Quantification of phosphorus entrainment in a lowland river by in situ and laboratory resuspension experiments   总被引：2，自引：0，他引：2  

Andreas Kleeberg  Michael Hupfer  Giselher Gust 《Aquatic Sciences - Research Across Boundaries》2008,70(1):87-99

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A 3100-year history of argon isotopic and compositional variation at El Chichón volcano     

D.A. Jones  P.W. Layer  R.J. Newberry 《Journal of Volcanology and Geothermal Research》2008

El Chichón volcano has produced at least 11 eruptive events in the past 8000 years, all of which display a relatively constant trachyandesitic composition. The constancy of the eruptive products attests to the tapping of a long-lived magma chamber and suggests a system held in steady state between the influx of basaltic magma and differentiation of resident magma. We have sampled eruptive products from eight of these events, subjecting their dominant phenocryst phases (plagioclase and hornblende) to argon isotopic analysis in order to investigate the dynamics of a steady state magmatic system. Plagioclase from the older eruptions, 1500 yr BP, 1600 yr BP, 2000 yr BP and 3100 yr BP, display variable enrichment of ⁴⁰Ar (excess argon), whereas hornblende from the same eruptions shows little or no enrichment. In contrast, both plagioclase and hornblende phenocrysts from the younger eruptions in 1982, 550 yr BP, 900 yr BP and 1250 yr BP have argon isotopic ratios near-atmospheric values. Isochron analysis of these mineral phases rules out xenocrystic contamination as the source of excess argon, while mafic enclaves and isotopic and compositional zoning evidence frequent recharge events, suggesting the source of this argon is most likely the same as the source of this basaltic magma; correlation with Cl points to melt/vapor inclusions as the primary host for Ar within the phenocrysts. Argon isotopic variations point to a disturbance of the system between 1500 yr BP and 1250 yr BP, while compositional evidence for a major mafic input is present in the 900 yr BP eruption, indicating a complex relationship between recharge and isotopic signature of eruptive products. The amount of excess argon within a plagioclase phenocryst are a function of variations in melt and vapor inclusion abundance, time elapsed between melt/vapor inclusion entrapment and eruption, variations in Ar abundance in melt (itself a function of vapor exsolution timing) and time variations in Ar isotopic composition of the melt; subdued behavior of hornblende is due to slower diffusion and minimal inclusions.  相似文献   

Behaviour of chlorine prior and during the 79 A.D. Plinian eruption of Vesuvius (southern Italy) as inferred from the present distribution in glassy mesostases and whole-pumices     

S. Signorelli  B. Capaccioni   《Lithos》1999,46(4):171-730

This study deals with the distribution of chlorine in glassy mesostases and whole-pumices from the 79 A.D. Plinian eruption (Somma–Vesuvius volcanic complex, Italy). This explosive event produced a prominent Plinian fall deposit followed by flows and surges. The fall deposit can be divided into two sub-units on the basis of an abrupt change in colour at approximately mid-level: a phonolitic white pumice layer at the base and a tephriphonolitic grey pumice layer at the top. Due to its hybrid nature (a mixture of k-tephritic, tephriphonolitic and phonolitic magmas), information on chlorine behaviour in tephriphonolitic magma has been inferred only by means of mass balance calculations. In the white pumices, chlorine concentrations show constant whole-pumice values, whereas glassy mesostases display significant compositional variations. These variations have been linked to the cryptocrystallisation of leucite in glassy mesostases, which affected the original melt compositions just before and during the eruptive event. In this framework, whole-pumice appears to better represent the pre-eruptive melt compositions. Using chlorine concentration in whole-pumices, a three-stage model of chlorine behaviour prior and during the eruptive event is predicted: (i) free variation during Rayleigh fractionation, according to a system with variance greater than zero; (ii) exsolution of volatile chlorine compounds (e.g., metal chlorides), when chlorine reaches its solubility limit in silicate melt, in coexisting hyper-saline and in dilute immiscible fluids; the variance of the system is zero at a given temperature and pressure; (iii) residual syn-eruptive variable enrichment of chlorine in the melt due to cryptocrystallization of leucite, suggesting a very minor loss of chlorine in the gas phase during the eruption. Although chlorine does not behave as a volatile element during the eruption, it is present in the volcanic plume. This is due to the postulated ‘excess' fluid phase containing chlorine that formed in the magma chamber prior to the eruption. The homogeneous distribution of chlorine in whole pumices, in contrast with a well-established chemical and isotopic layering in Vesuvian magmas prior to Pompei eruption, suggests that the trace element zonation is not directly linked to chlorine distribution in silicic melts.  相似文献   

A Light Portable Steam-driven Ice Drill Suitable for Drilling Holes in Ice and Firn     

Erich Heucke 《Geografiska Annaler: Series A, Physical Geography》1999,81(4):603-609

The purpose of this contribution is to explain the characteristics of a newly developed ice drill which is particularly geared to the needs of glaciologists. It is primarily designed for drilling holes for ablation stakes and for measuring water levels or temperatures in firn areas. Its distinguishing features are its light weight, making it easy to carry even over long distances, and the variety of tasks to which it can be adjusted. Furthermore, it is easy to operate even by one person.
Water is heated in a boiler by two gas flames to produce steam, which flows through an insulated hose to a nozzle. When the valve is opened the issuing steam condenses, and the heat released in the process melts the ice. The heater is constructed in such a way that it can easily be adapted to any form of gas supply locally available. It can be used for drilling in ice as well as in firn. The maximum drilling depth is 13 m in ice and 30 m in firn; hole diameters range from 25 to 45 mm. Mean drilling time is 16 min for 6 m, 35 min for 12 m in ice. The total weight is somewhat less than 16 kg, including all parts needed for drilling holes of 10 m in depth as well as the gas supply for one day. In recent years, devices of this type have been used successfully by scientists in various glaciated regions.  相似文献   

The Tarfala Mass Balance Programme     

Per Holmlund  & Peter Jansson 《Geografiska Annaler: Series A, Physical Geography》1999,81(4):621-631

The Tarfala mass balance programme currently comprises seven glaciers distributed in two, one southerly and one northerly, east-west trending profiles. Of the studied glaciers, Storglaciären has the longest record spanning 1945 to present. The purpose of the programme is to study gradients in mass balance parameters across the northern Scandinavian mountains. The measurements of both winter and summer balance are carried out with significant redundancy each year. In order to maintain such a large programme with limited personnel, different measurement techniques and strategies are applied to the different glaciers according to a priority scale. Storglaciären is the most important glacier in the network and is measured with high accuracy and measurement density. Storglaciren is also used as a reference for all other glaciers in the programme. The other glaciers have sparser measurement systems and are sometimes measured using alternative methods such as snow radar. In general, Swedish glaciers are still responding to the major climatic warming around 1910–1920 by retreat, and the effect of very long response times. However, measured volume change indicates that most glaciers are close to or varying around a quasi-steady state.  相似文献   

Evaluation of the ventilated chamber for measuring evaporation from a forest     

F. X. Dunin  E. A. N. Greenwood 《水文研究》1986,1(1):47-62

Evaporation from a regenerating forest was determined concurrently by atmospheric measurements of the Bowen ratio, soil water depletion, and by weighing lysimeter. The methods agreed closely over 18 days in spring and 11 days in summer. Accordingly, the Bowen ratio technique was then used as the control against which any effect on evaporation by enclosure of the lysimeter with a chamber of varied ventilation rate could be quantified hourly and daily. Accuracy of gas analysis was checked against lysimeter values. Daily evaporation by the lysimeter was generally unaffected by enclosure—on a few afternoons there was a statistically significant enhancement of hourly values by the chamber. This was accounted for by difference in turbulence between chamber and forest. The general agreement in daytime hourly values is attributed to the frequent occurrence of equilibrium evaporation (rate at which evaporation is independent of ventilation). At night, evaporation was higher during enclosure. Comparisons were not possible with rain or dew. Determination of evaporation by gas analysis agreed within about 5 per cent of lysimeter values during a dry period. We conclude that the ventilated chamber as used provides realistic estimates of evaporation by forests. We show how periods of bias can be anticipated and corrected by theory.  相似文献   

稠油注蒸汽热采过程中的水化学问题     

李雨新 《地球科学与环境学报》1993,(4)

本文简要论述了稠油注蒸汽采过程中所引发出的水化学问题,指出:在注蒸汽热采过程中,随着蒸汽的注入,将在储层内自注热井向四周逐渐形成一些连续过渡的温、压、pH值和水相状态不同的汽水浸润带,即蒸汽饱和带→蒸汽过热水混合带→过热水带→与储层温压条件相当的热水带,由于各带内状态条件的不同,故各带内所引发出的水-岩作用(包括矿物的溶解与沉淀作用)将是有所不同的,因而对各带内储层孔隙结构的影响程度也将是不同的。文中还扼要地介绍了对此进行水化学研究的方法原理和研究途径。  相似文献   

Finite element deformation of an elastic, non-uniform medium produced by a dilating or pressurized magma chamber     

F. Quareni 《Geophysical Journal International》1990,101(1):243-249

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居民区附近的深孔台阶控制爆破     

黄寅  李致宗  赵明特 《南方国土资源》1998,(3)

在南宁市五象岭住宅区平场工程中,采用深孔爆破技术进行石方开挖,所采取的技术措施和取得的经验是可行的、有效的,可供类似工程借鉴。  相似文献   

Study of the N, P and Si fluxes between fish farm sediment and seawater. Results of simulation experiments employing a benthic chamber under various redox conditions   总被引：2，自引：0，他引：2  

Christos Belias  Manos Dassenakis  Michael Scoullos   《Marine Chemistry》2007,103(3-4):266-275

The rapidly expanding industry of marine cage fish farming of sea bream (Sparus aurata) and sea bass (Dicentrarchus labrax) in the Mediterranean Sea over the last decade has often had damaging effects on the benthic aquatic environment near the fish farm installations. It has been observed that the food-remains, together with the pellets and metabolic products from fish, frequently form a “nepheloid” sediment layer covering large areas of the seabed. Under these conditions anoxia and/or hypoxia develop and affect benthic communities while the quality of the marine environment deteriorates for long periods, extending even beyond the life span of the fish farm itself. In most cases the affected areas act initially as sediment traps and in a second phase as secondary sources of organic carbon, nutrients and other substances.The aim of this paper is to explore the behaviour of such an affected area under different redox regimes by measuring the fluxes of ammonium, nitrite, nitrate, TDN, phosphate, TDP and silicate between the surface sediment and the overlying waters. To achieve this goal we constructed a prototype benthic chamber capable of sampling considerable quantities of affected undisturbed sediment along with its overlying water. The chamber was transported to the laboratory where simulation experiments reproducing the conditions occurring in nature, including the extreme ones, were carried out and studied carefully. The chamber allows the full and fine control of the dissolved oxygen concentration – and thus of the redox potential – as well as water temperature while subsamples of both water and sediment could be obtained and analysed for a series of chemical substances. The controlled laboratory chamber experiments reproduced four successional phases: 1) deoxygenation, 2) hypoxia, 3) reoxygenation and 4) anoxia.The results showed that even minor changes in the redox conditions at a relatively narrow zone near the water sediment interface have significant impacts on the concentrations of dissolved nitrogen, phosphorus and silicate compounds.With decreasing oxygen supply (phases 1, 2 and 4), the concentrations of ammonium, nitrite, TDN, phosphate, TDP and silicate rapidly increase, those of nitrate decrease. DON and DOP exhibit remarkable fluctuations.During reoxygenation (phase 3) the concentrations of ammonium stabilise, the nitrate concentration decreases while nitrite shows an increasing trend. Decreases in phosphate and silicate concentrations were also observed paralleled by TDP stabilization and DOP increasing trend. TDN shows a relatively small increase while the DON concentration fluctuates significantly.  相似文献