Biological Impacts of a Severn Barrage Les Batty

Outline  A. How important is the Severn?  B. The features of an estuary  C. What would change with a barrage?  D. What would be the biological effects?  E. Would it matter?  A. How important is the Severn?  B. The features of an estuary  C. What would change with a barrage?  D. What would be the biological effects?  E. Would it matter?

A. How Important is the Severn Estuary? One of largest intertidal zones in UK Ranks 15th in the UK for birds Covered by a suite of international nature conservation designations

Designated conservation areas Map 14: Designated Conservation Areas

Wetland of International Importance (Ramsar Convention)  Important run of migratory fish - salmon, sea trout, lampreys, allis shad, eel  One of most diverse fish communities in UK  Internationally important for birds  Important run of migratory fish - salmon, sea trout, lampreys, allis shad, eel  One of most diverse fish communities in UK  Internationally important for birds

Special Protection Area (EU Birds Directive)  Internationally important population Annex 1 species - Bewick’s swan  And other species: White-fronted Goose, Shelduck, Gadwall, Pintail, Dunlin, Redshank  Internationally important assemblage (>70,000)  Internationally important population Annex 1 species - Bewick’s swan  And other species: White-fronted Goose, Shelduck, Gadwall, Pintail, Dunlin, Redshank  Internationally important assemblage (>70,000)

Special Area of Conservation (EU Habitats & Species Directive)  Estuary, Saltmarshes, Intertidal flats;  Sabellaria alveolata reefs;  Shads and lampreys.  Estuary, Saltmarshes, Intertidal flats;  Sabellaria alveolata reefs;  Shads and lampreys.

B. The features of an estuary Physical features

Mudflats and their ecology  Most productive habitat in estuary  High water content, even at low tide  Organic matter from detritus, phytoplankton, benthic algae, saltmarshes  Most productive habitat in estuary  High water content, even at low tide  Organic matter from detritus, phytoplankton, benthic algae, saltmarshes

Mudflat fauna

Mudflat food web

Saltmarshes  Stabilize margins of estuary  Important source of primary production  Invertebrate fauna  Habitat for fish and birds

C. What would change? Tides  Tidal range & velocities reduced by 50%  Low water at present mid tide level  High water level reduced by c.1m  Possible increase in high water stand.  Tidal range & velocities reduced by 50%  Low water at present mid tide level  High water level reduced by c.1m  Possible increase in high water stand.

Processes  Longer period of wave action at HW  Reduced turbidity/ more light  Change in erosion/ accretion patterns  Redistribution of sediments  Longer period of wave action at HW  Reduced turbidity/ more light  Change in erosion/ accretion patterns  Redistribution of sediments

Zones  Saltmarsh - erosion in some places, expansion in others  Intertidal zones - decrease  Subtidal - more soft sediment  Saltmarsh - erosion in some places, expansion in others  Intertidal zones - decrease  Subtidal - more soft sediment

So...  The estuary would be altered...  But it would still be estuarine  The estuary would be altered...  But it would still be estuarine

D. What would be the biological effects? Changes in flora  More phytoplankton (more light)  More eelgrass (Zostera)  More deep water seaweeds  More phytoplankton (more light)  More eelgrass (Zostera)  More deep water seaweeds

Changes in fauna  More zooplankton and suspension feeders, eg.mussels, oysters, scallops  Changes in fish community  More fish-eating birds (clearer water)  Potentially fewer shorebirds  More zooplankton and suspension feeders, eg.mussels, oysters, scallops  Changes in fish community  More fish-eating birds (clearer water)  Potentially fewer shorebirds

So...  There would be an impact on the designated conservation areas  The biological communities would change,  but biodiversity may increase  There would be an impact on the designated conservation areas  The biological communities would change,  but biodiversity may increase

E. Does it matter?  If a significant effect on a Natura 2000 site (SPA/SAC) is likely  And the proposal goes ahead for “imperative reasons of over-riding public interest”  If a significant effect on a Natura 2000 site (SPA/SAC) is likely  And the proposal goes ahead for “imperative reasons of over-riding public interest”

 According to legislation...  Measures must be secured to “maintain the coherence of the Natura 2000 interest” (i.e. compensatory habitat provided)  According to legislation...  Measures must be secured to “maintain the coherence of the Natura 2000 interest” (i.e. compensatory habitat provided)

But what do you think?  How could you find compensatory habitat for the Severn estuary?! and...  From an ethical standpoint... Does it matter if the Severn estuary and its ecology changes as the result of a barrage?  How could you find compensatory habitat for the Severn estuary?! and...  From an ethical standpoint... Does it matter if the Severn estuary and its ecology changes as the result of a barrage?