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排序方式: 共有301条查询结果,搜索用时 15 毫秒
21.
René van Herwijnen Tim Laverye Jane Poole Mark E. Hodson Tony R. Hutchings 《Applied Geochemistry》2007
Organic materials such as compost are often proposed as suitable materials for the remediation of contaminated brownfield sites intended for soft end-use. In addition to vitalising the soil, they are also believed to immobilise metals thereby breaking contaminant-receptor pathways and reducing the ecotoxicity of the contaminants. However, some research has demonstrated contradictory effects between composts on metal immobilisation. In the present study, four different composts and a liming product containing organic matter (LimeX70) were tested to examine both their metal retention and toxicity reduction capabilities on three different metal contaminated soils. Leaching tests, a plant growth test with Greek cress (Lepidium sativum), an earthworm (Eisenia fetida) survival and condition test and a bacterial toxicity test using Vibrio fischeri were carried out. The leaching test results showed that spent mushroom compost caused an increase in metal concentration in the leachates, while LimeX70 caused a decrease. The variation in behaviour between different amendments for each soil was high, so a generic conclusion could not be drawn. Toxicity tests showed significant reduction of metal bioavailability and toxicity for Greek cress, earthworms and bacteria. The results also suggest that more research should be undertaken to understand the mechanisms involved in metal complexation using different types of organic matter, in order to optimise the use of organic materials like compost for soil remediation. 相似文献
22.
低温绿泥石成分温度计Fe/(Fe+Mg)校正的必要性问题 总被引:1,自引:0,他引:1
绿泥石是沉积岩、低级变质岩和水热蚀变岩中的常见矿物,基于四次配位Al含量的绿泥石成分温度计是确定古成岩或变质温度的最主要的手段之一。介绍了四种应用最为广泛的绿泥石成分温度计的原理,并从离子替代规律和比较研究的角度着重讨论了近年来关于绿泥石成分温度计校正的必要性。研究表明,在铝饱和的条件下,根据绿泥石中的Fe/(Fe Mg)值对绿泥石温度计进行校正并不能使计算值与实际值更为接近,而且从晶体化学的角度看,全岩的Fe/(Fe Mg)主要影响的是绿泥石中六次配位Fe与Mg的占位,而且偶合置换(Si4 )Ⅳ(Mg2 )Ⅵ—(Al3 )Ⅳ(Al3 )Ⅵ和(Si4 )Ⅳ(Fe2 )Ⅵ—(Al3 )Ⅳ(Al3 )Ⅵ共同控制着四次配位Al的占位。所以在铝饱和的岩石体系中可不必进行Fe/(Fe Mg)值的校正。 相似文献
23.
Hannes K. Brueckner Jane A. Gilotti Allen P. Nutman 《Contributions to Mineralogy and Petrology》1998,130(2):103-120
High-pressure metamorphic assemblages occur in mafic, ultramafic and a few intermediate rocks in a gneiss complex that covers
an area of approximately 400 × 100 km in the North-East Greenland Caledonides. Detailed petrologic and geochronologic studies
were carried out on three samples in order to clarify the P-T-t evolution of this eclogite province. Geothermobarometry yields temperature estimates of 700–800 °C and pressure estimates
of at least 1.5 GPa from an eclogite sensu stricto and as high as 2.35 GPa for a garnet websterite. The eclogite defines a garnet-clinopyroxene-amphibole-whole rock Sm-Nd isochron
age of 405 ± 24 Ma (MSWD 0.9). Isofacial garnet websterites define garnet-clinopyroxene-orthopyroxene-amphibole-whole rock-(biotite)
ages of 439 ± 8 Ma (MSWD =2.1) for a coarse-grained sample and 370 ± 12 Ma (MSWD=0.6) for a finer-grained variety. Overgrowths
on zircons from the fine-grained pyroxenite and the eclogite give a pooled 206Pb/238U SHRIMP age of 377 ± 7 Ma (n=4). Significantly younger Rb-Sr biotite ages of 357 ± 8, 330 ± 6 and 326 ± 6 agree with young Rb-Sr, K-Ar and 40Ar/39Ar mineral ages from the gneiss complex and indicate slow cooling of the eclogitic rocks. High-pressure metamorphism may have
been at least 439 Ma old (Siluro-Ordovician) with cooling through amphibolite-facies conditions in the Devonian and continued
crustal thinning and exhumation well into the Carboniferous. Sm-Nd whole rock model ages indicate the eclogite protoliths
are Early Proterozoic in age, while 207Pb/206Pb SHRIMP ages of 1889 ± 18 and 1981 ± 8 from anhedral zircon cores probably reflect Proterozoic metasomatism. The samples
have negative ɛNd values (−5 to −16) and elevated 87Sr/86Sr ratios (0.708–0.715), consistent with field evidence that the eclogite protoliths were an integral part of the continental
crust long before Caledonian metamorphism. The presence of a large Caledonian eclogite terrane in Greenland requires modification
of current tectonic models that postulate subduction of Baltica beneath Laurentia during the Caledonian orogeny.
Received: 9 October 1996 / Accepted: 7 July 1997 相似文献
24.
The formation and subsequent reactions of magnesiancalcite overgrowths on calcite were investigated bymeans of closed system seeded precipitationexperiments. These experiments demonstrated that(1) thin overgrowths of magnesian calcite are precipitatedon calcite seeds suspended in seawater;(2) the solubilities of the coatings increase outward from theseed crystals as a linear function of the log ofrelative coating thickness;(3) during the period ofthese experiments (up to 5.5 months), the magnesiancalcite coatings continued to increase in thickness,but became less soluble in composition. Thestabilization reaction, referred to asrecrystallization, can be described by the followingequation:Cax Mg(1-x) CO3 + [z + y(x + z)]Ca2++ 2yHCO3- ]= (1 + y)Ca(x + z)Mg(1 - x -z)CO3 + [z + y(x + z - 1)]Mg2++ y CO2 + yH20;]4) recrystallization rate is dependent on solutionsaturation state, with a reaction order of 3.2 forartificial seawater and 4.0 for natural seawater; and(5) by the cessation of the closed system experiments,overgrowth compositions approached that of the stablecalcite (a few mol % MgCO3).Armoring of suspended carbonate particles in thesurface oceans with magnesian calcite overgrowthswould provide an effective barrier to release of theoceanic supersaturation with respect to calcite. Thicknesses of such coatings would be limited by therecrystallization rate of the magnesian calcite. Estimates based on the recrystallization ratesdetermined in this work indicate coatings on the orderof 0.02 µm in thickness could form on particles asthey sink through the mixed layer. According to thesecalculations, the total amount of carbon precipitatedannually in magnesian calcite overgrowths iscomparable to the riverine flux of dissolved carbon tothe oceans. Field observations of severalinvestigators indicate the likely presence ofmagnesian calcite coatings on planktonic particles,and provide evidence for possible recrystallization ofbiogenic magnesian particles in the marineenvironment. 相似文献
25.
21Ne cosmic-ray exposure ages have been calculated from literature data for 201 H, 203 L and 38 LL chondrites, corrected for shielding differences when possible. The distributions of exposure ages again show the familiar peaks at 4.5 and 20 Myr for the H's, but no outstanding events for the L's and LL's. If the L-chondrite distribution is interpreted as a series of discrete events, then at least 6 peaks between 1 and 35 Myr are needed to model it. The observations, that every petrologic type occurs in every large peak and that even the higher petrologic types contain solar wind gases, suggest that the parent bodies have been fragmented and reassembled into a megabreccia. For the H chondrites, both large and small peaks contain about 15% solar-gas bearing meteorites, which could mean that surface material has been mixed to depths represented by the largest event, on the order of a kilometer. In contrast, only 3% of the L's contain solar wind, which may be related to breakup of their parent planet. Those L's with especially low radiogenic He (U,Th-He ages < 1 AE) tend to have low exposure ages: their distribution may be biased by a subgroup that had orbits coupling short capture lifetimes with significant solar heating. 相似文献
26.
Changes of atmospheric CO2 concentration since 1958 are shown to be related to sea surface temperature changes. The largest contribution to changes arises from the Pacific equatorial upwelling region, with the Indian Ocean and Atlantic contributing only small fractions to the variance. It is hypothesized that the observed relationship is related to the nutrients that are brought up by upwelling cold water, with photosynthesis contributing to a lowering of the partial pressure of CO2 in the sea and thus to a greater tendency for a flux from the air to the sea.Possible longer term variations of sea temperature and CO2 are discussed. 相似文献
27.
The economic impact of climate change on Kenyan crop agriculture: A Ricardian approach 总被引:3,自引:2,他引:1
This paper measures the economic impact of climate on crops in Kenya. We use cross-sectional data on climate, hydrological, soil and household level data for a sample of 816 households. We estimate a seasonal Ricardian model to assess the impact of climate on net crop revenue per acre. The results show that climate affects crop productivity. There is a non-linear relationship between temperature and revenue on one hand and between precipitation and revenue on the other. Estimated marginal impacts suggest that global warming is harmful for crop productivity. Predictions from global circulation models confirm that global warming will have a substantial impact on net crop revenue in Kenya. The results also show that the temperature component of global warming is much more important than precipitation. Findings call for monitoring of climate change and dissemination of information to farmers to encourage adaptations to climate change. Improved management and conservation of available water resources, water harvesting and recycling of wastewater could generate water for irrigation purposes especially in the arid and semi-arid areas. 相似文献
28.
29.
Reforestation Programs in Southwest China: Reported Success, Observed Failure, and the Reasons Why 总被引:4,自引:2,他引:2
Ever since the disastrous floods of 1998, the Chinese government has used the Natural Forest Protection and Sloping Land Conversion Programs to promote afforestation and reforestation as means to reduce runoff, control erosion, and stabilize local livelihoods. These two ambitious programs have been reported as large-scale successes, contributing to an overall increase in China’s forest cover and to the stated goals of environmental stabilization. A small-scale field study at the project level of the implementation of these two programs in Baiwu Township, Yanyuan County, Sichuan, casts doubt upon the accuracy and reliability of these claims of success; ground observations revealed utter failure in some sites and only marginal success in others. Reasons for this discrepancy are posited as involving ecological, economic, and bureaucratic factors. Further research is suggested to determine whether these discrepancies are merely local aberrations or represent larger-scale failures in reforestation programs. 相似文献
30.
Emily I. Curtis John S. Richer Jane V. Buckle 《Monthly notices of the Royal Astronomical Society》2010,401(1):455-472
We present submillimetre observations of the J = 3 → 2 rotational transition of 12 CO, 13 CO and C18 O across over 600 arcmin2 of the Perseus molecular cloud, undertaken with the Heterodyne Array Receiver Programme (HARP), a new array spectrograph on the James Clerk Maxwell Telescope. The data encompass four regions of the cloud, containing the largest clusters of dust continuum condensations: NGC 1333, IC348, L1448 and L1455. A new procedure to remove striping artefacts from the raw HARP data is introduced. We compare the maps to those of the dust continuum emission mapped with the Submillimetre Common-User Bolometer Array (SCUBA; Hatchell et al.) and the positions of starless and protostellar cores (Hatchell et al.). No straightforward correlation is found between the masses of each region derived from the HARP CO and SCUBA data, underlining the care that must be exercised when comparing masses of the same object derived from different tracers. From the 13 CO/C18 O line ratio the relative abundance of the two species ([13 CO]/[C18 O]∼ 7) and their opacities (typically τ is 0.02–0.22 and 0.15–1.52 for the C18 O and 13 CO gas, respectively) are calculated. C18 O is optically thin nearly everywhere, increasing in opacity towards star-forming cores but not beyond τ18 ∼ 0.9 . Assuming the 12 CO gas is optically thick, we compute its excitation temperature, T ex (around 8–30 K), which has little correlation with estimates of the dust temperature. 相似文献