Fractional calculus applied to the analysis of spectral electrical conductivity of clay-water system

The analysis of the low-frequency conductivity spectra of the clay-water mixtures is presented. The frequency dependence of the conductivity is shown to follow the power-law with the exponent n=0.67 before reaching the frequency-independent part. When scaled with the value of the frequency-independent part of the spectrum the conductivity spectra for samples at different water content values are shown to fit to a single master curve. It is argued that the observed conductivity dispersion is a consequence of the anomalously diffusing ions in the clay-water system. The fractional Langevin equation is then used to describe the stochastic dynamics of the single ion. The results indicate that the experimentally observed dielectric properties originate in anomalous ion transport in clay-water system characterized with time-dependent diffusion coefficient.     

Computer simulations of terrestrial carbon and atmospheric interactions

Terrestrial carbon modelling shows that the Goudriaan and Ketner and Esser simulations fit historical data well, but the results are sensitive to the decomposition rate coefficient of old sediment carbon. Modification of this rate constant over time, weighted by emission increases or linear increases, changes the model results to fit historic ice core data. Very old sediment carbon decomposition has an effect on the model postdictions only when the rate constant is 10 times greater than that predicted from sediment studies. Future estimates show that a maximum change from agriculture to forest has a small effect on abating emission increases. Controlling emission rates at 5.1 x 10(15) g C/a will result in almost a 50% increase in atmospheric CO(2) in 200 years, and reducing emission rates to 1960 levels (approximately 2.5 x 10(15) g C/a) immediately will still result in an increase in atmospheric CO(2).     

Electrosensory basis for individual recognition in a weakly electric, mormyrid fish, Pollimyrus adspersus (Günther, 1866)

Pollimyrus adspersus discriminates the individually variable waveforms of Electric Organ Discharges (EODs) of conspecifics of only 150–250 s duration. We examined: (1) the discrimination threshold for artificially generated EODs of similar waveform, (2) the mechanism of signal analysis (spectral vs temporal) present, by determining the discrimination between different waveforms of identical amplitude spectra, and (3) the threshold field intensity and reach of discrimination. The triphasic P. adspersus EOD waveform was artificially generated by superimposing two Gaussians, one wide, the second narrow, inverted, and of threefold amplitude. The natural variability among individual EOD waveforms was simulated by phase-shifting one Gaussian relative to the other. The symmetrical waveform where the peaks of the two Gaussians coincided was used as a reference (phase shift=0, rewarded stimulus S+). Results were: (1) in food-rewarded conditioning experiments, trained fish (N=7) detected a phase-shift in artificial EOD stimuli as low as 2 s (N=2 fish), 6 s (N=1) and 10 s (N=1). (2) All fish tested (N=3) discriminated between artificial EODs of identical amplitude spectra but different waveforms (hence, different phase spectra), demonstrating a temporal mechanism of signal analysis. (3) The maximum reach of waveform discrimination was 130 cm at 4.9 V_p-p/cm and 100 S/cm water conductivity (test signal generated at natural amplitude), that is, similar to the reach of EOD detection. Therefore, among the three kinds of electroreceptor organ present in mormyrids, we consider Knollenorgane the relevant sensory organs for EOD waveform discrimination.Communicated by J. Krause     

Electrosensory prey detection in the African sharptooth catfish, Clarias gariepinus (Clariidae), of a weakly electric mormyrid fish, the bulldog (Marcusenius macrolepidotus)

During their seasonal runs in the Okavango and other freshwater bodies in southern Africa, the sharptooth catfish, Clarias gariepinus, specialises on the bulldog, Marcusenius macrolepidotus, as its main prey. We examined whether the catfish can locate bulldogs by detecting their pulse-type electric organ discharges (EODs). The electrosensory threshold for single-cycle, monopolar square-wave pulses was exceedingly low (down to 13 μV_p–p/cm for 4-ms pulses) in trained, food-rewarded sharptooth catfish (n=4), confirming the results of Lissmann and Machin who were, however, unable to identify a biological function. Other stimulus pulse waveforms (single-cycle, monopolar as well as bipolar sine-wave pulses) were also effective stimuli according to their spectral low-frequency energy contents (0– 30 Hz). Male bulldogs display an EOD pulse approximately 10× the duration of female EODs (≈0.5 ms). The C. gariepinus threshold for field-recorded playbacks of a male bulldog EOD (of long duration) was 103 μV_p–p/cm, whereas the brief female and juvenile EODs were not detected (using intensities of natural EODs). EODs of other mormyrids were detected when either monopolar or of long duration. Signal source amplitude increased linearly with standard length (SL) in bulldogs. Signal reach, as calculated from signal source amplitude and receiver sensitivity, is up to 150 cm for a large male bulldog (SL 27.5 cm), and 83 cm for a male that has just turned sexually mature (SL 12.6 cm). Therefore, most bulldogs eaten by catfish are probably male, in agreement with the size distribution of bulldogs found in catfish stomachs. These results suggest that sharptooth catfish rely heavily on their acute electrical sense during hunting, and an important function for electroreception in an African catfish has been identified. Received: 13 December 1999 / Revised: 20 April 2000 / Accepted: 20 May 2000     

Arsenaufnahme von Wildpflanzen auf einem kampfstoffkontaminierten Rüstungsaltlastenstandort

The risk assessment of former ammunition factories, where chemical weapons consisting of diphenylarsenic compounds have been produced or stored is difficult because of the lack of data concerning bioavailability and metabolism of the residues of these sternutators. In order to estimate the contamination of fodder plants by typical pollutants of the former Heeresmunitionsanstalt Löcknitz, the total concentration of arsenic was determined in 186 samples of wild plants. The total arsenic concentration in plants of high feed value did not exceed 1 ppm, whereas 15% of the samples of plants of middle and little value in regard to animal fodder showed arsenic concentrations above 1ppm. The uptake of arsenic by wild plants, however, appears to be comparably low taken the high-grade contamination of the soil into account. A final toxicological evaluation of the risk potential is not yet possible because it requires the characterization of the anorganic and organic arsenic compounds in these plants.     

Management of Large Wood in Streams: An Overview and Proposed Framework for Hazard Evaluation

Instream and floodplain wood can provide many benefits to river ecosystems, but can also create hazards for inhabitants, infrastructure, property, and recreational users in the river corridor. We propose a decision process for managing large wood, and particularly for assessing the relative benefits and hazards associated with individual wood pieces and with accumulations of wood. This process can be applied at varying levels of effort, from a relatively cursory visual assessment to more detailed numerical modeling. Decisions to retain, remove, or modify wood in a channel or on a floodplain are highly dependent on the specific context: the same piece of wood that might require removal in a highly urbanized setting may provide sufficient benefits to justify retention in a natural area or lower‐risk urban setting. The proposed decision process outlined here can be used by individuals with diverse technical backgrounds and in a range of urban to natural river reaches so that opportunities for wood retention or enhancement are increased.     

Integrating Large Wood Jams into Hydraulic Models: Evaluating a Porous Plate Modeling Method

Large wood (LW) jams are key riverine habitat features that affect hydraulic processes and aquatic habitat. The hydraulic influence of LW jams is poorly understood due to the complexity of fluid dynamics around irregular, porous structures. Here we validated a method for two‐dimensional hydraulic modeling of porous LW jams using the open‐source modeling software Delft3D‐FLOW. We sampled 19 LW jams at three reaches across the Columbia River Basin in the United States. We used computer‐generated porous plates to represent LW jams in the modeling software and calibrated our modeling method by comparing model outputs to measured depths and velocities at validation points. We found that modeling outputs are error‐prone when LW jams are not represented. By representing LW jams as porous plates we reduced average velocity root mean square error (RMSE) values (i.e., improved model accuracy) by 42.8% and reduced average depth RMSE values by 5.2%. These differences impacted habitat suitability index modeling. We found a 15.1% increase in weighted useable area for juvenile steelhead at one test site when LW jams were simulated vs. when they were ignored. We investigated patterns in average RMSE improvements with varying jam size, bankfull obstruction, porosity, and structure type, and river complexity. We also identified research gaps related to field estimation of LW jam porosity and porous structure modeling methods.     

Recent introduction of an Asian estuarine copepod,Pseudodiaptomus marinus (Copepoda: Calanoida), into southern California embayments

Past studies made between 1938 and the mid-1970's of coastal embayments between northern Baja California and Oregon (USA) established the presence of only one species of the calanoid copepod genus Pseudodiaptomus, P. euryhalinus. This species is endemic to warm temperate latitudes of western North America. We now report the presence of breeding populations of the Asian calanoid copepod P. marinus in two Southern California embayments, Mission Bay and Agua Hedionda Lagoon. The Mission Bay population was monitored monthly from December 1986 to June 1987 and showed evidence of continuous breeding and growth. The regional, endemic species, P. euryhalinus, was not observed in either embayment. Mechanisms that might account for the apparent recent introductions of P. marinus into Southern California include dispersion by ocean circulations and transport by transoceanic ships. In the present case, the explanation is that the introduction is most likely a direct consequence of aquaculture projects. Remaining to be confirmed by systematic sampling is the apparent disappearance of P. euryhalinus from embayments dominated by P. marinus.     

Evaluation of the state-of-the-art of butyl- and phenyltin compound determinations in freshwater sediment prior to certification of a reference material

In order to control the quality of butyl- and phenyltin compound determinations in sediment, the Standards, Measurements and Testing Programme (formerly BCR) of the European Commission has started a project, the final aim of which is to certify a freshwater sediment for its contents of a range of organotin compounds (mono-, di- and tributyltin, and mono-, di- and triphenyltin). The first part of this project involved an interlaboratory study which aimed to test the feasibility of preparation of candidate freshwater sediment reference material and to detect and remove most of the pitfalls observed in organotin determinations. This paper presents the main results of this interlaboratory study carried out prior to the certification campaign. The agreement obtained among laboratories for the six compounds determined was considered to reflect the state-of-the-art and was encouraging enough to decide upon the organisation of a certification campaign, which will be concluded in June 1999.