How Clean is the Thames? Martin J Attrill Marine Biology & Ecology Research Centre University of...

How Clean is the Thames?

Martin J Attrill

Marine Biology & Ecology Research CentreUniversity of Plymouth

mattrill@plymouth.ac.uk

Plan of Lecture: How clean is the Thames

• Historical context– Background– Uses– History of pollution and

recovery

• Where are we now?– Trends from 1970s to

present day

• What about the future?– Current and impending

problems

Historical Context: Background • 110 km long Teddington Weir - Southend, via London

Change in the size of London

Major potential impact on the estuarine system

End of C19th – world’s largest city (4.7 million people)

Historical Context: main uses of the estuary and their impact

1. Navigation• Construction of weirs• By 1809 - 26 on

Thames• Impacted migratory

Romney weir - WindsorSalmon caught at Boulter’s lock

2. Bankside development• Loss of surrounding

marshes• Narrowed estuary –

deeper• Intensive Flood defences

• Removed natural foreshore

River Tyburn

ThorneyIsland

3. Drinking water supply

• Thames has always supplied London’s water

• Originally taken from upper estuary

• Water companies set up from 1600s to deliver water

1856 map of regions served by different water companies

4. Waste disposal• C19th – waste in streets &

tributaries flushed into estuary

• Cholera – 1849

4. Waste disposal• Major impact on

water quality in estuary

• 1858 – the year of the “Great Stink”

Come, my dear! Come to the old Thames and have a nice bath! - Punch, June, 1859

Historical Context: Plans to rehabilitate the estuary: 19th

Century

• 161 km gravity interceptor sewer constructed (1860s)

• Sewage discharged at Barking

• London cleaner…but not the mid-estuary

• Extensive “mud” banks• Fishery destroyed

(1320 men employed)

Historical Context: Plans to rehabilitate the estuary: 19th Century

• 1878 “Princess Alice” disaster

• Settlement ponds introduced – sludge dumped in outer estuary (continued until 1998)

Historical Context: Plans to rehabilitate the estuary: 19th Century

• By end of 19th Century water quality improved

• Fish returned (e.g. sprat)

Historical Context: It all goes wrong again: 20th Century

• Post WWI – massive increase in population

• WWII – huge damage to London infrastructure

• No funds for repair and improvement to old and damaged sewer system

Historical Context: It all goes wrong again: 20th Century

• 1950s – worse the Thames had ever been

• 52 km dissolved O2 <5%

• 20 km no measurable oxygen

• No fish populations for 69 km of estuary (Kew-Gravesend)

Tubifex

Historical Context: The second rehabilitation: 1960s-1970s

• 1960s – economic recovery

• Investment in sewage works – tertiary treatment at outfalls

• By 1976 all sewage fully treated - dramatic increase in water quality

Crossness STW outfall

Historical Context: Trends in fish recovery: 1960s-1980

• Fish used to monitor recovery of system

• Combination of methods, including power station intakes

• First returning fish recorded in early 1960s

Eel WhitingFlounder

Historical Context: Trends in fish recovery: 1960s-1980

• Steady increase in species recorded

64 66 68 70 72 74 76 78 80 82 84 86 88Year

• Some unusual species encountered

Where are we now? Trends in water quality since rehabilitation

1. Suspended solids (Kinks – “Dirty Old River”)

Naturally rivers and estuaries can carry lots of mud particles (e.g. Amazon). “Dirty” does not always mean polluted!

/l) Less muddy than pre-1992

Analysis of long-term data from Environment Agency

2. Heavy Metals (mainly from industry, since 1980)

Power, Attrill, Thomas (1999). Water Res. 33: 1672-1680

Can be toxic to estuary life, e.g. copper, nickel, mercury, zinc

Power, Attrill, Thomas (1999). Environ. Pollut. 104: 31-39

3. Pesticides (mainly from agriculture runoff, since 1988)

Exponential decrease in both metal and pesticide contamination since 1980s

4. Fertilisers (mainly from agriculture, since 1980)

Can cause eutrophication, algal blooms, etc.

Nitrogen

Significant decrease over last 30 years

4. Fertilisers (mainly from agriculture, since 1980)

Can cause eutrophication, algal blooms, etc.

g/l) Phosphate

Significant decrease over last 18 years

5. Dissolved Oxygen (essential for life, affected by bacteria breaking down organic material)

Lowest average oxygen since mid 1970s

5. Dissolved Oxygen

101520253035404550

Worrying decline in minimum oxygen

6. Fish community

1974 1992

Number of species in power station fish samples

More recent returns

Sea lamprey

Twaite Shad

Continued improvements to fish biodiversity

• Summary– Metals, pesticides and nutrients all show significant

declines. Thames now likely to be cleanest in living memory in terms of these pollutants.

– Amount of suspended solids in the water has stabilised at a lower level than previous years.

– Most expected fish species are present– Recent years, however, have seen a decrease in

levels of oxygen in the estuary.

– WHY?

Current problems in the Thames Estuary

1. Water temperatures – global warming

C) Average annual water temperature

2.7C increase in 30 years… linked to:

2. Dissolved Oxygen Sags in Summer

Sewer system cannot cope with summer flash floods

Aug 2004

Combined Sewer Overflow

• Warm water• Fast bacterial breakdown• Oxygen removed quickly• Elevated E. coli counts (health risk)

From Thames Tideway Strategic Study

•Thames Bubbler – treats symptoms• Build new interceptor system under estuary?

From Thames Tideway Strategic Study

Linked to…

3. Drought conditions

Kew, 1990

1976 – no water coming over Teddington Weir

• Increasing demand in drinking water for London.• Reduced flow impacts ecology of estuary and rate of pollution dispersal (e.g. CSO incidents)

3. Drought conditions

1900 1920 1940 1960 1980 2000

Rate of abstraction

Rate of Thames flow

1900 1920 1940 1960 1980 2000

flow rolling mean

Exacerbates CSO and STW input problem

4. Sea level rise

Current/Future problems in the Thames Estuary

Canvey Island 1953

London 2100?Annual Sea LevelSheerness

Global Sea Level Rise (mm)

Thermal exp

Glaciers etc

Greenland ice

UK Met. Office 1998UK Met. Office 1998

Thermal exp

Glaciers etc

Greenland ice

Thermal exp

Glaciers etc

Greenland ice

Thermal exp

Glaciers etc

Greenland ice

Predicted sea level rise

4. Sea level rise -

Need to plan now…but what to do?

Canvey Island

Example of managed realignment:

Example of a 'hard' flood defence option:

Managed realignment?

Build bigger defences?

4. Sea level rise -

Need to plan now…but what to do?

Outer EstuaryBarrier?

End of estuary as we know it

Thank you!

http://www.thamesweb.com/

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