FRESHWATER POLLUTION

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FRESHWATER POLLUTION

• The Effects of Pollution Caused by Treated
  Domestic Sewage on a Freshwater Ecosystem

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Specific Information

• The sewage treatment works is in St. Jean du
  Bleymard.
• It serves two settlements - St. Jean du Bleymard
  and Le Bleymard.
• These two settlements have a combined population
  of 446 (1999 census).
• It also receives waste from a small holiday
  village when it is open in July and August.
• The total population may then reach 1200 people.
• The liquid waste from the treatment works is
  discharged almost continuously in low volumes,
  and diluted by the river Lot.

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Map of Study Sites
Site 1 Upstream (control) Site 2 Outfall Site
3 5m downstream Site 4 50m downstream
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What is a Pollutant??

• A pollutant may be natural or unnatural.
• Pollutants are not necessarily highly toxic
  chemical compounds.
• It is the concentration of the substance that
  defines it as a pollutant.
• Domestic sewage is rich in ammonium from urine
  and faecal matter, phosphates from detergents and
  particulate matter.
• By proportion, it is approximately 45
  carbohydrate, 45 fat and 10 protein.

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Sewage Treatment Process
Tank 1
Tank 2
Tank 3

• Liquid and solid separation.
• Liquid continues onto biological treatment.

• Solid storage
• Farmers collect gtit in Autumn gtand
  Winter to gtbe used as gtorganic gtfertiliser.

• Sewage is stirred by a propeller.
• This increases its surface area.
• Air (esp. Oxygen) mixed with the sewage.

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Biological Treatment

• Urea from domestic sewage breaks down into
  Ammonium (NH4).
• Aerobic bacteria carry out oxidation reactions,
  converting the ammonium ions to nitrate.
• The reactions
• 2NH4 3O2 ? 2NO2- 4H
• (Carried out by nitrosomonas)
• Ammonium is used as food for Nitrosomonas to
  produce nitrite (NO2-).

• 2NO2- O2 ? 2NO3-
• (Carried out by nitrobacter)
• Nitrobacter use the Nitrites from the previous
  reaction and produce Nitrates (NO3-).
• Both reactions use up Oxygen.
• Nitrosomonas and nitrobacter occur naturally in
  watercourses therefore if the treatment process
  is insufficient, the ammonia will be converted to
  nitrate and cause Oxygen depletion in the
  receiving water.

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Abiotic Hypothesis
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Biotic Indicators

• There are a huge diversity of invertebrates
  living in rivers.
• They have a range of tolerances to different
  water qualities, especially different levels of
  oxygen concentrations.
• Therefore there are Indicator Species which can
  help determine the long term quality of the river
  water.
• Biological Monitoring Party Score (BMWP) can be
  used as a biotic index. Invertebrates with a low
  BMWP can tolerate low levels of Oxygen and are
  therefore good indicators of poor water quality.

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Aims

• To determine the effects of point source organic
  pollution from a small rural sewage treatment
  works on the water quality of an upland stream.
• To investigate the effects of water quality
  changes on stream fauna.

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Objectives

• To determine the susceptibility of freshwater
  invertebrates to organic pollution, using
  indicator species to give an indication of the
  extent of long term pollution.
• To determine the effects of pollution on species
  diversity and abundance.

• To determine how treated sewage affects the
  abiotic conditions
• Oxygen concentration
• Temperature
• pH
• Ammonium
• Nitrates
• Phosphates
• Dissolved Load

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Species we may find!!
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Stonefly nymph

• Stonefly nymphs prefer rocky, stony, or gravel
  bottoms in cool, well-oxygenated, swift-moving
  streams or small rivers. Any effluent that
  reduces the oxygen content of the stream quickly
  kills the nymphs.
• BMWP 10

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Flattened Mayfly Nymph

• These are only found in very clean water
  containing lots of oxygen. They absorb oxygen
  from the water through their gills.
• They are primary consumers that eat plants and
  algae.
• BMWP 10

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Cased caddis Fly Larvae

• Caddisflies use silk (like butterflies) to build
  cases from gravel, twigs, needles, or sand.
  Different species build distinct cases, but they
  often lose them when removed from a stream.
• BMWP 8 -10

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Cranefly Larvae

• Up to four inches long with a Fleshy, plump,
  rounded segmented body
• Its digestive track (internal organs) can be seen
  moving back and forth as it crawls.
• No legs and the back end usually has several
  extensions or finger-like lobes.
• BMWP 5

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Flatworms

• Flatworms are unsegmented worms with flattened
  bodies.
• Their flatness allows them to shelter beneath
  stones.
• Being flat increases the area of skin exposed to
  the water, which improves the flatworm's oxygen
  uptake.
• BMWP 5

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Freshwater Mite

• Tiny animals related to spiders.
• Up to 8mm.
• They have an oval body and 8 legs.
• Many are brightly coloured.
• BMWP 4

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Leeches

• Flat, Worm-like, segmented body.
• Many are scavengers or feed on other
  invertebrates.
• Suckers at both ends are used for attachment,
  feeding, and locomotion.
• They swim gracefully and quickly in an
  up-and-down motion.
• BMWP 3

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Red Midge Larvae (Bloodworms)

• These are sometimes called 'bloodworms' because
  of their bright red colour, but they are not
  worms at all.
• They are midge larvae.
• They eat dead organic matter and can tolerate
  very low oxygen levels.
• BMWP 2

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Tubifex Worms

• These are thread-like worms that live in the mud
  on stream bottoms.
• They are filterfeeders
• They can tolerate extremely low levels of oxygen
  and are therefore found in polluted water.
• BMWP 1

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• This shows freshwater fauna as indicators of
  river pollution.