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Plateau
Kinds of Plateau Terms modified by Plateau Selected AbstractsRUNOFF AND SEDIMENT RESPONSES TO CONSERVATION PRACTICES: LOESS PLATEAU OF CHINA,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 5 2003Mingbin Huang ABSTRACT: Soil erosion is the most significant threat to land productivity and environmental quality on the Loess Plateau of China. The annual total sediment load of the Yellow River is 1.6 billion tons, with about 90 percent coming from soil erosion from the Loess Plateau. To reduce soil erosion from the Loess Plateau, conservation practices, including tree planting, ridge construction between fields and around gullies, terrace and ditch construction perpendicular to the main slope, and dam construction are being implemented. An evaluation of these conservation practices is required before they are implemented at the large scale. The objective of this study is to evaluate the effectiveness of conservation practices to control runoff and sediment yield from paired watersheds in the hilly gully region of the Loess Plateau. The advantage of the paired watershed approach is its sensibility in detecting differences in runoff and sediment transport by monitoring both watersheds during two periods, an initial period with no conservation practices and a treatment period with only one watershed subjected to conservation practices. Implementation of the conservation practices resulted in (1) cumulative runoff and sediment yield that were, respectively, 25 and 38 percent less from the treatment watershed than from the control, (2) a decrease in the number of rainfall events producing runoff and sediment transport (94 in the control versus 63 in treatment), and (3) a reduction in the maximum discharge and maximum suspended sediment concentration. [source] STEPHEN HISLOP AND HIS 1860 CRETACEOUS CONTINENTAL MOLLUSCAN NEW SPECIES DESCRIPTIONS IN LATIN FROM THE DECCAN PLATEAU, INDIAPALAEONTOLOGY, Issue 6 2008JOSEPH H. HARTMAN Abstract:, In 1860, Stephen Hislop published a data-rich document on the infra- and intertrappean strata of the Deccan Plateau of central India, along with numerous new taxa of continental and marine molluscs. His scholarship interestingly blended antiquated, contemporary, and ahead-of-his-time palaeontological methods. Although his work established a completely adequate foundation upon which to build future end-Cretaceous Deccan molluscan studies, effectively no substantive work ensued, with only incidental subsequent reference to his effort. [source] Effectiveness of grass strips in trapping suspended sediments from runoffEARTH SURFACE PROCESSES AND LANDFORMS, Issue 9 2010Chengzhong Pan Abstract Little information is available concerning the performance of grass strips for erosion control from steep cropland. An experiment was conducted on 5-m-long grass strips with slopes of 3°,15° that were subjected to silt laden runoff and simulated rainfall, to investigate the sediment trapping processes. The grass strips had three treatments including intact grass control (C), no litter (dead grass material covering the soil surface was removed) (NL), and no litter or leaves (only 2,3,cm grass stems and roots were reserved) (NLL). Generally the grass strips had a high effectiveness in trapping sediment from steep cropland runoff. Sediment trapping efficiency (STE) decreased with increasing slope gradient, and even for a 15° slope, STE was still more than 40%. Most sediment deposited in the backwater region before each grass strips. The removal of grass litter or/and leaves had no significant influence on STE. The sediment median size (D50) in inflow was greater than that in outflow, and the difference (,D50) decreased with increasing slope. A positive power relationship between STE and ,D50 can be obtained. Grass strips were more effective in trapping sediments coarser than 10 or 25,µm, but sediments finer than 1,µm were more readily removed from runoff than particles in the range of 2 to approximately 10,µm. Grass litter had less influence on flow velocity than leaves because the deposited sediment partially covered the litter layer. Mean flow velocity and its standard deviation were negatively correlated with STE, and they can help make good estimation of STE. Results from this study should be useful in planting and managing forage grass to effectively conserve soil loss by runoff from steep slopes on the Loess Plateau of China. Copyright © 2010 John Wiley & Sons, Ltd. [source] High resolution quantification of gully erosion in upland peatlands at the landscape scaleEARTH SURFACE PROCESSES AND LANDFORMS, Issue 8 2010Martin Evans Abstract The upland peatlands of the UK are severely eroded, with large areas affected by gully erosion. The peatlands are important areas of carbon storage and provide a range of other ecosystem services including water supply and biodiversity all of which are negatively impacted by erosion of the upland surface. The magnitude of the gully erosion, and consequent adjustment of the peatland morphology, is such that in degraded peatlands the extent and magnitude of erosion is a major control on peatland function. Accurate mapping of gully form is therefore a necessary precondition to the understanding and management of these systems. This paper develops an approach to extracting gully maps from high resolution digital elevation models (DEMs). Gully maps of the Bleaklow Plateau in northern England were derived from a 2,m LiDAR DEM by combining areas of low difference from mean elevation and high positive plan curvature. Gully depth was modelled by interpolating between gully edges. Testing of the gully mapping and depth modelling against aerial photography, manual interpretation of the DEM and ground survey revealed that gully plan form is well represented and gully width and depth are modelled with tolerances close to the horizontal and vertical resolution of the LiDAR imagery. Estimates of gully width and depth were less reliable for gullies with total width of less than four pixels. The approach allows for the first time the derivation of accurate estimates of gully extent and magnitude over large areas and provides the basis for modelling a range of processes controlled by gullying. The approach has wider applicability to mapping gully erosion in a wide range of environments. Copyright © 2010 John Wiley & Sons, Ltd. [source] Evaluation of the SWEEP model during high winds on the Columbia Plateau ,EARTH SURFACE PROCESSES AND LANDFORMS, Issue 11 2009G. Feng Abstract A standalone version of the Wind Erosion Prediction System (WEPS) erosion submodel, the Single-event Wind Erosion Evaluation Program (SWEEP), was released in 2007. A limited number of studies exist that have evaluated SWEEP in simulating soil loss subject to different tillage systems under high winds. The objective of this study was to test SWEEP under contrasting tillage systems employed during the summer fallow phase of a winter wheat,summer fallow rotation within eastern Washington. Soil and PM10 (particulate matter ,10 µm in diameter) loss and soil and crop residue characteristics were measured in adjacent fields managed using conventional and undercutter tillage during summer fallow in 2005 and 2006. While differences in soil surface conditions resulted in measured differences in soil and PM10 loss between the tillage treatments, SWEEP failed to simulate any difference in soil or PM10 loss between conventional and undercutter tillage. In fact, the model simulated zero erosion for all high wind events observed over the two years. The reason for the lack of simulated erosion is complex owing to the number of parameters and interaction of these parameters on erosion processes. A possible reason might be overestimation of the threshold friction velocity in SWEEP since friction velocity must exceed the threshold to initiate erosion. Although many input parameters are involved in the estimation of threshold velocity, internal empirical coefficients and equations may affect the simulation. Calibration methods might be useful in adjusting the internal coefficients and empirical equations. Additionally, the lack of uncertainty analysis is an important gap in providing reliable output from this model. Published in 2009 by John Wiley & Sons, Ltd. [source] Windblown dust influenced by conventional and undercutter tillage within the Columbia Plateau, USA,EARTH SURFACE PROCESSES AND LANDFORMS, Issue 10 2009B. S. Sharratt Abstract Exceedance of the US Environmental Protection Agency national ambient air quality standard for PM10 (particulate matter ,10 µm in aerodynamic diameter) within the Columbia Plateau region of the Pacific Northwest US is largely caused by wind erosion of agricultural lands managed in a winter wheat,summer fallow rotation. Land management practices, therefore, are sought that will reduce erosion and PM10 emissions during the summer fallow phase of the rotation. Horizontal soil flux and PM10 concentrations above adjacent field plots (>2 ha), with plots subject to conventional or undercutter tillage during summer fallow, were measured using creep and saltation/suspension collectors and PM10 samplers installed at various heights above the soil surface. After wheat harvest in 2004 and 2005, the plots were either disked (conventional) or undercut with wide sweeps (undercutter) the following spring and then periodically rodweeded prior to sowing wheat in late summer. Soil erosion from the fallow plots was measured during six sampling periods over two years; erosion or PM10 loss was not observed during two periods due to the presence of a crust on the soil surface. For the remaining sampling periods, total surface soil loss from conventional and undercutter tillage ranged from 3 to 40 g m,2 and 1 to 27 g m,2 while PM10 loss from conventional and undercutter tillage ranged from 0·2 to 5·0 g m,2 and 0·1 to 3·3 g m,2, respectively. Undercutter tillage resulted in a 15% to 65% reduction in soil loss and 30% to 70% reduction in PM10 loss as compared with conventional tillage at our field sites. Therefore, based on our results at two sites over two years, undercutter tillage appears to be an effective management practice to reduce dust emissions from agricultural land subject to a winter wheat,summer fallow rotation within the Columbia Plateau. Copyright © 2009 John Wiley & Sons, Ltd. [source] Consequences of hyperconcentrated flow for process-based soil erosion modelling on the Chinese Loess PlateauEARTH SURFACE PROCESSES AND LANDFORMS, Issue 9 2006Rudi Hessel Abstract High sediment concentrations in runoff are a characteristic feature of the Chinese Loess Plateau, and are probably caused by factors such as the occurrence of erodible materials on steep slopes, the characteristics of the loess and the harsh climate that results in low plant cover. When sediment concentration increases, fluid density increases, viscosity increases and settling velocity decreases. These effects become increasingly important with increasing concentration and can result in flow behaviour that is quite different from that of clear water flow. Although the net effect of these changes on the flow is not always apparent, erosion models that deal with high sediment concentrations should consider such effects and could include corrections for some of these effects. A case study in a small catchment on the Loess Plateau indicated that sediment concentrations were considerable, and literature data suggested that for such sediment concentrations, corrections for settling velocity, fluid density and viscosity are needed. Furthermore, a number of corrections are necessary to be able to compare field measurements with results of soil erosion models: sediment volume should be subtracted from runoff volume and a density correction is needed to use data from a pressure transducer. For flumes that were used to measure discharge from smaller areas inside the catchment, the measured water level should be corrected by subtracting the sediment level in the flume from the water level, while the sediment volume should also be subtracted from the discharge. Finally, measured concentration should be corrected to give concentration expressed as grams per litre of clear water, since soil erosion models express sediment concentration in this way. Copyright © 2006 John Wiley & Sons, Ltd. [source] Palaeomonsoon variability in the southern fringe of the Badain Jaran Desert, China, since 130 ka BPEARTH SURFACE PROCESSES AND LANDFORMS, Issue 3 2006Quanzhou Gao Abstract Taking the Chagelebulu Stratigraphic Profile as a typical example, a comprehensive study has been conducted to elucidate the palaeoclimatic and geomorphic evolution patterns in the southern fringe of the Badain Jaran Desert, which were found to be complex and polycyclic in the past 130 ka. However, the fluctuating magnitude is not as remarkable as that in the eastern China sandy region. The shift in climate from interglacial to glacial and the uplift process of the Qinghai,Xizang Plateau are the two leading forces driving the evolution of the climate and desert landforms in this area. Seventeen cycles of cold, dry and warm, humid climatic stages were recognized in the Upper Pleistocene Series of the profile. The sharp uplift of the Qinghai,Xizang Plateau superimposed a cool and arid climatic trend in this area. As a result of the climatic changes, the desert in this area has undergone multiple stages of expansion and contraction since 130 ka bp. The middle Holocene Epoch and the early stage of the Late Pleistocene Period were the main periods when the sand dunes became stabilized, and the early and late phases of the Holocene Epoch and late phase of the Pleistocene Epoch were the main periods when the previously stabilized sand dunes became mobile. The late phase of the Pleistocene Epoch was the most mobile stage, when the aeolian sand activities formed the essential geomorphic pattern of the Badain Jaran Desert. Copyright © 2005 John Wiley & Sons, Ltd. [source] Penguins as oceanographers unravel hidden mechanisms of marine productivityECOLOGY LETTERS, Issue 3 2002Jean-Benoīt Charrassin ABSTRACT A recent concept for investigating marine ecosystems is to employ diving predators as cost-effective, autonomous samplers of environmental parameters (such as sea-temperature). Using king penguins during their foraging trips at sea, we obtained an unprecedented high resolution temperature map at depth off the Kerguelen Islands, Southern Ocean, a poorly sampled but productive area. We found clear evidence of a previously unknown subsurface tongue of cold water, flowing along the eastern shelf break. These new results provide a better understanding of regional water circulation and help explain the high primary productivity above the Kerguelen Plateau. [source] A key to the species of Spilogona Schnabl from China, with descriptions of four new species from the Qinghai,Xizang (Tibetan) Plateau (Diptera: Muscidae)ENTOMOLOGICAL SCIENCE, Issue 1 2008Wan-Qi XUE Abstract A generic diagnosis for Spilogona Schnabl and a key to the 38 species known from China are given. Four new species are described: Spilogona cordis sp. nov., Spilogona lobuliunguis sp. nov., Spilogona medilobulus sp. nov. and Spilogona ponti sp. nov., all four from the Qinghai,Xizang (Tibetan) Plateau, China. [source] Microbial response to salinity change in Lake Chaka, a hypersaline lake on Tibetan plateauENVIRONMENTAL MICROBIOLOGY, Issue 10 2007Hongchen Jiang Summary Previous investigations of the salinity effects on the microbial community composition have largely been limited to dynamic estuaries and coastal solar salterns. In this study, the effects of salinity and mineralogy on microbial community composition was studied by using a 900-cm sediment core collected from a stable, inland hypersaline lake, Lake Chaka, on the Tibetan Plateau, north-western China. This core, spanning a time of 17 000 years, was unique in that it possessed an entire range of salinity from freshwater clays and silty sands at the bottom to gypsum and glauberite in the middle, to halite at the top. Bacterial and archaeal communities were studied along the length of this core using an integrated approach combining mineralogy and geochemistry, molecular microbiology (16S rRNA gene analysis and quantitative polymerase chain reaction), cultivation and lipid biomarker analyses. Systematic changes in microbial community composition were correlated with the salinity gradient, but not with mineralogy. Bacterial community was dominated by the Firmicutes -related environmental sequences and known species (including sulfate-reducing bacteria) in the freshwater sediments at the bottom, but by halophilic and halotolerant Betaproteobacteria and Bacteroidetes in the hypersaline sediments at the top. Succession of proteobacterial groups along the salinity gradient, typically observed in free-living bacterial communities, was not observed in the sediment-associated community. Among Archaea, the Crenarchaeota were predominant in the bottom freshwater sediments, but the halophilic Halobacteriales of the Euryarchaeota was the most important group in the hypersaline sediments. Multiple isolates were obtained along the whole length of the core, and their salinity tolerance was consistent with the geochemical conditions. Iron-reducing bacteria were isolated in the freshwater sediments, which were capable of reducing structural Fe(III) in the Fe(III)-rich clay minerals predominant in the source sediment. These data have important implications for understanding how microorganisms respond to increased salinity in stable, inland water bodies. [source] An improved force-restore method for soil temperature predictionEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 5 2008Z. Gao Summary The force-restore method originally developed to enable soil temperature predictions assumes that soil is uniform with depth (i.e. the vertical gradient of thermal diffusivity is zero in soil) and that thermal conduction is the only heat transfer mechanism necessary for prediction of soil temperature. These assumptions hamper the applicability of the force-restore method to many natural soil conditions. The main objective of this study is to revise the force-restore method by extending it to include the possibility of soil heterogeneity with depth (i.e. non-zero vertical gradient of thermal diffusivity in soil) and to include the possible occurrence of convective heat transfer as well as conductive heat transfer in soil. Soil temperatures calculated by the current and the revised force-restore methods for a shallow soil layer were compared with measured soil temperatures at a bare soil site in the China Loess Plateau from 22 to 26 July 2005. Results showed that the revised method improved on the current force-restore method, which overestimated either the diurnal amplitude or the phase shift for the shallow soil layer. These results indicate that the revised force-restore method is more applicable than the current force-restore method for predicting soil temperatures in naturally occurring non-uniform soil. The revised force-restore method has potential application within many land-atmosphere numerical models. [source] SONG VARIATION IN AN AVIAN RING SPECIESEVOLUTION, Issue 3 2000Darren E. Irwin Abstract., Divergence of mating signals can occur rapidly and be of prime importance in causing reproductive isolation and speciation. A ring species, in which two reproductively isolated taxa are connected by a chain of intergrading populations, provides a rare opportunity to use spatial variation to reconstruct the history of divergence. I use geographic variation in the song of a likely ring species, the greenish warbler (Phylloscopus trochiloides) to reconstruct the microevolutionary steps that occurred during divergence of a trait that is often important in speciation in birds. Populations of a western Siberian (P. t. viridanus) and an eastern Siberian (P. t. plumbeitarsus) form of the greenish warbler meet, but do not interbreed in central Siberia; these forms are connected by a chain of interbreeding populations extending in a ring to the south around the treeless Tibetan Plateau. I show that: (1) song structure differs greatly between the two Siberian forms, which share the same habitat; (2) song structure changes gradually around the ring; (3) singing behavior is relatively simple in the Himalayas, but becomes increasingly complex to the north, both to the west and east of the Tibetan Plateau; and (4) song varies along independent axes of complexity in the western and eastern south-north clines. By comparing geographic variation in singing behavior and ecological variables, I distinguish among possible causes of song divergence, including selection based on the acoustic environment, stochastic effects of sexual selection, and selection for species recognition. I suggest that parallel south-to-north ecological gradients have caused a greater intensity of sexual selection on song in northern populations and that the stochastic effects of sexual selection have led to divergence in song structure. [source] The origins of food production in north China: A different kind of agricultural revolution,EVOLUTIONARY ANTHROPOLOGY, Issue 1 2010Robert L. Bettinger Abstract By roughly 8,000 calendar years before the present (calBP), hunter-gatherers across a broad swath of north China had begun small-scale farming of broomcorn millet (Panicum miliaceum) and foxtail millet (Setaria italica).1,6 According to traditional wisdom, this early millet farming evolved from the intensive hunter-gatherer adaptation represented by the late Pleistocene microblade tradition of northern China,2, 7 termed here the North China Microlithic. The archeological record of this hunter-gatherer connection is poorly documented, however, and as a result the early agricultural revolution in north China is not as well understood as those that occurred in other parts of the world. The Laoguantai site of Dadiwan, in the western Loess Plateau, Gansu Province, PRC, furnishes the first complete record of this transition, which unfolded quite differently from other, better known, agricultural revolutions. [source] Annual cycle and inter-annual variability of gross primary production and ecosystem respiration in a floodprone river during a 15-year periodFRESHWATER BIOLOGY, Issue 5 2006URS UEHLINGER Summary 1. Temporal variation in ecosystem metabolism over a 15-year period (1986,2000) was evaluated in a seventh order channelised gravel bed river (mean annual discharge 48.7 m3 s,1) of the Swiss Plateau. The river is subject to frequent disturbance by bed-moving spates. Daily integrals of gross primary production (GPP) and ecosystem respiration (ER) were calculated based on single-station diel oxygen curves. 2. Seasonal decomposition of the time series of monthly metabolism rates showed that approximately 50% of the variation of GPP and ER can be attributed to season. Annual GPP averaged 5.0 ± 0.6 g O2 m,2 day,1 and showed no long-term trend. 3. Ecosystem respiration, averaging 6.2 ± 1.4 g O2 m,2 day,1, declined from 8.8 to 4.1 g O2 m,2 day,1 during the 15-year period. This significant trend paralleled a decline in nitrate and soluble reactive phosphorus concentrations, and the biochemical oxygen demand discharged by sewage treatment facilities upstream of the study reach. The ratio of GPP to ER (P/R) increased from 0.53 to about 1 as consequence of ER reduction. 4. Bed moving spates reduced GPP by 49% and ER by 19%. Postspate recovery of GPP was rapid between spring and autumn and slow during winter. Recovery of ER lacked any seasonal pattern. Annual patterns of daily GPP and to a minor extent of daily ER can be described as a sequence of recovery periods frequently truncated by spates. 5. The study showed that disturbance by frequent bed-moving spates resulted in major stochastic variation in GPP and ER but annual patterns were still characterised by a distinct seasonal cycle. It also became evident that stream metabolism is a suitable method to assess effects of gradual changes in water quality. [source] Growth and population size of crayfish in headwater streams: individual- and higher-level consequences of acidificationFRESHWATER BIOLOGY, Issue 7 2004Steven M. Seiler Summary 1. Environmental stress may have indirect positive effects on population size through modification of food-web interactions, despite having negative effects on individuals. Here we evaluate the individual- and population-level effects of acidification on crayfish (Cambarus bartonii) in headwater streams of the Allegheny Plateau (PA, U.S.A.) with field experiments and survey data. Median baseflow pH of 24 study reaches in nine streams varied from 4.4 to 7.4, with substantial variation found both among and within streams. 2. Two bioassays were conducted to evaluate the relationship between stream pH and crayfish growth rates. Growth rates were always higher in circumneutral reaches than in acidic reaches. Crayfish originating in acidic water grew less when transplanted into neutral water than did crayfish originating in neutral water, providing some evidence for a cost of acclimation to acidity. 3. Stream surveys showed that fish were less abundant and crayfish more abundant in acidified streams than in circumneutral streams. Crayfish density was sixfold higher in reaches with the lowest pH relative to circumneutral reaches. Large crayfish made up a higher proportion of crayfish populations at sites with high fish biomass, consistent with the hypothesis that fish predation on small individuals may be limiting crayfish population size at these sites. 4. Although individual crayfish suffered lower growth in acidified streams, increased acidity appeared to cause an increase in crayfish population size and shifts in size structure, possibly by relieving predation pressure by fish. [source] Quaternary paleoenvironments and potential for human exploitation of the Jordan plateau desert interiorGEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 4 2005Caroline P. Davies The physical, chemical, numerical, and radiometric analyses of a 31-m sediment core from the Qa'el-Jafr basin provide an important record of Quaternary paleoenvironments for the Jordan Plateau and evidence for several significant changes in climate regime. Cluster and PCA analyses of the geochemical data support the designation of major sedimentation regimes identified by stratigraphic and sediment analyses. Multiple cycles of alluvial deposition, lacustrine units, and erosional unconformities characterize the deepest sediments, followed by a period(s) of intense evaporation. Radiocarbon ages of charcoal in the uppermost 7 m place the aeolian/alluvial phase between 16,030 ± 140 yr B.P. and 24,470 ± 240 yr B.P. Deflation processes may explain the lack of a Holocene sequence. Despite lacking radiometric ages for the lower sediments, the thickness and degree of calcium-carbonate cementation suggest considerable age for the basal sediments, which suggests that a very long terrestrial record of Quaternary climate changes has been preserved in the Jafr basin. This new record of paleoenvironments provides important context to the archaeological record of the Jordan Plateau during the Quaternary. Several archaeological surveys demonstrate extensive human exploitation of lakes and springs of the major wadis along the western margin of the Rift Valley. However, little is known of human exploitation of the desert interiors. Qa'el-Jafr sediments demonstrate significant lacustrine and high moisture phases sufficient for human exploitation of the eastern desert during the Pleistocene. © 2005 Wiley Periodicals, Inc. [source] Landforms, sediments, soil development, and prehistoric site settings on the Madaba-Dhiban Plateau, JordanGEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 1 2005Carlos E. Cordova This paper examines recurrent spatial patterns of prehistoric sites in relation to landforms, alluvial fills, and soil development in the uplands and valleys of the Madaba and Dhiban Plateaus of Jordan. Mousterian lithics (Middle Paleolithic) are largely found on high strath terraces plateaus, where they are associated with red Mediterranean soils. In valleys, Upper Paleolithic sites are often associated with reworked loess deposits of the Dalala allostratigraphic unit. Epipaleolithic occupations are found stratified in deposits of the Thamad Terrace, and Pre-Pottery Neolithic and Pottery Neolithic occupations are associated with colluvium mantling the Thamad Terrace. The Tur al-Abyad Terrace and the Iskanderite alluvial inset are the remnants of middle Holocene floodplains, which were attractive areas for Chalcolithic and Early Bronze Age settlements. Sometime around 4000 B.C., stream incision and further lateral erosion destroyed these floodplains. These historic terraces are underlain by alluvial deposits ranging in age from Roman to Early Islamic periods. The sequence of allostratigraphic units, paleosols, and terraces are the basis for reconstructing phases of fluvial aggradation and stream incision during the past 20,000 years. © 2005 Wiley Periodicals, Inc. [source] Wadi Bakht revisited: Holocene climate change and prehistoric occupation in the Gilf Kebir region of the Eastern Sahara, SW EgyptGEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 8 2004Jörg Linstädter Geoarchaeological and chronological evidence from the remote Gilf Kebir Plateau in southwest Egypt suggests a new model for the influence of early and mid-Holocene precipitation regimes on land-use strategies of prehistoric settlers in what is now the center of the largest hyperarid area on earth. We hypothesize that the quantitatively higher, daytime, monsoon summer rainfall characteristic of the early Holocene (9300,5400 14C yr B.P./8400,4300 yr B.C.) resulted in less grass growth on the plateau compared to the winter rains that presumably fell in the cool nights during the terminal phase of the Holocene pluvial (5400,4500 yr B.P./4300,3300 yr B.C.). The unparalleled climatic transition at 5400 yr B.P. (4300 yr B.C.) caused a fundamental environmental change that resulted in different patterns of human behavior, economy, and land use in the canyon-like valleys and on the plains surrounding the plateau. The model emphasizes the crucial impact of seasonal rainfall distribution on cultural landscapes in arid regions and the lower significance of annual precipitation rates, with implications for future numeric climate models. It also serves as an example of how past climate changes have affected human societies. © 2004 Wiley Periodicals, Inc. [source] Geochemistry and petrography of basalt grindstones from the Karak Plateau, central JordanGEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 1 2004Brandon G. Watts Seventeen basalt grindstone fragments from central Jordan's Karak Plateau were studied. Most of these artifacts are vesicular or amygdaloidal with calcite as the dominant mineral filling the voids. The major minerals are olivine (with iddingsite rims), plagioclase, clinopyroxene, magnetite, and apatite. Glass is present in some samples. One basalt fragment is quite different in appearance and composition and may have come from flows closer to the Dead Sea. Grindstone fragment compositions plot in the tephrite-basanite and basalt fields. A plot of the concentrations of niobium, zirconium, and yttrium reveal that the sample compositions plot in the "within-plate alkali basalt" and "within-plate tholeiite" fields. The acquisition of basalts for preparing such implements appears to have been random. Some may have been introduced through trade and migration. Archaeological and environmental studies on the Karak Plateau are urgently needed because Jordan's population growth and economic development are destroying many sites and their environmental contexts. © 2004 Wiley Periodicals, Inc. [source] ORIGINAL AND SECONDARY HIGH-FREQUENCY SANDSTORM ZONES IN THE LOESS PLATEAU REGION, CHINAGEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 2 2007JIONGXIN XU ABSTRACT. A study of sandstorms in the Loess Plateau and neighbouring areas is based on observations of sandstorms and precipitation. Through analysis of the relationship between the mean annual number of sandstorms and the mean annual precipitation, an original sandstorm zone and a secondary high-frequency zone of sandstorms have been defined. The latter is mainly formed as a result of human activities, such as vegetation destruction and waste-land cultivation, and not because of climatic change. The secondary sandstorm zone is located 350,500 km away from the original sandstorm zone, reflecting the fact that the sandstorm zone in the Loess Plateau area has shifted 350,500 km to the southeast, in response to human impact. Some abrupt change has been found in the area where the mean annual precipitation is 270 mm, where the original sandstorm zone ends and a secondary zone of high-frequency sandstorms begins. This transition area can be regarded as an abnormally unstable area. This study shows that destruction of the vegetation can cause changes in the environment similar to those attributed to climatic change. [source] Stratigraphic and structural evolution of the Blue Nile Basin, Northwestern Ethiopian PlateauGEOLOGICAL JOURNAL, Issue 1 2009N. DS. Abstract The Blue Nile Basin, situated in the Northwestern Ethiopian Plateau, contains ,1400,m thick Mesozoic sedimentary section underlain by Neoproterozoic basement rocks and overlain by Early,Late Oligocene and Quaternary volcanic rocks. This study outlines the stratigraphic and structural evolution of the Blue Nile Basin based on field and remote sensing studies along the Gorge of the Nile. The Blue Nile Basin has evolved in three main phases: (1) pre-sedimentation phase, include pre-rift peneplanation of the Neoproterozoic basement rocks, possibly during Palaeozoic time; (2) sedimentation phase from Triassic to Early Cretaceous, including: (a) Triassic,Early Jurassic fluvial sedimentation (Lower Sandstone, ,300,m thick); (b) Early Jurassic marine transgression (glauconitic sandy mudstone, ,30,m thick); (c) Early,Middle Jurassic deepening of the basin (Lower Limestone, ,450,m thick); (d) desiccation of the basin and deposition of Early,Middle Jurassic gypsum; (e) Middle,Late Jurassic marine transgression (Upper Limestone, ,400,m thick); (f) Late Jurassic,Early Cretaceous basin-uplift and marine regression (alluvial/fluvial Upper Sandstone, ,280,m thick); (3) the post-sedimentation phase, including Early,Late Oligocene eruption of 500,2000,m thick Lower volcanic rocks, related to the Afar Mantle Plume and emplacement of ,300,m thick Quaternary Upper volcanic rocks. The Mesozoic to Cenozoic units were deposited during extension attributed to Triassic,Cretaceous NE,SW-directed extension related to the Mesozoic rifting of Gondwana. The Blue Nile Basin was formed as a NW-trending rift, within which much of the Mesozoic clastic and marine sediments were deposited. This was followed by Late Miocene NW,SE-directed extension related to the Main Ethiopian Rift that formed NE-trending faults, affecting Lower volcanic rocks and the upper part of the Mesozoic section. The region was subsequently affected by Quaternary E,W and NNE,SSW-directed extensions related to oblique opening of the Main Ethiopian Rift and development of E-trending transverse faults, as well as NE,SW-directed extension in southern Afar (related to northeastward separation of the Arabian Plate from the African Plate) and E,W-directed extensions in western Afar (related to the stepping of the Red Sea axis into Afar). These Quaternary stress regimes resulted in the development of N-, ESE- and NW-trending extensional structures within the Blue Nile Basin. Copyright © 2008 John Wiley & Sons, Ltd. [source] BARGEN continuous GPS data across the eastern Basin and Range province, and implications for fault system dynamicsGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2004Nathan A. Niemi SUMMARY We collected data from a transect of continuous Global Positioning System (GPS) sites across the eastern Basin and Range province at latitude 39°N from 1997,2000. Intersite velocities define a region ,350 km wide of broadly distributed strain accumulation at ,10 nstr yr,1. On the western margin of the region, site EGAN, ,10 km north of Ely, Nevada, moved at a rate of 3.9 ± 0.2 mm yr,1 to the west relative to site CAST, which is on the Colorado Plateau. Velocities of most sites to the west of Ely moved at an average rate of ,3 mm yr,1 relative to CAST, defining an area across central Nevada that does not appear to be extending significantly. The late Quaternary geological velocity field, derived using seismic reflection and neotectonic data, indicates a maximum velocity of EGAN with respect to the Colorado Plateau of ,4 mm yr,1, also distributed relatively evenly across the region. The geodetic and late Quaternary geological velocity fields, therefore, are consistent, but strain release on the Sevier Desert detachment and the Wasatch fault appears to have been anomalously high in the Holocene. Previous models suggesting horizontal displacement rates in the eastern Basin and Range near 3 mm yr,1, which focused mainly along the Wasatch zone and Intermountain seismic belt, may overestimate the Holocene Wasatch rate by at least 50 per cent and the Quaternary rate by nearly an order of magnitude, while ignoring potentially major seismogenic faults further to the west. [source] A lock-in model for the complex Matuyama-Brunhes boundary record of the loess/palaeosol sequence at Lingtai (Central Chinese Loess Plateau)GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2003S. Spassov SUMMARY In most marine sedimentary records, the Matuyama-Brunhes boundary (MBB) has been found in interglacial oxygen isotope stage 19. In the magnetostratigraphic records of most Chinese loess/palaeosol profiles the MBB is located in loess layer L8, which was deposited during a glacial period. The MBB at Lingtai (central Chinese Loess Plateau) also occurs in L8 and is characterized by multiple polarity flips. The natural remanent magnetization is mainly carried by two coexisting components. The higher coercivity (harder) component dominates in loess layers and is thought to be of detrital origin. The lower coercivity (softer) component prevails in palaeosols and was most probably formed in situ by (bio-)chemical processes. A lock-in model for the Lingtai MBB record has been developed by extending the lithologically controlled PDRM model of Bleil & von Dobeneck (1999). It assumes two lock-in zones. The NRM of the magnetically harder component is physically locked by consolidation shortly after loess deposition, whereas the softer component is formed at greater depth by pedogenesis and acquires a chemical remanent magnetization of younger age. At polarity boundaries, grains carrying reversed and normal directions may therefore occur together within a single horizon. The model uses ARM coercivity spectra to estimate the relative contributions of the two components. It is able to explain the observed rapid multiple polarity flips and low magnetization intensities as well as the stratigraphic shift of the Lingtai MBB with respect to the marine records. [source] Magnetic grain-size distribution of the enhanced component in the loess,palaeosol sequences in the western Loess Plateau of ChinaGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2001Toshiaki Mishima SUMMARY Rock magnetic measurements of Chinese loess,palaeosol samples from the Beiyuan section in Linxia City suggest the presence of two magnetic components: a background component and an enhanced component. The magnetic properties of the enhanced component suggest strong grain-size control, which is in contrast with variable grain-size distribution in loess,palaeosol from the central Loess Plateau. Chemically formed magnetic grains do not fulfil the requirements in the case of the western Loess Plateau because they may show shifts in the grain-size distribution. The difference in climate between the western and central Loess Plateau may lead to different origins and different preservation conditions of the pedogenic magnetite. [source] Comprehensive geriatric assessment of elderly highlanders in Qinghai, China I: Activities of daily living, quality of life and metabolic syndromeGERIATRICS & GERONTOLOGY INTERNATIONAL, Issue 4 2009Kozo Matsubayashi Aim: To reveal the comparison of comprehensive geriatric functions of elderly highlanders in Qinghai Plateau in China among three different ethnic groups. Methods: Activities of daily living (ADL), screening-based depression, quality of life (QOL) and checking-up of metabolic syndrome including community-based oral glucose tolerance test were assessed in 393 community-dwelling elderly subjects aged 60 years or more (247 Han elderly subjects, 49 Mongolian ones and 97 Tibetan ones). Results: Tibetan elderly highlanders were more disabled in ADL, but had higher QOL than Han elderly ones in Qinghai Plateau. Blood pressure measurements, rate of hypertension and hemoglobin concentrations in Tibetan elderly highlanders were lower than Han ones. Rates of diabetes and impaired glucose tolerance in elderly highlanders were relatively lower than other Asian elderly lowlanders. Conclusion: Prevalence of metabolic syndrome in elderly highlanders in Qinghai was still not high, however, we should pay attention to its tendency related with socialglobalism in the near future. Further investigation on physiological adaptability to hypoxic environment and human ageing phenomena in a global context may open a new research frontier for ageing science. [source] Changes in topsoil carbon stock in the Tibetan grasslands between the 1980s and 2004GLOBAL CHANGE BIOLOGY, Issue 11 2009YUANHE YANG Abstract Climate warming is likely inducing carbon loss from soils of northern ecosystems, but little evidence comes from large-scale observations. Here we used data from a repeated soil survey and remote sensing vegetation index to explore changes in soil organic carbon (SOC) stock on the Tibetan Plateau during the past two decades. Our results showed that SOC stock in the top 30 cm depth in alpine grasslands on the plateau amounted to 4.4 Pg C (1 Pg=1015 g), with an overall average of 3.9 kg C m,2. SOC changes during 1980s,2004 were estimated at ,0.6 g C m,2 yr,1, ranging from ,36.5 to 35.8 g C m,2 yr,1 at 95% confidence, indicating that SOC stock in the Tibetan alpine grasslands remained relatively stable over the sampling periods. Our findings are nonconsistent with previous reports of loss of soil C in grassland ecosystems due to the accelerated decomposition with warming. In the case of the alpine grasslands on the Tibetan Plateau studied here, we speculate that increased rates of decomposition as soils warmed during the last two decades may have been compensated by increased soil C inputs due to increased grass productivity. These results suggest that soil C stock in terrestrial ecosystems may respond differently to climate change depending on ecosystem type, regional climate pattern, and intensity of human disturbance. [source] Storage, patterns and controls of soil organic carbon in the Tibetan grasslandsGLOBAL CHANGE BIOLOGY, Issue 7 2008YUANHE YANG Abstract The soils of the Qinghai-Tibetan Plateau store a large amount of organic carbon, but the magnitude, spatial patterns and environmental controls of the storage are little investigated. In this study, using data of soil organic carbon (SOC) in 405 profiles collected from 135 sites across the plateau and a satellite-based dataset of enhanced vegetation index (EVI) during 2001,2004, we estimated storage and spatial patterns of SOC in the alpine grasslands. We also explored the relationships between SOC density (soil carbon storage per area) and climatic variables and soil texture. Our results indicated that SOC storage in the top 1 m in the alpine grasslands was estimated at 7.4 Pg C (1 Pg=1015 g), with an average density of 6.5 kg m,2. The density of SOC decreased from the southeastern to the northwestern areas, corresponding to the precipitation gradient. The SOC density increased significantly with soil moisture, clay and silt content, but weakly with mean annual temperature. These variables could together explain about 72% of total variation in SOC density, of which 54% was attributed to soil moisture, suggesting a key role of soil moisture in shaping spatial patterns of SOC density in the alpine grasslands. [source] Large-scale pattern of biomass partitioning across China's grasslandsGLOBAL ECOLOGY, Issue 2 2010Yuanhe Yang ABSTRACT Aim, To investigate large-scale patterns of above-ground and below-ground biomass partitioning in grassland ecosystems and to test the isometric theory at the community level. Location, Northern China, in diverse grassland types spanning temperate grasslands in arid and semi-arid regions to alpine grasslands on the Tibetan Plateau. Methods, We investigated above-ground and below-ground biomass in China's grasslands by conducting five consecutive sampling campaigns across the northern part of the country during 2001,05. We then documented the root : shoot ratio (R/S) and its relationship with climatic factors for China's grasslands. We further explored relationships between above-ground and below-ground biomass across different grassland types. Results, Our results indicated that the overall R/S of China's grasslands was larger than the global average (6.3 vs. 3.7). The R/S for China's grasslands did not show any significant trend with either mean annual temperature or mean annual precipitation. Above-ground biomass was nearly proportional to below-ground biomass with a scaling exponent (the slope of log,log linear relationship between above-ground and below-ground biomass) of 1.02 across various grassland types. The slope did not differ significantly between temperate and alpine grasslands or between steppe and meadow. Main conclusions, Our findings support the isometric theory of above-ground and below-ground biomass partitioning, and suggest that above-ground biomass scales isometrically with below-ground biomass at the community level. [source] What caused the mid-Holocene forest decline on the eastern Tibet-Qinghai Plateau?GLOBAL ECOLOGY, Issue 2 2010Ulrike Herzschuh ABSTRACT Aim, Atmospheric CO2 concentrations depend, in part, on the amount of biomass locked up in terrestrial vegetation. Information on the causes of a broad-scale vegetation transition and associated loss of biomass is thus of critical interest for understanding global palaeoclimatic changes. Pollen records from the north-eastern Tibet-Qinghai Plateau reveal a dramatic and extensive forest decline beginning c. 6000 cal. yr bp. The aim of this study is to elucidate the causes of this regional-scale change from high-biomass forest to low-biomass steppe on the Tibet-Qinghai Plateau during the second half of the Holocene. Location, Our study focuses on the north-eastern Tibet-Qinghai Plateau. Stratigraphical data used are from Qinghai Lake (3200 m a.s.l., 36°32,,37°15, N, 99°36,,100°47, E). Methods, We apply a modern pollen-precipitation transfer function from the eastern and north-eastern Tibet-Qinghai Plateau to fossil pollen spectra from Qinghai Lake to reconstruct annual precipitation changes during the Holocene. The reconstructions are compared to a stable oxygen-isotope record from the same sediment core and to results from two transient climate model simulations. Results, The pollen-based precipitation reconstruction covering the Holocene parallels moisture changes inferred from the stable oxygen-isotope record. Furthermore, these results are in close agreement with simulated model-based past annual precipitation changes. Main conclusions, In the light of these data and the model results, we conclude that it is not necessary to attribute the broad-scale forest decline to human activity. Climate change as a result of changes in the intensity of the East Asian Summer Monsoon in the mid-Holocene is the most parsimonious explanation for the widespread forest decline on the Tibet-Qinghai Plateau. Moreover, climate feedback from a reduced forest cover accentuates increasingly drier conditions in the area, indicating complex vegetation,climate interactions during this major ecological change. [source] | |||||||||||||||||||||||||||||||||||||||||||||||||