Peat bog restoration: Implications of erosion and sediment transfer at Flow Moss, North Pennines

Abstract

The impacts of peatland management strategies used to restore degraded bare peat flats have received little attention. This study aims to improve the understanding of geomorphological processes acting on an upland bare peat flat which is undergoing restoration at Flow Moss, North Pennines, UK. A sediment budget is constructed which provides a baseline framework for assessing the effectiveness of peatland restoration measures in reducing peat erosion rates.

Erosion monitoring of aeolian and active slope processes was undertaken between October 2010 and July 2011 using a network of sediment traps and erosion pins installed across the 7 hectare site. Meteorological conditions were monitored using an Automatic Weather Station and local water table was recorded using a pressure transducer. This allowed relationships between weather patterns, hydrology and sediment transfer to be developed.

Meteorological conditions are important in controlling the wind erosion of peat with the highest rates of erosion occurring when heavy rainfall (> 5 mm hr-1) was combined with high wind-speeds (> 18 m s-1). Windward facing traps collected up to 8 times the peat collected by leeward facing traps. Freeze-thaw weathering and surface desiccation are important in generating loose material on the surface for subsequent sediment transport. A two-phase model is proposed to explain wind splash erosion dynamics where weathered material is transported preferentially before the intact peat layer is eroded. Sediment transport across bare peat flats is very active (3.2 t a-1) but the eroding flats are disconnected from the ephemeral channel system. Moreover, the channel system contains pools where the majority of suspended peat is deposited. This leads to a low net overall sediment yield for the catchment of approximately 0.01 t a-1.

The terrestrial carbon store (~2060 tonnes) at Flow Moss is relatively stable as, in the worst case scenario, it is losing 117 gC m-2 yr -1, amounting to just 0.4% of the total store. It is estimated that Flow Moss will become a carbon sink when 90% of the bare peat areas have been re-vegetated so it is therefore vital that the restoration measures are successful. Continued monitoring of sediment transfer will allow a full evaluation of the impact of the restoration measures in reducing erosion rates.