Validation of MODIS C6 AOD Products Retrieved by the Dark Target Method in the Beijing–Tianjin–Hebei Urban Agglomeration,China

The quality of the MODIS C6 3-km and 10-km aerosol optical depth(AOD) products retrieved by the Dark Target(DT)method is discussed using ground-based observations in the Beijing–Tianjin–Hebei region from 1 August 2007 to 31 July2008. Good consistency exists between the 3-km and 10-km products and ground-based observations. The retrieval accuracy of the two products both show distinctive seasonality. The percentage falling within the expected error(EE) is largest in the winter, moderate in the spring and autumn, and smallest in the summer. A worse overestimation appears in the spring and summer(27%–66%). However, the 3-km and 10-km products over different surfaces still exhibit obvious deviations. The 10-km product performs better in the large cities, while the 3-km product has advantages in the suburbs. In urban areas, the percentage falling within EE of the 3-km AOD product(18%–59%) is lower than that for the 10-km AOD product(31%–69%). However, in suburban areas, the percentage falling within EE of the 3-km AOD product(61%–84%) is higher than for the 10 km AOD product(54%–83%).The percentages falling within EE differ considerably when the AOD is greater than1.5(73% and 63% for the 3-km and 10-km products, respectively). On the whole, the 3-km(10-km) AOD product performs better in suburban(urban) areas.     

Geochemical Record of the Cenomanian–Turonian Anoxic Event in Tunisia: Is it Correlative and Isochronous to the Biotic Signal?

In Tunisia, five Bahloul spaced sections, Bargou, Jerisa, Guern Halfaya, Kherij and Gafsa were analyzed for biostratigraphy (foraminifera and radiolarians) and major and trace elements. This high-resolution biostratigraphic and chemostratigraphic integrated analyses for the Late Cenomanian–Early Turonian Bahloul Formation provide new insight into the palaeoceanographic evolution of the southern Tethyan margin. Relative low abundance of related terrigenous Ti/Al and K/Al ratios and enrichment of some productivity proxies such as Ba, Cu, and Ni (organic matter related trace elements) suggests that the Bahloul, deposited during a relatively short period (0.5 Ma), was of relatively elevated primary productivity and minimal detrital input. While higher D* values concurrent with lower Ti/Al ratios are interpreted as caused by enhanced fluvial material contribution, due to more humid climate during the OAE-2. Enhanced humidity triggered probably fluvial influxes, resulted in a sluggish water circulation and consequent anoxic/euxinic conditions favoring the preservation of organic matter at the bottom. Enrichments in redox-sensitive trace metals U, V, and Mo in the Bahloul Formation deposits and redox indices, such as V/(V+Ni), U/Th, V/Cr, and Ni/Co, indicate that oxygen-restricted conditions prevailed during the Late Cenomanian to earliest Turonian times and correlate well with relative abundances of some foraminiferal and radiolarian paleo-environmental relevant indicators. High Baxs values and Uauth may indicate anoxic conditions at least at the water–sediment interface during the Bahloul Formation deposition and provide information about low to moderate sulfate-reduction reactions.     

Salinity effect on the liquid limit of soils

Acta Geotechnica - Previous studies stated that, with increasing salinity, the decreased liquid limit for expansive soils was attributed to the shrinkage of diffuse double layer, while the...     

Comparison of linear solvers for equilibrium geochemistry computations

Equilibrium chemistry computations and reactive transport modelling require the intensive use of a linear solver under very specific conditions. The systems to be solved are small or very small (4 × 4 to 20 × 20, occasionally larger) and are very ill-conditioned (condition number up to 10¹⁰⁰). These specific conditions have never been investigated in terms of the robustness, accuracy, and efficiency of the linear solver. In this work, we present the specificity of the linear system to be solved. Several direct and iterative solvers are compared using a panel of chemical systems, including or excluding the formation of mineral species. We show that direct and iterative solvers can be used for these problems and propose computational keys to improve the chemical solvers.     

Phytoremediation assessment of native plants growing on Pb–Zn mine site in Northern Tunisia

Pollution by heavy metals presents an environmental concern, and their toxicity threats soil, water, animals and human health. Phytoremediation can be used as a solution to remediate contaminated soils. The aim of this study was to identify native plants collected from tailings: material of Pb–Zn mine sites of Fedj Lahdoum and Jebel Ressas (two abandoned mines located, respectively, in the northwest of Tunisia and in the south of Tunis City). The tolerance of plant to heavy metals (lead, zinc and cadmium) is evaluated. Soil samples were collected and analyzed for Pb, Zn and Cd concentration. The total soil Pb, Zn and Cd are, respectively, reached 6132 mg kg^?1, 11,052 mg kg^?1 and it doesn’t exceed 479 mg kg^?1 for Cd. The highest content of Zn in plants was detected in shoots of Rumex bucephalophorus (1048 mg kg^?1), and the highest Pb concentration was detected in roots of Chrysopogon zizanioides (381 mg kg^?1), while for Cd Silene colorata it accumulated the highest content in roots (51 mg kg^?1). From all plants, only 12 have a translocation factor for Pb which is higher than one. Among all plants, only 17 have a translocation factor that is higher than one for Zn, while for Cd only 13 plants indicate TF > 1. As for the biological absorption coefficient, all samples indicate a rate which is lower than one. These plants can be primarily hyper accumulators and useful in remediation of lead- and zinc-contaminated soils after further biochemistry researches in mechanism of accumulation and translocation of heavy metals in plants.