Trübeströme in Seen: Sauerstoffeintrag durch grundnah eingeschichtetes Flusswasser

Near-bottom current measurements in the main delta areas of the Walensee (Switzerland) and of Lake Constance yielded evidence that sporadic high influxes of clastic suspensions caused by flood stage discharges of tributaries generate turbidity underflows. Turbid suspensions plunge down the delta front as hyperpycnal inflows with speeds up to 130cm/s. These periodic intrusions of well oxygenated river water may influence the oxygen budget of the basal hypolimnion, thus possibly antagonizing eutrophication in marginal cases, supported by the adsorption of phosphate by suspended clay particles.      

Gravity study of the Djibouti area

In March and April 1972, 380 gravity stations were established in the T.F.A.I. The data were reduced to Bouguer anomalies of 5 mGal isolines. Qualitative and quantitative interpretation based on the gravity map, on seismic data and on the magnetics and physiography of the area revealed that: The crust of the Gulf of Tadjura and the central part of the T.F.A.I. is strongly oceanized and is the direct continuation of the Sheba Ridge.To the north of the Gulf, at the Dankali Mountains, the crust increases in thickness and most probably contains sialic fragments, indicating the continuation of the Danakil Chains in the T.F.A.I.To the south, the structure is bordered by a continental block, the Aysha Horst. The oceanization is concentrated only in the area of deep injections, marked by gravity maxima, whereas the rest of the area is to be described as sub-continental. The crust is attenuated from south (Aysha Horst) to north (Red Sea), from 30 to 15 km in thickness.The pattern of the gravity anomalies shows clearly liniations only along the coasts of the Gulf of Tadjura and the Straits of Bab el Mandeb. Inland the field breaks up into relative minima and maxima, indicating the fragmentation of the crust and the ‘triple junction’ nature of the area.The tectonic process is that of extension, with normal faults having maximum displacements at the northern border of the Gulf of Tadjura.The uppermost mantle has low velocity and density values due to thermal processes in the expanding zone. The state of the upper-mantle material must be that of partial melting due to high temperatures of the order of 800° to 1,000° C at about 15 km depth.     

Determinations of particle size distributions in natural waters use of Zeiss Micro-Videomat image analyzer

Use of a Zeiss Micro-Videomat electronic image analyzer for routine measurements of size distributions of particles found in natural waters greater than 0.3 μm has been investigated. Staining of particles with a solution of Gentiana-violet eliminated the multiple-count problem which has frustrated earlier attempts to use image analyzers for quantitative phytoplankton work. Concentration of samples from the lake water column was successfully achieved with an impact centrifuge. Losses of inorganic particles indicate that the centrifuge method must be evaluated on an individual case basis. Precision and accuracy of the Zeiss Micro-Videomat using either sedimentation (Utermöhl) or centrifugation for sample concentration were satisfactory for particles larger than 1 μm. The system appears promising for routine surveillance of raw water quality at water treatment plants, and performance of unit processes used for particulate removal, as well as for specific investigations of ecological phenomena in natural waters.     

Experimentelle Untersuchungen über die ökologische Wirkung der Strömungsgeschwindigkeit auf die Lebensgemeinschaften des fliessenden Wassers

Ohne Zusammenfassung     

Das dynamische Verhalten interstellarer Staubteilchen beim Wolkenstoß Teil I. Ohne Berücksichtigung von Masseänderungen

During the collision of interstellar clouds a partial separation between gas and dust occurs. It can be expected that also a separation between heavier and lighter dust particles takes place. To determine the ratio of this dynamical effect the way of dust particles with different values of the product a · ϱ_p (a radius; ϱ_p density of the particles) during the three successive cooling periods is numerically calculated. It is shown that the heavier particles (a · ϱ_p ⪊ 5 · 10⁻⁵ g/cm²) at the end of the collision and the expansion period are gathered in a thin sheet in the inner parts of the new-built cloud whereas the lighter ones (a · ϱ_p 1 · 10⁻⁵ g/cm²) are distributed more or less uniformly among the gas of the cloud. The growth or destruction of the dust particles are not taken into account in this paper.     

Evaluating effects of spectral training data distribution on continuous field mapping performance

Continuous field mapping has to address two conflicting remote sensing requirements when collecting training data. On one hand, continuous field mapping trains fractional land cover and thus favours mixed training pixels. On the other hand, the spectral signature has to be preferably distinct and thus favours pure training pixels. The aim of this study was to evaluate the sensitivity of training data distribution along fractional and spectral gradients on the resulting mapping performance.We derived four continuous fields (tree, shrubherb, bare, water) from aerial photographs as response variables and processed corresponding spectral signatures from multitemporal Landsat 5 TM data as explanatory variables. Subsequent controlled experiments along fractional cover gradients were then based on generalised linear models.Resulting fractional and spectral distribution differed between single continuous fields, but could be satisfactorily trained and mapped. Pixels with fractional or without respective cover were much more critical than pure full cover pixels. Error distribution of continuous field models was non-uniform with respect to horizontal and vertical spatial distribution of target fields. We conclude that a sampling for continuous field training data should be based on extent and densities in the fractional and spectral, rather than the real spatial space. Consequently, adequate training plots are most probably not systematically distributed in the real spatial space, but cover the gradient and covariate structure of the fractional and spectral space well.     

The hafnium isotope composition of Pacific Ocean water

The first Hf isotope data for seawater are reported for a series of stations in the Northwestern Pacific and define a range from ε_Hf = 3.5 ± 1.4 to 8.6 ± 1.6. Most samples have values within error of the average of ε_Hf = 5.9, but significant variations are found in intermediate waters at a depth of 600 m, as well as in deep waters. The Nd and Hf isotope compositions of the deep waters fall within the range of values found for surfaces of hydrogenetic ferromanganese crusts in the region, confirming that Hf in the Fe-Mn crusts has been derived from the overlying water column, which thus provide an archive of past seawater compositions. Although the seawater samples are generally close to the global ε_Nd-ε_Hf correlation obtained from ferromanganese crusts, there are significant deviations from this correlation indicating that there is some additional decoupling between Nd and Hf isotope signals, most likely caused by local water mass mixing and differences in residence times. This is not resolved in the crust samples, which integrate seawater signals over 10⁴ years. The combined use of these two isotope systems in seawater therefore provides an additional dimension for tracing water masses in the oceans. Studies of the distribution of oceanic Hf isotope compositions that have been confined to deep water and boundary waters, as recorded in seafloor ferromanganese crusts, can now be extended and aimed at characterising the entire present-day water column. Average Hf concentrations measured in this study are somewhat lower than previously reported, suggesting a shorter residence time for Hf in the global oceans, although the uncertainty in the extent of Hf removal from the water column during estuarine mixing as well as a lack of data on hydrothermal and dust inputs remains a limit on how well the residence time can be defined.     

Regeneration in Gap Models: Priority Issues for Studying Forest Responses to Climate Change

Recruitment algorithms in forest gap models are examined withparticular regard to their suitability for simulating forestecosystem responses to a changing climate. The traditional formulation of recruitment is found limiting in three areas. First, the aggregation of different regeneration stages (seedproduction, dispersal, storage, germination and seedling establishment) is likely to result in less accurate predictionsof responses as compared to treating each stage separately. Second, the related assumptions that seeds of all species are uniformly available and that environmental conditions arehomogeneous, are likely to cause overestimates of future speciesdiversity and forest migration rates. Third, interactions between herbivores (ungulates and insect pests) and forest vegetation are a big unknown with potentially serious impactsin many regions. Possible strategies for developing better gapmodel representations for the climate-sensitive aspects of eachof these key areas are discussed. A working example of a relatively new model that addresses some of these limitations is also presented for each case. We conclude that better modelsof regeneration processes are desirable for predicting effectsof climate change, but that it is presently impossible to determine what improvements can be expected without carrying outrigorous tests for each new formulation.     

A hydrochemical approach to quantify the role of return flow in a surface flow‐dominated catchment

Stormflow generation in headwater catchments dominated by subsurface flow has been studied extensively, yet catchments dominated by surface flow have received less attention. We addressed this by testing whether stormflow chemistry is controlled by either (a) the event‐water signature of overland flow, or (b) the pre‐event water signature of return flow. We used a high‐resolution hydrochemical data set of stormflow and end‐members of multiple storms in an end‐member mixing analysis to determine the number of end‐members needed to explain stormflow, characterize and identify potential end‐members, calculate their contributions to stormflow, and develop a conceptual model of stormflow. The arrangement and relative positioning of end‐members in stormflow mixing space suggest that saturation excess overland flow (26–48%) and return flow from two different subsurface storage pools (17–53%) are both similarly important for stormflow. These results suggest that pipes and fractures are important flow paths to rapidly release stored water and highlight the value of within‐event resolution hydrochemical data to assess the full range and dynamics of flow paths.