Detrital Amino Acids and the Growth of Sarotherodon mossambicus — a Reply to DABROWSKI

It depends on the trophic position of a species whether its growth is limited by the quantity or quality of diet: predators are frequently limited by the quantity of diet, primary consumers frequently by the quality of diet. The protein deficiency is of decisive importance for the growth of primary consumers. The digestible protein/digestible energy ratio is most important: 4 mg/kJ are sufficient for maintenance, 20… 30 mg/kJ are necessary for maximum growth. These values can be confirmed by feeding tests with Carassius auratus. According to measurements by different methods, the organic nitrogen is present in the detritus in the form of amino acids as bonded to organis matter. Thus, Sarotherodon mossambicus assimilates 25.6 mg amino acids/kJ from detritus, whereas only 25% of these amino acids can be identified as protein. Due to the utilization of this source of diet, detrivorous fish occupy a special position in the chain of diet, thus gaining a great importance for the aquatic culture.     

Toxicity of Interactions of Zinc —Nickel,Copper —Nickel and Zinc —Nickel —Copper to a Freshwater Teleost,Lebistes reticulatus (PETERS)1

The lethal toxicity of mixtures of Zn²⁺ —Ni²⁺, Cu²⁺ —Ni²⁺ and Zn²⁺ —Cu²⁺ —Ni²⁺ to common guppy at 21£C in hard water (total hardness = 260 mg/l as CaCO₃) was studied under static bioassays test conditions with renewal of the test solutions every 24 h. The heavy metals were tested separately and in mixtures. The 48 h median lethal concentrations (LC₅₀) for individual salts were 75 mg/l Zn²⁺, 37 mg/l for Ni²⁺ and 2.5 mg/l for Cu²⁺. Concentrations were expressed in “toxic units” by taking them as proportions of LC₅₀ values. Experiments showed that in the Zn²⁺-Ni²⁺ mixture, when Ni²⁺ was more in proportion, the toxicity was more than additive. The 48 h LC₅₀ value and 95% confidence limits in the Ni²⁺-Cu²⁺ mixture were 0.684 (0.484 … 0.807) toxic units and the mixture produced more than the additive toxicity (synergism.). The LC₅₀ value and its 95% confidence limits in a Zn²⁺?Cu²⁺?Ni²⁺ mixture also suggested that the mixture was again strictly additive. The results indicate that heavy metallic mixtures would pose a greater toxicological danger to fish than the respective individual metals.     

“REMOTE SENSING”— AN EVALUATION OF ITS IMPACT ON EARTH SCIENCE—*

“Remote sensing” techniques have been used for many years as an exploration tool; broadly speaking, any method using sensors not directly connected to the earth's surface falls into this group. It is preferable, however, to use the term solely with reference to a number of new sensors which have recently become available to earth scientists for the detection of various radiations of the electromagnetic spectrum in the wave length range from 0.1 micron (UV) to some centimeters including the visible and infrared regions. Radiations artificially induced in the earth (active sensing) or spontaneous radiations (passive sensing) can be detected. Some of the bands investigated seem promising for application to geological surveys, especially using sensors on aircraft and satellites, which allow synoptic and large scale investigations. A brief account is given of the results already achieved and of future developments such as the ERTS and manned satellite (post Apollo) “earth observation” programmes. The potential role of Europe in the field is discussed. Details are given of some applications of thermal I.R. imagery to geological and vulcanological problems, with special emphasis on the research carried out in Italy.     

Wasserqualität durch höhere Wasserpflanzen. — Übersicht zur ökotechnologischen Anwendung —

Improving Water Quality by submerged and emergent Macrophytes. — A Review of Ecotechnological Application. Measures of ecotechnology using submerged and emergent macrophytes in native stands or planted littoral stands on the one hand, ingenious swimming plant mats on the other, may be assessed to be successful if applied in combination with additional measures, for instance — reorganization (sanition) of all the area collecting water — biomanipulation of pelagic food chains. Plantation of submerged macrophytes as oxygenators in standing and impounded waters to improve water quality should be avoided. To the contrary, the strategy should be taking measures in order to maximize the light penetrated euphotic zone (z_eu) and simultaneously minimize the mixed zone (z_mix) in order to improve spontaneous settlements of submerged macrophyte stands.     

Riparian alder fens — source or sink for nutrients and dissolved organic carbon? — 2. Major sources and sinks

Natural riparian forest wetlands are known to be effective in their ability to remove nitrate by denitrification and sediments with attached phosphorus via sedimentation. On the other hand, litter input and decomposition is a process of crucial importance in cycling of nitrogen and phosphorus in a forest ecosystem.In this study we investigated the amount of nitrogen and phosphorus entering the alder fen ecosystem through leaf litter and its decomposition and the removal capacity of nitrogen and phosphorus by measuring denitrification and sedimentation in the alder fen.We found an average input of leaf litter during fall 1998 of 226 g m⁻² yr⁻¹ DW with nutrient concentration of 0.17% P and 1.6% N. This means a yearly input of 0.4 g m⁻² yr⁻¹ P and 3.6 g m⁻² yr⁻¹ N. The decomposition of leaf litter using litter bags with small and large mesh size resulted in bags with macroinvertebrates (large mesh size) and without macroinvertebrates (small mesh size). After 57 days the litter bags with macroinvertebrates had a decomposition rate of 79%.Denitrification was measured in May and June of 1997 using the acetylene inhibition technique on intact soil cores and slurry-experiments. The average annual denitrification rate was 0.2 g m⁻² yr⁻¹ N using data from the core experiments. The denitrification rate was higher after addition of nitrate, indicating that denitrification in the riparian alder fen is mainly controlled by nitrate supply.The sedimentation rate in the investigated alder fen ranged from 0.47 kg m⁻² yr⁻¹ DW to 4.46 kg m⁻² yr⁻¹ DW in 1998 depending on the study site and method we used. Sedimentation rates were lower in newly designed plate traps than in cylinder traps. The alder fen also showed lower rates than the adjacent creek Briese. Average phosphorus removal rate was 0.33 g m⁻² yr⁻¹ P.Input sources for the surface water of the alder fen are sediment mineralization and decomposition of leaf litter; output sources are sedimentation and denitrification. This study showed that a nutrient input of 24.58 kg ha⁻¹ yr⁻¹ N, 8.8 kg ha⁻¹ yr⁻¹ P and 419 kg ha⁻¹ yr⁻¹ DOC into the surface water of the alder fen is possible. Alder fens cannot improve water quality of an adjacent river system. This is only true for a nearly pristine alder fen with the hydrology of 10 months flooded conditions and 2 months non-flooding conditions a year.     

Wasser — Sphinx unter den Flüssigkeiten

Water is a rather peculiar substance with respect to a wide variety of static and dynamic properties. It can be considered as a highly organized complex liquid with a complicated structure determined by extended hydrogen bondings. Mixture models and continuum models have been developed to explain the structural features of liquid water, both of them being approximative and hitherto not at all convincing. Aqueous solutions can be discussed in terms of structure breaking and structure making solutes. The most surprising and fascinating properties of water and its outstanding importance require further detailed and unusual investigations.     

Riparian alder fens — Source or sink for nutrients and dissolved organic carbon? — 1. Effects of water level fluctuations

The biogeochemistry of riparian alder wetlands was studied from 1995 to 1997. Nutrient and DOC chemistry was related to water level changes. The spatial and temporal patterns of nutrients (P and N) and dissolved organic carbon (DOC) were measured in the surface water flowing through a riparian alder fen and in the adjacent creek. Nutrient and DOC concentrations were extremely variable temporally but not spatially within the wetland. In the wetland and the adjacent creek concentrations of NO₃-N, PO₄-P and DOC were homogenous during high-flow periods and frozen conditions. After low-flow conditions water bodies were isolated from the creek. The concentration of NH₄-N, PO₄-P and DOC in these isolated water bodies was significantly higher than in the adjacent creeks due to low oxygen levels.

Enclosures of different sizes were installed in the wetland to study possible release rates. A large enclosure experiment in the flooded alder fen showed the same concentrations as after high-flood conditions except for DOC. The DOC concentrations were enriched in the large enclosure after decomposition from leaf litter during fall season. Small enclosures with low oxygen levels confirmed data obtained from low-flow conditions. The release rates were calculated for low-flow conditions from small enclosure experiments for 2 months a year when the alder fen is not flooded. The rates for July and August were 11.6 kg/ha NH₄-N, 8.6 kg/ha PO₄-P and 57.6 kg/ha DOC. The DOC concentrations for fall estimated from the large enclosure-experiments were 168.2 kg/ha for the months September and October.

This means possible output rates of N, P and DOC during the summer and DOC during fall in the adjacent river system. This can cause eutrophication and organic pollution depending on the length of the low-flow conditions and the size of the alder fen. Water level changes must be regarded as important for the management of riparian wetlands such as alder fens. The riparian alder system may vary from a nutrient sink to a nutrient source at different times of a year depending on high or low water levels.     

Gas Chromatography for Determination of Pesticides in Aquatic Systems — Analytical Basis Gaschromatographie zur Bestimmung von Pestiziden in aquatischen Systemen — Analytische Grundlagen

High resolution gas chromatography (HRGC) with ECD, NFID and MSD is a very efficient determination method for pesticides in water. Because of their relatively low concentrations in aquatic systems enrichment and preconcentration procedures are essential. Some examples for pesticide determination by GC methods are given. Potentials and limitations of HRGC for pesticide analysis are also discussed. An extensive pesticide analysis in water has to include different methods like HRGC, HPLC and GC/MS.     

HOMOMORPHIC FILTERING — THEORY AND PRACTICE*

The application of homomorphic filtering in marine seismic reflection work is investigated with the aims to achieve the estimation of the basic wavelet, the wavelet deconvolution and the elimination of multiples. Each of these deconvolution problems can be subdivided into two parts: The first problem is the detection of those parts in the cepstrum which ought to be suppressed in processing. The second part includes the actual filtering process and the problem of minimizing the random noise which generally is enhanced during the homomorphic procedure. The application of homomorphic filters to synthetic seismograms and air-gun measurements shows the possibilities for the practical application of the method as well as the critical parameters which determine the quality of the results. These parameters are:

• a) the signal-to-noise ratio (SNR) of the input data
• b) the window width and the cepstrum components for the separation of the individual parts
• c) the time invariance of the signal in the trace.

In the presence of random noise the power cepstrum is most efficient for the detection of wavelet arrival times. For wavelet estimation, overlapping signals can be detected with the power cepstrum up to a SNR of three. In comparison with this, the detection of long period multiples is much more complicated. While the exact determination of the water reverberation arrival times can be realized with the power cepstrum up to a multiples-to-primaries ratio of three to five, the detection of the internal multiples is generally not possible, since for these multiples this threshold value of detectibility and arrival time determination is generally not realized. For wavelet estimation, comb filtering of the complex cepstrum is most valuable. The wavelet estimation gives no problems up to a SNR of ten. Even in the presence of larger noise a reasonable estimation can be obtained up to a SNR of five by filtering the phase spectrum during the computation of the complex cepstrum. In contrast to this, the successful application of the method for the multiple reduction is confined to a SNR of ten, since the filtering of the phase spectrum for noise reduction cannot be applied. Even if the threshold results are empirical, they show the limits fór the successful application of the method.     

Common-reflection-surface stack — a real data example

The simulation of a zero-offset (ZO) stack section from multi-coverage reflection data is a standard imaging method in seismic processing. It significantly reduces the amount of data and increases the signal-to-noise ratio due to constructive interference of correlated events. Conventional imaging methods, e.g., normal moveout (NMO)/dip moveout (DMO)/stack or pre-stack migration, require a sufficiently accurate macro-velocity model to yield appropriate results, whereas the recently introduced common-reflection-surface stack does not depend on a macro-velocity model. For two-dimensional seismic acquisition, its stacking operator depends on three wavefield attributes and approximates the kinematic multi-coverage reflection response of curved interfaces in laterally inhomogeneous media. The common-reflection-surface stack moveout formula defines a stacking surface for each particular sample in the ZO section to be simulated. The stacking surfaces that fit best to actual events in the multi-coverage data set are determined by means of coherency analysis. In this way, we obtain a coherency section and a section of each of the three wavefield attributes defining the stacking operator. These wavefield attributes characterize the curved interfaces and, thus, can be used for a subsequent inversion. In this paper, we focus on an application to a real land data set acquired over a salt dome. We propose three separate one-parametric search and coherency analyses to determine initial common-reflection-surface stack parameters. Optionally, a subsequent optimization algorithm can be performed to refine these initial parameters. The simulated ZO section obtained by the common-reflection-surface stack is compared to the result of a conventional NMO/DMO/stack processing sequence. We observe an increased signal-to-noise ratio and an improved continuity along the events for our proposed method — without loss of lateral resolution.     

Homeomorphic imaging approach — theory and practice

The homeomorphic imaging (HI) approach is a generalization of the common mid-point (CMP) stack to media of arbitrary structures with the following key properties: it collects and enhances useful waves; no knowledge about the velocity structure of the overburden is required for correlation and stacking; and neither the resolution of nor the information about the target objects is degraded by stacking the data. The so-called common reflecting element (CRE) method, which has all three properties, was proposed by Gelchinsky [Gelchinsky, B., 1988. Common reflecting element (CRE) method. Explor. Geophys. 19, 71–75]. However, the CRE method did not only provide a generalization of the CMP method with the key properties; it also has a topological feature that led to the creation of the HI approach. Today, HI can be regarded as a system of methods and schemes for the study of seismic structures that are based on asymptotic wave theory and on fundamental topological ideas. HI is based on a single supposition: it assumes that a target wave exists on the chosen central trace. The next step makes use of the ensemble of all possible wave fronts that can be formed in the vicinity of the central ray corresponding to the chosen central trace. This approach is applicable to a medium of arbitrary structure without the assumption of a seismic model or its parameters.