Hydrogeochemical Conditions Research Articles

Phylogenetic or environmental control on the elemental and organo-chemical composition of Sphagnum mosses?

Background and aimsPlant litter chemistry is a key driver of decomposition in peatlands. This study explored the relative contributions of phylogeny and environment to litter chemistry of peat mosses (Sphagnum), the key peat-forming plants on earth.MethodsFifteen Sphagnum species, representing three taxonomic sections ACUTIFOLIA, CUSPIDATA and SPHAGNUM, were sampled across a wide range of hydro-geochemical conditions. For all species we characterised chemical composition within (i) inorganic elements, (ii) carbohydrate polymers (iii) non-carbohydrates.ResultsThe variation in carbohydrates was mostly explained by taxonomic section, suggesting phylogenetic conservation of carbohydrate composition. ACUTIFOLIA species invested relatively more in pectins, whereas CUSPIDATA and SPHAGNUM species invested more in hemicellulose. The composition of non-carbohydrates was mainly influenced by environment, except for some constituents for which the variation was more correlated to phylogeny. Finally, the variation in inorganic element concentrations mostly reflected hydro-geochemical conditions within and between peatlands.ConclusionsThe separation into an environmentally independent, phylogenetically conserved group of compounds (structural carbohydrates) and an environmentally dependent, variable group of compounds (inorganic elements, non-carbohydrates) has important implications both for understanding patterns in and for upscaling of spatially variable ecosystem processes associated with peat decomposition such as carbon sequestration, nutrient cycling and greenhouse gas emissions.

Unstable convection flow as a controlling process of increasing salinity in the saline lake coastal aquifers: case of Maharlu Lake coastal aquifer

Deterioration of freshwater aquifers adjacent to saline lakes is a serious environmental and water resources management problem. Generally, different phenomena including saltwater intrusion, upconing, free and forced convection flow can lead to the salinization of fresh aquifers in the vicinity of saline lakes. The severity of this problem depends on hydrogeological and hydrogeochemical conditions of coastal saline lake aquifers. Accordingly, Maharlu Lake in the southeast of Shiraz plain is one of these saline lakes and has an important impact on its adjacent fresh aquifers so that the salinity of these aquifers has increased in recent years. Since the lake has special conditions such as very flat and low permeable floor and variable water level fluctuation during a year, with the onset of the rainy season after a long-term well pumping in the adjacent aquifer, the lake water covers a wide extent of the lake area in a short time. Then, because of the higher permeability of the surface of the lake in its southeast margin, conditions for convection flow are provided there. In this study, salinity distribution in one of the aquifers (Bokat aquifer) in the southeast of the lake is investigated using resistivity tomography along several profiles. Interpretation of inverse models of these profiles showed that convection flow is an important process in increasing the salinity of fresh aquifer. Comparison of the results of geo-tomography sections with convection index map of the Bokat aquifer showed that getting closer to the lake, free convection flow becomes the dominant process in the salinity distribution. In addition, in farther distances relative to the lake, due to increasing the pumping rate of the extraction wells, forced convection flow is an important process.

Applying numerical modeling for designing strategies of effective groundwater remediation

Selection of effective groundwater remediation scenarios is a complex issue that requires understanding of contaminants’ transport processes. The effectiveness of cleanup measures may be verified by fate and transport numerical modeling. The goal of this work was to present the usefulness of fate and transport modeling for planning, verification and fulfillment of effective groundwater remediation methods. Selection methodology was developed, which is based on results of numerical flow and transport modeling. A field site located in south-east Poland was selected as a case study, in which groundwater contamination of trichloroethene and tetrachloroethene was detected. The results indicated that “pump and treat” was the most effective among the studied remediation methods, followed by permeable reactive barrier and in situ chemical oxidation. Natural attenuation-based remediation was demonstrated to be the least suitable, as it requires the longest time to reach predefined remediation goals, principally due to low sorption capacity and unfavorable hydrogeochemical conditions for biodegradation. Fate and transport numerical modeling allowed simulating different remediation strategies, and thus the decision-making process was facilitated.

Impact of Road De-icing on the Hydrogeochemistry of Groundwater from a Mountain Area (Serra da Estrela, Central Portugal)

The importance of Mountains for the world's water supply has been increasingly recognized. However, in many cases the existing roads require regular de-icing operations which may have a severe impact on the natural hydrogeochemical conditions of the local hydrological systems due to the regular use of substances such as sodium chloride and calcium chloride. The Serra da Estrela Mountain is a strategic area for the water resources management in Portugal because of its geological, geomorphological and climatic framework. This study was carried out in the highest part of the mountain, where road de-icing is frequent during winter. The hydrogeochemical characteristics of several springs, located downstream from roads between 1500 m a.s.l. and 1990 m a.s.l., present clear anthropic signatures which disturbs the quality of the local water resources.

Spatial Distribution of Microbial Communities in the Alluvial Aquifer along the Oyodo River, Miyakonojo Basin, Japan

The hydrogeological properties of groundwater and behavior of nitrate attenuation in the nitrate-polluted alluvial aquifer, Miyakonojo Basin have been investigated in previous studies, but little knowledge is known about the spatially microbial communities especially associated with nitrate depletion. The objectives of the present study are to reveal the profile of microbial communities in the alluvial aquifer, Miyakonojo Basin, and the association with environmental variations based on cloning-library approach together with hydrogeochemical variables. The results showed that high bacterial diversity was characteristic of a large number of operational taxonomic units unique to the samples. The presence of some human-/livestock related bacteria was consistent with the distribution of high nitrate concentrations, which indicated an influence of hydrogeochemical variables on microbial composition. Methane-producing archaea and ammonia-oxidizing archaea were primarily found in the anoxic and oxic environments, respectively, reflected by the distribution of welded tuff. Additionally, heterotrophic and mixo-/autotrophic denitrifiers were ubiquitously distributed, but denitrification process only occurred under the anoxic environment. Microorganisms involved in the various metabolic processes were found to coexist in the same samples. Together, this study suggested that the description of microbial communities profile and associated putative metabolic processes could reflect the hydrogeochemical conditions of the alluvial aquifer, Miyakonojo Basin.

Influence of Humic Acid on the Transport and Deposition of Colloidal Silica under Different Hydrogeochemical Conditions

The transport and deposition of colloids in aquifers plays an important role in managed aquifer recharge (MAR) schemes. Here, the processes of colloidal silica transport and deposition were studied by displacing groundwater with recharge water. The results showed that significant amounts of colloidal silica transport occurred when native groundwater was displaced by HA solution. Solution contains varying conditions of ionic strength and ion valence. The presence of humic acid could affect the zeta potential and size of the colloidal silica, which led to obvious colloidal silica aggregation in the divalent ion solution. Humic acid increased colloidal silica transport by formation of non-adsorbing aqueous phase silica–HA complexes. The experimental and modeling results showed good agreement, indicating that the essential physics were accurately captured by the model. The deposition rates were less than 10−8 s−1 in deionized water and monovalent ion solution. Moreover, the addition of Ca2+ and increase of IS resulted in the deposition rates increasing by five orders of magnitude to 10−4 s−1. In all experiments, the deposition rates decreased in the presence of humic acid. Overall, the promotion of humic acid in colloidal silica was strongly associated with changes in water quality, indicating that they should receive greater attention during MAR.

Identification of hydrogeological windows based on large-scale mapping of the geological and hydrogeological conditions in Moscow

An original procedure for mapping hydrogeological windows is based on studying the geological structure of the massif overlaying the Podol’sko-Myachkovskii aquifer, changes in the hydrodynamic and hydrogeochemical conditions in the zone of “windows”; as well as calculating the travel time of contaminants in the vertical flow from the Meso-Cenozoic to Podol’sko-Myachkovskii Carboniferous aquifer. Both the areal and vertical distributions of low-permeability deposits are taken into account along with the variations of their thickness and permeability. The results obtained can be used in the development of groundwater protection measures and economic activity regulations in areas with hydrogeological windows.

CATAGENETIC ALTERATION HYDROGEOCHEMISTRY OF SEDIMENTARY ROCKS OF HYDROCARBON OCCURRENCES IN ARCTIC AREASOF THE WESTERN SIBERIAN MEGABASIN

For the first time a detailed analysis of the equilibrium-non-equilibrium state of ground waters of hydrocarbon occurrences in Arctic areas of the West Siberian megabasin based on physico-chemical modeling of equilibria in the «water-rock» revealed hydrogeochemical and thermodynamic conditions for the formation of authigenic minerals. For the first time equilibrated compositions of groundwaters and parameters of geochemical environment were identified, being a prerequisite for the mineral neoformations.

Transport of Silica Colloid through Saturated Porous Media under Different Hydrogeochemical and Hydrodynamic Conditions Considering Managed Aquifer Recharge

Colloids may have an important role in regulating the structure and function of groundwater ecosystems, and may influence the migration of low solubility contaminants in groundwater. There is, however, a degree of uncertainty about how colloids behave under the variable hydrogeochemical and hydrodynamic conditions that occur during managed aquifer recharge. We used an online monitoring system to monitor the transport of silica colloid in saturated porous media under different hydrogeochemical conditions, including a range of pH values (5, 7, and 9), ionic strengths (<0.0005, 0.02, and 0.05 M), cation valences (Na+, Ca2+), flow rates (0.1, 0.2, and 0.4 mL/min). The results showed that silica colloid was more likely to deposit on the surface of porous media in acidic conditions (pH = 5) than in alkaline conditions (pH = 9), indicating that the risks of pollution from colloidal interactions would be higher when the pH of the recharge water was higher. Colloid deposition occurred when the ionic strength of the colloidal suspension increased, and bivalent cations had a greater effect than monovalent cations. This suggests that bivalent cation-rich recharge water might affect the porosity of the porous medium because of colloid deposition during the managed aquifer recharge process. As the flow rate increased, the migration ability of silica colloid increased. We simulated the migration of silica colloid in porous media with the COMSOL Multiphysics model.

CHEMICAL COMPOSITION OF GROUNDWATER OF THE COLTOGOR- TOLKINSKAYA ZONE AND ADJACENT TECTONIC ELEMENTS

The comparison of hydrogeochemical conditions of Jurassic-Cretaceous sediments of Koltogor- Tolkinskaya suture zone and the adjacent tectonic structures was based on the results of the chemical composition analysis of almost 1,500 groundwater samples. The average values of the overall salinity of subsurface water and their content of basic components of ion-salt and microcomponent composition were compared for Aptian-Albian-Senomanian, Neocomian and Jurassic aquifer complexes of Koltogorsky, Tolkinsky, Yuzhno-Tolkinsky megatroughs and Tagrinsky, Bakhilovsky, Alexandrovsky, Srednevasyugansky megaswells, as well as Nizhnevartovsky, Kaymysovsky arches. Using Sulin’s classification and cluster analysis the type of groundwater was characterized by the hydrogeochemical parameters set. It was defined that the suture zone presence does not directly affect the hydrogeochemical conditions of deep horizons of this zone and adjacent areas.

Aquifer vulnerability assessment in the Bengal alluvial tract, India, using GIS based DRASTIC model

In the present study, an attempt has been made to evaluate the aquifer vulnerability in the central part of Bengal alluvial tract, covering 5324 km2 area by using DRASTIC model. Seven critical hydrogeological factors were taken into consideration. Initially, vulnerability index of individual factors were calculated on the basis of predefined weights and ratings. These indices were further combined to depict the actual vulnerability of the region. The model comprised of seven spatial parameters and their attributes and in handling of such diverse datasets, GIS played a significant role. For the depiction of the subsurface lithological characteristics, subsurface lotho-log data were used to generate 3 dimensional fence diagram of the entire region which was further helped in depicting the aquifer media condition. Entire eastern region of river Bhagirathi, a distributary of river Ganga, showed higher vulnerability index, which was about 29.65 % of the total study area, while the western portion had lesser vulnerability. Along with conventional modeling, map removal sensitivity analysis was also incorporated to examine the impact of different factors on the entire model. Depth to the water and impact of vadose zone were two important factors that contributed 46.93 % of the total variability of the model. Further, the generated model was incorporated with the locations of 156 groundwater samples, collected from the entire region and concentration of arsenic was determined to understand the probable relationship with the generated model through correlation coefficient. The model presented in the paper depicted recent hydrogeochemical condition of the aquifer which might help in further management of the region.

HYDROGEODYNAMIC AND HYDROGEOCHEMICAL CONDITIONS OF THE LOWER-MIDDLE JURASSIC COMPLEX IN TALINSKOYE OIL FIELD

Hydrogeodynamic and hydrogeochemical conditions of the Lower-Middle Jurassic complex are considered on the example of the oil field Talinskoye located in Krasnoleninsk oil and gas bearing area. The authors describe the complicated structures of the hydrogeodynamic and hydrogeochemical fields in the studied area. It is shown that the deficit reservoir pressure is in average 1.6 MPa. Within the field the zones of the waters ion-salt composition anomalies have been are identified. These zones are characterized by low values of mineralization (in average 5 g/l) as compared to the background value (8 - 9 g/l). The dependence of the hydrogeochemical anomalies formation on the faults position, the temperature of the basement top and the values of reservoir pressures is consistent with the model of the conjugated falling-rising mass transfer.

Chemical erosion of the bentonite buffer: do we observe it in nature?

Abstract It is planned to use bentonites as buffer materials in various types of geological repositories designed to host radioactive waste. For the bentonite materials, the hydrological and hydrogeochemical conditions are two of the main environmental factors affecting their evolution, assessed for a period of up to 1 Ma. Since it has been observed in laboratory tests that smectite, in particular montmorillonite, forms colloids and disperses in very dilute conditions, a scenario for chemical erosion has been discussed at length, especially in relation to geological repositories located in future glaciated terrains and locations otherwise potentially hosting dilute groundwaters. General understanding, based on laboratory experiments, is that bentonite erosion does not occur when the total charge equivalent of cations in groundwater is higher than 4 mM. However, based on current knowledge, it seems that chemical erosion is not observed in repository-relevant natural systems where groundwater conditions are below the given limit. Further investigation is therefore suggested to provide a better scientific understanding of the mechanisms involved in stabilizing smectites in these natural systems.

Hydrogeochemistry and coal-associated bacterial populations from a methanogenic coal bed

Biogenic coalbed methane (CBM), a microbially-generated source of natural gas trapped within coal beds, is an important energy resource in many countries. Specific bacterial populations and enzymes involved in coal degradation, the potential rate-limiting step of CBM formation, are relatively unknown. The U.S. Geological Survey (USGS) has established a field site, (Birney test site), in an undeveloped area of the Powder River Basin (PRB), with four wells completed in the Flowers-Goodale coal bed, one in the overlying sandstone formation, and four in overlying and underlying coal beds (Knoblach, Nance, and Terret). The nine wells were positioned to characterize the hydraulic conductivity of the Flowers-Goodale coal bed and were selectively cored to investigate the hydrogeochemistry and microbiology associated with CBM production at the Birney test site. Aquifer-test results indicated the Flowers-Goodale coal bed, in a zone from about 112 to 120m below land surface at the test site, had very low hydraulic conductivity (0.005m/d) compared to other PRB coal beds examined. Consistent with microbial methanogenesis, groundwater in the coal bed and overlying sandstone contain dissolved methane (46mg/L average) with low δ13C values (−67‰ average), high alkalinity values (22meq/kg average), relatively positive δ13C-DIC values (4‰ average), and no detectable higher chain hydrocarbons, NO3−, or SO42−. Bioassay methane production was greatest at the upper interface of the Flowers-Goodale coal bed near the overlying sandstone. Pyrotag analysis identified Aeribacillus as a dominant in situ bacterial community member in the coal near the sandstone and statistical analysis indicated Actinobacteria predominated coal core samples compared to claystone or sandstone cores. These bacteria, which previously have been correlated with hydrocarbon-containing environments such as oil reservoirs, have demonstrated the ability to produce biosurfactants to break down hydrocarbons. Identifying microorganisms involved in coal degradation and the hydrogeochemical conditions that promote their activity is crucial to understanding and improving in situ CBM production.

Enrichment and mechanisms of heavy metal mobility in a coastal quaternary groundwater system of the Pearl River Delta, China

The risks posed by heavy metal mobilization strongly depend on the pathways that the metals follow, with the sediment-water pathway representing a direct risk to groundwater contamination. Monitoring and sequential extraction experiments in the laboratory generally have limitations with respect to understanding the mechanisms of heavy metal mobilization in the field. The Quaternary coastal groundwater system of the Pearl River Delta, China was chosen as the study area to understand heavy metal enrichment and mobility. Heavy metals including V, Cr, Co, Ni, Cu, Zn, Ba, Pb, Mo, Cd, Sr, Ga, Ge, Rb, and Cs in both sediments and groundwater were analyzed. Geochemical parameters including Fe2O3, MnO, sedimentary organic matter, and carbonate content as well as hydrochemical parameters including K+, Na+, Ca2+, Mg2+, NH4+, SO42−, Cl−, HCO3−, pH, TDS, and dissolved organic carbon were also measured. The enrichment of heavy metals in the solid sediment phase as well as the mobilization mechanisms of heavy metals in groundwater are discussed as informed by Pearson's correlation analysis. Hydrochemical analyses demonstrated that the mobility of V, Ba, Cr, Rb, and Cs is closely related to the decomposition of buried sedimentary organic matter; the mobility of Co, Ni, Cu, Zn, Pb, and Cd is closely linked with the reductive dissolution of Fe–Mn oxides; and the mobility of Co, Ni, Cu, Ba, Zn, Pb, Cd, Mn, Sr and Ga is probably controlled by ion exchange processes. This study demonstrates that heavy metal mobility in the field is not entirely consistent with the potential mobility as indicated by sediment analysis, due to the complicated hydrogeochemical conditions in the groundwater system, and suggests that comprehensive geochemical and hydrochemical studies are useful ways to understand the mobility mechanisms of heavy metals in the field.

HYDROGEOCHEMICAL CONDITIONS OF FORMATION OLIGOTROPHIC BOG ECOSYSTEMS

On the basis of the analysis of data of geobotanical, hydrogeochemical and microbiological observation during 2002–2015 years on east part of Vasyugan bog complex (Western Siberia) is offered a hypothesis of formation of a convex relief of oligotrophic bog ecosystems as a result of the adaptation of system “a pine – bushes – sphagnum mosses” to hydrological and hydrogeochemical conditions and mutual influence of biotic and abiotic components. The pine forms “base” of ecosystems, bushes – “a force layer”, and sphagnum mosses act in a dual role “filler” of ecosystem and “stimulator” of a vertical gain of a surface. Oligotrophic bog ecosystem is not equilibrium and continuously changes depending on hydrogeochemical conditions which adjust quantity of accessible biogenic elements (the first – connections of Ca and P), an oxygen regime of a peat deposit, deducing or transformation of toxic products of biogeochemical and biochemical processes (for example, Al and NO 2 –). Concentration of toxic substances in many respects depends on functioning oxidizing and regenerative geochemical barriers, which, in turn, are connected with a water mode of a bog and properties of bog vegetation.

HYDROGEOLOGICAL, HYDROGEOCHEMICAL CHARACTERISTICS AND HYDROGEOCHEMICAL PROFILES IN COASTAL AREA IN VIETNAM

Vietnam has a long coastal line along which there are many plains that are composed of unconsolidated Kainozoic sediments in 5 granular aquifers overlying fissured ancient rock. The Holocene unconfined aquifer (qh) at the top of the profile contains fresh water lens with small potential water reserves. The Pleistocene (qp) and Neocene aquifers are confined with wide distribution and complicated hydrogeochemical condition: saline water in most areas, fresh water in small areas. There are 4 typical hydrogeochemical profiles in coastal areas: (I) fresh water in the whole profile, (II) fresh water in the upper part and saline water in the lower part, (IV) saline water in the whole profile, and (V) saline water in the upper part and fresh water in the lower part. Profiles (I), (II), (V) have effective use for drinking water. The profile type (Ib) has distribution in Thach Khe-Ha Tinh, Quang Tri and Thua Thien-Hue, (V) has distribution in Nam Dinh, Tra Vinh, Soc Trang, Bac Lieu, Ca Mau and South-East of Kien Giang in which the fresh water can be in shallow onshore areas.

Groundwater hydrogeochemical characteristics in rehabilitated coalmine spoils

The investigation aims to identify and describe hydrogeochemical processes controlling the evolution of groundwater chemistry in rehabilitated coalmine spoils and their overall influence on groundwater quality at a study area located in the Karoo basin of South Africa. A good understanding of the processes that controls the evolution of the mine water quality is vital for the planning, application and management of post-mining remedial actions. The study utilises scatter plots, statistical analysis, PHREEQC hydrogeochemical modelling, stoichiometric reaction ratios analysis, and the expanded Durov diagram as complimentary tools to interpret the groundwater chemistry data collected from monitoring boreholes from 1995 to 2014. Measured pH ranging between 6–8 and arithmetic mean of 7.32 shows that the groundwater system is characterised by circumneutral hydrogeochemical conditions period. Comparison of measured groundwater ion concentrations to theoretical reaction stoichiometry identifies Dolomite-Acid Mine Drainage (AMD) neutralisation as the main hydrogeochemical process controlling the evolution of the groundwater chemistry. Hydrogeochemical modelling shows that, the groundwater has temporal variations of calcite and dolomite saturation indices characterised by alternating cycles of over-saturation and under-saturation that is driven by the release of sulphate, calcium and magnesium ions from the carbonate-AMD neutralization process. Arithmetic mean concentrations of sulphate, calcium and magnesium are in the order of 762 mg/L, 141 mg/L and 108 mg/L. Calcium and magnesium ions contribute to very hard groundwater quality conditions. Classification based on total dissolved solids (TDS), shows the circumneutral water is of poor to unacceptable quality for drinking purposes. Despite its ability to prevent AMD formation and leaching of metals, the dolomite-AMD neutralisation process can still lead to problems of elevated TDS and hardness which mines should be aware of when developing water quality management plans.

Reactive transport modeling of subsurface arsenic removal systems in rural Bangladesh

Subsurface Arsenic Removal (SAR) is a technique for in-situ removal of arsenic from groundwater. Extracted groundwater is aerated and re-injected into an anoxic aquifer, where the oxygen in the injected water reacts with ferrous iron in the aquifer to form hydrous ferric oxide (HFO). Subsequent extraction of groundwater contains temporarily lower As concentrations, because As sorbs onto the HFO. Injection, storage, and extraction together is called a cycle. A reactive transport model (RTM) was developed in PHREEQC to determine the hydrogeochemical processes responsible for As (im)mobilization during experimental SAR operation performed in Bangladesh. Oxidation of Fe(II) and As(III) were modeled using kinetic-rate expressions. Cation exchange, precipitation of HFO, and surface complexation, were modeled as equilibrium processes. A best set of surface complexation reactions and corresponding equilibrium constants was adopted from previous studies to simulate all 20cycles of a SAR experiment. The model gives a reasonable match with observed concentrations of different elements in the extracted water (e.g., the r2 value of As was 0.59 or higher). As concentrations in the extracted water are governed by four major processes. First, As concentration decreases in response to the elevated pH of injection water and likewise increases when native neutral pH groundwater flows in. Second, the sorption capacity for As increases due to the gradual buildup of HFO. Third, As sorption is enhanced by preferential removal of As(V). Fourth, competitive sorption of Si limits the capacity of freshly precipitated HFO for As sorption. Transferability of the developed reactive transport model was demonstrated through successful application of the model, without further calibration, to two additional SAR sites in Bangladesh. This gives confidence that the model could be useful to assess potential SAR performance at locations in Bangladesh based on local hydrogeochemical conditions.

Hydrogeochemical processes of wastewater leakage purification from a thermal power plant

The hydrogeochemical conditions of a large flatland-type ash dump (Eastern Siberia, Russia) were studied. High-alkalinity sulphate water with high calcium content was found to infiltrate into the aquifer from the ash dump. The water was transformed into neutral bicarbonate solutions. Simulation of physicochemical interactions of the clarified water with ash, sandstone, and soil demonstrated that the composition of the resulting simulated solutions is similar to composition of the transformed clarified water leaking into the aquifer, and moving at various distances from their place of infiltration towards the discharge area.