Hydrometric and hydrochemicai evidence for fast flowpaths at La Cuenca, Western Amazonia     

Helmut Elsenbeer  Andreas Lack 《Journal of Hydrology》1996,180(1-4):237-250

A hydrological reconnaissance study in a first-order tropical rainforest catchment in western Amazonia implicated overland flow as an important hydrological pathway. A complementary hydrometric and hydrochemical approach that involved the recording of overland flow hydrographs and the determination of streamflow, overland flow, groundwater, soil water, and throughfall chemical signatures, was essential to establish unambiguously the importance of this pathway. Largely uncontrolled by topography, overland flow does occur in any season, regardless of antecedent moisture conditions, which only influence the volumes generated. The latter effect is also reflected in a close approximation of stormflow and overland flow chemical signatures, as expressed in the K/SiO ratio. We conclude that, despite its greater logistical demands, a complementary hydrometric/hydrochemical approach is essential to understand a catchment's hydrological behaviour, especially where fast pathways are at work; such pathways are apparently common in more forest ecosystems than has been previously assumed.  相似文献   

A NOTE ON THE APPLICATION OF LINEAR WAVE THEORY AT A CRITICAL LEVEL     

Andreas Dörnbrack  Carmen J. Nappo 《Boundary-Layer Meteorology》1997,82(3):399-416

The purpose of this note is to estimate the accuracy and practical limitations of applying linear theory at a critical level over a realistic range of atmospheric stabilities for an idealized surface terrain. These estimates are made by comparing the results of a linear model with a nonlinear numerical model at a critical level. Essentially similar results are obtained from each model for wave stress, wave breaking height and wave dissipation through the critical level. Because gravity waves can be either evanescent or internal depending on the relative sizes of the Scorer parameter and the wavenumber of the ground surface disturbance, the somewhat paradoxical result develops that wave breaking and non-linearity increase with increasing bulk Richardson number. It is recommended that steady linear wave theory be used in gravity wave drag parameterizations provided near real time profiles of background velocity and temperature are available.  相似文献   

Characterization of and correction for cultural noise   总被引：2，自引：0，他引：2  

Andreas Junge 《Surveys in Geophysics》1996,17(4):361-391

Surveys of time varying electromagnetic fields result in time series consisting of signals and noise, the latter defined as that part of the data which cannot be explained by a theory. Man-made contributions to noise can be subdivided into active and passive sources and are complex in character. As Szarka has treated this topic extensively in a recent review paper (Szarka, 1988), only a few further examples are presented here. Following discussion of noise correction in transient electromagnetic investigations which consists mainly of sophisticated stacking and filter procedures, several aspects of its correction in magnetotelluric and geomagnetic depth sounding data are considered. These include:

1. The methods of treatment of single time series in the presence of visible noise—its detection, removal and sometimes replacement by data predicted from undisturbed intervals.
2. The investigation of time series interrelations. This is mainly coherence based and—if possible—takes advantage of remote reference techniques.
3. The examination of the statistical properties of the time series by regression analysis. This leads to the weighting of time segments of data in order to achieve unbiased and minimum variance estimates based on identically and independently Gaussian distributed residuals.
4. The application of constraints. These can further improve the estimates' quality.
5. The use of simultaneously recorded multistation data. This can contribute remarkably to noise suppression as well as to the treatment of non-uniform source fields.
6. Leveraging and confidence limits. Problems relating to the former have not yet been solved satisfactorily while the Jacknife method seems to be an easy way of determining the latter.

Thanks to the modern processing techniques reviewed in this paper it should be possible to obtain a rather dense net of high quality data in spite of the world-wide increasing noise level. As most processing codes are widely accessible current problems are more related to availability of instruments, carrying out the measurements and reserving enough time for thorough data processing.  相似文献   

Toxic effects of decomposing red algae on littoral organisms   总被引：2，自引：0，他引：2  

Britta Eklund  Andreas P. Svensson  Conny Jonsson  Torleif Malm   《Estuarine, Coastal and Shelf Science》2005,62(4):621-626

Large masses of filamentous red algae of the genera Polysiphonia, Rhodomela, and Ceramium are regularly washed up on beaches of the central Baltic Sea. As the algal masses start to decay, red coloured effluents leak into the water, and this tinge may be traced several hundred meters off shore. In this study, possible toxic effects of these effluents were tested on littoral organisms from different trophic levels. Effects on fertilisation, germination and juvenile survival of the brown seaweed Fucus vesiculosus were investigated, and mortality tests were performed on the crustaceans Artemia salina and Idotea baltica, as well as on larvae and adults of the fish Pomatoschistus microps. Fucus vesiculosus was the most sensitive species of the tested organisms to the red algal extract. The survival of F. vesiculosus recruits was reduced with 50% (LC50) when exposed to a concentration corresponding to 1.7 g l⁻¹ dw red algae. The lethal concentration for I. baltica, A. salina and P. microps were approximately ten times higher. The toxicity to A. salina was reduced if the algal extract was left to decompose during two weeks but the decline in toxicity was not affected by different light or temperature conditions. This study indicates that the filamentous red algae in the central Baltic Sea may produce and release compounds with negative effects on the littoral ecosystem. The effects may be particularly serious for the key species F. vesiculosus, which reproduce in autumn when filamentous red algal blooms are most severe.  相似文献   

Three aspects of the law of the sea : Islands, delimitation and dispute settlement     

Andreas J. Jacovides 《Marine Policy》1979,3(4):278-288

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A simple boom assembly for the shipboard deployment of air-sea interaction instruments     

Edgar L. Andreas  John H. Rand  Stephen F. Ackley 《Ocean Engineering》1984,11(3):227-237

We have developed a simple boom for use in measuring meteorological variables from a ship. The main structural member of the boom, a triangular communications tower with rollers attached along its bottom side, is deployed horizontally from a long, flat deck, such as a helicopter deck, and will support a 100-kg payload at its outboard end. The boom is easy to deploy, requires minimal ship modifications, and provides ready access to the instruments mounted on it. And because it is designed for use with the ship crosswind, oceanographic work can go on at the same time as the air-sea interaction measurements.We describe our use of the boom on the Mikhail Somov during a cruise into the Antarctic sea ice and present some representative measurements made with instruments mounted on it. Theory, experiment, and our data all imply that instruments deployed windward from a rear helicopter deck can reach air undisturbed by the ship. Such an instrument site has clear advantages over the more customary mast, bow, or buoy locations.  相似文献   

Predicting significant wave height off the northeast coast of the United States   总被引：1，自引：0，他引：1  

Edgar L Andreas  Sinny Wang 《Ocean Engineering》2007,34(8-9):1328-1335

To develop a simple method to predict the significant wave height, we analyze 18 years of hourly observations from 12 different buoys that are off the northeast coast of the United States. Water depths ranged from 19 to 4427 m for these moored buoys. We find that, on average, all of these buoys exhibit a region of constant wave height for 10-m wind speeds between 0 and 4 m s⁻¹. That wave height does, however, depend on water depth. For wind speeds above 4 m s^–1, the wave height increases as the square of the wind speed; but the multiplicative factor is again a function of water depth. We synthesize these results in a prediction scheme that yields the significant wave height from simple functions of water depth and 10-m wind speed for wind speeds up to 25 m s^–1.  相似文献   

Sedimentary environment dynamics and the formation of coal in the Pennsylvanian Variscan foreland in the Ruhr Basin (Germany, Western Europe)     

M. Peter Suess  Guenter Drozdzewski  Andreas Schaefer   《International Journal of Coal Geology》2007,69(4):267-287

During the Pennsylvanian, formation of coal was a phenomenon that was spread over many continents. It is the aim of this paper to illustrate factors that led to the formation of coal seams in paralic clastic sedimentary environments in the Ruhr Basin (German Variscan foreland) during the Pennsylvanian in terms of sequence stratigraphy and the structural evolution of the basin. Lithostratigraphic sections from exploration wells in the currently explored zone of the coal basin allowed the generation of volumetric lithofacies models, using geostastical methods. These models support the analysis of sedimentary facies and a sequence stratigraphic interpretation of the successions that are widely correlated throughout the basin. We then evaluate the relation of the sequence stratigraphic elements derived from the facies models with the abundance of coal seams.  相似文献   

Geo- and cosmochemistry of the twin elements yttrium and holmium     

Andreas Pack  Sara S. Russell  Mark van Zuilen 《Geochimica et cosmochimica acta》2007,71(18):4592-4608

We have analyzed the Y/Ho-ratios in bulk chondrites, chondrules and four Ca- and Al-rich inclusions (CAIs) from carbonaceous and unequilibrated ordinary and enstatite chondrites (EC) by laser ablation inductively coupled mass spectrometry (LA-ICPMS). We demonstrate that bulk rock sample preparation by containerless melting is a suitable method for preparation of bulk rock samples for high-precision LA-ICPMS. Bulk chondrites have variable Y/Ho-ratios. Carbonaceous chondrites (CI1, CM2, CV3, and CK4) have a common Y/Ho-ratio (25.94 ± 0.08, 2σ) that is regarded as the solar system Y/Ho-ratio. The Y/Ho-ratio increases from carbonaceous, through ordinary (LL, L, H) to enstatite chondrites (EL6), which show the highest Y/Ho-ratio of 27.25. We discuss the result with respect to the origin of fractionation of Re and Os between chondrite groups. Within analytical error, Y and Ho show a good correlation in OC and CV3 chondrules and define an Y/Ho-ratio of 26.22 ± 0.40 (2σ). Y/Ho-fractionation in Ca- and Al-rich inclusions is related to differences in volatility. The bulk silicate Earth is suggested to have a solar Y/Ho-ratio and links the Earth with carbonaceous chondrites. Y/Ho variations in primitive and differentiated terrestrial igneous rocks are discussed in framework of incompatibility of Y and Ho during partial melting. Applicability of Y/Ho as tracer for or against a sedimentary origin of the putative host rock of the Earth’s oldest traces of life from the island of Akilia is briefly discussed.  相似文献   

Predicting particulate pools of nitrogen,phosphorus and organic carbon in lakes     

Andreas C. Bryhn  Dag O. Hessen  Thorsten Blenckner 《Aquatic Sciences - Research Across Boundaries》2007,69(4):484-494

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