Model of colloidal transportation of radionuclides by groundwater

The transportation of colloidal radionuclides by groundwater was subject to theoretical analysis. The far field of radioactive contamination of the underground environment (liquid waste pumping sites or storage of solidified waste) is dominated by pseudocolloids, i.e., colloidal particles of natural origin contaminated with radionuclides upon contact of groundwater with radioactive materials. Properties of real pseudocolloids were analyzed at sites of radioactive contamination of the underground environment. Based on a probabilistic approach, we developed a mathematical model of pseudocolloid transportation by groundwater, taking into account the difference in size of colloidal particles and the occurrence of nonradioactive natural particles with a similar composition in the groundwater. It is proved that nonuniform dimensions of the particles considerably affect the water transportation rate.     

Ways of investigating radionuclide migration processes in the lithosphere and hydrosphere

In Russia, until recently, it was considered that groundwater was protected from surface radioactive contamination by soil and rocks in the zone aeration. Groundwater was not a subject of radiation control. The accident at the Chernobyl Nuclear Power Plant showed, however, that groundwater is vulnerable to radioactive contamination. In this connection, the vulnerability of groundwater to and the problems of protecting groundwater from radioactive contamination became urgent. The assessment of natural protection of groundwater from radioactive contamination is now considered a top priority. The zone of aeration is generally considered to be the zone separating groundwater from surface contamination. In respect to radioactive contamination, soils that may fix a large quantity of radionuclides serve as a protection zone of a higher order. The mapping of protectibility was done for each radionuclide taking into consideration the specific structure of the flow medium and migration properties of a radionuclide.⁹⁰Sr and¹³⁷Cs have different mechanisms of transport; convective transport is characteristic of the former and diffusive transfer of the latter. This is conditioned by different physico-chemical properties of the radionuclides and principally by their sorption capacities. The coefficient of distribution of⁹⁰Sr is in many times less than the coefficient of distribution of¹³⁷Cs. The environmental protection problem in regions with nuclear power plants and in areas subjected to radioactive contamination may be solved using a monitoring, system including interrelated systems of observation and prediction of the lithosphere and the hydrosphere. The problem of mathematical modeling of migration processes is related to the complexities of modeling the processes of flow, mass transfer, and the accompanying physicochemical processes in zones of full and partial saturation, as well as difficulties in mathematical calculations.     

A comprehensive study of the spread of radioactive contamination in the geological medium near Lake Karachai,Chelyabinsk oblast

The spread of radioactive contamination in the subsurface medium near Lake Karachai is considered. The complexity of this process requires a comprehensive approach to its study. The source of radioactive contamination is overviewed. The map of faults in subsurface medium is considered in order to determine the prevailing direction of contaminated groundwater flow. Photometry in observation wells has been used for structural geological estimation of transport properties of the shallow aquifer, where contaminated groundwater is moving. This study was carried out along with hydrochemical logging, which makes it possible to estimate the dynamics of contamination of subsurface medium and vertical distribution of groundwater contamination. Special attention is paid to transport of radionuclides in the form of radiocolloid particles. Groundwater samples were taken from various depths corresponding to different contamination levels near Lake Karachai. The depth intervals of sampling were determined from the data of hydrochemical logging. Ultrafiltration through membranes with a specific pore size in combination with gamma spectrometry was used to characterize radionuclide transfer with colloidal particles differing in size. The local elemental composition of the radiocolloid surface was studied by Auger spectroscopy. The chemical composition and structure of radiocolloid particles were determined by X-ray photoelectron spectroscopy with consecutive etching of the particle surface by argon ions for a certain depth. The data obtained indicate that radiocolloid particles are heterogeneous and an organic shell consisting of humic and fulvic acids and technogenic organic compounds coat their surface.     

A model of radionuclide transfer by groundwater on the territory of the Russian Research Centre Kurchatov Institute

The convective transfer of ¹³⁷Cs and ⁹⁰Sr by groundwater on the territory of the Russian Research Centre Kurchatov Institute (RRCKI) was modeled. Geological data on the RRCKI site and possible sources of radionuclides show that the uppermost aquifer, composed of Quaternary sediments, is the most probable region of spreading of radioactive contamination. Since the lateral migration of radionuclides is predominant, a 2D horizontal model was used for the forecasting of spreading of radioactive contaminants in the subsurface medium. Transient or long-term repositories of radioactive materials at the RRCKI site (concentrated sources) and aquifer rocks contaminated in the course of removal of radionuclides from these repositories (distributed source) are responsible for groundwater pollution. The initial ¹³⁷Cs and ⁹⁰Sr distributions used in the forecasting of radionuclide migration were determined from their contents in core samples taken from wells drilled in contaminated areas of the RRCKI site. The zone of radionuclide migration is limited by poorly permeable moraine loam from below and by the water table from above. To determine the upper and lower boundaries, these surfaces were mapped in plan view. The data of meteorological observations over a long period were used to map the intensity of precipitation in the studied territory. The density of rocks in the uppermost aquifer and partition coefficients of radionuclides between rocks and groundwater were estimated from the data of laboratory examination of the core samples. The available data on the permeability of rock samples and the results of test pumping out of some wells were involved in the consideration. The results obtained and the data on the water table allowed us to define a gauge problem for determining the distribution of the filtration coefficient in the uppermost aquifer. This problem was solved taking the intensity of precipitation into account. The properties of the uppermost aquifer and the initial radionuclide distribution therein were used as initial data for modeling ¹³⁷Cs and ⁹⁰Sr migration on the territory of the RRCKI over 50 years.     

Sorption-desorption behavior of strontium-85 onto montmorillonite and silica colloids

Strontium-90 (⁹⁰Sr) is one of the major radioactive contaminants found in DP Canyon at Los Alamos, New Mexico, USA. Radioactive surveys found that ⁹⁰Sr is present in surface water and shallow alluvial groundwater environments in Los Alamos National laboratory (LANL). Colloids may influence the transport of this radionuclide in surface and groundwater environments in LANL. In this study, the authors investigated the sorption/desorption behavior of radioactive Sr on Ca-montmorillonite and silica colloids, and the effect of ionic strength of water on the sorption of Sr. Laboratory batch sorption experiments were conducted using ⁸⁵Sr as a surrogate for ⁹⁰Sr. Groundwater, collected from Well LAUZ-1 at DP Canyon and from Well J-13 at Yucca Mountain, Nevada, and deionized water, were used. The results show that 92–100% of the ⁸⁵Sr was rapidly adsorbed onto Ca-montmorillonite colloids in all three waters. Adsorption of ⁸⁵Sr onto silica colloids varied among the three waters. The ionic strength and Ca²⁺ concentration in groundwater significantly influence the adsorption of ⁸⁵Sr onto silica colloids. Desorption of ⁸⁵Sr from Ca-montmorillonite colloids is slower than from silica colloids. Desorption of ⁸⁵Sr from silica colloids was faster in LAUZ-1 groundwater than in J-13 groundwater and deionized water. The results suggest that clay and silica colloids may facilitate the transport of Sr along potential flowpaths from DP Canyon to Los Alamos Canyon.     

Stability assessment and characterization of colloids in coastal groundwater aquifer system at Kalpakkam

Natural colloids have a potential role in facilitating the transport of radionuclides in groundwater. To assess the role of mobile colloidal phases in radionuclide transport, characterization of colloids for size, size distribution, zeta potential, surface charge and elemental composition is required. Groundwater samples were collected from 12 borewells in the study area and were characterized with respect to physicochemical parameters. Water quality parameters such as pH, temperature, specific conductance, TDS and dissolved O₂ were measured in situ. Based on salinity, two groundwater types were identified in the study area: (1) freshwater type and (2) brackish type. Laboratory and field-scale turbidity measurements in addition to quantitative analysis of major ions were carried out. It was observed that the colloid concentrations are reduced at higher salinity. Zetasizer, particle size analyzer, scanning electron microscopy, energy dispersive X-ray analysis and X-ray diffraction techniques were used to characterize the colloidal particles in groundwater. Colloids were present in all the groundwater samples, the concentration varying between 0.05 and 6 mg/L. Colloid concentration was greater in wells with low ionic strength and the number of colloidal particles varied between 3 × 10⁹ and 4 × 10¹¹ particles/L. The average colloid size varied between 200 and 350 nm for various samples. The zeta potential of the colloidal particles varied between −25.5 and –34.0 mV. SEM analysis of colloidal particles revealed the presence of clays particularly kaolinite and that the mineral composition of colloids reflects the mineralogy of the aquifer. For proper risk assessment and remediation studies, the role of colloids in radionuclide transport assumes greater importance. This study highlights the need for, and relevance of, detailed colloid characterization to assess its role in the migration of radionuclides from near surface disposal facilities.     

Strontium incorporation into calcite generated by bacterial ureolysis

Strontium incorporation into calcite generated by bacterial ureolysis was investigated as part of an assessment of a proposed remediation approach for ⁹⁰Sr contamination in groundwater. Urea hydrolysis produces ammonium and carbonate and elevates pH, resulting in the promotion of calcium carbonate precipitation. Urea hydrolysis by the bacterium Bacillus pasteurii in a medium designed to mimic the chemistry of the Snake River Plain Aquifer in Idaho resulted in a pH rise from 7.5 to 9.1. Measured average distribution coefficients (D_EX) for Sr in the calcite produced by ureolysis (0.5) were up to an order of magnitude higher than values reported in the literature for natural and synthetic calcites (0.02-0.4). They were also higher than values for calcite produced abiotically by ammonium carbonate addition (0.3). The precipitation of calcite in these experiments was verified by X-ray diffraction. Time-of-flight secondary ion mass spectrometry (ToF SIMS) depth profiling (up to 350 nm) suggested that the Sr was not merely sorbed on the surface, but was present at depth within the particles. X-ray absorption near edge spectra showed that Sr was present in the calcite samples as a solid solution. The extent of Sr incorporation appeared to be driven primarily by the overall rate of calcite precipitation, where faster precipitation was associated with greater Sr uptake into the solid. The presence of bacterial surfaces as potential nucleation sites in the ammonium carbonate precipitation treatment did not enhance overall precipitation or the Sr distribution coefficient. Because bacterial ureolysis can generate high rates of calcite precipitation, the application of this approach is promising for remediation of ⁹⁰Sr contamination in environments where calcite is stable over the long term.     

Studies of colloids and suspended particles,Cigar Lake uranium deposit,Saskatchewan, Canada

The Cigar Lake U deposit is located in northern Saskatchewan in the eastern part of the Athabasca Sandstone Basin, and consists of a high-grade ore body (up to 55% U) located at a depth of ∼430 m. As part of a study to evaluate the analog features of this deposit with respect to a disposal vault for waste nuclear fuel, colloids (1–450 nm) and suspended particles (450nm) in groundwater have been investigated to evaluate their effect on element transport through the U deposit. Tangential-flow ultrafiltration was used to concentrate particles from 501 groundwater samples in order to characterize the size distribution, concentration, composition and natural radionuclide content of particles in representative parts of the U deposit. Although Cigar Lake groundwaters contain particles in all sizes ranging from 10 nm to slightly larger than 20 μm, most samples contained a relatively high concentration of colloids in the 100–400 nm size range. Particle compositions are similar to the composition of minerals in the sandstones and ore body, suggesting that particles in groundwater are generated by the erosion of fracture-lining minerals. As a result, particle concentrations in groundwater are affected by the integrity of the host rock. In some piezometers the high initial concentrations of suspended particles, which may have been drilling artifacts, decreased during the collection of the first 350 1. Although colloid concentrations fluctuated during sampling, there are no indications that these concentrations will be permanently reduced by continued groundwater pumping. The observed colloid and suspended particle concentrations in the deep groundwaters are too low to have a significant impact on radionuclide migration, provided that radionuclide sorption is reversible. If radionuclides are irreversibly sorbed to particles they cannot sorb to the host rock and their migration can only be evaluated with an understanding of particle mobility. The data for dissolved and particulate U, Th and Ra were used to calculate field-derived distribution ratios (R_d) between particles and groundwater. The wide range of observed R_d values indicates that these radionuclides in particulate form are not in equilibrium with groundwater. U-series isotope data indicated that most of the U and Ra on particles was derived from groundwater. Some particles could have retained their U for as long as 8000 a. The U and Ra contents of particles in the ore and surrounding clay zones are significantly higher than in particles from sandstone, suggesting that the clay has been an effective barrier to particle migration.     

Arsenic distribution in the dissolved, colloidal and particulate size fraction of experimental solutions rich in dissolved organic matter and ferric iron

Due to the widespread contamination of groundwater resources with arsenic (As), controls on As mobility have to be identified. In this study we focused on the distribution of As in the dissolved, colloidal and particulate size fraction of experimental solutions rich in ferric iron, dissolved organic matter (DOM) and As(V). Size fractions between <5 kDa and >0.2 μm were separated by filtration and their elemental composition was analyzed. A steady-state particle size distribution with stable element concentration in the different size classes was attained within 24 h. The presence of DOM partly inhibited the formation of large Fe-(oxy)hydroxide aggregates, thus stabilized Fe in complexed and colloidal form, when initially adjusted molar Fe/C ratios in solution were <0.1. Dissolved As concentrations and the quantity of As bound to colloids (<0.2 μm) increased in the presence of DOM as well. At intermediate Fe/C ratios of 0.02-0.1, a strong correlation between As and Fe concentration occurred in all size fractions (R² = 0.989). At Fe/C ratios <0.02, As was mainly present in the dissolved size fraction. These observations indicate that As mobility increased in the presence of DOM due to (I) competition between As and organic molecules for sorption sites on Fe particles; and (II) due to a higher amount of As bound to more abundant Fe colloids or complexes <0.2 μm in size. The amount of As contained in the colloidal size fractions also depended strongly on the initial size of the humic substance, which was larger for purified humic acids than for natural river or soil porewater samples. Arsenic in the particle size fraction >0.2 μm additionally decreased in the order of pH 4 ? 6 > 8. The presence of DOM likely increases the mobility of As in iron rich waters undergoing oxidation, a finding that has to be considered in the investigation of organic-rich terrestrial and aquatic environments.     

松嫩沙地Sr?Nd同位素组成特征

作为亚洲风尘源区的中国北方干旱—半干旱地区的Sr?Nd同位素组成已得到很好的研究,但位于欧亚黄土带最东端的松嫩沙地尚是空白,这影响了对该地区风尘系统的深入理解。为此,系统采集了松嫩沙地19个区域90个河流沙和风成沙样品,并对这些样品进行了分粒级处理（<63 μm、63~30 μm、30~10 μm、<10 μm和<30 μm）。对116个分粒级子样的酸不溶物（硅酸盐组分）进行了Sr?Nd同位素组成的测定。研究结果表明,松嫩沙地可划分出两个大区（嫩江水系和松花江水系）和七个小区,嫩江水系沉积物的Nd同位素组成显著高于松花江水系,而Sr同位素组成明显偏低。松嫩沙地8个剖面纵向上的同位素特征显示,Sr?Nd同位素组成存在“时间效应”,即随时间发生了明显变化,表明了源区地球化学组成的不稳定性。分粒级组成表明,粒度对87Sr/86Sr比值的影响很小,但对Nd同位素组成有明显影响,且存在Nd同位素比值富集在粗颗粒组分中的趋势,这与以往的研究结果不同。无论是地质历史时期还是现在,嫩江水系沉积物（大庆、杜蒙、齐齐哈尔、泰来、白城）对哈尔滨粉尘的贡献都很小。哈尔滨黄土与现代尘暴粉尘有不同的物源,哈尔滨黄土是春季尘暴天气作用的产物,有一个混合源,松花江水系沉积物（扶余、德惠、榆树等地）是哈尔滨黄土的主要粉尘源区,内蒙古中东部的沙地也为哈尔滨黄土贡献了部分的细颗粒粉尘。     

Mineralogical sources of the buffer capacity in a granite catchment determined by strontium isotopes

The role of different minerals in base cation release and thus the increase of buffering capacity of groundwater against acid deposition is controversially discussed in the literature. The ⁸⁷Sr/⁸⁶Sr ratios and base cation concentration were investigated in whole rock leachates, mineral separates, precipitation, soil solution, groundwater and stream water samples in the Lehstenbach catchment (Germany) to identify the weathering sequence of the granite bedrock. Three different approaches were followed in parallel. It was assumed that the contribution of different minerals to base cation supply of the groundwater with increasing weathering intensity would be observed by investigating (1) unweathered rock leachates, deep groundwater and shallow groundwater, (2) groundwater samples from new groundwater wells, reflecting the initial weathering of the drilled bedrock, and groundwater from wells that were drilled in 1988, (3) stream water during baseflow, dominated by deep groundwater, and stream water during high flow, being predominantly shallow groundwater. Whereas the first approach yielded consistent patterns, there was some evidence that groundwater from the new wells initially reflected contamination by the filter gravel rather than cation release in an initial stage of weathering. Time series samples of stream water and groundwater solute concentrations and isotope ratios turned out to reflect varying fractions of soil water and precipitation water at baseflow and high flow conditions rather than varying contributions of different minerals that prevail at different stages of granite weathering.     

Structure of colloid particles in groundwaters on the territory of the Mayak production association and its impact on the colloid transport of radionuclides in subsoil environments

Colloid particles were examined in groundwaters sampled at the large contamination area of the subsoil environment at the Mayak production association in the Southern Urals. Colloid particles were separated from groundwater samples by ultrafiltration, and their composition and structure were analyzed by X-ray photoelectron spectroscopy (XPS) and Auger spectroscopy (AS). Our results indicate that the chemical composition of the particles significantly varies at their surface and along their radii, from the peripheries to the cores of the particles. The data are used to estimate the possibility of utilizing properties of colloid particles contained in groundwaters (the composition, structure, and zeta potential of such particles) to numerically simulate the spreading of radioactive contamination with groundwaters with regard to the colloid mode of radionuclide transport. It is demonstrated that, along with transmitting electron spectroscopy (TEM) coupled with X-ray microprobe analysis and electron diffraction, the XPS and AS techniques make it possible to obtain information on heterogeneity in the distribution and modes of occurrence of various elements in colloid particles.     

Morphological characters and multi-element isotopic signatures of carbonates from Chinese loess-paleosol sequences

Morphological characters and multi-element isotopic compositions of carbonates from the loess-paleosol sequences in Northwestern China are examined to explore the origin of the minerals. Samples are collected from various sections ranging from Holocene to 0.9 Ma within the sequences and fractions with grain sizes >45 and <2 μm are separated from the bulk soil and examined by SEM and TEM. The results show that the grains >45 μm exhibit an almost perfect spherical shape while those <2 μm are dominated by nano-rods having diameters of 30-50 nm and lengths of 0.3-2 μm, presumably indicating the detrital origin of the coarse fractions and the authigenic characters of the fine ones. Such implications are corroborated by the multi-elemental isotopic compositions of the carbonate minerals. A comparison of the δ¹³C and δ¹⁸O values between minerals and biologically originated samples indicates that the <2 μm fractions have a similar composition to those of coexisting land snail shells. Additional differences between the two size fractions also manifest in the ratios of ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, ²⁰⁸Pb/²⁰⁴Pb, and ⁸⁷Sr/⁸⁶Sr. These results suggest the utility of fine carbonate particles in the soil profile in reconstructing a potentially higher resolution δ¹³C and δ¹⁸O time series to elucidate the paleoclimatic fluctuation in the Chinese Loess Plateau during Pleistocene. The discovery of the nano-rod calcite in Chinese loess, together with previous findings of the similar mineral form in Asian dust, strongly suggests the possibility that these highly reactive CaCO₃ form may alter the aerosol properties during transport.     

Results of Marine Radioecological Study of Fjords of Western Spitsbergen

The patterns of the distribution of technogenic radionuclides ¹³⁷Cs and ⁹⁰Sr in the water mass and bottom deposits of three fjords of Western Spitsbergen (Isfjorden and its arms Grønfjorden and Billefjorden) were studied. The hydrological processes affecting migration of radionuclides in these water bodies were described. It was shown that the ice sheet of the archipelago that accumulates atmospheric precipitation is a source of radioactive contamination of the marine environment of the coast. Technogenic isotopes were accumulated during nuclear weapon testing in the second half of the twentieth century. The current climatic changes strengthen the role of glaciers in the contamination of arctic seas. It was noted that extrema of the ¹³⁷Cs and ⁹⁰Sr specific activity is mainly concentrated in the areas of glacier runoff discharge.

     

Permeable reactive barriers based on natural zeolites from Kazakhstan in solving ecological problems: Mathematical model and simulation

In view of ecological problems stemming from the leakage of reservoirs with liquid radioactive wastes (LRW) and groundwater contamination with radioactive Cs⁺ and Sr²⁺, we have estimated the physicochemical (including sorption) characteristics of clinoptilolite-bearing tuff (CBT) from the Chankanai deposit in Kazakhstan. Data were obtained on the chemical and phase composition of CBT, its total cationexchange capacity, and equilibrium (exchange isotherms) and kinetic (diffusion coefficients) characteristics in sorbing radioactive Cs⁺ and Sr²⁺ from 0.07 n CaCl₂ solution (model solutions of groundwaters). We proved that CBT efficiently sorbs Cs from this solution and practically does not sorb Sr and elucidated the reasons for the low selectivity with respect to Sr²⁺. Based on the equilibrium and kinetic characteristics of the process, a mathematical model is suggested for Cs sorption under dynamic conditions. The protection lifetime of the clinoptilolite-based geochemical barrier is evaluated.     

Simulation of the nucleation and growth of binary solid solutions in aqueous solutions

We present a model which, for the first time, accounts for nucleation, growth and/or resorption of particles of variable composition in aqueous solutions (AS). Devised for describing the precipitation of binary solid solutions, it yields the time evolution of all ion activities in the AS, together with the particle population characteristics: number, size and composition profile of particles as a function of time and of their time of nucleation. We apply this numerical approach to the prototypical case of (Ba,Sr)CO₃ solid solution precipitation. We demonstrate the great sensitivity of the composition profiles and particle sizes to the initial conditions under which the AS is prepared, and thus illustrate the possibility of engineering the particle characteristics into a chosen state. Finally, by comparing the precipitation of two solid solutions (Ba,Sr)CO₃ and (Ba,Sr)SO₄, we evidence the sensitivity of the particle composition profiles to the ratio of the end-member solubility products, which leads to the formation of core-shell particles in the case of (Ba,Sr)SO₄.     

Migration of transuranic elements in groundwater from the near-surface radioactive waste site

Field experiments and laboratory studies were performed to investigate migration processes of plutonium isotopes from a near-surface radioactive waste trench to the underlying sandy aquifer at the Red Forest waste dump in the Chernobyl zone. The objectives of these experiments were to characterize the spatial distribution and possible migration mechanisms of plutonium in the aquifer. During 2002–2007 experimental investigations were carried out and spatial distributions of plutonium isotopes (^239,240Pu, ²³⁸Pu), ⁹⁰Sr and major ions in the aquifer in the direction of the groundwater flow were obtained. Specific activities of radionuclides in groundwater depended on the location of the piezometer and varied in the range of 1–360 mBq kg⁻¹ for ^239,240Pu, 0.5–180 mBq kg⁻¹ for ²³⁸Pu and n–n·10⁴ Bq kg⁻¹ for ⁹⁰Sr. It was found that the spatial features of the distributions of plutonium and strontium specific activities in the upper eolian aquifer were similar, i.e. there was a correlation between the positions of the activity maxima of the radionuclides. The Pu isotopes plume in the aquifer spreads about 15 m downstream of the radionuclides source. Characterization of the initial radionuclide composition of the waste showed that all plutonium in the aquifer originated from the trench. The ratio of plutonium isotopes (^239,240Pu/²³⁸Pu) at the sampling time was the same in waste material and in groundwater samples. In situ ultrafiltration of several groundwater samples was carried out. The size fractionation data obtained suggest that a significant part of plutonium (50–98%) in the groundwater sampled close to the source from the upper part of the aquifer is associated with a very low molecular weight fraction (<1 kDa).     

Identifying the Sources of Solutes in Karst Groundwater in Chongqing,China: a Combined Sulfate and Strontium Isotope Approach

Groundwater from karst subterranean streams is among the world’s most important sources of drinking water supplies, and the hydrochemical characteristics of karst water are impacted by both natural environment and people. Therefore, the study of hydrochemistry and its solutes’ sources is very important to ensure the normal function of life support systems. In this paper, thirty?five representative karst groundwater samples were collected from different aquifers (limestone and dolomite) and various land use types in Chongqing to trace the sources of solutes and relative hydrochemical processes. Hydrogeochemical types of karst groundwater in Chongqing were mainly of the Ca?HCO3 type or Ca (Mg)?HCO3 type. However, some hydrochemical types of karst groundwater were the K+Na+Ca?SO4 type (G25 site) or Ca?HCO3+SO4 type (G26 and G14 site), indicating that the hydrochemistry of these sites might be strongly influenced by anthropogenic activities or unique geological characteristics. The dissolved Sr concentrations of the studied groundwater ranged from 0.57 to 15.06 μmmol/L, and the 87Sr/86Sr varied from 0.70751 to 0.71627. The δ34S?SO42? fell into a range of ?6.8‰?21.5‰, with a mean value of 5.6‰. The variations of both 87Sr/86Sr and Sr values of the groundwater samples indicated that the Sr element was controlled by the weathering of limestone, dolomite and silicate rock. However, the figure of 87Sr/86Sr vs. Sr2+/[K++Na+] showed that the anthropogenic inputs also obviously contributed to the Sr contents. For tracing the detailed anthropogenic effects, we traced the sources of solutes collected karst groundwater samples in Chongqing according to the δ34S value of potential sulfate sources. The variations of both δ34S and 1/SO42? values of the groundwater samples indicated that the atmospheric acid deposition (AAD), dissolution of gypsum (GD), oxidation of sul?de mineral (OS) or anthropogenic inputs (SF: sewage or fertilizer) have contributed to solutes in karst groundwater. The influence of oxidation of sul?de mineral, atmospheric acid deposit and anthropogenic inputs to groundwater in Chongqing karst areas was much widespread.     

Properties of debris flow deposits and source materials compared: implications for debris flow characterization

In the Alps, debris flow deposits generally contain <5% clay‐size particles, and the role of the surface‐charged <2 μm particles is often neglected, although these particles may have a significant impact on the rheological properties of the interstitial fluid. The objective of this study was to compare debris flow deposits and parent materials from two neighbouring catchments of the Swiss Alps, with special emphasis on the colloidal constituents. The catchments are small in area (4 km²), 2·5 km long, similar in morphology, but different in geology. The average slopes are 35–40%. The catchments were monitored for debris flow events and mapped for surface aspect and erosion activity. Debris flow deposits and parent materials were sampled, the clay and silt fractions extracted and the bulk density, <2 mm fraction bulk density, particle size distribution, chemical composition, cation exchange capacity (CEC) and mineralogy analysed. The results show that the deposits are similar to the parent screes in terms of chemical composition, but differ in terms of: (i) particle size distribution; and (ii) mineralogy, reactivity and density of the <2 mm fraction. In this fraction, compared with the parent materials the deposits show dense materials enriched in coarse monocrystalline particles, of which the smallest and more reactive particles were leached. The results suggest that deposit samples should not be considered as representative of source or flow materials, particularly with respect to their physical properties.     

Using 87Sr/86Sr, δ18O and δ2H isotopes along with major chemical composition to assess groundwater salinization in lower Shire valley,Malawi

Groundwater resources in some parts of the lower section of Shire River valley, Malawi, are not useable for rural domestic water supply due to high salinity. In this study, a combined assessment of isotopic (⁸⁷Sr/⁸⁶Sr, δ¹⁸O and δ²H) and major ion composition was conducted in order to identify the hydro-geochemical evolution of the groundwater and thereby the causes of salinity. Three major end-members (representing fresh- and saline groundwater, and evaporated recharge) were identified based on major ion and isotopic composition. The saline groundwater is inferred to result from dissolution of evaporitic salts (halite) and the fresh groundwater shows influence of silicate weathering. Conservative mixing models show that brackish groundwater samples result from a three component mixture comprising the identified end-members. Hence their salinity is interpreted to result from mixing of fresh groundwater with evaporated recharge and saline groundwater. On the other hand, the groundwater with low TDS, found at some distance from areas of high salinity, is influenced by mixing of evaporated recharge and fresh groundwater only. Close to the Shire marshes, where there is shallow groundwater, composition of stable isotopes of water indicates that evaporation may also be an important factor.