Thu, 20 Sep 2012
New salt marshes created as part of managed coastal realignment are failing to meet European conservation regulations, according to a new study by the University of East Anglia.
Under the EU Habitats Directive, new salt marsh must be created each time natural salt marsh is lost to coastal development or to coastal erosion caused by sea-level rise. The new marshes must display “equivalent biological characteristics” to their natural counterparts - but the new findings, published today in the Journal of Applied Ecology, reveal that artificially created salt marshes suffer significantly reduced biodiversity.
The UEA researchers analysed the vegetation of 18 marshes created through deliberate coastal realignment since 1991 and 17 marshes created accidentally by storm surges since 1881. They compared the salt-tolerant plants at these sites with those at 34 natural salt marshes and found that some key species were very poorly represented. These included sea lavender, thrift, sea arrowgrass and sea plantain.
“Salt marshes such as those in North Norfolk, Essex and around much of the coast of England are loved by naturalists and tourists alike for their natural beauty and rare/rich ecology,” said lead author Dr Hannah Mossman of UEA’s School of Environmental Sciences.
“These unique tidal areas also provide vital habitat for invertebrates, a staging post for migrant birds, and the only environment in which a number of salt-tolerant plants can survive.”
Rising sea levels caused by global warming are posing a growing threat to the country’s coastal salt marshes and increasing the cost of maintaining sea defences. This challenge is increasingly being met in the UK by relocating sea walls further inland (managed coastal realignment) and allowing new salt marsh to develop.
Prior to this in-depth five-year study it had been assumed that this process caused no loss of species richness and that manmade marshes compensated well for the loss of natural ones. The researchers found, on the contrary, that plant life on artificially created salt marsh tended to be dominated by early-colonizing plants such as marsh samphire because of a lack of oxygen in the sediment. Shrubs such as sea purslane can also quickly become unduly dominant. The sites tended to be flat and featureless with scrappy vegetation. Even the older accidentally-created marshes were deficient in the characteristic salt marsh perennials such as sea lavender, thrift, sea arrowgrass and sea plantain.
“Our findings demonstrate very clearly that marshes created by managed realignment are not biologically equivalent to natural ones and therefore fail to satisfy the biodiversity requirements of the EU Habitats Directive,” said co-author Prof Alastair Grant, of UEA’s School of Environmental Sciences.
Prof Anthony Davy, of UEA’s School of Biological Sciences, added: “These created marshes are certainly better than losing our precious natural salt marsh altogether, but they are not a good enough replacement. We are currently developing ways of enhancing their biodiversity, such as improving local drainage conditions and planting the deficient species.”
The study was funded by the Natural Environment Research Council (NERC) and carried out by researchers from UEA’s schools of Environmental Sciences and Biological Sciences.
‘Does managed coastal realignment create salt marshes with “equivalent biological characteristics” to natural reference sites?’ by Hannah Mossman (UEA), Anthony Davy (UEA) and Alastair Grant (UEA) is published online by the Journal of Applied Ecology on September 20 2012.
Picture: A created salt marsh in Lincolnshire (left) dominated by annual seablite, common salt marsh grass and sea purslane, and a natural salt marsh (right) in Norfolk dominated by sea lavender. (A Grant/D White)
The UEA researchers analysed the vegetation of 18 marshes created through deliberate coastal realignment since 1991 and 17 marshes created accidentally by storm surges since 1881. They compared the salt-tolerant plants at these sites with those at 34 natural salt marshes and found that some key species were very poorly represented. These included sea lavender, thrift, sea arrowgrass and sea plantain.
“Salt marshes such as those in North Norfolk, Essex and around much of the coast of England are loved by naturalists and tourists alike for their natural beauty and rare/rich ecology,” said lead author Dr Hannah Mossman of UEA’s School of Environmental Sciences.
“These unique tidal areas also provide vital habitat for invertebrates, a staging post for migrant birds, and the only environment in which a number of salt-tolerant plants can survive.”
Rising sea levels caused by global warming are posing a growing threat to the country’s coastal salt marshes and increasing the cost of maintaining sea defences. This challenge is increasingly being met in the UK by relocating sea walls further inland (managed coastal realignment) and allowing new salt marsh to develop.
Prior to this in-depth five-year study it had been assumed that this process caused no loss of species richness and that manmade marshes compensated well for the loss of natural ones. The researchers found, on the contrary, that plant life on artificially created salt marsh tended to be dominated by early-colonizing plants such as marsh samphire because of a lack of oxygen in the sediment. Shrubs such as sea purslane can also quickly become unduly dominant. The sites tended to be flat and featureless with scrappy vegetation. Even the older accidentally-created marshes were deficient in the characteristic salt marsh perennials such as sea lavender, thrift, sea arrowgrass and sea plantain.
“Our findings demonstrate very clearly that marshes created by managed realignment are not biologically equivalent to natural ones and therefore fail to satisfy the biodiversity requirements of the EU Habitats Directive,” said co-author Prof Alastair Grant, of UEA’s School of Environmental Sciences.
Prof Anthony Davy, of UEA’s School of Biological Sciences, added: “These created marshes are certainly better than losing our precious natural salt marsh altogether, but they are not a good enough replacement. We are currently developing ways of enhancing their biodiversity, such as improving local drainage conditions and planting the deficient species.”
The study was funded by the Natural Environment Research Council (NERC) and carried out by researchers from UEA’s schools of Environmental Sciences and Biological Sciences.
‘Does managed coastal realignment create salt marshes with “equivalent biological characteristics” to natural reference sites?’ by Hannah Mossman (UEA), Anthony Davy (UEA) and Alastair Grant (UEA) is published online by the Journal of Applied Ecology on September 20 2012.
Picture: A created salt marsh in Lincolnshire (left) dominated by annual seablite, common salt marsh grass and sea purslane, and a natural salt marsh (right) in Norfolk dominated by sea lavender. (A Grant/D White)
