Towards continuous long-term measurements of suspended particulate matter (SPM) in turbid coastal waters   总被引：1，自引：1，他引：0  

Thomas H. Badewien  Elke Zimmer  Alexander Bartholomä  Rainer Reuter 《Ocean Dynamics》2009,59(2):227-238

The dynamics of sediment transport in the East Frisian Wadden Sea are important for the coastal zone and for ecosystem functioning. The tidal inlets between the East Frisian islands connect the back-barrier intertidal flats to the North Sea. Here, concentrations of suspended particulate matter (SPM) in the water column are highly variable, depending on weather conditions and tides. In order to estimate the nature and quantity of sediment transport, in situ measurements were carried out at a Time Series Station in the tidal inlet between the islands of Spiekeroog and Langeoog. This study shows the suitability of multispectral transmissometry (MST) for obtaining long-term SPM measurements with high resolution. The comparability of this technique to the standard filter method and the laser diffraction method [laser in situ scattering and transmissometry (LISST)] is demonstrated. In addition, the Junge coefficients derived from both MST and LISST measurements are compared. A time series of SPM data covering nearly 4 months is presented. As a major result, the data reveal that a single storm surge can have less impact on SPM dynamics than longer-lasting gales. This high-resolution long-term data set is very valuable for modelling suspended matter flux. It also provides background information for studying the influence of SPM dynamics on coastal sediments.  相似文献   

EXPLANATIONS FOR THE INTENSIFICATION OF COUNTERURBANIZATION IN THE FEDERAL REPUBLIC OF GERMANY *     

Thomas Kontuly  Roland Vogelsang 《The Professional geographer》1988,40(1):42-54

Evaluating yearly net migration for the Federal Republic of Germany establishes the importance of demographic restructuring and government policies as explanations for the counterurbanization phenomenon. Counterurbanization, the spatial demographic deconcentration of regional population, is measured as an inverse relationship between the net migration rate and population sizes of functional urban regions. A counterurbanization pattern filtered-down from older to younger age-groups of the population, and appears related to an increasing preference for small-sized regions with natural amenities. For foreigners, a counterurbanization direction of movement can be explained by changes in immigration laws. While counterurbanization may be slowing down during the 1980s in certain developed countries, such as the United States, in the Federal Republic the phenomenon intensifies throughout the 1970–84 time period. Based on broad national demographic changes in combination with agespecific patterns of movement, this strong counterurbanization trend should continue well into the future.  相似文献   

Rare earth element fractionation during the precipitation and crystallisation of hydrous ferric oxides from anoxic lake water     

Elke Bozau  Jrg Gttlicher  Hans-Joachim Strk 《Applied Geochemistry》2008,23(12):3473-3486

An enrichment of light rare earth elements (LREE) is characteristic for most of the acidic, Fe- and SO₄-rich pit lakes and groundwaters in the lignite mining area of Lower Lusatia (Germany). One of these acidic lakes – the pit lake “RL 1223” – has a strong thermal and chemical stratification. The upper water layer (0–9 m) shows pH values of about 3 during all seasons. The monimolimnion (10–17 m) of the lake is anoxic and has pH values of about 7. The rare earth element (REE) patterns of the upper lake water show enriched LREE (La_N/Yb_N = 1.6) whereas the opposite patterns (depletion of LREE, La_N/Yb_N = 0.4) are found in the anoxic water of the monimolimnion. Experiments were conducted to observe the behaviour of REE during Fe oxidation in water from the monimolimnion (depth 14 m). The sampled monimolimnion water was placed in plastic bottles, and the changing water chemistry was observed for 40 weeks after sampling. Due to the initial anoxic conditions almost all Fe precipitated in the investigated water, and the pH value decreased from about 7 to 3 during the oxidation. The Fe precipitates are identified as ferrihydrite which is transformed into goethite within the oxidation process. Stable pH conditions (pH 3.0) were reached after about 10 weeks of oxidation.The original REE patterns of the investigated water are generally reflected in the Fe precipitates collected at the beginning of the experiment as well as after up to 40 weeks of oxidation. However, in the corresponding water LREE were temporally enriched with a maximum La_N/Yb_N ratio of 1.0 and a maximum La_N/Sm_N ratio of 2.3 after 6 weeks of oxidation time (pH 3.8–4.9). Although complex geochemical changes took place between the start and the end of the experiment REE patterns observed at these points in time are nearly identical. These differences of the REE pattern can be explained by the sampling procedure. The experimental findings can be transmitted to the mining dump aquifers of the study area where geochemical conditions comparable to the experimental oxidation time from 3 to 6 weeks are found and hydrous ferric oxides are precipitating. Groundwater passing through the mining dumps can preferentially desorb LREE from the Fe precipitates and display the typical LREE enrichment and carry it to the epilimnion of the acidic pit lakes in Lower Lusatia.  相似文献   

Political unification and regional consequences of German East-West migration     

Kontuly T  Vogelsang R  Schon KP  Maretzke S 《International journal of population geography : IJPG》1997,3(1):31-47

"The purpose of this paper is to evaluate the impact of the post-unification East to West transfer of the German population on levels of spatial concentration and deconcentration in Eastern and Western Germany. Using 1991 internal migration data, it was found that German East-to-West migration served to deconcentrate regional population in the West, but concentrate population in the East. Regional variations in German East-to-West migration during 1991 can be explained by the availability of employment and housing, a distance-minimisation effect, and the location of relatives and friends."  相似文献   

Statements about climate researchers’ carbon footprints affect their credibility and the impact of their advice     

Shahzeen Z. Attari  David H. Krantz  Elke U. Weber 《Climatic change》2016,138(1-2):325-338

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The importance of three centuries of land-use change for the global and regional terrestrial carbon cycle   总被引：4，自引：0，他引：4  

Jelle G. Van Minnen  Kees Klein Goldewijk  Elke Stehfest  Bas Eickhout  Gerard van Drecht  Rik Leemans 《Climatic change》2009,97(1-2):123-144

Large amounts of carbon (C) have been released into the atmosphere over the past centuries. Less than half of this C stays in the atmosphere. The remainder is taken up by the oceans and terrestrial ecosystems. Where does the C come from and where and when does this uptake occur? We address these questions by providing new estimates of regional land-use emissions and natural carbon fluxes for the 1700–2000 period, simultaneously considering multiple anthropogenic (e.g. land and energy demand) and biochemical factors in a geographically explicit manner. The observed historical atmospheric CO₂ concentration profile for the 1700 to 2000 period has been reproduced well. The terrestrial natural biosphere has been a major carbon sink, due to changes in climate, atmospheric CO₂, nitrogen and management. Due to land-use change large amounts of carbon have been emitted into the atmosphere. The net effect was an emission of 35 Pg C into the atmosphere for the 1700 to 2000 period. If land use had remained constant at its distribution in 1700, then the terrestrial C uptake would have increased by 142 Pg C. This overall difference of including or excluding land-use changes (i.e. 177 Pg C) comes to more than half of the historical fossil-fuel related emissions of 308 Pg C. Historically, global land-use emissions were predominantly caused by the expansion of cropland and pasture, while wood harvesting (for timber and fuel wood) only played a minor role. These findings are robust even when changing some of the important drivers like the extent of historical land-use changes. Under varying assumptions, land-use emissions over the past three centuries could have increased up to 20%, but remained significantly lower than from other sources. Combining the regional land-use and natural C fluxes, North America and Europe were net C sources before 1900, but turned into sinks during the twentieth century. Nowadays, these fluxes are a magnitude smaller than energy- and industry-related emissions. Tropical regions were C neutral prior to 1950, but then accelerated deforestation turned these regions into major C sources. The energy- and industry-related emissions are currently increasing in many tropical regions, but are still less than the land-use emissions. Based on the presented relevance of the land-use and natural fluxes for the historical C cycle and the significance of fossil-fuel emissions nowadays, there is a need for an integrated approach for energy, nature and land use in evaluating possible climate change mitigation policies.  相似文献   

Experience-Based and Description-Based Perceptions of Long-Term Risk: Why Global Warming does not Scare us (Yet)   总被引：3，自引：2，他引：3  

Elke U. Weber 《Climatic change》2006,77(1-2):103-120

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Investigations in the Szczecin Lagoon during the Oder Flood (July – August 1997) from a biogeochemical perspective     

Christiane Fenske  Helmut Westphal  Alexander Bachor  Elke Breitenbach  Hinrich Meyer  Wladyslaw Buchholz  Wolf-Dieter Jülich 《Ocean Dynamics》1998,50(2-3):231-243

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Flood-triggered versus earthquake-triggered turbidites: A sedimentological study in clastic lake sediments (Eklutna Lake,Alaska)     

Elke Vandekerkhove  Maarten Van Daele  Nore Praet  Veerle Cnudde  Peter J. Haeussler  Marc De Batist 《Sedimentology》2020,67(1):364-389

Lake sediments in Eklutna Lake, Alaska, reveal the presence of turbidites within varved sequences. These turbidites, which result from flood events and earthquakes, show a similar macroscopic appearance. In order to use turbidites to reconstruct flood variability and/or seismic history in the lake basin, it is crucial to determine the trigger of the turbidity currents. This study examined the turbidite caused by the ad 1964 Great Alaska earthquake as well as turbidites linked to historical flood events in order to differentiate between these earthquake-triggered and flood-triggered turbidites. In a suite of samples from throughout the lake, distinctive proxies are identified that can be associated with event-specific flow characteristics. The study presents straightforward discrimination methods related to the sedimentology and geochemical components of the turbidites. These methods are also applicable to other lakes, particularly proglacial lakes where the sediment composition of onshore and offshore sources is similar. Finally, the discrimination of the turbidite trigger can be used to reconstruct the palaeoflood and seismic history.  相似文献   

Wakes of ram-pressure-stripped disc galaxies     

Elke Roediger  Marcus Brüggen  Matthias Hoeft 《Monthly notices of the Royal Astronomical Society》2006,371(2):609-618

We present a sample of 30 wide-angle tailed radio galaxies (WATs) that we use to constrain the jet speeds in these sources. We measure the distribution of the jet-sidedness ratios for the sample, and assuming that the jets are beamed, the jet speeds in the range (0.3–0.7) c are obtained. Whilst the core prominence of the sample, which ought to be a reliable indicator of beaming, shows little correlation with the jet sidedness, we argue that due to the peculiar nature of the WATs, core prominence is unlikely to be a good indicator of beaming in these sources. We further show that if the jets are fast and light, then the galaxy speeds required to bend the jets into C-shapes such as those seen in 0647+693 are reasonable for a galaxy in a merging or recently merged cluster.  相似文献