Interpretation of the behaviour of agrowell systems in Sri Lanka using radial flow models     

C. S. DE SILVA  K. R. RUSHTON 《水文科学杂志》2013,58(6):825-835

Abstract

This paper describes a study of the use of large diameter “agrowells” used for irrigation in Sri Lanka. Detailed field information for a single location is presented and a numerical radial flow model was used to interpret the field response. Initially the model was used to represent a pumping test in which the pumping and subsequent recovery were monitored. It was then used to investigate the operation of the well during a dry season. Satisfactory agreement could only be obtained when account was taken of the withdrawal of water from below the water table by trees. From the simulation it was possible to show that skilful farming practice could be used in steadily exploiting the resources for irrigation over the whole of the dry season.  相似文献   

Modelling solute leaching during fingered flow by integrating and expanding various theoretical and empirical concepts     

GERRIT H. DE ROOIJ  HIROYUKI CHO 《水文科学杂志》2013,58(3):447-465

Abstract

Wetting front instability (fingered flow) accelerates solute transport through the unsaturated zone to the groundwater table. Whether fingers widen or dissipate close to the groundwater is unclear. Water flow in a two-dimensional artificial capillary fringe below a dry layer exhibiting fingered flow was investigated. The flow diverged strongly in the wet soil, suggesting that fingers dissipate. Expressions for the finger radius in dry and wet soil were combined and adapted to a soil hydraulic property parameterization popular in numerical modelling. The modified equation provided finger radii for soils in humid and arid climates. The fingers in the arid soil were excessively wide. The finger radii were used to model solute transport, assuming fingers dissipated in the subsoil. Modelling was cumbersome for the arid climate. One shower may often be insufficient to trigger fingering in arid regions with short, heavy showers. In soils with shallow groundwater, the diverging subsoil flow determines solute leaching.  相似文献   

Younger Dryas – early Holocene transition in the south‐eastern Iberian Peninsula: insights from land snail shell middens     

YURENA YANES  MAGDALENA GÓMEZ‐PUCHE  MARCO A. ESQUEMBRE‐BEBIA  JAVIER FERNÁNDEZ‐LÓPEZ‐DE‐PABLO 《第四纪科学杂志》2013,28(8):777-788

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Evaporation of grass under non-restricted soil moisture conditions     

H. A. R. DE BRUIN  J. N. M. STRICKER 《水文科学杂志》2013,58(3):391-406

Abstract

The behaviour of various formulas for evapotranspiration of grass in Nonrestricted soil water conditions is considered. These are the expressions based on the Penman formula, i.e. “old” Penman, Penman-Monteith, Thorn-Oliver and the version recommended more recently by the FAO. Moreover, the Priestley-Taylor and the Makkink formulas are considered, which are radiation-based. Comparisons are made between daily mean values estimated with these formulas and direct measurements. The latter were collected over grass in the period 1979–1982 in the catchment area of the Hupselse Beek (The Netherlands). It was found that if all required input data were measured, the Priestley-Taylor and the “old” Penman formula yielded the best results. The assumption that soil heat flux can be neglected introduces a systematic and a random error of roughly 5%. The empirical estimates for net radiation from sunshine duration, temperature and humidity appear to perform rather poorly. These estimates improved significantly if solar radiation was measured directly. The empirical expression proposed by Slob (unpublished) that requires incoming solar radiation only as input, provided better results than the other more complicated expressions. Moreover, this study reveals that evaporation of unstressed grass is primarily determined by the available energy, i.e. good evaporation estimates can be obtained by using simply λE = 0.86(R_n ? G). The Makkink method appears to be attractive for practical applications. These findings support the use of Makkink's formula for routine calculations of crop-reference evapotranspiration as has been done by the Royal Netherlands Meteorological Institute since 1987.  相似文献   

DAMOCLES: a DAshing MOnolith Cutter for fine sectioning of peats and sediments into LargE Slices     

HANS JOOSTEN  PIM DE KLERK 《Boreas: An International Journal of Quaternary Research》2007,36(1):76-81

Simple cutting devices such as used in the printing industry allow precise and fine sectioning of frozen peats and sediments, thus enabling research with high temporal resolution. Large slices are useful in the collection of multiple synchronous subsamples for multidisciplinary research. This article describes the apparatus (called DAMOCLES) and its operation, and presents some examples from practice. These include combined microfossil, macrofossil and chemical analyses of the same sample with a sample resolution of 0.5 cm (temporal resolution c. 1 year): rapid changes occur that would have remained unnoticed with a coarser sampling distance. The final example presents a sample resolution of only 0.5 mm. These examples illustrate the possible uses of the DAMOCLES apparatus in palaeoecological research.  相似文献   

Late Holocene in central Brazil: vegetation changes and humidity variability in a tropical wetland     

SHIRLEY MARIA LIMA SABINO  RAQUEL FRANCO CASSINO  MAKÊNIA OLIVEIRA SOARES GOMES  ENEIDA MARIA ESKINAZI SANT'ANNA  CRISTINA HELENA RIBEIRO ROCHA AUGUSTIN  DIEGO ALVES DE OLIVEIRA 《第四纪科学杂志》2021,36(6):1028-1039

The Pandeiros wetland is a high biodiversity ecosystem located within a semiarid region of the Cerrado biome, a neotropical savanna. This large wetland is of key importance for ecological and hydrological balance in central Brazil and for the conservation of the Cerrado fauna and flora. In this study, we present the first palaeoecological investigation of the Pandeiros wetland based on pollen analysis of a palm swamp sediment core encompassing the Late Holocene. Our results show that the wetland was subject to multicentennial-scale oscillations in water availability during the Late Holocene; in particular, higher local humidity was documented between 4100 and 3100 cal a bp and from 2600 to 1000 cal a bp , and two events of drier local conditions occurred at approximately 2900 and 900 cal a bp. Our results also indicate a general decreasing trend in arboreal density in the Pandeiros River Basin from the beginning of the Late Holocene to the present, with the greatest expansion of dry forest occurring between 3600 and 3100 cal a bp.  相似文献   

Morphological patterns of Aptian Lithocodium–Bacinella geobodies: relation to environment and scale     

NIELS RAMEIL  ADRIAN IMMENHAUSER  GEORG WARRLICH  HEIKO HILLGÄRTNER  HENK J. DROSTE 《Sedimentology》2010,57(3):883-911

Lithocodium aggregatum and Bacinella irregularis are now extinct, shallow marine life forms of unknown taxonomic origin. Forming part of the tropical platform biota during much of the Mesozoic, these organisms experienced bloom periods and temporarily replaced rudist–coral assemblages during parts of the Early Aptian. Within the limitations of time resolution, this ‘out‐of‐balance’ facies is coeval with the Oceanic Anoxic Event 1a‐related black shale deposition in oceanic basins but the triggering factors remain poorly understood. Here, a platform‐wide comparison of Lithocodium–Bacinella geobodies and morphotypes from the Sultanate of Oman is presented and placed in its environmental, bathymetric and physiographic context. Lithocodium–Bacinella geobodies reach from kilometre‐scale ‘superstructures’ to delicate centimetre‐sized growth forms. Clearly, scale matters and care must be taken when drawing conclusions based on spatially limited observational data. Whilst the factors that cause Lithocodium–Bacinella expansion should probably be considered in a global context, regional to local factors affected growth patterns in a more predictable manner. Here, the unresolved taxonomic relationship remains the main obstacle in any attempt to unravel the response of Lithocodium–Bacinella to specific or interlinked environmental parameters as different organisms respond differently to changing environment. Acknowledging these limitations, the following tentative patterns are observed: (i) Lithocodium–Bacinella tolerated a wide range of hydrodynamic levels and responded to differences in energy level or physiographic settings (margin, intrashelf basin, inner platform) by obtaining characteristic growth forms. (ii) Lithocodium–Bacinella favoured low‐sediment input but had the ability to react to higher sedimentation rates by enhanced upward growth; a feature perhaps pointing to a phototrophic metabolism. Circumstantial evidence for continuous growth within the upper‐sediment column is debated. (iii) The availability of accommodation space had a direct influence on the maximum size of geobodies formed. (iv) Fluctuating nutrient levels and sea water alkalinity may have affected the growth potential of Lithocodium–Bacinella. Understanding the relationship between Lithocodium–Bacinella morphogenesis on a wide range of scales and local environmental parameters allows for better prediction of the spatial distribution of reservoir properties and also results in an improved interpretation of palaeoenvironments. This study might represent a useful first step in this direction.  相似文献   

New early winter f_CO2 data reveal continuous uptake of CO₂ by the Weddell Sea     

M. H. C. STOLL  H. J. W. DE BAAR  M. HOPPEMA  E. FAHRBACH 《Tellus. Series B, Chemical and physical meteorology》1999,51(3):679-687

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Relict Majoritic Garnet Microstructures from Ultra-Deep Orogenic Peridotites in Western Norway   总被引：9，自引：1，他引：9  

VAN ROERMUND  H. L. M.; DRURY  M. R.; BARNHOORN  A.; DE RONDE  A. 《Journal of Petrology》2001,42(1):117-130

Protogranular, porphyroclastic and equigranular (or equant-polygonal)garnet microstructures from Mg–Cr type orogenic garnetperidotites, Otrøy, Western Gneiss Region, Norway, havebeen studied using naked eye, light-optical, electron-opticaland confocal laser (fluorescence) microscopy techniques. Protogranularand porphyroclastic garnets contain microstructural evidencefor the former existence of majoritic (or super-silicic) garnet.The microstructural evidence consists of exsolution texturesinvolving pyroxene. Two types of exsolution microstructuresoccur—needles parallel to <111>_grt and interstitialgrains. The maximum volume percentage for intra-crystallinepyroxene exsolution is 2·7, and 3·6 for inter-crystallinepyroxene exsolution. The maximum pyroxene total volume percentagemeasured in one single protogranular or porphyroclastic garnetis 4·0. This value, at 1200°C, corresponds to minimumpressures of 6·4 GPa (  相似文献   

COMMENT ON 'SECONDARY SHEAR WAVES FROM SOURCE BOREHOLES’ BY J. A. MEREDITH,M. N. TOKSÖZ AND C. H. CHENG1     

J. A. DE BRUIN 《Geophysical Prospecting》1993,41(8):1067-1069

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