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Soil drainage water solute chemical composition showed not only increased losses of inorganic N with increasing N input but also substantially increased organic N losses from the soil system. These losses are important for water bodies both from the eutrophication and acidification view points, and may also be relevant in the context of trace metal transport via chelation. Preliminary studies showed that physical parameters such as hydraulic conductivity, bulk density and porosity could be important to assessment of damage occurring due to acidic N pollution load. Reduced soil microbial activity was clearly demonstrated from peat micromorphological studies and decomposition experiments. The micromorphological studies showed the thickening of the porous surface horizon in grossly polluted areas, where the decomposition process is slowed significantly. Under these conditions, however, NH4+ and NO3- leaching from microcosms is reduced, with greater use being made by biota of atmospheric N inputs as N mineralisation decreases. Two biotic components were studied. Enchytraeid worms showed sensitivity to soil acidity in the long term. Mycorrhizal infection studies showed that increasing N input, especially in the form of NH4+, could be injurious even in the short to mid term. Both studies suggested that more attention is needed in this area. aSignificant accumulation of NH4+ in peat was found in this study. Toxicity effects of high NH4+-N to plants or microflora may be manifesting themselves via discouraging infection in the Calluna root system. New plant generation for high NH4+- N treatment was also poor. It is suggested that, among the N species in N inputs, NH4+ could be most damaging.

This thesis relates to the mathematical modelling of biofilm in two primary areas: biofilm growth, and the effect of microbial immobilisation in biofilm on environmen- tal contaminant transport in the Earth's subsurface. For biofilm growth we construct a model based on polymer solution theory. Parameter estimates motivate a very different model from two published biofilm models also based on polymer solution theory. Analysis of ID solutions provides an expression for growth rate suitable for comparison with experiment. Stability analysis of spatial perturbations to a growing planar front reveals an interfacial instability mechanism similar to that found in a published theoretical study not based on a specific material model. We derive a stability criterion as a critical external nutrient boundary layer thickness, and for the travelling wave solution we identify the finite perturbation wavenumber selected by the instability. For environmental contaminant transport, we identify dissolution of organic phase contaminants and sorption of hydrocarbons onto solid grains as primary lim- itations on bioavailability. We build a pore scale model including both organic phase dissolution and micro- bial uptake and use it to parameterise pore scale Sherwood and Damkohler numbers with respect to pore Peclet number. We illustrate their relation to effective macro- scopic parameters for varying organic phase size relative to pore size. A simple intraparticle diffusion sorption model is extended by considering an external biofilm layer on the particles. A larger scale model considers contaminant transport in a ID flow through a bed of such particles. A physically reasonable pa- rameter regime is suggested, providing analytical solutions for breakthrough curves.