Land use and topography as predictors of nutrient levels in a tropical catchment     

María M. Castillo 《Limnologica》2010,40(4):322-329

The influence of landscape on nutrient concentration and yield was analyzed in a tropical catchment, the Guare River in northern Venezuela. Spatial and temporal variation in nitrate, SRP and total P were determined in 15 sites located along the river mainstem and tributaries. Higher nitrate concentrations and yields were reported from upper sites and both decreased in the downstream direction along the river mainstem. These trends appear to be related to more pronounced slopes and larger proportions of agricultural and forest lands in subcatchments located in the upper part of the basin, and dense algal mats in the lower reaches. Nitrate values were higher during periods of high discharge, suggesting that nitrate is primarily transported by shallow subsurface flow. SRP represented between 60 and 80% of total P. Phosphorus concentrations were homogeneous along the river mainstem and showed little seasonal variation, while yields were higher in the upper basin. Multiple regression identified slope, runoff and agriculture as primary predictors of nitrate and phosphorus across the watershed, which suggests that both natural and anthropogenic landscape characteristics have a strong influence on nutrient levels in the Guare catchment.  相似文献   

The impact of agriculture on solute and suspended sediment load on a Mediterranean watershed after intense rainstorms     

Luís Outeiro  Xavier Úbeda  Joaquim Farguell 《地球表面变化过程与地形》2010,35(5):549-560

The solute and suspended‐sediment load following five rainstorms (2005–2007) with varied intensities were studied at the Vernegà experimental watershed, north‐western Spain. Two land‐use areas are located within this watershed, the upstream one (forest) with 160 ha a 100% forested area, and the downstream one (agricultural) with 97 ha being 9 ha conventional agricultural field and 88 ha forest. This study investigates the capacity of each land‐use to yield water, suspended sediment concentration (SSC) and dissolved solid concentration (DSC). The hypothesis is that DSC and SSC from the agricultural area are greater than DSC and SSC of the forest area. Results showed that the agriculture area produced significantly greater mean DSC than in the forest area, the main contribution was the Ca²⁺ (24·68 ± 46·52 mg l^?1) ion at the agricultural area. A long‐term sediment production rate at the agricultural outlet was calculated (69·1 tonnes per 100 years) based on the total sediment discharge (TSD) and the recurrence interval of the largest event of the five rainstorms (October 2005). Geographic information system (GIS) spatial data layers of the watershed were produced to determine the relation of tracks, landforms, slopes and forest management to SSC yield in the forest outlet (133·89 ± 308·14 mg l^?1) during the five rainstorms. Agriculture practices are the main cause of soil erosion at the study area. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Accuracy assessment of the Mexican National Forest Inventory map: A study in four ecogeographical areas     

Stéphane Couturier  Jean‐François Mas  Erna López‐Granados  Jorge Benítez  Valdemar Coria‐Tapia  Álvaro Vega‐Guzmán 《Singapore journal of tropical geography》2010,31(2):163-179

The accuracy of the Mexican National Forest Inventory (NFI) map is derived in four distinct ecogeographical areas, using an assessment design tailored for the project. A main achievement of the design was to integrate the high diversity of classes encompassed at the most detailed subcommunity level of the classification scheme within a cost‐controlled statistically sound assessment. A hybrid double sampling strategy was applied to the 2.5 million‐ha study area. A total of 5955 reference sites were verified against their NFI map label. The availability of detailed quasi‐synchronous reference data for the 2000 Landsat‐derived NFI and the high diversity of mapped classes allowed a careful thematic analysis on the selected regions, relevant for national extrapolation. Global accuracy estimates of 64–78 per cent were registered among the four ecogeographical areas (two with mainly temperate climate and the other two with mainly tropical climate), with the lower accuracy levels found in areas more densely covered with forests. According to the estimates, the NFI map tends to underestimate the presence of temperate forest (especially oak) and overestimate the presence of tropical forest in the areas investigated. The analysis of confusions reveals difficulties in unambiguously interpreting or labelling forests with secondary vegetation, herbaceous and/or shrub‐like vegetation as well as distinguishing between aquatic vegetation types. The design proved useful from the perspective of accuracy assessments of regional maps in biodiverse regions.  相似文献   

Overwintering of terrestrial Arctic arthropods: the fauna of Svalbard now and in the future     

María Luisa Ávila-Jiménez  Stephen J. Coulson  Torstein Solhøy  & Anna Sjöblom 《Polar research》2010,29(1):127-137

There are over 500 species of arthropods recorded from Svalbard. These animals overwinter either within the soil or on the ground surface, and have to tolerate an environment where the ground is frozen for over 9 months each year. Three cold-tolerance strategies have been described from Svalbard invertebrates: freeze avoidance, freeze tolerance and desiccation. Once in a cold-tolerant state the animals can be extremely cold tolerant in terms of both minimum exposure temperature and period of exposure. How the overwintering capabilities of these animals will be affected by climate changes during the next 100 years, as predicted by climate models, is not yet known. Four principle factors with an impact on overwintering of the terrestrial arthropod fauna are outlined here: (1) warmer winter temperatures, with an increased frequency of extreme events such as freeze–thaw cycles and surface icing; (2) changes in snow fall and snow lie; (3) pollutant load; and (4) dispersal of invertebrates to Svalbard. Finally, areas where further research is required are highlighted: including the development of controlled multi-season field experiments; effect of freeze–thaw cycles; changes in thickness and distribution of snow lie, with the subsequent effects on duration of the summer period; chill susceptibility of soil arthropods; assessing potential colonizing species and the likelihood of these species becoming established; assessing the effect of gene flow from surrounding populations; interactions between pollution and cold tolerance; anoxia stress; and the genetics of cold tolerance.  相似文献   

Sky luminance distribution in Pamplona (Spain) during the summer period     

J.L. Torres  M. de Blas  A. García  A. Gracia  A. de Francisco 《Journal of Atmospheric and Solar》2010,72(5-6):382-388

In this work the outdoor daylight conditions in Pamplona (South Europe) during the summer period have been studied. The selected sky type (from fifteen standards) at a given moment is the one exhibiting the lowest RMSD when comparing the theoretical and experimental luminance distributions in the sky hemisphere. Two year data of luminance distribution registered every 10 min in 145 positions of the sky hemisphere have been used for selecting the sky type. The most frequent sky type in Pamplona is V.5 (cloudless polluted with a broad solar corona), with an occurrence of 29.5%. This result coincides with the one observed in a previous study in Athens.Six types of sky (V.5, IV.4, III.4, III.3, V.4 y II.2) out of the fifteen standards become practically the 80% of all the studied ones. Regarding a possible use in daylight climate studies, the frequency of occurrence of the fifteen types of sky for fourteen solar elevation intervals has been included.  相似文献   

Strong ground-motion relations for Mexican interplate earthquakes     

Danny Arroyo  Daniel García  Mario Ordaz  Mauricio Alexander Mora  Shri Krishna Singh 《Journal of Seismology》2010,14(4):769-785

We derive strong ground-motion relations for horizontal components of pseudo-acceleration response spectra from Mexican interplate earthquakes at rock sites (NEHRP B class) in the forearc region. The functional form is obtained from the analytical solution of a circular finite-source model. For the regression analysis we use a recently proposed multivariate Bayesian technique. The resulting model has similar accuracy as those models derived from regional and worldwide subduction-zone databases. However, there are significant differences in the estimations computed from our model and other models. First, our results reveal that attenuation in Mexico tends to be stronger than that of worldwide relations, especially for large events. Second, our model predicts ground motions for large earthquakes at close distances to the source that are considerably larger than the estimations of global models. Lack of data in this range makes it difficult to identify the most appropriate model for this scenario. Nevertheless, according to the available data at the city of Acapulco, our model seems to estimate seismic hazard more adequately than the other models. These new relations may be useful in computing seismic hazard for the Mexican forearc region, where no similar equations had been yet proposed.  相似文献   

Guest editorial: Structural seismic safety assessment     

Carlos Sousa Oliveira  Aníbal Costa  Raimundo Delgado 《Bulletin of Earthquake Engineering》2010,8(1):1-3

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A multi-scale hierarchical framework for developing understanding of river behaviour to support river management     

A. M. Gurnell  M. Rinaldi  B. Belletti  S. Bizzi  B. Blamauer  G. Braca  A. D. Buijse  M. Bussettini  B. Camenen  F. Comiti  L. Demarchi  D. García de Jalón  M. González del Tánago  R. C. Grabowski  I. D. M. Gunn  H. Habersack  D. Hendriks  A. J. Henshaw  M. Klösch  B. Lastoria  A. Latapie  P. Marcinkowski  V. Martínez-Fernández  E. Mosselman  J. O. Mountford  L. Nardi  T. Okruszko  M. T. O’Hare  M. Palma  C. Percopo  N. Surian  W. van de Bund  C. Weissteiner  L. Ziliani 《Aquatic Sciences - Research Across Boundaries》2016,78(1):1-16

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Surface dynamic deformation estimates from local seismicity: the Itoiz reservoir,Spain     

Miguel A. Santoyo  Patricia Martínez-Garzón  Antonio García-Jerez  Francisco Luzón 《Journal of Seismology》2016,20(3):1021-1039

We analyze the ground motion time histories due to the local seismicity near the Itoiz reservoir to estimate the near-source, surface 3D displacement gradients and dynamic deformations. The seismic data were obtained by a semipermanent broadband and accelerometric network located on surface and at underground sites. The dynamic deformation field was calculated by two different methodologies: first, by the seismo-geodetic method using the data from a three-station microarray located close to the dam, and second, by single station estimates of the displacement gradients. The dynamic deformations obtained from both methods were compared and analyzed in the context of the local free-field effects. The shallow 1D velocity structure was estimated from the seismic data by modeling the body wave travel times. Time histories obtained from both methods result quite similar in the time window of body wave arrivals. The strain misfits between methods vary from 1.4 to 35.0 % and rotational misfits vary from 2.5 to 36.0 %. Amplitudes of displacement gradients vary in the range of 10^?8 to 10^?7 strains. From these results, a new scaling analysis by numerical modeling is proposed in order to estimate the peak dynamic deformations for different magnitudes, up to the expected maximum M _w in the region (M5.5). Peak dynamic deformations due to local M _w5.5 earthquakes would reach amplitudes of 10^?5 strain and 10^?3 radians at the Itoiz dam. The single station method shows to be an adequate option for the analysis of local seismicity, where few three-component stations are available. The results obtained here could help to extend the applicability of these methodologies to other sites of engineering interest.  相似文献   

Numerically based proposals for the stiffness and strength of masonry infills with openings in reinforced concrete frames          下载免费PDF全文

Farhad Akhoundi  Paulo B. Lourenço  Graça Vasconcelos 《地震工程与结构动力学》2016,45(6):869-891

Aimed at investigating the effect of openings on the in‐plane behaviour of masonry infills in reinforced concrete frames, a parametric study is presented based on model calibration via experimental tests. Two types of openings are investigated: central window openings and different combinations of door and window openings based on the typologies of southern European countries. First, a finite element model of the structure is made using the DIANA software program. Then, after calibration with experimental results, a parametric analysis is carried out to investigate the effect of the presence and location of the different types of openings on the in‐plane behaviour of the infilled frame. Finally, different equations for predicting the initial stiffness and lateral strength of infilled frames with any types of openings were obtained. An α factor related to the geometry of the piers between openings is proposed to take into account the location of the openings in the developed equations. Subsequently, the masonry infill panel is replaced by a diagonal strut. An empirical equation is also proposed for the width of an equivalent strut to replace a masonry infill panel with openings in such a way that they possess the same initial stiffness. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献