No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

A linear multiple regression statistical model is applied to estimate the solar induced component of odd nitrogen variability in the stratosphere and lower mesosphere using UARS HALOE data for 1991–2003. Consistent with earlier studies, evidence is obtained for a decadal NOx variation at the highest available latitudes (50° – 70°) that projects positively onto the solar cycle. This variation, which is most statistically significant in the Southern Hemisphere, also correlates positively with the auroral Ap index. It is therefore probably caused by downward transport during the polar night of thermospheric and mesospheric odd nitrogen. In addition, at low latitudes near and above the stratopause, evidence is obtained for an inverse solar cycle NOx variation. It is suggested that this low-latitude response may be caused primarily by increased photolysis of NO under solar maximum conditions. Throughout most of the rest of the stratosphere, no statistically significant response is obtained.

European legislation has increased pressure on the use of land to represent the major disposal option for sewage sludge. Owing to their importance in regulating soil fertility, much research has been conducted into the effects of sewage sludge application on soil microorganisms. However, little knowledge is known about its effects on community dynamics of the beta-subgroup ammonia oxidising bacteria. This is despite the fact that nitrification activity of these bacteria plays an important role in soil nitrogen cycling. This investigation aimed to examine community dynamics of the beta-subgroup ammonia oxidising bacteria in sewage sludge amended soil by employing recently developed molecular based techniques. Firstly, a soil DNA extraction protocol was identified that allowed routine nested PCR amplification of 16S rDNA using beta-subgroup ammonia oxidiser directed primers. Reproducibility observed in denaturant gradient gel electrophoresis (DGGE) profiles suggested that 0.5 g samples used for DNA extraction allowed consistent detection of dominant beta-subgroup ammonia oxidiser community members. The effects of applying primary treatment sewage sludge to a variety of contrasting soils on (3-subgroup ammonia oxidiser community structure was unclear. This was partially hampered by lack of specificity of PCR primers for non ammonia oxidiser 16S rDNA sequences. Further, through measurement of net nitrification, there was no indication that sewage sludge addition stimulated the activity of nitrifier populations. Nevertheless, this study indicated the usefulness of DGGE for screening multiple environmental samples. A set of hierarchical oligonucleotide probes exhibiting specificity at the group, genus and cluster level were optimised using a non-radioactive system. These probes were used to assess the effects of application of aerobically digested sewage sludge to soil for 4 y on beta-subgroup ammonia oxidiser community structure. Despite significant changes in measurable soil parameters including net nitrification activity no changes were observed in beta-subgroup ammonia oxidiser community structure. This indicated resilience of these communities to change. A final study was conducted examining the effects of application of anaerobically digested sewage sludge to soil on beta-subgroup ammonia oxidiser community structure. Inhibition of nitrification by acetylene indicated the presence of a viable population of ammonia oxidising bacteria in continuously shaken samples of sludge. DGGE and oligonucleotide probing analysis provided evidence that sewage populations had the potential to outcompete indigenous soil populations of beta-subgroup ammonia oxidising bacteria. This was despite the fact that MPN enumeration suggested that soil populations of these bacteria were in some cases 10-fold greater than sludge populations. Evidence was also provided that suggested net nitrification to be an unreliable indicator of ammonia oxidiser activity in soil. It is possible to conclude that community structure of the beta-subgroup ammonia oxidising bacteria may be altered by application of sewage sludge to soil. The effects on community structure are likely to be influenced by both the type and level of sludge applied to soil.

No description available.

The spring application of fertiliser N often fails to stimulate grass growth in improved grass pastures on peaty soils. Fertiliser utilisation efficiencies under these conditions have been found to be low, suggesting that available N is not taken up by the plant. Previous work has suggested that in this type of system, the soil microbial biomass may function as a strong sink for fertiliser N and therefore limit plant growth in the Spring. A series of laboratory based experiments utilising reconstituted and intact cores, and homogenised peat, was set up to identify the factors controlling the competition between N uptake by plants and N immobilisation by soil microorganisms following the addition of fertiliser N to peat. Microbial biomass N concentrations were determined in order to quantify the amount of N present in the microbial pool. The use of 15N labelled fertilisers and selective biocides provides a powerful tool with which to characterise the microbial population responsible for the immobilisation of N under these conditions. Improvement of a grass pasture at Sletill Hill has resulted in the formation of a distinct layer comprised of partially decomposed roots, underneath the surface vegetation and it was within this layer, that microbial immobilisation of fertiliser N was found to occur. Approximately 30% of applied N (equivalent to ca 50 kgN ha-1) was found within the microbial biomass in this layer, 30 days after the addition of fertiliser N. Intact cores were removed from Sletill Hill and maintained under controlled abiotic conditions. Water table level and temperature were found to be important in controlling the extent of microbial immobilisation of applied N. Lowering the water table level increased the quantity of N present in plant and microbial N pools, particularly at lower temperatures (8°C). At higher temperatures (20°C), plant uptake of N tended to be less due to a restriction on plant growth caused by 'droughty' soil conditions.