The Influence of Atmospheric N Deposition on Nitrous Oxide and Nitric Oxide Fluxes and Soil Ammonium and Nitrate Concentrations

The deposition of atmospheric N to soils provides sources of available N to the nitrifying and denitrifying microbial community and subsequently influences the rate of NO and N₂O emissions from soil. We have investigated the influence of three different sources of enhanced N deposition on NO and N₂O emissions 1) elevated NH₃ deposition to woodlands downwind of poultry and pig farms, 2) increased wet cloud and occult N deposition to upland forest and moorland and 3) enhanced N deposition to trees as NO ₃ ^– and NH ₄ ⁺ aerosol. Flux measurements of NO and N₂O were made using static chambers in the field or intact and repacked soil cores in the laboratory and determination of N₂O by gas chromatography and of NO by chemiluminescence analysis. Rates of N deposition to our study sites were derived from modelled estimates of N deposition, NH₃ concentrations measured by passive diffusion and inference from measurements of the ²¹⁰Pb inventory of soils under tree canopies compared with open grassland. NO and N₂O emissions and KCl-extractable soil NH ₄ ⁺ and NO ₃ ^– concentrations all increased with increasing N deposition rate. The extent of increase did not appear to be influenced by the chemical form of the N deposited. Systems dominated by dry-deposited NH₃ downwind of intensive livestock farms or wet-deposited NH ₄ ⁺ and NO ₃ ^– in the upland regions of Britain resulted in approximately the same linear response. Emissions of NO and N₂O from these soils increased with both N deposition and KCl extractable NH ₄ ⁺ , but the relationship between NH ₄ ⁺ and N deposition (ln NH ₄ ⁺ = 0.62 ln N_deposition + 0.21, r ² = 0.33, n = 43) was more robust than the relationship between N deposition and soil NO and N₂O fluxes.     

Measuring Aerosol and Heavy Metal Deposition on Urban Woodland and Grass Using Inventories of 210Pb and Metal Concentrations in Soil

The deposition of aerosols to trees has proved very difficult to quantify, especially in complex landscapes. However, trees are widely quoted to be efficient scavengers of particles from the atmosphere, and a growing proportion of the pollutant burden in the atmosphere is present in the aerosol phase. In this study, the deposition of aerosols onto woodland and grass was quantified at a range of locations throughout the West Midlands of England. The sites included mature deciduous woodland in Edgbaston, and Moseley, and mixed woodland at sites within Sutton Park, a large area of semi-natural vegetation. Aerosol deposition to areas of grassland close to the woodland at each site was also measured. Detailed inventories of ²¹⁰Pb in soils within the woodland and in grassland soils, together with concentrations in the atmosphere and precipitation, provided the necessary data to calculate the long-term (about 40 years) annual deposition of sub-micron aerosols onto grassland and woodland. The soil inventories of ²¹⁰Pb under woodland exceeded those under grass, by between 22% and 60%, with dry deposition contributing 24% of the total input flux for grass and 47% for woodland. The aerosol dry deposition velocity to grassland averaged 3.3 mm s^-1 and 9 mm s^-1 for woodland. The large deposition rates of aerosols onto woodland relative to grass or other short vegetation (× 3), and accumulation of heavy metals within the surface horizons of organic soils, leads to large concentrations in soils of urban woodland. Concentrations in the top 10 cm of these woodland soils averaged 252 mg kg^-1 for Pb with peaks to 400 mg kg^-1. Concentrations of Cd averaged 1.4 mg kg^-1, Cu, 126 mg kg^-1, Ni 23 mg kg^-1 and Zn 173 mg kg^-1. The accumulated Pb in urban woodland soils is shown to be large relative to UK emissions.     

Determination and assessment of the characteristic values for the evaluation of the thermal safety of chemical processes

Experience gained in the chemical industry in testing and assessing the thermal safety of chemical processes is published in this paper. Isothermal and adiabatic tests, which are the most important methods for both small and large quantities, are described and discussed. Methods for testing the thermal hazards of primary or desired reactions are also included, e.g. reaction calorimetry, adiabatic methods, investigations using a sampling method. More important are the criteria for assessing the test results. On the basis of energies produced by primary and secondary reactions and the temperature ranges within which they take place, thermal hazards can be predicted. If the rules for the safe design of batch and semi-batch reactions are observed, it is possible to control the thermal behaviour of reactions.     

Conversion of temperate forests into heaths: Role of ecosystem disturbance and ericaceous plants

Fire and logging in nutrient-poor temperate forests with certain ericaceous understory plants may convert the forests into heaths. The process of disturbance-induced heath formation is documented by using examples ofCalluna in western Europe,Kalmia in Newfoundland, andGaultheria (salal) in coastal British Columbia. In a cool, temperate climate, rapid vegetative growth ofCalluna, Kalmia, and salal following disturbance results in increasing organic accumulation (paludification), nutrient sequestration, soil acidification, and allelochemicals. These are thought to be the main reasons to conifer regeneration failure in disturbed habitats. If continuation in forest is a land-use objective, then temperate forests with an ericaceous understory should not be logged unless effective silvicultural methods are devised to control the ericaceous plants and restore forest regeneration. Preharvest vegetation control may be considered as an option. Failure to control the understory plants may lead to a long-term vegetation shift, from forest to heathland, particularly in nutrient-poor sites. Successful methods of controllingKalmia andGaultheria, however, have yet to be developed. While theKalmia- andGaultheria- dominated heathlands are undesirable in Canada and the Pacific Northwest, a wide range ofCalluna heathlands of western Europe are being conserved as natural and seminatural vegetation.     

Flocculants—an Ecofriendly Approach

Although water-soluble synthetic polymers find wide applications as flocculants, the potential problem associated with their use is lack of biodegradability and high cost. Polysaccharides owing to their distinctive features like ability to undergo different chemical reactions, biodegradability and sustainability inspire hope to obtain effective, economical viable and safe substitute of the synthetic flocculants. In this regard, chemical modification of Cassia tora and guar gum was carried out through different substitution and grafting reactions. The modified products were tested against kaolin under laboratory conditions vis-a-vis polyacrylamide based synthetic flocculant.     

Action and composition of the alarm pheromone of the bedbugCimex lectularius L.

The Science of Nature -     

Relativitätstheorie als didaktische Herausforderung

The theory of relativity has been considered as one of the most abstract and most difficult theories at the turn of the century. Today relativity is taught at high schools. This process is explained here by the increased faith in this theory and by better verbal explanations of the twin paradox and other effects of relativity. The development of new audiovisual aides for the teaching of relativity and other fields of modern physics is seen here as one of the main didactical challenges for the future.     

Physiologische Anpassungen eines marinen insekts. II. Die Eigenschaften von schwimmenden und absinkenden Eigelegen

The gelatinous egg-masses of Clunio marinus (Diptera; Chironomidae) consist of a tube of jelly containing up to 175 eggs. The swimming egg-mass of the Atlantic populations (Race A) and the sinking egg-mass of the Baltic populations (Race B) have a higher density than the sea water, on which the female spawns; salinity is not important to the swimming or sinking of the egg-masses. Density and sinking velocity of gelatinous egg-masses from Atlantic midges are significantly higher than those from Baltic midges if the eggs are laid on water of the same salinity. The density of the eggs and the quantitative relation of eggs to jelly are the same in both races. The jelly of the egg-masses from the Baltic Sea race swells more than that from the Atlantic Sea race (increase of volume by absorption of water = 3-fold and 2.4-fold, respectively). During swelling the jelly alters from a trough-like shape into a tube-like from which closes around the eggs. If the surface tension of the spawning medium is lowered by use of detergents, the A-spawn will sink. A- and B-spawns occupy different positions at an oil-water interface. Interference contrast microscopy revealed that the A-jelly forms a well-defined outer line in relationship to the surrounding aqueous medium; this line is missing in the B-jelly. The morphological fine surface structures, as seen by the scanning electron microscope, do not explain the different properties of the A- and B-spawn. Extracts and hydrolysates of jelly material were separated by thin-layer chromatography. The results indicate that the spawn jelly of C. marinus consists of a polysaccharide-protein-complex, similar to the jellies of other invertebrates. It is rather probable that the chemical structure or the components of the jellies from A- and B-populations are not exactly the same; this would explain the different properties described. The ecological significance of swimming and sinking gelatinous egg-masses and the taxonomical position of both midge populations are discussed.