No description available.

No description available.

Organic nitrogen containing compounds represent the vast majority of natural N inputs to soils and of these, proteins, peptides and amino acids are the most significant. In order to facilitate the elucidation of both the nature and rates of the processes by which these vital nutrients are transformed in soils, an understanding of their fate at a mole; level is vital. This thesis aimed to utilise soil incubation experiments with dual (¹⁵N- and ¹³C-) labelled substrates, i.e. a suite of amino acids, individual amino acids and more complex substrates, i.e. protein and cow dung, as isotopically labelled trace enabling their N and C to be followed over time. A molecular level approach was adopted which included the application of chemically and isotopically defined substrates to soil and the use of compound-specific stable isotope (N and C) analysis to trace the fate of label into the soil amino acids (and in selected cases phospholipids, C only).

Outbreaks of viral disease in populations exposed to contaminated environments have been reported more frequently in recent years. Published studies had tried to explain virus removal based on soil properties; however, soil minerals and amorphous day minerals in the soil appear to have been overlooked. This has led to inconclusive and sometimes contradictory outcomes, which have often been compounded by small sample size. This study aims to improve the understanding of virus removal by natural soils, by examining the effect of soil property interactions on virus removal. A set of data analysis procedures was proposed to measure the effects of soil property interactions on the removal of bacteriophage MS2 and ~X174. The effects of crystalline soil minerals and amorphous content of the soils were also considered. Data analysis included univariate multiple linear and logistic regression modelling, partial correlation analysis, and means comparison. A total of 33 soil samples were collected across the county of Surrey, United Kingdom. Soil properties were examined using various physico-chemical tests. The removal of bacteriophage MS2 and 0X174 was assessed using these soils. The results showed that levels of aluminium, soil pH, total organic carbon, amorphous iron, amorphous silicon, and goethite significantly predicted the removal of MS2. For 0X174, it was aluminium, soil pH, free proton, smectite and vermiculite. Aluminium, calcium, amorphous silicon and total nitrogen divided the data into subgroups with the greatest contrast of bacteriophage removal values. Partial correlation analysis showed that calcium moderated the effect of many of the significant soil properties on the removal of both MS2 and 0X174. Verification tests performed as batch experiments using KSF, KID and nepheline syenite soils supported the finding of the regression models, while further highlighting the importance of amorphous day minerals on MS2 removal, and iron on ~X174 removal. This study showed that the influence of soil cations, soil minerals, organic matter and amorphous clay minerals should be considered together to explain virus removal in soils. This principle can also be applied to other microorganisms and land usage, in order to improve microbial risk assessment.

Concerns for soil carbon stocks with increasing global temperature have recently been raised. Adopting a multidisciplinary, reductionist approach and investigating the degradation and turnover of individual compound classes is essential in order to gain a greater knowledge of soil carbon dynamics and address the issue of soils becoming sources of carbon dioxide rather than sinks. The second most abundant natural biopolymer on earth is lignin and therefore its contribution to soil organic matter (SOM) is significant. The physical recalcitrance of lignin, together with its stability in laboratory studies has led many to assume that its degradation in soils must be slow. However, recent findings suggest that it is more easily degraded than conventionally perceived. This thesis investigates the molecular mechanisms involved in the degradation and turnover of lignin in the model system and the natural environment, linking together the associated biological and geochemical changes. White rot fungi are the primary degraders of lignin, secreting a complex array of extracellular enzymes that result in an oxidative attack of the biopolymer. Laboratory based, time-dependent growth experiments were performed and investigated the key enzymatic changes associated with lignin breakdown by the white rot fungus Pleurotus ostreatus cultivated on wheat straw (Triticum aestivum [L.]), ash (Fraxinus excelsior [L]) and Sitka spruce (Picea sitchensis [Bong.] Carr). The corresponding geochemical changes to lignin structure were also analysed using on- line thermally assisted hydrolysis and methylation (THM) in the presence of tetramethylammonium hydroxide (TMAH). Fungal growth, enzyme activity and lignin breakdown were substrate dependent, with higher levels of enzyme activity, lignin oxidation and side chain cleavage in the angiosperm (wheat straw and ash) systems than the gymnosperm (Sitka spruce) system. Early peaks in manganese dependent peroxidase and laccase activity were followed by a more gradual increase in lignin oxidation and side chain cleavage. On-line thermally assisted hydrolysis and methylation (THM) in the presence of 13C_ labelled/unlabelled tetramethylammonium hydroxide (TMAH) was used to investigate the phenolic distributions and their quantitative changes in soils beneath a Sitka spruce afforested moorland, an unforested moorland and an unimproved lowland grassland. \3C-labelled TMAH was successfully employed to distinguish between lignin- and non-lignin- derived (particularly tannin) phenols. Afforestation had a significant effect on phenolic degradation dynamics in these peaty gley soils. The Sitka spruce afforested moorland recorded a change in input and land preparation either as a result of changing vegetation input or due to land preparation prior to planting. Changes to soil carbon stocks were also investigated in these three soils and afforestation appeared to result in the accumulation of organic carbon in mineral horizons.

No description available.

Nitrogen (N) is an essential nutrient for plant growth and therefore a detailed mechanistic understanding of soil N cycling and plant N uptake is necessary to ensure sustainable food production. In addition, N availability can have significant effects on vegetation community structure and therefore climate-change induced shifts in N availability could affect ecosystem functioning and climate change feedbacks. The potential importance of organic N for plant nutrition has only recently been realised, and knowledge of its cycling and the competition for this resource in plant-soil systems is lacking. The first aim of this PhD thesis was to investigate the potential for plants to compete with soil microbes for N at an early stage in protein breakdown, rather than having to rely on the breakdown of proteins to amino acids and subsequent mineralization to NH/IN03-. The second aim of this thesis was to study N cycling processes in subsoil environments and their potential importance in plant N acquisition. The final aim was to examine how increased N inputs 'affected C and N cycling in Arctic tundra ecosystems, in order to gain a better understanding of potential climate change impacts on this vulnerable area. Experimentation with isotopically labelled N forms revealed differential mobility of the different N forms in soil. Firstly, N03- proved extremely mobile in comparison to ~ +, which was retained both on the exchange phase and rapidly captured by soil . microorganisms. High molecular weight (HMW) dissolved organic nitrogen (DON) showed greater potential for leaching than its low molecular weight (LMW) counterpart, which was also rapidly assimilated by soil microbes. Soil microbes showed a preference for peptide-N over other N forms, whilst wheat plants showed a greater affinity for NH4 + when grown under sterile conditions. When in competition with microbes, wheat mainly took up N03-, with the capture of alanine and peptides being comparatively low. The presence of peptide decreased the ability of wheat to use NH/, whilst the presence of other N forms depressed wheat's use of peptide-N. Studies of arable topsoil and subsoil revealed that C limitation was limiting microbial processes at depth, which was likely caused in part by low root length density and low rates of C input. This caused slower C and N mineralization processes at depth. Deep soils therefore appear unlikely to be a major N source for plants, but this could be stimulated by a labile C input. Surface moisture limitation appeared unlikely to cause a reliance on subsoil N, as there was no significant difference in the change in soil water content with depth during drought conditions. Increased organic N inputs to the Arctic significantly affected plant composition and increased plant litter degradation rates. This has implications for the Arctic's ability to store C and suggests a positive feedback to climate change. In conclusion, this thesis has shown that DON inputs are highly important for plant and microbial nutrition, and that DON can influence C degradation in the Arctic. Subsoil could potentially contribute to plant nutrition, but low inputs of organic material limits microbial activity, so wheat's main N supply appears to come from surface horizons where N cycling is greatest. Plants can readily uptake peptides, although the results suggest that agricultural plants may struggle to compete with microbes for this resource. Furthermore, when added in combination with other reduced forms ofN, the uptake of both peptide and the other N forms decreases.

The site of study (Pollok Park, Glasgow) features soil under both a coniferous canopy (predominantly Corsican Pine) and a deciduous canopy (predominantly Beech). There is a clear segregation between the two vegetation types which enables a direct comparison into the contribution of canopy type to the heavy metal distribution in soil. Average total metal contents of cores extracted from the two soil types indicated that the deciduous cores have a greater total content of Cr, Cu, Fe, and Mn, and that the two core types contain approximately the same Pb and Zn content. Concentration profiles for Cr, Cu, Fe, Mn, Pb and Zn were established for the two soil types. They showed enrichment of Cr, Cu, Pb and Zn at the surface. Correlation graphs [LOI vs. metal (Cr, Cu, Pb and Zn)] showed there to be a correlation between organic matter content and concentrations of these metals. Molar ratios (carbon : metal [Cr, Cu, Pb and Zn]) were estimated from the correlation graphs. In each case, these were found to be of considerable value, indicating that perhaps these metals are complexed by large organic molecules. Mn and Fe showed no enrichment to the surface and no correlation with organic matter. Speciation studies (Modified BCR sequential extraction procedure and cupric ISE investigations) were conducted on the surface soil (top 5cm), litter and leaves taken from below both vegetation types (deciduous and coniferous) in order to gain an understanding of soil-metal associations. The deciduous and coniferous soils were found to have virtually identical fractionation patterns of Cr, Cu, Pb and Zn (Modified BCR sequential extraction).

The aim of this work was to investigate the effect of soil properties on soil iodine dynamics and uptake to plants. Soil and vegetation samples were collected from across eastern Northern Ireland (NI) to form the basis of most experimental work; samples from the Rothamsted Park Grass archive were used to investigate the role of changing soil chemistry through time and due to selected fertiliser applications; and iodine dynamics in humic acid (HA) were studied to improve understanding of the role of organic matter in soils. Input of iodine in rainfall was considered in the context of samples from both locations, and the additional influences of coastal proximity, soil type and underlying geology were reviewed for the NI samples. Total iodine analysis was carried out using extraction with TMAH and quantification by ICP-MS; aqueous iodine speciation was determined using HPLC and SEC coupled with ICP-MS. The most important iodine inputs to both soil and vegetation were found to be directly from the sea in coastally-exposed locations, and from rainfall in other cases. Soil organic matter (measured as soil organic carbon, SOC) was determined to be involved in both retaining a portion of recalcitrant iodine in soil and HA, and in promoting sorption of both iodide and iodate in highly organic soils. Metal oxides (Fe, Mn and Al) were found to be important in rapid sorption of iodate to soils with SOC ≤ 38 %, and there was an indication that they may be involved in promoting the reaction of iodide with organic matter. Replenishment of a transient phyto-available pool was essential for provision of iodine to vegetation. The availability of recently added iodine (as 129IO3-) in the pot experiment was controlled by its sorption onto the solid phase, and near-constant input from irrigation water was the major source of vegetation iodine in most cases. Rainfall was shown to be important in controlling vegetation iodine concentrations in field situations. In soils collected from very coastally-exposed locations, the soil iodine concentration was extremely high and therefore a greater proportion of labile native iodine was available for uptake; irrigation sources were much less important. This work improves understanding of soil iodine dynamics and the important factors controlling iodine speciation and availability to plants. Results can be used to inform practices regarding provision of iodine to crops for both humans and grazing animals.

Sequential chemical extraction to fractionate metals in soils and sediments into different groups reflecting their "leachability" has been widely employed to determine distribution of metals in different physico-chemical phases. A large number of sequential extraction schemes have been reported, most of them modifications of Tessier's extraction protocol. Although this method has been widely accepted, it is important to highlight that sequential extraction procedures are often tedious and time consuming and that they also suffer from a number of limitations, such as the problem of achieving selective dissolution and the re-adsorption of trace metals during extraction. The objective of this study was to develop, optimise, characterise and apply a novel sequential extraction procedure for the evaluation of trace metal distribution in soils and sediments in order to speed up the process, but more importantly to provide robust data for further aid the chemical characterisation of such samples. The method developed used centrifugation to pass the extractant solution (HNO3) at increasing concentrations, through the soil/sediment sample. The sequential leachates were collected and analysed by ICP-AES for a suite of 18 analytes. The method then utilised chemometrics in order to facilitate processing of the data. Optimisation of the new extraction protocol was performed using an experimental design approach. This was important since the method employed multi-elemental analysis to predict the composition of the physico-chemical phases in a range of soils and sediments. The approach used for data processing was again novel and was based on a simple product of matrices. However many statistical and chemometric approaches are used throughout this thesis to aid both the design of the method and the interpretation of the data obtained. Once optimised, the methodology was evaluated using a range of reference materials and tentative assignments were made in order to characterise the different physico-chemical phases in the soils by comparison with previously obtained data following Tessier's protocol. Significant correlation was obtained for the exchangeable fraction, the fraction associated with carbonates and the iron and manganese oxides fraction. Hence the method proved to be effective in providing Important information in terms of metal distribution in agreement with established procedures. The method was then applied to the study of the effect of humic acids (HA) on trace metal distribution in two different samples. Both samples were spiked with increasing amounts of humic acids and the sequential extraction procedure was used to monitor the changes in metal distribution. Differences when HA were added were found for most of the physico-chemical components in both samples. This provided practical data to support the theoretical assumption that HA interact with the metals present in the soil samples changing their distribution. Using the new method, an evaluation of the trace metal distribution within the Arosa estuary (N.W. Spain) with respect to trace metal contamination was performed. Finally, an on-line automated multisequential extraction system was built "in-house", and coupled with the ICP-AES instrument to allow the fast characterisation of soils and sediment samples. The new system proved to be faster than the batch method and minimised the chance of sample mislabelling, sample contamination etc. Good agreement between results obtained from the on-line method, the batch method, and results using the Tessier scheme was obtained. The automated method clearly offers great potential for a range of environmental pollution studies aiding the quick identication of the physico-chemical components in geochemical samples.