Saltmarshes on the fringe : restoring the degraded shoreline of the Eden Estuary, Scotland
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Saltmarshes are highly valued habitats but the majority of the Eden Estuary’s saltmarsh was buried under sea defences and ad hoc rubbish dumps during the last century. Without saltmarsh, the degraded shoreline may be even more vulnerable to rising sea levels and increased wave and tidal energy. This study investigated planting native saltmarsh species, common in the estuaries of Eastern Scotland, to restore saltmarsh development and sedimentation to the Eden Estuary’s shoreline. The survival and growth of the sedge Bolboschoenus maritimus (Sea Club-rush) and the grasses Phragmites australis (Common Reed) and Puccinellia maritima (Common Saltmarsh Grass) were compared in planting trials. These were seeded or transplanted onto unvegetated upper mudflats in front of eroded P. maritima saltmarsh and a disused rubbish dump. The longer term sustainability of this practice was assessed by comparing sediment deposition and surface elevation in the transplant sites, natural saltmarsh and upper unvegetated mudflats. B. maritimus outperformed P. australis and P. maritima. Springtime, high density planting was successful, whereas seeds, planting in autumn and low density planting failed. Growth in the transplanted B. maritimus sites was relatively slow for the first three years but subsequently overtook growth of the seaward edge of natural B. maritimus marsh. Sediment was not deposited on natural P. maritima and was low on upper unvegetated mudflats and in young transplant sites. Most deposition occurred in four year old sites of B. maritimus. Sediment surface elevation in natural P. maritima remained constant throughout the year, but increased in all the other sites during the summer. The upper mudflat was the only site to erode during winter. A significant, positive association was found between tide height and sediment deposition, while winds from the south-east were associated with significantly more deposition than winds from the south-west. The direct planting of saltmarsh vegetation has restored a valuable and rapidly disappearing habitat to the degraded shoreline of the Eden Estuary. The low-cost and simplicity of this restoration practice give it great potential as a sustainable coastal management option that should be explored in other Scottish estuaries. This form of restoration could help to increase the resilience and reduce the vulnerability of degraded shorelines to climate change and rising sea levels.
Thesis, PhD Doctor of Philosophy
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