Study of wet and dry atmospheric deposition at two altitudes in central Switzerland

The analysis of various ions in atmospheric deposition at two altitudes (515 m and 950 m a.s.l.) in Switzerland during 1983/84 revealed that dry deposition depends more on altitude than wet deposition. During autumn and winter, when vertical air exchange is limited, dry deposition of substances from anthropogenic sources (e.g. SO₄-S) was higher at the lower site. In the course of the year, the pattern of wet deposition was independent of altitude and showed highest rates for S, N and Ca in summertime. A comparison between rates of wet, particulate and gaseous S and N deposition suggested that during the growing season wet deposition is the dominant flux. Total (wet + dry) deposition of S, N and Cl was lower than in other parts of Europe, but a substantial increase of NO₃-N deposition during the past 25 years must have occured.     

Quantifying soil organic carbon fractions by infrared-spectroscopy

Methods to quantify organic carbon (OC) in soil fractions of different stabilities often involve time-consuming physical and chemical treatments. The aim of the present study was to test a more rapid alternative, which is based on the spectroscopic analysis of bulk soils in the mid-infrared region (4000-400 cm⁻¹), combined with partial least-squares regression (PLS). One hundred eleven soil samples from arable and grassland sites across Switzerland were separated into fractions of dissolved OC, particulate organic matter (POM), sand and stable aggregates, silt and clay particles, and oxidation resistant OC. Measured contents of OC in each fraction were then correlated by PLS with infrared spectra to obtain prediction models. For every prediction model, 100 soil spectra were used in the PLS calibration and the residual 11 spectra for validation of the models. Correlation coefficients (r) between measured and PLS-predicted values ranged between 0.89 and 0.97 for OC in different fractions. By combining different fractions to one labile, one stabilized and one resistant fraction, predictions could even be improved (r=0.98, standard error of prediction=16%). Based on these statistical parameters, we conclude that mid-infrared spectroscopy in combination with PLS is an appropriate and very fast tool to quantify OC contents in different soil fractions.     

Ozone air pollution effects on tree-ring growth, delta(13)C, visible foliar injury and leaf gas exchange in three ozone-sensitive woody plant species

We assessed the effects of ambient tropospheric ozone on annual tree-ring growth, delta(13)C in the rings, leaf gas exchange and visible injury in three ozone-sensitive woody plant species in southern Switzerland. Seedlings of Populus nigra L., Viburnum lantana L. and Fraxinus excelsior L. were exposed to charcoal-filtered air (CF) and non-filtered air (NF) in open-top chambers, and to ambient air (AA) in open plots during the 2001 and 2002 growing seasons. Ambient ozone exposures in the region were sufficient to cause visible foliar injury, early leaf senescence and premature leaf loss in all species. Ozone had significant negative effects on net photosynthesis and stomatal conductance in all species in 2002 and in V. lantana and F. excelsior in 2001. Water-use efficiency decreased and intercellular CO(2) concentrations increased in all species in response to ozone in 2002 only. The width and delta(13)C of the 2001 and 2002 growth rings were measured for all species at the end of the 2002 growing season. Compared with CF seedlings, mean ring width in the AA and NF P. nigra seedlings was reduced by 52 and 46%, respectively, in 2002, whereas in V. lantana and F. excelsior, ring width showed no significant reductions in either year. Although delta(13)C was usually more negative in CF seedlings than in AA and NF seedlings, with the exception of F. excelsior in 2001, ozone effects on delta(13)C were significant only for V. lantana and P. nigra in 2001. Among species, P. nigra exhibited the greatest response to ozone for the measured parameters as well as the most severe foliar injury and was the only species to show a significant reduction in ring width in response to ozone exposure, despite significant negative ozone effects on leaf gas exchange and the development of visible foliar injury in V. lantana and F. excelsior. Thus, significant ozone-induced effects at the leaf level did not correspond to reduced tree-ring growth or increased delta(13)C in all species, indicating that the timing of ozone exposure and severity of leaf-level responses may be important in determining the sensitivity of tree productivity to ozone exposure.     

Crossed nanotube junctions

Junctions consisting of two crossed single-walled carbon nanotubes were fabricated with electrical contacts at each end of each nanotube. The individual nanotubes were identified as metallic (M) or semiconducting (S), based on their two-terminal conductances; MM, MS, and SS four-terminal devices were studied. The MM and SS junctions had high conductances, on the order of 0.1 e(2)/h (where e is the electron charge and h is Planck's constant). For an MS junction, the semiconducting nanotube was depleted at the junction by the metallic nanotube, forming a rectifying Schottky barrier. We used two- and three-terminal experiments to fully characterize this junction.     

Effects of nitric oxide and ozone on spring wheat (Triticum aestivum)

The hypothesis that stress ethylene production could determine plant sensitivity to ozone was tested with spring wheat (Triticum aestivum). The mechanism includes formation of radicals which induce peroxidative chain reactions. NO in the low ppb range could induce additional ethylene production. NO was added to three ozone levels in order to investigate its potential in enhancing ozone toxicity. Using malondialdehyde, ethane emission and activity of ascorbate peroxidase as indicators of peroxidation reactions, no indications for the postulated interaction was found. NO at low ozone concentrations induced effects on yield and physiological parameters similar to those of increased ozone concentrations, but this was not due to additional ethylene production. At higher ozone concentrations no adverse effect of NO addition could be detected.     

Equine motor neuron disease; a preliminary report

A spontaneous motor neuron disease or neuronopathy was identified in 10 horses from the northeastern United States. Signs of generalized weakness, muscle fasciculations, muscle atrophy and weight loss progressed over 1 to several months in young and old horses of various breeds. Pathologic studies revealed that degeneration and loss of motor neurons in the spinal cord and brain stem resulted in axonal degeneration in the ventral roots and peripheral and cranial nerves and denervation atrophy of skeletal muscle. Many spinal neurons were swollen, chromatolytic and contained neurofilamentous accumulations. Other cell bodies were shrunken and undergoing neuronophagia and some were lost and replaced by glia. This fatal equine motor neuron disease has not been reported previously and its cause has not been determined. The progressive weakness and wasting and the neuronal degenerative changes in these horses were similar to those described in people with sporadic amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig's disease.     

Critical level for ozone to protect agricultural crops: Interaction with water availability

A critical level for ozone has been established under the UN-ECE Convention on Long-Range Transboundary Air Pollutants (LRTAP) on the basis of data for spring wheat which ignores modifying factors. In this study, a correction factor (f[_water]) is derived for soil water availability by applying a simple model to predict the mean available soil water content (%FC) from precipitation and potential evapotranspiration, an empirical relationship between %FC and yield, and by assuming that the decrease in grain yield due to reduced soil water is proportional to the reduction in ozone sensitivity. Model inputs were temperature, radiation, and precipitation during June and July. f[_water] was tested with data obtained in years with non-limiting and limiting soil water. For a selected Swiss site, f[_water] was 1.0 in 1990 to 1993, but in 1989 and 1994, f[_water] was <1.0. the=" model=" was=" also=" used=" to=" analyze=" the=" variability=" of=">_water] across Europe, and to determine the distribution of the potential yield loss in Switzerland on a 0.5km × 0.5km scale. It is concluded that without introducing a correction factor, under dry conditions potential yield losses may be significantly overestimated.     

Monitoring Yield Loss from Ozone Pollution in a Mediterranean Environment: A Comparison of Methods

Yield losses from ozone pollution can be estimated by two methods: one involves the use of sensitive (S) and resistant (R) biotypes of white clover (Trifolium repens L., cv. Regal) exposed in ambient air, the other is based on the use of open-top chambers (OTC) supplied either with charcoal-filtered (CF) or non-filtered (NF) air. In southern Italy the two methods have been compared using the clover biotypes. The aim was (1) to compare the extent of ozone-induced yield reductions estimated by the two methods, (2) to evaluate the effect of the chamber enclosure on the growth of both biotypes, and (3) to compare plant water consumption in the different environments. On the average, the yield reduction was 23% when derived from the S/R yield ratio in ambient air, and 18% obtained by the CF/NF yield ratio of the S-type, without a significant difference between the two values. The slightly lower value for the OTC-based system may be due to the lower ozone levels in NF chambers due to losses in the ventilation system. Thus, both methods yielded equivalent yield reductions of about 20% due to ozone at this Mediterranean site. However, the higher air temperature inside OTCs influenced the plant growth, and this effect was stronger in the case of the R type. Therefore, R/S yield ratios in NF chambers differed from ambient air. Also, plant water consumption was higher in OTCs than in ambient air. The results suggest that the OTC-based method enables yield loss estimates at this Mediterranean site, in spite of chamber effects on plant growth and water use.     

Peatland subsidence and carbon loss from drained temperate fens

Peat‐forming organic soils lose large amounts of carbon and soil volume when drained. Although surface subsidence is often taken as a proxy for the associated carbon loss, other mechanisms also cause a change in volume. To infer the reliability of subsidence for estimating carbon loss, we compared long‐term subsidence rates of an 80 ha area of temperate fen that was drained 140 yr ago against estimates of subsidence based on soil bulk densities measured at four sites. Both methods correlate significantly, yield similar subsidence rates of 0.8–1.6 cm/yr and underpin the value of using profile information for inferring volumetric loss. Peat oxidation accounts for 28–64% of the loss in volume, which is equivalent to annual carbon loss rates of 2.5–5.5 t C/ha. Whereas the profile‐based method is also suitable for estimating carbon loss, the wide range of oxidative contribution to the overall subsidence indicates that subsidence alone cannot provide an unbiased estimate of carbon emission factors from drained fens.