Rivers and riparian zones are among the most threatened ecosystems globally, with modification of their natural flow regime a major source of change. Exposed riverine sediments (ERS) are characteristic of unregulated rivers in their upper and middle reaches and among the few remaining natural riparian habitats. However, they are in decline across the UK and Europe as a result of widespread modifications to channel structure and flow regimes. Studies of ERS and their dependent carabid beetles can help to understand how environmental change is affecting river ecosystems more generally, but prolonged research is scarce. This thesis reports on a three year study of carabid beetles at multiple sites in the Usk river system, Wales, during an extended period of low river discharge. Plot-scale experimentation and reach-scale surveys showed consistently that carabid assemblage structure and distribution varied more strongly in response to time and across the reach than to within-patch habitat character. There was no evidence of carabid assemblage succession, though generalist species richness appeared to increase through the study as specialist species richness declined, and general conditions for specialist species may have declined. It is suggested that specialist carabids of high conservation importance could be squeezed as land use encroachment and river regulation causes a decline in the ERS resource. Management interventions at the reach- or catchment scale are advocated to maintain and restore the ephemerality of ERS. Being responsive to reach- and catchment scale events, exposed riverine sediments and their dependent fauna should be the focus of long term study to appraise rates of environmental change or resilience to anthropogenic stressors. In particular, long term studies may not only reveal trends on ERS towards homogenisation, indicative of environmental decline within the wider river system, but might also help to detect the effectiveness of river restoration.

This thesis presents the first direct flux measurements of land/atmosphere carbon dioxide (CO[subscript 2]) exchange at managed lowland peatlands in the East Anglian Fens, UK. The dynamics and magnitude of land/atmosphere CO[subscript 2] exchange were quantified at semi-natural and regenerating ex-arable fens located at the Wicken Fen Nature Reserve in Cambridgeshire. Eddy covariance measurements were made at the semi-natural fen throughout two thermally and hydrologically dissimilar periods during 2009 and 2010, and at the regenerating former-arable fen over the complete annual cycle of 2010. The study sites were characterised by strong seasonal variation in CO[subscript 2] exchange. The semi-natural fen was a net source of 85.47±25.78 g CO[subscript 2]-C m[superscript -2] between 20th March and 31st December 2009, and a small net sink of -22.66±18.85 g CO[subscript 2]-C m[superscript -2] for the same period of 2010. Photosynthesis and ecosystem respiration were both higher during warm conditions of 2009 compared to 2010, but enhanced rates of ecosystem production were outweighed by large CO[subscript 2] losses during warm and dry conditions in autumn. The large interannual variability in CO[subscript 2] exchange illustrates the sensitivity of semi-natural fens to climatic variability and change, and highlights the need to maintain high water levels to prevent large losses of soil carbon to the atmosphere as CO[subscript 2]. The regenerating fen functioned as a small net source of 21.24±17.11 g CO[subscript 2]-C m[superscript -2] yr[superscript -1]. On the basis of values currently used to represent CO[subscript 2] losses from arable fens, the annual CO[subscript 2] balance for the ex-arable fen in 2010 indicates the net CO[subscript 2] benefit of fenland rehabilitation was an avoided loss of -87.7±17.11g CO[subscript 2]-C m[superscript -2] yr[superscript -1]. The results from the regenerating site imply that a more adaptive water management strategy will be needed if the environmental conditions required for peat formation and net carbon capture are to be restored.

This study investigates the biogeochemical controls on the release of phosphorus (P) from riparian wetland sediments to solution, and the subsequent delivery of P to receiving waters. The research was conducted at Strumpshaw Fen, a riparian wetland in the floodplain of the River Yare in the UK. Novel mesocosm work identifies the reductive-dissolution of iron-bound P as the dominant control on P release to solution. The timing of P release to pore water and surface water is also influenced by the concentration of nitrate-nitrogen in floodwater, because redox potential is poised above the level necessary for the reduction 0 f ferric iron whilst nitrate remains in solution. Field-based hydrochemical monitoring confirms the findings from laboratory mesocosm work on the controls on P release to solution, and indicates that P concentrations indicative of hyper eutrophic conditions may be established in the pore water and surface water of this riparian wetland. Sequential filtration establishes that the vast majority of the MRP fraction in 0.45 J.1m filtrates may be composed of free orthophosphate. An investigation of hydrological connectivity between the shallow peat and (i) the underlying mineral aquifer and (ii) the adjacent open-water network is used to indicate whether P in solution might be exported from the peat in large quantities. Reliable characterisation of the hydraulic conductivity (K) of the peat deposits at Strumpshaw Fen is achieved after a thorough evaluation of the piezometer technique, and the application of a novel laboratory-based method. K is found to be relatively high, indicating a potential for substantial flows of water between the near-surface peat and the ditch network at the site, given suitable hydraulic gradients. Field-based hydrological monitoring suggests that lateral exchanges between the peat and adjacent open-water bodies are more important than vertical exchanges between the peat and the underlying mineral aquifer. It is shown that the combination of P availability and hydrological connectivity between the peat and open water, will result in bioavailable P reaching the ditch network at Strumpshaw. In the light of these findings, riparian fen wetlands should not be assumed a priori to be 'protectors' of the chemical and ecological quality of receiving waters, but may in fact be sources for significant quantities of P that have the potential to be exported from the fen system.

No description available.

Papyrus swamps form ecological buffer zones at the land-water interface, protecting lake shallows from sedimentation and reducing the risk of eutrophication in open water. Many communities living near papyrus swamps, particularly in East Africa, derive socioeconomic benefits from these highly productive ecosystems. Loss of the buffering capacity of papyrus at Lake Naivasha, Kenya, explains much of the observed increase in the lake’s trophic state. Multiple authors have called for Naivasha’s wetlands to be restored; however, the social and ecological factors that would need to be considered before doing so have received insufficient attention. Case studies of recent restoration programmes at Lake Victoria illustrate the means by which degraded wetlands can be rehabilitated. Analysis of attitudes towards papyrus at Lake Naivasha reveals a general lack of awareness surrounding the benefits of local wetlands, forming a potential barrier to successful restoration there. An assessment of the lake’s riparian zone demonstrates that both anthropogenic and natural pressures present significant challenges for the survival of lake-fringing wetlands, highlighting changes that have occurred within the ecosystem over the last few decades. Potential means of addressing both the social and ecological limitations to papyrus restoration are offered, with explicit linkages to the benefits of doing so made clear. Floating islands are shown to be the most appropriate reference for ecological restoration at Lake Naivasha, which can be replicated through artificial technology. The establishment of a consumptive use value for harvested papyrus at Naivasha would help to raise stakeholders’ awareness of wetlands; a novel means of producing biomass briquettes was met with positive responses from local residents and may be used to encourage community participation in restoration. A vision for wise use of this internationally renowned Ramsar site is set out, with recommendations made as to how papyrus wetlands could be managed sustainably over the long term.

Introduction Recent global assessments of the impact of climate change have highlighted the current and future risks of increasing vector-borne disease incidence. The UK government has responded to climate change risks through various legislation and planning frameworks. Some of the main concerns include the need to mitigate storm surges, prevent inland and coastal flooding, provide sustainable urban drainage and expand defragmented wetlands to enhance biodiversity value. Wetlands provide a wealth of benefits for biodiversity, flood -risk management and human mental health. However they can harbour mosquito species of nuisance and/or disease vector concern. With the increasing trend in mosquito-borne disease in Europe this warrants further investigation. Aim This PhD aims to investigate the impact of the creation, expansion and management of three types of wetland (i.e. coastal, urban and arable reversion) on mosquitoes in England. Methods A range of sampling strategies were employed to investigate the impact of the creation, expansion and management of coastal, urban and arable reversion wetlands on mosquitoes. Aquatic dipping was used to survey immature mosquitoes, and mosquito magnet traps were used to survey adult mosquitoes. In a coastal environment, mosquito surveys were conducted during two visits by larval sampling at the eight largest coastal realignment sites on the Humber and in Essex. An urban wetland in Wiltshire was also studied over two years post construction, investigating the colonisation of mosquitoes at a range of urban wetland and sewage treatment habitats. Adult and pre-imaginal mosquito densities were also compared across a range of wetland types in the Cambridgeshire Fens to assess the relative roles of different seral stages of ecological succession. Studies were also conducted at Woodwalton Fen in Cambridgeshire to investigate the the impact of wetland management and expansion by arable reversion. This involved fortnightly larval sampling of a range of aquatic habitats and fortnightly (4 nights per week) adult trapping in six different wetland communities. Results The apparent absence of anopheline mosquitoes exploiting aquatic habitats at all of the coastal sites suggests that the risk of malaria associated with managed realignment sites is currently negligible. However, three of the eight sites supported populations of two nuisance and potential arboviral vector species, Aedes detritus and Aedes caspius. The aquatic habitats that supported mosquitoes resulted from specific design aspects of the new sea wall such as (a) an additional bank of ballast to mitigate wave action providing a linear habitat supporting significant numbers of mosquitoes, (b) constructed saline borrow ditches, excavated during construction, that receive brackish waters at spring high tides, with tidal waters collecting on vegetated banks in culverts with minimal tidal flushing and (c) isolated pools created through silt accretion or expansion of flooded zones to neighbouring pasture. In urban wetlands, Culex pipiensltorrentium dominated in temporary (pre-imaginal densities 33x higher than permanent wetlands) and vegetated (pre-imaginal densities 41 times higher than unvegetated) wetland habitats. The drying and re-wetting of habitats was significantly associated with Culex presence/abundance. In the sewage treatment reedbed, the stilling basin (i.e. sewage capture structure) accounted for >80% of all pre-imaginal mosquitoes collected during the study , with mean densities 80 times higher than all other wetland types. The presence of raw sewage and subsequent algal blooms is significant for high Culex densities.

The aim of this thesis is to investigate the use of Tellus airborne radiometric data in the development of peat thickness models for Northern Ireland. This involved exploring the complex relationships between peat and radiometric levels as well as optimising the modelling of peat and Tellus datasets. Laboratory and field-based experiments were utilised to determine how radiometric values are affected by changes in peat thickness, moisture content and bulk density. The laboratory results indicated an inverse exponential relationship between peat thickness and radiometric values, a general inverse relationship between peat moisture content and radiation levels and no clear relationship between bulk density and radiometric values. The field-based peat thickness experiment, devised to investigate how an active peat bog attenuates radiation, indicated an inverse relationship between the variables. Historical peat thickness measurements, digitised and collated to produce a peat thickness dataset for Northern Ireland, were used, in conjunction with other data, to determine suitable sites for analysis. At each field site, the relationship between peat thickness and radiometric levels was analysed using not only historical peat thickness and Tellus measurements but also newly acquired ground-penetrating radar and ground-based gamma-ray spectrometry data. The analysis indicated that stronger relationships between datasets were observed when data from different sites were not amalgamated. Historical peat thickness and Tellus radiometric data maps were generated using two techniques: inverse distance weighting (IDW) and ordinary kriging (OK). In each case, OK outperformed IDW, with the optimum model being determined using error statistics.

Peatlands are subject to multiple uses including farming, forestry, sites for renewable energy (wind farms) and recreation (including gun sports). To facilitate access, roads and tracks, both constructed and unsurfaced, are becoming an increasingly common feature in Northern peatlands. The impact that these linear features have on peatland ecohydrological functioning is poorly understood, especially within blanket peatlands which, unlike other peatland types, often occur on slopes. There is concern that disturbances could negatively impact important physical, hydrological and ecological peat properties, and consequently the wider functioning of these systems. Indeed, the ability of peatlands to capture and store carbon could be compromised following possible reductions in vegetation cover and a deepening of the water table. Likewise, the role of peatlands in flood management could be affected as a result of peat compaction and enhanced surface runoff. With respect to practical applications, the current lack of understanding and evidence for decision-making has made granting permission for track installation problematic. In this thesis, the first comprehensive study of track impacts on blanket peat is presented. A two strand approach was used to investigate the impact of tracks on blanket peat ecohydrology, involving (i) a regional survey of 29 track reaches (aggregate and plastic) across seven sites in the North Pennines and Cheviots of northern England and (ii) an intensive study over two years, covering 1.5 km of plastic mesh track, 30 m of articulated wooden track and 200 m of unsurfaced track located at Moor House in the North Pennines. Key properties for peatland ecohydrological functioning were measured including soil moisture, bulk density, hydraulic conductivity, water-table depth, overland flow occurrence and vegetation composition. The influence of track type, frequency of use and topographic location were considered, in addition to the spatial extent of track impacts. The regional survey found higher volumetric moisture content on the upslope side of stone tracks compared with the downslope side. Such an effect was not found around plastic tracks, where the upslope-downslope gradient was indistinct or did not exist, due to the orientation of the track to the contours. Topographic location and track age influenced spatial patterns in moisture content for stone tracks. Such effects could not be tested for plastic tracks. The influence of distance was considered for the stone tracks however no clear effect was observed. Findings from the intensive study showed variation in the responses to the tracks from the selected key properties for blanket peatland ecohydrological functioning. Clear impacts were observed for surface profile elevation and vegetation characteristics. Following track use a lowering of surface peat elevation directly under the track was recorded for all three track types and at all topographic locations. Compared with before disturbance data, reduced cover in C. vulgaris, E. vaginatum and S. capillifolium, a lowering in the height of the vegetation, and increased bare peat occurrence, were found 22 months after track installation and 13 months after the commencement of driving. These impacts were closely associated with the installation process of the tracks. Track type was a key influential variable in the magnitude of impact observed for both surface peat elevation and vegetation composition and height. Topographic location was influential for vegetation composition but not surface profile elevation. Track frequency of use had minimal influence on the responses of all of the properties measured in the intensive study. Expected impacts to bulk density, hydraulic conductivity, water-table depth and overland flow occurrence were found to occur under some conditions. The intensive study was undertaken over a two year period with 18 months of continuous monitoring (water-table depth and overland flow). The variation in the responses of a number of the key properties measured suggest a need for long-term studies (5+ years) to fully capture the impact of disturbances such as tracks. The results from this study will be used to inform decision-making with respect to the siting and use of tracks in blanket peatland environments. With better informed decision-making the future impacts of track installation and use can be mitigated against; resulting in healthy peatlands, where their multiple functions including carbon sequestration and flood alleviation can be maintained and supported.

Peatlands represent an important terrestrial pool of carbon, but are threatened by anthropogenic climate change, including a potential increase in drought events. Drought leads to the release of carbon dioxide from peat. It is well established that drought affects microbial communities, but so far insights into the microbial mechanisms underpinning the release of carbon from droughted peat are limited. In this project, temporally-explicit drought manipulations were carried out in two peatland habitats using a replicated and controlled series of mesocosm cores. ARISA fingerprinting was used to initially delimit shifts in microbial community composition, followed by shotgun metagenomic sequencing of a subset of samples and sequencing of SSU rRNA genes (marker gene analysis; MGA). DNA-based methodologies were accompanied by biogeochemical assays, which confirmed that drought conditions were achieved in treated cores relative to controls. ARISA fingerprinting demonstrated a significant effect of drought on bacterial and fungal community composition, with the most significant effect during the rewetting period. Conversely, sequencing-based methodologies detected a weak or non-existent effect of drought on overall community composition. However, MGA indicated that a subset of OTUs (operational taxonomic units) responded significantly to drought, particularly in the fen at 5cm depth. Where it was possible to assign taxonomy to drought-responsive OTUs, Proteobacteria and Bacteroidetes were overrepresented relative to their abundances in the community as a whole. In many cases, OTUs exhibiting negative responses to drought were closely related to obligate anaerobes. Rhizaria (a group of protists) also appeared to respond to drought. The abundance of hydA (a gene for the enzyme which catalyses the hydrogenic step in fermentation) fell during drought. To conclude, although the effect of drought on overall communities was weak, the analyses showed that a number of OTUs and functional genes responded to drought. The results provide numerous avenues for future research into the mechanisms underlying drought-driven carbon release from peatlands.

Rich fens are globally significant wetlands due to their high biodiversity and provision of multiple ecosystem services, such as water purification and climate mitigation. However, many U.K. rich fens have become botanically degraded. This is principally due to abandonment, following the cessation of management (mowing/grazing) and has led to a decline in plant species richness. Although the response to mowing on plant species richness has been well documented across Europe, there is no prior knowledge of this research being undertaken at U.K rich fens. Additionally, the effects of mowing on water quality are largely unquantified. Furthermore, the spatial heterogeneity of greenhouse gases across and within botanically rich and botanically poor sites is also unknown. Two rich fen plant communities: Cladio-Molinietum (n=9) and Scheonus nigricans - Juncus subnodulosus (n=8) were examined across three sites; chosen for their conservation value and current degraded condition. A 50 % success rate was achieved following mowing to increase species richness, which meant assumptions were not met for both plant communities. Nitrate, phosphate and dissolved organic carbon concentrations did not reduce following mowing, however there was a beneficial increase in concentration of base cations at both sites. The greenhouse gas investigation revealed that the net gaseous carbon flux between both sites was comparable, which did not meet expectations that the botanically impoverished site would have higher carbon emissions, however, expected differences between plant communities were observed at both sites. Therefore, this study shows the complexity of the botanical, hydro-chemical and greenhouse gas spatial heterogeneity at rich fens. Careful examination prior to restoration is needed to determine whether environmental/ecological barriers have been removed, so that restoration is not in any way inhibited. In addition, this study has demonstrated that objectives for biodiversity may be in conflict with objectives to manage for other ecosystem services, in these multi-functional wetlands.