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1.
The population growth of the freshwater chlorophyte, Scenedesmus acutus and the cladoceran Moina macrocopa cultured in the laboratory and in microcosms of a wastewater treatment plant was studied. S. acutus was cultured in a defined algal medium and mixed with wastewater. On diets of S. acutus cultured using Bold medium or a mixture with wastewater, the peak densities of M. macrocopa were 6–7 ind. mL?1, while on a diet of algae cultured on wastewater alone the cladoceran density fluctuated around 2 ind. mL?1. Population growth rates of M. macrocopa, which ranged from 0.3 to 0.4 d?1, were significantly lower on alga cultured in wastewater alone. The body size structure of M. macrocopa was larger on algae cultured in Bold medium than in wastewater. Peak densities of M. macrocopa were around 700 ind. L?1 when the organic matter in the containers was supplemented with algae but it reached lower densities (400 ind. L?1) when cultured on the organic matter in wastewater alone. Our study indicates that the nutrients in the final stages of wastewater treatment can support the growth of both phytoplankton and zooplankton.  相似文献   

2.
为了检验已记录的3种裸腹溞(发头裸腹溞(Moina irrasa)、短型裸腹溞(Moina brachiata)、微型裸腹溞(Moina micrura))的系统分类,用试剂盒法分别提取3种裸腹溞的基因组DNA.利用特异性引物,通过PCR扩增了3种裸腹溞的16S r DNA部分序列,并与来自Gen Bank中每个种类相似度较高的裸腹溞属序列进行分析.结果表明,3种裸腹溞的平均种间相似度为88.7%,碱基中A+T含量均明显高于G+C含量.本研究的发头裸腹溞的16S r DNA序列与Gen Bank所下载的多刺裸腹溞(Moina macrocopa)的16S r DNA序列相似度为99%,遗传距离(K2P双参考模型)为0.5%,属种内范围;两个地区的短型裸腹溞测得的16S r DNA序列与Gen Bank下载的欧洲短型裸腹溞的16S r DNA序列序列相似度相对较低(88%~90%),遗传距离较大(13.2%~13.5%左右),已达到属内种间分化水平.基于16S r DNA构建的NJ树和贝叶斯树也支持以上结论.结果表明,本研究的发头裸腹溞可能为多刺裸腹溞,本研究用的短型裸腹溞与Gen Bank下载的欧洲短型裸腹溞已经达到种间分化的标准.由于缺乏物种形态资料和其他分子标记的对比,3种裸腹溞的分类地位还需进行更深入的探讨.  相似文献   

3.
In the present work we tested the effect of Chlorella vulgaris and Scenedesmus acutus in different proportions on the population growth of Brachionus calyciflorus, Brachionus patulus, Ceriodaphnia dubia, and Moina macrocopa. In general, both rotifer species grew well on either type of algae. Regardless of algal mixture, B. calyciflorus had a shorter initial phase, while B. patulus needed more than a week to begin the exponential phase of growth. Both the rotifer species showed consistently better population growth with Chlorella than on Scenedesmus, or the mixture. At any given algal combination, B. patulus had higher peak values than B. calyciflorus. The rate of population increase (r) for both the rotifers varied from 0.18 to 0.48 d—1 depending on the algal type and combination. Regardless of algal type and combination, B. calyciflorus had a much higher value of r than B. patulus. Both C. dubia and M. macrocopa grew on the algal types, whether offered separately or in mixture. Regardless of the treatment type, C. dubia needed a longer period (about 2 weeks) than M. macrocopa to reach peak abundances. Thus, our study did not support the view that Scenedesmus is consistently superior to Chlorella as a basic diet to the tested species of zooplankton.  相似文献   

4.
Active layer thickness (ALT) is critical to the understanding of the surface energy balance, hydrological cycles, plant growth, and cold region engineering projects in permafrost regions. The temperature at the bottom of the active layer, a boundary layer between the equilibrium thermal state (in permafrost below) and transient thermal state (in the atmosphere and surface canopies above), is an important parameter to reflect the existence and thermal stability of permafrost. In this study, the Geophysical Institute Permafrost Model (GIPL) was used to model the spatial distribution of and changes in ALT and soil temperature in the Source Area of the Yellow River (SAYR), where continuous, discontinuous, and sporadic permafrost coexists with seasonally frozen ground. Monthly air temperatures downscaled from the CRU TS3.0 datasets, monthly snow depth derived from the passive microwave remote-sensing data SMMR and SSM/I, and vegetation patterns and soil properties at scale of 1:1000000 were used as input data after modified with GIS techniques. The model validation was carried out carefully with ALT in the SAYR has significantly increased from 1.8 m in 1980 to 2.4 m in 2006 at an average rate of 2.2 cm yr?1. The mean annual temperature at the bottom of the active layer, or temperature at the top of permafrost (TTOP) rose substantially from ?1.1°C in 1980 to ?0.6°C in 2006 at an average rate of 0.018°C yr?1. The increasing rate of the ALT and TTOP has accelerated since 2000. Regional warming and degradation of permafrost has also occurred, and the changes in the areal extent of regions with a sub-zero TTOP shrank from 2.4×104 to 2.2×104 km2 at an average rate of 74 km2 yr?1. Changes of ALT and temperature have adversely affected the environmental stability in the SAYR.  相似文献   

5.
Decompression experiments of a crystal-free rhyolitic liquid with ≈ 6.6 wt. % H2O were carried out at a pressure range from 250 MPa to 30–75 MPa in order to characterize effects of magma ascent rate and temperature on bubble nucleation kinetics, especially on the bubble number density (BND, the number of bubbles produced per unit volume of liquid). A first series of experiments at 800°C and fast decompression rates (10–90 MPa/s) produced huge BNDs (≈ 2 × 1014 m−3 at 10 MPa/s ; ≈ 2 × 1015 m−3 at 90 MPa/s), comparable to those in natural silicic pumices from Plinian eruptions (1015–1016 m−3). A second series of experiments at 700°C and 1 MPa/s produced BNDs (≈ 9×1012 m−3) close to those observed at 800°C and 1 MPa/s (≈ 6 × 1012 m−3), showing that temperature has an insignificant effect on BNDs at a given decompression rate. Our study strengthens the theory that the BNDs are good markers of the decompression rate of magmas in volcanic conduits, irrespective of temperature. Huge number densities of small bubbles in natural silicic pumices from Plinian eruptions imply that a major nucleation event occurs just below the fragmentation level, at which the decompression rate of ascending magmas is a maximum (≥ 1 MPa/s).  相似文献   

6.
Self-diffusion of oxygen in a natural phlogopite mica (annite 4%) has been measured under hydrothermal conditions at 2000 bars pressure and from 500 to 800°C using water enriched in18O. Diffusional transport is dominantly parallel to the c crystallographic axis. A linear Arrhenius plot was obtained with a pre-exponential term = (1.03 ± 0.38) × 10?9cm2sec?1 a and an activation energy of 29 ± 2kcal/g-atom O. The difference in transport rate between oxygens in the OH groups and those in tetrahedral sites is small to non-existent unless the OH oxygens diffuse much more slowly than the other oxygens, which we consider unlikely. A typical phlogopite crystal, 0.2 mm thick by 1 mm across will lose radiogenic argon faster than it will exchange oxygen at temperatures above 435°C, but the reverse holds at lower temperatures if the diffusion mechanism can be extrapolated to temperatures below 500°C. Such a crystal will lose only 5% of its argon if held at 380°C for 1 m.y., but could exchange 27% of its oxygen in that time. The rate at which phlogopite will undergo deformation by diffusional creep does not appear to be controlled by oxygen diffusion.  相似文献   

7.
武汉东湖超微藻生态学的初步研究   总被引：7，自引：2，他引：5  
王建  林婉莲 《湖泊科学》1998,10(4):71-76
论述了武汉东湖超微藻年数量,叶绿素含量,生产量分布,于室内模拟了不同光强与不同浓度Ｐ营养对超微藻光合性能的影响,同时与国外海洋与淡水超微藻的生产力,生物量和各自所占百分比进行了比较。文中还就东湖超微藻分布与生态环境之间关系进行了讨论。  相似文献   

8.
Recycling domestic wastewaters is one way to maximize the utilization of freshwater. Although sewage treatment plants help to remove particulate wastes, organic matter still remains, which can be used to harvest sizeable populations of zooplankton. In an effort to identify cladocerans which could grow on this organic matter, we tested the life table demography of the commonly found cladocerans (Alona rectangula, Ceriodaphnia dubia, Moina macrocopa, and Daphnia pulex) feeding on wastewater at three different stages of purification (tank that receives crude wastes (A), the biological reactor (B), and the penultimate stage of the treatment process (C)) from the Iztacalco water treatment plant in Mexico City. Experiments were conducted using the medium from each of the 3 tanks previously mentioned and a control of Chlorella vulgaris at 1.0 × 106 cells mL?1. We found that the average lifespan ranged from 5…30 days with D. pulex living the longest. The growth rate, which ranged from ?0.57 to +1.5 was highest for M. macrocopa. Our data indicate that Moina macrocopa, which had higher reproductive rates on wastewater than the controls, was most suited for growing in wastewaters.  相似文献   

9.
Data for the diffusion of cations in pyroxenes are relevant to a variety of sub-solidus processes including order-disorder and exsolution. Similar data must also be available if the reliability of geobarometers and geothermometers involving pyroxenes is to be assessed. Two types of diffusion experiment have been performed to determine cation diffusion rates in pyroxenes: (1) interdiffusion between single crystals of diopside and polycrystalline sinters enriched in Al and Fe, and (2) interdiffusion between single crystals of diopside and a glass of the same composition which was isotopically enriched in26Mg and43Ca. Following high-temperature annealing for periods up to several hundred hours, analysis of the diffusion couples, using an electron microprobe and an ion microprobe respectively, failed to show any measurable diffusion profiles. From these “null result” experiments the diffusion coefficients (D) for Al and Fe in diopside are estimated to be less than4×10?14cm2s?1 at 1200°C, and values ofD for Ca and Mg in diopside are estimated to be less than7 × 10?14cm2s?1 at 1250°C. These rates are significantly slower than published tracer-type diffusion data for Ca and Al.A review of studies of order-disorder, microstructural coarsening, and diffusion in pyroxenes suggest that activation energies for cation exchange are typically in excess of 60 kcal mol?1. Transport rates will be assisted, and activation energies lowered by sample non-stoichiometry, inhomogeneities, high dislocation densities and the presence of water.The collective data for Al, Mg and Ca diffusion in diopside indicate diffusion coefficients? 10?15cm2s?1 at 1200°C. A comparison with data for diffusion in garnet, olivine and spinel suggests that pyroxenes may have the highest blocking temperatures.  相似文献   

10.
The reaction of CO + OH? in aqueous solution to give formate was studied as a carbon monoxide sink on the primitive earth and in the present ocean. The reaction is first order in OH? and first order in the molar CO concentration. The second order rate constant is given by log k(M?1hr?1) = 15.83?4886/T between 25°C and 60°C. Using the solubility of CO in sea water, and assuming a pH of 8 for a primitive ocean of the present size, the halflife of CO in the atmosphere is calculated to be 12 × 106 yr at 0°C and 5.5 × 104 yr at 25°C.Three other CO sinks would have been important in the primitive atmosphere: CO + H2 → H2CO driven by various energy sources, CO + OH → CO2 + H, and the Fischer-Tropsch reaction of CO + H2 → hydrocarbons, etc. It is concluded that the lifetime of a CO atmosphere would have been very short on the geological time scale although the relative importance of these four CO sinks is difficult to estimate.The CO + OH? reaction to give formate is a very minor CO sink on the earth at the present time.  相似文献   

11.
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12.
To be used as proxies of seawater surface temperature(SST), the δ 18Oc values and Sr/Ca and Mg/Ca ratios of scleractinian coral skeletons must be verified by coral culture experiments in the laboratory. This paper describes a coral culture experiment that was conducted at several seawater temperatures T(21–28°C) using a tandem aquarium system and the new method for depositing coral skeletons grown under controlled conditions. The δ 18Oc values and the Sr/Ca and Mg/Ca ratios of the cultured coral were measured. We concluded that the δ 18Oc values and Sr/Ca and Mg/Ca ratios of the cultured coral are clearly correlated with T. The linear regression curve is δ18Oc(‰)=δ0.1427δT(°C)δ0.1495(n=18, r=0.955, p0.0001), and the slope of δ0.1427‰/°C is at the low end of the range of published values(δ0.13–δ0.29‰/°C). The Sr/Ca ratio decreases with increasing T, whereas the Mg/Ca ratio increases with increasing T, indicating a negative correlation between Sr/Ca and Mg/Ca. Their linear regression curves are Sr/Ca(mmol/mol)=δ0.04156δT+10.59(n=15, r=0.789, p0.005) and Mg/Ca(mmol/mol)= 0.04974δT+2.339(n=17, r=0.457, p0.05), respectively, which demonstrate that when Mg/Ca and Sr/Ca are increased by one unit, T increases by 5.19°C and decreases by 15.62°C, respectively. These variations are significantly lower than published values.  相似文献   

13.
We describe a simple method for nearly isotropic revelation of fission tracks in zircon. The etchant is an equivolume mixture of 48% HF and 98% H2SO4; etching is carried out under pressure at 150° – 180°C. For fossil track densities above ～ 5 × 106, the etching time is strongly anticorrelated with track density. The total etchable fission fragment track length (2 fragments) is 11 ± 0.5 μm. The length distribution is sharply peaked; the standard deviation in different samples is ± (0.7 – 0.8) μm. Thermal annealing studies indicate a lower activation energy for track fading than was previously repoted using a phosphoric acid etchant. A practical chemical dissolution method is described for quantitatively recovering zircon crystals from rock samples; this method should find application in fission track dating of even zircon poor rocks.  相似文献   

14.
The measurement of the176Lu/175Lu ratio in the Oklo uranium ore zones where nuclear reactions have been identified, can be related to the average equilibrium temperature of the neutrons at the time of the nuclear reactions; indeed, the effective neutron capture cross section of the isotope176Lu is particularly sensitive to temperature. A simple model has been developed to calculate the temperature. The results obtained on seven samples from three reactor zones are presented. From six samples an average value of280 ± 50°C is obtained, the corresponding integrated neutron flux τ varies from 0.06 × 1020 to 6 × 1020 n/cm2 and176Lu/175Lu from 0.0254 to 0.0054. From one sample a very high temperature is obtained:T > 1000°C, τ = 4.4 × 1020n/cm2,176Lu/175Lu= 0.0032. The validity of this result is sharply dependent on the relative stability of uranium and the rare earths during and after the nuclear reactions; so, it can be noticed that the two samples giving the highest temperatures present a surprisingly high enrichment in heavy rare earth elements.  相似文献   

15.
Illite clay particles with adsorbed137Cs were added as a submillimeter layer to the surface of silt-clay sediments contained in rectangular Plexiglas cells stored in a temperature-regulated aquarium, in order to trace the effect of the oligochaete, Tubifex tubifex, and the amphipod, Pontoporeia hoyi, on mass redistribution near the sediment-water interface. A well-collimated NaI gamma detector scanned each sediment column (～10 cm deep) at daily or weekly intervals for six months, depicting the time evolution of radioactivity with and without added benthos. In a cell with tubificids (～5 × 104 m?2), which feed below 3 cm and defecate on surface sediments, the labeled layer was buried at a rate of 0.052 ± 0.007 cm/day (20°C). When labeled particles entered the feeding zone,137Cs reappeared in surface sediments creating a bimodal activity profile. In time, the activity tended toward a uniform distribution over the upper 6 cm, decreasing exponentially below to undetectable levels by 9 cm. In a cell with amphipods (～1.6 × 104 m?2) uniform activity developed rapidly (～17 days) down to a well-defined depth (1.5 cm). The mixing of sediments by Pontoporeia is described by a simple quantitative model of eddy diffusive mixing of sediment solids. The value of the diffusion coefficient, 4.4 cm2/yr (7°C) was computed from a least squares fit of theoretical to observed profile broadening over time. In a cell without benthos, small but measurable migration of137Cs indicated an effective molecular diffusion coefficient of 0.02 cm2/yr.  相似文献   

16.
The experimental studies done at high temperature and high pressure find that increased temperature can lead to dramatic velocity and strength reductions of most of rocks at high confining pressure[1,2]. What causes this phenomenon? Is it due to dehydrati…  相似文献   

17.
Diffusion coefficients for Si, Ti, Al, Na, K, Ca, Mg and Fe between pairs of glasses of basaltic, rhyolitic or phonolitic compositions have been determinated experimentally. This method involves the heating of coaxial cylinders of paired glasses under atmospheric conditions, over a range of temperatures from 900 to 1300°C, followed by microprobe analysis determination of the concentration gradients across the interface.The measured diffusivities are similar for all cations and range from 10?13 cm2/s at 900°C to 5 × 10?9 cm2/s at 1300°C. Depending mainly on the composition contrast, the diffusion is characterized by asymmetrical concentration profiles. This peculiar feature increases with temperature and chemical gradients across the contact surface of the glasses and leads to higher diffusion coefficients (D) in the more “basic” glass of a given pair. In the case of the rhyolite-basalt couple, this variation increases by a factor of about 10 at 1300°C. Diffusion dependence on temperature follows an Arrhenius equation which gives activation energies ranging from 65 to 85 kcal/mole. Assuming a constant and overall D for the two glasses we have attempted to apply our results to some geological examples such as exchanges between molten enclaves and liquids of contrasting composition.  相似文献   

18.
Viscosity of anhydrous albite melt, determined by the falling-sphere method in the solid-media, piston-cylinder apparatus, decreases with increasing pressure from 1.13 × 105 P at 1 atm to 1.8 × 104 P at 20 kbar at 1400°C. The rate of decrease in viscosity is larger between 12 and 15 kbar than in other pressure ranges examined. The density of the quenched albite melt increases with increasing pressure of quenching from 2.38 g/cm3 at 1 atm to 2.53 g/cm3 at 20 kbar. The rate of increase in density is largest at pressures between 15 and 20 kbar. The melting curve of albite shows an inflexion at about 16 kbar. These observations strongly suggest that structural changes of albite melt would take place effectively at pressures near 15 kbar. Melt of jadeite (NaAlSi2O6) composition shows very similar changes in viscosity and density and a melting curve inflexion at pressures near 10 kbar. Difference in pressure for the suggested effective structural changes of albite and jadeite melts is 5–6 kbar, which is nearly the same as that between the subsolidus reaction curves nepheline + albite= 2jadeite and albite=jadeite + quartz. The structural changes of the melts are, however, continuous and begin to take place at pressures lower than those of the crystalline phases.  相似文献   

19.
— We have evaluated how the parameters prescribing the slip-dependent constitutive law are affected by temperature and effective normal stress, by conducting the triaxial fracture experiments on Tsukuba-granite samples in seismogenic environments, which correspond to a depth range to 15 km. The normalized critical slip displacement D c almost remains constant below 300oC (insensitive to both temperature and effective normal stress σ n eff); D c increases with increasing temperature above 300 °C, and the rate of D c increase with temperature tends to be largest at higher σ n eff. The breakdown stress drop Δτ b for the granite at constant σ n eff is roughly 80 MPa below 300 °C, and does not depend on σ n eff. Above 300 °C, Δτ b decreases gradually with increasing temperature, and the rate of Δτ b reduction with temperature increases at higher σ n eff. The peak shear strength τ p increases nearly linearly with increasing σ n eff below 300 °C. However, τ p becomes lower above 300 °C, deviating from the linear relation extrapolated from below 300 °C. This is consistent with the onset of crystal plastic deformation mechanisms of Tsukuba granite.  相似文献   

20.
河流中浮游植物的动态变化能够较好的指示河流水质状况.为探索水文气象过程对筑坝河流浮游植物群落结构的影响,2020年夏季,以钱塘江干流为例,对包括富春江水库在内的11个河段开展了浮游植物群落结构及相关环境因子的调查分析.结果 表明:夏季在钱塘江干流共鉴定出浮游植物6门59属95种,优势属为沟链藻(Aulacoseir、菱...  相似文献   

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