Understanding the link between tectonics and climate and their consequences in landscape evolution is a major current issue in Earth sciences. Bedrock rivers are an important component of the landscape because they transmit changes in tectonic and/or climatic conditions by setting bedrock incision rates to which the landscape must be adjusted. Nevertheless, there remain unresolved issues in relation to bedrock river processes and response to perturbation. The effects caused by propagation of a knickpoint triggered by a sudden drop in base-level remain to be fully clarified. Questions about rates of knickpoint recession, the control exerted by structure and lithology, the morphological response of rivers after knickpoint recession and whether bedrock incision rates are re-established after the passage of a knickpoint, as theory predicts, are all issues that need to be clarified. Moreover, the estimation of bedrock incision, which is key to understand transience in landscapes, has relied on the stream power model, mainly tested on large fluvial settings. Whether the stream power model is valid for small bedrock rivers is not well understood. Some of these questions are tackled in this research, by studying small bedrock river catchments. The case of a knickpoint propagation on a homogeneous resistant lithology (quartzite), triggered by an instantaneous base-level lowering ( 18 m in 13.6 ka), is evaluated here, as well as the effect of structure and the morphological response of rivers to base-level fall. Two approaches were followed: (1) stream profile analysis using slope-area and distance-slope plots and (2) the analysis of terrestrial cosmogenic nuclides to obtain erosion rates. The Isle of Jura, located in the west coast of Scotland, was selected as natural laboratory because bedrock rivers incise the landscape and rapid rock uplift resulting from glacio-isostatic rebound after the Last Glacial Maximum has left the Jura landscape in transience. The present research is organised in seven chapters. In chapter 1, the motivation for this research is presented. In chapter 2, a review of theory underpinning research on bedrock rivers, landscape evolution and knickpoint generation, is detailed. The relevant studies in the field are also reviewed. The physical setting of Jura is characterised in chapter 3, as well as the morphometry of catchments, stressing the effect of Quaternary glaciation on the landscape of Jura. Unpublished exposure ages and analysis of the resultant raised beaches (~35 m OD) of Jura’s west coast are used to demonstrate a sudden drop in base-level in Jura ~13.6 ka. Chapter 4 details how stream long profiles were extracted and how the slope-area (SA) and distance-slope (DS) analyses were undertaken. This chapter 4 shows that the Jura rivers have strong imprints related to glacial processes and base-level fall, making it difficult to use SA and DS models to estimate channel incision as has been done for large fluvial settings. Chapter 5 is explains how the base-level fall knickpoints were identified and it is shown that stream discharge is a first-order control on knickpoint propagation. Structure and lithology, on the other hand, are not first-order controls on knickpoint recession. Chapter 5 also evaluates the vertical distribution of knickpoints and morphological response of rivers after knickpoint migration, with the results indicating that stream power controls the vertical distribution of knickpoints and the morphological response of rivers to base-level fall. A threshold of ~5 km2, where rivers’ ability to modify their channel, resulting in a channel convex profile, is also identified. In chapter 6 the problem of bedrock incision and the role of sediment is tackled. Based on the sampling of sediment in fieldwork, it is demonstrated that the median fraction in the rivers of Jura is ≈45 mm and grain-size neither fines nor increases with stream discharge and channel slope, strongly indicating that detachment-limited conditions are likely to control bedrock incision. In the second part of chapter 6, the incision rates upstream and downstream of the base-level fall knickpoint are obtained to test whether incision rates are re-established after knickpoint propagation. Incision rates were obtained from the concentrations of cosmogenic 10Be in samples extracted from the river bed. The results indicate that incision rates are not re-established at an expected value of ≈ 0.1 m/k yr after knickpoint migration. Rather, incision rates below the knickpoint remain somewhat elevated (≈ 0.5 m/k yr) reflecting: (1) ongoing base-level fall, and/or (2) the propagation of younger knickpoints (< 13.6 ka) in those transient reaches. The cosmogenic-derived incision rates were tested with different bedrock incision rules. The results indicate that the stream power model is a good predictor for channel incision, even for the case of small catchments. In chapter 7 the conclusions of this research are provided.

Postglacial bedrock river erosion is likely to be a major control on the evolution of deglaciated landscapes. This study provides a quantitative assessment of bedrock channel change in a postglacial, post-orogenic terrain, encompassing the long-term evolution of bedrock channel distribution, geometry and the timing and rate of fluvial incision. In the NW Scottish Highlands, fluvial incision is focused on steep valley headwalls and at knickpoints formed at inherited glacial valley-floor steps (riegels). Holocene average incision rates of 0.4 – 1.3 m/kyr were measured using cosmogenic surface exposure dating (10-Be) at five strath terrace sites. Incision rates of 0.1 m/kyr were quantified from active channel beds and are lower than the Holocene average. This finding is consistent with a paraglacial decline in sediment supply being responsible for a reduction in fluvial incision in detachment-limited channels. Further support for a paraglacial sediment influence on bedrock channels is found in the long-term increase in the proportion of bedrock-exposure, reflecting a decrease in the critical slope threshold for the alluvial to bedrock channel transition. In reaches that have undergone a switch from alluvial to bedrock channel conditions, the onset of fluvial incision into bedrock was found to lag deglaciation by 2 – 4 kyr, suggesting that a substantial reduction in sediment availability occurred within several thousand years of ice retreat. Hydraulic conditions and substrate resistance are also major controls on the distribution and geometry of bedrock channels, and the rate of fluvial incision, in the NW Highlands. The geometry of both bedrock and alluvial channels was found to be strongly hydraulically scaled, with bedrock channels significantly narrower than coarse-grained alluvial channels. Lithology also governs the critical slope for alluvial to bedrock channel-transition; resistant metasedimentary bedrock produces relatively coarse-grained bed material with a high threshold for sediment entrainment, meaning that alluvial channels occur up to comparatively steep channel slopes. Lithological resistance also constrains the process and rate of fluvial incision. A new lithological resistance index, the ratio of joint spacing to intact rock strength, successfully discriminates between abrasion and plucking dominated channels and is non-linearly related to incision rate. The pulse of postglacial incision in bedrock channels has resulted in 2 – 8 m of entrenchment into valley floors since deglaciation. Bedrock channels narrow during entrenchment, achieving a consistent hydraulic geometry when entrenched to between 1 and 2 times the bankfull flow depth. Width adjustment occurs within 8 – 17 kyr of ice retreat, but adjustment of channel slope takes considerably longer and the long profiles of NW Highland rivers remain strongly glacially conditioned. Entrenchment disconnects channels from floodplains and may have contributed to the decline in paraglacial sediment flux, suggesting that fluvial incision may be a self-limiting process in post-orogenic postglacial terrains.

The impact of a 1 in 40 year flood on the morphology and sedimentology of the sandy braided South Saskatchewan River, Canada was assessed. Comparison of 2004 - 2007 repeat GPR surveys and the production of DEMs of difference allowed quantification of the initial and long-term 2005 flood impact on reach morphology and sedimentology. Main results show that even though a significant initial morphological impact was caused due to the flood through net erosion and channel incision across Bar A, subsequent low-magnitude high-frequency floods were able to rework morphology due to the ability to transport the medium sized sand bed load. In the subsurface, no distinct flood signature has been left, as flood deposits are similar to the scale and composition of deposits produced by low-magnitude high-frequency floods. Consequently, little evidence of such a flood event will be preserved in the sedimentary record. The research has also highlighted some important findings with respect to linking morphological processes to sedimentary deposits. In particular they have suggested the revision of depositional models for braided rivers, and further research on the relationship between bedform geometry and flow depth in natural rivers. The results have wider applications to other sand bed braided rivers and may aid interpretation and modelling of such deposits on a wider scale.

This thesis considers the geochemical links between geophysical survey results from, and responses of barley crop growth to, the existence of plough-levelled archaeological sites. It takes as a starting point the results of magnetic and resistivity surveys undertaken at three sites in the Upper Clyde Valley, Lanarkshire, Scotland. Two of the three sites produced geophysical results that closely matched the evidence for archaeological remains recorded using oblique aerial photography. The third site was largely unresponsive to geophysical prospection techniques. These mixed responses prompted a closer examination of why barley crops respond to plough-levelled remains, and why the geophysical data gathered tend to correlate with the growth responses. To allow an examination of the growth responses, a series of pot-based growth experiments were carried out under glasshouse conditions, and these were followed up by ICP-MS analysis of the plants and the archaeological soils in which they had grown, in an attempt to link any changes in elemental compositions with the growth responses, and to the geophysical responses recorded at the soil sampling points or for the features from which the soils were taken. The results of the experimental work revealed that although soil moisture content has a role in the development of both crop marks and geophysical anomalies, other factors are also involved, including changes in elemental concentrations in soils and plant material, soil pH changes and the redox potential of the archaeological soils.

Of numerous aeolian studies around the world, few have been dedicated to dust trapping in the Saharan regions and none is known in Libya. This research aims to explore the extent of dust activities in the western part of Libya, the main factors that influence dust entrainment and deposition, the likely regional emission sources transporting aerosol to this part of the country and ultimately to establish base line information in space and time based on a study area larger than the size of the UK. Dust trapping was carried out at thirty sites on a monthly basis starting from the beginning June 2000 until the end of May 2001. A physical characterization of 274 aeolian sediments were based on grain size distribution analysis and the mineral composition was based on XRD testing of 24 dust samples taken from extreme locations near the Mediterranean Sea and about 800 km inland. An assessment of dust emissions within the area of study, the vertical deposition rates in relation to The Total Ozone Mapping Spectrometer (TOMS) data have been investigated. Moreover, an attempt identify potential Saharan dust emission sources that have impacted the study area has also been made utilizing TOMS data. The area of study has been divided into three regions northern, central and southern according to the dominant factors controlling mobilization of dust particles on the bed surface. This study concludes that deposition rates in the northern coastal region are largely dominated by human activities. Rates in the central region were strongly affected by topographic irregularities whereas in the south deposition rates were less affected by topography and anthropogenic activity. However, deposition rates and particle size distributions are strongly controlled by wind regimes and correlate with the average atmospheric temperatures. Local sediments seem to be strongly affected by saltating particles in most of the study area and no evidence of long range aerosol emission from western Libya was found. Nevertheless, fine dust (<10 gm) is wide spread in the local atmosphere, however it is more pronounced during late spring and summer. TOMS data and the prevailing wind directions reveal that the depressions of the Libyan Desert and the Bodele Depression in Chad were the main sources of aerosol transported over the study area during the highest months of emission, transport and deposition, July and April. It is hoped that this baseline information can pave the way for future studies on dust impacts on soil fertility, human health, desertification, climate change and the validation of present day computer models.

In the past decades, engineers have started to realize the importance of the interaction between vegetation, biota and water flow, in riverine and marine environments; a discipline that has been named “Eco-Hydraulics”. Scientists have valued this coupled phenomenon for much longer than their engineering colleagues. As early as 1970, marine researchers presented the evidence that colonies of micro-organisms might alter the stability of fine cohesive sediments (Neuman et al., 1970). However traditional models of sediments transport (e.g. Shields, 1936) have been derived using abiotic sediments and did not consider that most wet surfaces would soon be colonized by micro-organisms and their extracellular polymeric substances (EPS), a combination called “biofilm” (Lock, 1993). Scientists during the 1990s, after observing this phenomenon in the field, coined the term “biostabilization”. During this period they showed that colonies of cyanobacteria and diatoms coating fine sand or cohesive sediments can increase their stability by up to 960% compared to abiotic sediments (Grant and Gust, 1987; Dade et al, 1990; Paterson 1997). Only recently have engineers started to take into consideration the effect of such increased cohesion and adhesion due to biogenic forces within the sediment transport model (Righetti and Lucarelli, 2007); yet all of those studies have low applicability because they are linked to specific environmental conditions. Moreover no data are available on the effect of biofilm on larger sediments (e.g. coarse sand and gravel). The present thesis provides experimental data carried out in a flume laboratory pertaining to biostabilization of non-cohesive coarse sand and gravels at a scale representation of a real river system (from 0.2m to 1m). Four sediment substratum (glass spheres of D50 = 1.09mm and 2.00mm; sand of D50 = 1.20mm and gravel of D50 = 2.20mm) were colonized under unidirectional flow by a cyanobacterium (Phormidium sp.) for between 1 and 10 weeks. The increase in erosion threshold for biotic sediment is then investigated using a series of different methods ranging from traditional sediment transport techniques (e.g. Yalin, 1972), to image thresholding and particle image velocimetry (PIV) assessments of flow modification due to biofilm presence. Moreover, tensile strength analysis of ex-situ biofilm/substratum specimens will be presented to understand better the mechanical property of this composite material. Data indicates that: i) biostabilization of sediments in the range of coarse sand and gravel occurs (9%-150% more shear stress required to induce entrainment compared to abiotic sediments) but to a lower extent compared to critical entrainment thresholds for fine sand and cohesive sediments (Paterson, 1997); ii) flume experimentation can be employed to control specific variables affecting biostabilization and could help to unfold the complicated interactions between environmental variables, and the affect of flow on the growth and strength of biofilm colonization over sediments; iii) strong biofilm growth generated a more uniform velocity field, with reduction in shear stress (up to 82% compared with abiotic sediments) and decreases in roughness length of the bed (up to 94% compared to abiotic sediments); iv) Composite biofilm/substratum specimens presented a clear elastic behaviour when tensile tested; v) Conventional models of sediment transport (e.g. Wiberg and Smith, 1987) do not consider the presence of biofilm and will not work in the case of bio-mats smoothing the surface of the bed; hence the need for new models which include the biofilm elasticity and the bio-mat smoothing process. This thesis suggests two theoretical examples where the biofilm action is considered at a grain to grain and bio-mat scale.