Partial pressures of CO2 in epikarstic zone deduced from hydrogeochemistry of permanent drips, the Moravian Karst, Czech Republic

Permanent drips from straw stalactites of selected caves of the Moravian Karst were studied during one-year period. A hypothetical partial pressure of CO2 that has participated in limestone dissolution, PCO2(H)=10-1.53±0.04, was calculated from the dripwater chemistry. The value significantly exceeds the partial pressures generally measured in relevant shallow karst soils, PCO2(soil)=10-2.72±0.02. This finding may have important implications for karst/cave conservation and paleoenvironmental reconstructions.Keywords: cave, carbon dioxide, dripwater, hydrogeochemistry,hypothetical partial pressure, karst processes, karstification model

Introduction to groundwater geochemistry and fundamentals of hydrogeochemical modeling

A wide diversity of physical and chemical processes control the distribution of species in waters in the vadose zone above the water table, and in the saturated zone below. The mineralogical composition of rocks or sediments, chemical reactions between solid, aqueous and gas phases, and oxidation/reduction (redox) processes are principal factors that influence the chemical composition of vadose-zone, ground- and surface waters, and the concentrations and mobilities of individual species. This chapter discusses the sampling of water, solids and gases, key steps in the investigation of groundwater systems, and then provides a brief summary of the thermodynamic fundamentals relevant for understanding geochemical processes in the vadose zone and in the aquifers and aquitards below it. This is followed by a short overview of important hydrogeochemical processes such as dissolution, precipitation, exsolution and redox processes, as well as sorption and ion exchange processes. These last two sections will help the reader understand the subsequent chapters on geochemical modeling. For more information on the fundamentals of aqueous and groundwater geochemistry, the reader is referred to standard textbooks such as Stumm and Morgan (1996) and Appelo and Postma (2005)

Mechanisms of arsenic enrichment in geothermal and petroleum reservoirs fluids in Mexico

The lack of chemical similarity between thermal fluids in geothermal and petroleum reservoirs in Mexico indicates a distinct origin for arsenic in both types of reservoirs. Deep fluids from geothermal reservoirs along the Transmexican Volcanic Belt (TMVB) are characterized by elevated arsenic concentrations, within a range between 1 and 100 mg L-1 at a depth from 600 to 3000 m b.s.l. Based on hierarchical cluster analysis (HCA), arsenic is linked to typical geothermal species like lithium, silica, and boron. The lack of correlation between arsenic and salinity reflects the importance of secondary water-rock interaction processes. The predominance of arsenic compared to Fe- and Cu-concentrations, and the occurrence of secondary minerals (sulfides and clay minerals) in temperature-dependent hydrothermal zones, supports this hypothesis. Neither magmatic fluids input, nor As mineralization is a prerequisite for As enrichment in Mexican geothermal fluids. In contrast, petroleum reservoir waters from sedimentary basins in SE-Mexico show maximum As concentrations of 2 mg L-1, at depths from 2900 to 6100 m b.s.l. The linear chloride-arsenic correlation indicates that evaporated seawater represents the major source for aqueous arsenic in oil reservoirs, and only minor arsenic proportions are derived from interaction with carbonate host rock. Speciation modeling suggests the lack of arsenic solubility control in both geothermal and petroleum reservoirs, but precipitation/co-precipitation of As with secondary sulfides could occur in petroleum reservoirs with high iron concentrations. Geothermal fluids from magmatic-type reservoirs (Los Azufres and Los Humeros at the TMVB and Las Tres Vírgenes with a granodioritic basement) show relative constant arsenic concentrations through varying temperature conditions, which indicates that temperatures above 230-250 °C provide optimal and stable conditions for arsenic mobility. In contrast, temperature conditions for sedimentary-type reservoirs are irrelevant for water-rock interaction processes, as suggested by low arsenic aqueous concentration for both Cerro Prieto geothermal fluids (high temperature - sedimentary type) and oil field formation water (low temperature - sedimentary type)

Geochemistry of groundwater and metal(loid) behavior in the costal aquifers of the Maharlu Lake, Iran.

Groundwater in coastal aquifers of the Maharlu Lake, southern Iran, has suffered from quality degradation and salinity increases in recent decades. These aquifers are important sources for drinking and agricultural uses in area around the lake. Hydrogeochemical analyses were carried out to identify the geochemical processes controlling groundwater chemistry and heavy metal concentrations in the coastal aquifer of the Maharlu Salt Lake. A total number of 54 water samples (45 samples from three coastal aquifers and 9 water samples from lake water) were collected for laboratory analysis of major ions and heavy metals three times from November-2014 to July-2015. In addition, physiochemical parameters of temperature, electrical conductivity, pH, and redox potential were measured in the field. The findings indicate three major controls of groundwater chemistry in the coastal aquifers of the Maharlu Lake including (1) lake water intrusions, (2) evaporites and carbonate dissolution-precipitation, and (3) input of organic matter probably linked to the seepage of domestic sewage with resulting sulfate reduction. In contrast, dissolution of minerals in surface sediments and direct evaporation of groundwater in the coastal aquifers seem to be insignificant based on geochemical ratios and water table depth. Concentrations of B, Li, Co, Cr, Cu, Ni, and U increase, but Zn concentrations decrease in groundwater due to the lake water intrusions into the costal aquifers. Gypsum dissolution and consequent carbonate reactions cause B, Co, Cr, Cu, Ni, Zn, and U enrichment in the groundwater samples. These findings can provide water managers and local authorities with a comprehensive framework of the coastal groundwater geochemistry, allowing a better understanding of the effects of current management practices and the implementation of mitigation approaches such as reduction of groundwater extraction to limit further lake saltwater intrusion and water resources deterioration

Pit Lakes Affected by a River Contaminated with Brines Originated from the Coal Mining Industry: Evolution of Water Chemistry in the Zakrzówek Horst Area (Krakow, Southern Poland)

Long-term coal mining activities in the Upper Silesia significantly affect the environment in southern Poland. Discharges of brines (with TDS reaching over 110 g/L) from mines are the main source of pollution of many rivers in Poland, including the Vistula River. The Zakrzówek horst is a small geological structure composed of the Upper Jurassic limestones. These limestones were exploited in several quarries. In the largest one (the “Zakrzówek” quarry), exploitation reached the depth of 36 m below the water table, i.e., about 32 m below the average water level in Vistula River which flows 700 m from the quarry. An important part of this inflow into quarries came from the contaminated Vistula River, with a chloride concentration over 2 g/L. The exploitation ceased in 1991, and dewatering ended in 1992. In the old quarry area, pit lakes appeared, which are unique because they present an example of a post-mining site affected by the riverine water contaminated with brines. Investigations of physicochemical parameters of water in the Zakrzówek area were carried out in the period of 1990–2020. Results showed that the largest pit lake was initially meromictic with a distinct stratification. After several years, holomictic conditions developed due to the surface layer freshening and convective mixing

Pit Lakes Affected by a River Contaminated with Brines Originated from the Coal Mining Industry: Evolution of Water Chemistry in the Zakrzówek Horst Area (Krakow, Southern Poland)

Long-term coal mining activities in the Upper Silesia significantly affect the environment in southern Poland. Discharges of brines (with TDS reaching over 110 g/L) from mines are the main source of pollution of many rivers in Poland, including the Vistula River. The Zakrzówek horst is a small geological structure composed of the Upper Jurassic limestones. These limestones were exploited in several quarries. In the largest one (the “Zakrzówek” quarry), exploitation reached the depth of 36 m below the water table, i.e., about 32 m below the average water level in Vistula River which flows 700 m from the quarry. An important part of this inflow into quarries came from the contaminated Vistula River, with a chloride concentration over 2 g/L. The exploitation ceased in 1991, and dewatering ended in 1992. In the old quarry area, pit lakes appeared, which are unique because they present an example of a post-mining site affected by the riverine water contaminated with brines. Investigations of physicochemical parameters of water in the Zakrzówek area were carried out in the period of 1990–2020. Results showed that the largest pit lake was initially meromictic with a distinct stratification. After several years, holomictic conditions developed due to the surface layer freshening and convective mixing

Geochemistry of natural chromium occurrence in a sandstone aquifer in Bauru Basin, Sao Paulo State, Brazil

Anomalous concentrations of Cr(VI) occur in groundwaters of the Adamantina Aquifer, in a large region in the western state of Sao Paulo, sometimes exceeding the potability limit (0.05 mg L(-1)). To identify the possible geochemical reactions responsible for the occurrence of Cr in groundwater in Urania, borehole rock samples were collected in order to carry out mineralogical and chemical analyses. In addition, multilevel monitoring wells were installed and groundwater samples were analyzed. Analyses of the borehole rock samples show the occurrence of a geochemical anomaly of Cr in the quartzose sandstones (average concentrations of 221 ppm). Chrome-diopside is one of the main minerals contributing to this anomaly, having an average Cr content of 1505 ppm. Sequential extraction experiments indicated weakly adsorbed Cr in the order of 0.54 ppm, and this quantity is enough to provide the Cr concentrations observed in groundwater. Groundwaters from the monitoring wells proved to be stratified, with the highest concentrations of Cr(VI) (0.13 mg L(-1)) being associated with high redox and pH values (over 10) and high concentrations of Na. Geochemical reactions that may explain the release of Cr from the solid phase to groundwater involve the release of Cr(III) from minerals (like chrome-diopside and Cr-Fe hydroxide), followed by oxidation of Cr(III) to Cr(VI), probably related to the reduction of Mn oxides present in the aquifer. Then cation exchange occurs and dissolution of carbonates which increases the pH of groundwater, resulting in the desorption and mobilization of Cr(VI) into groundwater. (C) 2011 Elsevier Ltd. All rights reserved.FAPESP[97/13879-6]Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)FAPESP[98/15340-0]Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)FAPESP[05/60502-3]Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)CNPq[154492/2006-0

Special issue: Environmental, Health and Social legacies of mining activities in Sub-Saharan Africa

Over > 40 years of implementation of the International Geoscience Programme (IGCP), a partnership and flagship programme between UNESCO and the International Union of Geological Sciences (IUGS), UNESCO realized that the involvement of Africa both in terms of projects devoted to the continent and leadership, was marginal. Between 2011 and 2013, UNESCO collaborated with the Swedish International Development Cooperation Agency (Sida) to support capacity-building activities aiming to increase the participation of Africa in IGCP. From this exercise, two projects (UNESCO/Sida IGCP-594 and IGCP-606) emerged as a research networking platform between scientists from Africa and Europe on the environmental and health challenges of mining activities in Africa. At the end of their implementation, the two projects jointly prepared and published a Special Issue on “Impacts of mining and mineral processing on the environment and human health in Africa” in the Journal of Geochemical Exploration in 2014 edited by Kříbek et al. (2014). However, it was obvious that the challenges facing African countries as a result of mining activities go well beyond simple IGCP projects, and need extensive mobilisation in terms of human re- sources, laboratory facilities and fund raising. The success of two major IGCP projects (IGCP-594 and IGCP-606) encouraged UNESCO to enter into a new Programme Cooperation Agreement with Sida for the period 2014–2018 to support an expanded project entitled “Mapping and Assessing the Environmental and Health Impacts of Abandoned Mines in Sub- Saharan African Countries”. The project aimed to reduce the adverse effects of mining activities on the ecosystem and health of adjacent communities while, at the same time, promote a peaceful mining atmosphere among industry, authorities and local communities. An important advancement in the mining sector is the legal ob- ligation for mining companies to rehabilitate former operational mine sites and ensure that they are restored to a safe environmental state after the mine is closed. While this concept is well rooted in mining legislation in many developed countries, this is not always the case in developing countries, especially in Sub-Saharan Africa. Apart from poor environmental governance as highlighted in the Africa Mining Vision, many African countries lack a precise inventory and assessment of abandoned and derelict mines. It is therefore important to make an assessment of the true extent of the detrimental effects of metal and metalloid pollutants and their impact on human and animal health, as well as on ecosystems. This is a pre-requisite for appropriate legislation development and enforcement. This new project intended to provide crucial scientific knowledge that will contribute to understanding of the factors that control cycling of pollutants from abandoned mines in soils, water and vegetation and the impact on the food chain. Development of appropriated technologies to mitigate environmental risk associated with mining activities was also at the heart of the project. Furthermore, influencing policies, training, education and awareness focusing on communities involved or living around mine sites were important aspects of the project. We anticipate that the results of the project will be used to improve the environmental norms in individual countries in Sub-Saharan Africa and the efficiency of governments in addressing the challenges related to the adverse effects of abandoned mines. The new project builds on a strong network of > 100 scientists working on 29 sites in 17 African countries, with focus on field assessment of pollution (soil, water, crops, health of human and animals), rehabilitation of degraded ecosystems, and policy issues for the attention of communities and governments. For the monitoring of the project, UNESCO put in place a scientific board composed of international experts in this field, some of whom have served as Co-Guest Editors of this Special Issue. An important meeting took place in April 2018 in Nairobi, Kenya, where all project leaders met with the members of the scientific board to evaluate the progress of the project. A key resolution by participants of this meeting was the preparation of another Special Issue to avail the new research contributions to the scientific community

Relation between sedimentary framework and hydrogeology in the Guarani Aquifer System in Sao Paulo state, Brazil

This paper presents the results of a new investigation of the Guarani Aquifer System (SAG) in Sao Paulo state. New data were acquired about sedimentary framework, flow pattern, and hydrogeochemistry. The flow direction in the north of the state is towards the southwest and not towards the west as expected previously. This is linked to the absence of SAG outcrop in the northeast of Sao Paulo state. Both the underlying Piramboia Formation and the overlying Botucatu Formation possess high porosity (18.9% and 19.5%, respectively), which was not modified significantly by diagenetic changes. Investigation of sediments confirmed a zone of chalcedony cement close to the SAG outcrop and a zone of calcite cement in the deep confined zone. The main events in the SAG post-sedimentary history were: (1) adhesion of ferrugineous coatings on grains, (2) infiltration of clays in eodiagenetic stage, (3) regeneration of coatings with formation of smectites, (4) authigenic overgrowth of quartz and K-feldspar in advanced eodiagenetic stage, (5) bitumen cementation of Piramboia Formation in mesodiagenetic stage, (6) cementation by calcite in mesodiagenetic and telodiagenetic stages in Piramboia Formation, (7) formation of secondary porosity by dissolution of unstable minerals after appearance of hydraulic gradient and penetration of the meteoric water caused by the uplift of the Serra do Mar coastal range in the Late Cretaceous, (8) authigenesis of kaolinite and amorphous silica in unconfined zone of the SAG and cation exchange coupled with the dissolution of calcite at the transition between unconfined and confined zone, and (9) authigenesis of analcime in the confined SAG zone. The last two processes are still under operation. The deep zone of the SAG comprises an alkaline pH, Na-HCO(3) groundwater type with old water and enriched delta(13)C values (<-3.9), which evolved from a neutral pH, Ca-HCO(3) groundwater type with young water and depleted delta(13)C values (>-18.8) close to the SAG outcrop. This is consistent with a conceptual geochemical model of the SAG, suggesting dissolution of calcite driven by cation exchange, which occurs at a relatively narrow front recently moving downgradient at much slower rate compared to groundwater flow. More depleted values of delta(18)O in the deep confined zone close to the Parana River compared to values of relative recent recharged water indicate recharge occur during a period of cold climate. The SAG is a ""storage-dominated"" type of aquifer which has to be managed properly to avoid its overexploitation. (C) 2011 Elsevier Ltd. All rights reserved.Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP)[03/08911-0]Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP