			Home About us Contact

Valley Bottom (valley + bottom)

Distribution by Scientific Domains

Earth and Environmental Science	66%
Humanities and Social Sciences	16%

Selected Abstracts

A conceptual model for the longitudinal distribution of wood in mountain streams

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 3 2009
Ellen Wohl
Abstract Wood load, channel parameters and valley parameters were surveyed in 50 contiguous stream segments each 25 m in length along 12 streams in the Colorado Front Range. Length and diameter of each piece of wood were measured, and the orientation of each piece was tallied as a ramp, buried, bridge or unattached. These data were then used to evaluate longitudinal patterns of wood distribution in forested headwater streams of the Colorado Front Range, and potential channel-, valley- and watershed-scale controls on these patterns. We hypothesized that (i) wood load decreases downstream, (ii) wood is non-randomly distributed at channel lengths of tens to hundreds of meters as a result of the presence of wood jams and (iii) the proportion of wood clustered into jams increases with drainage area as a result of downstream increases in relative capacity of a stream to transport wood introduced from the adjacent riparian zone and valley bottom. Results indicate a progressive downstream decrease in wood load within channels, and correlations between wood load and drainage area, elevation, channel width, bed gradient and total stream power. Results support the first and second hypotheses, but are inconclusive with respect to the third hypothesis. Wood is non-randomly distributed at lengths of tens to hundreds of meters, but the proportion of pieces in jams reaches a maximum at intermediate downstream distances within the study area. We use these results to propose a conceptual model illustrating downstream trends in wood within streams of the Colorado Front Range. Copyright © 2009 John Wiley & Sons, Ltd. [source]

The influence of plant cover and land use on slope,channel decoupling in a foothill catchment: a case study from the Carpathian Foothills, southern Poland

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 5 2002
Jolanta, chowicz
Abstract This paper examines the influence of plant cover and land use on slope,channel decoupling in the Stara Rzeka Stream catchment (22·4 km2) and its subcatchment Dworski Potok Stream (0·3 km2). The Stara Rzeka catchment is situated in the marginal part of the Carpathian Foothills and is characterized by a relief of low and medium hills. The catchment is used for agriculture but unlike other foothill catchments, it has a relatively extensive unfragmented area of forests (41·3 per cent). Grasslands and pastures (13·8 per cent) are mainly along the broad and flat valley floor. In the cultivated area (38·5 per cent) of the northern low hill part of the catchment, the fields are long, narrow and separated by boundary strips. They stretch from the hilltops to the valley bottom and are traditionally ploughed along the slopes. The research into slope wash was carried out at six sites downslope (August 1989 to October 1990) and on experimental plots (1989,1991). Transport of suspended matter was determined in the channels of the Stara Rzeka and Dworski Potok Streams (1987,1991). The results show that transport and export of the material on the slopes depend on the morphology of the slope and on the agricultural use of the area. The mosaic of fields which are used differently makes the soil wash process very intensive only if the slopes are ploughed and unprotected by a dense cover of vegetation. The material displaced is mostly accumulated at the foot of the slopes or at the bottom of the valley. Footslope areas and flat valley bottoms covered with grass function as a barrier separating the slope and the river bed. These features generally negate the transfer of slope-originated material to the bed of the stream. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Edaphic and physiographic factors affecting the distribution of natural gamma-emitting radionuclides in the soils of the Arnás catchment in the Central Spanish Pyrenees

EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 4 2002
A. Navas
Summary Gamma-emitting radionuclides are a natural source of radiation that can be a concern for human health, therefore it is important to know the radionuclide backgrounds in soils and to assess their mobility and transfer in ecosystems. Concentrations of natural radionuclides were determined in soils from a small catchment in the middle mountain environment of the Central Spanish Pyrenees. Radioisotope activities were well within the natural ranges for soil, averaging 27, 26, 32 and 500 Bq kg,1 for 238U, 226Ra, 208Tl and 40K, respectively. Their distributions in the soil profile were analysed along three transects of contrasting physiography and soil type. Uranium was depleted in upper layers of the soil and slightly enriched in deeper sections, while 226Ra, 40K and 208Tl were more uniformly distributed. Radionuclide activities in the Calcaric Regosols on the shrub slope were less than those in the deeper and better developed Haplic Kastanozems under forest and in Calcaric Fluvisols in the valley bottom. These spatial patterns seem to be affected by the soil type; other landscape features, such as slope orientation and vegetation cover, appeared to have an indirect effect. The results indicate that the depth distribution of the radionuclides is affected by some soil properties, including pH, carbonates, organic matter and particle size, and soil processes, such as leaching and adsorption. [source]

Near,surface ground temperature regime variability in selected microenvironments, Kärkevagge, Swedish Lapland

GEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 3-4 2002
Colin E. Thorn
The importance of topographic microvariability in influencing shallow (10,50 cm depths) soil temperature regimes in arctic,alpine Kärkevagge, northern Sweden, from August 1999 to July 2000 is demonstrated using six sites. The ground microclimate on the tops of very large boulders forming an extensive boulder field in the central valley bottom is more comparable to that at an alpine ridge,crest site 300 m higher than it is to the microclimate at the base of one of the boulders. The boulder crests also differ substantially from the more generalized valley,bottom conditions outside the boulder field. Assuming that chemical processes may be active at temperatures at or above 0°C, sites in the valley experience favorable conditions from 159 to 324 days of the year. Aside from the annual cycle, freeze,thaw cycles are infrequent within Kärkevagge. [source]

Positive and negative effects of livestock grazing on plant diversity of Mongolian nomadic pasturelands along a slope with soil moisture gradient

GRASSLAND SCIENCE, Issue 3 2009
Noboru Fujita
Abstract To examine different effects of herbivorous large mammals' grazing pressure on plant diversity along a slope in a Mongolian nomadic pasture, we compared species richness, Simpson's index of diversity, and the total plant coverage of plants between protected pasture from livestock grazing and grazed pasture on the near ridge, upper slope, lower slope, foot slope and valley bottom. The species richness and Simpson's index of diversity decreased and the total coverage increased downwardly with increase in pasture soil moisture along the slope. The species richness of the protected pasture decreased, changed little, and increased on the near ridge and the upper slope, the lower slope and the foot slope, and the valley bottom, respectively. Simpson's index of diversity of the protected pasture decreased compared with the grazed pasture only on the valley bottom. The total coverage became lower in the grazed pasture. As the reason for our results, we discuss positive and negative effects of livestock grazing on the species diversity of plants. The positive effect is shown on the valley bottom, where soil moisture and plant growth becomes high with the total coverage over 100%, due to relaxing indirectly the competitive exclusion among plants due to the grazing of dominant plants. The negative effect is obtained on the near ridge and the upper slope, where the soil moisture and the plant growth are low, because of elimination of some plants from the pasture by direct grazing damage. [source]

Investigating mechanisms of stormflow generation by natural tracers and hydrometric data: a small catchment study in the Black Forest, Germany

HYDROLOGICAL PROCESSES, Issue 2 2001
E. Hangen
Abstract The importance and interaction of various hydrological pathways and identification of runoff source areas involved in solute transport are still under considerable debate in catchment hydrology. To reveal stormflow generating areas and flow paths, hydrometric behaviour of throughfall, soil water from various depths, runoff, and respective concentrations of the environmental tracers 18O, Si, K, SO4 and dissolved organic carbon were monitored for a 14-week period in a steep headwater catchment in the Black Forest Mountains, Germany. Two stormflow hydrographs were selected and, based on 18O and Si, chemically separated into three flow components. Their sources were defined using mixing diagrams. Additional information about stormflow generating mechanisms was derived from recession analyses of the basin's complete 5-year hydrograph record. By providing insight into storage properties and residence times of outflowing reservoirs of the basin, recession analysis proved to be a valuable tool in runoff model conceptualization. Its results agreed well with hydrometric and hydrochemical data. Supported by evaluation of 30 hillslope soil profiles a coherent concept of stormflow generation could be derived: whereas in many steeply sloped basins in the temperate region soil water from hillslopes appears to have an immediate effect on the shape of the stormflow hydrograph, its role at this basin is basically restricted to the recharge of the groundwater reservoir in the near-channel area. Storm hydrograph peaks appear to be derived from a small direct runoff component supplemented by a fast delivery of baseflow from the groundwater reservoir in the valley bottom. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Farming flexibility and food security under climatic uncertainty: Manang, Nepal Himalaya

AREA, Issue 2 2010
Tor Halfdan Aase
Climate change is predicted to cause a substantial decrease in food production in poor regions during this century. But since reliable models of future climates have not been produced at local level as yet, this article focuses on the flexibility of farming systems in terms of adaptability to changing conditions of production, whatever those changes may turn out to be. Defining flexibility as ,uncommitted potentiality for change'Bateson 1972, the aim of the article is to identify such potentialities among subsistence farmers in a remote part of the Himalayas. Our analysis reveals four ,uncommitted potentialities' for adaptation to a future situation that will be climatologically different from the present. In order to maintain local food security under changing climate conditions, farmers in the study valley of Manang can reclaim abandoned land, they can depend more on barley, they may reduce the conspicuous exhibition of horses, and relocate farming from the slope to the valley bottom. The inherent flexibility in their farming system renders Mananges quite robust in facing future uncertainties. Thus, Manang is more appropriately labelled ,dynamic' than ,fragile', which is a term often ascribed to high Himalayan communities and environments. [source]

The influence of plant cover and land use on slope,channel decoupling in a foothill catchment: a case study from the Carpathian Foothills, southern Poland

Snow in the McMurdo Dry Valleys, Antarctica

INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 5 2010
Andrew G. Fountain
Abstract Snowfall was measured at 11 sites in the McMurdo Dry Valleys to determine its magnitude, its temporal changes, and spatial patterns. Annual values ranged from 3 to 50 mm water equivalent with the highest values nearest the coast and decreasing inland. A particularly strong spatial gradient exists in Taylor Valley, probably resulting from local uplift conditions at the coastal margin and valley topography that limits migration inland. More snow occurs in winter near the coast, whereas inland no seasonal pattern is discernable. This may be due, again, to local uplift conditions, which are common in winter. We find no influence of the distance to the sea ice edge. Katabatic winds play an important role in transporting snow to the valley bottoms and essentially double the precipitation. That much of the snow accumulation sublimates prior to making a hydrologic contribution underscores the notion that the McMurdo Dry Valleys are indeed an extreme polar desert. Copyright © 2009 Royal Meteorological Society [source]

Sediment sequences and paleosols in the Kyichu Valley, southern Tibet (China), indicating Late Quaternary environmental changes

ISLAND ARC, Issue 3 2009
Knut Kaiser
Abstract The Tibetan Plateau is highly sensitive to environmental changes and affects the settings of a far larger territory in Central Asia and beyond. Thus, knowledge on past environmental changes in that area is essential. Even though the Kyichu (Lhasa River) Valley and its tributaries is an easily accessible area, the Late Quaternary landscape evolution of southern Tibet is in general scarcely known. Therefore, 12 sedimentary sections in the middle and lower catchment were subjected to multidisciplinary analyses (sedimentology, paleopedology, AMS 14C and luminescence dating, and charcoal determination) aiming at results on regional paleoenvironmental changes. At the altitude studied (3600,4000 m above sealevel), no glacial relics could be detected, indicating that the valley positions have been unglaciated since the Last Interglacial. The lack of fluvial,lacustrine structures above the floodplain is due to the aggradational character of this tectonically (sub-)active valley, which caused an alluvial burying of older valley bottoms. During the Late Pleistocene the mouth area of the Kyichu was occupied by a lake which was part of a larger dam-lake in the superordinate Yarlung Zhangbo Valley. On the valley flanks, loesses were predominantly deposited before the Last Glacial Maximum (LGM), whereas eolian sands were predominantly deposited around and after the LGM. Paleosols of Last Interglacial, Last Glacial and Holocene ages regularly occur at terrestrial sites representing temperate to cool and humid to semiarid conditions during soil formation. Ages of colluvial sediments indicate that the widespread barren valley slopes were primarily formed by Late Pleistocene erosion followed by a secondary Holocene erosion phase. Charcoal spectra indicate a Late Holocene change from a forest environment to a pastoral environment with sparse grasses, herbs and dwarf shrubs. It is assumed that the Late Holocene environmental changes, such as loss of forests/woodlands and erosion, have at least been reinforced by humans, enhancing a regional climatic aridification and cooling trend. [source]

Spatial viability analysis of Amur tiger Panthera tigris altaica in the Russian Far East: the role of protected areas and landscape matrix in population persistence

JOURNAL OF APPLIED ECOLOGY, Issue 6 2006
CARLOS CARROLL
Summary 1The Amur or Siberian tiger Panthera tigris altaica forms a relatively small and disjunct population of less than 600 individuals in the Russian Far East. Because tigers in this region require large territories to acquire sufficient prey, current strictly protected areas, comprising 3·4% (10 300 km2) of the region, are unlikely to prevent extirpation of the subspecies in the face of expanding forestry and external demand for tiger parts. 2We used resource selection function models and spatially explicit population models to analyse the distribution and predict the demographic structure of the population to identify policy options that may enhance population viability. 3A resource selection function model developed from track distribution data predicted that tigers were most likely to occur in lower altitude valley bottoms with Korean pine forest and low human impacts. 4The results from the spatially explicit population model suggested that current tiger distribution is highly dependent on de facto refugia with low human impacts but without statutory protection, and that small increases in mortality in these areas will result in range fragmentation. Although an expanded reserve network only marginally increases tiger viability under current conditions, it dramatically enhances distribution under potential future scenarios, preventing regional extirpation despite a more hostile landscape matrix. 5The portion of tiger range most resistant to extirpation connects a large coastal reserve in the central portion of the region with largely unprotected watersheds to the north. A southern block of habitat is also important but more severely threatened with anthropogenic disturbances. The results suggest that preserving source habitat in these two zones and ensuring linkages are retained between blocks of habitat in the north and south will be critical to the survival of the tiger population. 6Synthesis and applications. Conservation priorities identified in this analysis differ from those suggested by a conservation paradigm focusing only on sustaining and connecting existing protected areas that has been applied to tiger conservation in more developed landscapes with higher prey densities. An alternative paradigm that assesses population viability in a whole-landscape context and develops priorities for both protected area expansion and increasing survival rates in the landscape matrix may be more appropriate in areas where tigers and other large carnivores coexist with low-density human populations. Although landscape connectivity merits increased emphasis in conservation planning, identification of landscape linkages should be tied to broad-scale recommendations resulting from spatial viability analyses in order to prevent misdirection of resources towards protecting corridors that add little to population persistence. [source]

Quaternary Lake Deposits of Nam Co, Tibet, with a Discussion of the Connection of Nam Co with Ring Co-Jiuru Co

ACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 3 2002
ZHU Dagang
Abstract Shorelines are widespread and lake deposits and lake geomorphology are well developed on the northern Tibetan Plateau. Through field observations of lacustrine deposits of Nam Co,the highest and largest Quaternary lake in Tibet, the authors found four-step shore terraces composed of sands and clays with well-developed horizontal bedding and 3,12 m, 15,22 m, 25,30 m and 35,45 m higher than the lake surface respectively, lacustrine deposits resting on the bedrocks and 60,150 m higher than the lake surface, and up to ,50 levees composed of oblate lakeshore gravels. Moreover they found lacustrine and lakeshore deposits making up the terraces and levees on the bottoms of wide dividing valleys connecting Nam Co with the Rencoyuema, Rencogongma and Jiuru Co northwest of Nam Co (the valley bottoms are 20 m, 90 m and 60 m higher than the above-mentioned three lakes) and on slopes north of it, i.e. terraces II and III of Nam Co. Thus they confirm that Nam Co and Ring Co-Jiuru Co had connected with each other several times, i.e. formed a unified large lake several times, rather than had been different lakes connected only by river channels. From indications such as the distribution of the highest shoreline and lake deposits and geomorphology, the authors conclude that the total area of the old large lakes on the northern Tibetan Plateau is a few times larger than that of the modern lakes and that the last-stage old large lakes formed in the interglacial interval of the last glaciation. [source]