No description available.

Clear links are known to exist between the terrestrial characteristics of catchments and the chemistry of their surface waters. During the last decade it has been established that atmospheric pollution, in the form of acidic deposition, can also influence the chemistry of waters draining sensitive upland sites. Furthermore, recent studies have suggested that reductions in these anion loads can have marked consequences for the surface-water quality of acidified catchments. However, many of these field experiments and model estimates have neglected other, potentially important realms of atmospheric influence. This thesis proposes that climate change over periods of up to one century can alter the hydrogen-ion budget of a catchment in two ways. First, variations in the relative frequency of large-scale synoptic features may significantly modify catchment chemical budgets by changing existing spatial and temporal patterns of acidic deposition. Secondly, as each major class of weather type is characterised by distinct precipitation and temperature regimes, the seasonal magnitude and frequency of acidic episodes may also be affected by long-term adjustments to the catchment water-balance. A hydtological perspective was employed in order to investigate these potential hydrochemical relationships. This involved hydrological modelling and hydrogen-ion budgeting, statistical analyses of climatic trends, the application of weather classification schemes, and the generation of synthetic input data from observed and historic meteorological data. These elements were combined by the development of a robust and comprehensive computer package (the Shifting Climate and Catchment Acidification Model, or SeAM) which enables the manipulation of a wide range of atmospheric and catchment properties. The model was calibrated and validated against data obtained from the Beacon experimental catchment in the East Midlands and then transferred to three contrasting watersheds in the Llyn Brianne region, Mid Wales. Using multiple climate and pollution scenarios, modelling experiments revealed that variations in the predominance of three key weather types modified the mean annual wet-deposited acid load by ±20% and the mean surface-water acidities by up to ±15%. Under the most extreme scenario the frequency of daily flows of less than pH 4.5 was increased by +90%. Whilst recognising the simplicity of the hydrologic ally-driven soil model, a feature common to all of the catchments was the exaggeration of existing seasonal discharge and acidity regimes. The sensitivity of individual catchments to a given climate change was found to be highly variable, depending upon the complex interaction of hydrology and catchment characteristics. It was concluded, therefore, that the effect of reduced emissions of acidifying substances on catchment recovery can be modified by climate change. Furthermore, acid-sensitive species occupying marginal sites, could be affected by the changes envisaged under the proposed BASE scenario. This underlines the need for a definition of the term 'critical load' that embraces desirable ecological responses with the required acidic deposition rates, for a given climatic context.

The thesis is devoted to a consideration of soil factors influencing the availability of trace metals for plant uptake, with particular reference to waterlogging. Chapter 1 includes a brief survey of the roles of trace metals in biological systems and the forms which exist in soil fractions. The forms of trace metals influenced by environmental factors are also discussed. The importance of waterlogging in influencing the distribution of trace metals is discussed in more detail, as are the relevant chemical changes taking place in the soil with various waterlogging times and depths. The objectives of the thesis are to investigate the effects of waterlogging on the redistribution of trace metals in soil and the implications for plant uptake. The case is made out for this study.

No description available.

This study examines the sedimentary and morphological flood record of the River Tyne, northern England, over the last 400 years. Temporal trends in flooding and spatial variations in the timing and nature of river response to floods (flood "effectiveness") are investigated at 3 reaches representative of upland, piedmont and lowland locations in the Tyne catchment. Deposition of coarse flood sediments in headwater tributaries of the River Tyne appears to be strongly related to flood water:sediment ratios that is primarily controlled by sediment supply. Cobble - boulder bars, sheets and splays are deposited under Newtonian flow conditions from flows with relatively low sediment concentrations. Boulder berms and lobes result from floods with high sediment loads, associated with slope-channel coupling. Flood sedimentation in lower reaches of the Tyne comprises vertical accretion of fine-grained, well-bedded sediments at overbank and within-channel locations. Larger floods can be identified on the basis of textural discontinuities that reverse the overall fining-upward sequence. Estimation and interpretation of flow magnitude in each setting is complicated by progressive river bed incision over the period of investigation and significant changes in sediment supply which have affected the nature of flood sedimentation. Trace metal dating of fine-grained, and lichenometric dating of coarsegrained, flood units has enabled detailed and temporally well-defined records of channel and floodplain response to flooding to be established within the Tyne catchment. Since 1600 A.D. fluvial activity at all 3 study reaches has been characterised by alternating periods of river bed incision and stability. Episodic changes in vertical channel stability appear to coincide with non-random decadalscale fluctuatiions in flood frequency: 3 periods with distinct clustering of large floods (1740-1790, 1860-1899, 1940-1965) were associated with vertical instability (channel trenching) throughout the Tyne basin, while intervening periods with relatively few exceptional floods were associated with channel accretion and floodplain rebuilding in general, but with significant upstream/downstream variation. Distinct clustering in the timing of large floods correspond with shortterm hydroclimate changes associated with fluctuations in the configuration of the upper atmosphere. These findings have significant implications for longer-term fluvial development and interpretaion of Holocene alluvial sequences.

There is currently worldwide interest in the effect of human activity on tile global environment, especially the effect of greenhouse gases and land-use change on the global climate, and models are being developed to study both global change and the local effects of global change. The research reported here (funded by CNPq-Brazil) involves the development of GRASP:Groundwater Recharge modelling Approach with a Scaling up Procedure. GRASP has been integrated into the UP (Upscaled Physically-based) macromodel, developed under the UK NERC TIGER programme, which is designed for studying the effects of climate and land-use change on the availability and quality of water resources. The UP macromodel will be coupled to the UK Meteorological. Office's Unified (weather and climate) model to create a state-of-the-art coupled atmospheric/hydrological model. Several important requirements for the design of new large-scale hydrological models are identified in a wide ranging review on GCMs; (General Circulation Models) and physically -based hydrological modelling, and these requirements have been applied in the development of GRASP(and UP). The main requirements are a physical basis, proper treatment of spatial variability, and simplicity. Using the concept of partial analysis, two point-scale models, SM (Soil Moisture content approach) and TF (Transfer Function approach), are developed for recharge, both based on the one-dimensional Richards' equation. SM is a simple two-parameter model relating recharge to water storage in the unsaturated zone, and several unsuccessful attempts are made to link its parameters to physical propcrties. TF is a transfer function model, and is parameterised using the matric potential and unsaturated hydraulic conductivity functions using a new approach developed especially for GRASP. Both SM and TF are verified against numerical solutions of Richards' equation.

An analysis of a number of flood routing methods has been carried out in this study. These methods are namely, the Muskingum-Cunge Method, the Variable Parameter Diffusion Method, the State Variable Kinematic Wave Model, and the state variable modelling of nonlinear Muskingum Model. The Muskingum-Cunge and Variable Parameter Diffusion Methods are recommended for use on British Rivers by the Natural Environment Research Council flood studies report, 1975.In using numerical flood routing model, it is very important to calculate the model parameters. For instance storage routing models require a suitable form of storage-discharge relationship. Past flow records were used for the above calculation. The state Variable Kinematic Wave Model has been applied for routing the flood hydrograph through river reaches. The stage and discharge are computed by a kinematic wave routing technique using the state variable approach in which the one-dimensional differential equations of unsteady flow are solved by state and output equations of the state variable model. The nonlinear Muskingum equation has been solved using the state variable modelling technique. Two parameter estimation techniques namely, Hooke-Jeeves and linear regression, are employed for the calibration of the nonlinear Muskingum model parameters (a, x, and m).The applicability of the flood routing model computer programs to different flood events of different seasons for reaches of both the Rivers Wear and Tees is demonstrated. Discriptions of the geology and hydrological data for reaches of both the Rivers Wear and Tees are given in this study. The computed and observed hydrographs of flood routing models used in this study are compared.

No description available.

This thesis investigates the inter-relationship between hydrological and water quality variations with reference to backwaters and dead zones in rivers. The examination of a series of controlled reservoir releases to an upland channel in Wales showed "in-channel" dead zones were important solute source and storage areas. Physico-chemical data have been presented to show the influence of main channel flow and quality variations on the hydrochemistry of a range of seven backwaters within the Trent basin. The hydrological regime of the mainstream seasonally modified backwater quality. The degree of main-flow influence declined with decreasing hydrological connectivity of the backwater environments with the mainstream. Furthermore other hydrological, biological and biogeochemical factors influenced backwater physico-chemistry. A generalised typology of permanent floodplain water bodies in the R. Trent catchment based upon water chemistry was established. An applied study examined the effect of reservoir cleaning/emptying operations and flood events on backwater hydrochemistry on the French Upper River Rhone. The simultaneous occurrence of decreasing mainstream discharge with the passage of the sediment laden release wave reduced its impact on backwater environments. Anthropogenic influences on riverine systems as a result of intensification of agriculture and urbanisation (e.g. nitrate pollution and river regulation) have influenced the hydrological and physico-chemical functioning of fluvial hydrosystems. In view of rising nitrate levels in many British rivers, trends within the Trent basin have been investigated. Rates of increase in concentration of 0.06 mg.l-1 N yr-1 were typical of rural catchments, whilst rates of up to 0.20 mg.l-1 N yr-1 were recorded in urbanised tributaries. Furthermore the impact of rising nitrate levels in the Trent catchment and river regulation on backwater hydrochemistry and ecology have been examined.

No description available.