Formation and development of salt crusts on soil surfaces

The salt concentration gradually increases at the soil free surface when the evaporation rate exceeds the diffusive counter transport. Eventually, salt precipitates and crystals form a porous sodium chloride crust with a porosity of 0.43 ± 0.14. After detaching from soils, the salt crust still experiences water condensation and salt deliquescence at the bottom, brine transport across the crust driven by the humidity gradient, and continued air-side precipitation. This transport mechanism allows salt crust migration away from the soil surface at a rate of 5 μm/h forming salt domes above soil surfaces. The surface characteristics of mineral substrates and the evaporation rate affect the morphology and the crystal size of precipitated salt. In particular, substrate hydrophobicity and low evaporation rate suppress salt spreading.     

Research Progress of Leaf-wax Hydrogen Isotope Paleoaltimetry

Leaf waxes/lipids which are derived from terrestrial higher plants are ubiquitous in fluvial, lake, and marine sediments. N-alkanes are an important component of leaf waxes. Modern leaf wax n-alkanes from terrestrial higher plants are characterized with long chains with 27 to 33 carbon atoms (nC₂₇-nC₃₁) and high carbon preference index (CPI) values (>5). The hydrogen isotopes in n-alkanes are determined by meteoric water compositions, which makes them a potential proxy in paleoaltimetry studies. The lapse rates at which n-alkane hydrogen isotopes in modern soils change with altitude vary in different areas, implying that local calibration has to be conducted. The enrichment due to evapotranspiration and difference in fractionation during biosynthesis also influence n-alkane hydrogen isotopes values. When using long-chain n-alkanes to reconstruct paleoaltitude, many factors such as paleoclimate, paleolatitude and paleobotany should be considered.     

Discrete element simulation of dynamic semi-circular bend flexure tests of rocks using split Hopkinson pressure bar

The semi-circular bending (SCB) using a split Hopkinson pressure bar system appears to be a promising method for measuring dynamic flexural strength of rock materials due to its distinct advantages. The quasi-static analysis is adopted for determining the dynamic flexural strength, of which several vital prerequisites have not been thoroughly examined yet. In this study, dynamic flexure tests regarding dynamic force equilibrium, interfacial friction effects, and energy partitioning are numerically investigated based on discrete element method (DEM) modeling. Results show that by virtue of the ramped wave loading, the force equilibrium of the specimen can be effectively achieved and the rupture is precisely measured to synchronize with the peak force, both of which guarantee the quasi-static data reduction method employed to determine the dynamic flexural strength; while the opposite occurs for the test under a rectangular wave loading. Furthermore, dynamic flexural strengths obtained by the numerical SCB tests exhibit approximately linear rate dependence that is identical with the experimental results. The interfacial friction, which is found to significantly influence the measuring results for rather high loading rates, contributes to enhancing the rate dependence of flexural strength and must be taken into account in dynamic flexure tests. In addition, energy partitioning is first numerically performed in the dynamic SCB tests and the nominal fracture energy manifests an S type of rate dependence with loading rates.     

Quality and quantity of pre-drainage methane and responding strategies in Chinese outburst coal mines

The potential sources of recharge of both water and solutes to the Quaternary aquifer in the area between Ismailia and El Kassara canals in northeastern Egypt include seepage from the irrigation canals and conduits, return flow after irrigation in the cultivated fields, local precipitation, and the upward flow of groundwater from the underlying Miocene aquifer system. Water isotopes, solute concentrations, and sulfate isotopes were used to investigate the geochemical sources, reactions, and the impacts of the hydraulic connections among recharge sources. The obtained results indicate a minimal influence of the underlying Miocene aquifer as a water and solute source while old and new contributions from the irrigation canals represent the main sources of recharge. The chemical reactions responsible for the chemical constituents and salinity in the aquifer include silicate weathering, evaporite dissolution, and carbonate precipitation. Most of groundwater samples appear to lie at/or close to equilibrium with montmorillonite, kaolinite, and illite where clay minerals are quite common in the local soils of the Quaternary aquifer.

     

南麂列岛海域沉积物中甲藻孢囊的多样性和分布

南麂列岛地处亚热带海域,是台湾暖流和江浙沿岸流的交汇处,因而呈现出很好的生物多样性。据调查,南麂列岛附近海域已鉴定的浮游植物甲藻有53种,而到目前为止,对南麂列岛海域甲藻的休眠孢囊种类和分布的调查仍为空白。本文通过对2014年南麂列岛附近海域沉积物中甲藻孢囊的调查研究,在该海域共发现甲藻孢囊10属26种,其中,种类最多的是原多甲藻属(Protoperidinium),有10种;其次是斯氏藻属(Scrippsiella)和亚历山大藻属(Alexandrium),分别有4种,膝沟藻属(Gonyaulax)2种,舌甲藻属(Lingulodinium)、易碎藻属(Fragilidium)、扁甲藻属(Pyrophacus)、翼藻属(Diplopsalis)、裸甲藻属(Gymnodinium)和多沟藻属(Polykrikos)各1种。这些甲藻孢囊中,异养型和自养型甲藻孢囊各13种,自养型甲藻孢囊在数量上所占比例较大(79%)。2014年南麂列岛海域甲藻孢囊丰度较低,每毫升沉积物能检测出2—33个;夏、秋季的孢囊丰富度较高;岙口等相对开放海域的孢囊丰度明显高于岙内各站点。值得注意的是,三种有毒甲藻孢囊,塔玛/相似亚历山大藻(Alexandrium tamarense/affine),具刺膝沟藻(Gonyaulax spinifera)和多边舌甲藻(Lingulodinium polyedra)的孢囊也在样品中检出,并且分别占春季、夏季和秋季孢囊总丰度的37%、23%和27%。本研究为完善南麂列岛甲藻的物种多样性提供了依据。