abstract: Nitrous oxide (N2O) is an important greenhouse gas and an oxidant respired by a diverse range of anaerobic microbes, but its sources and sinks are poorly understood. The overarching goal of my dissertation is to explore abiotic N2O formation and microbial N2O consumption across reducing environments of the early and modern Earth. By combining experiments as well as diffusion and atmospheric modeling, I present evidence that N2O production can be catalyzed on iron mineral surfaces that may have been present in shallow waters of the Archean ocean. Using photochemical models, I showed that tropospheric N2O concentrations close to modern ones (ppb range) were possible before O2 accumulated. In peatlands of the Amazon basin (modern Earth), unexpected abiotic activity became apparent under anoxic conditions. However, care has to be taken to adequately disentangle abiotic from biotic reactions. I identified significant sterilant-induced changes in Fe2+ and dissolved organic matter pools (determined by fluorescence spectroscopy). Among all chemical and physical sterilants tested, γ - irradiation showed the least effect on reactant pools. Targeting geochemically diverse peatlands across Central and South America, I present evidence that coupled abiotic and biotic cycling of N2O could be a widespread phenomenon. Using isotopic tracers in the field, I showed that abiotic N2O fluxes rival biotic ones under in-situ conditions. Moreover, once N2O is produced, it is rapidly consumed by N2O-reducing microbes. Using amplicon sequencing and metagenomics, I demonstrated that this surprising N2O sink potential is associated with diverse bacteria, including the recently discovered clade II that is present in high proportions at Amazonian sites based on nosZ quantities. Finally, to evaluate the impact of nitrogen oxides on methane production in peatlands, I characterized soil nitrite (NO2–) and N2O abundances along soil profiles. I complemented field analyses with molecular work by deploying amplicon-based 16S rRNA and mcrA sequencing. The diversity and activity of soil methanogens was affected by the presence of NO2– and N2O, suggesting that methane emissions could be influenced by N2O cycling dynamics. Overall, my work proposes a key role for N2O in Earth systems across time and a central position in tropical microbial ecosystems. / Dissertation/Thesis / Doctoral Dissertation Microbiology 2020

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Nitrous oxide (N2O) is a powerful greenhouse gas (GHG) which has a global warming potential 296 times greater than that of carbon dioxide (CO2). Agriculture is a major source of N2O and in the UK approximately 71 % of N2O emissions are produced by agricultural soils, mainly as a result of the application of nitrogenous fertilisers. Despite previous research into agricultural N2O emissions which has demonstrated that N2O emissions have high spatial and temporal variability, there is still a lack of knowledge surrounding the factors that influence the magnitude of emissions from agricultural soils. Agricultural N2O emissions for the UK’s annual GHG inventory are currently estimated using a 1.25 % emission factor (EF) (to be decreased to 1 % in 2015) which assumes that 1.25 % of applied nitrogen (N) fertiliser is emitted as N2O. The EF does not take into account influencing factors such as location or fertiliser type. Mitigation of N2O emissions is vital if future climate change is to be prevented, yet this must also be combined with the need to intensify agricultural production to feed the increasing global population. Biochar which is a carbon rich material produced during the pyrolysis of biomass has been identified as a potentially useful soil amendment with the ability to mitigate N2O emissions. However, most previous research has focused on laboratory scale experiments and there is a need to investigate the use of biochar in a field environment. Other N2O mitigation options such as nitrification inhibitors, or altering fertiliser management practices, require testing under different conditions to assess their suitability for use. This thesis aims to investigate a). The factors affecting N2O emissions from synthetically and organically fertilised arable soils, and b). To explore the potential of various N2O mitigation options for arable systems, including biochar. This thesis firstly investigates N2O emissions from synthetically fertilised arable soil. Varying application rates of ammonium nitrate fertiliser were applied to a Scottish arable soil during a year long field experiment and the effects of mitigation options such as a nitrification inhibitor (DCD) were assessed. N2O emissions were shown to be significantly affected by soil water filled pore space and the 1.25 % EF was demonstrated to be generally greater than those calculated in this experiment. The use of DCD significantly decreased N2O emissions and crop yields. A second year long field experiment was carried out to investigate N2O and NH3 emissions from an organically fertilised arable soil and to explore the effect of the timing, form and method of organic fertiliser application on emissions and EFs. Slurry, poultry litter, layer manure and farmyard manure were applied in the autumn and the spring. Cumulative N2O emissions were generally greater from the autumn applications and NH3 emissions were greater from the spring applications, due to wetter soil conditions and incorporation of fertiliser during the autumn. The type of fertiliser applied affected the magnitude of emissions with the greatest cumulative N2O and NH3 emissions from the layer manure. The method of fertiliser application had no effect on emissions. The following experiment investigated the ability of different biochars to retain N from a solution and the effect of biochar particle size on retention. A batch sorption experiment was used to test the affinity and capacity of six biochars for ammonium (NH4+) and nitrate (NO3-) from different concentrations of NH4NO3 solution. All of the biochars studied demonstrated the ability to retain NH4+ and NO3- from solution although greater NH4+ retention was observed. Differences in biochar affinity for N could be explained by pyrolysis temperature, but there was no effect of particle size or pH. Oil seed rape straw biochar was demonstrated to have the greatest NH4+ and NO3- retention capacity and as such was chosen for use in the next experiment. This work investigated the potential for oil seed rape straw biochar to decrease emissions of N2O, CH4 and CO2 from stored slurry and whether any GHG mitigation effects would continue following application of the slurry to arable soil. The effect on emissions of amending the biochar and slurry mixture with DCD after application to the soil was also explored. There was no significant effect of the biochar on GHG emissions from the stored slurry although the slurry initially acted as a sink for N2O and CO2. There were no significant differences between emissions from any treatments following application to the soil. The overall results of these studies indicate that N2O emissions are highly dependent on weather conditions, and hence location, in addition to fertiliser type and application timing. It was concluded that the use of a standard 1.25 % EF for synthetic and organic N fertiliser applications for the whole of the UK is inappropriate. Mitigation options such as the use of DCD, altering fertiliser application season or fertiliser type have been shown to possess the potential to mitigate N2O emissions but tradeoffs between N2O and NH3 emissions, and impacts on crop yields must be considered. Biochar was demonstrated to retain NH4+ and NO3- ions and this property may account for biochar’s N2O mitigation capabilities as observed by previous researchers. However, if N retention is taking place, the N appears to still be available for production of N2O and crop uptake.

Diffuse agricultural pollution is a major contributor to poor water quality in many parts of the world. Consequently agri-environment policy promotes the use of riparian buffer strips and/or denitrifying wetlands to intercept and remove diffuse NO3--N pollution. However, these methods have the potential to cause ‘pollution swapping’: the exchange of one form of pollution as a result of measures implemented to reduce another. Thus the benefits of intercepting NO3--N could be offset by enhanced emissions of the potent greenhouse gases, nitrous oxide (N2O) and methane (CH4), from buffer strips and wetlands. This research aimed to: (1) quantify the direct N2O emissions from an irrigated buffer strip (IBS), using nitrate-rich agricultural drainage water, compared to a non-irrigated control (CP); (2) improve the understanding of N2O production and consumption within soils using controlled soil monolith experiments; (3) assess the effectiveness of a small (60 m2) instream wetland at intercepting and removing diffuse NO3--N pollution, and quantify pollution swapping in the form of CH4 and N2O emissions; (4) assess the production of CH4 and N2O within the sediment, and their emissions as well as inorganic-N concentrations in the overlying water column in response to temperature and turbulence, using intact wetland sediment and membrane inlet mass spectrometry (MIMS). The research focused on mitigating diffuse NO3--N pollution from grazed pasture at a farm in north-east England. Annual N2O-N emissions from the IBS and CP were not statistically different (P > 0.05): 509 and 263 g N2O-N ha-1, respectively, in 2007 and 375 and 500 g N2O-N ha- 1 year-1, respectively, in 2008. Irrigation of the IBS increased spatial variability in flux and generated hotspots of denitrification compared to the CP. However, these changes were short-lived. Direct N2O emission factors (EF1) calculated using the available NO3--loading data (September 2007 - December 2008) for the IBS were lower (c.0.1%) than those calculated for the CP assuming N input from biological N fixation only (<1.9%). Soil monolith experiments under a variety of irrigation and NO3--N loading regimes confirmed low direct and indirect (of dissolved N2O-N in leachate) emissions (<3.1 and <2.3% of applied NO3--N emitted as N2O-N, respectively), similar to the IPCC default emission factors. However, N loss in leachate was high, up to 82% of added NO3--N with concentrations reaching 24 mg NO3--N L-1. Therefore even though no pollution swapping occurred the high leachate losses indicate irrigation of buffer strips are not effective mitigation methods. Monitoring for 2 years of the instream wetland that received median NO3--N concentrations of c. 6 mg N L-1, but up to c. 20 mg N L-1, showed it to be ineffective at intercepting diffuse NO3- pollution: likely a result of the relatively high discharge and short water residence time, as well as the direct input of NO3--N to the wetland from secondary sources: field drains and/or overland flow. The wetland was a net source of NH4+-N in both 2007 and 2008, and a net sink of NO3--N in 2007 only. Annual wetland CH4 and N2O emissions were 713 and 237 mg CH4 m-2 year-1, and 3.5 and 1.9 mg N2O-N m-2 year-1, for 2007 and 2008, respectively and were highly variable between seasons. N pollution swapping was minimal from either direct or indirect emissions, but CH4 emissions were found to be of greater importance at a net cost of ~ £600 ha-1 over the study period (2007 to 2008), compared to N2O emissions (~ £60 ha-1) and low NO3--N interception savings (~ £24 ha-1). Incubation experiments suggest that spatially variable microsites of nitrifying, denitrifying or methanogenic activity and CH4 oxidation occur within the wetland sediment. Therefore off-line, larger wetland systems offer the best prospects of enhanced NO3--N interception and potentially reduced CH4 emissions by maintaining shallow water depths (increased CH4 oxidation) and long residence times (increased opportunity for denitrification), within the wetland or wetland cells.

Texas’ Mass Emission Cap and Trade program is a mandatory Nitrous Oxide (NOx) abatement program for medium and large stationary sources located in the Houston-Galveston ozone non-attainment area. Effected companies are required to upgrade equipment to meet the current best achievable NOx control technology (BACT) standards or to purchase emission credits in sufficient quantity to cover the difference in emissions between existing equipment and equipment meeting the BACT standard. With over 260 participating companies, the market for emission credits is ever changing, making it difficult to evaluate whether the lowest cost decision is to upgrade equipment or to purchase NOx emission credits. Because equipment upgrades are capital investments, a well informed, rational decision can have a significant impact on the corporate balance sheet. The objective of this research is to aid the decision maker by predicting credit prices based on a Geometric Brownian Motion model based on historical NOx emission credit transactions. The predicted credit price is useful in evaluating the likelihood of the equipment upgrade option being a favorable or unfavorable decision. For the examined cases, modeled results indicate that equipment upgrade is the more cost effective option. / text

The aim of this study was to investigate the effects of biochar amendment on soil greenhouse gas (GHG) emissions and to elucidate the mechanisms behind these effects. I investigated the suppression of soil carbon dioxide (CO2) and nitrous oxide (N2O) emissions in a bioenergy and arable crop soil, at a range of temperatures and with or without wetting/drying cycles. More detailed investigation on the underlying mechanisms focused on soil N2O emissions. I tested how biochar altered soil physico-chemical properties and the subsequent effects on soil N2O emissions. In addition, 15N pool dilution techniques were used to investigate the effect of biochar on soil N transformations. Biochar amendment significantly suppressed soil GHG emissions for two years within a bioenergy soil in the field and for several months in an arable soil. I hypothesised that soil CO2 emissions were suppressed under field conditions by a combination of mechanisms: biochar induced immobilisation of soil inorganic-N (BII), increased C-use efficiency, reduced C-mineralising enzyme activity and adsorption of CO2 to the biochar surface. Soil CO2 emissions were increased for two days following wetting soil due to the remobilisation of biochar-derived labile C within the soil. Soil N2O emissions were suppressed in laboratory incubations within several months of biochar addition due to increased soil aeration, BII or increased soil pH that reduced the soil N2O: N2 ratio; effects that varied depending on soil inorganic-N concentration and moisture content. These results are significant as they consistently demonstrate that fresh hardwood biochar has the potential to reduce soil GHG emissions over a period of up to two years in bioenergy crop soil, while simultaneously sequestering C within the soil. They also contribute greatly to understanding of the mechanisms underlying the effect of biochar addition on soil N transformations and N2O emissions within bioenergy and arable soils. This study supports the hypothesis that if scaled up, biochar amendment to soil may contribute to significant reductions in global GHG emissions, contributing to climate change mitigation. Further studies are needed to ensure that these conclusions can be extrapolated over the longer term to other field sites, using other types of biochar.

Nitrous oxide (N2O) is a potent greenhouse gas mainly emitted from agriculture. In the biological process of denitrification, intermediates of the nitrogen cycle are reduced under oxygen limiting conditions thereby releasing N2O. Denitrification is influenced by various environmental factors and both bacteria and fungi are capable of denitrification. The ultimate aim of this thesis was to determine the significance of fungal and bacterial denitrification in arable soil and to investigate influences of soil pH and physical disturbance on potential denitrification rates and denitrifying communities. Long-term pH plots combined with a disturbance gradient have been utilised to investigate fungal and bacterial denitrification distinguished by application of selective inhibitors. Highest N2O production was measured from slightly acidic soil and soil with reduced disturbance. Fungi and bacteria contributed to N2O production with bacterial denitrification as dominant source. Fungal denitrification remained unaffected by soil pH and disturbance whereas bacterial denitrification was influenced by these factors. Bacterial denitrification was positively correlated with concentrations of fatty acids which suggested that these fatty acids were common to bacteria involved in N2O production in the soils investigated here. Bacterial community structure changed with soil pH and disturbance whereas fungal community structure was only influenced by disturbance. Bacterial denitrifier communities (nitrite reductases nirK and nirS) changed over the pH gradient but only the nirK community was affected by disturbance. This indicated that groups of bacterial denitrifiers follow different ecological strategies. Gene abundance of nirK and nirS was also correlated to concentrations of the fatty acids associated with denitrifying bacteria in the soils investigated here. In conclusion, fungal denitrification was significant in arable soil but remained unchanged by soil pH and disturbance. Therefore, fungal denitrification is important in agricultural ecosystems and should be considered when developing mitigation strategies for N2O production especially under conditions favourable for fungal denitrification.

Master of Science / Department of Agronomy / Peter J. Tomlinson / Growing cover crops (CCs) in rotation with cash crops has become popular in recent years for their many agroecosystem benefits, such as influencing nutrient cycling and reducing nutrient losses. This study aimed to (i) determine the long-term effects of no-till with CCs and varying nitrogen (N) rates on subsequent sorghum [Sorghum bicolor (L.) Moench] yield and yield components, (ii) assess how CCs affect the N dynamic in the soil-crop relationship during the growing season and N use efficiency (NUE) of sorghum, and (iii) define and evaluate important periods of nitrous oxide (N₂O) losses throughout the cropping system. Field experiments were conducted during the 2014-15 and 2015-16 growing season in a three-year no-till winter wheat (Triticum aestivum L.) – sorghum – soybean [Glycine max (L.) Merr] rotation. Fallow management consisted of a chemical fallow (CF) control plus four CCs and a double-crop soybean (DSB) grown after wheat harvest. Nitrogen fertilizer was subsurface banded at five rates (0, 45, 90, 135, and 180 kg ha⁻¹) after sorghum planting. On average, DSB and late-maturing soybean (LMS) provided one-third and one-half of the N required for optimum economic grain yield (90 kg N ha⁻¹), respectively; resulting in increased grain yield when compared to the other CCs and CF with 0-N application. Crimson clover (Trifolium incarnatum L.) and daikon radish (Raphanus sativus L.) had no or negative effects on sorghum yield and N uptake relative to CF across all N rates. Sorghum-sudangrass (SS) (Sorghum bicolor var. sudanese) significantly reduced N uptake and grain yield, even at higher N rates. Sorghum following CF had the lowest NUE at optimum grain yield when compared to all CC treatments, suggesting that CCs have a tendency to improve NUE. Cover crops reduced N₂O emissions by 65% during the fallow period when compared to CF; however, DSB and SS increased emissions when N was applied during the sorghum phase, indicating that N fertilization might be the overriding factor. Moreover, about 50% of the total N₂O emissions occurred within 3 weeks after N application, regardless of the cover crop treatment, indicating the importance of implementing N management strategies to reduce N₂O emissions early in the growing season. Overall, these results show that CC selection and N fertilizer management can have significant impacts on sorghum productivity and N₂O emissions in no-till cropping systems.

<p>Wetland ecosystems provide many valuable ecosystem services, including carbon (C) storage and improvement of water quality. Yet, restored and managed wetlands are not frequently evaluated for their capacity to function in order to deliver on these values. Specific restoration or management practices designed to meet one set of criteria may yield unrecognized biogeochemical costs or co-benefits. The goal of this dissertation is to improve scientific understanding of how wetland restoration practices and waterfowl habitat management affect critical wetland biogeochemical processes related to greenhouse gas emissions and nutrient cycling. I met this goal through field and laboratory research experiments in which I tested for relationships between management factors and the biogeochemical responses of wetland soil, water, plants and trace gas emissions. Specifically, I quantified: (1) the effect of organic matter amendments on the carbon balance of a restored wetland; (2) the effectiveness of two static chamber designs in measuring methane (CH4) emissions from wetlands; (3) the impact of waterfowl herbivory on the oxygen-sensitive processes of methane emission and coupled nitrification-denitrification; and (4) nitrogen (N) exports caused by prescribed draw down of a waterfowl impoundment.</p><p>The potency of CH4 emissions from wetlands raises the concern that widespread restoration and/or creation of freshwater wetlands may present a radiative forcing hazard. Yet data on greenhouse gas emissions from restored wetlands are sparse and there has been little investigation into the greenhouse gas effects of amending wetland soils with organic matter, a recent practice used to improve function of mitigation wetlands in the Eastern United States. I measured trace gas emissions across an organic matter gradient at a restored wetland in the coastal plain of Virginia to test the hypothesis that added C substrate would increase the emission of CH4. I found soils heavily loaded with organic matter emitted significantly more carbon dioxide than those that have received little or no organic matter. CH4 emissions from the wetland were low compared to reference wetlands and contrary to my hypothesis, showed no relationship with the loading rate of added organic matter or total soil C. The addition of moderate amounts of organic matter (< 11.2 kg m-2) to the wetland did not greatly increase greenhouse gas emissions, while the addition of high amounts produced additional carbon dioxide, but not CH4. </p><p>I found that the static chambers I used for sampling CH4 in wetlands were highly sensitive to soil disturbance. Temporary compression around chambers during sampling inflated the initial chamber CH4 headspace concentration and/or lead to generation of nonlinear, unreliable flux estimates that had to be discarded. I tested an often-used rubber-gasket sealed static chamber against a water-filled-gutter seal chamber I designed that could be set up and sampled from a distance of 2 m with a remote rod sampling system to reduce soil disturbance. Compared to the conventional design, the remotely-sampled static chambers reduced the chance of detecting inflated initial CH4 concentrations from 66 to 6%, and nearly doubled the proportion of robust linear regressions from 45 to 86%. The new system I developed allows for more accurate and reliable CH4 sampling without costly boardwalk construction. </p><p>I explored the relationship between CH4 emissions and aquatic herbivores, which are recognized for imposing top-down control on the structure of wetland ecosystems. The biogeochemical consequences of herbivore-driven disruption of plant growth, and in turn, mediated oxygen transport into wetland sediments, were not previously known. Two growing seasons of herbivore exclusion experiments in a major waterfowl overwintering wetland in the Southeastern U.S. demonstrate that waterfowl herbivory had a strong impact on the oxygen-sensitive processes of CH4 emission and nitrification. Denudation by herbivorous birds increased cumulative CH4 flux by 233% (a mean of 63 g CH4 m-2 y-1) and inhibited coupled nitrification-denitrification, as indicated by nitrate availability and emissions of nitrous oxide. The recognition that large populations of aquatic herbivores may influence the capacity for wetlands to emit greenhouse gases and cycle nitrogen is particularly salient in the context of climate change and nutrient pollution mitigation goals. For example, our results suggest that annual emissions of 23 Gg of CH4 y-1 from ~55,000 ha of publicly owned waterfowl impoundments in the Southeastern U.S. could be tripled by overgrazing. </p><p>Hydrologically controlled moist-soil impoundment wetlands provide critical habitat for high densities of migratory bird populations, thus their potential to export nitrogen (N) to downstream waters may contribute to the eutrophication of aquatic ecosystems. To investigate the relative importance of N export from these built and managed habitats, I conducted a field study at an impoundment wetland that drains into hypereutrophic Lake Mattamuskeet. I found that prescribed hydrologic drawdowns of the impoundment exported roughly the same amount of N (14 to 22 kg ha-1) as adjacent fertilized agricultural fields (16 to 31 kg ha-1), and contributed approximately one-fifth of total N load (~45 Mg N y-1) to Lake Mattamuskeet. Ironically, the prescribed drawdown regime, designed to maximize waterfowl production in impoundments, may be exacerbating the degradation of habitat quality in the downstream lake. Few studies of wetland N dynamics have targeted impoundments managed to provide wildlife habitat, but a similar phenomenon may occur in some of the 36,000 ha of similarly-managed moist-soil impoundments on National Wildlife Refuges in the southeastern U.S. I suggest early drawdown as a potential method to mitigate impoundment N pollution and estimate it could reduce N export from our study impoundment by more than 70%.</p><p>In this dissertation research I found direct relationships between wetland restoration and impoundment management practices, and biogeochemical responses of greenhouse gas emission and nutrient cycling. Elevated soil C at a restored wetland increased CO2 losses even ten years after the organic matter was originally added and intensive herbivory impact on emergent aquatic vegetation resulted in a ~230% increase in CH4 emissions and impaired N cycling and removal. These findings have important implications for the basic understanding of the biogeochemical functioning of wetlands and practical importance for wetland restoration and impoundment management in the face of pressure to mitigate the environmental challenges of global warming and aquatic eutrophication.</p> / Dissertation

Currently in the UK, spent nuclear fuel is reprocessed using the PUREX (Plutonium Uranium Reduction Extraction) process. This process generates large amounts of aqueous nitric acid based waste which is reduced in volume by evaporation before being stored in stainless steel tanks pending eventual disposal to a repository after conversion into a solid wasteform. The corrosivity of nitric acid solutions towards these stainless steel storage tanks is strongly affected by the presence of oxidants that can form in situ if certain dissolved metals such as cerium, chromium, ruthenium and neptunium are present, which is invariably the case in nuclear reprocessing plant liquors. Such liquors are, however, subject to radiolysis leading to the formation of nitrous acid and NOx species in equilibrium with nitric acid and water. The redox chemistry of irradiated reprocessing plant liquors is therefore complex, depending on a large number of factors including acidity, nitrate ion concentration, temperature, pressure, radiation dose rate and the nature/concentration of dissolved species. High acidities, high temperatures and low dose rates favour the oxidation of species such as Ce(III). For example, when Ce(IV) forms, the corrosion rate of stainless steel is strongly increased since the reduction of Ce(IV) forms a kinetically-favoured path way. Furthermore, the presence of nitrous acid (which is radiolytically formed from nitrate/nitric acid) can act to reduce potential corrosion accelerators (e.g. Ce(IV)) to their non-oxidising valency states. These dependencies are only semi-quantitatively understood at present, hampering useful prediction of actual effects when conditions are changed. The research presented within this thesis is divided between two experimental campaigns which are interrelated by their applicability to highly active storage tank conditions; I. An investigation into the conditions which effect the radiolytic production of nitrous acid in nitric acid based solutions was undertaken. This included the quantitative measurement of the steady state concentration of nitrous acid experienced under different conditions. The conditions investigated include temperature, dose rate, gaseous headspace and liquor composition in order to elucidate which factors are of importance in estimating the concentration of nitrous acid which can be expected at the base of a highly active storage tank. The major result of this campaign was that nitrous acid data collected could be used to formulate a g-value of nitrous acid formation (which was found to be 0.71) and this value was used to calculate the nitrous acid production rate expected within a highly active storage tank which is a pre-requisite of underpinning the corrosion chemistry within. II. Investigation into the potential formation of in situ corrosion accelerators in a reprocessing liquor simulant was undertaken. For this, a bespoke experimental rig has been designed, built and operated in order to identify the valency of potential corrosion accelerators at high temperatures while closely representing the conditions expected at the base of a highly active storage tank. This included the simulation of nitric acid radiolysis by means of an appropriate nitrite addition underpinned by the radiolysis studies described above in (I). It was found that none of the conditions investigated were oxidising enough to promote the generation of Ce(IV), which is contrary to the current understanding and should be favourable with regards to the storage tank remnant life expectations. Results reported in this thesis provide insight into the corrosivity of reprocessing liquors under representative storage tank conditions at various temperatures (up to the local liquor saturation temperature) and this knowledge will help improve remnant life predictions of the highly active storage tanks on the Sellafield site.