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21.
在氧化沉淀法去除铁的过程中,氧化反应分别在自然曝气、充气和除钙的条件下进行,对照结果进行分析,得出最佳的除铁配方,同时还着重对氧化反应速率及其影响因素(pH,Eh等)进行了探索性研究,为以后试验提供了一定的依据。 相似文献
22.
Analysis of fly-ash particles in lake sediments has become increasingly important in studies of environmental pollution and lake acidification history. Most fly-ash studies have concerned black spheroidal carbonaceous particles (SCP)(>5 m) produced from oil and coal combustion. This review paper provides a summary of this technique and its application, and focusses on our investigations in Sweden between 1979 and 1993. It consists of five parts: i) preparation and analysis methods, ii) historical trends in atmospheric deposition, iii) geographical surveys of atmospheric deposition, iv) sediment dating, and v) studies of sedimentation processes in lakes. Methods for preparation and analyses of SCP have been developed and applied to investigations using sediment, soil and snow samples. Stratigraphic trends of SCP concentrations in lake-sediment cores reflect the consumption history of fossil fuels. A characteristic temporal SCP pattern, with a marked concentration increase beginning after the 1940's and a peak in the early 1970's, has been recognized in most Swedish lakes and elsewhere in Europe. A survey of SCP concentrations in surface sediments of >100 lakes covering Sweden demonstrated that polluted areas in southern Sweden had >100 times higher SCP concentrations than clean areas in the north. The spatial distribution of SCP over Sweden is similar to the deposition pattern of long-range transported airborne pollutants, such as excess sulphate monitored by network stations. SCP also accumulate in soils, and soil analyses can be used for determining the integrated historical deposition of SCP at the local or regional scale. Finally, SCP have been used for indirect dating of sediment cores and as a marker to assess sediment distribution patterns within lake basins. 相似文献
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24.
Chantal Guillard Hervé Delprat Can Hoang-van Pierre Pichat 《Journal of Atmospheric Chemistry》1993,16(1):47-59
The photodegradation of naphthalene (NPH), chosen as a model of polynuclear aromatic pollutants, has been studied in the presence of a layer of four water-insoluble inorganic solids which can be found in the troposphere (TiO2, Fe2O3, muscovite, and a fly ash sample). Direct photolysis of NPH is negligible at >340 nm. Dark adsorption of NPH on TiO2 (mainly anatase, nonporous, 50 m2 g–1) at 293 K corresponds to a surface coverage ofca. 50% at equilibrium. Under these conditions (saturated surface), the stationary-state photocatalytic degradation reaches 0.4 molecule nm–2 h–1 (>340 nm, radiant fluxca. 22 mW cm–2). Dioxygen is required and its partial pressure in air is such that the degradation is zero order in O2. Water vapor markedly increases the rate. The other particulates have also an effect, less important than that of TiO2, however quite noticeable with respect to surface area unit for the fly ash sample which contains 3.2% Fe2O3. Apart from 1,4-naphthoquinone, which is the main intermediate product in all cases, 2-naphthol, phthalide, phthaldialdehyde, phthalic acid, acetophenone, benzaldehyde, benzoic acid are also formed on dry TiO2. Depending on their volatility, these compounds are transferred to the gas phase or remain principally adsorbed on the solid particles where they are further transformed. For instance, phthalic acid (or anhydride) and benzoic acid are generated from 1,4-naphthoquinone. Degradation mechanisms are briefly discussed. 相似文献
25.
26.
东北漫岗黑土区春季冻融期浅沟侵蚀 总被引:7,自引:0,他引:7
浅沟侵蚀是东北漫岗黑土区农耕地上常见的水蚀类型,往往对坡耕地造成严重的破坏。2005年春季,通过对两个小流域浅沟侵蚀的调查测量,发现该区浅沟侵蚀相当严重,两流域分别形成浅沟14条、16条,浅沟总长度分别达3 269 m、2 146 m,浅沟密度分别为908 m/km2、766 m/km2,侵蚀深度分别为0.17 mm、0.16 mm,侵蚀模数分别达181.8 t/km2、173.6 t/km2。2005年春季两流域浅沟侵蚀期的径流深分别是6.8 mm、7.7 mm。分析表明,研究区在春季表层土壤解冻、地表裸露和存在季节性冻土层的条件下,春季融雪及强降水易造成强烈的浅沟侵蚀。在分布上,浅沟一般位于坡面的中下部,而且多发育在瓦背状坡面的集流水路上。另外,耕作措施对浅沟的形成和发展也有重要影响。 相似文献
27.
Deformation-induced garnet zoning 总被引:1,自引:0,他引:1
Compositional zoning patterns in garnet porphyroblasts from kyanite-bearing samples of the Devonian Littleton Formation, north-central Massachusetts, reveal complex patterns of growth that are related to multiple deformation and metamorphic events. Garnet porphyroblasts exhibit asymmetrical and irregular zoning patterns in XMn, XCa and Fe/(Fe + Mg). Zoning reversals in Mn and Fe/(Fe + Mg) and patch distribution in Ca appear to occur around the boundaries of the textural zones. Also, the compositions of the garnet at the textural boundaries are variable for all traverses. These observations suggest that the garnet zoning was not only modified from diffusion processes, but was also influenced by pre-existing microfabrics through the effects of preferential dissolution and resorption in partial disequilibrium. Relationships between chemical and textural truncations indicate that the zoning patterns of garnet were strongly modified from preferential dissolution and precipitation during the development of successive foliations that occurred in zones of high strain/stress (cleavage seams) and zones of low strain/stress, respectively. 相似文献
28.
YANG Xuchao ZHANG Yili ZHANG Wei YAN Yuping WANG Zhaofeng DING Mingjun CHU Duo 《地理学报》2006,16(3):326-336
Using monthly average, maximum, minimum air temperature and monthly precipitation data from 5 weather stations in Mt. Qomolangma region in China from 1971 to 2004, climatic linear trend, moving average, low-pass filter and accumulated variance analysis methods, the spatial and temporal patterns of the climatic change in this region were analyzed. The main findings can be summarized as follows: (1) There is obvious ascending tendency for the interannual change of air temperature in Mt. Qomolangma region and the ascending tendency of Tingri, the highest station, is the most significant. The rate of increasing air temperature is 0.234 oC/decade in Mt. Qomolangma region, 0.302 oC/decade in Tingri. The air temperature increases more strongly in non-growing season. (2) Compared with China and the global average, the warming of Mt. Qomolangma region occurred early. The linear rates of temperature increase in Mt. Qomolangma region exceed those for China and the global average in the same period. This is attributed to the sensitivity of mountainous regions to climate change. (3) The southern and northern parts of Mt. Qomolangma region are quite different in precipitation changes. Stations in the northern part show increasing trends but are not statistically significant. Nyalam in the southern part shows a decreasing trend and the sudden decreasing of precipitation occurred in the early 1990s. (4) Compared with the previous studies, we find that the warming of Mt. Qomolangma high-elevation region is most significant in China in the same period. The highest automatic meteorological comprehensive observation station in the world set up at the base camp of Mt. Qomolangma with a height of 5032 m a.s.l will play an important role in monitoring the global climate change. 相似文献
29.
Environmental Changes at the Desert Margin: An Assessment of Recent Paleolimnological Records in Lake Qarun, Middle Egypt 总被引:1,自引:0,他引:1
R. J. Flower C Stickley N. L. Rose S Peglar A. A. Fathi P. G. Appleby 《Journal of Paleolimnology》2006,35(1):1-24
Lake Qarun has been profoundly affected by a combination of human activities and climatic changes during the past 5000 years.
Instrumental records available for the 20th century show that during most of this period both lake water level and salinity increased and that by the late 1980s lake water salinity was approximately that of seawater.
Sediment cores (c. 1 m long) were collected from this shallow (Zmax 8.4 m) saline lake in 1998 and the master core (QARU1) was used to examine the potential of paleolimnology for reconstructing
the recent environmental history of the site. According to 137Cs and 210Pb radio-assay, the recent sediment accumulation rate in QARU1 was around 5 mm year−1 during the latter half of the 20th century but radionuclide levels were low. Spheroidal carbonaceous particles (SCPs) were
present in the upper c. 30 cm of QARU1 and indicates contamination by low level particulate pollution, probably beginning
around 1950. The record of exotic pollen (Casuarina) indicated that sediment at 51–52 cm depth dated to around 1930. Otherwise the pollen spectra indicated a strongly disturbed
landscape with high ruderals and increased tree planting particularly since c. 1950. Diatom records were strongly affected
by taphonomic processes including reworking and differential preservation but typical marine diatoms increased after the 1920s.
Instrumental records show that the lake became more saline at this time. Freshwater taxa were present at approximately similar
abundances throughout the core. This distribution probably reflected a combination of processes. Reworking of ancient freshwater
diatomites is one likely source for freshwater diatoms in QARU1 but some taxa must also be contributed via the freshwater
inflows. Overall, the diatom stratigraphy indicated increasingly salinity since the 1920s but provided no firm evidence of
lake eutrophication. Diatom inferred salinity reconstructions were in only partial agreement with instrumental records but
inferred for the lower section of the core (pre 20th century to the 1960s) accord with measured water salinity values. Surficial
sediments of Lake Qarun contain environmental change records for the 20th century period but high sediment accumulation rate
and pollen reflect the high degree of human disturbance in the region. Because of poor preservation and evidence of reworking,
the relationships between diatom records and past water quality changes require careful interpretation, especially in the
upper section of the core. Nevertheless, early to mid 20th century measurements of increasing lake water salinity are well
supported by sediment records, a change that is probably linked to ingress of saline ground water 相似文献
30.
Diurnal Variations of Hydrochemistry in a Travertine-depositing Stream at Baishuitai, Yunnan, SW China 总被引:6,自引:0,他引:6
Zaihua Liu Qiang Li Hailong Sun Changjun Liao Huaju Li Jinliang Wang Kongyun Wu 《Aquatic Geochemistry》2006,12(2):103-121
Diurnal variations of hydrochemistry were monitored at a spring and two pools in a travertine-depositing stream at Baishuitai,
Yunnan, SW China. Water temperature, pH and specific conductivity were measured in intervals of 5 and 30 min for periods of
1 to 2 days. From these data the concentrations of Ca2+, HCO3−, calcite saturation index, and CO2 partial pressure were derived. The measurements in the spring of the stream did not show any diurnal variations in the chemical
composition of the water. Diurnal variations, however, were observed in the water of the two travertine pools downstream.
In one of them, a rise in temperature (thus more CO2 degassing) during day time and consumption of CO2 due to photosynthesis of submerged aquatic plants accelerated deposition of calcite, whereas in the other pool, where aquatic
plants flourished and grew out of the water (so photosynthesis was taking place in the atmosphere), the authors suggest that
temperature-dependent root respiration underwater took place, which dominated until noon. Consequently, due to the release
of CO2 by the root respiration into water, which dominated CO2 production by degassing induced by temperature increase, the increased dissolution of calcite was observed. This is the first
time anywhere at least in China that the effect of root respiration on diurnal hydrochemical variations has been observed.
The finding has implications for sampling strategy within travertine-depositing streams and other similar environments with
stagnant water bodies such as estuaries, lakes, reservoirs, pools and wetlands, where aquatic plants may flourish and grow
out of water. 相似文献