Northern peatlands are an important carbon store, with carbon dynamics and hydrology intrinsically linked. The riparian zone is the interface between the terrestrial and aquatic systems, situated adjacent to the stream and characterised by periodic flooding, near surface water tables and unique soil and plant species composition. Due to its unique biogeochemical environment, the riparian zone has the potential to modify significantly the production, mobilisation and transport of carbon via the land-atmosphere and aquatic pathways. Two contrasting headwater catchments, an ombrotrophic peatland (Auchencorth Moss, SE Scotland) and a forested, till dominated catchment (Västrabäcken, N Sweden), were investigated. In each carbon concentrations in soil and stream water and hydrological parameters were measured in transects connecting the wider catchment, riparian zone and stream. The overarching aim was to investigate the role of the riparian zone on the hydrological and bio-geochemical functioning of peatland and forested catchments, focusing on carbon export via the aquatic pathway. Specific objectives were to: a) examine the importance of soils, water table and vegetation composition on riparian biogeochemical cycling, b) investigate riparian-stream hydrological connectivity and the transport of carbon across the soil-water interface and c) assess riparian processes in relation to the net ecosystem carbon balance (NECB) across northern latitude ecosystems. Porewater total carbon (TC) concentrations (sum of dissolved organic and inorganic carbon (DOC, DIC), CO2 and CH4) were on average higher in Auchencorth Moss (78.8-140 mg C L-1) than the Västrabäcken (27.7-63.2 mg C L-1) catchment. In both catchments, higher TC concentrations were observed in the riparian zone compared to the wider catchment. The dominant control for differentiating between catchment and riparian biogeochemical processes was the higher average riparian water table with each carbon species displaying a positive relationship with water table height. A range of other factors, including soil temperature and the carbon content of catchment and riparian soils, also contributed to the complexity of riparian carbon biogeochemical cycles. Catchment specific phenomena, including the presence of aerenchymous vegetation and stream sediment deposition onto the riparian zone, modified riparian carbon dynamics in the Auchencorth Moss catchment. Isotopically, porewater DOC, CO2 and CH4 had a 14C content >100 %modern, indicating that the modern plant derived DOC is being transported down the soil profile, providing the source for CO2 and CH4 production at depth. In both catchments the riparian zone represented an important and dynamic source of carbon to stream waters. Total annual CO2 export from the riparian zone of the Västrabäcken catchment to the stream channel over the hydrological year was 2.7 g CO2-C m2 yr-1 with export predominantly from between 40 and 55 cm depth within the soil. Two monthly peaks in CO2 export occurred over the hydrological year related to either storm events or the spring snow melt period which accounted for 19 % of annual export, highlighting the temporal variability in soil-stream linkages, especially during high flow periods. In the generally wetter peatland catchment, riparian-stream linkages were driven by antecedent conditions and variation in riparian water table, with changes in water input, rather than changes in CO2 source concentrations, controlling stream water composition. The negative CO2 concentration-discharge relationship in the stream suggested that event water dominated, with small but important inputs from high concentration soil water during individual events. The importance of event water in transporting carbon was confirmed through the isotope result. CO2, CH4 and DOC exported via the aquatic pathway predominantly contained modern, plant derived carbon from the near surface soil horizons but with a small contribution (5-28 %) from deeper geological sources leading to aged evasion CH4 (310-537 years BP) and CO2 (36 years BP to modern). In both catchments the riparian zone was more important, relative to the wider catchment, in controlling the export of carbon via the aquatic pathway. At Auchencorth Moss, the riparian zone, plus an area of the catchment extending ~20 m from the stream, were hotspots for land-atmosphere fluxes of CH4, with mean flux of 1.08-7.70 mg m2 hr-1 in comparison to the catchment overall (0.05 mg m2 hr-1). In both catchments, combining detailed catchment hydrological models with high temporal resolution carbon concentration measurements, especially in riparian zone soils, has the potential to improve estimates of downstream and evaded carbon export in headwater catchments. Riparian zones should therefore be included more in studies investigating hydrological and biogeochemical processes in northern latitude headwater catchments. The processes within riparian zones suggest that despite the relatively small area that riparian zones represent, in relation to the wider catchment, they may play an important role in the NECB of peatland and forested catchments under future management and climate change scenarios.

Peatlands are a globally important, terrestrial store of carbon and the UK is recognised as an internationally significant holder of peatlands. Of all the kinds of peatland found in the UK, blanket bogs are dominant, representing 87% of the UK’s peatland area. The UK’s peatlands, in contrast to many other areas of boreal/temperate peat, are relatively accessible and as such have been subject to land-management pressures for many thousands of years. These management pressures have led to the deterioration of many peatlands in the UK, with only 1% of England’s peatlands being considered ‘pristine’ in a Natural England report (Natural England, 2010). Climate change and increasing land-use pressures are predicted to affect all UK peatlands in coming years. As such, studies of the drivers of carbon cycling on UK peatlands are being undertaken in order to help in the construction of models to predict the dynamics of peatland carbon balance. These models will subsequently enable land-managers and policy makers to take informed decisions regarding peatland management and carbon storage. One such model of peatland carbon balance is the Durham Carbon Model, which uses a mass balance between fluxes of carbon in and out of a peatland in order to estimate its net carbon budget. While the Durham Carbon Model is able to deal with the effects of some aspects of land-management on peatland carbon balance, there remain a number of important drivers as yet unaccounted for in the model. As such, the remit of this thesis was to conduct in-situ, experiments in order to provide additional data on peatland carbon cycling with a view to incorporating these drivers into the model. Specifically, this research examines three areas as yet unaccounted for in the Durham Carbon Model: altitude, vegetation and diurnal processes. These factors are considered relative to CO2 flux and, in some cases, soil pore water dissolved organic carbon concentration. Additional experiments were also performed to determine whether empirical models of CO2 flux can be physically interpretable. Results obtained for this thesis suggest that the most important factor in predicting CO2 flux on blanket peat soils is vegetation type and vegetation mediated processes, i.e. photosynthetic controls on respiration. Moreover, the relationship between respiration and photosynthesis was found across a range of other factors and temporal scales. In addition to vegetation, altitude was found to significantly affect CO2 for some vegetation types. Therefore, both of these factors are to be incorporated into the Durham Carbon Model. Experiments suggested that empirical models of CO2 flux can be physically interpretable. The results of the diurnal experiment gave evidence to support the hypothesis that some component of the relationship between photosynthesis and respiration is temporally lagged, perhaps by 3 hours. However, the results were not unequivocal and thus further work is needed to fully examine some of the results presented herein.

Inland waters including streams, rivers, reservoirs and lakes are regarded as a significant site of Organic Carbon (OC) cycling, and greenhouse gas production. As a result, there has been significant recent interest in the rates and fate of fluvial carbon exported from organic soils, such as peatlands. Additionally, peatlands can be subject to substantial degradation resulting in high rates of fluvial OC export, and this has led to efforts to repair degraded peatlands through restoration programmes. As a consequence, the study of degraded areas is useful to quantify the upper values of carbon release, understand processes of transformation, and evaluate the success of restoration programmes. Importantly peatlands are also collection areas for drinking water, which has implications for treatment, and requires better understanding of carbon cycling upstream of treatment works, in headwater rivers, reservoirs and pipes. UK upland blanket peat catchments are a key location in which to consider global questions surrounding fluvial carbon export and transformations, as they are highly degraded, provide a source of drinking water supply, and are currently undergoing pioneering methods of landscape scale restoration. This thesis considers Kinder Scout, an area of highly degraded and gullied blanket peatland in the South Pennines, UK. Using analysis of water samples collected over several years in the Kinder reservoir catchment and plateau, this thesis presents three novel contributions to global questions concerning OC cycling and peatlands. Firstly it provides (to date), the only carbon budget for a reservoir in a peat dominated catchment with high Particulate Organic Carbon (POC) export, which demonstrates that reservoirs may be net sources of Dissolved Organic Carbon (DOC), with the implication that POC-DOC interactions are important OC transformation mechanism in degraded systems. Secondly through use of a unique integrated combination of methods, it considers changes in carbon flux and composition in both river, lake and pipe locations, providing detailed understanding of the relative roles of river reaches, reservoirs and supply pipes, in controlling fluvial carbon cycling in peatland systems, and upstream of water treatment works. An important implication here, is that rate and direction of change in water treatability varies through a catchment. Finally, it includes results from the first widespread monitoring of the catchment scale effects of a new method of peatland revegetation. This restoration approach is being applied at landscape scale and the findings here, are that despite fears to the contrary, it does not lead to short term increases in fluvial carbon loss, which is an important piece of evidence supporting practical conservation approaches in these systems. To further enhance this research, a combination of field and laboratory investigations into carbon transformation processes, and ongoing restoration mentoring should be undertaken.

Methane is an important greenhouse gas that is relatively long-lived in the atmosphere, and wetlands are a major natural source of atmospheric methane. Methane emissions from wetlands are variable across both space and time at scales ranging from meters to continents and a comprehensive accounting of wetland methane efflux is critical for quantifying the atmospheric methane balance. Major uncertainties in quantifying methane efflux arise when measuring and modelling its physical and biological determinants, including water table depth, microtopography, soil temperature, the distribution of aerenchymous vegetation, and the distribution of mosses. Further complications arise with the nonlinear interaction between flux and derivers in highly-heterogeneous wetland landscape. A possible solution for quantifying wetland methane efflux at multiple scales in space (‘upscaling’) is repeated observations using remote sensing technology to acquire information about the land surface across time, space, and spectra. These scaling issues must be resolved to progress in our understanding of the role of wetlands in the global atmospheric methane budget from peatlands. In this thesis, data collected from multiple aircraft and satellite-based remote sensing platforms were investigated to characterize the fine scale spatial heterogeneity of a peatland in southwestern Scotland for the purpose of developing techniques for quantifying (‘upscaling’) methane efflux at multiple scales and space. Seasonal variation in pools such as expansion and contraction was simulated with the LiDAR data to investigate the expansion and contraction of the lakes and pools that could give an idea of increase or decrease in methane emissions. Concepts from information theory applied on the different data sets also revealed the relative loss in some features on peatland surface and relative gain on others and find a natural application for reducing bias in multi-scale spatial classification as well as quantifying the length scales (or scales) at which important surface features for methane fluxes are lost. Results from the wavelet analysis demonstrated the preservation of fine scale heterogeneity up to certain length scale and the pattern on peatland surface was preserved. Variogram techniques were also tested to determine sample size, range and orientation in the data set. All the above has implications on estimating methane budget from the peatland landscape and could reduce the bias in the overall flux estimates. All the methods used can also be applied to contrasting sites.