Description:
<jats:p> The biological and chemical regimes of the Severn Estuary are severely stressed by its physical regime. Estuarine flora and fauna naturally adapt to habitat conditions. The Severn is dynamic and turbid to such a degree, however, as to put it beyond the tolerance of most species. The foreshores have an exceptionally low carrying capacity for shorebirds and provide poor feeding and nursery areas for fish. Parts of the subtidal bed regime are barren and few support any live organisms. The turbid water excludes sunlight and suppresses dissolved oxygen. The ecosystem is limited to the most hardy and immature estuarine organisms and these are only present as a result of continual recruitment from the Bristol Channel. Furthermore, combined sea level rise, increased storminess and foreshore erosion are sustaining the downward spiral in ecosystem biodiversity. This severe suppression is natural; it is not induced by anthropogenic contaminants. Should a tidal power barrage be built, mean water level and shelter would increase and current strengths diminish. Large-scale reductions in suspended load and greater bed stability would encourage colonisation. Mixed substrates would develop, leading to biodiverse and abundant invertebrate and vertebrate communities. It is unusual for a major engineering project to result in the large-scale invasion of a suppressed ecosystem by organisms; this is an inevitable consequence of this project. </jats:p>