[Thesis]. Manchester, UK: The University of Manchester; 2017.
As conveyors of water and sediment, rivers play an instrumental role in landscape
evolution (Turner et al., 2015). River systems were traditionally considered as passive
pipes of terrestrial organic carbon (OC), but are now viewed as active sites of OC
processing, redistribution and storage (Aufdenkampe et al., 2011). Floodplains are
an important part of this system and have the capacity to act as sources or sinks
carbon (Zehetner et al., 2009), but most importantly active hotspots of organic matter
(OM) transformation (Hoffmann et al., 2009; Zocatelli et al., 2013). POC eroded
from highly-organic peat soils, may be interrupted in its transport through the fluvial
system, by temporary storage on floodplain landforms (Evans and Warburton, 2005;
Evans et al., 2006). It is important to investigate the fate of fluvial peatland POC,
order to fully close the terrestrial peatland carbon budget, to account for subsequent
mineralisation and explore the processes that lead to redistribution and storage.
The River Ashop in the southern Pennines, UK, drains the slopes of both Bleaklow
and Kinder Scout which are upland plateaux, which support an extensive cover of
blanket peat (Evans and Lindsay, 2010). These peatlands have been severely eroded
and are vulnerable to future erosion as they are marginal to the climatic space suitable
for growth of peat bogs in the UK (Clark et al., 2010). The wider peatland catchment
features cohesive, organic-rich floodplains, which are atypical in an upland landscape,
and thus suitable for investigation in their role in the fate of eroded carbon.
OM quality was an important focus of this research into the redistribution of
terrestrial organic carbon. As such, OM quality was conceptualised, by identifying
how different research disciplines identify with the term, and ultimately providing
classification scheme to assist individuals in their exploration of OM character.
A novel approach using ITRAX core scanning data was used to establish carbon
stocks of floodplains in the River Ashop catchment. Sedimentological characteristics
were insufficient to distinguish between allochthonous and autochthonous organic matter
storage. However, dating was used as a rapid and accurate tool to assess carbon
source on the 'off-site' floodplain, and could perhaps be used in the wider environment
where there are large discrepancies between the ages of source materials.
Investigations into the OM quality, provided suitably convincing evidence that
substantial overbank deposition of eroded 'old' peat had occurred. Despite this, viewing
these sites simply as areas of carbon storage is misleading. In fact, these systems
have potentially been turning over substantial quantities of carbon to the atmosphere.
Contextual information from modern-day fluvial POC fluxes showed that both 'off-site'
and 'on-site' floodplains only play a minor role in storing carbon.
Geomorphological events, particularly the substantial sediment flux generated from
peatland erosion were critical in the formation of these floodplains. In these peatland
systems, erosion, deposition and turnover of carbon are intimately linked at the
landscape scale, and floodplains are a dynamic component of this system.