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51.
Bernhard Krautzer Wilhelm Graiss Giovanni Peratoner Christian Partl Sonia Venerus Brigitte Klug 《Natural Hazards》2011,56(2):547-557
Control of erosion, and all of its after effects, from increased surface drainage and erosion to the formation of karst, is
one of the essential problems when undertaking recultivation following necessary interventions in the sub-alpine and alpine
vegetation stage (high zones). Average slope inclinations of 30–45% in the vicinity of ski runs, and far above in areas of
natural erosion and avalanche zones, make restoration processes with sufficient erosion protection the prerequisite for success.
Only a sufficient vegetation development of more than 70% ground cover stabilises the topsoil in the long term and reduces
soil erosion to an acceptable degree. From 1999 to 2002, an international EU project with the participation of research groups
and private firms from Austria, Italy and Germany was carried out under the direction of the Agricultural Research and Education
Centre Raumberg-Gumpenstein (AREC) on five different Alpine sites at altitudes from 1,245 to 2,350 m above sea level. The
aim of the work was the formulation of practice-relevant requirements for recultivation following intervention in high zones,
especially following constructional measures in the vicinity of ski runs and lifts, torrent- and avalanche barriers. In a
statistical comparison, the relationship between restoration techniques, seed mixtures of differing ecological value and vegetation
cover was observed. The influence of application technique on erosion processes after restoration was obvious for the first
two vegetation periods. Only with the additional use of mulch covers could increase surface drainage and noticeable soil loss
be avoided. At high altitudes, the choice of seed mixture, irrespective of whether rapid or slow growing and independent of
the extent of accompanying fertilisation, had no significance in the first two vegetation periods following sowing. In the
following growing seasons, however, higher cover values were obtained with site-specific seed mixtures at three of the five
experimental sites. While few species of the commercial seed mixture showed satisfactory persistency, most of the grasses
and in particular the alpine leguminosae of site-specific seed mixtures increased their share during the observation period.
In the long-term, sufficient protection against erosion is only guaranteed by the use of stable, enduring and ecologically
adapted species. 相似文献
52.
Yongbo Wang Ulrike Herzschuh Xingqi Liu Oliver Korup Bernhard Diekmann 《Journal of Paleolimnology》2014,51(2):303-312
Lacustrine sediments have been widely used to investigate past climatic and environmental changes on millennial to seasonal time scales. Sedimentary archives of lakes in mountainous regions may also record non-climatic events such as earthquakes. We argue herein that a set of 64 annual laminae couplets reconciles a stratigraphically inconsistent accelerator mass spectrometry (AMS) 14C chronology in a ~4-m-long sediment core from Lake Mengda, in the north-eastern Tibetan Plateau. The laminations suggest the lake was formed by a large landslide, triggered by the 1927 Gulang earthquake (M = 8.0). The lake sediment sequence can be separated into three units based on lithologic, sedimentary, and isotopic characteristics. Starting from the bottom of the sequence, these are: (1) unweathered, coarse, sandy valley-floor deposits or landslide debris that pre-date the lake, (2) landslide-induced, fine-grained soil or reworked landslide debris with a high organic content, and (3) lacustrine sediments with low organic content and laminations. These annual laminations provide a high-resolution record of anthropogenic and environmental changes during the twentieth century, recording enhanced sediment input associated with two phases of construction activities. The high mean sedimentation rates of up to 4.8 mm year?1 underscore the potential for reconstructing such distinct sediment pulses in remote, forested, and seemingly undisturbed mountain catchments. 相似文献
53.
Maik Grunwald Olaf Dellwig Gerd Liebezeit Bernhard Schnetger Rainer Reuter Hans-Jürgen Brumsack 《Marine Chemistry》2007
In autumn 2002 a time-series station was installed in the tidal inlet between the Islands of Langeoog and Spiekeroog (Southern North Sea, NW Germany) to continuously measure physical, chemical, and meteorological parameters, even during extreme weather conditions (gale-force storms, drifting ice). Inside the pole of the station sensor tubes are installed in direction of the prevailing tidal currents. The tubes are equipped with hydrographic sensors (pressure, temperature, conductivity) and allow retrieval of water for nutrient analysis by automated instruments located inside the pole. Dissolved methane and the nutrients ammonia, nitrite, nitrate, phosphate, and silicate are measured at the station. 相似文献
54.
55.
Basin evolution and palaeoenvironmental variability of the thermokarst lake El'gene‐Kyuele,Arctic Siberia 下载免费PDF全文
Philipp Schleusner Boris K. Biskaborn Frank Kienast Juliane Wolter Dmitry Subetto Bernhard Diekmann 《Boreas: An International Journal of Quaternary Research》2015,44(1):216-229
Thermokarst lakes are a widespread feature of the Arctic tundra, in which highly dynamic processes are closely connected with current and past climate changes. We investigated late Quaternary sediment dynamics, basin and shoreline evolution, and environmental interrelations of Lake El'gene‐Kyuele in the NE Siberian Arctic (latitude 71°17′N, longitude 125°34′E). The water‐body displays thaw‐lake characteristics cutting into both Pleistocene Ice Complex and Holocene alas sediments. Our methods are based on grain size distribution, mineralogical composition, TOC/N ratio, stable carbon isotopes and the analysis of plant macrofossils from a 3.5‐m sediment profile at the modern eastern lake shore. Our results show two main sources for sediments in the lake basin: terrigenous diamicton supplied from thermokarst slopes and the lake shore, and lacustrine detritus that has mainly settled in the deep lake basin. The lake and its adjacent thermokarst basin rapidly expanded during the early Holocene. This climatically warmer than today period was characterized by forest or forest tundra vegetation composed of larches, birch trees and shrubs. Woodlands of both the HTM and the Late Pleistocene were affected by fire, which potentially triggered the initiation of thermokarst processes resulting later in lake formation and expansion. The maximum lake depth at the study site and the lowest limnic bioproductivity occurred during the longest time interval of ~7 ka starting in the Holocene Thermal Maximum and lasting throughout the progressively cooler Neoglacial, whereas partial drainage and an extensive shift of the lake shoreline occurred ~0.9 cal. ka BP. Correspondingly, this study discusses different climatic and environmental drivers for the dynamics of a thermokarst basin. 相似文献
56.
Natacha Pasche Georges Alunga Keely Mills Fabrice Muvundja David B. Ryves Michael Schurter Bernhard Wehrli Martin Schmid 《Journal of Paleolimnology》2010,44(4):931-946
This study interprets the recent history of Lake Kivu, a tropical lake in the East African Rift Valley. The current gross
sedimentation was characterized from a moored sediment trap array deployed over 2 years. The past net sedimentation was investigated
with three short cores from two different basins. Diatom assemblages from cores were interpreted as reflecting changes in
mixing depth, surface salinity and nutrient availability. The contemporary sediment trap data indicate seasonal variability,
governed by diatom blooms during the annual mixing in the dry season, similar to Lakes Malawi and Tanganyika. The ratio of
settling fluxes to net sediment accumulation rates implies mineralization rates of 80–90% at the sediment-water interface.
The sediment cores revealed an abrupt change ~40 years ago, when carbonate precipitation started. Since the 1960s, deep-water
methane concentrations, nutrient fluxes and soil mineral inputs have increased considerably and diatom assemblages have altered.
These modifications probably resulted from a combination of three factors, commonly altering lake systems: the introduction
of a non-native fish species, eutrophication, and hydrological changes inducing greater upwelling. Both the fish introduction
and increased rainfall occurred at the time when the onset of carbonate precipitation was observed, whereas catchment population
growth accompanied by intensified land use increased the flux of soil minerals already since the early twentieth century due
to more intense erosion. 相似文献
57.
58.
Jean-Claude Vannay Zachary D. Sharp Bernhard Grasemann 《Contributions to Mineralogy and Petrology》1999,137(1-2):90-101
Inverted metamorphic field gradients are preserved in two amphibolite facies metapelitic sequences forming the crystalline
core zone of the Himalayan orogen in the Sutlej valley (NW India). In the High Himalayan Crystalline Sequence (HHCS), metamorphic
conditions increase upwards from the staurolite zone at the base, through the kyanite-in and sillimanite-in isograds, finally
to reach partial melting conditions at the top. The structurally lower Lesser Himalayan Crystalline Sequence (LHCS) shows
a gradual superposition of garnet-in, staurolite-in and kyanite + sillimanite-in isograds. Although phase equilibria constraints
imply inverted temperature field gradients in both units, garnet-biotite (GARB) rim thermometry indicates final equilibration
at a nearly uniform temperature around T ≈ 600 °C across these sequences. The P-T path and garnet zoning data show that this apparent lack of thermal field gradient is mainly the consequence of a resetting
of the GARB equilibria during cooling. In order to constrain peak temperature conditions, 20 samples along the studied section
have been analysed for oxygen isotope thermometry. The isotopic fractionations recorded by quartz-garnet and quartz-aluminosilicate
mineral pairs indicate temperatures consistent with phase equilibria and P-T path constraints for metamorphic peak conditions. Together with barometry results, based on net transfer continuous reactions,
the oxygen isotope thermometry indicates peak conditions characterized by: (1) a temperature increase from T ≈ 570 to 750 °C at a nearly constant pressure around P ≈ 800 MPa, from the base to the top of the HHCS unit; (2) a temperature increase from T ≈ 610 to 700 °C and a pressure decrease from P ≈ 900 to 700 MPa, from the base to the top of the LHCS metapelites. Oxygen isotope thermometry thus provides the first quantitative
data demonstrating that the Himalayan inverted metamorphism can be associated with a complete inversion of the thermal field
gradient across the crystalline core zone of this orogen.
Received: 1 April 1999 / Accepted: 12 July 1999 相似文献
59.
Svetlana S. Kostrova Hanno Meyer Hannah L. Bailey Anna V. Ludikova Raphael Gromig Gerhard Kuhn Yuri A. Shibaev Anna V. Kozachek Alexey A. Ekaykin Bernhard Chapligin 《Boreas: An International Journal of Quaternary Research》2019,48(2):361-376
This article presents a new comprehensive assessment of the Holocene hydrological variability of Lake Ladoga, northwest Russia. The reconstruction is based on oxygen isotopes of lacustrine diatom silica (δ18Odiatom) preserved in sediment core Co 1309, and is complemented by a diatom assemblage analysis and a survey of modern isotope hydrology. The data indicate that Lake Ladoga has existed as a freshwater reservoir since at least 10.8 cal. ka BP. The δ18Odiatom values range from +29.8 to +35.0‰, and relatively higher δ18Odiatom values around +34.7‰ between c. 7.1 and 5.7 cal. ka BP are considered to reflect the Holocene Thermal Maximum. A continuous depletion in δ18Odiatom since c. 6.1 cal. ka BP accelerates after c. 4 cal. ka BP, indicating Middle to Late Holocene cooling that culminates during the interval 0.8–0.2 cal. ka BP, corresponding to the Little Ice Age. Lake‐level rises result in lower δ18Odiatom values, whereas lower lake levels cause higher δ18Odiatom values. The diatom isotope record gives an indication for a rather early opening of the Neva River outflow at c. 4.4–4.0 cal. ka BP. Generally, overall high δ18Odiatom values around +33.5‰ characterize a persistent evaporative lake system throughout the Holocene. As the Lake Ladoga δ18Odiatom record is roughly in line with the 60°N summer insolation, a linkage to broader‐scale climate change is likely. 相似文献
60.