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排序方式: 共有302条查询结果,搜索用时 15 毫秒
91.
Martin Gude Gerhard Daut Susanne Dietrich Roland Mäusbacher Christer Jonasson Annett Bartsch & Dieter Scherer 《Geografiska Annaler: Series A, Physical Geography》2002,84(3-4):205-212
The analysis of Holocene geomorphic process activity demands long–term data sets, which are available for the Kärkevagge catchment due to 50 years of intensive geomorphologic field studies. This data set is used in combination with additional field measurements, remote sensing and digital elevation model (DEM) analysis to provide input data for modelling Holocene valley development. On the basis of this information, geomorphic process units (GPUs) are defined by means of GIS modelling. These units represent areas of homogeneous process composition that transfer sediments. Since the data base enables the quantification of single processes, the interaction of processes within the units can also be quantified. Applying this concept permits calculation of recent sediment transfer rates and hence leads to a better understanding of actual geomorphic landscape development activity. To extrapolate these data in time and space the process–related sediments in the valley are analysed for depth and total volume, primarily using geophysical methods. In this fashion the validity of measured process rates is evaluated for the Holocene time scale. Results from this analysis are exemplified in a cross–profile showing some of the principal sediment units in the valley. For example, the measured modern rates on a slush torrent debris fan seem to represent the Holocene mean rate. This approach should also be suitable for revealing Holocene geomorphic landscape development in terms of climate change. 相似文献
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93.
Artemi Cerda Susanne Schnabel Antonio Ceballos Dionisia Gomez-Amelia 《地球表面变化过程与地形》1998,23(3):195-209
Soil hydrology was investigated in the Guadelperalón experimental watershed in order to determine the influence of land use and vegetation cover on runoff and infiltration within the Dehesa land system. Five soil–vegetation units were selected: (1) tree cover, (2) sheep trials, (3) shrub cover, (4) hillslope grass and (5) bottom grass. The results of the simulated rainfall experiments performed at an intensity of 56·6 mm h−1 during one hour on plots of 0·25 m2, and the water drop penetration time test indicate the importance of water repellency in the Dehesa land system under drought conditions. Low infiltration rates (c. 9–44 mm h−1) were found everywhere except at shrub sites and in areas with low grazing pressure. Soil water repellency greatly reduced infiltration, especially beneath Quercus ilex canopies, where fast ponding and greater runoff rates were observed. The low vegetation cover as a consequence of a prolonged drought and grazing pressure, in conjunction with the soil water repellency, induces high runoff rates (15–70 per cent). In spite of this, macropore fluxes were found in different locations, beneath trees, on shrub-covered surfaces, as well as at sites with a dominance of herbaceous cover. Discontinuity of the runoff fluxes due to variations in hydrophobicity causes preferential flows and as a consequence deeper infiltration, especially where macropores are developed. © 1998 John Wiley & Sons, Ltd. 相似文献
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95.
David S. Johnson John W. Fleeger Kari A. Galván E. Barry Moser 《Estuaries and Coasts》2007,30(2):226-237
Coastal systems serve many human uses and as a result are susceptible to anthropogenic activities such as nutrient loading
and overfishing. In soft sediments, infauna frequently serve as key indicators of such activities. To use infauna effectively
as bioindicators, it is important to understand how infaunal abundances and community patterns vary naturally within ecosystems.
We examined the spatial and temporal dynamics of infaunal annelids in four tidal creeks of the Plum Island Estuary, Massachusetts,
USA, from June to October 2003, sampling along a tidal inundation gradient that crossed five distinct habitats from creek
bottoms to the vegetated high marsh platform. Annelids comprised 97% of the total number of macroinfauna. Highest densities
were found in creek wall habitats (33,418–65,535 individuals m−2), and lowest densities (2,421–10,668 individuals m−2) were found inSpartina patens habitats. Five numerically abundant species comprised 87% of the annelid assemblage and three species,Manayunkia aestuarina (Polychaeta),Paranais litoralis (Oligochaeta), andCernosvitoviella immota (Oligochaeta), were broadly distributed across the marsh landscape.Streblospio benedicti (Polychaeta) andFabricia sabella (Polychaeta) were abundant only in mudflat and creek wall habitats, respectively.P. litoralis experienced a summer decline in all habitats, whereasM. aestuarina abundance increased 4–5 fold, in October relative to June in creek wall and tall-formSpartina alterniflora habitats. Hierarchical spatial, analysis revealed that >90% of the variability in annelid abundances was found at the mesospatial
scale (<50 m). Variation among the four creeks, (>1 km) was relatively small. 相似文献
96.
Desert Potholes: Ephemeral Aquatic Microsystems 总被引:1,自引:0,他引:1
Marjorie?A.?ChanEmail author Katrina?Moser Jim?M.?Davis Gordon?Southam Kebbi?Hughes Tim?Graham 《Aquatic Geochemistry》2005,11(3):279-302
An enigma of the Colorado Plateau high desert is the “pothole”, which ranges from shallow ephemeral puddles to deeply carved
pools. The existence of prokaryotic to eukaryotic organisms within these pools is largely controlled by the presence of collected
rainwater. Multivariate statistical analysis of physical and chemical limnologic data variables measured from potholes indicates
spatial and temporal variations, particularly in water depth, manganese, iron, nitrate and sulfate concentrations and salinity.
Variation in water depth and salinity are likely related to the amount of time since the last precipitation, whereas the other
variables may be related to redox potential. The spatial and temporal variations in water chemistry affect the distribution
of organisms, which must adapt to daily and seasonal extremes of fluctuating temperature (0–60 °C), pH changes of as much
as 5 units over 12 days, and desiccation. For example, many species become dormant when potholes dry, in order to endure intense
heat, UV radiation, desiccation and freezing, only to flourish again upon rehydration. But the pothole organisms also have
a profound impact on the potholes. Through photosynthesis and respiration, pothole organisms affect redox potential, and indirectly
alter the water chemistry. Laboratory examination of dried biofilm from the potholes revealed that within 2 weeks of hydration,
the surface of the desiccated, black biofilm became green from cyanobacterial growth, which supported significant growth in
heterotrophic bacterial populations. This complex biofilm is persumably responsible for dissolving the cement between the
sandstone grains, allowing the potholes to enlarge, and for sealing the potholes, enabling them to retain water longer than
the surrounding sandstone. Despite the remarkable ability of life in potholes to persist, desert potholes may be extremely
sensitive to anthropogenic effects. The unique limnology and ecology of Utah potholes holds great scientific value for understanding
water–rock–biological interactions with possible applications to life on other planetary bodies. 相似文献
97.
Pascal Richet Alan Whittington François Holtz Harald Behrens Susanne Ohlhorst Max Wilke 《Contributions to Mineralogy and Petrology》2000,138(4):337-347
A review of published and newly measured densities for 40 hydrous silicate glasses indicates that the room-temperature partial
molar volume of water is 12.0 ± 0.5 cm3/mol. This value holds for simple or mineral compositions as well as for complex natural glasses, from rhyolite to tephrite
compositions, prepared up to 10–20 kbar pressures and containing up to 7 wt% H2O. This volume does not vary either with the molar volume of the water-free silicate phase, with its degree of polymerization
or with water speciation. Over a wide range of compositions, this constant value implies that the volume change for the reaction
between hydroxyl ions and molecular water is zero and that, at least in glasses, speciation does not depend on pressure. Consistent
with data from Ochs and Lange (1997, 1999), systematics in volume expansion for SiO2–M2O systems (M=H, Li, Na, K) suggests that the partial molar thermal expansion coefficient of H2O is about 4 × 10−5 K−1 in silicate glasses.
Received: 30 June 1999 / Accepted: 5 November 1999 相似文献
98.
99.
Susanne Bleisch Matt Duckham Antony Galton Patrick Laube Jarod Lyon 《International journal of geographical information science》2014,28(2):363-382
In many applications, the environmental context for and drivers of movement patterns are just as important as the patterns themselves. This article adapts standard data mining techniques, combined with a foundational ontology of causation, with the objective of helping domain experts identify candidate causal relationships between movement patterns and their environmental context. In addition to data about movement and its dynamic environmental context, our approach requires as input definitions of the states and events of interest. The technique outputs causal and causal-like relationships of potential interest, along with associated measures of support and confidence. As a validation of our approach, the analysis is applied to real data about fish movement in the Murray River in Australia. The results demonstrate that the technique is capable of identifying statistically significant patterns of movement indicative of causal and causal-like relationships. 相似文献
100.