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Cassiterite extraction in West Malaysia has left a legacy of some 80,000 hectares of nutrient-poor, drought-prone, quartz sandy tailings. Their proximity to urban centres has long made them a target for agricultural and forestry enterprises, and various techniques have been developed to overcome their intractability, including amendment with bulky organic matter and replacement with natural soils. Although reasonably successful, these approaches have often failed to acknowledge that a percentage of the original heavy mineral suite remains in sandy tailings, exerting possible phytotoxic effects and certainly raising concerns about the suitability of sandy tailings for agronomic crop production. To determine the nature and extent of trace element contamination of sandy tailings, ten different areas were identified and sampled in the states of Selangor and Perak. Preliminary analyses failed to corroborate earlier discoveries of elevated mercury and cadmium status, but lead, zinc, arsenic, uranium and rare earth elements were all common. However, greater concentrations of all these elements were found in clay (slime) tailings, which had been colonized by dense vegetation cover. This indicated that levels of trace elements in sandy tailings were not of themselves phytotoxic, but in the context of reduced nutrient availability, might exert a disproportionate influence on their colonization by plants. The colonization of sandy tailings by Melastoma malabathricum was therefore examined, revealing that in two of four sites, water contents were greater in colonized areas than the rest of each site. Macronutrient concentrations were also greater in colonized tailings, as were concentrations of zinc and manganese, but whether these were the cause or result of plant establishment could not be determined conclusively. Overall, trace element distribution in sandy tailings did not influence colonization by Melastoma, although in three of four populations, foliar concentrations of uranium were greater than those of a population growing on a natural soil. This has serious implications for the agronomic use of sandy tailings. The effects of bulky organic and clay amendment of sandy tailings on the availability and uptake of trace elements has never before been examined. A tropical greenhouse experiment was undertaken to examine the effects of peat and clay on the growth and trace element chemistry of Panicum miliaceum and Pueraria phaseoloides. The use of symbiotic mycorrhizal fungi was also included, since although these often improve the phosphorus nutrition of their hosts, they might also increase trace element uptake from pools sorbed by organic matter. Neither clay nor peat improved the growth of either plant species. However, addition of clay substantially increased the availability of aluminium and trace elements, and its use in rehabilitation attempts cannot be recommended. In contrast, peat reduced the availability of Co, Cu, As, La, Ce and U, whilst simultaneously improving the ECEC of sandy tailings. The effects of mycorrhizal inoculation were difficult to interpret, since the carrier medium used (predominantly zeolite) drastically altered the chemistry of soils to which it was added. Growth of Panicum and Pueraria was equally poor on two of three naturally sandy soils. Adding peat to sandy tailings produced plants with similar foliar chemistry to those grown on natural soils, suggesting that plant communities established on these natural siliceous media could act as models for the sustainable rehabilitation of anthropic mine tailings - something which has never before been suggested. A range of native species are recommended as having potential for further research into naturalistic rehabilitation.

20 m2 and the permeabilitycould be altered with the addition of different additives. Full analysis of the changes in permeability could be performed after a test time of one week compared with a test time of several months in a shale core experiment using the Hassler cell.

Lux-marked E. coli was responsive to a wide variety of chlorophenols with differing degrees of toxicity depending on number and position of chlorine substitution. The pH robustness of lux-marked E. coli was exploited in investigating the effect of pH on the sorption of 2,4-DCP to the bacterium. As the pH decreased, the accumulation of 2,4-DCP increased correlating with the amount of non-dissociated 2,4-DCP present, indicating that non-dissociated 2,4-DCP was preferentially sorbed. It was also shown that the toxicity of 2,4-DCP was increased at low pH values correlating with the increased sorption previously observed. The effect of an environmentally relevant matrix (soil pore water) on the toxicity of 2,4-DCP was investigated. The toxicity of 2,4-DCP was found to be enhanced in soil pore water, which questions the use of toxicity tests performed in pure aqueous systems. The effect of soil pH on the adsorption of 2,4-DCP was investigated using pH plots maintained at different pH values for 30 years. The pH had very little effect on the adsorption and desorption of 2,4-DCP but it does have a high affinity and is not easily desorbed. A solid phase toxicity assay was developed to measure the toxicity of 2,4-DCP sorbed to soil. It was found that 2,4-DCP was not toxic to lux-marked E. coli, demonstrating the ameliorative effect of sorption of pollutants to soil. This has major implications for the field of soil toxicity testing as soil toxicity testing is commonly performed using soil extracts or elutriates.

In semi-arid environments, the combination of a non-uniform distribution of vegetation, an often highly irregular terrain and complex geological, pedological and management histories have frequently given rise to considerable spatial variability in the physical and hydrological properties of soils. Heterogeneity within the soil's physical and hydrological properties can result in pronounced differences in infiltration and soil moisture. The hydrological response of semi-arid landscapes to rainfall events may therefore be spatially non-uniform. Quantifying the spatial pattern of hydrological response is important for identifying those areas within the landscape which arc vulnerable to runoff and erosion. Since soil moisture is considered to be a key factor in determining hydrological response and its spatial distribution is a function of the soil's physical and hydrological properties, the spatial and temporal measurement of soil moisture may be used to identify contrasting areas of hydrological response. In a badlands environment located approximately 70 km north of Madrid, central Spain, an experiment was established to describe the temporal and spatial variability in soil moisture at three scales, with the primary aim of furthering the understanding of the hydrological and geomorphological processes operating in semi-arid landscapes. At each measurement scale, the macroscale (25m sampling interval), the mesoscale (gully catchments, 5m sampling interval) and the microscale (1 m sampling interval), two distinct groups of soil moisture conditions emerged related to dry and wet weather conditions. At each measurement scale the maximum variability in soil moisture is similar (>20% volumetric content difference between immediately adjacent sampling points). At the meso and microscale the spatial pattern of soil moisture could be described as a mosaic pattern which during the dry period was more fragmented and variable than during the wet period. The spatial pattern of soil moisture during wet conditions is more uniform due to the development of extensive wet areas within the catchments. During these conditions the range of spatial correlation in soil moisture may double (to greater than 30m) compared to dry conditions, indicating an increase in the spatial continuity of soil moisture. The spatial variability in soil moisture therefore displays a temporal dependency; the mosaic soil moisture pattern is more fragmented and spatially discontinuous during dry than wet conditions. A striking characteristic of the study area is the near horizontal interbedding of sediment horizons which may strongly contrast in their textural composition over relatively short distances. This variability in soil texture and the associated changes in pore size characteristics, were the principal controlling factors in determining the spatial patterns of soil moisture and overrides the known influence of vegetation and topography on soil moisture. During dry conditions the non-uniform uptake of soil moisture by vegetation may partly explain the greater variability in soil moisture observed during this period. The mosaic patterns of soil moisture represent areas of contrasting hydrological response. During dry periods when the mosaic pattern is more fragmented, source areas of overland flow are spatially isolated and surrounded by 'sink' areas capable of re-absorbing runoff and sediment deposition. Hydrological pathways are therefore discontinuous resulting in minimal runoff reaching the catchments channels. Since soil moisture values during this period are below saturation, any runoff which does occur is generated as infiltration excess overland flow. In semi-arid areas spatial variability in soil properties or vegetation patterns may therefore be beneficial for runoff and erosion control by creating a self-regulating system in which runoff producing areas are surrounded by buffer zones capable of re-absorbing the runoff. During wet periods extensive areas of the catchments may be saturated. source areas are no longer spatially isolated and continuous hydrological pathways may develop rapidly during this period. During the wet period when conditions arc above a critical saturation threshold value widespread runoff will occur regardless of the spatial variability in the soil's physical and hydrological properties. The creation of a mosaic pattern in which buffer zones are adjacent to potential runoff producing areas, as identified from spatial soil moisture patterns, may provide the most effective management strategy in runoff and erosion control for degraded semi-arid environments. The creation of a mosaic pattern is most applicable at the watershed scale allowing several land uses, including those which are potentially degrading, to co-exist. Increasing the critical threshold value above which widespread runoff occurs should also.be included as part of this management strategy.

Flow through soil into groundwater has been classically conceptualised as taking place through a set of aligned capillary tubes. In solute transport models these approximations are also present. Pore-Cor (a network model) has been used to model the void structure of soil by using water retention and mercury porosimetry curves. The model successfully predicts trends in saturated hydraulic conductivity. The effect of the assumptions used in the Pore-Cor geometry have been investigated by comparing of two dimensional slices of the simulated networks with two dimensional image analysis data. The geometric limitations of the model cause packing inefficiencies which prevent the model from representing the size distribution of voids found in real samples. The observation of environmental events is dependent upon the implementation of rapid and reliable analytical techniques. This work presents an adaptation of an FI method for the determination of dissolved reactive phosphorus (DRP) and a new method for the determination of total dissolved phosphorus (TDP). Both are ideally suited to the detection of phosphorus species in soil leachate and runoff waters over the concentration range 3 to 1000 Ilg ri. The effect of compaction on solute transport is described and the experimental data have been modelled using a modified form of the convection dispersion equation (CDE). The parameters of the CDE have been given structural interpretation by the network model. The model was used to interpret a change in dispersivity and the behaviour of reactive phosphorus species on compaction.

Previous work has suggested that soil conditioners can provide environmentally beneficial aids to agriculture and soil conservation. To investigate this further, studies were carried out on soil conditioner effects on soil erosion, soil structure and crop performance. The main soil conditioner investigated was an anionic, hydrophilic conditioner based on ammoniurn-laureth-sulphate. Several objectives were established, in order to test the hypothesis that ammonium-laureth-sulphate can establish treatment effects by decreasing soil erosion and improving soil structure and crop performance. Subsequently, initial attempts were made to elucidate the mode of action. The field experiments were established on loamy sand soil (Bridgnorth series) at the Hilton Experimental Site, east Shropshire and on sandy silt loam soil (Salwick series) at the Plant and Environment Research Unit at Compton Park, Wolverhampton. The main soil conditioner applied was 'Agri-SC' at manufacturer recommended application rates and three other soil conditioners were used for some comparative studies. Following applications of ammonium-laureth-sulphate to bare and cropped plots, effects on the topsoil (0-5 cm) included significantly decreased bulk-densities, soil moisture contents and splash erosion and significantly increased soil porosity and infiltration rates. Other effects included decreased runoff and erosion rates from 100 slopes and penetrometer resistance and increased aggregate stability and drainage capacities. Responses in a winter wheat crop (cv. Beaver) included apparent suppressed seedling emergence, followed by apparent enhanced growth and development. Initial laboratory studies indicated conditioner treatment altered cation exchange capacities, mineral and elemental compositions and provided evidence for chemical interparticle bonds. ' The soil conditioner appeared to function through a mechanism involving several stages. Upon application, the charged polymer molecules were electrostatically attracted to clay or silt particles and their attached ions. It is postulated that ammonium ions could then replace Ca and possibly Mg and Na, causing the polymer molecules to adhere to soil particles. This might be associated with mineral deposition. The laureth polymer strings could thus bridge individual particles and increase internal aggregate stability. This mechanism may be relevant for further understanding of the mode of action of other hydrophilic, polymer-based soil conditioners.

The study aimed to determine the interrelationship between aggregate stability and microbial biomass in restored soils, and to investigate if the development of the two parameters in soils disturbed by opencast mining could be influenced by the application of slow release organic amendments. These objectives were tested using two microbiological methods; determination of adenosine triphosphate and dehydrogenase activity, and three structural measurements; determination of aggregate stability by wet-sieving, shear vane and bulk density. Soil carbon and nitrogen were also determined. The first part of the study involved a survey of 16 field areas located in Britain, 12 disturbed and four not disturbed by opencast coal mining. The areas were all grasslands which varied in the time since restoration, which was between 0-16 years. A log linear relationship between the soil biomass and stable aggregates > 2 mm was found for all field areas (y = 38 In x - 69, r = 0.51). The variation in both properties was also affected by the restoration practices at the individual sites. A cluster analysis of the measured soil properties separated the restored areas into "good" restorations, involving progressive restoration, topsoil replacement and early underdrainage, and "poor" restorations, restored without topsoil or with soil forming material. The second part of the study reported on the first 16 months of a field trial set up on a recently restored opencast coal site situated near Denby in Derbyshire in 1991. A 3 x 4 factorial design involved two organic amendments (straw and wood), and four vegetation covers. The treatment effects were obscured by natural fluctuations in the soil properties over the period studied. However, the presence of the organic amendments alleviated some of the physical problems of the soil, such as waterlogging and frost damage, which drastically affected the results in 1992. The soil properties generally improved in the order straw>wood>no amendment for the majority of soil parameters (structure, C and N), the notable exception being the soil microbiological parameters which varied substantially throughout the experiment. Differences between the vegetation covers (a MAFF, a ruderal and a species rich seed mixture) were small.

This thesis reports the interactions of (poly)cations with a variety of clay minerals and the application of the resultant organoclays as both sorbents and catalysts. The behaviour of organoclays containing tetramethylammonium cations (TMA[+]), is compared to the behaviour of organoclays containing polycations of the formula [(Me[2]NCH[2]CHOHCH[2])[n]][n+] (Magnafloc 206), which are shown to form two distinct types of organoclay. To investigate the interactions of the (poly)cations with clay surfaces, several dry powder analysis techniques have been employed including Kjeldahl nitrogen analysis, variable temperature x-ray diffraction and thermogravimetric analysis. The studies have shown that the (poly)cations reside between the clay layers and that the nature of the clay and the resident exchange cation have a significant effect on the amount adsorbed. It is also shown that the polycations have a higher affinity than tetramethylammonium cations for all the clay minerals investigated. Sorbents exchanged with various amounts of (poly)cation are investigated for their ability to adsorb benzene and rho-nitrophenol from water. The adsorption by polycation containing sorbents is reduced compared to TMA[+] containing sorbents and the latter is comparable with that reported in the literature. The adsorption site in such sorbents is the siloxane surface in the clay interlayers, as shown by the observation that the uptake of both benzene and / rho-nitrophenol by TMA[+] exchanged SAz-1, a high charge montmorillonite, was reduced compared to TMA[+] exchanged SWy-1, a low charge montmorillonite. In SAz-1 there is closer packing of adsorbed TMA[+] cations resulting in less siloxane surface area being available. Hydration of the TMA[+] cations also increases steric constraints. High polycation loadings prevent the clay layers from expanding and thus accessibility of rho-nitrophenol to the clay surface is reduced. Partition into the organic carbon content of the polymer occurs but uptake does not increase with organic carbon content as expected. Also, TMA[+] exchanged Westone-L was expected to behave similarly to TMA[+] exchanged SWy-1 as Westone-L and SWy-1 have very similar cation exchange capacities. However, it is shown that TMA[+] exchanged Westone-L behaves more like TMA[+] exchanged SAz-1 which has a much higher cation exchange capacity. A range of organoclays containing either tetraalkylammonium cations or polycations at differing exchange levels have been subjected to acid leaching at either 25 or 90°C. The activity of these acid-activated (poly)cation-exchanged clays for the conversion of alpha-pinene to camphene and limonene was determined and compared with those from clay samples (without (poly)cations), acid-treated in the same manner. The presence of the polycation had a more marked influence on the activity of samples derived from SAz-1 than for corresponding samples derived from SWy-2, which was attributed to the increased hydrophobicity of the polycation loaded clay. Comparable yields for SWy-2 in the absence and presence of polycation suggest that SWy-2 disperses well in the nonpolar alpha-pinene. Also, octadecyltrimethylammonium and dodecyltrimethylammonium exchanged clays were generally less active than TMA[+] exchanged clays which were comparable to the most active polymer containing catalysts. It has also been shown that the octahedral iron content of the clay affects its catalytic activity. Finally, a competitive adsorption method of catalyst preparation has been developed which may replace more conventional high temperature techniques.

The impact of land use on the N and P status of three contrasting river catchments within the north east of Scotland was studied over time and along the length of each river. Annual mean NO₃-N concentrations increased significantly in the Ythan, Don (P<0.001) and Dee (P<0.05), from 1958 to 1992. Concentrations in the predominantly agricultural Ythan catchment showed the largest increase from 1.9 mg l^-1 in 1958 to 7.0 mg l^-1 in 1992. A significant increase in mean NO₃-N concentrations in the spring from 1980 to 1992 in the Ythan appeared to reflect the increased N fertiliser usage associated with a change from winter to spring cropping which was evident over this period. Annual mean NO₃-N loads over the period 1980-1992 were 1305, 2010 and 623 t yr^-1 for the Ythan, Don and Dee, respectively. Annual PO₄-P loads were 17.6, 40-1 and 16.8 t yr^-1 over the same time period for the Ythan, Don and Dee respectively. These loads were found to have associated errors in the range 16-24, 16-17 and 18-32% for NO₃-N, PO₄-P and total P respectively. Annual loss coefficients, calculated for NO₃-N, PO₄-P total P, Si and suspended sediment were 27.2, 0.180, 0.319, 26.1 and 73.5 kg ha^-1, respectively. Annual losses of N and P from forestry were calculated in the Kirkhill catchment, a small subcatchment of the Don and ranged from 0.6 to 2.5 kg ha^-1 depending on flow. Annual total P losses were also related to flow and ranged from 0.029 to 0.06 kg ha^-1. A nutrient budget calculated for the Kirkhill catchment found the annual loss of N from the catchment accounted for 44.5% of N inputs, in contrast, only 2.7% of P input to the catchment was detected in the output.

It is proposed that microbial polysaccharides behave anion-exclusively, permitting the transport of cations, but excluding the diffusion of anions. This hypothesis has been investigated in the context of polysaccharides produced by microorganisms in the rhizosphere. The anion-exclusive behaviour of exopolysaccharides, extracted from broth cultures of a range of rhizosphere microorganisms together with several commercial polysaccharides (i.e., xanthan, scleroglucan, dextran, guar gum) was investigated by measuring the electrochemical potential which developed as a result of the diffusion of KC1 across a polymer layer. Considering xanthan as a 'model' microbial polysaccharide, polymer concentration, layer thickness and the presence of either O-acetyl or pyruvyl groups were found to positively affect the degree of anion exclusion. The anion-exclusive behaviour of xanthan was verified by direct ion analysis of solutions either side of the polymer layer. It was found that in a range of ionic environments, the diffusion of anions was reduced by ~70% by the presence of a 3% w/w xanthan layer. The influence of xanthan on the diffusion of cations was studied using magnetic resonance imaging. In contrast to the proposed theory of anion exclusion, the rate of cation (Mn2+) diffusion through a 3% w/w xanthan layer was found not to be greater than that through free aqueous solution. The possible occurrence of anion exclusion and consequences thereof in the rhizosphere were assessed by studying the effect of substitution of the water films in soil with a layer of 3% xanthan on the growth of wheat seedlings. The phosphate, but not potassium content of those plants grown in soil with xanthan was ~20% lower than in the control plants. Those plants grown in xanthan-amended soil produced ~30% more biomass by dry weight. The anion-exclusive properties of polysaccharides produced naturally in bulk soil, the rhizosphere and root surface of pea was studied by the measurement of diffusion potentials. All three were found to show a high level of anion exclusion. The influence of O-acetyl groups in xanthan on the rate of water transport and degree of water binding was studied using stray field NMR methods. It was found that removal of O-acetyl groups reduces the rate of water transport and increases the rate of water binding at any given xanthan concentration. It is proposed that microoganisms produce anion-exclusive polysaccharides in the rhizosphere to protect themselves against the potentially lethal effects of water stress.

Roots and their associated mycorrhizal fungi have long been recognised as major determinants of nutrient cycling. Their measurement has been limited because soil limits accessibility. The use of in-situ camera techniques in conjunction with minirhizotrons and image analysis software now make the acquisition of accurate root longevity data possible. The current literature was reviewed in relation to root longevity - both measurement techniques and available data. Four main experiments were employed to study the root longevity of a number of tree species, grass and clover subject to differing environmental conditions and grass and clover and poplar roots with and without colonisation by Arbuscular Mycorrhizal fungi. The data was analysed in a number of different ways including the use of the powerful statistical technique for censored data - survival analysis. This technique proved to be very useful for analysing temporal changes to root longevity. The data indicate that root longevity can be extremely short but is dependent upon environment and for some species, colonisation by Arbuscular Mycorrhizal fungi. Preliminary calculations were completed to determine the role of root death in nutrient cycling and these predict that large quantities of nitrogen, phosphorus and carbon are flowing from the live to the dead root pool on an annual basis.

The relationship between soil structure and microorganisms is a unique two way interaction. Whilst soil structure influences microbial transport, activity and predation, microorganisms affect soil structure by playing a major role in its genesis and stabilisation. Microorganisms are largely thought to influence structural genesis and stabilisation through the exudation of polysaccharides, which act to bind soil particles together as well as microorganisms to soil particles. Filamentous microorganisms are also thought to influence structural genesis and stabilisation by enmeshing soil particles together. A laboratory-based experimental system was developed whereby the structural heterogeneity of soil cracking patterns, generated from homogeneous soil slurries, was quantified using fractal concepts. A fractal approach was used because it provided a theoretical framework in which structural heterogeneity could be quantified and linked to soil processes such as gaseous diffusion, water movement and microbial population dynamics. This study demonstrated the potential of fractal geometry to functionally quantify soil structure. A greater understanding was gained of some of the processes acting to direct the formation of particular structural geometries. The latter is particularly important since it is the geometry of soil structure which will regulate processes such as gaseous diffusion and water movement. Microbial activity (mainly through the production of polysaccharides) was shown to have a significant effect on the generation of soil structure as well as on its water retention properties. The nutritional management of the microbial population was also shown to be a key factor regulating its contribution to structural genesis. Microorganisms can play a significant role in structural genesis ultimately impacting upon all aspects of the soil-plant-microbe ecosystem. It will be essential to understand how to effectively manage the indigenous microbial population if their potential as soil conditioners is to be fully reached.

Long-term changes in soil profile characteristics and important soil physical, chemical and biological properties were evaluated and compared at 4 paired sites in NE Scotland, 44-61 years after the afforestation of agricultural soils planted with either Norway spruce (Picea abies (L.)) or Scots pine (Pinus sylvestris (L.)). At each paired site five profiles were studied in the afforested and five in the control agricultural soils. Comparison made between various properties in the pairs of soils showed a number of significant changes, which are summarised in Tables 2.18-2.20. The surface (O) horizon of the afforested soil could be differentiated into L, F and H horizons. The O horizon was rich in organic matter, crumb structured, porous and well-drained and was differentiated from the A horizon below by an irregular boundary. The A horizon was moderately well to excessively well-drained with a subangular blocky to crumb structure. This horizon was differentiated from the B horizon below by an irregular boundary. The agricultural soil profile was characterised by compact O and A horizons with a subangular blocky structure; each horizon was separated from the one below by a gradual, smooth horizon boundary. Afforestation increased the combined thickness of the O and A horizon by 0.21 cm yr-1. It caused a significant decrease in bulk density and had no effect on particle size distribution. At most sites % organic matter, C, C/N ratio, CEC and NH4+ concentration were higher and extractable P concentration lower in the O horizon and most of the A horizons of forest soils, compared to the agricultural soil. The concentration of N increased significantly in the O horizon. Soil pH, exchangeable Ca, Mg and K and % base saturation decreased significantly in most forest soil horizons compared to the agriculated soils. Exchangeable Na concentration increased in the B horizon. Accumulation rates of each element since afforestation were also calculated.

Traditionally, soil scientists have ignored the spatial dimension concentrating upon the physics of soil water movement at points/sites. The development of geographic information systems (GIS) provides an opportunity to develop soil-water models taking into account differences (spatially and temporally) in land cover and soil type. This thesis has attempted to integrate traditional soil water modelling within a GIS for estimating soil water drainage rates for a typical water catchment with spatially varied soil type and land cover. The Campbell soil model has been adopted for its simplicity and accuracy for estimating soil water infiltration/distribution. However, Campbell's model fails to take into account sufficiently the role of vegetation ininfiltration/distribution. The Meteorological Office Rainfall and Evaporation Calculation System provides effective ways of deriving potential evapotranspiration under various vegetated surfaces. The integration of these two models has resulted in the development of the Soil Water Drainage Model which is more accurate and capable of incorporating spatial soil and vegetation data. The model was developed and tested for the south-west Reading study area. The model's behaviour under various conditions was examined and its performance evaluated. It has found that a bare soil surface has a significant water drainage difference from a vegetated one and soil type affects soil drainage rate, especially when the soil is bare or abnormal climatic events occur. It has also shown that grassland reduces greatly the quantity of soil water loss as drainage and most drainage occurred in winter months and early spring. The accuracy of the model's prediction for estimating soil water drainage was validated on the small Winterbourne catchment (45km2) near Newbury, based on the catchment water mass equilibrium. The water drainage rates predicted by the model are reliable and consistent with the observed river discharge data. However, the results suggest a number of ways in which the methodology could be improved.

The effects of adhesion to surfaces on the specific growth rates of Nitrosomonas europaea and Nitrobacter sp. were determined in batch culture systems both in monoculture and co-culture. It was found that the presence of a glass slide in co-cultures of these bacteria significantly reduced the specific growth rates of both species of bacteria. In monoculture, the specific growth rate of N. europaea was significantly lower in a mature biofilm system. The specific rates of production of ammonia by these four species of Pseudomonas were investigated in minimal medium. All four species converted approximately 60 - 80% of the provided L-alanine to ammonia, and this production of ammonia raised the pH of the medium. All four strains were capable of this when the initial pH of the medium was 5.5 or 7.5, however, lowering the initial pH of the medium reduced the specific rate of production of ammonia for P. cepacia, P. fluorescens and P. syringae, and reduced the final concentration of ammonia produced by P. cepacia. Ammonia produced by P. fluorescens could support the growth of N. europaea in liquid batch culture. The growth of the pseudomonad increased the pH of the medium from 5.5 to 6.8 and this increase in pH allowed growth of the nitrifier in the medium with the lower initial pH. The growth of N. europaea and P. fluorescens in continuous flow biofilm reactors was examined, and the addition of P. fluorescens to a nitrifying biofilm raised the pH of the bulk medium, thus removing the effects of pH inhibition on the ammonia oxidiser. Further investigations were carried out in continuous flow sand column systems and it was found that the rapid growth of the pseudomonad caused obstruction of the column.