Enrichment characteristics and risk assessment of Hg in bird feathers from Caohai wetland in Guizhou Province,China

Based on the analysis of the enrichment characteristics of Hg and MeHg in bird feathers from Caohai National Nature Reserve in Guizhou, the risks of Hg pollution to the birds from Caohai wetland have been evaluated. The total Hg content of bird feathers ranges from 40 to 5058 ng/g with an average of 924 ng/g. The content of MeHg is significantly correlated with total Hg (r = 0.68, p < 0.01), and the content are among 0.75 and 113 ng/g. The total Hg content in the birds feathers is significantly dependent on their feeding habits, which is mainly in accordance with the following rule: carnivorous birds > omnivorous birds that are mainly carnivorous > omnivorous birds that are mainly herbivorous. There are also differences in the Hg enrichment ability in the different parts of bird feathers, and the total Hg and MeHg content in the wing feathers are significantly higher than that in the other parts of feathers. The bioaccumulation coefficients of aqueous Hg and MeHg by bird feathers are 0.9 × 10⁴–112.13 × 10⁴ (mean value is 20.47 × 10⁴) and 0.47 × 10⁴–70.4 × 10⁴ (mean value is 9.52 × 10⁴), respectively. Although the whole Hg level in Caohai bird feathers is not too high, the Hg content in some carnivorous birds exceeds over or approaches the abnormal threshold when birds are breeding (5 μg/g), which indicates that the birds in Caohai wetland are faced with some risks of ecological Hg pollution.     

Evaluation of CBM reservoir fracture characteristics by azimuthal AVA inversion

Exploitation of coalbed methane (CBM) is directly affected by the strike and density of fractures, particularly because fractures can act as conduits for water and gas (after desorption). To realize the azimuthal amplitude versus angle (AVA) inversion for a CBM reservoir, we treated reservoirs whose fractures are aligned vertically as being equivalent to a horizontal transverse isotropic medium and simplified the P-P wave reflection coefficient formula to an approximately linear equation. Then, we adopted a modified damping least squares algorithm to solve the azimuthal AVA inversion problem. With edited macro-bins, corrected residual moveout, and normalized amplitude, the azimuthal gathers exhibited unambiguous azimuthal AVA characteristics. The #3 CBM reservoir in the Qinshui Basin was selected for a case study. The density and strike of the reservoir fractures were obtained and analyzed, and the reservoir was divided into three classes according to fracture density. Finally, in comparison with the gas production data, we confirmed that the inversion results and reservoir classification were both reasonable and credible.     

Solar-, monsoon- and Kuroshio-influenced thermocline depth and sea surface salinity in the southern Okinawa Trough during the past 17,300 years

Factors influencing millennial-scale variability in the thermocline depth (vertical mixing) and sea surface salinity (SSS) of the southern Okinawa Trough (OT) during the past 17,300 years were investigated based on foraminifer oxygen isotope records of the surface dweller Globigerinoides ruber sensu stricto and the thermocline dweller Pulleniatina obliquiloculata in the AMS ¹⁴C dated OKT-3 core. The thermocline depth is influenced by surface thermal buoyancy (heat) flux, in turn controlled by the annual mean insolation at 30°N and the strength of the East Asian winter monsoon (EAWM). Strong insolation and weak EAWM tend to increase buoyancy gain (decrease buoyancy loss), corresponding to shallow thermocline depths, and vice versa. Regional SSS is influenced by the global ice volume, the Kuroshio Current (KC), and vertical mixing. A deep thermocline coincides with a high SSS because strong vertical mixing brings more, saltier subsurface KC water to the surface, and vice versa. Local SSS (excluding the global ice volume effect) became lower in the northern OT than in the southern OT after ~9.2 ka, implying that Changjiang diluted water had stronger influence in the northern sector. SSS show no major changes during the Bølling/Allerød and Younger Dryas events, probably because the KC disturbed the North Atlantic signals. This argues against earlier interpretations of sea surface temperature records of this core. Wavelet and spectral analyses of the Δδ¹⁸O_P-G (δ¹⁸O of P. obliquiloculata minus G. ruber s.s.) and δ¹⁸O_local records display 1,540-, 1,480-, 1,050-, 860-, 640-, and 630-year periods. These are consistent with published evidence of a pervasive periodicity of 1,500 years in global climate as well as EAWM and KC signatures, and a fundamental solar periodicity of 1,000 years and intermediary derived periodicity of 700 years.     

BVOC emissions from mechanical wounding of leaves and branches of <Emphasis Type="Italic">Eucalyptus sideroxylon</Emphasis> (red ironbark)

Emissions of biogenic volatile organic compounds (BVOCs) from mechanical wounding of leaves and branches of plants can contribute to the atmospheric burden of volatile organic compounds (VOCs) in both (a) urban airsheds (from urban garden maintenance) and (b) the global atmosphere (from large scale forest harvesting). These emissions of BVOCs are poorly understood and quantified, and their role in urban and global emissions inventories neglected. This paper presents measurements of the magnitude, duration and composition of emissions of BVOCs, carbon dioxide (CO₂) and methane (CH₄) from freshly cut leaf mulch and wood chips derived from a common eucalypt tree, Eucalyptus sideroxylon (red ironbark), found in southeastern Australian forests and gardens. The emissions of BVOCs from freshly cut and shredded leaves and wood of E. sideroxylon were found to be 2.3 ± 0.6 and 0.05 ± 0.04 mg g^-1 DM (Dry Mass) from leaf mulch and wood chips respectively and to last typically for 1 day following cutting. Three sampling techniques were used for VOC speciation and the 12 most abundant BVOCs released from the mulch materials were identified. The specific BVOCs emitted in order of decreasing abundance from leaf mulch are: (a) stored plant oils, 1,8-cineole, α–pinene and o-cymene which make up the major part of the emissions, (b) a minor contribution from chemicals associated with environmental stress and wound defence, (Z)–3–hexenyl acetate, (E)-2-hexenal and (Z)-3-hexen-1-ol, and (c) a second minor contribution from metabolic products, acetaldehyde and acetone. The observed integrated emissions of BVOCs from leaves following mulching are equivalent to more than half and perhaps all of the likely stored plant oils in the leaves. For the two comparable studies available, one of a plant with stored oils (this study) and one of a plant without stored plant oils, the emissions of leaf wound defence BVOCs are in the same range for both plants. In the plant with stored plant oils, the plant oil emissions are about a factor of 11 larger in emission rate than the plant wound defence BVOCs. A compilation of available leaf wounding BVOC emission studies indicates that for plants with stored plant oils, plant oil emissions dominate, whereas with other plants, leaf wound defence BVOCs dominate the emissions.     

Incorporating space,time, and magnitude measures in a network characterization of earthquake events

We investigate the structural properties of a spatio-temporal network of earthquake events that incorporates magnitude information between the connected events. The network creates temporally directed links from an origin event towards a later event if it breaks the record closest distance from the origin among all the events in the catalog so far. Additionally, the links are conditionally classified based on the magnitude difference between connected events: “up” (“down”) connections point from a weaker (stronger) to a stronger (weaker) event. Using earthquake records from the Philippines from 1973 to 2012 and southern California from 1982 to 2012, we observe that the out-degree distributions show slight deviations from the corresponding Poisson distribution of the same mean. The space and time separations of connected earthquakes both show power-law regimes, suggesting spatio-temporal (self-)organization. More importantly, the conditional distributions of “up” and “down” connections in space, time, and network structure point to a higher likelihood of a stronger event triggering a nearby weaker event for the first few connections, as in the case of aftershocks. The results are captured by a sandpile-based model where a small but finite probability of preferentially targeting the most susceptible grid site is introduced. Our analysis, coupled with the discrete model analog, provides a quantitative picture of the spatio-temporal and magnitude organization of seismicity beyond just the successive events. The technique may be extended to further characterize similar long-period earthquake records to yield a more complete picture of the underlying processes involved in seismicity.     

Three-dimensional forward modeling of DC resistivity using the aggregation-based algebraic multigrid method

To speed up three-dimensional (3D) DC resistivity modeling, we present a new multigrid method, the aggregation-based algebraic multigrid method (AGMG). We first discretize the differential equation of the secondary potential field with mixed boundary conditions by using a seven-point finite-difference method to obtain a large sparse system of linear equations. Then, we introduce the theory behind the pairwise aggregation algorithms for AGMG and use the conjugate-gradient method with the V-cycle AGMG preconditioner (AGMG-CG) to solve the linear equations. We use typical geoelectrical models to test the proposed AGMG-CG method and compare the results with analytical solutions and the 3DDCXH algorithm for 3D DC modeling (3DDCXH). In addition, we apply the AGMG-CG method to different grid sizes and geoelectrical models and compare it to different iterative methods, such as ILU-BICGSTAB, ILU-GCR, and SSOR-CG. The AGMG-CG method yields nearly linearly decreasing errors, whereas the number of iterations increases slowly with increasing grid size. The AGMG-CG method is precise and converges fast, and thus can improve the computational efficiency in forward modeling of three-dimensional DC resistivity.     

Dispersion features of transmitted channel waves and inversion of coal seam thickness

In-seam seismic survey currently is a hot geophysical exploration technology used for the prediction of coal seam thickness in China. Many studies have investigated the relationship between the group velocity of channel wave at certain frequency and the actual thickness of exposed coal beds. But these results are based on statistics and not universally applicable to predict the thickness of coal seams. In this study, we first theoretically analyzed the relationship between the depth and energy distribution of multi-order Love-type channel waves and found that when the channel wave wavelength is smaller than the thickness of the coal seam, the energy is more concentrated, while when the wavelength is greater than the thickness, the energy reduces linearly. We then utilized the numerical simulation technology to obtain the signal of the simulated Love-type channel wave, analyzed its frequency dispersion, and calculated the theoretical dispersion curves. The results showed that the dispersion characteristics of the channel wave are closely related to the thickness of coal seam, and the shear wave velocity of the coal seam and its surrounding rocks. In addition, we for the first time realized the joint inversion of multi-order Love-type channel waves based on the genetic algorithm and inversely calculated the velocities of shear wave in both coal seam and its surrounding rocks and the thickness of the coal seam. In addition, we found the group velocity dispersion curve of the single-channel transmitted channel wave using the time–frequency analysis and obtained the phase velocity dispersion curve based on the mathematical relationship between the group and phase velocities. Moreover, we employed the phase velocity dispersion curve to complete the inversion of the above method and obtain the predicted coal seam thickness. By comparing the geological sketch of the coal mining face, we found that the predicted coal seam thickness is in good agreement with the actual thickness. Overall, adopting the channel wave inversion method that creatively uses the complete dispersion curve can obtain the shear wave velocities of the coal and its surrounding rocks, and analyzing the depth of the abruptly changed shear wave velocity can accurately obtain the thickness of the coal seam. Therefore, our study proved that this inversion method is feasible to be used in both simulation experiments and actual detection.     

Preliminary comparison of trace metals in coastal aerosols between Qingdao and Liverpool

Aerosol samples were collected at two coastal suburban stations, Qingdao （China） in 1995-1996 and Liverpool （U.K.） in 1995, respectively. The samples were analyzed to determine the concentrations of trace metals （Cr, Zn, Cu, Co, Ni, Pb, V, and Cd） as well as A1, Fe and Mn. Data were examined to understand the difference of trace metals in aerosols between coastal zones downwind the developing area （near the Yellow Sea） and developed region （near the Irish Sea）. The results show that most elements at Qingdao have levels 4-5 times higher than those at Liverpool, particularly for the crust-dominated elements （e.g. Al, Fe and Mn）. Moreover, the aerosol composition at Qingdao is higher in spring than in summer, underlying the influence of westerlies and local emissions in combination, whereas seasonal change of aerosol composition is not significant at Liverpool. The enrichment factors for the crustal source elements （EFcrust） at Liverpool are much higher than those at Qingdao. The contributions from the pollutant source （Rp） for some trace metals like Cu, Pb, Zn and Cd are 〉90% at Qingdao and Liverpool, suggesting overwhelming anthropogenic contributions to these metals. The contributions from crustal source （Re） for trace metals tend to increase with higher aerosol levels and Al concentration at Qingdao, indicating a good correlation between the crust-dominated component and the air mass. At Liverpool, the Rc values for trace metals are positively correlated with Al concentrations instead of with aerosol mass, suggesting that Al in aerosols represents the crustal component even though the aerosols come from different sources.     

Joint probability density function of the stochastic responses of nonlinear structures

The joint probability density fimction （PDF） of different structural responses is a very important topic in the stochastic response analysis of nonlinear structures. In this paper, the probability density evolution method, which is successfully developed to capture the instantaneous PDF of an arbitrary single response of interest, is extended to evaluate the joint PDF of any two responses. A two-dimensional partial differential equation in terms of the joint PDF is established. The strategy of selecting representative points via the number theoretical method and sieved by a hyper-ellipsoid is outlined. A two-dimensional difference scheme is developed. The free vibration of an SDOF system is examined to verify the proposed method, and a flame structure exhibiting hysteresis subjected to stochastic ground motion is investigated. It is pointed out that the correlation of different responses results from the fact that randomness of different responses comes from the same set of basic random parameters involved. In other words, the essence of the probabilistic correlation is a physical correlation.     

∼3,850 Ma tonalites in the Nuuk region,Greenland: geochemistry and their reworking within an Eoarchaean gneiss complex

The Eoarchaean (>3,600 Ma) Itsaq Gneiss Complex of southern West Greenland is dominated by polyphase orthogneisses with a complex Archaean tectonothermal history. Some of the orthogneisses have c. 3,850 Ma zircons, and they vary from rare single phase metatonalites to more common complexly banded migmatites. This is due to heterogeneous strain, in situ anatexis and granitic veining superimposed during younger tectonothermal events. In the single-phase tonalites with c. 3,850 Ma zircon, oscillatory-zoned prismatic zircon is all 3,850 Ma old, but shows patchy ancient loss of radiogenic Pb. SHRIMP spot analyses and laser ablation ICP-MS depth profiling show that thin (usually < 10 μm) younger (3,660–3,590 Ma and Neoarchaean) shells of lower Th/U metamorphic zircon are present on these 3,850 Ma zircons. Several samples with this simple zircon population occur on islands near Akilia. In contrast, migmatites usually contain more complex zircon populations, with often more than one generation of igneous zircon present. Additional zircon dating of banded gneisses across the Complex shows that samples with c. 3,850 Ma igneous zircon are not just a phenomenon restricted to Akilia and adjacent islands. For example, migmatites from Itilleq (c. 65 km from Akilia) contain variable amounts of oscillatory-zoned 3,850 Ma and 3,650 Ma zircon, interpreted, respectively, as the rock age and the time of crustal melting under Eoarchaean metamorphism. With only 110–140 ppm Zr in the tonalites and likely magmatic temperatures of >850°C, zircon solubility–melt composition relationships show that they were only one-third saturated in zircon. Any zircon entrained in the precursor magmas would thus have been highly soluble. Combined with the cathodoluminesence imaging, this demonstrates that the c. 3,850 Ma oscillatory zoned zircon crystallised out of the melt and hence gives a magmatic age. Thus the rare well-preserved tonalites and palaeosome in migmatites testify that c. 3,850 Ma quartzo–feldspathic rocks are a widespread (but probably minor) component in the Itsaq Gneiss Complex. C. 3,850 Ma zircon with negative Eu anomalies (showing growth in felsic systems) also occurs as detrital grains in rare c. 3,800 Ma metaquartzites and as inherited grains in some 3,660 Ma granites (sensu stricto). These demonstrate that still more c. 3,850 Ma rocks were present, but were recycled into Eoarchaean sediments and crustally derived granites. The major and trace element characteristics (e.g. LREE enrichment, HREE depletion, low MgO) of the best-preserved c. 3,850 Ma rocks are typical of Archaean TTG suites, and thus argue for crust formation processes involving important contributions from melting of hydrated mafic crust to the earliest Archaean. Five c. 3,850 Ma tonalites were selected as the best preserved on the basis of field criteria and zircon petrology. Four of these samples have overlapping initial ɛ_Nd (3,850 Ma) values from +2.9 to +3.6± 0.5, with the fourth having a slightly lower value of +0.6. These data provide additional evidence for a markedly LREE-depleted early terrestrial mantle reservoir. The role of c. 3,850 Ma crust should be considered in interpreting isotope signatures of the younger (3,800–3,600 Ma) rocks of the Itsaq Gneiss Complex. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.