首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 500 毫秒
1.
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).  相似文献   

2.
Estimation of Rn transfer from water to indoor air based on multi-day measurements may underestimate alpha exposure that occurs at short time scales in confined spaces, such as from showering, in houses with high Rn activities in the water supply. In order to examine one such incremental increase in exposure, variations in Rn in water and indoor air in 18 houses with private wells in western North Carolina (USA) were investigated. Radon in well water ranged from 158 to 811 Bq L−1 (median 239 Bq L−1). After 20-min showers in bathrooms with closed doors, peak Rn in air increases (above background) ranged from 71 to 4420 Bq m−3 (median 1170 Bq m−3). Calculated transfer coefficients at the scale of a 40-min closed bathroom (20-min shower plus 20 min post-shower) are described by a lognormal distribution whose geometric mean exceeds the widely-used ∼10−4 whole-house transfer coefficient by about one order of magnitude. As short-lived decay products grow from shower-derived Rn, short-term alpha energy exposure occurs in bathrooms in addition to the exposure caused by Rn mixed throughout the volume of the house. Due to the increasing ratio of Rn decay products to Rn, alpha energy exposure is greatest several minutes after the shower is turned off. For a 7.2-min shower with 10 min of additional exposure before opening the door, a geometric mean 5.6% increase in exposure over the ∼10−4 whole-house transfer coefficient derived from longer measurement periods was estimated. In addition to Rn activity in water, short-term shower exposure to Rn progeny depends on exposure time, ventilation, attachment and deposition, among other variable factors that characterize individual houses and residents.  相似文献   

3.
Before the Kobe earthquake, an anomalous increase in atmospheric Rn concentration was observed. By separating the measured concentration of atmospheric Rn into three components according to the distance from the monitoring station, the variation of Rn exhalation rate can be estimated for the respective area using the daily minimum and maximum concentrations. The mean rate of Rn exhalation gradually increased in an area of 20 km around the monitoring station, becoming five times higher than normal in the period between October 1994 and the date of the earthquake. This area had a large co-seismic displacement of up to 30 cm, which roughly corresponds to the crustal strain of 10−6-order, and it is considered the main source for the atmospheric Rn prior to the Kobe earthquake. Analyses revealed that the pre-seismic change in the atmospheric Rn concentration exhibited an anomalous pattern which would yield information on the spatial distribution of the mechanical response of the ground.  相似文献   

4.
Solubility experiments were performed on nanocrystalline scorodite and amorphous ferric arsenate. Nanocrystalline scorodite occurs as stubby prismatic crystals measuring about 50 nm and having a specific surface area of 39.88 ± 0.07 m2/g whereas ferric arsenate is amorphous and occurs as aggregated clusters measuring about 50–100 nm with a specific surface area of 17.95 ± 0.19 m2/g. Similar to its crystalline counterpart, nanocrystalline scorodite has a solubility of about 0.25 mg/L at around pH 3–4 but has increased solubilities at low and high pH (i.e. <2 and >6). Nanocrystalline scorodite dissolves incongruently at about pH > 2.5 whereas ferric arsenate dissolution is incongruent at all the pH ranges tested (pH 2–5). It appears that the solubility of scorodite is not influenced by particle size. The dissolution rate of nanocrystalline scorodite is 2.64 × 10−10 mol m−2 s−1 at pH 1 and 3.25 × 10−11 mol m−2 s−1 at pH 2. These rates are 3–4 orders of magnitude slower than the oxidative dissolution of pyrite and 5 orders of magnitude slower than that of arsenopyrite. Ferric arsenate dissolution rates range from 6.14 × 10−9 mol m−2 s−1 at pH 2 to 1.66 × 10−9 mol m−2 s−1 at pH 5. Among the common As minerals, scorodite has the lowest solubility and dissolution rate. Whereas ferric arsenate is not a suitable compound for As control in mine effluents, nanocrystalline scorodite that can be easily precipitated at ambient pressure and temperature conditions would be satisfactory in meeting the regulatory guidelines at pH 3–4.  相似文献   

5.
We have performed holographic interferometry measurements of the dissolution of the (0 1 0) plane of a cleaved gypsum single crystal in pure water. These experiments have provided the value of the dissolution rate constant k of gypsum in water and the value of the interdiffusion coefficient D of its aqueous species in water. D is 1.0 × 10−9 m2 s−1, a value close to the theoretical value generally used in dissolution studies. k is 4 × 10−5 mol m−2 s−1. It directly characterizes the microscopic transfer rate at the solid-liquid interface, and is not an averaged value deduced from quantities measured far from the surface as in macroscopic dissolution experiments. It is found to be two times lower than the value obtained from macroscopic experiments.  相似文献   

6.
The importance of accessing safe aquifers in areas with high As is being increasingly recognized. The present study aims to investigate the sorption and mobility of As at the sediment-groundwater interface to identify a likely safe aquifer in the Holocene deposit in southwestern Bangladesh. The upper, shallow aquifer at around 18 m depth, which is composed mainly of very fine, grey, reduced sand and contains 24.3 μg/g As, was found to produce highly enriched groundwater (190 μg/L As). In contrast, deeper sediments are composed of partly oxidized, brownish, medium sand with natural adsorbents like Fe- and Al-oxides; they contain 0.76 μg/g As and impart low As concentrations to the water (4 μg/L). These observations were supported by spectroscopic studies with SEM, TEM, XRD and XRF, and by adsorption, leaching, column tests and sequential extraction. A relatively high in-situ dissolution rate (Rr) of 1.42 × 10−16 mol/m2/s was derived for the shallower aquifer from the inverse mass-balance model. The high Rr may enhance As release processes in the upper sediment. The field-based reaction rate (Kr) was extrapolated to be roughly 1.23 × 10−13 s−1 and 6.24 × 10−14 s−1 for the shallower and deeper aquifer, respectively, from the laboratory-obtained adsorption/desorption data. This implies that As is more reactive in the shallower aquifer. The partition coefficient for the distribution of As at the sediment-water interface (Kd-As) was found to range from 5 to 235 L/kg based on in-situ, batch adsorption, and flow-through column techniques. Additionally, a parametric equation for Kd-As (R2 = 0.67) was obtained from the groundwater pH and the logarithm of the leachable Fe and Al concentrations in sediment. A one-dimensional finite-difference numerical model incorporating Kd and Kr showed that the shallow, leached As can be immobilized and prevented from reaching the deeper aquifer (∼150 m) after 100 year by a natural filter of oxidizing sand and adsorbent minerals like Fe and Al oxides; in this scenario, 99% of the As in groundwater is reduced. The deeper aquifer appears to be an adequate source of sustainable, safe water.  相似文献   

7.
地震活动断裂带能够向大气释放大量的温室气体、放射性气体和有毒气体(CO_2、CH_4、Rn和Hg),并对大气环境的影响产生复杂的影响。利用静态暗箱法,对汶川M_s8.0地震破裂带CO_2、Rn和Hg脱气强度进行实地测量,并计算了CO_2和Hg脱气对大气的年贡献量。结果表明:(1)破裂带土壤气中CO_2、CH_4、Rn和Hg异常浓度最大值分别可以达到7.98%、2.38%、524.30k Bq/m~3和161.00ng/m~3;破裂带CO_2、Rn和Hg脱气平均通量是34.95g·m~(-2)d~(-1)、36.11m Bq·m~(-2)s~(-1)和26.56ng·m~(-2)h~(-1),最大值分别达到259.23g·m~(-2)d~(-1)、580.35m Bq·m~(-2)s~(-1)和387.67ng·m~(-2)h~(-1);(2)汶川Ms8.0地震破裂带向大气脱气的CO_2年贡献量是0.95Mt,Hg的年贡献量是15.94kg。汶川Ms8.0地震破裂带破裂CO_2、CH_4、Rn和Hg等的脱气强度,不仅与破裂带渗透率有关,还与断裂带浅部存在的气藏、煤层以及磷矿层等气体源有重要的联系。  相似文献   

8.
The pool of iron oxides, available in sediments for reductive dissolution, is usually estimated by wet chemical extraction methods. Such methods are basically empirically defined and calibrated against various synthetic iron oxides. However, in natural sediments, iron oxides are present as part of a complex mixture of iron oxides with variable crystallinity, clays and organics etc. Such a mixture is more accurately described by a reactive continuum covering a range from highly reactive iron oxides to non-reactive iron oxide. The reactivity of the pool of iron oxides in sediment can be determined by reductive dissolution in 10 mM ascorbic acid at pH 3. Parallel dissolution experiments in HCl at pH 3 reveal the release of Fe(II) by proton assisted dissolution. The difference in Fe(II)-release between the two experiments is attributed to reductive dissolution of iron oxides and can be quantified using the rate equation J/m0 = k′(m/m0)γ, where J is the overall rate of dissolution (mol s−1), m0 the initial amount of iron oxide, k′ a rate constant (s−1), m/m0 the proportion of undissolved mineral and γ a parameter describing the change in reaction rate over time. In the Rømø aquifer, Denmark, the reduction of iron oxides is an important electron accepting process for organic matter degradation and is reflected by the steep increase in aqueous Fe2+ over depth. Sediment from the Rømø aquifer was used for reductive dissolution experiments with ascorbic acid. The rate parameters describing the reactivity of iron oxides in the sediment are in the range k′ = 7·10−6 to 1·10−3 s−1 and γ = 1 to 2.4. These values are intermediate between a synthetic 2-line ferrihydrite and a goethite. The rate constant increases by two orders of magnitude over depth suggesting an increase in iron oxide reactivity with depth. This increase was not captured by traditional oxalate and dithionite extractions.  相似文献   

9.
The western Tianshan range is a major Cenozoic orogenic belt in central Asia exposing predominantly Paleozoic rocks including granite. Ongoing deformation is reflected by very rugged topography with peaks over 7000 m high. Active tectonic deformation is tied to an E–W trending fracture and fault system that sections the mountain chain into geologically diverse blocks that extend parallel to the orogen. In the Muzhaerte valley upwelling hot water follows such a fault system in the Muza granite. About 20 L min−1 Na–SO4–Cl water with a temperature of 55 °C having a total mineralization of about 1 g L−1 discharge from the hot spring. The water is used in a local spa that is frequented by the people of the upper Ili river area. Its waters are used for balneological purposes and the spa serves as a therapeutic institution. The major element composition of the hot water is dominated by Na and by SO4 and Cl, Ca is a minor component. Dissolved silica (1.04 mmol L−1) corresponds to a quartz-saturation temperature of 116 °C and a corresponding depth of the source of the water of about 4600 m. This temperature is consistent with Na/K and Na/Li geothermometry. The water is saturated with respect to fluorite and contains 7.5 mg L−1 F− as a consequence of the low Ca-concentration. The water is undersaturated with respect to the primary minerals of the reservoir granite at reservoir temperature causing continued irreversible dissolution of granite. The waters are oversaturated with respect to Ca–zeolite minerals (such as stilbite and mesolite), and it is expected that zeolites precipitate in the fracture pore space and in alteration zones replacing primary granite.  相似文献   

10.
Laboratory determined mineral weathering rates need to be normalised to allow their extrapolation to natural systems. The principle normalisation terms used in the literature are mass, and geometric- and BET specific surface area (SSA). The purpose of this study was to determine how dissolution rates normalised to these terms vary with grain size. Different size fractions of anorthite and biotite ranging from 180-150 to 20-10 μm were dissolved in pH 3, HCl at 25 °C in flow through reactors under far from equilibrium conditions. Steady state dissolution rates after 5376 h (anorthite) and 4992 h (biotite) were calculated from Si concentrations and were normalised to initial- and final- mass and geometric-, geometric edge- (biotite), and BET SSA. For anorthite, rates normalised to initial- and final-BET SSA ranged from 0.33 to 2.77 × 10−10 molfeldspar m−2 s−1, rates normalised to initial- and final-geometric SSA ranged from 5.74 to 8.88 × 10−10 molfeldspar m−2 s−1 and rates normalised to initial- and final-mass ranged from 0.11 to 1.65 molfeldspar g−1 s−1. For biotite, rates normalised to initial- and final-BET SSA ranged from 1.02 to 2.03 × 10−12 molbiotite m−2 s−1, rates normalised to initial- and final-geometric SSA ranged from 3.26 to 16.21 × 10−12 molbiotite m−2 s−1, rates normalised to initial- and final-geometric edge SSA ranged from 59.46 to 111.32 × 10−12 molbiotite m−2 s−1 and rates normalised to initial- and final-mass ranged from 0.81 to 6.93 × 10−12 molbiotite g−1 s−1. For all normalising terms rates varied significantly (p ? 0.05) with grain size. The normalising terms which gave least variation in dissolution rate between grain sizes for anorthite were initial BET SSA and initial- and final-geometric SSA. This is consistent with: (1) dissolution being dominated by the slower dissolving but area dominant non-etched surfaces of the grains and, (2) the walls of etch pits and other dissolution features being relatively unreactive. These steady state normalised dissolution rates are likely to be constant with time. Normalisation to final BET SSA did not give constant ratios across grain size due to a non-uniform distribution of dissolution features. After dissolution coarser grains had a greater density of dissolution features with BET-measurable but unreactive wall surface area than the finer grains. The normalising term which gave the least variation in dissolution rates between grain sizes for biotite was initial BET SSA. Initial- and final-geometric edge SSA and final BET SSA gave the next least varied rates. The basal surfaces dissolved sufficiently rapidly to influence bulk dissolution rate and prevent geometric edge SSA normalised dissolution rates showing the least variation. Simple modelling indicated that biotite grain edges dissolved 71-132 times faster than basal surfaces. In this experiment, initial BET SSA best integrated the different areas and reactivities of the edge and basal surfaces of biotite. Steady state dissolution rates are likely to vary with time as dissolution alters the ratio of edge to basal surface area. Therefore they would be more properly termed pseudo-steady state rates, only appearing constant because the time period over which they were measured (1512 h) was less than the time period over which they would change significantly.  相似文献   

11.
We report the application of an in situ method to obtain field dissolution rates of fine mineral particles in soils. Samples with different metal-containing mineral and slag particles (lead oxide, copper concentrate and copper slag) from the mining and smelting industry were buried in the topsoil of an acidic forest soil for up to 18 months. In addition we studied the dissolution of these particles in samples of the same soil, in a sand matrix and in acid solution under constant temperature and moisture conditions in the laboratory. Under field conditions the PbO particles dissolved quite rapidly (2.4 ± 0.7 × 10−10 mol Pb m−2 s−1), whereas the copper concentrate (<1 × 10−11 mol Cu m−2 s−1) and the copper slag particles (4.3 ± 0.8 × 10−11 mol Cu m−2 s−1) proved to be more resistant to weathering. In addition to qualitative information on dissolution features (SEM), the method yielded quantitative data on in situ dissolution rates. The dissolution rates followed the order: sand with acid percolation (pH 3.5; lab) < soil (lab) < soil (field) < acid solution (pH 3.5; lab). Dissolution rates in soil were found to be lower under laboratory than under field conditions. The faster field rates may in part be attributed to the higher biological activity in the field soil compared to the same soil in the laboratory.  相似文献   

12.
The shallow aquifer beneath the Western Snake River Plain (Idaho, USA) exhibits widespread elevated arsenic concentrations (up to 120 μg L−1). While semi-arid, crop irrigation has increased annual recharge to the aquifer from approximately 1 cm prior to a current rate of >50 cm year−1. The highest aqueous arsenic concentrations are found in proximity to the water table (all values >50 μg L−1 within 50 m) and concentrations decline with depth. Despite strong vertical redox stratification within the aquifer, spatial distribution of aqueous species indicates that redox processes are not primary drivers of arsenic mobilization. Arsenic release and transport occur under oxidizing conditions; groundwater wells containing dissolved arsenic at >50 μg L−1 exhibit elevated concentrations of O2 (average 4 mg L−1) and NO3 (average 8 mg L−1) and low concentrations of dissolved Fe (<20 μg L−1). Sequential extractions and spectroscopic analysis of surficial soils and sediments indicate solid phase arsenic is primarily arsenate and is present at elevated concentrations (4–45 mg kg−1, average: 17 mg kg−1) relative to global sedimentary abundances. The highest concentrations of easily mobilized arsenic (up to 7 mg kg−1) are associated with surficial soils and sediments visibly stained with iron oxides. Batch leaching experiments on these materials using irrigation waters produce pore water arsenic concentrations approximating those observed in the shallow aquifer (up to 152 μg L−1). While As:Cl aqueous phase relationships suggest minor evaporative enrichment, this appears to be a relic of the pre-irrigation environment. Collectively, these data indicate that infiltrating irrigation waters leach arsenic from surficial sediments to the underlying aquifer.  相似文献   

13.
Dissolution experiments on a serpentinite were performed at 70 °C, 0.1 MPa, in H2SO4 solution, in open and closed systems, in order to evaluate the overall dissolution rate of mineral components over different times (4, 9 and 24 h). In addition, the serpentinite powder was reacted with a NaCl-bearing aqueous solution and supercritical CO2 for 24 h at higher pressures (9-30 MPa) and temperatures (250-300 °C) either in a stirred reactor or in an externally-heated pressure vessel to assess both the dissolution rate of serpentinite minerals and the progress of the carbonation reaction. Results show that, at 0.1 MPa, MgO extraction from serpentinite ranges from 82% to 98% and dissolution rate varies from 8.5 × 10−10 mole m−2 s−1 to 4.2 × 10−9 mole m−2 s−1. Attempts to obtain carbonates from the Mg-rich solutions by increasing their pH failed since Mg- and NH4- bearing sulfates promptly precipitated. On the other hand, at higher pressures, significant crystallization (5.0-10.4 wt%) of Ca- and Fe-bearing magnesite was accomplished at 30 MPa and 300 °C using 100 g L−1 NaCl aqueous solutions. The corresponding amount of CO2 sequestered by crystallization of carbonates is 9.4-15.9 mole%. Dissolution rate (from 6.3 × 10−11 mole m−2 s−1 to 1.3 × 10−10 mole m−2 s−1) is lower than that obtained at 0.1 MPa and 70 °C but it is related to pH values much higher (3.3-4.4) than that (−0.65) calculated for the H2SO4 solution.Through a thorough review of previous experimental investigations on the dissolution kinetics of serpentine minerals the authors propose adopting: (i) the log rate [mole m−2 s−1] value of −12.08 ± 0.16 (1σ), as representative of the neutral dissolution mechanism at 25 °C and (ii) the following relationship for the acidic dissolution mechanism at 25 °C:
log rate=-0.45(±0.09)×pH-10.01(±0.30).  相似文献   

14.
Halogen diffusion in a basaltic melt   总被引：2，自引：0，他引：2  
The diffusion of the halogens fluorine, chlorine and bromine was measured in a hawaiitic melt from Mt. Etna at 500 MPa and 1.0 GPa, 1250 to 1450 °C at anhydrous conditions; the diffusion of F and Cl in the melt was also studied with about 3 wt% of dissolved water. Experiments were performed using the diffusion-couple technique in a piston cylinder. Most experiments were performed with only one halogen diffusing between the halogen-enriched and halogen-poor halves of the diffusion couple, but a few experiments with a mixture of halogens (F, Cl and Br) were also performed in order to investigate the possibility of interactions between the halogens during diffusion. Fluorine and chlorine diffusivity show a very similar behavior, slightly diverging at low temperature. Bromine diffusion is a factor of about 2-5 lower than the other halogens in this study. Diffusion coefficients for fluorine range between 2.3 × 10−11 and 1.4 × 10−10 m2 s−1, for chlorine between 1.1 × 10−11 and 1.3 × 10−10 and for bromine between 9.4 × 10−12 and 6.8 × 10−11 m2 s−1. No pressure effect was detected at the conditions investigated. In experiments involving mixed halogens, the diffusivities appear to decrease slightly (by a factor of ∼3), and are more uniform among the three elements. However, activation energies for diffusion do not appear to differ between experiments with individual halogens or when they are all mixed together. The effect of water increases the diffusion coefficients of F and Cl by no more than a factor of 3 compared to the anhydrous melt (DF = 4.0 × 10−11 to 1.6 × 10−10 m2 s−1; DCl = 3.0 × 10−11 to 1.9 × 10−10 m2 s−1). Comparing our results to the diffusion coefficients of other volatiles in nominally dry basaltic melts, halogen diffusivities are about one order of magnitude lower than H2O, similar to CO2, and a factor of ∼5 higher than S. The contrasting volatile diffusivities may affect the variable extent of volatile degassing upon melt depressurization and vesiculation, and can help our understanding of the compositions of rapidly grown magmatic bubbles.  相似文献   

15.
Sediments from the Aquia aquifer in coastal Maryland were collected as part of a larger study of As in the Aquia groundwater flow system where As concentration are reported to reach levels as high as 1072 nmol kg−1, (i.e., ∼80 μg/L). To test whether As release is microbially mediated by reductive dissolution of Fe(III) oxides/oxyhydroxides within the aquifer sediments, the Aquia aquifer sediment samples were employed in a series of microcosm experiments. The microcosm experiments consisted of sterilized serum bottles prepared with aquifer sediments and sterilized (i.e., autoclaved), artificial groundwater using four experimental conditions and one control condition. The four experimental conditions included the following scenarios: (1) aerobic; (2) anaerobic; (3) anaerobic + acetate; and (4) anaerobic + acetate + AQDS (anthraquinone-2,6-disulfonic acid). AQDS acts as an electron shuttle. The control condition contained sterilized aquifer sediments kept under anaerobic conditions with an addition of AQDS. Over the course of the 27 day microcosm experiments, dissolved As in the unamended (aerobic and anaerobic) microcosms remained constant at around ∼28 nmol kg−1 (2 μg/L). With the addition of acetate, the amount of As released to the solution approximately doubled reaching ∼51 nmol kg−1 (3.8 μg/L). For microcosm experiments amended with acetate and AQDS, the dissolved As concentrations exceeded 75 nmol kg−1 (5.6 μg/L). The As concentrations in the acetate and acetate + AQDS amended microcosms are of similar orders of magnitude to As concentrations in groundwaters from the aquifer sediment sampling site (127-170 nmol kg−1). Arsenic concentrations in the sterilized control experiments were generally less than 15 nmol kg−1 (1.1 μg/L), which is interpreted to be the amount of As released from Aquia aquifer sediments owing to abiotic, surface exchange processes. Iron concentrations released to solution in each of the microcosm experiments were higher and more variable than the As concentrations, but generally exhibited similar trends to the As concentrations. Specifically, the acetate and acetate + AQDS amended microcosm typically exhibited the highest Fe concentrations (up to 1725 and 6566 nmol kg−1, respectively). The increase in both As and Fe in the artificial groundwater solutions in these amended microcosm experiments strongly suggests that microbes within the Aquia aquifer sediments mobilize As from the sediment substrate to the groundwaters via Fe(III) reduction.  相似文献   

16.
The quaternary volcanic complex of Mount Amiata is located in southern Tuscany (Italy) and represents the most recent manifestation of the Tuscan Magmatic Province. The region is characterised by a large thermal anomaly and by the presence of numerous CO2-rich gas emissions and geothermal features, mainly located at the periphery of the volcanic complex. Two geothermal systems are located, at increasing depths, in the carbonate and metamorphic formations beneath the volcanic complex. The shallow volcanic aquifer is separated from the deep geothermal systems by a low permeability unit (Ligurian Unit). A measured CO2 discharge through soils of 1.8 × 109 mol a−1 shows that large amounts of CO2 move from the deep reservoir to the surface. A large range in δ13CTDIC (−21.07 to +3.65) characterises the waters circulating in the aquifers of the region and the mass and isotopic balance of TDIC allows distinguishing a discharge of 0.3 × 109 mol a−1 of deeply sourced CO2 in spring waters. The total natural CO2 discharge (2.1 × 109 mol a−1) is slightly less than minimum CO2 output estimated by an indirect method (2.8 × 109 mol a−1), but present-day release of 5.8 × 109 mol a−1 CO2 from deep geothermal wells may have reduced natural CO2 discharge. The heat transported by groundwater, computed considering the increase in temperature from the infiltration area to the discharge from springs, is of the same order of magnitude, or higher, than the regional conductive heat flow (>200 mW m−2) and reaches extremely high values (up to 2700 mW m−2) in the north-eastern part of the study area. Heat transfer occurs mainly by conductive heating in the volcanic aquifer and by uprising gas and vapor along fault zones and in those areas where low permeability cover is lacking. The comparison of CO2 flux, heat flow and geological setting shows that near surface geology and hydrogeological setting play a central role in determining CO2 degassing and heat transfer patterns.  相似文献   

17.
To advance understanding of hydrological influences on As concentrations within groundwaters of Southeast Asia, the flow system of an As-rich aquifer on the Mekong Delta in Cambodia where flow patterns have not been disturbed by irrigation well pumping was examined. Monitoring of water levels in a network of installed wells, extending over a 50 km2 area, indicates that groundwater flow is dominated by seasonally-variable gradients developed between the river and the inland wetland basins. While the gradient inverts annually, net groundwater flow is from the wetlands to the river. Hydraulic parameters of the aquifer (K ≈ 10−4 ms−1) and overlying clay aquitard (K ≈ 10−8 ms−1) were determined using grain size, permeameter and slug test analyses; when coupled with observed gradients, they indicate a net groundwater flow velocity of 0.04–0.4 ma−1 downward through the clay and 1–13 ma−1 horizontally within the sand aquifer, producing aquifer residence times on the order 100–1000 a. The results of numerical modeling support this conceptual model of the flow system and, when integrated with observed spatial trends in dissolved As concentrations, reveal that the shallow sediments (upper 2–10 m of fine-grained material) are an important source of As to the underlying aquifer.  相似文献   

18.
Hydrochemical patterns resulting from differing bedrock geochemistry were ascertained by concurrent streamwater sampling in three small catchments, each underlain by geochemically contrasting silicate rock types in the western Czech Republic, Central Europe in 2001–2010. The catchments are situated 5–7 km apart in the Slavkov Forest and are occupied by Norway spruce (Picea abies) plantations. They have similar altitude, area, topography, mean annual air temperature, and atmospheric deposition fluxes. The amount of base cations oxides (Ca + Mg + Na + K) is markedly different among the three studied rocks (leucogranite 8%, amphibolite 22%, serpentinite 36%). The leucogranite contains a very small amount of MgO, while the serpentinite contains extremely large amounts of MgO. The amphibolite contains an intermediate amount of MgO and elevated CaO. The Lysina, on leucogranite, exhibited very small concentrations of Mg (median 0.4 mg L−1) in streamwater; Pluh?v Bor, on serpentinite, contained extremely high concentrations of streamwater Mg (18 mg L−1). Streamwater in the Na Zeleném catchment, on amphibolite, contained an intermediate amount of Mg and an elevated Ca. Very low pH (4.2), negative alkalinity (−60 μeq L−1) and high inorganic monomeric Al concentrations (0.3 mg L−1) were found in the stream draining leucogranite. Serpentinite streamwater exhibited the highest pH (7.6), alkalinity (+940 μeq L−1) and Ni concentrations (100 μg L−1). Aquatic chemistry reflected the composition of the underlying rocks within the studied catchments. Contrasting streamwater compositions of the studied catchments were generated according to the MAGIC model simulations mainly by differences in chemical weathering rates of base cations (65 meq m−2 a−1 at Lysina, 198 meq m−2 a−1 at Na Zeleném, and 241 meq m−2 a−1 at Pluh?v Bor).  相似文献   

19.
The mass of pore water present in the rock matrix of a crystalline rock mass is significant and its influence on fracture groundwater and future deep repositories needs to be understood. Yet, the rock matrix has a hydraulic transmissivity generally well below 10−10 m2 s−1 inhibiting sampling of pore water by conventional sampling techniques. Various innovative techniques for the chemical and isotopic characterisation of pore water in crystalline rocks are applied and evaluated. Direct sampling of pore water was facilitated by collecting seepage water in a specially designed borehole located at a depth of 420 m in the Äspö underground research laboratory (Äspö HRL), Sweden, over a period of 7.5 a. During the entire time span, seepage waters collected from different sampling sections showed constant, but individual chemical and isotopic compositions. Compositional differences compared to nearby fracture groundwaters indicate that the collected waters originated from the low-permeability rock mass without mutual influence via more conductive microfractures within the metre scale. They are interpreted as representing pore water in a transient state of diffusive interaction with different types of old palaeowaters which have periodically characterised the fracture network at the Äspö HRL over geological times (thousands to hundreds of thousands of years).  相似文献   

20.
Gaseous elemental mercury (GEM) and reactive gaseous mercury (RGM) were measured over 2-week seasonal field campaigns near Salmon Falls Creek Reservoir in south-central Idaho from the summer of 2005 through the fall of 2006 and over the entire summer of 2006 using automated Tekran Hg analyzers. GEM, RGM, and particulate Hg (HgP) were also measured at a secondary site 90 km to the west in southwestern Idaho during the summer of 2006. The study was performed to characterize Hg air concentrations in the southern Idaho area for the first time, estimate Hg dry deposition rates, and investigate the source of observed elevated concentrations. High seasonal variability was observed with the highest GEM (1.91 ± 0.9 ng m−3) and RGM (8.1 ± 5.6 pg m−3) concentrations occurring in the summer and lower values in the winter (1.32 ± 0.3 ng m−3, 3.2 ± 2.9 pg m−3 for GEM, RGM, respectively). The summer-average HgP concentrations were generally below detection limit (0.6 ± 1 pg m−3). Seasonally averaged deposition velocities calculated using a resistance model were 0.034 ± 0.032, 0.043 ± 0.040, 0.00084 ± 0.0017 and 0.00036 ± 0.0011 cm s−1 for GEM (spring, summer, fall and winter, respectively) and 0.50 ± 0.39, 0.40 ± 0.31, 0.51 ± 0.43 and 0.76 ± 0.57 cm s−1 for RGM. The total annual RGM + GEM dry deposition estimate was calculated to be 11.9 ± 3.3 μg m−2, or about 2/3 of the total (wet + dry) deposition estimate for the area. Periodic elevated short-term GEM (2.2–12 ng m−3) and RGM (50–150 pg m−3) events were observed primarily during the warm seasons. Back-trajectory modeling and PSCF analysis indicate predominant source directions to the SE (western Utah, northeastern Nevada) and SW (north-central Nevada) with fewer inputs from the NW (southeastern Oregon and southwestern Idaho).  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号