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In this thesis an examination is made of the ecology of the meiofauna in a slow sand filter used for the purification of river derived water for industrial and domestic supply. The physical and operational features of the filter are described in relation to the biology of the organisms inhabiting it. Problems encountered with sampling the meiofauna of such a system are discussed and a criticism of the sampling methods employed is presented. A discussion is made of the uses of total particulate organic carbon as a parameter for characterising the biomass changes in the system. An evaluation of the horizontal and vertical distributions of the meiofauna in the filter is presented. Similar observations are made regarding the distributional heterogeneity of the organic carbon in the system. Special attention is directed to the oligochaetes present. A relationship is determined between length and dry weight and also segment number and dry weight of Enchytraeus buchholzi, the only actively sexually reproducing oligochaete worm present. The segment number - dry weight relationship is exploited to obtain quick estimates of the dry weight of the worm for biomass estimates. Seasonal changes in population abundance of the meiofauna are presented. The need to obtain estimates of parameters not easily measured in an operational filter is discussed. The design and functioning of an experimental small-scale filter is described and criticised. A method is detailed for obtaining interstitial water samples without them coming into contact with air. An account of a micro-Winkler oxygen analysis is given. The results of redox potential measurements and dissolved oxygen analyses, made in the pilot filter, are presented together with a discussion on the insight which these measurements give as far as bacterial activity in the filter is concerned. A discussion is made of the ecology of the meiofauna in slow sand filters and further suggestions for research investigations are made.

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The conversion of arsenic into organoarsenic compounds is affected by the action of organisms, particularly marine organisms. These arsenic species require a suitable technique to distinguish the species and quantify their abundance. The ICP-MS coupled to either HPLC or HG-CT are the most popular techniques for arsenic species could be separated, but the limit of detection (LOD) was not satisfactory for the concentration of arsenic in natural waters and the chloride interference in the marine samples was high. While the HG-CT-ICP-MS, the LOD was sufficient to detect very low concentrations of arsenic, particularly for methylated arsenic species, and there was no chloride interference, however the inorganic arsenic in the reagents was high and only the reducible arsenic species could be detected. The transformation of organoarsenic compounds, specifically the conversion of arsenosugars by micro-organisms in sediment, was studied by analysing porewater from decaying seaweed in a mesocosm experiment. Arsenosugars degraded to DMAE further to DMAA to MMAA and finally to As(V) and As(III), but not as previously proposed to AsB, AsC and TMAO. Arsenic was released by the dissolution of manganese and iron clay particles in a pristine area but much more by anaerobic degradation in an industrial area. Arsenic was removed from the water phase to the sediment by precipitation, particularly with manganese at the surface sediment only in the pristine area but with iron in the industrial area.

At the end of 1995 work was completed on a low level intersecting foul sewer for the upper Pymme' s Brook catchment (north London), known as the East Barnet foul water sewerage scheme. Commissioned by Thames Water Utilities Limited (TWUL), it was intended that this would both resolve flooding problems in the area, and address environmental concerns raised by the Environment Agency (EA). The key element of the scheme was the removal of seven combined sewer overflows (CSOs) that the EA had defined as 'unsatisfactory'. Consequently, the present study assesses the scheme's impact on the brook's environmental status, and considers the results in light of the pollutant generation, transport and dispersal properties of the catchment. The pollutant generation, transport and dispersal processes operating in the catchment were explored at a range of spatial and temporal scales, in order to assess the contributions made by a range of urban non-point sources of pollution (CSOs, misconnections and urban runofl), under differing weather conditions, and to determine the way in which they interacted to control water quality. Considerable temporal and spatial variability was identified in the quality of both the brook, and the effluents discharging to it. A first flush of contamination was noted for both solid and dissolved pollutants, during many of the studied storm events; although the studied determinants (pH, conductivity, suspended solids, biochemical oxygen demand, dissolved oxygen, ammonia-N, chloride and E. coli count) responded to storm driven processes in different ways. A holistic approach was adopted to define the environmental status of the studied watercourse; incorporating its benthic macro-invertebrate community structure (BMWP score and ASPT), bacteriology (E. coli count) and water chemistry. Temporal change was then identified in each data set by performing an ANOVA between years, and between the periods prior to, during and after the scheme's construction. The scheme's impact on catchment hydrology was also explored by assessing temporal changes in the catchment's unit hydrograph parameters, using both linear regression for, and ANOVA between the periods related to the scheme's construction. In addition, regression analysis was used to explore the relationship between climatically induced hydrological change and both BMWP score and water column E. coli count, in which both variables were related to the mean discharge recorded at the EA's Silver Street gauging station on a range of temporal scales. It was concluded that climatically driven hydrological change was the major factor in determining the environmental status ofPymme's Brook, whereas the East Barnet foul water sewerage scheme produced only a limited improvement. This was because as well as removing several pollutant sources, the scheme had a hydrological effect that negated some of the expected improvements in water qUality. In addition, the large number and variety of pollutant sources operating in the catchment meant that a scheme designed to address just one element of the problem was unlikely to have a wtifonnly positive effect. Consequently, the magnitude of the temporal changes observed varied between the eight sites sampled in a way that was determined by a combination of the sensitivity of the benthic macro-invertebrate community inhabiting a site, the contamination processes prevalent within its local catchment area and its location within the catchment as a whole. Methodological recommendations for the future are made.

A method of quantifying the susceptibility of upland catchments to acidification, utilizing the influence of atmospheric sea-salt deposition in maritime dominated climates, is evaluated. Inputs of marine-derived Sodium (Na) provide a scale against which to measure inputs of alternative base cations, principally Ca and Mg, which are released through weathering reactions. Hence, the use of a Na base cation dominance index, as a means of quantifying catchment weathering rates, is proposed. Mineral weathering is important as it provides the only long-term sink for acid inputs including those of anthropogenic pollution. The Critical Loads approach provides a scientific tool with which to address appropriate levels of pollution control legislation by deriving acceptable levels of pollution below which sensitive components of various ecosystems will not be damaged. Critical loads for soils and freshwaters currently rely on methods to determine crucial base weathering rates and associated alkalinity generation. Existing methods are complicated and data intensive and have attracted a level of criticism from scientists in this field. The calibration of the index for streamwaters against both catchment weathering rates and alkalinity production is described across a major river system in Northeast Scotland. Clear differences are demonstrated between relative base cation proportions in streamwaters, soil solutions and on soil exchange sites. Atmospheric base cation inputs are generally shown to exceed those from internal weathering sources. The %Na dominance approach is proposed as being a cost-effective, field-based determination method capable of achieving a greater degree of reliability in the determination of weathering rates. This research has shown that the index has the benefit of providing a unifying approach between catchment soils and surface waters, which is currently lacking in critical loads methodology. The index has potential to describe both spatial and temporal variations in catchment weathering at a range of scales.

No description available.