Habitat Creation Opportunities for Landward Coastal Re‐alignment: Essex Case Studies

Abstract

Relative sea‐level fluctuations during the Holocene period have combined with medieval to present saline floodplain embanking to reduce the inter‐tidal saltmarsh area in Essex from 40 000 ha to 4400 ha. The present loss by erosion is estimated at 2%/annum for the country, and the reduction in these areas is not only detrimental to related habitats but has caused an increasing requirement for flood‐defence financial investment. Recent initiatives by the Ministry of Agriculture, Fisheries and Food, the Environment Agency and English Nature have created mechanisms and opportunities to develop sustainable flood‐control structures where coastal re‐alignment has been the preferred option. The Orplands frontage covers 2 km of sea wall which have been deliberately breached to allow 40 ha of rare saltmarsh to re‐establish. At Abbotts Hall, an arable field of 20 ha has been converted to its former saltmarsh by creek re‐establishment and tidal inundation by reversal of existing sluices. These two schemes have (a) regenerated habitats for halophytic and semi‐halophytic plants, marine and brackish invertebrates, and (b) provided roost, feed and breeding areas for birds and nursery areas for marine fish fry. Apart from flood control and habitat creation, particular features were incorporated to provide niche locations for targeted types of wildlife.

Remedial habitat creation: does Nereis diversicolor play a confounding role in the colonisation and establishment of the pioneering saltmarsh plant, Spartina anglica ?

“…Regarding this, it is not clear whether other species might refer to plants or animals; both could potentially compete for the same resourcespace within the sediment. Dixon et al (1998) report some preliminary results as being earlier than expected colonisation by halophytic plants and rapid take-up by marine invertebrates. Marine bioturbators are major controllers of sediment ecosystems, their impact on human attempts at ecosystem engineering and manipulations of the "natural environment" towards some desired end state should be considered carefully.…”

“…The suggestion by Dixon et al (1998) that "managed retreat" or "coastal realignment" schemes represent a minimalist approach and provide a cost-effective solution to the problem of seawall maintenance through a process of sustainable natural development that ensures evolution towards a natural system, may well be true. However, evidence from the present study detailing the effects of N. diversicolor on S. anglica, and other studies (Gerdol and Hughes 1993) detailing the negative effects of C. volutator on Salicornia europaea distribution, contribute to a growing body of evidence that indicates the importance of bioturbating infaunal invertebrates in limiting the distribution of pioneering saltmarsh plants and hence saltmarsh development.…”

“…These schemes known variously as "coastal realignment" and "managed retreat" strategies have involved removal or breaching, of certain existing, but deteriorated, seawalls and make use of enhanced low level counterwalls to limit the extent of saline flooding. The philosophy behind this approach has been "to allow natural processes to work, with as little human engineering and interference as possible" (Dixon et al 1998).…”

“…Previous studies have reported significant seed predation by Corophium volutator on another pioneer saltmarsh species, Salicornia europaea (Gerdol and Hughes 1993). An understanding of the effects of intertidal invertebrates on these species is important if proposed management strategies to allow the development of saltmarsh communities in areas of managed retreat (Dixon et al 1998) are to be properly evaluated…”

Cross-sectoral interactions of adaptation and mitigation measures

“…Long-term improvement in water quality 56 ; short-term may be negative, 53,57 Increased habitat 39,58 ; benefits most species 59 Increase/decrease urban protection 60,61 Loss of agricultural land 50,62,63 Increase carbon sequestration 42 ; increase in CH 4 and N 2 O emissions 53,55 Managed retreat Possible short-term reduction in water quality followed by overall improvement 64 Habitat gains 47 /loss 58,65 ; benefits most species Increase/decrease urban protection 60,61 Loss of agricultural land 62,63 Increase carbon sequestration 42 ; increase in CH 4 [66][67][68] ; fish nursery ground 69 ; increase in algae, but can prevent species settling on structure 67 ; coastal squeeze 70 …”