Arsenic distribution in the environment: The effects of scale

The distribution of As in a variety of sample materials was studied at different scales, from continental to local, combining published data sets with the aim of delineating the impact and relative importance of geogenic vs. anthropogenic As sources. Geochemical mapping of As with a variety of sample materials demonstrates that variation is high at all scales (local to continental) – from sample densities of 400 sites per km² to 1 site per 5000 km². Different processes govern the As distribution at different scales. A high sample density is needed to reliably detect mineralisation or contamination in soil samples. In both cases the impact on the much larger geochemical background variation is limited to a local scale. Distribution patterns in geochemical maps on the sub-continental to continental scale are dominated by natural variation. Given that the geochemical background is characterised by a high variation at all scales, it appears impossible to establish a reliable single value for “good soil quality” or a “natural background concentration” for As for any sizeable area, e.g., for Europe. For such a differentiation, geochemical maps at a variety of scales are needed.     

Top-/bottom-soil ratios and enrichment factors: What do they really show?

High top-/bottom-soil ratios, or high values of “enrichment factors” (EFs), are used as a proof for major anthropogenic impact on the geochemistry of the Earth surface. The idea behind calculating such ratios is that soils taken at depth or “average crust” can provide the geochemical background for the soils collected at the Earth surface. However, a soil profile is not a closed system, element exchange between the different layers, depending on and varying with the chemical properties of the different elements, and their turnover in the biosphere is the essence of soil formation. High top-/bottom-soil ratios, or EFs, may thus highlight the geochemical de-coupling of the lithosphere from the biosphere rather than contamination. This is demonstrated by using regional data from 258 soil O- and B-horizon samples collected from the Czech Republic (76,800 km²). Results show no relationship between the ratios and the magnitude of anthropogenic emissions. The visible relationship between element concentrations and sources in a map of the spatial distribution of the elements is lost when maps for the top-/bottom-soil ratio or EFs are constructed. The value of the data lies in the spatial elemental distribution, and not in ratios calculated based on misconceptions.     

Arsenic and antimony contamination of waters,stream sediments and soils in the vicinity of abandoned antimony mines in the Western Carpathians,Slovakia

Environmental contamination with As and Sb caused by past mining activities at Sb mines is a significant problem in Slovakia. This study is focused on the environmental effects of the 5 abandoned Sb mines on water, stream sediment and soil since the mines are situated in the close vicinity of residential areas. Samples of mine wastes, various types of waters, stream sediments, soils, and leachates of the mine wastes, stream sediments and selected soils were analyzed for As and Sb to evaluate their geochemical dispersion from the mines. Mine wastes collected at the mine sites contained up to 5166 mg/kg As and 9861 mg/kg Sb. Arsenic in mine wastes was associated mostly with Fe oxides, whereas Sb was present frequently in the form of individual Sb, Sb(Fe) and Fe(Sb) oxides. Waters of different types such as groundwater, surface waters and mine waters, all contained elevated concentrations of As and Sb, reaching up to 2150 μg/L As and 9300 μg/L Sb, and had circum-neutral pH values because of the buffering capacity of abundant Ca- and Mg-carbonates. The concentrations of Sb in several household wells are a cause for concern, exceeding the Sb drinking water limit of 5 μg/L by as much as 25 times. Some attenuation of the As and Sb concentrations in mine and impoundment waters was expected because of the deposition of metalloids onto hydrous ferric oxides built up below adit entrances and impoundment discharges. These HFOs contained >20 wt.% As and 1.5 wt.% Sb. Stream sediments and soils have also been contaminated by As and Sb with the peak concentrations generally found near open adits and mine wastes. In addition to the discharged waters from open adits, the significant source of As and Sb contamination are waste-rock dumps and tailings impoundments. Leachates from mine wastes contained as much as 8400 μg/L As and 4060 μg/L Sb, suggesting that the mine wastes would have a great potential to contaminate the downstream environment. Moreover, the results of water leaching tests showed that Sb was released from the solids more efficiently than As under oxidizing conditions. This might partly explain the predominance of Sb over As in most water samples.     

Relative spatial soil geochemical variability along two transects across the United States and Canada

To support the development of protocols for the proposed North American Soil Geochemical Landscapes project, whose objective is to establish baselines for the geochemistry of North American soils, two continental-scale transects across the United States and Canada were sampled in 2004. The sampling employed a spatially stratified random sampling design in order to estimate the variability between 40-km linear sampling units, within them, at sample sites, and due to sample preparation and analytical chemical procedures. The 40-km scale was chosen to be consistent with the density proposed for the continental-scale project. The two transects, north–south (N–S) from northern Manitoba to the USA–Mexico border near El Paso, Texas, and east–west (E–W) from the Virginia shore north of Washington, DC, to north of San Francisco, California, closely following the 38th parallel, have been studied individually. The purpose of this study was to determine if statistically significant systematic spatial variation occurred along the transects. Data for 38 major, minor and trace elements in A- and C-horizon soils where less than 5% of the data were below the detection limit were investigated by Analysis of Variance (ANOVA). A total of 15 elements (K, Na, As, Ba, Be, Ce, La, Mn, Nb, P, Rb, Sb, Th, Tl and W) demonstrated statistically significant (p < 0.05) variability at the between-40-km scale for both horizons along both transects. Only Cu failed to demonstrate significant variability at the between-40-km scale for both soil horizons along both transects.The patterns of relative variability differ by transect and horizon. The N–S transect A-horizon soils show significant between-40-km scale variability for 29 elements, with only 4 elements (Ca, Mg, Pb and Sr) showing in excess of 50% of their variability at the within-40-km and ‘at-site’ scales. In contrast, the C-horizon data demonstrate significant between-40-km scale variability for 26 elements, with 21 having in excess of 50% of their variability at the within-40-km and ‘at-site’ scales. In 36 instances, the ‘at-site’ variability is statistically significant in terms of the sample preparation and analysis variability. It is postulated that this contrast between the A- and C- horizons along the N–S transect, that is dominated by agricultural land uses, is due to the local homogenization of Ap-horizon soils by tillage reducing the ‘at-site’ variability. The spatial variability is distributed similarly between scales for the A- and C-horizon soils of the E–W transect. For all elements, there is significant variability at the within-40-km scale. Notwithstanding this, there is significant between-40-km variability for 28 and 20 of the elements in the A- and C-horizon data, respectively. The differences between the two transects are attributed to (1) geology, the N–S transect runs generally parallel to regional strikes, whereas the E–W transect runs across regional structures and lithologies; and (2) land use, with agricultural tillage dominating along the N–S transect. The spatial analysis of the transect data indicates that continental-scale maps demonstrating statistically significant patterns of geochemical variability may be prepared for many elements from data on soil samples collected on a 40 × 40 km grid or similar sampling designs resulting in a sample density of 1 site per 1600 km².     

National-Scale Geochemical Mapping Projects in China

Regional, national and global scale geochemical mapping projects have been carried out in China since the late 1970s, due to the development of cost‐effective, low detection limit analytical methods. These projects have provided a huge mass of high‐quality, informative and comparable data for mineral resource exploration and are now making contributions to environmental assessment. In this paper, four national‐scale geochemical mapping projects are described. (1) The Regional Geochemistry‐National Reconnaissance Project (RGNR project), which is China's largest national geochemical mapping project, has covered 6 million km² of upland regions since 1978. Generally, stream sediment samples were collected at a density of 1/km² and four samples were composited into one sample and analysed for thirty‐nine elements. (2) The deep‐penetrating geochemical mapping project (DEEPMAP Project) has been conducted since 1994 in covered terrains, including sedimentary basins, at a density of 1 sample per 100 km² with thirty to seventy elements determined per sample. In the past 10 years, an area of approximately 800 000 km² has been covered and this project has played an important role in finding sandstone‐type uranium deposits in basins. (3) The seventy‐six geochemical element mapping project (76 GEM project) has been carried out since 1999 and involved the collection of stream sediment samples from the RGNR project targets which were analysed for seventy‐six elements. Samples from each 1:50 000 map sheet were composited into one analytical sample (approximately one composite sample per 400 km²). Approximately 1 million km² have been surveyed to date. (4) The multi‐purpose eco‐geochemical mapping project has been conducted since 1999 in Quaternary plain areas for environmental and agricultural applications. Surface soils (depths from 0–20 cm) were collected at a density of one sample per km², and four samples were composited into one for analysis. Deep soils (from a depth of 150 to 200 cm) were collected at a density of one sample per 4 km² and four samples were composited into one analytical sample. All the composite samples were analysed for fifty‐four elements.     

平原区中大比例尺土壤地球化学调查采样方法--浙江省平湖市试验研究

文章以浙江省平湖市为典型三角洲平原区,开展了多种尺度、不同采样方法的对比试验。结果表明,田块内土壤元素分布较为均匀,小范围内元素的空间分异性较小,而田块之间土壤元素含量差异性明显增加;Hg,Cd等典型污染元素空间分异性较强,而人为污染扰动较弱的元素的空间分布较为均一;不同采样方法取得的区域性资料,其统计值接近,空间分布模式也相似,但有些元素仍有较明显差异。因此,中大比例尺地球化学调查时,应根据调查研究的目标任务,充分考虑地块分布、土壤类型和土地利用方式,选择合理的采样点。土壤样品可采取多坑点采集、多子样组合的方式,以保证样品的代表性,同时减少分析测试工作量。     

Deep-penetrating geochemistry for sandstone-type uranium deposits in the Turpan–Hami basin, north-western China

The Turpan–Hami basin, covering an area of approximately 50,000 km² in NW China, contains concealed sandstone-type U deposits in a Jurassic sequence of sandstone, mudstone and coal beds. Sampling of soil profiles over the Shihongtan concealed U deposit in this basin shows that fine-grained soil collected from the clay-rich horizon contains U concentrations three times higher than similar soils at background areas. Selective leaching studies of these soils show that U is mainly associated with clay minerals, which comprise from 17.9% to 40% (average 30.4%) of the total mineral content. This may indicate that U is converted to uranyl ions [UO₂]²⁺ under oxidizing conditions and is sorbed on clay minerals to accumulate in anomalous concentrations. Fine-grained soil (<120 mesh, <0.125 mm) from the clay-rich horizon, generally occurring at a depth of 0–40 cm, is shown to be an effective sampling medium for deep-penetrating geochemical surveys. A wide-spaced geochemical survey at a density of approximately 1 site per 100 km² was carried out throughout the whole basin using this sampling medium. Samples were analyzed for 30 elements by ICP-MS following a 4-acid extraction. Three large-scale geochemical anomalies of U and Mo were delineated over the whole basin. One of the anomalies is consistent with the known U deposit at Shihongtan in the western part of the basin. A new potential target in the eastern part of the basin was selected for a follow-up survey at a density of 1 sample per 4 km². A drilling exploration programme at the center of the geochemical anomaly delineated by this follow-up survey discovered a new U deposit.     

Downstream changes in antimony and arsenic speciation in sediments at a mesothermal gold deposit in British Columbia,Canada

This study investigates Sb speciation in sediments along the drainage of the Upper Peter adit at the Bralorne Au mine in southern British Columbia, Canada, and compares the behavior of Sb with that of As. The Upper Peter mineralization consists of native Au in quartz-carbonate veins with 1 wt.% sulfides dominated by pyrite and arsenopyrite although stibnite, the primary Sb-bearing sulfide mineral, can be locally significant. Dissolved Sb concentrations can reach up to 349 μg L⁻¹ in the mine pool. Sediments were collected for detailed geochemical and mineralogical characterization at locations along the 350-m flow path, which includes a 100-m shallow channel within the adit, a sediment settling pond about 45 m beyond the adit portal and an open wetland another 120 m farther downstream. From the mine pool to the wetland outlet, dissolved Sb in the drainage drops from 199 μg L⁻¹ to below the detection limit due to the combined effect of dilution and removal from solution. Speciation analyses using X-ray absorption near-edge structure (XANES) spectroscopy indicate that Sb(III)–S accounts for around 70% of total Sb in the sediments in the main pool at the far end of the adit. At a short distance (24 m) downstream of the main adit pool, however, Sb(III)–O and Sb(V)–O species represent ?50% of total Sb in the bulk sediments, indicating significant oxidation of the primary sulfides inside the adit. Although Sb appears largely oxidized in the bulk samples collected near the portal, Sb(III)–S species are nevertheless present in the <53-μm fraction, suggesting a higher oxidation rate for stibnite in the coarser grains, possibly due to galvanic interaction with pyrite. Secondary Sb species released from the sulfide oxidation are most likely sorbed/co-precipitated with Fe-, Mn-, and Al-oxyhydroxides along the flow channel in the adit and in the sediment settling pond, with the Fe phase being the dominant sink for Sb.     

Low-density geochemical mapping in Hungary

Guidelines for a low-density geochemical survey were described in 1990 by the Western European Geological Surveys. A low-density geochemical survey of Hungary was carried out in 1991–1995. The results are useful for future surveys and for the IGCP 360 project ‘Global Geochemical Baseline’. In regions with well-developed drainage systems in Hungary, 196 catchment basins of approx. 400 km² were delineated and flood-plain deposits sampled at their outlets. The samples were taken from 0 to 10 cm and from 50 to 60 cm depths. Samples were analysed by ICP-AES and AAS techniques in two laboratories. A Geochemical Atlas of Hungary is in preparation that will show the distribution of 25 elements in the two sampled layers. Maps for the lower layer represent regional geochemical baseline values and a geochemical subdivision of the country (maps showing the distribution of element associations) was made on the basis of factor variables. Maps constructed from the data of the upper sampling level show us the present state of contamination of the surface. The results of this survey have contributed to the establishment of guidance values for soils prepared by the Hungarian Ministry of the Environment in 1995. Safe levels were established for As, Cd, Cr, Cu, Hg, Pb and Zn and regional environmental loads plotted. Differences between the median values of the two levels are generally small. However, the concentrations of certain elements like P, Pb and S are significantly greater in the upper layer reflecting contamination from agriculture. In certain regions, the rate of sedimentation was fairly fast such that the environmental effects of ore mining in Transylvania and southern Slovakia as well as those of heavy industry in northern Hungary can be observed in samples from the lower level. The main factor controlling the geochemical pattern in Hungary is the predominance of young (Pleistocene or Miocene) clastic sediments at the surface. Approx. 90% of the surface is covered by these young sediments. This kind of survey has the disadvantage of not providing enough contrast to differentiate geologically dissimilar areas but it has the advantage to provide regional surface background geochemical data and it helps to outline areas of possible surface contamination. Based on the results of this survey we conclude that it would be much better to sample smaller, but geologically homogeneous areas in mountainous terrain to obtain data characteristic of the geochemical background of lithologic units. This approach would mean a sampling density of a few tens of km²/sample for hilly areas, and a few hundred km²/sample for lowland areas.     

Lanthanoid behaviour in an acidic landscape

Lanthanoids were studied in a boreal landscape where an abundance of acid sulfate soils and Histosols provide a unique opportunity to increase the understanding of how these metals behave in acidic soils and waters and interact with soil and aqueous organic matter. In the acid sulfate soils lanthanoids are mobile as reflected in high to very high concentrations in soil water and runoff (typically a few mg l⁻¹ but up to 12 mg l⁻¹) and abundant release by several relatively weak extractants (ammonium acetate EDTA, sodium pyrophosphate, hydroxylamine hydrochloride) applied on bulk soil. Normalisation with the lanthanoid pool in the underlying parent materials (sulphide-bearing sediments deposited in brackish-water) and soil water showed that the extensive release/retention in the acidic soil was accompanied by large, and variable, fractionation trends across the lanthanoid series. In low-order streams draining these soils, the lanthanoid concentrations were high and, as indicated by frontal ultrafiltration and geochemical modelling, largely dissolved (<1 kDa) in the form of the species LnSO₄⁺ and Ln³⁺. In other moderately acidic stream waters (pH 4.3-4.6), organic complexation was predicted to be important in the <1 kDa fraction (especially for the heavy lanthanoids) and strongly dominating in the colloidal phase (1 kDa-0.45 μm). Along the main stem of a stream in focus (catchment area of 223 km²), lanthanoid concentrations increased downstream, in particular during high flows, caused by a downstream increase in the proportion of acid sulfate soils which are extensively flushed during wet periods. The geochemical models applied to the colloidal Ln-organic phase were not successful in predicting the measured fractionation patterns.     

The variety of lithologies in the Yamato-86032 lunar meteorite: Implications for formation processes of the lunar crust

We performed a petrologic, mineralogical, geochemical, and isotopic study of several lithologies in the Y-86032 feldspathic breccia. This study leads us to conclude that Y-86032 likely originated on the lunar farside. Y-86032 is composed of several types of feldspathic clasts, granulitic breccias, and minor basaltic clasts set in a clastic matrix. We identify an “An97 anorthosite” that has An contents similar to those of nearside FANs. Mg′ (= molar Mg/(Mg + Fe) × 100) values vary significantly from ∼45 to ∼80 covering the ranges of both nearside FANs and the Mg′ gap between FANs and the Mg-suite. A light-gray feldspathic (LG) breccia making up ∼20% of the investigated slab (5.2 × 3.6 cm²) mainly consists of fragments of anorthosites (“An93 anorthosite”) more sodic than nearside FANs. LG also contains an augite-plagioclase clast which either could be genetically related to the An93 anorthosite or to slowly-cooled basaltic magma intruded into the precursor rock. The Na-rich nature of both An93 anorthosite and this clast indicates that the LG breccia was derived from a relatively Na-rich but incompatible-element-poor source. The Mg′ variation indicates that the “An97 anorthosite” is a genomict breccia of several types of primary anorthosites. Granulitic breccias in Y-86032 have relatively high Mg′ in mafic minerals. The highest Mg′ values in mafic minerals for the “An97 anorthosite” and granulitic breccias are similar to those of Mg-rich lithologies recently described in Dhofar 489. Basaltic clasts in the dark-gray matrix are aluminous, and the zoning trends of pyroxene are similar to those of VLT or LT basalts. The crystallization of these basaltic clasts pre-date the lithification age of the clastic matrix at ∼3.8 Ga. The low K contents of plagioclase in both the anorthositic and basaltic clasts and generally low incompatible element abundances in all the lithologies in Y-86032 indicate that KREEP was not involved during the formation of the precursor lithologies. This observation further suggests that urKREEP did not exist in the source regions of these igneous lithologies. All these facts support the idea that Y-86032 was derived from a region far distant from the PKT and that the lithic clasts and fragments are indigenous to that region. An An97 anorthositic clast studied here has distinct Sm-Nd isotopic systematics from those previously found for another An97 anorthositic clast and “An93 anorthosite”, and suggests either that An97 anorthosites come from isotopically diverse sources, or that the Sm-Nd isotopic systematics of this clast were reset ∼4.3 Ga ago. These lines of geochemical, isotopic, and petrologic evidence suggest that the lunar crust is geochemically more heterogeneous than previously thought.     

Fate and groundwater impacts of produced water releases at OSPER “B” site,Osage County,Oklahoma

For the last 5 a, the authors have been investigating the transport, fate, natural attenuation and ecosystem impacts of inorganic and organic compounds in releases of produced water and associated hydrocarbons at the Osage-Skiatook Petroleum Environmental Research (OSPER) “A” and “B” sites, located in NE Oklahoma. Approximately 1.0 ha of land at OSPER “B”, located within the active Branstetter lease, is visibly affected by salt scarring, tree kills, soil salinization, and brine and petroleum contamination. Site “B” includes an active production tank battery and adjacent large brine pit, two injection well sites, one with an adjacent small pit, and an abandoned brine pit and tank battery site. Oil production in this lease started in 1938, and currently there are 10 wells that produce 0.2–0.5 m³/d (1–3 bbl/d) oil, and 8–16 m³/d (50–100 bbl/d) brine. Geochemical data from nearby oil wells show that the produced water source is a Na–Ca–Cl brine (∼150,000 mg/L TDS), with high Mg, but low SO₄ and dissolved organic concentrations. Groundwater impacts are being investigated by detailed chemical analyses of water from repeated sampling of 41 boreholes, 1–71 m deep. The most important results at OSPER “B” are: (1) significant amounts of produced water from the two active brine pits percolate into the surficial rocks and flow towards the adjacent Skiatook reservoir, but only minor amounts of liquid petroleum leave the brine pits; (2) produced-water brine and minor dissolved organics have penetrated the thick (3–7 m) shale and siltstone units resulting in the formation of three interconnected plumes of high-salinity water (5000–30,000 mg/L TDS) that extend towards the Skiatook reservoir from the two active and one abandoned brine pits; and (3) groundwater from the deep section of only one well, BR-01 located 330 m upslope and west of the site, appear not to be impacted by petroleum operations.     

Influence of geological setting on geochemical baselines of trace elements in soils. Application to soils of South–West Spain

A collection of 235 samples were taken from 115 sites (representing a density of 1 sampling site ca. 130 km²) on rural soils derived from the major rock types in the southern Iberian Massif. The geochemical baselines of selected trace elements (As, Co, Cr, Cu, Ni, Pb and Zn) were determined on the < 2 mm soil fraction. The sampling sites were not directly influenced by external pollution. Soil geochemical baseline and threshold values were calculated for each element in two geologically different zones: the Ossa-Morena Zone (OMZ) and the South-Portuguese Zone (SPZ).     

A δS isoscape of total sulphur in soils across Northern Ireland

A map of the spatial variation in isotopic composition of a substrate, or isoscape, provides a tool to address a range of research questions, such as the use of isotope fingerprinting to identify the origin of compounds. The focus of this study was to establish a soil S isotope map for Northern Ireland in order to investigate spatial variability within the isotopic composition of total soil sulphur (S). The sample resolution was about one sample every 141 km². δ³⁴S values were grouped based on soil type and soil parent material. Total soil S δ³⁴S data were grouped according to soil type, to evaluate whether a soil’s characteristics affect its isotopic composition. Gleyed soils had a mean δ³⁴S value of +6.3 ± 6.1‰, lower than the means for other soil types. A trend towards higher δ³⁴S values (mean δ³⁴S of +13.8 ± 6.0‰) was observed in soils with a high organic matter content. No trends in δ³⁴S value were observed for other soil types. There were no discernible correlations between total soil S δ³⁴S and soil parent material, with the exception of shale and mudstones. The majority of soils derived from shale and mudstones had δ³⁴S values at or close to the mean of +4.9‰. A spatially coherent pattern of relatively high soil total S δ³⁴S values in the west and north, and low in the SE, is discernible in Northern Ireland. Based on the observed spatial distribution, it has been concluded that the quantity and source (anthropogenic or marine) of wet atmospheric S deposition is a controlling factor on regional variation of soil δ³⁴S in Northern Ireland. This S isoscape will assist studies of S cycling in Northern Ireland and may assist in the creation of an ‘isotopic fingerprint’ for a potential ‘input’ source needed to interpret data in traceability studies.     

A national-scale geochemical and mineralogical survey of soils of the conterminous United States

In 2007, the US Geological Survey initiated a low-density (1 site per 1600 km², c. 4800 sites) geochemical and mineralogical survey of soils of the conterminous USA. The ideal sampling protocol at each site includes a sample from 0–5 cm depth, a composite of the soil A horizon, and a sample from the soil C horizon. The <2-mm fraction of each sample is analyzed for Al, Ca, Fe, K, Mg, Na, S, Ti, Ag, Ba, Be, Bi, Cd, Ce, Co, Cr, Cs, Cu, Ga, In, La, Li, Mn, Mo, Nb, Ni, P, Pb, Rb, Sb, Sc, Sn, Sr, Te, Th, Tl, U, V, W, Y and Zn by inductively coupled plasma-mass spectrometry and inductively coupled plasma-atomic emission spectrometry following a near-total digestion in a mixture of HCl, HNO₃, HClO₄ and HF. Separate methods are used for As, Hg, Se and total C on this same size fraction. The major mineralogical components are determined by a quantitative X-ray diffraction method. Sampling was completed in 2010 with chemical and mineralogical analysis currently underway. Preliminary results for a swath from the central USA to Florida clearly show the effects of soil parent material and climate on the chemical and mineralogical composition of soils. A sample archive will be established and made available for future investigations.     

Mercury, arsenic, antimony, bismuth and boron as geochemical indicators for geothermal areas

From 1982 to 1983, 131 soil samples were collected within an area of 60 km² in known geothermal field and their vicinities in Tengchong, Yunnan Province. Distinct anomalies of Hg, As, Sb and Bi were found on the known geothermal fields. The contour of the multiplicative anomaly of Hg × As × Sb encircled the two known geothermal fields, Reshuitang and Rehai, within its extent, disclosing the interrelation between these two fields, and enlarging their future prospects. The B anomaly is related to structural features. Significant correlations among Hg, As and Sb are shown by correlation analysis. It was concluded that a geochemical survey with a density of two samples per km² could be carried out effectively to delineate promising targets of geothermal resources.     

吉林中西部地区土壤有机碳储量及其时空变化特征

利用多目标区域地球化学调查的实测数据,估算了吉林中西部地区表层土壤的有机碳密度和储量.结果表明,在不同深度的分布层次上,表层(0～0.2m)土壤对有机碳的积累较弱,SOC储量占到全层(0～1.8m)储量的23.8%,中上层(0～1.Om)储量则占到全层储量的95.7%.从上壤类型看,表层SOC密度较高的有暗棕壤(636...     

In situ Atomic Force Microscopy study of dissolution of the barite (0 0 1) surface in water at 30 °C

The dissolution behavior of the barite (0 0 1) surface in pure water at 30 °C was investigated using in situ Atomic Force Microscopy (AFM), to better understand the dissolution mechanism and the microtopographical changes that occur during the dissolution, such as steps and etch pits. The dissolution of the barite (0 0 1) surface started with the slow retreat of steps, after which, about 60 min later, the <hk0> steps of one unit cell layer or multi-layers became two-step fronts (fast “f” and slow “s” steps) with a half-unit cell layer showing different retreat rates. The “f” step had a fast retreat rate (≈(14 ± 1) × 10⁻² nm/s) and tended to have a jagged step edge, whereas the “s” step (≈(1.8 ± 0.1) × 10⁻² nm/s) had a relatively straight front. The formation of the “f” steps led to the formation of a new one-layer step, where the front of the “s” step was overtaken by that of the immediate underlying “f” step. The “f” steps also led to the decrease of the <hk0> steps and the increase in the percentage of stable steps parallel to the [0 1 0] direction during the dissolution.Etch pits, which could be observed after about 90 min, were of three types: triangular etch pits with a depth of a half-unit cell, shallow etch pits, and deep etch pits. The triangular etch pits were bounded by the step edges parallel to [0 1 0], [1 2 0], and [] and had opposite orientations in the upper half and lower half layers. Shallow etch pits that had a depth of two or more half-unit cell layers had any two consecutive pits pointing in the opposite direction of each other. The triangular etch pit appeared to grow by simultaneously removal of a row of ions parallel to each direction from the three step edges. At first, deep etch pits were elongated in the [0 1 0] direction with a curved outline and then gradually developed to an angular form bounded by the {1 0 0}, {3 1 0}, and (0 0 1) faces. The retreat rate of the (0 0 1) face was much slower than those of the {1 0 0} and {3 1 0} and tended to separate into two rates ((0.13 ± 0.01) × 10⁻² nm/s for the deep etch pits derived from a screw dislocation and (0.07 ± 0.01) × 10⁻² nm/s for those from other line defects).The changes in the dissolution rate of a barite (0 0 1) surface during the dissolution were estimated using the retreat rates and densities of the various steps as well as the growth rates, density, and areas of the lateral faces of the deep etch pits that were obtained from this AFM analysis. Our results showed that the dissolution rate of the barite (0 0 1) surface gradually increased and approached the bulk dissolution rate because of the change in the main factor determining the dissolution rate from the density of the steps to the growth and the density of the deep etch pits on the surface.     

The isotopic evolution of atmospheric Pb in central Ontario since AD 1800, and its impacts on the soils, waters, and sediments of a forested watershed, Kawagama Lake

A peat core from an ombrotrophic bog documents the isotopic evolution of atmospheric Pb in central Ontario since AD 1804 ± 53 (²¹⁰Pb dating). Despite the introduction of unleaded gasoline in the mid-1970’s, the ratio ²⁰⁶Pb/²⁰⁷Pb in atmospheric deposition has not increased as expected, but rather continues to decline. In fact, snowpack sampling (2005 and 2009) and rainwater samples (2008) show that the isotopic composition of atmospheric Pb today is often far less radiogenic than the gasoline lead that had been used in Canada in the past. The peat, snow, and rainwater data presented here are consistent with the Pb isotope data for aerosols collected in Dorset in 1984 and 1986 which were traced by Sturges and Barrie (1989) to emissions from the Noranda smelter in northern Quèbec, Canada’s largest single source of atmospheric Pb. Understanding atmospheric Pb deposition in central Ontario, therefore, requires not only consideration of natural sources and past contributions from leaded gasoline, but also emissions from metal smelting and refining.Lead in the streams which enter Kawagama Lake today (²⁰⁶Pb/²⁰⁷Pb = 1.16 − 1.19) represents a mixture between the natural values (1.191 − 1.201 estimated using pre-industrial lake sediments) and the values found in the humus layer of the surrounding forest soils (²⁰⁶Pb/²⁰⁷Pb = 1.15 − 1.19). In the lake itself, however, Pb is much less radiogenic (²⁰⁶Pb/²⁰⁷Pb as low as 1.09) than in the streams, with the dissolved fraction less radiogenic than particulate material. The evolution of Pb isotope ratios within the watershed apparently reflects preferential removal by sedimentation of comparatively dense, radiogenic, terrestrial particles (derived from the mineral fraction of soils) from the humus particles with lower ratios of ²⁰⁶Pb/²⁰⁷Pb (because of atmospheric Pb contamination). Despite the contemporary enrichments of Pb in rain and snow, concentrations of dissolved Pb in the lake are extremely low (sometimes below 10 ng/l), with Pb concentrations and Pb/Sc ratios approaching “natural” values because of efficient binding to particles, and their subsequent removal in the watershed.     

The potential of mid- and near-infrared diffuse reflectance spectroscopy for determining major- and trace-element concentrations in soils from a geochemical survey of North America

In 2004, soils were collected at 220 sites along two transects across the USA and Canada as a pilot study for a planned soil geochemical survey of North America (North American Soil Geochemical Landscapes Project). The objective of the current study was to examine the potential of diffuse reflectance (DR) Fourier Transform (FT) mid-infrared (mid-IR) and near-infrared (NIRS) spectroscopy to reduce the need for conventional analysis for the determination of major and trace elements in such continental-scale surveys. Soil samples (n = 720) were collected from two transects (east–west across the USA, and north–south from Manitoba, Canada to El Paso, Texas (USA), n = 453 and 267, respectively). The samples came from 19 USA states and the province of Manitoba in Canada. They represented 31 types of land use (e.g., national forest, rangeland, etc.), and 123 different land covers (e.g., soybeans, oak forest, etc.). The samples represented a combination of depth-based sampling (0–5 cm) and horizon-based sampling (O, A and C horizons) with 123 different depths identified. The set was very diverse with few samples similar in land use, land cover, etc. All samples were analyzed by conventional means for the near-total concentration of 49 analytes (C_total, C_carbonate and C_organic, and 46 major and trace elements). Spectra were obtained using dried, ground samples using a Digilab FTS-7000 FT spectrometer in the mid- (4000–400 cm⁻¹) and near-infrared (10,000–4000 cm⁻¹) at 4 cm⁻¹ resolution (64 co-added scans per spectrum) using a Pike AutoDIFF DR autosampler. Partial least squares calibrations were develop using: (1) all samples as a calibration set; (2) samples evenly divided into calibration and validation sets based on spectral diversity; and (3) samples divided to have matching analyte concentrations in calibration and validation sets. In general, results supported the conclusion that neither mid-IR nor NIRS would be particularly useful in reducing the need for conventional analysis of soils from this continental-scale geochemical survey. The extreme sample diversity, likely caused by the widely varied parent material, land use at the site of collection (e.g., grazing, recreation, agriculture, etc.), and climate resulted in poor calibrations even for C_total, C_organic and C_carbonate. The results indicated potential for mid-IR and NIRS to differentiate soils containing high concentrations (>100 mg/kg) of some metals (e.g., Co, Cr, Ni) from low-level samples (<50 mg/kg). However, because of the small number of high-level samples, it is possible that differentiation was based on factors other than metal concentration. Results for Mg and Sr were good, but results for other metals examined were fair to poor, at best. In essence, it appears that the great variation in chemical and physical properties seen in soils from this continental-scale survey resulted in each sample being virtually unique. Thus, suitable spectroscopic calibrations were generally not possible.