Climate effects on soil erodibility   总被引：3，自引：0，他引：3  

M. P. Salvador Sanchis  D. Torri  L. Borselli  J. Poesen 《地球表面变化过程与地形》2008,33(7):1082-1097

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Modelling increased soil cohesion due to roots with EUROSEM   总被引：3，自引：0，他引：3  

S. De Baets  D. Torri  J. Poesen  M. P. Salvador  J. Meersmans 《地球表面变化过程与地形》2008,33(13):1948-1963

As organic root exudates cause soil particles to adhere firmly to root surfaces, roots significantly increase soil strength and therefore also increase the resistance of the topsoil to erosion by concentrated flow. This paper aims at contributing to a better prediction of the root effects on soil erosion rates in the EUROSEM model, as the input values accounting for roots, presented in the user manual, do not account for differences in root density or root architecture. Recent research indicates that small changes in root density or differences in root architecture considerably influence soil erosion rates during concentrated flow. The approach for incorporating the root effects into this model is based on a comparison of measured soil detachment rates for bare and for root‐permeated topsoil samples with predicted erosion rates under the same flow conditions using the erosion equation of EUROSEM. Through backwards calculation, transport capacity efficiencies and corresponding soil cohesion values can be assessed for bare and root‐permeated topsoils respectively. The results are promising and present soil cohesion values that are in accordance with reported values in the literature for the same soil type (silt loam). The results show that grass roots provide a larger increase in soil cohesion as compared with tap‐rooted species and that the increase in soil cohesion is not significantly different under wet and dry soil conditions, either for fibrous root systems or for tap root systems. Power and exponential relationships are established between measured root density values and the corresponding calculated soil cohesion values, reflecting the effects of roots on the resistance of the topsoil to concentrated flow incision. These relationships enable one to incorporate the root effect into the soil erosion model EUROSEM, through adapting the soil cohesion input value. A scenario analysis shows that the contribution of roots to soil cohesion is very important for preventing soil loss and reducing runoff volume. The increase in soil shear strength due to the binding effect of roots on soil particles is two orders of magnitude lower as compared with soil reinforcement achieved when roots mobilize their tensile strength during soil shearing and root breakage. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Diagnosis of trace metal contamination in sediments: the example of Ensenada and El Sauzal, two harbors in Baja California, Mexico   总被引：1，自引：0，他引：1  

Huerta-Diaz MA  Delgadillo-Hinojosa F  Hernández-Ayón M  Segovia-Zavala JA  García-Esquivel Z  López-Zárate H  Siqueiros-Valencia A  Galindo-Bect S 《Marine environmental research》2008,66(3):345-358

Total metal concentrations in sediments from within Ensenada and El Sauzal Harbors are generally higher than at the mouths. Grain-size analyses suggested that this enrichment could be due to the presence of fine-grained sediments in the inner part of the harbors rather than to anthropogenic perturbations. The (Me/Al)(sample) ratios for Pb, Co, Ni and Fe were significantly higher for Ensenada Harbor relative to El Sauzal Harbor, whereas the ratios for Cd, Mn, Zn and Cu were statistically equivalent for both harbors. Calculated enrichment factors [EF(Me)=(Me/Al)(sample)/(Me/Al)(shale)] indicated that the metals showing slight enrichment were those associated with anthropogenic contamination (Pb, Zn), or probably related to primary productivity in the water column (Cd, Co). The levels of most of the metals were not greatly enriched, a consideration that is of the utmost importance when contamination issues are at stake.  相似文献   

Nutrient Concentrations are High in the Turbid Waters of the Colorado River Delta     

J. Martín Hernndez-Ayn  M. Salvador Galindo-Bect  Bernardo P. Flores-Bez  Saúl Alvarez-Borrego 《Estuarine, Coastal and Shelf Science》1993,37(6)

We studied the seasonal change of the spatial distribution of nitrite (NO^-₂), nitrate (NO^-₃), reactive phosphate (PO^3-₄), and silicate (SiO₂) in the Colorado River Delta. We also generated 24-h time series at one location to study their short-period variability. The delta is a negative estuary. During summer, salinity may be as high as 40. Amplitude of spring tides is as large as 9 m, and this causes great water turbidity by sediment resuspension. Nutrient concentrations were high throughout the whole year, with lower values towards the oceanic region. Maximum nutrient values in the river delta were 15, 53, 11·5 and 92 μM, for NO^-₂, NO^-₃, PO^3-₄, and SiO₂, respectively. Most values were under 2, 40, 5, and 60 μM, for NO^-₂, NO^-₃, PO^3-₄, and SiO₂, respectively. Our nutrient data show no clear seasonal pattern. Possibly, high NO^-₃ values in the delta are due to groundwater input, mostly at the internal extreme, and high NO^-₂, PO^3-₄, and SiO₂ values are due to resuspension of sediments and mixing of porewaters with the water column, caused mainly during spring tides. In the case of NO^-₂, oxidation of NH⁺₄ in the water column would be part of the mechanism. This would explain the high negative correlation between NO^-₃ and sea-level, and the relatively low correlation between the other nutrients and sea-level, for the time series generated at a single location.  相似文献   

Evaluation of the use of photochemical indicators to assess ozone—NOx—VOC sensitivity in the Southwestern Iberian Peninsula     

Nuria Castell  Ariel F. Stein  Enrique Mantilla  Rosa Salvador  Millán Millán 《Journal of Atmospheric Chemistry》2009,63(1):73-91

Understanding the chemical links between ozone (O₃) and its two main precursors, nitrogen oxides (NOx) and volatile organic compounds (VOC), is important for designing effective photochemical smog reduction strategies. This chemical relationship will determine which precursor (NOx or VOC) emission reduction will be more effective for decreasing the ozone formation. Under certain conditions, ozone levels decrease as a result of a reduction in NOx emissions but do not respond significantly to changes in VOC emissions (NOx-sensitive condition), while under other conditions ozone concentrations decrease in response to reductions in VOCs and may even increase when NOx emissions are reduced (VOC-sensitive conditions). Indicator species can be used to assess the sensitivity of ozone to changes in the emissions of its precursors. These indicators are species or species ratios involved in ozone photochemistry which reflect the primary chemical process through which the ozone was formed. In this work we use the MM5-CAMx model system to explore the behaviour of various indicator species during two meteorological situations featuring different atmospheric conditions in a complex terrain area. The results show that indicators based on nitrogen compounds (i.e,. NOy and NOz) are suitable for defining the transition range from VOC- to NOx-sensitive chemistry, and that despite the uncertainties associated with the use of chemical indicators, the ratios O₃/NOy and O₃/NOz may provide a simple and useful way to summarize the response of ozone to changes in NOx and VOC emissions in Southwestern Spain.  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   

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   

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   

Schooling behaviour and environmental forcing in relation to anchoveta distribution: An analysis across multiple spatial scales   总被引：7，自引：4，他引：3  

Arnaud Bertrand  Franois Gerlotto  Sophie Bertrand  Mariano Gutirrez  Luis Alza  Andres Chipollini  Erich Díaz  Pepe Espinoza  Jesús Ledesma  Roberto Quesqun  Salvador Peraltilla  Francisco Chavez 《Progress in Oceanography》2008,79(2-4):264

The Peruvian anchovy or anchoveta (Engraulis ringens) supports the highest worldwide fishery landings and varies in space and time over many scales. Here we present the first comprehensive sub-mesocale study of anchoveta distribution in relation to the environment. During November 2004, we conducted a behavioural ecology survey off central Peru and used a series of observational and sampling tools including SST and CO₂ sensors, Niskin bottles, CTD probes, zooplankton sampling, stomach content analysis, echo-sounder, multibeam sonar, and bird observations. The sub-mesoscale survey areas were chosen from mesoscale acoustic surveys. A routine coast-wide (2000 km) acoustic survey performed just after the sub-mesoscale surveys, provided information at an even larger population scale. The availability of nearly concurrent sub-mesoscale, mesoscale and coast-wide information on anchoveta distribution allowed for a unique multi-scale synthesis. At the sub-mesoscale (100s m to km) physical processes (internal waves and frontogenesis) concentrated plankton into patches and determined anchoveta spatial distribution. At the mesoscale (10s km) location relative to the zone of active upwelling (and age of the upwelled water) and the depth of the oxycline had strong impacts on the anchoveta. Finally, over 100s km the size of the productive area, as defined by the upwelled cold coastal waters, was the determining factor. We propose a conceptual view of the relative importance of social behaviour and environmental (biotic and abiotic) processes on the spatial distribution of anchoveta. Our ecological space has two y-axis; one based on self-organization (social behaviour), and the other based on the environmental processes. At scales from the individual (10s cm), to the nucleus (m), social behaviour (e.g. the need to school) drives spatial organization. At scales larger than the school, environmental forces are the main driver of fish distribution. The conceptual ecosystem models presented in this paper may provide the final links needed to develop accurate forecasts of the spatial distribution of anchoveta over multiple scales.  相似文献   

Quantification of bank erosion in a drained agricultural lowland catchment          下载免费PDF全文

Anthony Foucher  Sébastien Salvador‐Blanes  Rosalie Vandromme  Olivier Cerdan  Marc Desmet 《水文研究》2017,31(6):1424-1437

The long‐term and current volumes of sediment exported from stream banks were calculated as potential sources of sediment in a large pond located at the catchment outlet of a small agricultural lowland basin strongly affected by anthropogenic pressure in France. Bank erosion was measured over a short period using a network of erosion pins along a small stream (1400 m long) to quantify the material exported during a single winter (2012–2013). The material exported by this same stream over the last 69 years was quantified using an original approach involving the comparison of a compilation of three‐dimensional historical stream redesign plans that date back to 1944 with the state of the banks in 2013 (differential global positioning system and LiDAR data). The results suggest that a global trend of material loss along the stream banks monitored by erosion pins, with an average erosion rate of 17.7 mm year^?1 and an average volume of exported material of 75 t km^?1. Over 69 years, this same stream exported an average of 36 t km^?1 year^?1, and the average loss of material from the banks throughout the whole catchment was estimated to be 14 t km^?1 year^?1. The contribution of bank material to the filling of the pond over the last 10 years is between 46% and 52% based on an extrapolation of erosion pin dynamics or between 27% and 30% based on the comparison of LiDAR data to the average historical profile extrapolated for the catchment. These results suggest that bank erosion represents a major source of sediment in degraded waters in traditionally understudied agricultural lowland catchments, where anthropogenic pressures are high.  相似文献