Drought impacts on water quality and potential implications for agricultural production in the Maipo River Basin,Central Chile     

M. D. Peña-Guerrero  A. Nauditt  C. Muñoz-Robles  L. Ribbe  F. Meza 《水文科学杂志》2020,65(6):1005-1021

ABSTRACT

Droughts can have serious negative impacts on the water quality needed for irrigated agriculture. The Metropolitan region of Chile is a relevant producer of high-value crops and is prone to droughts. Standardized Drought Indices were used to characterize meteorological and hydrological droughts for the period from 1985 to 2015. To understand the relationship between droughts and water quality, we evaluated the correlations between daily discharge and surface water quality observations. The threshold level method was used to compare physicochemical parameters during hydrological drought periods with the Chilean water quality thresholds for agricultural uses. A significant (p < 0.05) negative relationship between discharge and electrical conductivity and major ions was found in most of the basin. Hydrological stations located in irrigation districts exceeded the official thresholds for these parameters during hydrological drought periods seriously threatening irrigated agriculture of the region.  相似文献   

New controversies on Columbus' “cosmographic” ideas     

M. Peñaloza  A. Marcos 《GeoJournal》1994,32(4):415-423

This paper examines the spatial distribution of the functional systems in the different belts of settlements around Budapest. The surburban belts have an important role in the capital's labour market, places of employment and recreation with 45 settlements. The paper reviews the structure of the Budapest agglomeration from the core to the three inner, middle and outer belts comprising the suburbs, the semi-urban settlements, the suburban villages, the satellite towns, and the satellite villages. Then the system of the functional urban centres are reviewed, The author establishes the concept of the main, the division, the district and the settlement group centres in the Budapest agglomeration. The different levels of attached functions, such as international, national, regional and local are also described with each centre type. The areal distribution of the centre system of Budapest is shown in maps too.  相似文献   

Le champ électrique atmosphérique à Dakar     

O. Salvador  H. Masson 《Meteorology and Atmospheric Physics》1957,10(2-3):216-223

Résumé Les mesures de champ électrique atmosphérique sont jusqu'à présent assez rares dans les régions de faible latitude. Il nous a semblé intéressant d'entreprendre des observations à Dakar afin de pouvoir comparer les résultats recueillis avec ceux obtenus ailleurs et de mettre en évidence les anomalies éventuelles.

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Summary Atmospheric potential gradient measurements are rare enough up to now in low latitude. It seemed interesting to undertake observations at Dakar in order to compare the results obtained with those obtained elsewhere and to consider possible anomalies.

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Zusammenfassung Messungen des luftelektrischen Potentialgefälles sind in niedrigen Breiten bisher ziemlich selten. Wir haben daher Beobachtungen in Dakar angestellt und die Ergebnisse mit den in anderen Gegenden ausgeführten Messungen verglichen.

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Avec 6 Figures  相似文献   

Gravity ideal-body analysis     

Pavel Peška  Reviewers J. Švancara  Reviewers K. Pěč 《Studia Geophysica et Geodaetica》1989,33(4):405-408

Summary This short note contributes to the methods of computing the bounds on some properties of the source of measured data.  相似文献   

Overcoring measurements in the příbram mine area and their relation to the regional stress field     

Pavel Peška 《Studia Geophysica et Geodaetica》1993,37(2):141-150

Summary A set of overcoring measurements in deep mines near Píbram is re-interpreted in order to obtain information on the regional component of in situ stress. This is achieved by averaging 17 complete stress tensors measured at the deepest level of the mine, at a depth of 1240 m. The computations indicate that (1) the mean principal stresses act roughly in the horizontal and vertical directions, and (2) the maximum principal stress is horizontal, acting NW - SE, which was also confirmed by the data from all 42 sites of the mine area. The NW - SE orientation of S_H is consistent with the stress pattern in Western Europe and also with borehole breakouts observed within the Bohemian Massif, but the quality of the stress indicator obtained is poor — the standard deviation of the S_H direction is 26°. High variance of the directional data is discussed with respect to stress redistribution due to the mine workings and the contact separating Proterozoic sediments from the Variscan pluton.  相似文献   

Simulating a century of soil erosion for agricultural catchment management          下载免费PDF全文

Hugh G. Smith  Andrés Peñuela  Heather Sangster  Haykel Sellami  John Boyle  Richard Chiverrell  Daniel Schillereff  Mark Riley 《地球表面变化过程与地形》2018,43(10):2089-2105

Agricultural land management requires strategies to reduce impacts on soil and water resources while maintaining food production. Models that capture the effects of agricultural and conservation practices on soil erosion and sediment delivery can help to address this challenge. Historic records of climatic variability and agricultural change over the last century also offer valuable information for establishing extended baselines against which to evaluate management scenarios. Here, we present an approach that combines centennial‐scale reconstructions of climate and agricultural land cover with modelling across four lake catchments in the UK where radiometric dating provides a record of lake sedimentation. We compare simulations using MMF‐TWI, a catchment‐scale model developed for humid agricultural landscapes that incorporates representation of seasonal variability in vegetation cover, soil water balance, runoff and sediment contributing areas. MMF‐TWI produced mean annual sediment exports within 9–20% of sediment core‐based records without calibration and using guide parameter values to represent vegetation cover. Simulations of land management scenarios compare upland afforestation and lowland field‐scale conservation measures to reconstructed historic baselines. Oak woodland versus conifer afforestation showed similar reductions in mean annual surface runoff (8–16%) compared to current moorland vegetation but a larger reduction in sediment exports (26–46 versus 4–30%). Riparian woodland buffers reduced upland sediment yields by 15–41%, depending on understorey cover levels, but had only minor effect on surface runoff. Planting of winter cover crops in the lowland arable catchment halved historic sediment exports. Permanent grass margins applied to sets of arable fields across 15% or more of the catchment led to further significant reduction in exports. Our findings show the potential for reducing sediment delivery at the catchment scale with land management interventions. We also demonstrate how MMF‐TWI can support hydrologically‐informed decision making to better target conservation measures in humid agricultural environments. Copyright © 2018 John Wiley & Sons, Ltd.  相似文献   

A model for catchment soil erosion management in humid agricultural environments          下载免费PDF全文

Andrés Peñuela  Haykel Sellami  Hugh G. Smith 《地球表面变化过程与地形》2018,43(3):608-622

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Estimates of Horizontal Groundwater Flow Velocities in Boreholes     

Martí Bayer-Raich  Anthony Credoz  Jordi Guimerà  Salvador Jordana  Diego Sampietro  Jordi Font-Capó  Nathalie Nief  Matthieu Grossemy 《Ground water》2019,57(4):525-533

Currently, monitoring tools can be deployed in observation boreholes to better assess groundwater flow, flux of dissolved contaminants and their mass discharge in an aquifer. The relationship between horizontal water velocity in observation boreholes and Darcy fluxes in the surrounding aquifer has been studied for natural flow conditions (i.e., no pumping). Interpretation of measurements taken with dilution tests, the colloidal borescope, the Heat Pulse Flowmeter, and other techniques require the conversion of observed borehole velocity u to aquifer Darcy flux q_∞ . This conversion is typically done through a proportionality factor α = u/q_∞ . In experimental studies as well as in theoretical developments, reported values of α vary almost three orders of magnitude (from 0.5 to 10). This large variability in reported values of α could be explained by: (1) unclear distinction between Darcy flux and water seepage velocity, (2) unclear definition of water velocity in the borehole, (3) effects of well screen and the presence of the measurement device itself on the observable velocities, and (4) hydraulic conditions in the borehole annulus. We address (1), (2) from a conceptual/theoretical perspective, and (3) by means of numerical simulations. We show that issue (1) in low porosity aquifers can yield to order-of-magnitude discrepancies in estimates of q_∞ ; (2) may result in discrepancies of up to 50%, and (3) can cause differences up to 20% of water velocity in the borehole void space compared to the theoretical case of an open borehole.  相似文献   

Upward infiltration–evaporation method to estimate soil hydraulic properties     

C. Peña-Sancho  T.A. Ghezzehei  B. Latorre  C. González-Cebollada  D. Moret-Fernández 《水文科学杂志》2017,62(10):1683-1693

Determination of saturated hydraulic conductivity, K_s, and the van Genuchten water retention curve θ(h) parameters is crucial in evaluating unsaturated soil water flow. The aim of this work is to present a method to estimate K_s, α and n from numerical analysis of an upward infiltration process at saturation (Cap0), with (Cap0 + h) and without (Cap0) an overpressure step (h) at the end of the wetting phase, followed by an evaporation process (Evap). The HYDRUS model as well as a brute-force search method were used for theoretical loam soil parameter estimation. The uniqueness and the accuracy of solutions from the response surfaces, K_s–n, α–n and K_s–α, were evaluated for different scenarios. Numerical experiments showed that only the Cap0 + Evap and Cap0 + h + Evap scenarios were univocally able to estimate the hydraulic properties. The method gave reliable results in sand, loam and clay-loam soils.  相似文献   

Effects of water quality on infiltration,runoff and interrill erosion processes during simulated rainfall     

Lorenzo Borselli  Dino Torri  Jean Poesen  Pilar Salvador Sanchis 《地球表面变化过程与地形》2001,26(3):329-342

This paper discusses the effects of water quality on the hydrological and erosion response of non‐saline, non‐sodic soils during simulated rain experiments. It is well known that rain water quality affects the behaviour of saline soils. In particular, rain simulation experiments cannot be run using tap water if realistic values of infiltration rates and soil erosion are to be found. This paper reports on similar effects for non‐saline, non‐sodic soils. Two soils – a well‐aggregated clay‐rich soil developed on marine silty clay deposits and a soil developed on silt loam – were selected and subjected to a series of simulated rainstorms using demineralized water and tap water. The experiments were conducted in two different laboratories in order to obtain results independent of the tap water quality or the rainfall simulator characteristics. The results indicate that time‐to‐ponding is largely delayed by solute‐rich water (tap water). When tap water is used, infiltration rates are significantly overestimated, i.e. by more than 100 per cent. Interrill erosion rates increase by a factor of 2·5–3 when demineralized water is used. The silty clay soil was more affected by the water quality than the silt loam soil, with respect to infiltration and runoff production. Regarding interrill erosion rates, the two tested soils were similarly affected by the water quality. Therefore, it can be concluded that rainfall simulation experiments with non‐dispersive soils (e.g. non‐saline, non‐sodic) must also be conducted using water with very low electrical conductivity (i.e. less than 30–50 µS cm⁻¹), close to that of distilled water. The use of tap water certainly hampers comparisons and the relative ranking of the hydrological and erosion response of different soils, while parameter values, such as final infiltration rate or time‐to‐ponding, cannot be extrapolated and extended to natural situations. Therefore, the majority of hydrological and erosion models and parameter values measured during rainfall simulations in the past should be used with caution for all types of soils. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献