Water Geochemistry Research Articles

Efflorescent Sulphates with M+ and M2+ Cations from Fumarole and Active Geothermal Fields of Mutnovsky Volcano (Kamchatka, Russia)

In this study, sulphate efflorescent minerals covering the surface of the Donnoe and Dachnoe fields of the Mutnovsky volcano are described. The minerals were precipitated on the argillic facies as the result of water–rock interaction and fumarole emission. A chemical composition of Ca, Ba, (NH4)+, Na-Fe3+, (NH4)+-Al, (NH4)+-Fe3+, Na-Al, K-Al, and K-Fe3+ sulphates was reported. Elements such as Sr, Mg, Co, Ni, Ti and P were found as isomorphic impurities. Ammonia species were concentrated around fumaroles. The mineral assemblage described herein is unique in relation to other geological settings and reflects the process of low-temperature mineral formation associated with volcanism. The thermal water contains cations such as H, Na, K, NH4, Ca, Mg, Fe2+, Fe3+, and Al in different proportions with pH ranging from 2.4 to 6.5 and the dominance of acidic waters. The gas condensate bears such cations as (NH4)+, Ca, and Mg and has a pH of ~5. Thus, the rest of the main cations are derived from the leaching of the host rocks. Among the identified phases, the alunite-supergroup minerals are more prone to isomorphism. The Ti, Co, and Ni impurities mark the unique geochemistry of thermal water at the Mutnovsky volcano. We postulate that the chemical composition of alunite-supergroup minerals reflects the types of hydrothermal occurrences and contains important information on the geochemistry of the hydrothermal process.

Geochemistry and Radioecology of Waters and Bottom Sediments of the Mzymta River, the Black Sea Coast

Geochemistry and Radioecology of Waters and Bottom Sediments of the Mzymta River, the Black Sea Coast

Hydrogeochemical characteristics of fresh waters in the springs of salt dome territories of the Cis-Urals region

The article presents the results of a study on the geochemistry of fresh water from natural sources (springs) in the salt dome territories of the Pre-Ural Artesian Basin. Spring waters are understudied; they are not classified according to their chemical composition and purpose. The research area is the territory of the Pre-Ural Artesian Basin in Orenburg Region with salt-gypsum tectonics. There are numerous springs with fresh water suitable for household and drinking purposes there. Springs with mineralization from 156 to 806 mg/dm3 of mixed composition, sulfate-chloride, sulfate-bicarbonate, bicarbonate and calcium and magnesium-calcium, sodium-magnesium-calcium are related to gypsum fields and salt dome structures. The total hardness varies from 3.5 to 10.27 mg/eq/l from moderately hard to extremely hard. The conclusion on the quantitative and qualitative assessment of spring waters should be made by prospecting and exploration activities with experimental filtration activities and assessment of reserves.

Household and community systems for groundwater remediation in Bihar, India: Arsenic and inorganic contaminant removal, controls and implications for remediation selection

The presence of arsenic (As) and other inorganic contaminants in groundwater is a key public health issue in India and many other parts of the world. Whilst a broad range of remediation technologies exist, performance can be highly variable, and appropriate selection and management of remediation approaches remains challenging. Here, we have identified and tested the performance of a range of small-scale remediation technologies (e.g. sand filters, multi-stage filtration and reverse osmosis (RO)-based systems; n = 38) which have been implemented in Bihar, India. We have undertaken spot-assessments of system performance under typical operating conditions in household and non-household (e.g. community, hospital, hostel/hotel) settings. The removal of As and other inorganic contaminants varied widely (ranging from ~0–100%), with some solutes generally more challenging to remove than others. We have evaluated the relative importance of technology type (e.g. RO-based versus non-RO systems), implementation setting (e.g. household versus non-household) and source water geochemistry (particularly concentrations and ratios of As, Fe, P, Si and Ca), as potential controls on remediation effectiveness. Source water composition, particularly the ratio ([Fe] – 1.8[P])/[As], is a statistically significant control on As removal (p < 0.01), with higher ratios associated with higher removal, regardless of technology type (under the site-specific conditions observed). This ratio provides a theoretical input which could be used to identify the extent to which natural groundwater composition may be geochemically compatible with higher levels of As removal. In Bihar, we illustrate how this ratio could be used to identify spatial patterns in theoretical geochemical compatibility for As removal, and to identify where additional Fe may theoretically facilitate improved remediation. This geochemical approach could be used to inform optimal selection of groundwater remediation approaches, when considered alongside other important considerations (e.g. technical, managerial and socio-economic) known to impact the effective implementation and sustainability of successful groundwater remediation approaches.

Geochemistry of Thermal and Cold Mineral Water and Gases of the Tien Shan and the Pamir

This study presents the first regional hydrogeochemical portrait of the mineral waters and associated gases of the Central Asia region, shaped by the Tien Shan and the Pamir. A geochemical survey of more than 50 fluid discharges from the Northern Tien Shan to the Pamir was carried out between 2018 and 2019. Isotopic (δD, δ18O, d15N2, d13CCO2, d13CCH4) and chemical data allow elucidating fluid genesis and general evolution in the continental collision zone. Geothermometric estimations as well as the content of the chemical components in waters (Cl, Li, B, Br) and gases (N2, CO2) suggest that the studied waters are not related to the presence of any active hydrothermal systems at shallow depth. Silica and cation geothermometers along with thermodynamic equilibrium calculations indicate that the temperature of unmixed deep fluids does not exceed 110 to 150 °C. The determination of d15N2 and d13CCO2 has revealed that the mantle genesis of gas flux matches with the areas of CO2-rich waters manifestations. The dislocation of mineral and thermal waters of Central Asia along the major regional tectonic structures is provided by topographically driven and well-developed long circulation of waters at the depth of 1 to 4 km.

Geochemistry of Formation Water and Its Implications for Petroleum Source Rocks in the Fengcheng Formation, Mahu Depression, Xinjiang, China

Geochemical properties of formation water reflect the sedimentary environments and the sealing conditions of the formation, which are of great significance for oil and gas exploration. In this research, the formation waters in the deep Permian Fengcheng Formation in the Mahu Depression were studied by analysis of chemical composition, stable isotopes, and the homogenization temperatures and salinities of fluid inclusions. The results show that the formation water is NaHCO3-type with high salinity, high HCO3-, low concentrations of Ca2+ and Mg2+ and high pH. The overall sealing of the formation is well maintained. Na2SO4-type water was found in some places with poor preservation of oil and gas. The fluid geochemistry and alkaline mineral distribution in the strata, which are dominated by deep fine-grain mixed deposits, indicate that the main body of the Fengcheng Formation was deposited in an alkaline lake sedimentary environment. The isotopic signatures are characterized by high δ13C, negative δ18O, and light strontium and heavy boron isotopes in the strata near the deep fault zone, which indicate that the Fengcheng formation may have been affected by deep hydrothermal fluids. From the first member to the third member of the formation, the salinity first increases and then decreases. This low-high-low trend corresponds to the initial stage of alkaline lake development followed by strong alkali formation and a final stage of water retreat. The coincidence between the spatial distribution of alkaline minerals, high-salinity formation water and source rocks indicates that the alkaline lake environment can form high-quality source rocks with good petroleum generation capacity.

Geochemistry of formation waters and crude oils in the Shulu Sag, Bohai Bay Basin, NE-China, to assess quality and accumulation of hydrocarbons

Geochemical fingerprinting of formation waters and hydrocarbons can be utilized to track the migration, accumulation, and preservation of hydrocarbons. The present case study from the Shulu Sag, Bohai Bay Basin, NE-China analyzes the origin of the formation waters and the relationship between water chemistry and hydrocarbon preservation by combining the geochemical characteristics of formation waters and crude oils. There are three geochemical groups of formation waters with different origins, which represent different hydrodynamic environments and hydrocarbon preservation conditions. Group 1 waters are related to meteoric water with the lowest total dissolved solids (TDS), γ(Cl–Na)/γMg and the highest γNa/γCl, representing an open environment with poor hydrocarbon preservation conditions, accompanied by super heavy oils. Group 3 waters are connate water with the highest TDS, γ(Cl–Na)/γMg and the lowest γNa/γCl, representing a closed environment with the best hydrocarbon preservation conditions, accompanied by light oils. Group 2 waters are intermediate between Group 1 and Group 3 waters, representing a semi-open environment with intermediate hydrocarbon preservation conditions, accompanied by light, medium, and heavy oils. The clear corresponding relationship between oil quality and associated water type shows that water chemistry significantly affects the oil quality and accumulation in the Shulu Sag through secondary changes. Biodegradation is the dominant effect in the strata above 2100 m. Water washing is dominant in the depth range of 2100–3400 m, and there are no noticeable secondary changes in the strata below 3400 m. A model for the origin, evolution, and flow of formation waters in the Shulu Sag is established to analyze the hydrocarbon accumulation process. Meteoric waters flow into the buried hills from Ningjin Uplift as a result of gravity flow, resulting in modification of oil composition, destruction of the oil reservoirs, and the formation of Group 1 waters. During the hydrocarbon charging, the centrifugal flow driven by overpressure flows in two directions from the source rocks, one is to the western slope and mixes with meteoric waters to form Group 2 waters and heavy oil reservoirs, and the other is to the paleo-uplift to form Group 2 and Group 3 waters and light oil reservoirs. Water chemistry is sensitive to the hydrodynamic environment change and can be an important reference for oil and gas exploration. Buried hills with Group 3 waters should be the highest priority for further exploration, whose oil reservoirs are dominated by light oil with high commercial value. Although the oil quality is poor, buried hills with Group 2 waters in the slope can be secondary targets. In comparison, the buried hills with Group 1 waters should be avoided for oil and gas exploration. The geochemistry of formation waters helps understand the origin and evolution of formation waters, predict oil quality and distribution, and further aids oil and gas exploration.

Aquaculture production of hatchling Hawaiian Bobtail Squid (Euprymna scolopes) is negatively impacted by decreasing environmental microbiome diversity.

AimsThe Hawaiian Bobtail Squid (Euprymna scolopes) is a model organism for investigating host–symbiont relationships. The current scientific focus is on the microbiome within E. scolopes, while very little is known about the microbiome of the tanks housing E. scolopes. We examined the hypothesis that bacterial communities and geochemistry within the squid tank environment correlate with the production of viable paralarval squid.Methods and ResultsTotal DNA was extracted from sediment and filtered water samples from ‘productive’ squid cohorts with high embryonic survival and paralarval hatching, ‘unproductive’ cohorts with low embryonic survival and paralarval hatching. As a control total DNA was extracted from environmental marine locations where E. scolopes is indigenous. Comparative analysis of the bacterial communities by the 16S rRNA gene was performed using next generation sequencing. Thirty‐eight differentially abundant genera were identified in the adult tank waters. The majority of the sequences represented unclassified, candidate or novel genera. The characterized genera included Aquicella, Woeseia and Ferruginibacter, with Hyphomicrobium and Rhizohapis were found to be more abundant in productive adult tank water. In addition, nitrate and pH covaried with productive cohorts, explaining 67% of the bacterial populations. The lower abundance of nitrate‐reducing bacteria in unproductive adult tank water could explain detected elevated nitrate levels.ConclusionsWe conclude that microbiome composition and water geochemistry can negatively affect E. scolopes reproductive physiology in closed tank systems, ultimately impacting host‐microbe research using these animals.Significance and Impact of studyThese results identify the tight relationship between the microbiome and geochemistry to E. scolopes. From this study, it may be possible to design probiotic counter‐measures to improve aquaculture conditions for E. scolopes.

HYDROGEOLOGICAL CONCEPTUAL MODEL OF 'AFH' GEOTHERMAL FIELD AT SALAHUTU REGENCY, MALUKU PROVINCE USING WATER AND GAS GEOCHEMISTRY METHODS

The research area is a geothermal field located in the Tulehu area, Salahutu District, Maluku Province. The purpose of this research is to interpret the conceptual model of the geothermal system with the data that has been obtained. The first method is water geochemistry which includes ion balance, water type, water source, water geothermometer and water geoindicator. Theremore, the isotopic geochemical method is applied, which is to determine the source of the fluid. Then using gas geochemical methods including gas sources, gas geothermometers, and gas geoindicators. Based on the descriptive provisions, the research area is included in the low relief liquid dominated system. Based on the heat source, the research area is included in seawater. The research area is a medium temperature geothermal system with reservoir temperatures ranging from 185˚C to 240˚C with reservoir temperature parameters. Based on geological and geochemical interpretations, the upflow area in the study area is in the middle of the study area in the Hatuasa regionor between Mt. Salahutu and Mt. Erikawang, while the outflow area is in the eastern part of the study area, or towards the coastal line in Tulehu region

Thermal springs and active fault network of the central Colca River basin, Western Cordillera, Peru

Thermal waters and vapor discharges (hot springs, geysers, solfataras, and fumaroles) are common phenomena in volcanic regions at active plate boundaries, and the Central Andes are no exception. The Colca River basin in S Peru is a highly diversified and complex thermal region with unresolved questions on the origin of thermal fluids, reservoir temperature, and connections with tectonic and/or volcanic activity. To answer these, we used hydrogeochemical analysis of 35 water samples from springs and geysers, together with isotopic (δ18O and δD) analysis, chemical and mineral studies of precipitates collected in the field around these outflows, and field observations. We aimed (1) to recognize the geochemistry of thermal waters and precipitates in the central part of the Colca River basin, (2) to identify fluid sources and their origin, (3) to estimate the temperature of a potential geothermal reservoir, and (4) to discuss the regional active tectonic and volcanic framework of this geothermal region and mutual relationships.Our results corroborate a heterogeneous and complex geothermal system in the central part of the Colca River basin, with contrasting hydrogeochemical and physical properties, variable isotope composition, different reservoir temperatures, and associated precipitates around thermal springs. Processes controlling water chemistry are closely related to the Ampato-Sabancaya magmatic chamber's activity and tectonic structures that allow complex interactions of meteoric waters with magmatic fluids and gases. With a considerable gradient of pressure owing to local relief and deep incision in the Colca Canyon, these processes led to the differentiation of the thermal waters into three main groups. (1) Chloride-rich, mainly sodium chloride, thermal waters are of meteoric origin but mature within the geothermal reservoir possibly fed by magma degassing. These waters' chemical and isotopic composition results from water-rock interaction and mixing with magmatic waters within the reservoir. These waters discharge at the bottom of the Colca Canyon and Valley, presenting a broad hydrogeochemical spectrum and highly variable mineral phases precipitating at the outflows. The reservoir temperature estimated for these waters ranges from 180 to 200 °C. The group of hottest springs and geysers at the bottom of the Colca Canyon waters are fully equilibrated, with the reservoir temperature ~ 240 °C. (2) Sulfate-rich waters are shallow meteoric waters heated by ascending gases that form an independent group referring to the local water circulation, often controlled by tectonic barriers. (3) Bicarbonate-rich waters are the intermediate meteoric waters, divided into two hydrochemical groups: waters partially equilibrated with reservoir rocks and more similar to chloride-rich waters or additionally enriched with SO4 and more similar to sulfate-rich waters.Studied thermal springs show a clear spatial correlation with active and seismogenic crustal W- to NW-tracing normal and strike-slip faults. These act as barriers to infiltrating meteoric waters, provide pathways to hydrothermal solutions and gases assisting in meteoric water heating, and yield passages for pressured by lithostatic load and heated waters to ascend to the surface.

Geochemistry and Utilization of Water from Thermal Springs of Tawang and West Kameng Districts, Arunachal Pradesh

ABSTRACT The hydrogeochemical studies provide insights about reservoir conditions of geothermal springs along with utilization of thermal waters for domestic, livestock and irrigation purposes. Most of the hot springs of Tawang and West Kameng districts of Arunachal Pradesh emanated through garnet bearing high grade gneissmigmatite-schist-quartzite sequence of the Se La Group, except for Dirang hot springs which emanate from river terrace deposits lying on the footwall of deformed quartzite-phyllite. The thermal waters are of mixed Na-Ca-HCO3-SO4-Cl type, meteoric in origin and at the same time immature in nature, moving sluggishly towards mineral-fluid equilibration zone with slow rock-water interactions. Chemical geothermometry showed wide variation in estimation of sub-surface reservoir temperature and quartz geothermometry model fits prominently to provide the most reliable reservoir temperature varying within 90±40°C. The studies recorded highest reservoir temperature of Thingbu hot spring with 133°C with very high fluoride concentration in all the hot springs except Bishum and Phudung as per BIS (2012) IS: 10500 specifications. High fluoride and sulfate concentration in thermal spring waters make it unsuitable for drinking purpose. The applicability of thermal waters for irrigation is predicted through sodium adsorption ratio (SAR) calculations which showed that waters of Dirang-2, Sorbe and Kitpi-1&amp;2 are not suitable for irrigation purpose due to high salinity and SAR values.

Sediment and water geochemistry record of water-rock interactions in King George Island, Antarctic Peninsula

AbstractWe used a multidisciplinary approach integrating major, trace and rare earth element geochemistry, mineralogy of rocks and sediments along with the ionic composition of water reservoirs of Admiralty Bay, King George Island, to evaluate the record of water-rock interactions under Maritime Antarctic conditions. Our results showed that the ionic compositions of the streams and meltwaters predominantly reflect the atmospheric inputs, while lake waters have higher Na/Cl, Ca/Mg and HCO3/Cl ratios related to chemical weathering in lake sediments, but this did not allow for distinguishing purely silicate sources. Consistent with the trace and rare earth element data, various alteration indices and Index of Compositional Variability values denote the low degree of chemical weathering in the lake sediments. The records from the previously unexplored Mud Lake and Upper Lake suggest that the lakes of Admiralty Bay are better places to trace the impacts of a succession of environmental changes that have occurred in the watershed, while the stream channel sediments, when accompanied by water chemistry data, may provide a more representative composition of the source rocks than the lake sediments. These findings may help revealing the intensity of contemporary weathering in a colder climate with relatively few mineralogical changes accompanied by a lesser degree of elemental loss.

Geochemistry and therapeutic properties of Caucasian mineral waters: a review.

The Caucasian mineral water (CMW) region is a unique area where mineral waters differ by their chemical composition and balneological properties. The presence of a wide range of mineral waters with various ions and gas components and different genesis and their therapeutic properties in the restricted area is explained by complicated geological and tectonic settings. The dominant type of mineral water in the CMW region is CO2-bearing water with H2SiO3 and H3BO3 as the specific components. According to ion composition, gas phases' content into groundwater, total dissolved solids, and balneological characteristics, we would distinguish 9 groups and 16 types of these mineral waters, with each water type being of particular therapeutic interest. The CMW region includes four spa cities with a different therapeutic profile: Zheleznovodsk, Kislovodsk, Pyatigorsk, and Essentuki. Spa treatment is based on the use of different types of mineral waters, therapeutic muds within the region's diverse landscapes, and climatic conditions. Mineral waters are utilized in the form of baths, swimming pools, showers, various irrigations, inhalation, as well as drinking therapy. Therapeutic mineral waters are used to treat gastrointestinal problems, metabolic and nervous system disorders, as well as various diseases of liver, kidney, urinary tract, circulatory system, respiratory organs, and skin.

Tellus regional stream water geochemistry: environmental and mineral exploration applications

Regional stream water geochemistry acquired as part of the Tellus programme in Ireland has been analysed to assess its potential for application to environmental assessment and mineral exploration. Interpolated geochemical maps and multivariate statistical analysis, including principal component analysis and random forest classification, demonstrate broad geogenic control of stream water chemistry, with both bedrock and subsoil contributing to the patterns observed. Surface water regulations set Environmental Quality Standard values for individual Priority Substances and Specific Pollutants that may depend on background concentrations and/or water hardness. The high resolution of Tellus stream water data and their location on low-order streams have allowed estimation of background concentrations and water hardness in the survey area, with significant implications for water monitoring programmes. Anthropogenic inputs to stream water in the survey area come mainly from agricultural sources and Tellus data suggest few catchments are unaffected. Comparison of Tellus stream water geochemistry with stream sediment and topsoil geochemistry suggest that stream water geochemistry has strong potential for use in mineral exploration, with the same base metal and gold pathfinder anomalies apparent in all three data sets. Cluster analysis indicates that base metals in stream water are associated with organic matter but statistical analysis may be employed to distinguish mineralization-related signatures. Supplementary material: Comparison of cation/anion associations using Piper plots and principal component analysis is available at https://doi.org/10.6084/m9.figshare.c.5683094 Thematic collection: This article is part of the Hydrochemistry related to exploration and environmental issues collection available at: https://www.lyellcollection.org/cc/hydrochemistry-related-to-exploration-and-environmental-issues

Geochemical Markers as a Tool for the Characterization of a Multi-Layer Urban Aquifer: The Case Study of Como (Northern Italy)

The analysis of geochemical markers is a known valid tool to explore the water sources and understand the main factors affecting natural water quality, which are known issues of interest in environmental science. This study reports the application of geochemical markers to characterize and understand the recharge areas of the multi-layer urban aquifer of Como city (northern Italy). This area presents a perfect case study to test geochemical markers: The hydrogeological setting is affected by a layered karst and fractured aquifer in bedrock, a phreatic aquifer hosted in Holocene sediments and connected with a large freshwater body (Lake Como); the aquifers recharge areas and the water geochemistry are unknown; the possible effect of the tectonic setting on water flow was overlooked. In total, 37 water samples were collected including water from two stacked aquifers and surface water to characterize hydrochemical features. Moreover, six sediment samples in the recent palustrine deposits of the Como subsurface were collected from cores and analyzed to understand the main geochemistry and mineralogy of the hosting material. The chemical analyses of water allow to observe a remarkable difference between the shallow and deep aquifers of the study area, highlighting different recharge areas, as well as a different permanence time in the aquifers. The sediment geochemistry, moreover, confirms the differences in trace elements derived from sediment-water interaction in the aquifers. Finally, an anomalous concentration of As in the Como deep aquifer was observed, suggesting the need of more detailed analyses to understand the origin of this element in water. This study confirms the potentials of geochemical markers to characterize main factors affecting natural water quality, as well as a tool for the reconstruction of recharge areas.

Geochemistry of surface waters around four hard-rock lithium deposits in Central Europe

There are several Li-mica and spodumene deposits in Central Europe. The Cínovec deposit on the border of the Czech Republic and Germany is the largest known hard-rock Li deposit in Europe and is currently being explored. Weathering and mining of such deposits could release Li and F to the environment. Both elements are associated with potential health effects when ingested via drinking water, yet little is known about the aqueous geochemistry of streams and creeks around Li hard-rock deposits. In this study, we sampled surface waters (n = 47) near three Li-mica and one spodumene deposit to examine a potential public health risk resulting from the weathering of Li-minerals. At the Cínovec and Homolka (also in the Czech Republic) sites, several water samples have elevated Li contents relative to those in typical surface waters, but they are all below the U.S. EPA-recommended threshold of 0.7 mg/L. Three of the ten samples from Cínovec contain F in concentrations that are above World Health Organization's 1.5 mg/L drinking water limit, and thus these waters (max. concentration: 3.8 mg/L) may represent a public health hazard. Based on geochemical modeling and statistical analysis, the lithium in the water comes from Li-micas and the fluoride is derived from a combination of Li-micas and fluorite, depending on the specific site analyzed. Lithium seems to be scavenged by clay minerals.

Humus substances in the swamp ecosystems of taiga zone of Western Siberia

Eutrophic peatlands with a predominantly humate type of humus is dominated according to content of hydrophobic humus substances accumulated in the solid phase of peat. Oligotrophic peatlands with fulvate type of humus are characterized by minimal storages. Mesotrophic peatlands occupy a transitional position, both in terms of storage and in terms of the humus type – humate-fulvate. Hydrophilic components of the water phase are characterized by fulvate humus, regardless of the type of peatland, but differ in the proportion of the contribution of humus substances in the amphiphilic system of swamp ecosystems. It is the highest in the thickness of the oligotrophic peatland almost 31%, slightly lower in the mesotrophic – 25% and much less in the eutrophic – 6%. Structural features of macromolecules of humic acids of swamp waters of various genesis are determined. The humic acids of mesotrophic waters are adjacent to the group of reduced compounds, they are more enriched with aromatic structures and carboxyl groups in relation to oligotrophic waters. The humic acids of oligotrophic waters belong to a group of oxygenated compounds, have low enrichment of nitrogen, contain more methoxyl carbon and carbohydrates (polysaccharides). These structural features are caused by geochemistry of waters feeding the peatlands and specific mechanisms of humic acids synthesis on the swamps of different genesis. The volume of dissolved organic carbon stock from wetland ecosystems through system of taiga rivers of left bank of Middle Ob is 805 kt per year.

Geochemistry of Water and Gas Emissions From Cuicocha and Quilotoa Volcanic Lakes, Ecuador

There are hundreds of volcanic lakes around the world that represent an important hazard due to the potential occurrence of phreatomagmatic or limnic eruptions. Variations in geochemical and geophysical parameters could help to identify potential risks for these events. Cuicocha and Quilota volcanic lakes, located at the North Andean Volcanic Zone of Ecuador, are geologically young, with gas emissions manifested mainly as CO2via bubbling gases. Both lakes present a limited monitoring record. Therefore, volcanic monitoring is a priority task due to the potential hazard they represent by the possibility of water stratification and CO2accumulation. During 2012-2018 period, geochemical investigation based mainly on diffuse CO2surveys and analyzing the chemical and isotopic composition of bubbling gases has been carried out at Cuicocha and Quilotoa lakes. Additionally, vertical profiles of water columns were conducted in both lakes to investigate the possibility of water stratification and CO2accumulation in the lakes. A bathymetric study was also carried out in Quilotoa in 2017, giving further information about the degasification processes and the morphology of the lake bottom. The computed diffuse CO2output for Cuicocha volcanic lake (3.95 km2) showed a range from 53 to 652 t d−1for the period 2006–2018, with a maximum value in 2012, coinciding with a maximum of the3He/4He ratio measured at the bubbling gases and an increase in the seismic activity with an episode of long-period seismicity recorded in 2011–2012. For Quilotoa volcanic lake (3.50 km2) diffuse CO2output was estimated between 141 and 536 t d−1for the period 2014–2018. The chemical and isotopic data show that Cuicocha has a chemical composition typical of worldwide superficial shallow waters and aquifers, while Quilotoa shows a chemical composition typical of crater lakes in active volcanic systems. The distribution of the dissolved gas composition along the vertical profiles shows the existence of different water masses in both lakes, with an increase in the concentration of dissolved gases with depth. The carbon isotopic signature indicates an endogenous origin of the CO2, with a greater contribution in the stratification zone in both lakes. This study shows methods applicable to other volcanic lakes of the world to monitor their activity and potential risks.

Use of water isotopes and chemistry to infer the type and degree of exchange between groundwater and lakes in an esker complex of northeastern Ontario, Canada

Abstract. While interactions between groundwater and lake-water influence water chemistry, water balance, aquatic organisms, biochemical cycles and contamination levels, they remain a poorly studied component of lake hydrology. Identifying the controls of groundwater and lake-water interactions at the landscape level and classifying lakes into categories based on their degree of interaction with the groundwater can provide insights into a lake's sensitivity and vulnerability to environmental stressors. Such information can also provide baseline conditions for comparison to future changes that are important for water management and conservation. To this end, water chemistry and water isotopic composition were investigated in a set of 50 boreal lakes located at different elevations in an esker system near Timmins, Ontario. Analyses focused on stable isotopic ratios of hydrogen and oxygen and specific conductance as indicators of the position of a lake with respect to the influence of groundwater. Both isotopic composition and specific conductance distinguished higher-elevation groundwater-recharge lakes from lower-elevation groundwater-discharge lakes. Groundwater-recharge lakes were high-elevation lakes characterized by enriched isotopic values and low values of specific conductance. In contrast, groundwater-discharge lakes were isotopically depleted and had higher values of specific conductance and occurred at lower elevations. An intermediate group of lakes was also defined (termed seepage lakes) and had intermediate isotopic and water-chemistry characteristics compared to recharge and discharge lakes. Differences in water geochemistry between field campaigns revealed that upland groundwater-recharge lakes showed evidence of evaporative drawdown, indicating sensitivity to short-term changes in climate, whereas the lower-elevation groundwater-discharge lakes showed little variation between seasonal samples and consequently would likely be affected only by hydroclimatological changes of greater duration and magnitude.

Indigenous microbial communities in heavy oil show a threshold response to salinity.

ABSTRACTMicrobial degradation influences the quality of oil resources. The environmental factors that shape the composition of oil microbial communities are largely unknown because most samples from oil fields are impacted by anthropogenic oil production, perturbing the native ecosystem with exogenous fluids and microorganisms. We investigated the relationship between formation water geochemistry and microbial community composition in undisturbed oil samples. We isolated 43 microliter-sized water droplets naturally enclosed in the heavy oil of the Pitch Lake, Trinidad and Tobago. The water chemistry and microbial community composition within the same water droplet were determined by ion chromatography and 16S rRNA gene amplicon sequencing, respectively. The results revealed a high variability in ion concentrations and community composition between water droplets. Microbial community composition was mostly affected by the chloride concentration, which ranged from freshwater to brackish-sea water. Remarkably, microbial communities did not respond gradually to increasing chloride concentration but showed a sudden change to less diverse and uneven communities when exceeding a chloride concentration of 57.3 mM. The results reveal a threshold-regulated response of microbial communities to salinity, offering new insights into the microbial ecology of oil reservoirs.