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 31 毫秒
1.
Mountain soils store huge amounts of carbon which may be highly vulnerable to the strong land use and climate changes that mountain areas currently experience worldwide. Here, we tested the Rock–Eval (RE) pyrolysis as a proxy technique to (i) quantify soil organic carbon (SOC) stocks, (ii) bring insights into SOC bulk chemistry and (iii) investigate biogeochemical stability at the landscape scale in a mountain area of the French calcareous Prealps. A total of 109 soils from 11 eco-units representing the variety of ecosystems of the study area were analyzed with RE pyrolysis. RE pyrolysis showed an excellent predictive performance (R2 = 0.99) for SOC content even in calcareous soils. The technique revealed specific chemical fingerprints for some eco-units and soil types, with decreasing hydrogen index values from Anthroposols (425 ± 62 mg HC/g SOC) to Umbrisols, Leptosols (311 ± 49 mg HC/g SOC) and to Cambisols (278 ± 35 mg HC/g SOC), associated with an increase in SOC maturation. Newly developed RE pyrolysis indices revealed the high stability of SOC in most eco-units developed on Cambisols (acidic grasslands, alpine meadows, bushy facies) and a significantly lower stability of SOC in mountain ridges, sheepfold areas and coniferous forest soils. The persistence of SOC in this mosaic of ecosystems may depend not only on its chemistry or thermal stability, but also on local environmental factors such as climatic conditions or pH, especially for high altitude soils. Overall, RE pyrolysis appears as an appropriate tool for landscape scale carbon inventories and could become a standardized proxy for assessing the vulnerability of SOC stocks.  相似文献   

2.
Soil inorganic carbon (SIC) and organic carbon (SOC) levels can change with forest development, however, concurrent changes in soil carbon balance and their functional differences in regulating soil properties are unclear. Here, SIC, SOC, and other physicochemical properties of soil (N, alkali-hydrolyzed N, effective Si, electrical conductivity, pH, and bulk density) in 49 chronosequence plots of larch plantation forests were evaluated, by analyzing the concurrent changes in SIC and SOC storage during growth of plantation and the functional difference of these levels in maintaining soil sustainability. These soils had characteristically high SOC (15.34 kg m?2) and low SIC storage (83.38 g m?2 on average). Further, 28 of 30 linear regressions between SIC and SOC storage and larch growth parameters (age, tree size, and biomass density) were not statistically significant (p > 0.05). However, significant changes were observed in ratios of SIC and SOC with these growth parameters (between 0–40 cm and 40–80 cm, respectively; p < 0.05). These results were more useful for determining the changes in SIC and SOC vertical distribution than changes in storage. Moreover, larch growth generally decreased SIC and increased SOC. Linear correlation and multiple-regression analysis showed that the SIC influences soil acidity, whereas SOC affects soil nitrogen. This clearly indicates that larch growth could result in divergent changes in SIC and SOC levels, particularly in their vertical distribution; further, changes in SIC and SOC may variably affect soil physicochemical properties.  相似文献   

3.
Oxygen isotope systematics for co-existing pairs of gem-spinel and calcite in marble from Vietnam and other worldwide deposits have been determined in order to characterize the O-isotope fractionation between calcite and spinel. In Vietnam, the Δ18Occ–sp (= 3.7 ± 0.1‰ for six samples from the An Phu and Cong Troi deposits) is remarkably constant. The combination of these data with those obtained on calcite–spinel pairs of Paigutan (Nepal, n = 2), Ipanko (Tanzania, n = 1), and Mogok (Myanmar, = 2) are also consistent with an overall Δ18Occ–sp of 3.6 ± 0.3‰ for all the spinel samples (n = 11). The straight line correlation δ18Occ = 0.96 δ18Osp + 4.4 is excellent despite their worldwide geographic spread. The increment method of calculating oxygen isotope fractionation gave a geologically unreasonable temperature of formation for both minerals at 1374 °C when compared to temperatures obtained by mineral assemblage equilibrium of these marble type deposits, between 610 and 750 °C. The constant Δ18Occ–sp reflects a constant temperature for this amphibolite facies assemblage, whose current best estimate is calculated at 620 ± 40 °C, but unquantified uncertainties remain.  相似文献   

4.
Soil organic carbon (SOC) storage and erosion in South China at the regional scale in the past decades remains far from being understood. This paper calculated the SOC density, storage and erosion in 14 soil classes in Guangdong Province, South China, based on statistical data from the soil survey and soil erosion survey of Guangdong, which was performed in the 1990s. The purpose of this study is to understand the relationships between soil classes and SOC erosion at the regional scale. The results indicated that the SOC density in the soils of Guangdong varied from 12.7 to 144.9 Mg ha?1 over the entire profile and from 12.6 to 68.4 Mg ha?1 in the top 20-cm soil layer. The average area-weighted SOC density in the topsoil (0–20 cm) and the entire profile was 32 ± 3 and 86 ± 4 Mg ha?1, respectively. The total SOC storage was 1.27 ± 0.06 Pg, with 35.6 % (0.46 ± 0.04 Pg) located in the topsoil. The average area-weighted strength of the SOC erosion in the 1990s was 20.6 ± 0.8 Mg km?2 year?1. The results indicated that SOC erosion was strongly related to soil class.  相似文献   

5.
The main limiting factor in obtaining precise and accurate uranium-series (U-series) ages of corals that lived during the last few hundred years is the ability to constrain and correct for initial thorium-230 (230Th0), which is proportionally much higher in younger samples. This is becoming particularly important in palaeoecological research where accurate chronologies, based on the 230Th chronometer, are required to pinpoint changes in coral community structure and the timing of mortality events in recent time (e.g. since European settlement of northern Australia in the 1850s). In this study, thermal ionisation mass spectrometry (TIMS) U-series dating of 43 samples of known ages collected from living Porites spp. from the far northern, central and southern inshore regions of the Great Barrier Reef (GBR) was performed to spatially constrain initial 230Th/232Th (230Th/232Th0) variability. In these living Porites corals, the majority of 230Th/232Th0 values fell within error of the conservative bulk Earth 230Th/232Th atomic value of 4.3 ± 4.3 × 10?6 (2σ) generally assumed for 230Th0 corrections where the primary source is terrestrially derived. However, the results of this study demonstrate that the accuracy of 230Th ages can be further improved by using locally determined 230Th/232Th0 values for correction, supporting the conclusion made by Shen et al. (2008) for the Western Pacific. Despite samples being taken from regions adjacent to contrasting levels of land modification, no significant differences were found in 230Th/232Th0 between regions exposed to varying levels of sediment during river runoff events. Overall, 39 of the total 43 230Th/232Th0 atomic values measured in samples from inshore reefs across the entire region show a normal distribution ranging from 3.5 ± 1.1 to 8.1 ± 1.1 × 10?6, with a weighted mean of 5.76 ± 0.34 × 10?6 (2σ, MSWD = 8.1). Considering the scatter of the data, the weighted mean value with a more conservative assigned error of 25% (i.e. 5.8 ± 1.4 × 10?6) that encompasses the full variation of the 39 230Th/232Th0 measurements is recommended as a more appropriate value for initial 230Th corrections for U-series dating of most Porites samples from inshore regions of the GBR. This will result in significant improvement in both the precision and accuracy of the corrected 230Th ages related to those based on the assumed bulk Earth 230Th/232Th0 value of 4.3 ± 4.3 × 10?6. However, several anomalously high 230Th/232Th0 values reaching up to 28.0 ± 1.6 × 10?6 occasionally found in some coral annual bands coinciding with El Niño years imply high 230Th/232Th0 sources and highlight the complexities of understanding 230Th/232Th0 variability. For U-series dating of young coral samples from such sites where anomalous 230Th/232Th0 values occur, we suggest replicate dating of multiple growth bands with known age difference to verify age accuracy.  相似文献   

6.
Effective radium-226 concentration (ECRa) has been measured in soil samples from seven horizontal and vertical profiles of terrace scarps in the northern part of Kathmandu Valley, Nepal. The samples belong to the Thimi, Gokarna, and Tokha Formations, dated from 50 to 14 ky BP, and represent a diverse fluvio-deltaic sedimentary facies mainly consisting of gravelly to coarse sands, black, orange and brown clays. ECRa was measured in the laboratory by radon-222 emanation. The samples (n = 177) are placed in air-tight glass containers, from which, after an accumulation time varying from 3 to 18 days, the concentration of radon-222, radioactive decay product of radium-226 and radioactive gas with a half-life of 3.8 days, is measured using scintillation flasks. The ECRa values from the seven different profiles of the terrace deposits vary from 0.4 to 43 Bq kg?1, with profile averages ranging from 12 ± 1 to 27 ± 2 Bq kg?1. The values have a remarkable consistency along a particular horizon of sediment layers, clearly demonstrating that these values can be used for long distance correlations of the sediment horizons. Widely separated sediment profiles, representing similar stratigraphic positions, exhibit consistent ECRa values in corresponding stratigraphic sediment layers. ECRa measurements therefore appear particularly useful for lithologic and stratigraphic discriminations. For comparison, ECRa values of soils from different localities having various sources of origin were also obtained: 9.2 ± 0.4 Bq kg?1 in soils of Syabru–Bensi (Central Nepal), 23 ± 1 Bq kg?1 in red residual soils of the Bhattar-Trisuli Bazar terrace (North of Kathmandu), 17.1 ± 0.3 Bq kg?1 in red residual soils of terrace of Kalikasthan (North of Trisuli Bazar) and 10 ± 1 Bq kg?1 in red residual soils of a site near Nagarkot (East of Kathmandu). The knowledge of ECRa values for these various soils is important for modelling radon exhalation at the ground surface, in particular in the vicinity of active faults. Importantly, the study also reveals that, above numerous sediments of Kathmandu Valley, radon concentration in dwellings can potentially exceed the level of 300 Bq m?3 for residential areas; a fact that should be seriously taken into account by the governmental and non-governmental agencies as well as building authorities.  相似文献   

7.
Pyrogenic carbon (PyC), a by-product of recurrent boreal wildfires, is an important component of the global soil C pool, although precise assessment of boreal PyC stock is scarce. The overall objective of this study was to estimate total C stock and PyC stock in forest floors of Eastern Canada boreal forests. We also investigated the environmental conditions controlling the stocks and characterized the composition of the forest floor layers. Forest floor samples were collected from mesic black spruce sites recently affected by fire (3–5 yr) and analyzed using elemental analysis and solid state 13C nuclear magnetic resonance (NMR) spectroscopy. PyC content was further estimated using a molecular mixing model. Total C stock in forest floors averaged 5.7 ± 2.9 kg C/m2 and PyC stock 0.6 ± 0.3 kg C/m2. Total stock varied with position in the landscape, with a greater accumulation of organic material on northern aspects and lower slope positions. In addition, total stock was significantly higher in spruce-dominated forest floors than stands where jack pine was present. The PyC stock was significantly related to the atomic H/C ratio (R2 0.84) of the different organic layers. 13C NMR spectroscopy revealed a large increase in aromatic carbon in the deepest forest floor layer (humified H horizon) at the organic-mineral soil interface. The majority of the PyC stock was located in this horizon and had been formed during past high severity fires rather than during the most recent fire event.  相似文献   

8.
Carbohydrates are major organic components of dung and are likely to contribute substantially to increased carbon stocks in manured soils. To investigate this hypothesis, a field-scale experiment was conducted on a temperate grassland site in Devon, UK. C4 dung (bulk δ13C value ?12.6‰) was applied to a temperate grassland C3 soil (bulk δ13C value ?30.3‰) in April and the surface soil beneath cow pats sampled at seven dates over a year. Total carbohydrates were extracted as their monosaccharide components and analysed as the alditol acetates using gas chromatography. The δ13C values of the major monosaccharides glucose (?11.5 ±0.6‰), xylose (?10.4 ±0.4‰), arabinose (?10.4 ±0.5‰) and galactose (?8.3 ±1.6‰) extracted from the C4 dung via acid hydrolysis were indicative of their source. Their weighted mean δ13C value was ?10.8‰, 1.8‰ more 13C-enriched than the bulk dung value. The δ13C values of individual monosaccharides recovered by acid hydrolysis in the 0–1 cm and 1–5 cm soil horizons beneath C4 cow pats, compared with control soils determined over 372 days, allowed assessment of the extent of incorporation and fluxes of dung-derived monosaccharides. A maximum of 60% of the dung C in soil was derived from carbohydrates after 56 days, declining to around 20% after 372 days. Incorporation dynamics varied between monosaccharide species. Glucose, xylose and arabinose behaved in a similar manner because of their predominantly plant cell wall derived provenance in the dung, whilst dung-derived galactose and mannose appeared to have a microbial source in the soil. The dynamics of total dung-derived monosaccharides in the top 5 cm was comparable to incorporation and flux of bulk dung C, previously estimated using bulk δ13C values. The movement of dung-derived carbohydrates into the soil was inequivalent between the 0–1 cm and 1–5 cm horizons. The lack of a significant difference in concentration, but the evidence for the persistence of dung-derived monosaccharides in soil based on δ13C values, indicated replacement of existing pools in the soil, suggesting that the ability of this particular soil to sequester further C derived from carbohydrates was limited.  相似文献   

9.
During the past 50 years, the amount of agricultural fertilizer used in Northern China increased from about 7.5 kg ha?1 in the 1950s to approximately 348 kg ha?1 in the 1990s. Given that little is known about the effects of nitrogen fertilization on soil labile carbon fraction in Northern China, this paper evaluated such effects in terms of microbial biomass and dissolved organic carbon in the Sanjiang Plain located in Northeast China. Soils with different cultivation time and undisturbed marsh with Deyeuxia angustifolia were selected to study the effects of nitrogen fertilization on the soil labile organic fractions microbial C (biomass C, microbial quotient, and basal respiration) and to estimate the contributions of nitrogen input on the dynamics of soil labile carbon. Continuous nitrogen application decreased total organic and dissolved organic carbon concentrations significantly, leading to the lack of carbon source for microbes. Therefore, continuous nitrogen fertilizer application induced negative effects on measured soil microbiological properties. However, a moderate nitrogen application rate (60 kg N ha?1) stimulated soil microbial activity in the short term (about 2 months), whereas a high nitrogen application rate (150 kg N ha?1) inhibited measured soil microbiological properties in the same period.  相似文献   

10.
This paper presents geochemical, Sr–Nd isotopic, and U–Pb zircon geochronological data on the Alvand plutonic complex in Sanandaj–Sirjan zone (SSZ), Western Iran. The gabbroic rocks show a trend of a calc-alkaline magma suite and are characterized by low initial 87Sr/86Sr ratios (0.7023–0.7037) and positive εNd(t) values (2.9–3.3), which suggest derivation from a moderately depleted mantle source. Geochemical features of the granites illustrate a high-K calc-alkaline magma series, whereas the leucocratic granitoids form part of a low-K series. Granites have intermediate 87Sr/86Sr ratios (0.707–0.719) and negative εNd(t) values (−1.0 to −3.4), while leucocratic granitoids have higher initial 87Sr/86Sr ratio (0.713–0.714) and more negative εNd(t) values (−3.5 to −4.5). Potential basement source lithologies for the granites are Proterozoic granites and orthogneisses, and those for the leucocratic granites are plagioclase-rich sources such as meta-arkoses or tonalites. The U–Pb dating results demonstrate that all granitoids were exclusively emplaced during the Jurassic instead of being Cretaceous or younger in age as suggested previously. The pluton was assembled incrementally over c. 10 Ma. Gabbros formed at 166.5 ± 1.8 Ma, granites between 163.9 ± 0.9 Ma and 161.7 ± 0.6 Ma, and leucocratic granitoids between 154.4 ± 1.3 and 153.3 ± 2.7 Ma. Granites and leucocratic granitoids show some A-type affinity. It is concluded that the Alvand plutonic complex was generated in a continental-arc-related extensional regime during subduction of Neo-Tethyan oceanic crust beneath the SSZ. The U/Pb zircon age data, recently corroborated by similar results in the central and southern SSZ, indicate that Jurassic granitoids are more areally extensive in this belt than previously thought.  相似文献   

11.
The Sirstan granitoid (SG), comprising diorite and granodiorite, is located in the Shalair Valley area, in the northeastern part of Iraq within the Sanandaj–Sirjan Zone (SSZ) of the Zagros Orogenic Belt. The U–Pb zircon dating of the SG rocks has revealed a concordia age of 110 Ma, which is interpreted as the age of crystallization of this granitoid body during the Middle Cretaceous. The whole-rock Rb–Sr isochron data shows an age of 52.4 ± 9.4 Ma (MSWD = 1.7), which implies the reactivation of the granitoid body in the Early Eocene due to the collision between the Arabian and Iranian plates. These rocks show metaluminous affinity with low values of Nb, Ta and Ti compared to chondrite, suggesting the generation of these rocks over the subduction zone in an active continental margin regime. The SG rocks are hornblende-bearing I-type granitoids with microgranular mafic enclaves. The positive values of ?Nd (t = 110 Ma) (+0.1 to +2.7) and the low (87Sr/86Sr)i ratios (0.7044 to 0.7057) indicate that the magma source of the SG granitoids is a depleted subcontinental mantle. The chemical and isotope compositions show that the SG body originated from the metasomatic mantle without a major role for continental contamination. Our findings show that the granitoid bodies distributed in the SSZ were derived from the continuous Neo-Tethys subduction beneath the SSZ in Mesozoic times and that the SSZ was an active margin in the Middle Cretaceous.  相似文献   

12.
The solubility of synthetic ZnS(cr) was measured at 25–250 °C and P = 150 bars as a function of pH in aqueous sulfide solutions (~ 0.015–0.15 m of total reduced sulfur). The solubility determinations were performed using a Ti flow-through hydrothermal reactor. The solubility of ZnS(cr) was found to increase slowly with temperature over the whole pH range from 2 to ~ 10. The values of the Zn–S–HS complex stability constant, β, were determined for Zn(HS)20(aq), Zn(HS)3?, Zn(HS)42?, and ZnS(HS)?. Based on the experimental values the Ryzhenko–Bryzgalin electrostatic model parameters for these stability constants were calculated, and the ZnS(cr) solubility and the speciation of Zn in sulfide-containing hydrothermal solutions were evaluated. The most pronounced solubility increase, about 3 log units at m(Stotal) = 0.1 for the temperatures from 25 to 250 °C, was found in acidic solutions (pH ~ 3 to 4) in the Zn(HS)20(aq) predominance field. In weakly alkaline solutions, where Zn(HS)3? and Zn(HS)42? are the dominant Zn–S–HS complexes, the ZnS(cr) solubility increases by 1 log unit at the same conditions. It was found that ZnS(HS)? and especially Zn(HS)42? become less important in high temperature solutions. At 25 °C and m(Stotal) = 0.1, these species dominate Zn speciation at pH > 7. At 100 °C and m(Stotal) = 0.1, the maximum fraction of Zn(HS)42? is only 20% of the total Zn concentration (i.e. at pHt ~ 7.5), whereas at 350 °C and 3 <pHt <10, the fraction of Zn(HS)42? and ZnS(HS)? is less than 0.05% and 2.5% respectively, of the total Zn concentration and Zn(HS)20 and Zn(HS)3? predominate. The measured equilibrium formation constants were combined with the literature data on the stability of Zn–Cl complexes in order to evaluate the concentration and speciation of Zn in chloride solutions. It was found that at acidic pH, and in more saline fluids having total chloride > 0.05 m, Zn–Cl complexes are responsible for hydrothermal Zn transport with no significant contribution of Zn–S–HS complexes. The hydrosulfide/sulfide complexes will play a more important role in lower salinity (< 0.05 m chloride) hydrothermal solutions which are characteristic of many epithermal ore depositing environments. The value of ΔfG° (β-ZnS(cr)) = ? 198.6 ± 0.2 kJ/mol at 25 °C was determined via solubility measurements of natural low-iron Santander (Spain) sphalerite.  相似文献   

13.
Lumbricus terrestris earthworms exposed to 11 soils of contrasting properties produced, on average, 0.8 ± 0.1 mgCaCO3 earthworm?1 day?1 in the form of granules up to 2 mm in diameter. Production rate increased with soil pH (r2 = 0.68, p < 0.01). Earthworms could be a significant source of calcite in soils.  相似文献   

14.
This work describes the in situ analysis of loparite [(Na,REE)Ti2O6], a perovskite group mineral with extremely low Rb/Sr ratios and high rare earth contents, by LA-(MC)-ICP-MS for the determination of U–Pb ages together with Sr and Nd isotopic composition. The reliability of these data were validated by analysis of a loparite standard by TIMS solution methods. Data are given for loparite from the Lovozero and Khibiny peralkaline complexes of the Kola Alkaline Province (Russia). For Lovozero loparite the Tera–Wasserburg intercept age for 15 loparites analysed is 373 ± 11 Ma, and the weighted 207Pb corrected 206Pb/238U age is 373 ± 2 Ma. For Khibiny loparite, the intercept age for 5 loparites analysed is 375 ± 10 Ma, and the weighted 207Pb corrected 206Pb/238U age is 374 ± 3 Ma. The common Pb compositions for Lovozero and Khibiny loparites are identical i.e. 207Pb/206Pb = 0.898 ± 0.009 and 0.898 ± 0.007, respectively. The 87Sr/86Sr initial ratios of Lovozero loparite range from 0.703552 to 0.703682 (av. 0.703611), and εNd (t370) from + 3.8 to + 4.4 (av. + 4.0). The 87Sr/86Sr initial ratios of Khibiny loparite range from 0.703560 to 0.703871, and εNd (t730) from + 4.0 to + 4.8. Our data indicate that in situ LA-(MC)-ICP-MS analysis of loparite provides accurate and precise estimates of the intrusion ages and isotopic composition of peralkaline rocks.  相似文献   

15.
The linkage between the iron and the carbon cycles is of paramount importance to understand and quantify the effect of increased CO2 concentrations in natural waters on the mobility of iron and associated trace elements. In this context, we have quantified the thermodynamic stability of mixed Fe(III) hydroxo-carbonate complexes and their effect on the solubility of Fe(III) oxihydroxides. We present the results of carefully performed solubility measurements of 2-line ferrihydrite in the slightly acidic to neutral–alkaline pH ranges (3.8–8.7) under constant pCO2 varying between (0.982–98.154 kPa) at 25 °C.The outcome of the work indicates the predominance of two Fe(III) hydroxo carbonate complexes FeOHCO3 and Fe(CO3)33−, with formation constants log*β°1,1,1 = 10.76 ± 0.38 and log β°1,0,3 = 24.24 ± 0.42, respectively.The solubility constant for the ferrihydrite used in this study was determined in acid conditions (pH: 1.8–3.2) in the absence of CO2 and at T = (25 ± 1) °C, as log*Ks,0 = 1.19 ± 0.41.The relative stability of the Fe(III)-carbonate complexes in alkaline pH conditions has implications for the solubility of Fe(III) in CO2-rich environments and the subsequent mobilisation of associated trace metals that will be explored in subsequent papers.  相似文献   

16.
Chromophoric dissolved organic matter (CDOM) is an important component in the aquatic environment and plays a key role in light attenuation and in carbon biogeochemical cycles. We examined CDOM production in each of two laboratory experiments in which phytoplankton and macrophyte degradation were monitored using absorption and excitation–emission matrix fluorescence spectroscopy (EEMs). During the incubation period, CDOM was produced from phytoplankton and macrophytes, and partly decomposed by microorganisms. The absorption spectra of the phytoplankton derived and the macrophyte derived CDOM were distinct and characterized by peaks and shoulders in the UV bands. Production of CDOM absorption at 350 nm, a(350), was 0.0125 m2/g per unit of chlorophyll a from phytoplankton CDOM from 0–3 d. Meanwhile a(350) production was 2.708 × 10−4 m2/g per unit of wet biomass from macrophytes CDOM from 1–7 d. Despite the high production of CDOM by phytoplankton and macrophytes, extrapolation of these values to the field indicated that about 15% of total CDOM was produced from phytoplankton during algal blooms in Meiliang Bay in summer and about 8% of total CDOM was produced from macrophytes in the macrophyte dominated littorals. The mean value of the spectral slope (S) describing the exponential decrease of the absorption spectrum, which was strongly correlated to an optical index of molecular size, for the phytoplankton derived CDOM was 10.26 ± 2.05 μm−1, which was significantly lower than the mean S of 14.47 ± 2.88 μm−1 for the macrophyte derived CDOM (t-test, p < 0.001). The mean value of the spectral slope ratio (SR) for the phytoplankton derived CDOM was 1.79 ± 0.52, which was significantly higher than that of 0.35 ± 0.58 for the macrophyte derived CDOM (t-test, p < 0.001). Three fluorescent components were validated in parallel factor analysis (PARAFAC) models calculated separately for phytoplankton derived and macrophyte derived CDOM, each CDOM source resulting in distinct excitation and emission maxima for each component. The significant differences in CDOM absorption spectra, S, SR and PARAFAC fluorescence component characteristics, all showed that phytoplankton derived CDOM was compositionally distinct from macrophyte derived CDOM. Overall both sources were important to the CDOM pool in the shallow temperate lake.  相似文献   

17.
This study was conducted on recent desert samples—including (1) soils, (2) plants, (3) the shell, and (4) organic matter from modern specimens of the land snail Eremina desertorum—which were collected at several altitudes (316–360 m above sea level) from a site in the New Cairo Petrified Forest. The soils and shellE. desertorum were analyzed for carbonate composition and isotopic composition (δ18O, δ13C). The plants and organic matterE. desertorum were analyzed for organic carbon content and δ13C. The soil carbonate, consisting of calcite plus minor dolomite, has δ18O values from −3.19 to −1.78‰ and δ13C values −1.79 to −0.27‰; covariance between the two values accords with arid climatic conditions. The local plants include C3 and C4 types, with the latter being dominant. Each type has distinctive bulk organic carbon δ13C values: −26.51 to −25.36‰ for C3-type, and −13.74 to −12.43‰ for C4-type plants.The carbonate of the shellE. desertorum is composed of aragonite plus minor calcite, with relatively homogenous isotopic compositions (δ18Omean = −0.28 ± 0.22‰; δ13Cmean = −4.46 ± 0.58‰). Most of the δ18O values (based on a model for oxygen isotope fractionation in an aragonite-water system) are consistent with evaporated water signatures. The organic matterE. desertorum varies only slightly in bulk organic carbon δ13C values (−21.78 ± 1.20‰) and these values suggest that the snail consumed more of C3-type than C4-type plants. The overall offset in δ13C values (−17.32‰) observed between shellE. desertorum carbonate and organic matterE. desertorum exceeds the value expected for vegetation input, and implies that 30% of carbon in the shellE. desertorum carbonate comes from the consumption of limestone material.  相似文献   

18.
The Bastar Craton of Central India has a thick sequence of volcano–sedimentary rocks preserved in Kotri–Dongargarh belt that developed on a tonalite-trondhjemite-granodiorite (TTG) basement followed upwards by the Amgaon, Bengpal, Bailadila, and Nandgaon Groups of rocks. Here, we report the U-Pb geochronology and Lu-Hf isotope systematics and whole rock geochemistry of volcanic rocks and associated granitoids belonging to the Pitepani basalts, Bijli rhyolites, and Dongargarh granite in the Nandgaon Group of the Kotri belt. The volcanic rocks of the Nandgaon Group are bimodal in nature in which the basalts exhibit intergranular, porphyritic to spherulitic texture composed of pyroxenes, plagioclase, tremolite, actinolite, and chlorite ± Fe oxides. The rhyolites display porphyritic texture consisting of K-feldspar, quartz, and plagioclase as phenocrysts. The associated porphyritic granitoids have K-feldspar, microcline, plagioclase, and biotite phenocrysts within a groundmass of similar composition. The bimodal suite displays LILE, LREE enrichment, and HFSE depletion with significant negative Nb-Ta anomalies combined with slightly fractionated REE patterns in the basalts and highly fractionated patterns and prominent negative Eu anomalies in the rhyolites endorsing their generation in an island-arc/back-arc tectonic setting. The geochemical features of the associated granitoids indicate that these are potassic and classify as within-plate A-type granites. Zircons from the basalts show clear oscillatory zoning in their CL images. They cluster as a coherent group with 207Pb/206Pb spot ages ranging from 2446 to 2522 Ma and weighted mean age of 2471 ± 7 Ma. Zircons from the rhyolite samples are subhedral to euhedral and show simple oscillatory zoning with some heterogeneous fractured domains. The data from two samples define upper intercept ages of 2479 ± 13 Ma and 2463 ± 14 Ma. Zircon grains in the granite show clear oscillatory zoning and their U-Pb data define an upper intercept age of 2506 ± 50 Ma. The Lu-Hf isotopic data on the zircons from the basalts show initial 176Hf/177Hf ratios from 0.280925 to 0.281018. Their εHf(t) values are in the range of − 10.0 to − 6.7. The Hf-depleted model ages (TDM) are between 3038 Ma and 3171 Ma, and Hf crustal model ages (TDMC) vary from 3387–3589 Ma. The zircons from the rhyolites show initial 176Hf/177Hf ratios from 0.280919 to 0.281020 and from 0.281000 to 0.281103, respectively, with εHf(t) values varying from − 10 to − 6.4 and from − 7.5 to − 3.9. Among these, one sample shows TDM between 3038 Ma and 3182 Ma, and TDMC varies from 3377 to 3596 Ma, whereas the other sample shows ages of 2925 Ma and 3072 Ma with TDMC varying from 3208 to 3432 Ma. The initial 176Hf/177Hf ratios of the granites range from 0.280937 to 0.281062 with εHf(t) values of − 8.8 to − 4.3. The TDM shows a range of 2979 Ma and 3170 Ma, and TDMC varies from 3269 to 3541 Ma. The predominant negative εHf(t) values of zircons from these rocks suggest that the source material was evolved from the Paleoarchean crust. The geological, geochemical, and geochronological evidence suggests coeval tectonic and magmatic episodes of volcanic and plutonic activity in an island-arc setting where the arc migrated toward the continental margin and played a significant role in the Neoarchean–Paleoproterozoic crustal growth of the Kotri belt of Central India.  相似文献   

19.
Porphyry Cu deposits occurred in the southern West Junggar of Xinjiang, NW China and are represented by the Baogutu and newly-discovered Jiamantieliek porphyry Cu deposits. Petrographical and geochemical studies show that both Jiamantieliek and Baogutu ore-bearing intrusions comprise main-stage diorite stock and minor late-stage diorite porphyry dikes and are the calc-alkaline intermediate intrusions. Based on U–Pb zircon SHRIMP analyses, the Jiamantieliek intrusion formed in 313 ± 4 Ma and 310 ± 5 Ma, while, based on U–Pb zircon SIMS analyses, the Baogutu intrusion formed in 313 ± 2 Ma and 312 ± 2 Ma. Rocks in the Jiamantieliek intrusion are enriched in light rare earth elements (LREE) and large ion lithophile elements (LILE) with negative Nb anomaly. Their isotopic compositions (εNd(t) = +1.6 to +3.4, (87Sr/86Sr)i = 0.70369–0.70401, (207Pb/204Pb)i = 15.31–5.41) suggest a mixing origin from depleted to enriched mantle sources. In the Baogutu intrusion, the rocks are similar to those of the Jiamantieliek intrusion. Their Sr-Nd-Pb isotopic composition (εNd(t) = +4.4 to +6.0, (87Sr/86Sr)i = 0.70368–0.70385, (207Pb/204Pb)i = 15.34–5.42) shows a more depleted mantle source. These features suggest generation in an island arc. The Jiamantieliek and Baogutu intrusions have similar characteristics, indicating that a relatively uniform and integrated source region has existed in the southern West Junggar since the Palaeozoic. A larger contribution of calc-alkaline magma would be required to generate the Jiamantieliek intrusion, which may reflect the development of magma arc maturation towards the western section of the southern West Junggar.  相似文献   

20.
A series of 30-day biochemical oxygen demand (BOD) experiments were conducted on water column samples from a reach of the upper Klamath River that experiences hypoxia and anoxia in summer. Samples were incubated with added nitrification inhibitor to measure carbonaceous BOD (CBOD), untreated to measure total BOD, which included demand from nitrogenous BOD (NBOD), and coarse-filtered to examine the effect of removing large particulate matter. All BOD data were fit well with a two-group model, so named because it considered contributions from both labile and refractory pools of carbon: BODt = a1(1 ? e? a0t) + a2t. Site-average labile first-order decay rates a0 ranged from 0.15 to 0.22/day for CBOD and 0.11 to 0.29/day for BOD. Site-average values of refractory zero-order decay rates a2 ranged from 0.13 to 0.25 mg/L/day for CBOD and 0.01 to 0.45 mg/L/day for BOD; the zero-order CBOD decay rate increased from early- to mid-summer. Values of ultimate CBOD for the labile component a1 ranged from 5.5 to 28.8 mg/L for CBOD, and 7.6 to 30.8 mg/L for BOD. Two upstream sites had higher CBOD compared to those downstream. Maximum measured total BOD5 and BOD30 during the study were 26.5 and 55.4 mg/L; minimums were 4.2 and 13.6 mg/L. For most samples, the oxygen demand from the three components considered here were: labile CBOD > NBOD > refractory CBOD, though the relative importance of refractory CBOD to oxygen demand increased over time. Coarse-filtering reduced CBOD for samples with high particulate carbon and high biovolumes of Aphanizomenon flos-aquae. There was a strong positive correlation between BOD, CBOD, and the labile component of CBOD to particulate C and N, with weaker positive correlation to field pH, field dissolved oxygen, and total N. The refractory component of CBOD was not correlated to particulate matter, instead showing weak but statistically significant correlation to dissolved organic carbon, UV absorbance at 254 nm, and total N. Particulate organic matter, especially the alga A.flos-aquae, is an important component of oxygen demand in this reach of the Klamath River, though refractory dissolved organic matter would continue to exert an oxygen demand over longer time periods and as water travels downstream.  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