Validation of a vegetated filter strip model (VFSMOD)   总被引：2，自引：0，他引：2  

Majed Abu‐Zreig  R. P. Rudra  H. R. Whiteley 《水文研究》2001,15(5):729-742

Vegetated filter strips (VFS) are designed to reduce sediment load and other pollutants into water bodies. However, adaptation of VFS in the field has been limited owing to lack of data about their efficiency and performance under natural field conditions. A number of models are available that simulate sediment transport and trapping in VFS, but there is a general lack of confidence in VFS models owing to limited validation studies and model limitations that prevent correct application of these models under field conditions. The objective of this study is to test and validate a process‐based model (VFSMOD) that simulates sediment trapping in VFS. This model links three submodels: modified Green–Ampt's infiltration, Quadratic overland flow submodel based on kinematic wave approximation and University of Kentucky sediment filtration model. A total of 20 VFS, 2, 5, 10 and 15 m long and with various vegetation covers, were tested under simulated sediment and runoff conditions. The results of these field experiments were used to validate the VFS model. The model requires 25 input parameters distributed over five input files. All input parameters were either measured or calculated using experimental data. The observed sediment trapping efficiencies varied from 65% in the 2‐m long VFS to 92% in the 10‐m long filters. No increase in sediment removal efficiency was observed at higher VFS length. Application of the VFS model to experimental data was satisfactory under the condition that actual flow widths are used in the model instead of the total filter width. Predicted and observed sediment trapping efficiencies and infiltration volume fitted very well, with a coefficient of determination (R²) of 0·9 and 0·95, respectively. Regression analyses revealed that the slope and intercept of the regression lines between predicted versus observed infiltration volume and trapping efficiency were not significantly different than the line of perfect agreement with a slope of 1·0 and intercept of 0·0. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

Theoretical investigation of iron isotope fractionation between Fe(H₂O)₆ and Fe(H₂O)₆: Implications for iron stable isotope geochemistry     

A.D. Anbar  A.A. Jarzecki  T.G. Spiro 《Geochimica et cosmochimica acta》2005,69(4):825-837

The magnitude of equilibrium iron isotope fractionation between Fe(H₂O)₆³⁺ and Fe(H₂O)₆²⁺ is calculated using density functional theory (DFT) and compared to prior theoretical and experimental results. DFT is a quantum chemical approach that permits a priori estimation of all vibrational modes and frequencies of these complexes and the effects of isotopic substitution. This information is used to calculate reduced partition function ratios of the complexes (10³ · ln(β)), and hence, the equilibrium isotope fractionation factor (10³ · ln(α)). Solvent effects are considered using the polarization continuum model (PCM). DFT calculations predict fractionations of several per mil in ⁵⁶Fe/⁵⁴Fe favoring partitioning of heavy isotopes in the ferric complex. Quantitatively, 10³ · ln(α) predicted at 22°C, ∼ 3 ‰, agrees with experimental determinations but is roughly half the size predicted by prior theoretical results using the Modified Urey-Bradley Force Field (MUBFF) model. Similar comparisons are seen at other temperatures. MUBFF makes a number of simplifying assumptions about molecular geometry and requires as input IR spectroscopic data. The difference between DFT and MUBFF results is primarily due to the difference between the DFT-predicted frequency for the ν₄ mode (O-Fe-O deformation) of Fe(H₂O)₆³⁺ and spectroscopic determinations of this frequency used as input for MUBFF models (185-190 cm⁻¹ vs. 304 cm⁻¹, respectively). Hence, DFT-PCM estimates of 10³ · ln(β) for this complex are ∼ 20% smaller than MUBFF estimates. The DFT derived values can be used to refine predictions of equilibrium fractionation between ferric minerals and dissolved ferric iron, important for the interpretation of Fe isotope variations in ancient sediments. Our findings increase confidence in experimental determinations of the Fe(H₂O)₆³⁺ − Fe(H₂O)₆²⁺ fractionation factor and demonstrate the utility of DFT for applications in “heavy” stable isotope geochemistry.  相似文献   

Experimental investigation of runoff reduction and sediment removal by vegetated filter strips   总被引：2，自引：0，他引：2  

Majed Abu‐Zreig  Ramesh P. Rudra  Manon N. Lalonde  Hugh R. Whiteley  Narinder K. Kaushik 《水文研究》2004,18(11):2029-2037

The impact of vegetated filter strips (VFS) on sediment removal from runoff has been studied extensively in recent years. Vegetation is believed to increase water infiltration and decrease water turbulence thus enhancing sediment deposition within filter media. In the study reported here, field experiments have been conducted to examine the efficiency of vegetated filter strips for sediment removal from cropland runoff. Twenty filters with varying length, slope and vegetated cover were used under simulated runoff conditions with an average sediment concentration of 2700 mg/L. The filters were 2, 5, 10 and 15 m long with a slope of 2·3 and 5% and three types of vegetation. Three other strips with bare soil were used as a control. The experimental results showed that the average sediment trapping efficiency of all filters was 84% and ranging from 68% in a 2‐m filter to as high as 98% in a 15‐m long filter compared with only 25% for the control. The length of filter has been found to be the predominant factor affecting sediment deposition in VFS up to 10 m. Increasing filter length to 15 m did not improve sediment trapping efficiency under the present experimental conditions. The rate of incoming flow and vegetation cover percentage has a secondary effect on sediment deposition in VFS. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

Iron isotope fractionation during planetary differentiation   总被引：4，自引：0，他引：4  

Stefan Weyer  Ariel D. Anbar  Carsten Münker  Alan B. Woodland 《Earth and Planetary Science Letters》2005,240(2):251-264

The Fe isotope composition of samples from the Moon, Mars (SNC meteorites), HED parent body (eucrites), pallasites (metal and silicate) and the Earth's mantle were measured using high mass resolution MC-ICP-MS. These high precision measurements (δ⁵⁶Fe ≈ ± 0.04‰, 2 S.D.) place tight constraints on Fe isotope fractionation during planetary differentiation.Fractionation during planetary core formation is confined to < 0.1‰ for δ⁵⁶Fe by the indistinguishable Fe isotope composition of pallasite bulk metal (including sulfides and phosphides) and olivine separates. However, large isotopic variations (≈ 0.5‰) were observed among pallasite metal separates, varying systematically with the amounts of troilite, schreibersite, kamacite and taenite. Troilite generally has the lightest (δ⁵⁶Fe ≈ − 0.25‰) and schreibersite the heaviest (δ⁵⁶Fe ≈ + 0.2‰) Fe isotope composition. Taenite is heavier then kamacite. Therefore, these variations probably reflect Fe isotope fractionation during the late stage evolution and differentiation of the S- and P-rich metal melts, and during low-temperature kamacite exsolution, rather than fractionation during silicate-metal separation.Differentiation of the silicate portion of planets also seems to fractionate Fe isotopes. Notably, magmatic rocks (partial melts) are systematically isotopically heavier than their mantle protoliths. This is indicated by the mean of 11 terrestrial peridotite samples from different tectonic settings (δ⁵⁶Fe = + 0.015 ± 0.018‰), which is significantly lighter than the mean of terrestrial basalts (δ⁵⁶Fe = + 0.076 ± 0.029‰). We consider the peridotite mean to be the best estimate for the Fe isotope composition of the bulk silicate Earth, and probably also of bulk Earth. The terrestrial basaltic mean is in good agreement with the mean of the lunar samples (δ⁵⁶Fe = + 0.073 ± 0.019‰), excluding the high-Ti basalts. The high-Ti basalts display the heaviest Fe isotope composition of all rocks measured here (δ⁵⁶Fe ≈ + 0.2‰). This is interpreted as a fingerprint of the lunar magma ocean, which produced a very heterogeneous mantle, including the ilmenite-rich source regions of these basalts.Within uncertainties, samples from Mars (SNC meteorites), HED (eucrites) and the pallasites (average olivine + metal) have the same Fe isotope compositions as the Earth's mantle. This indicates that the solar system is very homogeneous in Fe isotopes. Its average δ⁵⁶Fe is very close to that of the IRMM-014 standard.  相似文献   

DIVERSITY OF EPHEMEROPTERA, PLECOPTERA AND TRICHOPTERA IN VARIOUS TRIBUTARIES OF TEMENGGOR CATCHMENT, PERAK, MALAYSIA     

Che Salmah M R Abu Hassan A Jongkar G 《湿地科学》2007,5(1):20-31

Ephemeroptera(mayfly),Plecoptera(stonefly)and Trichoptera(caddisfly)(EPT,3 kinds of insectorders)reach their maximum development in streamsand contain families that are entirely or almost con-fined to running water.Ross(1963)suggested thatthe early evolut…  相似文献   

The active Kalabsha Fault Zone in Southern Egypt: detecting faulting activity using field-structural data and EMR-technique,and implications for seismic hazard assessment     

Z. Hamimi  W. Hagag  R. Osman  M. El-Bialy  I. Abu El-Nadr  M. Fadel 《Arabian Journal of Geosciences》2018,11(15):421

Since November 14, 1981 earthquake (ML 5.6), about 60 km southwest of Aswan High Dam, the seismic hazard raised and the Aswan Local Seismic Network (ALSN) has recorded and precisely monitored the seismic activity in the vicinity of the High Dam. The major source of seismic activity in this region is the active Kalabsha Fault Zone (KFZ). The focal mechanism solutions indicate that two nodal planes strike E to ENE, with subordinate right-lateral strike-slip component and N to NNW, with left-lateral movement. The directions of tectonic extension (T) and compression (P) are NNE-SSW and NNW-SSE, respectively. Structural investigations and application of the Electromagnetic Radiation (EMR) technique reveal ongoing activity on the KFZ. Kinematic evolution of the KFZ implies faulting events with a strong movement intervened with periods of severe crushing, grinding, and even pulverization. Such tectonic processes have resulted in fault-breccia and fault-gouge. Results obtained from the present study indicate that the KFZ is not a single transcurrent wrench fault with dextral sense of movement but, instead, it represents a major dextral transtensional shear or fault zone deforming southern Egypt and plays a significant role in the structural shaping of the area to the west of Nasser Lake. Furthermore, the activity on the KFZ is most probably controlling the seismic cycle in the area. Topographic expression of KFZ is evidently realized at Sinn El-Kaddab scarp, as well as at Gebel Marawa. Frequent surface rupturing and newly recorded strong seismic activity advocate faulting reactivation supported by the EMR data, which suggest an active fault system oriented ENE-WSW and NNW-SSE affecting the KFZ, with a maximum horizontal stress (σ1) perturbing between ENE and NNW directions.  相似文献   

Geological evolution of Nile Valley,west Sohag,Upper Egypt: a geotechnical perception     

El-Sayed Sedek Abu Seif 《Arabian Journal of Geosciences》2015,8(12):11049-11072

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Fertile Lithospheric Mantle Beneath the North African Plate: Evidence from Gharyan Lherzolite Xenoliths (Northern West Libya)     

Mohamed M. Hamdy  Youngwoo Kil  Hassan Abu Arabia 《Petrology》2018,26(5):546-563

The late-stage basanite (～12–1 Ma) of the NNW-SSE extending Gharyan Cenozoic volcanics (Northern West Libya) contains numerous fresh lherzolite xenoliths. These xenoliths display magmatic protogranular and porphyroclastic textures. Chemistry of olivine (forsterite content –90–91, NiO = 0.26–0.39 wt %), orthopyroxene (Mg# = 0.91–0.92, Cr# = 0.03–0.07, Al₂O₃ = 3.64–4.43 wt %), clinopyroxene ((Wo_{45.59–48.61}, En_{45.89–48.80}, Fs_4.47–5.81), Mg# = 0.82–0.92, Al₂O₃ = 5.14–6.58 wt % and Cr₂O₃ = 0.5–0.95 wt %) and spinel (hercynite–picotite–Al-rich chromite spinels with Cr# = 0.08–0.11) refer to the fertile nature of Gharyan peridotites. Mantle source region was close to the primitive composition with low degrees of melting and depletion in melt (1.5% in average). However, it underwent metasomatism as illustrated by formation of secondary clinopyroxene (Wo_{37.96–44.77}, En_{47.44–54.18}, Fs_7.59–8.03) with high contents of Na₂O, and enrichment of the Al-spinel in TiO₂. The estimated pre-eruptive temperature ranges from 1066 to 837°C. Despite the Gharyan peridotite is similar to mantle components in many districts in Saharan belt of North Africa, it represents juvenile mantle source with minor refractory residues. This compositional heterogeneity is mainly attributed to the local effect of the interaction of the Gharyan mantle with the host basanite magma that may be related to the Cenozoic rifting of the Pan-African basement.  相似文献   

The photochemistry of manganese and the origin of Banded Iron Formations     

Anbar AD  Holland HD 《Geochimica et cosmochimica acta》1992,56(7):2595-2603

The photochemical oxidation of Fe(2+) -hydroxide complexes dissolved in anoxic Precambrian oceans has been suggested as a mechanism to explain the deposition of Banded Iron Formations (BIFs). Photochemical studies have not yet addressed the low levels of manganese in many of these deposits, which probably precipitated from solutions bearing similar concentrations of Fe2+ and Mn2+. Depositional models must also explain the stratigraphic separation of iron and manganese ores in manganiferous BIFs. In this study, solutions containing 0.56 M NaCl and approximately 180 micromoles MnCl2 with or without 3 to 200 micromoles FeCl2 were irradiated with filtered and unfiltered UV light from a medium-pressure mercury-vapor lamp for up to 8 hours. The solutions were deaerated and buffered to pH approximately 7, and all experiments were conducted under O2-free (< 1 ppm) atmospheres. In experiments with NaCl + MnCl2, approximately 20% of the Mn2+ was oxidized and precipitated as birnessite in 8 hours. Manganese precipitation was only observed when light with lambda < 240 nm was used. In experiments with NaCl + MnCl2 + FeCl2, little manganese was lost from solution, while Fe2+ was rapidly oxidized to Fe3+ and precipitated as gamma-FeOOH or as amorphous ferric hydroxide. The Mn:Fe ratio of these precipitates was approximately 1:50, similar to the ratios observed in BIFs. A strong upper limit on the rate of manganese photo-oxidation during the Precambrian is estimated to be 0.1 mg cm-2 yr-1, a factor of 10(3) slower than the rate of iron photo-oxidation considered reasonable in BIF depositional basins. Thus, a photochemical model for the origin of oxide facies BIFs is consistent with field observations, although models that invoke molecular O2 as the oxidant of Fe2+ and Mn2+ are not precluded. Apparently, oxide facies BIFs could have formed under anoxic, as well as under mildly oxygenated atmospheres.  相似文献   

Hunza river watershed landslide and related features inventory mapping     

M. Farooq Ahmed  J. David Rogers  Muhammad Zubair Abu Bakar 《Environmental Earth Sciences》2016,75(6):523

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