Biological Impacts of a Severn Barrage

Les Batty

Biological Impacts of a Severn Barrage

Les Batty

OutlineOutline

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?

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

One of largest intertidal zones in UK Ranks 15th in the UK for birds Covered by a suite of international

nature conservation designations

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Designated conservation areasDesignated conservation areasMap 14: Designated Conservation Areas

Wetland of International Importance

(Ramsar Convention)

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)

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)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

B. The features of an estuary

Physical features

Mudflats and their ecologyMudflats 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 faunaMudflat fauna

Mudflat food webMudflat food web

SaltmarshesSaltmarshes

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

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

C. What would change?Tides

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.

ProcessesProcesses

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

ZonesZones

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 . . .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

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 faunaChanges 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 . . .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? 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?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?