Assessing the Impact of Peat Bog Restoration in Mitigating Carbon Loss by Upland Erosion

Abstract

Demonstrating the impact of peat bog restoration in mitigating carbon loss by upland erosion requires careful field monitoring. This thesis presents results of a year-long field monitoring project at Flow Moss, a 7 ha area of eroding upland blanket bog in the North Pennines, UK.

The aim of the project was to estimate the size of the carbon store at Flow Moss, identify the main drivers and pathways through which peat and carbon were leaving the site, and investigate the effectiveness of restoration methods in reducing peat loss. Three main approaches were used:
1) A subsurface Ground Penetrating Radar (GPR) survey to quantify peat depths. This was coupled with results from peat core analysis (loss on ignition, bulk density, total organic carbon and heavy metal analysis of 298 peat samples) to estimate the amount of peat and carbon stored at Flow Moss.
2) Surface erosion monitoring using sediment traps, fixed pole transects, erosion pins and Terrestrial Laser Scanning (TLS) to establish through which mechanisms peat is eroded and transported. A dGPS survey was implemented and the results compared to historic satellite and UAV imagery to monitor changes in surface vegetation cover.
3) Environmental monitoring of rainfall, wind speed / direction, temperature and water table height. The results are compared with those collected during surface monitoring to identify the drivers of erosion at Flow Moss.

Results show that currently there are 4004 (±0.03) tonnes of carbon stored at Flow Moss, which equates to 572 tonnes per ha. At present this is relatively stable, but the site is a slight net source of carbon emitting approximately two tonnes or 0.05% of the stored carbon each year. The bare peat flats are actively eroding with 35 tonnes of sediment being transported by wind-related processes annually. High wind speed and high intensity rainfall are the main drivers of erosion at Flow Moss and their effectiveness increases when they occur concurrently. Sediment and carbon loss from the channel system, although small, has significantly decreased (a reduction of 98%) since the start of restoration. This is most likely due to vegetation encroachment from the margins of the bare peat with a reduction in the bare peat area of 21% occurring since 2007 and a reduction of 997 m2 or 12% occurring since restoration began in 2010. This suggests that that restoration attempts have shown some limited success, however for Flow Moss to become a net carbon store, full re-vegetation of the bare peat is necessary.