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Causes and underlying processes of measurement variability in field erosion plots in Mediterranean conditions 总被引：1，自引：0，他引：1
C. Boix‐Fayos M. Martínez‐Mena A. Calvo‐Cases E. Arnau‐Rosalén J. Albaladejo V. Castillo 《地球表面变化过程与地形》2007,32(1):85-101
An understanding of the sources of variation in the use of erosion plots and of their feasibility to meet the objectives of each specific research project is key to improving future field designs, selecting data for modelling purposes and furthering knowledge of soil erosion processes. Our own field experiences from ongoing research on soil erosion processes since 1989, have allowed us to detect several methodological problems that cause measurement variability. Here several examples are presented concerning: (i) differences in long‐term soil erosion data between open and closed plots; (ii) differences in soil loss derived from replica soil erosion plots; and (iii) differences in soil loss data derived from plots at a range of spatial scales. Closed plots are not the most suitable method for long‐term monitoring of soil erosion rates due to the risk of exhaustion of available material within the plot. The difference in time after which exhaustion occurs depends on the surface soil characteristics, the climatological conditions and the size of the plots. We detected four and seven years as ‘time to exhaustion’. Different results are frequently obtained between pairs of replica plots. Differences up to a factor of nine have been detected in total soil loss between replica plots due to different spatial patterns of surface components. Different constraints appear depending on the spatial scale of measurement of soil loss. We obtained lower runoff percentages at coarser scales; however, larger sediment concentrations are observed at coarser scales (1·32 g l?1, catchment; 0·30 g l?1, 30 m2; 0·17 g l?1, 1 m2 scales). The smaller the plot, the larger the hydrological disconnection within the system, the lower the energy flows due to short distances and the quicker the response to runoff due to an artificial decrease of concentration times for continuous flow. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
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S. De la Cruz-Reyna M. Mena N. Segovia J. F. Chalot J. L. Seidel M. Monnin 《Pure and Applied Geophysics》1985,123(3):407-421
Radon (222Em) emanation measurements in soil gases are reported in connection with the 1982 eruptions of El Chichón Volcano.222Em detection is performed with LR-115 cellulose nitrate track detectors. Results show a general decreasing pattern of222Em concentration in soil with time after the eruptions. Activity measurements of radon daughters in ashes show that a large amount of222Em and220Em was released from magma degassing during the eruptions, and that only a fraction of the degassed magma was erupted. An important fluid interaction between the magma chamber and the surrounding sedimentary rock is also suggested. 相似文献
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F. Pelaez P. Mandrou M. Niel B. Mena N. Vilmer G. Trottet F. Lebrun J. Paul O. Terekhov R. Sunyaev E. Churazov M. Gilfanov D. Denisov A. Kuznetsov A. Dyachkov N. Khavenson 《Solar physics》1992,140(1):121-138
The anti-coincidence shield of the SIGMA telescope aboard GRANAT provides observations of solar X-ray and -ray bursts in the energy range 200 keV–15 MeV. The characteristics of the experiment are presented here as well as the observations of the solar bursts detected during the first year of operation. Among these events, two of these bursts associated respectively with a limb and a disk flare were observed with significant flux above 10 MeV. Advantage is taken of the experiment large detector area to examine fine time structures even at high energies ( 10 MeV). 相似文献
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S. K. Singh E. Mena J. G. Anderson R. Quaas J. Lermo 《Pure and Applied Geophysics》1990,133(3):447-474
Strong motion (SM) data of six Mexican subduction zone earthquakes (6.4M
S8.1) recorded near the epicentral zone are analyzed to estimate their far-field source acceleration spectra at higher frequencies (f0.3 Hz). Apart from the usual corrections such as geometrical spreading (1/R), average radiation pattern (0.6), free surface amplification (a factor of 2), and equal partitioning of the energy into two orthogonal horizontal components (a factor of 1/
), the observed spectra are corrected for a frequency dependentQ(Q=100f), a site dependent filter (e
–kf
), and amplification ofS waves near the surface (a factor of about 2 atf2Hz). We takeR as the average distance from the rupture area to the site. If we model the high frequency plateau (f1 Hz) of the source spectra, by a point source –2-model, and interpret them in terms of Brune's model we obtain between 50 and 100 bars for all earthquakes. The low-frequency broadband teleseismicP wave spectra, corrected witht
*=1.0 s, agrees within a factor of two with SM source spectra near 1 Hz. The –2-model is inadequate to explain the observed source spectra in a broad frequency range; these resemble spectra given byGusev (1983) with some differences.SM source acceleration spectra require significant corrections to explain observed spectra and RMS acceleration (arms) (a) at farther coastal sites for extended sources due to directivity effect and (b) at inland sites (100R200 km) because of unaccounted path and site amplification and/or invalidity of body-wave approximation. The observed spectra and arms at these sites are significantly greater than the predicted values from the estimated source spectra. 相似文献
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Evolution of the Galicia Interior Basin over the last 60 ka: sedimentary processes and palaeoceanographic implications 
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下载免费PDF全文 Anxo Mena Guillermo Francés Marta Pérez‐Arlucea Till J. J. Hanebuth Vera B. Bender Miguel A. Nombela 《第四纪科学杂志》2018,33(5):536-549
The Galicia Interior Basin (GIB; NW Iberian Peninsula) is located near a critical transition between the subtropical (temperate) and subpolar (cold) gyres of the North Atlantic. It therefore witnesses oceanographic changes driven by global climatic events. This study reports on the recent (latest Pleistocene) sedimentary, palaeoceanographic and palaeoclimatic history of the basin. We integrated analysis of deep‐sea sediment cores retrieved from an E–W transect across the GIB. The analysis indicated three types of sedimentary processes recording glacial (Marine Isotope Stage 2–4) and deglacial events: along‐slope bottom currents (forming contourite deposits), pelagic and hemipelagic sedimentation, and gravitational dislocation. Variation in depositional patterns and sedimentation rates indicate distinctive transport (along‐slope and down‐slope) and depositional processes. These in turn reflect climatic and oceanographic drivers. We interpret changes in sea level from core evidence showing changes in sediment supply. The cores exhibited conspicuous sedimentary evidence of Heinrich events (HEs). The stratigraphic intervals associated with HEs showed significant lateral variation. We suggest that the lateral variation may result from the development of an oceanographic boundary between surface water masses with different temperature and salinity parameters or changes in surface currents which may have introduced relatively warmer water into the GIB during the last glacial period. 相似文献
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Observations of gravity and atmospheric pressure variations during the total solar eclipse of 11 July 1991 in Mexico City
are presented. An LCR-G402 gravimeter equipped with a feedback system and a digital data acquisition system scanned gravity
and pressure every second around the totality. On the pressure record an oscillation, starting at the totality, with a peak
to peak amplitude of 0.5 hPa and a periodicity of 40 to 50 min, can clearly be seen. This oscillation results from the thermal
shock wave produced by the Moon shadow travelling at supersonic speed. At the 0.1 μGal (1 nm · s−2) level all gravity perturbations are explained by the atmospheric pressure effect.
Received: 10 February 1995 / Accepted: 7 June 1996 相似文献