| Coastal Saltmarsh - Gloucestershire |
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| Extent/Distribution The Severn Estuary is an internationally important conservation area. The estuary is one of the largest in Britain with an extremely large tidal range which, combined with its funnel shape creates a unique, highly dynamic environment. It supports a range of distinctive communities, a number of which have been identified as priority habitats under the UK Biodiversity Action Plan. The section within Gloucestershire holds extensive areas of mudflats and saltmarsh. These habitats are intimately linked together by coastal processes. Saltmarsh is a significant and threatened habitat of the estuary’s fringes. Gloucestershire holds approximately 350 ha of saltmarsh. There are several different community types present with both gradual and the more unusual stepped transitions from bare mud to upper saltmarsh. The Atlantic salt meadows of the lower, middle and upper saltmarsh are of international significance. Most areas of saltmarsh exist south of Arlingham, significant areas occurring at Slimbridge (the Dumbles) and around Lydney Beachley and Sedbury, there are numerous smaller areas along the estuary often confined to narrow belts. At Lancaut in the Wye Valley, there is a rare example of the natural transition of saltmarsh into woodland. Erosion and Coastal Squeeze It has been predicted that sea level rise will result in the loss of 8,000 to 10,000 ha of mudflat in England between 1993 and 2013, while saltmarsh may be being lost in the UK at the rate of 100 ha per year. This sea level rise coupled with changing prevailing winds results in the land-ward movement of the estuary. The limited opportunities for the natural expansion of the estuary means that intertidal flats and saltmarshes are squeezed between the flood defence and the eroding seashore. There has been a net loss of saltmarsh over the last 10 years. Significant areas of saltmarsh (probably in excess of 20 hectares) have been lost from the Gloucestershire section of the Severn Estuary, particularly at Frampton and Lydney, in the last 10-20 years outweighing small local gains elsewhere. Opportunities for coastal realignment are limited within the Gloucestershire section of the estuary and may only be realised where changes in flood defence policy are possible without affecting significant natural or man made assets. Agri-environment incentives have become available to encourage farmers/landowners to facilitate managed retreat. In addition important infrastructure ( i.e. major roads and railways) and the value of agricultural land within the Severn Vale significantly affect opportunities for coastal realignment. Proposals for a Severn Barrage still pose a potential threat to the ecological integrity of the estuary. Sediment dynamics Local sediment budgets may be affected by coastal protection works or by changes in estuary morphology caused by ldredging and impacts of flood defence over the years. Mudflats deposited in the past may erode due to changing estuarine dynamics and be deposited elsewhere within the estuary. Accretion and development of saltmarsh is occurring in some areas of the estuary; however, this is unlikely to offset the overall loss of saltmarsh. Grazing Grazing has a marked effect on the structure and composition of saltmarsh vegetation. Too little grazing can lead to the domination of saltmarshes by rank grasses and overgrazing to poaching, loss of sward diversity (only very tolerant species will remain) and enhanced erosion. Land claim and development In Gloucestershire’s section of the Estuary most reclamation of land has been for agriculture and current policy would be unlikely to allow similar activity in the future. Land claim for development has only removed a few small areas of mudflat and saltmarsh. Regulation There are significant difficulties in securing the integrated management of the estuary due to the large number of regulatory authorities/bodies with a remit in the Severn Estuary (EN/CCW, EA, GHT, UK Government, Welsh Assembly and numerous local authorities). Pollution Diffuse or point source discharges from agriculture, industry and urban areas, including polluted storm water run-off can create abiotic areas or produce algal mats which may affect invertebrate communities. Eutrophication due to sewage effluent and agricultural run-off can lead to localised excessive algal growth. The total loading of effluents and nutrients into the estuary is currently undefined. Disturbance Human disturbance may be a localised problem, such as around the Severn Way, however, most areas of the estuary suffer only a minimal amount of disturbance. Development proposals adjacent to the estuary may have an impact on ground nesting birds and high tide roosting areas, particularly through disturbance by pets. Fishing operations (predominantly for salmon and elvers) on the estuary are mainly small scale,and therefore unlikely to have a significant effect on community structure and substratum. Salmon and elvers, however, appear to be in decline. OBJECTIVE 1 OBJECTIVE 2 To maintain at least the present extent and regional distribution of the Severn EstuaryÕs mudflats. This will require compensation of predicted losses to development by the restoration of mudflats within the whole estuary. OBJECTIVE 3 To create 50 ha of saltmarsh using the few currently remaining opportunities
for managed realignment by 2010. OBJECTIVE 4 OBJECTIVE 5 OBJECTIVE 6 To restore estuarine water quality to ensure that existing mudflats fulfill their important ecological and conservation role. Target: ongoing OBJECTIVE 7 To maintain and expand the populations of internationally and nationally
important species in the estuary. To increase awareness, understanding and appreciation of the estuaryÕs
biodiversity. [see above] {Current action} Policy and legislation {policy}Management
{Management} Research and monitoring
{Research} Education and awareness
raising
{Education} {Progress} |
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