Vertical mixing in Überlinger See,western part of Lake Constance

Depth variable vertical eddy diffusion coefficients for heat (K _z) were calculated from continuously measured temperature profiles in Überlinger See (western part of Lake Constance). The temperatures were averaged over vertical intervals of 10 m yielding 14 discrete values (maximum depth of Überlinger See: 147 m). A linear fit from 10 June to 29 September 1987 was used to smooth the significant temperature fluctuations caused by internal seiches of Lake Constance.Assuming horizontal homogeneity for the smoothed data the Gradient-Flux-Method was applied to compute vertical diffusion coefficientsK _z at different depths using the depth variable volumes and surfaces of the 14 layers. The resulting mean diffusion coefficients for the period from June to September are 0.04 cm²/s near the thermocline and up to 0.8 cm²/s in deeper strata (accuracy: ± 50%). It is shown that horizontal mixing between Überlinger See and Obersee (main lake) alters the computation ofK _z by less than 50%.A relationship betweenK _z and stability (Brunt-Väisälä) frequencyN is found which corresponds well to the theory of internal wave induced turbulence.Combining the diffusion coefficients with measured phosphorus profiles, a phosphorus flux from the hypolimnion to the epilimnion of (0.7 ± 0.4) mg P m^–2 d^–1 was calculated, corresponding to about 20% of the average external loading per area of Lake Constance in 1986.     

Vertical mixing in Überlingersee (Lake Constance) traced by SF6 and heat

Vertical mixing in Überlingersee is studied by releasing sulfur hexafluoride (SF₆) as a tracer at a central hypolimnic depth of 60 m and measuring its subsequent vertical dispersion over a period of three months. The experiment started with a streaky tracer injection of 1 liter gaseous SF₆ (STP) in August 1990. At that time the lake showed a typical strong summer stratification which in a weakened form lasts until November. From the SF₆ profiles of fifteen surveys at three sampling sites vertical diffusivitiesK _z are calculated compensating internal seiche displacement and horizontal tracer loss. Except of the bottom region no sampling site or time period is marked by significant differences in the hypolimnicK _z profile. So vertical mixing in the whole Überlingersee is described by mean diffusivities decreasing from 1.7 cm²/s at 120 m depth to 0.4 cm²/s in 30 m. The minimal value of 0.3 cm²/s in the thermocline region at 20 m depth is only based on observations in autumn. For a strong summer stratification it is certainly lower. The gradient-flux-method for heat was applied to compute a meanK _z (T) profile from continuously measured temperature profiles. Significant differences resulting from the two tracers showed, that theK _z (T) values are underestimated by up to a factor of 5 if cooling by lateral exchange is neglected. Particularly, internal seiche pumping of colder water from the adjacent Lake Obersee over the separating sill of Mainau into the deep Überlingersee basin is observed in 1990 from August onward, obviously controlling the heat budget below the sill level.     

Interaction of trace metals with natural particle surfaces: Comparison between adsorption experiments and field measurements

The distribution of the metal ions Zn and Pb between particulate and dissolved phase in river Glatt was studied by field measurements and compared with calculated simulations, using parameters obtained by adsorption experiments with natural suspended particulate material. Differences in distribution coefficients obtained from field data are observed in function of the sampling locations and of the composition of the particulate matter.Experiments in which metal ion solutions are titrated with a suspension of natural particles and analyzed by anodic stripping voltammetry, are interpreted in terms of binding capacities and conditional stability constants of Zn and Pb with the surface sites. Binding constants of a particular metal ion varied very little for all samples. We obtained mean values for the conditional average complex formation constants at pH 8 of: log^cond K _Pb = 9.44 ± 0.18 and log^cond K _Zn = 8.17 ± 0.20. At this pH, binding capacities of 5 10^–3 – 1.7 10^–2 mol/kg of particles were obtained for samples collected at different locations and times; organic material, iron and manganese oxides are considered to be the main components that control the adsorption to the particles.Distribution coefficients are calculated from the experimentally obtained binding capacities and conditional stability constants. Calculated distribution coefficients for Zn agree with those obtained from the field data and are not very sensitive to changes in the composition of the solution. Good agreement was obtained for lead as well; for some samples it was important to take two types of sites with different affinity into consideration.     

Hypolimnetic density currents traced by sulphur hexafluoride (SF6)

The artificial tracer sulphur hexafluoride (SF₆) has been used to study the density-driven deep water exchange between two sill-separated basins of Lake Lucerne, Gersauersee and Urnersee. The sources of the density gradients between the two basins are (1) salinity differences between the major inlets due to the different geology of their drainage areas, and (2) temperature differences due to spatial variation of wind forcing. Wind speeds are generally larger in Urnersee, especially in spring during the so-called Föhn events, when winds blow from the south. In contrast, Gersauersee is protected form these winds. In spring 1989, a total of 630 g of SF₆ was released at 80 to 120 m depth in the small Treib Basin located between Urnersee and Gersauersee. During about 100 days the distribution of SF₆ in the lake was determined by gaschromatography. Two models are used to quantify the exchange flow, (1) a one-box mass balance model for SF₆ in the deep part of Treib Basin, and (2) a one-dimensional diffusion/advection model describing the temporal and vertical temperature variation in Urnersee. According to the first model, the flow into the deep hypolimnion of Urnersee, decreases from 21·10⁶ m³·d^?1 at the end of March to about 8·10⁶ m³·d^?1 in late April. The second model yields similar flow rates. The decrease of the flow rate during spring, confirmed by both approaches, is consistent (1) with the decreasing strength of the density gradient above the sill during spring and early summer, and (2) with hydrographic information collected in Lake Lucerne during other years.     

Gravity field determination using boundary element methods

The Boundary Element Method (BEM), a numerical technique for solving boundary integral equations, is introduced to determine the earth's gravity field. After a short survey on its main principles, we apply this method to the fixed gravimetric boundary value problem (BVP), i.e. the determination of the earth's gravitational potential from measurements of the intensity of the gravity field in points on the earth's surface. We show how to linearize this nonlinear BVP using an implicit function theorem and how to transform the linearized BVP into a boundary integral equation using the single layer representation. A Galerkin method is used to transform the boundary integral equation using the single layer representation. A Galerkin method is used to transform the boundary integral equation into a linear system of equations. We discuss the major problems of this approach for setting up and solving the linear system. The BVP is numerically solved for a bounded part of the earth's surface using a high resolution reference gravity model, measured gravity values of high density, and a 50 50 m² digital terrain model to describe the earth's surface. We obtain a gravity field resolution of 1 1 km² with an accuracy of the order 10^–3 to 10^–4 in about 1 CPU-hour on a Siemens/Fujitsu SIMD vector pipeline machine using highly sophisticated numerical integration techniques and fast equation solvers. We conclude that BEM is a powerful numerical tool for solving boundary value problems and may be an alternative to classical geodetic techniques.     

平流及层结在阿尔卑湖泊风成扩散问题中的作用

A semi-implicit semi-spectral hydrodynamic primitive equation model is used to study tracer diffusion in homogeneous and stratified lakes. Impulsively applied spatially uniform wind is applied in the long direction of a rectangular basin with constant depth and Lake Constance. Tracer mass is released at various locations of the free surface and its spreading under the action of dijfusion and advection is studied. We show that for homogeneous basins the tracer quickly spreads over the entire water depth. Inertial waves can also be detected in the tracer concentration. On the other hand for stratified waters the tracer mass is largely confined to the epilimnion with occasional penetration into the hypolimnion where large downwelling occurs. Here Kelvinand Poincar ''e-type wave dynamics is discernable in the tracer-concentratwn-time series, the former more conspicuously at nearshore, the latter at off-shore positions.     

Biogeochemistry of iron in an acidic lake

In this paper, the fate of iron in Lake Cristallina, an acidic lake in the Alps of Switzerland, is discussed. A simple conceptual model is developed in order to explain the observed diel variation in dissolved iron(II) concentration. Biotite weathering provides reduced iron that is oxidized and subsequently precipitated in the lake. The amorphous Fe(III)hydroxide (FeOOH xH₂O), found in the sediments of Lake Cristallina, is an Fe(II) oxidation product. This oxygenation reaction is most probably catalyzed by bacteria surfaces, as indicated by the relatively high estimated oxidation rate compared to the oxidation rate of the homogeneous oxidation of inorganic Fe(II) species at the ambient pH of Lake Cristallina (pH 5.4 at 4 °C) and by the scanning electron micrograph pictures. Under the influence of light, these amorphous iron(III)hydroxide phases are reductively dissolved. The net concentration of Fe(II) reflects the balance of the reductive dissolution and the oxidation/precipitation reactions and tends to parallel the light intensity, leading to a diurnal variation in the Fe(II) concentration. The rate of the photochemical reductive dissolution of Lake Cristallina iron(III)hydroxides is greatly enhanced in situ and in the laboratory by addition of oxalate to the lake water.     

Estimation du débit de SO2, HCl et HF émis par le volcan Vulcano (Italie)

The flow rate of SO₂, HCl and HF was calculated from a transfer coefficient obtained by measuring the concentration of a tracer gas (SF₆) emitted at the plume and analysed down wind with a field gas chromatograph. The results obtained are: $$\begin{gathered} SO_2 = 2.3 \pm 0.4 t/day \hfill \\ HCl = 6.4 \pm 0.4 t/day \hfill \\ HF = 0.11 \pm 0.3 t/day \hfill \\ \end{gathered} $$      

Die Windverhältnisse am Bodensee

Summary Within the programme sponsored by the Deutsche Forschungsgemeinschaft (Bad Godesberg) in which different branches of scientific disciplines cooperated in order to investigate Lake Constance in Southern Germany, meteorology was mainly dealing with the wind situation round the Lake.Investigations by the Aerological Observatory of Friedrichshafen which was destroyed during the last war, yielded fundamental contributions to the problem of air currents on the Lake and in the outer regions of the Alps in its vicinity. With regard to the various problems in the common achievements of the Lake Constance Project of the Deutsche Forschungsgemeinschaft it proved necessary to extend the investigations across the whole region of the Lake in order to elaborate the synoptic situations of the daily and annual periodical wind systems.The vertical structure of the air currents could not be inferred but by an indirect manner, whilst its confirmation by direct aerological means is going to be studied in an additional research programme. The results of the comprehensive observational material of several years will be published in a final report by the Deutsche Forschungsgemeinschaft.Here some special results of the wind observations are presented.     

Partikelgrössenverteilung und Natürliche Koagulation im Zürichsee

The size distribution of suspended particles in Lake Zürich water shows always the same shape, irrespective of the total concentration of particles, depth or season. The particle size distribution can be described by a function of the form $$\frac{{\Delta {\rm N}(d_p )}}{{\Delta d_p }} = n(d_p ) = {\rm A}d_p^{ - m} $$ where N (d_p)=concentration of particles with diameters between d_p and d_p+Δd_p [cm^?3], d_p=particle diameter [μm], A=constant of the particle size distribution, n(d_p)=particle size distribution function. m was found to be about 3.5. Model calculations show that coagulation determines the particle size distribution. The lake model consists in three completely mixed parts: the epilimnion, the thermocline and the hypolimnion. The effect of outflow of particles by a river, sedimentation and coagulation on the particle size distribution were investigated.     

Dispersion of surface plumes in the Southern North Sea

Summary Continuous releases of fluorescent dye were made in the southern North Sea and the power law dependence of the plume width, represented by _y , against the diffusion time determined. The spreading was non-Fickian and could be represented in the form _y ² =B ² t whereB was a diffusion velocity of magnitude 1.4×10^–2 m/s. Such spreading was reproduced in both particle tracking and finite difference plume models by allowing the horizontal diffusivity,K _H, to depend linearly on diffusion time. The weakness of this method is that it is not clear how the diffusion parameters can be extrapolated to weather conditions that are different to those prevailing at the time of the experiments. However, comparable spreading rates were obtained by combining a Fickian diffusion model with an advective field that represented the near-surface current shears due to wind and waves. The resulting shear diffusion effect produced realistic simulation of the observed dispersion rates. An advantage of this approach is that it enables predictions to be made over a range of weather conditions provided that the wind and wave shears can be accurately parameterized.

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Ausbreitung von Tracerwolken an der Oberfläche in der südlichen Nordsee

Zusammenfassung Fluoreszierender Farbstoff wurde in der südlichen Nordsee kontinuierlich freigesetzt und die Breite der Wolke, repräsentiert durch _y , in Abhägigkeit von der Ausbreitungszeit bestimmt. Die Ausbreitung folgte nicht dem Fickschen Ansatz und konnte in der Form _y ² =B ² t dargestellt werden, wobeiB eine Ausbreitungsgeschwindigkeit von der Größenordnung 1.4×10^–2 m/s darstellt. Eine derartige Ausbreitung wurde sowohl mit Modellen des Partikel-Tracking als auch mit Modellen der finiten Differenzen reproduziert, wobei die horizontale AusbreitungsgrößeK _H linear von der Diffusionszeit abhängig war. Die Schwäche dieser Methode ist, daß es nicht klar ist, wie die Diffusions-Parameter für andere Wetterbedingungen als zur Zeit des Experiments zu extrapolieren wären. Vergleichbare Ausbreitungsverhältnisse werden durch die Kombination eines Fickschen Diffusionsmodells mit einem advektiven Feld erreicht, welches die oberflächennahen durch Wind und Wellen verursachten Stromscherungen berücksichtigt. Der so resultierende Scher-Diffusions-Effekt erbrachte ein realistische Simulation der beobachteten Ausbreitung. Ein Vorteil dieses Vorgehens ist, daß es Vorhersagen über einen Bereich von Wetterbedingungen ermöglicht, vorausgesetzt, daß die durch Wind und Wellen verurschte Scherung zutreffend parameterisiert werden kann.

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La dispersion de la panache de surface dans la partie sud de la Mer du Nord

Résumé A partir de déversements continus de produits fluorescents effectués dans la partie sud de la Mer du Nord, on a pu déterminer l'expression de la largeur du panache _y , par son carré en fonction du temps de diffusion. La dispersion n'était pas du type Fickian et était représentée sous la forme _y ² =B ² t aB était une vitesse de diffusion de grandeur égale 1.4×10^–2 m/s. Une telle dispersion peut être reproduite par une modélisation du panache à la fois par suivi de particules et aux différences finies en admettant que le coefficient de diffusion horizontaleK _H dépendait linéairement du temps. L'inconvénient de cette méthode est qu'il n'est pas facile de savoir comment les paramètres de diffusion peuvent être extrapolés à des conditions météorologiques différentes de celles prévalant au moment des expériences. Quoi qu'il en soit, des taux de dispersion comparables ont été obtenus en combinant un modèle de diffusion Fickian avec un champ d'advection qui représentait les cisaillements de courant de surface dus au vent et aux vagues. L'effet de diffusion du cisaillement résultant produisit une simulation réaliste des taux de dispersion observés. Un avantage de cette approche est de rendre possible des prédictions réalisées à travers un éventail de conditions météorologiques à condition que les cisaillements liés au vent et aux vagues puissent être paramétrisés avec précision.

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Numerical simulations of non-ergodic solute transport in three-dimensional heterogeneous porous media

Numerical simulations of non-ergodic transport of a non-reactive solute plume by steady-state groundwater flow under a uniform mean velocity, , were conducted in a three-dimensional heterogeneous and statistically isotropic aquifer. The hydraulic conductivity, K(x), is modeled as a random field which is assumed to be log-normally distributed with an exponential covariance. Significant efforts are made to reduce the simulation uncertainties. Ensemble averages of the second spatial moments of the plume and the plume centroid variances were simulated with 1600 Monte Carlo (MC) runs for three variances of log K, _Y²=0.09, 0.23, and 0.46, and a square source normal to of three dimensionless lengths. It is showed that 1600 MC runs are needed to obtain stabilized results in mildly heterogeneous aquifers of _Y²0.5 and that large uncertainty may exist in the simulated results if less MC runs are used, especially for the transverse second spatial moments and the plume centroid variance in transverse directions. The simulated longitudinal second spatial moment and the plume centroid variance in longitudinal direction fit well to the first-order theoretical results while the simulated transverse moments are generally larger than the first-order values. The ergodic condition for the second spatial moments is far from reaching in all cases simulated and transport in transverse directions may reach ergodic condition much slower than that in longitudinal direction.     

Sulfur Hexafluoride and Potassium Bromide as Groundwater Tracers for Managed Aquifer Recharge

Sulfur hexafluoride (SF₆) is an established tracer for use in managed aquifer recharge projects. SF₆ exsolves from groundwater when it encounters trapped air according to Henry's law. This results in its retardation relative to groundwater flow, which can help determine porous media saturation and flow dynamics. SF₆ and the conservative, nonpartitioning tracer, bromide (Br⁻ added as KBr), were introduced to recharge water infiltrated into stacked glacial aquifers in Thurston County, Washington, providing the opportunity to observe SF₆ partitioning. Br⁻, which is assumed to travel at the same velocity as the groundwater, precedes SF₆ at most monitoring wells (MWs). Average groundwater velocity in the unconfined aquifer in the study area ranges from 3.9 to 40 m/d, except in the southwestern corner where it is slower. SF₆ in the shallow aquifer exhibits an average retardation factor of 2.5 ± 3.8, suggesting an air-to-water ratio on the order of 10⁻³ to 10⁻² in the pore space. Notable differences in tracer arrival times at adjacent wells indicate very heterogeneous conductivity. One MW exhibits double peaks in concentrations of both tracers with different degrees of retardation for the first and second peaks. This suggests multiple flowpaths to the well with variable saturation. The confining layer between the upper two aquifers appears to allow intermittent connection between aquifers but serves as an aquitard in most areas. This study demonstrates the utility of SF₆ partitioning for evaluating hydrologic conditions at prospective recharge sites.     

Correlated seasonal and climatic variations of trace constituents in the stratosphere

Summary Spectrometric experiments performed, in November 1976, within the framework of the Latitude Survey Mission on board the NASA Convair 990 from Ames Research Center are briefly deseribed. The results presented concern odd nitrogen molecules, HCl and water vapor. In terms of vertical column density, HNO₃ is predominant over NO+NO₂ at all latitudes higher than 40 degrees. A seasonal variation of NO₂ abundance is observed, with larger values in the summer hemisphere at high latitude. The mean zenith column density of HCl above 11 km is 1.5×10¹⁵ mol.cm^–2, with no evidence for any seasonal or climatic variation. Local number densities as high as 1.4×10¹⁰ mol.cm^–3 for HNO₃ and 5.4×10¹⁴ mol.cm^–3 for water vapor have been measured during the same flight near 11 km.     

L'ordre du coefficient de récombinaison dans la coucheE

Résumé On propose une méthode de détermination de l'ordre du coefficient équivalent de récombinaison en n'utilisant que les données ionosphériques. A cette fin on évalue l'apport de la vitesse des changements passagersdN _m E/dt dans la densité électroniqueN _m E. L'évaluation se fait en présence d'une série de valeurs choisies de , on observe laquelle des courbes définis _m (t) dans cette étude coïncidera de plus près avec _m (t) mesurée. Les changements de montrés sur la figure 4 sont obtenus de cette manière. La valeur diurne de varie de (0.5÷1) 10^–7 cm³ sec^–1; peu après le lever et peu avant le coucher du soleil devient >10^–7 cm³ sec^–1. Lorsque cos>0, d'après la règle décrcit et devient 10^–8 cm³ sec^–1. Les explications des changements de obtenus de cette manière sont données en rendant compte des changements par rapport aux ions atomiques et moléculaires, à la disparition rapide des ions positifs pendant le coucher du soleil en présence d'un coefficient de récombinaison plus grand et des changements de température eventuels. La symétrie ou l'asymétrie des fréquences critiquesf ₀ E quand cos sont égaux permettent dans la marche diurne de juger de l'ordre de . Toutes ces évaluations indiquent également des valeurs de environ 10^–7 cm³ sec^–1. En précisant des mesures def ₀ E il est possible de définir non seulement l'ordre, mais aussi la valeur de elle-même.

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Summary A method for the determination of the order of the equivalent recombination coefficient is suggested, by using ionospheric data only. The increase in the speed of temporary changes indN _m /dt in the electronic densityN _m E is estimated for this purpose. The estimation is done with series of selected for the sake of expediency values of , following at the same time which curves _m (t), determined in the course of work, will coincide most closely with the _m (t) measured. The changes in , shown in figure 4, have been obtained in this way. The diurnal value of is in the range of (0.5 to 1) 10^–7 cm³ sec, being >10^–7 cm³ sec a little after sunrise and a little prior to sunset. At cos<0, by rule decreases and becomes 10^–8 cm³ sec. Explanations of the changes thus obtained in are indicated, taking into consideration the relation of atomic and molecular ions, the rapid disappearance of positive ions at sunset with a higher recombination coefficient and eventual temperature changes. From the symmetry or asymmetry of the critical frequencies off ₀ E at equal cos in the course of the day it can also be judged for the order of . All those estimates show values of in the range of 10^–7 cm³ sec. In the case of precise measurements off ₀ E, not only the determination of the order but also the real value of is possible.

     

Groundwater dating with 3H and SF6 in relation to mixing patterns,transport modelling and hydrochemistry

A comprehensive study of a sandy aquifer of deltaic origin in southern Poland included water chemistry, isotopes, dissolved trace gases and transport modelling. Tritium, sulphur hexafluoride (SF₆) and freons (F‐11, F‐12 and F‐113) showed the presence of modern waters in the recharge areas and shallow confined parts of the aquifer. The presence of older Holocene waters farther from the recharge areas was indicated by lack of ³H, SF₆ contents ≤0·02 fmol l⁻¹ and relatively low ¹⁴C values. The discharge from the system is by upward seepage in the valley of a major river. Pre‐Holocene waters of a cooler climate, identified on the basis of δ¹⁸O, δ²H, ¹⁴C, Ne and Ar data, were found in some distant wells. Concentrations of N₂, Ne and Ar determined by gas chromatography were used for calculating the noble gas temperatures, air excess needed for correction of SF₆, and nitrogen content released by denitrification process. The time series of ³H content available for some wells supplied quantitative information on age distributions and the total mean ages of flow through the unsaturated and saturated zones. The derived ³H age distributions turned out to be very wide, with mean values in the range of about 30 to 160 years. For each well with determined ³H age, the SF₆ data showed either a lower age range or the possibility of a lower age as expected due to shorter travel times of SF₆ through the unsaturated zone, which most probably also resulted in different types of age distributions of these tracers. Freons appeared to be of little use for individual age determinations. A quantitative estimation of two‐component mixing from SF₆ ³H relations is not possible unless the travel time of ³H through the unsaturated zone is comparable to that of SF₆. The ratio of integrals of the response function over the age range with tracer and the whole response function yields the ratio of water with tracer to total flow of water. That ratio is a tracer‐dependent function of time. Transport modelling of SF₆ tracer done with MT3D code yielded initially large discrepancies between calculated and measured tracer concentrations. Some discrepancies remained even after calibration of the transport model with SF₆. Simulation of tritium contents with a calibrated transport model yielded reasonable agreement with measured contents in some wells and indicated a need for further investigations, particularly in the eastern part of the aquifer. The existence of distinct hydrochemical zones is consistent with the tracer data; young waters with measurable ³H and SF₆ contents are aerobic and of HCO₃ Ca or HCO₃ SO₄ Ca types. Slightly elevated Na and Cl contents, as well as the highest concentrations of SO₄ and NO₃ within this zone are due to anthropogenic influences. Anaerobic conditions prevail in the far field, under the confining cover, where pre‐bomb era Holocene waters dominate. In that zone, dissolved oxygen, NO₃ and U contents are reduced, and Fe, Mn and NH₄ contents increase. In the third zone, early Holocene and glacial waters occur. They are of HCO₃ Ca Na or HCO₃ Na types, with TDS values higher than 1 g l⁻¹ and Na content higher than 200 mg l⁻¹, due to either small admixtures of ascending or diffusing older water or freshening of marine sediments, a process that is probably occurring till the present time. Copyright © 2005 John Wiley & Sons, Ltd.     

Low genetic variation in perch (Perca fluviatilis L.) from three major European drainage systems in Switzerland

Previous genetic studies on perch (Perca fluviatilis L.) in northern and southern regions of Europe have shown low heterozygosity. No such investigation has been conducted in the central part of Europe. The genetic variability ofP. fluviatilis in four Swiss lakes (Lake Constance, Lake Zürich, Lake Geneva and Lake Maggiore) was investigated. These four lakes belong to three different drainage systems (Rhine, Rhone and Po) without connections. A total of 136 fish were analysed electrophoretically. Only one locus (SOD ^*) was highly polymorphic in Lake Constance among the 27 loci studied. The expected heterozygosities for each population and for the total population were higher than in the previous studies but low (H _S= 0.38–2.7%;H _T=1.22%) and Nei's genetic distances were small (0.000–0.003). However, the jack-knifed mean of the Wright'sF _STwas calculated as 0.142, which indicates modest genetic differentiation among the perch populations in Switzerland, due to the differentiated population in Lake Constance.     

Effectivity of dissolved SF6 tracer for clarification of rainfall–runoff processes in a forested headwater catchment

Understanding rainfall‐runoff processes is crucial for prevention and prediction of water‐related natural disasters. Sulfur hexafluoride (SF₆) is a potential tracer, but few researches have applied it for rainfall‐runoff process studies. We observed multiple tracers including SF₆ in spring water at 1‐ to 2‐hr intervals during rainstorm events to investigate the effectivity of SF₆ tracer in rainfall–runoff studies through the clarification of rainfall–runoff process. The target spring is a perennial spring in a forested headwater catchment with an area of 0.045 km² in Fukushima, Japan. The relationship between the SF₆ concentration in spring water and the spring discharge volume was negative trend; the SF₆ concentration in spring water becomes low as the spring discharge volume increases especially during rainstorms. The hydrograph separation using SF₆ and chloride ion tracers was applied for determining the contribution of principal sources on rainfall–runoff water. It suggested more than 60% contribution of bedrock groundwater at the rainfall peak and high percentage contribution continued even in the hydrograph recession phase. Based on observed low SF₆ concentration in groundwater after heavy rainfall, the replacement of groundwater near the spring with bedrock groundwater is indicated as a mechanism for water discharge with low SF₆ concentration during rainfall events. Consequently, rainstorm events play an important role as triggers in discharging water stored in the deeper subsurface area. In addition, SF₆ tracer is concluded as one of the strongest tracers for examining rainfall–runoff process studies. And, therefore, this study provided new insights into the dynamics of groundwater and its responses to rainfall in terms of SF₆ concentration variance in water in headwater regions.     

Box and Gaussian plume models of the exhaust composition evolution of subsonic transport aircraft in- and out of the flight corridor

A box and a Gaussian plume model including gas-phase photochemistry and with plume dispersion parameters estimated from the few available plume observations are proposed and used for evaluation of photochemical transformations of exhausts from a single subsonic transport aircraft. The effects of concentration inhomogeneities in the plume cross section on the photochemical sources and sinks in the plume are analyzed for various groups of compounds. The influence of these inhomogeneities on the rate and on the mass of ambient air entrainment into the plume are studied also by comparing the box and the Gaussian plume model simulations during the first hours of their life. Due to the enterance of HO_X and NO_X from ambient air into the plume with rates varying from the wind shear and turbulence conditions, the rate of emitted NOX oxidation in the plume is dependent on these and also on the background concentration levels of HO_X and NO_X.     

Sauerstoffzehrungsraten von Profundalsediment des Bodensee-Obersees unter oxischen und anoxischen Bedingungen

Oxygen uptake rates by the sediment have been determined in a natural stratified sediment-water system from Lake Constance (Obersee, max. depth). After oxic preconditioning of the system the uptake rates ranged between 855 and 1,062 mg·m^?2·d^?1; after anoxic preconditioning of the system they ranged between 3,405 and 3,794 mg·m^?2·d^?1. These data, and the electron activity buffer capacity and oxygen consumption intensity as found in Lake Constance profundal water, show that the oxic-anoxic transition will happen here at the earliest after 142 days (about 4.5 months) of total oxygen isolation. Reoxygenation requires at least 3.7 times higher O₂ input than supposed for a ‘normal’ winter circulation in Obersee.