Na-Cl Water Type Research Articles

Hydrogeochemical and ecological risk assessments of trace elements in the coastal surface water of the southern Caspian Sea.

This study investigates the occurrence, distribution, and potential ecological risk of trace elements (TEs) along with the hydrogeochemical characteristics of coastal surface water collected from the southern Caspian coasts in the Mazandaran province of Iran. Eighteen coastal water sites were sampled and analyzed using inductively coupled plasma-mass spectrometry and ion chromatography to determine concentrations of TEs and major ions, respectively. Mean concentrations (µg/l) of TEs in the water followed the order: Al (154.3) > Fe (73.6) > Zn (67.8) > Mn (29.9) > Cu (5.7) > Mo (3.7) > Cd (2.8) > Se (2.3) > V (1.9) > Co = As (1.8) > Sb (1.2) > Pb (0.6). TEs displayed high variations within samples, reflecting many sources that control their concentrations in the coastal water. Most TEs displayed elevated concentrations in the east and west of the study area. The Na-Cl water type in the majority of investigated sites indicates excess alkaline elements and strong acid anions relative to alkaline earth cations and weak acid anions. Considering the saturation states of minerals, carbonate and evaporite minerals are oversaturated and unsaturated in surface water, respectively. Compositional interrelations between aqueous species showed that reverse cation exchange may have occurred. The excess SO42- content, derived from irrigation return flow and domestic greywater, probably plays a crucial role in the mobilization and transport of Zn and Pb by binding to sulfate ligands and forming aqueous complexes. Ecological risk assessment of TEs revealed that water in the majority of sites is safe in terms of As, Se, Pb, and Cd content, and unsuitable with respect to Zn and Cu. Acute and chronic toxicities of Cu and Zn are reported in several sites, thus coastal water cannot be used for fishery and protecting "nature reserve" purposes. However, industrial activity and tourism are safe to be conducted in most coastal water sites.

Environmental Effects of Water Product from Coalbed Methane Wells: A Case Study of the Songhe Well Group, Western Guizhou, China

Based on water chemistry analyses of five batches of water product samples from eight coalbed methane (CBM) wells of the Songhe well group in the western Guizhou province in 2017, the single-factor index method, the Nemerow index method and the health risk assessment method were used to evaluate the environmental effects of the water product. The results show that the water co-product of the Songhe well group was characterized mainly by high Na+ and Cl− concentrations, alkalinity, high total dissolved solids and Na–Cl water types. The concentrations of carcinogens (i.e., As, Cd and Cr) were low, but the non-carcinogen Ba was enriched abnormally. The single-factor index method and the Nemerow index method were used to evaluate the water co-product from the eight CBM wells, and the results show a serious pollution level of up to grade 5. The ions Na+, Cl− and Ba2+ were the main sources of pollution. The pollution is more serious in the deeper part than in the shallow part of the well group. The health risk evaluation method was used to calculate the health risk index of carcinogenic factors (i.e., As, Cr, Cd) and non-carcinogenic factors (i.e., Pd, Fe, Cu, Zn, Mn, Hg, F, Ba). The results show that the spatial distribution regularity of these metals in the well group is weak. There were mainly two CBM wells with slight risk throughout the year. With increase in drainage time, the risk gradually decreased, but in the rainy season, the risk index increased abnormally to medium risk.

Influence of surface geology on phosphorus export in coastal forested headwater catchments in Akita, Japan

ABSTRACT Surface geology is a key factor regulating the geographical patterns of P export; however, geographically extensive data on P export mechanisms from natural coastal mountain regions are lacking. We compared stream-water characteristics in forested headwater catchments with different types of surface geology (marine sedimentary rocks [MSRs] and igneous rocks [IRs]) and evaluated the factors regulating soluble reactive phosphorus (SRP) concentrations in stream water. Geographically extensive stratified sampling was conducted: stream-water and sediment samples were obtained from 66 MSR catchments and 55 adjacent IR catchments along the coastal forested mountain regions in Akita, Japan. SRP and major cations and anions in stream waters were analyzed. To evaluate the effect of ionic composition on SRP, sediments were extracted with NaCl and CaCl2 solutions and the SRP concentrations in the extracts were measured. Stream SRP was significantly higher in MSR catchments (median 23 µg L−1) than in IR catchments (median 8 µg L−1) (P < 0.001), and tended to be higher in MSR catchments with younger rocks. Dissolved inorganic nitrogen (DIN) did not differ between catchments with different geologies; therefore, DIN/SRP was significantly lower in MSR catchments (median 18), close to the Redfield ratio. On a Piper diagram, high-SRP stream waters were of the NaCl water type, and stream SRP was significantly correlated with Na+ (r = 0.642, P < 0.0001). In IR catchments, stream waters had relatively higher Ca2+ and Mg2+ concentrations. SRP in the sediment extracts was significantly higher in MSR catchments and samples obtained by NaCl extraction than in IR catchments and CaCl2-extracted samples. Exchangeable Na+ in sediments was significantly higher in MSR catchments, decreasing Ca2+ in the liquid phase by an ion-exchange reaction, which is likely also key in maintaining high SRP levels. We conclude that MSR catchments in coastal Akita are a significant P source for streams even in headwater forests, and that site-specific NaCl water types and higher exchangeable Na+ concentrations in sediments result in higher SRP concentrations in stream waters. These results have critical implications for P cycles in freshwater ecosystems influenced by Na+.

Critical Tectonic Limits for Geothermal Aquifer Use: Case Study from the East Slovakian Basin Rim

The Pannonian basin is a major geothermal heat system in Central Europe. Its peripheral basin, the East Slovakian basin, is an example of a geothermal structure with a linear, directed heat flow ranging from 90 to 100 mW/m2 from west to east. However, the use of the geothermal source is limited by several critical tectono-geologic factors: (a) Tectonics, and the associated disintegration of the aquifer block by multiple deformations during the pre-Paleogene, mainly Miocene, period. The main discontinuities of NW-SE and N-S direction negatively affect the permeability of the aquifer environment. For utilization, minor NE-SW dilatation open fractures are important, which have been developed by sinistral transtension on N–S faults and accelerated normal movements to the southeast. (b) Hydrogeologically, the geothermal structure is accommodated by three water types, namely, Na-HCO3 with 10.9 g·L−1 mineralization (in the north), the Ca-Mg-HCO3 with 0.5–4.5 g·L−1 mineralization (in the west), and Na-Cl water type containing 26.8–33.4 g·L−1 mineralization (in the southwest). The chemical composition of the water is influenced by the Middle Triassic dolomite aquifer, as well as by infiltration of saline solutions and meteoric waters along with open fractures/faults. (c) Geothermally anomalous heat flow of 123–129 °C with 170 L/s total flow near the Slanské vchy volcanic chain seems to be the perspective for heat production.

Origin of solutes in a regional multi-layered sedimentary aquifer system (a case study from the Rub’ al Khali basin, Saudi Arabia)

An isotope and solute evaluation was applied to identify the origin and mechanisms of groundwater salinization in three major Tertiary aquifers in the Rub’ al Khali topographic basin. We demonstrate that the groundwater chemistry evolved from a low- (1800 ppm) to high- (>120,000 ppm) salinity Na–Cl water type, regardless of the aquifer. The similarity in water types between the groundwater from the different formations suggests that the same origin and geochemical processes may be controlling the salinity and major ion chemistry in these aquifers. The suite of hydrogeological, hydrochemical (Cl vs. Br), and isotopic (Cl vs δ18O and Br vs δ81Br) data indicates that the source of solutes is associated with the entrapment of evaporated paleo-seawater (connate water) in nearshore and lagoonal environments during the time of deposition. Moreover, the results from the 87Sr/86Sr ratios show no evidence of significant vertical connectivity between the three Tertiary aquifers. Instead, the data support that evaporated paleo-seawater was trapped in each aquifer individually during the time of deposition, and that each has evolved similarly through water-rock and redox reactions. The stable isotopic compositions of δ18O, δ2H, and 14C show that the entrapped paleo-seawater was partially flushed out by fresh meteoric water during the Late Pleistocene and Early Holocene periods.

Groundwater Quality Characterisation of Selected Hand-dug Wells and Geological Implications in the Assin North Municipality, Ghana

Water from ten hand-dug wells from Assin North Municipality in Ghana were analysed at Ghana Water Company Limited Quality Assurance Laboratory, Ho in Ghana for various physico-chemical parameters. The analyses used standard methods with chemicals of AR grade; pH was measured with the Horiba Compact B-122 and Inolab 7300 Conductivity/TDS portable meter. Colour, turbidity, aluminium, copper, sulphate and total iron were analysed by spectrophotometry using Hach DR/2500 following standard methods. Flame photometer was used for determination of metal ions Na+, K+ and Ca2+. Silver nitrate method was used to estimate chloride, sulphate was determined by turbidimetric method. Total hardness was calculated by complexometric titration using EDTA. The results of the analyses show pH 6.0 to 7.2 with a mean of 6.5, conductivity from 300 to 800 μS/cm, TDS range from 90 to 400 mg/l. Piper Trilinear diagram revealed three main water types - calcium bicarbonate (Ca+Mg-HCO3) possibly sourced from Ca-plagioclase, biotite and amphibole; sodium chloride (Na-Cl) from Na-plagioclase, muscovite and chlorite; and mixed water types which may be due to the combined effect of Birimian metasedimentary rocks, Belt granitoid and pegmatites that released into the water through cation exchange and accounted for Na+ in the Na-Cl water type. Chloride in a few hand-dug wells may be linked to mineralogy crystallised from marine deposited sediments and infiltration of rainwater along fractures in the rocks. Hence most of the water samples have Na/Cl ratios&lt;0.86. The rainwater in the area with weak acidity possibly infiltrated into the soil to cause appreciable concentration of HCO3- in the studied water. The total coliform values in water were less harmful as there was no faecal coliforms, though total microbial values in hand-dug wells X4 and X10 with total coliform values of 2.2 and 5.1 MPN/100ml respectively exceed the WHO guidelines. Hand-dug wells X4 and X6 in the study probably ended in aquifers in the weathered zone with the rest of the wells in fresh fractured horizons of the granitoids. Na/Cl ratios&gt;1 (for water samples X1, X7 and X8) might have been due to contamination from anthropogenic sources. Pearson correlation indicates strong and positive correlation of TDS&lt;Mg&lt; Na with conductivity. All the water samples were safe for human consumption.

Evaluation of natural background levels of high mountain karst aquifers in complex hydrogeological settings. A Gaussian mixture model approach in the Port del Comte (SE, Pyrenees) case study

The hydrogeological processes driving the hydrochemical composition of groundwater in the alpine pristine aquifer system of the Port del Comte Massif (PCM) are characterized through the multivariate statistical techniques Principal Component Analysis (PCA) and Gaussian Mixture Models (GMM) in the framework of Compositional Data (CoDa) analysis. Also, the groundwater Natural Background Levels (NBLs) for NO3 and SO4 and Cl are evaluated, which are specially important for indicating the occurrence of groundwater contamination derived from the anthropic activities conducted in the PCM.The different hydrogeochemical facies found in the aquifer system of the PCM comprises low mineralized Ca-HCO3 water for the main Eocene karst aquifer, and Ca-SO4 and highly mineralized NaCl water types in the minor aquifers discharging from the PCM. The NBL values of SO4, Cl and NO3 obtained for the main karst aquifer are 14.33, 4.06 and 6.55 mg/L, respectively. These values are 35, 3 and 1.2 times lower than the respective official NBLs values that were determined by the water administration to be compared with in the case of conducting a pollution assessment characterization in the main karst aquifer. Official overestimation of NBLs can put important groundwater resources in the PCM at risk.

Groundwater quality assessment for different uses using various water quality indices in semi-arid region of central Tunisia

The Hajeb Layoun-Jelma basin, located in the central Tunisia, is the principal source of water supply for Sidi Bouzid and Sfax region. The over-abstraction from this groundwater, since 1970, and the intensive agriculture activities led to the degradation of the water quantity and quality. The quality evaluation for this groundwater is very important tool for sustainable development and decision for water management. A total of 28 groundwater samples, from shallow, springs, and deep aquifers, were collected, storage and analyzed to evaluate its quality suitability for domestic and agriculture purposes using geographic information system and geochemical methods. For the both aquifers, the abundance of cations: Na > Mg > Ca > K, and of anions in the order: Cl > HCO3 > SO4. The dominant hydrochemical facies, for the shallow aquifer and springs, are Na-Cl and Ca-Mg-Cl; for the deep aquifer, the geochemical facies are Na-Cl, Ca-Mg-Cl, and Ca-Cl. The comparison of the major parameters and the chemical data with the World Health Organization standards and the national standards indicate that this groundwater is suitable for drinking, except in some samples, with high salinity concentrations. The water quality was assessed, for drinking uses, using “water quality index,” “entropy,” and “improved water quality index.” The results mentioned that the improved water quality index is the best method which indicated that the poor water quality coincide with the Na-Cl water type. The entropy method and the water quality index present the optimistic methods. The irrigation suitability assessment was made using various parameters (SAR, TH, % Na, PI, MH, KR, EC). The results revealed that the majority of samples in Hajeb Layoun-Jelma basin are not appropriate for irrigation uses.

Medium to low enthalpy geothermal reservoirs estimated from geothermometry and mixing models of hot springs along the Malawi Rift Zone

We investigated the major ion and stable isotope geochemistry and used silica and cation concentrations to assess the geothermometry of hot springs along the Malawi Rift Zone (MRZ). The MRZ is a magma-poor rift, where potential geothermal energy is postulated from elevated heat flow and the occurrence of hot springs. Our objectives were to (1) estimate hot spring reservoir temperatures, (2) identify processes that could affect hot spring water during the ascent from their geothermal reservoirs, and (3) identify the most promising areas for geothermal energy generation. New geochemistry data from 27 hot springs were analyzed and classified as Na-HCO3, Na-SO4, or Na-Cl (SO4) water types controlled mainly by the mineralogy of the host rocks. The hot springs in the MRZ are associated with the local meteoric waters that infiltrate at depth and are heated by an anomalously high geothermal gradient. Our findings indicate that a parent geothermal fluid is mixed and diluted with a proportion of more than ∼45 % of cold water from shallow aquifers. Additionally, other processes such as water-rock interaction, and CO2 outgassing take place during the ascent of the geothermal fluid to the surface. The quartz conductive silica geothermometer indicates reservoir temperatures that range from 60 °C to 130 °C, with enthalpies ranging from 250 kJ/kg to 537 kJ/kg, respectively. However, the Na-K cation geothermometer indicates reservoir temperatures from 92 °C to 190 °C with enthalpies from 388 kJ/kg to 808 kJ/kg. Three areas of potential geothermal energy generation were identified: (1) The Chiweta area, (2) Nkhotakota area, and (3) the Shire graben area. We conclude that the hot springs along the MRZ have geothermal energy capabilities of medium to low enthalpy that can be exploited for electricity generation or other direct uses.

Hydrogeochemical processes and suitability assessment of surface water in the Grouz Dam Basin, northeast Algeria

Surface water is the principal source of water for domestic use and agricultural irrigation in Grouz Dam Basin and adjacent regions. This research aims to evaluate hydrochemical characteristics and suitability for domestic and agricultural irrigation purposes of the Grouz Dam Basin surface waters. The surface waters were categorized as alkaline hard freshwater and are classified into Na-Cl and mixed water types. The values of measured parameters are below the maximum allowable limits for drinking except for Na+, NO32- and turbidity. Dissolution and anthropogenic activity are the dominant hydrogeochemical processes controlled surface water chemistry. Overall, it was found that surface waters are unsuitable for drinking by cons they are suitable for irrigation. The results of this study will be useful in regional surface water management and protection.

Hydrogeochemistry of a strategic alluvial aquifer system in a semi-arid setting and its implications for potable urban water supply: The Lodwar Alluvial Aquifer System (LAAS)

Lodwar Municipality is one of the fastest-growing urban areas of Sub-Saharan Africa that depends mainly on groundwater for its municipal water supply. Most of the groundwater sources are located within the riparian zones of the Turkwel River. With limited understanding of its aquifers, the groundwater of Lodwar may be at risk of natural processes and anthropogenic activities. Statistical techniques and geochemical methods were applied to determine the aquifer hydrogeochemistry. Three distinct aquifers, which we collectively refer to as the Lodwar Alluvial Aquifer System, underlie Lodwar and its environs, the shallow alluvial, intermediate, and deep aquifers which are the main source of fresh water. A fourth, the shallow aquifer of the Turkana grit, is highly saline and with fluoride contamination. Just as the Turkwel River, the shallow alluvial aquifer (SAA) was dominated by Ca–HCO3 water type, while the TGSA was Na–Cl water type and became Na–HCO3 near the Holocene sediments. The intermediate aquifer (IA) was Na–HCO3water type. Pockets of Mg–HCO3 water occurred in the shallow alluvial and intermediate aquifers. The natural processes in the SAA include rock-water interaction, recharge by surface water, and oxidation reactions, while evaporation and dissolution are the major factors controlling the chemistry of the TGSA. Ion exchange, dilution, and dissolution are the major processes in the IA. Elevated levels of NO3− and SO42− during the wet season within the SAA and the IA reflects their vulnerability to pollution. Saline intrusion into the shallow and intermediate aquifers from the Turkana grit aquifers is likely to occur.

Assessment of coastal surface water quality for irrigation purpose

Abstract The study aimed to assess the coastal surface water quality for irrigation purposes through the analysis of the water samples of some selected estuaries, rivers, and ponds. The analysis results showed that the mean value of typical water quality parameters like electrical conductivity (EC), total dissolved solids (TDS), sodium (Na+), and chloride (Cl−) ions exceeded the permissible limit of the Department of Environment (DoE), Bangladesh 2010, and FAO, 1985 for the pre- and post-monsoon seasons. The Piper diagram indicated a Na-Cl water type, especially during the pre- and post-monsoon seasons. The water quality parameters in the areas showed a higher amount than the standard permissible limits, indicating that the quality is deteriorating. The water quality index values for domestic uses showed very poorly to unsuitable in most of the surface waters except pond water, especially during the pre- and post-monsoon periods. The surface water quality index for irrigation purpose usages was found to be high and/ or severely restricted (score: 0–55) during the pre- and post-monsoon seasons. The study observed that due to saline water intrusion, the water quality deterioration started from post-monsoon and reached its highest level during the pre-monsoon season, which gradually depreciates the water quality in coastal watersheds of Bangladesh.

Hydrogeochemical Processes and Trace Metal Contamination in Groundwater: Impact on Human Health in the Maputaland Coastal Aquifer, South Africa

The main objective of the study is to evaluate the hydrogeochemical processes and potential health risk assessment for humans in groundwater of Maputaland coastal aquifer, South Africa. In this study, 53 and 42 groundwater samples were collected from bore wells during 2018 and 2019 and were analysed for major ions, minor ions, nutrients and trace metals. Na–Cl water type was dominant in groundwater followed by Ca–HCO3. Cross plots revealed that ion exchange, reverse ion exchange, silicate weathering, seawater mixing and anthropogenic inputs from agricultural activities govern the groundwater chemistry. GIS methods were adopted to produce spatial distribution maps of major ions through which locations of groundwater contamination and the intensity of hydrogeochemical processes were identified. Mean concentration of trace metals were in the order: Zn > Li > Al > Fe > Mn > Cu > Pb > As > Co > Cd in 2018, Fe > Zn > Mn > Sr > B > Pb > Cu > Co > Cr > Cd > Ag > Al > Ni in 2019. Most of the trace metals were found to be within the WHO standards for drinking water except Cd, Zn, Pb, Mn, Al and Fe. Health risk assessment of trace metals in groundwater via ingestion and dermal absorption pathways were carried out. Hazard Quotients (HQs) and Hazard Index (HI) of all trace metals were below 1, except HQingestion and HI for Co and Pb which were greater than 1 in children. This suggests that these metals pose adverse risks to local people, and children were more sensitive to risks than adults. HI values for adults and children were medium indicating high risk. This is the first baseline study conducted in the study area which identifies the chemical characterization and the potential health risk due to trace metals contamination.

Aksaray Üniversitesi Kampüs Alanının Hidrojeokimyasal, Jeoteknik ve Toprak Jeokimyası Karakteristikleri, Aksaray

Bu çalışma, Aksaray Üniversitesi kampüs alanının, hidrojeolojik, jeokimyasal ve jeoteknik bakımdan incelenmesini konu almaktadır. Bu kapsam doğrultusunda, kampüs alanı içerisinden 4 farklı su noktasından toplanan su örneklerine ait analiz sonuçları, 17 adet toprak numunesinin jeokimyasal analizi ve 2008 yılında gerçekleştirilen sondajlardan elde edilen kuyu log-tanımlamaları ile kaya numunelere ait jeoteknik özellikler incelenmiştir. Hidrojeolojik çalışmalar, inceleme alanında Na-Cl ve Ca-Cl su tiplerine sahip iki farklı su fasiyesinin geliştiğini göstermiştir. Bu sular, sulama suyu standartlarına ve elektriksel iletkenlik değerlerine göre sulama suyu kalitesi düşük ancak kullanılabilir III. kalite sulama suyu olarak sınıflandırılmıştır. Jeoteknik incelemelere göre, kampüs alanı örtü tabakasının altında geniş yayılım gösteren killi kireçtaşlarının güvenli taşıma gücü değerinin 36,5 kg/cm2 olduğu ve mukavemeti düşük dayanımlı kayaç sınıfına girdiği belirlenmiştir. Toprak örneklerinin As ve Pb içerikleri, ortalama üst kabuk değerlerine göre yüksek sayılabilecek değerlerdedir. Cl ve Na elementleri için hazırlanan anomali dağılım haritalarına göre, kampüs alanının doğu, güney batı ve kuzey batı kesimlerinin Na ve Cl elementleri bakımından diğer bölgelere oranla daha yüksek değerler içerdiği belirlenmiştir. Bu çalışmanın sonuçları, kampüs alanı içerisinde gerçekleştirilecek yeşil alan çalışmalarının daha planlı ve verimli bir şekilde yapılabilmesine olanak tanıyacak ve yeşil alanların geliştirilmesine katkı sağlayacaktır.

Degradation of groundwater quality in the coastal aquifers of the USA

The objective of this study is to analyze groundwater types and the extent of seawater intrusion in terms of ion concentrations in groundwater sample using USGS monitoring wells. Groundwater quality indices [fsea, GQI (dom), GQI (mix), GQI (swi)] were used to estimate the spatial distributions of groundwater types in the US coastal aquifers. Results showed that the dominating groundwater chemistry in the study area was Na+ and Cl−. Results also indicated that seawater intrusion of groundwater occurred in the US coastal aquifers. Based on the results of GQI (mix) and GQI (dom), most of the wells fell under domain II in the Piper diagram, indicating that they were of the Na–Cl water type. Na–Cl and mixed Ca–Mg–Cl were determined to be the two dominant groundwater types in the coastal aquifers of the US seawater intrusion evident in the Palm Beach and Miami-Dade counties of Florida, the San Diego and Santa Barbara areas of California, and within Virginia and New Jersey on the east coast. As the sea level continues to rise further inland, Na–Cl concentration in groundwater will increase, particularly in aquifers along low-lying coasts.

Analysis and evaluation of the spatial and temporal variabilities of river water quality parameters

This study aimed to analyze the status and evaluate the spatiotemporal variabilities of water quality in the Awash River, Ethiopia. The study also aims to identify the origin and geochemical composition of the river water. Temporal variabilities of similar water quality parameters in the Lake Beseka, a dramatically rising lake (0.2 m/year) in the Awash River basin, which is being channeled into the Awash River system in order to control the lake level rise, were also considered in this study. To do this, laboratory measurements and a 10-year consecutive record of physicochemical parameters, major ions, nutrients and minor ions of the Awash River and Lake Beseka waters, graphical methods and factor analysis approaches were used. The origin of the Awash River was found to be shallow-medium depth aquifer with a geochemical composition of Ca(HCO3)2 and NaHCO3, while the origin of Lake Beseka was found to be deep, ancient groundwater with a geochemical composition of NaCl and NaHCO3. However, mixing the lake water with Awash River in the downstream sites shifted the geochemical composition of the river water to a mixture of Ca(HCO3)2, NaHCO3 and NaCl water types. The results also showed that the river water quality varies spatially and temporally, controlled by three major factors: the combined effects of anthropogenic activities and mineral dissolutions (Factor-1), anthropogenic activities and ion exchange (Factor-2) and ion exchange (Factor-3). While Factor-1 was the main controlling factor of the river water quality, and Factor-3 was the least, all three factors equally controlled the temporal variabilities of water quality in Lake Beseka. The observed temporal and spatial variabilities of the river water quality suggest that frequent water quality evaluations are important in designing appropriate water management strategies in river systems near intensive agricultural, industrial, and urban development areas.

CO2 emissions from Fogo intracaldera volcanic lakes (São Miguel Island, Açores): A tool for volcanic monitoring

A geochemical study was carried out at Fogo Lake during June 2016, in one of the deepest lakes on São Miguel Island, as well as on small associated pond, in order to identify possible anomalous degassing areas. Fogo Lake is located inside the summit caldera of Fogo Volcano, one of the three active central volcanoes that dominate São Miguel geology.The hydrogeochemical profile carried out along the water column of the Fogo Lake suggests that the lake was thermally stratified, corresponding to poorly mineralized and cold Na-Cl type waters. The same composition is found in the small pond, but with a slight Ca-enrichment.To measure the CO2 flux at the lake surface, the modified accumulation chamber method was used, and a total of 1696 measurements were accomplished, covering an area of approximately 1.56 km2. Measured CO2 flux values are relatively low, ranging from 0 to 28.4 g m−2 d−1 (mean = 2.6 g m−2 d−1) and from 2.1 to 15.0 g m−2 d−1 (mean = 6.3 g m−2 d−1), respectively at Fogo Lake and at the small pond. The very low values measured in the central area of Fogo Lake are associated with the monomictic character of the lake, as the CO2 is not able to ascend into the surface when the water column is stratified during the warmer period.Statistical analyses suggest that the CO2 emission is associated with a single source of CO2, probably biogenic; a similar signature is pointed by the water δ13C isotopic content. The estimated total CO2 emissions from the Fogo Lake was approximately 4.04 t d−1, much higher than the value observed at the small pond (0.19 t d−1).

Geophysical and hydrogeochemical investigations of Nubian sandstone aquifer, South East Sinai, Egypt: Evaluation of groundwater distribution and quality in arid region

The expansion in human activities, the absence of running water in South Sinai province in northeastern Egypt and the high cost of seawater desalination render groundwater the essential source for potable water in this arid region. This contribution represents the integration of geophysical and hydrochemical investigations to delineate groundwater distribution and evaluate the water quality of the Cretaceous sandstone aquifer of Wadi Barqa area, Southeastern Sinai. The locations of sites, suitable for geophysical sounding measurements, were selected using digital elevation map. Vertical electrical sounding (VES) and time-domain electromagnetic sounding (TEM) measurements were carried out to determine the depth and thickness of the unsaturated and water-saturated zones as well as the groundwater quality, which were verified by calibrating the estimated electrical resistivity values with the design and logs data of eleven drilled wells next to the sites of geophysical soundings. The VES and TEM data revealed the presence of relatively thick zoned aquifer, overlain by unsaturated zone with variable thickness (83-65 m). The upper aquifer zone (25–43 m thick) is characterized by higher resistivity values (16–163 Ohm.m), reflecting fresh water signature, whereas the lower aquifer zone (122–150 m thick) has lower resistivity values (16–24 Ohm.m), indicating saturation with semi-fresh to relatively brackish water. Water samples, collected from wells taping the Nubian Sandstone aquifer, have average total dissolved solids (TDS) value of 544 mg/l. The hydrochemical parameters of these samples are consistent with NaCl water type with the majority of samples belonging to high salinity with low sodium categories. This suggests that the groundwater of the aquifer was dominated by old meteoric origin. The compositional characteristics of the groundwater of the investigated aquifer indicate suitability for domestic and irrigation purposes. However, due to the arid nature of Southeastern Sinai province, it is recommended to use this groundwater as potable water.

Hydrogeochemical processes controlling the mobilization and enrichment of fluoride in groundwater of the North China Plain

Fluoride enrichment in groundwater at the North China Plain (NCP) is posing a potential health risk to human being. To better understand the enrichment mechanism of fluoride in the groundwater systems, the groundwater, sediments samples and pore water compacted from clayey sediments were collected to perform the chemistry analysis and geochemical inverse modeling. The results showed that fluoride concentration in groundwater from the NCP has a range of 0.38–7.35 mg/L, and 67.8% of groundwater samples have the fluoride concentration higher than 1.5 mg/L. High fluoride groundwater was mainly distributed in the central plain and coastal area of the NCP, and characterized by the Na-HCO3 or Na-Cl type water, lower Ca and higher TDS concentrations. Along groundwater flow-path from the mountainous to coastal areas, several hydrogeochemical processes control the mobilization and enrichment of fluoride in groundwater, including cation exchange between Ca and Na on the surface of clay minerals, precipitation/dissolution of carbonates, dissolution of fluorite, marine transgressions, and release of pore water trapped in clayey sediments caused by land subsidence. The fluoride concentrations in the pore water compacted from the sediments ranged from 2.92 to 4.48 mg/L. At the central plain and coastal area, the wide occurrence of land subsidence resulted from the groundwater over-exploration leads to the release of pore water rich in fluoride into surrounding aquifers, thereby elevating the concentration of groundwater fluoride. The resulted groundwater environment with high salinity and some newly-introduced ions, such as Mg, promote the dissolution of fluorite, which was under-saturated in the groundwater samples from the NCP, further enhancing the fluoride enrichment in the groundwater at the coastal area. The findings of this study will provide new insights on the generation of high fluoride groundwater.

Kestanbol Jeotermal Akışkanının Hidrokimyasının ve Çevresel Etkilerinin Belirlenmesi

Kestanbol geothermal field, located in the ancient town of Alexandria Troas, is at the contact between plutonic intrusions and neighboring metamorphic rocks in the Biga Peninsula. This area is also controlled by an ENE-WSW striking right lateral strike-slip fault segment representing the extension of the southern branch of the North Anatolian Fault to the west and is one of the geothermal fields with highest temperature in the Biga Peninsula. Kestanbol geothermal fluid from a well is used to heat facilities for thermal tourism and balneological purposes. The geothermal fluid continuously seeps into the environment with low flow rate and additionally, wastewater from the facility is discharged into Ilica stream. This study was conducted to determine the hydrochemical characteristics of the well and springs located in Kestanbol geothermal field and to evaluate the environmental effects of geothermal fluids on the soil and stream sediment. The temperature, electrical conductivity (EC) and pH of Kestanbol geothermal fluids are 59.5-74.1oC, 30.3-35.5 mS/cm, and 6.45-6.71, respectively. The geothermal fluids are NaCl water type, with mean NaCl concentration of 19511 mg/L. In addition to higher EC values, and total dissolved solid content, Na + , Cl - , B, Ba, Fe and Mn concentrations of the Kestanbol geothermal fluid are above the tolerance limit of TS 266. Moreover, the geothermal fluid is heavily polluted water (class IV) according to the Turkish Inland Water Quality Regulations in terms of EC, Na + , Cl - , B and Fe. There is a scaling problem in the Kestanbol geothermal field. XRD and SEM-EDX analyses identified the minerals causing scale as calcite, halite and siderite. Arsenic, Fe and Mn concentration of scale, soil and stream sediment samples are higher than the mean value of world continental crust. According to the enrichment factor and geoaccumulation index, the geothermal fluid with intense rock interaction enriches soil and stream sediment in terms of As and Mn metal(loid)s as a result of discharge. It is recommended that geothermal fluids and waste waters from the facility should not be discharged into the soil and Ilica stream.