Search

Fluid flows effected by surface tension variations are considered. A discussion of the various agencies causing these variations is given together with laboratory, industrial and natural illustrations of such flows. The equations of motion, mass transfer and state for the surface phase are described and discussed. The various theoretical models produced for Bernard's cells are described and compared. Yih's model for two dimensional variable surface tension driven flow when the variation is caused by an insoluble contaminant is discussed and an analysis of a singular point in a phase plane is used to examine' the possible instabilities in such a flow. By extending Yih's analysis, a model is produced for the flow in a shallow fuel layer near, but not close to, a burning wick. The solutions for the variations of surface tension and fuel depth with distance from the wick are obtained numerically. A separate solution, developed from slow viscous corner flow theory, is provided for the flow close to the wick. Neglecting the variation of depth associated with these flows, a model is produced for the effect of a heat source placed at the corner of a rectangular cell. The solutions are found using a Green's function which is obtained as a series of eigenfunctions and eigenvalues. A model produced for flow owing to a moving heat source involves the solution in a fast moving boundary layer close to the surface by formulating Yih's basic equations in a moving frame and then obtaining' numerical solutions for surface tension and liquid depth, and the solution in the layer below using a Von Karman-Pohlhausen technique. Using this Von Karman-Pohlhausen technique again, an analysis for the flow in an aqueous solution on contact with a hot gas is presented.

Eurasian beavers (Castor fiber) were extirpated from Great Britain (GB) ca. 400 years ago. Harvested for their meat, pelts and castoreum, their numbers across Eurasia were reduced to a few isolated populations. In recent years, beavers have been reintroduced in GB and their numbers have increased across Europe due to conservation efforts. However, the landscapes that beavers are now returning to have been significantly altered by anthropogenic landuse. This land use change has had hugely detrimental impacts for natural riverine and riparian processes, with respect to their structure and function. Beavers are well known for their industrious behaviours: building dams and lodges, excavating burrows and canals, and felling trees. Beavers therefore act as a significant ecological and hydrological disturbance, creating dynamic, structurally heterogeneous wetland ecosystems. Not only do the impacts of beaver enhance biodiversity through the provision of diverse habitats, but they also help to restore natural hydrological, geomorphic and ecological processes that are all but lost across intensively-farmed, densely populated European landscapes. Beavers may therefore play an important role in restoring this ecosystem function and could potentially help to mitigate the harm caused by anthropogenic landuse. However, we now rely on agriculture and infrastructure; the expansion of beaver populations can consequently result in conflict where their impacts intersect anthropogenic activity. As such, there is a requirement to better understand the impact of beavers on the structure and function of natural processes, to inform their management and conservation. Further, there is a need to develop methods that can allow us to predict the spatial and temporal changes in beaver populations across modern landscapes to underpin the recovery of the species in such a way that their benefits can be maximised whilst minimising the risk of potential conflict. This thesis presents four papers to advance our scientific understanding in this regard, as follows: The hydrological mechanisms that cause storm event peak flow attenuation in beaver wetlands were explored at a beaver dam complex on a third order stream. Data from 612 discrete flow events were measured at a flow gauge, downstream of a beaver dam complex, seven years before and three years after it was constructed; 634 events from a neighbouring control catchment, over the same time period, were also extracted from the time series. A selection of general linear models were fitted between event peak flow and total event rainfall. The differences in the slope of the regression, before and after beavers, indicate that flow attenuation, due to beaver activity, increases with greater rainfall. This increasing attenuation effect is attributed to floodplain flow diversion and transient storage because the observed attenuation volumes greatly exceed the available storage capacity of the beaver ponds alone. Drone-derived structure from motion photogrammetry surveys were carried out, providing a high-resolution understanding of changes in woodland canopy structure, over a one-year period. Riparian woodland has a complex structure and uncertainty in estimated point elevations can be spatially patchy and locally high. The adoption of robust error propagation methods to accurately estimate canopy height change was found to be very important. Beaver foraging slightly reduced mean canopy height but significantly increased the variability in canopy height change. Quantile regression was used to quantify the difference in canopy elevation change across two regions of riparian woodland: with and without evidence of beaver foraging. The rates of canopy growth and height decline were greater in regions where beavers were actively foraging, indicating that beaver foraging may increase canopy height variability which could have varying implications for riparian/aquatic species and woodland management. In order to better predict the landscape scale impact of beavers on ecosystem structure and function, it is necessary to develop methods to accurately predict their potential habitat distribution and where dams, which have the largest environmental impact, are likely to occur. To address this, we developed a modelling approach using high resolution, nationally-available datasets to create a Beaver Forage Index (BFI) model - a raster dataset describing the suitability of landcover for beaver forage and; a Beaver Dam Capacity (BDC) model which describes the density of dams that could be supported within a given reach. Beaver preferentially foraged in regions with higher BFI values and are more likely to dam (and build more dams) in reaches with higher BDC. Using these models, it is possible to estimate the number of dams that might occur at the catchment scale at beaver population capacity. Though beavers have only been living in the wild in GB for a short period of time, their populations are growing rapidly. It is essential to build a stronger understanding of how beaver populations expand, at what rates and how management interventions, such as translocations or lethal control, might impact population dynamics. To gain this insight, we conducted annual beaver feeding sign surveys to map the distribution of beaver impacts throughout the River Otter catchment, SW England. Using a semi-automated approach, that combines kernel density estimates and expert knowledge, the number of territories in the River Otter catchment was estimated over a 5-year period. A spatially explicit method for predicting the catchment population carrying capacity was developed which uses BDC and BFI models in combination with empirical understanding on territory sizes from across Europe. Adopting the assumption of logistic growth in beaver populations, we use the observed rates of population increase, constrained by the estimated carrying capacity range to model the expansion rate of the beaver population. A range of theoretical management scenario simulations were carried out revealing that, even low-moderate management interventions may have very uncertain outcomes for population viability and therefore any management plan, involving translocation or culling of animals, should be carefully designed. The findings presented in this thesis advance our understanding on the impacts of beaver on hydrological function, riparian woodland structure and provide methods for understanding the spatio-temporal distribution of beavers and their impacts. This understanding has already been used to inform management policies within national agencies and non-governmental organisations across GB and has the potential to inform the management of beavers across Europe.

The natural capital (NC) approach presents a structured framework for sustainable decision-making and evaluation, requiring an understanding of how different decisions impact NC and the flow of multiple ecosystem services (ES). The approach has been placed at the heart of delivering the UK Government's 25 year Environment Plan, which states their intention to "set gold standards in protecting and growing natural capital - leading the world in using this approach as a tool in decision-making". There is now growing advocacy for its incorporation into local-scale land management decision-making (e.g. individual farm or estate businesses). Despite this growing interest, evidence of its application at the farm scale is limited. Existing studies have often only partially applied the approach and nearly always rely on existing data (irrespective of its suitability at local scales), modelled data or data from other studies. Previous research has suggested that failing to underpin the approach with site-specific, fit-for-purpose, data brings into question its usefulness in decision-making and evaluation at the local scale. The research in this PhD represents one of the first attempts to implement a complete application of the NC approach, including detailed measurement of NC condition, ecosystem function (EF) and ES value at the farm scale. The study focuses on four ES pathways - climate regulation, food production, drinking water provision and pollinator services - in the context of land management decisions on the Clinton Devon Estate in Devon. Its core contributions are both methodological and empirical; it explores how the NC approach can be applied robustly at the farm scale and how the adoption of different land management practices, including organic agriculture and intensive farm management, impact NC and ES. The key findings are that: 1.) there are a number of significant challenges that need to be addressed before the NC approach will be practical in routine farm-management decision-making (e.g. availability of suitable data, access to expertise), 2.) land management intensity can degrade soil NC presenting on-going risks to future soil condition in the UK and 3.) organic farming has the capacity to increase soil carbon storage, enhance pollinator stocks and improve the supply of clean drinking water whilst delivering similar producer welfare compared to conventional farming.

Natural flood management (NFM) is an emerging form of land management which works with natural processes to reduce flood risk. The evidence basis for NFM schemes is immature but is growing, with wetland unimproved grassland being a particularly understudied ecosystem in need of evidence-based research. The research presented in this thesis aimed to assess the extent to which unimproved grassland, a formerly extensive habitat that has been greatly reduced by intensive agriculture, could provide NFM benefits. This study specifically focused on unimproved grassland in southwest England known as Culm grassland; comprising of purple moor grass (Molinia caerulea) and rush pasture (Juncus effusus). Improved grassland (Lolium perenne) fields were used as a comparison/control as the grassland species which now dominates North-west European agricultural landscapes. The study was divided into four objectives spanning a range of spatial scales to gain a multi-scale understanding of unimproved grassland hydrology. Objective 1 focused upon soil and water table properties using soil sampling and water table monitoring via dipwells. Results showed that M. caerulea and J. effusus dominated fields had on average significantly less compacted soil and slowly released water after rainfall events, compared to the more compacted and flashier L. perenne dominated sites. The research was continued in Objective 2 which used a rainfall simulator to mimic a 40 mm/hr rainfall event over plots of the three grassland types. Results showed a significant relationship between soil compaction and when saturation was reached, but volume of runoff was likely influenced by vegetation density within each plot, as no clear relationship between grassland type and overland flow was found. Objective 3 quantified surface flow pathway length in a field of M. caerulea and L. perenne using an unpiloted aerial vehicle and structure from motion photogrammetry to produce a detailed surface model through which surface flow pathways could be measured. The M. caerulea field had on average 1.4 times greater flow pathway length than the L. perenne control field and a rougher round/vegetation surface which could delay and store surface water. All three field experiments fed into Objective 4: sub-catchment rainfall-runoff response modelling of the Upper Tamar. Scenarios of 0, 10, 20 and 30% unimproved grassland restoration were modelled to assess potential impacts on within river flood hydrographs. Results showed peak flow and peak volume were reduced with increasing unimproved grassland extent. The four objectives of this study showed that unimproved grassland restoration has a place in the NFM toolkit, and that unimproved grassland can deliver other environmental benefits such as greater carbon storage and a diverse habitat for wildlife.

Coexistence is the adaptive but sustainable behaviour of humans and animals living together, which can be beneficial for humans. Conflicts can occur between humans and wildlife or among humans about wildlife which require effective and socially acceptable management solutions to achieve coexistence. Wildlife reintroduction is where species are returned to landscapes where they previously existed but are no longer present. A knowledge of how to anticipate and address conflicts in reintroduction scenarios would aid the development of sustainable solutions in this unique coexistence context, as would an understanding of how social benefits occur and can be maximised post-reintroduction. Further, understanding how reintroduction governance compares to the governance of coexistence with species that are already present would help aid the integration of reintroduced species into anthropogenic landscapes. In this thesis, these questions are addressed with a pragmatic, mixed-methods approach to investigating the human dimensions of Eurasian beaver (Castor fiber) reintroduction in England. Informed by a foundational nationwide attitudinal survey, the research consists of a series of studies: two of potential conflicts, two of social benefits, and one exploring the experiences of stakeholders involved in a reintroduction project. The thesis finds: 1) potential conflicts can be anticipated and addressed with early and appropriate engagement, and by seeking to understand social attitudes towards potential management solutions beyond just reintroduction itself; 2) social benefits occur naturally to some extent, but are greatest where there is active investment in the opportunities; 3) lessons from existing literature can be applied to governance of coexistence with reintroduced species, but key differences arise from the 'future-thinking' needed in reintroduction. The thesis concludes reintroduction is both an ecological and social science, and defines 'Renewed Coexistence' as coexistence between a species which was formerly resident and humans in the locality today to whom the species is a 'new' presence.

Accelerated soil erosion and the subsequent decline in soil depth has negative environmental, and consequently financial, impacts that have implications across all land cover classifications and scales of land management. Ironically, although attempts to quantify soil erosion nationally have illustrated that soil erosion can occur in the UK, understanding whether or not the UK has a soil erosion problem still remains a question to be answered. Accurately quantifying rates of soil erosion requires capturing both the volumetric nature of the visible, fluvial pathways and the subtle nature of the less-visible, diffuse pathways, across varying spatial and temporal scales. Accordingly, as we move towards a national-scale understanding of soil erosion in the UK, this thesis aims to explore some of the multiple techniques available for developing an understanding of soil erosion in the UK. The thesis first explored the information content of existing UK-based soil erosion studies, ascertaining the extent to which these existing data and methodological approaches can be used to develop an empirically derived understanding of soil erosion in the UK. The second research chapter then assessed which of two proximal sensing technologies, Terrestrial Laser Scanning and Structure-from-Motion Multi-view Stereo (SfM-MVS), is best suited to a cost-effective, replicable and robust assessment of soil erosion within a laboratory environment. The final research chapter built on these findings, using both Rare Earth Oxide tracers and SfM-MVS to elucidate retrospective information about sediment sources under changing soil erosion conditions, also within a laboratory environment Given the biased nature of the soil erosion story presented within the existing soil erosion research in the UK, it is impossible to ascertain if the frequency and magnitude of soil erosion events in the UK are problematic. However, this study has also identified that without ‘true’ observations of soil loss i.e. collection of sediment leaving known plot areas, proxies, such as the novel techniques presented in the experimental work herein and the methods used in the existing landscape scale assessments of soil erosion as included in the database chapter, are not capable of providing a complete assessment of soil erosion rates. However, this work has indicated that despite this limitation, each technique can present valuable information on the complex and spatially variable nature of soil erosion and associated processes, across different observational environments and scales.

This study advances understanding of how the changes in ecosystem structure and function associated with woody shrub encroachment in semi-arid grasslands alter ecosystem carbon (C) dynamics. In terms of both magnitude and dynamism, dryland ecosystems represent a major component of the global C cycle. Woody shrub encroachment is a widespread phenomenon globally, which is known to substantially alter ecosystem structure and function, with resultant impacts on C dynamics. A series of focal sites were studied at the Sevilleta National Wildlife Refuge in central New Mexico, USA. A space-for-time analogue was used to identify how landscape structure and function change at four stages over a grassland to shrubland transition. The research had three key threads: 1. Soil-associated carbon: Stocks of organic and inorganic C in the near-surface soil, and the redistribution of these C stocks by erosion during high-intensity rainfall events were quantified using hillslope-scale monitoring plots. Coarse (>2 mm) clasts were found to account for a substantial proportion of the organic and inorganic C in these calcareous soils, and the erosional effluxes of both inorganic and organic C increased substantially across the vegetation ecotone. Eroded sediment was found to be significantly enriched in organic C relative to the contributing soil with systematic changes in OC enrichment across the vegetation transition. The OC enrichment dynamics observed were inconsistent with existing understanding (derived largely from reductionist, laboratory-based experiments) that OC enrichment is largely insignificant in the erosional redistribution of C. 2. Plant biomass: Cutting-edge proximal remote sensing approaches, using a remotely piloted lightweight multirotor drone combined with structure-from-motion (SfM) photogrammetry were developed and used to quantify biomass carbon stocks at the focal field sites. In such spatially heterogeneous and temporally dynamic ecosystems existing measurement techniques (e.g. on-the-ground observations or satellite- or aircraft-based remote sensing) struggle to capture the complexity of fine-grained vegetation structure, which is crucial for accurately estimating biomass. The data products available from the novel SfM approach developed for this research quantified plants just 15 mm high, achieving a fidelity nearly two orders of magnitude finer than previous implementations of the method. The approach developed here will revolutionise the study of biomass dynamics in short-sward ecogeomorphic systems. 3. Ecohydrological modelling: Understanding the effects of water-mediated degradation processes on ecosystem carbon dynamics over greater than observable spatio-temporal scales is complicated by significant scale-dependencies and thus requires detailed mechanistic understanding. A process-based, spatially-explicit ecohydrological modelling approach (MAHLERAN - Model for Assessing Hillslope to Landscape Erosion, Runoff and Nutrients) was therefore comprehensively evaluated against a large assemblage of rainfall runoff events. This evaluation highlighted both areas of strength in the current model structure, and also areas of weakness for further development. The research has improved understanding of ecosystem degradation processes in semi-arid rangelands, and demonstrates that woody shrub encroachment may lead to a long-term reduction in ecosystem C storage, which is contrary to the widely promulgated view that woody shrub encroachment increases C storage in terrestrial ecosystems.

Water resources managers are required to develop comprehensive water resource plans based on severely uncertain information of the effects of climate change on local hydrology and future socio-economic changes to localised demand. In England and Wales, current water resource planning methodologies include a headroom estimation process separate from water resources simulation modelling. This process quantifies uncertainty based on only one point of an assumed range of deviations from the expected climate and projected demand 25 years into the future. The research presented herein addresses this problem by developing an integrated the Water Resources Planning Robustness Assessment (WRP-RA) method based on Information-Gap Decision Theory (IGDT) to quantitatively assess the robustness of various supply side and demand side management options over a broad range of plausible futures. Findings show that beyond the uncertainty range explored with the headroom method, a preference reversal can occur, i.e. some management strategies that underperform at lower uncertainties, outperform at higher levels of uncertainty. Also, some management strategies that perform relatively well within the headroom range of uncertainty, fail just beyond this range. Additionally, this thesis demonstrates that when 50% or more of the population adopts demand side management in the form of efficiency related measures and/or innovative options such as rainwater collection and/or greywater reuse, the robustness of a management strategy can be greatly improved as can its ability to recover after a drought episode. The use of Multi-Criteria Decision Analysis shifts the focus away from reservoir expansion options and large-scale river abstractions that perform best in regards to water availability, to strategies that include innovative demand side management actions of rainwater collection and greywater reuse as well efficiency measures along with more traditional supply-side schemes. Therefore, this thesis illustrates how the WRP-RA can offer a comprehensive picture of the relative robustness of management strategies to more extreme supply/demand futures. The knowledge of which options and collections of options perform better in response to higher demands and lower supplies offers insight into more secure long term investment strategies.

Over the last millennium peatlands have accumulated significant carbon stores. Drainage for agricultural use has been widespread and has altered the functioning of these mires: shifting them towards carbon release. Recently, in recognition of the range of ecosystem services derived from these landscapes peatland restoration projects have been initiated. Carbon storage is often cited amongst the aims of these projects, especially since the inclusion of rewetting wetlands in the Kyoto Protocol. However, little is known about the effects of ditch blocking on CO2 fluxes, particularly in Molinia caerulea dominated peatlands, a species common on degraded peatlands which tolerates a range of water table depths. This thesis aims firstly to quantify CO2 fluxes from a drained Molinia caerulea dominated blanket bog and to improve understanding of the temporal and spatial controls on these fluxes and secondly, to quantify the immediate effects of ditch blocking. Closed chamber measurements of net ecosystem exchange and partitioned below-ground respiration from control-restored paired sites were collected over the growing seasons immediately pre- (2012) and post-restoration (2013/2014). These flux data were coupled with remotely sensed data quantifying vegetation phenology and structure with a fine resolution (daily/cm) over large extents (annual/catchment). Although temporal variation in water table depth was not related to CO2 fluxes, the seasonal average related to vegetation composition suggesting raising water tables may promote a change in vegetation composition within these species-poor ecosystems. The distribution of water table depths, vegetation composition and CO2 fluxes did not vary with proximity to drainage ditches despite their prominence. An empirical model suggests in a drained state these peatlands are CO2 sources, indicating carbon previously accumulated is gradually being lost. Data suggest restoration does not always significantly affect water tables and consequently CO2 fluxes in the short-term. Where shallower water tables were maintained during dry conditions photosynthesis decreased and heterotrophic respiration increased: enhancing carbon release. Research undertaken during atypical weather has been unable to determine if restoration will be able to raise water tables sufficiently to protect the existing peat store and promote the vegetation change required to reinstate CO2 sequestration in the longer-term.

Peatlands are unique and important landscape systems, providing valuable ecosystem services such as water and carbon storage, water supply and flood attenuation. They are known to account for more than 10% of the world’s terrestrial carbon store and represent 50 – 70% of the global wetland resource. The UK government’s decision to support the IUCN, UK Peatland Program Commission of Inquiry on Peatlands, recognises the importance and urgency with which action is needed to understand and restore damaged peatland landscapes, and their associated ecosystem services. To meet this need, it is recognised that peatlands in the South West of the UK are important as bio-climatically and functionally marginal peatlands that are undergoing extensive restoration to reinstate key ecological and hydrological function. This thesis aims to improve understanding of the temporal and spatial variability of the ecohydrological structure and function of peatland ecosystems in the South West UK, and will provide the first baseline for the spatially distributed extrapolation of change across larger landscape extents. The research seeks to characterise the structure and function of peatland ecohydrology across multiple spatial and temporal scales. This is accomplished by bringing together remote sensing analyses of ecohydrological structure and function coupled with an integrated and high resolution hydrological monitoring system to characterise the spatial and temporal variability of runoff production and water storage across two headwater catchments. Key outcomes of this research are: 1. The development of novel methods to assess the spatial distribution of near surface hydrology in upland ecosystems using airborne thermal imaging data, 2. Improved understanding of how laser altimetry data can be used to measure the ecohydrology of landscapes more appropriately. 3. An empirical understanding of both the spatial and temporal variability of hydrology across representative sites within the moorlands of the South West UK. The high-resolution monitoring data are the first to describe the hydrological processes operating in these peatlands systems effectively, and provide an insight into how these processes are controlled by the anthropogenic drainage networks that are present throughout this shallow marginal peatland system.

One of the major challenges for agriculture today is to manage soil properties and their spatial distribution to optimize productivity and minimize environmental impacts, such as diffuse pollution. To identify best management practices, the effects of different agricultural management practices on pollutant sources, mobilization, transfer and delivery to water bodies need to be understood. Grasslands managed for dairy and meat production, despite being widespread, have received less research attention than other agricultural land uses. Therefore, this thesis studies the effects of different grassland management practices on soil properties and their spatial distribution and the mobilization and delivery of multiple diffuse pollutants. As a grassland case study, monitoring for this thesis was conducted across three fields (6.5 – 7.5 ha) on the North Wyke Farm Platform, a grassland experimental farm in the UK. First, the effects of permanent grassland management (permanent for at least 6 years, but different grassland management > 6 years ago) were characterized as a baseline, followed by quantifying the short-term effects of ploughing and reseeding of permanent grassland fields. Throughout those management periods, i) a range of soil physical (bulk density [BD]) and chemical (soil organic matter [SOM], total N [TN], total phosphorus [TP], total carbon [TC]) soil properties and their spatial distribution were sampled and analysed by geostatistics, and ii) hydrological characteristics and multiple pollutant fluxes (suspended sediment [SS] and the macronutrients: total oxidized nitrogen-N [TONN], total phosphorus [TP], and total carbon [TC]) were monitored at high temporal resolution (monitoring up to every 15 minutes). The permanent grassland fields (or areas within fields) can be considered to be functioning differently. Past management legacy (more than 6 years ago) has affected soil properties and their distribution with subsequent effects on sediment and macronutrient delivery from the fields to surface waters. Overall, permanent grasslands were found to contribute significantly to agricultural diffuse pollution. The estimated erosion and macronutrient losses were similar to or exceeded the losses reported for other grasslands, mixed land use and even arable sites, and sediment and TP concentrations exceeded those recommended by EU / UK water quality guidelines. Ploughing and reseeding did not homogenize spatial variation and did not override past management effects. Long-term management differences affected soil properties and altered soil processes, so that the fields subsequently responded differently to ploughing and reseeding. All nutrient concentrations were significantly reduced in the older grassland field (no ploughing for 20 years), but not in the younger grassland field (no ploughing for 6 years). Ploughing and reseeding significantly accelerated the losses of sediment and macronutrients and sediment, TP and TONN exceedance frequencies of EU / UK water quality guidelines increased. Additionally, ploughing and reseeding caused a shift in the relative importance of nutrients, by increasing the relative importance of N. Such large sediment and nutrient losses from intensively managed grasslands should be acknowledged in land management guidelines and advice for future compliance with surface water quality standards. The between-field and within-field variation highlights the importance of baseline characterization and paired catchment studies. The long-term effects of management still acting on soil properties and subsequently water quality indicates how long it may take to see soil and water quality improvements after implementing mitigation measures. Therefore, long-term management history always has to be included when interpreting soil and water quality data.

This study develops understanding of vegetation change and water, sediment and carbon dynamics in semi-arid environments. Objectives were addressed using an integrated ecohydrological and biogeochemical approach. Fieldwork, over two contrasting grass-woody transitions at the Sevilleta National Wildlife Refuge, New Mexico, USA; quantified vegetation structure, soil structure and the spatial distribution of soil carbon resources. Over both transitions; woody sites showed a lower percentage vegetation cover and a greater heterogeneity in vegetation pattern, soil properties and soil carbon. Soil organic carbon differed in both quantity and source across the sites; with levels higher under vegetation, particularly at the woody sites. Biogeochemical analysis revealed soil organic carbon to be predominantly sourced from grass at the grassland sites. In contrast, at the woody sites soil organic carbon under vegetation patches was predominantly sourced from woody vegetation, whilst inter-patch areas exhibited a strong grass signature. Investigation of function focussed on the hydrological response to intense rainfall events. Rainfall-runoff monitoring showed woody sites to exhibit greater; runoff coefficients, event discharge, eroded sediment and event carbon yields. In contrast to grass sites, biogeochemical analysis showed the loss of organic carbon from woody sites to exhibit a mixed source signal, reflecting the loss of carbon originating from both patch and interpatch areas. To examine the linkages between vegetation structure and hydrological function, a flow length metric was developed to quantify hydrological connectivity; with woody sites shown to have longer mean flow pathways. Furthermore, in addition to rainfall event characteristics, flow pathway lengths were shown to be a significant variable for explaining the variance within fluxes of water, sediment and carbon. Results demonstrating increased event fluxes of sediment and carbon from woody sites have important implications for the quality of semi-arid landscapes and other degrading ecosystems globally. It is thus necessary to translate the understanding of carbon dynamics developed within this study to the landscape scale, so changing fluvial carbon fluxes can be incorporated into carbon budgets, research frameworks and land management strategies at policy-relevant scales.

The European Water Framework Directive 2000 established a new emphasis for the management of freshwaters by setting ecologically-based water quality targets that are to be achieved through holistic, catchment-scale, ecosystem management. However, significant knowledge gaps exist in the understanding of the cumulative effectiveness of multiple mitigation measures on a number of pollutants at a catchment scale. This research contributes to improved understanding of the effectiveness of an ecosystem management approach to deliver catchment-scale water quality improvements on the National Trust Holnicote Estate on Exmoor, UK. This research is part of a larger multi-objective project funded by the UK Department for Environment, Food and Rural Affairs (Defra), to demonstrate the benefits of land use interventions for the management of flood risk. This thesis evaluates the effects of upland ditch blocking on physico-chemical and biological parameters of water quality in an upland Horner Water catchment one year after habitat restoration, and establishes a solid baseline for the monitoring of the effects of current and future land management changes in a lowland, intensively managed, agricultural Aller catchment. The spatial variability of soil physical and chemical properties (bulk density, total carbon (TN), nitrogen (TN), C:N ratio, δ15N, total phosphorus (TP), inorganic phosphorus (IP), organic phosphorus (OP)) and water quality determinands (suspended sediment (SS), dissolved organic carbon (DOC), total particulate carbon (TPC), total oxidised nitrogen (TON) and dissolved reactive phosphorus (DRP)) in the two study catchments with contrasting land use has been characterised and linked to the prevailing land use. Agricultural land use resulted in extensive homogenisation of soil properties. The spatial dependence of all soil properties, except for bulk density and δ15N, was stronger in the agricultural than the semi-natural catchment (nugget:sill ratio 0.10-0.42 in the Aller and 0.15-0.94 in Horner Water), while bulk density, TP, inorganic phosphorus (IP), organic phosphorus (OP), C:N ratio, δ15N and carbon storage showed a longer range of spatial auto-correlation in the agricultural catchment (2,807-3,191 m in the Aller and 545-2,599 m Horner Water). The central tendency (mean, median) of all soil properties, except for IP and δ15N, also differed significantly between the two catchments (P < 0.01). The observed extensive alteration of soil physical and chemical properties in the agricultural catchment is likely to have long-term implications for the restoration of ecosystem functioning and water quality management. The intensive land use seems to have resulted in an altered ‘catchment metabolism’, manifested in a proportionally greater total fluvial carbon (dissolved and particulate) export from the agricultural than the semi-natural catchment. The agricultural catchment supported significantly higher DOC concentrations (P < 0.05) and the quality of DOC differed markedly between the two study catchments. The prevalence of more humic, higher molecular weight compounds in the agricultural catchment and simpler, lower molecular weight compounds in the semi-natural catchment, indicated enhanced microbial turnover of fluvial DOC in the agricultural catchment as well as additional allochtonous terrestrial sources. During an eight month period for which a comparable continuous turbidity record was available, the estimated SS yields from the agricultural catchment (25.5-116.2 t km2) were higher than from the semi-natural catchment (21.7-57.8 t km2). Further, the agricultural catchment exported proportionally more TPC (0.51-2.59 kg mm-1) than the semi-natural catchment (0.36-0.97 kg mm-1) and a similar amount of DOC (0.26-0.52 kg mm-1 in the Aller and 0.24-0.32 kg mm-1 in Horner Water), when normalised by catchment area and total discharge, despite the lower total soil carbon pool, thus indicating an enhanced fluvial loss of sediment and carbon from the intensively managed catchment. Whilst detection of catchment-scale effects of mitigation measures typically requires high resolution, resource-intensive, long term data sets, this research has found that simple approaches can be effective in bridging the gap between fine scale ecosystem functioning and catchment-scale processes. Here, the new macro-invertebrate index PSI (Proportion of Sediment-sensitive Invertebrates) has been shown to be more closely related to a physical measure of sedimentation (% fine bed sediment cover) (P = 0.002) than existing non-pressure specific macro-invertebrate metrics such as the Lotic Index for Flow Evaluation (LIFE) and % Ephemeroptera, Plecoptera & Trichoptera abundance (% EPT) (P = 0.014). Further testing of PSI along a pronounced environmental gradient is recommended as PSI and % fine bed sediment cover have the potential to become a sensitive tool for the setting and monitoring of twin sedimentation targets. Upland ditch management has not had any discernible effect on water quality in the semi-natural upland catchment one year after restoration, which may be due to the short-term post-restoration monitoring period but may also reflect benign effects of large-scale earth moving works on this high quality environment. The conceptual understanding of catchment processes developed in this thesis suggests that cumulatively, the recently completed mitigation works in the lowland agricultural catchment will likely result in reduced sediment and nutrient input into the aquatic environment. However, further research is needed to build on this detailed baseline characterisation and inform the understanding of the effectiveness of combined mitigation measures to reduce the flux of multiple contaminants at the catchment scale.

Recent researches on the effects of environmental degradation on food security suggest that a better understanding of the relationship between agricultural intensification and pollutant transfer is urgently required to support the implementation of sustainable agricultural policies, globally. Poor understanding of the hydrological behaviour of clay-rich soils in intensively managed agricultural regions is highlighted as an important problem. The study therefore evaluated precipitation-soil water chemistry relationships, soil variability and concentration-discharge relationships at the farm-scale based on datasets from the North Wyke Farm Platform between 2011 and 2013. The three main hypothesis were that (1) precipitation and soil water chemistry are significantly related (2) significant relationships exists between the distribution of soil physiochemical characteristics and the managments of the fields, and that (3) hydrological behaviour of fields underlain by certain dominant soils in the study area are different from that of other fields. The basis of this work was to elucidate links between sources of pollutants and water quality, further understanding of the effect that management of the soil may have upon the quality of the water and improve understanding of the pathways of pollutants within intensively managed landscapes. Precipitation chemistry of the study area was chemically different from that of the other regions in the United Kingdom, and was influenced by contributions from sea salts and terrestrial dusts. The soil chemistry was rich in organic matter which contributed significantly (r2>0.60; p<0.05) to the distribution of total carbon and total nitrogen in the fields. Mean total carbon and nitrogen stocks ranged 32.4 - 54.1 t C ha-1, and 4 - 6.2 t Na ha-1, respectively in the entire farm platform while runoff coefficient at four selected fields (Pecketsford, Burrows, Middle and Higher Wyke Moor, and Longlands East) varied between 0.1 and 0.28 in January and November, 2013. The study rejected the first and third hypotheses, and concluded that the study area is largely influenced by contributions from the surface runoff mechanisms. The study also noted that sodium and chloride ions were dominant in the precipitation chemistry, and therefore suggests their further investigation as conservative tracers in the soil and runoff chemistry.