Perturbation of natural environments through anthropogenic nitrogen (N) inputs and climate change significantly alter soil systems. Few pristine environments remain in which to study natural controls on the development of soil N cycling over time and thus increase our understanding of the natural development of such mechanisms. This study took place in Glacier Bay National Park and Preserve (GBNP), southeast Alaska. This area presented a unique opportunity to study microbial cycling in near pristine soil systems. Six river catchments were selected for study across a chronosequence of 200 years of primary succession. Within each watershed soil nutrient content and microbial processes where evaluated to determine a time frame for development. Samples were collected from riparian and wider catchment areas in order to investigate the effects of dominant vegetation types and slope steepness. These data were coupled with percent vegetation type generated by analysis of satellite imagery allowing the scaling up of soil variables. A key finding of this research was that vegetation type is the primary influence on nitrogen cycling processes and soil characteristics. With increasing age potential microbial activity increased in particular nitrification, which linked with the low soil NO\(_3\)- indicated a large heterotrophic microbial community in older soils.

A physically-based, distributed sediment yield component has been developed for the SHE hydrological modelling system. This new component models the hillslope processes of soil detachment by raindrop impact, leaf drip impact and overland flow, and transport by overland flow. If the eroded soil reaches a river system it is routed downstream along with any inobilised river bed material. Deposition on land or in a river is simulated and the river bed material size distribution is continuously updated with allowance for armour layer development. The equation developed for soil detachment by raindrop and leaf drip impact was successfully tested using data from a field plot with a range of soybean canopy covers and rainfall intensities. The soil detachment coefficient in this equation was determined for a range of soil types and showed a variation consistent with that which may be expected from a consideration of the physics of a soils resistance to detachment. At present two soil detachment coefficients need calibration. In order to investigate the variation in these coefficient values, as well as to test the component, various applications were carried out. The hilislope sub-component was applied to rainfall simulator plots with a variety of surface conditions. Two sets of calibration parameters, distinguishable on a physical basis according to the degree of soil disturbance, were found to be appropriate for all the plots. To investigate scale effects, parameters calibrated at the rainfall simulator plot scale were transferred to a 1-ha rangeland sub-catchment. With no further calibration, the catchmerit response for four events was poorly simulated for both water and sediment. However, with reasonable variations in the antecedent soil moisture content but no variation in plot calibrated sediment parameters, the sediment yield for two of the four events could be successfully simulated. These applications suggest that parameter transfer is feasible if the sediment yield characteristics at the different scales are similar. Further applications of the hilislope sub-component were carried out for two small agricultural catchments. The sediment response could be simulated to at least the same accuracy as achieved by two existing distributed soil erosion models. The channel sub-component was applied to the East Fork River, Wyoming. Although the complex sediment storage/supply effects could not be reproduced completely, the simulated response was nevertheless of similar accuracy to that achieved by two existing alluvial river models. The new component is considered to be a valuable contribution to sediment yield modelling as a physically-based approach is used for both the hilislope and channel phases of the catchinent sediment system, within the framework of an advanced hydrological modelling system.

Lake sediments from inland endoreic (saline) lakes in the semi-arid Ebro Basin, NE Spain have been analysed to provide a history of lake level, vegetation, catchment erosion and anthropogenic activity over the last 10,000 years. Analysis was undertaken for pollen, macrofossils (seeds, Cladocera ephippia, Chironomid head capsules etc), charcoal, geochemistry (total cations/trace metals, sulphate, carbonate & LOI) and sediment composition. Fourteen AMS radiocarbon dates provide dating control. Seven cores were investigated from 4 seasonal playa lakes, I shallow (<1.5m) semi-permanent salt lake, 1 deep (5.0m) permanent salt lake and 1 Medieval-age reservoir. Over 40 surface samples were also taken to investigate modern analogue environments. A review of the use and interpretation of saline lake macrophytes (seeds & pollen), Cladocera and Chironomids in palaeolimnology is provided, with special emphasis on those found in Spanish salt lakes. Taphonomic problems and nearshore-offshore facies were also investigated using a surface sample transect across a small playa lake. A surface sample pollen data set from 30 lakes in the Ebro Basin is presented and the implications for palaeo-interpretation discussed. The sensitivity of the pollen record as a climate indicator is investigated using 6 sites across a climatic gradient from sub-humid to semi-arid. Lake level reconstruction is based on an 8 stage semi-quantitative palaeohydrological model, developed from a surface sample data set from 32 lakes ranging from temporary to permanent, and hypersaline to freshwater. A simple hydrological model for groundwater fed lakes is also discussed which can be used to quantify these palaeohydrological changes. The early Holocene (<9.3-8.6Kyr BP) was characterised by semi-arid extreme continental conditions in the Ebro Basin, with an extensive Juniper thurifera woodland. Lake levels rose to their highest point in the Holocene between 8.6-7.2Kyr BP when evergreen oak and pine forest dominated. This is interrupted by a short recession in lake level between 8.2-7.6Kyr BP. A distinct regional early-Neolithic fire and clearance event occurs between 7.7-7.3Kyr BP. A drop in lake level and development of a monospecific pine forest (P. halepensis) indicates warmer and drier conditions in the mid Holocene (7.2-5.4Kyr BP). Evergreen oak reappears as forest cover declines after 5.4Kyr BP, although this is not marked by any increase in charcoal or cultivation indicators. Low groundwater but moderate lake levels (4.0-2.7Kyr BP) may be linked to high summer storm frequency and low winter rainfall. This coincides with catchment erosion and valley floor alluviation. Lake level rises again significantly between 2.7-1.8Kyr BP during Iberian and Roman times when archaeological evidence indicates a peak in population. Agriculture changes from small scale pastoral to small scale arable without any further decline in woodland cover. A rapid fall in lake level at ca. 1.8Kyr BP is followed by complete forest recovery (P. halepensis) and depopulation, until major deforestation around 1.4Kyr BP marks the arrival of the Visigoths/Arabs and extensive nomadic pastoralism. Intensive grazing pressure or lower temperatures resulted in Juniperus increasing again between 1.4-0.4Kyr BP. This also coincides with a second period of catchment erosion and valley floor alluviation. After ca. 0.4Kyr BP, lake levels have increased along with extensive olive cultivation and the development of modern (irrigated) arable agriculture.

The management of large scale strategic urban combined drainage systems is becoming increasingly dependent upon weather radar systems which can provide quantitative precipitation information to improve the overall efficiency of a system's operational performance. Thus, there has been an increasing requirement for a more detailed knowledge of the radar rainfall data accuracy and the development of a mathematical rainfall-runoff model that can be used to analyse and control a system in real-time. Within this context, several important factors including signal attenuation, temporal and spatial data resolutions and rainfall quantisation schemes that determine the accuracy of radar rainfall estimates were examined in this thesis. In order to facilitate real-time flow simulation and forecast, a Conceptually Parametrised Transfer Function (CPTF) model has been developed based on Dynamic Linear Reservoir theory. The model is structurally simple and operationally reliable. It can be easily identified and robustly updated following a pulse response-to-CPTF procedure in which Genetic Algorithms play a key role. Using the model, the accuracy of areal rainfall estimates obtained by the Hameldon Hill radar has been assessed, firstly by comparing the radar rainfall estimates with `ground truth', and then by comparing the simulated hydrographs with the actual flow observations. Finally, a case study was conducted using radar rainfall data to highlight the potential benefit of real-time control for the strategic urban drainage system in the Fylde Coast. The major achievements documented in this thesis are: 1) A rule for determination of an appropriate input data resolution for hydrological models; 2) A general probability density function for describing the sampled radar rainfall intensities; 3) An efficient quantising law (ß-Law) and an associated adaptive rainfall quantisation scheme; 4) Three general conceptual pulse-response functions developed based on Dynamic Linear Reservoir theory; 5) CPTF model; and 6) A case study on the potential benefit of real-time control in the Fylde urban drainage system.

Suspended sediments were collected from 3 rivers, the Rheidol, Ystwyth and Tywi on a regular basis. The sediment samples were studied for a number of physical and chemical properties to identify characteristics which might distinguish between source areas. These properties included mineralogy, magnetic properties, sediment colour, and the trace element composition of .sediments. Point-sources for heavy metals can be identified for all three catchments, and the metal content, and partitioning was studied. The metal content, and the site on the sediment to which the metal is bound has been found to vary with discharge. The response to discharge is not the same for all metals, but in general, at peak discharge the lead was in the Fe/Mn oxide and organic fractions, and these fractions became important for cadmium. Prior to the flood peak however, up to 70% of the cadmium was in easily exchangeable form. The organic fraction was the most important for copper throughout the flood. j Sediments which had been deposited in floodplain features and in lakes were also studied, as they recorded the pattern of sediment transport during floods over an extended period. In the Ystwyth catchment the metal content and ratios between metals was used to determine the importance of two mining areas for the supply of sediment to a floodplain during the mining period (1860-1890). Sediments from profiles in fossil alluvial channels on a floodplain in the Rheidol showed a dramatic increase in metal .concentrations in the mid-profile, and recorded the period of concerted mining in the catchment. Mining operations in the Ystwyth catchment caused widespread lateral aggradation of floodplains, as established at Trawscoed. The historic record of catchment changes as contained in the sedimentary profile of reservoirs in the Mendips was studied. The record in Blagdon and Chew Valley lakes in the Mendips was deciphered using a combination of sedimentological, magnetic and chemical data. A catastrophic flood which is documented for the area, which occurred in July 1968, caused the mobilisation and transportation of sediments from dry valleys in the catchment. Sediments deposited during the floods were distinguished by their coarse nature, by an increase in magnetic susceptibility and the parameter'S', which indicated a topsoil source, and by a change in the partitioning of lead and zinc, where the organic fraction was absent.

The River Thurne catchment on the north-cast coast of Norfolk contains large areas of marshland, including several Ramsar-designated sites. Land drainage of much of the marshland over the previous centuries has lowered groundwater levels to below sea-level. Consequently, saline groundwater has intruded into a large proportion of the underlying Norwich Crag aquifer, thereby raising the salinity of the surface water networks. Changes in the economics of arable farming and the perception that changes in the land drainage regimes will produce beneficial effects on the water quality of the River Thume and its associated Broads have necessitated the need for a better understanding of the hydrogeology of this complex, highly managed aquifer. To provide the necessary understanding, this study has investigated the hydrogeology, hydrology and land management of the catchment using a variety of geophysical techniques, including electrical resistivity soundings EM surveys and reflection seismology to supplement information collected using standard hydrogeological measurements The distribution of dyke water levels as maintained by the drainage pumps are shown to exert important controls on the extent and depth of saline intrusion. In the north of the catchment a further control is the internal structure of the Crag aquifer. A clay layer of probable Baventian age divides the Crag aquifer into two units and appear to prevent the salinization of the aquifer above this layer. A catchment water balance has shown that land drainage pumps discharge about 95% of the catchment recharge, so that raising dyke water levels will also result in raised groundwater levels. Futurel and use change to grazing marsh, while improving the water quality of drainage water entering the River Thurne may lead to increased salinization of the aquifer, as a result of changes in the distribution of dyke water levels.

The study traces the history and development of Loe Pool, a 50 hectare freshwater coastal lake near Helston, Cornwall. using a wide variety of palaeolimnological and associated research techniques. The principle upon which such research is based is that there is an intimate relationship between the history of a catchment and the lake into which it drains. In addition, the history of the shingle bar which now isolates Loe Pool from the sea is explored, as this has also had a significant bearing on the lake's physical and ecological development. The study uses a combination of lines of evidence to interpret the development of the lake-catchment system. Palaeolimnological techniques. employed include the examination of the physical nature of the lake sediments themselves, and chemical and biological analyses, in particular for sub-fossil diatoms. These are used to establish both a chronology of sediment deposition, and also a detailed history of the principal ecological changes experienced by the Pool. In addition, a considerable amount of historical documentary and cartographic 'material is incorporated in the study, in order to provide corroborative evidence of the major events that have taken place in the history of the lake and catchment. The results highlight the main influences on the lake, and in particular, those of the last two hundred years. Marine incursions dominated the lake's history up until the late 19th century, when both natural overspill of lake water and the customary practise by local residents of 'breaching the bar' ceased. Tin mining within the catchment has also had a major impact on the lake and has given rise to several periods of very rapid sediment accumulation, the most significant of which took place in the 1930's and 1930's. Following the cessation, in 1939, of all mining activity within the catchment, the discharge of treated sewage effluent, which had begun in 1930, became the dominant influence upon the lake's ecology. It is hoped that such an historical background will allow a more sympathetic management of the lake in future years.

Geophysical, hydrochemical and hydrogeological investigations were undenaken to evaluate the groundwater prospects in the study area. The factors which affect/determine the spatial development of ground water in the area was also examined. The results show that the essential conditions for groundwater availability in hard rock terrains are satisfied. The average weathering depth is 34 m, rainfall is high and seasonal and the geological evolutionary sequence included tectonic phases during which suitable geological structures are expected to have been developed. Analysis of borehole drilling records revealed that each borehole encountered at least one water strike. The clay mineral stable in the prevailing physico-chemical conditions is kaolinite, an evidence that weathering sites are being flushed presumably by flowing groundwater. Available results of isotope analysis also show that the stable isotope concentration in the groundwater is similar to that of current meteoric water. It is therefore concluded that the ground water is receiving current recharge. Infact water balance calculations and results of baseflow analysis indicate that this recharge is substantial. The yields of the boreholes varied greatly spatially ranging between 0.7 and 10.9 I/s. This may be low compared with values quoted for sedimentary rock terrains, but in view of the present low level of water supply in the area, it is considered that exploitation of this resource would represent a significant improvement on the present situation. A physical catchment hydrogeological model is presented to explain the observed spatial variation in yields. In this model, a threshold elevation is considered to exist in each catchment. At elevations below this threshold, borehole yield is sustained entirely by fracture flow. At elevations above this threshold, borehole yield is sustained by storage in the weathered rocks. Pumping tests on large diameter wells show that groundwater abstration using these wells would be greatly improved by repeated pumping after every 60 - 80 minutes recovery. An equation is presented for calculating the number of times a well can be repeatedly pumped in an operating day. The drawdown of the boreholes contained a large well loss component. This well loss was incurred during the early stages of pumping when water had to be withdrawn from well storage to supplement the aquifer flow in order to meet the pumping capacity. Field results presented indicated that the drawdown can be minimised by stepping the discharge rather than imposing it all at once at the onset of pumping. Field results indicate that the use of well water levels for mapping the water table may not be valid in weathered hard rocks.

No description available.

No description available.