Throughout the last two centuries large areas of northern(i.e. not tropical)peatlands have been subject to extensive drainage, typically carried out through the digging of ditches. Ecosystem restoration now focuses on blocking these ditches, with various aims such as increasing biodiversity or sequestering carbon. Despite the increasing number of restoration projects taking place, there are still large knowledge gaps concerning the effects of ditch blocking on biogeochemistry. This thesis presents the results from a ditch blocking experiment on a Welsh blanket bog, and compares two methods of ditch blocking: damming using peat dams, and a reprofiling method that uses peat dams as well as infilling the ditch. Following ditch blocking,results suggested that water tables had risen by approximately 2 cm. Post-rewettingCH4fluxes increased substantially, with blocked ditches (and pools within blocked ditches) releasing large amounts of CH4. This increase was most notable for reprofiled ditches, although fluxes from dammed ditches were also larger than those from unblocked control ditches. Upscaling CH4fluxes to the catchment area suggested that before rewettingthe catchment-scale flux was 2.89 g CH4m-2yr-1. Post-rewettingfluxeswere calculated as 3.55 g CH4m-2yr-1if all ditches were blocked using a damming method, and 4.21g CH4m-2yr-1if all ditches were blocked using a reprofiling method. A detailed survey of bog pools that formed behind ditch dams showed that Eriophorumspecies colonised shallower pools (< 50 cm depth) whilst Sphagnumspecies dominated in deeper pools. Considering that Eriophorumis well-documented as a species associated with high CH4fluxes, and that certain Sphagnumspecies have been observed to consumeCH4, we argue that deeper pools are desirable to facilitate the colonisation of preferential plant species that might have the capacity to mediate large post-blocking CH4fluxes. In addition to CH4fluxes, we also present a limited amount of carbon dioxide (CO2) flux data, obtained using static chambers in conjunction with an infra-red gas analyser. Results were very variable butCO2uptakefrom Sphagnumwithin unblocked ditches was extremely high, and this therefore suggests that Sphagnumcolonisation is a favourable outcome for both a CH4and CO2perspective. A certain degree of the lowsoildecomposition rates that are found in northern peatlands has been attributed to constraints on the activity of the extracellular enzyme phenol oxidase, and the associated ‘enzymic latch’ mechanism. To test how extracellular enzymes respond to drainage and ditch blocking, soil samples were analysed from three different sites on the Migneint. The results from one site suggested that historical peatland drainage had stimulated phenol oxidase activity and enhanced hydrolase activities in comparison to enzyme activities at an undrained site. Results from a second drained site showed no change in phenol oxidase activity, but a decrease in hydrolase activity compared to the undrained site. We hypothesised that this was due to vegetation differences at the second site; that large areas of Juncusand Eriophorumwere supplying low-molecular weight root exudates to the soil, thus negating the demand for hydrolase enzymes that are responsible for the production of low molecular weight compounds. Following ditch blocking there was no evidence of changes to enzyme activities, implying that activities remain enhanced as a legacy of previous, drained conditions. The effect of ditch blocking on water chemistry was examined through regular sampling of ditch water, pore water, and overland flow (OLF) water. For ditch water there was no difference between treatments in the concentration or composition of dissolved organic carbon (DOC), particulate organic carbon (POC) concentration, pH, electrical conductivity (EC), or sulphate concentration. For pore water there was some evidence for higher DOC concentrations associated with blocked ditches occurring in summer 2011.This enhancement occurred one month before an increase in DOC concentration in the stream draining the blocked catchment (relative to an unblocked control catchment). These results suggest that ditch blocking stimulates a brief flush of DOC from a catchment, possibly due to ecosystem disturbance during the physical act of rewetting. Although there was no effect of rewettingon OLF water chemistry, we noted that the concentrations of DOC in OLF were very similar to ditch water DOC concentrations. As such, we hypothesise that ditch blocking diverts water out of ditches, resulting in increased OLF. We therefore suggest that ditch blocking studies must measure this pathway, as previous work has largely ignored it.In addition to elucidating the effects of ditch blocking, investigations into the use of spectrophotometric proxies for DOC were undertaken. These investigations consistently showed that light absorbance at 254 nm is a more accurate and reliable proxythan400 nm. We also propose a new DOC proxy, the concentration of phenolic compounds in a water sample, and show how this compares to traditional light absorbance proxies.