消融的冰川：加拿大班夫国家公园亚高山带鲍湖中持久性有机氯的主要来源

有机氯杀虫剂和多氯联苯（PCB）是环境中普遍而稳固的化合物。现已查明，由于它们从温暖的地区逐渐蒸发出来，并在较冷的地区凝聚下来，因而它们富集在寒冷的环境中。在本研究中，我们的结果是，消融的冰川供给阿尔伯达亚高山带湖泊中的有机氯输入量为50%～97％，而提供的水量为73％。对氚的分析结果表明，在夏季的中、晚期，至少10％的冰川消融物是在1950～1970年期间沉积下来的，这期间它受到有机氯更多的污染。这一发现表明，气候变暖可能会使消融的冰川成为日益增多的淡水污染物来源。由于有机物贫乏的冰川粘土对多氯联苯这样的疏水化合物的吸附能力有限，因此冰川水流带来的有机氯大多呈溶解状态。     

Influence of acidity level in simulated rain on disease progress in four plant pathosystems

Field investigations were performed in 1984-1985 on the effects of acidity level in simulated rain on disease dynamics in four pathosystems: alfalfa leaf spot (ALS), peanut leaf spot (PLS), potato late blight (PLB), and soybean brown spot (SBS). Studies were performed in an ambient rain exclusion apparatus with simulated rain acidity levels of pH 2.8, 3.6, 4.2, 4.8, or 5.6 and four plots per pH level. In 1984 for ALS and PLB, rain was simulated three times a week at 6-8 mm per event. For PLS and SBS in 1984 and for PLB, PLS, and SBS in 1985, rain was simulated twice a week at 13-16 mm per event with a 10 min pause halfway through each event. Disease was assessed three times a week. In 1984, no significant effect of acidity level in simulated rain on disease severity was detected in any pathosystem. Severity of PLB differed among treatments in 1985 with significant quadratic and cubic components for the dose-response relationship. PLS severity decreased with increasing level of acidity in simulated rain in 1985 and the dose-response relationship was linear. No differences in severity of ALS or SBS due to acidity of simulated rain were found. Thus, disease response to acidity of simulated rain is system dependent.     

A combination of ion exchange and electrochemical reduction for nitrate removal from drinking water. Part II: electrochemical treatment of a spent regenerant solution.

The process of electrochemical treatment of a solution after strong basic anion exchanger regeneration was studied. The goal of the study was to reduce the nitrate content in the solution to allow its use in a closed loop. Diaphragmless, flow-through cells in a recirculation mode with and without a fluidizing bed of inert particles in the interelectrode space equipped with copper (Cu) cathodes and activated titanium anodes were used. The temperature was maintained at 20 degrees C. To assess the influence of recirculation of the regenerant solution on the quality of the treated water, the effect of the addition of copper ions to the solution, postelectrolysis cathode treatment, and enhanced mass transfer on the electrolysis results with respect to current efficiency and residual nitrate and nitrite concentration were investigated using an artificial solution. On the basis of the experimental results, a laboratory-scale unit for selective nitrate removal was designed and constructed that integrated ion exchange and electrochemical cell to one assembly. The process of recirculation of regenerant solution was tested using groundwater.     

Solute transport in crystalline rocks at Aspö--I: geological basis and model calibration

Water-conducting faults and fractures were studied in the granite-hosted Asp? Hard Rock Laboratory (SE Sweden). On a scale of decametres and larger, steeply dipping faults dominate and contain a variety of different fault rocks (mylonites, cataclasites, fault gouges). On a smaller scale, somewhat less regular fracture patterns were found. Conceptual models of the fault and fracture geometries and of the properties of rock types adjacent to fractures were derived and used as input for the modelling of in situ dipole tracer tests that were conducted in the framework of the Tracer Retention Understanding Experiment (TRUE-1) on a scale of metres. After the identification of all relevant transport and retardation processes, blind predictions of the breakthroughs of conservative to moderately sorbing tracers were calculated and then compared with the experimental data. This paper provides the geological basis and model calibration, while the predictive and inverse modelling work is the topic of the companion paper [J. Contam. Hydrol. 61 (2003) 175]. The TRUE-1 experimental volume is highly fractured and contains the same types of fault rocks and alterations as on the decametric scale. The experimental flow field was modelled on the basis of a 2D-streamtube formalism with an underlying homogeneous and isotropic transmissivity field. Tracer transport was modelled using the dual porosity medium approach, which is linked to the flow model by the flow porosity. Given the substantial pumping rates in the extraction borehole, the transport domain has a maximum width of a few centimetres only. It is concluded that both the uncertainty with regard to the length of individual fractures and the detailed geometry of the network along the flowpath between injection and extraction boreholes are not critical because flow is largely one-dimensional, whether through a single fracture or a network. Process identification and model calibration were based on a single uranine breakthrough (test PDT3), which clearly showed that matrix diffusion had to be included in the model even over the short experimental time scales, evidenced by a characteristic shape of the trailing edge of the breakthrough curve. Using the geological information and therefore considering limited matrix diffusion into a thin fault gouge horizon resulted in a good fit to the experiment. On the other hand, fresh granite was found not to interact noticeably with the tracers over the time scales of the experiments. While fracture-filling gouge materials are very efficient in retarding tracers over short periods of time (hours-days), their volume is very small and, with time progressing, retardation will be dominated by altered wall rock and, finally, by fresh granite. In such rocks, both porosity (and therefore the effective diffusion coefficient) and sorption K(d)s are more than one order of magnitude smaller compared to fault gouge, thus indicating that long-term retardation is expected to occur but to be less pronounced.     

Cadmium in naturally-occurring water hyacinths

Water hyacinth [$\text{Eichhornia}$$\text{crassipes}$ (Mart.) Solms] is an effective fertillizer, mulch, soil amendment and fodder for cattle and sheep. The consequences of the ability of the plant to accumulate heavy metals needs consideration. Small and large water hyacinth ecotypes collected from two “rural” rivers in Florida, the Peace and Withalachoochee respectively, were examined for an accumulation of cadmium from the natural environment. Less than trace amounts (below limits of detection, 2.5ppb) were present. Water hyacinths tested for cadmium accumulation under laboratory conditions exhibited a pronounced ability to absorb and accumulate the metal. The roots contained 0.982 mg of the 2.0 mg cadmium presented to the plant. The distribution of the metal within the plant was 76.7% in the roots, 22.4% in the stems with the remainder in the leaves. Of the total cadmium presented to the plant, 80.8 ± 3.0% was recovered by the plant after 7 days, the mean generation time of the plant. With increasing urbanization, accumulation of cadmium by water hyacinths exists. It is either an asset or a potential hazard and needs to be appreciated.     

Time of flight secondary ion mass spectrometry studies of the distribution of metals between the soil, rhizosphere and roots of Populus tremuloides Minchx growing in forest soil

Time of flight secondary ion mass spectroscopy has been used to study the metal distribution at the soil/root interface of tree roots extracted from smelter-impacted soils. The results, augmented by scanning electron microscopy, show that the technique is capable of resolving metal distributions at the cellular level. In addition, the distribution of metals between the root plaque and the root interior may be useful in interpreting local metal transport mechanisms.     

A combination of ion exchange and electrochemical reduction for nitrate removal from drinking water. Part I: nitrate removal using a selective anion exchanger in the bicarbonate form with reuse of the regenerant solution.

The process of selective nitrate removal from drinking water by means of ion exchange was studied. A commercial strong base anion exchanger with triethylammonium (-N+Et3) functional groups was used in the bicarbonate (HCO3-) and carbonate (CO3(2-)) form. The aim of this study was to optimize ion-exchanger regeneration in view of the subsequent electrochemical reduction of nitrates in the spent regenerant solution. The effects of ion-exchanger form, concentration of regenerant solution, and presence of nitrates, chlorides, and sulphates in the regenerant solution were studied. The strong base anion exchanger in HCO3- form that was investigated was able to treat 270 bed volumes of model water solution containing 124 mg dm(-3) nitrates. To achieve adequate regeneration of the saturated anion exchanger, it is necessary to use approximately 30 bed volumes of fresh 1-M sodium bicarbonate (NaHCO3) regenerant solution. The presence of residual 50-mg dm(-3) nitrates in the regenerant solution, treated by electrolysis, resulted in an increase in the dose of regenerant solution to 35 bed volumes and a decrease in the subsequent sorption run of approximately 13%. The volume of applied regenerant solution was high, but the consumption of NaHCO3 for regeneration was low.     

Klima?nderungen: M?gliche Ursachen in Vergangenheit und Zukunft

In this overview two definitions of climate are presented, from the meteorological point of view and from the climate system’s point of view. The origin of climate change is discussed, i.e., externally forced variability and free, or internal variability that is caused without external trigger by internal instabilities of the system. Both, forced and free variability can appear as periodic, randomly quasi-periodic, and abrupt climate change. Finally, various possibilities of climate forecast are considered.

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Klima?nderungen: M?gliche Ursachen in Vergangenheit und Zukunft

Zusammenfassung  In diesem übersichtsartikel werden zwei Klimadefinitionen, die meteorologische und die systemanalytische, vorgestellt. Verschiedene Ursachen für Klima?nderungen werden vergleichend diskutiert: die extern angetriebene Klimavariabilit?t und die ohne ?u?eren Ansto?, aufgrund von internen Instabilit?ten im System ausgel?ste, freie oder interne Klimavariabilit?t. Sowohl die angetriebene als auch die freie Klimavariabilit?t kann sich durch periodische, zuf?llig periodische und abrupte Klima?nderungen bemerkbar machen. Abschlie?end werden die verschiedenen M?glichkeiten der Klimavorhersage betrachtet.

Professor Dr. Martin Claussen ist amtierender Direktor des Potsdam-Instituts für Klimafolgenforschung und Vorsitzender der Deutschen Meteorologischen Gesellschaft (Amtsperiode 2003–2005). Sein aktuelles Forschungsgebiet umfasst die Klimasystemmodellierung einschlie?lich der Pal?oklimamodellierung, wobei die Wechselwirkung zwischen dem physikalischen Klimasystem und der Biosph?re im Vordergrund der Forschung steht. Professor Claussen ist ausgebildeter Meteorologe und lehrt zurzeit Klimaphysik an der Universit?t Potsdam.