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Providing evidence to improve practice

Individual study: Translocation of a nationally scarce aquatic plant, grass-wrack pondweed Potamogeton compressus, at South Walsham Marshes, Norfolk, England

Published source details

Markwell H.J. & Halls J.M. (2008) Translocation of a nationally scarce aquatic plant, grass-wrack pondweed Potamogeton compressus, at South Walsham Marshes, Norfolk, England. Conservation Evidence, 5, 69-73

Summary

To mitigate for loss of a dyke supporting a population of the nationally rare grass-wrack pondweed Potamogeton compressus due to be infilled during flood defence works, a new section of dyke was excavated. Grass-wrack pondweed turions were collected prior to infilling of the old dyke and grown on, both indoors and outdoors, for transplanting into the new dyke once completed. The pondweed was also present within adjoining dykes potentially at risk to increased turbidity/siltation and/or water pollution, plus hydrological changes during construction works. Therefore, to reduce these risks, measures were implemented, including bunding of internal dykes and installation of 'silt curtains' to minimise such impacts. Finally, as the old dyke was infilled, the majority of the green material was removed by hand using grapnels, and sections of silt (including turions) where the plant was growing were sequentially removed mechanically and placed into the adjacent new length of replacement dyke. Monitoring of the new dyke in 2007 and 2008 (one and two years after creation) indicated successful grass-wrack pondweed establishment; in 2007 it was the dominant taxa. In 2008 its density was lower, however cover of other aquatic species had significantly increased. The results are consistent with those of another translocation, where good populations were present during the first 2-3 years of establishment, with populations tailing off as the new habitat is colonised i.e. the species is considered a primary coloniser.