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1.
The proper selection of the background electrolyte is of special importance studying element availability and mobility in the laboratory. The determination of the background solution composition can be done with the equilibrium soil solution method ESS (Matschonat and Vogt, 1997). The ESS method is a procedure to find out a salt solution of major cations and anions that does not undergo changes in its composition when brought into contact with a specific soil sample. This composition is experimentally approximated in an iterative procedure until certain quality criteria are fulfilled. We tested if the ESS method, which was developed for forest soils, can successfully be applied also to agricultural soils. The solution composition was confirmed by an independent method. We used samples of a glasshouse and an arable loess soil. Because the ESS method is relatively time and work consuming, we tested modifications which should simplify the procedure: the use of dried and frozen samples instead of field fresh soil, an approximation according to the solution's electric conductivity only, and the modeling of cation exchange to omit iteration steps. The ESS method caused slight overestimation (10–25 %) in cation concentrations, but in general, these were well met. Individual anion concentrations, however, were not buffered in this soil and could not unequivocally be determined. We recommend to adjust the anion concentrations in the ESS procedure according to their proportions in an initial water extract. As ion concentrations are functions of the soil : solution ratio, any method based on addition of water to the soil, like the so‐called soil saturation extract (Germany: Bodensättigungsextrakt), runs a risk to seriously underestimate ion concentrations at field conditions. The ESS method may therefore be especially well suited for soils with a low water content. The use of frozen soil gave good results and the omission of iteration steps by cation exchange modeling was promising and will be explored with the aim to operationalize it in forthcoming work. 相似文献
2.
This paper describes the movement of anions and cations through soils at the regional scale using block‐scale and regional simulations of one‐dimensional ion transport through cultivated soils. The simulations were based on field experiments in a region of about 10 km2 in Lower Saxony, Germany. Transport was modelled with the convection–dispersion equation, and the cation exchange was described using the Gapon equation. We evaluated the spatial variation of cation exchange parameters, obtained estimates valid at the block scale, and simulated the one‐dimensional transport of anions and cations. The movement of anions and cations was simulated over blocks using effective transport parameters calculated from local transport parameters. The approach led to a good agreement between measured and predicted concentrations of Br–, Na+, K+, Ca2+ and Mg2+ on four different 1 ha blocks. However, the mean concentrations of K+ in the soil solution in the uppermost horizons could not be described satisfactorily by the model. For the regional simulations, transport and exchange parameters were estimated by block kriging. All variograms of the exchange parameters were spatially structured with correlation lengths varying from 100 m to 300 m. Results of the regional simulations imply that Cl– and K+ were transported substantially deeper in the southern part than in the northern part of the area. The transport depth of the ions strongly depended on the pore water velocities. The simulation of solute transport to the water table showed the influence of the depth of water table on the estimated travel times, superimposing the influence of the transport parameters in the region. The results of the regional simulations also emphasize the importance of careful fertilization, especially in regions with shallow water tables such as in the north of the area. 相似文献
3.
Allgayer MC Lima-Rosa CA Weimer TA Rodenbusch CR Pereira RA Streck AF Oliveira SD Canal CW 《The Veterinary record》2008,162(25):816-819
Cloacal swabs were collected from 280 captive psittacine birds belonging to 13 species. Samples of dna were tested by PCR using a pair of primers that amplify a 284 base pair fragment of the Salmonella genus invA gene, and the PCR-positive samples were tested by standard microbiological techniques. Thirteen per cent of the samples were positive by PCR, but negative by microbiological techniques. The infection rates were significantly different among the 13 species, the most commonly infected being Amazona amazonica (28 per cent) and Amazona pretrei (20 per cent). Specific tests for Salmonella Typhimurium Salmonella Enteritidis, Salmonella Pullorum and Salmonella Gallinarum did not produce positive results. 相似文献
4.
Hanno Zielke Thomas-Benjamin Seiler Sabine Niebergall Erik Leist Markus Brinkmann Denise Spira Georg Streck Werner Brack Ute Feiler Thomas Braunbeck Henner Hollert 《Journal of Soils and Sediments》2011,11(2):352-363
Purpose
Traditionally, methods for sediment extractions are characterised using chemical analyses. However, in order to evaluate sediment extracts with regard to biological effects and, thus, bioaccessibility, extraction methods have to be compared to effect data obtained from experiments with in situ exposure scenarios, i.e., sediment contact tests. This study compares four extraction methods and sediment contact test data from a previous project with respect to predictive power in the fish embryo test with zebrafish (Danio rerio).Materials and methods
A natural and an artificial sediment spiked with a mixture of six organic pollutants (2,4-dinitrophenol, diuron, fluoranthene, nonylphenol, parathion and pentachlorophenol) were extracted using (a) membrane dialysis extraction (MDE), (b) a Soxhlet procedure, (c) hydroxypropyl-??-cyclodextrin (HPCD) or (d) Tenax®-TA. Whereas the former two are regarded being exhaustive with respect to non-covalently bound contaminants, the latter two are considered to predict bioaccessibility. Resulting extracts were tested in the fish embryo assay with D. rerio for embryotoxic and teratogenic potential.Results and discussion
Mortalities caused by organic extracts from Soxhlet extraction and MDE were high. However, HPCD extracts turned out to be at least as effective as extracts obtained with these two methods. One possible reason might be short ageing time of the spiked sediments. Only Tenax®-TA extracts gave results comparable to the sediment contact assay for natural sediment, but revealed low reproducibility. Significant differences between natural and artificial sediment were found for extracts obtained with techniques using native (i.e., non-freeze-dried) sediments, i.e., HPCD and Tenax®-TA. In contrast, MDE and Soxhlet extracts used freeze-dried sediment and did not differentiate between natural and artificial sediment. Therefore, freeze-drying has likely altered and equalised sediment properties that influence accessibility, such as composition of bacterial communities and organic matter quality.Conclusions
Four extraction methods were successfully characterised with respect to their stringency and predictiveness for bioaccessibility. MDE was confirmed as an alternative to Soxhlet extraction. High mortalities induced by HPCD extracts underline the need to include ageing into consideration when assessing sediments. Although Tenax®-TA may basically be used to predict bioaccessibility in the fish embryo test, the high variability observed warrants further investigation of the relation between effect and extractability. Apparently, freeze-drying can severely affect sediment properties, potentially eliminating individual properties of natural sediments. 相似文献5.
Crop residues and tillage are being advocated for their potential effectiveness to modify the soil hydrothermal regime. This study was carried out to quantify the effect of straw mulching and rotary hoeing on the soil water and thermal regimes of a loess soil. The field experiment consisted of four treatments: (1) no mulching and no rotary hoeing as control, (2) rotary hoeing, (3) wheat straw mulching, and (4) wheat straw mulching with rotary hoeing. During the study period from 5 August to 20 September 2002, soil water content and pressure head were measured daily at five soil depths (0.05, 0.15, 0.30, 0.45 and 0.60 m). Soil temperatures were measured at hourly resolution at three depths (0.05, 0.15 and 0.30 m). Mulching decreased soil water loss on an average by 0.39 mm d−1 and rotary hoeing increased water loss on an average by 0.12 mm d−1 as compared to control. Volumetric soil water contents at pF 1, 1.8 and 2.5 up to 30 cm depth were highest (0.418, 0.390, and 0.360 m3 m−3, respectively) with the application of wheat straw mulch and lowest (0.393, 0.363, and 0.333 m3 m−3, respectively) with the rotary hoeing. Soil thermal conductivity measured at pF 1, 1.8, 2.5, 3, and 3.7 decreased with increasing suctions in all the treatments. However, the tillage and mulching did not affect the soil thermal conductivity. Further, compared with the control, mulching reduced average soil temperatures by 0.74, 0.66, 0.58 °C at 0.05, 0.15, and 0.30 m, respectively, during the study period. The rotary hoeing tillage slightly increased the average soil temperature by 0.21 °C at 0.05 m depth compared to control. The tillage effect did not transmit to deeper depths. The numerical model Hydrus-1D was used to simulate the water and temperature regimes of the treatments. Simulations with hydraulic parameters derived from laboratory measurements did not yield satisfactory results. Only when the hydraulic parameters were optimized by the inverse method, simulations performed well. The largest deviations were observed in the wheat straw mulching treatment. Simulations were further improved by adjusting the potential evaporation rate from the measured data which was achieved by linking the inversion code UCODE to the Hydrus-1D. Soil temperatures at 0.05 and 0.15 m in all the treatments were modeled well, yielding root mean square errors between 0.3 and 1.7 °C. As for soil water, the largest temperature deviations were found for the mulching treatment. All simulations underestimated soil temperatures at 0.30 m. In conclusion, crop residue can be utilized as mulching to improve the soil hydrothermal regime and the Hydrus-1D model can be used as a tool for analyzing water and heat transport processes and for estimating hydraulic transport parameters under field conditions. 相似文献
6.
Streck AF Gava D Souza CK Gonçalves KR Bortolozzo FP Wentz I Canal CW 《Berliner und Münchener tier?rztliche Wochenschrift》2011,124(5-6):242-246
Porcine parvovirus (PPV) is a widespread DNA virus that causes reproductive failure in swine. The aim of the present study was to investigate the presence of PPV in sera of nursery piglets (healthy n = 191 and wasting n = 132) and regularly vaccinated sows (with different parity rank [PR] n = 129), collected from different herds. Altogether, 452 animals were sampled in 27 herds owned by five companies. All sera were analyzed for the presence of PPV DNA by nested-PCR. The samples from sows were in addition tested for the presence of antibodies by Hemagglutination Inhibition (HI). PPV DNA was detected in healthy piglets (15.7%), wasting piglets (18.2%) and sows (17.8%). 25 herds had at least one positive sample and four companies had positive animals. The serology revealed that 84.7% of the sows had detectable antibodies and the fourth PR sows had the highest mean PPV antibody titers. Thirteen sows (19.1%) were found to be positive for DNA detection in the presence of high levels of antibody titers (> 512). This finding indicates that PPV DNA can be detected in different swine production categories irrespective of antibody titers. 相似文献
7.
Stephan Schulz Tatiana Yuyunkina Holger Pagel Lukas Y. Wick Christian Poll Thilo Streck Ellen Kandeler Michael Schloter 《Biology and Fertility of Soils》2012,48(8):933-940
In the present study, the temporal and spatial variation of the abundance of the alkane monooxygenase gene alkB and 16S rRNA genes in different soil compartments was analysed in the presence or absence of 2-methyl-4-chlorophenoxyacetic acid (MCPA) after the addition of pea litter to soil in a microcosm study. Samples were analysed shortly after litter addition (T0) and 1?week (T1), 3?weeks (T3) and 6?weeks (T6) after the addition of litter. In addition also, the quantity and quality of litter-derived alkanes was analysed and measured. The results revealed a fast and complete degradation of MCPA in all compartments throughout the experiment. Nevertheless, significant changes in the distribution patterns of short- and middle-chained alkanes suggest an interaction of MCPA and alkane degradation. alkB gene copy numbers were highly influenced by the time point of analysis and by the investigated soil compartment. Overall, an increase in alkB gene copy numbers from T0 to T3 was visible in the upper soil compartments whereas a decrease compared to T0 was measured in the deeper soil compartments. MCPA addition resulted in an increase of alkB abundance at T6. Gene copy numbers of 16S rRNA were not influenced by sampling time and soil compartment. In contrast to the control treatments, a slight increase in 16S rRNA gene copy numbers was visible at T1 and T3 compared to T0 in all soil compartments. 相似文献
8.
Ayoup M. Ghrair Joachim Ingwersen Thilo Streck 《Water, air, and soil pollution》2009,203(1-4):155-168
Nanoparticles derived from natural materials are promising compounds in the field of environmental remediation. The present study produces and characterizes Na-zeolitic tuff in the nanorange, stabilizes the nanotuff in suspension, and investigates the effect of Na-zeolitic nanotuff on sorption of Cd. Breakdown of raw zeolitic tuff with a mean particle size of 109 μm to the nanorange was achieved by attrition milling. In the first stage of grinding, a mixture of Al-oxide beads of 1 to 2.6 mm diameter was used. The milling process lasted 4 h. In the second stage, the dried powder was milled again using a mixture of a fine zirconia beads (0.1 mm) and Al-oxide beads (1.0 mm). The powder was treated with 1 M NaCl solution. Finally, the powder was sonicated in water. After this procedure, the mean and median particle diameters were 47.6 and 41.8 nm, respectively. The nanoparticulate zeolitic tuff had a surface area of 82 m2 g?1. The estimated zero charge point of the nanoparticle suspension was 3.2. The surface zeta potential was pH dependent. The Na-zeolitic nanotuff increased Cd sorption by a factor of up to 3 compared to the raw zeolitic tuff. Our results indicate that zeolitic nanoparticles can be produced by grinding using a mixture of fine beads in an attrition mill and that this procedure increases their metal immobilizing potential. 相似文献
9.
Joachim Ingwersen Christian Poll Thilo Streck Ellen Kandeler 《Soil biology & biochemistry》2008,40(4):864-878
The detritusphere is a very thin but microbiological highly active zone in soil. To trace the fate of litter carbon in the detritusphere we developed a new 1D dynamic mechanistic model. In a microcosm experiment soil cores were incubated with 13C labelled rye residues (δ13C=299‰), which were placed on the surface. Microcosms were sampled after 3, 7, 14, 28, 56 and 84 days and soil cores were separated into layers of increasing distance to the litter. Gradients in soil organic carbon (TOC), dissolved organic carbon (DOC), microbial biomass and activity were detected over a distance of 3 mm from the litter layer. The newly developed 1D model simulates both the total carbon and the 13C carbon pools and fluxes, so that it was possible to include the 13C data in model optimisation. The special feature of the model is that it operates with two decomposer populations; the first one is assumed to be dominated by bacteria (initial-stage decomposer) and second one by fungi (late-stage decomposer). Moreover, in the model the DOC pool is divided into two sub pools. Each DOC pool is consumed by one of the decomposer populations. After parameter optimisation the model was well suited to simulate the experimental data. The model explained 92% of the observed variance. The model output provides a comprehensive insight into the carbon cycling within the detritusphere. The simulation results showed among others that after 84 days about 10% of total litter C was transferred to the soil organic matter (SOM) pool. Only 3% was located in the microbial biomass. From the evolved CO2 71% was litter-derived and 29% was soil-derived. From the litter-derived CO2, 69% was directly formed in the litter layer. The remaining 31% was transported to soil before mineralisation. Our study shows that a combination of experimental work and mathematical modelling is a powerful approach to provide a comprehensive insight into the small-scale carbon turnover in soil. 相似文献
10.