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Saltmarsh creation and growing foredunes: Four decades of change at Saltfleetby-Theddlethorpe NNR

Cliff Morrison

For nearly 40 years Cliff Morrison has been walking the NNR and has watched how this dynamic dune landscape has changed over time - with some new habitats created and others lost.

In the 38 years that we have lived close to the dunes here, we have seen massive changes to the shoreline along the whole length of the NNR. Our most regular walks are between Churchill Lane (CL)in the north Brickyard Lane (BYL) in the centre and Crook Bank (CB) in the south, and some of the changes here will be highlighted.

A walk down to the beach along the tracks from the car parks firstly reveals a clearly demarcated line where maturing sea buckthorn ends, with marram covered foredunes beyond and then a new line of younger buckthorn running along the foredune edge.

What might not be too obvious to the casual visitor is that the foredunes have developed seawards at a pace, particularly since the new millennium. John Walker MBE, the reserve manager at the time, placed a marker at the foredune edge midway between BYL and CL; it is now about 30 metres in from the current foredune and it has disappeared under new buckthorn. This expansion of the dunes’ seaward is not new since a wartime defence blockhouse is to be found here over 100metres in from the foredunes along a valley bottom with 3 dune ridges in front of it.

SB 1
SB 2

Sea Buckthorn develops to edge of expanding foredunes and at top of new blown sand dunes but does not like ‘getting its feet wet’, so only grows above spring tide levels.

Whilst this has been an ongoing process for decades, what is totally new along this stretch is the development of saltmarsh and new mobile dunes centred out from the Brickyard Lane entrance. The beach here used to be clean yellow sand, much as can still be found at the Crook Bank entrance, but saltmarsh development has been particularly rapid over the past 20 years. It began with salicornia, also known as samphire, growth trapping muddy sediment on spring tides, annual sea blight growth entrapping further sediment and blown sand, saltmarsh grass arrival, followed by infill with further blown sand. Many typical saltmarsh plants, such as sea-lavender, lax-flowered sea-lavender, sea aster, sea-purslane have gradually arrived via wind and tide.

samphire 1
Samphire 2

Salicornia (samphire) traps sediment and sand and is quickly followed by annual sea blight. The sea blight in this photograph (right) has an upright growth but tends to more common as a prostrate plant. Many people cutting samphire for culinary purpose mistakenly collect sea blight as well.

Weather patterns in recent years have produced long periods of onshore winds, resulting in sand blow and new mobile dune formation well out from the existing foredunes. These new dune ridges are rapidly colonised by sea buckthorn, which despite its name, doesn’t like getting ‘its feet wet’ by the sea. Hence it only develops when the dunes reach a height where normal high spring tides no longer reach. This why there are buckthorn delineated growth lines along the existing foredunes marking spring tide heights.

Currently new saltmarsh development is halting sand blow at its outer edge so that dunelets are forming, consequently the saltmarsh is at a lower level than these and seawater is held after spring tide flooding, only slowly draining away. Sedimentation occurs during spring tides, but with blocked blown sand ingress to the marsh or existing foredune edge 400+metres beyond. The spring tides used to reach the foredunes along the whole stretch of this coast, but whilst it still does at Churchill and Crook Bank, only the highest tides Brickyard Lane do so.

It will be interesting to see, how long this saltmarsh and dune development continues, because the low tide profile does not appear to be changing. Saltmarsh is globally one of the least common habitat types, is being lost at an increasing rate elsewhere due to climate change and rising sea level but is also extremely beneficial for carbon capture. Only a little further south from Mablethorpe, the coast is subject to rising sea levels, requiring constant and expensive sand nourishment to protect from flooding. Perhaps in many decades to come, should dunes develop around the saltmarsh, it akin eventually become a freshwater marsh akin to the areas

sea lavender1
sea lavender2

Common sea-lavender in wetter areas of the new saltmarsh with the much less common lax-flowered sea-lavender on the drier areas, such as new dune slopes.

sea aster
sea club

Common sea-lavender in wetter areas of the new saltmarsh with the much less common lax-flowered sea-lavender on the drier areas, such as new dune slopes.