Managed coastal realignment in Essex saltmarsh : Monitoring the development of vegetation on former agricultural land following sea-water inundation

Managed coastal realignment is an integral feature of the UK’s coastal sea defence policy. The approach has potential to compensate for natural loss of salt-marsh, to facilitate compliance with EU demands for creation of habitat, and to be cost-effective as a flood defence strategy. Managed coastal realignment has been undertaken at several sites in south-east England, and in 2002 the largest managed coastal realignment project commenced on the Blackwater estuary, Essex. This paper presents the findings from the monitoring of vegetation in 2004, 2007 and 2010 at Brickfield, Great Wigborough, following the sea wall breach in 2002. A mature, established salt-marsh nearby (Old Marsh) was used as a reference site. Data were obtained from fixed point transects and quadrats over a number of elevation zones in both sites. The floristic assemblages at Old Marsh were generally stable over time, and consisted of the NVC SM14 (Sea-purslane salt-marsh) community. At Brickfield, floristic assemblages were consistent for the two lowest elevation ranges (SM8 common glasswort community and SM10 transitional lowmarsh vegetation). However, marked changes were observed in the two higher elevation zones, with a transformation from either a SM10 or SM25 (Shrubby Sea-blite drift-line community), to a SM14 community (comparable to that of Old Marsh) over time. The findings suggest that following initial rapid colonization of Brickfield by salt-marsh species, this restoration site has undergone change in its floristic assemblage, and is becoming increasingly similar to the nearby reference site, Old Marsh. Introduction Embankments and sea walls provide major defence mechanisms against coastal flooding, with many of these constructions used to reclaim salt-marsh for grazing and agriculture (Boorman, 2003; Wolters et al. 2005a). In Essex, many sea walls were constructed circa 1700, and the enclosed marshes converted into rich coastal grazing land, although since World War II much (up to 70%) has been converted to arable land (Essex Wildlife Trust 2004). These sea walls (approximately 450 km in length), are composed largely of earth banks colonised by unimproved grassland swards, and are recognised as being of high conservation value for flora and invertebrates, and as wildlife corridors (Gardiner 2012; Gardiner & Benton 2011). However, the presence of physical barriers, such as sea walls, has further exacerbated losses of salt-marsh by erosion,which has been linked to ‘coastal squeeze’ (Boorman 2003; van der Wal et al. 2008; Adnitt et al. 2007; Doody 2004, 2012) and / or changes to intertidal biota (Hughes & Paramor 2004; Paramor & Hughes 2005), although the issue is complex (Wolters et al. 2005b). The extensive land reclaim over past centuries, and losses through more recent erosion, has resulted in only 4400 ha of coastal saltmarsh (of the original 40000 ha) remaining in south-east England (Hughes & Paramor 2004). Specifically in Essex, some 25% of total salt-marsh was lost between 1973 and 1998, primarily due to coastal erosion (Cooper et al. 2001). However, a recent assessment of Essex salt-marsh covering the period 1997 to 2008 suggested overall losses within seven Essex