Dissolution Of Carbonate Rocks Research Articles

Land-use change and managed aquifer recharge effects on the hydrogeochemistry of two contrasting atoll island aquifers, Roi-Namur Island, Republic of the Marshall Islands

Freshwater resources on low-lying atoll islands are highly vulnerable to climate change and sea-level rise. In addition to rainwater catchment, groundwater in the freshwater lens is a critically important water resource on many atoll islands, especially during drought. Although many atolls have high annual rainfall rates, dense natural vegetation and high evapotranspiration rates can limit recharge to the freshwater lens. Here we evaluate the effects of land-use/land-cover change and managed aquifer recharge on the hydrogeochemistry and supply of groundwater on Roi-Namur Island, Republic of the Marshall Islands. Roi-Namur is an artificially conjoined island that has similar hydrogeology on the Roi and Namur lobes, but has contrasting land-use/land-cover and managed aquifer recharge only on Roi. Vegetation removal and managed aquifer recharge operations have resulted in an estimated 8.6 × 105 m3 of potable groundwater in the freshwater lens on Roi, compared to only 1.6 × 104 m3 on Namur. We use groundwater samples from a suite of 33 vertically nested monitoring wells, statistical testing, and geochemical modeling using PHREEQC to show that the differences in land-use/land-cover and managed aquifer recharge on Roi and Namur have a statistically significant effect on several groundwater-quality parameters and the controlling geochemical processes. Results also indicate a six-fold reduction in the dissolution of carbonate rock in the freshwater lens and overlying vadose zone of Roi compared to Namur. Mixing of seawater and the freshwater lens is a more dominant hydrogeochemical process on Roi because of the greater recharge and flushing of the aquifer with freshwater as compared to Namur. In contrast, equilibrium processes and dissolution-precipitation non-equilibrium reactions are more dominant on Namur because of the longer residence times relative to the rate of geochemical reactions. Findings from Roi-Namur Island support selective land-use/land-cover change and managed aquifer recharge as a promising management approach for communities on other low-lying atoll islands to increase the resilience of their groundwater supplies and help them adapt to future climate change related stresses.

Assessment of the Combined Effect of Temperature and Time on Calcium and Magnesium Release in Carbonate Rocks, Central Luconia Province, Offshore Sarawak, Malaysia

Dissolution of carbonate rocks indicated by the release of calcium and magnesium ions was evaluated for a number of six samples of carbonate rocks representing three microfacies. Dissolution was measured progressive periods of time under different temperature ranges. The main objective of this paper was to evaluate the individual and collective effect of time and temperature on the dissolution trends for any facies. The method applied was the surface response method, in which, temperature, and time represented the factors, while amounts of calcium and magnesium released (in ppm) represented the responses. Dissolution was carried out experimentally under a constant pH of 0.1 m Hcl, continuous stirring. The resulting data in terms of concentration (ppm) of the Ca and Mg was used as input data for the model. Response surface method provided models for the dissolution of carbonates, optimization of dissolution, and individual-and-combined effect of each factor (Time and temp).

Hydrogeochemical Characteristics of Groundwater in the Karst Region, Southwest China

Groundwater is a very important source for drinking and irrigation in the karst area, and therefore understanding the hydrogeochemistry of karst water is extremely significant. Groundwater were collected, and major chemical compositions were measured to analyse the geochemical processes in Guiyang-Anshun, southwest China. The chemical compositions of the groundwater of the study area are dominated by Ca2+, Mg2+, HCO3-, SO42-, which have been derived largely from dissolution of carbonate rocks (limestone and dolomite). Compared to the rural areas, TDS value is higher in the city centre. Chloride as a conservative tracer can be used to discuss the source of main ions in the groundwater. In this case, we support that high concentrations of Ca2+, Mg2+, Na+ are observed with low Chloride concentration in the regional groundwater.

Hydrothermal Dissolution of Deeply Buried Cambrian Dolomite Rocks and Porosity Generation: Integrated with Geological Studies and Reactive Transport Modeling in the Tarim Basin, China

The burial dissolution of carbonate rocks has long been an interesting topic of reservoir geologists. Integrated with geological studies and reactive transport modeling, this study investigated the Cambrian dolomites that were buried at depths up to 8408 m and still preserved a large amount of unfilled dissolution vugs from the borehole TS1 in the northern Tarim Basin. Studies indicate that these vugs were formed in association with fault-channeled hydrothermal fluids from greater depth through “retrograde dissolution” as the fluid temperature dropped during upward migration. The reactive transport modeling results suggest an important control of the vertical permeability of wall-rock on fluid and temperature patterns which, in turn, would control the spatial distribution of dissolving-originated porosity. The hydrothermal dissolution mainly occurred in dolomite wall-rocks with higher vertical permeability (extensive development of tensional fractures and connected pore spaces), producing additional dissolved porosity there during deep burial. This study implicates the importance of multidisciplinary approaches for understanding the burial/hydrothermal dissolution of dolomite rocks and predicting favourable deep/ultradeep carbonate reservoirs.

An Approach towards the Determination of Alkalinity in Water, Its Experimental Consideration & Comparison with Traditional Method: An Overview

<em>Alkalinity is equal to the stoichiometric sum of the bases in solution therefore it includes all the acid neutralizing bases in water namely OH</em><em>ˉ</em><em>, CO</em><em><sub>3</sub></em><em>²ˉ</em><em> & HCO</em><em><sub>3</sub></em><em>ˉ</em><em> ions. In the natural environment carbonate alkalinity tends to make up most of the total alkalinity due to the common occurrence and dissolution of carbonate rocks and presence of CO</em><em>2</em><em> in the atmosphere. Alkalinity varies with the location Acid-base titration is performed for their estimation but the theoretical determination for the type and extent of these ions is tedious process through traditional formulas known to us, (Volume of acid used up till Phenolphthalein & Methyl orange end point). Here in this paper we are trying to simplify the method and reporting the direct determination of the extent of ions by simple calculation without using the formulas for specific ions under different conditions of alkalinity. Thus a comparative aspect of this approach with traditional method will be covered by us in this paper.</em>

Foreword

A special section of Acta Carsologica is dedicated to the successfully concluded 5-year-long global UNESCO IGCP Project No. 598.IGCP/SIDA 598 “Environmental Change and Sustainability in Karst Systems (2011−2015)” is the 5th karst-related IGCP project sponsored by UNESCO/IUGS and the Swedish International Development Cooperation Agency (SIDA). It is a successor to IGCP 299, IGCP 379, IGCP 448, and IGCP 513 projects. The project was proposed and co-led by Zhang Cheng (China), Chris Groves (USA), Martin Knez (Slovenia), Jiang Yongjun (China), Augusto Auler (Brazil), Bartolome Andreo-Navarro (Spain), and Yuan Daoxian (China). The main objectives of the project are to better estimate the carbon sink potential from carbonate rock dissolution on continents by improving the approaches; to reveal the responses of the hydrogeological behavior of karst aquifers and water resource processes under the influence of different weather and climate events; to improve assessments methods for groundwater vulnerability to contamination; to quantify the records of environmental change within karst water, sediments, and speleothems that provide information over various timescales.During the implementation of the project, more than 200 scientists from 40 countries were involved in the project’s annual meetings, symposia, and field excursions. In line with the four objectives of the project, the new developments of IGCP/SIDA 598 were published in the journal Episodes in 2015 as the project’s final report.

Changes in the geochemical parameters of karst lakes over the past three decades – The case of Plitvice Lakes, Croatia

One of the major reasons for the increase in global air temperature since the early 20th century is considered to be the increase in the atmospheric CO2 concentration. Karst relief is considered an important carbon sink, but it can also be a natural source of carbon and CO2 emission. Aquatic systems in karst areas facilitate carbon exchange between the karst and the atmosphere, often through groundwater geochemical carbonate rock dissolution (carbon sink) and in the form of secondary calcium carbonate precipitation (possible carbon source).The protected area of Plitvice Lakes National Park, located in the karst region of Croatia, was chosen as a case study on karst geochemical processes. The lakes are also specific for their authigenic calcite precipitation in the form of tufa barriers and lake sediment. Physical and chemical data (temperature, pH, Ca2+, HCO3−, Mg2+ and CO2 concentrations, calcite saturation index (SIcalc), calcite dissolution ionic ratio (IRcalc), and Mg/Ca ratio) from water samples collected at 8 locations (2 springs, 2 rivers, and 4 lakes) from 1981 to 2014 were studied.The data were not collected systematically, so long-term changes have been mostly assessed through comparison between parameters from two selected periods (1981–1986 and 2010–2014) and through temporal correlations for each observed parameter in each calendar month.For the 33 years studied, an increase in air and water temperature, Ca2+ and HCO3− concentrations, calcite saturation index (SIcalc), calcite dissolution ionic ratio (IRcalc), and a decrease in the Mg/Ca ratio were observed. No statistically significant change was observed for pH or CO2 and Mg2+ concentrations. Average discharge rates did not display any significant change over the past three decades, however there was a change in their seasonal distribution.The significant increase in Ca2+ and HCO3− concentrations at lake locations were primarily caused by an increase in Ca2+ and HCO3− values in the water of the springs. Simultaneously, Mg2+ concentrations remained constant, which indicates higher levels of limestone (calcite) dissolution than dolomite dissolution. One of the reasons for this could be higher air/soil temperatures, resulting in higher soil CO2 production, which appears to result in the higher dissolution of calcite exclusively. An increase in HCO3− concentrations at the springs implies that karst groundwater is a carbon sink. Furthermore, the fact that the spatial decrease in HCO3− concentration in downstream waters was the same during the 1981–1986 and 2010–2014 periods implies that the entire observed karst lake system itself is a carbon sink.Temporal and spatial changes in SIcalc and IRcalc values in surface waters were mainly attributed to an increase in the intensity of bioactivity, which is in turn connected with an increase in water temperature.

Subnetworks of Percolation Backbones to Model Karst Systems Around Tulum, Mexico

Karstic caves, which play a key role in groundwater transport, are often organized as complex connected networks resulting from the dissolution of carbonate rocks. In this work, we propose a new model to describe and study the structures of the two largest submersed karst networks in the world. Both of these networks are located in the area of Tulum (Quintana Roo, Mexico). In a previous work \cite{hendrick2016fractal} we showed that these networks behave as self-similar structures exhibiting well-defined scaling behaviours. In this paper, we suggest that these networks can be modeled using substructures of percolation clusters ($\theta$-subnetworks) having similar structural behaviour (in terms of fractal dimension and conductivity exponent) to those observed in Tulum's karst networks. We show in addition that these $\theta$-subnetworks correspond to structures that minimise a global function, where this global function includes energy dissipation by the viscous forces when water flows through the network, and the cost of network formation itself.

Groundwater flow and residence time in a karst aquifer using ion and isotope characterization

In order to identify the origin of the main processes that affect the composition of groundwater in a karstic aquifer, a hydrogeochemical and isotopic study was carried out of water from numerous observation wells located in Sierra de Gador, a semiarid region in SE Spain. Several natural and anthropogenic tracers were used to calculate groundwater residence time within this complex aquifer system. Analysis of major ions enabled the principal geochemical processes occurring in the aquifer to be established, and the samples were classified into four distinctive solute groups according to this criterion. Dissolution of carbonate rocks determines the chemical composition of less mineralized water. In another group, the concurrent dissolution of dolomite and precipitation of calcite in gypsum-bearing carbonate aquifer, where the dissolution of relatively soluble gypsum controls the reaction, are the dominant processes. Marine intrusion results in highly mineralized waters and leads to base exchange reactions. The groundwater enrichment of minor and trace elements allowed classification of the samples into two classes that are linked to different flow patterns. One of these classes is influenced by a slow and/or deep regional flow, where the temperature is generally elevated. The influence of sulphate reduces by up to 40 % the barium concentration due to the barite precipitation. Isotope data (T, 14C) confirm the existence of recent local flows, and regional flow system, and ages of ground water may reach 8000 years. The importance of gypsum dissolution in this aquifer is proved by the δ34S content.

Geochemical characteristics and isotopic reversal of natural gases in eastern Kopeh-Dagh, NE Iran

Natural gas samples from two gas fields located in Eastern Kopeh-Dagh area were analyzed for molecular and stable isotope compositions. The gaseous hydrocarbons in both Lower Cretaceous clastic reservoir and Upper Jurassic carbonate reservoir are coal-type gases mainly derived from type III kerogen, however enriched δD values of methane implies presence of type II kerogen related material in the source rock. In comparison Upper Jurassic carbonate reservoir gases show higher dryness coefficient resulted through TSR, while presence of C1C5 gases in Lower Cretaceous clastic reservoir exhibit no TSR phenomenon. Carbon isotopic values indicate gas to gas cracking and TSR occurrence in the Upper Jurassic carbonate reservoir, as the result of elevated temperature experienced, prior to the following uplifts in last 33–37 million years. The δ13C of carbon dioxide and δ34S of hydrogen sulfide in Upper Jurassic carbonate reservoir do not primarily reflect TSR, as uplift related carbonate rock dissolution by acidic gases and reaction/precipitation of light H2S have changed these values severely. Gaseous hydrocarbons in both reservoirs exhibit enrichment in C2 gas member, with the carbonate reservoir having higher values resulted through mixing with highly-mature-completely-reversed shale gases. It is likely that the uplifts have lifted off the pressure on shale gases, therefore facilitated the migration of the gases into overlying horizons. However it appears that the released gases during the first major uplift (33–37 million years ago) have migrated to both reservoirs, while the second migrated gases have only mixed with Upper Jurassic carbonate reservoir gases. The studied data suggesting that economic accumulations of natural gas/shale gases deeper than Upper Jurassic carbonate reservoir would be unlikely.

Hydrothermal dissolution of Ordovician carbonates rocks and its dissolution mechanism in Tarim Basin, China

The dissolution of carbonate rocks has a significant control on reservoir quality under deep burial conditions, which has become a focus of studies in recent years. A series of hydrothermal minerals and combinations, such as fluorite, dickite, barite and hydrothermal dolomite, were discovered in the Ordovician strata in some exploration wells in the Tahe area. Moreover, the analysis results of carbon and oxygen isotope, REE, strontium isotope and inclusion homogenization temperature further confirmed that hydrothermal fluids existed in the Ordovician strata of Tahe areas. In this paper, the dissolution mechanism of carbonate rocks under deep burial conditions is discussed. It was considered that the hydrothermal dissolution required three conditions, i.e., the development of fault system, the presence of acidic fluids and a fall in temperature. The major theoretical foundation was the retrograde solubility of carbonate rocks that could be achieved through temperature drop and the upward migration of hydrothermal fluids. The dissolution of carbonate rocks caused by hydrothermal fluids normally occurred in the vicinity of migration pathways (faults or other pathways), which could be identified as good reservoir development zones.

Investigation of groundwater hydrochemical characteristics using the multivariate statistical analysis in Ain Djacer area, Eastern Algeria

The hydrochemical and multivariate statistical techniques such as the factor analysis (FA), the principal component analysis (PCA), and the cluster analysis (CA) were used to determine the main factors and mechanisms controlling groundwater chemistry of Ain Djacer Mio-Plio-Quaternary aquifer, Eastern Algeria. Twenty-one groundwater samples of this aquifer were monitored, during March 2013, with the objective of identifying the geochemical processes and their relation with groundwater quality as well as to get an insight into the hydrochemical evaluation of groundwater. The Piper diagram showed that water facies are of a Ca-HCO3-type near limestone limits and SO4–Na in the center part of the plain. The FA and the PCA revealed two factors that explained 65.1% of the total variance in water quality dataset. The first factor is salinization, which shows strong associations between total dissolved solids (TDS), SO42-, Cl–, Ca2+, Mg2+, and Na+. The second factor is mostly associated with chemical fertilizers and represents the high positive load of NO3- and K+ and the high negative load of pH and HCO3-. However, the CA, based on major ion contents, defined three main groups, reflecting different hydrochemical processes. The first group has low salinity (TDS < 1,000 mg/l) and a Ca-HCO3 water type. Samples of this group are mostly located in recharge areas and suggest dissolution of carbonate rocks. The third group has high salinity (TDS > 2,000 mg/l) and a SO4–Na water type. Samples from this group are mostly located in the center part of the plain which constitutes the discharge area. The second group has intermediate salinity (1,000 < TDS < 2,000 mg/l) and Ca-Na water type. These three groups present a salinity increasing with groundwater flow direction. The chemical monitoring allowed relating the presence of nitrates in the study area to agricultural activity. This study highlights that reactions responsible for the hydrochemical evolution in this area are of three categories: (1) dissolution of evaporite minerals, (2) precipitation of carbonate minerals, and (3) anthropogenic action.

Experimental investigation of the impact of rock dissolution on carbonate rock properties in the presence of carbonated water

Carbon dioxide (CO2) storage in aquifers or injection to petroleum reservoirs for enhanced oil recovery purposes are the ways of mitigation of global warming. Dissolution of carbon dioxide in water forms carbonic acid. This acid would react with the carbonate components in carbonate rocks (i.e., CaCO3, MgCO3) and cause dissolution of salts thereafter changing carbonate rocks intrinsic properties. Dissolution changes the properties of carbonate rocks. To investigate these phenomena, two carbonate rock samples were saturated with brine and brought in contact with carbonated water for about 12 days. After each 72-h period, porosity, permeability, the mass of the cores and concentration of released ions in brine were measured. Concentrations of released ions were calculated by titration in each period. A considerable change on rock properties was observed. Porosity and permeability changes were about +8.09 and ±9.73 %, respectively, and core weight loss was about 0.82 Wt %. Besides, intensity of the concentration of released magnesium ions in brine with comparison to calcium ions indicates that the core samples are dolomite. The results of this study show that carbonate rock dissolution should be considered in water alternative CO2 injection, carbonated water injection and CO2 storage projects.

Chemical and isotopic (O, H, C) composition of surface waters in the catchment of Lake Donggi Cona (NW China) and implications for paleoenvironmental reconstructions

The oxygen, hydrogen, and carbon isotope ratios and major and trace element concentrations of surface waters are reported for the catchment of Lake Donggi Cona, Qinghai Province, China. The chemistry of the surface waters in the southeastern catchment is reflecting the dissolution of carbonate rocks, whereas thermal waters add sodium and chlorine to the waters in the northern catchment. The Dongqu River, draining the southeast catchment, contributes 87 to 94% to the water budget of the lake. Thermal waters and waters from the northern catchment add 6 to 13%. The combination of hydrogen and oxygen isotopes provides evidence that only small amounts of recycled lake water contribute to the precipitation in the catchment. Most of the moisture may be transported by the East Asian summer monsoon or an eastern branch of the South Asian monsoon into the Donggi Cona region. From oxygen isotope ratios it is calculated that about 45% of the lake water input is evaporated and 55% leaves the lake through a channeled outflow. The carbon isotope ratios identifies microbial respiration of organic matter, probably in soils and sediments of the catchment, as the major source of dissolved inorganic carbon in most surface waters and the lake. An isotope effect, from biological processes, in the lake is minor, and can be neglected in order to explain isotope ratios of inorganic carbon in lake water. The results imply that oxygen isotope ratios in the lake sediment archives mainly mirror the relation between precipitation and evaporation (P/E), which may be controlled by changes in the global water cycle like monsoon intensity or by tectonically driven local changes affecting the outflow flux. A comparison between lake archives based on ostracod shells and the modern system indicates similar δ18O values for the lake water since 4.3ka but different δ13CDIC values. This discrepancy between carbon isotope ratios in ostracod shells and modern lake water samples may be due to thermal waters with high δ13CDIC emerging near the coring site. It is suggested that carbon isotopes of ostracods from a sediment drill core reflect the activity of a local thermal spring at the lake bottom, whereas oxygen isotopes provide evidence for an open lake system since about 11ka and that the climate and environment of the Donggi Cona region changed very little over the last 4300years.

Spatiotemporal Characterization of Land Subsidence and Uplift (2009–2010) over Wuhan in Central China Revealed by TerraSAR-X InSAR Analysis

The effects of ground deformation pose a significant geo-hazard to the environment and infrastructure in Wuhan, the most populous city in Central China, in the eastern Jianghan Plain at the intersection of the Yangtze and Han rivers. Prior to this study, however, rates and patterns of region-wide ground deformation in Wuhan were little known. Here we employ multi-temporal SAR interferometry to detect and characterize spatiotemporal variations of ground deformation in major metropolitan areas in Wuhan. A total of twelve TerraSAR-X images acquired during 2009–2010 are used in the InSAR time series analysis. InSAR-derived results are validated by levelling survey measurements and reveal a distinct subsidence pattern within six zones in major commercial and industrial areas, with a maximum subsidence rate up to −67.3 mm/year. A comparison analysis between subsiding patterns and urban developments as well as geological conditions suggests that land subsidence in Wuhan is mainly attributed to anthropogenic activities, natural compaction of soft soil, and karst dissolution of subsurface carbonate rocks. However, anthropogenic activities related to intensive municipal construction and industrial production have more significant impacts on the measured subsidence than natural factors. Moreover, remarkable signals of secular land uplift are found along both banks of the Yangtze River, especially along the southern bank, with deformation rates ranging mostly from +5 mm/year to +17.5 mm/year. A strong temporal correlation is highlighted between the detected displacement evolutions and the water level records of the Yangtze River, inferring that this previously unknown deformation phenomenon is likely related to seasonal fluctuations in water levels of the Yangtze River.

Pressure transients to characterize cavities dissolved for natural gas storage

This paper describes an analysis of pressure transients in conduits that includes effects of variable conduit diameter and contrasts in fluid material properties. The analysis considers pressure applied to the outside of a submerged conduit, as well as that transmitted along the submerged conduit's interior with potential applications such as analysis of submerged pipelines or tubing in oil wells or in wells used in solution mining.In this work, we present a method for monitoring the dissolution of carbonate rock with acid to create a cavern for storing natural gas. This process includes an acid injection pipe and a brine production pipe submerged in the fluid-filled cavern. The motivation is to characterize the geometry of the cavern by analyzing pressure transients traveling down the acid injection pipe, interacting with the walls of the cavern and compressing the brine pipe, and traveling to a pressure transducer in the brine pipe. The conventional water-hammer equations were modified to include the pressure applied to the outside of a submerged conduit, and the resulting boundary value problems were solved with perturbation analysis. The results show that peak pressure at an observation point decreases more than one order of magnitude when the cavern diameter increases one order of magnitude. This suggests that the proposed approach is sensitive to cavern diameter. Consideration of the external loading provides a potential mechanism for locating an interface between fluids of different properties, such as the interface between acid/CO2 mixture and underlying brine.

Experimental determination of natural carbonate rock dissolution rates with a focus on temperature dependency

The denudation of carbonate rocks at landscape scale is controlled by factors like mineral composition, temperature, precipitation, runoff, fracture spacing and vegetation cover. Knowledge on carbonate denudation is important in order to understand landscape development and long-term terrestrial/marine carbon transport, but there are few laboratory studies done on weathering rates of natural carbonate rocks under the low temperatures relevant for glacial-interglacial periods. To enhance the understanding of carbonate dissolution kinetics we studied low-temperature dissolution reactions of various natural Triassic carbonate rocks belonging to the Lower Muschelkalk in Germany. We conducted batch and flow-through experiments investigating the direct correlation of dissolution rates with temperature, and to establish whether the fine-grained carbonate rocks (micrite) are more reactive than the coarser-grained sparitic limestones. By increasing the temperature from 5 to 26°C far-from-equilibrium dissolution rates of micritic and sparitic limestone samples increased from 2.42×10−07 to 10.88×10−07 and 4.19×10−07 to 7.74×10−07molm−2s−1, respectively (Specific Surface Areas (SSA) of about 0.006–0.01m2/g). The dissolution rates of dolomite rock samples varied only slightly from 1.06×10−07 to 2.02×10−07molm−2s−1 (SSA approximately 0.002m2/g) in the temperature range 5–25°C at circum-neutral pH. The obtained apparent activation energies are in the range of earlier experiments done at higher temperatures, but there is a distinct difference between the calcite in the micrite (~51kJ/mol) and sparitic (~20–22kJ/mol) lithologies, indicating that the dissolution mechanisms are not the same. Using these activation energies in modelling of natural carbonate denudation we see that there is a clear effect of changing temperature, but this is mostly through the increased solubility at lower temperatures and not through the increasing far-from-equilibrium dissolution rates at higher temperatures. Formation of fluid pathways by preferential dissolution of framework calcite crystals is suggested to form infiltration pathways and affect denudation rates. The difference in crystal size between the micritic and sparitic limestones will affect the formation of such pathways (larger crystals may create fewer and larger conduits) and this is expected to be more important for the long-term denudation than the differences in activation energies.

Statistical analysis of water discharging from rocks of different origin: a case study from Turkey

The present study was conducted in Sivas, Karabuk and Bartin regions of Turkey, which have rocks of different origins, agricultural and mining activities. Correlation, principal components, hierarchical cluster and multidimensional scaling analyses were applied to determine the processes controlling the chemical composition of groundwater. The results show that dissolution-weathering process, agricultural activities, oxidation processes of sulfide minerals, mining activities, coal levels, alteration of volcanics and progressive silicate hydrolysis effects the physicochemical properties of groundwater in the study areas. Principal components and multidimensional scaling analyses provided excellent visual representations of the grouping of the waters. The significant variables in the first factor are SO4, Mn, Fe, Al, and pH. The factor represents the groundwater reached by these elements via the dissolution and oxidation processes of sulfide minerals (especially pyrite). Ca, EC, and HCO3 are generally grouped under the second factor representing the dissolution of carbonate rocks. The third factor represented by Na, CO3, and pH is mostly related to alteration of volcanics, progressive silicate hydrolysis and dissolution, and probably ion exchange between Ca and Na. The fourth factor of NO3 and Cl is strongly influenced by agricultural activity. The measurement, analyses and evaluation results showed that the groundwater contamination is caused by (1) NO3 in waters discharging from clastic rocks in areas where intensive agricultural activities are conducted; (2) Al, Fe, Mn, and SO4 ions in water emerging from volcanics containing Pb–Zn–Cu ore deposits; and (3) Al, Fe, and Mn in water issuing from coal levels and altered volcanics. Some of these waters are used by adjacent towns for drinking, domestic, and irrigation purposes.

Hidrogeological features of carbonate karst

On the example of loamy-chalky Upper Cretaceous strata (K2cm) of Sviatogirsk brachyanticline it has been found out that carbonate karst forms with the participation of different on dynamics and chemical composition kinds of groundwater.Basic chemical reactions that lead to leaching and dissolution of carbonate rocks during their interaction with groundwater have been characterized. Geological, hydrogeological and geochemical conditions of formation of various morphogenetic types of karst - surface (epikarst) and deep (hypokarst) have been well-grounded.

A refined dissolution method for rare earth element studies of bulk carbonate rocks

Extraction of primary geochemical signals from bulk carbonate rocks is a key task in palaeoenvironmental studies. REE behaviour is investigated during stepwise dissolution of carbonate rocks. The experiment is designed to achieve total carbonate dissolution in ten steps, aiming for approximately 10% of the total carbonate to be dissolved in each step using acetic acid. An additional eleventh step using excess acid completed each experiment. Results show that calcite is preferentially dissolved before dolomite though no significant effect on the REE pattern of the rock is observed. Secondary carbonate phases and adsorbates are likely to be dissolved at the beginning of the dissolution process but this does not increase REE concentration though the REE pattern may be altered e.g. lessening of negative Ce anomaly, altering of Eu anomaly, Y/Ho ratio and relative fractionation between LREE and HREE. Non-carbonate minerals e.g. terrestrial particulate matter, Fe–Mn oxyhydroxides and phosphates, are likely to be dissolved towards the end of the total dissolution, especially in the final excess acid step. This should increase REE concentrations and alter REE distribution patterns greatly. In contrast, solutions from intermediate steps are less contaminated. Further, compared with using 10% v/v acetic acid, the solutions obtained using 5%v/v acid return more pristine REE information from the carbonate.A proposed method for REE studies of bulk carbonate rocks requires an initial dissolution of 30%–40% followed by the sampling dissolution of 30%–40% of total carbonate using 5%v/v acetic acid to produce REE information considered to best represent that of the carbonate source water. Following these steps 20%–30% of the carbonate should remain undissolved, thus minimising contamination from non-carbonate minerals.