A spectroelectrochemical study of factor F<SUB>430</SUB> nickel(II/I) from methanogenic bacteria in aqueous solution
The nickel(II) ion in factor F<sub>430</sub> pentacarboxylic acid, both in the native form and in the 12,13-di-epimer, in solution can be reversibily in a one-electron to the monovalent state by the action of titanium-(III) citrate. The 3d<sup>9</sup> Ni(I) is quantitatively detected by EPR spectroscopy as a tetragonally distorted octahedral system with the in the d(<I>x</I><sup>2</sup>-<I>y</I><sup>2</sup>) orbital resulting in an <I>S</I> = <sup>1</sup>/<sub>2</sub> spin with <I>g</I><sub>∥</sub> = 2.244, <I>g</I><sub>⊥</sub> = 2.061, (<I>g</I><sub>∥</sub> = 2.238, <I>g</I><sub>⊥</sub> = 2.057 for the di-epimer), subject to isotropic superhyperfine interaction from the four in-plane nitrogen ligand with <I>A</I> = 1.0 mT. The UV-visible spectrum of the reduced native F<sub>430</sub> has peaks (extinction coefficients in mM<sup>-1</sup> cm<sup>-1</sup>) at 268 (24.0), 378 (34.7), and 715 nm (2.3), In the reduced di-epimer these values are 265 (23.7), 376 (27.6), and 710 nm (1.6). Complete reduction is achieved only at alkaline pH; the process an apparent p<I>K</I> of 8.9 (native) or 9.4 (di-epimer). The Ni(II)/Ni(I) in <I>F</I><sub>430</sub> has a reduction <I>E</I><sub>m,10.4</sub> = -0.65 (native) or -0.62 V(diepimer). Three-pulse stimulated ESEEM spectroscopy on the reduced complexes reveals a single, near isotropic proton at ≈13 MHz. In <sup>2</sup>H<sub>2</sub>O solution this line is replaced by a quadrupole-split deuterium resonance around ≈2 MHz, indicating that the Ni(I) in and 12,13-di-epimeric F<sub>430</sub> is weakly coordinated by water. The absence of a strong axial bond with water would leave the ability of the d(<I>z</I><sup>2</sup>) pair for nucleophilic attack on substrate carbon largely intact.
Upflow anaerobic filtration of a sugar containing wastewater
Pretreatment of a sugar containing wastewater from a date processing plant was tested for COD removal in an anaerobic pilot filter over a period of eight months. The filter was operated in the upflow mode and randomly packed with a plastic pipe carrier material. Initial start and restart after a 6-week break, steady state performance on seven different COD load levels ranging from 1.6 to 25 kg COD/m<sup>3</sup><B>·</B>d, and filter behavior during reactor acidification were observed. In all examined experimental cases, the anaerobic filter rapidly adapted (5-7 days) to new operating conditions, thus indicating its high process flexibility. Below COD loads of 20 kg COD/m<sup>3</sup><B>·</B>d, a COD removal of 90% or more was achieved. The specific CH<sub>4</sub> gas production was measured at 0.40-0.53 m<sup>3</sup> CH<sub>4</sub>/kg COD removed, and the specific sludge production was quantified at 0.1 kg particulate COD/kg COD removed throughout the experimental periods. Biomass distribution revealed that 60% was attached to the packing media and 40% was suspended in the pore space. Based on COD profiles along the filter height, conclusions on the reactor flow pattern could be drawn. With the help of a simple reactor model, the experimental results could be used to simulate other process conditions for design considerations.
Comparison of the results of tracer experiments in lakes with predictions based on horizontal mixing models
Experiments in Lake Lucerne indicate growth of tracer patches to be approximately proportional to elapsed time raised to the power 1.3. Published data from Lake Ontario can be interpreted to be in agreement with this result. This suggests that an inertial subrange model of horizontal diffusion, such as that commonly used in the ocean, does not apply in lakes. A shear-diffusion model including small-scale (Fickian) diffusion appears to provide a better prediction of patch growth and patch asymmetries.
The influence of a hierarchy in time scales on the dynamics of, and the coexistence within, ensembles of predator-prey pairs
One approach to developing general model concepts for ecological systems is to base them on the properties associated with the body weight of the component organisms. The dynamic characteristics of species may be described according to allometric relationships. In the model presented here an ensemble of predator-prey pairs, which share a common pool of an abiotic nutrient, are distributed along the body weight axis, introducing thus a hierarchy of different time scales. Model versions comprising a single predator-prey pair are chararacterized by a time-invariant steady state. As soon as further pairs are added the system becomes instable, exhibiting first periodic and then chaotic oscillations. In spite of the chaotic dynamics, certain statistical trends are independent of the initial conditions chosen. The variability in global system variables (nutrient concentration, metabolic activity) decreases with increasing number of pairs, revealing thus an increase in the efficiency of nutrient utilization. In the non-equilibrium situation an unlimited number of differently sized predator-prey pairs may coexist, the time-averaged biomass being evenly distributed among all pairs. Such observations contrast with expectations derived from the steady state.
The non-linear influence of wind-speed variability on gas transfer in lakes
The analytical representation of wind-speed probabilities by the Weibull distribution allows the empirical characterization of a scalar wind field on the basis of two Weibull parameters. Such a parameterization obviates the necessity of including wind data in time-series form explicitly in air-water interaction models when accounting for non-linear wind effects. By combining the Weibull wind-speed distribution with commonly employed trilinear and power-law expressions for the dependence of the gas transfer velocity on wind speed, analytical expressions for the mean value of the transfer velocity are obtained. These expressions predict the non-linearity of the dependence of gas transfer velocity on wind speed to be responsible for an increase in the mean transfer velocity which will normally not exceed 100% of the value obtained when non- linear wind effects are neglected. In the specific case of the winter oxygenation of a typical subalpine Swiss lake (Aegerisee), the commonly employed trilinear and power-law expressions are found to underestimate the mean O<sub>2</sub> transfer velocity considerably. It is evident that such expressions cannot be employed to determine gas transfer velocities in sheltered lakes without considerable modification at low wind speeds. The extent of the modification required, however, suggests that the role played by the instantaneous wind speed in determining the gas transfer velocity in such lakes may be much less significant than is usually assumed.
Food webs and ecological networks across temporal and spatial scales
A coherent description of ecosystems across a range of temporal and spatial scales is obtained by introducing non-dimensional coordinates normalized by the intrinsic scales of the populations of the organisms involved. Organisms are aggregated into dynamic classes irrespective of taxonomic identity. The basic food web units, the trophic dynamic modules, are defined in terms of the dynamic properties of the component organisms, their location in time and space and their functional embedding within the network of energy transfers. As a result one obtains a hierarchical modular description of the spatio-temporal structure of food web interactions. Such a description can be employed as a quantitative basis for the analysis of general food web patterns. Comparisons between terrestrial and aquatic systems, and among systems exposed to different schemes of environmental variability, become feasible. Valuable information can be provided to resolve the controversy concerning the interpretation of food webs in terms of trophic levels or as a trophic continuum. This approach, motivated by a view of ecosystems as dynamic nonequilibrium systems characterized by local interactions and distributed control, contrast with the more common view of ecosystems as equilibrium systems characterized by centralized control.
Scavenging of Chernobyl <SUP>137</SUP>Cs and natural <SUP>210</SUP>Pb in Lake Sempach, Switzerland
Radioactive fallout from the burning Chernobyl nuclear reactor provided a pulsed release of <sup>137</sup>Cs to Lake Sempach at the beginning of May 1986. The time-dependent removal of <sup>137</sup>Cs from the water column into the sediments has been investigated by analyzing water samples, settling particles and sediment cores. A flux balance has been established to determine and to quantify the removal processes in the epilimnion and hypolimnion of Lake Sempach. Between May 1986 and March 1988, removal residence times of <sup>137</sup>Cs averaged 150 days in the epilimnion and 280 days in the hypolimnion. <sup>137</sup>Cs accumulated in the hypolimnion during stratification and its scavenging from the hypolimnion into the sediments was the rate-limiting step of the overall process of removing <sup>137</sup>Cs from the water column. Resuspension of sedimentary <sup>137</sup>Cs occurred during circulation periods in winter. Scavenging by settling particles was the dominant removal process of <sup>137</sup>Cs in epilimnion and hypolimnion. Sediment trap fluxes of <sup>137</sup>Cs and <sup>210</sup>Pb linearly correlated with increasing particle fluxes up to a maximum of about 2.5 g m<sup>-2</sup> d<sup>-1</sup>. Higher particle fluxes, likely due to calcite precipitation, did not enhance removal fluxes and scavenging efficiency for these nuclides. The distribution coefficient for the partition of <sup>137</sup>Cs between lake water and settling particles, K<sub>d</sub>, was determined to 7.0 ± 1.0 × 10<sup>4</sup> cm<sup>3</sup> g<sup>-1</sup> for epilimnetic particles and to 5.3 ± 1.1 × 10<sup>4</sup> cm<sup>3</sup> g<sup>-1</sup> for hypolimnetic particles. The distribution coefficient for <sup>210</sup>Pb was estimated to 1.1 × 10<sup>6</sup> cm<sup>3</sup> g<sup>-1</sup>. The possibility of postdepositional mobility of Chernobyl and nuclear weapons <sup>137</sup>Cs and natural <sup>210</sup>Pb in sediments was proved.
Kinetics of redox cycling of iron coupled with fulvic acid
The kinetics of conversion of iron(III) (hydr)oxides to ferrous iron mediated by fulvic acid have been investigated in order to improve the understanding of the redox cycling of iron at the oxic-anoxic boundary in natural waters. Under the conditions similar to natural waters, fulvic acid is able to reduce the iron(III) (hydr)oxide. The kinetics of the reaction depend on the reactivity of iron(III) (hydr)oxides and the reducing power of the fulvic acid. The rate of reaction is 60 nm/h obtained under following conditions: total concentration of Fe(III) 1.0 × 10<sup>-4</sup> M, pH 7.5, fulvic acid 5 mg/L. The rate is considered as a net result of reduction and oxidation in the > Fe<sup>III</sup>-OH/Fe(II) "wheel" coupled with fulvic acid. In a real natural water system, reductants other than fulvic acid may be of importance. The results obtained in the laboratory, however, provide evidence that the Fe(OH)<sub>3</sub>(s)/Fe(II) redox couple is able to act as an electron-transfer mediator for the oxidation of natural organic substances, such as fulvic acid by molecular oxygen either in the absence of microorganisms or as a supplement to microbial activity.
The photo-oxidation of diethyl ether in smog chamber experiments simulating tropospheric conditions: product studies and proposed mechanism
The products formed by the hydroxyl radical initiated photo-oxidation of diethyl ether have been investigated by irradiating synthetic air mixtures containing diethyl ether and nitrous acid in amounts approaching ppbv levels in a smog chamber. The decay of reactants and formation of products were monitored by gas chromatography, HPLC, and by chemiluminescent analysis. The major products are ethyl formate and formaldehyde, minor products include ethyl acetate, acetaldehyde, peroxyacetyl nitrate, methyl nitrate, and ethyl nitrate. The products observed arise from the decomposition reactions of the 1-ethoxyethoxy radical and its reaction with oxygen. One molecule of nitric oxide appears to be oxidized per molecule of diethyl ether reacted. This is lower than would be expected on the basis of the proposed mechanism and possible reasons for the discrepancy are discussed.
Aquatic colloids as chemical reactants: surface-structure and reactivity
Colloids are ubiquitous; they occur in natural waters, even in seawater, groundwater and interstitial soilwater, in relatively large concentrations (more than 10<sup>9</sup> colloids per liter). We consider first an idealized α-Fe<sub>2</sub>O<sub>3</sub> (hematite) colloid and consider how its surface chemistry, surface speciation and surface charge is affected by its interaction H<sup>+</sup>, OH<sup>−</sup>, metal ions and ligands. The interaction is modeled with the help of the surface complex formation theory; effects of electrostatic interaction are taken care of with the Gouy—Chapman diffuse double layer theory.<br/>
The surface charge of a particle can be estimated from the extent of isomorphic substitution, and from H<sup>+</sup>, OH<sup>−</sup>, metal ions and ligands bound to the surface. Competitive surface complex formation equilibria can be used to estimate surface charge and, in turn, surface potential. Steric stabilization by polymer segments needs to be considered when the thickness of the polymer layer is larger than the thickness of the electric double layer, e.g. in seawater, δ<sub>h</sub>(polymer) > δ<sub>D</sub>(debye length).<br/>
Most surface-controlled processes depend on the identity of the surface species and the geometry of the coordinating shell. The overlapping orbital of the inner-sphere surface complex interconnects the solid phase (ionic or covalent solid, polymer) with the aqueous solution phase. Surface complex formation concepts have been extended to carbonates, sulfides, phosphates and organic particles (cells). The surface structure can be modified by hydrophobic adsorption and the sorption of polymers. Colloid surfaces can mediate electron transfer (including light-induced) processes. Electron cycling mediated by surfaces often complements or substitutes for an enzymatic mechanism.
Degradation of 2-<em>sec</em>-butylphenol: 3-<em>sec</em>-butylcatechol, 2-hydroxy-6-oxo-7-methylnona-2,4-dienoxic acid, and 2-methylbutyric acid as intermediates
<em>Pseudomonas</em> sp. strain HBP1 Prp, a mutant of strain HBP1 that was originally isolated on 2-hydroxybiphenyl, was able to grow on 2-<em>sec</em>-butylphenol as the sole carbon and energy source. During growth on 2-<em>sec</em>-butylphenol, 2-methylbutyric acid transiently accumulated in the culture medium. Its concentration reached a maximum after 20 hours and was below detection limit at the end of the growth experiment. The first three enzymes of the degradation pathway — a NADH-dependent monooxygenase, a metapyrocatechase, and a <em>meta</em>-fission product hydrolase — were partially purified. The product of the the monooxygenase reaction was identified as 3-<em>sec</em>-butylcatechol by mass spectrometry. This compound was a substrate for the metapyrocatechase and was converted to 2-hydroxy-6-oxo-7-methylnona-2,4-dienoic acid which was identified by gas chromatography-mass spectrometry of its trimethylsilyl-derivative. The cofactor independent <em>meta</em>-cleavage product hydrolase used 2-hydroxy-6-oxo-7-methylnona-2,4-dienoic acid as a substrate. All three enzymes showed highest activities for 2-hydroxybiphenyl and its metabolites, respectively, indicating that 2-<em>sec</em>-butylphenol is metabolized via the same pathway as 2-hydroxybiphenyl.
O<SUB>2</SUB><SUP>-</SUP> decay catalyzed by Cu<SUP>2+</SUP> and Cu<SUP>+</SUP> ions in aqueous solutions: a pulse radiolysis study for atmospheric chemistry
The catalytic decay of O<sub>2</sub><sup>−</sup> radicals due to Cu<sup>+</sup> and Cu<sup>2+</sup> ions in O<sub>2</sub> saturated solutions of low ionic strength was studied by pulse radiolysis and computer simulation of the entire reaction mechanism. Phosphate was used as buffer and formate was used to convert OH radicals into O<sub>2</sub><sup>−</sup>. At pH ≈ 6, the very low solubility products of Cu<sup>2+</sup> with OH<sup>−</sup> and PO<sub>4</sub><sup>3-</sup> limited the copper concentration to the order of μM. In experiments with [Cu<sup>2+</sup>] > [O<sub>2</sub><sup>−</sup>], the rate constant <em>k</em> (Cu<sup>2+</sup>+O<sub>2</sub><sup>−</sup>) = (8.0±0.5)·10<sup>9</sup> M<sup>−1</sup> s<sup>−1</sup> was determined. In systems with [O<sub>2</sub><sup>−</sup>]≫[Cu]<sub>tot</sub>, steady state for the copper ions is attained with apparent first-order kinetics, which correlates <em>k</em> (Cu<sup>2+</sup>+O<sub>2</sub><sup>−</sup>) with <em>k</em> (Cu<sup>+</sup>+O<sub>2</sub><sup>−</sup>). The O<sub>2</sub><sup>−</sup> decay rate decreased with increasing pH due to Cu<sup>2+</sup> complexation with HPO<sub>4</sub><sup>2-</sup>. Correspondingly the pK(CuHPO<sub>4</sub>) was found to be -4.0±0.2 under the assumption that <em>k</em> (CuHPO<sub>4</sub>+O<sub>2</sub><sup>−</sup>)≤0.01·<em>k</em> (Cu<sup>2+</sup>+O<sub>2</sub><sup>−</sup>. With this value, <em>k</em> (Cu<sup>+</sup>+O<sub>2</sub><sup>−</sup>) could be determined as (9.4±0.8)·10<sup>9</sup> M<sup>−1</sup> s<sup>−1</sup> by an iterative procedure. The consequences for the chemistry of atmospheric waters are discussed.
Grundsätze der Gewässerentwicklung - neue Ansätze im Gewässerschutzgesetz
Der Gewässerschutz wird immer wieder als Erfolgsgeschichte gepriesen. Tatsächlich konnten die Fliessgewässer und Seen vor katastrophalen Verunreinigungen bewahrt und ihre Wasserqualität verbessert werden. Zu lange allerdings verharrte man beim vornehmlich technischen Gewässerschutz. Im Schatten des Erfolgs wuchsen neue, grosse Probleme heran. Damit steht der Gewässerschutz auch als Paradebeispiel für die Defizite des herkömmlichen Umweltschutzes. <BR/>
Das neue Gewässerschutzgesetz soll nun mithelfen, die Situation der Gewässer zu verbessern. Darüber hinaus müssen die Massnahmen zum Schutz der Gewässer mit weiteren Belangen des Umwelt- und Naturschutzes koordiniert werden. Für die Schweiz besteht zudem eine zunehmende Verpflichtung, sich an internationalen Umweltschutz-Programmen zu beteiligen. Bei alledem geht es darum, eine langfristig tragfähige Umweltentwicklung einzuleiten. Das wiederum wird nicht möglich sein ohne Einführung von marktwirtschaftlichen Instrumenten, deren Zweck es ist, umweltgerechtes Verhalten und eine verursachergerechte Finanzierung des Umweltschutzes zu fördern.
Biogeochemical cycles in lakes are strongly influence by thin biofilms at the sediment-water interface. Rapid transformation reactions at this boundary determine the fate of chemical species: Dissolved components diffuse back into the lake, solid fractions are buried with the sediments and remain isolated from the biosphere for geological time scales. High resolution in-situ sampling with dialysis samplers and direct measurements of diffusive fluxes with sediment landers yield quantitative estimates of the dominant processes at the sediment water interface. The application of such methods is illustrated with results from a study in Lake Sempach, an eutrophic Lake in central Switzerland. This lake is artificially oxygenated in order to keep oxygen concentrations in the deep waters above a limit of 4 mg O<SUB>2</SUB>/l. However, this technology cannot prevent that the sediment surface turns anoxic in summer. As a consequence manganese and iron oxides dissolve and the adsorption capacity of the sediments for phosphorus remains low. A decrease in external phosphorus loading from agriculture is necessary in order to diminish the sedimentation rates of organic carbon and to restore the phosphorus binding capacity of the sediments.
Wehrli, B. (1993) Chemie am Seegrund, Vierteljahrsschrift der Naturforschenden Gesellschaft in Zürich, 69 - 79
Characterization of an inducible, membrane-bound iminodiacetate dehydrogenase from <em>Chelatobacter heintzii</em> ATCC 29600
Iminodiacetate (IDA) is a xenobiotic intermediate common to both aerobic and anaerobic metabolism of nitrilotriacetate (NTA). It is formed by either NTA monooxygenase or NTA dehydrogenase. In this paper the detection and characterization of a membrane-bound iminodiacete dehydrogenase (IDA-DH) from <em>Chelatobacter heintzii</em> ATCC 29600 is reported, which oxidizes IDA to glycine and glyoxylate. Out of 15 compounds tested, IDA was the only substrate for the enzyme. Optimum activity of IDA-DH was found at pH 8.5 and 25°C, respectively, and the K<sub>m</sub> for IDA was found to be 8mM. Activity of the membrane-bound enzyme was inhibited by KCN, antimycine and dibromomethylisopropyl-benzoquinone. When inhibited by KCN IDA-DH was able to reduce the artificial electron acceptor iodonitrotetrazolium (INT). It was possible to extract IDA-DH from the membranes with 2% cholate, to reconstitute the enzyme into soybean phospholipid vesicles and to obtain IDA-DH activity (more than 50% recovery) using ubiquinone Q<sub>1</sub> as the intermediate electron carrier and INT as the final electron acceptor. Growth experiments with different substrates revealed that in all NTA-degrading strains tested both NTA monooxygenase and IDA-DH were only expressed when the cells were grown on NTA or IDA. Furthermore, in <em>Cb. heintzii</em> ATCC 29600 growing exponentially on succinate and ammonia, addition of 0.4 g l<sup>-1</sup> NTA led to the induction of the two enzymes within an hour and NTA was utilized simultaneously with succinate. The presence of IDA-DH was confirmed in ten different NTA-degrading strains belonging to three different genera.
Lake oxygenation: application of a one-box model with ice cover
A one-box exponential model with constant coefficients is capable of giving a good description of the winter oxygen uptake of a lake not subject to freezing over. A simple modification of the model accounts well for the effects of ice cover. The modified model predicts that, all else being equal, the oxygen regimes of eutrophic lakes will tend to be affected more by ice cover than those of oligotrophic lakes; that a short period of ice cover is of no great consequence for the oxygen regime of the lake, whereas a long period of ice cover results in a disproportionately large decrease in the mean lake oxygen concentration; and that the later break-up occurs, the greater will be the effect of the ice cover on the oxygen regime of the lake.
A new method for processing clay-rich unconsolidated sediments for paleoecological investigations
A method is described for processing flocculated clay-rich sediments which avoids acetolysis and heavy liquid separation. Twin 80 (Merck index 1983) is used for deflocculation. Microsieves separate the recovered organisms according to size. Taxonomic identification and quantitative evaluation of the organisms can be performed in counting chambers or on permanent slides. Algae, cysts and exospores of dinoflagellates, pollen grains and zooplankton remains can be recovered.
Selection of <I>Pseudomonas</I> sp. strain HBP1 Prp for metabolism of 2-propylphenol and elucidation of the degradative pathway
A mutant of <I>Pseudomonas</I> sp. strain HBP1, originally isolated on 2-hydroxybiphenyl, was selected for the ability to grow on 2-propylphenol as the sole carbon and energy source. In the mutant strain, which was designated as <I>Pseudomonas</I> sp. strain HBP1 Prp, the cellular induction mechanism involved in the synthesis of the NADH-dependent monooxygenase is changed. 2-Propylphenol, which is known to be a substrate of the monooxygenase, does not induce formation of the monooxygenase in the wild type but does have an induction effect in the mutant strain. Furthermore, in contrast to the wild type, mutant strain HBP1 Prp constitutively produces a small amount of monooxygenase and metapyrocatechase. The enzymes from strain HBP1 Prp catalyzing the first three steps in the degradation of 2-propylphenol—the NADH-dependent monooxygenase, the metapyrocatechase, and the <I>meta</I> fission product hydrolase—were partially purified, and their activities were measured. The product of the monooxygenase activity was identified by mass spectrometry as 3-propylcatechol. The metapyrocatechase used this compound as a substrate and produced a yellow <I>meta</I> fission product that was identified by mass spectrometry as 2-hydroxy-6-oxo-nona-2,4-dienoate. Butyrate could be detected as a product of the <I>meta</I> fission product hydrolase in crude cell extract of 2-propylphenol-grown cells, as well as an intermediate in culture broths during growth on 2-propylphenol. All three enzymes expressed highest activities for the metabolites of the degradation of 2-hydroxybiphenyl.
Description of the Gram-negative, obligately aerobic, nitrilotriacetate (NTA)-utilizing bacteria as <I>Chelatobacter heintzii</I>, gen. nov., sp. nov., and <I>Chelatococcus asaccharovorans</I>, gen. nov., sp. nov.
Nine obligately aerobic, Gram-negative, nitrilotriacetate (NTA)-utilizing isolates and the two NTA-utilizing reference strains <em>Pseudomonas</em> spp. ATCC 29600 and ATCC 27109 were investigated by a polyphasic taxonomic approach. The presence of sym-homospermidine as the major polyamine excluded all NTA-utilizing bacteria from the authentic genus <em>Pseudomonas</em> and suggested their allocation into the alpha-2 subclass of the <em>Proteobacteria</em>. Protein patterns and DNA hybridization studies revealed two unrelated groups, neither of which could be allocated to any currently recognized genus. The 16S rRNA fragment sequences (position 1220–1377, <em>Escherichia coli</em>-nomenclature) of representative strains from both groups differ by 13 nucleotides. This indicates that they are not closely related, and justifies placement of the NTA-utilizing bacteria in two different genera, <em>Chelatobacter</em>, gen. nov., and <em>Chelatococcus</em>, gen. nov. These taxa are formally described below. A difference of 10 nucleotides indicated that <em>Rhodopseudomonas acidophila</em> is the most closely related neighbour of <em>Chelatococcus asaccharovorans</em> TE2. Oligonucleotide cataloguing places <em>Chelatobacter heintzii</em> ATCC 29600 next to the carbon monoxide oxidizing bacterium “<em>Alcaligenes carboxydus</em>” DSM 1086, within the <em>Agrobacterium-Rhizobium</em> branch.
Evidence for photochemical formation of H<SUB>2</SUB>O<SUB>2</SUB> and oxidation of SO<SUB>2</SUB> in authentic fog water
When samples of rain and fog water were exposed to ultraviolet and visible light, reactive transients such as hydrogen peroxide were formed and dissolved organic matter and sulfur dioxide were depleted. These results, in conjunction with those from previous studies, imply that dissolved organic compounds and transition metals such as iron ions are involved in the photochemical formation of hydrogen peroxide and other photooxidants in atmospheric waters.
Metabolism of 2,2'-dihydroxybiphenyl by <I>Pseudomonas</I> sp. strain HBP1: production and consumption of 2,2',3-trihydroxybiphenyl
Cells of <I>Pseudomonas</I> sp. strain HBP1 grown on 2-hydroxy- or 2,2'-dihydroxybiphenyl contain NADH-dependent monooxygenase activity that hydroxylates 2,2'-dihydroxybiphenyl. The product of this reaction was identified as 2,2',3-trihydroxybiphenyl by <sup>1</sup>H nuclear magnetic resonance and mass spectrometry. Furthermore, the monooxygenase activity also hydroxylates 2,2',3-trihydroxybiphenyl at the C-3' position, yielding 2,2',3,3'-tetrahydroxybiphenyl as a product. An extradiol ring cleavage dioxygenase activity that acts on both 2,2',3-tri- and 2,2',3,3'-tetrahydroxybiphenyl was partially purified. Both substrates yielded yellow <I>meta</I>-cleavage compounds that were identified as 2-hydroxy-6-(2-hydroxyphenyl)-6-oxo-2,4-hexadienoic acid and 2-hydroxy-6-(2,3-dihydroxyphenyl)-6-oxo-2,4-hexadienoic acid, respectively, by gas chromatography-mass spectrometry analysis of their respective trimethylsilyl derivatives. The <I>meta</I>-cleavage products were not stable in aqueous incubation mixtures but gave rise to their cyclization products, 3-(chroman-4-on-2-yl)pyruvate and 3-(8-hydroxychroman-4-on-2-yl)pyruvate, respectively. In contrast to the <I>meta</I>-cleavage compounds, which were turned over to salicylic acid and 2,3-dihydroxybenzoic acid, the cyclization products are not substrates to the <I>meta</I>-cleavage product hydrolase activity. NADH-dependent salicylate monooxygenase activity catalyzed the conversions of salicylic acid and 2,3-dihydroxybenzoic acid to catechol and pyrogallol, respectively. The partially purified extradiol ring cleavage dioxygenase activity that acted on the hydroxybiphenyls also produced 2-hydroxymuconic semialdehyde and 2-hydroxymuconic acid from catechol and pyrogallol, respectively.
Observations of the second vertical mode of the internal seiche in an alpine lake
The analysis of wind and temperature data from Alpnacher See (Switzerland) shows the second vertical mode of the internal (baroclinic) seiche to dominate over the first vertical mode. Resonance with diurnal wind is responsible for the high amplitudes of the second mode. Two different models are used to calculate the periods and velocity distribution of the various modes of the internal seiche. First, as a natural extension of Mortimer's two-layer model, the eigenvalues of a three-layer model for a rectangular basin are calculated analytically. The period of the second vertical mode is found to depend strongly on the thickness of the metalimnion. Second, in order to better represent the vertical structure of the water column, a continuous stratification model is adopted and solved analytically for realistic density profiles. The resulting vertical variation of the horizontal velocity is used to calculate local gradient Richardson numbers (Ri) and relate them to the vertical eddy diffusivity estimated with the temperature microstructure method.
The effect of herbivorous crustacean zooplankton on epilimnetic carbon and phosphorus cycling
Plastic limnocorrals (LCs; volume 70 m<sup>3</sup>) in oligo-mesotrophic Lake Lucerne, Switzerland were used to manipulate planktonic communities by (1) removing large zooplankton at the start of the experiment, and (2) adding phosphate during experiments of two weeks duration.<br />
Primary production (<sup>14</sup>C-assimilation), chlorophyll, standing crops and sedimentation of particulate organic carbon (POC) and of particulate phosphorus, as well as plankton composition were assessed simultaneously in two to four differently treated LCs. Carbon and phosphorus mass balances were calculated from assimilation, temporal change in standing crop of particulate matter, and sedimentation.<br />
A quick elimination of crustaceans by screening hardly increased primary production, but decreased sedimentation and mineralisation of particulate organic carbon, and thus significantly enhanced the standing crop of POC, but decreased POC turnover. The exclusion of crustaceans increased the mean residence time of total phosphorus by a reduced P loss by sedimentation.<br />
Increased grazing pressure during the experiment showed little grazing induced effect on plankton composition and primary production except at the very end.<br />
We conclude that in an oligo-mesotrophic lake, buffering mechanisms attenuate the impact of changing grazing pressures on primary production.
Reductive dechlorination of polychlorinated biphenyls in anaerobic sediments
To better understand the conditions which control PCB dechlorination in anaerobic sediments we examined the microbial activity in two freshwater sediments, Hudson River (NY) and Silver Lake (MA), and one estuarine sediment, New Bedford Harbor (MA). Two different reducing conditions were established, methanogenic and sulfidogenic; in addition, the effect of added organic substrates and the differences in the fate of preexisting and freshly added PCBs (100-400 ppm Aroclor 1242 or 1260) were examined. The most rapid dechlorination occurred in the methanogenic cultures established with Hudson River sediment to which Aroclor 1242 was added and supplemented with a fatty acid mixture. Meta and para chlorines were preferentially removed, resulting in accumulation of ortho-substituted mono-, di-, and trichlorobiphenyls. In cultures established with New Bedford Harbor sediment, dechlorination was slower and not as extensive, with di-, tri-, and tetrachlorobiphenyls accumulating. Dechlorination was observed with spiked Aroclor 1242 and with preexisting PCBs alone. In Silver Lake sediment cultures spiked with Aroclor 1260, dechlorination with accumulation of tri- and tetrachlorobiphenyls was observed. Dechlorination was slower than that for the Hudson River cultures. Both the Hudson River and Silver Lake cultures showed no additional dechlorination for the preexisting PCBs. The addition of fatty acids did not enhance activity in the New Bedford Harbor or Silver Lake cultures. No activities were detected under sulfate-reducing conditions with any of the sediments.
Roughing filters are used in European groundwater recharge plants and applied in rural water supplies of developing countries. Four case studies of roughing filter application in Europe, presented at an international workshop held in Zurich in June 1992, are summarized in this paper. The roughing filter technology which has been further improved in developing countries, is briefly described. The new and hardly known filter designs could be used as innovative elements in future rural water treatment systems.
Filtration through roughing gravity filters at low filtration rates between 0,5 and 2 m/h has shown to be able to produce a water with low particulate concentrations which allow further treatment in slow sand filters without the danger of solids overloads. Theoretical considerations on particulate transport mechanisms in granular media filters revealed that sedimentation is the main transport mechanism for particle separation in gravel type filters. Model calculations of particle transport trajectories in horizontal and vertical flow filters showed that horizontal pores are more efficient particle collectors. High removal rates for particulates down to colloidal size without the need for flocculant chemicals and the large solids storage capacity at low headloss as well as the simple and reliable technology make roughing filters appropriate for applications in third world countries.
Roughing filters are used for the separation of solid particles. Similar to slow sand filters, they rely on natural water treatment processes. In Europe, roughing filters are applied in combination with slow sand filters for the artificial recharge of groundwater whereas in developing countries, the filter combination is used in rural water treatment plants. Since the roughing filter technology has been greatly developed over the last 10 years, an international workshop was held in Zurich last year to enhance the information exchange. The roughing filter technology will be presented hereafter in a somewhat larger context with a few selected papers and a summary of the practical field experience.
Das Verursacherprinzip: Eine Anwendung bei der Siedlungsabfallentsorgung
The Polluter Pays Principle has become a widely accepted political guideline for dealing with environmental problems. In order to apply this principle to the municipal solid waste management three questions are discussed:<br/>
– who are the polluters,<br/>
– what are the costs they have to pay,<br/>
– and where should these costs be imposed on the polluters?<br/>
The determination of the polluter is mainly a juridical problem while the two other questions lie in the center of economic theory. The imposition of the total social costs of waste disposal is theoretically convincing but practically not feasible.<br/>
Therefore another approach is chosen: the costs to be intemalized are the costs that result from reaching a politically set environmental standard.<br/>
It is argued that for an efficient compliance with this standard it is not enough to intemalize the operational costs of waste treatment.<br/>
An additional charge should be levied to influence the quantity of municipal solid waste directly.
Die Stoffbilanzierung landwirtschaftlicher Böden. Eine Methode zur Früherkennung von Bodenveränderungen
Material balances of agricultural soil - a method for early recognition of soil alterations. For agricultural soils of a lowland region in Switzerland the input and output of the elements nitrogen, phosphorus, copper, zinc, cadmium and lead were measured over two years. In spite of the fact that the emission standards are met there is a slow and steady increase of the P, Cu, Zn and Pb concentrations found in the plough layer. In accordance with the principle of prevention the metabolism of the soil should be controlled on a large scale in such a way that this concentration increase can be substantially reduced within decades.<br/>
With the available analytical methods the observed concentration increases in the soil are clearly detectable only after decades. Regional annual material balancing of the relevant anthropogenic processes (farming, private households, industry and trade), however, allows early detection of small changes in concentration. Consequently, a soil protection strategy which obeys the principle of early prevention should be completed by regional material balances.
The feasibility of real time control of combined sewer overflows
Urban drainage systems (UDSs) are
often plagued with pollution problems
due to flooding and combined
sewer overflows (CSOs). The agencies responsible
for these systems have become hardpressed
to come up with solutions to these
problems. These agencies are also under public
constraints to implement these solutions with
the lowest possible cost, and to maximize other
potential benefits that can be applied to other
problems such as reducing energy costs and
improving wastewater treatment and in-sewer
sediment control. Real time UDS.control offers
one way to reduce flooding and pollution problems
with relatively little investment cost.
The hierarchical organization of the aquatic ecosystem: an outline how reductionism and holism may be reconciled
The aquatic ecosystem is viewed from the perspective of a hierarchical system of positive feedback cycles. The system's behaviour is governed by the dualism between cooperative phenomena at the level of the ecological network as a whole and processes at the level of its components. The former are characterized by the network's spatiotemporal organization; the latter are characterized by what is here referred to as the spatiotemporal niche, determined mainly by body-weight. Accordingly, the hierarchical structure of the system cannot be simply based on body-weight in a reductionist fashion, but must be interpreted from a holistic point of view taking into account the feedback structure of the whole network.<br/>
The perspective outlined is that of a self-organizing system operating far from its equilibrium state. Possible consequences associated with such a view are suggested for research and management decisions. For instance the focus may be shifted from the investigation of single processes of control to questions dealing with the system's potential for spatiotemporal self-organization and its associated adaptibility.
Quantification of species as functional units within an ecological network
A new index referred to as “scope for change in ascendency” has been suggested recently by Genoni and Pahl-Wostl to measure overall ecosystem performance. In this paper we derive an amended version of their original formulation that we suggest be called the “scope for growth and development.” The amended measure can be decomposed into terms that correspond to the contribution of each system component toward total system performance. Those system compartments that are acknowledged often to exert top-down trophic control on their supporting resources make strong positive contributions to the community scope, whereas those thought to limit the availability of resources from below impart negative terms to the new scope index. On a per unit flow basis, system performance seems to be most sensitive to exports of usable materials from the system and least affected by losses due to dissipation. The qualitative description of the system performance in terms of contributions by its components appears to be robust with respect to the level of aggregation of system elements.
Mathematical modelling of anaerobic mesophilic sewage sludge treatment
A mathematical model was developed to describe the dynamic behaviour of the anaerobic mesophilic digestion. Special emphasis was given to the acetate degradation kinetics, as the step that determines the stability of anaerobic digestion. From the safety factor (maximum/average degradation rate) of acetate degradation in the range of 5.3 to 23 days hydraulic detention time, a maximum observed growth rate of 0.37 d<sup>-1</sup> and decay rate of 0.10 d<sup>-1</sup> were estimated. Temperature and pH dependence of acetate conversion was also determined and included in the model. The model was verified with load variation experiments on laboratory and full scale digesters. Mesophilic digestion with anaerobic thermophilic pretreatment is more sensitive to load variation than single mesophilic digestion. However two stage treatment leads to better sludge characteristics (thickening, viscosity, COD, TSS) of the treated sludge.
Umweltverträgliche Landwirtschaft - ein Vorhaben von vielen Weggefährten
Die schweizerische Landwirtschaft befindet sich im Umbruch. Sie muss umweltfreundlichere Produktionsweisen realisieren und gleichzeitig die darauf abgestimmte Neuorientierung der Agrarmarktordnung adaptieren. Diese schwierige Entwicklung soll durch spezielle Anstrengungen aller auf die Landwirtschaft einwirkenden Kreise erleichtert werden. Der VGL-Präsident Ueli Bundi steckt im folgenden Artikel den Wirkungsbereich ab.
<SUP>10</SUP>Be and magnetic susceptibility in Chinese loess
<sup>10</sup>Be and magnetic susceptibility have been measured in the top 12 m of a loess profile from Luochuan, Central China. Comparison of the <sup>10</sup>Be concentration record with the SPECMAP δ<sup>18</sup>O profile of the last 130 ka (Imbrie et al., 1984] results in a new time scale which is in good agreement with that of Kukla et al. . The calculated loess accumulation rates can be compared with existing records of dust falls in Pacific deep sea sediments and Antarctic ice cores. A simple model for the <sup>10</sup>Be dust flux demonstrates that a significant part of the magnetic susceptibility signal in palaeosol horizons is due to in situ pedogenic production. During times of high loess accumulation (cold palaeoclimate) this contribution is negligible.
Molecular mechanisms of genetic adaptation to xenobiotic compounds
Microorganisms in the environment can often adapt to use xenobiotic chemicals as novel growth and energy substrates. Specialized enzyme systems and metabolic pathways for the degradation of man-made compounds such as chlorobiphenyls and chlorobenzenes have been found in microorganisms isolated from geographically separated areas of the world. The genetic characterization of an increasing number of aerobic pathways for degradation of (substituted) aromatic compounds in different bacteria has made it possible to compare the similarities in genetic organization and in sequence which exist between genes and proteins of these specialized catabolic routes and more common pathways. These data suggest that discrete modules containing clusters of genes have been combined in different ways in the various catabolic pathways. Sequence information further suggests divergence of catabolic genes coding for specialized enzymes in the degradation of xenobiotic chemicals. An important question will be to find whether these specialized enzymes evolved from more common isozymes only after the introduction of xenobiotic chemicals into the environment. Evidence is presented that a range of genetic mechanisms, such as gene transfer, mutational drift, and genetic recombination and transposition, can accelerate the evolution of catabolic pathways in bacteria. However, there is virtually no information concerning the rates at which these mechanisms are operating in bacteria living in nature and the response of such rates to the presence of potential (xenobiotic) substrates. Quantitative data on the genetic processes in the natural environment and on the effect of environmental parameters on the rate of evolution are needed.
Characterization of two phosphate transport systems in <I>Acinetobacter johnsonii</I> 210A
The transport of P<sub>i</sub> was characterized in <I>Acinetobacter johnsonii</I> 210A, which is able to accumulate an excessive amount of phosphate as polyphosphate (polyP) under aerobic conditions. P<sub>i</sub> is taken up against a concentration gradient by energy-dependent, carrier-mediated processes. <I>A. johnsonii</I> 210A, grown under P<sub>i</sub> limitation, contains two uptake systems with <I>K<sub>t</sub></I> values of 0.7 ± 0.2 μM and 9 ± 1 μM. P<sub>i</sub> uptake via the high-affinity component is drastically reduced by <I>N,N'</I>-dicyclohexylcarbodiimide, an inhibitor of H<sup>+</sup>-ATPase, and by osmotic shock. Together with the presence of P<sub>i</sub>-binding activity in concentrated periplasmic protein fractions, these results suggest that the high-affinity transport system belongs to the group of ATP-driven, binding-protein-dependent transport systems. Induction of this transport system upon transfer of cells grown in the presence of excess P<sub>i</sub> to P<sub>i</sub>-free medium results in a 6- to 10-fold stimulation of the P<sub>i</sub> uptake rate. The constitutive low-affinity uptake system for P<sub>i</sub> is inhibited by uncouplers and can mediate counterflow of P<sub>i</sub>, indicating its reversible, secondary nature. The presence of an inducible high-affinity uptake system for P<sub>i</sub> and the ability to decrease the free internal P<sub>i</sub> pool by forming polyP enable <I>A. johnsonii</I> 210A to reduce the P<sub>i</sub> concentration in the aerobic environment to micromolar levels. Under anaerobic conditions, polyP is degraded again and P<sub>i</sub> is released via the low-affinity secondary transport system.
Synthesis of cyclic β-(1,2)-glucans by <I>Rhizobium leguminosarum</I> biovar trifolii TA-1: factors influencing excretion
The synthesis of cyclic β-(1,2)-glucans from UDP-[<sup>14</sup>C]glucose by a crude membrane preparation and whole cells of Rhizobium leguminosarum bv. trifolii TA-1 was investigated. The crude membrane system needed Mn<sup>2+</sup>, ATP, and NAD<sup>+</sup> for optimal activity. Hardly any difference in biosynthetic activity between membrane fractions of TA-1 cells grown in the presence (200 mM) or absence of NaCl was observed. Whole TA-1 cells grown in the presence of NaCl excreted labeled, neutral cyclic β-(1,2)-glucan during incubation with added UDP-[<sup>14</sup>C]glucose. With NaCl-free cultured TA-1 cells, no excretion was observed; however, after these cells were alternately frozen and thawed eight times, they excreted glucans. Glucan formation in vitro and glucan excretion by whole cells were strongly inhibited in the presence of 50 mg of cyclic glucan per ml (about 15 mM), indicating that biosynthesis of cyclic β-(1,2)-glucans in strain TA-1 is controlled by end-product inhibition. These observations indicate that TA-1 cells become more permeable to cyclic glucans at high NaCl concentrations. The constant loss of glucans from cells grown in the presence of 200 mM NaCl prevented end-product inhibition and resulted in glucan accumulation of up to 1,600 mg/liter in the medium.
<em>In vitro</em> effects of cadmium, zinc and lead on calmodulin-dependent actions in <em>Oncorhynchus mykiss</em>, <em>Mytilus</em> sp., and <em>Chlamydomonas reinhardtii</em>
The potential of cadmium, zinc, and lead to interact with calmodulin (CaM) was investigated by examining in vitro CaM- dependent protein phosphorylation in tissues from rainbow trout (<em>Oncorhynchus mykiss</em>) and sea mussel (<em>Mytilus</em> sp.) and CaM- dependent phosphodiesterase (PDE) activation by algal (<em>Chlamydomonas reinhardtii</em>) extracts. Cadmium, zinc, and lead proved effective in sustaining CaM-dependent protein phosphorylation in systems containing calcium, whereas only lead was capable of CaM activation in systems depleted of calcium. Cadmium lead to a small activation of CaM-dependent PDE activity by algal extracts, corresponding to approximately 25% of that induced by calcium. Cadmium-induced PDE-activation could be attributed to the residual calcium present in the extract. The results indicate that metal-induced CaM activation is primarily mediated in the case of cadmium and zinc by resulting calcium/CaM complexes and in the case of lead by lead/CaM complexes.
Quantitative determination of sulfonated aliphatic and aromatic surfactants in sewage sludge by ion-pair/supercritical fluid extraction and derivatization gas chromatography/mass spectrometry
Secondary alkanesulfonate (SAS) and linear alkylbenzene-sulfonate (LAS) surfactants were quantitatively (>90%) extracted from sewage sludges as their tetrabutylammonium Ion pairs using 400 atm of supercritical CO<sub>2</sub> for 5 min of static extraction followed by 10 min of dynamic extraction at 80 °C. Ion pairs of SAS and LAS quantitatively formed butyl esters in the injection port of the gas chromatograph and were determined by gas chromatography/mass spectrometry without class fractionation of the sewage sludge extracts. Concentrations of SAS and LAS in sludges from five different sewage treatment plants ranged from 0.27 to 0.80 g/kg of dry sewage sluge and from 3.83 to 7.51 g/kg, respectively. Good reproducibility was achieved with RSDs of typically 5% for replicate extractions and analyses. Homologue and isomer distributions of SAS in sewage sludge indicated an enrichment of the more Hydrophobic components in sewage sludge during sewage treatment.
A steady bubble plume model is developed to describe a weak air (or oxygen) bubble injection system used for the restoration of deep stratified lakes. Since the model is designed for two modes of operation, i.e., oxygenation and artificial mixing, gas exchange between water and bubbles has to be included. The integral model is based on the entrainment hypothesis and a variable buoyancy flux determined by the local plume properties and the ambient water column. Fluxes of eight properties are described by nonlinear differential equations which can be numerically integrated. In addition, five equations of state are used. The model leaves open two initial conditions, plume radius and plume velocity. Model calculations with real lake water profiles demonstrate the range of applicability for both modes of operation. The model agrees reasonably well with field data and with laboratory experiments conducted by various investigators.
Trophic state and its implications for natural reproduction of salmonid fish
Natural propagation of all fish species native to a particular lake is an ecological requirement of prime importance. Salmonid fish are particularly vulnerable to environmental degradation since egg development takes place on or in the bottom substrate. Dissolved oxygen concentration on the spawning site is commonly considered the main factor limiting egg development. In order to assess the relationship between trophic state, hypolimnetic oxygen concentration, and salmonid egg development, whitefish (<em>Coregonus</em> sp.) eggs were sampled just prior to hatching in late winter. Eggs were collected in 13 Swiss lakes of different trophic state, using a sled-dredge. The proportion of viable eggs among the total number of eggs found was taken as a measure of reproductive success. The results indicate that successful <em>in situ</em> embryogenesis is not primarily governed by hypolimnetic oxygen concentration which tends to be high anyway during egg incubation, but by trophic state in terms of total phosphorus concentration in spring. The findings are explained by the production-related oxygen uptake of the sediment, creating an oxygen gradient of varying steepness in the diffusive boundary layer. Implications for the restoration of lacustrine ecosystems are discussed.
Density structure and tritium-helium age of deep hypolimnetic water in the northern basin of Lake Lugano
Long-term stratification of the deep hypolimnetic waters of the northern basin of Lake Lugano (Lago di Lugano) has resulted in a lack of deep-water renewal which has persisted for decades. Tritium-helium age measurements reveal that deep water has not been in contact with the atmosphere since the 1960s. Higher primary production associated with the significant increase in phosphorus concentration which occurred at this time resulted in greater autochthonous gross sedimentation rates, increasing the rate of mineralization and, consequently, the rate of release of dissolved solids (mainly HCO<sub>3</sub><sup>-</sup> and Ca<sup>2+</sup>) into the deep hypolimnion. This gave rise to an intensification of the stratification and to a consequent reduction in the vertical exchange of hypolimnetic water layers. Today, the density stabilizing effect of ion release due to mineralization in the deep water is four to five times greater than the destabilizing effect of the geothermal heat flux from the earth's interior. It is known from laboratory experiments that such small density gradient ratios are likely to give rise to double-diffusive instabilities. However, even rudimentary mass balance calculations of biogeochemical components indicate that shear- induced turbulence, most likely generated by bottom currents, mixes far more efficiently than double diffusion. In the future, the biogenic density stratification is likely to persist in the deep water, unless the upward ion flux, driven by primary production, decreases by a factor of four to five.
Further studies of the temperature dependence of the rate coefficients for the reactions of OH with a series of ethers under simulated atmospheric conditions
The following temperature-dependent rate coefficients (<i>k</i>/cm<sup>3</sup> molecule<sup>−1</sup> s<sup>−1</sup>) of the reactions of hydroxyl radicals with aliphatic ethers have been determined over the temperature range 247–373 K by a competitive flow technique: diethyl ether, <i>k</i><sub>OH</sub>=5.2×10<sup>−12</sup> exp[(262±150)/T]; methyl-<i>n</i>-butyl ether, <i>k</i><sub>OH</sub>=5.4×10<sup>−12</sup> exp[(309±150)/T]; ethyl-<i>n</i>-butyl ether, <i>k</i><sub>OH</sub>=7.3×10<sup>−12</sup> exp[(335±150)/T]; di-<i>n</i>-butyl ether, <i>k</i><sub>OH</sub>=5.5×10<sup>−12</sup> exp[(502±150)/T] and di-<i>n</i>-pentyl ether, <i>k</i><sub>OH</sub>=8.5×10<sup>−12</sup> exp[(417±150)/T]. The data have been measured relative to the rate coefficient <i>k</i>(OH + 2,3-dimethylbutane)=6.2×10<sup>−12</sup> cm<sup>3</sup> molecule<sup>−1</sup> s<sup>−1</sup> independent of temperature.<br/>
Previous discrepancies in the room-temperature rate coefficients for the OH reactions with ethyl-<i>n</i>-butyl ether and di-<i>n</i>-butyl ether, obtained in the flow and static experiments of Bennett and Kerr (<i>J. Atmos. Chem.</i> 8, 87–94, 1989; 10, 29–38, 1990) compared with those of Wallington <i>et al.</i> (<i>Int. J. Chem. Kinet.</i> 20, 541–547, 1988; 21, 993–1001, 1989) and of Nelson <i>et al.</i> (<i>Int. J. Chem. Kinet.</i> 22, 1111–1126, 1990) have been resolved. The results are considered in relation to the available literature data and evaluated rate expressions are deduced where possible. The data are also discussed in terms of structure-activity relationships.
The fish species inhabiting
the river Rhine near Basel before the year 1900 and today are reported. Originally, some 29
fish species and three cyclostome species were known to occur. Changes in species diversity
and abundance during the past 150 years are related to human activities such as water
pollution, river canalization, hydropower development, and species introductions. Changes
in the fish fauna, as documented by catch statistics, are characterized by a pronounced
decrease in rheophilic species, and a moderate increase in limnophilic species. All anadromous
fish species in the upper reaches of the Rhine have become extinct: sturgeon around 1850,
Allis shad shortly before 1900, and sea lamprey, sea trout and atlantic salmon between 1950
and 1960. The fate of these fish species is exemplified by that of the salmon whose decline is
closely related to the construction of hydropower dams which obstructed access to the
spawning grounds. The fish fauna of present days is relatively rich, with about 37 fish and one
or two cyclostome species. Six fish specics are introductions. lt seems that improvements in
water quality since 1970 are having a positive effect on the fish. However, rheophilic species
still suffer from silting of the river bed, and from the lack of fast-flowing stretches and other
suitable habitats. A two-step rehabilitation programme initiated by the International Commission
for the Protection of the Rhine is aiming, first, at restoring salmon stocks in the Rhine
by improving upstream passage of the fish by the year 2000. In a second step, the creation of
a more diverse watercourse, with backwaters, shallow and deep areas, and refuge zones for
aquatic organisms is expected to help increase species diversity.
Reduction of substituted nitrobenzenes in aqueous solutions containing natural organic matter
Natural organic matter (NOM) from a variety of sources has been shown to mediate the reduction of substituted nitrobenzenes in aqueous solution containing hydrogen sulfide. Pseudo-first- order rate constants were proportional to NOM concentrations and increased with increasing pH and decreasing reduction potential (<i>E</i><sub>h</sub>) of the solution. At fixed pH and <i>E</i><sub>h</sub>, the carbon-normalized rate constants (<i>k</i><sub>NOM</sub>) of a given compound varied less than 1 order of magnitude among NOMs derived from various natural waters. The effect of substituents on the reaction rate could be described by a linear free energy relationship (LFER) of the general form log <i>k</i><sub>NOM</sub> = <I>a</I><i>E</i><sub>h</sub><sup>1'</sup>(ArNO<sub>2</sub>) + <I>b</I>, where <i>E</i><sub>h</sub><sup>1'</sup>(ArNO<sub>2</sub>) is the one-electron reduction potential of the nitroaromatic compound. Such LFERs were applied successfully to predict the <i>k</i><sub>NOM</sub> values of previously untested compounds. The results of this study suggest that hydroquinone moieties within the NOM may play a pivotal role in the mediation of electron-transfer reactions involving organic pollutants.
Improvement of secondary clarifiers efficiency by porous walls
Parameters influencing the flow field in final settling tanks are discussed. The effects of a porous wall on the hydraulics as well as on the flocculation of activated sludge are described. The flow upstream of the wall is rendered more uniform by the increased overall pressure and by deflecting the bottom current to the upward direction, while the hole jets beyond the wall induce velocity gradients to enhance flocculation and improve settling properties of the sludge. Installing several porous walls improves the effects, such as increasing the volume with forward flow, preventing strong density currents and improving the stability of tank performance at wet-weather flow. A method to optimize the porosity and the hole size is introduced.