Impact of soil and water conservation measures on catchment hydrological response—a case in north Ethiopia     

Jan Nyssen  Wim Clymans  Katrien Descheemaeker  Jean Poesen  Ine Vandecasteele  Matthias Vanmaercke  Amanuel Zenebe  Marc Van Camp  Mitiku Haile  Nigussie Haregeweyn  Jan Moeyersons  Kristine Martens  Tesfamichael Gebreyohannes  Jozef Deckers  Kristine Walraevens 《水文研究》2010,24(13):1880-1895

Impact studies of catchment management in the developing world rarely include detailed hydrological components. Here, changes in the hydrological response of a 200‐ha catchment in north Ethiopia are investigated. The management included various soil and water conservation measures such as the construction of dry masonry stone bunds and check dams, the abandonment of post‐harvest grazing, and the establishment of woody vegetation. Measurements at the catchment outlet indicated a runoff depth of 5 mm or a runoff coefficient (RC) of 1·6% in the rainy season of 2006. Combined with runoff measurements at plot scale, this allowed calculating the runoff curve number (CN) for various land uses and land management techniques. The pre‐implementation runoff depth was then predicted using the CN values and a ponding adjustment factor, representing the abstraction of runoff induced by the 242 check dams in gullies. Using the 2006 rainfall depths, the runoff depth for the 2000 land management situation was predicted to be 26·5 mm (RC = 8%), in line with current RCs of nearby catchments. Monitoring of the ground water level indicated a rise after catchment management. The yearly rise in water table after the onset of the rains (ΔT) relative to the water surplus (WS) over the same period increased between 2002–2003 (ΔT/WS = 3·4) and 2006 (ΔT/WS >11·1). Emerging wells and irrigation are other indicators for improved water supply in the managed catchment. Cropped fields in the gullies indicate that farmers are less frightened for the destructive effects of flash floods. Due to increased soil water content, the crop growing period is prolonged. It can be concluded that this catchment management has resulted in a higher infiltration rate and a reduction of direct runoff volume by 81% which has had a positive influence on the catchment water balance. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Temporal patterns and controls on runoff magnitude and solution chemistry of urban catchments in the semiarid southwestern United States     

Erika L. Gallo  Paul D. Brooks  Kathleen A. Lohse  Jean E. T. McLain 《水文研究》2013,27(7):995-1010

Urban expansion and the scarcity of water supplies in arid and semiarid regions have increased the importance of urban runoff to localized water resources. However, urban catchment responses to precipitation are poorly understood in semiarid regions where intense rainfall often results in large runoff events during the short summer monsoon season. To evaluate how urban runoff quantity and quality respond to rainfall magnitude and timing, we collected stream stage data and runoff samples throughout the 2007 and 2008 summer monsoons from four ephemeral drainages in Tucson, Arizona. Antecedent rainfall explained 20% to 30% of discharge (mm) and runoff ratio in the least impervious (22%) catchment but was not statistically related to hydrologic responses at more impervious sites. Regression models indicated that rainfall depth, imperviousness and their combined effect control discharge and runoff ratios (p < 0.01, r² = 0.91 and 0.75, respectively). In contrast, runoff quality did not vary with imperviousness or catchment size. Rainfall depth and duration, time since antecedent rainfall and event and cumulative discharge controlled runoff hydrochemistry and resulted in five specific solute response patterns: (i) strong event and seasonal solute mobilization (solute flush), (ii) event chemostasis and strong seasonal flush, (iii) event chemostasis and weak seasonal flush, (iv) event and seasonal chemostasis and (v) late seasonal flush. Our results indicate that hydrologic responses of semiarid catchments are controlled by rainfall partitioning at the event scale, whereas wetting magnitude, frequency and timing alter solute stores readily available for transport and control temporal runoff quality. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Contamination of the Marcy Anorthosite Massif,Adirondack Mountains,NY: petrologic and isotopic evidence     

Jean Morrison  John W. Valley 《Contributions to Mineralogy and Petrology》1988,98(1):97-108

Oxygen isotope analyses of 101 samples from the Marcy Anorthosite Massif (61 from this study, 40 from Taylor 1969), indicate that two major and distinct processes of crustal contamination have affected the massif. Ninety percent of the 93 samples with over 65% plagioclase are enriched in ¹⁸O by 2.6 relative to normal anorthosites or gabbros: the average ¹⁸O for 83 enriched samples is 9.5 Depletions in ¹⁸O occur in 8% of the samples which have values ranging from 3.0 to 5.8 Only 2 of the samples fall within the normal magmatic range for anorthosites.Low ¹⁸O values of 3.0 to 5.8 in the anorthosite occur only near contacts, and a gradient in ¹⁸O occurs near the contact within the border zone of the massif. Low ¹⁸O values in both the anorthosite and adjacent wollastonite skarns (with ¹⁸O down to –1.3) were probably caused by isotopic exchange with heated meteoric water when the anorthosite intruded at shallow levels, prior to Grenvilleage ( 1.1 by) granulite facies metamorphism.The ¹⁸O-enrichment was ascribed to exchange between anorthosite and ¹⁸O-rich marble by means of a pervasive, H₂O-CO₂ fluid during the regional metamorphism by Taylor (1969). However, a number of lines of evidence argue against this hypothesis: 1) the preservation of premetamorphic low ¹⁸O values in anorthosite from the border zone as well as preserved gradients in ¹⁸O from a number of localities, 2) mass balance calculations of the amount of marble necessary to produce the ₁₈O enrichment 3) metamorphic phase equilibria which buffer and to low values, and, 4) recent oxygen isotope analyses show homogeneity which indicates that magmatic oxygen isotope compositions have been preserved. We evaluated the importance of magmatic assimilation of country rock at the present level of intrusion as an alternative cause of the ¹⁸Oenrichment. Samples from 2 distinct lobes of the massif were analyzed: the NE lobe where xenoliths of metasedimentary country rock are common, and the NW lobe, where xenoliths are scarce and the country rock is dominantly granitic. The mean values of ¹⁸O for these two lobes are 9.6 in the NE and 9.3 in the NW. Thus, magmatic assimilation at the present level of exposure probably had only localized and relatively minor effects on the oxygen isotope composition of the massif. This conclusion is supported by Rb/Sr data: variations in Rb content and (₈₇Sr/ ₈₆Sr)_i show that such crustal contamination is localized, generally occurring only in samples near the border zone. All of the available results suggest that the ¹⁸O-enrichment is a magmatic feature, acquired prior to intrusion at the present level of exposure.  相似文献   

Origin and evolution of 2 Ga old carbonatite complex (Ihouhaouene,Ahaggar, Algeria): Nd and Sr isotopic evidence     

Jean Bernard-Griffiths  Jean -Jacques Peucat  Serge Fourcade  Jean -Robert Kienast  Khadidja Ouzegane 《Contributions to Mineralogy and Petrology》1988,100(3):339-348

Associated syenitic rocks and carbonatites from Ihouhaouene, Algeria, have been investigated for their Sr and Nd isotope and trace element geochemistry. A zircon U-Pb emplacement age (1994 +22 -17 Ma) has been obtained from the carbonatites. The REE characteristics, among which the significant and approximately constant negative Eu anomaly and the evolution of (La/Ce)N and (Yb/Lu)N ratios which increase sympathetically with total REE abundances, are considered to be of purely magmatic origin. They are used to constrain the genetic links between syenites and carbonatites. Sr and Nd isotopes suggest a similar source for carbonatites and syenites, which is enriched compared to a chondritic reference: Nd(T)=-6.4 to -8.6 and ISr(T)=0.7097. These features are interpreted as evidence of contamination of a mantle-derived magmatic precursor by continental crust, occurring in a magmatic chamber.  相似文献   

Some aspects of the tectonics of subduction zones     

Jean Aubouin 《Tectonophysics》1989,160(1-4):1-3

The main structures of a subduction zone are as follows.

1. (1) On the outer wall: faults, formed either by reactivation of the structural grain of the oceanic plate, when the latter is slightly oblique to the trench, or by a new fault network parallel to the trench, or both. The width of the faulted zone is about 50 miles.

2. (2) On the inner wall: either an accretionary prism or an extensional fault network, or both; collapsed structures and slumps are often associated, sometimes creating confusion with the accretionary structures.

3. (3) The overall structure of the trench itself is determined by the shape of the edge of the continental crust or of the island arc. Its detailed structure, however, is related to the oceanic plate, namely when the structural grain of the latter is slightly oblique to the trench, which then takes an “en echelon” form. Collapsed units can fill up the trench which is, in that case, restricted to an irregular narrow depression; the tectonic framework of the trench can be buried under a sedimentary blanket when the sedimentation rate is high and the trench bottom is a large, flat area.

Two extreme types of active margins can be distinguished: convergent compressive margins, when the accretionary mechanism is strongly active; and convergent extensional margins where the accretionary mechanism is absent or only weakly active.

The status of a given margin between these two extreme types is related to the convergence rate of the plates, the dip of the subduction zone, the sedimentation activity and the presence of a continental obstacle, because oceanic seamounts and aseismic ridges are easily subducted.

Examples are taken from the Barbados, Middle America, Peru, Kuril, Japan, Nankai, Marianna, Manila, New Hebredes and Tonga trenches.  相似文献   

Extension of Penman's formulae to multi-layer models     

Jean Paul Lhomme 《Boundary-Layer Meteorology》1988,42(4):281-291

In this paper, the well-established multi-layer model originally devised by Waggoner and Reifsnyder (1968) is used. This steady-state model based on an electrical analogue simulates the energy exchange between the vegetation and the atmosphere. A purely mathematical development of the basic equations of this model yields explicit expressions of the total fluxes of sensible and latent heat at the top of the canopy as a function of the net radiation absorbed in each layer, the soil heat flux, the water vapour pressure deficit at a reference height and the whole set of elementary conductances (stomatal, boundary-layer and aerodynamic). These new equations can be considered as a generalization of the familiar Penman's formulae to a multi-layer model.  相似文献   

Description de deux nouvelles Cyclotelles (Bacillariophyceae) de milieux alcalins et eutrophes:Cyclotella costei nov. sp. etCyclotella wuethrichiana nov. sp.     

Jean Claude Druart  François Straub 《Aquatic Sciences - Research Across Boundaries》1988,50(2):182-188

Two new species of the genus Cyclotella are presented which have been discovered during ecological and paleoecological research studies in the littoral zone of two small alkaline eutrophic lakes in France (Lake Paladru) and in Switzerland (Lake Le Loclat). These new species are namedCyclotella costei nov. sp. andCyclotella wuethrichiana nov. sp.  相似文献   

Numerical Modeling of Axisymmetric Flow   总被引：1，自引：0，他引：1  

Ashok Pandit  Jean M. Abi Aoun 《Ground water》1994,32(3):458-464

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Numerical Modeling of Ground-Water Resource Management Options in Kuwait   总被引：1，自引：0，他引：1  

Amitabha Mukhopadhyay  Jawad Al-Sulaimi  Jean Marie Barrat 《Ground water》1994,32(6):917-928

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Uptake of macroelements by the helophytePhalaris arundinacea L.     

Jean Paul Dubois 《Aquatic Sciences - Research Across Boundaries》1994,56(1):70-79

Helophytes are often incorporated into biological wastewater treatment plants. In favourable situations, they can take up large amounts of nutrients. One helophyte, the reed canarygrass (Phalaris arundinacea L.), is fast growing when supplied with sufficient light and nutrients. Experiments were carried out under natural climatic conditions in small plastic tanks filled with sand with regular additions of a balanced and concentrated nutrient solution. In the growing season (May–October), plant production reached 10.5 kg m^–2 of dry biomass, of which 66% was in the aerial parts. Maximum nutrient uptake capacity was reached just after flowering and before senescence (beginning of October): 49% N, 34% P, 52% K and 34% Mg of the input was fixed in the aerial parts, which are easily harvestable. The corresponding values for the below ground parts were 12%, 10%, 11% and 11% respectively. Excretion of K and Mg has been observed when nutrients are translocated to the storage organs.  相似文献