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1.
Annett Bartsch Martin Gude Christer Jonasson & Dieter Scherer 《Geografiska Annaler: Series A, Physical Geography》2002,84(3-4):171-178
Sediment transport processes in the Kärkevagge are investigated concerning their spatial and temporal characteristics due to long–term monitoring. Within this study remote sensing techniques and GIS modelling in connection with geomorphic mapping are applied for identification and characterization of geomorphic process units. Relationships between geomorphometric parameters and slope processes like solifluction, talus creep and rockfall have been analysed. Multitemporal Landsat–TM5 scenes are used as source for landcover characteristics (Normalized Difference Vegetation Index) after preprocessing involving orthorectification and topographic normalization in order to remove possible terrain–induced effects. Additionally, a digital elevation model with a resolution of 20 m for the Kärkevagge catchment is developed and parameters like slope gradient, slope aspect and profile curvature are extracted as input for the analysis of the sediment transport system. The combination of landcover information, geomorphometrical and topological features allows the definition of areas for single process activities. They show specific sediment displacement characteristics depending on material conditions, topological and geometrical features. Geomorphic process units, which show a homogenous composition, are extracted from these available layers. 相似文献
2.
Yannick Garcin Annett Junginger Daniel Melnick Daniel O. Olago Manfred R. Strecker Martin H. Trauth 《Quaternary Science Reviews》2009,28(9-10):911-925
The Late Pleistocene to Middle Holocene African Humid Period (AHP) was characterized by dramatic hydrologic fluctuations in the tropics. A better knowledge of the timing, spatial extent, and magnitude of these hydrological fluctuations is essential to decipher the climate-forcing mechanisms that controlled them. The Suguta Valley (2°N, northern Kenya Rift) has recorded extreme environmental changes during the AHP. Extensive outcrops of lacustrine sediments, ubiquitous wave-cut notches, shorelines, and broad terrace treads along the valley margins are the vestiges of Lake Suguta, which once filled an 80 km long and 20 km wide volcano–tectonic depression. Lake Suguta was deep between 16.5 and 8.5 cal ka BP. During its maximum highstand, it attained a water depth of ca 300 m, a surface area of ca 2150 km2, and a volume of ca 390 km3. The spatial distribution of lake sediments, the elevation of palaeo-shorelines, and other geomorphic evidences suggest that palaeo-Lake Suguta had an overflow towards the Turkana basin to the north. After 8.5 cal ka BP, Lake Suguta abruptly disappeared. A comparison of the Lake Suguta water-level curve with other reconstructed water levels from the northern part of the East African Rift System shows that local insolation, which is dominated by precessional cycles, may have controlled the timing of lake highstands in this region. Our data show that changes of lake levels close to the Equator seem to be driven by fluctuations of spring insolation, while fluctuations north of the Equator are apparently related to variations in summer insolation. However, since these inferred timings of lake-level changes are mostly based on the radiocarbon dating of carbonate shells, which may have been affected by a local age reservoir, alternative dating methods are needed to support this regional synthesis. Between 12.7 and 11.8 cal ka BP, approximately during the Northern Hemisphere high-latitude Younger Dryas, the water level of Lake Suguta fell by ca 50 m, suggesting that remote influences also affected local hydrology. 相似文献
3.
A series of 30-day biochemical oxygen demand (BOD) experiments were conducted on water column samples from a reach of the upper Klamath River that experiences hypoxia and anoxia in summer. Samples were incubated with added nitrification inhibitor to measure carbonaceous BOD (CBOD), untreated to measure total BOD, which included demand from nitrogenous BOD (NBOD), and coarse-filtered to examine the effect of removing large particulate matter. All BOD data were fit well with a two-group model, so named because it considered contributions from both labile and refractory pools of carbon: BODt = a1(1 ? e? a0t) + a2t. Site-average labile first-order decay rates a0 ranged from 0.15 to 0.22/day for CBOD and 0.11 to 0.29/day for BOD. Site-average values of refractory zero-order decay rates a2 ranged from 0.13 to 0.25 mg/L/day for CBOD and 0.01 to 0.45 mg/L/day for BOD; the zero-order CBOD decay rate increased from early- to mid-summer. Values of ultimate CBOD for the labile component a1 ranged from 5.5 to 28.8 mg/L for CBOD, and 7.6 to 30.8 mg/L for BOD. Two upstream sites had higher CBOD compared to those downstream. Maximum measured total BOD5 and BOD30 during the study were 26.5 and 55.4 mg/L; minimums were 4.2 and 13.6 mg/L. For most samples, the oxygen demand from the three components considered here were: labile CBOD > NBOD > refractory CBOD, though the relative importance of refractory CBOD to oxygen demand increased over time. Coarse-filtering reduced CBOD for samples with high particulate carbon and high biovolumes of Aphanizomenon flos-aquae. There was a strong positive correlation between BOD, CBOD, and the labile component of CBOD to particulate C and N, with weaker positive correlation to field pH, field dissolved oxygen, and total N. The refractory component of CBOD was not correlated to particulate matter, instead showing weak but statistically significant correlation to dissolved organic carbon, UV absorbance at 254 nm, and total N. Particulate organic matter, especially the alga A.flos-aquae, is an important component of oxygen demand in this reach of the Klamath River, though refractory dissolved organic matter would continue to exert an oxygen demand over longer time periods and as water travels downstream. 相似文献
4.
Carbon storage and catchment hydrology are influenced both by land use changes and climatic changes, but there are few studies
addressing both responses under both driving forces. We investigated the relative importance of climate change vs. land use change for four Alpine catchments using the LPJ-GUESS model. Two scenarios of grassland management were calibrated
based on the more detailed model PROGRASS. The simulations until 2100 show that only reforestation could lead to an increase
of carbon storage under climatic change, whereby a cessation of carbon accumulation occurred in all catchments after 2050.
The initial increase in carbon storage was attributable mainly to forest re-growth on abandoned land, whereas the stagnation
and decline in the second half of the century was mainly driven by climate change. If land was used more intensively, i.e.
as grassland, litter input to the soil decreased due to harvesting, resulting in a decline of soil carbon storage (1.2−2.9 kg C
m–2) that was larger than the climate-induced change (0.8–1.4 kg C m−2). Land use change influenced transpiration both directly and in interaction with climate change. The response of forested
catchments diverged with climatic change (11–40 mm increase in AET), reflecting the differences in forest age, topography
and water holding capacity within and between catchments. For grass-dominated catchments, however, transpiration responded
in a similar manner to climate change (light management: 23–32 mm AET decrease, heavy management: 29–44 mm AET decrease),
likely because grassroots are concentrated in the uppermost soil layers. Both the water and the carbon cycle were more strongly
influenced by land use compared to climatic changes, as land use had not only a direct effect on carbon storage and transpiration,
but also an indirect effect by modifying the climate change response of transpiration and carbon flux in the catchments. For
the carbon cycle, climate change led to a cessation of the catchment response (sink/source strength is limited), whereas for
the water cycle, the effect of land use change remains evident throughout the simulation period (changes in evapotranspiration
do not attenuate). Thus we conclude that management will have a large potential to influence the carbon and water cycle, which
needs to be considered in management planning as well as in climate and hydrological modelling. 相似文献
5.
Flat sharers are one of the most distinct representatives of the ‘new’ household types, but have received only very limited
attention from researchers. Back in the 1960s shared flats were usually founded with a strong ideological impetus, whereas
flat sharing nowadays is just one household type among many others. Typically, this housing arrangement consists of at least
two young adult individuals without children. Sharing the flat and the housing costs is the basis of their relationship but
living with others is an additional motive. As a rule, flat sharing bridges two distinct events in the course of one’s life:
the leaving of the parental home and the foundation of the first independent household. Thus for a restricted period in time,
it is a flexible household type adapted to the situational needs of its members. Germany has one of the strongest and longest
traditions of flat sharing in Europe, especially among university students. An explorative study was conducted in Leipzig
to come to a deeper understanding of what flat sharing means in its ambivalence of being both an economic unit and a social
arrangement. Based on qualitative and quantitative evidence from group discussions and Internet adverts, we shed light on
the highly under-researched social practice of flat sharing. We will show that despite the structural flexibility of this
household type, there is also evidence for its socio-demographic selectivity, spatial concentration and temporal limitation
over the individual life courses. 相似文献
6.
Clarissa Glaser Marc Schwientek Tobias Junginger Benjamin Silas Gilfedder Sven Frei Martina Werneburg Christian Zwiener Christiane Zarfl 《水文研究》2020,34(24):4712-4726
Understanding groundwater–surface water (GW–SW) interactions is vital for water management in karstic catchments due to its impact on water quality. The objective of this study was to evaluate and compare the applicability of seven environmental tracers to quantify and localize groundwater exfiltration into a small, human-impacted karstic river system. Tracers were selected based on their emission source to the surface water either as (a) dissolved, predominantly geogenic compounds (radon-222, sulphate and electrical conductivity) or (b) anthropogenic compounds (predominantly) originating from wastewater treatment plant (WWTP) effluents (carbamazepine, tramadol, sodium, chloride). Two contrasting sampling approaches were compared (a) assuming steady-state flow conditions and (b) considering the travel time of the water parcels (Lagrangian sampling) through the catchment to account for diurnal changes in inflow from the WWTP. Spatial variability of the concentrations of all tracers indicated sections of preferential groundwater inflow. Lagrangian sampling techniques seem highly relevant for capturing dynamic concentration patterns of WWTP-derived compounds. Quantification of GW inflow with the finite element model FINIFLUX, based on observed in-stream Rn activities led to plausible fluxes along the investigated river reaches (0.265 m3 s−1), while observations of other natural or anthropogenic environmental tracers produced less plausible water fluxes. Important point sources of groundwater exfiltration can be ascribed to locations where the river crosses geological fault lines. This indicates that commonly applied concepts describing groundwater–surface water interactions assuming diffuse flow in porous media are difficult to transfer to karstic river systems whereas concepts from fractured aquifers may be more applicable. In general, this study helps selecting the best suited hydrological tracer for GW exfiltration and leads to a better understanding of processes controlling groundwater inflow into karstic river systems. 相似文献
7.
The dynamic vegetation model (LPJ-GUESS) is used to project transient impacts of changes in climate on vegetation of the Barents
Region. We incorporate additional plant functional types, i.e. shrubs and defined different types of open ground vegetation,
to improve the representation of arctic vegetation in the global model. We use future climate projections as well as control
climate data for 1981–2000 from a regional climate model (REMO) that assumes a development of atmospheric CO2-concentration according to the B2-SRES scenario [IPCC, Climate Change 2001: The scientific basis. Contribution working group I to the Third assessment report of the IPCC. Cambridge University Press, Cambridge (2001)]. The model showed a generally good fit with observed data, both qualitatively when model outputs were compared to vegetation
maps and quantitatively when compared with observations of biomass, NPP and LAI. The main discrepancy between the model output
and observed vegetation is the overestimation of forest abundance for the northern parts of the Kola Peninsula that cannot
be explained by climatic factors alone. Over the next hundred years, the model predicted an increase in boreal needle leaved
evergreen forest, as extensions northwards and upwards in mountain areas, and as an increase in biomass, NPP and LAI. The
model also projected that shade-intolerant broadleaved summergreen trees will be found further north and higher up in the
mountain areas. Surprisingly, shrublands will decrease in extent as they are replaced by forest at their southern margins
and restricted to areas high up in the mountains and to areas in northern Russia. Open ground vegetation will largely disappear
in the Scandinavian mountains. Also counter-intuitively, tundra will increase in abundance due to the occupation of previously
unvegetated areas in the northern part of the Barents Region. Spring greening will occur earlier and LAI will increase. Consequently,
albedo will decrease both in summer and winter time, particularly in the Scandinavian mountains (by up to 18%). Although this
positive feedback to climate could be offset to some extent by increased CO2 drawdown from vegetation, increasing soil respiration results in NEE close to zero, so we cannot conclude to what extent
or whether the Barents Region will become a source or a sink of CO2. 相似文献
8.
Christoph Zöckler Lera Miles Lucy Fish Annett Wolf Gareth Rees Fiona Danks 《Climatic change》2008,87(1-2):119-130
Climate change is expected to alter the distribution of habitats and thus the distribution of species connected with these
habitats in the terrestrial Barents Sea region. It was hypothesised that wild species connected with the tundra and open-land
biome may be particularly at risk as forest area expands. Fourteen species of birds were identified as useful indicators for
the biodiversity dependent upon this biome. By bringing together species distribution information with the LPJ-GUESS vegetation
model, and with estimates of future wild and domestic reindeer density, potential impacts on these species between the present
time and 2080 were assessed. Over this period there was a net loss of open land within the current breeding range of most
bird species. Grazing reindeer were modelled as increasing the amount of open land retained for nine of the tundra bird species. 相似文献
9.
Barbara Seth Richard A. Armstrong Annett Büttner Igor M. Villa 《Earth and Planetary Science Letters》2005,230(3-4):355-378
This study presents the chronological evolution of the upper amphibolite facies Orue Unit in NW Namibia. Metasedimentary and meta-igneous rocks of the Orue Unit were investigated using the Pb–Pb stepwise leaching technique on garnet and rutile, U–Pb multi-grain analysis on rutile, Sm–Nd–Lu–Hf leaching technique on garnet, SHRIMP analysis on zircon and Ar–Ar dating on amphibole. Each of these techniques pertains to different processes that occurred before, during, or after the metamorphic peak. Our age data can be integrated with petrological constraints to provide a more complete understanding of the metamorphic cycle. Our pre-peak metamorphic zircon ages, peak metamorphic garnet ages and peak to late peak metamorphic amphibole 39Ar–40Ar ages bracket the upper amphibolite facies metamorphic event including hydration or dehydration processes into a time span of only ca. 20 Ma. The age data obtained by peak metamorphic mineral analyses cluster around 1340–1320 Ma. Based on age data and field observation, we interpret the upper amphibolite facies metamorphism as a large-scale regional mid-crustal event. Spot analyses of inherited zircon cores obtained by SHRIMP reflect the sedimentary origin of the respective rocks of the Orue Unit and derivation from Palaeoproterozoic protoliths. The metamorphic rocks south of the anorthositic Kunene Intrusive Complex (KIC) have previously been ascribed to the Palaeoproterozoic Epupa Complex at the SW margin of the Congo craton and were thus thought to be older than the Mesoproterozoic KIC. Our data show that the high-grade metamorphic overprint took place 30–50 Ma after emplacement of the KIC. Rutile growth ages of 1248 Ma in one sample reflect fluid activity which seems to be a local phenomenon since there is no other evidence of geological activity throughout the Orue Unit at that time. The rutile ages predate the emplacement of satellite intrusions in that area by 30 Ma and there is no causal relation between these two events. 相似文献
10.
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