent recharge.

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